Bipyridine- and Phenanthroline-Based Metal–Organic Frameworks for Highly Efficient and Tandem Catalytic Organic Transformations via Directed C–H Activation

We report here the synthesis of a
series of robust and porous bipyridyl-
and phenanthryl-based metal–organic frameworks (MOFs) of UiO
topology (BPV-MOF, mBPV-MOF, and mPT-MOF) and their postsynthetic
metalation to afford highly active single-site solid catalysts. While
BPV-MOF was constructed from only bipyridyl-functionalized dicarboxylate
linker, both mBPV- and mPT-MOF were built with a mixture of bipyridyl-
or phenanthryl-functionalized and unfunctionalized dicarboxylate linkers.
The postsynthetic metalation of these MOFs with [Ir­(COD)­(OMe)]2 provided Ir-functionalized MOFs (BPV-MOF-Ir, mBPV-MOF-Ir,
and mPT-MOF-Ir), which are highly active catalysts for tandem hydrosilylation
of aryl ketones and aldehydes followed by dehydrogenative ortho-silylation of benzylicsilyl ethers as well as C–H
borylation of arenes using B2pin2. Both mBPV-MOF-Ir
and mPT-MOF-Ir catalysts displayed superior activities compared to
BPV-MOF-Ir due to the presence of larger open channels in the mixed-linker
MOFs. Impressively, mBPV-MOF-Ir exhibited high TONs of up to 17000
for C–H borylation reactions and was recycled more than 15
times. The mPT-MOF-Ir system is also active in catalyzing tandem dehydrosilylation/dehydrogenative
cyclization of N-methylbenzyl amines to azasilolanes
in the absence of a hydrogen acceptor. Importantly, MOF-Ir catalysts
are significantly more active (up to 95 times) and stable than their
homogeneous counterparts for all three reactions, strongly supporting
the beneficial effects of active site isolation within MOFs. This
work illustrates the ability to increase MOF open channel sizes by
using the mixed linker approach and shows the enormous potential of
developing highly active and robust single-site solid catalysts based
on MOFs containing nitrogen-donor ligands for important organic transformations.