PALLADIUM-CATALYZED AND PLATINUM-CATALYZED COUPLING REACTIONS OF ALLYLOXY AROMATICS WITH HYDRIDOSILANES AND HYDRIDOSILOXANES - NOVEL LIQUID-CRYSTALLINE ORGANOSILANE MATERIALS

Pt- and Pd-catalyzed reactions of a set of allyloxyaromatic mono- and diesters with selected silanes were examined to develop simple, mild m ethods of forming liquid crystal (LC)/siloxane and LC/silsesquioxane p olymers. Pt complexes catalyze hydrosilylation to give primarily (less than or equal to 80% selectivity at 100% conversion) terminal silylat ion of the allyloxys. The catalyst, platinum-1,3-divinyltetramethyldis iloxane [Pt(dvs)], gives the cleanest reactions, fewest side products, under the mildest conditions. Model studies of Pt(dvs) catalyzed hydr osilylation of 4-allyloxy methylbenzoate gave relative reactivities (H SiO1.5)(8) much greater than Et(3)SiH > HMe(2)Si-O-SiMe(2)H > Ph(2)SiH (2). The cubic silsesquioxane, (HSiO1.5)(8), is so reactive hydrosilyl ation is over in 1-3 h at 0 degrees C. All other reactions required > 40 degrees C and longer reaction times. Initial efforts to form high p olymers by Pt-catalyzed reactions of bis-allyloxy aromatics with Ph(2) SiH(2) provide polymers with bimodal MW distributions (polystyrene), M (w)s approximate to 30 kDa, and PDIs approximate to 5. Pd catalysis gi ves quite different products resulting from loss of propene with coinc ident formation of Si-O bonds, ''oxysilylation.'' The same products ap pear (10-15%) in some Pt catalyzed reactions. Palladium dibenzylidenea cetone/Ph(3)P [Pd(dba)(2)/Ph(3)P], gives the cleanest oxysilylation re actions. Relative oxysilylation activities are: Ph(2)SiH(2) > HMe(2)Si OSiMe(2)H > Et(3)SiH. Polymerization with Pd catalysts provides polyme rs with M(w)s approximate to 11 kDa, and PDIs approximate to 2. Reacti on of 1 equiv. of (HSiO1.5)(8) with 4 equiv. of 4-( 4-allyloxy-benzoyl oxy)biphenyl gives relatively pure tetrasubstituted LC/silsesquioxane [M(n) approximate to 1860 Da, PDI approximate to 1.09 (styrene equiv.) vs. 1746 Da calcd.]. A detailed analysis of the products formed, the catalytic reactivity patterns of the bis(allyloxy) aromatic diesters a nd their LC transitions is presented. (C) 1994 John Wiley & Sons, Inc.