9,10-Phenanthrenesemiquinone radical complexes of ruthenium(iii), osmium(iii) and rhodium(iii) and redox series

Abstract

Reactions of 9,10-phenanthrenequinone (PQ) in toluene with [M(II)(PPh3)3X2] at 298 K afford green complexes, trans-[M(PQ)(PPh3)2X2] (M = Ru, X = Cl, 1; M = Os, X = Br, 2) in moderate yields. Reaction of anhydrous RhCl3 with PQ and PPh3 in boiling ethanol affords the dark brown paramagnetic complex, cis-[Rh(PQ)(PPh3)2Cl2] (3) in good yields. Diffusion of iodine solution in n-hexane to the trans-[Os(PQ) (PPh3)2(CO)(Br)] solution in CH2Cl2 generates the crystals of trans-[Os(PQ)(PPh3)2(CO)(Br)](+)I3(-), (4(+))I3(-)), in lower yields. Single crystal X-ray structure determinations of 1·2toluene, 2·CH2Cl2 and 4(+)I3(-), UV-vis/NIR absorption spectra, EPR spectra of 3, electrochemical activities and DFT calculations on 1, 2, trans-[Ru(PQ)(PMe3)2Cl2] (1Me), trans-[Os(PQ)(PMe3)2Br2] (2Me), cis-[Rh(PQ)(PMe3)2Cl2] (3Me) and their oxidized and reduced analogues including trans-[Os(PQ)(PMe3)2(CO)(Br)](+) (4Me(+)) substantiated that 1-3 are the 9,10-phenanthrenesemiquinone radical (PQ(˙-)) complexes of ruthenium(III), osmium(III) and rhodium(III) and are defined as trans/cis-[M(III)(PQ(˙-))(PPh3)2X2] with a minor contribution of the resonance form trans/cis-[M(II)(PQ)(PPh3)2X2]. Two comparatively longer C-O (1.286(4) Å) and the shorter C-C lengths (1.415(7) Å) of the OO-chelate of 1·2toluene and 2·CH2Cl2 and the isotropic fluid solution EPR signal at g = 1.999 of 3 are consistent with the existence of the reduced PQ(˙-) ligand in 1-3 complexes. Anisotropic EPR spectra of the frozen glasses (g11 = g22 = 2.0046 and g33 = 1.9874) and solids (g11 = g22 = 2.005 and g33 = 1.987) instigate the contribution of the resonance form, cis-[Rh(II)(PQ)(PPh3)2Cl2] in 3. DFT calculations established that the closed shell singlet (CSS) solutions of 1Me and 2Me are unstable due to open shell singlet (OSS) perturbation. However, the broken symmetry (BS) (1,1) Ms = 0 solutions of 1Me and 2Me are respectively 22.6 and 24.2 kJ mole(-1) lower in energy and reproduced the experimental bond parameters well prompting the coordination of PQ(˙-) to the M(III) ions. The comparatively shorter C-O lengths, 1.268(4) and 1.266(5) Å and the longer C-C length, 1.466(6) Å, are consistent with the PQ chelation to osmium(II) ion in 4(+). The reversible anodic waves at 0.22, 0.22, and 0.18 V of 1-3, referenced by the Fc(+)/Fc couple, are assigned to the PQ(˙-)/PQ couple forming PQ complexes as trans/cis-[M(III)(PQ)(PPh3)2X2](+) while the cathodic waves at -0.92 and -0.89 V of 2 and 3 are due to formations of PQ(2-) complexes as trans-[M(III)(PQ(2-))(PPh3)2X2](-). 1 displays two overlapping cathodic waves at -0.72(89), -1.0(120) V. EPR spectrum of the frozen glass of 1(-) along with DFT calculations detected the contribution of both the valence tautomers, trans-[Ru(III)(PQ(2-))(PPh3)2Cl2](-) (g1 = g2 = 2.456; g3 = 1.983) and trans-[Ru(II)(PQ(˙-))(PPh3)2X2](-) (g(iso) = 1.999) in the anion. The characteristic lower energy absorption bands of 1 and 2 at 700 nm were assigned to CSS-OSS perturbation MLCT those are absent in paramagnetic 3, 1(+), 2(+), 1(-), 2(-) and 4(+)...

Rational Design of Electronically Labile Dinuclear Fe and Co complexes with 1,10‐Phenanthroline‐5,6‐Diimine: A DFT study

“…The density functional theory (DFT) calculations were performed using the Gaussian 09 program package with the standard 6‐311++G(d,p) basis set including diffuse and polarization functions at all atoms. As it was shown in the previously published works, depending on the central ion, the type of the magnetic bistability mechanism resulting in switching the magnetic characteristics, and the presence of charge of the complex, the best agreement with the experiment is achieved when using hybrid functionals UB3LYP* or UTPSSh . Due to the electroneutrality of the modeled compounds, all the calculations were performed with the use of modified UB3LYP functional—UB3LYP* .…”

Theoretical modeling of valence tautomeric dinuclear cobalt complexes. Adducts of CoIIdiketonates with cyclic redox-active tetraone ligands

“…The DFT calculations were performed using the Gaussian 09 program package 22 with the modified B3LYP* functional, 23 which differs from the standard hybrid B3LYP functional by the reduction of the Hartree-Fock term of the exchange part from 0.20 to 0.15, and the 6-311++G(d,p) basis set. This methodology has been shown to accurately reproduce stabilization energies of the adducts formed by diketonate and Schiff base cobalt complexes with quinones and other redox-active ligands 12,24 as well as experimental data on energy parameters of a variety of intramolecular spin-forbidden rearrangements of transition metal complexes. 25 The spin-forbidden reactions were studied by implementation of the program code developed by Harvey et al 26 The stationary points on the PESs were located by full geometry optimization with the calculation of the force constant matrix, and checked for the stabilities of the Hartree-Fock solutions.…”

The semiquinone radical anion of 1,10-phenanthroline-5,6-dione: synthesis and rare earth coordination chemistry

“…These transitions are diagnostic of the singly-reduced radical pd À , [17][18][19] as also observed for related 9,10-phenanthrenesemiquinone (pq À ) complexes [MX(pq À )(PPh 3 ) 2 (CO)] (M = Ru, X = Cl; M = Os, X = Br) where the dominant feature is also assigned as a pp* ILCT. 21,22 In conclusion, this work represents the discovery and success of a novel approach to the synthesis of rare earth-transition metal complexes. The stability of the bridging pd À ligand, and the selectivity of N,N 0 -binding for Y(III) have been demonstrated.…”