S u p e r v i s o r ! ' Dr, S. R. S t o b a r t
ABSTRACT
The p r e p a r a t i o n and s p e c t r o s c o p i c p r o p e r t i e s o f s i x p.oly-c y p.oly-c l o p e n t a d i e n y l and - m e t h y l p.oly-c y p.oly-c l o p e n t a d i e n y l d e r i v a t i v e s o f germane
* * 1 '
and s t a n n a n e a r e d e s c r i b e d . The t e m p e r a t u r e dependence of H and NMR d a t a a r e d i s c u s s e d , l e a d i n g t o c o n c l u s i o n s r e g a r d i n g t h e
n a t u r e o f m e t a l l o t r o p i ç m i g r a t i o n s i n b o t h r i n g s y s t e m s . M e t a l l o t r o p i c s h i f t s w i t h i n t h e m e t h y l c y c l o p e n t a d i e n y l d e r i v a t i v e s r e s u l t i n
' t h e i n t e r c o n v e r s i o n o f d i f f e r e n t - i s o m e r s , t h e r e l a t i v e c o n c e n t r a t i o n s o f w hich depend on Jjoth t h e s i z e o f t h e m e ta l''a to m and s t e r i c
. r e q u i r e m e n t s o f t h e s y b s t i t u e n t s . ■ .
The NMR p r o p e r t i e s
« i
a number o f p o l y i n d e n y l d e r i v a t i v e so f germane and s t a n n a n ^ a r e exam ined o v e r a wide ra n g e o f t e m p e r a t u r e s . The r e l a t i v e c o n c e n t r a t i o n s o f is o m e r s p r e s e n t i n s o l u t i o n s of
t h q s e compounds a r e c o n s i s t e n t V i f h z e r o f r e e e n e rg y d i f f e r e n c e s betw een t h e g round s t a t e s o f t h e is o m e r s f o r . a n y p a r t i c u l a r
compound. I n t e r c o n v e r s i o n b e tw e e n ^ h e s e is o m e rs o c c u r s as a
* ' ,
r e s u l t o f f a c i l e m i g r a t i o n o f th f e ,m e ta l s u b s t i t u e n t a c r o s s eac h in d e n y l r i / i g . The soJ,id s t a t e g t r j i c t u r e of ope is o m e r 'of t e t r a ( l
-i n d e n y -i ) s t a n n a n e , th p - m e s o -f o r m , pas b e e n d e t e r m -i n e d by X -ra y
*
■
c r y s t a l l o g r a p h y ; s o d i e ; , - C o m m e n t a r y o h t h e s i g n i f i c a n c e - o f t h i s
s t r u c t u r e w h i c h b e l o n g s t o t h e s y m m e t r y ' p o i n t g r o u p i s g i v e n * . ,
■ TABLE OF CONTENTS ABSTRACT'... i i TABLE OF CONTENTS ... ' i v ■ *
•
LIST OF Cables v i i i ^ LIST OF f i g u r e sp x i ‘
l i s t o f a b b r e v i a t i o n s ...)
... x l v • ACKNOWLEDGEMENTS ...% . ... ’ xv DEDICATION ... ; ... x v i PREFACE ... -... . . x v i i ' ' ' • ,«è' % ■ , C h a p te r . , , • ’ i INTRODUCTION ... ; ... 1 ' a. general ... ■...‘ ... 1 • - ^B. STRUCTURE AND REACTIVITY OF ORGANOMETALLIC AND
■
%GANIC DERIVATIVES OF BIVALENT GERMANIUM, TIN,
> » AND LEAD... ...t .
.
b
. ’ ■ : . *
B , l . S y n t h e s i s 8 .
B .2 . S t r u c t u r e A . ... A . 11
B .3 . R e a c t i v i t y ... j ... 21
C. SIGMATROPIC MIGRATIONS IN METALLOlr-CARBOCYCLIC
SYSTEMS ... 26 » • i
*
C . l . I n t r o d u c t i o n . ...% 26 , . , C .2 . T h e o r e t i c a l C o n s i d e r a t i o n s ... 27 , ' - ' ')C.'3.' The NMR T e c h n iq u e as A p p lie d to* .
' A '
S t e r e o c h e t n i c a l l y n o n - r i g i d M o le d u le s . . . ... 31 K . ( i ) T heory ... 31
y
%
t
♦
V•
.
_
V
.( i i ) The u s e *of d i a s t e r e o t o p i c groupa ■ .. •, i n d e t e r m i n i n g t h e mechanism o f ' r e a r r a n g e m e n t i n m e t a l l o c y c l o p e n t a d i e n e s . . . 34'< f ' % . C .4 . E x p e r i m e n t a l O b s e r v a t i o n s o f S i g m a t t o p i c . -s h i f t -s i n M e ta llo m o n o h a p to c y c lo p o ly e n e
/
Sy’stem s ...' . ... 38 % ( i ) H e t a l l o c y c l o p e n t a d i e n e s ... 38 ( i i ) M e t a l l o m e t h y l c y c l o p e n t a d i e n e s ... 41 ( i i i ) M e t a l l o p e n t a m e t h y l c y c l o p e n t a d i e n e s ... 45 ( i v ) M é t a l l o ( 1 - i n d e n e s ) ... 46 (v) l l e t a l l o c y c l o h e p t a ' t s i e n e s ■... ... '50 ( v i ) M e t a l l o c y c l o n o n a t e t r a e n é s ...' . . . 1 . ... 52 ^ ( v i i ) M e t a l l o c y c l o p r o p e n e s ... 52 ' ' ’ p . GENERAL EXPERIMENTAL ... 54 D . I . ' S p e c t r o s c o p i c Methods f o r C h a r a c t e r i z a t i o n ' Based on t h e N u c le a r P r o p e r t i e s o f I s o t o p e sI
o f t h e Group IVA E le m e n ts ... 54" ( i ) N u c l e a r M a g n e tic R esonance 54 ^ ( i i ) - Maisg S p e c t T o m e t r y ... ; . . . s . 56 ( i i i ) M ossbauer S p e c t ro é c o p y '59 D»2. , G e n e r a l E x p e r i m e n t a l P r o c e d u r e s *■ and I n s t r u m e 'n £ ^ t i o n * ... 61 INTRAMOLECULAR'REARRANGEMENT BEHAVIOUR OF TËÏiyUCIS(GYCLOPENTADIENYL) AND TETRAKIS(METHYLCYCLOPENTADIENYL) f DERIVATIVES OP'GERMANIUMCIV) AND TIN,(IV)... 6464
68 68
72 A. INTRODUCTION ... ) ... .
RESULTS AND DISCUSSION ... 3 , 1 . Mass S p e c t r a l D ata ... \ : ' B.'Z. M ossbauer S p e c t r a l D a ta ... . . . I . . » . . / e 3 . 3 . V i b r a t i o n a l S p e c t r a l D ata ... ‘ 3 . 4 . NMR D a t a ... 75 ( i ) M o n o h a p to c y c lo p e n ta d ie n y l, D e r i v a t i v e s ... 75 . ■ * ( i i ) M o n o h a p to in e th y lc y c lo p e n ta d ife n y l D e r i v a t i v e s . . . 80 C. EXPERIMENTAL ... 91 METALLOTROPISM AND STEREOMUTATION IN POLY(INDENYL) DERIVATIVES
OF GERMANIUM AND TIN' ... A. INTRODUCTION... ... B. RESULTS AND DISCUSSION... i ... ...
. 1 . Mass S p e c t r a l D a té . 13, 3 . 2 . C NMR D ata (i) SnPh3 (n -CgH^), (3^ ^ .... (ii) SnPh2 (n^-CgR^)2 ,(3 .3 ) . - . ( i i i ) ’ SnPh(n^-CgH.p3,(3.4) and Sn3u^(ri-CgHy) 2 » ( ^ . ^ ) . . . . ( iv ) Sn(n^“ CgHy)^, 0 . 6 , ) and 1 G e ( n 93 93 95 ' 9 5 9 8 9 8 1 0 4 1 0 8 112 3 . 3 . 1
.
H NMR D a t a ... »...C. THE CRYSTAL AND-MOLECULAR STRUCTURE OF ''
R,R,S,S-TETRA( 1-INDENYL)STANNANg...^... :... 124
*5 ’
v i i »
V
k
CONSEQUENCES OF CHIRALITY AT TIN IN SOME. STANNYLCYCLOPENTADIENE ANALOGUES... ' --- 132 . A. INTRODUCTION... 132 B. RESULTS... . 132 ♦ B . l . Mass S p e c t r a l D a t a ... 135 B .2 . ' NMR D a t a ... ... .. 135 ( i ) P r o t o n NMR D a t a . . . ... 139 ( i i ) 'C arb o n -1 3 NMR D a t a . . . ' . ... 147-C. DISCUSSION... ’. . ... 149 D. EXPERIMENTAL... ; ... 156
5 SYNTHESIS AND PROPERTIES OF SOME BIVALENT DERIVATIVES OF GERMANIUM AND TIN.*... 158
A. INTRODUCTION... : ... '... .’ . 1 5 8 B. RESULTS AND D IS C U S S IO N ... : ... 161 B . l . S y n t h e s i s and P r o p e r t i e s of ' * ^
k
Bis,(n - m e t h y l c y c l o p e n t a d i 'e n y l ) g e r m a n i u m ( l l ) . . . 161 B .2 . S y n t h e s i s and P r o p e r t i e s o f 1 , 3 - D i k e t o n a t o and R e l a t e d D e r i v a t i v e s o f G e r m a n iu in ( I I ) ...175 B .3 . S y n t h e s i s and S t r u c t u r e o f B i s ( t r i p h e n y l p h o s - p h i n e ) b i s [ b i s ( a c e t y l a c e t o n a t o ) g e r m y l e n e ] - and B i s ( t r i p h e n y l p h o s p h i n e ) b i s [ b i s ( a c e t y l a c e t o n a t o ) - ' I • s t a n n y l e n e ] - p l a t i n u m ( G ) ... ‘ ... 191J
\ REFERENCES C. EXPERIMENTAL... ... ... 197LIST OF TABLES \ -T a b l e No. « 1..1(a) S e l e c t i o n r u l e s f o r an a llo w e d s i g m a t r o p i c s h i f t o f o r d e r [ l , j } o f a h y d ro g en a t o m ... 29 1 . 1 ( b ) G e n e r a l s e l e c t i o n r u l e s f o r t h e r m a l l y a llo w e d s i g m a t r o p i c s h i f t s . . . ' ... 30 1 .2 A pproxim ate tim e s c a l e s f o r some d i f f e r e n t
e x p e r i m e n t a l t e c h n i q u e s ... .'... 33 1 .3 P e r c e n t a g e n a t u r a l abundance o f NMR a c t i v e
i s o t o p e s of t h e group IVA e le m e n ts h av in g . 1 « 1/2 .*... 54
29 i l 9
1 .4 R e p r e s e n t a t i v e exam ples of (a)^ S i a n d ( b ) , Sn
c h e m ic a l s h i f t s ... 55 * 4 1 .5 P e r c e n t a g e n a t u r a l ab undance o f i s o t o p e s o f , t h e group IVA e le m e n ts ... '... ] ... 57 1 . 6 I o n i z a t i o n p o t e n t i a l s f o r . t h e group IVA e l e m e n t s ...58 1 .7 T y p i c a l v a l u e s o f t h e is o m e r s h i f t and q u a d r u p o l e s p l i t t i n g f ^ some t i n - c o n t a i n i n g compounds ... 58 1 . 8 I n s t r u m e n t a t i o n , ... X ... 62 1 .9 S t a r t i n g ^ m a t e r i a l s , ... 63
\
i . l E s t i m a t e d c o n c e n t r a t i o n s o f is o m e rs 1 and 2 i n , 1 ^ \ , ■ MR^(n -C ^ H ^ C H ^ )- ty ^ s y s te m s ... 65 , \ 2 . 2 p h y s i c a l and a n a l y t i c a l d a t a f o r ^ompounds 2 : ^ - 2 . 6 .692 . 3 Mass s p e c t r a l d a t a f o r (a) HR and (b) MR^Cl ... 70 119
2 . 4 Sn M dsdbauer d a t a fo r'c o m p o u n d s X 2 a n d ... 72 2 . 5 Is o m e r s h i f t v a l u e p f o r some S nR ^-type compounds ... 73
I X . 2 . 6 Q u ad ru p o le s p l i t t i n g v a l u e s f o r sbme , SnR„Cl - t y p e compounds ... ...) 73 * . 2 . 7 I n f r a r e d s p e c t r a , 2800 - 3200 cm r é g i o n # f o r com pounas_^._1 - 2 -A ... ... 74 2 . 8 H NMR d a t a f o r compounds
- 2 . ^
...76 2 . 9 NMR d a t a f o r t e t r a k i s , ( s i ^ - m e t h y l c y c l o p e n t â d i e n y l )- germane and - s t a n n a n e ^ compounds 2 -A
r e s p e c t i v e l y ...i ... 84 3.1 P h y s i c a l and a n a l y t i c a l d a t a f o r compounds _3*Ji. “
—‘È.
... 96 3 .2 Mass s p e c t r a l d a t a o b t a i n e d f o r compounds _3*A “A'È.
... 97L3_ ^ „1 2 , „3
3 .6 S t e r e o i s o m e r i s m i n p o l y i n d e n y l d e r i v a t i v e s . . . . ' ... 117
3 .7 NMR d a t a f o r compounds 3^*1. ~ 119
3 . 8 Bond d i s t a n c e s d e t e r m i n e d f o r R , R , S , S - t e t r a ( l - i n d e n y l ) t i n . 126 3 .9 Bond a n g l e s d e t e r m in e d f o r R , R , S , S - t e t r a ( l - l n d e n y l ) t i n . . . . 127. 4 .1 P h y s i c a l and a n a l y t i c a l d a t a f o r compounds A*A “ 4 . ^ . . . 134 4 .2 M a s s ‘s p e c t r a l d a t a f o r compounds “ A 'A
( S n ( M e ) ( i - P r ) ( P h ) C p ' ) ... 136 3 . 3 C NMR r e s o n a n c e s a s s i g n e d t o C , C a n d C of t h e ;
i n d e n y l r i n g s i n compounds _3*i. “
A'È.
... 101 3 .4 NMR r e s o n a n c e s a s s i g n e d t o a n d ' o f th e i n d e n y l r i n g s i n -compounds _3*A “ ' 102 13 3 .5 C NMR r é s o n a n c e s f o r t h e p h e n y l g ro u p s o f 1 ‘ • SnPh^ -C gH ^)^, n = 0 , 1 , 2 , 3 , and t i - b u t y l g roup o f S n (B u^)(n^-C gH ^)^ ... n ... 103/ s :
^ . * i ^ -\ 4 . 3 “InMR .data f o r t h e m e t h y l c y c l o p e n t a d i e n y l , ' p e n t a m e t h y l c y c l o p e n t a d i e n y l and i n d e j i y l g ro u p s o f c o m p o u n d s ^ « 2 “ !L ‘!L * • • *... 4 . 4 . NMR d a t a f o r tlie m e t h y l , i s o p r o p y l and p h e n y l g ro u p s o f compounds * 1^5 4 .5 . NMR d a t a f o r t h e m e t h y l , i s o p r d p y l a n d 'p h e n y l g ro u p s i • o f compounds ^._2 - _ • • 146 P h y s i c a l and a n a l y t i c a l d a t a f o r compounds _5«1 5.'3 - 5 . 1 2 ... 5 .2 Mass s p e c t r a l d a t a f o r b i s ( n ^ - m e t h y l c y c l o p e n t a d i e n y l ) - g e r m a n iu m ( I I ) aqd - t i n ( I I ) , ... 1^3 5 . 3 NMR d a t a f o r compounds _5.J^ and _5.^... 5^4 Mass s p e c t r a l d a t a f o r compounds ^ . 2 “ 2 'É " " ' - \ ... 5 . 5 . I n f r a r e d c a r b o n y l , s t r e t c h i n g f r e q u e n c i e s f o r 171 compounds 2 ' 2 ' 2 "A...2 * 2 ... ... .. Î 173 5 .6 NMR d a t a f o r compounds _5*2... 2 ^ 2 ...‘
5 , 7 ’ NMR d a t a f o r compounds 2 * 2 ... 2 * 2 ... * A • 5 . 8 Mass s p e c t r a l d a t a f o r compounds 2 * 2 “ 2 * 2 2 ... 5 .9 . I n f r a r e d c a r b o n y l s t r e t c h i n g f r e q u e n c i e s f o r ■ 179 compounds 2 * 2 “ 2 *i2 * * *... *... 1 182 5 .1 0 H NMR d a t a f o r compounds 2 * 2 " 2 ' 2 2 ... 5.11 NMR s p e c t r a l d a t a f o r compounds 2 * 2 " ..2 * 2 2 ... 5 .1 2 I n f r a r e d s t r e t c h i n g f r e q u e n c i e s f o r compounds 185 5 . 1 3 a n d ' 5 . 1 4 . ... » 185 5 .1 3 - NMR d a t a f o r compounds 2 * 2 2 2 * 2 2 ... S' , ' 186 ■ 5 ,1 4 S t r u c t u r a l d a t a f o r s o m e p l a t i q u m ( O ) / c o m p l e x e s ...x i
’ . LIST OF FIGURES F i g u r e 1 .1 Prop.osed(<in—pit o v e r l a p i n some s i l i c o n compounds ...I
... 2 1 .2 The s o l i d s t a t e s t r u c t u r e o f b i s ( n ^ - c y c l o p e n ' t a d i e n y l ) l e a d ( I I ) ... 1 2 1 .3 The c r y s t a l s t r u c t u r e o f ( p e n t a h a p t o c y c l o p e n t a d i e n y l ) -t i n c h l o r i d e .'...-... I ■ 1 .4 The c r y s t a l s t r u c t u r e o f ( n^-CgH^)Pb(AlCl^) 2 * . . . 15 / 1 . 5 The c r y s t a l s t r u c t u r e o f Cr(CO) c-M[CIJ.(-SiMe>iL^ * M = Ge and Sn ... . '. 16 t ” 1 .6 The c r y s t a l s t r u c t u r e o f Cr(CO)^Sn(Bu“ ) 2 ( p y r i d i n e ) ... 17 1 .7 The c r y s t a l s f r u c t u r e o f S n (IV )P h 2S n ( I I ) N 0 2 ... 18 1 . 8 ( a ) S u p r a f a c i a l m i g r a t i o n o f a h y d ro g e n atom ‘. ... 28 1 . 8 ( b ) A n t a r a f a c i a l m i g r a t i o n o f a h y d ro g e n a t o m ) .." ... 28 , • \ ' . - ' 1 . 9 ( a ) P o s s i b l e [ 1 ,3 ] s i g m a t r o p i c m i g r a t i o n s ... 30 1 . 9 ( b ) P o s s i b l e [ 1 , 5 ] s i g m a t r o p i c m i g r a t i o n s ... 30 / 1 .1 0 The ^^^Sn M ossbauer is o m e r ë h i f t c s c a l e ... 60 1 2 . 1 F r a g m e n t a t i o n pathw ays f o r Ge(n ^Cl ... 711 ■ 2 . 2 ■ V a r i a b l e t e m p e r a t u r e 9CMHz H MMR s p e c tru m o f G e ( n ^ - C 'H .) ' 2 .1 ... 78
J D 4 ' — 1 -2 . 3 R o o m -tem p era tu re 90MHar H NMR s p e c tr u m o f I " Sn(ri —C^H^CH^)^ ... 81
* I , 2 . 4 R o o m -te m p e ra tu re NMR s p e c tru m o f SnCr/^CgH^CHg)^ ... ... / 82
f 2 . 5 2 . 6 ' 3 . 1 ' , / - T \ 3 . 2 . 3 .3 3 . 4 3 .5 ■ 3 .6 ' 3 .7 3 . 8 3 . 9 3 .1 0 3.11 3 .1 2 ë 90MHz E NMR s p ectru m , o f ^ ^ ./ ■ 'v. ' 1 o Ge(n -C^H^CHg)^ a t 27°C ... 86 13 f ' V a r i a b l e t e m p e r a t u r e C NMR s p e c tr u m o f
'
1^
w
Ge(n -CgH^CHg)^... ... 87 H • ^ X 3 ^ ' a, • V a r i a b l e t e m p e r a t u T e ^ G.NMR s p e c tr u m o f I-SnPh ( n ‘ -C H ) , 3 . 2 , . . . . ; . . . . r . . . ... 99 a - ? - : , 13 ■ 1 ■ ' .. - V a r i a b l e t e m p e r a t u r e , ë NMR s p e c tr u m o f ’ SnPhg(n^-CgH^)^, _ 3 - i“ *... . 105 The p o s s i b l e is o m e r s p r e s e n t i n MR^Cn^-CgHy)g - ... 107 ' 1*3 V a r i a b l e t e m p e r a t u r e C NMR s p e c tr u m o f ' ' . / SnCBuS^Cnl-CgH,)], 3 ^ 5 ... / ...: . . . . t . . 109 / The p o s s i b l e is o m e r s p r e s e n t i n MR(n^-CQH.,) „,R=Bu2^, P h . . i . . , . l i c r y / J 6 1 O « 1 The p o s s i b l e is o m e r s p r e s e n t i n , ' t r i s - l “ ( 2- m e t h y l n a p h t h y l ) b o r a n e . ... ; ...m * ■ 5 -13 - V a r i a b l e t e m p e r a t u r e C NMR s p e c tr u m of S n X n l-C g H ,)4 ,^ 3 ^ & ;... ...113. 1' The p o s s i b l e is o m e r s p r e s e n t i n M(n -C gH ^)^, M=Ge, Sn... 115 13 ■ 1 ‘ C o m p a r^o n o f C NMR s i g n a l s , a t t r i b u t a b l e t o in d e n y l - C n u c l e i i n compounds ^hJL_ - ,3._6. ... I . . . . IJLB 1 ' V a r i a b l e temperature*-90MHz H NMR s p e c tr u m o f S n ( B u ^ ) ( n ^ - C g H p 2 i n CDCl^'... . . . 1 2 0 ' 2 V a r i a b l e t e m p e r a t u r e 9CIMHz H NMR s p e c tru m o f « S n(n^-C Hy)^ i n CDCl ___ '... ' ...'...121 The m o l e c u l a r s t r u c t u r e f o r R , R , S , S - t e t r a ( l - i n d e n y l ) t i n ( I V ) .125' % . '
' x i i i
4 .1 S y n t h e t i c scheme u sed t o p r e p a r e 4n(Me) ( i - P r ) (Ph) (B r) ,_4.J^... ,...133 ’ 1 ' , 4 . 2 90MHz H NMR s p e c tr u m o f. . . . * ' y S n (M e ) ( i - P r ^ P h ) [n - C g C G H g ) ^ ] , ^.2^ a t 2 7 C ...1 3 7 ’ 1 3 4 . 3 C NMR s p e c t r u m o f Sn(M e) ( i - P r ) (P h ) [ n ^ ' C C H ^ ) g ] , 4 . 2 ... 1 3 8 4 . 4 - 30MHz ^H NMR s p e c t r u m d f S n ( M e ) ' ( t - P r ) ( P h ) , 4._3 a t 2 7 ° C ...‘... 4 . 5 NMR s p e c t r u m o f S n (M e ) ( i - P r ) ( P h ) (fi^-C^H^CH^) , ^._3* • • 1^1 4 . 6 90MHz v a r i a b l e t e m p e r a t u r e ^H NMR s p e c t r u m o f S n (M e) ( i - P r ) ( P h ) ( n ^ - C g H ^ , 4 . 4 ... 1 4 2 13 4 . 7 V a r i a b l e t e m p e r a t u r e C NMR s p e c t r u m o f S n (M e) ( i - P r ) (P h ) ( n ^ - C ^ H ^ ) , 4 . 4 • • 14 3 4 . 8 I s o m e r s p r e s e n t i n s i g n i f i c a n t c o n c e n t r a t i o n i n ^ S n ( M e ) ( i - P r ) ( P h ) ( n l - C 5 H 4 C H 2 ) , 4 / 3 ... 15 1 4 . 9 T h e d i a s t e r e o i s o m e r s ^ an d ^ p r e s e n t i n S n ( M e ) ( t - P r ) ( P h ) ( n ^ - C g H , ) , 4 ^ 4 ... f . . ... 1 5 2 1 3 ' ' * ' 5 . 1 , Ç NMR s p e c t r u m o f ' b i s ( n ^ - m e t h y l c y c l o p e n t a d i e n y l ) g e r m a n i u m ( I I ) a t 2 5 C . . . 1 6 5 5 . 2 ^H NM R ^spectrum o f b i s ( a c e t y l a c e t o n a t o ) g e r m a h i u m ( I X ) i n CDCl^ a t 2 7 C . . . 1 8 1 5 . 3 T h e m o l e c u l a r s t r u c t u r e o f 5 . 1 4 , b i s ( t r i p h e n y l p h o s -p h i n e ) b i s [ b i s ( a c e t y l a c e t o n a t o ) s t a n n y l e n e ] -p l a t i n u m ( 0 ) ... 1 8 9 5 4 ^ h e l o c a l g e o m e t r y a b o u t t i n i n b i s ( t r i p h e n y l p h o s -p h i n e ) b i s [ b i s ( a c e t y l a c e t o n a t o ) s t . a -p n y l e n e ] -p l a t i n u m ( 0 ) . . y . . 1 9 0x i v LIST OF ABBREVIATIONS acacH Bu^ E t IR i - P r Me MS ' NMR Ph ppm R THF TMP TMS a c e t y l a c e t o n e
tertiaryh xxtyl
e t h y l i n f r a r e d i s o p r o p y l m e th y l mass s p e c tru m n u c l e a r m a g n e t i c r e s o n a n c e p h e n y l Af
p a r t s p e r m i l l i o n ^ a l k y l o r a r y l t e t r a h y d r o f u r a n t r i m e t h y l p h o s p h i t e t e t r a m e t h y l s i l a n e%
' J • à XV ■ACKNOWLEDGEMENTS < I would- l i k e ' t o th a n k Dr. S. R. S t o b a r t f o r h i s a d v i c e and s u p p o r t t h r o u g h o u t t h e p a s t ^-several y e a p s
i---I would a l s o l i k e ‘s t o ,th a n k t h e . U n i v e r s i t y of V i c t o r i a and " th e R e s e a r c h C o r p o r a t i o n ( C o t t r e l l F o u n d a tio n ) f o r f i n a n c i a l
( .
^ v i
-4A
To H elen . ;I
. %^
x v i i
PREFACE
The work d e s c r i b e d i n t f t l s ^ h e s i s d e a l s w i t h t h e s y n t h e s i s and p r o p e r t i e s o f a v a r i e t y o f compounds o f germanium and t i n . C h a p t e r One o u t l i n e s t h e s c o p e o f t h e t h e s i s and p r o v i d e s b ack g ro u n d
. i n f o r m a t i o n t o work c o n t a i n e d . i n t h e s u b s e q u e n t c h a p t e r s . I n C h a p t e r Two t h e n o n - r i g i d p r o p e r t i e s a s s o c i a t e d j^ ith m e t a l l o c y c l o p e n t a d i e n e s and m e t a l l o m e t h y l c y c l o p e n t a d i e n è s is ,, . 1 13 examined th ro u g h th e u se of v a r i a b l é t e m p e r a t u r e H and C NMR s p e c t r o s c o p y . R e l a t e d m i g r a t i o n s i n p o l y i n d e n y l d e r i v a t i v e s o f germanium and t i n a r e r e p o r t e d i n C h a p te r T h r e e . C h a p t e r F our l i s t s i n f o r m a t i o n d e r i v e d a b o u t t h e r e a r r a n g e m e n t p r o c e s s e s i n p e n t a m e t h y l c y c l o p e n t a d i e n e , m e t h y l c y c l o p e n t a d i e n e and i n d e n e r i n g s y s te m s b e a r i n g a c h i r a l t i n s u b s t i t u e n t . C h a p te r F iv e d e s c r i b e s both- t h e p h y s i c a l and c h e m ic a l
p r o p e r t i e s of*a number o f new d e r i v a t i v e s o f b i v a l e n t germanium,
and t i n i ' .
INTRODUCTION
A. ^GENERAL ' '
The u n iq u e p o s i t i o n o f c a rb o n among t h e n i n e t y n a t u r a l e le m e n ts i s p r i m a r i l y t h e r e s u l t o f i t s a b i l i t y t o form s t a b l e l o n g - c h a i n and x y c l i c compounds h a v i n g a d j a c e n t ' c a r b o n atoms, c^ nrfected by s i n g l e , d o u b le o r t r i p l e b o n d s . The v a l e n c e s t a t e o f c a rb o n i n su ch compounds i s i n v a r i a b l y f o u r , a s i t u a t i o n p a r a l l e l e d by t h e lo w er group IVA e le m e n ts i n t h e m a j o r i t y o f t h e i r known compounds. I n t h e l a t t e r t h e c o o r d i n a t i o n ^
^
number i s a l s o o f t e n f o u r , t h e c e n t r a l ' a t o m assum ing a geometry w hich c l o s e l y a p p r o x im a te s t o t e t t a h e d r a l , b u t t h e te n d e n c y
to w a rd s a d o p in g h i g h e r c o o r d i n a t i o n numbers i n c r e a s e s w i t h
1 2 3 2 3
i n c r e a s i n g atOTiic number. ’ ’ ■ T h i s i s th o u g h t to be f a c i l i t a t e d i n p a r t by u t i l i z a t i o n of v a c a n t o u t e r
nd
o r b i t a l s , and l e a d s t o c o o r d i n a t i o n numbers of f i v e and s i x th r o u g h b o t h i n t e r - and i n t r a - m o l e c u l a r c o o r d i n a t i o n . E i g h t d o o r d i n a t e • s p e c i e s have b e e n c h a r a c t e r i z e d’
f o r b o th t i n and l e a d .T h e m u l t i p l e bonds o b s e r v e d in ' c a rb o n c h e m i s t r y w hich . r e s u l t |ro m o v e r l a p b e tw e e n s i n g l y o c c u p ie d 2p o r b i t a l s on ,
a d j a c e n t c a rb o n atoms a r e n o t a f e a t u r e o f t h e c h e m i s t r y o f t h e o t h e r g roup IVA e l e m e n t s . R e c e n t l y , how ever, a v a r i e t y of i n t e r m e d i a t e s c o n t a i n i n g s i l i c o n - c a r b o n d o u b le bonds have b e e n p o s t u l a t e d ; and a t h e r m a l l y s t a b l e example
J , .
^ M u lti^ 'le - b o n d c h a r a c t e r o f a d i f f e r e n t t y p e , a r i s i n g from o v e rla p /.b e tw e e n v a c a n t
3d
o r b i t a l s on s i l i c o n and f i l l e d "non b o n d in g " o r b i t a l s on a d j a c e n t ' a t o m s , (F ig 'u re 1 . 1 ) h a s b een7 8 “ 5 * * ^ ^
p ro p o s e d ’ feo e x p l a i f i t h e s t r o n g e r s i l i c o n - h a l o g e n bonds compared to* c o r r e s p o n d in g c a r b o n - h a l o g e n b o n d s , and t h e s t r u c t u r a l
,
p l a n a r i t y and low er b a s i c i t y o f s i i y l a m i n e s compared t o carb o n a n a l o g u e s . ' T h is e f f e c t i s g r e a t e s t f o r s i l i c o n and much l e s s C a p p a r e n t i n t h e c h e m i s t r y o f germanium, t i n , a n d l e a d .
S i
\
FIGURE 1 . 1 . P ro p o se d
d»
- p " o v e r l a p i n some s ili c o n .p o m p o u n d s .The g roup IVA e le m e n ts h a v e an o u t e r v a l e n c e g h e l l g r o u n d
-^
2 1 1
s t a t e e l e c t r o n i c c o n f i g u r a t i o n o f ns np
np
, w here n changes from 2 f o r carb o n t q 6 f o r l e a d . The b i v a l e n t s t a t e r e q u i r e s o n ly two e l e c t r o n s t o form t h e two bonds i n , f o r exam p le,, w h i l e f o r t h e q u a d r i v a l e n t s t a t e one e l e c t r o n must be prom oted from t h e n s o r b i t a l to t h e np o r b i t a l t o g i v e t h e o u t e r e l e c t r o n
'
2
1
1
1
-
'
.
c o n f i g u r a t i o n ns np np np : t h i s a l lo w s f o r t h e f o r m a t i o n
Ni
The r e l a t i v e s t a b i l i t i e s o f t h e s e two o x i d a t i o n s t a t e s a r e t h u s . c o n t r o l l e d by ( i ) s i z e o f p ro m o tio n e n e r g y , and ( i i ) i b o n d s t r e n g t h s , i.e. f o r m a t i o n o f f o u r bonds i n as compared t o o n ly two in.MA^. D e c r e a s e i n t h e (group I V A ) - ( o t h e r e le m e n t) bond s t r e n g t h as t h e group i s d e s c e n d e d a l lo w s a b a l a n c e t o b e s t r u c k whereby t h e e n e rg y r e q u i r e d f o r e l e c t r o n p ro m o tio n i s co m parable to t h a t a c h i e v e d by a d d i t i o n a l bond f o r m a t i o n .pnd Q i s t h e b a s i s ^ o f t h e s o - c a l l e d " i n e r t p a i r e f f e c t " . Compounds h a v in g carb o n i n t h e b i v a l e n t s t a t e ( c a r b e n e s ) 10 w ere f i r s t p ro p o s e d as i n t e r m e d i a t e s a b o u t t h e end o f t h e n i n e t e e n t h c e n t u r y . T h ese h i g h l y r e a c t i v e s p e c i e s a r e used e x t e n s i v e l y as
in s i t u
r e a g e n t s i n o r g a n i c c h e n i s t r y , t y p i c a l l y Aindergoing a v a r i e t y o f i n s e r t i o n r e a c t i o n s and a d d i t i o n st o o l e f i n s g i v i n g c y c l b p r o p a n e s . C arb en e s can have e i t h e r a s i n g l e t (_1) o r t r i p l e t ( ^ and _3) s p l n ^ t a t e . ' R e s u l t s
from e x p e r i m e n t a l o b s e r v a t i o n and t h e r e o r e t i c a l c a l c u l a t i o n s i n d i c a t e t h a t most c a r b e n e s have a n o n - l i n e a r t r i p l e t ground
s t a t e (i.e. ^ ) , how ever d i h a l o g e n o c a r b e n e s and c a r b e n e s w i t h oxygen, n i t r o g e n o r s u l f u r a t t a c h e d t o t h e b i v a l e n t c a rb o n may have
s i n g l e t g round s t a t e s (ie , 1) .
C arbenes a r f m ost o f t e n p r e p a r e d f r o m . t h e c o r r e s p o n d in g d i a z o a l k a n e ( e q n a t i o p ( 1) ) ; how ever t h e r e a r e a v a r i e t y
R^R^C = Ng ---:CR^R^ + N g ... ( 1 )
o f o t h e r u s e f u l m ethods and t h e s e h a v e b e e n d i s c u s s e d i n d e t a i l e l s e w h e r e . T r a n s i t i o n m e t a l com plexes have b e e n used
t o s t a b i l i z e a v a r i e t y of c a r b e n e s , t h e c a r b e n e f u n c t i o n i n g as a two e l e c t r o n d onor (Lewis b a s e ) to w a rd s t h e m e t a l . T hese compounds have b e e n p r e p a r e d by s e v e r a l d i f f e r e n t methods
12 one o f t h e m ost c o n v e n i e n t i n v o l v i n g a d d i t i o n o f an o r g a n o - l i t h i u m r e a g e n t t o a c o o r d i n a t e d c a r b o n monoxide m o le c u le f o ll o w e d by a l k y l a t i o n ( e q u a t i o n ( 2 ) ) . RgO"^ M(CO) + L i R > L i ' ^ [ M - c t ° ] " --- ^2) I n c o n t r a s t w i t h t h e s p e c i a l c h a r a c t e r o f c a r b e n e s , t h e f e ' -1 3 “
a r e numerous exam ples o f s t a b l e i n o r g a n i c d e r i v a t i v e s of b i v a l e n t germanium ( g e r m y l e n e s ) , t i n (s ta n n y le n e s % and l e a d
( p l u m b y l e n e s ) . W hile t h e s e compounds do n o t c o n t a i n m e t a l - m e t a l b o n d s , .th e y f r e q u e n t l y have s t r u c t u r e s b a s e d on b r i d g e d p o ly m e r ic -arr.ays i n t h e s o l i d s t a t e . The g a s p h a s e s t r u c t u r e s of two e x a m p le s ,
S i p 2 and S n C l ^ j ^ ^ h a v e b e e n d e t e r m in e d and b o th have t h e b e n t s t r u c t u r e ^ c o n s i s t e n t w i t h s t e r e o c h e m i c a l a c t i v i t y o f
___M: 4
t h e n o n - b o n d in g e l e c t r o n p a i r . T h e s e compounds a r e s i g n i f i c a n t l y l e s s r e a c t i v e th a n t h e c o r r e s p o n d i n g c a r b e n e d e r i v a t i v e s a l t h o u g h t h e y u ndergo s i m i l a r r e a c t i o n s : f o r exaA ple ge.rmanium(II)
16 and t ï n ( I I ) d i h a l i d e s r e a d i l y i n s e r t i n t o c a r b o n - h a l o g e n b o n d s . I n t e r e s t i n g l y , t h e r e a c t i o n o f G eig w i t h c e r t a i n a c e t y l e n e s h ad 17 * b e e n r e p o r t e d t o g i v e t h e t h r e e membered r i n g (_5) . I t 18 h a s s u b s e q u e n t l y b een shown*' t h a t t h e p r o d u c t i s i n f a c t t h e s i x membered r i n g ( 6)- c o n t a i n i n g two germanium atom s.
R-" R
5 ' 6
G erm anium (II) and t i n ( I I ) d i c h l o r i d e s a r e e a s i l y c o n v e r t e d 9 t o t h e t e t r a c h l o r i d e s by r e a c t i o n w i t h C I 2 , ( e q u a t i o n s (3) and ( 4 ) ) 9 however i n t h e c a s e o f l e a d f o r c i n g c o n d i t i o n s a r e n e c e s s a r y , t h e t e t r a c h l o r i d e r e v e r t i n g e x p l o s i v e l y t o t h e d i c h l o r i d e a t t e m p e r a t u r e s above c a ,2 0 ° C ( e q u a t i o n (5) ) , r e f l e c t i n g t h e g r e a t e r therm odynam ic s t a b i l i t y o f t h e lo w er o x i d a t i o n s t a t e f o r l $ a d . r a p i d " O e C l , " + U t 2 5 ° C ) " - < 3 ) =" “ 2 " “ 2 ' " " 4 ... •'... PbCl^ PbClg + C l g ...(5)
The f i r s t a u t h e n t i c o r g a n o m e t a l l i c d e r i v a t i v e s t o be p r e p a r e d i n w hich t h e m e t a l ( m e t a l l o i d ) i s i n t h e b i v a l e n t
19
s t a t e w ere t h e c y c l o p e n t a d i e n y l d e r i v a t i v e s , M(CgHg)2 , M = Ge, S n , ^ ^ and P b, a l t h o u g h o l i g o m e r i c q u a d r i v a l e n t o r g a n o m e t a l l i e s 21 had b e e n i n c o r r e c t l y i d e n t i f i e d as su ch p r e v i o u s l y . - S t r u c t u r e s i n w hich t h e m e t a l ( m e t a l l o i d ) i s bonded t o two q^ -C ^H ^-rings,,22 23 a s shown i n
1_,
h av e b e e n e s t a b l i s h e d . ’ A summary o f t h e p r o p e r t i e s o f compounds l i k e 7_ i s g i v e n i n S e c t i o n B t o g e t h e r w i t h a r e v ie w o f t h e c h e m i s t r y o f o t h e r d e r i v a t i v e s i n w hich t h e g roup IVA e le m e n t i s i n t h e b i v a l e n t s t a t e . M M = Ge, Sn, and Pb. By c o n t r a s t w i t h _7, c y c l o p e n t a d i e n y l d e r i v a t i v e s in^ w hich t h e m e t a l i s in t h e +4 o x i d a t i o n s t a t e i n v o l v e b o n d in g t o t h e ^ / s a t u r a t e d c a rb o n atom o f t h e C ^ - r i n g , as shown i n . M = Ge, Sn, and Pb. T hqse m o l e c u le s e x h i b i t n o n - r i g i d c h a r a c t e r i s t i c s a s s o c i a t e d w i t h t h e m i g r a t i o n o f t h e m e t a l atom around t h e f i v e carb o n9A * * '
atoms o f ' t h e C ^ - r i n g ( e q u a t i o n ( 6) ) .
^
c x
“
Hf i v e r i n g p r o t o n s ^and r i n g c a r b o n s ) , and b r i n g s a b o u t o b s e r v a b l e e f f e c t s i n t h e ahd ^^C’ NMR s p e c t r a o f many r e p r e s e n t a t i v e s . The n o g r r i g i d c h a r a c t e r o f m e t a l l o c y c l o p e n t a d i e n y l s and r e l a t e d c y c l o p o l y e n y l s y s t e n E x p e r i m e n t a l t e ts i s r e v ie w e d i n * S e c t i o n C. Echniques r e q u i r e d by t h e c h a r a c t e r i s t i c p r o p e r t i e s o f g roup IV A -elem ent compounds, t o g e t h e r w i t h a s s o c i a t e d s p e c t r o s c o p i c and s y n t h e t i c m e th o d s , a r e d i s c u s s e d
B. STRUCTURE AND' REACTIVITY OF ORGANOMETALLIC AND ORGANIC w
DERIVATIVES OF BIVALENT GERMANIUM, TIN, AND LEAD.
B . l . S y n t h e s i s . A tte m p ts t o s y n t h e s i z e o r g a n o d e r i v a t i v e s o f b i v a l e n t t i n ». n 1 d a t e b a c k t o t h e m i d d le o f t h e n i n e t e e n t h c e n t u r y , when V r e a c t i o n s o f o r g a n o l i t h i u m o r organomagnesium h a l i d e s w i t h t i n ( j [ I ) . h a l i d e s y i e l d e d h i g h - m e l t i n g , r e l a t i v e l y i n s o l u b l e , ^ t i n c o n t a i n i n g p r o d u c t s . I t was l a t e r shown^^’ ^^ t h a t t h e s e m a t e r i a l s w ere i n f a c t m i x t u r e s o f compounds c o n t a i n i n g e i t h e r r i n g s , and o r ^ s t r a i g h t o r b r a n c h e d c h a i n s ,
e,ff, n
, o f t i n a to m s , t h u s i n v o l v i n g t h e m e t a l i n a f o r m a l l y q u a d r i v a l e n t s t a t e . RgSn RgSn SnR„ SnR„ SnR„ RgSn '•SnR., SrtR. SnR, RgSn S n SnR^ SnR, 10 11Group IVA compounds' may be c a t e g o r i z e d as f o l l o w s ;
.
(1) Organogroup IVA compounds; compounds w hich c o n t a i n a t l e a s t one g ro u p IVA e le m e n t - c a rb o n b o nd.
(2) O rg a n ic compounds; compounds w hich c o n t a i n one o r more o r g a n i c g r o u p s , b u t h a v e no g ro u p ,IV A - c a rb o n bond. (3) I n o r g a n i c compounds; compounds w hich do n o t b e lo n g to
/
2 9 ,3 0
t
^do however r# g z t, w i t h b i v a l e n t germanium, t i n , and l e a d h a l i d e s t o g i v e t h e c o r r e s p o n d i n g B i v a l e n t g roup IVA compound, e q u a t i o n s (7) and ( 8 } r e s p e c t i v e l y . SnCl2 +,2Li(C gH g) --- ÿ " S nC n^-C ^H ^g + Z p iC l (?) P b C l . + . Z l i C H C S i M e ^ ) ^— ^ P b [CH(SiMe^ ) 2 • •... ...(&) ’ S i m i l a r r e a c t i o n s u s i n g t h e l i t h i u m o r 'sodium s a l t s o f a c e t y l a c e t o n ç ^ 3 Ï ( e q u a t i o n (9) ) o r h e x a m e t h y l d i s i l 'a z a n e (HN (SiMe^) g) , ( e q u a t i o n (10)
)■ ,
a l s o a f f o r d b i v a l e n t group IVA d e r i v a t i v e s . C s G e C l g + 2Na(acac) ——> - , G e ( a c a c ) ^ • ! • • • • / ...(9) SnClg + 2Li[N^SiMe2)2]2 — ^ Sn[N(SiMe2) 2] 2 ... (1°)The t i n c y c lo p en ta d ien y ls^ ..* S n (n ^ -G ^ H ^ )2^ anà Sn(ri -G^H^CHg)2 , h av e been shown ^ * t o b è u s e f u l p r e c u r s o r s t o a v a r i e t y o f p r e v i o u s l y unknown, o r o t h e r w i s e d i f f i c u l t t o p r e p a r e d e r i v a t i v e s _ o f b i v a l e n t t i n , e q u a t i o n s ( 11 ) and ( 12) . ^ < S n ( n -CgH ) 2 + 2HCN *---^ S n ( C N ) 2 ... ( 1 1 ) * + 2 I ^ ( 12) I
The r e a c t i o n of t i n ( I I ) halid#% w i t h compounds h a v in g an a c i d i c h y d ro g e n , i n thfe p r e s e n c e p f t r i e t r h y la m in e g i v e s t h e c o r r e s p o n d i n g
t ■* _ ' ' ' ' *■
35 36
^
^ t i n ( I I ) d e r i v a t i v e ( e q u a t i o n (13) ) , ’ ‘ '
SnCl2 + 2MeOH + 2 N E tg ^ S n ( 0Me) 2 + TMEt^HCl. . ... ("l3)
_ . ' '
10 w h i l e r e l a t e d ^ r e a c t i o i i s _ , f ^ g e rm a n iu m (II) h a l i d e s h av e r e c e n t l y b e e n r e p o r t e d , e q u a t i o n ( 1 4 ) . CsGeClg + 2 2NEt„ -2NEt_HCl -C sC l . . ( 1 4 ) A l t e r n a t i v e methods f o r t h e s y n t h e s i s o f t h e s e t y p e s o f compound a r e g e n e r a l l y l i m i t e d i n s c o p e , and have b e e n rev ie w e d e l s e w h e r e . 3?
A number o f compounds h a v e b e e n r e p o r t e d i n w hich t h e
« •
b i v a l e n t group IVA m e t a l ( m e t a l l o i d ) f u n c t i o n s as a n e u t r a l
! 38 39
t w o - e l e c t r o n d onor to w a rd s t h e t r a n s i t i o n m e t a l c e n t e r . ’
Where t h e b i v a l e n t group IVA d e r i v a t i v e i s s t a b l e , t h e t r a n s i t i o n m e t a l compound i s e a s i l y formed by d is p l a c e m e n t r e a c t i o n s 38 ‘ 39 s i m i l a r t o t h o s e shown i n e q u a t i o n s (15) and (16) 'M(CO)c.THF + Sn(n^-CfHc)2 (M = C r, Mo, and W) M(CO), + Sn[CH(SiMe_)2]2 ' (M = Cr and Mo) M(CO>^Sn(n - C . 11^)2... (15)
hv
M(CO)^Sn[CH(SlMe2)2J2-* • (16) S o m e - t r a n s i t i o n m e t a l d e r i v a t i v e s , f o r w hich t h e f r e e b i v a l e n t m e t a l com pound.is u n s t a b l e , h a v e b e e n p r e p a r e d b y " i n d i r e c t m e th o d s " . T h u s’ r e a c t i o n o f a c o o r d i n a t e d germanium d i h a l i d e k ' I w i t h two é q u i v a l e n t s o f an alkylma^nesl^ini h a l i d e g i v e s \ h e 40 ^o rg a n p g e rm a n iu m (II ) t r a n s i t i o n m e t a l complex a s shown i n e q u a t i o n (17.)
S i m i l a r l y t h e r e d u c t i o n o f q u a d r i v a l e n t t i n i n s u i t a b l y s u b s t i t u t e d 2— d i a l k y l t i n d i h a l i d e s by Cr(CO)^ , g i v e s t h e b a s e s t a b i l i z e d 41 compounds R.2 Sn(THF)Cr(C0 ) g ( e q u a t i o n ( 1 8 ) ) . , ‘ 9— THF Cr(CO)c + SnRgClg — Cr (CO) ^SnR2 (THF)... ^16) (R = Me, Bu^) B. 2. S t r u c t u r e *5 "The t r u e o r g a n o - t i n ( I I ) and l e a d ( I I ) d e r i v a t i v e s , b i s ( n -20 c y c l o p e n t a d i e n y l ) - t i n ( I I ) and - l e a d ( I I ) , w ere f i r s t r e p o r t e d by F i s c h e r and G ru b e r# i n 1956. W i l k i n s o n ' e t
al.
s u b s e q u e n t l y 42 r e p o r t e d t h e s y n t h e s i s o f t h e m e t h y l c y c l o p e n t a d i e n y l 5 19a n a l o g u e s , w h i l e t h e germanium compounds Ge(q -C jH ^ ) 2 and
5 s43
■ e,Ge(n h a v e ' b e e n i s o l a t e d more r e c e n t l y . A lth o u g h i t
20
was i n i t i a l l y s u g g e s t e d t h a t t h e t i n and l e a d c y c l o p e n t a d i e n y l s have t h e
sigma-hoxiàeà
s t r u c t u r e shown i n , c o m p ariso n o ft h e i r IR s p e c t r a w i t h t h a t o f f e r r o c e n e l e d P i p e r and W i lk in s o n
, ‘ 24
■to p r o p o s e t h a t t h e s e compounds had t h e a n g u l a r s a n d w ic h »
s t r u c t u r e shown i n 13.
M
12
■ 5 ' 5 * E l e c t r o n d i f f r a c t i o n s t u d i e s o f Sn(n and P b (n “ *^5^ 5 ) 2 22 h âv e shown t h a t t h e s e m o l e c u l e s a s s u m e , s t r u c t u r e j U U i n t h e g a s ' 5 23 p h a s e . The s o l i d s t a t e s t r u c t u r e o f Sn(n -C ^H ^)2h a s r e c e n t l y b e e n r e p o r t e d t o be m onom eric, h a v i n g d i s c r e t e u n i t s w i t h t h e a n g u l a r sandw ich s t r u c t u r e however t h e s o l i d s t a t e s t r u c t u r e. . .
*
.
44 o f t h e . l e a d compound h a s b e e n s h o r n by X -ra y c r y s t a l l o g r a p h y
'
t o be p o l y m e r i c . I n t h i s , compound eac h p a i r of l e a d atom s i s b r i d g e d b y . a c y e l o p e n t a d i e n y l r i n g , t h e p l a n e o f w hich i s a t r i g h t a n g l e s t o t h e l e a d - l e a d a x i s ; c o o r d i n a t i o n o f eac h m e t a l atom i s c o m p lete d by a t e r m i n a l n ^ -C ^ H ^ - r in g , ap shown i n F i g u r e 1 . 2 . P b Pb Pb FIGURE 1 . 2 . The s o l i d s t a t e s t r u c t u r e o f b i s ( n - c y e l o p e n t a d i e n y l ) l e a d ( I I ) The c r y s t a l s t r u c t u r e s o f t h e p e n t a m e t h y l c y c l o p e n t a d i e n y l s , \ 5 ‘ 4S 2 3 M [ r, -C_(CH_)_ ] „ , M = Sn and Pb, c o n s i s t o f d i s c r e t e monomeric 5 j C) Z u n i t s h a v in g t h e a n g u l a r , sa n d w ic h s t r u c t u r e d e p i c t e d i n 14 . 14 I
The r e l a t e d compound, Sn [n^-C^CCH^) ^ , formed by t h e r e a c t i o n o f Sn[n^-C^(CH2 ) ^ ] 2 w i t h HBF^, hp s a c r y s t a l s t r u c t u r e h a v in g p e n t a g o n a l p y r a m i d a l SnCn^-C^(CH^)^3 u n i t s i n w hich a l l f i v e t i n - c a r b o n d i s t a n c e s a r e a p p r o x i m a t e l y e q ü a l ( a v e r a g e 2 .4 6 S ) . The t i n atom o f t h e s e u n i t s i s f u r t h e r a s s o c i a t e d w i t h ' t w o f l u o r i n e atoms' o f t h e BF, c o u n t e r i o n . s ' 4 « 15 Sn ♦ '
/
5 47 The c r y s t a l s t r u c t u r e of Sn(n -C^H^)C1 c o n s i s t s of g ^ * Sn(n -C^H^)C1 u n i t s i n w hich t h e c y e l o p e n t a d i e n y l i s a s y m m e t r i c a l l y bound t o t i n , w i t h Sn-C bond d i s t a n c e s r a n g i n g from 2 .4 5 t o 2 . 7 4R.
The t i n atoms of a l t e r n a t e u n i t s a r e b r i d g e d by c h l o r i n e atoms • o f a d j a c e n t Sn(n^-C^Hg>Cl g r o u p s , a s s h o w n ,in F ig u r e 1 . 3 . ' Sn Sn Cl Cl Sn FIGURE 1 . 3 . The c r y s t a l s t r u c t u r e o f ( p e n t a h a p t o c y c l o p e n t a d i e n y l ) t i n c h l o r i d e .
A p a rt from t h e c y e l o p e n t a d i e n y l d e r i v a t i v e s . , t h e r e a r e r a t h e r few exam ples o f s t a b l e compounds w hich have a t i v a l e n t g e rm a n iu m , t i n , o r l e a d atom bonded d i r e c t l y t o c a r b o n . The
f i r s t , and somewhat e x o t i c ex am ples o f s u c h compounds w ere b i s t 2-p h e n y l“l , 2- d i c a r b a - c l o S ( ? - d o d e c a r b o r a n ( 1 2) - l - y l ] t i n ( I I ) 1 6 ajid I - g e r m a - , 1 - s t a n n a - , and l - p l u m b a - 2 , 3 - d i c a r b a - c Z o o O - d o d e ~ c a b o r a n e ( I I ) ,
14
Sn 1 6' Ph - ' , 2 17 M = G e ,S n , and Pb. c . 0 = B 27 28 L a p p e r te t al,
have r e p o r t e d ■’ t h e f i r s t s t a b l e a l k y l d e r i v a t i v e s - of b i v a l e n t germanium,, t i n , and l e a d ,M[CH(SiMe„)„ L , M = G e,S n, and Pb. A lth o u g h t h e germ a n iu m ' 28
and t i n compounds have b een shown t o be monomeric i n t h e
l i q u i d and v a p o u r p h a s e s , t h e c r y s t a l s t r u c t u r e o f Sn[ (CHCSlHe^)2^2 c o n s i s t s o f d i m e r i c u n i t s , w hich h av e b e e n s u g g e s t e d t o r e s u l t
from i n t e r a c t i o n betw een t h e o r b i t a l c o n t a i n i n g t h e n o n - b o n d in g e l e c t r o n p a i r on each t i n ato m ,a n d t h e v a c a n t o r b i t a l . o n t h e
a d j a c e n t t i n a to m ,a s shçwn i n 1_8 . ’ /
18
V * The f i r s t s t a b l e a r y l s t a n n y l e n e ( 19) was p r e p a r e d r e c e n t l y , i t s s t a b i l i t y to w ard s' p o l y m e r i z a t i o n b e i n g a t t r i b u t e d t o t h e p r e s e n c e o f t h e t r i f l u o r o m e t h y l s u ^ t i t u e n t s ^ ^ i n t h e 2- and 6- p o s i t i o n s .
52
19 r C F Sn CF 2 53 ,5 4 . ,Amma and c o -w o rk e rs have r e p o r t e d t h e n o v e l compounds Rn*-C,H^)M(A^C1^ ) 2 . ( C 6H^X^ M = Sn, P b. The c r y s t a l s t r u c t u r e
5A
o f t h e l e a d d e r i v a t i v e c o n s i s t s o f a p o ly m e r ic a r r a y , i n w hich eac h l e a d atom i s bound t o a t e r m i n a l , s y m m e tric , rj^—b en z e n e r i n g . The l e a d atom i s f u r t h e r a s s o c i a t e d w i t h s i x c h l o r i n e a to m s , two from eac h o f th e t h r e e AlCl^ u n i t s , w i t h two of j : h e s e A lCl^ u n i t s fo rm in g b r i d g e s betw een a d j a c e n t l e a d a to m s, as sho™ i n F i g u r e 1 . 4 .
: 6
16
S e v e r a l o t h e r ji - a r e n e com plexes o f b i v a l e n t t i n and le a d 55
w ere s u b s e q u e n t l y r e p o r t e d , and t h e c r y s t a l s t r u c t u r e s o f (n^-CgH g)SnCl(A lCl^) a n d ^ n ^ - p - ( C H 3 ) 2C gH ^)SnCl(A lCl^) h ave
55 6 - “
been d e t e r m in e d . Asymmetry i n t h e n - C ^ - r i n g , o b s e r v e d
f o r b o th t h e s e compounds was a t t r i b u t e d t o c r y s t a l p a c k in g f o r c e s . T h e ' C r y s t a l s t r u c t u r e s o f t h e t r a n s i t i o n m e t a l d e r i v a t i v e s o f MCCHfSiMegïgLz, Cr(C0 )^M[CH(SiMe2) 2 ] 2 , M = Ge^* and S n ,^ ? have been d e t e rm in e d - ( F i g u r e 1 . 5 ) . S i g n i f i c a n t l y t h e atoms C ( l ) , C ( 2 ) , M and Cr a l l l i e i n a p p r o x i m a t e l y t h e same p l a n e , a r e s u l t which has b een i n t e r p r e t e d i n te rm s o f b a c k d o n a t i o n from t h e t r a n s i t i o n m e t a l t o t h e s t a n n y l e n e ( o r g e rm y le n e ) l i g a n d . ■ . H Me^Si II I' gQ MeiSl H Me^Si ' M [ ) C ( 2 ) ' CO Cr CO CO CO Me S i FIGURE 1 . 5 . The c r y s t a l s t r u c t u r e o f C r(C O )^ [C H (S iM e2 ) 2 ) 2 > M = Ge and Sn.
The c r y s t a l s t r u c t u r e o f t h e p y r i d i n e a d d u c t Cr(CO)^Sn(Bu^) ( p y r i d i n e ) j { F i g u r e 1 * 6 ) , h a s a l s o been d e t e r m in e d ^ ^
and shows, t h e Sn atom t o be o u t o t t h e C ( 1 ) , ’C ( 2 ) , Cr p l a n e , c o n s i s t e n t w i t h a d e c r e a s e i n b a c k d o n a t i o n from Cr t o Sn upon i n c o r p o r a t i o n o f t h e p y r i d i n e m o l e c u l e .
CO
\
\
Me_C(l) III' I'-Sn---C r CO
^ / f " ^ c o
CO Me^CfZ)
FIGURE 1 . 6 . The c r y s t a l s t r u c t u r e o f Cr(CO )^Sn(Bu-) ^ ( p y r i d i n e )
A v a r i e t y o f g e r m a n i u m ( I I ) - , t i n ( I I ) - , and l e a d ( I I ) - h a l i d e s 59 ( and
p se u d o -h a lid e s)
have been s t r u c t u r a l l y c h a r a c t e r i z e d . T h e s e compounds a r e g e n e r a l l y p o l y m e r i c , h a v in g h a l o g e n atoms(p eew d b -h alo g e n g ro u p s ) b r i d g i n g a d j a c e n t m e t a l c e n t e r s . Such s t r u c t u r e s a r e complex and have bfien rev ie w e d i n d e t a i l
59 ' 14
e l s e w h e r e . By c o n t r a s t , t h e g a s p h a s e s t r u c t u r e s o f S i F 2
15 o
( ■
and SnCl. a r e monomeric, h a v in g t h e " b e n t " g e o m etry shown i n
M
J .
18 B i v a l e n t t i n and l e a d d e r i v a t i v e s o f s i m p l e o x y - a c i d s 59 have b e e n s u b j e c t e d t o e x t e n s i v e s t r u c t u r a l c h a r a c t e r i z a t i o n . T h e s e compounds a r e a g a i n p o l y m e r i c and o f t e n h av e b r i d g i n goxygen atoms b e tw e e n a d j a c e n t m e t a l c e n t e r s . The s t r u c t u r e o f one compound o f t h i s ty p e S n (IV )P h 2S n ( I I ) N 0 2 > i s of i n t e r e s t , s i n c e i t c o n t a i n s b o th b i v a l e n t and q u a d r i v a l e n t t i n c o n n e c te d by a t i n - t i n b ond. The c r y s t a l s t r u c t u r e i s p o l y m e r i c , w i t h b r i d g i n g NO^ g ro u p s b etw ee n a d j a c e n t b i v a l e n t t i n atoms
( F i g u r e 1 . 7 ) .
The 1 , 3 - d i k e t o n a t o - d e r i v a t i v e s o f g e rm a n iu m (II) and t i n ( I I ) , w h ic h a r e motiomeric i n t h e v a p o u r , l i q u i d and s o l i d p h a s e s ,
2 9 , 3 0 ,3 4
h av e b e e n r e p o r t e d . , The c r y s t a l s t r u c t u r e o f t h e t i n compound, d i ( b e n z o y l a c e t o n a t o ) t i n ( I I ) , c o n s i s t s o f t h e d i s c r e t e monomeric u n i t s shown i n 2 1 , i n w hich eac h m e t a l
Sfi Ph
Ph 21
atom i s f o u r
(p se u d o -fiv e )
c o o r d i n a t e . The c h e l a t i n g e f f e c t o f t h e two k e t o e n o l a t e g r o u p s , a p p a r e n t l y r e s u l t s i n a t i n c e n t e r w hich i s c o o r d i n a t i v e i y s a t u r a t e d , and t h u s p r o h i b i t s i n t e r m o l e c u l a r a s s o c i a t i o n . The c r y s t a l s t r u c t u r e o f a r e l a t e d germanium compound, ( a c e t y l a c e t o n a t o ) g e r m a n i u m ( I I ) i o d i d e h a s ' 62 a l s o b e e n d e t e r m i n e d , and c o n s i s t s o f t h e u n i t s shown i n 2 2 , i n w hich each germanium atom i s t h r e e(p se i^ o -fo u r)
c o o r d i n a t e .'Ge
I
22
20
The s t r u c t u r e s o f t h e d i - t e r û - b u t y l p h e n o x i d e s , 23 ^
M(OC^H^Me-t • 63
4 - B u ^ 2 , 6 ) M = Ge o r Sn, have r e c e n t l y b e e n d e t e r m in e d by X -ray c r y s t a l l o g r a p h y . T h e s e a r e t h e f i r s t exam ples o f compounds t o h av e b e e n s t r u c t u r a l l y c h a r a c t e r i z e d i n t h e s o l i d
s t a t e f o r w hich t h e b i v a l e n t g ro u p IVA e le m e n t h a s t h e low c o o r d i n a t i o n number o f two
{pseudo
t h r e e ) . The s t r u c t u r e sshown i n 21 t o
2^
c l e a r l y d e m o n s t r a t e d t h e s t r o n g s t e r e o c h e m i c a l e f f e c t o f t h e n o n -b o n d in g e l e c t r o n p a i r i n eéch c a s e . M 23 P o s s i b l y t h e m ost i n t e r e s t i n g n i t r o g e n d e r i v a t i v e s o f t h e b i v a l e n t g roup IVA e l e m e n t s a r e b i s [ b i s ( t r i m e t h y l s i l y l ) ] a m i d o 31 - g e r m a n i u m ( I I ) , - t i n ( L I ) a n d - l e a d ( I I ) . Whi l e t h e s e compounds a r e monomeric i n t h e v a p o u r and l i q u i d p h a s e s , t h e31 s o l i d s t a t e s t r u c t u r e o f t h e t i n compound h a s b e e n s u g g e s t e d t o be d i m e r i c , p a r a l l e l i n g e x a c t l y t h e s i t u a t i o n fôund f o r t h e i s o e l e c t r o n i c t i n a l k y l , Sn[CH(SiMe2) 2 ] 2 ' M
24
SiMe, 'SiMe,5 . 3 . R e a c t i v i t y The r e a c t i o n s o f i n o r g a n i c t i n ( I I ) compounds w i t h o r g a n i c ( h a l i d e s , t o g i v e t h e c o r r e s p o n d i n g t i n ( I V ) compounds, have 2 21 . b e e n khown s i n c e 1851 ’ ( e q u a t i o n (19) ) . " S nig + Mel V- M e S n l ^ . . . . ’. ...(19) T h is ty p e o f r e a c t i o n h a s b e e n u sed e x t e n s i v e l y i n i n d u s t r y f o r t h e p r e p a r a t i o n o f m o n o o rg a n o tin (IV ) t r i h a l i d e s , w hich a r e i m p o r t a n t c o n s t i t u e n t s o f P .V .C . s t a b i l i z e r s . S i m i l a r r e a c t i o n s ^ i n v o l v i n g u n s a t u r a t e d o r g a n i c compounds hav e a l s o b e e n r e p o r t e d , ( e q u a t i o n ( 2 0) ) . P h v • , P h ' 2GeI‘2 + 2 P h C = C P h --- > I^Ge G el (20) Ph . Ph • V. . 3 0 The r e a c t i o n - o f Sn[CH(SiMeg)2 ] 2 w i t h a l k y l h a l i d e s o r h a l o g e n s a l s o g i v e s t h e c o r r e s p o n d i n g t i n ( I V ) p r o d u c t , e q u a t i o n s (21) and (22). Mel Sn[CH(SiMeg)2 ] 2 - V S n [ C H ( S i M e 2 ) 2 ] 2 ( M e ) ( I ) (21) Br ^ S n[C H (S iM eg)2]2B r2...(22)
/
22
T i n ( I I ) h a l i d e s r e a d i l y i n s e r t i n t o t r a n s i t i o n m e t a l - m e t a l bonds ^ ^ ’’^ ^ t o g i v e t h e c o r r e s p o n d i n g t i n ( I V ) d e r i v a t i v e ,eg
e q u a t i o n ( 2 3 ) . [ F e ( n ^ - C g H g ) (0 0)2 )2 '+ S n C l g ---- :— S n [ F e ( n ^ - C ^ H ^ ) ( C O ) 2 ] C l 2 . . . ( 2 3 ) T h e s e t y p e s o f r e a c t i o n s a r e o f t e n c o m p l i c a t e d by t h e f u r t h e rr e a c t i o n o f t h e t i n ( I V ) compound i n i t i a l l y form ed; t h u s Sn[Co(CO)^]^
38 *
was i s o l a t e d as one o f t h e p r o d u c t s from t h e r e a c t i o n o f Sn(n^-C^H^0 8 2 ) 2 w i t h Co2 (C0 )g ( e q u a t i o n ( 2 4 ) ) . Sn^n^-CgH^CHg) + Co2(C0)g ---
>■
Sn[Co(CO^^]^ + . . . (24) 5 5 S i m i l a r l y , t h e r e a c t f p n o f g n (n ^ 0 ^8 ^ 0 8 2 ) 2 w i t h ^/(n-Cgh^) (CO)2 ( H ) , 32 w hich h ad b e e n r e p o r t e d t o g iv e t h e b i v a l e n t t i n compound Sn[W(n^-C2H2 ) ( 0 0 ) 2 1 2 » r e c e n t l y b e e n shown^^ t o g i v e t h e t i n ( I V ) 5 compound S n(8 )[W(n -O^H^)(CO)2 ] ^ ( e q u a t i o n ( 2 5 ) ) . \ S n ( 11- 0^8 ^0 8 2 ) 2 + 3W(n^-Cg8 2 )(C 0 ) 2 (H) Sn(H$ [W(n^02H2 ) (CO) 2 ] 3 . . (25) -I n s e r t i o n i n t o a m e ta l- h y d r o g e n and m e t a l - c a r b o n bonds 39 have a l s o b e e n r e p o r t e d , t h u s S n [ 0 8 ( 811462) 2 ] 2 i n s e r t s i n t o e i t h e r a Mo- 8 o r a Mo-0 bond a c c o r d i n g t o e q u a t i o n ( 2 6 ) .Sn[C8 (S iM e.) 1 ' .
Mo(n^-05Hg)(C0 ^2-R =--- ^ Sn[CM(SiMe2)2l2[Mo(n -02H2) (00)2lR
23
^ 67 S e v e r a l t i n ( I I ) compounds h av e b e e n shown t o r e a c t w i t h d i i r o n e n n e a c a r b o n y l t o g iv e four-raerabered FSgSn^ r i n g compounds, i n w hich t h e t i n i s i n a f o r m a l l y q u a d r i v a l e n t s t a t e ( e q u a t i o n ( 2 7 ) ) . •^2 . Sn. Sn%2 + F e 2 (C0 )g --- (OC)^Fe ' Fe(CO)^ . (27) X = C l, B r, CgHc, CrH^CHg, X^ and 1 , 3 ' d i k e t o n â t o .The b i v a l e n t group IVA e l e m e n t i n t h e s e d e r i v a t i v e s o f
J . ;
germanium, t i n , a n d l e a d can a l s o S a n c t i o n a s a / tw o e l e c t r o n
donor t o s u i t a b l e a c c e p t o r s i t e s , t h u s S n(n^-C gH ^)2 forms com plexes w i t h t h e Lewis a c i d s BF^^^ an.d A lC l^ ( e q u a t i o n ( 2 8 ) ) .
Sn(n^-CgHg)2 + MX^ —---^ (n^-C^H^)2Sn-^MX^...é - <28)
MX. = BFg, A lC lg .
V ' , 39
I n t e r e s t i n g l y Sn[CH(SiMeg)2 ] 2 d o es n o t r e a c t w i t h B F g .E t2 0 ,
however w i t h A lC l^ , below - 3 0 ° C , i t forms a w h i t e s o l i d , w hich ■ decomposes a t more e l e v a t e d t e m p e r a t u r e s , the" o n ly i s o l a b l e
p r o d u c t b e i n g Sn[CH(SiMe2) 2 ] ’ ^ o r e s t r a i g h t f o r w a r d l y , Sn[CH(SiMe2) 2 ] 2 f u n c t i o n s a s ' a two e l e c t r o n d o n o ^ ^ to g ^ h e m e t a l c a r b o n y l s , M(CO)^, M = Cr and Mo,^^ and a l s o d i s p l a c e s ^
e t h y l e n e from PPh^frotn RhClCPPh^)^ ( e q u a t i o n (2 9 )) . ct V ■ R h(C _È .yci(P P h_) Sn[CH(SiMe2) 2J 2 RhCl(PPh2)^n[CH(SiMe2)2] (2 9 )
24
F o r most d e r i v a t i v e s o f b i v a l e n t germanium, t i n and l e a d , - t h e m e t a l ( m e t a l l o i d ) can f u n c t i o n as a Lewis a c i d , a c c e p t i n g -an e l e c t r o n p a i r i n t o -an u n o c c u p ie d
fisnp nd ■
ty p e m o l e c u l a rX y
o r b i t a l . Thus iri t h e c r y s t a l s t r u c t u r e o f S nC l„.2H „0,
- - ^ ^ . '
t h e oxygen o f one o f t h e w a t e r m o l e c u le s can be view ed as
d o n a t i n g two e l e c t r o n s t o t i n , a s shown i n
2^
. G erm anium (II)V c r ' ' ' , 11' Sn
H C l
_25
and t i n ( I I ) h a l i d e s r e a d i l y a c c e p t a f u r t h e r h a l i d e i o n t o fotm t h e complex i o n s GeX^ and SnX~ ( e q u a t i o n ( 3 0 ) ) .
[GeClg]* + CsCl --- > Cs"*" G eCl".-... (30) 5 ■ 73 Both b i s ( n - c y e l o p e n t a d i e n y l ) t i n ( I I ) and b i s ( a c e t y l -a c e t o n -a t o ) t i n ( I I ) . u n d e r g o . r e d i s t r i b u t i o n r e a c t i o n s w i t h t i n ( I I ) h a l i d é s ( e q u a t i o n ( 3 1 ) ) , _ * 5 " c s n ( n - C ^ H ^ ) 2 + SnClg ---:---^ 2 S n ( n - C ^ H ^ ) C 1...(31) GeClg i s p r e p a r e d
, s z t u
from t h e r e d u c t i o n o f G eC l^ in a c i d i c m e d ia . /■w h i l e s i m i l a r exchange r e a c t i o n s h a v e a l s o b e e n o b s e r v e d w i t h 74 ' t i n ( I V ) h a l i d e s , ( e q u a t i o n ( 3 2 ) ) . - ' 1 5 Sn(n -C^H^ ) 2 + SnMe^Cl^ SnMe2 (h -C^H^)C1 + Sn(n -C^H^)C1 . . ( 32)
1
26
C. SIOATROPIC MIGRATIONS IN METALLO-CARBOCYCLIC SYSTEMS.
0 . 1 . I n t r o d u c t i o n .
The d i s c o v e r y o f t h é phenomenon o f s t e r e o c h e m i c a l n o n - r i g i d i t y added a new d im e n s io n to t h e c o n c e p t o f m o l e c u l a r s t r u c t u r e .
The e s t a b l i s h m e n t o f v a r i a b l e t e m p e r a t u r e NMR s p e c t r o s c o p y a s a r o u t i n e method f u r t h e r f a c i l i t a t e d t h e r a p i d d ev elopm ent o f t h e s tu d y o f s t e r e , o c h e m i c a l l y n o n - r i g i d m o l e c u le s w here '
- _1 +9 - 1 75
t h e r a t e o f r e a r r a n g e m e n t i s o f t h e o r d e r o f 10 - 10 s . T h i s has l e d i n p a r t i c u l a r t o t h e i d e n t i f i c a t i o n o f m i g r a t i o n s o f -bonded m e t a l atoms betw een some, o r a l L , o f t h e - c a r b o n atoms i n c e r t a i n c y c l o p o l y e n y l s y s t e m s . S i g m a t r o p i c s h i f t s o f t h i s ty p e have b e e n th o r o u g h l y docum ented^^ f o r t h e c y c l o - „
» p e n t a d i e n y l - r i n g system^shown i n 26 w h i l e more r e c e n t l y m i g r a t i o n s i n o t h e r r i n g s y s te m s
ie,
C^, 27, , 28, and Cg h av e a l s o b e e n o b s e r v e d . T h i s s e c t i o n r e v i e y s tjh is t o p i c , d i s c u s s i n g f i r s t t h e t h e o r e t i c a l a s p e c t s ( C . 2 ) , s e c o n d ly t h e m ethods used t o c h a r a c t e r i z e t h e s e p r o c e s s e s ( C . 3 ) , and f i n a l l y su m m a rizin g t h e . e x p e r im e n ta l r e s u l t s a v a i l a b l e ^ ( C . ^ ) . H M 26 27 28 29 '■C . 2 . T h e o r e t i c a l C o n s i d e r a t i o n s .
S e v e r a l t y p e s o f s i g m a t r o p i c s h i f t s hay e b e e n d i s t i n g u i s h e d b y Woodward and Hoffmann. F or t h e p u r p o s e s o f t h i s d i s c u s s i o n , h o w ev er, o n ly r e a r r a n g e m e n t s o f o r d e r [ h , j ] w i l l be c o n s i d e r e d ,
c o r r e s p o n d i n g t o t h e m i g r a t i o n o f a
sigma-honàeà
atom o r group (R) from one end t o t h e o t h e r o f a p o l 'y e n y l i c c h a i n a s shown i ne q u a t i o n ( 3 3 ) . R ,R \ r 1 I* ■■11 c - t - c = c — f - --- > - . . . ( 3 3 ) n ( j = 2n + 1)
Woodward and Hoffmann h av e d e f i n e d a s i g m a t r o p i c
change p f o r d e r ' { i , j ] as t h e m i g r a t i o n o f a s ig m a b ond, f l a n k e d ' b y one o r more i r - e ^ e c t r o n s y s t e m s , to a new p o s i t i o n whose t e r m i n i
a r e i - 1 and j - 1 atoms removed from t h e o r i g i n a l Bonded l o c i , i n an u n c a t a l y z e d i n t r a m o l e c u l a r r e a c t i o n . ThTen p r o v i d e d t h e m i g r a t i n g g roup R re m a in s bonded t o b o th ends o f t h e u n s a t u r a t e d s y ste m th r o u g h o u t ( c o n c e r t e d r e a c t i o n ) , o r b i t a l symmetry c o n s t r a i n t s
would b e d e r i v e d from t h e form o f t h e h i g h e s t o c c u p ie d m o l e c u l a r o r b i t a l (HOMO) o f t h e h y d r o c a r b o n r a d i c a l c o r r e s p o n d i n g t o t h e p o l y e n y l i c c h a i n . .T he HOMO f o r t h i s s y ste m i s t h e n o n - b o n d in g a l l y l i e o r b i t a l w hich p o s s e s s e s t h e f o l l o w i n g symmetry.
28 5 , • i ■
^""~A^roup R, when bound t o t h e c h a i n by a s y m m e tric o r b i t a l
{eg,
an, s o r b i t a l f o r R = H ) .c a n m i g r a t e from one end o f t h e c h a i n ■ \ to t h e o t h e r i n two d i s t i n c t w a y s ; ’ c o n s i d e r t h e c a s e of a 1 ,5 m i g r a t i o n f o r t h e f o l l o w i n g p e n t a d i e n y l : A •H/
B C D FIGURE 1 . 8 ( a ) . S u p r a f a c i a l m i g r a t i o n o f a h y d ro g e n atom. -ST H FIGURE 1 . 8 ( b ) . A n t a r a f a c i a l m i g r a t i o n o f a h y d ro g en atom.»
f o r a s u p r a f a c i a l p r o c e s s ( F i g u r e 1.'8 ( a ) ) ,th e t r a n s f e r r e d h y d ro g e n atom i s a s s o c i a t e d a t a l l tim e s w i t h t h e same f a c e o f t h e Tf s y s t e m ; f o r t h e a n t a r a f a c i a l p r o c e s s ( F i g u r e 1 . 8 ( b ) ) , t h e m i g r a t i n g atom p a s s e s f r o n r t h e t1fp f a c e of one carb o n
t e r m i n u s t o t h e b o tto m f a c e o f t h e o t h e r . The s e l e c t i o n r u l e s f o r s u c h a s i g m a t r o p i c r e a c t i o n o f o r d e r [ I , j ] a r e g iv e n i n T a b l e 1 . 1 ( a ) . X TABLE 1.1(a). S e l e c t i o n r u l e s f o r an a llo w e d s i g m a t r o p i c s h i f t o f o r d e r [ l , j ] o f a h y d ro g en atom.
L
( c n e r m a i; [ 1 , 3 ] antara [ 1 , 5 ] ' Gupra [ 1 , 7 ] a n t a r a [ 1 , 9 ] s u p r a *= ■* Where R i s a group o t h e r t h a n ' a h y d ro g e n atom (eg m e t i y r l ) ,the orbital by which R is bound to the polyenyl system may be antisymmetric (3 9. possess some p character). Alternate processes
a t t h e m i g r a t i n g c e n t e r as shown i n e q u a t i o n ( 3 4 ) .
30 The s e l e c t i o n r u l e s a r e t h e n p r e c i s e l y r e v e r s e d i f i n v e r s i o n t a k e s p l a c e a t t h e m i g r a t i n g c e n t e r ( T a b l e 1 . 1 ( b ) ) . TA3LE 1 . 1 ( b ) . G e n e r a l s e l e c t i o n r u l e s f o r t h e r m a l l y a llo w e d s i g m a t r o p i c s h i f t s . [l,j] S u p r a f a c i a l A n t a r a f a c i a l [1,3] i n v e r s i o n r e t e n t i o n [1,5] r e t e n t i o n i n v e r s i o n [1,7] i n v e r s i o n - r e t e n t i o n [1,9] r e t e n t i o n • i n v e r s i o n Thus a [ l , 3 ] s h i f t may b e e i t h e r a n t a r a f a c i a l w i t h r e t e n t i o n , o r s u p r a f a c i a l w ith i n v e r s i o n ( F i g u r e 1 . 9 ( a ) ) , w h i l e a ( 1 , 5 ] s h i f t w i l l be s u p r a f a c i a l w i t h r e t e n t i o n , o r a n t a r a f a c i a l w i t h i n v e r s i o n ( F i g u r e 1 . 9 ( b ) ) . 1 , 3 : a n t a r a f a c i a l :
