Alkyne Metathesis Reactions of Rhenium(V) Carbyne Complexes

Although alkyne metathesis reactions mediated by high-valent d(0) carbyne complexes are well established, similar reactions mediated by well-defined low-valent (non-d(0)) carbyne complexes are rare. This work demonstrates that d(2) Re(V) carbyne complexes Re( CR)Cl-2(PMe2Ph)(3) (R = CH2(o-C6H4Br), Ph, CO2Et) can undergo stoichiometric alkyne metathesis reactions. For example, reactions of Re{ CCH2(o-C6H4Br)}Cl-2(PMe2Ph)(3) with TMSC CR (R = CO2Et, CH2Ph) and PhC CPh produced carbyne complexes Re( CR)Cl-2(PMe2Ph)(3) and Re( CPh)Cl-2(PMe2Ph)(3), respectively. Theoretical studies suggest that the metathesis reactions most likely proceed through six-coordinate alkyne-carbyne intermediates Re( CR)Cl-2(eta(2)-alkyne)(PMe2Ph)(2) that undergo reversible cydoaddition reactions.