Siliciumhaltige Carben-Komplexe: X. Ethoxy- und Ethylthio(triphenylsilyl)keten aus CarbenKomplexen (CO)5WC(XEt)SiPh3 (X O,S)

Abstract The carbene complex (CO) 5 WC(SEt)SiPh 3 ( 1 ) decomposes at 0°C to give the isolable ketene Ph 3 Si(EtS)(CCO ( 3 ) and a metal complex ( 4 ), in which 3 is coordinated to a (CO) 5 W fragment via its sulfur atom. The ketene ligand in 4 can be cleaved from the metal by tetraethylammonium bromide or by CO. The much more reactive ketene Ph 3 Si(EtO)CCO ( 7 ) is formed on treatment of (CO) 5 WC(OEt)-SiPh 3 ( 2 ) with 50 atm CO at room temperature. The ketenes 3 and 7 are readily hydrolyzed to give the corresponding acids Ph 3 Si(EtX)CHCOOH ( 5 : X  S; 9 : X  O). The anhydride [Ph 3 Si(EtO)CHCO] 2 O ( 8 ), which is obtained from 7 after addition of an appropriate amount of water, and the ketene 3 have been characterized by X-ray crystallography. Upon in situ reaction of 7 with 2,3-dihydrofuran the [2 + 2]-cycloaddition product 10 is formed in high yields. Two isomers, with the Ph 3 Si group in endo or exo position, are found in a 16 1 ratio.