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 [(R n Cp) 2 ZrH 2 ] x having substituted cyclopentadienyl ligands has been prepared by hydrogenation of the corresponding dimethyl complexes. The most sterically crowded members (Cp*(η 5 -C 5 HMe 4 )ZrH 2, (Cp* = (η 5 -C 5 Me 5 )), Cp*{η 5 -C 5 H 3 -1,3-(CMe 3 ) 2 }ZrH 2 and {η 5 -C 5 H 3 -1,3-(CMe 3 ) 2 } 2 ZrH 2 ) are monomeric; those less crowded members ([Cp*{η 5 -C 5 H 4 (CMe 3 )}ZrH 2 ] 2, [Cp*(THI)ZrH 2 ] 2 (THI = η 5 -tetrahydroindenyl), and [{η 5 -C 5 H 3 -1,3-(CHMe 2 ) 2 } 2 ZrH 2 ] 2 ) are predominantly dimeric in benzene solution. Cp*{η 5 -C 5 H 3 -1,3-(CHMe 2 ) 2 }ZrH 2 and (η 5 -C 5 HMe 4 ) 2 ZrH 2 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* 2 HfH 2, Cp*{η 5 -C 5 H 4 (CMe 3 )}ZrCl 2, Cp*{η 5 -C 5 H 3 -1,3-(CHMe 2 ) 2 }ZrCl 2 and {η 5 -C 5 H 3 -1,3-(CMe 3 ) 2 } 2 ZrCl 2 are reported.