Unsymmetric Dinuclear Rh and RhRh Complexes Supported by Tetraphosphine Ligands and Their Reactivity of Oxidative Protonation and Reductive Dechlorination.

Two linear tetradentate phosphine ligands, -PhPCHP(Ph)CHCHP(Ph)CHPPh ( = CH (-dpmppp), NBn (-dpmppmNBn; Bn = benzyl)) were utilized to synthesize unsymmetrical dinuclear Rh complexes, [RhCl(-dpmppp)(L)] (L = XylNC (), CO ()) and [RhCl(-dpmppmNBn)(L)] (L = XylNC (), CO ()), where electron-deficient Rh → Rh centers with 30 valence electrons are supported by a tetraphosphine in an unusual /- coordination mode. The Rh dimers of - were treated with HCl under air to afford the Rh → Rh dimers with 32 e, [RhCl(-dpmppp)(L)] (L = XylNC (), CO ()) and [RhCl(-dpmppmNBn)(L)] (L = XylNC (), CO ()), via intermediate hydride complexes, [{RhCl(μ-H)RhCl(L)}(-dpmppp)] (L = XylNC (), CO ()) and [{RhCl(μ-H)RhCl(L)}(-dpmppmNBn)] (L = XylNC (), CO ()), and [{Rh(H)Cl(μ-Cl)Rh(L)}-dpmppp)] (L = XylNC (), CO ()) and [{Rh(H)Cl(μ-Cl)Rh(L)}-dpmppmNBn)] (L = XylNC (), CO ()). The hydride intermediates and were monitored under nitrogen by H{P} and P{H} NMR techniques to reveal two reaction pathways depending on the terminal auxiliary ligand L. Further, the reductive dechlorination converting RhRh (,) to Rh (,) was accomplished with a CO terminal ligand by reacting with various amines that acted as one-electron reducing agents through an inner-sphere electron transfer mechanism. DFT calculations were performed to elucidate the electronic structures of - and - and to estimate the structures of the hydride intermediate complexes and .