Intrazeolite metal carbonyl kinetics:12CO substitution in Mo(12CO)6-Na56Y by PMe3and13CO

Ozin, Geoffrey A.; Özkâr, Saim; Pastore, Heloise O.; Poë, Anthony J.; Vichi, Eduardo J. S.

doi:10.1039/c39910000141

Cited by 10 publications

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“…Pooling the variances from all 61 rate constants leads to a value of 24%. Similar values were found when all the individual rate constants were used in Eyring analyses (Table 2), and previous studies [2][3][4]8 led to comparable values. This relatively low reproducibility is evidently a function of the nature of the zeolitic environment and should not be surprising.…”

Section: Discussionsupporting

confidence: 86%

“…This, and the direct formation of the subcarbonyl [Mo(CO) 3 ], coordinated by three neighboring oxide ions in the cavity walls, was taken to indicate that the rate determining step involved a concerted attack by those oxide ions on the carbon atoms of three fac CO ligands (Scheme 1). This conclusion differed from that previously reached [2][3][4] where interaction between the Na + ions and the oxygen atoms of the CO ligands was considered the source of activation. However, the same rate determining step, to form a common intermediate, was implied for the reactions of the undissociated [Mo(CO) 6 ] in which it became "anchored" within a "12-ring window" between two alpha cages in the zeolite by as many as six sodium ions.…”

Section: Introductioncontrasting

confidence: 88%

“…The fact that this is not observed, and that even the deliberate addition of water molecules has only minor effects, 15 serves to support the importance in the activation process of the oxide ions, rather than the Na + ions as previously postulated. 2 There have been other indications of the negligible effect of water molecules as shown by the nature of products in such situations. 16 The importance of the high electric fields associated with the bare cations in the surface of the cavities may therefore be less than previously envisaged.…”

Section: Discussionmentioning

confidence: 99%

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Zeolite activation of organometallics: revisiting substitution kinetics of [Mo(CO)6] with chemisorbed PMe3 in dehydrated Na56Y zeolite

Fernandez

Parkes

Poë

et al. 2008

J. Braz. Chem. Soc.

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2 ] são produzidas sob CO. Reações sob vácuo exibem fatores entálpicos baixos e fatores entrópicos muito negativos ( H ‡ = 71,4 ± 3,5 kJ mol -1 and S ‡ = -102 ± 11 J K -1 mol -1 ), comparados com fatores entálpicos muito mais altos e fatores entrópicos positivos para reações de substituição dissociativa de CO por P(n-Bu) 3 em xileno observadas em outros trabalhos. A reação a 66 C sob vácuo é cerca de 10 3 vezes mais rápida do que reações dissociativas 'espontâneas'de CO em solução. Conclui-se que a substituição intrazeólito ocorre por um mecanismo "assistido por zeólito" em que dois íons óxidos nas paredes da cavidade deslocam simultaneamente dois ligantes CO vizinhos do [Mo(CO) 6 ]. Isso contrasta com valores de entalpia ainda menores e de entropia mais negativos para o deslocamento simultâneo de três ligantes CO vizinhos em reações de descarbonilação térmica. As cavidades comportam-se como ligantes "zeolato" aniônicos multidentados, com números variáveis de íons O 2-participando da criação de estados de transição altamente ordenados. Os resultados enfatizam o alto grau com que estes estudos cinéticos podem revelar detalhes íntimos da natureza dos efeitos ativadores. Reactions under vacuum exhibit low enthalpic and very negative entropic factors ( H ‡ = 71.4 ± 3.5 kJ mol -1 and S ‡ = -102 ± 11 J K -1 mol -1 ) compared with much higher enthalpic and positive entropic factors for CO dissociative reactions with P(n-Bu) 3 in xylene observed elsewhere. Reaction at 66 C under vacuum is ca.10 3 times faster than "spontaneous" CO dissociative reactions in solution. Intrazeolite substitution is concluded to occur by a "zeolite assisted" mechanism in which two oxide ions in the cavity walls simultaneously displace two neighbouring CO ligands from the [Mo (CO) 6 ]. This contrasts with even lower enthalpy, and more negative entropy values, for simultaneous displacement of three neighbouring CO ligands in thermal decarbonylation reactions. The -cages behave as multidentate anionic "zeolate" ligands with varying numbers of O 2-ions participating to create highly ordered transition states. These results emphasize the high degree to which such kinetic studies can reveal intimate details of the nature of these activating effects.Keywords: hexacarbonylmolybdenum(0), Na 56 Y zeolite, intrazeolite kinetics, PMe 3 substitution IntroductionThe catalytic effect of zeolite cavities on many chemical reactions has been well known for over 60 years. 1 However, it was not until much later 2-4 that the intrazeolite kinetics Fernandez et al. 863 Vol. 19, No. 5, 2008 of some simple stoichiometric reactions were reported, reactions that had previously been thoroughly studied in homogeneous solution and the gas phase. 5 136 ). Preliminary studies of the reactions in other M 56 Y zeolites were also reported. 4 Apart from the detection 3 of what were essentially bimolecular substitution reactions with physisorbed PMe 3 , a very striking observation was the very low activation enthalpy of the CO exchange reaction which was offset, b...

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Section: Discussionsupporting

confidence: 86%

Section: Introductioncontrasting

confidence: 88%

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confidence: 99%

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Zeolite activation of organometallics: revisiting substitution kinetics of [Mo(CO)6] with chemisorbed PMe3 in dehydrated Na56Y zeolite

Fernandez

Parkes

Poë

et al. 2008

J. Braz. Chem. Soc.

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“…As experimental techniques become available, the dynamics of intrazeolite reactions, such as catalysis, ligand exchange, 95 electron transfer and radical reactions, and polymerizations will be explored in more detail. As molecular sieves with ever larger pores are being discovered, the future potential to assemble and understand supramolecular structures is enormous.…”

Section: Discussionmentioning

confidence: 99%

Zeolite Inclusion Chemistry

Bein

1992

ACS Symposium Series

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The zeolate ligand; zeolite encapsulated semiconductor nanomaterials

Ozin

Steele

1994

Macromolecular Symposia

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Consolidation of the results of structural, spectroscopic and kinetic studies of a range of intrazeolite guests and their reactions have led to the development of the “crown ether‐zeolite ligand analogy” and the concept of the “zeolate” as a macrospheroidal or macrocylindrical multidentate anionic ligand. This view of a zeolite cavity or channel as a collection of interconnected aluminosilicate crown ether‐like building blocks, permits a coordination chemistry approach to the understanding of metal‐ligand bonding (capping, anchoring, complexing, stabilizing and structure‐directing phenomena) in a variety of zeolite guest‐host inclusion systems. In this paper we focus attention on the role that the zeolate ligand plays in the organization of semiconductor precursors and their assembly to semiconductor nanoclusters with particular reference to II‐VI nanomaterials.

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Intrazeolite metal carbonyl kinetics:¹²CO substitution in Mo(¹²CO)₆-Na₅₆Y by PMe₃and¹³CO

Cited by 10 publications

References 11 publications

Zeolite activation of organometallics: revisiting substitution kinetics of [Mo(CO)6] with chemisorbed PMe3 in dehydrated Na56Y zeolite

Zeolite activation of organometallics: revisiting substitution kinetics of [Mo(CO)6] with chemisorbed PMe3 in dehydrated Na56Y zeolite

Zeolite Inclusion Chemistry

The zeolate ligand; zeolite encapsulated semiconductor nanomaterials

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