SILICON-CARBON UNSATURATED-COMPOUNDS .57. PHOTOLYSIS OF MESO-1,2-DIETHYL-1,2-DIMETHYLDIPHENYLDISILANE AND RACEMIC-1,2-DIETHYL-1,2-DIMETHYLDIPHENYLDISILANE, DIRECT EVIDENCE FOR A CONCERTED 1,3-SILYL SHIFT TO ORTHO-CARBON IN THE PHENYL RING

meso- and racemic-1,2-diethyl-1,2-dimethyldiphenyldisilane (2a) and (2 b) were synthesized respectively by hydrogenation of meso- and racemic -1,2-diethynyl-1,2-dimethyldiphenyldisilane in the presence of a IrCl( CO)(PPh(3))(2) catalyst. Irradiation of 2a with a low-pressure mercury lamp in the presence of isobutene in hexane proceeded with high diast ereospecificity to give (R,S)- and thylmethylsilyl)-1-(ethylmethylphen ylsilyl)benzene in 77% yield. Similar irradiation of 2b with isobutene produced (R,R)- and (S,S)-isomer. The photolysis of 2a and 2b in the presence of 1,1-diphenylethylene also proceeded diastereospecifically to give the respective adducts. With 2,3-dimethylbutadiene, 2a and 2b produced the corresponding adducts, whose spectrometric analysis showe d the presence of two diastereomers. Results on theoretical studies wh ich were carried out using PhSiH(2)SiH(3) as a model have also been re ported.