[1,3]-Metal Shifts in Rhenium Alkynyl Carbene Complexes

The electron-withdrawing SO 2 CF 3 substituent of Cp(CO) 2 Re C(Tol)(C⋮CC 6 H 4 - p -SO 2 CF 3 ) ( 1d ) greatly accelerates rearrangement via a [1,3]-rhenium shift. The [1,3]-rhenium shift is proposed to proceed via an 18-electron dehydrometallacyclobutadiene intermediate formed by alkyne coordination concerted with an η 5 −η 3 Cp ring slip.