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Experiments were performed to characterize the structural evolution of the glassy and polycrystalline alkali binary thioborate system xNa2S + (1-x)B2S3 using magic angle spinning nuclear magnetic resonance (MAS NMR) and by two-dimensional multiple-quantum analysis. The results described the short range order of the fundamental network structures in glass compositions. Moreover, the dominant 11B resonances in glassy samples exhibited similarities with the structural units found in the the polycrystalline compounds.

Multiple-quantum magic angle spinning (MQMAS) NMR spectrum of super27A1 via superH cross polarization (CP) was produced. The new technique was applied to the study of a fully hydrated A1POsub4-11 aluminophosphate. The combination of MQMAS and CPMQMAS gave new insights into the sample structure.

A method combining multiple-quantum magic angle spinning (MQMAS) with S-observe, I-dephase rotational echo double resonance (REDOR), is presented. The MQ-REDOR technique was used in (super19)F-(super27)A1 spin pairs within a fluorinated aluminophosphate sample. It would be useful for spectral editing and in the study of internuclear distances in complex systems, that involve quadrupolar spins in conditions of high resolution.

Nanoconfinement imposes physical constraints and chemical effects on reactivity in nanoporous catalyst systems. In the present study, we lay the groundwork for quantitative single-molecule measurements of the effects of chemical environment on heterogeneous catalysis in nanoconfinement. Choosing hydrophobicity as an exemplary chemical environmental factor, we compared a range of essential parameters for an oxidation reaction on platinum nanoparticles (NPs) confined in hydrophilic and hydrophobic nanopores. Single-molecule experimental measurements at the single particle level showed higher catalytic activity, stronger adsorption strength, and higher activation energy in hydrophobic nanopores than those in hydrophilic nanopores. Interestingly, different dissociation kinetic behaviors of the product molecules in the two types of nanopores were deduced from the single-molecule imaging data.

Single-site organolanthanum complexes supported on mesoporous silica nanoparticles, La{C(SiHMe 2 ) 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(SiHMe 2 ) 3 } 3 and SBA-type MSN treated at 700 °C (MSN 700 ), are mostly monopodal ≡SiO-La{C(SiHMe 2 ) 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 29 Si measurements, diffuse reflectance IR, and elemental analysis. These rigorous analyses also established that grafting reactions in pentane provide a preponderance of ≡SiO-La{C(SiHMe 2 ) 3 } 2 sites and are superior to those in benzene and THF, and that grafting onto MSN treated at 550 °C (MSN 550 ) 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(SiHMe 2 ) 3 } n @MSN and HBpin, species including ≡SiO-La{C(SiHMe 2 ) 3 }(H 2 Bpin) and ≡SiO-La{C(SiHMe 2 ) 3 }{κ 2 -pinB-O(CMe 2 ) 2 OBH 3 } are identified by detailed 1D and 2D 11 B SSNMR experiments.

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 ( dm Phebox)Ir(III) ( dm 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. Tetrabutylammonium acetate was found to remove the organometallic species from the surface, enabling solution-phase analytical techniques in conjunction with traditional surface methods. Cationic character was imparted to the iridium center by its grafting onto sulfated zirconia, imbuing high levels of activity in electrophilic C-H bond functionalization reactions such as the stoichiometric dehydrogenation of alkanes, with density functional theory (DFT) calculations showing a lower barrier for β-H elimination. Catalytic hydrogenation of olefins was also facilitated by the sulfated zirconia-supported ( dm Phebox)Ir(III) complex, while the homologous complex on silica was inactive under comparable conditions.

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 3 )IrMe 2 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 ([Ph 3 C] + ), a Lewis acid known to effect formal hydride abstraction by one-electron oxidation followed by hydrogen abstraction. Organometallic deuterium incorporation was found to be correlated with surface sulfate concentration as well as the extent of dehydration under thermal activation conditions of SA and SZ supports. Surface sulfate concentration dependence, in conjunction with a computational study of surface electron affinity, indicates an electron-deficient pyrosulfate species as the redox-active moiety. These results provide further evidence for the ability of sulfated metal oxides to participate in redox chemistry not only toward organometallic complexes but also in the larger context of their application as catalysts for the transformation of light alkanes.

Well-defined organoplatinum(IV) sites were grafted on a Zn(II)-modified SiO 2 support via surface organometallic chemistry in toluene at room temperature. Solid-state spectroscopies including XAS, DRIFTS, DRUV-vis, and solid-state (SS) NMR enhanced by dynamic nuclear polarization (DNP), as well as TPR-H 2 and TEM techniques revealed highly dispersed (methylcyclopentadienyl)methylplatinum(IV) sites on the surface ((MeCp)PtMe/Zn/SiO 2 , 1). In addition, computational modeling suggests that the surface reaction of (MeCp)PtMe 3 with Zn(II)-modified SiO 2 support is thermodynamically favorable (Δ G = -12.4 kcal/mol), likely due to the increased acidity of the hydroxyl group, as indicated by NH 3 -TPD and DNP-enhanced 17 O{ 1 H} SSNMR. In situ DRIFTS and XAS hydrogenation experiments reveal the probable formation of a surface Pt(IV)-H upon hydrogenolysis of Pt-Me groups. The heterogenized organoplatinum(IV)-hydride sites catalyze the selective partial hydrogenation of 1,3-butadiene to butenes (up to 95%) and the reduction of nitrobenzene derivatives to anilines (up to 99%) with excellent tolerance of reduction-sensitive functional groups (olefin, carbonyl, nitrile, halogens) under mild reaction conditions.

The characterization of nanometer-scale interactions between carbon-containing substrates and alumina surfaces is of paramount importance to industrial and academic catalysis applications, but it is also very challenging. Here, we demonstrate that dynamic nuclear polarization surface-enhanced NMR spectroscopy (DNP SENS) allows the unambiguous description of the coordination geometries and conformations of the substrates at the alumina surface through high-resolution measurements of 13 C- 27 Al distances. We apply this new technique to elucidate the molecular-level geometry of 13 C-enriched methionine and natural abundance poly(vinyl alcohol) adsorbed on γ-Al 2 O 3 -supported Pd catalysts, and we support these results with element-specific X-ray absorption near-edge measurements. This work clearly demonstrates a surprising bimodal coordination of methionine at the Pd-Al 2 O 3 interface.

Due to its extremely low natural abundance and quadrupolar nature, the (17)O nuclide is very rarely used for spectroscopic investigation of solids by NMR without isotope enrichment. Additionally, the applicability of dynamic nuclear polarization (DNP), which leads to sensitivity enhancements of 2 orders of magnitude, to (17)O is wrought with challenges due to the lack of spin diffusion and low polarization transfer efficiency from (1)H. Here, we demonstrate new DNP-based measurements that extend (17)O solid-state NMR beyond its current capabilities. The use of the PRESTO technique instead of conventional (1)H-(17)O cross-polarization greatly improves the sensitivity and enables the facile measurement of undistorted line shapes and two-dimensional (1)H-(17)O HETCOR NMR spectra as well as accurate internuclear distance measurements at natural abundance. This was applied for distinguishing hydrogen-bonded and lone (17)O sites on the surface of silica gel; the one-dimensional spectrum of which could not be used to extract such detail. Lastly, this greatly enhanced sensitivity has enabled, for the first time, the detection of surface hydroxyl sites on mesoporous silica at natural abundance, thereby extending the concept of DNP surface-enhanced NMR spectroscopy to the (17)O nuclide.

Organozirconium complexes are chemisorbed on Brønsted acidic sulfated ZrO2 (ZrS), sulfated Al2O3 (AlS), and ZrO2-WO3 (ZrW). Under mild conditions (25 °C, 1 atm H2), the supported Cp*ZrMe3, Cp*ZrBz3, and Cp*ZrPh3 catalysts are very active for benzene hydrogenation with activities declining with decreasing acidity, ZrS ≫ AlS ≈ ZrW, arguing that more Brønsted acidic oxides (those having weaker corresponding conjugate bases) yield stronger surface organometallic electrophiles and for this reason have higher benzene hydrogenation activity. Benzene selective hydrogenation, a potential approach for carcinogenic benzene removal from gasoline, is probed using benzene/toluene mixtures, and selectivities for benzene hydrogenation vary with catalyst as ZrBz3(+)/ZrS(-), 83% > Cp*ZrMe2(+)/ZrS(-), 80% > Cp*ZrBz2(+)/ZrS(-), 67% > Cp*ZrPh2(+)/ZrS(-), 57%. For Cp*ZrBz2(+)/ZrS(-), which displays the highest benzene hydrogenation activity with moderate selectivity in benzene/toluene mixtures. Other benzene/arene mixtures are examined, and benzene selectivities vary with arene as mesitylene, 99%, > ethylbenzene, 86% > toluene, 67%. Structural and computational studies by solid-state NMR spectroscopy, XAS, and periodic DFT methods applied to supported Cp*ZrMe3 and Cp*ZrBz3 indicate that larger Zr···surface distances are present in more sterically encumbered Cp*ZrBz2(+)/AlS(-) vs Cp*ZrMe2(+)/AlS(-). The combined XAS, solid state NMR, and DFT data argue that the bulky catalyst benzyl groups expand the "cationic" metal center-anionic sulfated oxide surface distances, and this separation/weakened ion-pairing enables the activation/insertion of more sterically encumbered arenes and influences hydrogenation rates and selectivity patterns.

The conformations of (pentafluorophenyl)propyl groups (-CH(2)-CH(2)-CH(2)-C(6)F(5), abbreviated as PFP), covalently bound to the surface of mesoporous silica nanoparticles (MSNs), were determined by solid-state NMR spectroscopy and further refined by theoretical modeling. Two types of PFP groups were described, including molecules in the prone position with the perfluorinated aromatic rings located above the siloxane bridges (PFP-p) and the PFP groups denoted as upright (PFP-u), whose aromatic rings do not interact with the silica surface. Two-dimensional (2D) (13)C-(1)H, (13)C-(19)F and (19)F-(29)Si heteronuclear correlation (HETCOR) spectra were obtained with high sensitivity on natural abundance samples using fast magic angle spinning (MAS), indirect detection of low-gamma nuclei and signal enhancement by Carr-Purcell-Meiboom-Gill (CPMG) spin-echo sequence. 2D double-quantum (DQ) (19)F MAS NMR spectra and spin-echo measurements provided additional information about the structure and mobility of the pentafluorophenyl rings. Optimization of the PFP geometry, as well as calculations of the interaction energies and (19)F chemical shifts, proved very useful in refining the structural features of PFP-p and PFP-u functional groups on the silica surface. The prospects of using the PFP-functionalized surface to modify its properties (e.g., the interaction with solvents, especially water) and design new types of the heterogeneous catalytic system are discussed.

The structure of the silica supported palladium(II) complex [Pd(dppp)(S2C-NEt2)]BF4 (abbreviated as [Pd(dppp)(dtc)]BF4, where dppp is Ph2P(CH2)3PPh2) and interactions between the [Pd(dppp)(dtc)]+ cation, the BF4(-) anion, and the silica surface are studied using solid-state NMR spectroscopy. The unsupported, crystalline form of [Pd(dppp)(dtc)]BF4 is also investigated, both by X-ray diffraction and NMR. The structures of the cation and anion are found to be essentially the same in both unsupported and supported complex. The [Pd(dppp)(dtc)]BF4 loading has been determined by quantitative measurements of 11B, 19F, and 31P intensities, whereas the arrangement of anions and cations on the surface of silica has been established by two-dimensional heteronuclear correlation experiments involving 1H, 11B, 13C, 19F, 29Si, and 31P nuclei. At low coverages, the [Pd(dppp)(dtc)]+ cations are located near the BF4(-) anions, which in turn are immobilized directly on the surface near the Q4 sites. At higher loadings, which in this study corresponded to 0.06-0.15 mmol/g, the complexes stack on top of each other, despite the fact that the directly adsorbed molecules take up less than 10% of the silica surface. The relevance of these findings to heterogeneous catalysis is discussed.

A new nucleophilic catalytic system comprised of dialkylaminopyridine-functionalized mesoporous silica nanosphere (DMAP-MSN) has been synthesized and characterized. We have demonstrated that this material is an efficient heterogeneous catalyst for Baylis-Hillman, acylation, and silylation reactions with good reactivity, product selectivity, and recyclability. We envision that this DMAP-functionalized mesoporous silica material can also serve as an effective heterogeneous catalyst for many other catalytic nucleophilic reactions.

Highly resolved solid-state HETCOR NMR spectra between protons and low gamma nuclei ((13)C and (29)Si) can be suitably obtained on surfaces using a "brute force" (1)H-(1)H decoupling by MAS at rates > or =40 kHz. Despite a small rotor volume (<10 microL), a (1)H-(13)C HETCOR spectrum of allyl groups (AL, -CH(2)-CH=CH(2)) covalently anchored to the surface of MCM-41 silica was acquired without using isotope enrichment. The advantages of using fast MAS in such studies include easy setup, robustness, and the opportunity of using low RF power for decoupling. In the case of the (1)H-(29)Si HETCOR experiment, the sensitivity can be dramatically increased, in some samples by more than 1 order of magnitude, through implementing into the pulse sequence a Carr-Purcell-Meiboom-Gill train of pi pulses at the (29)Si spin frequency. The use of low-power heteronuclear decoupling is essential in the (1)H-(29)Si CPMG-HETCOR experiment, due to unusually long acquisition periods. These methods provided detailed structural characterization of the surface of AL-MCM mesoporous silica.

A systematic study of the surface of MCM-41-type mesoporous silica nanoparticles prepared under low surfactant concentration was carried out using high-resolution solid-state nuclear magnetic resonance spectroscopy. The structures and concentrations of various species present during dehydration and rehydration of mesoporous silicas between -25 and 500 degrees C were detailed by employing one-dimensional and two-dimensional (1)H, (13)C, and (29)Si NMR, including (1)H signal intensity measurements, (1)H-(1)H homonuclear correlation experiments (double quantum, exchange, and RFDR), and (1)H-(29)Si heteronuclear correlation NMR. These experiments employed high MAS rates of up to 45 kHz. The study shows that the surfactant (CTAB) was almost completely removed by acid extraction. The residual molecules assumed prone positions along the pores, with the tailgroup being most mobile. The weakly adsorbed water was hydrogen bonded to the silanol groups, all of which were involved in such bonds under ambient humidity. Specific structures involving water and silanol groups were proposed for various stages of thermal treatment, which included dehydration, dehydroxylation, and subsequent rehydration.

We have synthesized a poly(lactic acid) coated MCM-41-type mesoporous silica nanosphere (PLA-MSN) material can serve as a fluorescence sensor system for detection of amino-containing neurotransmitters in neutral aqueous buffer. Utilizing the PLA layer as a gatekeeper, we investigated the molecular recognition events between several structurally simple neurotransmitters, i.e., dopamine, tyrosine, and glutamic acid and a pore surface-anchored o-phthalic hemithioacetal (OPTA) group, which functions as a fluorescence-sensing group that can react with the neurotransmitters with primary amine groups and form the corresponding fluorescent isoindole products. The poly(lactic acid) layer of the PLA-MSN sensor showed a unique "sieving" effect that regulates the rates of diffusion of the amino acid-based neurotransmitters into the sensor mesopores of the material.

A series of bifunctionalized mesoporous silica nanosphere-based (MSN) heterogeneous catalysts for the nitroaldol (Henry) reaction have been synthesized. A common 3-[2-(2-aminoethylamino)ethylamino]propyl (AEP) primary group and three different secondary groups, ureidopropyl (UDP), mercaptopropyl (MP), and allyl (AL) functionalities, were incorporated to these mesoporous silica materials by introducing equal amounts of AEP-trimethoxysilane with UDP-, MP-, or AL-trialkoxysilane precursors to our previously reported co-condensation reaction. Structures and relative concentrations of the functional groups were detailed by solid-state NMR and other spectroscopic techniques. The AEP group served as a catalyst, and the other secondary groups provided different noncovalent interactions to reactants and thereby controlled the reaction selectivity. By varying the secondary group in these bifunctionalized MSN catalysts, we investigated the selectivity of a nitroaldol reaction of two competing benzaldehydes reacting with nitromethane by measuring the molar ratio of the nitroalkene products. The selectivity of the bifunctionalized MSN catalysts could be systematically tuned simply by varying the physicochemical properties of the pore surface-bound secondary groups, i.e., polarity and hydrophobicity.

A polyalkynylene-based conducting polymer (molecular wire) has been synthesized within the Cu-functionalized mesoporous MCM-41 silica catalyst. Fluorescence and 13C solid-state NMR provided spectroscopic evidence that the synthesis of extended polymeric chains with a high degree of alignment requires homogeneously distributed catalytic sites throughout the entire MCM matrix. This type of homogeneity has been achieved via co-condensation of the catalytic groups in narrow pores. In addition, our results indicated that proper adjustment of the pore diameter is vital to prevent clogging of the pores with aggregated or cross-linked polymers or both.

The environments for oxygen sites in crystalline V(2)O(5) and in layered vanadia gels produced via sol-gel synthesis have been investigated using (17)O MAS and 3QMAS NMR. For crystalline V(2)O(5), three structural oxygen sites were observed: V=O (vanadyl), V(2)O (doubly coordinated), and V(3)O (triply coordinated). Line-shape parameters for these sites were determined from numerical simulations of the MAS spectra. For the vanadia gels at various stages of dehydration, assignments have been proposed for numerous vanadyl, doubly coordinated, and triply coordinated oxygen sites. In addition, by correlating the (17)O MAS and 3QMAS NMR, (51)V MAS NMR, and thermogravimetric analysis data, the coordination of water sites has been established. On the basis of these results, the gel structure and its evolution at various stages of hydration have been detailed. Upon rehydration of the layered gel, we observed a preferred site for initial water readsorption. The oxygen atoms of these readsorbed water molecules readily exchanged into all types of oxygen sites even at room temperature.

We describe the nearly quantitative preparation of phosphorus ylides and the Wittig reaction occurring in the solid sate during high-energy mechanochemical processing. Initial insights into the details of the discovered chemical transformations indicate that high-energy mechanical processing supports the interaction of reacting centers by breaking crystallinity of the reactants and by providing mass transfer without a solvent.