Zirconium and hafnium polyhedral oligosilsesquioxane complexes – green homogeneous catalysts in the formation of bio-derived ethers via a MPV/etherification reaction cascade. Issue 1 (17th November 2020)

• Record Type: Journal Article
• Authors: Garg, Shipra; Unruh, Daniel K.; Krempner, Clemens
• Is Part Of: Catalysis science & technology. Volume 11:Issue 1(2021)
• Page Start: 211
• Page End: 218
• Publication Date: 2020-11-17
• Subjects: Catalysis -- Periodicals; 541.395
• DOI: 10.1039/d0cy01864c
• Languages: English
• ISSNs: 2044-4753

Abstract

Abstract : Newly designed POSS supported zirconium and hafnium isopropoxides are robust, durable and selective homogeneous catalysts for the conversion of hydroxymethylfurfural to bis(isopropoxymethyl)furane via MPV/etherification reaction with isopropanol as a green solvent/reagent. Abstract : The polyhedral oligosilsesquioxane complexes, {[(isobutyl)7 Si7 O12 ]ZrOPr i ·(HOPr i )}2 (I ), {[(cyclohexyl)7 Si7 O12 ]ZrOPr i ·(HOPr i )}2 (II ), {[(isobutyl)7 Si7 O12 ]HfOPr i ·(HOPr i )}2 (III ) and {[(cyclohexyl)7 Si7 O12 ]HfOPr i ·(HOPr i )}2 (IV ), were synthesized in good yields from the reactions of M(OPr i )4 (M = Zr, Hf) with R-POSS(OH)3 (R = isobutyl, cyclohexyl), resp. I –IV were characterized by 1 H, 13 C and 29 Si NMR spectroscopy and their dimeric solid-state structures were confirmed by X-ray analysis. I –IV catalyze the reductive etherification of 2-hydroxy- and 4-hydroxy and 2-methoxy and 4-methoxybenzaldehyde and vanillin to their respective isopropyl ethers in isopropanol as a "green" solvent and reagent. I –IV are durable and robust homogeneous catalysts operating at temperatures of 100–160 °C for days without significant loss of catalytic activity. Likewise, I –IV selectively catalyze the conversion of 5-hydroxymethylfurfural (HMF) into 2, 5-bis(isopropoxymethyl)furane (BPMF), a potentially high-performance fuel additive. Similar results were achieved by using a combination of M(OPr i )4 and ligand R-POSS(OH)3 as a catalyst system demonstrating the potential of this " in situ " approach for applications in biomass transformations. A tentative reaction mechanism for the reductive etherification of aldehydes catalysed by I –IV is proposed.