Alkyl Substituent Effects on Reductive Elimination Reactions in Zirconocene Alkyl Hydride Complexes. Manipulation of the Alkyl Steric Environment Allows the Synthesis of a Zirconocene Dinitrogen Complex

Abstract

The rate of reductive elimination as a function of alkyl ligand has been measured for a series of zirconocene alkyl hydride complexes, Cp*Cp‘ ‘Zr(R)H (Cp* = η5-C5Me5, Cp‘ ‘ = η5-C5H3-1,3-(SiMe3)2, R = CH3, CH2(CH2)2CH3, CH2(CH2)6CH3, CH2cC6H11, CH2CHMe2, CH2CMe3), where the steric disposition of the alkyl ligand has been systematically varied. The rate of reductive elimination increases modestly as the steric bulk of the alkyl ligand is increased. This trend is attributed to ground state destabilization arising from unfavorable steric interactions between the alkyl ligand and the cyclopentadienyl substituents. The effect is magnified when more voluminous cyclopentadienyl ligands are incorporated into the metallocene framework. Thus, the Cp*Cp‘ ‘‘Zr(R)H (Cp‘ ‘‘ = η5-C5H2-1,2,4-(SiMe3)3, R = CH3, CH2(CH2)2CH3, CH2(CH2)6CH3) series of alkyl hydride complexes lose alkane more readily than the corresponding Cp*Cp‘ ‘Zr(R)H complexes. In addition, the rate of reductive elimination has also been examined for Cp*C...