University of Groningen Exploring coordination chemistry and reactivity of formazanate ligands Travieso Puente, Raquel
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(2) . Chapter 3 Bis(formazanate)calcium and magnesium complexes Various bis(formazanate)calcium and magnesium complexes with a large variety of steric and electronic properties were synthesized and characterized by NMR, single crystal structure determination and UV/Vis spectroscopy. These complexes are compared with the previously reported zinc analogues. The differences in the coordination sphere due to harder Lewis acidity of magnesium and calcium versus zinc is also discussed. Cyclic voltammetry studies differ markedly from those in the bis(formazanate)zinc analogues reported previously.. Part of this chapter will be published in a manuscript that is under preparation. Great contribution on the bis(formazanate)magnesium complexes presented in this chapter was made by Peter Roewen, MSc student in our group. .
(3) . 3.1 Introduction Although transition metal chemistry still constitutes the heart of homogeneous catalysis, main group organometallic chemistry is not limited to classical Lewis-acidic or -basic catalysis. However, studies of rock forming elements have been poorly explored and little attention has been focused on the alkaline-earth group in spite of its potential higher reactivity due to the large metal-carbon bond polarity. Different studies on magnesium based complexes showed the wide applicability of those complexes: ranging from β-diiminate magnesium alkoxides as catalysts for lactide polymerization1 to homoleptic magnesium amidinate as molecular precursors for MOCVD and ALD processes2 among others. The abundance of calcium and magnesium in the earth’s crust (fifth (3.4 wt%) and eight (1.5 wt%), respectively. Chapter 1, Figure 1.1) makes them extremely attractive elements with effectively endless supply and worldwide accessibility. Their straightforward isolation and reduction makes it also one of the cheapest metals. In spite of that, organocalcium chemistry has not being highly studied.3 Despite of the interesting properties of formazanate complexes, relatively little work has been done in this area. Thus, it is of interest to develop insight into this new system in terms of coordination and redox behaviour. Our group has reported recently the synthesis and the ligand-based reduction chemistry of several bis(formazanate)zinc complexes, which exhibit two sequential, reversible one electron reductions to form isolable complexes that were crystallographically characterized in a manifold of available redox states [ZnL2]0/1–/2– (L = formazanate anion).4 In an effort to extend the coordination chemistry of formazanate complexes, in this chapter we provide novel insight into the first formazanate complexes involving alkaline-earth metal centers. Thus, a series of bis(formazanate)magnesium complexes (n-Mg), their corresponding monoTHF adducts (n-MgTHF) and bis(formazanate)calcium complexes (n-Ca) complexes are presented and compared with the previously reported bis(formazanate)zinc analogues.. " .
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(6) . 3.2 Synthesis and characterization of bis(formazanate) complexes 3.2.1 Synthesis of bis(formazanate) complexes Bis(formazanate)magnesium complexes n-Mg are conveniently prepared by stirring a toluene solution of the free formazans n-H with MgBu2 (as a commercially available 1.0 M solution in heptane) in a 2:1 molar ratio (Scheme 3.1). Removing the volatiles under vacuo afford the magnesium (bis)formazanate complexes n-Mg. The products are obtained in good yields (> 60%) and can be purified by crystallization from toluene/pentane to afford crystals suitable for X-ray analysis for compounds 1,3,4,6,8,9-Mg. Due to the Lewis acidity of magnesium and in contrast to the corresponding Zn complexes, dissolution of n-Mg complexes in THF lead to the coordination of THF to the base-free compounds 1,3,4,6-Mg resulting in rapid formation of the mono-THF adducts 1,3,4,6-MgTHF, which were crystallographically characterized (Scheme 3.1). R5. R3 2 R1. N. N. N. HN. MgBu 2 - 2 BuH. N N Mg. R3 N N. R5. R5. R5 N N N N. R3. THF. R1 R1 n-Mg. n-H 1-Mg: R1 3-Mg: R1 4-Mg: R1 6-Mg: R1 8-Mg: R1 9-Mg: R1. N N R3. O Mg. R5 N N N N. N N R1. R3. R1. n-Mg THF. = R5 = Ph; R3 = p-tol = R5 = Ph; R3 = tBu = Ph, R5 = Mes; R3 = p-tol = Mes, R5 = C6F 5; R3 = p-tol = Ph, R5 = Mes; R3 = C6F 5 = C6F 5, R5 = Mes; R3 = C6F 5. Scheme 3.1 Synthesis of bis(formazanate)magnesium complexes (n-Mg) and their corresponding THF adduct (n-MgTHF). The analogous bis(formazanate)calcium complexes could be obtained via two different pathways: (i) metathesis of 2.0 equivalents of the corresponding n-Na/n-K formazanate salt5 with one equivalent of CaI2 in THF, or (ii) treatment of one equivalent of Ca(NTMS)2(THF)2 (NTMS = N(SiMe3)2) with two equivalents of formazan n-H leads to the desired bis(formazanate)calcium compound. However, some amount of free ligand n-H is still present after all Ca(NTMS)2(THF)2 is consumed. To achieve complete conversion of both starting materials 1.5 equivalents of Ca(NTMS)2(THF)2 were needed (Scheme 3.2). This is in agreement with the work previously reported by Hanusa et. al.6 and Henderson et. al.7 who. #.
(7) claimed that Ca(NTMS)2(THF)x is often contaminated with the heterobimetallic complex K[Ca(NTMS)3](THF)x, which is difficult to detect by NMR spectroscopy. For comparison, compound 1-Ca was synthesized testing both pathways (Scheme 3.2), where full conversion and good isolated yields were achieved (route (i) 83% yield, route (ii) 94% yield). The first route i) required a two step synthesis: (1) synthesis and purification of the corresponding (mono)formazanate salt 1-K5 and (2) subsequent metathesis of the purified salt with CaI2 and purification of the product 1-Ca. The second route ii) only required a one step synthesis which is easily followed by 1H NMR due to the disappearance of the acidic NH proton present on the ligand by deprotonation with bis(trimethylsilyl)amide and easy purification by removing the co-product HNTMS under vacuo. Due to a greater efficiency, the second alternative was chosen for the synthesis of n-Ca bis(formazanate)calcium complexes here reported. p-tol Ph i). N. N. N. 2. N. K O. O. Ph Ph. CaI 2 - 2 KI. N N p-tol N N. R3. R1. N. N. N. HN. p-tol. N N. O. Ph. 1-Ca. 1-K. 2. N N. Ca Ph. ii). Ph. O. 1.5 Ca(NTMS)2(THF) 2 - 2 HNTMS R5. R3. R5 (THF)n R5 N N Ca N N N N. N N R1. R3. R1. n-Ca. n-H 1-Ca (n=2): R1 3-Ca (n=2): R1 4-Ca (n=1): R1 5-Ca (n=1): R1. = R5 = Ph; R3 = p-tol = R5 = Ph; R3 = tBu = Ph, R5 = Mes; R3 = p-tol = R5 = Mes; R3 = p-tol. Scheme 3.2 Synthesis of bis(formazanate) calcium complexes (n-Ca) via i) salt metathesis pathway (top) and ii) direct deprotonation of the ligand (bottom).. 3.2.2 NMR spectroscopy analysis The NMR spectroscopic features for the symmetrical compounds 1,3,4,5,8-Mg/MgTHF/Ca are straightforward and display one chemically equivalent set of N-Ar groups, which can be .
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(10) attributed to the symmetrical coordination of two ligand systems to the metal site, consistent with both 1H and 13C NMR spectra. In contrast, the 1H NMR of 6-Mg complex shows clear resonances of a major compound and small, slightly broadened signals for a minor compound. This minor compound might be another isomer of the complex in solution. Heating the sample resulted in broadening and shifting of the resonances from the major compound and the small broad resonances towards each other to eventually merge into one broad peak (Figure 3.1). Further heating to 100 °C resulted in a single broadened doublet. Cooling the solution back to room temperature gave the same spectrum as before heating. The. 19. F NMR also shows one major compound and. some other small peaks.. . Figure 3.1 VT 1H NMR of o-p-tol proton of 6-Mg at 25 °C (red), 40 °C (yellow), 55 °C (green), 70 °C (light blue), 85 °C (dark blue) and 100 °C (purple) in toluene-d8. This implies that both sets of resonances present at room temperature belong to two isomers of 6-Mg that are present in a dynamic equilibrium. The most probable structure of these two isomers is a complex with two six-membered chelating rings as shown in the crystal structure of 6-Mg (see section 3.2.3), and a complex with a five- and a six-membered chelating ring similar to that observed for 6-Zn8, with a ratio of about 7:1. Addition of THF to compound 6-Mg results in formation of 6-MgTHF. In the 1H NMR, there are only small changes in the peak positions. Also for 6-MgTHF there are small broad peaks that belong to another isomer in solution where the isomers have a ratio of about 14:1 with the complex with two six-membered chelating rings as the major compound. The o-CH3 signals of the mesityl substituent are slightly broadened, indicating restricted rotation of the nitrogencarbon bond that connects this mesityl substituent to the formazanate. In C6D6 solution, the .
(11) THF resonances of 6-MgTHF are broadened, but they are very similar to the resonances of free THF (3.55 ppm and 1.31 ppm versus 3.57 ppm and 1.40 ppm), so in solution they don’t bind strongly to the metal center and most of the THF is dissociated. The 19F NMR spectrum also shows one major compound and small broad peaks belonging to the other isomer in solution. Similarly, complex 9-Mg also shows one major compound and additional small peaks in the 1. H NMR spectrum, indicating an equilibrium between isomers.. Attemps to synthesize 6-Ca were unsuccessful and instead an air-stable unknown species was cleanly formed, which is discussed in detail in Chapter 4. Dissolution of 8-Mg in THF does not lead to formation of 8-MgTHF, but instead gives the same product that is formed when Ca(NTMS)2(THF)2 reacts with 8-H. The nature of this compound is also discussed in Chapter 4. NMR spectroscopy in C6D6 solution for the magnesium and calcium complexes where one or two molecules are present show the THF resonances shifted and broadened with respect to free THF, indicating that the complexes are in a rapidly exchanging equilibrium with the base-free compounds. Similar equilibria were studied in detail by Chisholm and co-workers for β-diketiminate magnesium complexes.9–11. 3.2.3 X-Ray crystallography studies Single crystals of compounds 1,3,4-Ca were grown from slow diffusion of hexane into THF, slow evaporation of hexane or pentane, respectively. X-ray diffraction studies showed, in all cases, a central calcium atom surrounded by two chelating formazanate ligands, which is supplemented by the coordination of THF in all the cases. The modification of the steric properties in the formazanate backbone determines the possible number of molecules coordinated to the central atom and therefore the geometry (vide infra) (Figure 3.3 and Table 3.4). The molecular structure of n-Mg obtained from single-crystal X-ray diffraction studies show the compounds to contain a Mg center surrounded by 4 N atoms in a pseudo-tetrahedral coordination environment. The structures for 1,3,4-Mg are very similar to those observed in related bis(formazanate) zinc complexes recently reported by Otten et al.4,8. .
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(14) In all cases, the formazanate ligands are bound via the terminal N-atoms to give 6-membered chelate rings (Figures 3.2-3.5) with the exception for 9-Mg, where two binding modes are found 6- and 5-membered chelate ring (Figure 3.5). Compounds n-Mg/n-MgTHF/n-Ca show virtually identical N-N and N-C bond lengths throughout the formazanate ligand backbone indicative of significant charge delocalization (Tables 3.1-3.4). Despite the similar ionic radii of Zn and Mg, the latter element is more electropositive and more Lewis acidic, resulting in complexes in which the bonding is more ionic and consequently slightly larger N-M distances are observed for Mg than for Zn.12 For example, the Mg-N bond distances in 3-Mg range between 2.031(1) and 2.045(1) Å, whereas in the corresponding Zn compound these are 1.977(2)-1.990(2) Å (Table 3.1).4. 1-Mg. 1-Zn. 3-Zn. 4-Zn. . 3-Mg. 4-Mg. Figure 3.2 X-ray crystallographic data steric hindrance comparison between bis(formazanate)zinc8 (left) and magnesium (right), showing 50% probability ellipsoids. All hydrogen atoms are omitted for clarity. .
(15) The solid state structures of the THF adducts show significant structural deformation as a result of THF binding: the Mg centers are displaced significantly out of the formazanate NNCNN plane and all Mg-N bond distances are elongated by 0.05-0.10 Å in comparison to the base-free precursors n-Mg (except for 6-MgTHF). The higher ionic radius of Ca2+ in comparison to Mg2+ leads to an octahedral coordination environment due to the presence of two THF molecules for compounds 1-Ca and 3-Ca (R1 = R5 = Ph; R3 = p-tol and tBu, respectively), as evidenced by X-ray crystallography and NMR studies. This follows the trend for previously reported guanidinates13–16, amidinates2 and benzamidinates17. Although both possess very similar structures, in 1-Ca the THF molecules show a cis coordination whereas complex 3-Ca shows a trans disposition to each other (Figure. 3.3).. This. is. in. accordance. with. bis[phosphaguanidinates] by Westerhausen, et. al.. 13. the. previously. reported. calcium. where it is shown that the cis/trans. disposition of the THF molecules is dependent on the substituents involved (R = iPr/Cy, respectively). Another example was reported by Barret et. al.15 showing cisoid geometry of two guanidinates complexes. An increase in the ligand steric bulk by substitution of the phenyl substituent/s on N1 or/and N4 (1-Ca) to a more steric demanding mesityl (4-Ca/5-Ca) results in formazanate complexes that contain only one molecule of THF. In 4-Ca the coordinated THF molecule occupies the apical position suggesting a distorted trigonal bipyramidal geometry by using the method described by Reedijk et al. for five coordinated complexes (τ = 0.80)18 (Figure 3.3). A similar complex with guanidinate ligands has been published by Barman et. al.16. !. 1-MgTHF. . . . 1-Ca. ". ! !.
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(18) . ! !. !. ". . . . . 3-Ca. 3-MgTHF. . ! . . !. . 4-MgTHF. . . . ". !. 4-Ca. Figure 3.3 X-ray crystallographic data steric hindrance comparison between bis(formazanate)magnesium THF adduct (left) and calcium (right), showing 50% probability ellipsoids. All hydrogen atoms are omitted for clarity and in the 4-Ca pentane molecule also omitted for clarity. Two of the four N-Ph rings in compounds 1,3-Ca were found to be approximately coplanar with the ligand backbone (NNCNN / Ph dihedral angles < 20°), which maximizes conjugation. However, the dihedral angles increase considerable for the other two N-Ph present in compounds 1,3-Ca (dihedral angles 28-47°) due to the steric effects of a nearby THF molecule. In complexes where mesityl is present as a substituent (4-Mg/MgTHF/Ca and 5-MgTHF/Ca), steric interactions of the 2,6-Me groups on the N-Mes and the ligand backbone causes these Mes groups to have much larger dihedral angles (av. Ca, 62.73°, 65.80° in 4-Zn and av. 74.64° in 5-Zn). This orthogonality decreases the length of the conjugated system in comparison with the phenyl analogues. In the solid-state structure of complex 4-Mg(THF) the. .
(19) N-Mes rings are oriented nearly parallel and stack in an off-center fashion as is usually observed for electron-rich aromatic rings.19,20 For compound 6-Mg, which contains a ligand with two electronically disparate N-substituents (N-Mes and N-C6F5), the X-ray structure suggests the formazanate to be less delocalized with N-N bond lengths that have clear double (1.270(3)/1.292(2) Å) and single bond character (1.329(2)/1.325(2) Å, Table 3.3). The solid-state structure of 6-Mg is different than that for its Zn congener,8 in which one of the formazanates adopts a 5-membered chelate ring, this is not observed for 6-Mg and instead, the Mg center is shown to interact with an ortho-CF moiety of the N-C6F5 ring (Mg...F = 2.251(1) to result in a five-coordinate geometry with a distorted trigonal bipyramidal geometry (τ = 0.75) 18 (Figure 3.4).. 6-Zn. 6-Mg. 6-MgTHF. Figure 3.4 X-ray crystallographic data electronic effect comparison between bis(formazanate)-zinc8 (6-Zn, left), -magnesium (6-Mg, center) and –magnesium THF adduct (6-MgTHF, right) showing 50% probability ellipsoids. All hydrogen atoms are omitted for clarity. Addition of THF to compound 6-Mg results in loss of the Mg-F interaction and formation of a new Mg-O(THF) bond, 6-MgTHF, also shows a five-coordinate geometry but instead a distorted tetragonal pyramidal geometry (τ = 0.12)18 (Figure 3.4, Table 3.3). Compound 8-Mg, which contains a C6F5 substituent in the backbone, is very similar to 4-Mg (with a p-tol instead), suggesting that the C6F5 substituent in the backbone only has an electronic effect on the complex (Figure 3.5). A formazan with a mesityl substituent and two C6F5 substituents; one in the backbone of the formazan and the other connected to one of the terminal nitrogens, was used to synthesize complex 9-Mg. This is the first bis(formazanate)magnesium complex that shows a formazanate chelating in a five-membered ring. In the formazanate chelated as a 5-membered ring, distances for the nitrogen in the pendant arm are much shorter than those in the chelate .
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(22) ring (N7-N8 = 1.287(5) Å vs. N5-N6 = 1.352(7) Å) indicating double vs. single bond characters, respectively. This can be extended for the C-N distances where N6-C2 shows double character (1.307(7) Å) versus the single one for C2-N7 (1.404(7) Å). Similarly to 6Mg, the solid-state structure presents an unusual Mg-F interaction, which leads also to a distorted tetragonal pyramidal geometry.. 9-Mg. 8-Mg. Figure 3.5 X-ray crystallographic data of complex 8,9-Mg (left and right, respectively) showing 50% probability ellipsoids. All hydrogen atoms are omitted for clarity. Table 3.1 Selected bond lengths (Å) and angles (°) for compounds 1-Zn/Mg and 3,4-Mg. Distance (Å) M1-N1/M1-N4 M1-N5/M1-N8 N1-N2/N3-N4 N5-N6/N7-N8 N2-C1/C1-N3 N6-C2/C2-N7 Bond angle (°) N1-M1-N4/N5-M1-N8 Out of plane distance (Å) M1-NNCNN. 1.985(1) 2.001(1) 1.307(2) 1.303(2) 1.346(2) 1.350(2). 1-Zn 1.995(1) 1.983(1) 1.305(2) 1.312(2) 1.352(2) 1.346(2). 1-Mg 2.037(1) 2.048(1) 2.053(1) 2.041(1) 1.316(2) 1.308(2) 1.310(2) 1.306(2) 1.344(2) 1.350(2) 1.349(2) 1.350(2). 2.045(1) 2.036(1) 1.310(2) 1.303(2) 1.346(2) 1.347(2). 3-Mg 2.031(1) 2.042(1) 1.318(2) 1.319(2) 1.337(2) 1.336(2). 2.050(1). 4-Mg 2.045(1). 1.308(1). 1.316(1). 1.345(2). 1.351(2). 92.21(5). 90.37(5). 86.95(5). 88.60(5). 87.38(5). 86.07(5). 84.65(4). 0.124. 0.581. 0.147. 0.660. 0.627. 0.725. 0.776. Table 3.2 Selected bond lengths (Å) and angles (°) for compounds 1-Mg/MgTHF and 3,4MgTHF. Distance (Å) M1-N1/M1-N4 M1-N5/M1-N8 N1-N2/N3-N4 N5-N6/N7-N8 N2-C1/C1-N3 N6-C2/C2-N7 Mg1-O1 Bond angle (°) N1-M1-N4/N5-M1-N8 Out of plane distance (Å) M1-NNCNN. 1-Mg 2.037(1) 2.048(1) 2.053(1) 2.041(1) 1.316(2) 1.308(2) 1.310(2) 1.306(2) 1.344(2) 1.350(2) 1.349(2) 1.350(2). 1-MgTHF 2.136(3) 2.047(2) 2.150(2) 2.057(2) 1.310(3) 1.326(3) 1.310(3) 1.334(3) 1.362(3) 1.338(4) 1.366(3) 1.327(3) 2.047(2). 3-MgTHF 2.091(2) 2.114(2) 2.099(2) 2.120(3) 1.315(3) 1.316(3) 1.320(3) 1.320(3) 1.339(3) 1.350(4) 1.338(4) 1.337(4) 2.114(2). 4-MgTHF 2.094(2) 2.163(2) 2.161(2) 2.091(2) 1.322(2) 1.301(2) 1.297(2) 1.311(2) 1.337(3) 1.358(2) 1.347(2) 1.344(2) 2.097(2). 86.95(5). 88.60(5). 79.57(9). 80.48(9). 84.60(9). 78.6(1). 77.58(6). 83.60(6). 0.147. 0.660. 1.224. 1.271. 0.597. 1.121. 0.010. 1.290. !.
(23) Table 3.3 Selected bond lengths (Å) and angles (°) for compounds 6-Zn/Mg/MgTHF and 8,9Mg.. .
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(34) Out of plane distance (Å) . . ! ! !! ! !! !!. !!. ! ! ! . ! ! ! . . . ! . ! . . . . . . . . . . . . . . . . !. . . . . . . . . ! . Table 3.4 Selected bond lengths (Å) and angles (°) for compounds 1,3,4-Ca. .
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(38) . 1-Ca 2.459 2.429 2.459 2.429 1.295(2) 1.314(2) 1.295(2) 1.314(2) 1.359(2) 1.338(1) 1.359(2) 1.338(1) 2.373 2.373 71.00. 71.00 84.00. 3-Ca 2.443(1) 2.438(1) 2.421(1) 2.447(1) 1.316(2) 1.311(2) 1.314(2) 1.310(2) 1.341(2) 1.345(2) 1.345(2) 1.343(2) 2.409(1) 2.417(1). 4-Ca 2.362 2.400 2.425 2.352 1.320 1.291 1.312 1.296 1.342 1.365 1.341 1.361 2.327. 70.43(4) 70.17(4) 141.53(3). 68.63. 71.49. 3.3 UV/Vis spectroscopy of bis(formazanate) complexes The solution electronic spectra of bis(formazanate)calcium complexes (n-Ca) are presented in Figure 3.6. The intense colorful THF solution of the complexes is reflected in the intense visible bands (460-510 nm), which show extinction coefficients ranging from 22000-45000 L.mol−1.cm−1. The p-tol substituted compound 1-Ca has a low energy absorption max at 510 nm, red-shifted by 21 nm compared to 3-Ca where a more donating group tBu is present within the backbone. The replacement of phenyl substituents (510 nm, 1-Ca) by the more donating mesityl results in a blue shift of 37 nm (473 nm, 4-Ca). This is consistent with the solid-state structures (vide infra), which show coplanarity between the phenyl substituents and the formazanate backbone. However, when mesityl are present the perpendicular orientation of the mesityl with respect to the formazanate backbone reduces the length of the conjugated system.21,22 Accordingly, the complex 5-Ca with two mesityl substituents possess the shortest conjugated system and therefore exhibits the shortest wavelength absorption. " .
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(43) . Figure 3.6 Absorption spectra for bis(formazanate)calcium complexes (n-Ca).. 3.4 Cyclic voltammetry studies of bis(formazanate) complexes Studies of the redox-active properties of various bis(formazanate)zinc complexes (n-Zn) have shown two quasi-reversible redox couples8,23, indicating that each formazanate ligands can store one electron. These reduced species could be synthesized and isolated.4 Because the magnesium ionic radius is similar to that of zinc, and the solid state structures of various bis(formazanate)magnesium complexes (n-Mg) presented in this chapter are closely related to their Zn congeners, cyclic voltammetry studies were performed for comparison. The redox chemistry of bis(formazanate)magnesium differs markedly from that in the zinc analogues: nMg/Ca do not show clean, reversible cyclic voltammograms. We suggest this to be due to their increased ionic character, which results in subsequent chemical transformations that to date could not be characterized in detail.. 3.5 Conclusions A study of the first bis(formazanate) alkaline-earth complexes is presented in this chapter. This. study. comprises. the. synthesis. and. characterization. of. a. series. of. bis(formazanate)magnesium and calcium complexes (n-Mg/MgTHF/Ca), where the steric and electronic properties of the formazan backbone (NNCNN) were manipulated. The increased acidity of the metal centers, in contrast with the analogue zinc, allows coordination of THF (n-MgTHF/Ca), increasing the coordination number by one or two depending on the steric effect of the substituents and the ionic radius of the metal center. The solid-state structures showed N-phenyl groups that are coplanar with the NNCNN backbone. However, when the bulkier N-mesityl substituent is present, they displayed an almost perpendicular orientation, #.
(44) disrupting conjugation with the backbone. UV/Vis absorption studies for the intensely colored complexes n-Ca indicated absorption maxima between 460 and 510 nm due to π-π* transitions within the formazanate framework. An increase in the steric effects implies a decrease in conjugation within the backbone, which is translated into hypsochromic shifts. Cyclic voltammetry studies on bis(formazanate)magnesium and calcium complexes show markedly different redox-behaviour between these alkaline earth complexes and their zinc analogues. While the latter show well-behaved, reversible electrochemistry, the Mg and Ca complexes studied in this chapter result in complex voltammograms. Although the details of this difference are currently not well-understood, it is likely that it relates to the more ionic bonding for Mg/Ca.. 3.6 Experimental 3.6.1 General considerations All manipulations were carried out under nitrogen atmosphere using standard glovebox, Schlenk, and vacuum-line techniques. Toluene, hexane, and pentane (Aldrich, anhydrous, 99.8%) were passed over columns of Al2O3 (Fluka), BASF R3-11-supported Cu oxygen scavenger, and molecular sieves (Aldrich, 4 Å). Diethyl ether and THF (Aldrich, anhydrous, 99.8%) were dried by percolation over columns of Al2O3 (Fluka). Deuterated solvents were vacuum transferred from Na/K alloy (C6D6, toluene-d8, Aldrich) and stored under nitrogen. Ca(NTMS)2(THF)2 was prepared according to published procedures and added in an excess of 1.5 equivalents due to previously reported side reactions.6 Dimethylzinc (Aldrich, 2.0 M in toluene) was used as received. NMR spectra were recorded on Varian Gemini 200, VXR 300, Mercury 400 or Varian 500 spectrometers. The 1H and 13C NMR spectra were referenced internally using the residual solvent resonances and reported in ppm relative to TMS (0 ppm); J is reported in Hz. Assignment of NMR resonances was aided by gradient-selected COSY, NOESY, HSQC and/or HMBC experiments using standard pulse sequences. All electrochemical measurements were performed under an inert N2 atmosphere in a glove box using an Autolab PGSTAT 100 (or PGSTAT 302N) computer-controlled potentiostat. Cyclic voltammetry (CV) was performed using a three-electrode configuration comprising of a Pt wire counter electrode, a Ag wire pseudoreference electrode and a Pt disk working electrode (CHI102, CH Instruments, diameter = 2 mm). The Pt working electrode was polished before experiment using alumina slurry (0.05 μm), rinsed with distilled water .
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(47) and subjected to brief ultrasonication to remove any adhered alumina microparticles. The electrodes were then dried in an oven at 75 °C overnight to remove any residual traces of water. The CV data was calibrated by adding ferrocene in THF solution at the end of experiments. In all cases, there is no indication that addition of ferrocene influences the electrochemical behaviour of products. All electrochemical measurements were performed at ambient temperatures under an inert N2 atmosphere in THF containing 0.1 M [nBu4N][PF6] (or [nBu4N][B(C6F5)4]) as the supporting electrolyte. Data were recorded with Autolab NOVA software (v.1.8). UV/Vis spectra were recorded in THF solution (~ 10-5 M) using a Avantes AvaSpec 3648 spectrometer and AvaLight-DHS lightsource inside a N2 atmosphere glovebox. Elemental analyses were performed at the Microanalytical Department of the University of Groningen or Kolbe Microanalytical Laboratory (Mülheim an der Ruhr, Germany).. 3.6.2 Synthesis and characterization 3.6.2.1 Bis(formazanate)magnesium complexes [PhNNC(p-tol)NNPh]2Mg (1-Mg) 1,5-Diphenyl-3-para-tolyl formazan24 1-H (3.056 g, 9.720 mmol) was dissolved in toluene (20 mL) and a 1.0 M solution of di-n-butyl magnesium in heptane (4.9 mL, 4.9. Ph N N p-tol. Ph. Mg N N. mmol) was added. The solution turned from dark red to dark. Ph Ph. violet and gas evolution was observed. The solution was. 1-Mg. N N N N. p-tol. stirred for 30 minutes and removing the solvent under vacuo afforded the product (3.031 g, 4.655 mmol, yield: 96%). Crystals suitable for X-ray analysis were obtained from toluene/pentane. 1H NMR (C6D6, 500 MHz): δ 8.47 (4H, d, J = 7.8 Hz, p-tol m-H), 7.62 (8H, d, J = 8.0 Hz, Ph o-H), 7.31 (4H, d, J = 7.8 Hz, p-tol o-H), 6.82 (8H, t, J = 7.7 Hz, Ph m-H), 6.68 (4H, t, J = 7.3 Hz, Ph p-H), 2.27 (6H, s, p-tol p-CH3).. 13. C NMR (C6D6, 126 MHz): δ. 153.6 (Ph i-C), 146.25 (p-tol i-C), 138.11 (NNCNN), 137.49 (p-tol p-C), 130.25 (Ph m-C), 130.02 (p-tol o-C), 128.11 (Ph p-C), 126.91 (p-tol m-C), 120.35 (Ph o-C), 21.64 (p-tol p-CH3).. .
(48) [PhNNC(p-tol)NNPh]2Mg(THF) (1-MgTHF) Complex 1-Mg was dissolved in THF and removed solvent. H NMR (C6D6, 500 MHz): δ 8.51 (4H, d, J = 7.8 Hz, p-tol. Ph Ph THF N N Mg N N N N Ph Ph. m-H), 7.70 (8H, d, J = 7.8 Hz, Ph o-H), 7.33 (4H, d, J = 7.8. 1-Mg THF. under vacuo to afford 1-MgTHF in quantitative yield. Crystals suitable for X-ray analysis were obtained from THF/pentane. 1. N N p-tol. p-tol. Hz, p-tol o-H), 6.90 (8H, t, J = 7.6 Hz, Ph m-H), 6.76 (4H, t, J = 7.2 Hz, Ph o-H), 3.25 (4H, THF), 2.27 (6H, s, p-tol p-CH3), 0.75 (4H, THF). 13C NMR (C6D6, 126 MHz): δ 154.06 (Ph iC), 146.21 (p-tol i-C), 138.27 (NNCNN), 137.19 (p-tol p-C), 130.01 (p-tol o-C), 129.53 (Ph m-C), 127.22 (Ph p-C), 126.45 (p-tol m-C), 121.37 (Ph o-C), 69.85 (THF), 25.07 (THF), 21.64 (p-tol p-CH3). Elemental analysis calculated for C44H44N8OMg: C, 73.08; H, 5.85; N, 15.49. Found: C, 73.28; H, 5.57; N, 15.68. [PhNNC(tBu)NNPh]2Mg (3-Mg) 1,5-Diphenyl-3-tert-butyl formazan25 3-H (1.048 g, 3.738 mmol) was dissolved in toluene (20 mL) and a 1.0 M solution of di-n-. Ph tBu. butyl magnesium in heptane (1.9 mL, 1.9 mmol) was added. The. N N. Ph. Mg N N. solution turned from yellow to dark violet and gas evolution was. Ph Ph. observed. The solution was stirred for 30 minutes and removing. 3-Mg. N N N N. tBu. the solvent under vacuo afforded the product (1.072 g, 1.832 mmol, yield: 98%). Crystals suitable for X-ray analysis were obtained from toluene/pentane. 1H NMR (C6D6, 400 MHz): δ 7.56 (8H, d, J = 7.8 Hz, Ph o-H), 6.88 (8H, t, J = 7.6 Hz, Ph m-H), 6.71 (4H, t, J = 7.2 Hz, Ph p-H), 1.73 (18H, s, tBu). 13C NMR (C6D6, 126 MHz): δ 154.44 (NNCNN), 154.02 (Ph i-C), 130.09 (Ph m-C), 127.60 (Ph p-C), 120.06 (Ph o-C), 39.96 (C(CH3)3), 31.81 (C(CH3)3). [PhNNC(tBu)NNPh]2Mg(THF) (3-MgTHF) Compound 3-Mg was dissolved in THF and removed solvent. NMR (C6D6, 500 MHz): δ 7.63 (8H, d, J = 7.8 Hz, Ph o-H), 6.91. Ph Ph THF N N Mg N N N N Ph Ph. (8H, t, J = 7.6 Hz, Ph m-H), 6.75 (4H, t, J = 7.2 Hz, Ph p-H),. 3-MgTHF. under vacuo to afford 3-MgTHF in quantitative yield. Crystals suitable for X-ray analysis were obtained from THF/pentane. 1H. t. tBu. N N. tBu. 13. 3.28 (4H, THF) 1.75 (18H, s, Bu), 0.94 (4H, THF). C NMR (C6D6, 126 MHz): δ 154.44 (Ph i-C), 154.24 (NNCNN), 128.58 (Ph m-C), 126.62 (Ph p-C), 121.01 (Ph o-C), 69.53 (THF),. .
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(51) 39.34 (C(CH3)3), 31.87 (C(CH3)3), 25.30 (THF). Elemental analysis calculated for C38H46N8OMg: C, 69.67; H, 7.08; N, 17.10. Found: C, 70.00; H, 7.11; N, 17.11. [MesNNC(p-tol)NNPh]2Mg (4-Mg) 1-Phenyl-3-para-tolyl-5-mesityl formazan8 4-H (985.6 mg,. Ph. 2.765 mmol) was dissolved in toluene (20 mL) and a 1.0 M solution of di-n-butyl magnesium in heptane (1.38 mL, 1.38. N N p-tol. Ph. Mg N N. N N N N. mmol) was added. The solution turned from dark red to dark. Mes Mes. violet and gas evolution was observed. The solution was. 4-Mg. p-tol. stirred for 30 minutes and removing the solvent under vacuo afforded the product (686.9 mg, 0.932 mmol, yield: 68%). Crystals suitable for X-ray analysis were obtained from toluene/pentane. 1H NMR (C6D6, 500 MHz): δ 8.32 (4H, d, J = 7.7 Hz, p-tol m-H), 7.60 (4H, d, J = 7.8 Hz, Ph o-H), 7.21 (4H, d, J = 7.7 Hz, p-tol o-H), 6.90 (4H, t, J = 7.6 Hz, Ph m-H), 6.75 (2H, t, J = 7.1 Hz, Ph o-H), 6.39 (4H, s, Mes m-H), 2.20 (6H, s, p-tol o-CH3), 1.96 (6H, s, Mes p-CH3), 1.90 (12H, s, Mes o-CH3).. 13. C NMR (C6D6, 126 MHz): δ 153.64 (Ph i-C),. 148.32 (Mes i-C), 146.39 (p-tol i-C), 137.59 (NNCNN), 137.33 (p-tol p-C), 136.70 (Mes p-C), 131.16 (Mes o-C), 130.31 (Mes m-C), 130.09 (Ph m-C), 129.96 (p-tol o-C), 127.40 (Ph p-C), 126.35 (p-tol m-C), 120.19 (Ph o-C), 21.57 (p-tol CH3), 21.14 (Mes p-CH3), 18.75 (Mes oCH3). [MesNNC(p-tol)NNPh]2Mg(THF) (4-MgTHF) Compound 4-Mg was dissolved in THF and removed solvent. H NMR (C6D6, 500 MHz): δ 8.31 (4H, d, J = 7.8 Hz, p-tol o-. Ph Ph THF N N Mg N N N N Mes Mes. H), 7.64 (4H, d, J = 7.8 Hz, Ph o-H), 7.22 (4H, d, J = 7.8 Hz,. 4-MgTHF. under vacuo to afford 4-MgTHF in quantitative yield. Crystals suitable for X-ray analysis were obtained from THF/hexane. 1. N N p-tol. p-tol. p-tol m-H), 6.94 (4H, t, J = 7.6 Hz, Ph m-H), 6.78 (2H, t, J = 7.2 Hz, Ph p-H), 6.41 (4H, s, Mes m-CH), 3.49 (THF), 2.20 (6H, s, p-tol p-CH3), 1.99 (6H, s, Mes p-CH3), 1.93 (12H, 2, Mes o-CH3), 1.21 (THF).. 13. C NMR (C6D6, 126 MHz): 153.99 (Ph i-C), 149.10 (Mes i-C),. 146.43 (p-tol i-C), 137.47 (NNCNN), 137.27 (p-tol p-C), 136.36 (Mes p-C), 131.41 (Mes oC), 130.18 (Mes m-C), 129.94 (p-tol o-C), 129.80 (Ph m-C), 126.91 (Ph p-C), 126.23 (p-tol m-C), 120.65 (Ph o-C), 68.83 (THF), 25.88 (THF), 21.58 (p-tol CH3), 21.16, (Mes p-CH3), 18.97 (Mes o-CH3).. .
(52) [C6F5NNC(p-tol)NNMes]2Mg (6-Mg) 1-Mesityl-3-para-tolyl-5-pentafluorophenyl formazan8 6-H (840.1 mg, 1.882 mmol) was dissolved in toluene (20 mL) and a 1.0 M solution of di-n-butyl magnesium in heptane. C6F 5. Mes. N N p-tol. Mg N N. N N N N. (0.94 mL, 0.94 mmol) was added. The solution turned from. C6F 5 Mes. dark red to dark violet and gas evolution was observed. The. 6-Mg. p-tol. solution was stirred for 30 minutes and removing the solvent under vacuo afforded the product (718.0 mg, 0.783 mmol, yield: 83%). Crystals suitable for X-ray analysis were obtained from toluene/pentane. 1H NMR (C6D6, 500 MHz): Major isomer: δ 8.24 (4H, d, J = 7.8 Hz, p-tol m-H), 7.20 (4H, d, J = 7.8 Hz, Ph o-H), 6.39 (4H, s, Mes m-H), 2.17 (6H, s, p-tol o-CH3), 1.96 (6H, s, Mes p-CH3), 1.87 (12H, s, Mes o-CH3). Minor isomer: δ 8.07 (br), 7.04 (br), 1.66. 13C NMR (C6D6, 126 MHz): δ 148.42 (Mes i-C), 146.55 (p-tol i-C), 141.18 (d, J = 245.42 Hz), 138.89 (d, J = 252.73 Hz), 138.28 (Mes p-C), 138.05 (p-tol p-C), 136.70 (NNCNN), 131.06 (Mes o-C), 130.11 (p-tol m-C), 129.88 (Mes m-C), 126.21 (p-tol o-C), 21.54 (p-tol p-CH3), 20.79 (Mes p-CH3), 18.06 (Mes o-CH3).. 19. F NMR (C6D6, 376 MHz):. Major isomer: δ -155.24 (2F, br, C6F5 o-F), -163.43 (2F, br, C6F5 m-F), -164.76 (1F, t, J = 21.0 Hz, C6F5 p-F). Minor isomer: δ -158.80 (br), -162.10 (br), -164.35 (t), -165.35 (br), 170.78 (t). [C6F5NNC(p-tol)NNMes]2Mg(THF) (6-MgTHF) Compound 6-Mg was dissolved in THF and removed solvent. H NMR (C6D6, 500 MHz): Major isomer: δ 8.21 (4H, d, J =. C6F 5 Mes THF N N Mg N N N N C6F 5 Mes. 7.8 Hz, p-tol m-H), 7.18 (4H, d, J = 7.8 Hz, Ph o-H), 6.44 (4H,. 6-Mg THF. under vacuo to afford 6-MgTHF in quantitative yield. Crystals suitable for X-ray analysis were obtained from THF/pentane. 1. N N p-tol. p-tol. s, Mes m-H), 3.55 (THF), 2.15 (6H, s, p-tol o-CH3), 2.01 (6H, s, Mes p-CH3), 1.91 (12H, s, Mes o-CH3) 1.31 (THF). Minor isomer: δ 8.08 (br), 7.01 (br), 6.20 (br), 1.66 (br). 13C NMR (C6D6, 126 MHz): δ 148.81 (Mes i-C), 146.88 (p-tol i-C), 141.34 (d, J = 241.34 Hz), 138.77 (d, J = 241.34 Hz) 138.21 (Mes p-C), 137.97 (p-tol p-C), 136.37 (NNCNN), 131.00 (Mes oC), 130.11 (p-tol m-C), 129.84 (Mes m-C), 126.08 (p-tol o-C), 68.74 (THF), 25.99 (THF), 21.54 (Mes p-CH3), 20.80 (p-tol p-CH3), 18.21 (Mes o-CH3).. 19. F NMR (C6D6, 376 MHz):. Major isomer: δ -154.07 (2F, br, C6F5 o-F), -163.45 (2F, br, C6F5 m-F), -164.50 (1F, t, J = 21.6 Hz, C6F5 p-F). Minor isomer: δ -153.71 (d), -158.79 (br), -162.61 (br), -165.35 (br), 170.70 (br). .
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(55) [PhNNC(C6F5)NNMes]2Mg (8-Mg) 1-Phenyl-3-pentafluorophenyl-5-mesityl. formazan26. 8-H. Ph N N. (1.189 g, 2.750 mmol) was dissolved in toluene (20 mL) and a 1.0 M solution of di-n-butyl magnesium in heptane (1.38. Ph. Mg. C6F 5 N N. N N N N. mL, 1.38 mmol) was added. The solution turned from dark. Mes Mes. red to dark violet and gas evolution was observed. The. 8-Mg. C6F 5. solution was stirred for 30 minutes and removing the solvent under vacuo afforded the product (1.022 g, 1.150 mmol, yield: 84%). Crystals suitable for X-ray analysis were obtained from toluene/pentane. 1H NMR (C6D6, 400 MHz): δ 7.59 (4H, d, J = 7.7 Hz, Ph o-H), 7.11 (4H, t, J = 7.5 Hz, Ph m-H), 6.87 (2H, t, J = 7.2 Hz, Ph p-H), 6.36 (4H, s, Mes m-H), 1.93 (6H, s, Mes p-CH3), 1.91 (12H, s, Mes o-CH3).. 13. C NMR (C6D6, 126 MHz): δ 152.59 (Ph i-C),. 147.45 (Mes i-C), 146.73 (d, J = 244.2 Hz, C6F5), 141.29 (d, J = 251.3 Hz, C6F5 p-C), 138.39 (d, J = 251.1 Hz, C6F5), 137.35 (Mes p-C), 135.60, 130.81 (Mes o-C), 130.44 (Ph m-C), 130.26 (Mes m-C), 128.80 (Ph p-C), 120.08 (Ph o-C), 21.06 (Mes p-CH3), 18.57 (Mes o-CH3). 19. F NMR (C6D6, 376 MHz): δ -143.65 (2F, dd, J = 24.5 Hz and 7.5 Hz, C6F5 m-F), -156.59. (1F, t, J = 21.4 Hz, C6F5 p-F), -163.15 (2F, dt, J = 22.8 Hz and J = Hz, C6F5 o-F). [C6F5NNC(C6F5)NNMes]2Mg (9-Mg) 1,3-dipentafluorophenyl-5-mesityl formazan23 9-H (1.017 g, 1.947 mmol) was dissolved in toluene (20 mL) and a 1.0 M solution of di-n-butyl magnesium in heptane (0.98 mL, 0.98 C6F 5 mmol) was added. The solution turned from dark red to dark violet and gas evolution was observed. Removing the solvent. C6F 5 Mes N N N N Mg N N N N C6F 5 Mes. C6F 5. 9-Mg. under vacuo afforded the product (653.2 mg, 0.611 mmol, yield: 63%). Crystals suitable for X-ray analysis were obtained from toluene/pentane. Elemental analysis calculated for C44H22F20N8Mg: C, 49.53; H, 2.08 5; N, 10.50. Found: C, 49.66; H, 2.45; N, 10.09.. .
(56) . 3.6.2.2 Bis(formazanate)calcium complexes [PhNNC(p-tol)NNPh]2Ca(THF)2 (1-Ca) To a red solution of LH24 (1-H, 176.2 mg, 0.561 mmol) in THF (15 ml), Ca(NTMS)2(THF)2 (212.6 mg, 0.421 mmol). Ph THF. N N p-tol. was added. After stirring at room temperature overnight, the. Ca N N Ph. volatiles were removed under vacuo and the residue was. Ph N N N N. p-tol. THF Ph. 1-Ca. subsequently extracted three times into an intense violet. toluene solution (15 ml). Removal of all volatiles and subsequent washing with hexane resulted in a dark purple powder of 1-Ca (214.1 mg. 0.264 mmol, 94%). Crystals suitable for X-ray analysis were obtained by slow diffusion of hexane into a THF solution of 1-Ca. 1H NMR (C6D6, 25 ºC, 500 MHz): δ 8.57 (d, 4H, J = 7.6, p-tol o-H), 7.89 (d br, 8H, J = 7.4, Ph oH), 7.36 (d, 4H, J = 7.6, p-tol m-H), 7.06 (t, 8H, J = 7.7, Ph m-H), 6.86 (t, 4H, J = 7.2, Ph pH), 3.29 (q, 8H, THF), 2.29 (s, 6H, CH3), 0.76 (q, 8H, THF).. 13. C NMR (C6D6, 25 ºC, 126. MHz): δ 155.06 (Ph ipso-C), 146.05 (NCN), 138.76 (p-tol ipso-C), 136.28 (p-tol p-C), 129.56 (p-tol m-CH), 129.28 (Ph m-CH), 126.05 (p-tol o-CH and Ph p-CH), 120.80 (Ph o-CH), 69.25 (THF), 24.86 (THF), 21.36 (p-tol CH3). Anal. calcd. for C48H50N8CaO2: C 71.08, H 6.21, N 13.82; found: C 70.93, H 6.23, N 13.38. [PhNNC(tBu)NNPh]2Ca(THF)2 (3-Ca) To an orange solution of LH25 (3-H, 149.3 mg, 0.533 mmol) in THF (15 ml), Ca(NTMS)2(THF)2 (201.3 mg, 0.399 mmol) was added. After stirring at room temperature overnight, the volatiles were removed under vacuo and the residue was subsequently extracted into an intense blue-violet toluene solution (15 ml). Ph tBu. THF. N N. Ca N N Ph. Ph N N N N. tBu. THF Ph. 3-Ca. three times. Removal of all volatiles and subsequent washing with hexane resulted in a dark purple powder of 3-Ca (191.2 mg, 0.257 mmol, 96%). Crystals suitable for X-ray analysis were obtained by slow evaporation of hexane. 1H NMR (C6D6, 25 ºC, 400 MHz): δ 7.73 (d, 8H, J = 7.2, Ph o-H), 7.18 (t, 8H, J = 7.0, Ph m-H), 6.92 (t, 4H, J = 6.8, Ph p-H), 3.31 (br, 8H, THF), 1.83 (s, 18H, tBu), 0.88 (br, 8H, THF).. 13. C NMR (C6D6, 25 ºC, 101 MHz): δ 173.84. (NCN), 155.77 (Ph ipso-C), 129.24 (Ph m-CH), 125.36 (Ph p-CH), 120.14 (Ph o-CH), 68.88 (THF), 38.91 (C(CH3)3), 31.71 (C(CH3)3), 24.95 (THF). Anal. calcd. for C42H54N8CaO2: C 67.89, H 7.33, N 15.08; found: C 67.38, H 6.98, N 15.09.. .
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(59) [MesNNC(p-tol)NNPh]2Ca(THF) (4-Ca) To a red solution of LH8 (4-H, 128.0 mg, 0.359 mmol) in THF (15 ml), Ca(NTMS)2(THF)2 (135.9 mg, 0.269 mmol) was added. After stirring at room temperature overnight, the. Ph N N p-tol. THF. N N. Ca. N N. N N. volatiles were removed under vacuo and the residue was. Ph p-tol. Mes. Mes. 4-Ca. subsequently extracted into an intense violet toluene solution. (15 ml) three times. Removal of all volatiles and subsequent washing with hexane resulted in a dark brown powder of 4-Ca (100.9 mg, 0.123 mmol, 68%). Crystals suitable for X-ray analysis were obtained by slow evaporation of pentane. 1H NMR (C6D6, 75 ºC, 500 MHz): δ 8.28 (d, 4H, J = 7.6, p-tol o-H), 7.55 (d, 4H, J = 7.4, Ph o-H), 7.22 (d, 4H, J = 7.9, p-tol m-H), 7.08 (t, 4H, J = 7.5, Ph m-H), 6.87 (t, 2H, 7.4, Ph p-H), 6.60 (s, 4H, Mes m-H), 3.36 (s br, 8H, THF), 2.25 (s, 6H, p-tol CH3), 2.08 (s, 6H, Mes p-CH3), 2.03 (s, 12H, Mes o-CH3), 1.17 (s br, 8H, THF).. 13. C NMR (C6D6, 75 ºC, 126 MHz): δ 155.54 (Ph ipso-C), 150.46 (Mes ipso-C),. 147.02 (p-tol ipso-C), 137.80 (NCN), 136.68 (p-tol p-C), 135.72 (Mes p-C), 130.95 (Mes oC), 130.50 (Mes m-CH), 129.91 (Ph m-CH), 129.67 (p-tol m-CH), 126.43 (p-tol o-CH), 125.43 (Ph p-CH), 120.43 (Ph o-CH), 68.88 (THF), 25.70 (THF), 21.53 (p-tol CH3), 21.15 (Mes p-CH3), 19.09 (Mes o-CH3). Anal. calcd. for C54H62N8CaO2: C 72.45, H 6.98, N 12.52. Satisfactory elemental analysis could not be obtained, despite repeated attempts.. [MesNNC(p-tol)NNMes]2Ca(THF) (5-Ca) To an orange solution of LH8 (5-H, 168.5 mg, 0.423 mmol) in THF (15 ml), Ca(NTMS)2(THF)2 (159.5 mg, 0.316 mmol) was added. After stirring at room temperature overnight, the volatiles were removed under vacuo and the residue was subsequently extracted into a dark orange toluene solution. p-tol. Mes Mes THF N N N N Ca N N N N Mes. p-tol. Mes. 5-Ca. (15 ml) three times. Removal of all volatiles resulted in a dark orange powder of 5-Ca (95.4 mg, 0.105 mmol, 49%). Crystalline material was obtained by slow diffusion of hexane into a THF solution of 5-Ca. Crystals suitable for X-ray analysis could not be obtained 1H NMR (C6D6, 25 ºC, 400 MHz): δ 8.21 (d, 4H, J = 7.6, p-tol o-H), 7.17 (d, 4H, p-tol m-H), 6.58 (s, 8H, Mes m-H), 3.02 (br, 4H, THF), 2.18 (s, 6H, p-tol CH3), 2.14 (s, 24H, Mes o-CH3), 2.11 (s, 12H, Mes p-CH3), 0.81 (br, 4H, THF). 13C NMR (C6D6, 25 ºC, 101 MHz): δ 150.69 (Mes ipso-C), 145.64 (p-tol ipso-C), 138.32 (NCN), 135.69 (p-tol p-C), 134.53 (Mes p-C), 130.53 (Mes o-C), 129.96 (Mes m-CH), 129.34 (p-tol m-CH), 125.29 (p-tol o-CH), 68.91 (THF), !.
(60) 25.04 (THF), 21.24 (p-tol CH3), 20.94 (Mes p-CH3), 19.69 (Mes o-CH3). Satisfactory elemental analysis could not be obtained, despite repeated attempts.. Crystallographic data Suitable crystals of 1,3,4,6,8,9-Mg, 1,3,4,6-MgTHF and 1,3,4-Ca were mounted on a cryo-loop in a drybox and transferred, using inert-atmosphere handling techniques, into the cold nitrogen stream of a Bruker D8 Venture diffractometer. Intensity data were corrected for Lorentz and polarisation effects, scale variation, for decay and absorption: a multiscan absorption correction was applied, based on the intensities of symmetry-related reflections measured at different angular settings (SADABS).27 The structures were solved by direct methods using the program SHELXS.28 The hydrogen atoms were generated by geometrical considerations and constrained to idealise geometries and allowed to ride on their carrier atoms with an isotropic displacement parameter related to the equivalent displacement parameter of their carrier atoms. Structure refinement was performed with the program package SHELXL.28 Crystal data and details on data collection and refinement are presented in following tables.. " .
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(63) 1-Mg chem formula Mr cryst syst color, habit size (mm) space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å3) Z ρcalc, g.cm-3 Radiation [Å] µ(Mo K ), mm-1 F(000) temp (K) θ range (°) data collected (h,k,l) min, max transm rflns collected indpndt reflns observed reflns Fo ≥ 2.0 σ (Fo) R(F) (%) wR(F2) (%) GooF weighting a,b params refined min, max resid dens α. 4-Mg. 6-Mg. 583.03 monoclinic black, block 0.39x0.32x0.30 P21/n 14.0728(10) 9.6417(6) 24.4136(15) 90.00 100.719(2) 90.00 3254.8(4) 4 1.190 Mo Kα 0.71073 0.091 1240 200(2) 2.80 - 28.34 -18:18; -12:12; 32:32 0.9656, 0.9734 128928 8081. C46 H46 Mg N8 735.22 monoclinic purple, block 0.25x0.22x0.10 C2/c 17.7960(8) 11.5035(6) 19.4349(9) 90.00 97.971(2) 90.00 3940.2(3) 4 1.239 Mo Kα 0.71073 0.089 1560 100(2) 2.88 - 27.18 -22:22; -14:14; 24:24 0.9780, 0.9911 44914 4371. C46 H36 F10 Mg N8 915.14 triclinic dark red, platelet 0.29x0.13x0.03 P-1 11.5549(8) 14.8006(10) 15.1629(9) 68.145(2) 74.116(3) 73.402(3) 2265.3(3) 2 1.342 Mo Kα 0.71073 0.123 940 100(2) 2.85 - 26.37 -14:14; -18:18; 18:18 0.9653, 0.9963 67338 9265. 6456. 5844. 3782. 8021. 4.45 9.92 1.042 0.0426, 8.8605 496. 4.70 12.55 1.031 0.0555, 1.0369 425. 3.84 9.92 1.046 0.0447, 4.1116 253. 5.05 13.68 1.068 0.0603, 2.2576 594. -0.248, 0.045. -0.195, 0.039. -0.257, 0.045. -0.317, 0.059. C43.50 H38 Mg N8 697.13 monoclinic dark violet, needle 0.30x0.09x0.03 C2/c 31.6676(15) 13.0632(7) 18.7138(9) 90.00 106.284(2) 90.00 7431.0(6) 8 1.246 Mo Kα 0.71073 0.091 2936 100(2) 2.68 - 27.15 -40:40; -16:16; 24:24 0.9732, 0.9973 103535. 3-Mg C34 H38 Mg N8. . #.
(64) . chem formula Mr cryst syst color, habit size (mm) space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å3) Z ρcalc, g.cm-3 Radiation [Å] µ(Mo K ), mm-1 F(000) temp (K) θ range (°) data collected (h,k,l) min, max transm rflns collected indpndt reflns observed reflns Fo ≥ 2.0 σ (Fo) R(F) (%) wR(F2) (%) GooF weighting a,b params refined min, max resid dens α. . . 8-Mg. 1-MgTHF. 3-MgTHF. C44 H32 F10 Mg N8 887.09 monoclinic. C44 H42 Mg N8 O 723.17 monoclinic. C38 H46 Mg N8 O 655.14 monoclinic. 0.16x0.13x0.12 C2/c 18.1013(8) 11.3625(4) 19.4233(8) 90.00 90.786(2) 90.00 3994.5(3) 4 1.475 Mo Kα 0.71073 0.136 1816 100(2) 2.97 - 27.17 -23:23; -14:14; 24:24 0.9785, 0.9838 29551 4434. 0.41x0.21x0.17 P 21/c 17.4561(18) 10.8846(11) 20.048(2) 90.00 97.493(4) 90.00 3776.6(7) 4 1.272 Mo Kα 0.71073 0.094 1528 100(2) 2.91 - 26.37 -21:21; -13:13; -24:24 0.9625, 0.9842 27683 28081. 0.46x0.15x0.11 P 21/c 37.4564(19) 10.5950(6) 18.9930(11) 90.00 104.6834(18) 90.00 7291.2(7) 8 1.194 Mo Kα 0.71073. -42:46; -13:13; 23:23 0.682, 0.732 167434 14814. 3735. 20761. 13854. 3.72 9.91 1.035 0.0474, 4.3373 288. 7.10 22.19 1.062 0.1154, 3.4107 490. 6.17 11.83 1.277 0, 8.4232 876. -0.221, 0.049. -0.586, 0.124. -0.321, 0.060. 2800 100(1).
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(67) . chem formula Mr cryst syst. 4-MgTHF. 6-MgTHF. 1-Ca. C50 H54 Mg N8 O 807.32 monoclinic. C50 H44 F10 Mg N8 O 987.24 triclinic. C24 H25 Ca0.50 N4 O 405.52 monoclinic. color, habit. dark red, block. size (mm) space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å3) Z ρcalc, g.cm-3. 0.43x0.22x0.11 0.29x0.13x0.08 P21/c P-1 10.6361(5) 10.5671(5) 29.3572(16) 14.5535(7) 15.5548(9) 16.4424(9) 90.00 72.545(2) 108.441(2) 85.812(2) 90.00 70.726(2) 4607.5(4) 2276.1(2) 4 2 1.164 1.441 Mo Kα Mo Kα 0.71073 0.71073. Radiation [Å] µ(Mo K ), mm-1 F(000) temp (K) θ range (°) data collected (h,k,l) min, max transm rflns collected indpndt reflns observed reflns Fo ≥ 2.0 σ (Fo) R(F) (%) wR(F2) (%) GooF α. weighting a,b params refined min, max resid dens. 3-Ca. 4-Ca. C42 H54 Ca N8 O2 743.01 tetragonal dark red, purple, block platelet 0.35x0.26x0.10 0.25x0.20x0.07 C2/c I4(1)/a 25.3861(17) 28.525(2) 9.1463(6) 28.525(2) 20.9726(13) 20.2590(18) 90.00 90.00 121.399(2) 90.00 90.00 90.00 4156.5(5) 16484(2) 8 16 1.296 1.198. C52.50 H60 Ca N8 O 859.16 monoclinic. MoKα 0.71073 MoKα 0.71073. MoKα 0.71073. brown, block 0.26x0.23x0.12 P 21/c 10.9601(9) 29.707(2) 15.2607(13) 90.00 108.531(3) 90.00 4711.1(7) 4 1.211. 0.084. 0.129. 0.202. 0.197. 0.180. 1720 100(2) 2.78 - 26.37 -13:12; -36:36; -19:19. 1020 100(2) 2.69 - 27.16 -13:13; -18:18; -21:21. 1720 100(2) 2.87 - 27.15 -32:32; -11:11; -26:26. 6368 100(2) 2.76 - 27.12 -36:36; -36:36; -25:25. 1836 100(2) 2.743 - 26.022 -13:13; -36:36; -15:15. 0.9649, 0.9909. 0.9635, 0.9897. 0.9328, 0.9801. 0.9524, 0.9863. 0.7134, 0.7454. 76728 9415. 61599 10070. 58683 4607. 169271 9092. 203862 8670. 7122. 7879. 4135. 7493. 7049. 5.29 14.03 1.024. 3.83 9.92 1.022. 3.57 9.01 1.035. 0.0730, 1.8022. 0.0470, 1.0090. 0.0390, 4.5205. 3.66 9.06 1.047 0.0351, 18.3537. 6.82 16.05 1.138 0.0314, 11.8144. 550. 639. 268. 515. 596. -0.235, 0.052. -0.293, 0.050. -0.245, 0.043. -0.268, 0.041. -0.546, 0.064. . .
(68) . 3.7 References (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28). . Chamberlain, B. M.; Cheng, M.; Moore, D. R.; Ovitt, T. M.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 3229–3238. Moxey, G. J.; Ortu, F.; Goldney Sidley, L.; Strandberg, H. N.; Blake, A. J.; Lewis, W.; Kays, D. L. Dalton Trans. 2014, 43 (43), 4838. Harder, S. Chem. Rev. 2010, 110 (7), 3852–3876. Chang, M. C.; Dann, T.; Day, D. P.; Lutz, M.; Wildgoose, G. G.; Otten, E. Angew. Chemie - Int. Ed. 2014, 53, 4118–4122. Travieso-Puente, R.; Chang, M.-C.; Otten, E. Dalt. Trans. 2014, 43, 18035–18041. Johns, A. M.; Chmely, S. C.; Hanusa, T. P. Inorg. Chem. 2009, 48, 1380–1384. He, X.; Noll, B. C.; Beatty, A.; Mulvey, R. E.; Henderson, K. W. J. Am. Chem. Soc. 2004, 126, 7444– 7445. Chang, M.-C.; Roewen, P.; Travieso-Puente, R.; Lutz, M.; Otten, E. Inorg. Chem. 2015, 54 (1), 379–388. Chisholm, M. H.; Choojun, K.; Gallucci, J. C.; Wambua, P. M. Chem. Sci. 2012, 3 (12), 3445. Chisholm, M. H.; Choojun, K.; Chow, A. S.; Fraenkel, G. Angew. Chemie Int. Ed. 2013, 52 (11), 3264– 3266. Chisholm, M. H.; Choojun, K.; Chow, A. S.; Fraenkel, G.; Gallucci, J. C. Inorg. Chem. 2013, 52 (19), 11302–11310. Armstrong, D. R.; Forbes, G. C.; Mulvey, R. E.; Clegg, W.; Tooke, D. M. J. Chem. Soc. Dalt. Trans. 2002, No. 8, 1656–1661. Al-Shboul, T. M. A.; Volland, G.; Görls, H.; Westerhausen, M. Zeitschrift für Anorg. und Allg. Chemie 2009, 635, 1568–1572. Barrett, A. G. M.; Crimmin, M. R.; Hill, M. S.; Hitchcock, P. B.; Procopiou, P. A. Dalt. Trans. 2008, 4474. Barrett, A. G. M.; Crimmin, M. R.; Hill, M. S.; Hitchcock, P. B.; Lomas, S. L.; Mahon, M. F.; Procopiou, P. A. Dalton Trans. 2010, 39, 7393–7400. Barman, M. K.; Baishya, A.; Nembenna, S. J. Organomet. Chem. 2015, 785, 52–60. Westerhausen. Coord. Chem. Rev. 1998, 176, 157. Anthony W. Addison, T. Nageswara Rao, Jan Reedijk,’ Jacobus van Rijn, and G. C. V. J. Chem. Soc., Dalt. Trans., 1984, 0, 1349–1356. Martinez, C. R.; Iverson, B. L. Chem. Sci. 2012, 3 (7), 2191. Salonen, L. M.; Ellermann, M.; Diederich, F. Angew. Chemie Int. Ed. 2011, 50 (21), 4808–4842. Barbon, S. M.; Reinkeluers, P. A.; Price, J. T.; Staroverov, V. N.; Gilroy, J. B. Chem. - A Eur. J. 2014, 11340. Barbon, S. M.; Price, J. T.; Reinkeluers, P. A.; Gilroy, J. B. Inorg. Chem. 2014, 53, 10585–10593. Chang, M.-C. Thesis: Formazanate as a Redox-Active, Structurally Versatile Ligand Platform; 2016. Gilroy, J. B.; Ferguson, M. J.; McDonald, R.; Patrick, B. O.; Hicks, R. G. Chem. Commun. (Camb). 2007, 126–128. Neugebauer, F. A.; Trischmann, H. Justus Liebigs Ann. Chem. 1967, 706, 107–111. Chang, M.-C.; Otten, E. Chem. Commun. (Camb). 2014, 50, 7431–7433. Bruker, APEX2 (v2012.4-3), SAINT (Version 8.18C) and SADABS (Version 2012/1), Bruker AXS Inc., Madison, Wisconsin, USA, 2012. Sheldrick, G. M. Acta Crystallogr. Sect. A Found. Crystallogr. 2008, 64 (1), 112–122..
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