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

Abstract

A wide variety of ruthenium porphyrin carbene complexes, including [Ru(tpfpp)(CR 1R 2)] (CR 1R 2 = C(p-C 6H 4Cl) 2 1b, C(p-C 6H 4Me) 2 1e, C(p-C 6H 4OMe) 2 1d, C(CO 2Me) 2 1e, C(p-C 6H 4NO 2)CO 2Me 1f, C(p-C 6H 4OMe)CO 2Me 1g, C(CH= CHPh)CO 2CH 2(CH=CH) 2CH 3 1h), [Ru(por)(CPh 2)] (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)CO 2Et}] (por = tdcpp 2j, tmp 2k), [Ru(tpfpp)(CPh 2)(L)1 (L = MeOH 3a, EtSH 3b, Et 2S 3c, Melm 3d, OPPh 3 3e, py 3f), and [Ru(tpfpp){C(Ph)-CO 2R}(MeOH)] (R = CH 2CH=CH 2 4a, Me 4, b, Et 4c), were prepared from the reactions of [Ru(por)(CO)] with diazo compounds N 2CR 1R 2 in dichloromethane and, for 3 and 4, by further treatment with reagents L. A similar reaction of [Os(tpfpp)(CO)] with N 2CPh 2 in dichloromethane followed by treatment with MeIm gave [Os(tpfpp)(CPh 2)(MeIm)] (3d-Os). All these complexes were characterized by 1H 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 E 1/2 values in the range of 0.06-0.65 V (vs Cp 2Fe +/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.