FACILE ALKYNE COUPLING REACTIONS IN DIRHENIUM CARBONYL-COMPLEXES

The complex (OC)4Re[trans-mu-HC=C(CO2Me)]Re(CO).5 (1) was converted to the reactive acetonitrile complex (OC)4Re[trans-mu-HC=C(CO2Me)]Re(CO)4(NCMe) (2) by reaction with Me3NO in acetonitrile. Under an atmosphere of CO, complex 2 reacts with HC=CCO2Me in refluxing CH2Cl2 to yield the new complexes (OC)4Re[mu-C(H)=C(CO2Me)C(H)=C(CO2Me)]-Re(CO)5 (3; 11 %) and (OC)4Re[C(H)=C(CO2Me)C(H)=C(CO2Me)C(H)=C(CO2Me)]Re(CO)4 (4a,b; 49 %, existing in solution as a mixture of isomers) by the head-to-tail coupling of two and three HC=CCO2Me molecules, respectively. In the absence of CO only compound 4 and a small amount of the new compound Re(CO)4[C6H2(CO2Me)(CO2Me)2] (5;6 %) were obtained. Complex 3 was converted into 4 by reaction with additional HC=CCO2Me in the presence of Me3NO. When heated to 98-degrees-C, 4 was transformed into 5 in 22 % yield. Three of the products, 3, 4a, and 5 were characterized crystallographically. In complex 3 the two linked HC=CCO2Me groups form a four-carbon chain between the metal-containing groups. One of the carboxylate substituents is also coordinated to form a five-membered metallacyclic ring. In complex 4a the metal-containing groups are joined by a six-carbon chain formed from the three alkynes, and two of the carboxylate groups are coordinated to form five- and six-membered metallacyclic rings. The six-carbon chain in 4 was transformed into a 2,4,6-tris(methoxycarbonyl)phenyl group that is a-coordinated to the metal atom and also has one of its carboxylate groups coordinated. Crystal data: for 3, space group P1BAR, a = 13.792(2) angstrom, b = 14.009(2) angstrom, c = 6.2734(6) angstrom, a = 91.47(1)-degrees, beta = 92.95(1)-degrees, gamma = 114.764(8)-degrees, Z = 2, 2120 reflections, R = 0.023; for 4a, space group P1BAR, a = 10.7738(8) angstrom, b = 13.179(2) angstrom, c = 9.024(1) angstrom, alpha = 96.52(1)-degrees, beta = 101.467(8)-degrees, gamma = 84.604(9)-degrees, Z = 2, 2428 reflections, R = 0.024; for 5, space group P1BAR, a = 9.947(1) angstrom, b = 11.840(2) angstrom, c = 7.977(1) angstrom, alpha = 106.99(1)-degrees, beta = 102.98(1)-degrees, gamma = 89.52(1)-degrees, Z = 2,1968 reflections, R = 0.022.