Inorganic Chemistry p. 1859 - 1866 (1981)
Update date:2022-09-26
Topics:
Chisholm, Malcolm H.
Huffman, John C.
Tan, Loon-Seng
Ta(NMe2)5 and Me3SiCl (2 equiv) in pentane solvents react to give a microcrystalline precipitate of [TaCl2(NMe2)3]2 according to the stoichiometric reaction Ta(NMe2)5 + 2Me3SiCl → 1/2[TaCl2(NMe2)3]2 + 2Me3SiNMe2. Addition of HNMe2 to [TaCl2(NMe2)3]2 yields TaCl2(NMe2)3(HNMe2) quantitatively. From the reaction between TaCl5 and HNMe2 (5 equiv) in benzene, TaCl3(NMe2)2(HNMe2), TaCl2(NMe2)2(HNMe2), and [TaCl2(NMe2)2(HNMe2)]2O have been isolated and characterized. The first compound was originally prepared by Carnell and Fowles; the latter two compounds are new ones and are formed as minor products in the reaction. The rapid (NMR time scale) and reversible reaction between TaCl3(NMe2)2(HNMe2) and HNMe2 to give TaCl2(NMe2)3(HNMe2) and Me2NH2+Cl- has been established. All the compounds have been characterized by elemental analyses, IR spectroscopy, variable-temperature 220-MHz 1H NMR spectroscopy, and mass spectroscopy. The solid-state molecular structures of [TaCl2(NMe2)3]2, TaCl3(NMe2)2(HNMe2), and [TaCl2(NMe2)2(HNMe2)]2O have been determined by single-crystal X-ray studies. In each compound, tantalum is in a distorted octahedral environment. The Ta-NMe2 groups contain short Ta-N bond distances (1.96 ? averaged) and have planar Ta-NC2 groups indicative of extensive nitrogen p to tantalum d π bonding. The disposition of Me2N- ligands about tantalum is such that tantalum achieves the maximum effect of this π donation, viz., fac in [TaCl2(NMe2)3]2, which has a planar central Ta2(μ-Cl)2 moiety and cis in both TaCl3(NMe2)2(HNMe2) and [TaCl2(NMe2)2(HNMe2)]2O. The latter compound has a nearly linear Ta-O-Ta moiety (174°) with short Ta-O bond distances (1.92 ? averaged) indicative of oxygen p to tantalum d π bonding. The spectroscopic data are consistent with the view that TaCl2(NMe2)3(HNMe2) adopts a similar structure with a fac-Ta(NMe2)3 group. Crystal data are as follows. For [TaCl2(NMe2)3]2: space group = P21/n, a = 10.464 (3) ?, b = 13.224 (4) ?, c = 8.450 (2) ?, β = 98.07 (1)°, Z = 2, V = 1157.6 (1) ?3. For TaCl3(NMe2)2(HNMe2): space group = P21/c, a = 9.750 (3) ?, b = 10.330 (2) ?, c = 14.300 (4) ?, β = 112.05 (1)°, Z = 4, V = 1335.0 (1) ?3. For [TaCl2(NMe2)2(HNMe2)]2O: space group = P21/c, a = 8.314 (1) ?, b = 20.480 (4) ?, c = 15.778 (3) ?, β = 112.22 (1)°, Z = 4, V = 1243.5 (1) ?3.
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