Structural and Voltammetric Studies on the Reduction of the Bis(2,2‘-bipyridyl)platinum(II) Cation in Aprotic Media

The reduction of the bis(2,2‘-bipyridyl)platinum(II) cation, [Pt(bpy)₂]²⁺, in aprotic media has been studied electrochemically. Voltammetry at scan rates above 500 V s^-1 reveals three reversible reductions at −1.14, −1.45, and −2.07 V versus the ferrocenium/ferrocene couple. The first of these couples shows only a moderately fast electron transfer. At lower scan rate, e.g., 0.1 V s^-1, or on the time scale of an electrosynthesis, the product of the first one-electron reduction is shown to be the previously unknown homoleptic platinum(I) dimeric cation (μ₂-2,2‘-bipyridyl)bis(2,2‘-bipyridyl)bisplatinum(I), [Pt₂(bpy)₃]²⁺, an X-ray crystal structure of which is presented along with 2-D NMR and EXAFS results showing this is also the major species in solution. The formation of [Pt₂(bpy)₃]²⁺ is shown by digital simulation of voltammetric results to be by a first-order process initiated by one-electron reduction of [Pt(bpy)₂]²⁺, and subsequent ligand loss before insertion into the Pt−N bond of another molecule of reduced monomer. Electrolysis in the absence of inert electrolyte is shown to be a viable means of producing pure samples of the products of electrode reactions, even in cases where these are delicate or unstable.