Carbon Dioxide Solubility Enhancement through Silicone Functionalization: “CO2-philic” Oligo(dimethylsiloxane)-substituted Diphosphonates∗

Abstract

Carbon dioxide has received significant attention as a potential environmentally benign medium to replace hazardous organic compounds, but is a relatively poor solvent. The addition of siloxane substituents provides an attractive and inexpensive means to solubilize a wide variety of compounds in CO₂. By synthesizing and testing a family of gem-diphosphonate ligands that have been rendered CO₂-philic by incorporation of a number of related, discrete dimethylsiloxane oligomers, we show that small variations in substituents have a significant effect on the CO₂-philicity of the ligand. To our knowledge, this is the first systematic study of the effect of siloxane substituent size, branching, and position on the affinity of a ligand for CO₂. In addition, we present a general approach to the preparation of novel gem-diphosphonate ligands.