Coordination of alkenes and alkynes to a cationic d0 zirconocene alkoxide complex

This paper describes the synthesis of base-free (C5R5)2Zr(OtBu)+ cations, the direct observation of nonchelated alkene and alkyne adducts of these cations, and studies of the thermodynamic and dynamic properties of these novel species. Reaction of Cp2′ZrMe2 (Cp′ = C5H4Me) with tert-butyl alcohol followed by [Ph3C][B(C6F5)4] in benzene yields [ Cp2′Zr(O′Bu) ][B(C6F5)4] (1), which exists as Cp2′Zr(O′Bu)(CIR)+ solvent adducts in C6D5Cl and CD2Cl2 solutions. Addition of ligands L (L = ethylene, propylene, propyne, 2-butyne, CO, phenylacetylene, allene, 1-hexene, cis-2-butene) to 1 in CD2Cl2 at -89 °C results in reversible formation of Cp2′Zr(O′Bu)(L)+ adducts. NMR data for Cp2′Zr(O′Bu)(H2C=CHMe)+ (4) indicate that the propylene coordinates unsymmetrically and is polarized with positive charge buildup at Cint. Equilibrium constants, defined by Keq = [Zr-L][1]-1[L]-1, vary in the order CO > propyne > 2-butyne > phenylacetylene > ethylene > allene > propylene > 1-hexene > cis-2-butene > vinyl chloride. Loss of L from Cp2′Zr(O′Bu)(L)+to give 1 appears to proceed via associative displacement by CD2Cl2 in most cases. Copyright © 2003 American Chemical Society.