Formation and reactivity of 1,3-cyclohexadiene complexes of niobium and tantalum containing aryloxide ligation: Selectivity differences in the hydrogenation of 1,3-cyclohexadiene
作者:Valerie M. Visciglio、Mindy T. Nguyen、Janet R. Clark、Phillip E. Fanwick、Ian P. Rothwell
DOI:10.1016/0277-5387(95)00252-n
日期:1996.2
The sodium amalgam reduction (2 Na per M) of hydrocarbon. solutions of [M(OAr)(3)Cl-2] (M = Nb, Ta) or [Nb(OAr)(2)Cl-3](2) (OAr = 2,6-di-isopropylphenoxide) in the presence of either 1,3- or 1,4-cyclohexadiene yielded the complexes [M(OAr)(3)(eta(4)-C6H8)] (1a: M = Nb; 1b: M = Ta) and [Nb(OAr)(2)Cl(eta(4)-C6H8)], 2, respectively. The solid state structures of la, isomorphous Ib and 2 showed the 1,3-cyclohexadiene strongly bound to the metal. The ligand is not symmetrically bound to the metal in 1 but in 2 there is a crystallographic mirror plane. The solution NMR spectra of la and Ib show only one set of aryloxide ligand signals and only four proton and three carbon resonances for the C6H8 group. The hydrolysis of 1 or 2 yielded 2,6-di-isopropylphenol and one equivalent of cyclohexane (H-1 NMR). The niobium compounds 1a and 2 will catalyse the disproportionation and hydrogenation of 1,3-cyclohexadiene with differing selectivity.