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

Protonation of the amido groups of M(NMe2)(5) (M = Ta or Nb) with trialkylg uanidines, (RNH)(2)CNR (R = i-Pr or Cy), directly produced a series of five -co-ordinated complexes, M(NMe2)(3)[(RN)(2)CNR] 1-4. Single crystal X-ray a nalysis confirmed that 1 contained a dianionic N,N',N "-triisopropylguanidi nate ligand which was co-ordinated in a chelating bidentate mode. In contra st, protonation of the amido groups of Ta(NMe2)(4)Cl with triisopropylguani dine gave the six-co-ordinated complex Ta(NMe2)(3)Cl[(i-PrN)(2)CNHi-Pr] 5 w hich possessed a bidentate monoanionic guanidinate ligand. Complex 5 can be converted into 1 by reaction with either LiNMe2 or MeMgBr.