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)]

Abstract

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)Å] is asymmetrically bridged by the CH₂ group [µ-C–Fe 2.016(3), µ-C–Mo 2.239(3)Å], and the C(C₆H₄Me-4)CH₂ fragment is σ-bonded to molybdenum [C–Mo 2.209(2)Å] and η-co-ordinated to iron [C–Fe 2.055(2) and 2.127(3)Å]. The molecule of [FeMo{µ-C(C₆H₄Me-4)C(OMe)C(H)}(CO)₅(η-C₅H₅)] has an Fe–Mo bond [2.704(1)Å] 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.