Investigations of the magnitude of steric and α deuterium kinetic isotope effects in a carbon-carbon bond-forming reaction of a permethylscandocene complex

Article abstract of DOI:10.1016/0022-328X(91)80181-I

No measurable isotope effect is observed in the reaction of (Cp^*-d₁₅)2Sc-CH3 (1a, Cp^* = η⁵-C5(CH3)5) with CD3C<*>CCH3 to yield a mixture of (Cp^*-d₁₅)2Sc-C(CD3)C=C(CH3)2 (2a) and (Cp^*-d₁₅)2Sc-C(CH3)C=C(CH3)(CD3) (2b) (2b:2a = 1.01 +/- 0.02:1).Thus steric repulsions between the 2-butyne methyl group and the scandium-bound methyl group are not sufficiently severe to give rise to a measurable steric deuterium kinetic isotope effect.Similarly, 1a reacts with CH3C<*>CCH3 at approximately the same rate as does (Cp^*-d₁₅)2Sc-CD3 (1b), producing a mixture of (Cp^*-d₁₅)2Sc-C(CH3)C=C(CH3)2 (2c) and (Cp^*-d₁₅)2Sc-C(CH3)C=C(CD3)(CH3) (2d) (k_2c/k_2d=1.02+/-0.07).The implication from the latter finding is that a 2-CH2-H)> α agostic interaction is likely not present in the transition state for 2-butyne insertion into the scandium methyl bond of 1.