HYDRAZIDO(2-) COMPLEXES OF NIOBOCENE

The new compounds [Nb(eta-C5H4R)(eta-C5H4R')Cl(NNMe2)] (R = H or Me); R' = H or Me), [Nb eta(5)-C5H4R)(2)-(eta(1)-C5H4R)(NNMe2)] (R-3 = H-x or Me-y, x + y = 3), [Nb{CMe2(eta(5)-C5H4)(eta(1)-C5H4)} (eta(5)-C5H5) (NNMe2)] and [Nb(eta-C5H2),(thf)(NNMe,)][BPh,] (thf = tetrahydrofuran) have been prepared. The crystal structure of [Nb(eta-C5H5Me)(2)Cl(NNM e2)] has been determined, A variable-temperature NMR study of [Nb(eta 5-C5H5)(2)-(eta(1)-C5H5)(NNMe2)] reveals a fluxional interchange of th e three cyclopentadienyl rings. This compound has been shown to react with the electrophiles SiMe3Cl, FeCl2 . 1.5thf, [NMe3H]Cl and [Nb(eta- C5H5)Cl-2(NNMe2)] to form in each case [Nb(eta-C5H5)Cl(NNMe2)]. A vari able-temperature NMR study of 2(eta(5)-C5H4)(eta(1)-C5H4)}-(eta(5)-C5H 5)(NNMe2)] shows the presence of two interconvertible diastereomers. T he bis- and tris-cyclopentadienyl compounds have been shown to undergo exchange of their cyclopentadienyl rings in solution with each other or Li(C5H4R). The compound [Nb(eta-C5H5)(OBut)(2)(NNMe2}] has also bee n shown to undergo a cyclopentadienyl ligand-exchange reaction.