Unsymmetric Dinuclear RhI 2 and RhIRhIII Complexes Supported by Tetraphosphine Ligands and Their Reactivity of Oxidative Protonation and Reductive Dechlorination

• Published in: Inorganic chemistry 2022-01, Vol.61 (2), p.1102-1117
• Main Authors: Nakajima, Takayuki, Maeda, Mami, Matsui, Aya, Nishigaki, Mariko, Kotani, Momoko, Tanase, Tomoaki
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.1c03278

Two linear tetradentate phosphine ligands, meso-Ph2PCH2P­(Ph)­CH2 XCH2P­(Ph)­CH2PPh2 (X = CH2 (meso-dpmppp), NBn (meso-dpmppmNBn; Bn = benzyl)) were utilized to synthesize unsymmetrical dinuclear RhI complexes, [Rh2Cl2(meso-dpmppp)­(L)] (L = XylNC (1a), CO (1b)) and [Rh2Cl2(meso-dpmppmNBn)­(L)] (L = XylNC (1c), CO (1d)), where electron-deficient RhI → RhI centers with 30 valence electrons are supported by a tetraphosphine in an unusual cis-/trans-P,P coordination mode. The RhI dimers of 1a–d were treated with HCl under air to afford the RhI → RhIII dimers with 32 e–, [Rh2Cl4(meso-dpmppp)­(L)] (L = XylNC (4a), CO (4b)) and [Rh2Cl4(meso-dpmppmNBn)­(L)] (L = XylNC (4c), CO (4d)), via intermediate hydride complexes, [{RhCl2(μ-H)­RhCl­(L)}­(meso-dpmppp)] (L = XylNC (2a), CO (2b)) and [{RhCl2(μ-H)­RhCl­(L)}­(meso-dpmppmNBn)] (L = XylNC (2c), CO (2d)), and [{Rh­(H)­Cl2(μ-Cl)­Rh­(L)}(meso-dpmppp)] (L = XylNC (3a), CO (3b)) and [{Rh­(H)­Cl2(μ-Cl)­Rh­(L)}(meso-dpmppmNBn)] (L = XylNC (3c), CO (3d)). The hydride intermediates 2 and 3 were monitored under nitrogen by 1H­{31P} and 31P­{1H} NMR techniques to reveal two reaction pathways depending on the terminal auxiliary ligand L. Further, the reductive dechlorination converting RhIRhIII (4b,d) to RhI 2 (1b,d) 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 1a–d and 4a–d and to estimate the structures of the hydride intermediate complexes 2 and 3.