Angewandte Chemie International Edition
10.1002/anie.201901599
COMMUNICATION
from the NIH (GM 098395), DOE (DE-SC0008313), and Harvard
University. Solid-state structures of 2 and 4 were obtained at
ChemMatCARS Sector 15. ChemMatCARS Sector 15 is
supported by the National Science Foundation under grant
number NSF/CHE-1834750. This research used resources of the
Advanced Photon Source, a U.S. Department of Energy (DOE)
Office of Science User Facility operated for the DOE Office of
Science by Argonne National Laboratory under Contract No. DE-
AC02-06CH11357.
Keywords: cluster compounds • azides • bridging ligands •
chromium complexes • multi-electron reactivity
Figure 4. a) Solid-state structure of 10 at 100K with 30% probability ellipsoids.
Solvent molecules and most hydrogen atoms omitted for clarity. b) Core
geometry of 10. Proposed mechanisms of formation of c) 2 and d) 4.
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procedure analogous to that used by Lešetický to synthesize
1
5
[15]
PhNN N.
To determine whether the reaction of 1 with
[2]
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MesNN N in THF produced (tbsL)Cr
1
5
3
15
15
3
(µ – N) (5– N) the product
of the reaction was decomposed using HCl to produce ammonium
chloride and then treated with base to liberate ammonia, which
1
was vacuum transferred into a solution of HCl in diethyl ether. H
NMR of the re-formed ammonium chloride in DMSO-d
6
showed
the characteristic splitting pattern of 5NH
1
4
Cl (Figure S16),
. To our
knowledge, the only previously reported transition metal complex
confirming that 5 is formed from the ɣ-N of MesN
3
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to undergo this transformation is Mo(NAr)
3
(R=C(CD
3
)
2
CH
3
16]
, Ar =
It is
[
4]
[
3
,5-C Me ) as reported by the Cummins group.
6
H
3
2
4
638; b) B. Wu, K. M. Gramigna, M. W. Bezpalko, B. M. Foxman, C. M.
remarkable that the steric protection afforded by the ligand results
in a change from typical azide decomposition to this unusual
mode of azide reactivity for larger azide substrates.
The foregoing results highlight the divergent reactivity
resulting from both templating ligand and azide substrate steric
control. The secondary coordination sphere control imposed by
the tbs groups of the tbsL6 template gates how azides can
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CCDC1895532, 1895533, and 1895569-1895577 contain the
supplementary crystallographic data for this paper.These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre. See also Supporting Information.
[
5]
approach the reactive [Cr
BnN
larger azides such as MesN
3
] core. While the small azide substrate
reacts rapidly with the trinuclear face of 1 to form a µ imido,
3
[6]
[7]
3
3
and DippN
3
do not afford the
corresponding bridging imido products. Rather, the sterically
hindered azides react faster at the THF-bound site, aided by THF
dissociation in benzene solution, to form terminal imido products.
When the reaction media is switched to THF and THF lability from
[8]
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Chem. Soc. 2013, 135, 14448.
the cluster is minimized, mesityl azide reacts with the [Cr
3
] face
leading to N-atom extrusion from the azide to form the neutral
bridging nitride 5. Reactivity of organic azides with 1 allows
controlled access to two, three, and four-electron oxidation of the
[
[
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Cr ] core. Research is underway to understand if the divergent
reaction pathways lead to fully site-isolated oxidation of the cluster.
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[
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[
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Acknowledgements
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The authors are grateful for the assistance of Dr. Shao-Liang
Zheng with X-ray analysis. This work was supported by grants
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