ALKYLIDYNE-ALKYNE COUPLING REACTIONS - REACTIONS OF MO2CO(CO)7CP2(MU-3-CH) WITH ETC2ET AND PHC2PH

The reaction of Mo2Co(CO)7Cp2(mu-3-CH) with EtC2Et has yielded two isomeric products Mo2Co(CO)5Cp2[mu-3-OCC(Et)C(Et)CH] (2a, 3%, 2b, 18%). Both products were characterized crystallographically and were found to contain triply bridging OCC(Et)C(Et)CH ligands formed by the coupling of the methylidyne ligand to one EtC2Et molecule and one CO ligand. The CO group bridges the face of a Mo2Co triangular cluster with the oxygen atom coordinated to one of the molybdum toms, Mo-O = 21.142 (5) angstrom in 2a and 2.150 (4) angstrom in 2b. The isomers were equilibrated as 1.0/1.7 2a/2b at 52-degrees-C in 7 days. The reaction of 1 with PhC2Ph yielded two products Mo2Co(CO)2Cp2[mu-3-C(Ph)C(H)C(Ph)C(Ph)](mu-3-CPh) (3, 18% and Mo2Co(CO)2Cp2(mu-3-CO)(mu-PhC2Ph)[mu-3-C(H)C(Ph)C(Ph)] (4, 30%). Compound 3 contains a dimetallatriphenylbutadiene ligand and a triply bridging benzylidyne ligand. These were formed by the coupling of two PhC2Ph molecules to the methylidyne ligand and the splitting off of one CPh group. Compound 4 contains a triply bridging dimetalladiphenylallyl ligand formed by the coupling of one PhC2Ph molecule to the methylidyne ligand. Compounds 3 and 4 are both electron deficient and both contain Mo2Co clusters with unusually short Mo-Mo bonds. Compound 3 also contains an unusual agostic phenyl interaction. Crystal Data: for 2a, space group = P2(1)/a, a = 15.035 (3) angstrom, b = 9.373 (4) angstrom, c = 16.494 (3) angstrom, beta = 100.65 (1)-degrees, Z = 4, 1659 reflections, R = 0.029; for 2b, space group = Pbca, a = 16.966 (3) angstrom, b = 25.777 (5) angstrom, c = 10.310 (1) angstrom, Z = 8, 2349 reflections, R = 0.027; for 3, space group = C2/c, a = 34.08 (2) angstrom, b = 11.436 (4) angstrom, c = 18.80 (1) angstrom, beta = 118.62 (4)-degrees, Z = 8, 2254 reflections, R = 0.040; for 4, space group = C2/c, a = 35.896 (9) angstrom, b = 13.243 (5) angstrom, c = 16.899 (3) angstrom, beta = 96.62 (2)-degrees, Z = 8, 2535 reflections, R = 0.048.