PREPARATION OF 4-MEMBERED AND 5-MEMBERED DIRUTHENACYCLES AND AN UNUSUAL DOUBLE INSERTION OF CARBON-MONOXIDE - CRYSTAL AND MOLECULAR-STRUCTURES OF RU2(ME2PCH2PME2)2(CO)3[MU-C2(CO2ME)2][C(O)C(O)C2-(CO2ME)2] AND RU2(ME2PCH2PME2)2(CO)4[MU-C(O)C2(CO2ME)2]

The reaction of Ru2(dmpm)2(CO)5, where dmpm = bis(dimethylphosphino)methane, with dimethyl acetylenedicarboxylate (DMAD) resulted in the formation of three isolable products, each of which can be prepared in approximately 80% yield by varying the reaction conditions. In very concentrated solutions at room temperature, the presence of excess DMAD led to Ru2(dmpm)2(CO)3[mu-C2(CO2Me)2][C(O)C(O)C2(CO2Me)2] in 81% yield. The X-ray crystal structure [P2(1)2(1)2(1) (No. 19) space group, a = 13.932 (5) angstrom, b = 14.360 (3) angstrom, c = 17.854 (3) angstrom, V = 3572 (3) angstrom3, Z = 4] established that one alkyne was bound as a cis-dimetalated alkene, while the other was incorporated into a five-membered metallacycle. This metallacycle appeared to have formed by the insertion of two carbon monoxide ligands into a metal-alkyne bond. When the reaction was conducted at room temperature in dilute solution, the product, Ru2(dmpm)2(CO)4[mu-C(O)C2(CO2Me)2] contained only 1 equiv of DMAD. X-ray crystallography [P2(1)/n. (No. 14) space group, a = 10.845 (5) angstrom, b = 27.82 (1) angstrom, c = 10.447 (5) angstrom, beta = 109.90 (4)-degrees, V = 2964 (5) angstrom3, Z = 4] showed the alkyne had again been incorporated into a five-membered metallacycle, in a 1,2-diruthenacyclopentenone arrangement. When the reaction of Ru2(dmpm)2(CO)5 with DMAD was conducted at elevated temperatures or when Ru2(dmpm)2(CO)4[mu-C(O)C2(CO2Me)2] was heated, loss of one CO ligand to form a 1,2-diruthenacyclobutene resulted. Methyl propiolate was also found to react slowly (25-30 h at room temperature) with Ru2(dmpm)2(CO)5 yielding a product that was analogous to the 1,2-diruthenacyclobutene described for DMAD.