Radical and Non-Radical States of the [Os(PIQ)] Core (PIQ = 9,10-Phenanthreneiminoquinone): Iminosemiquinone to Iminoquinone Conversion Promoted o‑Metalation Reaction

The coordination and redox chemistry of 9,10-phenanthreneiminoquinone (PIQ) with osmium ion authenticating the [OsII(PIQ•–)], [OsIII(PIQ•–)], [OsIII(C,N-PIQ)], [OsIII(PIQ)], and [OsIII(PIQ2–) ] states of the [Os­(PIQ)] core in the complexes of types trans-[OsII(PIQ•–)­(PPh3)2(CO)­Br] (1), trans-[OsIII(PIQ•–)­(PPh3)2Br2] (2), trans-[OsIII(C,N-PIQ)­(PPh3)2Br2]·2CH2Cl2 (3·2CH2Cl2), trans-[OsIII(C,N-PIQBr)­(PPh3)2Br2]·2CH2Cl2 (4·2CH2Cl2), trans-[OsIII(C,N-PIQCl2)­(PPh3)2Br2] (6), trans-[OsIII(PIQ•–)­(PPh3)2Br2]+1/2I3–1/2Br– (1+1/2I3–1/2Br–), [OsIII(PIQ)­(PPh3)2Br2]+ (2+), and [OsIII(PIQ2–)­(PPh3)2Br2]− (2–) are reported (PIQ•– = 9,10-phenanthreneiminosemiquinonate anion radical; C,N-PIQ = ortho-metalated PIQ, C,N-PIQBr = ortho-metalated 4-bromo PIQ, and C,N-PIQCl2 = ortho-metalated 3,4-dichloro PIQ). Reduction of PIQ by [OsII(PPh3)3(H)­(CO)­Br] affords 1, while the reaction of PIQ with [OsII(PPh3)3Br2] furnishes 2. Oxidation of 1 with I2 affords 1+1/2I3–1/2Br–, while the similar reactions of 2 with X2 (X = I, Br, Cl) produce the ortho-metalated derivatives 3·2CH2Cl2, 4·2CH2Cl2, and 6. PIQ and PIQ2– complexes of osmium­(III), 2+ and 2‑, are generated by constant-potential electrolysis. However, 2+ ion is unstable in solution and slowly converts to 3 and partially hydrolyzes to trans-[OsIII(PQ•–)­(PPh3)2Br2] (2PQ), a PQ•– analogue of 2. Conversion of 2+ → 3 in solution excludes the formation of aryl halide as an intermediate for this unique ortho-metalation reaction at 295 K, where PIQ acts as a redox-noninnocent ambidentate ligand. In the complexes, the PIQ•– state where the atomic spin is more localized on the nitrogen atom is stable and is more abundant. The reaction of 2PQ, with I2 does not promote any ortho-metalation reaction and yields a PQ complex of type trans-[OsIII(PQ)­(PPh3)2Br2]+I5–·2CH2Cl2 (5+I5–·2CH2Cl2). The molecular and electronic structures of 1–4, 6, 1+, and 5+ were established by different spectra, single-crystal X-ray bond parameters, cyclic voltammetry, and DFT calculations.