From H-bonding Hydrides to Organic Electrides
James E. Jackson
Department of Chemistry, Michigan State University, East Lansing, MI 48824
jackson@cem.msu.edu
www.cem.msu.edu/~jackson
X H
H
BH3
­
X BH3
­
rX-B ~ 3-3.5 
(X = O, N)
rX-B ~ 1.5 H2
X H :Y­
rX-Y ~ 2.5-3.5 
(X, Y = O, N, Hal)
1 2 3
Unlike classical X-H...
:Y­
hydrogen bonds 1, those of type 2 between protonic and
hydridic hydrogens X-H...
H-M (AKA dihydrogen bonds) can react via proton transfer
from X-H to H-M (X electronegative; M electropositive, e.g. B), triggering irreversible
H2 loss and formation of new X-M bonds 3. Study of the reaction and crystal engineering
consequences of this difference (see Radu Custelcean's Chem. Rev. 2001, 101, 19631980)
called for molecular crystals designed to allow the solid state H-bond to covalent
switch while maintaining crystalline order--i.e. synthesis of networks primed to cross-link
into crystalline covalent 3D structures via a crystal-to-crystal reaction (see Custelcean &
Vlassa's Chem. Eur. J. 2002, 8, 302-308.)
In the hydrogen loss reaction X-H...
H-M -> H2 + X-M the elements that move
most are both hydrogens, light atoms capable of quantum mechanical tunneling. Ab Initio
modeling of the dynamics in this process are encouraging (see Simona Marincean's J.
Phys. Chem. A 2004, 108, 5521-5526.) More recent simulations suggest that such
processes may be relevant in the context of biological hydride transfer reactions as well.
Among unusual and reactive anions, beyond
hydrides lie alkalides and electrides. In collaboration with J.
L. Dye, synthetic studies (see Misha Redko's Synthesis
2006, 759-761) guided by ab initio modeling have recently
enabled construction of the first room-temperature-stable
organic electride and its isostructural sodide salts 4 (see M.
Redko's J. Am. Chem. Soc. 2005, 127, 12416-12422).
N
N
N
N
N
N
N
N
Na+
e­, Na­
4