Synthesis, Structure, and Redox Properties of the Extremely Crowded Triarylpnictogens: Tris(2,4,6-triisopropylphenyl)phosphine, Arsine, Stibine, and Bismuthine

A series of the extremely crowded triarylpnitogens, tris(2,4,6-triisopropylphenyl)phosphine (1), arsine (2), stibine (3), and bismuthine (4), were synthesized by the reaction of 2,4,6-triisopropylphenylcopper(I) with the corresponding pnictogen trichlorides. Introducion of the three bulky aryl groups resulted in the unusual structures and redox properties, which were studied by X-ray crystallography and cyclic voltammetry. The triarylpnictogens 1, 2, and 3 had extremely large bond angles around pnictogen atoms (1:  111.5°, 2:  109.2°, 3:  106.7°), and not only 1 and 2, but also stibine 3 displayed a reversible redox wave in the cyclic voltammograms at very low potentials (1:  0.16 V, 2:  0.50 V, 3:  0.57 V vs Ag/Ag+), which suggests considerable stability of the corresponding cation radicals.