ChemComm
Communication
Scholar. We thank Dr Jeff W. Kampf for X-ray assistance, and
Dr Cameron M. Moore for helpful discussions.
Notes and references
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Fig. 2 Catalyst recycling experiments with 1, 2, and 3. Yields calculated by
GC and are the average of two independent runs.
One of the decomposition pathways that hindered hydrogen
transfer reactions with 2 (formation of multinuclear aggregates)
was overcome using 1 and demonstrated through catalyst
recycling experiments. Catalysts 1–3 were subjected to three
cycles of dehydrogenative oxidation of benzyl alcohol to assess
the overall catalyst stability (Fig. 2). Complexes 2 and 3 show
significant loss in activity over three cycles (total TON = 1120
and 790, cycle three = 9% and 10% yield, respectively). In
contrast, the stability provided by the secondary mesityl amino
groups in 1 allows for a fully recyclable catalyst (total TON =
2500, cycle three = 85% yield). These data illustrate that
catalytic stability across a series of otherwise structurally analogous
complexes is dramatically affected by modifications to the metal’s
secondary coordination sphere environment.
In conclusion, we have demonstrated that the simple sub-
stitution from –H to –OH to –NH(Ar) in the secondary sphere of
the terpyridine framework can impart dramatic improvements
in catalyst lifetime and activity for Ru-catalyzed hydrogen
transfer reactions. This study outlines a design principle to
use steric protection around polar secondary groups to stabilize
reactive Ru–H intermediates and circumvent catalyst decom-
position to impart markedly improved stability and activity
for hydrogen transfer reactions. Further efforts will focus on
the mechanistic underpinnings that govern these reactivity
trends.
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data, isomerization of cinnamyl alcohol is an alternative plausible
route to 3-phenyl propionic acid.
This work was supported by an NSF-CAREER grant (CHE-
1350877) and an NSF grant CHE-0840456 for X-ray instrumentation.
N. K. S. is an Alfred P. Sloan Research Fellow and a Camille Dreyfus 12 K. D. Collins and F. Glorius, Nat. Chem., 2013, 5, 597–601.
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