Chloro(dimethylamido) compounds of tantalum(V): Preparations, properties, and structures of [Ta(NMe2)3Cl2]2, TaCl3(NMe2)2(HNMe2), Ta(NMe2)3Cl2(HNMe2), and [TaCl2(NMe2)2(HNMe2)]2O

Article abstract of DOI:10.1021/ic50220a049

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.