Constructing a Catalytic Cycle for C–F to C–X (X = O, S, N) Bond Transformation Based on Gold-Mediated Ligand Nucleophilic Attack

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)
Å] than bicoordinated linear gold complexes (2.27–2.30
Å) and tricoordinated XantphosAuCl [2.462(1) Å]. Single-crystal
X-ray diffraction analysis of a cocrystal of tBuXantphosAuCl and pentafluoronitrobenzene
(PFNB) and UV–vis spectroscopic titration experiments revealed
the existence of an anion−π 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, NEt2) 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).