New photoswitchable
pyridyl-azo-phenyl-decorated tripodal host
ligands (Laz) that belong to the cyclotriveratrylene family
have been synthesized, and their photoswitching behavior and crystal
structures determined. The latter includes a remarkable 7-fold Borromean-weave
entanglement of π–π stacked layers. Trigonal bipyramidal
{[Pd(en)]3(Laz)2}6+ metallo-cryptophanes
(en = ethylenediamine) were formed from these and a previously known
pyridyl-azo-phenyl-decorated tripodal host ligand. These coordination
cages dissociate at low concentrations and are less robust to photoswitching
of the Laz ligands than were previously reported Ir(III)-linked
metallo-cryptophanes with similar ligands, reflecting the greater
lability of the Pd–N bonds. The {[Pd(en)]3(Laz)2}6+ cages all act as hosts, binding
octyl sulfate anions, or N-[2-(dimethylamino)ethyl]-1,8-naphthalimide
in a dimethyl sulfoxide solution.
Trimetallic Pd–NHCs with a cyclotriguaiacylene scaffold display variable host–guest interactions and, along with monomeric analogues, catalyse cross-coupling reactions with a switch in the normal regioselectivity.
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