Yoshitaro Miyashita

Layered transition metal carboxylates: efficient reusable heterogeneous catalyst for epoxidation of olefins.

Layered metal carboxylates [M(malonato)(H(2)O)(2)](n) (M = Ni(II) and Mn(II)) that have a claylike structure have been synthesized hydrothermally and characterized. The interlayer separation in these layered carboxylates is comparable to that of the intercalation distance of the naturally occurring clay materials or layered double hydroxides (LDHs). In this study, we have demonstrated that, instead of intercalating the metal complex into layers of the clay or LDH, layered transition metal carboxylates, [M(malonato)(H(2)O)(2)](n), as such can be used as a recyclable heterogeneous catalyst in olefin epoxidation reaction. Metal carboxylates [M(malonato)(H(2)O)(2)](n) exhibit excellent catalytic performance in olefin epoxidation reaction.

Group 12 metal(II) complexes with 1-methylimidazoline-2(3H)-thione (mitH): correlation between crystal structure and physicochemical property

The crystal structures of [ZnX2(mitH)2] (X = Cl (1), Br (2)), [ZnI(mitH)3]I (3), and [CdX2 (mitH)2] (X = Cl (4), Br (5), I (6)) (mitH = 1-methylimizadoline-2(3H)-thione) were determined by X-ray crystallography and all complexes were characterized by IR, far-IR, Raman, and UV–Vis absorption (solid) spectroscopies. All complexes except 3, which have a different ZnIS3 coordination mode, have a distorted tetrahedral geometry with an MX2S2 coordination mode. Each π-character of the C=S bonds (from 37.7 to 45.4%) is smaller than that of free mitH (51.9%). Their M–S–C bond angles (from 97° to 109°) support that the C=S bonds are not a full double bond. Their stretching vibration frequencies of M–S (300–320 cm−1) and M–X (229–290 cm−1) in both far-IR and Raman spectra show the lower energy shifts with increasing weight of metal(II) or halide ions. Similarly, some shifts (from 275 nm for 1 to 293 nm for 6) are also observed in CT transition bands in UV-Vis absorption spectra.

Crystal structures, electronic absorption and reflectance spectral behaviors, and electrochemical properties of five-coordinated chlorocopper(II) complexes with 5,6-disubstituted-1,10-phenanthroline

Abstract The five-coordinated geometries around the Cu(II) centers in [CuCl(dmphen)2]PF6 (1; dmphen=5,6-di-methyl-1,10-phenanthroline) and [CuCl(phendione)2]PF6·H2O (2; phendione=1,10-phenanthroline-5,6-dione) are distorted square-pyramidal in contrast to the distorted trigonal-bipyramidal [CuCl(phen)2]PF6 (phen=1,10-phenanthroline), reflecting introductions of substituents into the 5- and 6-positions on phen. It has been found that these geometries in 1 and 2 are considerably dependent on the interactions between the π-electronic systems of the phen frameworks. The diffuse reflectance spectra significantly reflect geometrical differences of 1 and 2 from [CuCl(phen)2]PF6. The electronic absorption spectra suggest that the geometries of 1 and 2 in solution are similar to those in the crystalline state, while the geometry of [CuCl(phen)2]PF6 seems to be changed from distorted trigonal-bipyramid to square-pyramid. The electrochemical experiments indicate that the redox properties of these complexes are appreciably influenced by the electronic characters of the substituents on the phen frameworks.

M–S vibrational study in three-coordinate thiolato compounds (NEt4)2[M(SC6H4-p-X)3] and (NEt4)2[M4(μ-SC6H4-p-Cl)6]: M=Cu(I) and Ag(I), X=Cl and Br

By using p-substituted benzenethiolate ligands, the novel three-coordinate copper(I) and silver(I) thiolato complexes (NEt4)2[Cu(SC6H4-p-X)3] (X=Cl (1) and Br (2)), (NEt4)2[Ag(SC6H4-p-X)3] (X=Cl (3) and Br (4)) and novel clusters (NEt4)2[M4(mu-SC6H4-p-Cl)6] (M=Cu (5) and Ag(6)) have been prepared and structurally characterized by single crystal X-ray diffraction. All the complexes have three-coordinate sites having point-group D3h symmetry. The three-coordinate mononuclear silver(I) complexes 3 and 4 are the first examples. The M-S stretching bands were determined by far-IR and FT-Raman spectroscopies; nu(Cu-S) 363-372 cm(-1) and nu(Ag-S) 353-363 cm(-1). These results indicate that M-S stretching vibration energy in the three-coordinate metal(I) site of the mononuclear compounds or clusters is around 340-380 cm(-1), and it is a useful tool for determining their coordination modes.

Syntheses, structures, and properties of oxorhenium(V) complexes with 2-, 5-, and/or 7-substituted 8-quinolinolato ligands

Abstract Five mononuclear oxorhenium(V) complexes containing 8-quinolinolato derivatives, [ReOCl2(2-X-5-Y-7-Z-8-Oqn)(PPh3)] (qn= quinoline; PPh3=triphenylphosphine; X=Me, Y=Z=H, 1; X=Z=H, Y=Cl, 2; X=H, Y=Z=Cl, 3; X=H, Y=Cl, Z=I, 4; X=H, Y=Z=Br, 5), were newly synthesized by the reaction of [ReOCl3(PPh3)2] with the corresponding 8-hydroxyquinoline ligands. From X-ray crystal structural analyses, all the obtained complexes have the same geometry; the ReaO bond occupies the trans position to the O atom of the deprotonated 8-hydroxyquinoline ligand. The complexes, which retain their structures in solution, were characterized on the basis of IR, UV–vis, 31P NMR spectra, and cyclic voltammetry. Depending on the existence of 2-Me substituent in the ligands, some stereochemical and electrochemical differences were observed. In contrast to the case of the corresponding 2-methylquinolin-8-ylamido complex [ReOCl2(2-Me-8-HNqn)(PPh3)], substitution reaction of PPh3 to OPPh3 (Ztriphenylphosphine oxide) or pyridine did not take place, reflecting the high stability of the present 8-quinolinolato complexes.

Optically active sulfur-bridged Co(III)–M(II) (M=Pd, Pt) dinuclear complexes with square-planar [M(μ-S)2(bpy)] (bpy=2,2′-bipyridine) frameworks derived from octahedral bidentate sulfur-donating Co(III) metalloligands

Abstract The reactions of the optically active octahedral mononuclear complex, trans(N)-[Co( d -pen)2]− ( d -pen= d -penicillaminate), with [PdCl2(bpy)] (bpy=2,2′-bipyridine) and [PtCl2(bpy)] stereoselectively gave the S-bridged dinuclear complexes, [Pd(bpy){Co( d -pen)2}]+ (1a) and [Pt(bpy){Co( d -pen)2}]+ (1b), respectively. A similar optically active S-bridged dinuclear complex, Δ-[Pt(bpy){Co(aet)2(R-pn)}]3+ (2b; aet=2-aminoethanethiolate, pn=1,2-propanediamine), was also obtained by the substitution reaction of ΔΔ-[Ni{Co(aet)2(R-pn)}2]4+ with [PtCl2(bpy)]. The crystal structures of 1a, 1b, and 2b were determined by X-ray crystallography, and compared with that of the previously reported Δ-[Pd(bpy){Co(aet)2(R-pn)}]3+ (2a). The Co(III) equatorial planes and the PdN2S2 or PtN2S2 square planes in the 1a and 1b are almost coplanar, while those in 2a and 2b are somewhat bent from each other. In addition, the distortions from the square planes to tetrahedrons in 2a and 2b are more pronounced than those in 1a and 1b. Furthermore, all of the bridging S atoms in 1a and 1b are stereoselectively unified to the S configuration, in contrast to those in 2a and 2b with the R configuration. These reflect the differences of the optically active Co(III) units in these complexes. The electronic absorption, CD, and 13C NMR spectral behaviors of these complexes are also discussed in relation to their crystal structures.

Oxalato-bridged di- and trinuclear Co(III)–Dy(III) complexes derived from mononuclear Co(III) complex with nitrilotriacetate

Abstract The divalent mononuclear complex anion, [Co(nta)(ox)] 2− (nta=nitrilotriacetate, ox=oxalate) functions as an effective building-block for construction of the oxalato-bridged heteropolynuclear lanthanide(III) complexes, and reacts with Dy 3+ ion by the molar ratio of 1:1 to form a novel dinuclear Co(III)–Dy(III) complex, [Dy{Co(nta)(μ-ox)}(H 2 O) 7 ] + ( 1 ). A similar reaction by the ratio of 2:1 results in the formation of trinuclear species, [Dy{Co(nta)(μ-ox)} 2 (H 2 O) 5 ] − ( 2 ). The X-ray structural analyses for 1 and 2 revealed that each of the Dy(III) atoms in these complexes takes a nine-coordinated tricapped trigonal-prismatic geometry. The two characteristic bands for the Dy 3+ ions in the diffuse reflectance spectra reflect differences in the coordination environments of Dy(III) atoms between 1 and 2 . Although no significant distinctions are recognized for the geometries of the Co(III) units between 1 and 2 , furthermore, the reflectance spectra indicate distinguishable electronic states of Co(III) atoms from each other.

Syntheses, stereochemistry, reactivity, and some properties of sulfur-bridged cobalt(III)-cadmium(II) polynuclear complexes derived from mononuclear cobalt(III) complex with D-penicillaminate

Abstract A reaction of the octahedral bidentate metalloligand, trans(N)-[Co( d -pen)2]− ( d -pen= d -penicillaminate) with Cd(NO3)2 or Cd(ClO4)2 gave a novel S-bridged trinuclear complex, [Cd(H2O){Co( d -pen)2}2] (1). In this complex molecule, the central Cd atom is surrounded by four S atoms from two [Co( d -pen)2]− units and one O atom of a H2O molecule to form a distorted five-coordinated geometry. Each of two terminal [Co( d -pen)2]− units takes an approximately octahedral geometry and has a similar trans(N) geometry to that of the starting material. On the other hand, the reaction of trans(N)-[Co( d -pen)2]− with CdCl2 in the molar ratio of 1:1 gave an S-bridged dinuclear complex, [CdCl{Co( d -pen)2}(H2O)m]·nH2O (m+n=4) (2). The reactivity of trans(N)-[Co( d -pen)2]− toward CdCl2 is significantly influenced by the ratio of two components, and the formation of a similar trinuclear species to 1 is also suggested under the condition with excess amount of trans(N)-[Co( d -pen)2]−. Some spectrochemical properties of these complexes are also discussed in relation to their structures.

Characterization and electrochemical properties for rhenium(III) ion incorporated into linear-type S-bridged trinuclear complexes. Crystal structures of ΔΛ- and ΔΔ/ΛΛ-[Re{Ir(aet)3}2]3+ (aet=2-aminoethanethiolate)

Abstract The meso (1a) isomer of the IrIIIReIIIIrIII trinuclear complex [Re{Ir(aet)3}2]3+ (aet=2-aminoethanethiolate) was newly prepared by SnCl2·2H2O reduction of an acidic mixture of fac(S)-[Ir(aet)3] and NH4ReO4, and purified by column chromatography. The racemic (1b) isomer was isolated by the reaction of fac(S)-[Ir(aet)3] with [Re(Metu)6]Cl3 (Metu=N-methylthiourea). The crystal structures of 1aBr3 and 1bBr3·H2O were determined by X-ray crystallography. Both isomers consist of two terminal fac(S)-[Ir(aet)3] units and a central Re atom, forming the linear-type S-bridged trinuclear structure. The central Re atom is situated in an octahedral environment with ReIIIS6 chromophore. Both 1a and 1b are fairly stable in water under aerobic condition and they were characterized spectrochemically. Further, 1b was optically resolved by a column chromatographic method, and it is characterized by CD spectroscopy. The ReIII ion, which has a d4-electronic configuration, in 1b indicates a lower magnetic moment (1.11μB) at room temperature, reflecting well the paramagnetic shifts for 1H and 13C NMR signals. Each cyclic voltammogram of [Re{M(aet)3}2]3+ (M=IrIII, RhIII) shows a reversible redox process (MIV/III) in a positive region and they are confirmed by a spectroelectrochemical technique. Their redox potentials at E0′=+0.34–+0.60 V (vs. Ag/AgCl) are lower than those for the corresponding complexes, whereas it was elucidated that the oxidation state of the ReIII ion is highly stabilized in the S-bridged trinuclear structures.

Regulation of the physiological effects of peroxidovanadium(V) complexes by the electronic nature of ligands.

Although the physiological effects of peroxidovanadium(V) complexes (pVs) have been extensively investigated both in vitro and in vivo with regard to their pharmacological activity, such as insulin-mimetic and antitumor activities, the relationship between the chemical and pharmacological properties of pVs is still unclear. Rational drug design with pVs depends on a full understanding of this relationship. Toward this end, the current report evaluates the physiological effects of 13 pVs were evaluated bound to a variety of ligand. Six of these ligands are tripodal tetradentate ligands, one is a linear tetradentate ligand, one boasts two pendant groups, three are tridentate ligands, and two are alkoxido-bridging, dinucleating ligands. The cytotoxicities of these pVs could be classified into three groups: significantly toxic, moderately toxic, and non- or negligibly toxic. Further, IC50 values could be related with the LMCT transition energies of the peroxido group, particularly among complexes with similar ligands. This relation indicates that the electronic properties of the peroxido group affected the physiological activity of the pV complex. We also investigated the insulin-signaling intensity of each pV. Phosphorylation of protein kinase B and extracellular signal-regulated kinase 1/2, two major insulin-signaling proteins, was observed after treating cells with pV for 30 min. Phosphorylation was particularly remarkable for complexes that exhibited high cytotoxicity. The present results demonstrate that the toxicity and physiological effects of pVs can be controlled by selecting an appropriate ancillary ligand. These findings provide a guide for synthesis of new pVs that may be used as candidate therapeutic agents.