1 H, 13 C, and IR spectroscopy and gas chromatography3mass spectrometry were used to study addition of hydrosiloxanes to vinylsiloxanes in the presence of Pt(II) complexes. Along with hydrosilylation, dehydrocondensation and disproportionation of hydrosiloxanes occur.Hydrosilylation of vinylsiloxanes with hydrosiloxanes, as well as of most unsaturated compounds, occurs by the Farmer rule (b-addition) or against this rule (a-ÄÄÄÄÄÄÄÄÄÄÄÄ addition) and adheres to general regularities of such reactions [133]. The ratio of the a-and b-isomers depends on the reagent structure, reaction temperature, and catalyst nature.3Si3O3Si3H + CH 2 =CH3Si3O3Si3 g g g g g g g g 7 9 9 9 9 76 76 3Si3O3Si3CH3Si3O3Si3 g g g g g g g g g CH 3a-addition 3Si3O3Si3CH 2 3CH 2 3Si3O3Si3 g g g g g g g g b-addition
ÄÄÄÄÄÄÄÄÄÄÄÄThe activity of hydrosiloxanes decreases with their molecular weight, reverse the situation with vinylsiloxanes [436].Previously [7] we showed that the activity of hydrosiloxanes in hydrosilylation of vinylsiloxanes with hydrosiloxanes in the presence of sulfoxide, sulfide, phosphine sulfide, and cyclooctadiene Pt(II) complexes increases with increasing effective positiove charge on the silicon atom of the Si3H bond and decreasing size of the substituent at Si3H. Moreover, the product of hydrosilylation of vinylsiloxanes with 1,1,3,3-tetramethyldisiloxane (HMe 2 Si) 2 O increased in molecular weight and viscosity on standing in air, on account of spontaneous dehydrocondensation of terminal Si3H groups [7]. The tendency of silicon hydrides for dehydrocondensation has also been noted in [8311], but there has been no systematic research into this problem with regard to siloxanes.The objects for study were hydro-and vinylsiloxanes, whose reaction in the presence of sulfurcontaining Pt(II) complexes we earlier considered in [7].The available data on the catalytic hydrosilylation in siloxane systems are controversial, and this prompted us to a more detailed study of this reaction and attendant processes with the aid of various spectral methods. For the reaction catalysts we took squareplanar Pt(II) complexes with phosphine, sulfide, sulfoxide, pyridine sulfoxide, and cyclooctadiene ligands of the general formulas [Pt(L)(L`)Hlg 2 ] and [Pt(L``)Hlg 2 ] (L = Ph 3 P, t-Bu 3 P, i-Pr 3 P, Et 2 SO, (+)-Me-p-TolSO, Et 2 S; L`= Py or L`= L; L``h 4 -COD, h 4 -MeCOD).The hydrosilylation progress was controlled by GLC and, for comparison, volumetrically by the amount of hydrogen evolved on the reaction of residual Si3H groups with alcoholic alkali. Further control of the selectivity of the process and the struc-
