Iodenium or Phosphonium: The Ambi-Valent Character of Iodophosphonium Complexes

The ambi-valent character of the
P–I bond in iodophosphonium
complexes ensures that it can be electrophilic at either P or I. Herein,
we use an ensemble of computational tools and methodologies to probe
the nature of this ambi-valent bond. Geometric and atomic electron
population analyses yielded strong trends between the electron donating
ability of the phosphine and the strength and polarity of the P–I
bond. Quasi-atomic orbital analysis demonstrated the near homo-polarity
of the P–I bond, and energy decomposition analysis calculations
demonstrated the ability to tune the polarization of the bond with
only mild changes in secondary structural features. Finally, the ambi-valent
nature of the P–I bond was demonstrated to follow hard–soft
considerations in reactions with nucleophiles, with harder nucleophiles
preferentially forming products of addition to P and softer nucleophiles
to I.