Mononuclear Rh(II) PNP-type complexes. Structure and reactivity

The Rh(II) mononuclear complexes [(PNP^tBu)RhCl][BF₄] (2), [(PNP^tBu)Rh(OC(O)CF₃)][OC(O)CF₃] (4), and [(PNP^tBu)Rh(acetone)][BF₄]₂ (6) were synthesized by oxidation of the corresponding Rh(I) analogs with silver salts. On the other hand, treatment of (PNP^tBu)RhCl with AgOC(O)CF ₃ led only to chloride abstraction, with no oxidation. 2 and 6 were characterized by X-ray diffraction, EPR, cyclic voltammetry, and dipole moment measurements. 2 and 6 react with NO gas to give the diamagnetic complexes [(PNP^tBu)Rh(NO)Cl][BF₄] (7) and [(PNP^tBu)Rh(NO) (acetone)]-[BF₄]₂ (8) respectively. 6 is reduced to Rh(I) in the presence of phosphines, CO, or isonitriles to give the Rh(I) complexes [(PNP^tBu)Rh(PR₃)][BF₄] (11, 12) (R = Et, Ph), [(PNP^tBu)Rh(CO)][BF₄] (13) and [(PNP^tBu)Rh(L)] [BF₄] (15, 16) (L = tert-butyl isonitrile or 2,6-dimethylphenyl isonitrile), respectively. On the other hand, 2 disproportionates to Rh(I) and Rh(III) complexes in the presence of acetonitrile, isonitriles, or CO. 2 is also reduced by triethylphosphine and water to Rh(I) complexes [(PNP ^tBu)RhCl] (1) and [(PNP^tBu)Rh(PEt₃)][BF ₄] (11). When triphenylphosphine and water are used, the reduced Rh(I) complex reacts with a proton, which is formed in the redox reaction, to give a Rh(III) complex with a coordinated BF₄, [(PNP ^tBu)Rh(Cl)(H)(BF₄)] (9).