A Simple Micellar Gold Catalyst Supported by a Hydrophilic Phosphinoferrocene Amidosulfonate Ligand

A phosphinoferrocene amidosulfonate and its chlorogold complex form micelles in water. The complex can be used as a self-activating Au catalyst, as demonstrated for the model cyclization of N-propargyl benzamide into 4,5-dihydro-5-methylene-2-phenyloxazole.

The design of micellar catalysts is instrumental in transferring metal-catalyzed organic reactions into aqueous reaction media and enabling catalyst reuse. Herein, it is reported that phosphinoferrocene amidosulfonate Ph₂PfcC(O)NHCH₂SO₃(HNEt₃) (1, fc = ferrocene-1,1′-diyl) and its chlorogold(I) complex [AuCl(1-κP)] (8) form stable micelles in water. The latter compound is found to be an efficient, self-activating catalyst for the gold-catalyzed cyclization of N-propargyl benzamide into 4,5-dihydro-5-methylene-2-phenyloxazole in a water-ethyl acetate mixture. Structure determination of 8·½CH₂Cl₂ reveals extensive hydrogen bonding between the polar amidosulfonate pendants, in line with the compound's surfactant-like behavior. Density functional theory calculations of the plausible LAu⁺ type catalyst suggest a possible in situ self-activation of complex 8 in water via chloride loss, possibly facilitated by the amidosulfonate group and the formation of Au(I)-aqua species.

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