Keisuke Umakoshi

Heteropolynuclear Complexes of 3,5-Dimethylpyrazolate [Pt2M4(Me2pz)8] (M = Ag, Cu). Highly Luminescent Character of the Triplet Excited State Based on Mixed-Metal Cores

The platinum dimer and heteropolynuclear platinum complexes of 3,5-dimethylpyrazolate, [Pt2M4(mu-Me2pz)8] [M = H (1), Ag (2), Cu (3)], were synthesized and structurally characterized. They exhibit yellow, sky-blue, and orange luminescence, respectively, in the solid state. The absorption bands of 2 and 3 are mainly assigned to the combination of the metal-metal-to-ligand charge-transfer and [Pt2 --> Pt2M4] transitions by the time-dependent density functional theory (DFT) method. DFT calculations also indicate that the emissive states of 2 and 3 are 3[Pt2 --> Pt2Ag4] and 3[Cu(d) --> Pt2Cu4], respectively.

A europium(III)-N,N,N′,N′-tetrakis(2-pyridylmethyl)-(R)-propylenediamine complex as a new chiral lanthanide NMR shift reagent for aqueous neutral solution

A new chiral lanthanide shift reagent [EuIIICl2{R)-tppn}]ClO4 which is structurally characterized by X-ray crystallography, resolves the enantiomer signals of α-amino acids in neutral aqueous solution and affords a good relation between the relative signal position of enantiomers and their absolute configurations.

Luminescent Heteropolynuclear Complexes of 3,5‐Dimethylpyrazolate [Pt2Au2M2(Me2pz)8] (M=Ag, Cu) Showing the Synergistic Effect of Three Transition Elements in the Excited State

Swap the coins! The Pt(2)Au(2), Pt(2)Au(2)Cu(2), and Pt(2)Au(2)Ag(2) complexes of 3,5-dimethylpyrazolate exhibit yellow-green, orange, and sky-blue luminescence, respectively (see figure). The emission energies of Pt(2)Au(2)M(2) complexes can be controlled by the change of the third coinage metal ions M. The Pt(2)Au(2)M(2) complexes take the cis configuration with respect to the Au(2)M(2) plane.

Preparation, spectroscopic properties, and dynamic behavior of a μ-oxo dirhenium(III) complex [Re2(μ-O)Cl2(tpa)2](PF6)2 (tpa=tris(2-pyridylmethyl)amine)

Abstract An oxo-bridged dirhenium(III,III) complex of tris(2-pyridylmethyl)amine (tpa) and its one-electron oxidized (III,IV) species, [Re2(μ-O)Cl2(tpa)2]3+,4+ have been prepared. They are new members to a series of rhenium tpa complexes in various oxidation states. X-ray structural determination of the Re2(III,IV) complex revealed practically linear ReORe bridge (178(1)°) with short ReO distances of 1.85(2) A indicative of some multiple bonded character. The 1H NMR spectrum disclosed the relatively slow rotation around the ReORe axis in CH3CN solution in the timescale of 1H NMR. The complex undergoes two consecutive reversible one electron oxidations Re2(III,III)/(III,IV) and Re2(III,IV)/(IV,IV) at E1/2=0.23 and 0.90 V vs Ag/AgCl, respectively. Strong visible absorption bands are observed for the Re2(III,III) species at 448 (e=31 160) and 563 nm (19 550) which are tentatively assigned to MLCT transitions. A unique oxidation product, Re2(μ-O)(O)2Cl2(bpaO2)2 (bpaO2H=1,3-bis(2-pyridyl)-2-aza-propanedione) has also been isolated and its crystal structure was determined. The complex is dirhenium(V) species with linear OReOReO moiety. Ligand tpa has been oxidized to ketone with simultaneous dissociation of one of the 2-pyridylmethyl arms.

Syntheses and Luminescent Properties of 3,5-Diphenylpyrazolato-Bridged Heteropolynuclear Platinum Complexes. The Influence of Chloride Ligands on the Emission Energy Revealed by the Systematic Replacement of Chloride Ligands by 3,5-Dimethylpyrazolate

Heteropolynuclear Pt(II) complexes with 3,5-diphenylpyrazolate [Pt(2)Ag(4)(μ-Cl)(2)(μ-Ph(2)pz)(6)] (3), [Pt(2)Ag(2)Cl(2)(μ-Ph(2)pz)(4)(Ph(2)pzH)(2)] (4), [Pt(2)Cu(2)Cl(2)(μ-Ph(2)pz)(4)(Ph(2)pzH)(2)] (5), [Pt(2)Ag(4)(μ-Cl)(μ-Me(2)pz)(μ-Ph(2)pz)(6)] (7), and [Pt(2)Ag(4)(μ-Me(2)pz)(2)(μ-Ph(2)pz)(6)] (8) have been prepared and structurally characterized. These complexes are luminescent except for 5 in the solid state at an ambient temperature with emissions of red-orange (3), orange (4), yellow-orange (7), and green (8) light, respectively. Systematic red shift of the emission energies with the number of chloride ligands was observed for 3, 7, and 8. DFT calculations indicate that the highest occupied molecular orbital (HOMO) as well as HOMO-1 of the heterohexanuclear complexes, 3, 7, and 8, having Pt(2)Ag(4) core, mainly consist of dδ orbital of Pt(II) and π orbitals of Ph(2)pz ligands, while the lowest unoccupied molecular orbital (LUMO) of these complexes mainly consists of in-phase combination of 6p of two Pt(II) centers and 5p of four Ag(I) centers. It is likely that the emissions of 3, 7, and 8 are attributed to emissive states derived from the Pt(2)(d)/π → Pt(2)Ag(4) transitions, the emission energy of which depends on the ratio of chloride ligands to pyrazolate ligands.

Reactivity of pentamethylcyclopentadienyltetrachloromolybdenum(V). Synthesis, structure and electrochemical properties of [(η5-C5Me5)MoOCl]2O

Abstract The reaction of [(η 5 -C 5 Me 5 )Mo V Cl 4 ] with Na 2 WO 4 in THF provides red-brown [(η 5 -C 5 Me 5 )Mo V OCl] 2 O, while in water yellow [(η 5 -C 5 Me 5 )Mo VI O 2 ] 2 O is formed. Single-crystal X-ray diffraction analysis has revealed that [(η 5 -C 5 Me 5 )MoOCl] 2 O has an anti configuration with a linear MoOMo skeleton. A cyclic voltammogram of [(η 5 -C 5 Me 5 )MoOCl] 2 O in CH 2 Cl 2 shows both a reversible and an irreversible two-electron process centered at -0.70 V and +1.03 V vs Ag/AgCl, respectively. Crystal data: monoclinic, space group P 2 1 / n, a 10.621(1), b 14.371(3), c 7.689(1) A, β 93.24(2) o , Z = 2.

Chiral-at-Metal Phosphorescent Square-Planar Pt(II)-Complexes from an Achiral Organometallic Ligand

The synthesis and characterization of a new kind of cis- and trans-cyclometalated square-planar platinum(II) complexes is reported. Uncharged organometallic compounds carrying one or two of the C∧N-donor ligand LCN were prepared. Due to the heterobidentate coordination of the achiral chelate ligand, the formed [PtLCNCl(SEt2)], cis- and trans-[PtLCN2] complexes are chiral with the metal serving as the stereo center. The enantiomers of complex trans-[PtLCN2] could be separated and their absolute configuration was determined by anomalous X-ray diffraction, in accordance with CD spectroscopic results and TD-DFT calculations. All compounds were fully characterized by NMR spectroscopy, mass spectrometry and X-ray structure determination. The photophysical properties of trans-[PtLCN2] have been investigated showing phosphorescence in solution and in the solid state with a moderate quantum yield. For the enantiomers, strong circular dichroism (CD) and circularly polarized luminescence (CPL) effects were observed, rendering this new structural motif suitable for application in chiroptical and luminescent materials.

Redox behaviour of the oxo-bridged diruthenium(III) complex, [Ru2(µ-O)(µ-MeCO2)2(bpy)2(mim)2]2+ in acetonitrile in the presence of various proton donors (bpy = 2, 2′-bipyridine, mim = 1-methylimidazole)

Redox potentials of the Ru2III,III–Ru2III,II and Ru2III,II–Ru2II,II processes of [Ru2(µ-O)(µ-MeCO2)2(bpy)(mim)2]2+ in acetonitrile, move to the positive direction remarkably on addition of a strong acid such as toluene-p-sulfonic acid, while two processes are coalesced to show apparent one-step two-electron reduction on addition of weaker proton donors.

Synthesis and Properties of Oxo-carboxylato- and Dioxo-Bridged Diosmium Complexes of Tris(2-pyridylmethyl)amine

A series of oxo-bridged diosmium complexes with tpa ligand (tpa = tris(2-pyridylmethyl)amine) are synthesized. The hydrolytic reaction of the mononuclear osmium complex [Os(III)Cl(2)(tpa)]PF(6) in aqueous solution containing a sodium carboxylate yields a μ-oxo-μ-carboxylato-diosmium(III) complex, [Os(III)(2)(μ-O)(μ-RCOO)(tpa)(2)](PF(6))(3) (R = C(3)H(7) (1), CH(3) (2), or C(6)H(5) (3)). One-electron oxidation of 1 with (NH(4))(2)Ce(IV)(NO(3))(6) gives a mixed-valent [Os(III)Os(IV)(μ-O)(μ-C(3)H(7)COO)(tpa)(2)](PF(6))(4) complex (4). A mixed-valent di-μ-oxo-diosmium complex, [Os(III)Os(IV)(μ-O)(2)(tpa)(2)](PF(6))(3) (5), is also synthesized from 1 in an aerobic alkaline solution (pH 13.5). All the complexes exhibit strong absorption bands in a visible-near-infrared region based on interactions of the osmium dπ and oxygen pπ orbitals of the Os-O-Os moiety. The X-ray crystallographic analysis of 1, 3, and 4 shows that the osmium centers take a pseudo-octahedral geometry in the μ-oxo-μ-carboxylato-diosmium core. The mixed-valent osmium(III)osmium(IV) complex 4 has a shorter osmium-oxo bond and a larger osmium-oxo-osmium angle as compared with those of the diosmium(III) complex 1 having the same bridging carboxylate. Crystal structure of 5 reveals that the two osmium ions are bridged by two oxo groups to give an Os(2)(μ-O)(2) core with the significantly short osmium-osmium distance (2.51784(7) Å), which is indicative of a direct osmium-osmium bond formation with the bond order of 1.5 (σ(2)π(2)δ(2)δ*(2)π*(1) configuration). In the electrochemical studies, the μ-oxo-μ-carboxylato-diosmium(III) complexes exhibit two reversible Os(III)Os(III)/Os(III)Os(IV) and Os(III)Os(IV)/Os(IV)Os(IV) oxidation couples and one irreversible redox wave for the Os(III)Os(III)/Os(II)Os(III) couple in CH(3)CN. The irreversible reductive process becomes reversible in CH(3)CN/H(2)O (1:1 Britton-Robinson buffer; pH 5-11), where the {1H(+)/2e(-)} transfer process is indicated by the plot of the redox potentials against the pH values of the solution of 1. Thus, the μ-oxo-μ-butyrato-diosmium(III) center undergoes proton-coupled electron transfer to yield a μ-hydroxo-μ-butyrato-diosmisum(II) species. The di(μ-oxo) complex 5 exhibits one reversible Os(III)Os(IV)/Os(IV)Os(IV) oxidation process and one reversible Os(III)Os(IV)/Os(III)Os(III) reduction process in CH(3)CN. The comproportionation constants K(com) of the Os(III)Os(IV) states for the present diosmium complexes are on the order of 10(19). The values are significantly larger when compared with those of similar oxo-bridged dimetal complexes of ruthenium and rhenium.

Synthesis, structure, and properties of sulfido-bridged dinuclear tungsten(V) complex of dithiolene, (Pr4N)2[W2(μ-S)2{S2C2(CO2Et)2}4]

Abstract The reaction of tetrathiotungstate (WS42−) with diethyl acetylenedicarboxylate, EtO2CCCCO2Et, in the presence of dinuclear Pt(III) complex [Pt2Cl2(5-mpyt)4] (5-mpyt=5-methylpyridine-2-thiolato) as an oxidant gave a sulfido-bridged dinuclear tungsten(V) complex of dithiolene, (Pr4N)2[W2(μ-S)2{S2C2(CO2Et)2}4] (1). The absence of an appropriate oxidant in the reaction system afforded tris(dithiolene) complex (Pr4N)2[W{S2C2(CO2Et)2}3] (2). The complex 1 was characterized structurally and spectroscopically. The complex anion in 1 has an edge-shared bioctahedral structure with two bridging sulfide ions, WW distance being 2.9425(7) A. The fluxionality of the dithiolene ligand was observed by 1H-NMR even at −50°C for 1.