Reactions of the (2-Pyridyl) Pyrrolide Platinum(II) Complex Driven by Sterically Encumbered Chelation: A Model for the Reversible Attack of Alcohol at the Coordinated Carbon Monoxide

Treatment of 3,5-bis(trifluoromethyl)-2-(2'-pyridyl)pyrrole (fpyroH) with Pt(DMSO)2Cl2 and Na2CO3 in THF solution gave a light-yellow complex denoted as [Pt(fpyro)2] (1). A single-crystal X-ray diffraction study on 1 revealed a large conformational distortion around the platinum(II) center, which is attributed to interligand repulsion between the pyridyl groups and the CF3 substituents of the nearby pyrrolides. Reaction of 1 with N- and C-donor ligands such as acetonitrile, pyridine, isocyanide, and CO affords the adducts [Pt(fpyro)2(L)], L = NCMe (2), pyridine (3), CNBut (4), and CO (5), showing formation of one monodentate fpyro ligand by release of the strain energy. The variable-temperature 1H NMR studies showed a static structure for the N-substituted adducts 2 and 3, whereas the C-adducts 4 and 5 are shown to be more labile, displaying a pairwise exchange of bidentate and monodentate fpyro ligands in solution. Addition of ethanol to the coordinated CO in 5 during recrystallization is also established, affording an ethoxycarbonyl complex [Pt(fpyro)(fpyroH)(CO2Et)] (6), which was isolated as a crystalline solid and can be readily converted back to 5 and free ethanol upon dissolution at room temperature.