Guanidinate anions and dianions. Reactions involving alkylguanidines, (RNH)2CNR (R = i-Pr or Cy), and metal amido complexes M(NMe2)5 (M = Ta or Nb)

Abstract

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.