DIMETALLATED OLEFINS FORMED BY THE INSERTION OF AN ALKYNE INTO AN RE-RE BOND - THE REACTION OF ETO2CC-EQUIVALENT-TO-CCO2ET WITH RE2(CO)9(NCME)

The complex Re(CO)4[mu-(Z)-(EtO2C)C=C(CO2Et)]Re(CO),5, 2, obtained from the reaction of Re2(CO)9(NCMe), 1, with EtO2CC=CCO2Et was analyzed by single crystal X-ray diffraction analysis and was found to be a Z-dimetalated olefin complex formed by the insertion of the alkyne into the rhenium-rhenium bond. One of the carboxylate groups is coordinated to one of the rhenium atoms through the ketonic oxygen atom to form a four membered metallacyclic ring. The absence of crossover in a reaction of a mixture of fully (CO)-C-13 labeled 1 and unlabeled 1 indicates that the insertion of the alkyne into the metal-metal bond occurs by an intramolecular mechanism. When irradiated (UV-vis), compound 2 was isomerized to the complex Re(CO)4[mu-(E)-(EtO2C)C=C(CO2Et)]Re(CO)5, 3, and the ketonic oxygen atom of the carboxylate group became coordinated to the other rhenium atom to form a five membered metallacyclic ring. Decarbonylation of 3 by irradiation yielded the new complex Re(CO)4[mu-(E)-(EtO2C)C=C(CO2Et)]Re(CO)4, 4, by coordination of the oxygen atom of the second carboxylate group. Compound 2 was found to add CO at 700 psi/25-degrees-C by opening the Re-O bond of the metallacycle to form the simple Z-dimetalated olefin complex Re(CO)5[mu-(Z)-(EtO2CC=C(CO2Et)]Re(CO)5,5, in 93% yield. Compound 2 reacts with a mixture of HCl/CO (gas) by cleaving off one of the rhenium groupings as Re(CO)5Cl and forming the new complex [(E)-(EtO2C)HC=C(CO2Et)]Re(CO)5, 6, in 97% yield. Crystal data: (for 2) space group = P2(1)/c, a = 10.292(2) angstrom, b = 11.731(2) angstrom, c = 18.704(4; angstrom, beta = 100.14(2)degrees, Z = 4, 2133 reflections, R = 0.025; (for 3) space group = Fdd2, a = 24.498(3) angstrom, b = 35.102(5) angstrom, c = 10.681(1) angstrom, Z = 16, 1843 reflections, R = 0.027; (for 4) space group = P1BAR, a = 7.838(3) angstrom, b = 9.830(3) angstrom, c = 7.047(2) angstrom, alpha = 106.93(2)degrees, beta = 94.84(3)degrees, gamma = 84.28(3), Z = 2, 1927 reflections, R = 0.037; (for 5) space group = Pbca, a = 14.275(2) angstrom, b = 33.00(1) angstrom, c = 10.114(2) angstrom, Z = 8, 2124 reflections, R = 0.036; (for 6) space group = P2(1)/c, a = 9.637(1) angstrom, b = 8.340(1) angstrom, c = 20.821(2) angstrom, beta = 102.10(1)degrees, Z = 4, 1686 reflections, R = 0.021.