Spectral, structural, and electrochemical properties of ruthenium porphyrin diaryl and aryl(alkoxyrcarbonyl) carbene complexes: Influence of carbene substituents, porphyrin substituents, and trans-axial ligands

A wide variety of ruthenium porphyrin carbene complexes, including [Ru(tpfpp)(CR1R2)] (CR1R2= C(p-C6H4Cl)21b, C(p-C6H4Me)21e, C(p-C6H4OMe)21d, C(CO2Me)21e, C(p-C6H4NO2)CO2Me 1f, C(p-C6H4OMe)CO2Me 1g, C(CH= CHPh)CO2CH2(CH=CH)2CH31h), [Ru(por)(CPh2)] (por=tdcpp 2a, 4-Br-tpp 2b, 4-Cl-tpp 2c, 4-F-tpp 2d, tpp 2e, ttp 2f, 4-MeO-tpp 2g, tmp 2h, 3,4,5-MeO-tpp 2i), [Ru(por){C(Ph)CO2Et}] (por = tdcpp 2j, tmp 2k), [Ru(tpfpp)(CPh2)(L)1 (L = MeOH 3a, EtSH 3b, Et2S 3c, Melm 3d, OPPh33e, py 3f), and [Ru(tpfpp){C(Ph)-CO2R}(MeOH)] (R = CH2CH=CH24a, Me 4, b, Et 4c), were prepared from the reactions of [Ru(por)(CO)] with diazo compounds N2CR1R2in dichloromethane and, for 3 and 4, by further treatment with reagents L. A similar reaction of [Os(tpfpp)(CO)] with N2CPh2in dichloromethane followed by treatment with MeIm gave [Os(tpfpp)(CPh2)(MeIm)] (3d-Os). All these complexes were characterized by1H NMR,13C NMR, and UV/Vis spectroscopy, mass spectrometry, and elemental analyses. X-ray crystal structure determinations of 1d, 2a,i, 3a,b, d,e, 4a-c, and 3d-Os revealed Ru=C distances of 1.806(3)-1.876(3) Å and an Os=C distance of 1.902(3) Å. The structure of 1d in the solid state features a unique "bridging" carbene ligand, which results in the formation of a one-dimensional coordination polymer. Cyclic voltammograms of 1a-c,g, 2a-d,g-k, 3b-d, 4a,b, and 3d-Os show a reversible oxidation couple with E1/2values in the range of 0.06-0.65 V (vs Cp2Fe+/0) that is attributable to a metal-centered oxidation. The influence of carbene substituents, porphyrin substituents, and trans-ligands on the Ru=C bond was examined through comparison of the chemical shifts of the pyrrolic protons in the porphyrin macrocycles (1H NMR) and the M=C carbon atoms (13C NMR), the potentials of the metal-centered oxidation couples, and the Ru=C distances among the various ruthenium porphyrin carbene complexes. A direct comparison among iron, ruthenium, and osmium porphyrin carbene complexes is made.