ALKYNE AND CO COUPLING REACTIONS WITH THE VINYLIDENE LIGAND IN THE COMPLEX MN2(CO)7[MU-ETA-2-C=CME(CO2ET)]

Reaction of the vinylidene complex Mn2(CO)8[mu-eta2-C = CMe(CO2Et)] (1a) with CO (at 1000 psi) at 87-degrees-C yielded the new compound (OC)4Mn[(EtO2C)MeC = CC = OC = OC = CMe(CO2-Et)]Mn(CO)4 (2) in 59% yield and Mn2(CO)10. COMPound 2 is believed to have been formed by the carbonylation of the vinylidene ligand, cleavage of a Mn(CO)5 fragment, and a coupling of two metal groupings containing carbonylated vinylidene ligands. The reaction of la with a combination of MeC = COEt and CO yielded only the compound (OC)4Mn[(EtO2C)-MeC = CC = CMe(CO2Et)]Mn(CO)4 (3) in 72% yield. Compound 3 contains a 3,4-dimetallo-2,5-bis(ethoxycarbonyl)-2,4-hexadiene group formed by the coupling of two vinylidene ligands at the vinylidene carbon atoms. When the reaction of la with MeC = COEt was performed in the absence of CO, the three isomeric products Mn2(CO)7{C(Me)C(OEt)C[= CMe(CO2Et)]C-(Me)C(OEt)} (4a), Mn2(CO)7{C(Me)C(OEt)C[=CMe(CO2Et)]C(OEt)C(Me)} (4b), and Mn2(CO)7-{C(OEt)C(Me)C[= CMe(CO2Et)]C(Me)C(OEt)} (4c) were formed in low yields. All three products contain a metallacyclohexadiene grouping that was formed by the addition and coupling of two MeC = COEt molecules to the carbon atom of the vinylidene ligand in la. Compounds 2, 3, and 4a-c were characterized by single-crystal X-ray diffraction analyses. Crystal data: for 2, space group P1BAR, a = 12.056(2) angstrom, b = 18.016(3) angstrom, c = 9.729(2) angstrom, a = 91.96(1)-degrees, beta = 111.82(1)-degrees, gamma = 85.13(2)-degrees, Z = 3, 4273 reflections, R = 0.029; for 3, space group P2(1)/n, a = 8.532(2) angstrom, b = 19.431(4) angstrom, c = 14.331(3) angstrom, beta = 91.34(2)-degrees, Z = 4, 1562 reflections, R = 0.036; for 4a, space group P1BAR, a = 10.570(l) angstrom = 13.930(6) angstrom, c = 9.497(3) angstrom, alpha = 91.57(3)-degrees, beta = 98.48(3)-degrees, gamma = 72.63(4)-degrees, Z = 2, 1556 reflections R = 0.042; for 4b, space group = P2(1)/c, a = 12.080(3) angstrom, b = 12.929(5) angstrom, c = 16.723(4) angstrom, beta = 99.22(2)-degrees, Z = 4, 1473 reflections, R = 0.040; for 4c, space group P2(1)2(1)2(1), a = 13.876(3) angstrom, b = 17.443(3) angstrom, c = 10.871(2) angstrom, Z = 4, 1574 reflections, R = 0.035.