Siloxyaluminate and Siloxygallate Complexes as Models for Framework and Partially Hydrolyzed Framework Sites in Zeolites and Zeotypes. Issue 1 (3rd December 2020)

• Record Type: Journal Article
• Authors: Dombrowski, James P.; Ziegler, Micah S.; Phadke, Neelay M.; Mansoor, Erum; Levine, Daniel S.; Witzke, Ryan J.; Head‐Gordon, Martin; Bell, Alexis T.; Tilley, T. Don
• Is Part Of: Chemistry. Volume 27:Issue 1(2021)
• Page Start: 307
• Page End: 315
• Publication Date: 2020-12-03
• Subjects: hydrogen transfer -- molecular modeling -- zeolites; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.202002926
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: Anionic molecular models for nonhydrolyzed and partially hydrolyzed aluminum and gallium framework sites on silica, M[OSi(O t Bu)3 ]4 − and HOM[OSi(O t Bu)3 ]3 − (where M=Al or Ga), were synthesized from anionic chlorides Li{M[OSi(O t Bu)3 ]3 Cl} in salt metathesis reactions. Sequestration of lithium cations with [12]crown‐4 afforded charge‐separated ion pairs composed of monomeric anions M[OSi(O t Bu)3 ]4 − with outer‐sphere [([12]crown‐4)2 Li] + cations, and hydroxides {HOM[OSi(O t Bu)3 ]3 } with pendant [([12]crown‐4)Li] + cations. These molecular models were characterized by single‐crystal X‐ray diffraction, vibrational spectroscopy, mass spectrometry and NMR spectroscopy. Upon treatment of monomeric [([12]crown‐4)Li]{HOM[OSi(O t Bu)3 ]3 } complexes with benzyl alcohol, benzyloxide complexes were formed, modeling a possible pathway for the formation of active sites for Meerwin–Ponndorf–Verley (MPV) transfer hydrogenations with Al/Ga‐doped silica catalysts. Abstract : Zeotype framework sites : The synthesis and characterization of anionic molecular models for aluminum and gallium framework sites and partially hydrolyzed framework sites on silica with M[OSi(O t Bu)3 ]4 − and HOM[OSi(O t Bu)3 ]3 − cores are reported. Upon treatment of partially hydrolyzed framework‐site models with alcohols, alkoxide complexes were formed, reminiscent of proposed precatalyst activation for transfer hydrogenations.