Reactions of Platinum Carbonyl Chini Clusters with Ag(NHC)Cl Complexes: Formation of Acid-Base Lewis Adducts and Heteroleptic Clusters.

The reactions of anionic platinum carbonyl Chini clusters [Pt(CO)] [n = 2 (1), 3 (2), 4 (3)] with Ag(IPr)Cl [IPr = CNH(CHPr)] afford the neutral acid-base Lewis adducts [Pt(CO)(AgIPr)] (4) and [Pt(CO)(AgIPr)] (5). These are thermally transformed into the homometallic heteroleptic neutral cluster [Pt(CO)(IPr)] (6). Alternatively, 6 can be obtained from the reactions of 1-3 with an excess of the free IPr carbene ligand. The formation of 6 is sometimes accompanied by trace amounts of [Pt(CO)(IPr)] (7). The reaction of 6 with free IPr affords the closely related [Pt(CO)(IPr)] (8) heteroleptic cluster by substitution of the unique terminal CO ligand with a third IPr ligand. The reactions of 1-3 with Ag(IMes)Cl [IMes = CNH(CHMe)] proceed differently from those involving Ag(IPr)Cl. Indeed, the only product isolated after workup is the bimetallic tetranuclear cluster [Pt(CO)(IMes)(AgCl)] (9). 9 slowly reacts under a CO atmosphere, resulting in the pentanuclear [Pt(CO)(IMes)] (10) complex. All of the new clusters 4-10 have been spectroscopically characterized and their molecular structures determined by X-ray crystallography. 4 and 5 retain the original trigonal-prismatic structures of the parent anionic Chini clusters, which are capped by two [Ag(IPr)] moieties. Conversely, 6-9 are based on a Pt triangular core decorated by CO and N-heterocyclic carbene ligands as well as Pt(CO) (in the case of 7) and AgCl (9) moieties. 10 displays an edge-bridged tetrahedral geometry.