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Type: Artigo de periódico
Title: Zeolite activation of organometallics: Revisiting substitution kineticsof [Mo(CO)(6)] with chemisorbed PMe3 in dehydrated Na56Y zeolite
Author: Fernandez, AL
Hao, J
Parkes, RL
Poe, AJ
Vichi, EJS
Abstract: Reactions of [Mo(CO)(6)] under vacuum in alpha-cages of Na56Y zeolite fully loaded with chemisorbed PMe3 form cis-[Mo(CO)(4)(PMe3)(2)] but mixtures of [Mo(CO)(5)(PMe3)] and cis-[Mo(CO)(4)(PMe3)(2)] are formed under CO. Reactions under vacuum exhibit low enthalpic and very negative entropic factors (Delta H-double dagger = 71.4 +/- 3.5 kJ mol(-1) and Delta S-double dagger = -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 degrees 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 alpha-cages behave as multidentate anionic "zeolate" ligands with varying numbers of O2- 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.
Subject: hexacarbonylmolybdenum(0)
Na56Y zeolite
intrazeolite kinetics
PMe3 substitution
Country: Brasil
Editor: Soc Brasileira Quimica
Rights: aberto
Identifier DOI: 10.1590/S0103-50532008000500009
Date Issue: 2008
Appears in Collections:Artigos e Materiais de Revistas Científicas - Unicamp

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