Journal of the American Chemical Society, Vol.118, No.45, 11134-11141, 1996
Ether Complexes of Tungsten with 2 Different Binding Modes - An O-Bound Ether and an Eta(2)-(C=c) Vinyl Ether - Evidence for C-H-Center-Dot-Center-Dot-Center-Dot-O Hydrogen-Bonding of Vinylic C-H Groups
The reaction of PhCH(OCH3)(2) with Cp(CO)(3)WH and HOTf gives [Cp(CO)(3)W(PhCH(2)OCH(3))](+)OTf(-). The structure of this benzyl methyl ether complex was determined by single crystal X-ray diffraction and was shown to have the ether bonded to tungsten through the oxygen. This compound was isolated as a kinetic product of the reaction; it decomposes in solution by releasing free PhCH(2)OCH(3) and forming Cp(CO)(3)WOTf. An analog with the BAr4’(-) counterion [Ar’=3,5-bis(trifluoromethyl)phenyl] is more stable. The reaction of the vinyl acetal CH2=CHCH(OEt)(2) with Cp(CO)(3)WH and HOTf produces [Cp(CO)(3)W(eta(2)-EtOCH=CHCH3)](+)OTf(-), in which the ether is bonded to tungsten through the C=C bond of the vinyl ether. The crystal structure of this compound shows that the W-C(OEt) distance (2.69(3) Angstrom) is significantly longer than the W-C(CH3) distance (2.37(3) Angstrom). There are weak C-H ... O hydrogen bonds between both vinyl CH’s and oxygens of triflate counterions. Evidence is presented that some of these weak hydrogen bonds are maintained in CD2Cl2 solution but not in CD3CN.
Keywords:REDUCTIVE CLEAVAGE;ORGANOMETALLIC CRYSTALS;IONIC HYDROGENATION;CATION EQUIVALENTS;HYDRIDE TRANSFER;IRON COMPLEXES;LEWIS-ACIDS;ACETALS;OLEFINS;KETALS