Complexation of aldehydes and ketones by trimeric perfluoro-ortho-phenylene mercury, a tridentate Lewis acid

A series of adducts formed by the interaction of trimeric perfluoro-ortho-phenylene mercury (2) with various organic carbonyls including acetaldehyde, acetone, acetophenone, and benzophenone have been characterized. The crystal structures. of [2(.),mu(3)-acetaldehydel (3) and [2(.)mu(3)-benzophenone] (7), respectively, reveal the formation of 1:1 complexes in which one. molecule of the organic carbonyl is concomitantly coordinated to the three mercury centers of 2 via the oxygen atom. In the benzophenone adduct 7, one of the phenyl rings of the coordinated benzophenone molecule engages in an intramolecular arene-fluoroarene interaction with a tetrafluorophenylene ring of 2 (intercentroid distance: 3.687 Angstrom). When 2 is combined with acetone and acetophenone, adducts [2(.)(acetone)(mu(3)-acetone)(2)] (4) and [2(.)(mu(3)-acetophenone)(2)] (6) are obtained. In both cases, two molecules of the ketone are positioned on each side of the planar trifunctional Lewis acid and are complexed via their respective oxygen atom to the three mercury centers of 2. In 4, a third molecule of acetone acts as a terminal ligand and forms a relatively long bond with one of the mercury atoms. In 3, 4, 6, and 7 the Hg-O bonds formed by the triply bridging carbonyl substrate range from 2.813(6) to 3.056(14) and are within the sum of the van der Waals radii of oxygen and mercury. In all cases, the carbonyl stretching vibration of the carbonyl substrate is shifted to a lower wavenumber, which suggests a weakening of the C=O bond.