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Abstract
An exceptionally mild and efficient method was developed for the preparation of (hetero)aryl‐AuI‐L complexes using ethanol or water as the reaction medium at room temperature and Ar‐B(triol)K boronates as the transmetalation partner. The reaction does not need an exogeneous base or other additives, and quantitative yields can be achieved through a simple filtration as the only required purification method, which obviates considerable waste associated with alternative workup methods. A broad reaction scope was demonstrated with respect to both the L and (hetero)aryl ligands on product Au complexes. Despite the polar reaction medium, large polycyclic aromatic hydrocarbon units can be incorporated on the Au complexes in very good to excellent yields. The approach was demonstrated for the chemoselective manipulation of orthogonally protected aryl boronates to afford a new class of N‐heterocyclic carbene‐Au‐aryl complexes. A mechanistic rationale was proposed.
Highlights
Synthetic chemistry is under increasing pressure to provide environmentally benign routes to functional molecules
We compared a range of 3-tolyl boronates (2 a–d) in transmetalation to the AuI center of Ph3PAuCl (3 a) in various solvents (Table 1, entries 1–8)
We extensively investigated the scope with respect to both five- and six-memberedaryl boronates using 3 a as the gold precursor (Scheme 1)
Summary
Synthetic chemistry is under increasing pressure to provide environmentally benign routes to functional molecules. We set out to develop a protocol to prepare LAuI-Ar complexes that can tolerate a wide variety of functional groups and ligands, require only environmentally benign/nontoxic solvent media, and, importantly, work efficiently without any other exogeneous additives or heating using well-defined reagents. The triol itself, 2-(hydroxymethyl)-2-methylpropane-1,3-diol, has low toxicity, is significantly cheaper than pinacol,[16] and is produced on a multi-ton scale annually.[17] We anticipated that the transmetalation of (hetero)aryl groups from such boronates to an AuI center should be efficient on account of their significantly enhanced nucleophilicity[11,18] and because they have been shown to benefit transmetalation to other transition metals.[15e,f,19] For example, Chan–Lam aminations using [PhB(triol)]K proceed at three times the rate of the equivalent reactions using PhB(OH) or PhBF3K as the arylating reagent.[20] We envisaged the prospect of an alternative intramolecular transmetalation pathway through intermediate alkoxide adducts (see below)
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