α-Cationic Arsines: Synthesis, Structure, Reactivity, and Applications

A series of structurally differentiated cationic arsines containing imidazolium, cyclopropenium, formamidinium, and pyridinium substituents have been synthesized through short and scalable routes. Evaluation of the donor properties of these compounds by IR spectroscopy and DFT calculations reveals similar sigma-electron-releasing abilities for all of them; however, their pi-acceptor properties are strongly influenced by the nature of the positively charged group. We describe the coordination chemistry of the newly prepared alpha-cationic arsines toward different metal centers and their reactivity in the presence of strong oxidants to afford cationic As(V) species. Their unique electronic properties have been exploited in Pt(II) catalysis to develop a new catalyst with remarkable activity in the cycloisomerization of enynes to trisubstituted cyclopropanes. To the best of our knowledge, this is the first report on the use of a-cationic arsine ligands in catalysis.