Dai Ooyama

Multi-electron reduction of CO2 via RuCO2, C(O)OH, CO, CHO, and CH2OH species

Abstract A series of [Ru(bpy)2(CO)L]n+ (L=CO2, C(O)OH, CO, CHO, CH2OH, CH3, and C(O)CH3; n=0, 1, 2) were prepared and their molecular structures determined by X-ray analyses. These complexes are reasonable models of reaction intermediates in the multi-electron reduction of CO2 catalyzed by metal complexes, since reductive cleavage of the RuL bonds of the complexes in protic media affords HCOOH, CO, HCHO, CH3OH, and CH4 as two-, four-, six- and eight-electron reduction products of CO2. Thermodynamically, the free energy required in the reduction of CO2 progressively decreases with an increase of the number of electrons participating in the reduction of CO2. The RuL bond character of the series of [Ru(bpy)2(CO)L]n+ was assessed by the ν(RuL) bands and the RuL bond distances from the viewpoint of elucidation of a correlation between free energy changes in the multi-electron reduction of CO2 catalyzed by metal complexes and the metalcarbon bond strength of each intermediate. The rutheniumcarbon bond distance of [Ru(bpy)2(CO)L]n+ largely depends on the hybrid orbital of the carbon atom bonded to ruthenium and lengthens in the order RuCsp

Structural and spectroscopic characterization of ruthenium(II) complexes with methyl, formyl, and acetyl groups as model species in multi-step CO2 reduction

Abstract The molecular structures of Ru(II) complexes with methyl, formyl, and acetyl groups [Ru(bpy)2(CO)L]+ (L=CH3, C(O)H and C(O)CH3) were examined from the view point of active species in multi-step reduction of CO2 on Ru. The methyl complex was prepared by the reaction of [Ru(bpy)2(OH2)2]2+ with trimethylsilyl acetylene and fully characterized by infrared, Raman, 13C-NMR and single-crystal X-ray crystallography. Disorder of the RuCO and RuC(O)H bonds in the crystal structure of the formyl complex made it difficult to determine the bond parameters of the two groups accurately, but the molecular structure of the analogous acetyl complex, which was obtained by the reaction of [Ru(bpy)2(CO3)] with propiolic acid, was determined by X-ray analysis. The ruthenium–carbonyl (RuCO) bond angles of the methyl and acetyl complex with 174(1) and 175.5(5)°, respectively, are in the ranges of those of previously characterized [Ru(bpy)2(CO)L]n+ (L=CO2, C(O)OH, CO and CH2OH). On the other hand, the RuCH3 and RuC(O)CH3 bond distances showed unusual relationship against the stretching frequency in the Raman spectra.

Regulation of electron donating ability to metal center: isolation and characterization of ruthenium carbonyl complexes with N, N- and/or N, O-donor polypyridyl ligands

Abstract Polypyridyl ruthenium(II) dicarbonyl complexes with an N,O- and/or N,N-donor ligand, [Ru(pic)(CO)2Cl2]− (1), [Ru(bpy)(pic)(CO)2]+ (2), [Ru(pic)2(CO)2] (3), and [Ru(bpy)2(CO)2]2+ (4) (pic=2-pyridylcarboxylato, bpy=2,2′-bipyridine) were prepared for comparison of the electron donor ability of these ligands to the ruthenium center. A carbonyl group of [Ru(L1)(L2)(CO)2]n (L1, L2=bpy, pic) successively reacted with one and two equivalents of OH− to form [Ru(L1)(L2)(CO)(C(O)OH)]n−1 and [Ru(L1)(L2)(CO)(CO2)]n−2. These three complexes exist as equilbrium mixtures in aqueous solutions and the equilibrium constants were determined potentiometrically. Electrochemical reduction of 2 in CO2-saturated CH3CN–H2O at −1.5 V selectively produced CO.

Synthesis and characterization of polypyridineruthenium(II) complexes containing a linear ambidentate ligand, NCO− or NCS−, and reaction of isocyanato complexes under acidic conditions

Abstract Isocyanato and isothiocyanatopolypyridineruthenium complexes, [Ru(NCX)Y(bpy)(py)2]n+ (bpy=2,2′-bipyridine, py=pyridine; X=O, Y=NO2 for n=0, and Y=py for n=1; X=S, Y=NO2 for n=0, Y=NO for n=2, and Y=py for n=1), were synthesized by the reaction of polypyridineruthenium complexes with potassium cyanate or sodium thiocyanate salt. Isocyanatoruthenium(II) complexes, [Ru(NCO)(NO2)(bpy)(py)2] and [Ru(NCO)(bpy)(py)3]+, react under acidic conditions to form the corresponding ammineruthenium complexes, [Ru(NO)(NH3)(bpy)(py)2]3+. The molecular structures of [Ru(NCO)(bpy)(py)3]ClO4, [Ru(NCS)(NO)(bpy)(py)2](PF6)2 and [Ru(NO)(NH3)(bpy)(py)2](PF6)3 were determined by X-ray crystallography.

A Ru–carbene complex with a metallacycle involving a 1,8-naphthylidine framework

The reaction of [Ru(bpy)2(napy-κ2N,N′)](PF 6)2 [1](PF6)2 (napy = 1,8-naphthyridine) with propiolic acid yielded a Ru–carbene complex with a five-membered metallacycle involving a 1,8-naphthylidine framework.