Reactions of the metallabromoalkane [Mo{(CH2)3Br}(CO)3(η-C5H5)] and the carbene complexes trans-[MoI{C(CH2)3O}(CO)2(η-C5H4R)](R = H or Me) with Li(BEt3H). The synthesis (R = H or Me) and X-ray structure (R = Me) of [Mo{CH(CH2)3O}(CO)2(η-C5H4R)] containing an unusual oxygen–molybdenum donor interaction

Abstract

The reaction of [Mo{(CH₂)₃Br}(CO)₃(η-C₅H₅)] with Li(BEt₃H) leads to the spectroscopically characterised [[graphic omitted]}(CO)₂(η-C₅H₅)]. This compound is also formed in the reaction of the carbene complex trans-[MoI{[graphic omitted]}(CO)₂(η-C₅H₅)] with Li(BEt₃H). In both reactions small quantities of the known η³-ally[Mo(CO)₂(η³-C₄H₇)(η-C₅H₅)] are also isolated. The methylcyclopentadienyl analogues are available through reaction of trans-[MoI{[graphic omitted]}(CO)₂(η-C₅H₄Me)] with Li(BEt₃H) and the resulting molecule [[graphic omitted]}(CO)₂(η-C₅H₄Me)] is the subject of an X-ray crystal structure determination. It crystallises as irregular red lumps, a= 8.416(9), b= 11.541(12), c= 7.063(3)Å, α= 105.23(3), β= 105.71(3), and γ= 104.938(12)°; R converged to 0.0299 for 1 805 independent reflections for which I > 3.0 σ(I). The bonding of the C₄H₇O ring is unusual and formulated as a metal–alkyl interaction adjacent to a O → Mo bond. The molybdenum–oxygen bond is labile, thus [[graphic omitted]}(CO)₂(η-C₅H₅)] reacts readily with PPh₃ to give the phosphine complex trans-[Mo{[graphic omitted]}(CO)₂(PPh₃)(η-C₅H₅)] in good yield. Formation of [[graphic omitted]}(CO)₂(η-C₅H₅)] from the alkyl complex proceeds by the initial formation of a metal formyl complex [Mo(CHO){(CH₂)₃Br}(CO)₂(η-C₅H₅)]^– which rearranges through two further intermediates to the ultimate product. Formation of [[graphic omitted]}(CO)₂(η-C₅H₄R)] from the appropriate carbene complex is apparently by direct attack of the hydride reagent at the carbene atom. Reaction of the alkyl trans-[Mo{(CH₂)₃Br}(CO)₂(PPh₃)(η-C₅H₅)] with Li(BEt₃H) leads only to the η³-allyl [Mo(CO)(PPh₃)(η³-C₄H₇)(η-C₅H₅)].