FLASH-PHOTOLYSIS STUDIES OF THE PHOTOCHEMICAL-REACTIONS OF SILANES WITH CHROMIUM HEXACARBONYL

The photochemical reactions following flash photolysis of n-hexane solutions containing silanes and Cr(CO)6 have been studied. The silane adducts vary widely in stability. The kinetics of silane elimination from Cr(CO)5(silane) in hexane solutions under a CO atmosphere were investigated. For HSiClMe2 and HSiClPh2, two distinct first-order decay processes were observed, corresponding to elimination of H-Si- and Cl-Si-bonded adducts. Decay is faster for the Cl-Si form of bonding. The rates of elimination at 25-degrees-C were measured for a series of 14 silanes differing widely in steric and electronic properties. The stabilities of the Cr(CO)5(H-SiR'R2) adducts increase with increasing electron-donor character of the silane, the opposite order from that observed for (eta-5-C5H5)(CO)2Mn(silane) and other related systems. The reversal of order reflects the relatively greater importance of sigma-donation to the metal in bonding to the more electrophilic Cr metal center.