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 LiNHBu^t gave the monomeric complex TaCl(NBu^t)[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.