This contribution reports a synthetic and kinetic study of CO migratory insertion for the series of thorium hydrocarbyls Th(ƞ5-C5H5)3R, R = i-C3H7, sec-C4H9, neo-C5H11, n-C4H9, CH2Si(CH3)3, CH3, and CH2C6H5. Under the conditions employed, the reaction was found to be first order in Th(C5H5)3R and first order in CO. In the above order, the relative rates of migratory insertion were found to be 42:18:1.3:1.0:0.02:0.01:<0.01. In the case of R = CH3, i-C3H7, n-C4H9, neo-C5H11, and sec-C4H9, carbene-like (by spectroscopic and chemical properties) ƞ2-acyl insertion products, Th(C5H5)3(ƞ2-COR), could be isolated and characterized. In the case of R = i-C3H7and CH2Si(CH3)3, enolate rearrangement products were isolated and characterized. The relative rates of CO insertion reflect both steric and electronic effects; there is a significant correlation with experimentally determined Th-R bond disruption enthalpies. For Th(C5H5)3CH2Si(CH3)3, it was also found that the rate of migratory CO insertion could be significantly accelerated by photolysis. However, secondary reactions of the insertion product are also observed. A comparative study of CO2migratory insertion to yield bidentate carboxylates revealed that carboxylation is significantly slower than carbonylation (a factor of 50 for Th(C5H5)3CH3; a factor of 105for Th(C5H5)3(i-C3H7)) and that for the above two compounds sensitivity of the rate to the nature of R is considerably altered vis-à-vis CO migratory insertion.
ASJC Scopus subject areas
- Colloid and Surface Chemistry