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

Abstract

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 (HSiO 1.5 ) 8 ≫ Et 3 SiH > HMe 2 SiOSiMe 2 H > Ph 2 SiH2. The cubic silsesquioxane, (HSiO 1.5 ) 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 Ph 2 SiH 2 provide polymers with bimodal MW distributions (polystyrene), M w s ≈ 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/ Ph 3 P[Pd(dba) 2 /Ph 3 P], gives the cleanest oxysilylation reactions. Relative oxysilylation activities are: Ph 2 SiH 2 > HMe 2 SiOSiMe 2 H > Et 3 SiH. Polymerization with Pd catalysts provides polymers with M w s ≈ 11 kDa, and PDIs ≈ 2. Reaction of 1 equiv. of (HSiO 1.5 ) 8 with 4 equiv. of 4‐(4‐allyloxy‐benzoyloxy) biphenyl gives relatively pure tetrasubstituted LC/silsesquioxane [ M n ≈ 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.