Because of the continually rising levels CO2 in atmosphere, research for conversion into fuels using carbon-neutral energy is an important and current topic catalysis. Recent on molecular catalysts has led to improved rates formate, but are based precious metals such as iridium, ruthenium rhodium require high temperatures pressures. Using established thermodynamic properties hydricity (ΔGH(-)) acidity (pKa), we designed a cobalt-based catalyst system production formate from H2. The complex...

The complex Co(dmpe)2H catalyzes the hydrogenation of CO2 at 1 atm and 21 °C with significant improvement in turnover frequency relative to previously reported second- third-row transition-metal complexes. New studies are presented elucidate catalytic mechanism as well pathways for catalyst deactivation. rate was optimized through choice base match pKa [Co(dmpe)2(H)2]+ intermediate. With a strong enough base, has zeroth-order dependence on concentration pressure hydrogen first-order CO2....

We report the first discrete molecular Cr-based catalysts for reduction of N2. This study is focused on reactivity Cr-N2 complex, trans-[Cr(N2)2(PPh4NBn4)] (P4Cr(N2)2), bearing a 16-membered tetraphosphine macrocycle. The architecture [16]-PPh4NBn4 ligand critical to preserve structural integrity catalyst. P4Cr(N2)2 was found mediate N2 at room temperature and 1 atm pressure by three complementary reaction pathways: (1) Cr-catalyzed N(SiMe3)3 Na Me3SiCl, affording up 34 equiv N(SiMe3)3; (2)...

This study examines the use of transition-metal hydride complexes that can be generated by heterolytic cleavage H(2) gas to form B-H bonds. Specifically, these studies are focused on providing a reliable and quantitative method for determining when transfer from hydrides three-coordinate BX(3) (X = OR, SPh, F, H; R Ph, p-C(6)H(4)OMe, C(6)F(5), (t)Bu, Si(Me)(3)) compounds will favorable. involves both experimental theoretical determinations abilities. Thermodynamic donor abilities...

We report a rare example of Cr-N2 complex supported by 16-membered phosphorus macrocycle containing pendant amine bases. Reactivity with acid afforded hydrazinium and ammonium, representing the first N2 reduction complex. Computational analysis examined thermodynamically favored protonation steps Cr leading to formation hydrazine.

The geometric constraints imposed by a tetradentate P4N2 ligand play an essential role in stabilizing square planar Fe complexes with changes metal oxidation state. pyramidal Fe0(N2)(P4N2) complex catalyzes the conversion of N2 to N(SiR3)3 (R = Me, Et) at room temperature, representing highest turnover number any Fe-based silylation catalyst date (up 65 equiv N(SiMe3)3 per center). Elevated pressures (>1 atm) have dramatic effect on catalysis, increasing solubility and thermodynamic binding...

Catalysts for the oxidation of NH3 are critical utilization as a large-scale energy carrier. Molecular catalysts capable oxidizing to N2 rare. This report describes use [Cp*Ru(PtBu2 NPh2 )(15 )][BArF4 ], (PtBu2 =1,5-di(phenylaza)-3,7-di(tert-butylphospha)cyclooctane; ArF =3,5-(CF3 )2 C6 H3 ), catalytically oxidize dinitrogen under ambient conditions. The cleavage six N-H bonds and formation an N≡N bond was achieved by coupling H+ e- transfers net hydrogen atom abstraction (HAA) steps using...

We report ammonia oxidation by homolytic cleavage of all three H atoms from a [Mo-NH3]+ complex using the 2,4,6-tri-tert-butylphenoxyl radical to yield Mo-alkylimido ([Mo═NR]+) (R = 2,4,6-tri-tert-butylcyclohexa-2,5-dien-1-one). Chemical reduction [Mo═NR]+ generates terminal Mo≡N nitride upon N-C bond cleavage, and [Mo═NH]+ is formed protonation nitride. Computational analysis describes energetic profile for stepwise removal formation [Mo═NR]+.

Abstract Energy storage and conversion schemes based on environmentally benign chemical fuels will require the discovery of faster, cheaper, more robust catalysts for oxygen‐evolution reaction (OER). Although incorporation pendant bases into molecular hydrogen production utilization has led to enhanced turnover frequencies, analogous water oxidation received little attention. Herein, syntheses, structures, catalytic activities new iron complexes with are reported. Of these complexes, [Fe( L...

Catalysts that are able to reduce carbon dioxide under mild conditions highly sought after for storage of renewable energy in the form a chemical fuel. This study describes systematic kinetic and thermodynamic series cobalt rhodium bis(diphosphine) complexes capable hydrogenating formate ambient temperature pressure. Catalytic CO2 hydrogenation was studied 1.8 20 atm pressure (1:1 CO2/H2) at room tetrahydrofuran with turnover frequencies (TOF) ranging from 74 000 h–1. The catalysis followed...

Abstract The molecular complexes described herein use main‐group elements or transition metals to control the stoichiometric cleavage of N−H bonds ammonia (NH 3 ) and/or catalyze chemical and electrochemical NH oxidation dinitrogen (N 2 ). We highlight phenomenon coordination‐induced bond weakening a variety mechanisms including H atom abstraction, inter‐ intra‐molecular deprotonation reactions, oxidative addition, σ ‐bond metathesis that have been demonstrated with systems. provide an...

Cis and trans-Cr–N2 complexes supported by the diphosphine ligand PPh2NBn2 have been prepared. Positioned pendant amines in second coordination sphere influence thermodynamically preferred geometric isomer. Electronic structure calculations indicate negligible Cr–N2 back-bonding; rather, electronic polarization of N2 is thought to stabilize binding.

Hydrides of numerous transition metal complexes can be generated by the heterolytic cleavage H2 gas such that they offer alternatives to using main group hydrides in regeneration ammonia borane, a compound has been intensely studied for hydrogen storage applications. Previously, we reported HRh(dmpe)2 (dmpe = 1,2-bis(dimethylphosphinoethane)) was capable reducing variety BX3 compounds having hydride affinity (HA) greater than or equal HA BEt3. This study examines reactivity less expensive...

The study of metal‐dinitrogen complexes has lent valuable insight into the nature dinitrogen (N 2 ) reduction to ammonia (NH 3 ), known as “nitrogen fixation.” Even so, understanding this difficult transformation continues be an elusive goal for chemists. N chemistry chromium (Cr) is exceptional its diversity, rarity, and richness depth. Hans Karsch opined in 1977 that “ Almost all transition metals are form with molecular nitrogen, but case some ‐ notably examples few far between .”...

Abstract We report a nickel complex for catalytic oxidation of ammonia to dinitrogen under ambient conditions. Using the aryloxyl radical 2,4,6‐tri‐ tert ‐butylphenoxyl ( t Bu 3 ArO⋅) as H atom acceptor cleave N−H bond coordinated NH ligand up 56 equiv N 2 per Ni center can be generated. Employing ‐oxyl 2,2,6,6‐(tetramethylpiperidin‐1‐yl)oxyl (TEMPO⋅) H‐atom acceptor, 15 are formed. A bridging Ni‐hydrazine product identified by isotopic nitrogen N) studies and supported computational models...

A series of low-coordinate, paramagnetic iron complexes in a tris(thioether) ligand environment have been prepared. Reduction ferrous {[PhTttBu]FeCl}2 [1; PhTttBu = phenyltris((tert-butylthio)methyl)borate] with KC8 the presence PR3 (R Me or Et) yields high-spin, monovalent phosphine [PhTttBu]Fe(PR3) (2). These provide entry into other low-valent derivatives via substitution. Carbonylation led to smooth formation low-spin dicarbonyl [PhTttBu]Fe(CO)2 (3). Alternatively, replacement...

The reduction of fac-[CrCl3(PPh3NBn3)], (1(Cl3)), (PPh3NBn3 = 1,5,9-tribenzyl-3,7,11-triphenyl-1,5,9-triaza-3,7,11-triphosphacyclododecane) with Mg in the presence dmpe (dmpe 1,2-bis(dimethylphosphino)ethane) affords first example a monodinitrogen Cr0 complex, Cr(N2)(dmpe)(PPh3NBn3), (2(N2)), containing pentaphosphine coordination environment. 2(N2) is supported by unique facially coordinating 12-membered phosphorus macrocycle pendant amine groups second sphere. Treatment at −78 °C 1 equiv...

Here we describe maturation of the [FeFe]-hydrogenase from its [4Fe-4S]-bound precursor state by using synthetic complex [Fe2(μ-SH)2(CN)2(CO)4]2- together with HydF and components glycine cleavage system, but in absence maturases HydE HydG. This semisynthetic fully-defined provides new insights into nature H-cluster biosynthesis.

Cr(N 2 ) (diphosphine) complexes catalyze the reduction of dinitrogen at room temperature using SmI and ethylene glycol or H O to form hydrazine ammonia.

Molybdenum and tungsten bis(dinitrogen) complexes of the formula M(N2)2(PNP)2 (M = Mo W) W(N2)2(dppe)(PNP), supported by diphosphine ligands containing a pendant amine (CH2PR2)2NR′ PRNR′PR (R Et, Ph; R′ Me, Bn), have been prepared Mg reduction metal halides under an N2 atmosphere. The characterized NMR IR spectroscopy, X-ray crystallography, cyclic voltammetry. Reactivity target W compounds with CO results in formation dicarbonyl complexes.

Treatment of trans-[W(N2)2(dppe)(PEtNMePEt)] (dppe = Ph2PCH2CH2PPh2; PEtNMePEt Et2PCH2N(Me)CH2PEt2) with 3 equiv tetrafluoroboric acid (HBF4·Et2O) at −78 °C generated the seven-coordinate tungsten hydride trans-[W(N2)2(H)(dppe)(PEtNMePEt)][BF4]. At higher temperatures, protonation a pendant amine is also observed, affording trans-[W(N2)2(H)(dppe)(PEtNMe(H)PEt)][BF4]2, formation hydrazido complex [W(NNH2)(dppe)(PEtNMe(H)PEt)][BF4]2 as minor product. A similar product mixture was obtained...

The first complete structurally and spectroscopically characterized series of isostructural Group 6 N2 complexes is reported. Protonolysis experiments on cis-[M(N2)2(P(Et)N(R)P(Et))2] (M = Cr, Mo, W; R 2,6-difluorobenzyl) reveal that only Cr affords N2H5(+) NH4(+) from the reduction ligands.

While diamagnetic transition metal complexes that bind and split H2 have been extensively studied, paramagnetic exhibit this behavior remain rare. The square planar S = 1/2 FeI(P4N2)+ cation (FeI+) reversibly binds H2/D2 in solution, exhibiting an inverse equilibrium isotope effect of KH2/ KD2 0.58(4) at -5.0 °C. In the presence excess H2, dihydrogen complex FeI(H2)+ cleaves 25 °C a net hydrogen atom transfer reaction, producing dihydrogen-hydride trans-FeII(H)(H2)+. proposed mechanism...

The addition of acids to ferrous dinitrogen complexes [FeX(N2)(P(Et)N(Me)P(Et))(dmpm)](+) (X = H, Cl, or Br; P(Et)N(Me)P(Et) Et2PCH2N(Me)CH2PEt2; and dmpm Me2PCH2PMe2) gives protonation at the pendent amine diphosphine ligand rather than ligand. This increased νN2 band complex by 25 cm(-1) shifted Fe(II/I) couple 0.33 V a more positive potential. A similar IR shift slightly smaller (0.23 V) was observed for related carbonyl [FeH(CO)(P(Et)N(Me)P(Et))(dmpm)](+). [FeH(P(Et)N(Me)P(Et))(dmpm)](+)...