Stabilization of Tricoordinate Pyranmidal Boron: Theoretical Sudies on CBSiH_5, CBGeH_5, and CBSnH_5

摘要

The dramatic computational discoveries~[1] and experimental realizations~[2] of planar tetracoordinate carbon and planar tetracoordinate boron~[3] species have set the stage for other rule-breaking structures. Preference for the trigonal planar arrangement in carbenium ions and tricoordinate boron species is one of the tenets of main-group chemistry that remains unchallenged. An unconstrained pyramidal carbenium ion or its boron equivalent has, so far, remained elusive. We report here, for the first time, the computationa~[4] discovery of a neutral-ground-state molecule, silaborane 1, which contains a tricoordinate pyramidal boron center. The conventional planar geometry 2 is a transition state with the imaginary frequency corresponding to pyramidalization around the boron atom. Similar results are obtained when the Si atom in 1 is replaced by Ge and Sn.