The insertion reactions of CNMe and CN-t-Bu with Cp * CpHf(CH 2 SiMe 2 CH 2 ),1 , have been investigated to evaluate the stereoelectronic influence of the Cp * ligand on the competitive 1,2-silyl shift and reduction coupling pathways previously observed for Cp 2 Hf(CH 2 SiMe 2 CH 2 ). Under ambient conditions the addition of CNMe to 1 proceeds with the sequential formation of Cp * CpHf(N(Me)C( CH 2 )SiMe 2 CH 2 ), 2, and Cp * CpHf(N(Me)C( CH 2 )SiMe 2 (CH 2 )CN(Me)),3 . Alternatively, the addition of excess CNMe below -5°C to 1 occurs with reductive coupling to produce Cp * CpHf(N(Me)C(CH 2 SiMe 2 CH 2 ) CN(Me)),4 . In contrast, the addition of two equivalents of CN-t-Bu to 1 does not afford the corresponding cyclic enamide species but proceeds with the sequential formation of Cp * CpHf(N(CMe 3 )CCH 2 SiMe 2 CH 2 ), 5, and Cp * CpHf(N(CMe 3 )C--C( NCMe 3 )CH 2 SiMe 2 CH 2 ),6 . The molecular structures of 3 and 6 have been determined by X-ray crystallography. The puckered 1-sila-3,5-diaza-4-hafnacyclohexane ring of 3 adopts a chair conformation with the folding along the N N vector being 19.3° out of the N , Hf, N plane toward the smaller Cp ligand and the folding along the C(1) C(1) vector being 43.3° in the opposite direction toward the Cp * ligand. The molecular structure of 6 is consistent with nucleophilic attack of CN-t-Bu at the η 2 -iminoacyl carbon of 5 occurring exclusively from the side opposite to the Cp * ligand. The second equivalent of CN-t-Bu displaces the η 2 -iminoacyl group away from the Hf atom, eventually placing the resultant imine group of 6 syn to the Cp * ligand.