Insertion Routes to Tetrasubstituted Guanidinate Complexes of Ta(V) and Nb(V).

The preparation and characterization of guanidinate-containing complexes of Nb and Ta is described. The direct reactions of M(NMe(2))(5) with either dicyclohexylcarbodiimide (CyN=C=NCy) and diisopropylcarbodiimide ((i)PrN=C=N(i)Pr) proceeded smoothly at room temperature under nitrogen to yield [RNC(NMe(2))NR]M(NMe(2))(4) (M = Ta, Nb; R = Cy, (i)Pr). The spectroscopic characterization of these materials is consistent with a symmetrical chelating bidentate guanidinate anion bonded to a pseudo-octahedral metal center.

Transition Metal Complexes of Guanidinate Dianions: Reactions between Guanidines and M(NMe(2))(5) (M = Ta, Nb).

The protonation of two metal-amido groups of M(NMe(2))(5) with trialkylguanidines yielded a series of novel complexes with formulas [RNC(NR)NR]M(NMe(2))(3) (1-4) (M = Ta, Nb; R = isopropyl, cyclohexyl). These complexes contained dianionic N,N',N' '-trialkylguanidinate ligands which were coordinated in a chelating bidentate mode. A single-crystal X-ray study of [CyNC(NCy)NCy]Ta(NMe(2))(3) (3) (C(25)H(51)N(6)Ta, triclinic, P&onemacr;, a = 9.