Stable Pentacoordinate Carbocations: Structure and Bonding

摘要

We report that only elements more electropositive than carbon (Group 13, 14, and Be) form stable symmetrical H_nE-CH_3-EH_n~+ structures (E = Group 1, 2, 13, or 14 element) with a planar CH_3 group symmetrically bonded to two EH_n moieties, in analogy with prototypical S_N2 transition structures. Analysis of the bonding situation of these pentacoordinate carbon molecules was studied by means of an energy decomposition analysis (EDA) of the interaction energy. This shows that H_nE-CH3- EH_n~+ molecules can be viewed as being composed of one CH3 group that is sigma-covalently bonded to two EH_n groups forming a three-center, two-electron bond.