Tailoring the Binding Properties of Phosphazane Anion Receptors and Transporters

The
binding and sensing of anions is an important cross-disciplinary
field, which impacts broad areas such as biology, supramolecular chemistry
and catalysis. To date, however, this area has been dominated by organic
architectures which function as H-bonding, anion receptor molecules.
Inorganic anion receptors have largely been based on Lewis acidic
metals, with very few examples of H-bonding counterparts of organic
systems having been systematically studied. This paper develops strategies
for enhancing the anion binding properties of phosphazanes of the
type [(RNH)­(E)­P­(μ-NtBu)]2 (E = O, S, Se) which are bench-stable, H-bond receptors that can
be regarded as inorganic analogues of squaramides (a key class of
organic anion receptor). The distinct advantages of these inorganic
receptors over organic counterparts is the ease by which their functionality
and electronic character can be altered (by means of the R group,
chalcogenide, or metal present). Se substitution at the P centers,
the presence of electron-withdrawing R groups, and metal coordination
to the soft donor centers can be used to modulate and enhance anion
binding. The water stability and superior anion binding properties
of the seleno-phosph­(V)­azanes give them applications as synthetic
anion transporters through phospholipid layers.