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 σ-electron-releasing abilities
for all of them; however, their π-acceptor properties are strongly
influenced by the nature of the positively charged group. We describe
the coordination chemistry of the newly prepared α-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 α-cationic arsine ligands
in catalysis.