Reactions of alkynes having electron-withdrawing substituents with Re2(CO)9(NCMe). Formation of trans dimetalated olefins by alkyne insertion into a rhenium-rhenium bond

Abstract

The reaction of the dirhenium complex Re[sub 2](CO)[sub 9](NCMe), 1, with electrophilic alkynes, RC[quadruple bond]CCO[sub 2]R[prime], proceeds by displacement of the NCMe ligand and addition of the alkyne with insertion into the rhenium-rhenium bond to yield the dimetalated olefin complexes, Re(CO)[sub 4-][trans-[mu]-RC=C(CO[sub 2]R[prime])]Re(CO)[sub 5], R = H, R[prime] = Me, 2a, R = Me, 2b, and R = CO[sub 2]Et, R[prime] = Et, 2c, that have a trans stereochemistry at the C-C double bond. The carboxylate group is coordinated to one of the rhenium atoms through the ketonic oxygen atom to form a metallacycle. The reaction is insensitive to radical scavengers, solvent polarity, and light. The absence of crossover in a reaction of a mixture of labeled and unlabeled 1 is consistent with the insertion of the alkyne into the metal-metal bond by an intramolecular mechanism. Compound 2a was found to add CO (reversibly) to open the metallocycle and form the simple dimetalated olefin complex Re(CO[sub 5][trans-[mu]-HC=C(CO[sub 2]Me))]Re(CO)[sub 5], 3. When irradiated, 2a underwent a shift of the alkenyl hydrogen atom to the carboxylate-substituted carbon atom to form the carboxylate-substituted vinylidene complex Re[sub 2](CO)[sub 8][[mu]C=CH(CO[sub 2]Me)], 4, in which the ketonic oxygen atom of the carboxylate group is coordinated tomore » one of the metal atoms. The metal-metal bond in 4 was cleaved (reversibly) by addition of CO at 1 atm/25[degrees]C to yield the complex Re[sub 2](CO)[sub 9][[mu]-C=CH(CO[sub 2]Me)], 5, and under a high pressure of CO (1000 psi/100[degrees]C), compound 5 underwent a CO insertion (reversible) into one of the Re-C bonds to form the complex Re(CO)[sub 4][[mu]O=CC=CH(CO[sub 2]/Me)]Re(CO)[sub 5], 6. Compounds 1, 2a and 3-6 were characterized by single-crystal X-ray diffraction analysis. Crystal data are provided. 21 refs., 6 figs., 6 tabs.« less