Ma K. T. Tin, Natesan Thirupathi, Glenn P. A. Yap and Darrin S. Richeson
Protonation of the amido groups of M(NMe2)5 (M = Ta or Nb) with trialkylguanidines, (RNH)2CNR (R = i-Pr or Cy), directly produced a series of five-co-ordinated complexes, M(NMe2)3[(RN)2CNR] 1–4. Single crystal X-ray analysis confirmed that 1 contained a dianionic N,N′,N
″-triisopropylguanidinate ligand which was co-ordinated in a chelating bidentate mode. In contrast, protonation of the amido groups of Ta(NMe2)4Cl with triisopropylguanidine gave the six-co-ordinated complex Ta(NMe2)3Cl[(i-PrN)2CNHi-Pr] 5 which possessed a bidentate monoanionic guanidinate ligand. Complex 5 can be converted into 1 by reaction with either LiNMe2 or MeMgBr.