Exploration of Hypervalent Lewis Acid/Base Interactions in 2-(2'-Thiazolyl)-3-thienylphosphanes

The synthesis of a series of conjugated organophosphorus materials with intramolecular Lewis acid/base interactions and the exploration of the electronic nature of the bonding around the resulting hypervalent phosphorus centers are reported. To further establish the influence of increasing the size of the π-conjugated backbone, two scaffolds, thiazolyl-thiophene and benzothiazolyl-thiophene, were included in this study. Single-crystal X-ray crystallography of several of the compounds supports the hypervalent nature of the phosphorus center in the new species. Surprisingly, altering the Lewis acidity of the phosphorus center via oxidation or methylation impacts the coordinating mode of the thiazolyl substituent, which also has considerable impact on the photophysical and electrochemical properties of the π-conjugated molecular scaffolds. Through theoretical calculations involving natural bond orbital (NBO) analysis and atom-in-molecules (AIM) correlation, the existence and electronic nature of weak hypervalent bonding interactions around the phosphorus center was solidified as weak 3c-4e and/or σ-hole bonds, depending on the coordination mode of the peripheral thiazolyl substituent as well as the Lewis acidity of the phosphorus center.