Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 61. Reactions of iron–molybdenum compounds with tertiary phosphines

Treatment of [FeMo(µ-CR)(CO)6(η-C5H5)](R = C6H4Me-4) with PMe3 affords the compound [FeMo(µ-CR)(CO)5(PMe3)(η-C5H5)], which readily releases a molecule of CO to give the unsaturated species [FeMo(µ-CR)(CO)4(PMe3)(η-C5H5)]; a process which can be readily reversed. The compound [Mo(CR)(CO)2(η-C5H5)] reacts with PMe3 to give [Mo(CR)(CO)(PMe3)(η-C5H5)]. The latter on treatment with one equivalent of [Fe2(CO)9] yields a mixture of the complexes [FeMo(µ-CR)(CO)n(PMe3)(η-C5H5)](n= 4 or 5), and with excess of [Fe2(CO)9] affords [Fe2Mo(µ3-CR)(µ-CO)(CO)7(PMe3)(η-C5H5)]. This di-ironmolybdenum compound may also be obtained from the reaction of PMe3 with [Fe2Mo(µ3-CR)(µ-CO)(CO)8(η-C5H5)], while the latter with dppm (Ph2PCH2PPh2) affords [Fe2Mo(µ-CR)(µ-CO)(µ-dppm)(CO)6(η-C5H5)]. The reaction between PMe3 and [FeMo2(µ3-RC2R)(CO)6(η-C5H5)2] gives [FeMo2(µ3-RC2R)(CO)5(PMe3)(η-C5H5)2]. Spectroscopic data for the new compounds are reported and discussed in the context of the structures proposed.