Synthesis and characterization of metallocalixarenes as precursors for the SOHIO model catalyst

Abstract

The Standard Oil of Ohio Company (SOHIO) process refers to the selective oxidation and ammoxidation of propene to produce acrolein and acrylonitrile, used on large scales in industry. The outstanding performance of the SOHIO process has stimulated much fundamental research on its mechanistic details, but four decades after its discovery, the mode of action of the "simple" Bi2O3*MoO3 catalyst remains controversial (Chapter 1). For several years now, we have sought to prepare soluble complexes featuring BiIII(m-O)MoVI interactions in pure oxo environments, in order to resemble the proposed SOHIO catalyst active site. During our quest, we have employed calixarene ligands as oxygen rich platforms that can hold the Bi and Mo centers simultaneously.^We took advantage of the oxygen-donor lower rim of the calixarenes to prepare a series of BiIII and SbIII metallated complexes that display a broad structural diversity.^We synthesized a series of deprotonated calixarenes "calix[n]anions" (including mono- to pentaanionic species) by the reaction of parent calix[n]arenes (n = 5, 7) with alkali metal bases (Chapter 2). The calix[5]arene anions were employed to successfully synthesize for the first time, mono- and bimetallic BiIII and SbIII calix[5]arene complexes containing unreacted OH groups (Chapter 3). In order to expand the number of bismuth and antimony precursors, we decided to explore the reactivity of the calix[n]arenes (n = 6-8) taking advantage of the larger cavity size and conformational exchange.^The treatment of parent calix[n]arenes (n = 6-8) with several bismuth and antimony precursors allowed the preparation of a series of metal complexes featuring mono- to tretranuclear structures (Chapter 4).^As the chemistry of bismuth and antimony complexes usually has an issue of low solubility, we synthesized mono-silylated calix[5]arenes that upon treatment with bismuth and antimony alkoxides permitted the preparation of highly soluble BiIII and SbIII compounds (Chapter 5). The reactivity of the monometallic BiIII and SbIII calixarene complexes was tested and successfully utilized on the synthesis of the first M/Mo (M = Sb, Bi) heterometallic models supported by calixarene ligands (Chapter 6). Finally, as part of our studies on C-H activation (rate determining step in the SOHIO process) observed in BiIII bisphenolates, we have synthesized the analogous SbIII complexes and discovered that they are able to undergo such bond activations under similar reaction conditions (Chapter 7).