Publication: Phenylcyanamide Ruthenium Scorpionate Complexes

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Title Phenylcyanamide Ruthenium Scorpionate Complexes
Authors/Editors* C. Harb,P. Kravtsov,M. Choudhuri,E.R. Sirianni, G.P. A. Yap, A. B. P. Lever and R. J. Crutchley
Where published* Inorganic Chemistry
How published* Journal
Year* 2013
Volume 52
Number 00
Pages 00
Publisher ACS
Keywords Scorpionate ligands, DFT, ruthenium, mixed valence
Abstract: Nine [Ru(Tp)(dppe)L] complexes, where Tp is hydrotris(pyrazol-1-yl)borate, dppe is ethylenebis(diphenylphosphine) and L is 4-nitrophenylcyanamide (NO2pcyd-), 2-chlorophenylcyanamide (2-Clpcyd-), 3-chlorophenylcyanamide (3-Clpcyd-), 2,4-dichlorophenylcyanamide (2,4-Cl¬2pcyd-), 2,3-dichlorophenylcyanamide (2,3-Cl¬2pcyd-), 2,5-dichlorophenylcyanamide (2,5-Cl2pcyd-), 2,4,5-trichlorophenylcyanamide (2,4,5-Cl3pcyd-), 2,3,5,6-tetrachlorophenylcyanamide (2,3,5,6-Cl4pcyd-), pentachlorophenyl= cyanamide (Cl5pcyd-) and the dinuclear complex [{Ru(Tp)(dppe)}2(-adpc)], where adpc2- is azo-4,4-diphenylcyanamide, have been prepared and characterized. Crystal structures of [Ru(Tp)(dppe)(Cl5pcyd)] and [{Ru(Tp)(dppe)}2(-adpc)] reveal the Ru(II) ion to occupy a pseudo-octahedral coordination sphere in which the cyanamide ligand coordinates to Ru(II) by its terminal nitrogen. For both complexes, the cyanamide ligands are planar indicating significant  mixing between the cyanamide and phenyl moieties as well as the azo group in the case of adpc2-. The optical spectra of the nominally Ru(III) species [Ru(Tp)(dppe)L]+ were obtained through spectroelectrochemistry measurements and showed an intense NIR absorption band. TD-DFT calculations of these species revealed that oxidation of the Ru(II) species led to species where partial oxidation of the cyanamide ligand had occurred, indicative of non-innocent character for these ligands. The spin densities reveal that while the 3-Clpycd species has substantial Ru(II)-(3-Clpycd0) character, the Cl5pycd species is a much more localised Ru(III) complex of the Cl5pycd mono-anion. Some bond order and charge distribution data are derived for these Ru(III) species. The NIR band is assigned as a quite complex mix of d-d, 4d to L(NCN) MLCT, L(NCN) to Ru 4d LMCT with even a scorpionate ligand component. Spectroelectrochemistry was also performed on [{Ru(Tp)(dppe)}2(-adpc)] to generate the mixed-valence state. The intense intervalence transition that is observed in the NIR is very similar to that previously reported for [{Ru(trpy)(bpy)}2(-adpc)]2+, where trpy is 2,2′:6′,2′′-terpyridine, bpy is 2,2′-bipyridine, and by analogy identifies [{Ru(Tp)(dppe)}2(-adpc)]+ as a delocalized mixed-valence complex.
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