Inorganic Chemistry, Vol.54, No.4, 1384-1394, 2015
Orthometalation of Dibenzo[1,2]quinoxaline with Ruthenium(II/III), Osmium(II/III/IV), and Rhodium(III) Ions and Orthometalated [RuNO](6/7) Derivatives
A new family of organometallics of ruthenium(II/III), osmium(II/III/IV), and rhodium(III) ions isolated from CH 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)(2)Br-2] (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)(2)Cl]Cl (6( +)Cl), isoelectronic to 2 , with a byproduct, [Ru(NO)(PPh3)2Cl3] (7 ). Complexes 15 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 13 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) angstrom 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-[OsIV(DBQ)(PPh3)(2)Br-2](+) (3 +), and trans-[Os-III(DBQ)(CO)(PPh3)2Br](+) (4 +) ions. Complex 3 + incorporates an OsIV(d4 ion)C bond. The 6( +)/trans-[Ru(DBQ)(NO)(PPh3)(2)Cl] (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 99,101Ru and N-14 nuclei. DFT calculations on trans-[Os-III(DBQ)(PMe3)(2)Br-2] (3( Me)), S-t = 1/2 and trans-[Os-IV(DBQ)(PMe3)(2)Br-2](+) (3( Me+)), S-t = 0, trans-[Ru(DBQ)(NO)(PMe3)(2)Cl](+) (6( Me+)), S-t = 0 and trans-[Ru(DBQ)(NO)(PMe3)(2)Cl] (6( Me)), S-t = 1/2, authenticated a significant mixing between dOs and paromatic* orbitals, which stabilizes (MC)-C-II/III/IV 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)(PPh 3)(2)Cl] and trans-[Ru-I(DBQ)(NO+)(PPh3)(2)Cl] states.