Stepwise Sulfite Reduction on a Dinuclear Ruthenium Complex Leading to Hydrogen Sulfide.

Sulfite reduction by dissimilatory sulfite reductases is a key process in the global sulfur cycle. Sulfite reductases catalyze the 6e reduction of SO to HS using eight protons (SO + 8H + 6e → HS + 3HO). However, detailed research into the reductive conversion of sulfite on transition-metal-based complexes remains unexplored.

Noncovalent tailoring of coordination complexes by resorcin[4]arene-based supramolecular hosts.

Molecular recognition of guest molecules in a confined cavity is one of the important phenomena in biological and artificial molecular systems. When the guest is trapped within an artificial nano-space, its conformation is fixed in an unusual fashion by noncovalent interactions with host frameworks, and also the guest is kept away from the bulk solvent by the steric effect of the host. Therefore, host-guest formations lead to the effective modulation of the chemical and physical properties of guests noncovalent interactions.

Symmetry-breaking host-guest assembly in a hydrogen-bonded supramolecular system.

Bio-inspired self-assembly is invaluable to create well-defined giant structures from small molecular units. Owing to a large entropy loss in the self-assembly process, highly symmetric structures are typically obtained as thermodynamic products while formation of low symmetric assemblies is still challenging. In this study, we report the symmetry-breaking self-assembly of a defined C-symmetric supramolecular structure from an O-symmetric hydrogen-bonded resorcin[4]arene capsule and C-symmetric cationic bis-cyclometalated Ir complexes, carrying sterically demanding tertiary butyl (Bu) groups, on the basis of synergistic effects of weak binding forces.

An asymmetric Pt diimine acetylide complex providing unique luminescent multinuclear sandwich complexes with Cu salts.

The formation and photophysical properties of two types of sandwich complexes supported by asymmetric Pt complex units having two different acetylide moieties are reported. The asymmetric Pt complex unit was obtained acetylide metathesis reaction between two types of symmetric Pt complexes. The reversible acetylide exchange reaction was effectively suppressed by the incorporation of Cu ions to give unique chiral PtCu and achiral PtCuBr sandwich complexes.

Integrative Assembly of Heteroleptic Tetrahedra Controlled by Backbone Steric Bulk.

A bent fluorenone-based dipyridyl ligand L reacts with Pd cations to a solvent-dependent dynamic library of [PdL] assemblies, constituted by a [PdL] ring and a [PdL] tetrahedron as major components, and a [PdL] octahedron as minor component. Introduction of backbone steric hindrance in ligand L allows exclusive formation of the [PdL] octahedron. Combining equimolar amounts of both ligands results in integrative self-sorting to give an unprecedented [PdLL] heteroleptic tetrahedron.

Multinuclear Ag Clusters Sandwiched by Pt Complex Units: Fluxional Behavior and Chiral-at-Cluster Photoluminescence.

Multinuclear Ag clusters sandwiched by Pt complex units were synthesized and characterized by single crystal X-ray diffraction and NMR studies. The sandwich-shaped multinuclear Ag complexes showed two different types of fluxional behavior in solution: rapid slippage of Pt complex units on the Ag core and a reversible demetalation-metalation reaction by the treatment with Cl anion and Ag ion, respectively. The Ag complex obtained by demetalation reaction from the Ag complex displayed U to Z isomerization.

Bridging-arylene effects on spectroscopic and photophysical properties of arylborane-dipyrrinato zinc(ii) complexes.

Novel bis(dipyrrinato)zinc(ii) derivatives having 4-[bis(2,4,6-trimethylphenyl)boryl]phenyl (ZnBph) or 4-[bis(2,4,6-trimethylphenyl)boryl]-2,3,5,6-tetramethylphenyl groups (ZnBdu) at the 5-position of the dipyrrinato ligands were designed and synthesized. In ZnBph with the smaller dipyrrinate-arylene and arylene-dimesitylboryl dihedral angles, an intramolecular charge transfer arising from the presence of the vacant p orbital on the boron atom participates in the ππ* excited state in character in contrast to the pure ππ* excited state of ZnBdu. The synergistic ππ*/ILCT excited state was weakly fluorescent, and the fluorescence was enhanced upon binding of fluoride to the boron atom.

A Heteropolynuclear Pt-Ag System Having Cycloplatinated Rollover Bipyridyl Units.

The synthesis and photophysical properties of the heteropolynuclear Pt-Ag complex having cyclometalated rollover bipyridine ligands (bpy*) and bridging pyrazolato ligands are reported. The PtAg complex was synthesized by two step reactions from a Pt(II) complex precursor having the rollover bpy* ligand, [Pt(bpy*)(dmso)Cl], with 3,5-dimethylpyrazole (MepzH) and a subsequent replacement of NH protons in the MepzH moieties with the Ag(I) ion. The PtAg complex exists as a mixture of U- and Z-shaped isomers in solution, whose structures were clearly determined by single-crystal X-ray structural analyses.

Emissive Supramolecular Systems Based on Reversible Bond Formation and Noncovalent Interactions.

Noncovalent interactions and reversible bond formations are widely seen in natural systems for the construction of sophisticated molecular systems that perform various biological processes. Inspired by the natural systems, luminescent supramolecular systems constructed by coordination-driven self-assembly and homometallic metal-metal interations have been studied increasingly. These supramolecular systems show fascinating luminescent behaviors that are not observed from single components.

Anion-mediated encapsulation-induced emission enhancement of an Ir complex within a resorcin[4]arene hexameric capsule.

Understanding of encapsulation processes in confined inner spaces of self-assembled hosts is important for the rational creation of supramolecular systems showing unusual reactivities and physical properties through molecular recognition. Herein we report the formation of luminescent supramolecular host-guest complexes consisting of a hydrogen-bonded resorcin[4]arene hexameric capsule and a variety of emissive Ir complex salts. The Ir complexes, accompanied by small counter anions (Cl, Br, NO, I and NO), are trapped effectively to show large encapsulation-induced emission enhancement (EIEE) behavior, while Ir complexes having large counter anions (ClO, PF and OTf) are not stabilized within the capsule, suggesting that the Ir complex cation is trapped together with its counter anion to form an ion-pair in the capsule.

Photocatalytic CO Reduction under Visible-Light Irradiation by Ruthenium CNC Pincer Complexes.

Photocatalytic CO reduction using a ruthenium photosensitizer, a sacrificial reagent 1,3-dimethyl-2-(o-hydroxyphenyl)-2,3-dihydro-1H-benzo[d]imidazole (BI(OH)H), and a ruthenium catalyst were carried out. The catalysts contain a pincer ligand, 2,6-bis(alkylimidazol-2-ylidene)pyridine (CNC) and a bipyridine (bpy). The photocatalytic reaction system resulted in HCOOH as a main product (selectivity 70-80 %), with a small amount of CO, and H .

Controlling the Electronic Structures and Excited-State Characteristics of Dipyrrinatoiridium(III) Complexes by an Arylborane or an Arylamino Unit.

Novel dipyrrinatoiridium(III) complexes, in which a typical element substituent (i.e., arylborane or arylamino group) was introduced at the meso position of the 5-phenyldipyrrinato ligand, were designed and synthesized.

Encapsulation condition dependent photophysical properties of polypyridyl Ru(ii) complexes within a hydrogen-bonded capsule.

Controlling the encapsulation equilibrium is a key strategy to affect host-guest associations. Ruthenium(ii) polypyridyl complex salts suspended in a chloroform solution of resorcin[4]arene afforded a host-guest complex which showed structured emission spectra even in the solution state. In contrast, a host-guest complex obtained through homogeneous encapsulation conditions by using soluble ruthenium(ii) polypyridyl complex salts showed broadened emission spectra which strongly depended on the amount of the host owing to the encapsulation equilibrium.

A synthetic NO reduction cycle on a bis(pyrazolato)-bridged dinuclear ruthenium complex including photo-induced transformation.

A synthetic NO reduction cycle (2NO + 2H+ + 2e- → N2O + H2O) on a dinuclear platform {(TpRu)2(μ-pz)2} (Tp = HB(pyrazol-1-yl)3) was achieved, where an unusual N-N coupling complex was included. Moreover, an interesting photo-induced conversion of the N-N coupling complex to an oxido-bridged complex was revealed.

U- to Z-shape isomerization in a PtAg framework containing pyridyl-NHC ligands.

Synthesis and isomerization of a heteropolynuclear Pt2Ag2 complex containing pyridyl N-heterocyclic carbene (NHC) ligands are reported. The Pt2Ag2 complex could take two geometrical isomers possessing a twisted U-shaped structure and a Z-shaped structure. The rate of the isomerization reaction depended on the concentration of the solution, implying that the reaction took place through an intermolecular process.

Nitrite Reduction Cycle on a Dinuclear Ruthenium Complex Producing Ammonia.

The fundamental biogeochemical cycle of nitrogen includes cytochrome c nitrite reductase, which catalyzes the reduction of nitrite ions to ammonium with eight protons and six electrons (NO + 8H + 6e → NH + 2HO). This reaction has motivated researchers to explore the reduction of nitrite. Although a number of electrochemical reductions of NO have been reported, the synthetic nitrite reduction reaction remains limited.

Reversible formation and cleavage of Pt→Ag dative bonds in a pre-organized cavity of a luminescent heteropolynuclear platinum(ii) complex.

A U-shaped PtAg complex [PtAg(ppy)(Phpz)] with a pre-organized cavity (ppy = 2-phenylpridinate and Phpz = 3,5-diphenylpyrazolate) and related complexes have been prepared. The PtAg complexes react with Ag(i) ions to give the corresponding PtAg complexes containing Pt→Ag dative bonds. It became obvious that the existence of the C(ipso) atom in the chelate ligand is important as the driving force for forming Pt→Ag dative bonds.

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 CN-donor ligand L were prepared. Due to the heterobidentate coordination of the achiral chelate ligand, the formed [PtLCl(SEt)], cis- and trans-[PtL] complexes are chiral with the metal serving as the stereo center.

Encapsulation and Enhanced Luminescence Properties of Ir Complexes within a Hexameric Self-Assembled Capsule.

Encapsulation and luminescence studies of [Ir(ppy) (bpy)]Cl (ppy=2-phenylpyridinate, bpy=2,2'-bipyridine) within a hexameric resorcinarene capsule are reported. One Ir complex cation was encapsulated within the capsule, as demonstrated by NMR and dynamic light scattering (DLS) studies. The emission color of the Ir complex was drastically changed from orange to yellow by encapsulation, in contrast with the lack of significant changes in the absorption spectrum.

Different structural preference of Ag(I) and Au(I) in neutral and cationic luminescent heteropolynuclear platinum(II) complexes: Z (U)-shaped Pt2M2 type vs. trinuclear PtM2 type.

The reactions of monocationic Pt(II) complexes bearing N^C chelate ligands and Me2pzH, [Pt(N^C)(Me2pzH)2]PF6 (N^C = 2-phenylpyridinate (ppy(-)), 2-(2,4-difluorophenyl)pyridinate (dfppy(-)), benzo[h]quinolinate (bzq(-)); Me2pzH = 3,5-dimethylpyrazole), with Ag(I) ions gave Z (or U)-shaped neutral tetranuclear Pt2Ag2 complexes [Pt2Ag2(N^C)2(Me2pz)4], while those with Au(I) ions gave neutral trinuclear PtAu2 complexes [PtAu2(N^C)(Me2pz)3]. On the contrary, the reactions of the dicationic Pt(II) complex bearing a N^N chelate ligand and Me2pzH, [Pt(bpy)(Me2pzH)2](PF6)2 (bpy = 2,2'-bipyridine), with Ag(I) and Au(I) ions both gave Z (or U)-shaped dicationic tetranuclear Pt2M2 complexes, [Pt2M2(bpy)2(Me2pz)4](PF6)2 (M = Ag, Au). The structures of heteropolynuclear Pt(II) complexes were dominated by the nature of incorporated group 11 metal ions and the charge of complexes.

Preparation and Luminescent Property of the Self-Assembled Nanoscale Network Systems Combined Tetracyanoplatinate(II) and Copper(II)-Polyaza Complexes.

Complexes 1 and 2 were obtained by the reaction of [Cu(L1)](ClO4)2 (1) or [Cu(L2)](ClO4)2 (2) (L1 = 8-acetyl-1,3,6,8,10,13,15-heptaazatricyclo[13.1.1.

Fixation of atmospheric carbon dioxide by ruthenium complexes bearing an NHC-based pincer ligand: formation of a methylcarbonato complex and its methylation.

A methylcarbonato ruthenium complex was prepared by capture of CO2 from air using the (CNC)(bpy)Ru scaffold. The methylcarbonato complex was relatively inert to decarboxylation. Treatments with methylating reagents released dimethylcarbonate.

Reactivity of a nitrosyl ligand on dinuclear ruthenium hydrotris(pyrazolyl)borato complexes toward a NO molecule.

A cationic mononitrosyl dinuclear ruthenium complex was prepared by removing one NO ligand of a dicationic dinitrosyl ruthenium complex using NaN3. Reduction and oxidation reactions of the mononitrosyl complex led to the isolation of a neutral nitrosyl-bridged complex and a dicationic mononitrosyl complex, respectively, as expected from the cyclic voltammogram. According to the electron count, their reactions with a second NO molecule resulted in an N-N coupling complex from the nitrosyl-bridged complex and the dicationic dinitrosyl complex from the dicationic mononitrosyl complex.