Synthesis and characterization of niobium(IV) and tantalum(V) guanidinates and benzamidinates -: Molecular structure of the first Nb(IV) guanidinate NbCl2{CyNC(N(SiMe3)2)NCy}2

The reactions between niobium pentachloride or NbCl4(THF)(2) and [(Et2N)(2)TaCl3](2) with various lithium guanidinates or benzamidinates were investigated. [NbCl2{RNCR'NR}(2)] [R=Cy (Cyclohexyl), R'=N(SiMe3)(2) (1); R=SiMe3, R'=p-tolyl (2)] [TaCl3{Me3SiNC(p-tolyl)NSiMe2}(3)] (3) and [(Et2N)(2)TaCl2{RNCR'NR}] [R=SiMe3, R'=p-tolyl (4) and R=Cy, R'=N(SiMe3)(2) (5)] were isolated and characterized by elemental analyses, FT-IR and H-1 NMR or ESR spectroscopy. The molecular structure of 1 corresponds to a centrosymmetric, monomeric [NbCl2{CyNC(N(SiMe3)(2))NCy}(2)] species as established by X-ray diffraction studies with the chloride ligands in trans positions. The guanidinate ligand displays a symmetrical sigma,sigma'-coordination behaviour (Nb-N 2.161(8) Angstrom av.) (C) 1999 Elsevier Science Ltd. All rights reserved.