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)]PF(6) (2), [Ru(II)(bppa)Cl]PF(6) (3), [Ru(III)(bnpa)Cl(2)]PF(6) (4), [Ru(II)(mppa)Cl]PF(6) (5), and [Ru(III)(mnpa)Cl(2)]PF(6) (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.
Jitsukawa
Koichiro
K
Department of Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan. jitsukawa.koichiro@nitech.ac.jp
Oka
Yoshiyuki
Y
Yamaguchi
Syuhei
S
Masuda
Hideki
H