Phenylcyanamidoruthenium
Scorpionate Complexes
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Abstract
Nine [Ru(Tp)(dppe)L] complexes, where Tp is hydrotris(pyrazol-1-yl)borate,
dppe is ethylenebis(diphenylphosphine), and L is (4-nitrophenyl)cyanamide
(NO<sub>2</sub>pcyd<sup>–</sup>), (2-chlorophenyl)cyanamide
(2-Clpcyd<sup>–</sup>), (3-chlorophenyl)cyanamide (3-Clpcyd<sup>–</sup>), (2,4-dichlorophenyl)cyanamide (2,4-Cl<sub>2</sub>pcyd<sup>–</sup>), (2,3-dichlorophenyl)cyanamide (2,3-Cl<sub>2</sub>pcyd<sup>–</sup>), (2,5-dichlorophenyl)cyanamide (2,5-Cl<sub>2</sub>pcyd<sup>–</sup>), (2,4,5-trichlorophenyl)cyanamide
(2,4,5-Cl<sub>3</sub>pcyd<sup>–</sup>), (2,3,5,6-tetrachlorophenyl)cyanamide
(2,3,5,6-Cl<sub>4</sub>pcyd<sup>–</sup>), and (pentachlorophenyl)cyanamide
(Cl<sub>5</sub>pcyd<sup>–</sup>), and the dinuclear complex
[{Ru(Tp)(dppe)}<sub>2</sub>(μ-adpc)], where adpc<sup>2–</sup> is azo-4,4-diphenylcyanamide, have been prepared and characterized.
The crystal structures of [Ru(Tp)(dppe)(Cl<sub>5</sub>pcyd)] and [{Ru(Tp)(dppe)}<sub>2</sub>(μ-adpc)] reveal the Ru<sup>II</sup> ion to occupy a
pseudooctahedral coordination sphere in which the cyanamide ligand
coordinates to Ru<sup>II</sup> by its terminal nitrogen atom. For
both complexes, the cyanamide ligands are planar, indicating significant
π mixing between the cyanamide and phenyl moieties as well as
the azo group in the case of adpc<sup>2–</sup>. The optical
spectra of the nominally ruthenium(III) species [Ru(Tp)(dppe)L]<sup>+</sup> were obtained through spectroelectrochemistry measurements
and showed an intense near-IR absorption band. Time-dependent density
functional theory calculations of these species revealed that oxidation
of the ruthenium(II) species led to species where partial oxidation
of the cyanamide ligand had occurred, indicative of noninnocent character
for these ligands. The spin densities reveal that while the 3-Clpycd
species has substantial Ru<sup>II</sup>(3-Clpycd<sup>0</sup>) character,
the Cl<sub>5</sub>pycd species is a much more localized ruthenium(III)
complex of the Cl<sub>5</sub>pycd monoanion. Some bond order and charge
distribution data are derived for these ruthenium(III) species. The
near-IR band is assigned as a quite complex mixture of d–d,
4d<sub>π</sub> to L(NCN) MLCT, and L(NCN) to Ru 4d LMCT with
even a scorpionate ligand component. Spectroelectrochemistry was also
performed on [{Ru(Tp)(dppe)}<sub>2</sub>(μ-adpc)] to generate
the mixed-valence state. The intense intervalence transition that
is observed in the near-IR is very similar to that previously reported
for [{Ru(trpy)(bpy)}<sub>2</sub>(μ-adpc)]<sup>2+</sup>, where
trpy is 2,2′:6′,2″-terpyridine and bpy is 2,2′-bipyridine,
and by analogy identifies [{Ru(Tp)(dppe)}<sub>2</sub>(μ-adpc)]<sup>+</sup> as a delocalized mixed-valence complex
