Youichi Ishii

Syntheses and Phosphorescent Properties of Blue Emissive Iridium Complexes with Tridentate Pyrazolyl Ligands

Novel neutral mixed-ligand Ir(N=C=N)(N=C)X complexes (N=C=N = 1,3-bis(3-methylpyrazolyl)benzene (bpzb), 1,5-dimethyl-2,4-bis(3-methylpyrazolyl)benzene (dmbpzb), and 1,5-difluoro-2,4-bis(3-methylpyrazolyl)benzene (dfbpzb); N=C = 2-phenyl pyridine (ppy); and X = Cl or CN) have been synthesized and characterized. An X-ray single-crystal structure of the complex Ir(dmbpzb)(ppy)Cl shows that the nitrogen atom in the ppy ligand occupied the trans position to the carbon atom in the tridentate N=C=N ligand of dmbpzb with the Ir-C bond length of 1.94(1) A, whereas the coordinating carbon atom occupied the trans position of chlorine. Electrochemical data show that the complexes exhibit an oxidation Ir(III/IV) process in the potential range of +0.5 approximately 0.9 V and two irreversible reductions at approximately -2.6 and -3.0 V against Fc (0)/Fc (+), respectively. All of the Ir(III) complexes do not emit phosphorescence at room temperature, although strong phosphorescence is exhibited at 77 K with the 0-0 transition centered at around 450 nm and lifetimes of 3-14 mus. DFT calculations indicate that the HOMOs are mainly localized on iridium 5dpi and chlorine ppi*, whereas the LUMOs are mainly from the ppy ligand pi* orbitals. The phosphorescence originates from a (3)LC state mixed with the (3)MLCT and (3)XLCT ones. Temperature-dependent lifetime measurements of Ir(dfbpzb)(ppy)Cl reveal the existence of a thermal deactivation process with a low activation energy (1720 cm (-1)) and very high frequency factor (2.3 x 10 (13) s (-1)). An unrestricted density functional theory indicates that the dd state, in which both the Ir-N (pyrazolyl) bond lengths increase considerably, exists almost at the same energy as that for the phosphorescent state. A thorough analysis based on the potential energy surfaces for the T 1 and S 0 states allows us to determine the reaction pathway responsible for this thermal deactivation. The calculated activation energies of 1600 approximately 1800 cm (-1) are in excellent agreement with the observed values.

Synthesis of novel chiral ruthenium complexes of 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl and their use as asymmetric catalysts

Reactions of [RuCl2(COD)]n(COD = cyclo-octa-1,5-diene) with the chiral bidentate phosphine ligands 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl, BINAP, and 2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl, p-tolyl-BINAP, give new chiral ruthenium(II) complexes, Ru2Cl4(BINAP)2(NEt3)and Ru2Cl4(p-toly-BINAP)2(NEt3) respectively, which serve as excellent catalysts for asymmetric hydrogenation of alkenes and some cyclic anhydrides.

Synthesis and reactivities of diazoalkane complexes

Abstract Diazoalkane complexes have been attracting wide interest because of their rich coordination chemistry. Diazoalkane ligands, derived from either free diazoalkanes or other precursors such as coordinated dinitrogen, azines, and hydrazones, display numerous coordination modes acting as π− and/or σ-bound terminal, bridging, or chelating ligands to form mono- or multimetallic complexes. The reactivities of coordinated diazoalkanes are largely affected by their coordination modes. The variety of reactivities observed for these coordinated diazoalkanes is quite different from those of free diazoalkanes. In this review are described the synthesis, structures, and reactivities of diazoalkane complexes.

Ruthenium (II)-BINAP complex catalyzed asymmetric hydrogenation of unsaturated dicarboxylic acids

Abstract Asymmetric hydrogenation of unsaturated dicarboxylic acids employing ruthenium-BINAP complexes as catalyst gave optically active 2-alkylsuccinic acids with high enantioselectivities.

Formation of Vinylidenes from Internal Alkynes at a Cyclotriphosphato Ruthenium Complex

A ruthenium cyclotriphosphato (P(3)O(9)(3-)) complex with a labile MeOH ligand can affect the vinylidene rearrangement of general internal alkynes via the 1,2-migration of alkyl, aryl, and acyl groups. This provides the first internal alkyne-to-vinylidene isomerization with high generality. Several intermediary eta(2)-alkyne complexes could be isolated and were successfully transformed into the corresponding vinylidene complexes. The reaction mechanism is also discussed on the basis of a kinetic study and migratory aptitude of alkyl, aryl, and acyl groups; the present reaction proceeds via an intramolecular process and is viewed as an uncommon electrophilic rearrangement.

Stereoselective addition of carboxylic acids to electron deficient acetylenes catalyzed by the PdMo3S4 cubane-type cluster

Abstract The mixed-metal sulfide cubane-type cluster complex [PdMo 3 S 4 (tacn) 3 Cl][PF 6 ] 3 ( 1 ; tacn = 1,4,7-triazacyclononane) was found to be a highly efficient and selective catalyst for the addition of carboxylic acids to acetylenes with electron-withdrawing groups. The corresponding trans addition products were exclusively obtained in good yields under mild reaction conditions in the presence of a catalytic amount of triethylamine.

Organometallic synthesis and magnetic properties of ferromagnetic Sm-Co nanoclusters

We have successfully prepared Sm–Co composite nanoclusters using liquid-phase organometallic synthesis. The chemical composition was determined by quantitative x-ray fluorescence analysis and it is found that the composition of synthesized Sm–Co nanoclusters was Sm poor while the Sm–Co nanoclusters with required composition could be obtained in starting from the excess Sm(acac)3. From the transmission electron microscopy measurements, the Sm–Co nanoclusters have the uniform size with the diameter of 9 nm. The crystalline structure was fcc which is different from that of bulk SmCo alloy with the same Sm and Co content. The magnetic property was observed by superconducting quantum interference magnetometer and shows the ferromagnetic characteristics.

Syntheses, structures and properties of hydrosulfido-bridged diiridium and dirhodium complexes,

Abstract The reaction of [ Cp ∗ MCl (μ 2 - Cl ) 2 MCp ∗ Cl ] ( M  Ir , Rh ; Cp ∗ = η 5 - C 5 Me 5 ) with excess H2S gas for 5 min afforded the dobly bridged hydrosulfido complexes [ Cp ∗ MCl (μ 2 - SH ) 2 MCp ∗ Cl ] (3: M = Ir, 4: M = Rh) which were further transformed into the triply bridged cationic hydrosulfido complexes [ Cp ∗ M (μ 2 - SH ) 3 MCp ∗ ] Cl (5·Cl: M = Ir, 6·Cl: M = Rh) by continuous stirring under H2S. The molecular structures of 3, 4, 5 · [BPh4] and 6·Cl·C6H6 were determined by X-ray analyses. The SH ligands in complexes 3 and 4 take anti configuration in the solid state, whilst these complexes exist as mixtures of the syn and anti isomers in solution. Strong hydrogen bonds between the Cl anion and two of the SH ligands were found in 5·Cl and 6·Cl, and were maintained in CDCl4 solution. When complexes 3 and 4 were treated with NEt3 at room temperature, the cubane-type sulfido clusters [ Cp ∗ M ) 4 (μ 4 - S ) 4 ] (M = Ir, Rh) were produced in high yields. In the reaction of 3, an intermediary complex, most probably [ Cp ∗ Ir (μ 2 - S ) 2 IrCp ∗ ] , was detected by 1H NMR.

Asymmetric hydrogenation of prochiral carboxylic acids catalyzed by the five-coordinate ruthenium(II)-hydride complex [RuH(binap)2]PF6 (binap = (R)- or (S)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl)

Abstract The five-coordinate complex [RuH(binap)2]PF6 (I, binap = (R)- or (S)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) has been found to have sufficient catalytic activity for asymmetric hydrogenation of itaconic acid and other prochiral carboxylic acids under mild conditions. The catalytic hydrogenation of itaconic acid by I was examined under a variety of conditions, and the addition of triethylamine was found to effect high enantioselectivities (> 90% ee). 1H and 31P NMR examinations of reaction mixtures of I and itaconic acid under conditions similar to the hydrogenation suggested the formation of ruthenium species containing one binap chelate.

Asymmetric hydrogenation of prochiral alkenes catalysed by ruthenium complexes of (R)-(+)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl

Two chiral ruthenium(II) complexes containing (R)-(+)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl[(R)-BINAP] were found to be effective catalysts for the asymmetric hydrogenation of 2-acylaminoacrylic and 2-acylaminocinnamic acids under mild conditions, to afford N-acyl-(R)-α-amino acids with 49–95% optical purity. The differences between the asymmetric hydrogenations effected by RuII- and RhI-(R)-BINAP systems are discussed. Asymmetric hydrogenation of methylenesuccinic acid and its derivatives with Ru-(R)-BINAP is also described.