title: Orthometalation of dibenzo[1,2]quinoxaline with ruthenium(II/III), osmium(II/III/IV), and rhodium(III) ions and orthometalated [RuNO](6/7) derivatives.
abstract: A new family of organometallics of ruthenium(II/III), osmium(II/III/IV), and rhodium(III) ions isolated from C-H activation reactions of dibenzo[1,2]quinoxaline (DBQ) using triphenylphosphine, carbonyl, and halides as coligands is reported. The CN-chelate complexes isolated are trans-[Ru(III)(DBQ)(PPh3)2Cl2] (1), trans-[Ru(II)(DBQ)(CO)(PPh3)2Cl] (2), trans-[Os(III)(DBQ)(PPh3)2Br2] (3), trans-[Os(II)(DBQ)(PPh3)2(CO)Br] (4), and trans-[Rh(III)(DBQ)(PPh3)2Cl2] (5). Reaction of 1 with NO affords trans-[Ru(DBQ)(NO)(PPh3)2Cl]Cl (6(+)Cl(-)), isoelectronic to 2, with a byproduct, [Ru(NO)(PPh3)2Cl3] (7). Complexes 1-5 and 6(+) were characterized by elemental analyses, mass, IR, NMR, and electron paramagnetic resonance (EPR) spectra including the single-crystal X-ray structure determinations of 1-3 and 5. The Ru(III)-C, Ru(II)-C, Os(III)-C, and Rh(III)-C lengths are 2.049(2), 2.074(3), 2.105(16), and 2.012(3) Å in 1, 2, 3, and 5. In cyclic voltammetry, 2, 3, and 4 undergo oxidation at 0.59, 0.39, and 0.46 V, versus Fc(+)/Fc couple, to trans-[Ru(III)(DBQ)(CO)(PPh3)2Cl](+) (2(+)), trans-[Os(IV)(DBQ)(PPh3)2Br2](+) (3(+)), and trans-[Os(III)(DBQ)(CO)(PPh3)2Br](+) (4(+)) ions. Complex 3(+) incorporates an Os(IV)(d(4) ion)-C bond. The 6(+)/trans-[Ru(DBQ)(NO)(PPh3)2Cl] (6) reduction couple at -0.65 V is reversible. 2(+), 3(+), 4(+) and 6 were substantiated by spectroelectrochemical measurements, EPR spectra, and density functional theory (DFT) and time-dependent (TD) DFT calculations. The frozen-glass EPR spectrum of the electrogenerated 6 exhibits hyperfine couplings due to (99,101)Ru and (14)N nuclei. DFT calculations on trans-[Os(III)(DBQ)(PMe3)2Br2] (3(Me)), St = 1/2 and trans-[Os(IV)(DBQ)(PMe3)2Br2](+) (3(Me+)), St = 0, trans-[Ru(DBQ)(NO)(PMe3)2Cl](+) (6(Me+)), St = 0 and trans-[Ru(DBQ)(NO)(PMe3)2Cl] (6(Me)), St = 1/2, authenticated a significant mixing between dOs and πaromatic* orbitals, which stabilizes M(II/III/IV)-C bonds and the [RuNO](6) and [RuNO](7) states, respectively, in 6(+) and 6, which is defined as a hybrid state of trans-[Ru(II)(DBQ)(NO(•))(PPh3)2Cl] and trans-[Ru(I)(DBQ)(NO(+))(PPh3)2Cl] states.
authors.affiliation: Department of Chemistry, R. K. Mission Residential College , Narendrapur, Kolkata-103, India.
authors.forename: Suvendu
authors.initials: S
authors.lastname: Maity
authors.forename: Suman
authors.initials: S
authors.lastname: Kundu
authors.forename: Amit
authors.initials: A
authors.lastname: Saha Roy
authors.forename: Thomas
authors.initials: T
authors.lastname: Weyhermüller
authors.forename: Prasanta
authors.initials: P
authors.lastname: Ghosh