Evaluating the impacts of amino acids in the second and outer coordination spheres of Rh-bis(diphosphine) complexes for CO2 hydrogenation.

To explore the influence of a biologically inspired second and outer coordination sphere on Rh-bis(diphosphine) CO2 hydrogenation catalysts, a series of five complexes were prepared by varying the substituents on the pendant amine in the P(Et)2CH2NRCH2P(Et)2 ligands (PEtNRPEt), where R consists of methyl ester modified amino acids, including three neutral (glycine methyl ester (GlyOMe), leucine methyl ester (LeuOMe), and phenylalanine methyl ester (PheOMe)), one acidic (aspartic acid dimethyl ester (AspOMe)) and one basic (histidine methyl ester (MeHisOMe)) amino acid esters. The turnover frequencies (TOFs) for CO2 hydrogenation for each of these complexes were compared to those of the non-amino acid containing [Rh(depp)2]+ (depp) and [Rh(PEtNMePEt)2]+ (NMe) complexes. Each complex is catalytically active for CO2 hydrogenation to formate under mild conditions in THF. Catalytic activity spanned a factor of four, with the most active species being the NMe catalyst, while the slowest were the GlyOMe and the AspOMe complexes. When compared to a similar set of catalysts with phenyl-substituted phosphorous groups, a clear contribution of the outer coordination sphere is seen for this family of CO2 hydrogenation catalysts.

Crystal structures of a manganese(I) and a rhenium(I) complex of a bi-pyridine ligand with a non-coordinating benzoic acid moiety.

The structures of two facially coordinated Group VII metal complexes are reported, namely: fac-bromido-[2-(2,2'-bipyridin-6-yl)benzoic acid-κ2N,N']tricarbonyl-manganese(I) tetra-hydro-furan monosolvate, [MnBr(C17H12N2O2)(CO)3]·C4H8O, I, and fac-[2-(2,2'-bipyridin-6-yl)benzoic acid-κ2N,N']tricarbonyl-chlorido-rhenium(I) tetra-hydro-furan monosolvate, [ReCl(C17H12N2O2)(CO)3]·C4H8O, II. In both complexes, the metal ion is coordinated by three carbonyl ligands, a halide ion, and a 2-(2,2'-bipyridin-6-yl)benzoic acid ligand, in a distorted octa-hedral geometry. In manganese complex I, the tetra-hydro-furan (THF) solvent mol-ecule could not be refined due to disorder. The benzoic acid fragment is also disordered over two positions, such that the carb-oxy-lic acid group is either positioned near to the bromide ligand or to the axial carbonyl ligand. In the crystal of I, the complex mol-ecules are linked by a pair of C-H⋯Br hydrogen bonds, forming inversion dimers that stack up the a-axis direction. In the rhenium complex II, there is hydrogen bonding between the benzoic acid moiety and a disordered co-crystallized THF mol-ecule. In the crystal, the mol-ecules are linked by C-H⋯Cl hydrogen bonds, forming layers parallel to (100) separated by layers of THF solvent mol-ecules.

Crystal structures of fac-tri-carbonyl-chlorido-(6,6'-dihy-droxy-2,2'-bi-pyridine)-rhenium(I) tetra-hydro-furan monosolvate and fac-bromido-tricarbon-yl(6,6'-dihy-droxy-2,2'-bi-pyridine)-manganese(I) tetra-hydro-furan monosolvate.

The structures of two facially coordinated Group VII metal complexes, fac-[ReCl(C10H8N2O2)(CO)3]·C4H8O (I·THF) and fac-[MnBr(C10H8N2O2)(CO)3]·C4H8O (II·THF), are reported. In both complexes, the metal ion is coordinated by three carbonyl ligands, a halide ligand, and a 6,6'-dihy-droxy-2,2'-bi-pyridine ligand in a distorted octa-hedral geometry. Both complexes co-crystallize with a non-coordinating tetra-hydro-furan (THF) solvent mol-ecule and exhibit inter-molecular but not intra-molecular hydrogen bonding. In both crystal structures, chains of complexes are formed due to inter-molecular hydrogen bonding between a hy-droxy group from the 6,6'-dihy-droxy-2,2'-bi-pyridine ligand and the halide ligand from a neighboring complex. The THF mol-ecule is hydrogen bonded to the remaining hy-droxy group.

Covalent attachment of diphosphine ligands to glassy carbon electrodes via Cu-catalyzed alkyne-azide cycloaddition. Metallation with Ni(II).

Covalent tethering of P(Ph)2N(C6H4C≡CH)2 ligands (P(Ph)2N(C6H4C≡CH)2 = 1,5-di-(4-ethynylphenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) to planar, azide-terminated glassy carbon electrode surfaces has been accomplished using a Cu(I)-catalyzed alkyne-azide cycloaddition (CuAAC) coupling reaction, using a BH3←P protection-deprotection strategy. Deprotected, surface-confined ligands were metallated using [Ni(II)(MeCN)6](BF4)2. X-ray photoelectron spectroscopic measurements demonstrate that metallation introduced 1.3 equivalents Ni(II) per diphosphine onto the electrode surface. Exposure of the surface to a second diphosphine ligand, P(Ph)2N(Ph)2, resulted in the removal of Ni from the surface. Protection, coupling, deprotection, and metallation conditions were optimized using solution-phase model systems, with benzyl azide as a model for the azide-terminated carbon surface; these reactions generate a [Ni(II)(diphosphine)2](2+) complex.

Enzyme design from the bottom up: an active nickel electrocatalyst with a structured peptide outer coordination sphere.

Catalytic, peptide-containing metal complexes with a well-defined peptide structure have the potential to enhance molecular catalysts through an enzyme-like outer coordination sphere. Here, we report the synthesis and characterization of an active, peptide-based metal complex built upon the well-characterized hydrogen production catalyst [Ni(P(Ph)2N(Ph))2](2+) (P(Ph)2N(Ph)=1,3,6-triphenyl-1-aza-3,6-diphosphacycloheptane). The incorporated peptide maintains its ß-hairpin structure when appended to the metal core, and the electrocatalytic activity of the peptide-based metal complex (≈100,000 s(-1)) is enhanced compared to the parent complex ([Ni(P(Ph)2N(APPA))2](2+); ≈50,500 s(-1)). The combination of an active molecular catalyst with a structured peptide provides a scaffold that permits the incorporation of features of an enzyme-like outer-coordination sphere necessary to create molecular electrocatalysts with enhanced functionality.

A proton channel allows a hydrogen oxidation catalyst to operate at a moderate overpotential with water acting as a base.

We report the incorporation of a simple enzyme-inspired proton channel onto a hydrogen oxidation catalyst. This modification facilitates proton transfer and lowers the overpotential for oxidation of H2 by 300 mV when using water as a base.

Minimal proton channel enables H2 oxidation and production with a water-soluble nickel-based catalyst.

Hydrogenase enzymes use first-row transition metals to interconvert H2 with protons and electrons, reactions that are important for the storage and recovery of energy from intermittent sources such as solar, hydroelectric, and wind. Here we present Ni(P(Cy)2N(Gly)2)2, a water-soluble molecular electrocatalyst with the amino acid glycine built into the diphosphine ligand framework. Proton transfer between the outer coordination sphere carboxylates and the second coordination sphere pendant amines is rapid, as observed by cyclic voltammetry and FTIR spectroscopy, indicating that the carboxylate groups may participate in proton transfer during catalysis. This complex oxidizes H2 (1-33 s(-1)) at low overpotentials (150-365 mV) over a range of pH values (0.1-9.0) and produces H2 under identical solution conditions (>2400 s(-1) at pH 0.5). Enzymes employ proton channels for the controlled movement of protons over long distances-the results presented here demonstrate the effects of a simple two-component proton channel in a synthetic molecular electrocatalyst.

Water oxidation catalyzed by a new tetracobalt-substituted polyoxometalate complex: [{Co4(µ-OH)(H2O)3}(Si2W19O70)]11-.

A new polyoxometalate of earth adundant elements [{Co(4)(µ-OH)(H(2)O)(3)}(Si(2)W(19)O(70))](11-) has been synthesized, characterized and shown to be a water oxidation catalyst. The initial catalytic complex is unstable and slowly undergoes hydrolysis. The hydrolysis products have been isolated and characterized, and their catalytic water oxidation activity is assessed.

Incorporating peptides in the outer-coordination sphere of bioinspired electrocatalysts for hydrogen production.

Four new cyclic 1,5-diaza-3,7-diphosphacyclooctane ligands have been prepared and used to synthesize [Ni(P(Ph)(2)N(R)(2))(2)](2+) complexes in which R is a mono- or dipeptide. These complexes represent a first step in the development of an outer-coordination sphere for this class of complexes that can mimic the outer-coordination sphere of the active sites of hydrogenase enzymes. Importantly, these complexes retain the electrocatalytic activity of the parent [Ni(P(Ph)(2)N(Ph)(2))(2)](2+) complex in an acetonitrile solution with turnover frequencies for hydrogen production ranging from 14 to 25 s(-1) in the presence of p-cyanoanilinium trifluoromethanesulfonate and from 135 to 1000 s(-1) in the presence of protonated dimethylformamide, with moderately low overpotentials, ∼0.3 V. The addition of small amounts of water results in rate increases of 2-7 times. Unlike the parent complex, these complexes demonstrate dynamic structural transformations in solution. These results establish a building block from which larger peptide scaffolding can be added to allow the [Ni(P(R)(2)N(R')(2))(2)](2+) molecular catalytic core to begin to mimic the multifunctional outer-coordination sphere of enzymes.

Catalytic dioxygen activation by Co(II) complexes employing a coordinatively versatile ligand scaffold.

The ligand bis(2-isobutyrylamidophenyl)amine has been prepared and used to stabilize both mononuclear and dinuclear cobalt(II) complexes. The nuclearity of the cobalt product is regulated by the deprotonation state of the ligand. Both complexes catalytically oxidize triphenylphosphine to triphenylphosphine oxide in the presence of O(2).

A new family of sandwich-type polytungstophosphates containing two types of metals in the central belt: M'2M2(PW9O34)(2)(12-) (M' = Na or Li, M = Mn2+, Co2+, Ni2+, and Zn2+).

A new family of sandwich-type polytungstophosphates containing two different types of metals in the central belt, M'(2)M(2)(PW(9)O(34))(2)(12-) (M' = Na or Li, M = Mn(2+), Co(2+), Ni(2+), and Zn(2+)), have been synthesized and characterized by infrared spectroscopy, (31)P solution NMR spectroscopy, and elemental analysis. Compounds Na(2)Co(2)(PW(9)O(34))(2)(12-) (Na2Co2), Na(2)Ni(2)(PW(9)O(34))(2)(12-) (Na2Ni2), Li(2)Ni(2)(PW(9)O(34))(2)(12-) (Li2Ni2), Na(2)Mn(2)(PW(9)O(34))(2)(12-) (Na2Mn2), and Li(2)Zn(2)(PW(9)O(34))(2)(12-) (Li2Zn2) were characterized by X-ray crystallography. All these compounds have similar structures, in which two transition-metal ions and two alkali metal ions (sodium or lithium) are sandwiched between two [B-alpha-PW(9)O(34)](9-) units; the transition and alkali metals reside in the internal and external (solvent exposed) positions of the central belt, respectively. By adding LiCl to aqueous solutions of compounds Na2M2, lithium-sodium exchanges in the external belt positions are observed by (31)P solution NMR spectroscopy and X-ray crystallography. Magnetic measurements indicate ferromagnetic exchange interactions between the two Ni(2+) ions in Na2Ni2 at 10-300 K and the two Co(2+) ions in Na2Co2 at 6-30 K. In contrast, Na2Mn2 exhibits an antiferromagnetic interaction between the Mn(2+) ions at 2-50 K.

Cs(9)[(gamma-PW(10)O(36))(2)Ru(4)O(5)(OH)(H(2)O)(4)], a new all-inorganic, soluble catalyst for the efficient visible-light-driven oxidation of water.

The tetraruthenium-substituted polyoxometalate Cs(9)[(gamma-PW(10)O(36))(2)Ru(4)O(5)(OH)(H(2)O)(4)] was synthesized and structurally, spectroscopically and electrochemically characterized; it was shown to be a catalyst for visible-light-induced water oxidation.

Biomimetic syntheses from squalene-like precursors: synthesis of ent-abudinol B and reassessment of the structure of muzitone.

We achieved the stereoselective syntheses of two different structural patterns corresponding to the enantiomers of the marine natural products abudinol B and muzitone, by developing two-directional tandem biomimetic cyclizations of polyepoxides of squalene analogues in which one alkene was functionalized as an enolsilane. In the course of this work, we demonstrated that the structure of muzitone was misassigned.

3-Chloro-6-{4-[3-(trifluoro-meth-yl)phen-yl]piperazin-1-yl}pyridazine.

The title compound, C(15)H(14)ClF(3)N(4), was synthesized from 3,6-dichloro-pyridazine and 1-[3-(trifluoro-meth-yl)phen-yl]piper-azine. The piperazine ring is flanked by 3-chloro-pyridazine and 3-trifluoro-methyl-phenyl rings and adopts a chair conformation, whereas the 3-chloro-pyridazine and 3-trifluoro-methyl-phenyl rings are planar, with maximum deviations of 0.0069 (13) and 0.0133 (14) Å, respectively. The crystal structure is stabilized by weak inter-molecular C-H⋯N hydrogen-bond inter-actions.

Effect of methylene spacers on the spectral, electrochemical, and structural properties of bis(4,4'-disubstituted-2,2'-bipyridyl) ruthenium(II) dye analogues.

Two new ruthenium complexes, [Ru(L1OMe)2(NCS)2] and [Ru(L2OMe)2(NCS)2] (where L1OMe = 2,2'-bipyridine-4,4'-di(methyl ethanoate) and L2OMe = 2,2'-bipyridine-4,4'-di(methyl propionate)), have been synthesized and characterized using spectroscopic and electrochemical techniques. The [Ru(L2OMe)2(NCS)2] complex has also been characterized by X-ray diffraction studies and reveals a distorted octahedral coordination geometry about the ruthenium center. Cyclic voltammetry studies of both complexes exhibit quasi-reversible Ru(II/III) couples and a number of ligand reduction events. The complex with one methylene spacer between the bipyridyl ligand and the methyl ester functional group, [Ru(L1OMe)2(NCS)2], was particularly unstable under reducing conditions. The properties of these complexes are compared with the ethyl ester analogue of the N3 photosensitizer [Ru(L0OEt)2(NCS)2].

3-Chloro-6-[4-(2-pyrid-yl)piperazin-1-yl]pyridazine.

In the title compound, C(13)H(14)ClN(5), the piperazine ring adopts a chair conformation and the dihedral angle between the aromatic rings is 13.91 (7)°. The crystal structure is stabilized by weak inter-molecular C-H⋯N hydrogen-bond inter-actions.