Molecular Intracage Chemistry: [Rh6(CO)15]2− in Zeolite NaX

Weber, William A.; Phillips, Brian L.; Gates, Bruce C.

doi:10.1002/(sici)1521-3765(19991001)5:10<2899::aid-chem2899>3.0.co;2-j

Cited by 24 publications

(17 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Consistent with this suggestion, oxidative fragmentation of Rh 6 and Ir 4 clusters supported on MgO 55 led to the formation of metal oxide like species under conditions similar to those reported here. Comparable results have been observed for the oxidative fragmentation of [Rh 6 (CO) 15 ] 2-in NaX zeolite, 56 Pt clusters in KLTL zeolite, 57 and Ir clusters on MgO, for example. 57…”

Section: Discussionmentioning

confidence: 99%

Oxidation States of Gold in MgO-Supported Complexes and Clusters: Characterization by X-ray Absorption Spectroscopy and Temperature-Programmed Oxidation and Reduction

and

Gates

2003

J. Phys. Chem. B

View full text Add to dashboard Cite

X-ray absorption near edge structure (XANES) spectroscopy, temperature-programmed reduction (TPR), and temperature-programmed oxidation (TPO) were used in combination to determine the oxidation states of gold in clusters and complexes supported on MgO. The samples were also characterized by X-ray absorption fine structure (EXAFS) spectroscopy to determine the structure of the supported gold species. The samples were prepared by adsorption of Au III (CH 3 ) 2 (C 5 H 7 O 2 ) on MgO followed by treatment in He or H 2 for 2 h at 573 K and 1 atm. The XANES and TPR results identify Au 3+ in supported gold complexes and show that treatment in H 2 caused reduction at 480 K to metallic gold, which could be reoxidized to Au 3+ at about 490 K by treatment in O 2 , as shown by TPO and XANES. Treatment of the sample containing supported Au(III) complexes with CO led to the formation of partially reduced gold (Au + , 40 ( 5%) and zerovalent gold (60 ( 5%), as shown by the combination of XANES, TPR, and TPO. The results demonstrate how XANES and TPR/TPO used in combination can effectively determine the oxidation states of metals on supports, even when the metals are present in various oxidation states.

show abstract

Section: Discussionmentioning

confidence: 99%

Oxidation States of Gold in MgO-Supported Complexes and Clusters: Characterization by X-ray Absorption Spectroscopy and Temperature-Programmed Oxidation and Reduction

and

Gates

2003

J. Phys. Chem. B

View full text Add to dashboard Cite

show abstract

“…Similarly, EXAFS data show that the Rh-Rh distance shrinks from 2.75 to 2.65 Å upon decarbonylation of NaX-zeolite-and NaY-zeolite-supported Rh 6 (CO) 16 . 5, 22 A similar shrinkage of the cluster frame upon decarbonylation was shown by EXAFS data 4 characterizing TiO 2 -supported Rh 6 (CO) 16 . We infer that the observed pattern is a common feature of rhodium clusters.…”

Section: Discussionmentioning

confidence: 99%

Carbonylation and Decarbonylation of γ-Al₂O₃-Supported Hexarhodium Clusters: Characterization by Infrared, ¹³C NMR, and Extended X-ray Absorption Fine Structure Spectroscopies

et al. 2003

View full text Add to dashboard Cite

Rh6(CO)16 adsorbed on γ-Al2O3 that had been calcined at 400°C was decarbonylated in steps by treatment in He at increasing temperatures. The metal frame in the supported clusters remained largely intact during the decarbonylation process as evidenced by extended X-ray absorption fine structure (EXAFS) spectroscopy. The face-bridging CO ligands were removed first when the temperature was raised to 100°C and held for 2 h, as shown by infrared and 13 C NMR data. Treatment in He at 300°C led to complete removal of the carbonyl ligands and the formation of supported rhodium clusters with structures modeled on the basis of EXAFS data as Rh 6 (along with some other species inferred to be cationic rhodium). These clusters were stable in He at temperatures as high as 400°C. The infrared and 13 C NMR data show that when the fully decarbonylated Rh6 clusters were exposed to CO at 25-200°C, they were partially recarbonylated. Subsequent treatment of the partially recarbonylated clusters in He at 300°C again led to complete decarbonylation. The reversibility of the carbonylation and decarbonylation is suggestive of the behavior of extended metal surfaces, and the restriction of the reversibility to only a fraction of the CO ligands that can bond to Rh 6 indicates a role of the support and a contrast in reactivity between the supported metal clusters and extended metal surfaces.

show abstract

“…[10][11][12][13][14][15][16][17] The organometallic guests in zeolite hosts become polarized by electrostatic fields resulting from the interplay between positively charged extra-framework cations and negatively charged zeolite walls and are expected to show substantially enhanced reactivity compared to the parent compounds. 18 Therefore, as demonstrated in the past, 18 zeolitic voids would function as "nanoscale reaction chambers", where the reactivity of guest organometallic complexes can provide molecular insights into the elementary steps of heterogeneous catalysis.…”

Section: Introductionmentioning

confidence: 99%

Structure and Enhanced Reactivity of Chromocene Carbonyl Confined inside Cavities of NaY Zeolite

et al. 2009

View full text Add to dashboard Cite

Chromocene (Cp 2 Cr) hosted inside the supercage cavities of a NaY zeolite undergoes a structural distortion induced by the strong local electric fields generated by charge-balancing counterions. This effect, clearly observed by an in situ Cr K-edge extended X-ray absorption fine structure (EXAFS) study, is the key factor in enhancing the reactivity of Cp 2 Cr toward CO. The Cp 2 Cr(CO) adducts initially formed are not as stable as when hosted in nonpolar environments such as toluene solution or polystyrene. The presence of strong anionic/ cationic pairs (Y -/Na + ) favors, in a CO atmosphere, the loss of a Cp ring driven by an electron transfer mechanism (accompanied by ligand rearrangement) that results in the formation of the charged [CpCr(CO) 3 ] - and [Cp 2 Cr(CO)]+ carbonyl species that are stabilized by Na + and Y -pairs. Shape selectivity of the supercage cavity of the Y zeolite is necessary for this reaction, as it can host the two Cp 2 Cr molecules needed for disproportionation. Fast Fourier transform infrared (FTIR) spectroscopy, working in operando conditions, allows us to follow the time evolution of the IR stretching modes peculiar of reactants and products and thus to infer a reaction mechanism. The combination of quantum mechanical calculation with an in situ EXAFS study supports the hypothesis made on the basis of IR results. The work is further demonstration that zeolitic voids act as "nanoscale reaction chambers", where the reactivity of guest organometallic complexes can provide molecular insights into the elementary steps of heterogeneous catalysis. In this context, the investigation of metallocene reactivity inside a polar matrix can be extremely useful to understanding their properties in polymerization conditions, where they are usually found as part of an ion pair, together with the anionic form of the activator (e.g., MAO).

show abstract

Molecular Intracage Chemistry: [Rh6(CO)15]2− in Zeolite NaX

Cited by 24 publications

References 33 publications

Oxidation States of Gold in MgO-Supported Complexes and Clusters: Characterization by X-ray Absorption Spectroscopy and Temperature-Programmed Oxidation and Reduction

Oxidation States of Gold in MgO-Supported Complexes and Clusters: Characterization by X-ray Absorption Spectroscopy and Temperature-Programmed Oxidation and Reduction

Carbonylation and Decarbonylation of γ-Al₂O₃-Supported Hexarhodium Clusters: Characterization by Infrared, ¹³C NMR, and Extended X-ray Absorption Fine Structure Spectroscopies

Structure and Enhanced Reactivity of Chromocene Carbonyl Confined inside Cavities of NaY Zeolite

Contact Info

Product

Resources

About

Molecular Intracage Chemistry: [Rh6(CO)15]2− in Zeolite NaX

Cited by 24 publications

References 33 publications

Oxidation States of Gold in MgO-Supported Complexes and Clusters: Characterization by X-ray Absorption Spectroscopy and Temperature-Programmed Oxidation and Reduction

Oxidation States of Gold in MgO-Supported Complexes and Clusters: Characterization by X-ray Absorption Spectroscopy and Temperature-Programmed Oxidation and Reduction

Carbonylation and Decarbonylation of γ-Al2O3-Supported Hexarhodium Clusters: Characterization by Infrared, 13C NMR, and Extended X-ray Absorption Fine Structure Spectroscopies

Structure and Enhanced Reactivity of Chromocene Carbonyl Confined inside Cavities of NaY Zeolite

Contact Info

Product

Resources

About

Carbonylation and Decarbonylation of γ-Al₂O₃-Supported Hexarhodium Clusters: Characterization by Infrared, ¹³C NMR, and Extended X-ray Absorption Fine Structure Spectroscopies