Osazone Anion Radical Complex of Rhodium(III)

One electron paramagnetic parent osazone complex of rhodium of type trans-Rh(LNHPhH2)(PPh3)2Cl2 (1), defined as an osazone anion radical complex of rhodium(III), trans-RhIII(LNHPhH2•−)(PPh3)2Cl2, 1(t-RhL•), with a minor contribution (∼2%) of rhodium(II) electromer, trans-RhII(LNHPhH2)(PPh3)2Cl2, 1(t-Rh•L), and their nonradical congener, trans-[RhIII(LNHPhH2)(PPh3)2Cl2]I3 ([t-1]+I3−), have been isolated and are substantiated by spectra, bond parameters, and DFT calculations on equivalent soft complexes [Rh(LNHPhH2)(PMe3)2Cl2] (3) and [Rh(LNHPhH2)(PMe3)2Cl2]+ (3+). 1 is not stable in solution and decomposes to [t-1]+ and a new rhodium(I) osazone complex, [RhI(LNHPhH2)(PPh3)Cl] (2). 1 absorbs strongly at 351 nm due to MLCT and LLCT, while [t-1]+ and 2 absorb moderately in the range of 300−450 nm, respectively, due to LMCT and MLCT elucidated by TD-DFT calculations on 3(t-RhL•), [t-3]+, and RhI(LNHPhH2)(PMe3)Cl (4). EPR spectra of solids at 295 and 77 K, and dichloromethane−toluene frozen glass at 77 K of 1 are similar with g = 1.991, while g = 2.002 for the solid at 25 K. The EPR signal of 1 in dichloromethane solution is weaker (g = 1.992). In cyclic voltammetry, 1 displays two irreversible one electron transfer waves at +0.13 and −1.22 V, with respect to Fc+/Fc coupling, due to oxidation of 1(t-RhL•) to [t-1]+ at the anode and reduction of rhodium(III) to rhodium(II), i.e., [t-1]+ to electromeric 1(t-Rh•L) at the cathode.