1003323-35-0Relevant academic research and scientific papers
Diorganoruthenium complexes incorporating noninnocent [C6H 2(CH2ER2)2-3,5]2 2-- (E = N, P) bis-pincer bridging ligands: Synthesis, spectroelectrochemistry, and DFT studies
Gagliardo, Marcella,Amijs, Catelijne H. M.,Lutz, Martin,Spek, Anthony L.,Havenith, Remco W. A.,Hartl, Frantisek,Van Klink, Gerard P. M.,Van Koten, Gerard
, p. 11133 - 11144 (2008/10/09)
The dinuclear complex [(tpy)RuII(PCP-PCP)RuII(tpy)] Cl2 (bridging PCP-PCP = 3,3′,5,5′- tetrakis(diphenylphosphinomethyl)biphenyl, [C6H2(CH 2PPh2)2-3,5]22-) was prepared via a transcyclometalation reaction of the bis-pincer ligand [PC(H)P-PC(H)P] and the Ru(II) precursor [Ru(NCN)(tpy)]Cl (NCN = [C 6H3(CH2NMe2)2-2,6] -) followed by a reaction with 2,2′:6′,2″- terpyridine (tpy). Electrochemical and spectroscopic properties of [(tpy)Ru II(PCP-PCP)RuII-(tpy)]Cl2 are compared with those of the closely related [(tpy)RuII(NCN-NCN)Ru II(tpy)](PF6)2 (NCN-NCN = [C6H 2(CH2-NMe2)2-3,5]2 2-) obtained by two-electron reduction of [(tpy)Ru III(NCN-NCN)RuIII(tpy)](PF6)4. The molecular structure of the latter complex has been determined by single-crystal X-ray structure determination. One-electron reduction of [(tpy)Ru III(NCN-NCN)RuIII(tpy)](PF6)4 and one-electron oxidation of [(tpy)RuII(PCP-PCP)RuII(tpy)] Cl2 yielded the mixed-valence species [(tpy)RuIII(NCN-NCN) RuII(tpy)]3+ and [(tpy)RuIII(PCP-PCP)Ru II(tpy)]3+, respectively. The comproportionation equilibrium constants Kc (900 and 748 for [(tpy)Ru III(NCN-NCN)RuIII(tpy)]4+ and [(tpy)Ru II(PCP-PCP)RuII(tpy)]2+, respectively) determined from cyclic voltammetric data reveal comparable stability of the [RuIII-RuII] state of both complexes. Spectroelectrochemical measurements and near-infrared (NIR) spectroscopy were employed to further characterize the different redox states with special focus on the mixed-valence species and their NIR bands. Analysis of these bands in the framework of Hush theory indicates that the mixed-valence complexes [(tpy)RuIII(PCP-PCP)RuII(tpy)]3+ and [(tpy)RuIII(NCN-NCN)RuII(tpy)]3+ belong to strongly coupled borderline Class II/Class III and intrinsically coupled Class III systems, respectively. Preliminary DFT calculations suggest that extensive derealization of the spin density over the metal centers and the bridging ligand exists. TD-DFT calculations then suggested a substantial MLCT character of the NIR electronic transitions. The results obtained in this study point to a decreased metal-metal electronic interaction accommodated by the double-cyclometalated bis-pincer bridge when strong σ-donor NMe 2 groups are replaced by weak σ-donor, π-acceptor PPh 2 groups.
