Synthesis, structure, redox properties, and catalytic activity of new ruthenium complexes containing neutral or anionic and facial or meridional ligands: an evaluation of electronic and geometrical effects.
The synthesis of a family of new Ru complexes containing meridional or facial tridentate ligands with the general formula [Ru(II)(T)(D)(X)](n+) [T = 2,2':6',2' '-terpyridine or tripyrazolylmethane; D = 4,4'-dibenzyl-4,4',5,5'-tetrahydro-2,2'-bioxazole (S,S-box-C) or 2-[((1'S)-1'-(hydroxymethyl)-2'-phenyl)ethylcarboxamide]-(4S)-4-benzyl-4,5-dihydrooxazole (S,S-box-O); X = Cl, H(2)O, MeCN or pyridine] has been described. All complexes have been spectroscopically characterized in solution through (1)H NMR and UV-vis techniques. Furthermore, all of the chloro complexes presented here have also been characterized in the solid state through monocrystal X-ray diffraction analysis. The oxazolinic S,S-box-C ligands undergo a Ru-assisted hydrolysis reaction generating the corresponding amidate anionic oxazolinic ligands S,S-box-O, which are also strongly attached to the metal center and produce a strong sigma-donation effect over the Ru metal center. The redox properties of all complexes have also been studied by means of cyclic voltammetry, strongly reflecting the nature of the ligands; both effects, geometrical (facial vs meridional) and electronic (neutral vs anionic), can be unveiled and rationalized. Finally, the reactivity of the Ru-OH(2) complexes has been tested with regard to the epoxidation of trans-stilbene, and it has been shown that, in this particular case, the reactivity is practically not dependent on the redox potentials of the catalyst but, in sharp contrast, it is strongly dependent on the geometry of the tridentate ligands.
Serrano
Isabel
I
Departament de Química, Universitat de Girona, Campus de Montilivi, E-17071 Girona, Spain.
Sala
Xavier
X
Plantalech
Elena
E
Rodríguez
Montserrat
M
Romero
Isabel
I
Jansat
Susanna
S
Gómez
Montserrat
M
Parella
Teodor
T
Stoeckli-Evans
Helen
H
Solans
Xavier
X
Font-Bardia
Mercè
M
Vidjayacoumar
Balamurugan
B
Llobet
Antoni
A