Catalytic Hydrogenolysis by Atomically Dispersed Iron Sites Embedded in Chemically and Redox Non-innocent N-Doped Carbon.

Atomically dispersed first-row transition metals embedded in nitrogen-doped carbon materials (M-N-C) show promising performance in catalytic hydrogenation but are less well-studied for reactions with more complex mechanisms, such as hydrogenolysis. Their ability to catalyze selective C-O bond cleavage of oxygenated hydrocarbons such as aryl alcohols and ethers is enhanced with the participation of ligands directly bound to the metal ion as well as longer-range contributions from the support. In this article, we describe how Fe-N-C catalysts with well-defined local structures for the Fe sites catalyze C-O bond hydrogenolysis. The reaction is facilitated by the N-C support. According to spectroscopic analyses, the as-synthesized catalysts contain mostly pentacoordinated FeIII sites, with four in-plane nitrogen donor ligands and one axial hydroxyl ligand. In the presence of 20 bar of H2 at 170-230 °C, the hydroxyl ligand is lost when N4FeIIIOH is reduced to N4FeII, assisted by the H2 chemisorbed on the support. When an alcohol binds to the tetracoordinated FeII sites, homolytic cleavage of the O-H bond is accompanied by reoxidation to FeIII and H atom transfer to the support. The role of the N-C support in catalytic hydrogenolysis is analogous to the behavior of chemically and redox-non-innocent ligands in molecular catalysts based on first-row transition metal ions and enhances the ability of M-N-Cs to achieve the types of multistep activations of strong bonds needed to upgrade renewable and recycled feedstocks.

Population Balance Equations for Reactive Separation in Polymer Upcycling.

Many polymer upcycling efforts aim to convert plastic waste into high-value liquid hydrocarbons. However, the subsequent cleavage of middle distillates to light gases can be problematic. The reactor often contains a vapor phase (light gases and middle distillates) and a liquid phase (molten polymers and waxes with a suspended or dissolved catalyst). Because the catalyst resides in the liquid phase, middle distillates that partition into the vapor phase are protected against further cleavage into light gases. In this paper, we consider a simple reactive separation strategy, in which a gas outflow removes the volatile products as they form. We combine vapor-liquid equilibrium models and population balance equations (PBEs) to describe polymer upcycling in a two-phase semibatch reactor. The results suggest that the temperature, headspace volume, and flow rate of the reactor can be used to tune selectivity toward the middle distillates, in addition to the molecular mechanism of catalysis. We anticipate that two-phase reactor models will be important in many polymer upcycling processes and that reactive separation strategies will provide ways to boost the yield of the desired products in these cases.

Two Mesoporous Domains Are Better Than One for Catalytic Deconstruction of Polyolefins.

Catalytic hydrogenolysis of polyolefins into valuable liquid, oil, or wax-like hydrocarbon chains for second-life applications is typically accompanied by the hydrogen-wasting co-formation of low value volatiles, notably methane, that increase greenhouse gas emissions. Catalytic sites confined at the bottom of mesoporous wells, under conditions in which the pore exerts the greatest influence over the mechanism, are capable of producing less gases than unconfined sites. A new architecture was designed to emphasize this pore effect, with the active platinum nanoparticles embedded between linear, hexagonal mesoporous silica and gyroidal cubic MCM-48 silica (mSiO2/Pt/MCM-48). This catalyst deconstructs polyolefins selectively into ∼C20-C40 paraffins and cleaves C-C bonds at a rate (TOF = 4.2 ± 0.3 s-1) exceeding that of materials lacking these combined features while generating negligible volatile side products including methane. The time-independent product distribution is consistent with a processive mechanism for polymer deconstruction. In contrast to time- and polymer length-dependent products obtained from non-porous catalysts, mSiO2/Pt/MCM-48 yields a C28-centered Gaussian distribution of waxy hydrocarbons from polyolefins of varying molecular weight, composition, and physical properties, including low-density polyethylene, isotactic polypropylene, ultrahigh-molecular-weight polyethylene, and mixtures of multiple, post-industrial polyolefins. Coarse-grained simulation reveals that the porous-core architecture enables the paraffins to diffuse away from the active platinum site, preventing secondary reactions that produce gases.

Zirconium-Catalyzed C-H Alumination of Polyolefins, Paraffins, and Methane.

C-H/Et-Al exchange in zirconium-catalyzed reactions of saturated hydrocarbons and AlEt3 affords versatile organoaluminum compounds and ethane. The grafting of commercially available Zr(OtBu)4 on silica/alumina gives monopodal ≡SiO-Zr(OtBu)3 surface pre-catalyst sites that are activated in situ by ligand exchange with AlEt3. The catalytic C-H alumination of dodecane at 150 °C followed by quenching in air affords n-dodecanol as the major product, revealing selectivity for methyl group activation. Shorter hydrocarbon or alcohol products were not detected under these conditions. Catalytic reactions of cyclooctane and AlEt3, however, afford ring-opened products, indicating that C-C bond cleavage occurs readily in methyl group-free reactants. This selectivity for methyl group alumination enables the C-H alumination of polyethylenes, polypropylene, polystyrene, and poly-α-olefin oils without significant chain deconstruction. In addition, the smallest hydrocarbon, methane, undergoes selective mono-alumination under solvent-free catalytic conditions, providing a direct route to Al-Me species.

Structure and Magnetic Properties of Homoleptic Trivalent Tris(alkyl)lanthanides.

Six new solvent-free, homoleptic paramagnetic tris(alkyl)lanthanides Ln{C(SiHMe2)3}3 (1Ln) and Ln{C(SiHMe2)2Ph}3 (2Ln) (Ln = Gd, Dy, and Er) were synthesized to investigate the magnetic properties of 4f organometallic compounds stabilized by secondary Ln↼H-Si and benzylic interactions. The unit cell of 1Gd contains one independent molecule (Z = 2), while 1Dy and 1Er crystallize with four independent isostructural molecules per unit cell (Z = 16). In all molecules, as in other 1Ln compounds, the three tris(dimethylsilyl)methyl ligands form a trigonal planar LnC3 core, and six secondary interactions involving Ln↼H-Si bonding in Ln{C(SiHMe2)3}3 form above and below the equatorial plane. Two and five crystallographically independent molecules of each 2Ln (2Gd, Z = 8; 2Dy, Z = 20) form with three π-coordinated phenyl groups in addition to either one or two secondary Ln↼H-Si interactions per molecule. The packing of these midseries organolanthanide compounds contrasts the single crystallographically unique molecules in previously reported La{C(SiHMe2)3}3 (1La, Z = 2, Z' = 1) and La{C(SiHMe2)2Ph}3 (2La, Z = 2, Z' = 1/3). 2La doped with 2Dy can adopt the crystallographic structure of 2La, which promotes magnetic properties, namely a higher χmT value at low temperatures as well as stronger magnetic anisotropy. The ac susceptibility data for 10% 2Dy doped into 2La suggests slow relaxation at low temperatures with a relaxation barrier of ∼45 K. The computed saturated magnetization of 1Er (M ≈ 4.5 µB) and 1Dy (M ≈ 6 µB) matches the experimental values, while the computed value for 2Dy better matches the value measured for 2Dy diluted in 2La (M ≈ 5 µB). Gas-phase calculations predict that the ground-state and first excited-state multiplet separations are larger for 1Er than 2Er, while the ordering for dysprosium is 1Dy > 2Dy.

Size-Controlled Nanoparticles Embedded in a Mesoporous Architecture Leading to Efficient and Selective Hydrogenolysis of Polyolefins.

A catalytic architecture, comprising a mesoporous silica shell surrounding platinum nanoparticles (NPs) supported on a solid silica sphere (mSiO2/Pt-X/SiO2; X is the mean NP diameter), catalyzes hydrogenolysis of melt-phase polyethylene (PE) into a narrow C23-centered distribution of hydrocarbons in high yield using very low Pt loadings (∼10-5 g Pt/g PE). During catalysis, a polymer chain enters a pore and contacts a Pt NP where the C-C bond cleavage occurs and then the smaller fragment exits the pore. mSiO2/Pt/SiO2 resists sintering or leaching of Pt and provides high yields of liquids; however, many structural and chemical effects on catalysis are not yet resolved. Here, we report the effects of Pt NP size on activity and selectivity in PE hydrogenolysis. Time-dependent conversion and yields and a lumped kinetics model based on the competitive adsorption of long vs short chains reveal that the activity of catalytic material is highest with the smallest NPs, consistent with a structure-sensitive reaction. Remarkably, the three mSiO2/Pt-X/SiO2 catalysts give equivalent selectivity. We propose that mesoscale pores in the catalytic architecture template the C23-centered distribution, whereas the active Pt sites influence the carbon-carbon bond cleavage rate. This conclusion provides a framework for catalyst design by separating the C-C bond cleavage activity at catalytic sites from selectivity for chain lengths of the products influenced by the structure of the catalytic architecture. The increased activity, selectivity, efficiency, and lifetime obtained using this architecture highlight the benefits of localized and confined environments for isolated catalytic particles under condensed-phase reaction conditions.

Determining the Three-Dimensional Structures of Silica-Supported Metal Complexes from the Ground Up.

The immobilization of molecularly precise metal complexes to substrates, such as silica, provides an attractive platform for the design of active sites in heterogeneous catalysts. Specific steric and electronic variations of the ligand environment enable the development of structure-activity relationships and the knowledge-driven design of catalysts. At present, however, the three-dimensional environment of the precatalyst, much less the active site, is generally not known for heterogeneous single-site catalysts. We explored the degree to which NMR-based surface-to-complex interatomic distances could be used to solve the three-dimensional structures of three silica-supported metal complexes. The structure solution revealed unexpected features related to the environment around the metal that would be difficult to discern otherwise. This approach appears to be highly robust and, due to its simplicity, is readily applied to most single-site catalysts with little extra effort.

Supported Lanthanum Borohydride Catalyzes CH Borylation Inside Zeolite Micropores.

The zeolite-supported lanthanide La(BH4 )x -HY30 catalyzes C-H borylation of benzene with pinacolborane (HBpin), providing a complementary approach to precious, late transition metal-catalyzed borylations. The reactive catalytic species are generated from La grafted at the Brønsted acid sites (BAS) in micropores of the zeolite, whereas silanoate- and aluminoate-grafted sites are inactive under the reaction conditions. During typical catalytic borylations, conversion to phenyl pinacolborane (PhBpin) is zero-order in HBpin concentration. A turnover number (TON) of 167 is accessed by capping external silanols, selectively grafting at BAS sites, and adding HBpin slowly to the reaction.

Hydrosilane σ-Adduct Intermediates in an Adaptive Zinc-Catalyzed Cross-dehydrocoupling of Si-H and O-H Bonds.

Three-coordinate Ph BOX Me 2 ZnR (Ph BOX Me 2 =phenyl-(4,4-dimethyl-oxazolinato; R=Me: 2 a, Et: 2 b) catalyzes the dehydrocoupling of primary or secondary silanes and alcohols to give silyl ethers and hydrogen, with high turnover numbers (TON; up to 107 ) under solvent-free conditions. Primary and secondary silanes react with small, medium, and large alcohols to give various degrees of substitution, from mono- to tri-alkoxylation, whereas tri-substituted silanes do not react with MeOH under these conditions. The effect of coordinative unsaturation on the behavior of the Zn catalyst is revealed through a dramatic variation of both rate law and experimental rate constants, which depend on the concentrations of both the alcohol and hydrosilane reactants. That is, the catalyst adapts its mechanism to access the most facile and efficient conversion. In particular, either alcohol or hydrosilane binds to the open coordination site on the Ph BOX Me 2 ZnOR catalyst to form a Ph BOX Me 2 ZnOR(HOR) complex under one set of conditions or an unprecedented σ-adduct Ph BOX Me 2 ZnOR(H-SiR'3 ) under other conditions. Saturation kinetics provide evidence for the latter species, in support of the hypothesis that σ-bond metathesis reactions involving four-centered electrocyclic 2σ-2σ transition states are preceded by σ-adducts.

Silica-Supported Organolanthanum Catalysts for C-O Bond Cleavage in Epoxides.

Single-site organolanthanum complexes supported on mesoporous silica nanoparticles, La{C(SiHMe2)3}n@MSNs, catalyze the ring-opening hydroboration reaction of aliphatic and styrenic epoxides with pinacolborane (HBpin). The surface-bound complexes, synthesized by reaction of the homoleptic tris(alkyl)lanthanum La{C(SiHMe2)3}3 and SBA-type MSN treated at 700 °C (MSN700), are mostly monopodal ≡SiO-La{C(SiHMe2)3}2 and contain an average of one bridging La↼H-Si per alkyl ligand. This structure was established through a combination of solid-state NMR (SSNMR) experiments, including J-resolved SiH coupling and quantitative 29Si measurements, diffuse reflectance IR, and elemental analysis. These rigorous analyses also established that grafting reactions in pentane provide a preponderance of ≡SiO-La{C(SiHMe2)3}2 sites and are superior to those in benzene and THF, and that grafting onto MSN treated at 550 °C (MSN550) results in a mixture of surface species. The single-site supported catalysts are more selective and in most cases more active than the homogeneous analogue, allow easy purification of products from the catalyst, are strongly resistant to leaching into solution phase, and may be recycled for reuse at least five times. After reaction of La{C(SiHMe2)3}n@MSN and HBpin, species including ≡SiO-La{C(SiHMe2)3}(H2Bpin) and ≡SiO-La{C(SiHMe2)3}{κ2-pinB-O(CMe2)2OBH3} are identified by detailed 1D and 2D 11B SSNMR experiments.

Rare-Earth Catalyzed C-H Bond Alumination of Terminal Alkynes.

Organoaluminum reagents' application in catalytic C-H bond functionalization is limited by competitive side reactions, such as carboalumination and hydroalumination. Herein, rare-earth tetramethylaluminate complexes are shown to catalyze the exclusive C-H bond metalation of terminal alkynes with the commodity reagents trimethyl-, triethyl-, and triisobutylaluminum. Kinetic experiments probing alkyl-group exchange between rare-earth aluminates and trialkylaluminum, C-H bond metalation of alkynes, and catalytic conversions reveal distinct pathways of catalytic aluminations with triethylaluminum versus trimethylaluminum. Most significantly, kinetic data point to reversible formation of a unique [Ln](AlR4 )2 ⋅AlR3 adduct, followed by turnover-limiting alkyne metalation. That is, C-H bond activation occurs from a more associated organometallic species, rather than the expected coordinatively unsaturated species. These mechanistic conclusions allude to a new general strategy for catalytic C-H bond alumination that make use of highly electrophilic metal catalysts.

Suppressing 1H Spin Diffusion in Fast MAS Proton Detected Heteronuclear Correlation Solid-State NMR Experiments.

Fast magic angle spinning (MAS) and indirect detection by high gyromagnetic ratio (γ) nuclei such as proton or fluorine are increasingly utilized to obtain 2D heteronuclear correlation (HETCOR) solid-state NMR spectra of spin-1/2 nuclei by using cross polarization (CP) for coherence transfer. However, one major drawback of CP HETCOR pulse sequences is that 1H spin diffusion during the back X→1H CP transfer step may result in relayed correlations. This problem is particularly pronounced for the indirect detection of very low-γ nuclei such as 89Y, 103Rh, 109Ag and 183W where long contact times on the order of 10-30 ms are necessary for optimal CP transfer. Here we propose two methods that eliminate relayed correlations and allow more reliable distance information to be obtained from 2D HETCOR NMR spectra. The first method uses Lee-Goldburg (LG) CP during the X→1H back-transfer step to suppress 1H spin diffusion. We determine LG conditions compatible with fast MAS frequencies (νrot) of 40-95 kHz and show that 1H spin diffusion can be efficiently suppressed at low effective radiofrequency (RF) fields (ν1,eff ≪ 0.5νrot) and also at high effective RF fields (ν1,eff ≫ 2νrot). We describe modified Hartmann-Hahn LG-CP match conditions compatible with fast MAS and suitable for indirect detection of moderate-γ nuclei such as 13C, and low-γ nuclei such as 89Y. The second method uses D-RINEPT (dipolar refocused insensitive nuclei enhanced by polarization transfer) during the X→1H back-transfer step of the HETCOR pulse sequence. The effectiveness of these methods for acquiring HETCOR spectra with reduced relayed signal intensities is demonstrated with 1H{13C} HETCOR NMR experiments on l-histidine⋅HCl⋅H2O and 1H{89Y} HETCOR NMR experiments on an organometallic yttrium complex.

CO Displacement in an Oxidative Addition of Primary Silanes to Rhodium(I).

The rhodium dicarbonyl {PhB(OxMe2)2ImMes}Rh(CO)2 (1) and primary silanes react by oxidative addition of a nonpolar Si-H bond and, uniquely, a thermal dissociation of CO. These reactions are reversible, and kinetic measurements model the approach to equilibrium. Thus, 1 and RSiH3 react by oxidative addition at room temperature in the dark, even in CO-saturated solutions. The oxidative addition reaction is first-order in both 1 and RSiH3, with rate constants for oxidative addition of PhSiH3 and PhSiD3 revealing kH/ kD ∼ 1. The reverse reaction, reductive elimination of Si-H from {PhB(OxMe2)2ImMes}RhH(SiH2R)CO (2), is also first-order in [2] and depends on [CO]. The equilibrium concentrations, determined over a 30 °C temperature range, provide Δ H ° = -5.5 ± 0.2 kcal/mol and Δ S ° = -16 ± 1 cal·mol-1K-1 (for 1 ⇄ 2). The rate laws and activation parameters for oxidative addition (Δ H⧧ = 11 ± 1 kcal·mol-1 and Δ S⧧ = -26 ± 3 cal·mol-1·K-1) and reductive elimination (Δ H⧧ = 17 ± 1 kcal·mol-1 and Δ S⧧ = -10 ± 3 cal·mol-1K-1), particularly the negative activation entropy for both forward and reverse reactions, suggest the transition state of the rate-determining step contains {PhB(OxMe2)2ImMes}Rh(CO)2 and RSiH3. Comparison of a series of primary silanes reveals that oxidative addition of arylsilanes is ca. 5× faster than alkylsilanes, whereas reductive elimination of Rh-Si/Rh-H from alkylsilyl and arylsilyl rhodium(III) occurs with similar rate constants. Thus, the equilibrium constant Ke for oxidative addition of arylsilanes is >1, whereas reductive elimination is favored for alkylsilanes.

Heteroleptic Four-Coordinate Tris(oxazolinyl)borato Iron(II) Compounds.

The reaction of FeBr2 and 1 equiv of thallium tris(4,4-dimethyl-2-oxazolinyl)phenylborate (TlToM) in THF provides ToMFeBr (1), whereas FeBr2 and 2 equiv of TlToM react to give (ToM)2Fe (2). Two νCN bands at 1604 and 1548 cm-1 indicated bidentate coordination of ToM to iron in 2. Homoleptic 2 and FeBr2 react in THF overnight through an unusual ligand exchange process to give compound 1, which is apparently the thermodynamic product. The salt metathesis reaction of 1 and KCH2Ph affords ToMFeCH2Ph (3). The effective magnetic moments of compounds 1-3 range from 4.9 to 5.4 µB, and these values are consistent with high-spin iron(II) ( S = 2). A single 1H NMR signal assigned to the methyl groups of the ToM ligand suggested tridentate coordination of the ToM ligand to iron in 1 and 3. X-ray crystallography studies of 1-3 establish their structure as four-coordinated tetrahedral iron complexes. ToMFeBn and CO (1 atm) react to afford isolable ToMFe{C(═O)Bn}(CO)2 (4) as a yellow solid. Complex 4 is diamagnetic ( S = 0), and the three distinct methyl signals in the 1H NMR spectrum are consistent with a six-coordinate, C s-symmetric species. This assignment is supported by its IR spectrum, which revealed intense bands at 2004 and 1935 cm-1 (symmetric and asymmetric νCO), at 1680 and 1662 cm-1 (acyl rotamers, νCO), and at 1593 and 1553 cm-1 (νCN) and is confirmed by a single-crystal X-ray diffraction study.

Interconverting Lanthanum Hydride and Borohydride Catalysts for C=O Reduction and C-O Bond Cleavage.

The high catalytic reactivity of homoleptic tris(alkyl) lanthanum La{C(SiHMe2 )3 }3 is highlighted by C-O bond cleavage in the hydroboration of esters and epoxides at room temperature. The catalytic hydroboration tolerates functionality typically susceptible to insertion, reduction, or cleavage reactions. Turnover numbers (TON) up to 10 000 are observed for aliphatic esters. Lanthanum hydrides, generated by reactions with pinacolborane, are competent for reduction of ketones but are inert toward esters. Instead, catalytic reduction of esters requires activation of the lanthanum hydride by pinacolborane.

A Quasi-Atomic Analysis of Three-Center Two-Electron Zr-H-Si Interactions.

A comprehensive analysis of the bonding structure of the disilyl zirconocene amide cation {Cp2Zr[N(SiHMe2)2]}+ is conducted by application of an intrinsic orbital localization method that yields quasi-atomic orbitals (QUAOs). An emphasis is placed on describing a previously characterized three-center two-electron interaction between zirconium, hydrogen, and silicon that presents structural and spectroscopic features similar to that of agostic bonds. Expressions of the first-order density matrix in terms of the QUAOs yields bond orders (BOs), kinetic bond orders (KBOs), and the extent of transfer of charge that are useful to determine the electronic nature of the Zr-H-Si bond. The interactions between the QUAOs demonstrate the importance of vicinal interactions in the stabilization of the molecule. In addition, the evolution of the QUAOs during reactions with Lewis bases reveals the role of the Zr-H-Si interaction in facilitating the reaction.

Enhancing the Sensitivity of Solid-State NMR Experiments with Very Low Gyromagnetic Ratio Nuclei with Fast Magic Angle Spinning and Proton Detection.

Many transition metals commonly encountered in inorganic materials and organometallic compounds possess NMR-active nuclei with very low gyromagnetic ratios (γ) such as 89Y, 103Rh, 109Ag, and 183W. A low-γ leads to poor NMR sensitivity and other experimental challenges. Consequently, nuclei with low-γ are often impossible to study with conventional solid-state NMR methods. Here, we combine fast magic angle spinning (MAS) and proton detection to enhance the sensitivity of solid-state NMR experiments with very low-γ nuclei by 1-2 orders of magnitude. Coherence transfer between 1H and low-γ nuclei was performed with low-power double quantum (DQ) or zero quantum (ZQ) cross-polarization (CP) or dipolar refocused insensitive nuclei enhanced by polarization transfer (D-RINEPT). Comparison of the absolute sensitivity of CP NMR experiments performed with proton detection with 1.3 mm rotors and direct detection with 4 mm rotors shows that proton detection with a 1.3 mm rotor provides a significant boost in absolute sensitivity, while requiring approximately 1/40th of the material required to fill a 4 mm rotor. Fast MAS and proton detection were applied to obtain 89Y and 103Rh solid-state NMR spectra of organometallic complexes. These results demonstrate that proton detection and fast MAS represents a general approach to enable and accelerate solid-state NMR experiments with very low-γ nuclei.

Homoleptic Trivalent Tris(alkyl) Rare Earth Compounds.

Homoleptic tris(alkyl) rare earth complexes Ln{C(SiHMe2)3}3 (Ln = La, 1a; Ce, 1b; Pr, 1c; Nd, 1d) are synthesized in high yield from LnI3THFn and 3 equiv of KC(SiHMe2)3. X-ray diffraction studies reveal 1a-d are isostructural, pseudo-C3-symmetric molecules that contain two secondary Ln↼HSi interactions per alkyl ligand (six total). Spectroscopic assignments are supported by comparison with Ln{C(SiDMe2)3}3 and DFT calculations. The Ln↼HSi and terminal SiH exchange rapidly on the NMR time scale at room temperature, but the two motifs are resolved at low temperature. Variable-temperature NMR studies provide activation parameters for the exchange process in 1a (ΔH⧧ = 8.2(4) kcal·mol-1; ΔS⧧ = -1(2) cal·mol-1K-1) and 1a-d9 (ΔH⧧ = 7.7(3) kcal·mol-1; ΔS⧧ = -4(2) cal·mol-1K-1). Comparisons of lineshapes, rate constants (kH/kD), and slopes of ln(k/T) vs 1/T plots for 1a and 1a-d9 reveal that an inverse isotope effect dominates at low temperature. DFT calculations identify four low-energy intermediates containing five ß-Si-H⇀Ln and one γ-C-H⇀Ln. The calculations also suggest the pathway for Ln↼HSi/SiH exchange involves rotation of a single C(SiHMe2)3 ligand that is coordinated to the Ln center through the Ln-C bond and one secondary interaction. These robust organometallic compounds persist in solution and in the solid state up to 80 °C, providing potential for their use in a range of synthetic applications. For example, reactions of Ln{C(SiHMe2)3}3 and ancillary proligands, such as bis-1,1-(4,4-dimethyl-2-oxazolinyl)ethane (HMeC(OxMe2)2) give {MeC(OxMe2)2}Ln{C(SiHMe2)3}2, and reactions with disilazanes provide solvent-free lanthanoid tris(disilazides).

Improved strategies for DNP-enhanced 2D 1H-X heteronuclear correlation spectroscopy of surfaces.

We demonstrate that dynamic nuclear polarization (DNP)-enhanced 1H-X heteronuclear correlation (HETCOR) measurements of hydrogen-rich surface species are better accomplished by using proton-free solvents. This approach notably prevents HETCOR spectra from being obfuscated by the solvent-derived signals otherwise present in DNP measurements. Additionally, in the hydrogen-rich materials studied here, which included functionalized mesoporous silica nanoparticles and metal organic frameworks, the use of proton-free solvents afforded higher sensitivity gains than the commonly used solvents containing protons. We also explored the possibility of using a solvent-free sample formulation and the feasibility of indirect detection in DNP-enhanced HETCOR experiments.

Cerium-Catalyzed Hydrosilylation of Acrylates to Give α-Silyl Esters.

The homoleptic organocerium complex Ce{C(SiHMe2 )3 }3 (1) reacts with B(C6 F5 )3 to produce the zwitterionic bis(alkyl) hydridoborato Ce{C(SiHMe2 )3 }2 HB(C6 F5 )3 (2). NMR and IR spectroscopy and X-ray crystallography indicate that each alkyl ligand contains two bridging Ce↼H-Si interactions in both 1 and 2. Compound 2 serves as a precatalyst for the hydrosilylation of acrylates to give α-silyl esters at room temperature with a turnover number of 2200.