[Fp(CH₄)]⁺, [η⁵-CpRu(CO)₂(CH₄)]⁺, and [η⁵-CpOs(CO)₂(CH₄)]⁺: A Complete Set of Group 8 Metal–Methane Complexes

Abstract

Here, we report the NMR spectroscopic analysis of the group 8 transition metal methane σ-complexes [η5-CpM(CO)2(CH4)][Al(OC(CF3)3)4] (M = Fe, Ru) at −90 °C in the weakly coordinating solvent 1,1,1,3,3,3-hexafluoropropane. The iron(II)–methane complex has a 1H resonance at δ −4.27, a 13C resonance at δ −53.0, and 1JC–H = 126 Hz for the bound methane fragment. The ruthenium(II)–methane complex has a 1H resonance at δ −2.10, a 13C resonance at δ −48.8, and a 1JC–H = 126 Hz for the bound methane fragment. DFT and ab initio calculations support these experimental observations and provide further detail on the structures of the [η5-CpM(CO)2(CH4)]+ (M = Fe, Ru) complexes of the Group 8 metals. Both the iron centered methane complex, [η5-CpFe(CO)2(CH4)][Al(OC(CF3)3)4], and the ruthenium centered methane complex, [η5-CpRu(CO)2(CH4)][Al(OC(CF3)3)4], are significantly less stable than the previously reported osmium–methane complex [η5-CpOs(CO)2(CH4)][Al(OC(CF3)3)4].

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