Stoichiometric and catalytic C–F bond activation by the trans-dihydride NHC complex [Ru(IEt2Me2)2(PPh3)2H2] (IEt2Me2 = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene)

Abstract

The room temperature reaction of C₆F₆ or C₆F₅H with [Ru(IEt₂Me₂)₂(PPh₃)₂H₂] (1; IEt₂Me₂ = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene) generated a mixture of the trans-hydride fluoride complex [Ru(IEt₂Me₂)₂(PPh₃)₂HF] (2) and the bis-carbene pentafluorophenyl species [Ru(IEt₂Me₂)₂(PPh₃)(C₆F₅)H] (3). The formation of 3 resulted from C–H activation of C₆F₅H (formed from C₆F₆via stoichiometric hydrodefluorination), a process which could be reversed by working under 4 atm H₂. Upon heating 1 with C₆F₅H, the bis-phosphine derivative [Ru(IEt₂Me₂)(PPh₃)₂(C₆F₅)H] (4) was isolated. A more efficient route to 2 involved treatment of 1 with 0.33 eq. of TREAT-HF (Et₃N·3HF); excess reagent gave instead the [H₂F₃]⁻ salt (5) of the known cation [Ru(IEt₂Me₂)₂(PPh₃)₂H]⁺. Under catalytic conditions, 1 proved to be an active precursor for hydrodefluorination, converting C₆F₆ to a mixture of tri, di and monofluorobenzenes (TON = 37) at 363 K with 10 mol% 1 and Et₃SiH as the reductant.