Masahiro Ebihara

Synthesis and Fluorescence Properties of a Pyridomethene−BF2 Complex

A fluorescent dye, the pyridomethene-BF(2) complex, has been synthesized. Although pyridomethenes did not exhibit fluorescence, pyridomethene-BF(2) complexes exhibited fluorescence both in solution and in the solid state. The trifluoromethyl-substituted BF(2) complex formed a J-aggregate and showed the highest fluorescence quantum yield in the solid state among all pyridomethene-BF(2) complexes.

Two-Step Adsorption on Jungle-Gym-Type Porous Coordination Polymers: Dependence on Hydrogen-Bonding Capability of Adsorbates, Ligand-Substituent Effect, and Temperature

A preliminary study of isopropanol (IPA) adsorption/desorption isotherms on a jungle-gym-type porous coordination polymer, [Zn(2)(bdc)(2)(dabco)](n) (1, H(2)bdc = 1,4-benzenedicarboxylic acid, dabco =1,4-diazabicyclo[2.2.2]octane), showed unambiguous two-step profiles via a highly shrunk intermediate framework. The results of adsorption measurements on 1, using probing gas molecules of alcohol (MeOH and EtOH) for the size effect and Me(2)CO for the influence of hydrogen bonding, show that alcohol adsorption isotherms are gradual two-step profiles, whereas the Me(2)CO isotherm is a typical type-I isotherm, indicating that a two-step adsorption/desorption is involved with hydrogen bonds. To further clarify these characteristic adsorption/desorption behaviors, selecting nitroterephthalate (bdc-NO(2)), bromoterephthalate (bdc-Br), and 2,5-dichloroterephthalate (bdc-Cl(2)) as substituted dicarboxylate ligands, isomorphous jungle-gym-type porous coordination polymers, {[Zn(2)(bdc-NO(2))(2)(dabco)]·solvents}(n) (2 ⊃ solvents), {[Zn(2)(bdc-Br)(2)(dabco)]·solvents}(n) (3 ⊃ solvents), and {[Zn(2)(bdc-Cl(2))(2)(dabco)]·solvents}(n) (4 ⊃ solvents), were synthesized and characterized by single-crystal X-ray analyses. Thermal gravimetry, X-ray powder diffraction, and N(2) adsorption at 77 K measurements reveal that [Zn(2)(bdc-NO(2))(2)(dabco)](n) (2), [Zn(2)(bdc-Br)(2)(dabco)](n) (3), and [Zn(2)(bdc-Cl(2))(2)(dabco)](n) (4) maintain their frameworks without guest molecules with Brunauer-Emmett-Teller (BET) surface areas of 1568 (2), 1292 (3), and 1216 (4) m(2) g(-1). As found in results of MeOH, EtOH, IPA, and Me(2)CO adsorption/desorption on 2-4, only MeOH adsorption on 2 shows an obvious two-step profile. Considering the substituent effects and adsorbate sizes, the hydrogen bonds, which are triggers for two-step adsorption, are formed between adsorbates and carboxylate groups at the corners in the pores, inducing wide pores to become narrow pores. Interestingly, such a two-step MeOH adsorption on 2 depends on the temperature, attributed to the small free-energy difference (ΔF(host)) between the two guest-free forms, wide and narrow pores.

Mixed metal complexes of groups 10 and 11 elements. The structure and properties of [M(mnt)2{Ag(PR3)2}2] (MNi, Pd, Pt; mnt2− = maleonitriledithiolate)

Abstract The reaction of [Ag(PR2)2]+ (RPh, Bun) and [M(mnt)2]2− (MNi, Pd, Pt; mnt2− = maleonitriledithiolate) gave mixed-metal complexes with the general formula of [M(mnt)2{Ag(PR3)2}]. X-ray structures of [Pt(mnt)2{Ag(PPh3)2}2] (1), [Pd(mnt)2{Ag(PPh3)2}2] (2) and [Pd(mnt)2{Ag(PBun3)2}2] (5) are similar to one another. The Ag atoms have distorted tetrahedral AgP2S2 arrangement. All complexes have MAg distances shorter than van der Waals contacts. Complex 1 dissociates in solution, whereas [Pt(mnt)2{Ag(PBun3)2}2] (4) does not appreciably. UV-Vis absorption spectra of the mixed-metal completes are not much different from those of the corresponding free [M(mnt)2]2− ions. The first oxidation potential of each mixed-metal compound shifted about 0.15 V positively from that of the corresponding free [M(mnt)2]2− ion. 31P NMR chemical shift and PAg coupling of these mixed-metal complexes do not depend significantly on the Group 10 metal atom.

One-dimensionally extended paddlewheel dirhodium complexes from metal-metal bonds with diplatinum complexes.

We have succeeded in obtaining unique one-dimensional (1D) chain complexes (1, 2, and 3) comprised of two types of metal species: rhodium and platinum. These compounds are constructed from a dinuclear rhodium complex (i.e., [Rh(2)]) and a pivalamidate-bridged platinum complex (i.e., [Pt(2)]), forming an attractive quasi-1D infinite chain, expressed as -{[Rh(2)]-[Pt(2)]-[Pt(2)]}(n)-. Interestingly, the bridging ligands of [Rh(2)] can be varied with trifluoroacetate, acetate, and acetamidate groups, indicating the possibility of electronic structure modulation in the 1D chain.

Paramagnetic one-dimensional chains comprised of trinuclear Pt-Cu-Pt and paddlewheel dirhodium complexes with metal-metal bonds.

One-dimensional (1-D) chain complexes constructed by metal-metal bonds containing three types of metal species-platinum, rhodium, and copper-have been rationally synthesized and characterized by single-crystal X-ray analyses and physical measurements. The paddlewheel or lantern type complex, [Rh2(O2CCH3)4] (i.e., [Rh2]), has a vacant σ* orbital which accepts the electrons from the filled dz(2) orbital of cis-[Pt(piam)2(NH3)2]·2H2O (1, i.e. [Pt], where piam = pivalamidate) to afford a tetranuclear complex, [{Rh2(O2CCH3)4}{Pt(piam)2(NH3)2}2]·2H2O (2). Compound 2 forms a linear alignment as [Pt]-[Rh2]-[Pt] with unbridged Rh-Pt bonds, where the oxygen atoms of the piam ligands in the [Pt] are noncoordinated, showing the capability of binding another metal ion. Simply mixing [Rh2] and the heterometallic trinuclear complex [Pt2Cu(piam)4(NH3)4](PF6)2 (3, i.e. [Pt-Cu-Pt]) in a ratio of 1:1 in MeOH, EtOH, or Me2CO affords [{Rh2(O2CCH3)4}{Pt2Cu(piam)4(NH3)4}]n(PF6)2n (4), [{Rh2(O2CCH3)4}{Pt2Cu(piam)4(NH3)4}]n(PF6)2n (5), or [{Rh2(O2CCH3)4}{Pt2Cu(piam)4(NH3)4}]n(PF6)2n·6nMe2CO (6), respectively. Compounds 4-6 form infinite chains with the repetition of -{[Rh2]-[Pt-Cu-Pt]}n-, which to our knowledge, are the first examples of heterometallic 1-D chains comprised of three types of metal species with direct metal-metal bonds. The CF3CO2(-), ClO4(-), and water molecules influence the crystal packing to form an octanuclear complex of [{Rh2(O2CCH3)4}{Pt2Cu(piam)4(NH3)4}2](CF3CO2)2(ClO4)2·2H2O (7) with [Pt-Cu-Pt]-[Rh2]-[Pt-Cu-Pt] alignment. Considering the crystal structures and X-ray photoelectron spectra (XPS) measurements in 4-7, the oxidation states of the metal atoms are -{[Rh2(II,II)]-[Pt(II)-Cu(II)-Pt(II)]}n- or [Pt(II)-Cu(II)-Pt(II)]-[Rh2(II,II)]-[Pt(II)-Cu(II)-Pt(II)], which are unchanged from those in the starting compounds. Electron paramagnetic resonance spectra of 4-7 show axially symmetric spectra with g∥ > g⊥, indicating that the HOMO (SOMO) is a Cu d(x(2)-y(2)) orbital. In 7, the hyperfine coupling in the spectrum indicates that the unpaired spin on Cu is perturbed by the Pt atoms.

Synthesis, Crystal Structure, and Characterization of a Heterometallic One-Dimensional Complex with Metal−Metal Bonds

The quasi-one-dimensional chain [{PtRh(TCM)(2)(NH(3))(2)Cl(2.5)}(2){Pt(2)(PVM)(2)(NH(3))(4)}(2)](n)(PF(6))(6n).2nH(2)O (Chain-2; TCM = Cl(3)CCONH(-), PVM = (t)BuCONH(-)), which consists of Pt and Rh atoms, has been obtained from two dinuclear compounds, [Pt(2)(PVM)(2)(NH(3))(4)](PF(6))(2).H(2)O (1) and [PtRh(TCM)(2)(NH(3))(2)Cl(3)] (2). Single-crystal X-ray analysis showed that the dinuclear compounds stack with metal-metal bonds to form octameric units, Pt-Rh-Pt-Pt-Pt-Pt-Rh-Pt (Pt(6)Rh(2)), that are bridged by the Cl(-) ion to be a quasi-one-dimensional chain. Elemental analysis, X-ray photoelectron spectroscopy, electron paramagnetic resonance (EPR), and magnetic susceptibility measurements showed that Chain-2 has a mixed valency and one unpaired electron per octameric Pt(6)Rh(2) unit. Taking into account the small observed g(av) value (g(av) = 2.01 at room temperature) obtained by EPR measurement and B3LYP density functional theory calculations of the model complex, oxidation states of the octameric unit are postulated to be Pt(3+)-Rh(2.5+)-Pt(2+)-Pt(2+)-Pt(2+)-Pt(2+)-Rh(2.5+)-Pt(3+), where the EPR isotropic signal showed that the unpaired electron resides in the Rh d(xy) orbitals (delta* orbitals in Pt-Rh dinuclear parts) and hops from one Rh atom to another.

Preparation, structure and electrochemical behavior of dinuclear cyclooctadiene-chelated Ir(I) complexes with 2-aminopyridinato bridges

Abstract Dinuclear iridium(I) complexes with two bridging aminopyridinato ligands, [Ir(μ-L)(COD)]2 (COD=1,5-cyclooctadiene (1): L=2-aminopyridinato (ap) (2): L=2-anilinopyridinato (anp)), were prepared from [Ir(μ-Cl)(COD)]2 and Li+L− in a 24–36% yield. These compounds were characterized by X-ray structure analysis and 1H NMR spectroscopy. Two iridium atoms were bridged by two aminopyridinato ligands and each iridium atom was coordinated by one chelating COD. The coordination sphere of each Ir(I) center, which was formed by two N atoms and two olefinic π bonds, was square planar. Ir⋯Ir separations in 1 and 2 were 3.0998(6) and 3.0681(3) A, respectively. Cyclic voltammetry of 1 and 2 in n-Bu4NPF6/CH2Cl2 exhibited a chemically reversible oxidation wave at −0.41 and −0.36 V versus Fc+/Fc, respectively. These potentials were lower than those of [Ir(μ-form)(COD)]2 (form=anion of N,N′-di-p-tolylformamidine), [Ir(μ-hp)(COD)]2 (hp=anion of 2-hydroxypyridine), [Ir(μ-mhp)(COD)]2 (mhp=anion of 6-methyl-2-hydroxypyridine) and [Ir(μ-pz)(COD)]2 (pz=anion of pyrazole). Electrolytic one-electron oxidation of 2 gave its stable cationic radical, [Ir(μ-anp)(COD)]2 +, of which frozen solution ESR spectrum was rhombic with g1=2.43, g2=2.30 and g3=2.08 and no hyperfine splitting was resolved.

Homogeneous hydrogenation of olefins catalyzed by a novel tetrarhodium(II) complex as precursor in aqueous solution

Abstract Hydrogenation of α,β-unsaturated alcohol, nitrile, aldehyde, ketone, carboxylic acid and amide catalyzed by a novel water-soluble complex [Rh 4 (O 2 CPr n ) 4 Cl 4 (CH 3 CN) 4 ] was investigated. The reactions were carried out in aqueous solution at room temperature under 1 atm of H 2 . The results showed that this tetrarhodium(II) complex is efficient for the hydrogenation of both terminal and internal double bond with the selectivity of unhydrogenated carbonyl groups. Unsaturated ketone, amide and carboxylic acid were readily hydrogenated, and nitrile and aldehyde were slowly hydrogenated. The hydrogenation of allyl alcohol was accompanied with isomerization to propanal. The rate of the hydrogenation was first-order to the catalyst precursor.

Palladium complex-catalysed carbocyclization–distannylation, –disilylation and –silastannylation of bis-dienes using distannanes, disilanes and silylstannanes

Bis-dienes 4 react with distannanes 1, disilanes 2, and silylstannanes 3 in the presence of a catalytic amount of a palladium complex to afford carbocyclization–distannylation, –disilylation and –silastannylation products in high yields. Reaction of distannanes 1a, b with bis-dienes 4a, b as well as reaction of disilane 2b with bis-diene 4d proceeded regio- and stereo-selectively to afford a single product: trans-(E),(Z) isomers. Regio- and stereo-selective reaction was also realized with the disilane 2b and bis-diene 4e to provide only trans-(E),(E) isomer. In other cases, the reactions proceeded regioselectively, but the stereoselectivity was modest. The X-ray crystal structures of the cyclopropanes 10 and 11 have been determined.

Two types of heterometallic one-dimensional alignment composed of acetamidate-bridged dirhodium and pivalamidate-bridged diplatinum complexes.

Two types of heterometallic one-dimensional chains, [{Rh2(acam)4}{Pt2(piam)2(NH3)4}2]n(CF3SO3)4n·2nMeOH (2, where acam = acetamidate, piam = pivalamidate) and [{Rh2(acam)4}{Pt2(piam)2(NH3)4}]n(CF3CO2)2n·2nEtOH (3), have been synthesized and characterized by single-crystal X-ray analyses. The chain structures in 2 and 3 are composed of two kinds of dinuclear complexes, [Rh2(acam)4] (i.e., [Rh2]) and [Pt2(piam)2(NH3)4] (i.e., [Pt2]), where Rh and Pt atoms are axially linked by metal-metal bonds. In 2 and 3, each complex is one-dimensionally aligned as -{[Rh2]-[Pt2]-[Pt2]}n- or -{[Rh2]-[Pt2]}n-, respectively, in which different alignments are caused by different isomers of [Pt2] that are HH (head-head) and HT (head-tail) orientation of piam ligands and their hydrogen bonding modes. Considering the crystal structures and X-ray photoelectron spectra (XPS) measurements in 2 and 3, the oxidation states of the metal atoms are -{[Rh2(II,II)]-[Pt2(II,II)]-[Pt2(II,II)]}n- and -{[Rh2(II,II)]-[Pt2(II,II)]}n-, which are unchanged from those in the starting compounds. The diffuse reflectance spectra show that LUMOs are M-M σ-type orbitals. The gap between filled and vacant σ-type orbitals in 3 is narrower than that in 2, and is attributed to the relative higher destabilized filled σ-type orbitals caused by lower numbers of linking platinum atoms.