ISOLOBAL BORON CARBONYL CARBOCATION ANALOGS

Abstract

The isolobal [Formula: see text] relationship has been applied computationally to create a new family of positively charged boron carbonyls. These are generated by replacing one or more of the CH's in carbocations by BCO groups. The boron carbonyl cations can be hypercoordinated (e.g. H4BCO +, isolobal with [Formula: see text]), hydrogen bridged (e.g. ( BCO )2 H +, isolobal with the bridged vinyl cation [Formula: see text]), carbon bridged (e.g. [Formula: see text], isolobal with the 2-norbornyl cation), and polyhedral (e.g. [Formula: see text], isolobal with C 4 v [Formula: see text]). Furthermore, the BCO analogs have geometries and electronic structures similar to those of their carbocation counterparts, for example, characterized by 3c-2e multicenter and aromatic six interstitial electron bonding. The nucleus-independent chemical shifts (NICS) at the centers of three-membered rings or the pyramidal clusters are highly diatropic, ranging from -28 to -45 ppm. The replacement of CH by BCO favors the hypercoordinate bonding characteristic of boron compounds due to the more diffuse orbitals and lower electronegativity of boron.