Solid state and solution structure of the hetero-dimetallic complexes [Cp(CO)2Re{μ-C(OMe)(Ph)}Pt(COD)] and [Cp(CO)2Re{μ-CPh}Pt(COD)]+, containing bridging carbene and carbyne ligands

The reaction of the carbene complex [Cp(CO)2ReC(OMe)(Ph)] with [Pt(COD)2] affords in high yield the novel complex [Cp(CO)2Re{μ-C(OMe)(Ph)}Pt(COD)] (2), containing a bridging carbene ligand. Reaction of 2 with (Me3O)BF4 results in removal of the carbene-bound methoxy group, with formation of the cation [Cp(CO)2Re{μ-CPh}Pt(COD)]+ (3), in which a bridging carbyne is present. Both the complexes contain only ligands coordinated through carbon atoms and represent the highest members, as far as the Pt:Re ratio is concerned, of the small family of phosphorous-free Pt–Re mixed metal complexes containing PtRe bonds. Their full 1H and 13C NMR characterization in solution and their single-crystal solid state diffractometric analysis are reported and discussed. The X-ray analysis evidenced the substantially symmetric nature of the carbene bridge in the dimetalla-cyclopropane ring of complex 2 [RePt 2.7188(3), Re-(μ-C) 2.166(4) and Pt-(μ-C) 2.055(4) Å]. In complex 3 the bond length pattern within the three-membered ring is suggestive of a significant double-bond character for the Re-(μ-C) interaction [RePt 2.707(1), Re-(μ-C) 1.904(9) and Pt-(μ-C) 1.981(8) Å]. Both complexes show a semi-bridging CO ligand, with Pt⋯C distances of 2.452(4) and 2.299(9) Å, in 2 and 3, respectively. The 13C NMR characterization showed that the Pt⋯CO interaction is also maintained in solution in both complexes. In cation 3 a libration of the ReCp(CO)2 fragment around the PtRe axis, fast down to 193 K, interchanges the two carbonyl locations observed in the solid state, as well as the environments of couples of COD carbon atoms, leading to an apparent Cs symmetry. The correlation between spectroscopic data and structural features (concerning bridging carbenes or carbynes and semi-bridging carbonyls) in the class of heterodimetallic M–Pt complexes is discussed.