New evidence on the factors affecting bridging and semibridging character of carbonyl ligands.: The structures of Mn2(CO)7(μ-SCH2CH2S) and its phosphine derivatives Mn2(CO)7-x(PMe2Ph)x(μ-SCH2CH2S), X=1,2

The new ethanedithiolate-dimanganese carbonyl complex, Mn-2(mu-SCH2CH2S)(CO)(gamma), 1, was prepared in 28% yield from the reaction of 1,2,5,6-tetrathiacyclooctane with Mn-2(CO)(9)(NCMe). Complex 1 was characterized crystallographically. It contains two Mn(CO)(3) groups joined by a Mn-Mn bond of 2.6470(6) Angstrom in length, a dihapto-bridging ethanedithiolate ligand, and one strong semibridging CO ligand. The reaction of 1 with PMe2Ph yielded two derivatives: Mn-2(mu-SCH2CH2S)(CO)(6)(PMe2Ph), 2, and gem-Mn-2(mu-SCH2CH2S)(CO)(5)(PMe2Ph)(2), 3a, in 48% and 6% yields, respectively. When heated at 40 degreesC, compound 3a was transformed into three isomers, iso-gem-Mn-2(mu-SCH2CH2S)(CO)(5)(PMe2Ph)(2), 3b, 1,2-Mn-2(mu-SCH2CH2S)(CO)(5)(PMe2Ph)(2), 3c, and cis-Mn-2(mu-SCH2CH2S)(CO)(5) PMe2Ph)(2), 3d. Compounds 3b and 3c were characterized by single-crystal X-ray diffraction analyses. The introduction of phosphine ligand into the complexes strongly affects the semibridging character of the carbonyl ligand.