STEREOCHEMICAL LABILITY OF DIPHOSPHINES AND DIARSINES

Nuclear magnetic resonance experiments have been performed to detect pyramidal inversion about the heavy atom in diphosphines and diarsines. Doubling of the methyl and the phenyl resonances in the spectrum of 1,-2-dimethyl-1,2-diphenyldiphosphine has been attributed to the presence in solution of diastereomeric modifications. The reversible coalescence of each doublet above 150° is interpreted in terms of an interconversion between the meso and the dl forms through inversion about phosphorus. Appropriate kinetic data have been gathered. Similar observations have been made with the arsenic analog of this system. The Arrhenius activation energies were found to be 26 ± 2 and 27 ± 1 kcal/mol for the diphosphine and the diarsine, respectively. Detailed consideration is given to viable mechanistic alternatives, such as bimolecular inversion and rotational isomerism. © 1968, American Chemical Society. All rights reserved.