Hydrogen bonding to carbonyl hydride complex Cp*Mo(PMe3)2(CO)H and its role in proton transfer

Abstract

The interaction of the carbonyl hydride complex Cp*Mo(PMe₃)₂(CO)H with Brønsted (fluorinated alcohols, (CF₃)_nCH_3−nOH (n = 1–3), and CF₃COOH) and Lewis (Hg(C₆F₅)₂, BF₃·OEt₂) acids was studied by variable temperature IR and NMR (¹H, ³¹P, ¹³C) spectroscopies in combination with DFT/B3LYP calculations. Among the two functionalities potentially capable of the interaction – carbonyl and hydride ligands – the first was found to be the preferential binding site for weak acids, yielding CO⋯HOR or CO⋯Hg complexes as well as CO⋯(HOR)₂ adducts. For stronger proton donors ((CF₃)₃COH, CF₃COOH) hydrogen-bonding to the hydride ligand can be revealed as an intermediate of the proton transfer reaction. Whereas proton transfer to the CO ligand is not feasible, protonation of the hydride ligand yields an (η²-H₂) complex. Above 230 K dihydrogen evolution is observed leading to decomposition. Among the decomposition products compound [Cp*Mo(PMe₃)₃(CO)]⁺[(CF₃)₃CO·2HOC(CF₃)₃]⁻ resulting from a phosphine transfer reaction was characterized by X-ray diffraction. Reaction with BF₃·OEt₂ was found to produce [Cp*Mo(PMe₃)₂(CO)BF₄] via initial attack of the hydride ligand.