Trapping the Dirhenium Alkynyl Fischer Type Carbene through Michael Addition. Unexpected Room-Temperature E/Z Isomerization of (CO)5Re(CO)4Re(C(OMe)CHC(NMe2)TMS)

The reaction of Re2(CO)10 with LiC⋮CTMS and Me3O+BF4- results in a low-stability Fischer type alkynyl carbene complex, (CO)5Re(CO)4Re(C(OMe)C⋮CTMS). This easily reacts with HNMe2 to give the stable (CO)5Re(CO)4Re(C(OMe)CHC(NMe2)TMS) in 82% yield, which exhibits unrestrained rotation around the carbon−carbon “double bond”, resulting in room-temperature E/Z isomerization. The aminolysis product (CO)5Re(CO)4Re(C(NMe2)C⋮CTMS) was also generated from (CO)5Re(CO)4Re(C(OMe)C⋮CTMS) and could be desilylated to form the acetylene carbene (CO)5Re(CO)4Re(C(NMe2)C⋮CH).