Phosphine-nickel(II), -cobalt(II), -palladium(0) and -palladium(II) complexes as catalysts in cross-coupling reactions of aryl- and alkyl-grignard reagents with organic tellurides

Abstract

Some alkyl- and aryl-tellurides react with Grignard reagents (RMgBr; R  aryl and alkyl) in the presence of NiCl 2(PPh 3) 2, NiCl 2(Ph 2PCH 2CH 2CH 2PPh 2), or CoCl 2(PPh 3) 2 as catalyst in THF or diethyl ehter as solvent to give the cross-coupling products together with the homo-coupling products of the tellurides in good to moderate yields, with elemental tellurium being formed as a black precipitate. A catalytic reduction-oxidation cycle involving a Ni or Co complex bearing an organotellurium moiety (RTe; R  alkenyl, aryl, and alkyl) is proposed for the reaction. Palladium catalysts such as Pd(PPh 3) 4, PdCl 2(PPh 3) 2, and PdCl 2(PhCN) 2 are revaled to be much less effective than the Ni and Co catalysts in both the yield and the stereoselectivity of the product.