Organoimido-complexes of tantalum(V). Preparation and X-ray crystal structure of bis[bis(trimethylsilyl)amido]chloro(t-butylimido)-tantalum(V) and bis[bis(trimethylsilyl)amido]-di-µ-bromo-dibromobis-(trimethylsilylimido)ditantalum(V)
Abstract
Some novel organoimido-complexes of tantalum have been obtained from reactions of TaCl3-[N(SiMe3)2]2 with various reagents. Thus addition of LiNHBut gave the monomeric complex TaCl(NBut)[N(SiMe3)2]2(molecular geometry parameters: Ta N 1.763, Ta – N 1.988 and 2.029, Ta – Cl 2.322 Å; Ta NC 165.8°, from crystal structure analysis) corresponding to replacement of two chlorines. Reaction with Me3SiBr led to the formation of the centrosymmetric five-co-ordinated dimer [Ta2(µ-Br)2Br2(NSiMe3)2{N(SiMe3)2}2](for which X-ray structure analysis gave Ta N 1.761, Ta–N 1.965, Ta–Br 2.502; Ta–µ-Br 2.655 and 2.713 Å; TaNSi 166.1°) where two chlorines were replaced by bromines and one N(SiMe3)2 ligand was cleaved to generate the TaNSiMe3 moiety. The unsymmetrical bromine bridge was readily disrupted by addition of neutral donor ligands which produced the compounds TaBr2(NSiMe3)[N(SiMe3)2](C5H5N) and TaBr2(NSiMe3)[N(SiMe3)2]-(PMe3). Reaction of TaCl3[N(SiMe3)2]2 with NaS2CNMe2 gave the adduct Ta(NSiMe3)(S2CNMe2)3-(CH2Cl2) which may involve a seven-co-ordinated tantalum imido-complex.