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

Abstract

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.

Inverting Pt–I Bond Polarization to Generate Iodonium Character

“…To assess the polarization of the Pt–I bond before and after iodide abstraction, energy decomposition analysis (EDA) was employed. ,, EDA allows us to split a bond heterolytically, placing the electrons on either end of the Pt–I bond without perturbing the geometry of the system, to generate the Pt­(II)/I + or Pt­(IV)/I – extreme formulations of the Pt–I bond. This methodology is inspired by the work of Frenking et al Computing the energy of their respective interactions in a geometry-optimized environment allows one to compare the two extreme polarization models, with the lowest interaction energy being the polarization mode closest to the actual bonding situation.…”

“…The most illustrative examples of this are metal hydrides that cleave the M–H bond to yield H – , H • , or H + equivalents. , The generation of an acidic metal hydride requires inversion of its formal bond polarization (hydride) and can occur when the metal is reducible and the supporting ligand environment is electron-withdrawing, e.g., CO. Although bond inversions are common in p-block compounds (Wittig reagents, N–X (X = I, Br, Cl, F, S) compounds, pseudo-halogens, iodophosphoniums, etc), − few unbridged M–X complexes display reactivity that signals a functional inversion of the normal bond polarization. − To the extent that a bonding analysis supports such a formulation, the electrophilic behavior of such a ligand would tend to classify it as Z-type. Goldberg’s study of the 5-coordinate Pt­(IV) intermediate from oxidative addition/reductive elimination of MeI revealed an electrophilic apical Pt–Me bond that was otherwise unreactive when coordinatively saturated .…”