Isolation and X‑ray Crystal Structures of Triarylphosphine Radical Cations

Abstract

Salts containing triarylphosphine radical cations <b>1</b>^<b>•+</b> and <b>2</b>^<b>•+</b> have been isolated and characterized by electron paramagnetic resonance (EPR) and UV–vis absorption spectroscopy as well as single-crystal X-ray diffraction. Radical <b>1</b>^<b>•+</b> exhibits a relaxed pyramidal geometry, while radical <b>2</b>^<b>•+</b> becomes fully planar. EPR studies and theoretical calculations showed that the introduction of bulky aryl groups leads to enhanced p character of the singly occupied molecular orbital, and the radicals become less pyramidalized or fully flattened