Unsymmetric Ir2 and RhIr Dinuclear Complexes Supported by a Linear Tetraphosphine meso-dpmppp, Showing High Reactivity for O2, H2, and HCl.

Unsymmetric dinuclear Ir(I) complexes, [Ir2Cl2(L)(meso-dpmppp)] (L = XylNC (1aIr2), tBuNC (1bIr2), CO (1cIr2)), were synthesized using meso-Ph2PCH2P(Ph)(CH2)3P(Ph)CH2PPh2 (meso-dpmppp), which supports cis-P,P (M1) and trans-P,P (M2) metal sites, and exhibited high reactivity for O2, H2, and HCl. The IrRh heterodinuclear complexes, [M1M2Cl2(L)(meso-dpmppp)] (1xM1M2) (M1M2 = IrRh, RhIr; L = XylNC, CO (x = a, c)), were also synthesized and used together with the Rh2 complexes (1a,cRh2) to elucidate the role of each metal site. For the reactions of O2, 1aIr2 and 1aRhIr showed higher reactivity than those of 1aIrRh and 1aRh2, giving η2-peroxide complexes [{M1Cl2}{M2(η2-O2)(XylNC)}(meso-dpmppp)] (2aIr2, 2aRhIr), from which O2 would not dissociate. All the CO complexes 1cM1M2 (M1, M2 = Ir or Rh) showed no reactivity for O2. In the reactions with H2, 1aIr2 reacted with H2 to give the dihydride complex, [{IrCl2}{Ir(H)2L}(meso-dpmppp)] (11aIr2) and the tetrahydride complex, [{Ir(H)Cl2}(µ-H){Ir(H)2L}(meso-dpmppp)] (12aIr2), while 1aRhIr gave the dihydride complex, and 1aIrRh and 1aRh2 gave no hydride complexes. Reactions of 1a,cM1M2 with HCl afforded the dihydride complexes, [{IrCl3}(µ-H){Ir(H)Cl(XylNC)}(meso-dpmppp)] (14aIr2), [{Ir(H)Cl2}(µ-H){M2Cl2(L)}(meso-dpmppp)] (M2 = Ir, L = CO (15cIr2); M2 = Rh, L = XylNC (15aIrRh), CO (15cIrRh)), and [{Rh(H)Cl2}(µ-Cl){Ir(H)Cl(XylNC)}(meso-dpmppp)] (18aRhIr), the structures varying depending on M1 and M2 as well as L.

Unsymmetric Dinuclear RhI2 and RhIRhIII Complexes Supported by Tetraphosphine Ligands and Their Reactivity of Oxidative Protonation and Reductive Dechlorination.

Two linear tetradentate phosphine ligands, meso-Ph2PCH2P(Ph)CH2XCH2P(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 RhI2 (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.