Cyclo-hydrosilylation: A novel route to siloxetanes and silanones

A novel and convenient method for the apparent liquid phase generation of dimethylsilanone, Me2SiO (D1), based on readily obtainable reactants and employing conventional temperatures (50–150°) is reported herein. Platinum catalyzed hydrosilylation of vinyldimethylcaarbinoxydimethylsilane (I) appears to proceed by an exclusively intramolecular path to produce not only the expected 5-membered heterocyclic, 1,1,3,3-tetramethyl-2-oxa-1 silacyclopentane (V), but also the isomeric and highly unstable 4-membered siloxetane, 1,1,3,3,4-pentamethyl-2-oxa-1-silacyclobutane (IV). The intermediacy of IV is suggested by the products: i.e., 2-methyl-2-butene which is believed to arise along with Me2SiO from fragmentation of IV; D3 and D4 from D1 self-coupling; a 6-membered cyclic derived from insertion of D1 into the Si-O bond of IV, i.e., 1,1,3,3,5,5,6-heptamethyl-2,4-dioxa-1,3-disilacyclohexane (VI); a polymer which upon alkaline cracking produces more 6-ring (VI) but little or no 5-ring (V) suggesting that the polymer arose from copolymerization of D1, D2, and siloxetane (IV). Compound I is also an excellent thermolytic source of D1 as evidenced by the formation of the expected derivatives upon heating in the presence of known silanone traps.