Catalytic consequences of open and closed grafted Al(III)-calix[4]arene complexes for hydride and oxo transfer reactions

Partha Nandi, Wenjie Tang, Alexander Okrut, Xueqian Kong, Son Jong Hwang, Matthew Neurock, Alexander Katz

Research output: Contribution to journalArticlepeer-review

20 Scopus citations

Abstract

An approach for the control and understanding of supported molecular catalysts is demonstrated with the design and synthesis of open and closed variants of a grafted Lewis acid active site, consisting of Al(III)-calix[4] arene complexes on the surface of silica. The calixarene acts as a molecular template that enforces open and closed resting-state coordination geometries surrounding the metal active sites, due to its lower-rim substituents as well as site isolation by virtue of its steric bulk. These sites are characterized and used to elucidate mechanistic details and connectivity requirements for reactions involving hydride and oxo transfer. The consequence of controlling open versus closed configurations of the grafted Lewis acid site is demonstrated by the complete lack of observed activity of the closed site for Meerwein-Ponndorf-Verley (MPV) reduction; whereas, the open variant of this catalyst has an MPV reduction activity that is virtually identical to previously reported soluble molecular Al(III)-calix[4]arene catalysts. In contrast, for olefin epoxidation using tert-butyl-hydroperoxide as oxidant, the open and closed catalysts exhibit similar activity. This observation suggests that for olefin epoxidation catalysis using Lewis acids as catalyst and organic hydroperoxide as oxidant, covalent binding of the hydroperoxide is not required, and instead dative coordination to the Lewis acid center is sufficient for catalytic oxo transfer. This latter result is supported by density functional theory calculations of the transition state for olefin epoxidation catalysis, using molecular analogs of the open and closed catalysts.

Original languageEnglish (US)
Pages (from-to)2484-2489
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume110
Issue number7
DOIs
StatePublished - Feb 12 2013

Keywords

  • MPVO reaction
  • Molecular catalysis
  • Organic-inorganic interface
  • Selective oxidation
  • Single-site catalysts

Fingerprint Dive into the research topics of 'Catalytic consequences of open and closed grafted Al(III)-calix[4]arene complexes for hydride and oxo transfer reactions'. Together they form a unique fingerprint.

Cite this