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A series of mononuclear nickel­(II) thiolate complexes (Et₄N)­Ni­(X-pyS)₃ (Et₄N = tetraethylammonium; X = 5-H (<b>1a</b>), 5-Cl (<b>1b</b>), 5-CF₃ (<b>1c</b>), 6-CH₃ (<b>1d</b>); pyS = pyridine-2-thiolate), Ni­(pySH)₄(NO₃)₂ (<b>2</b>), (Et₄N)­Ni­(4,6-Y₂-pymS)₃ (Y = H (<b>3a</b>), CH₃ (<b>3b</b>); pymS = pyrimidine-2-thiolate), and Ni­(4,4′-Z-2,2′-bpy)­(pyS)₂ (Z = H (<b>4a</b>), CH₃ (<b>4b</b>), OCH₃ (<b>4c</b>); bpy = bipyridine) have been synthesized in high yield and characterized. X-ray diffraction studies show that <b>2</b> is square planar, while the other complexes possess tris-chelated distorted-octahedral geometries. All of the complexes are active catalysts for both the photocatalytic and electrocatalytic production of hydrogen in 1/1 EtOH/H₂O. When coupled with fluorescein (Fl) as the photosensitizer (PS) and triethylamine (TEA) as the sacrificial electron donor, these complexes exhibit activity for light-driven hydrogen generation that correlates with ligand electron donor ability. Complex <b>4c</b> achieves over 7300 turnovers of H₂ in 30 h, which is among the highest reported for a molecular noble metal-free system. The initial photochemical step is reductive quenching of Fl* by TEA because of the latter’s greater concentration. When system concentrations are modified so that oxidative quenching of Fl* by catalyst becomes more dominant, system durability increases, with a system lifetime of over 60 h. System variations and cyclic voltammetry experiments are consistent with a CECE mechanism that is common to electrocatalytic and photocatalytic hydrogen production. This mechanism involves initial protonation of the catalyst followed by reduction and then additional protonation and reduction steps to give a key Ni–H^–/N–H⁺ intermediate that forms the H–H bond in the turnover-limiting step of the catalytic cycle. A key to the activity of these catalysts is the reversible dechelation and protonation of the pyridine N atoms, which enable an internal heterocoupling of a metal hydride and an N-bound proton to produce H₂

Luminescence Tribochromism and Bright Emission in Gold(I) Thiouracilate Complexes

New dinuclear Au(I) complexes containing bridging thiouracilate and bis(diphenylphosphino)methane ligands have been synthesized and characterized structurally and spectroscopically. The compounds exhibit a unique behavior of solid-state luminescence tribochromism in which photoemission turns on upon gentle grinding of the sample and a sensitivity to pH in fluid solution. The emissive form in the solid state exhibits a bright blue or cyan emission upon irradiating at 375 nm. Structural studies show that the nonemissive form of the complexes has an extended helical ···Au···Au···Au··· structure in the solid with weak aurophilic interactions, whereas the blue emissive form has a strong intermolecular aurophilic interaction in the solid that leads to an arrangement of dimers of dinuclear (Au2) complexes. Interconversion between the two forms can be carried out by either recrystallization for solid-state samples or by exposure to vapors of volatile acid or base for fluid solutions of the complexes

Tuning the Excited-State Properties of Platinum(II) Diimine Dithiolate Complexes

Two series of Pt(diimine)(dithiolate) complexes have been prepared in order to investigate the effects of molecular design on the excited-state properties of this chromophore. The first series comprises Pt(dbbpy)(dithiolate) complexes where dbbpy = 4,4‘-di-tert-butyl-2,2‘-bipyridine and the dithiolates are 1-(tert-butylcarboxy)-1-cyanoethylene-2,2-dithiolate (tbcda), 1-diethylphosphonate-1-cyanoethylene-2,2-dithiolate (cpdt), 6,7-dimethyl-quinoxaline-2,3-dithiolate (dmqdt), maleonitriledithiolate (mnt), and toluene-3,4-dithiolate (tdt). The second series comprises Pt(diimine)(tdt) complexes where the diimines are 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen), 4,4‘-di-tert-butyl-2,2‘-bipyridine (dbbpy), 4,4‘-dimethyl-2,2‘-bipyridine (dmbpy), 2,2‘-bipyridine (bpy), 1,10-phenanthroline (phen), 5-chloro-1,10-phenanthroline (Cl-phen), 4,4‘-dichloro-2,2‘-bipyridine (Cl2bpy), and 4,4‘-bis(ethoxycarbonyl)-2,2‘-bipyridine (EC-bpy). All of the compounds display solvatochromic absorption bands and solution luminescence, which are attributed to a common charge-transfer-to-diimine excited state. The excited-state energies can be tuned by approximately 1 eV through ligand variation. Solution lifetimes range from 1 ns to over 1000 ns and Φem range from 6.4 × 10-3 to less than 10-5 in CH2Cl2. Based on these data, the nonradiative and radiative decay rate constants have been calculated. For the Pt(diimine)(tdt) series, the nonradiative decay rate constants increase exponentially with decreasing energy, in agreement with the Energy Gap Law, while those for the Pt(dbbpy)(dithiolate) complexes do not exhibit a similar correlation. Excited-state redox potentials have been estimated for all of the complexes from spectroscopic and electrochemical data. The ability to tune the driving force for bimolecular excited-state electron-transfer reactions has been demonstrated for eight of the complexes using reductive and oxidative quenching experiments

Luminescence Tribochromism and Bright Emission in Gold(I) Thiouracilate Complexes

New dinuclear Au(I) complexes containing bridging thiouracilate and bis(diphenylphosphino)methane ligands have been synthesized and characterized structurally and spectroscopically. The compounds exhibit a unique behavior of solid-state luminescence tribochromism in which photoemission turns on upon gentle grinding of the sample and a sensitivity to pH in fluid solution. The emissive form in the solid state exhibits a bright blue or cyan emission upon irradiating at 375 nm. Structural studies show that the nonemissive form of the complexes has an extended helical ···Au···Au···Au··· structure in the solid with weak aurophilic interactions, whereas the blue emissive form has a strong intermolecular aurophilic interaction in the solid that leads to an arrangement of dimers of dinuclear (Au2) complexes. Interconversion between the two forms can be carried out by either recrystallization for solid-state samples or by exposure to vapors of volatile acid or base for fluid solutions of the complexes

One-Hydrogen Polarization in Hydroformylation Promoted by Platinum−Tin and Iridium Carbonyl Complexes: A New Type of Parahydrogen-Induced Effect

The first use of parahydrogen-induced polarization (PHIP) in hydroformylation is described including a novel one-hydrogen polarization (oneH-PHIP) in the product RCHO proton. Observed in propanal formed in the reaction of trans-PtCl(COEt)(PPh3)2 + SnCl2 under parahydrogen, oneH-PHIP was examined using the model hydroformylation catalyst Ir(COEt)(CO)2(dppe) (dppe = bis(diphenylphosphino)ethane) that yields the characterized acyl dihydride IrH2(COEt)(CO)(dppe). It is found that oneH-PHIP occurs as a consequence of second-order effects in the acyl dihydride species coupled with stereospecific reductive elimination of aldehyde. Thus, even though hydrogen transfer to substrate in hydroformylation is nonpairwise, parahydrogen effects prove useful mechanistically

Tuning the Excited-State Properties of Platinum(II) Diimine Dithiolate Complexes

Two series of Pt(diimine)(dithiolate) complexes have been prepared in order to investigate the effects of molecular design on the excited-state properties of this chromophore. The first series comprises Pt(dbbpy)(dithiolate) complexes where dbbpy = 4,4‘-di-tert-butyl-2,2‘-bipyridine and the dithiolates are 1-(tert-butylcarboxy)-1-cyanoethylene-2,2-dithiolate (tbcda), 1-diethylphosphonate-1-cyanoethylene-2,2-dithiolate (cpdt), 6,7-dimethyl-quinoxaline-2,3-dithiolate (dmqdt), maleonitriledithiolate (mnt), and toluene-3,4-dithiolate (tdt). The second series comprises Pt(diimine)(tdt) complexes where the diimines are 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen), 4,4‘-di-tert-butyl-2,2‘-bipyridine (dbbpy), 4,4‘-dimethyl-2,2‘-bipyridine (dmbpy), 2,2‘-bipyridine (bpy), 1,10-phenanthroline (phen), 5-chloro-1,10-phenanthroline (Cl-phen), 4,4‘-dichloro-2,2‘-bipyridine (Cl2bpy), and 4,4‘-bis(ethoxycarbonyl)-2,2‘-bipyridine (EC-bpy). All of the compounds display solvatochromic absorption bands and solution luminescence, which are attributed to a common charge-transfer-to-diimine excited state. The excited-state energies can be tuned by approximately 1 eV through ligand variation. Solution lifetimes range from 1 ns to over 1000 ns and Φem range from 6.4 × 10-3 to less than 10-5 in CH2Cl2. Based on these data, the nonradiative and radiative decay rate constants have been calculated. For the Pt(diimine)(tdt) series, the nonradiative decay rate constants increase exponentially with decreasing energy, in agreement with the Energy Gap Law, while those for the Pt(dbbpy)(dithiolate) complexes do not exhibit a similar correlation. Excited-state redox potentials have been estimated for all of the complexes from spectroscopic and electrochemical data. The ability to tune the driving force for bimolecular excited-state electron-transfer reactions has been demonstrated for eight of the complexes using reductive and oxidative quenching experiments

A Homogeneous System for the Photogeneration of Hydrogen from Water Based on a Platinum(II) Terpyridyl Acetylide Chromophore and a Molecular Cobalt Catalyst

A Homogeneous System for the Photogeneration of Hydrogen from Water Based on a Platinum(II) Terpyridyl Acetylide Chromophore and a Molecular Cobalt Catalys

Excited-State Self-Quenching Reactions of Square Planar Platinum(II) Diimine Complexes in Room-Temperature Fluid Solution

Excited-State Self-Quenching Reactions of Square Planar Platinum(II) Diimine Complexes in Room-Temperature Fluid Solutio

Synthesis and Characterization of (Di-<i>tert</i>-butylbipyridine)bis(pyridine-4-thiolato)platinum(II), Pt(dbbpy)(S-4-py)₂: A Synthon for Supramolecular Systems Containing the Platinum Diimine Bis(Thiolate) Chromophore

Synthesis and Characterization of (Di-tert-butylbipyridine)bis(pyridine-4-thiolato)platinum(II), Pt(dbbpy)(S-4-py)2: A Synthon for Supramolecular Systems Containing the Platinum Diimine Bis(Thiolate) Chromophor

Unsymmetrical 1,4-Diazabutadiene Complexes of Platinum(II)

The new unsymmetrical 1,4-diazabutadiene ligand glyoxal bis(2-(methoxymethyl)-4,6-di-tert-butylphenyl)diimine (L) and its reduced analog (LH4) were synthesized. The reactions of both ligands with bis(benzonitrile) complexes of palladium and platinum, MCl2(PhCN)2, were investigated. Two isomers of formula MCl2L were isolated from the reaction of L with MCl2(PhCN)2 (1a and 1b for Pd, 2a and 2b for Pt), while only a single product, MCl2(LH4), formed in the reaction with LH4 (3 for M = Pd, 4 for M = Pt). All new compounds were characterized by elemental analyses and IR and NMR spectroscopies. The molecular structures for L, LH4, 2b, 3, and 4 were determined by single-crystal X-ray diffraction. The metal complexes exhibit distorted square-planar geometry. The aryl groups of the L and LH4 ligands lie out of the coordination plane in a manner that blocks potential axial ligation sites. Ligand L crystallizes in the triclinic space group P1̄ with a = 5.760(1) Å, b = 9.383(2) Å, c = 14.954(3) Å, α = 89.38(2)°, β = 79.67(2)°, γ = 88.14(2)°, and Z = 1. The reduced ligand LH4 crystallizes in the monoclinic space group P21 with a = 5.9758(1) Å, b = 17.4272(2) Å, c = 15.6222(1) Å, β = 99.063(1)°, and Z = 2. Complex 2b crystallizes in the monoclinic space group P21/c with a = 16.9599(2) Å, b = 18.4985(2) Å, c = 12.4976(0) Å, β = 100.945(0)°, and Z = 4. Complex 3 crystallizes in the monoclinic space group C2/c with a = 36.1506(8) Å, b = 8.0994 (2) Å, c = 15.5671(1) Å, β = 113.988(1)°, and Z = 4. Complex 4 crystallizes in the monoclinic space group C2/c with a = 36.0649(3) Å, b = 8.1787(2) Å, c = 15.7585(3) Å, β = 112.610(1)°, and Z = 4