Surface-supported group 5 metal organometallic compounds for catalytic arene hydrogenation

Profilet, Robert D.; Rothwell, Arlene P.; Rothwell, Ian P.

doi:10.1039/c39930000042

Cited by 33 publications

(22 citation statements)

References 9 publications

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“…These surface complexes ( 25 and 29 – 31 ), probably generated in situ from their alkyl derivatives, catalyze the hydrogenation of aromatics very efficiently [Eq. (15)] 100. 101 For example, 4000 equivalents of benzene are converted into cyclohexane in 240 min in the presence of 30 and H 2 (80 atm) at 120 °C. …”

Section: Application Of Surface Organometallic Chemistry To Heteromentioning

confidence: 93%

Homogeneous and Heterogeneous Catalysis: Bridging the Gap through Surface Organometallic Chemistry

et al. 2003

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Surface organometallic chemistry is an area of heterogeneous catalysis which has recently emerged as a result of a comparative analysis of homogeneous and heterogeneous catalysis. The chemical industry has often favored heterogeneous catalysis, but the development of better catalysts has been hindered by the presence of numerous kinds of active sites and also by the low concentration of active sites. These factors have precluded a rational improvement of these systems, hence the empirical nature of heterogeneous catalysis. Catalysis is primarily a molecular phenomenon, and it must involve well-defined surface organometallic intermediates and/or transition states. Thus, one must be able to construct a well-defined active site, test its catalytic performance, and assess a structure-activity relationship, which will be used, in turn-as in homogeneous catalysis-to design better catalysts. By the transfer of the concepts and tools of molecular organometallic chemistry to surfaces, surface organometallic chemistry can generate well-defined surface species by understanding the reaction of organometallic complexes with the support, which can be considered as a rigid ligand. This new approach to heterogeneous catalysis can bring molecular insight to the design of new catalysts and even allow the discovery of new reactions (Ziegler-Natta depolymerization and alkane metathesis). After more than a century of existence, heterogeneous catalysis can still be improved and will play a crucial role in solving current problems. It offers an answer to economical and environmental problems faced by industry in the production of molecules (agrochemicals, petrochemicals, pharmaceuticals, polymers, basic chemicals).

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Section: Application Of Surface Organometallic Chemistry To Heteromentioning

confidence: 93%

Homogeneous and Heterogeneous Catalysis: Bridging the Gap through Surface Organometallic Chemistry

et al. 2003

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“…As a control, studies of benzene hydrogenation in homogenous solution using Cp*Zr(CH 3 ) 3 + B(C 6 F 5 ) 3 ) under far more drastic conditions (120°C, 80-95 atm H 2 ), and little is known about their structures (19).…”

Section: Resultsmentioning

confidence: 99%

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

Williams

Guo

Motta

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Structural characterization of the catalytically significant sites on solid catalyst surfaces is frequently tenuous because their fraction, among all sites, typically is quite low. Here we report the combined application of solid-state 13 C-cross-polarization magic angle spinning nuclear magnetic resonance ( 13 C-CPMAS-NMR) spectroscopy, density functional theory (DFT), and Zr X-ray absorption spectroscopy (XAS) to characterize the adsorption products and surface chemistry of the precatalysts (η 5 O rganometallic molecule-derived heterogeneous catalysts are of increasing interest owing to their enhanced thermal stability and activity vs. their homogeneous analogs, and their atomically precise tailorable metal-ligand structures vs. other heterogeneous catalysts (1, 2). Furthermore, it is becoming increasingly evident that the inorganic support in many systems is noninnocent and can function as both a ligand and an activator, with the chemically important but poorly understood nature of the catalyst-support interaction strongly modulating catalytic activity and selectivity (3, 4). When adsorbed on Lewis acidic, dehydroxylated alumina surfaces, group 4 complexes such as Cp 2 ZrR 2 (Cp = η 5 -C 5 H 5 ; A, R = H; B, R = CH 3 ) and Cp*Zr (CH 3 ) 3 [C, Cp* = η 5 -C 5 (CH 3 ) 5 ] were argued on the basis of highresolution solid-state NMR spectroscopy to transfer an alkyl anion to unsaturated, Lewis acidic surface sites as in Fig. 1 (complexes B, C → qualitative model D) (5, 6). The resulting catalysts are extremely active for olefin hydrogenation and polymerization, and analogous ion-paired species form the basis for large-scale industrial polymerization processes (7,8). However, kinetic poisoning experiments in which the catalytic sites are titrated in situ with H 2 O or t BuCH 2 OH indicate that ≤5% of D-type sites are catalytically significant, likely reflecting, among other factors, the established heterogeneity of alumina surfaces (5, 6, 9), hence rendering active site structural and chemical descriptions necessarily imprecise. In contrast to these results, chemisorption of such organozirconium precursors on SiO 2 , Al 2 O 3 , and SiO 2 -Al 2 O 3 surfaces having appreciable coverage by weakly acidic OH groups predominantly yields covalently bound, poorly electrophilic Etype species via Zr-CH 3 protonolysis with CH 4 evolution (5, 6, 10, 11). Although the E-type sites may be characterized in some detail by high-resolution solid-state NMR and extended X-ray adsorption fine structure spectroscopy (EXAFS), they display minimal catalytic turnover in the absence of added, complicating activators [e.g., methylalumoxane or B(C 6 F 5 ) 3 ], and the fraction of catalytically significant sites is unknown (12, 13). In such situations, it is experimentally impossible to unambiguously distinguish catalytically significant sites from inactive "spectator" sites, hence to fully understand the catalytic chemistry.-In marked contrast to the above results, chemisorption of these same organozirconium molecules on highly Brønsted "super...

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“…[1][2][3][4][5] Notably, they also catalyze the hydrogenolysis of polyolefins and alkanes, except ethane, and this reaction corresponds to the reverse of the polymerization of olefins. [6][7][8][9] Under similar conditions, alkanes, including ethane, are transformed into their lower homologues in the presence of a catalytic amount of silica-supported tantalum hydride.…”

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confidence: 99%

Homologation of Propane Catalyzed by Oxide‐Supported Zirconium Dihydride and Dialkyl Complexes

et al. 2007

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Zirconium hydrides supported on oxide materials catalyze several classical reactions, such as hydrogenation, reductive cyclization, cyclotrimerization, and olefin polymerization. [1][2][3][4][5] Notably, they also catalyze the hydrogenolysis of polyolefins and alkanes, except ethane, and this reaction corresponds to the reverse of the polymerization of olefins. [6][7][8][9] Under similar conditions, alkanes, including ethane, are transformed into their lower homologues in the presence of a catalytic amount of silica-supported tantalum hydride.[10] Cleavage of the carbon-carbon bond is different for both catalysts (Group 4 vs. Group 5): b-alkyl transfer for d 0 zirconium catalysts versus a-alkyl transfer for d 2 tantalum catalysts so that hydrogenolysis of a C À C bond in the skeleton of an alkane occurs by removal of one carbon atom at a time for tantalum catalysts and of at least two carbon atoms for zirconium catalysts, hence the difference in the selectivity of the final product (Scheme 1). [9,11,12] Silica-supported tantalum hydrides also catalyze the conversion of alkanes into their direct lower and higher homologues. This reaction, named alkane metathesis, [13] involves carbene and metallacyclobutane intermediates, [14,15] and it explains the selective formation of the directly lower and higher linear homologues of the starting alkane through the transfer of one carbon atom at a time, thereby preventing the formation of long-chain alkanes. We have exploited the specific properties of Zr, which is able to 1) activate C À H bonds of alkanes through s-bond metathesis, 2) carry out hydrogenolysis (the transfer of at least two carbon atoms through b-alkyl transfer), and 3) polymerize olefins by insertion. [16,17] Herein, we report on the transformation of propane into longer-chain higher homologues (up to C 10 ) at moderate temperatures.In an autoclave, zirconium hydride supported on silicaalumina was brought into contact with 500 equivalents of propane under supercritical conditions (43 bar, d = 510 Kg m À3 ). After 48 h at 200 8C, 12.6 % of the propane was converted into lower (39.1 %) and higher homologues (60.9 %). Notably, the major product was 2-methylpropane (20.7 %), and overall branched higher homologues up to C 10 are favored, and particularly the iso homologues, except for pentanes (see the Supporting Information, Table S1 for detailed selectivities). This selectivity is in contrast with that reported with tantalum hydride or tungsten hydride supported on oxide supports: [13,18] 1) linear higher homologues are the major products; 2) higher homologues are mainly butanes and pentanes along with trace amounts of hexanes.The reaction was studied in a flow reactor to identify primary products by investigating the effect of inverse space velocity (contact time) on product selectivity.First, using a constant flow of propane (600 kPa, 3 N mL) at 216 8C, we observed the formation of H 2 , methane, and ethane, which resulted from the C À H bond activation of propane, and its subsequent hydrogenolysis (Supportin...

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Surface-supported group 5 metal organometallic compounds for catalytic arene hydrogenation

Abstract: The Group 5 metal alkylidyne bridged compounds [(Me3SiCH2)2M(y-CSiMe3)2M(CH$SiMe3)2] (M = Nb, Ta) supported on silica will catalyse the exhaustive hydrogenation of a variety of aromatic substrates.

Cited by 33 publications

References 9 publications

Homogeneous and Heterogeneous Catalysis: Bridging the Gap through Surface Organometallic Chemistry

Homogeneous and Heterogeneous Catalysis: Bridging the Gap through Surface Organometallic Chemistry

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

Homologation of Propane Catalyzed by Oxide‐Supported Zirconium Dihydride and Dialkyl Complexes

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Surface-supported group 5 metal organometallic compounds for catalytic arene hydrogenation

Abstract: The Group 5 metal alkylidyne bridged compounds [(Me3SiCH2)2M(y-CSiMe3)2M(CH$SiMe3)2] (M = Nb, Ta) supported on silica will catalyse the exhaustive hydrogenation of a variety of aromatic substrates.

Cited by 33 publications

References 9 publications

Homogeneous and Heterogeneous Catalysis: Bridging the Gap through Surface Organometallic Chemistry

Homogeneous and Heterogeneous Catalysis: Bridging the Gap through Surface Organometallic Chemistry

Surface structural-chemical characterization of a single-site d 0 heterogeneous arene hydrogenation catalyst having 100% active sites

Homologation of Propane Catalyzed by Oxide‐Supported Zirconium Dihydride and Dialkyl Complexes

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Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites