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

The Rh(II) mononuclear complexes [((PNPBu)-Bu-t)RhCl][BF4] (2), [((PNPBu)-Bu-t)Rh(OC(O)CF3)][OC(O)CF3] (4), and [(PNPt-Bu)Rh(acetone)][BF4](2) (6) were synthesized by oxidation of the corresponding Rh(l) analogs with silver salts. On the other hand, treatment of ((PNPBu)-Bu-t)RhCl with AgOC(O)CF3 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 [((PNPBu)-Bu-t)Rh(NO)Cl][BF4] (7) and [((PNPBu)-Bu-t)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(l) complexes [((PNPBu)-Bu-t)Rh(PR3)][BF4] (11, 12) (R = Et, Ph), [((PNPBu)-Bu-t)Rh(CO)][BF4] (13) and [((PNPBu)-Bu-t)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 [((PNPBu)-Bu-t)RhCl] (1) and [((PNPBu)-Bu-t)Rh(PEt3)][BF4] (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, [((PNPBu)-Bu-t)Rh(Cl)(H)(BF4)] (9).