Preparation and characterization of monomeric and dimeric group IV metallocene dihydrides having alkyl-substituted cyclopentadienyl ligands

A series of zirconocene dihydride complexes of the general form [(RnCp)(2)ZrH2](x) having substituted cyclopentadienyl ligands has been prepared by hydrogenation of the corresponding dimethyl complexes. The most sterically crowded members (Cp*(eta(5)-C5HMe4)ZrH2, (Cp* = (eta(5)-C5Me5)), Cp*{eta(5)-C5H3-1,3-(CMe3)(2)}ZrH2 and {eta(5)-C5H3-1,3-(CMe3)(2)}(2)ZrH2) are monomeric; those less crowded members ([Cp*{eta(5)-C5H4(CMe3)}ZrH2](2), [Cp*(THI)ZrH2](2) (THI = eta(5)-tetrahydroindenyl), and [{eta(5)-C5H3-1,3-(CHMe2)(2)}(2)ZrH2](2)) are predominantly dimeric in benzene solution. Cp*{eta(5)-C5H3-1,3-(CHMe2)(2)}ZrH2 and (eta(5)-C5HMe4)(2)ZrH2 exist as equilibrium mixtures of monomer and dimer in benzene solution. The hydride ligands rapidly exchange with D-2, affording the dideuteride complexes. Deuterium incorporation into some of the substituents on the cyclopentadienyl rings of the monomeric dihydride complexes is also observed. The X-ray structures of Cp*2HfH2, Cp*{eta(5)-C5H4(CMe3)}ZrCl2, Cp*{eta(5)-C5H3-1,3-(CHMe2)(2)}ZrCl2 and {eta(5)-C5H3-1,3-(CMe3)(2)}(2)ZrCl2 are reported.