Trapping the Dirhenium Alkynyl Fischer Type Carbene through Michael Addition. Unexpected Room-Temperature <i>E</i>/<i>Z</i> Isomerization of (CO)<sub>5</sub>Re(CO)<sub>4</sub>Re(C(OMe)CHC(NMe<sub>2</sub>)TMS)

The reaction of Re<sub>2</sub>(CO)<sub>10</sub> with LiC⋮CTMS and Me<sub>3</sub>O<sup>+</sup>BF<sub>4</sub><sup>-</sup> results in a low-stability Fischer type alkynyl carbene complex, (CO)<sub>5</sub>Re(CO)<sub>4</sub>Re(C(OMe)C⋮CTMS). This easily reacts with HNMe<sub>2</sub> to give the stable (CO)<sub>5</sub>Re(CO)<sub>4</sub>Re(C(OMe)CHC(NMe<sub>2</sub>)TMS) in 82% yield, which exhibits unrestrained rotation around the carbon−carbon “double bond”, resulting in room-temperature <i>E</i>/<i>Z</i> isomerization. The aminolysis product (CO)<sub>5</sub>Re(CO)<sub>4</sub>Re(C(NMe<sub>2</sub>)C⋮CTMS) was also generated from (CO)<sub>5</sub>Re(CO)<sub>4</sub>Re(C(OMe)C⋮CTMS) and could be desilylated to form the acetylene carbene (CO)<sub>5</sub>Re(CO)<sub>4</sub>Re(C(NMe<sub>2</sub>)C⋮CH).