Palladium(II) Weak-Link Approach Complexes Bearing Hemilabile N‑Heterocyclic Carbene–Thioether Ligands

A new
class of homoligated palladium­(II) weak-link approach (WLA) complexes
bearing hemilabile N-heterocyclic carbene (NHC)–thioether ligands
is reported that, unlike previous tweezer-like WLA complexes, expand
and contract in a linear fashion when switching between configurational
states. These complexes can be chemically switched between a trans
open state and a trans closed state via the addition or subsequent
extraction of Cl–. These bis­(NHC) complexes also
display unusual isomerization behavior. For example, an NMR spectroscopic
investigation into the solution-state configuration of the open complex
reveals the presence of interconverting syn,trans and anti,trans isomers,
and a kinetic study shows that the barrier is large enough to isolate,
store, and study the anti,trans isomer at room temperature. Notably,
the linker length between the NHC and thioether moieties can be tailored
with additional −CH2– groups, which affords
considerable control over the geometric changes imposed by switching.
Therefore, this class of complexes may be useful in the construction
of allosterically regulated supramolecular assemblies and materials.