Palladium-catalyzed formation and reactions of iodo- and bromosiloxane intermediates
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Polysiloxanes are useful materials because of their functionality, such as high thermal stability, electrical resistance, and hydrophobicity. In this regard, we studied palladium-catalyzed formation of iodo-and bromopolysiloxanes from two types of hydrosiloxanes, alpha,omega-dihydropoly(dimethylsiloxane) (1) and cyclotetra(hydromethylsiloxane) (2), and their reactions. Treatment of 1 with mixtures of cyclic ethers or lactones and MeI or allylBr in the presence of a catalytic amount of PdCl2 gave the corresponding alpha,omega-bis(haloalkoxy and haloalkanoyloxy) poly(dimethylsiloxane)s in good yields, via iodo-and bromopoly(dimethylsiloxane) intermediates. Transformation of the iodobutoxy-terminal units in the resulting poly(dimethylsiloxane) into aminoalkoxy groups was examined. The formation of alpha,omega-diiodo- and dibromopoly(dimethylsiloxane)s from 1 was confirmed by spectrometric analysis as well as by quenching experiments with ethanol. A reaction of alpha,omega-dibromopoly(dimethylsiloxane) with 2,5-dilithiothiophene gave a polydimethylsiloxane-thiophene alternating polymer. Similar palladiumcatalyzed reactions of 2 with THF/MeI, THF/allylBr, and delta-valerolactone/allylBr afforded cyclo(halobutoxy- and bromobutanoyloxymethylsiloxane) s in moderate yields. This would provide a new strategy for the introduction of various substituents to the terminal positions of linear polysiloxane and to the cyclosiloxane core.
Journal of Organometallic Chemistry
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Graduate School of Engineering