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Characterization of Catalytically Active Octahedral Metal Halide Cluster Complexes
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Metals 2014, 4(2), 235-313; doi:10.3390/met4020235

Catalytic Reactions over Halide Cluster Complexes of Group 5–7 Metals

1
Graduate School of Science and Engineering, Saitama University, Shimo-Okubo, Sakura-Ku, Saitama City, Saitama 338-8570, Japan
2
Organometallic Chemistry Laboratory, RIKEN, 2-1 Hirosawa, Wako City, Saitama 351-0198, Japan
3
Advanced Catalysis Research Group, RIKEN Center for Sustainable Resource Science, 2-1 Hirosawa, Wako City, Saitama 351-0198, Japan
*
Author to whom correspondence should be addressed.
Received: 9 January 2014 / Revised: 1 June 2014 / Accepted: 4 June 2014 / Published: 23 June 2014
(This article belongs to the Special Issue Metal and Molecular Clusters)

Abstract

Halide clusters of Group 5–7 metals develop catalytic activity above 150–250 °C, and the activity is retained up to 350–450 °C by taking advantage of their thermal stability, low vapor pressure, and high melting point. Two types of active site function: the solid Brønsted acid site and a coordinatively unsaturated site that catalyzes like the platinum metals do. Various types of catalytic reactions including new reactions and concerted catalyses have been observed over the clusters: hydrogenation, dehydrogenation, hydrogenolysis, isomerization of alkene and alkyne, and alkylation of toluene, amine, phenol, and thiol. Ring-closure reactions to afford quinoline, benzofuran, indene, and heterocyclic common rings are also catalyzed. Beckmann rearrangement, S-acylation of thiol, and dehydrohalogenation are also catalyzed. Although the majority of the reactions proceed over conventional catalysts, closer inspection shows some conspicuous features, particularly in terms of selectivity. Halide cluster catalysts are characterized by some aspects: cluster counter anion is too large to abstract counter cation from the protonated reactants, cluster catalyst is not poisoned by halogen and sulfur atoms. Among others, cluster catalysts are stable at high temperatures up to 350–450 °C. At high temperatures, apparent activation energy decreases, and hence weak acid can be a catalyst without decomposing reactants. View Full-Text
Keywords: weak Brønsted acid; oxo acid; large cation; coodinatively unsaturated site; platinum-like catalysis; alkylation; ring closure reaction; activation of hydrogen; high temperature catalysis weak Brønsted acid; oxo acid; large cation; coodinatively unsaturated site; platinum-like catalysis; alkylation; ring closure reaction; activation of hydrogen; high temperature catalysis
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This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Nagashima, S.; Kamiguchi, S.; Chihara, T. Catalytic Reactions over Halide Cluster Complexes of Group 5–7 Metals. Metals 2014, 4, 235-313.

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