Constructing a catalytic cycle for c-f to c-x (x = o, s, n) bond transformation based on gold-mediated ligand nucleophilic attack

Article abstract of DOI:10.1021/acs.inorgchem.5b02634

A tricoordinated gold(I) chloride complex, tBuXantphosAuCl, supported by a sterically bulky 9,9-dimethyl-4,5-bis(di-Tert-butylphosphino)xanthene ligand (tBuXantphos) was synthesized. This complex features a remarkably longer Au?Cl bond length [2.632(1) ?] than bicoordinated linear gold complexes (2.27-2.30 ?) and tricoordinated XantphosAuCl [2.462(1) ?]. Single-crystal Xray diffraction analysis of a cocrystal of tBuXantphosAuCl and pentafluoronitrobenzene (PFNB) and UV-vis spectroscopic titration experiments revealed the existence of an anion-φ interaction between the Cl anion ligand and PFNB. Stoichiometric reaction between PFNB and tBuXantphosAuOtBu, after replacement of Cl by a more nucleophilic tBuO anion ligand, showed higher reactivity and para selectivity in the transformation of C-F to C-OtBu bond, distinctively different from that when only KOtBu was used (ortho selectivity) under the identical condition. Mechanistic studies including density functional theory calculations suggested a gold-mediated nucleophilic ligand attack of the C?F bond pathway via an SNAr process. On the basis of these results, using trimethylsilyl derivatives TMS-X (X = OMe, SEt, NEt) as the nucleophilic ligand source and the fluorine acceptor, catalytic transformation of the C-F bond of aromatic substrates to the C-X (X = O, S, N) bond was achieved with tBuXantphosAuCl as the catalyst (up to 20 turnover numbers).