Palladium‐ and platinum‐catalyzed coupling reactions of allyloxy aromatics with hydridosilanes and hydridosiloxanes: Novel liquid crystalline/organosilane materials

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Abstract
Pt‐and Pd‐catalyzed reactions of a set of allyloxyaromatic mono‐and diesters with selected silanes were examined to develop simple, mild methods of forming liquid crystal (LC)/ siloxane and LC/silsesquioxane polymers. Pt complexes catalyze hydrosilylation to give primarily (≤ 80% selectivity at 100% conversion) terminal silylation of the allyloxys. The catalyst, platinum‐1,3‐divinyltetramethyldisiloxane [Pt (dvs), gives the cleanest reactions, fewest side products, under the mildest conditions. Model studies of Pt(dvs) catalyzed hydrosilylation of 4‐allyloxy methylbenzoate gave relative reactivities (HSiO1.5)8≫ Et3SiH > HMe2SiOSiMe2H > Ph2SiH2. The cubic silsesquioxane, (HSiO1.5)8, is so reactive hydrosilylation is over in 1–3 h at 0°C. All other reactions required > 40°C and longer reaction times. Initial efforts to form high polymers by Pt‐catalyzed reactions of bis‐allyloxy aromatics with Ph2SiH2provide polymers with bimodal MW distributions (polystyrene),Mws ≈ 30 kDa, and PDIs ≈ 5. Pd catalysis gives quite different products resulting from loss of propene with coincident formation of SiO bonds, “oxysilylation.” The same products appear (10–15%) in some Pt catalyzed reactions. Palladium dibenzylideneacetone/ Ph3P[Pd(dba)2/Ph3P], gives the cleanest oxysilylation reactions. Relative oxysilylation activities are: Ph2SiH2> HMe2SiOSiMe2H > Et3SiH. Polymerization with Pd catalysts provides polymers withMws ≈ 11 kDa, and PDIs ≈ 2. Reaction of 1 equiv. of (HSiO1.5)8with 4 equiv. of 4‐(4‐allyloxy‐benzoyloxy) biphenyl gives relatively pure tetrasubstituted LC/silsesquioxane [Mn≈ 1860 Da, PDI ≈ 1.09 (styrene equiv.) vs. 1746 Da caled.] A detailed analysis of the products formed, the catalytic reactivity patterns of the his (allyloxy) aromatic diesters and their LC transitions is presented. © 1994 John Wiley & Sons, Inc.

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