Electronic Structures of Ruthenium and Osmium Complexes of 9,10-Phenanthrenequinone
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The reaction of 9,10-phenanthrenequinone (PQ) with [MII(H)(CO)(X)(PPh3)3] in boiling toluene leads to the homolytic cleavage of the MII–H bond, affording the paramagnetic trans-[M(PQ)(PPh3)2(CO)X] (M = Ru, X = Cl, 1; M = Os, X = Br, 3) and cis-[M(PQ)(PPh3)2(CO)X] (M = Ru, X = Cl, 2; M = Os, X = Br, 4) complexes. Single-crystal X-ray structure determinations of 1, 2·toluene, and 4·CH2Cl2, EPR spectra, and density functional theory (DFT) calculations have substantiated that 1–4 are 9,10-phenanthrenesemiquinone radical (PQ•–) complexes of ruthenium(II) and osmium(II) and are defined as trans-[RuII(PQ•–)(PPh3)2(CO)Cl] (1), cis-[RuII(PQ•–)(PPh3)2(CO)Cl] (2), trans-[OsII(PQ•–)(PPh3)2(CO) Br] (3), and cis-[OsII(PQ•–)(PPh3)2(CO)Br] (4). Two comparatively longer C–O [average lengths: 1, 1.291(3) Å; 2·toluene, 1.281(5) Å; 4·CH2Cl2, 1.300(8) Å] and shorter C–C lengths [1, 1.418(5) Å; 2·toluene, 1.439(6) Å; 4·CH2Cl2, 1.434(9) Å] of the OO chelates are consistent with the presence of a reduced PQ•– ligand in 1–4. A minor contribution of the alternate resonance form, trans- or cis-[MI(PQ)(PPh3)2(CO)X], of 1–4 has been predicted by the anisotropic X- and Q-band electron paramagnetic resonance spectra of the frozen glasses of the complexes at 25 K and unrestricted DFT calculations on 1, trans-[Ru(PQ)(PMe3)2(CO)Cl] (5), cis-[Ru(PQ)(PMe3)2(CO)Cl] (6), and cis-[Os(PQ)(PMe3)2(CO)Br] (7). However, no thermodynamic equilibria between [MII(PQ•–)(PPh3)2(CO)X] and [MI(PQ)(PPh3)2(CO)X] tautomers have been detected. 1–4 undergo one-electron oxidation at −0.06, −0.05, 0.03, and −0.03 V versus a ferrocenium/ferrocene, Fc+/Fc, couple because of the formation of PQ complexes as trans-[RuII(PQ)(PPh3)2(CO)Cl]+ (1+), cis-[RuII(PQ)(PPh3)2(CO)Cl]+ (2+), trans-[OsII(PQ)(PPh3)2(CO)Br]+ (3+), and cis-[OsII(PQ)(PPh3)2(CO)Br]+ (4+). The trans isomers 1 and 3 also undergo one-electron reduction at −1.11 and −0.96 V, forming PQ2– complexes trans-[RuII(PQ2–)(PPh3)2(CO)Cl]− (1–) and trans-[OsII(PQ2–)(PPh3)2(CO)Br]− (3–). Oxidation of 1 by I2 affords diamagnetic 1+I3– in low yields. Bond parameters of 1+I3– [C–O, 1.256(3) and 1.258(3) Å; C–C, 1.482(3) Å] are consistent with ligand oxidation, yielding a coordinated PQ ligand. Origins of UV–vis/near-IR absorption features of 1–4 and the electrogenerated species have been investigated by spectroelectrochemical measurements and time-dependent DFT calculations on 5, 6, 5+, and 5–.
创建时间：
2016-02-20
