Synthesis, reactions and characterization of mu-alkyne molybdenum complexes containing a functionally substituted cyclopentadienyl ligand. The crystal structure of [(eta(5)-MeO(2)CC(5)H(4))(CO)(2)Mo](2)(mu-eta(2)eta(2)-C2H2)

Through reaction of acetylene with an in situ generated mixture of three metal-metal triply bonded complexes [eta(5)-R(1)C(5)H(4)(CO)(2)Mo](2), [eta(5)-R(2)C(5)H(4)(CO)(2)Mo](2) and eta(5)-R(1)C(5)H(4)(CO)(2)Mo=Mo(CO)(2)C(5)H(4)R(2)-eta(5), five new mu-alkyne bridged molybdenum compounds [eta(5)-R(1)C(5)H(4)(CO)(2)Mo](2)(mu-eta(2),eta(2)-C2H2) (1a, R(1) = C(O)Me), [eta(5)-R(2)C(5)H(4)(CO)(2)Mo](2)(mu-eta(2),eta(2)-C2H2) (2a, R(2) = CO(2)Me) and [eta(5)-R(1)C(5)H(4)(CO)(2)MoMo(CO)(2)C(5)H(4)R(2)-eta(5)](mu-eta(2),eta(2)-C2H2) (3a: R(1) = C(O)Me, R(2) = CO(2)Me; 3b: R(1) = C(O)Me, R(2) = H; 3c: R(1) = CO(2)Me, R(2) = H) were prepared. Further reaction of 1a, 3a or 3b with NaBH4 in MeOH gave three new corresponding acetyl reduction products [eta(5)-MeCH(OH)C5H4(CO)(2)Mo](2)(mu-eta(2),eta(2)-C2H2)(4), [eta(5)-MeCH(OH)C5H4(CO)(2)MoMo(CO)(2)C(5)H(4)CO(2)Me-eta(5)](mu-eta(2),eta(2)-C2H2)(5) or [eta(5)-MeCH(OH)C5H4(CO)(2)MoMo(CO)(2)C5H5-eta(5)](mu-eta(2),eta(2)-C2H2 (6), respectively, whereas reaction of 2a with KOH/MeOH/H2O afforded two products resulting from mono- and dihydrolysis of the ester groups [eta(5)-HO2CC5H4(CO)(2)MoMo(CO)(22)C(5)H(4)CO(2)Me-eta(5)]-(mu-eta(2),eta(2)-C2H2)(7) and [eta(5)-HO2CC5H4(CO)(2)Mo](2)(mu-eta(2),eta(2)-C2H2 (8). All of these new complexes were fully characterized by elemental analysis, IR, H-1 NMR and mass spectroscopy. The crystal structure of 2a was determined by X-ray diffraction techniques. 2a crystallized in the triclinic space group <P(1)over bar> (No. 2) with a = 7.135(2), b = 14.794(2), c = 20.133(4) Angstrom; alpha = 107.98(1), beta = 98.58(2), gamma = 93.12(2)degrees; V = 1987(2) Angstrom(3) and Z = 4.