cicCartuja Centro de Investigaciones Científicas de la cartuja
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Juan Miranda-Pizarro, Zhongwen Luo, Juan J. Moreno, Diane A. Dickie, Jesús Campos, and T. Brent Gunnoe J. Am. Chem. Soc. 2021, Vol. 143, 2509–2522
Organometallic gold complexes are used in a range of catalytic reactions, and they often serve as catalyst precursors that mediate C–C bond formation. In this study, we investigate C–C coupling to form ethane from various phosphine-ligated gem-digold(I) methyl complexes including [Au2(μ-CH3)(PMe2Ar′)2][NTf2], [Au2(μ-CH3)(XPhos)2][NTf2], and [Au2(μ- CH3)(tBuXPhos)2][NTf2] {Ar′ = C6H3-2,6-(C6H3-2,6- Me)2, C6H3-2,6-(C6H2-2,4,6-Me)2, C6H3-2,6-(C6H3-2,6- iPr)2, or C6H3-2,6-(C6H2-2,4,6-iPr)2; XPhos = 2- dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl; tBuXPhos = 2-di-tert-butylphosphino-2′,4′,6′- triisopropylbiphenyl; NTf2 = bis(trifluoromethyl sulfonylimide)}. The gem-digold methyl complexes are synthesized through reaction between Au(CH3)L and Au(L)(NTf2) {L = phosphines listed above}. For [Au2(μ- CH3)(XPhos)2][NTf2] and [Au2(μ- CH3)(tBuXPhos)2][NTf2], solid-state X-ray structures have been elucidated. The rate of ethane formation from [Au2(μ-CH3)(PMe2Ar′)2][NTf2] increases as the steric bulk of the phosphine substituent Ar′ decreases. Monitoring the rate of ethane elimination reactions by multinuclear NMR spectroscopy provides evidence for a second-order dependence on the gem-digold methyl complexes. Using experimental and computational evidence, it is proposed that the mechanism of C–C coupling likely involves (1) cleavage of [Au2(μ- CH3)(PMe2Ar′)2][NTf2] to form Au(PR2Ar′)(NTf2) and Au(CH3)(PMe2Ar′), (2) phosphine migration from a second equivalent of [Au2(μ-CH3)(PMe2Ar′)2][NTf2] aided by binding of the Lewis acidic [Au(PMe2Ar′)]+, formed in step 1, to produce [Au2(CH3)(PMe2Ar′)][NTf2] and [Au2(PMe2Ar′)]+, and (3) recombination of [Au2(CH3)(PMe2Ar′)][NTf2] and Au(CH3)(PMe2Ar′) to eliminate ethane.
https://doi.org/10.1021/jacs.0c11296
Juan Miranda
