Understanding the Nature and Properties of Hydrogen–Hydrogen Bonds: The Stability of a Bulky Phosphatetrahedrane as a Case Study

Abstract

Recently, the first mixed C/P phosphatetrahedranes (^<i>t</i>BuC)₃P and (^<i>t</i>BuCP)₂ were reported. Unlike (^<i>t</i>BuCP)₂, (^<i>t</i>BuC)₃P exhibits remarkable thermal stability, which can be partially attributed to a network of nine hydrogen-hydrogen bonds (HHBs) localized between the <i>tert</i>-butyl substituents. The stabilizing contribution arising from this network of HHBs was obtained from local energy decomposition (LED) analysis calculated at the domain-based local pair natural orbital CCSD(T) (DLPNO-CCSD(T)) level of theory. These calculations suggest that each HHB contributes approximately -0.7 kcal/mol of stabilization; however, the net stabilization energy likely lies between -0.25 and -0.5 kcal/mol because of steric repulsion. Spatial analysis of the London dispersion energy via a dispersion interaction density (DID) plot reveals that the DID surface is localized at key C-H groups involved in HHBs, consistent with London dispersion interactions predominantly arising from HHBs. In addition, we present a computed mechanism that supports a phosphinidenoid species as a key reaction intermediate in the synthesis of (^<i>t</i>BuC)₃P.