SELECTIVE ADDITION OF HYDROSILANES TO 1,3-DIENES CATALYZED BY POLYAMIDE-SUPPORTED METAL-COMPLEX CATALYSTS

Four transition metal complexes [RhCl(CO)(2)](2), PdCl2(PhCN)(2), PtCl2(PhCN)(2) and RuCl2(bipy)(2) were immobilized on polyamides bearing a pyridine moiety in their repeat units and displaying a relatively uniform distribution of micropores with voids from 1.0 to 3.0 nm. The polymer-supported catalysts were used in the hydrosilylation of isoprene and 2-methyl-1,3-pentadiene with the purpose of investigating the effect of polymer morphology on the catalyst selectivity. The addition of HSiMe(2)Ph and HSi(EtO)(3) to both 1,3-dienes catalyzed by the polymer-supported Rh(I) catalysts was found to proceed highly regioselectively and stereoselectively to give (Z)-(2-methyl-but-en-2-en-1-yl)silanes and (Z)-(2-methyl-pent-2-en-1-yl)silanes as the predominant products (85-95%). The stereochemical assignment of the products was carried out by H-1 NMR spectroscopy employing the nuclear Overhauser effect. A similar 1,4-addition of Me(2)PhSiH to isoprene and 2-methyl-1,3-pentadiene was found to produce Z isomers as the main products for the polymer-supported Pd(II) catalysts. In contrast the same reaction with HSi(EtO)(3) proceeded via a 1,2 route with 79-85% selectivity. As a general feature, in all the reactions studied, exception for the hydrosilylations catalyzed by polymer-supported rhodium catalysts, the 1,4 mode of addition prevailed with HSiMe(2)Ph, but 1,2 addition with HSi(EtO)(3). Essentially the same regioselectivity was found for reactions under the homogeneous conditions. These results demonstrated that the microporous structure of the polyamide supports did not exert any particular effect on the regioselective and stereoselective course of the reaction. The explanation was based on a good match of the dimensions of the reaction intermediate to those of the polymer micropores. The constant selectivity of the supported catalysts demonstrated during recycling tests showed that they could be useful for practical application.