Lithium 2,2,6,6‐Tetramethylpiperidinoselenolate: An Unsymmetrical Dimer with an Unusually Coordinated Lithium

Abstract

AbstractLithium 2,2,6,6‐tetramethylpiperidide inserts elemental selenium into its Li–N bond with the formation of lithium 2,2,6,6‐tetramethylpiperidinoselenolate 1. In the crystal 1 is an unsymmetric dimer. One lithium atom is coordinated tetrahedrally by two molecules of tetrahydrofuran and two selenium atoms, the other lithium atom exhibits an approximately rectangular‐planar coordination by two N,Se‐chelating groups. The lithium atoms are bridged by two selenium atoms thus forming a planar Li2Se2 core. Ab initio Hartree‐Fock calculations show 1 and the hypothetical symmetric dimer 2 to be of equal energy, whereas the non‐chelated dimer 3 is of distinctly higher energy. Exclusive crystallization of 1 is most likely a consequence of its large dipole moment of 6.18 D. Calculations also show that the deformation of the observed geometry around the uniquely coordinated lithium atom in 1 towards distorted tetrahedral or complete planarity leads to an increase of energy. Excessive charge transfer from selenium to nitrogen explains the overwhelming tendency for the N,Se‐chelating bonding.