Sterically Tunable Phosphenium Cations: Synthesis and Characterization of Bis(arylamino)phosphenium Ions, Phosphinophosphenium Adducts, and the First Well-Defined Rhodium Phosphenium Complexes

Abstract

A family of bis(arylamino)chlorophosphines of the general formula (Ar = 4-MeO-C6H4, 3a; Ar = 2,4,6-Me3-C6H2, 3b; Ar = 2,6-(CHMe2)2-C6H3, 3c) has been prepared from PCl3 and the appropriate diamine. Steric interactions involving the 2,6-aryl substituents in 3b,c result in hindered rotation about the N−CAr bond, as evidenced by 1H NMR spectroscopy. Treatment of halophosphines 3a−c with AgOSO2CF3 (AgOTf) or Tl{B[3,5-(CF3)2-C6H3]4} (TlBArF) affords the cationic bis(arylamino)phosphenium compounds (4a−e; A = OTf, BArF), in high yield. Phosphenium cations 4a−d reversibly form adducts with trimethylphosphine. The structure of the phosphinophosphenium adduct 5c (Ar = 2,6-(CHMe2)2-C6H3) has been determined by single-crystal X-ray diffraction techniques, revealing both the steric influences of the 2,6-Ar substituents and the electronic nature of the bonding in 5. Treatment of Wilkinson's catalyst, RhCl(PPh3)3, with 1 equiv of 4a gives the first well-defined Rh phosphenium complex, (6), which is isolated in 80% yiel...