Studies aimed at synthesizing surfactants from biomass-based feedstocks using Pd-catalyzed telomerization of 1,3-butadiene resulted in the development of a highly active catalyst system. A ligand screening was performed, and Pd/tris(2-methoxyphenyl)phosphine (TOMPP) was identified as the most promising catalyst. A solvent- and base-free protocol was developed, which allows efficient and selective conversion of a wide variety of polyol substrates (e.g., glycerol, diols, carbohydrates, and sugar alcohols). In the case of hemi-acetal bearing sugars, catalyst deactivation was observed and mechanistic studies showed that extensive formation of ligand-derived phosphonium species depleted the amount of available ligand. Stoichiometric coordination reactions gave insight into the phosphine alkylation mechanism and demonstrated the reversibility of the observed reaction. A simple and efficient one-pot synthesis method was developed for the preparation of [Pd((1-3,7,8η)-(E)-octa-2,7-dien-1-yl)(PR3)]+ complexes, which are key reactive intermediates. Based on these studies, an extended telomerization mechanism is proposed, which accounts for the formation of ligand-derived phosphonium species and the reversibility of reaction pathways.
Pd/TOMPP-catalyzed telomerization of 1,3-butadiene: From biomass-based substrates to new mechanistic insights