Photochemistry of Group 14 1,1,1-Trimethyl-2,2,2-triphenyldimetallanes (Ph3MM‘Me3; M, M‘ = Si, Ge). Direct Detection and Characterization of Silene and Germene Reactive Intermediates

The photochemistry of trimethylsilyltriphenylgermane (Ph 3 GeSiMe 3 ), triphenylsilyltrimethylgermane (Ph 3 SiGeMe 3 ), and 1,1,1-trimethyl-2,2,2-triphenyldigermane (Ph 3 GeGeMe 3 ) has been studied in hydrocarbon solution by steady state and laser flash photolysis methods and is compared to previously reported data for the homologous disilane Ph 3 SiSiMe 3 . A variety of products are formed upon photolysis of the three compounds in the presence of 2,3-dimethyl-1,3-butadiene or chloroform, but in each case the major ones are derived from M−M‘ bond homolysis and dimethyl- or diphenylgermylene extrusion. The trapping products of the 1,3,5-(1-metalla)hexatriene derivatives formed by [1,3]-MMe 3 migration into the ortho-position of one of the phenyl rings are formed as well, in yields of 9−30%. While these experiments indicate that germylenes are formed in at least twice the yield of the 1,3,5-(1-metalla)hexatrienes, only the latter and triphenylsilyl or triphenylgermyl radicals can be detected by laser flash photolysis techniques. The metallaenes have been identified on the basis of their time-resolved UV absorption spectra and absolute rate constants for reaction with 2,3-dimethylbutadiene, methanol, acetone, acetic acid, oxygen, and carbon tetrachloride and can be distinguished from germylenes by their lack of reactivity toward triethylsilane and chloroform. Radical formation is shown to result from reaction of the triplet states of these compounds, and a triplet lifetime is estimated for Ph 3 GeSiMe 3 and compared to that of the disilane homologue. The results of time-resolved experiments on other, related compounds are discussed in light of these results.