Synthesis, Characterization, and Electrochemistry of Biorelevant Photosensitive Low-Potential Orthometalated Ruthenium Complexes

Abstract

Redox potentials of photosensitive cyclometalated RuII derivatives of 2-phenylpyridine or 2-(4-tolyl)pyridine are controllably decreased by up to 0.8 V within several minutes. This is achieved by irradiation of the ruthena(II)cycles cis-[Ru(o-X-2-py)(LL)(MeCN)2]PF6 (2, X = C6H4 (a) or 4-MeC6H3 (b), LL = 1,10-phenanthroline or 2,2'-bipyridine). The cis geometry of the MeCN ligands has been confirmed by the X-ray structural studies. The sigma-bound sp2 carbon of the metalated ring is trans to LL nitrogen. Complexes 2 are made from [Ru(o-X-2-py)(MeCN)4]PF6 (1) and LL. This "trivial" ligand substitution is unusual because 1a reacts readily with phen in MeCN as solvent to give cis-[Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 (2c) in a 83% yield, but bpy does not afford the bpy-containing 2 under the same conditions. cis-[Ru(o-C6H4-2-py)(bpy)(MeCN)2]PF6 (2e) has been prepared in CH2Cl2 (74%). Studies of complexes 2c,e by cyclic voltammetry in MeOH in the dark reveal RuII/III quasy-reversible redox features at 573 and 578 mV (vs Ag/AgCl), respectively. A minute irradiation 2c and 2e converts them into new species with redox potentials of -230 and 270 mV, respectively. An exceptional potential drop for 2c is accounted for in terms of a photosubstitution of both MeCN ligands by methanol. ESR, 1H NMR, and UV-vis data indicate that the primary product of photolysis of 2c is an octahedral monomeric low-spin (S = 1/2) RuIII species, presumably cis-[RuIII(o-C6H4-2-py)(phen)(MeOH)2]2+. The primary photoproduct of bpy complex 2e is cis-[RuII(o-C6H4-2-py)(bpy)(MeCN)(MeOH)]+, and this accounts for a lower decrease in the redox potential. Irradiation of 2c in the presence of added chloride affords [(phen)(o-C6H4-2-py)ClRuIIIORuIVCl(o-C6H4-2-py)(phen)]PF6, a first mu-oxo-bridged mixed valent dimer with a cyclometalated unit. The structure of the dimer has been established by X-ray crystallography.

Strategies for Optimizing the Performance of Cyclometalated Ruthenium Sensitizers for Dye‐Sensitized Solar Cells

“…2-phenylpyridine (ppy), 2-(2,4-difluorophenyl)pyridine (ppy-F 2 ) and 2,2Ј-bipyridine (bpy) were used as supplied from Aldrich. [Ru(C 6 H 6 )Cl 2 ] 2 , [60] 5-[3-(pyridin-2-yl)phenyl]thiophene-2-carbaldehyde (ppy4thio), [42] diethyl 2,2Ј-bipyridine-4,4Ј-dicarboxylate (deeb), [61] 2,2Ј-bipyridine-4,4Ј-dicarboxylic acid (dcbpy), [61] complexes 1a, [35] 1b, [62] 4d, [42] 5d [42] and 6d [42] were prepared as previously reported. Purification by column chromatography was carried out using silica (Silicycle: Ultrapure Flash Silica), and basic alumina (Fluka).…”

Comparison Between Polypyridyl and Cyclometalated Ruthenium(II) Complexes: Anticancer Activities Against 2D and 3D Cancer Models

“…Polypyridyl complexes 1 a-4 a [31][32][33] and the cyclometalated complex 4 b [34] have been synthesized previously. Complexes 1 b-3 b were synthesized by reacting [Ru(ppy)(bpy)-(NCCH 3 ) 2 ]PF 6 [35] with an equimolar amount of the requisite aromatic ligand in refluxing ethanol. All of these complexes were purified by column chromatography and characterized by ES-MS, 1 H NMR, and elemental analysis (Figures S1-S6).…”

Selective Preparation of a Heteroleptic Cyclometallated Ruthenium Complex Capable of Undergoing Photosubstitution of a Bidentate Ligand

“…The developmento fs tereoselective syntheses is an important but challenging goal in coordination and organometallic chemistry,w hereby the number of isomers of octahedral complexesb earing dissymmetric bidentate chelate ligands can be very high. In this work, the ring size resulting from the coordination of ad issymmetric N,S bidentate ligand to ac yclometallated ruthenium complex was found to have acritical influence on the number of isomers obtained in syntheses of [2] [28,30,37] Electrospray ionization mass spectra (ESI-MS) were recorded on an MSQ Plus spectrometer.U V/Vis spectra were recorded on aC ary Varian spectrometer.A ll 1 HNMR spectra were recorded on Bruker DPX-300 or DMX-400 spectrometers. Chemical shifts are indicated in ppm relative to the residual solvent peak.…”

“…As shown by Ryabove tal.,o nly the isomer having the s-bound Ca tom trans to bpy ([1a]PF 6 ) is thereby obtained. [30] Coordination of the respective N,S bidentate ligand (mtpa,m tea, mtep, or mtmp) was performed by heatingt he precursor [1a]PF 6 at 70 8Ci nE tOH in the presence of about 4equiv.e ach of the N,S ligand andE t 3 N( to ensure coordinationo ft he amine group of the N,S ligand)f or 22 hu nder N 2 .T he syntheses of [2]PF 6 and [3]PF 6 proved to be very air-sensitive, with at race of air leadingt of ormation of a dark-green ruthenium(III)-containing solid. No such oxidation occurredw hen preparing complexes [4] Octahedralc omplexes bearing three differentb identate ligands,two of which are dissymmetric, have many isomers.T he carbon donor atom can be either trans or cis to the nitrogen donor atoms of the bpy ligand, andi ne ach of these cases the nitrogen atom of the N,S ligand can be trans to either the bpy or the phpy À ligand, generating up to four coordination isomers, each of which exists as an enantiomeric pair L/D (Scheme1).…”