Observation of radical intermediates for unusual carbon-nitrogen bond formation of .alpha.-aminomalonate to give an .alpha.-diamine linkage. ESR studies on electron transfer reactions in cobalt(III)-polyamine complexes

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.

Synthesis and Characterization of Mononuclear and Dinuclear Ruthenium Complexes with Tris(2-pyridylmethyl)amine and Tris(5-methyl-2-pyridylmethyl)amine

Novel Ru(II) and Ru(III) complexes having TPA (tris(2-pyridylmethyl)amine, L1) and 5-Me(3)-TPA (tris(5-methyl-2-pyridylmethyl)amine, L2) were prepared to establish their synthetic routes and to elucidate coordination geometry and interactions between tightly bound tripodal tetradentate ligands and Ru(II)/Ru(III) centers. They include mononuclear Ru(II) complexes [RuCl(DMSO)(L)]ClO(4) (1 (L1), 2 (L2)), dinuclear bis-&mgr;-chloro Ru(II) complexes [RuCl(L)](2)(ClO(4))(2) (3 (L1), 4 (L2)), and mononuclear Ru(III) complexes [RuCl(2)(L)]ClO(4) (5 (L1), 6 (L2)). They were characterized by X-ray crystallography (for 2, 3, and 5), (1)H NMR spectroscopy, and cyclic voltammetry. For compound 2, the crystal structure was determined to possess S-bound DMSO ligand which was trans to pyridine and Cl(-) trans to the tertiary amino group of L2, and this isomer was obtained exclusively. Complex 1 was also isolated as a single isomer. Complex 3 was revealed to be a dinuclear bis-&mgr;-chloro Ru(II) species with the center of symmetry midway between two Cl(-). (1)H NMR spectra of Ru(II) complexes 1-4, the molecular structure of 2, and comparison of the molecular structure of 3 with 5 suggest that the interaction between the Ru(II) center, pyridyl moieties, and the DMSO ligand is strengthened by pi-back-bonding from the Ru(II) center to the ligands in addition to sigma-bonding of the tertiary amino group. Electrochemical measurements on 1-6 in CH(3)CN revealed that the methyl groups on pyridyl rings exert electron-donating effects onto the Ru centers to lower each redox process and such effect strengthens the Ru-S bonding in 2 compared with that in 1, accommodating pi-back-bonding from Ru(II) center to other pi-acceptors such as DMSO in 2 enough to prevent isomerization of DMSO binding mode. The dinuclear complexes 3 and 4 showed relatively large comproportionation constants, which suggest mixed-valent Ru(II)Ru(III) states would be stabilized.