The energetics of the oxidative addition of trisubstituted silanes to photochemically generated (η5-C5R5)Mn(CO)2

The rates for the oxidative addition reaction of trisubstituted silanes (Et3SiH, Et2MeSiH, EtMe2SiH, Et2SiH2) to photochemically generated (η5-C5R5)Mn(CO)2 (R5 = H5, Me5, H4Me) species have been measured for the temperature range 70–125 K. The reactions were carried out in either neat silane or a 50/50, by volume, mixture of methylcyclohexane and silane. The activation energies, determined using Arrhenius law, varied from 2 to 35 kj/mol. The kinetic data fit an isokinetic relationship with an isokinetic temperature of 102 ± 6 K. The results are interpreted in terms of a variation in the loss of solvation prior to the oxidative addition. When the solvating molecule is methylcyclohexane, then loss of the solvent molecule precedes oxidative addition. In cases where solvation is by the silane, the incomplete loss of this silane precedes the oxidative addition. Key words: mechanism, oxidative addition, solvation.