Divergent Reactivity of a Phosphinidene-Bridged Dimolybdenum Complex Toward 1-Alkynes: P–C, P–H, C–C, and C–H Couplings

Abstract

The ability of complex [Mo2Cp2{μ-P(2,4,6-C6H2tBu3)}(CO)4] to promote P–C and subsequent coupling processes has been analyzed by examining reactions with alkynes. The title compound reacted at room temperature with different terminal alkynes HC≡CR under visible-UV light irradiation to give, in a selective way, the corresponding phosphapropenediyl derivatives [Mo2Cp2(μ–κ1C:η3C,C,P-CRCHPR*)(CO)4] for R groups of varied electron-withdrawing nature, but low to medium size, such as Pr, CO2Me, and p-tol. These products follow from formal insertion of the alkyne into one of the Mo-phosphinidene bonds in the parent compound, with selective P–C coupling to the terminal carbon of the alkyne. In contrast, when R was the bulky tBu group, the corresponding photochemical reactions yielded a mixture of the cis and trans isomers of the phosphanyl- and formylalkenyl-bridged complex [Mo2Cp2{μ–κ2C,O:η2C,C-CHC(tBu)C(O)H}{μ-P(CH2CMe2)C6H2tBu2}(CO)2], which follow from a complex reaction sequence involving an H–C(sp3) bond clea...