Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 64. Addition of methylene groups to iron–molybdenum complexes; crystal structures of [FeMo(µ-CH2){µ-σ:η-C(C6H4Me-4)CH2}(CO)5(η-C5H5)] and [FeMo{µ-C(C6H4Me-4)C(OMe)C(H)}(CO)5(η-C5H5)]

The reaction between [FeMo(µ-CC6H4Me-4)(CO)6(η-C5H5)] and CH2N2 in diethyl ether at ambient temperatures affords the complex [FeMo(µ-CH2){µ-σ:η-C(C6H4Me-4)CH2}(CO)5(η-C5H5)], whereas if the reaction is carried out at ca.–40 °C the product is [FeMo{µ-C(C6H4Me-4)C(OMe)C(H)}(CO)5(η-C5H5)]. Both species correspond to the addition of two CH2 fragments to the precursor, and their molecular structures have been established by single-crystal X-ray diffraction studies. In [FeMo(µ-CH2){µ-σ:η-C(C6H4Me-4)CH2}(CO)5(η-C5H5)] the Fe–Mo bond [2.717(1)A] is asymmetrically bridged by the CH2 group [µ-C–Fe 2.016(3), µ-C–Mo 2.239(3)A], and the C(C6H4Me-4)CH2 fragment is σ-bonded to molybdenum [C–Mo 2.209(2)A] and η-co-ordinated to iron [C–Fe 2.055(2) and 2.127(3)A]. The molecule of [FeMo{µ-C(C6H4Me-4)C(OMe)C(H)}(CO)5(η-C5H5)] has an Fe–Mo bond [2.704(1)A] transversely bridged by a C(C6H4Me-4)C(OMe)C(H) fragment, with the latter η3-co-ordinated to the iron and with the two end carbons of the C3 chain σ-bonded to the molybdenum. Reactions between the complexes [FeMo(µ-CC6H4Me-4)(CO)n( PMe3)(η-C5H5)](n= 4 and 5) and CH2N2 have also been investigated, and the compounds [FeMo(µ-CH2){µ-σ:η-C(C6H4Me-4)CH2}(CO)4(PMe3)(η-C5H5)] and [FeMo{µ-C(C6H4Me-4)C(OH)C(H)}(CO)4(PMe3)(η-C5H5)] thereby obtained. The 1H and 13C-{1H} n.m.r. spectra of the new compounds are reported and discussed, and pathways proposed for their formation.