UNPRECEDENTED METATHESIS OF METAL-CARBON AND CARBON-CARBON BONDS IN ALPHA-AGOSTIC N-ALKYL NIOBIUM ALKYNE COMPLEXES

The alpha-agostic n-ethyl and n-propyl niobium alkyne complexes [NbL(C l)(mu-H-CHR)(PhC=CR')] [L = hydridotris(3,5-dimethylpyrazolyl)borate; R = Me, Et; R' = Me, Et, Pr-n] undergo a thermolytic exchange of the n iobium and alkyne-bound alkyl groups to give [NbL(Cl)(R')(PhC=CCH(2)R] ; first-order kinetic parameters have been obtained when R = R' = Me ( Delta H-double dagger = 113 kJ mol(-1), Delta S-double dagger = 4J K-1 mol(-1)).