Inorganic Chemistry, Vol.43, No.25, 8119-8129, 2004
Preparation, structure characterization, and oxidation activity of ruthenium complexes with tripodal ligands bearing noncovalent interaction sites
Ruthenium(II/III) complexes with tripodal tris(pyridylmethyl)amine ligands bearing one, two, or three pivalamide groups (MPPA, BPPA, TPPA: amide-series ligands) or neopentylamine ones (MNPA, BNPA, TNPA: amine-series ligands) at the 6-position of the pyridine ring have been synthesized and structurally characterized. The X-ray structure analyses of the single crystals of these complexes reveal that they complete an octahedral geometry with the tripodal ligand and some monodentate ligands. The amide-series ligands prefer to form a Ru(II) complex, while the amine-series ones give a Ru(III) complex. In the presence of PhIO oxidant, the catalytic activities for epoxidation of olefins, hydroxylation of alkane, and dehydrogenation of alcohol have been investigated using the six ruthenium complexes [Ru-II(tppa)Cl-2] (1), [Ru-III(tnpa)Cl-2]PF6 (2), [Ru-II(bppa)Cl]PF6 (3), [Ru-III(bnpa)Cl-2]PF6 (4), [Ru-II(mppa)Cl]PF6 (5), and [Ru-III(mnpa)Cl-2]PF6 (6). Among them, the amide-series complexes, 1, 3, and 5, showed a higher epoxidation activity in comparison with the amine-series ones, 2, 4, and 6. On the other hand, the latter showed a higher reactivity for hydroxylation, allylic oxidation, and C=C bond cleavage reactions compared with the former. Such a complementary reactivity is interpreted by the character of the ruthenium-oxo species involving electronically equivalent formulas, Ru(V)=O and Ru(IV)-O-..