Proton-Responsive Ligands Promote CO Capture and Accelerate Catalytic CO/HCO Interconversion.

The synthesis and investigation of [Rh(DHMPE)][BF] () are reported. features proton-responsive 1,2-bis[(dihydroxymethyl)phosphino]ethane (DHMPE) ligands, which readily capture CO from atmospheric sources upon deprotonation. The protonation state of the DHMPE ligand was observed to have a significant impact on the catalytic reactivity of with CO.

Silicon Nitride Surface Enabled Propane Dehydrogenation Catalyzed by Supported Organozirconium.

Mesoporous silicon nitride (SiN) is a nontraditional support for the chemisorption of organometallic complexes with the potential for enhancing catalytic activity through features such as the increased Lewis basicity of nitrogen for heterolytic bond activation, increased ligand donor strength, and metal-ligand orbital overlap. Here, tetrabenzyl zirconium (ZrBn) was chemisorbed on SiN, and the resulting supported organometallic species was characterized by Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), Dynamic Nuclear Polarization-enhanced Solid State Nuclear Magnetic Resonance (DNP-SSNMR), and X-ray Absorption Spectroscopy (XAS). Based on the hypothesis that the nitride might enable facile heterolytic C-H bond activation along the Zr-N bond, this material was found to be a highly active (1.

Oxidative Grafting for Catalyst Synthesis in Surface Organometallic Chemistry.

The development of new methods of catalyst synthesis with the potential to generate active site structures orthogonal to those accessible by traditional protocols is of great importance for discovering new materials for addressing challenges in the evolving energy and chemical economy. In this work, the generality of oxidative grafting of organometallic and well-defined molecular metal precursors onto redox-active surfaces such as manganese dioxide (MnO) and lithium manganese oxide (LiMnO) is investigated. Nine molecular metal precursors are explored, spanning groups 4-11 and each of the three periods of the transition metal series.

Homogeneous MOF-supported catalysis: a direct comparison of catalytic hydroboration with Ni tripodal PE (E = Si, Ge) complexes.

The MOF material NU-1000 was employed to host Ni tripodal complexes prepared from new organometallic precursors [HNi((,,,)-E(-CHCHPPh)], E = Si (Ni-1), Ge (Ni-2). The new heterogeneous catalytic materials, Ni-1@NU-1000 and Ni-2@NU-1000, show the advantages of both homogeneous and heterogeneous catalysts. They catalyze the hydroboration of aldehydes and ketones more efficiently than the homogeneous Ni-1 and Ni-2, under aerobic conditions and show recyclability.

Structural and reactive evolution of oxidatively grafted Pd catalysts on MnO for the low-temperature oxidation of CO.

Isolated Pd atoms supported on high surface area MnO, prepared by the oxidative grafting of (bis(tricyclohexylphosphine-palladium(0)), catalyze (>50 turnovers, 17 h) the low temperature (≤325 K) oxidation of CO (7.7 kPa O, 2.6 kPa CO) with results of / and spectroscopic characterization signifying a synergistic role of Pd and MnO in facilitating redox turnovers.

Silica Supported Organometallic Ir Complexes Enable Efficient Catalytic Methane Borylation.

Catalytic C-H borylation is an attractive method for the conversion of the most abundant hydrocarbon, methane (CH), to a mild nucleophilic building block. However, existing CH borylation catalysts often suffer from low turnover numbers and conversions, which is hypothesized to result from inactive metal hydride agglomerates. Herein we report that the heterogenization of a bisphosphine molecular precatalyst, [(dmpe)Ir(cod)CH], onto amorphous silica dramatically enhances its performance, yielding a catalyst that is 12-times more efficient than the current standard for CH borylation.

Sulfated Zirconium Metal-Organic Frameworks as Well-Defined Supports for Enhancing Organometallic Catalysis.

Understanding heterogeneous catalysts is a challenging pursuit due to surface site nonuniformity and aperiodicity in traditionally used materials. One example is sulfated metal oxides, which function as highly active catalysts and as supports for organometallic complexes. These applications are due to traits such as acidity, ability to act as a weakly coordinating ligand, and aptitude for promoting transformations via radical cation intermediates.

Phosphorus-Atom Transfer from Phosphaethynolate to an Alkylidyne.

A low-spin and mononuclear vanadium complex, ( nacnac)V(CO)(η -P≡C Bu) (2) ( nacnac =[ArNC(CH )] CH, Ar=2,6- Pr C H ), was prepared upon treatment of the vanadium neopentylidyne complex ( nacnac)V≡C Bu(OTf) (1) with Na(OCP)(diox) (diox=1,4-dioxane), while the isoelectronic ate-complex [Na(15-crown-5)]{([ArNC(CH )]CH[C(CH )NAr])V(CO)(η -P≡C Bu)} (4), was obtained via the reaction of Na(OCP)(diox) and ([ArNC(CH )]CH[C(CH )NAr])V≡C Bu(OEt ) (3) in the presence of crown-ether. Computational studies suggest that the P-atom transfer proceeds by [2+2]-cycloaddition of the P≡C bond across the V≡C Bu moiety, followed by a reductive decarbonylation to form the V-C≡O linkage. The nature of the electronic ground state in diamagnetic complexes, 2 and 4, was further investigated both theoretically and experimentally, using a combination of density functional theory (DFT) calculations, UV/Vis and NMR spectroscopies, cyclic voltammetry, X-ray absorption spectroscopy (XAS) measurements, and comparison of salient bond metrics derived from X-ray single-crystal structural characterization.

Surface immobilized copper(I) diimine photosensitizers as molecular probes for elucidating the effects of confinement at interfaces for solar energy conversion.

Heteroleptic copper(i) bis(phenanthroline) complexes with surface anchoring carboxylate groups have been synthesized and immobilized on nanoporous metal oxide substrates. The species investigated are responsive to the external environment and this work provides a new strategy to control charge transfer processes for efficient solar energy conversion.

Functionalized NU-1000 with an Iridium Organometallic Fragment: SO Capture Enhancement.

A new material, MOF-type [Ir]@NU-1000, was accessed from the incorporation of the iridium organometallic fragment [Ir{κ(P,Si,Si)PhP(-CHCHSiPr)}] into NU-1000. The new material incorporates less than 1 wt % of Ir(III) (molar ratio Ir to NU-1000, 1:11), but the heat of adsorption for SO is significantly enhanced with respect to that of NU-1000. Being a highly promising adsorbent for SO capture, [Ir]@NU-1000 combines exceptional SO uptake at room temperature and outstanding cyclability.

Electrophilic Organoiridium(III) Pincer Complexes on Sulfated Zirconia for Hydrocarbon Activation and Functionalization.

Single-site supported organometallic catalysts bring together the favorable aspects of homogeneous and heterogeneous catalysis while offering opportunities to investigate the impact of metal-support interactions on reactivity. We report a ( Phebox)Ir(III) ( Phebox = 2,6-bis(4,4-dimethyloxazolinyl)-3,5-dimethylphenyl) complex chemisorbed on sulfated zirconia, the molecular precursor for which was previously applied to hydrocarbon functionalization. Spectroscopic methods such as diffuse reflectance infrared Fourier transformation spectroscopy (DRIFTS), dynamic nuclear polarization (DNP)-enhanced solid-state nuclear magnetic resonance (SSNMR) spectroscopy, and X-ray absorption spectroscopy (XAS) were used to characterize the supported species.

Catalytic Applications of Vanadium: A Mechanistic Perspective.

The chemistry of vanadium has seen remarkable activity in the past 50 years. In the present review, reactions catalyzed by homogeneous and supported vanadium complexes from 2008 to 2018 are summarized and discussed. Particular attention is given to mechanistic and kinetics studies of vanadium-catalyzed reactions including oxidations of alkanes, alkenes, arenes, alcohols, aldehydes, ketones, and sulfur species, as well as oxidative C-C and C-O bond cleavage, carbon-carbon bond formation, deoxydehydration, haloperoxidase, cyanation, hydrogenation, dehydrogenation, ring-opening metathesis polymerization, and oxo/imido heterometathesis.

Evidence for Redox Mechanisms in Organometallic Chemisorption and Reactivity on Sulfated Metal Oxides.

The chemical and electronic interactions of organometallic species with metal oxide support materials are of fundamental importance for the development of new classes of catalytic materials. Chemisorption of Cp*(PMe)IrMe on sulfated alumina (SA) and sulfated zirconia (SZ) led to an unexpected redox mechanism for deuteration of the ancillary Cp* ligand. Evidence for this oxidative mechanism was provided by studying the analogous homogeneous reactivity of the organometallic precursors toward trityl cation ([PhC]), a Lewis acid known to effect formal hydride abstraction by one-electron oxidation followed by hydrogen abstraction.

Conformational Selection as the Mechanism of Guest Binding in a Flexible Supramolecular Host.

This study offers a detailed mechanistic investigation of host-guest encapsulation behavior in a new enzyme-mimetic metal-ligand host and provides the first observation of a conformational selection mechanism (as opposed to induced fit) in a supramolecular system. The GaL host described features a C-symmetric ligand motif with meta-substituted phenyl spacers, which enables the host to initially self-assemble into an S-symmetric structure and then subsequently isomerize to a T-symmetric tetrahedron for better accommodation of a sufficiently large guest. Selective inversion recovery H NMR studies provide structural insights into the self-exchange behaviors of the host and the guest individually in this dynamic system.

Scope and Mechanism of Cooperativity at the Intersection of Organometallic and Supramolecular Catalysis.

The scope and mechanism of the microenvironment-catalyzed C(sp(3))-C(sp(3)) reductive elimination from transition metal complexes [Au(III), Pt(IV)] is explored. Experiments detailing the effect of structural perturbation of neutral and anionic spectator ligands, reactive alkyl ligands, solvent, and catalyst structure are disclosed. Indirect evidence for a coordinatively unsaturated encapsulated cationic intermediate is garnered via observation of several inactive donor-arrested inclusion complexes, including a crystallographically characterized encapsulated Au(III) cation.

A supramolecular microenvironment strategy for transition metal catalysis.

A self-assembled supramolecular complex is reported to catalyze alkyl-alkyl reductive elimination from high-valent transition metal complexes [such as gold(III) and platinum(IV)], the central bond-forming elementary step in many catalytic processes. The catalytic microenvironment of the supramolecular assembly acts as a functional enzyme mimic, applying the concepts of enzymatic catalysis to a reactivity manifold not represented in biology. Kinetic experiments delineate a Michaelis-Menten-type mechanism, with measured rate accelerations (k(cat)/k(uncat)) up to 1.

Enabling New Modes of Reactivity via Constrictive Binding in a Supramolecular-Assembly-Catalyzed Aza-Prins Cyclization.

Supramolecular assembly 1 catalyzes a bimolecular aza-Prins cyclization featuring an unexpected transannular 1,5-hydride transfer. This reaction pathway, which is promoted by constrictive binding within the supramolecular cavity of 1, is kinetically disfavored in the absence of 1, as evidenced by the orthogonal reactivity observed in bulk solution. Mechanistic investigation through kinetic analysis and isotopic labeling studies indicates that the rate-limiting step of the transformation is the encapsulation of a transient iminium ion and supports the proposed 1,5-hydride transfer mechanism.