J.M. Basset

Surface-supported metal cluster carbonyls. Chemisorption, decomposition and reactivity of Os3(CO)12, H2Os3(CO)10 and Os6(CO)18 supported on silica and alumina and the investigation of the fischer-tropsch catalysis with these systems

Abstract On silica and alumina, Os 3 (CO) 12 , H 2 Os 3 (CO) 10 and Os 6 (CO) 18 are physisorbed (or weakly adsorbed) at room temperature. When the physisorbed cluster Os 3 (CO) 12 is thermally decomposed at ca. 150°C, there is an oxidative addition of a surface MOH group (M  Al???, Si???) to the OsOs bond of Os 3 (CO) 12 with formation of the surface species Os 3 (H)(CO) 10 (OM) (M  Al???, Si???) in which the cluster is covalently bonded to the surface by MOOs 3 bonds.Such a grafted cluster was also obtained was also obtained by bringing Os 3 (CO) 10 (CH 3 CN) 2 or H 2 Os 3 (CO) 10 into reaction with the surface of silica and alumina. On silica the grafted cluster, when treated with CO + H 2 O, can regenerate the starting Os 3 (CO) 12 cluster. The structure of the covalently bonded cluster was also confirmed by the synthesis of the model compound Os 3 (H)(CO) 10 (OSi(Ph) 3 ). Such covalent attachment of a cluster to a surface can be regarded as a model for the metal—support interaction which is frequently involved in heterogeneous catalysis. When the physisorbed clusters Os 3 (CO) 12 , H 2 Os 3 (CO) 10 , Os 6 (CO) 18 or the chemisorbed cluster Os 3 (H)(CO) 10 (OM), (M  Al???, Si???), are heated at about 200°C, there is a breakdown of the cluster cage with simultaneous oxidation of the osmium to two osmium(II) carbonyl species by the surface proton with simultaneous release of hydrogen. The [Os II (CO) 3 X 2 ] 2 and [Os II (CO) 2 X 2 ] n surface species in which X is a surface oxygen atom can be interconverted by a reversible carbonylation-decarbonylation process at 200°C. These two species can be also obtained by decomposition of [Os(CO) 3 X 2 ] 2 , (X  Cl, Br) onto silica or alumina surface or by CO reduction at 200°C of OsX 3 adsorbed on silica or alumina. The structure of one these surface compounds was confirmed by synthesis of the model compound [Os(CO) 3 (OSiPh 3 ) 2 ] m . These surface osmium carbonyl species exhibit a rather high thermal and chemical stability. They appear to be reduced by H 2 to metallic osmium only at 400°C. The thermal decomposition of the supported clusters is followed by a stoichiometric water gas shift reaction as well as a stoichiometric formation of methane. Under CO + H 2 , a Fischer-Tropsch catalyst, which exhibits a high selectivity for methane, is obtained. From the range of temperatures over which those stoichiometric and catalytic reactions are observed it seems reasonable to assume that they involve the Os II carbonyl species rather than metallic osmium.

Surface supported metal cluster carbonyls. Chemisorption decomposition and reactivity of Rh4(CO)12 supported on silica and alumina

Abstract Chemisorption of Rh 4 (CO) 12 on to a highly divided silica (Aerosil “0” from Degussa), Leads to the transformation: 3 Rh 4 (CO) 12 → 2 Rh 6 (CO) 16 + 4 CO. Such an easy rearrangement of the cluster cage implies mobility of zerovalent rhodium carbonyl fragments on the surface. Carbon monoxide is a very efficient inhibitor of this reaction, and Rh 4 (CO) 12 is stable as such on silica under a CO atmosphere. Both Rh 4 (CO) 12 and Rh 6 (CO) 16 are easily decomposed to small metal particles of higher nuclearity under a water atmosphere and to rhodium(I) dicarbonyl species under oxygen. From the Rh I (CO) 2 species it is possible to regenate first Rh 4 (CO) 12 and then Rh 6 (CO) 16 by treatment with CO ( P co ⩾ 200 mm Hg) and H 2 O ( P H 2 O ⩾ 18 mm Hg). The reduction of Rh I (CO) 2 surface species by water requires a nucleophilic attack to produce an hypothetical [Rh(CO) n ] m species which can polymerize to small Rh 4 or Rh 6 clusters in the presence of CO but which in the absence of CO lead to metal particles of higher nuclearity. Similar results are obtained on alumina.

Surface-supported metal cluster carbonyls. Chemisorption, decomposition and reactivity of Rh6(C0)16 supported on silica

Abstract A partially decarbonylated metal cluster is quickly formed on the surface of silica by oxidation at room temperature; it is possible to regenerate the initial cluster compound under a carbon monoxide atmosphere at 200°C. Decarbonylation of Rh 6 (CO) 16 at higher temperature produces a new metallic material on the surface, characterized by two v (CO) vibration bands at 2048 ± 7 cm −1 and 1893 ± 10 cm −1 . These two bands have been respectively assigned to a terminal carbonyl group and a bridged carbonyl group bonded to two rhodium atoms. Oxidation of this compound occurs very easily under oxygen at room temperature and gives an oxidized material presumably of the same nuclearity; adsorption of carbon monoxide produces two intense sharp bands at 2093 and 2038 cm −1 which have been assigned to the symmetric and asymmetric stretching modes of two CO molecules bonded to a single oxidized Rh site as Rh I (CO) 2 . The conversion from the oxidized surface species to the metallic one can be performed under mild conditions, but attempts to regenerate the initial cluster compound were unsuccessful.

A surface organometallic approach to the synthesis of rhenium-based catalysts for the metathesis of olefins: CH3ReO3/Nb2O5☆

Abstract The reaction of methyltrioxorhenium with the surface of niobium oxide leads to an active catalyst for the metathesis of acyclic olefins. The activity is related to the niobia surface acidity and to a methylrhenium surface species that resonates at 25 ppm on the 13 C MAS NMR spectrum.

Surface supported metal cluster carbonyls. Chemisorption, reactivity, and decomposition of Ru3(CO)12 on silica

Abstract Ru3(CO)12 supported on silica is oxidised by surface SiOH groups in presence of water and/or dioxygen to form oxidised species, probably incorporated into the silica surface, such as RuII(CO)n(OSi )2 (n = 2, 3). The presence of air (involving both water and dioxygen) greatly accelerates this oxidative process. When supported in total absence of dioxygen, Ru3(CO)12 reacts with surface silanol groups to produce the grafted cluster HRu3(CO)10(OSi ), which has been characterized by chemical methods and by infrared and Raman spectroscopies. The grafted cluster is not very stable; it is an intermediate in the formation, by controlled thermal decomposition, of both small metallic particles and some RuII(CO)n(OSi )2 (n = 2, 3) carbonyl surface species (this oxidation by surface protons is also evidenced by the formation of molecular hydrogen). The formation of metallic ruthenium accounts for the production of hydrocarbons during the thermal decomposition.

Formation and Characterization of Zwitterionic Stereoisomers from the Reaction of B(C6F5)3 and NEt2Ph: (E)- and (Z)-[EtPhN+=CHCH2-B−(C6F5)3]

The stoichiometric reaction of B(C6F5)3 and NEt2Ph I, at room temperature, in an aromatic solvent, has been investigated by 1D and 2D NMR spectroscopy (1H, 11B,13C, 15N and 19F). No Et2PhN·B(C6F5)3 adduct was observed. An equilibrium between free B(C6F5)3, NEt2Ph, [HB(C6F5)3]−(HNEt2Ph)+ and two zwitterionic stereoisomers (E)- and (Z)-[EtPhN+=CH-CH2-B−(C6F5)3] (30%) in an E/Z ratio of 3:2 was observed. Whatever the protic reagent Z-OH [Z = H, SiPh3, (c-C5H9)7O12Si8, or silanol group of silica], all the equilibria involved in solutions of I are quantitatively displaced towards the ionic form [Z-O-B(C6F5)3]−(HNEt2Ph)+. In the case of dimethylaniline, besides free B(C6F5)3 and Me2NPh, the 1:1 adduct (C6F5)3B·NMe2Ph and an iminium salt [PhCH3N=CH2]+[HB(C6F5)3]− have been identified. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Synthesis and characterization of ionic liquids based upon 1-butyl-2,3-dimethylimidazolium chloride/ZnCl2

Trialkylimidazolium chlorozincate molten salts resulting from the combination of zinc chloride and 1-butyl-2,3-dimethylimidazolium chloride, [BMMI][Cl], have been prepared with a mole percent of ZnCl2, R (R = nZnCl2/nZnCl2 + n[BMMI][Cl]) equal to 0, 0.1, 0.25, 0.33, 0.5, 0.66, 0.75. Their analyses by DSC, 13C, 1H and 35Cl solid state and solution NMR, and mass spectrometry (ESI, MS/MS) are consistent with the presence of [BMMI][Cl] and [BMMI][ZnCl3] for R < 0.5; pure [BMMI][ZnCl3] for R = 0.5, and [BMMI][ZnCl3] with [BMMI][Zn3Cl7] for R > 0.5. Infrared spectra realized in the presence of pyridine show that the Lewis acidity of ZnCl2–[BMMI][Cl] increases with R. High temperature (110 °C) 13C and 35Cl NMR experiments on neat [BMMI][ZnCl3] (R = 0.5) evidenced that its structure varies with time from [BMMI][ZnCl3] to [BMMI⋯Cl⋯ZnCl2].

The water gas shift reaction catalyzed by Rh6(CO)16 adsorbed on alumina or [Rh(CO)2Cl]2 adsorbed on alumina, Na-Y zeolite and H-Y zeolite

Abstract Rh 6 (CO) 16 chemisorbed on η-alumina or [Rh(CO) 2 Cl] 2 chemisorbed on η-alumina, Na-Y zeolite and H-Y zeolite catalyze the water gas shift reaction to various degrees. The following order of activity was observed: alumina > Na-Y > H-Y zeolite. With alumina the reaction occurs between 25 and 100°C. Turnover numbers as high as 255/Rh atom/h are obtained at 50°C and under 50 atm. These turnover numbers are the same whether the precursor complex is Rh 6 (CO) 16 or [Rh(CO) 2 Cl] 2 . The mechanism of such a reaction has been deduced from infrared studies, mass balance and labeling experiments. It involves three steps: electrophilic attack by surface protons on the metallic frame with formation of Rh I (CO) 2 (OAl )(HOAl ) and possibly Rh III (H)(H)(OAl )HOAl ); reductive elimination of H 2 from Rh(H)(H)(OAl )(HOAl ) under CO pressure; and nucleophilic attack by water on CO coordinated to rhodium(I) with formation of CO 2 , H + and regeneration of Rh 6 (CO) 16 . If the CO pressure is too low or if liquid water is used, aging of the catalyst occurs which seems to be due to the formation of metallic rhodium. The intermediacy of [Rh(CO) 4 ] − is also suspected in the step of metal-metal bond formation.

Immobilization of η5-cyclopentadienyltris(dimethylamido)zirconium polymerization catalysts on a chlorosilane- and HMDS-modified mesoporous silica surface: a new concept for supporting metallocene amides towards heterogeneous single-site-catalysts

Abstract The modification of a mesoporous silica surface with Si(Ind)(CH 3 ) 2 Cl and the immobilization of CpZr(NMe 2 ) 3 on this surface was studied via IR-spectroscopy. To reduce side reactions, the indenyl-modified silica was reacted with hexamethyldisilazane (HMDS) under IR-control before the CpZr(NMe 2 ) 3 -immobilization. The role of the hydroxyl group protection with HMDS is discussed. The surface modifications have been repeated via Schlenk technique at the same conditions and the surface modifications were studied with 13 C CP MAS–NMR, 1 H MAS–NMR, elemental-, SEM- and BET-analysis. The surface species of the resulting catalysts are discussed. The precatalysts have been treated with methylaluminoxane (MAO) (Al:Zr (mol:mol)=500:1) and the resulting Zr contents (leaching-effect) are discussed. All catalysts have been tested in ethylene and propylene polymerization.

Surface supported metal cluster carbonyls. the surface organometallic chemistry of polymetallic and monometallic osmium carbonyl species formed by depositing various osmium clusters on silica and alumina

Abstract On highly hydroxylated silica, Os 3 (CO) 12 , H 2 Os 3 (CO) 10 or Os 6 (CO) 18 are simply physisorbed at room temperature. At 150°C there is an oxidative addition of the surface SiOH group to the OsOs bond of Os 3 (CO) 12 with formation of the surface species: HOs 3 (CO) 10 (OSi). Such a structure was confirmed by the synthesis of the model compound HOs 3 (CO) 10 (OSi Ph 3 ). When the physisorbed clusters Os 3 (CO) 12 , H 2 Os 3 (CO) 10 , Os 6 (CO) 18 or the chemisorbed clusters HOs 3 (CO) 10 (OSi ), are heated at 200°C, a breakdown of the cluster frame occurs, with formation of osmium(II) carbonyl species of the type [Os(CO) 2 (OSi ) 2 ] n or [Os(CO) 3 (OSi ) 2 ] 2 . Similar reactions are observed on alumina.