Development of Group Vi Compounds as Potential Catalysts for Deoxydehydration

Open Access
Author:
Byrne, Ryan Michael
Graduate Program:
Chemistry
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
September 10, 2013
Committee Members:
  • Alexander Thomas Radosevich, Thesis Advisor
Keywords:
  • Molybdenum
  • Tungsten
  • Deoxydehydration
Abstract:
In line with a growing for sustainability in chemistry, there has been much interest in the conversion of cellulosic biomass into carbon feedstock chemicals, which are typically obtained from non-renewable fossil sources. Given the highly oxygenated nature of cellulosic biomass, reductive methods that transform this abundant renewable resource into valuable carbon-containing compounds with high efficiency and selectivity are required. This thesis describes progress toward the development of a catalytic method to reduce biomass-derived vicinal diols through a deoxydehydration approach. Specifically, we have attempted to reduce these diols to the corresponding olefins using transition metal complexes of the Group VI metals Mo and W. Both stoichiometric and catalytic chemistry related to the desired transformation is described. In a stoichiometric sense, the synthesis and characterization of seven target Tp’Mo(V) diolates was achieved, and attempts to convert these to Tp’Mo(IV) diolates capable of cycloreversion by one-electron reduction are detailed. In catalytic studies, an effect of catalyst on product distributions for the conversion of (R,R)-hydrobenzoin was observed. Utilizing a bis-oxomolybdenum(VI) catalyst, an unanticipated oxidative cleavage of the 1,2-diol substrate to two equivalents of benzaldehyde was observed. Conversely, the use of low valent Group VI catalysts, specifically molybdenum hexacarbonyl, reductively transforms hydrobenzoin derivatives into olefins in moderate yields in the presence of 4Å molecular sieves. The scope of these two disparate processes is described. While optimization and mechanistic understanding are still on-going, the results substantiate the hypothesis that Group VI compounds may serve as new catalysts for conversion of carbohydrate-like polyols to useful organic products.