Revisiting the Preparation and Catalytic Performance of a Phosphine-Modified Co(II) Hydroformylation Precatalyst.

In light of recent conflicting reports regarding the hydroformylation catalytic activity derived from cationic Co(II) precatalysts of the form [Co(acac)(bis(phosphine))]BF, the synthetic procedures and characterization of [Co(acac)(dppBz)]BF, , are evaluated. Leveraging calibrated ESI-TOF MS methodologies, substantial quantities of Co(acac)(dppBz), , were observed within samples of . The source of the impurity, , is determined to derive from incomplete protonolysis of the Co(acac) precursor and ligand scrambling occurring during the synthesis of .

Direct photocatalytic C-H functionalization mediated by a molybdenum dioxo complex.

Direct photocatalytic C-H activation mediated by MoOCl(bpy-Bu), a unique photoactive metal OXO, is presented. The limiting step, reoxidation to the Mo dioxo, is evaluated and proposed to occur a key Cl loss event. Photocatalyst degradation occurs upon substitution of bpy-Bu with HO generated during catalysis.

Catalyst self-assembly accelerates bimetallic light-driven electrocatalytic H evolution in water.

Hydrogen evolution is an important fuel-generating reaction that has been subject to mechanistic debate about the roles of monometallic and bimetallic pathways. The molecular iridium catalysts in this study undergo photoelectrochemical dihydrogen (H) evolution via a bimolecular mechanism, providing an opportunity to understand the factors that promote bimetallic H-H coupling. Covalently tethered diiridium catalysts evolve H from neutral water faster than monometallic catalysts, even at lower overpotential.

The Role of Anionic Ligands on Photoreactivity in Mo(VI) Dioxo Complexes of the Form MoO X (NN).

The photoreactivity of d metal dioxo complexes in activating C-H bonds has been recently studied. We have previously reported that MoO Cl (bpy- Bu) is an effective platform for light initiated C-H activation with unique product selectivity for the overall functionalization. Herein we expand on these studies and report the synthesis and photoreactivity of several new Mo(VI) dioxo complexes with the general formula MoO (X) (NN); where X=F , Cl , Br , CH , PhO , BuO and NN=2,2'-bipyridine (bpy) or 4,4'-tert-butyl-2,2'bipyridine (bpy- Bu).

Light-Initiated C-H Activation via Net Hydrogen Atom Transfer to a Molybdenum(VI) Dioxo.

MoOCl(bpy-Bu) () is shown to be a potent one-electron oxidant upon irradiation with 365 nm light in various solvents, while being a weak two-electron oxidant in the dark. Complex is characterized to activate various types of C-H bonds photochemically, including allylic and benzylic positions as well as alkanes and aldehydes. In all of these oxidations, ultimately forms a bimetallic Mo(V)/Mo(V) species with a μ-oxo ligand ().

"May the Force Be with You!" Force-Volume Mapping with Atomic Force Microscopy.

Information of the chemical, mechanical, and electrical properties of materials can be obtained using force volume mapping (FVM), a measurement mode of scanning probe microscopy (SPM). Protocols have been developed with FVM for a broad range of materials, including polymers, organic films, inorganic materials, and biological samples. Multiple force measurements are acquired with the FVM mode within a defined 3D volume of the sample to map interactions (i.

Mechanistic basis for tuning iridium hydride photochemistry from H evolution to hydride transfer hydrodechlorination.

The photochemistry of metal hydride complexes is dominated by H evolution, limiting access to reductive transformations based on photochemical hydride transfer. In this article, the innate H evolution photochemistry of the iridium hydride complexes [Cp*Ir(bpy-OMe)H] (, bpy-OMe = 4,4'-dimethoxy-2,2'-bipyridine) and [Cp*Ir(bpy)H] (, bpy = 2,2'-bipyridine) is diverted towards photochemical hydrodechlorination. Net hydride transfer from and to dichloromethane produces chloromethane with high selectivity and exceptional photochemical quantum yield ( ≤ 1.

Maximizing the Photocatalytic Activity of Metal-Organic Frameworks with Aminated-Functionalized Linkers: Substoichiometric Effects in MIL-125-NH.

Despite the promise of utilizing metal-organic frameworks (MOFs) as highly tunable photocatalytic materials, systematic studies that interrogate the relationship between their catalytic performances and the amount of functionalized linkers are lacking. Aminated linkers are known to enhance the absorption of light and afford photocatalysis with MOFs under visible-light irradiation. However, the manner in which the photocatalytic performances are impacted by the amount of such linkers is poorly understood.

Molecular polypyridine-based metal complexes as catalysts for the reduction of CO.

Polypyridyl transition metal complexes represent one of the more thoroughly studied classes of molecular catalysts towards CO reduction to date. Initial reports in the 1980s began with an emphasis on 2nd and 3rd row late transition metals, but more recently the focus has shifted towards earlier metals and base metals. Polypyridyl platforms have proven quite versatile and amenable to studying various parameters that govern product distribution for CO reduction.

Efficient Photochemical Dihydrogen Generation Initiated by a Bimetallic Self-Quenching Mechanism.

Artificial photosynthesis relies on coupling light absorption with chemical fuel generation. A mechanistic study of visible light-driven H production from [Cp*Ir(bpy)H] (1) has revealed a new, highly efficient pathway for integrating light absorption with bond formation. The net reaction of 1 with a proton source produces H, but the rate of excited state quenching is surprisingly acid-independent and displays no observable deuterium kinetic isotopic effect.

Thermodynamic Hydricity of Transition Metal Hydrides.

Transition metal hydrides play a critical role in stoichiometric and catalytic transformations. Knowledge of free energies for cleaving metal hydride bonds enables the prediction of chemical reactivity, such as for the bond-forming and bond-breaking events that occur in a catalytic reaction. Thermodynamic hydricity is the free energy required to cleave an M-H bond to generate a hydride ion (H(-)).

A Simple and Non-Destructive Method for Assessing the Incorporation of Bipyridine Dicarboxylates as Linkers within Metal-Organic Frameworks.

As a novel avenue for applications, metal-organic frameworks (MOFs) are increasingly used for heterogenizing catalytic molecular species as linkers into their crystalline framework. These multifunctional compounds can be accessed with mixed linkers synthesis or postsynthetic-exchange strategies. Major limitations still reside in their challenging characterization; in particular, to provide evidence of the genuine incorporation of the functionalized linkers into the framework and their quantification.

Turning it off! Disfavouring hydrogen evolution to enhance selectivity for CO production during homogeneous CO reduction by cobalt-terpyridine complexes.

Understanding the activity and selectivity of molecular catalysts for CO reduction to fuels is an important scientific endeavour in addressing the growing global energy demand. Cobalt-terpyridine compounds have been shown to be catalysts for CO reduction to CO while simultaneously producing H from the requisite proton source. To investigate the parameters governing the competition for H reduction CO reduction, the cobalt bisterpyridine class of compounds is first evaluated as H reduction catalysts.

Photocatalytic carbon dioxide reduction with rhodium-based catalysts in solution and heterogenized within metal-organic frameworks.

The first photosensitization of a rhodium-based catalytic system for CO2 reduction is reported, with formate as the sole carbon-containing product. Formate has wide industrial applications and is seen as valuable within fuel cell technologies as well as an interesting H2 -storage compound. Heterogenization of molecular rhodium catalysts is accomplished via the synthesis, post-synthetic linker exchange, and characterization of a new metal-organic framework (MOF) Cp*Rh@UiO-67.

Versatile functionalization of carbon electrodes with a polypyridine ligand: metallation and electrocatalytic H(+) and CO2 reduction.

A strategy is proposed for immobilization of homogeneous catalysts whereby a glassy carbon electrode is functionalized by electro-grafting of a ligand, terpyridine. The modified electrode can easily be metallated with cobalt and shows activity towards catalytic proton and CO2 reduction. The metal can be removed and the electrode re-metallated at will.

Role of pendant proton relays and proton-coupled electron transfer on the hydrogen evolution reaction by nickel hangman porphyrins.

The hangman motif provides mechanistic insights into the role of pendant proton relays in governing proton-coupled electron transfer (PCET) involved in the hydrogen evolution reaction (HER). We now show improved HER activity of Ni compared with Co hangman porphyrins. Cyclic voltammogram data and simulations, together with computational studies using density functional theory, implicate a shift in electrokinetic zone between Co and Ni hangman porphyrins due to a change in the PCET mechanism.

Terpyridine complexes of first row transition metals and electrochemical reduction of CO₂ to CO.

Homoleptic terpyridine complexes of first row transition metals are evaluated as catalysts for the electrocatalytic reduction of CO2. Ni and Co-based catalytic systems are shown to reduce CO2 to CO under the conditions tested. The Ni complex was found to exhibit selectivity for CO2 over proton reduction while the Co-based system generates mixtures of CO and H2 with CO : H2 ratios being tuneable through variation of the applied potential.

Halogen Photoelimination from Dirhodium Phosphazane Complexes via Chloride-Bridged Intermediates.

Halogen photoelimination is a critical step in HX-splitting photocatalysis. Herein, we report the photoreduction of a pair of valence-isomeric dirhodium phosphazane complexes, and suggest that a common intermediate is accessed in the photochemistry of both mixed-valent and valence-symmetric complexes. The results of these investigations suggest that halogen photoelimination proceeds by two sequential photochemical reactions: ligand dissociation followed by subsequent halogen elimination.

Iron in a trigonal tris(alkoxide) ligand environment.

Mononuclear Fe(II) and Fe(III) complexes residing in a trigonal tris(ditox) (ditox = (t)Bu2(Me)CO(-)) ligand environment have been synthesized and characterized. The Fe(III) ditox complex does not react with oxidants such as PhIO, whereas NMe3O substitutes a coordinated tetrahydrofuran (THF) in the apical position without undergoing oxo transfer. In contrast, the Fe(II) ditox complex reacts rapidly with PhIO or Me3NO in THF or cyclohexadiene to furnish a highly reactive intermediate, which cleaves C-H bonds to afford the Fe(III)-hydroxide complex.

Cobalt in a bis-β-diketiminate environment.

The reaction of Co(2)(mesityl)(4) with acetonitrile leads to the formation of a planar, low spin, bis-β-diketiminate cobalt(II) complex, (1-mesitylbutane-1,3-diimine)(2)Co (1). EPR spectroscopy, magnetic studies, and DFT calculations reveal the Co(II) ion to reside in a tetragonal ligand field with a (2)B(2)(d(yz))(1) ground state electronic configuration. Oxidation of 1 with ferrocenium hexafluorophosphate furnishes (1-mesitylbutane-1,3-diimine)(2)Co(THF)(2)PF(6) (2).

Stability-enhanced hydrogen-evolving dirhodium photocatalysts through ligand modification.

The two-electron mixed-valent complex Rh(2)(0,II)(tfepma)(2)(CN(t)Bu)(2)Cl(2) (tfepma = CH(3)N[P(OCH(2)CF(3))(2)](2)) photocatalytically splits HCl to generate H(2). Whereas this catalyst degrades rapidly, with H(2) production ceasing after about 36 hours (3 turnovers), a modified complex, Rh(2)(0,II)(tfepma)(2)(CNAd)(2)Cl(2) (CNAd = 1-adamantylisocyanide) displays enhanced stability with sustained H(2) production continuing for >144 h (7 turnovers).