New metallocene complexes of Nb and Ta with functionalized diazoalkanes

The reaction of Cp2MH3, where M  Nb or Ta, with N2CPh2, N2CPh(o-C6H4Br) and N2CHCOOEt was thoroughly studied. It was shown that the primary products of the reaction are the complexes Cp2M(H)(η1-N2CRR′) (2). The complexes 2 are readily oxidized by air to give polymeric (Cp2MO)n, N2CRR′ and RR′CN2CRR′. Interaction of an excess of N2CPh(o-C6H4Br) with Cp2NbH3 leads to a 17-electron complex Cp2Nb( NNCPho-C6H4)2 (6) with two σ-N pyrazole ligands. Finally the reaction of Cp2NbH3 with N2CHCOOEt gives an unusual dimeric complex Cp2Nb2(η5-C5H4C(COOEt)N μ-N)2. The complexes 2 were found to undergo easily substitution of a hydride ligand for a halogen atom. The results of X-ray analysis of the complexes 6 and Cp2Nb(Cl)-η1-N2CPh(o-C6H4Br) are provided.