Dinuclear Cobalt(II) Bis-Dipyrromethane Complexes: Synthesis via Divergent Transmetalation Reactions.

A bis-dipyrromethane ligand, 4,4'-bis(1,1-bis(3,5-dimethyl-1H-pyrrol-2-yl)ethyl)-1,1'-biphenyl, [H-BDPM-BPh] (), is synthesized via acid-catalyzed electrophilic aromatic substitution of 2,4-dimethylpyrrole with 4,4'-diacetylbiphenyl. Subsequent deprotonation of with -BuLi yields the corresponding Li-salt [Li-BDPM-BPh] (). Transmetalation involving and either CoCl or [Co(HMDS)] (HMDS = -N(Si(CH))) results in dinuclear Co(II) complexes.

A High-Throughput Approach to Repurposing Olefin Polymerization Catalysts for Polymer Upcycling.

Efficient and economical plastic waste upcycling relies on the development of catalysts capable of polymer degradation. A systematic high-throughput screening of twenty-eight polymerization catalyst precursors, belonging to the catalyst families of metallocenes, ansa-metallocenes, and hemi- and post-metallocenes, in cis-1,4-polybutadiene (PB) degradation reveals, for the first time, important structure-activity correlations. The upcycling conditions involve activation of the catalysts (at 0.

Molecular and supported Ti(iii)-alkyls: efficient ethylene polymerization driven by the π-character of metal-carbon bonds and back donation from a singly occupied molecular orbital.

While Ti(iii) alkyl species are the proposed active sites in Ziegler-Natta ethylene polymerization catalysts, the corresponding well-defined homogeneous catalysts are not known. We report that well-defined neutral β-diiminato Ti(iii) alkyl species, namely [Ti(nacnac)(CH Bu)] and its alumina-grafted derivative [(AlO)Ti(nacnac)(CH Bu)], are active towards ethylene polymerization at moderate pressures and temperatures and possess an electron configuration well-adapted to insertion of ethylene. Advanced EPR spectroscopy showed that ethylene insertion into a Ti(iii)-C bond takes place during polymerization from Ti(nacnac)(CH Bu).

Well-Defined, Silica-Supported Homobimetallic Nickel Hydride Hydrogenation Catalyst.

There is an increasing interest to replace precious metal-based catalysts by earth-abundant nonprecious metals due to higher costs, toxicity, and declining availability of the former. Here, the synthesis of a well-defined supported nickel hydrogenation catalyst prepared by surface organometallic chemistry is reported. For this purpose, [LNi(μ-H)] (L = HC(CMeNCH(Pr))) was grafted on partially dehydroxylated silica to give a homobimetallic H- and O(silica)-bridged Ni complex.

A Formulation Protocol with Pyridine to Enable Dynamic Nuclear Polarization Surface-Enhanced NMR Spectroscopy on Reactive Surface Sites: Case Study with Olefin Polymerization and Metathesis Catalysts.

Dynamic nuclear polarization surface-enhanced NMR spectroscopy (DNP-SENS) has emerged as a powerful characterization tool in material chemistry and heterogeneous catalysis by dramatically increasing, by up to 2 orders of magnitude, the NMR signals associated with surface sites. DNP-SENS mostly relies on using exogenous polarizing agents (PAs), typically dinitroxyl radicals, to boost the NMR signals. However, the PAs may interact with the surface or even react with surface sites, thus leading to loss or quenching of DNP enhancements.

Unusual Dinitrogen Binding and Electron Storage in Dinuclear Iron Complexes.

A rare example of a dinuclear iron core with a non-linearly bridged dinitrogen ligand is reported in this work. One-electron reduction of [(pyrrpy)Fe(OEt)] () (pyrrpy = 2,6-bis((3,5-di--butyl)pyrrol-2-yl)pyridine) with KC yields the complex [K][(pyrrpy)Fe](μ-η:η-N) (), where the unusual -divacant octahedral coordination geometry about each iron and the η-cation-π coordination of two potassium ions with four pyrrolyl units of the ligand cause distortion of the bridging end-on μ-N about the FeNFe core. Attempts to generate a EtO-free version of resulted instead in a dinuclear helical dimer, [(pyrrpy)Fe] (), via bridging of the pyridine moieties of the ligand.

Enhanced CHOH selectivity in CO hydrogenation using Cu-based catalysts generated SOMC from Ga single-sites.

Small and narrowly distributed nanoparticles of copper alloyed with gallium supported on silica containing residual Ga sites can be obtained surface organometallic chemistry in a two-step process: (i) formation of isolated Ga surface sites on SiO and (ii) subsequent grafting of a Cu precursor, [Cu(O Bu)], followed by a treatment under H to generate CuGa alloys. This material is highly active and selective for CO hydrogenation to CHOH. X-ray absorption spectroscopy shows that gallium is oxidized under reaction conditions while copper remains as Cu.

Silica-supported, narrowly distributed, subnanometric Pt-Zn particles from single sites with high propane dehydrogenation performance.

The development of highly productive, selective and stable propane dehydrogenation catalysts for propene production is strategic due to the increasing need for propene and the availability of shale gas, an abundant source of light alkanes. In that context, the combination of surface organometallic chemistry (SOMC) and a thermolytic molecular precursor (TMP) approach is used to prepare bimetallic subnanometric and narrowly distributed Pt-Zn alloyed particles supported on silica grafting of a Pt precursor on surface OH groups present in a Zn single-site containing material followed by a H reduction treatment. This material, that exhibits a Zn to Pt molar ratio of 3 : 2 in the form of alloyed Pt-Zn particles with a 0.

Monomeric Copper(II) Sites Supported on Alumina Selectively Convert Methane to Methanol.

Monomeric Cu sites supported on alumina, prepared using surface organometallic chemistry, convert CH to CH OH selectively. This reaction takes place by formation of CH O surface species with the concomitant reduction of two monomeric Cu sites to Cu , according to mass balance analysis, infrared, solid-state nuclear magnetic resonance, X-ray absorption, and electron paramagnetic resonance spectroscopy studies. This material contains a significant fraction of Cu active sites (22 %) and displays a selectivity for CH OH exceeding 83 %, based on the number of electrons involved in the transformation.

Selective Hydrogenation of CO to CH OH on Supported Cu Nanoparticles Promoted by Isolated Ti Surface Sites on SiO.

Small and narrowly distributed Cu nanoparticles, supported on SiO decorated with isolated Ti sites, prepared through surface organometallic chemistry, showed significantly improved CO hydrogenation activity and CH OH selectivity compared to the corresponding Cu nanoparticles supported on SiO . These isolated Lewis acid Ti sites, evidenced by UV/Vis spectroscopy, are proposed to stabilize surface intermediates at the interface between Cu nanoparticles and the support.

Highly Productive Propane Dehydrogenation Catalyst Using Silica-Supported Ga-Pt Nanoparticles Generated from Single-Sites.

The development of more effective alkane dehydrogenation catalysts is a key technological challenge for the production of olefins from shale gas, an abundant source of light hydrocarbons. Surface organometallic chemistry provides an original approach to generate nanometric Ga-Pt bimetallic particles supported on partially dehydroxylated silica containing gallium single-sites, which displays high activity, selectivity, and stability in propane dehydrogenation. This catalyst was prepared via sequential grafting of a platinum precursor onto silica possessing site-isolated gallium sites followed by H reduction.

Metal alkyls programmed to generate metal alkylidenes by α-H abstraction: prognosis from NMR chemical shift.

Metal alkylidenes, which are key organometallic intermediates in reactions such as olefination or alkene and alkane metathesis, are typically generated from metal dialkyl compounds [M](CHR) that show distinctively deshielded chemical shifts for their α-carbons. Experimental solid-state NMR measurements combined with DFT/ZORA calculations and a chemical shift tensor analysis reveal that this remarkable deshielding originates from an empty metal d-orbital oriented in the M-C-C plane, interacting with the C p-orbital lying in the same plane. This π-type interaction inscribes some alkylidene character into C that favors alkylidene generation α-H abstraction.

Bridging the Gap between Industrial and Well-Defined Supported Catalysts.

Many industrial catalysts contain isolated metal sites on the surface of oxide supports. Although such catalysts have been used in a broad range of processes for more than 40 years, there is often a very limited understanding about the structure of the catalytically active sites. This Review discusses how surface organometallic chemistry (SOMC) engineers surface sites with well-defined structures and provides insight into the nature of the active sites of industrial catalysts; the Review focuses in particular on olefin production and conversion processes.

Silica-supported isolated gallium sites as highly active, selective and stable propane dehydrogenation catalysts.

Single-site gallium centers on the surface of silica are prepared grafting of [Ga(OSi(OBu))(THF)] on SiO followed by a thermolysis step. The resulting surface species corresponds to well-defined tetra-coordinate gallium single-sites, [([triple bond, length as m-dash]SiO)Ga(XOSi[triple bond, length as m-dash])] (X = -H or [triple bond, length as m-dash]Si) according to IR, X-ray absorption near-edge structure and extended X-ray absorption fine structure analysis. These gallium sites show high activity, selectivity and stability for propane dehydrogenation with an initial turnover frequency of 20 per h per gallium center, propylene selectivity of ≥93% and remarkable stability over 20 h.

Isolated Surface Hydrides: Formation, Structure, and Reactivity.

Surface hydrides are ubiquitous in catalysis. However, their structures and properties are not as well-understood as those of their molecular counterparts, which have been extensively studied for the past 70 years. Hydrides isolated on surfaces have been characterized as stable entities on oxide surfaces or in zeolites.

Formation and Redox Interconversion of Niobium Methylidene and Methylidyne Complexes.

The niobium methylidene [{(Ar'O)2 Nb}2 (μ2 -Cl)2 (μ2 -CH2 )] (2) can be cleanly prepared via thermolysis or photolysis of [(Ar'O)2 Nb(CH3 )2 Cl] (1) (OAr'=2,6-bis(diphenylmethyl)-4-tert-butylphenoxide). Reduction of 2 with two equivalents of KC8 results in formation of the first niobium methylidyne [K][{(Ar'O)2 Nb}2 (μ2 -CH)(μ2 -H)(μ2 -Cl)] (3) via a binuclear α-hydrogen elimination. Oxidation of 3 with two equiv of ClCPh3 reforms 2.

Phosphinoalkylidene and -alkylidyne Complexes of Titanium: Intermolecular C-H Bond Activation and Dehydrogenation Reactions.

The ethylene complex (PNP)Ti(η(2)-H2C═CH2)(CH2(t)Bu) or (PNP)Ti═CH(t)Bu(CH2(t)Bu) (PNP(-) = N[2-P(CHMe2)2-4-methylphenyl]2) reacts with H2CPPh3 to form the κ(2)-phosphinoalkylidene (PNP)Ti═CHPPh2(Ph) (1). Compound 1 activates benzene via the transient intermediate [(PNP)Ti≡CPPh2] (C). By treatment of (PNP)Ti═CH(t)Bu(OTf) with LiCH2PPh2, 1 or its isotopologue (PNP)Ti═CDPPh2(C6D5) (1-d6) can be produced by an independent route involving intermediate C, which activates benzene or benzene-d6 and dehydrogenates cyclohexane-d12.

Niobium-nitrides derived from nitrogen splitting.

The easy-to-prepare Nb(V) aryloxide complex [(ArO)2Nb(μ-Cl)Cl2]2 (OAr = 2,6-bis(diphenylmethyl)-4-tert-butylphenoxide) is a precursor to both Nb(IV), [trans-(ArO)2NbCl2(THF)2], and Nb(III), K3[(ArO)4Nb2(μ-Cl)3Cl2], molecules. The Nb(IV) and (V) complexes readily split atmospheric nitrogen at room temperature and 1 atmosphere, under reducing conditions, to produce the low-coordinate nitride dimer [(ArO)2Nb(μ-N)]2 and its radical anion, K[(ArO)2Nb(μ-N)]2.

A cis-divacant octahedral and mononuclear iron(IV) imide.

A rare, low-spin Fe(IV)  imide complex [(pyrr2py)Fe=NAd] (pyrr2 py(2-) = bis(pyrrolyl)pyridine; Ad = 1-adamantyl) confined to a cis-divacant octahedral geometry, was prepared by reduction of N3Ad by the Fe(II)  precursor [(pyrr2py)Fe(OEt2)]. The imide complex is low-spin with temperature-independent paramagnetism. In comparison to an authentic Fe(III) complex, such as [(pyrr2py)FeCl], the pyrr2py(2-) ligand is virtually redox innocent.

Binary role of an ylide in formation of a terminal methylidene complex of niobium.

The first structurally characterized niobium(v) complex possessing a terminal methylidene ligand is reported in high yield from the reaction of [(Ar'O)2Nb(CH3)2Cl] (Ar' = (2,6-CHPh2)2-4-tBu-C6H2) and two equivalents of H2CPPh3.

Total reflection infrared spectroscopy of water-ice and frozen aqueous NaCl solutions.

Liquid-like and liquid water at and near the surface of water-ice and frozen aqueous sodium chloride films were observed using attenuated total reflection infrared spectroscopy (ATR-IR). The concentration of NaCl ranged from 0.0001 to 0.

3d early transition metal complexes supported by a new sterically demanding aryloxide ligand.

The bulky aryloxide 2,6-bis(diphenylmethyl)-4-tert-butylphenol [HOAr(tBu)] (1) can be synthesized from 4-tert-butylphenol and benzhydrol in solvent-free conditions and obtained pure in 91% yield. Deprotonation of HOAr(tBu) is accomplished with M(N(SiMe3)2) (M = Na, Li), yielding the corresponding salts of the aryloxide [MOAr(tBu)] (M(+) = Na (2), Li(3)) in 83% and 73% yield, respectively. Facile salt formation of the aryloxide ligand allows for transmetalation to a variety of metal halides.