A Molybdenum(0) Isocyanide Analogue of Ru(2,2′-Bipyridine)32+: A Strong Reductant for Photoredox Catalysis

Article abstract of DOI:10.1002/anie.201605571

We report the first homoleptic Mo⁰complex with bidentate isocyanide ligands, which exhibits metal-to-ligand charge transfer (³MLCT) luminescence with quantum yields and lifetimes similar to Ru(bpy)₃²⁺(bpy=2,2′-b

Full text of DOI:10.1002/anie.201605571

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201605571
German Edition: DOI: 10.1002/ange.201605571
Photoredox Catalysis
2+
3
A Molybdenum(0) Isocyanide Analogue of Ru(2,2’-Bipyridine) :
A Strong Reductant for Photoredox Catalysis
Laura A. Bꢀldt, Xingwei Guo, Alessandro Prescimone, and Oliver S. Wenger*
0
2+
Abstract: We report the first homoleptic Mo complex with
the luminescence and photoredox properties of Ru(bpy)3 -
bidentate isocyanide ligands, which exhibits metal-to-ligand
type complexes are tunable through ligand variation, there
are limitations to this approach. In view of the continued
great interest in the above-mentioned research areas ranging
from synthetic organic chemistry to materials applications
and solar-energy conversion, the development of new photo-
sensitizers is highly desirable.
3
charge transfer ( MLCT) luminescence with quantum yields
2
+
and lifetimes similar to Ru(bpy)3 (bpy = 2,2’-bipyridine).
0
This Mo complex is a very strong photoreductant, which
manifests in its capability to reduce acetophenone with
essentially diffusion-limited kinetics as shown by time-resolved
laser spectroscopy. The application potential of this complex
for photoredox catalysis was demonstrated by the rearrange-
ment of an acyl cyclopropane to a 2,3-dihydrofuran, which is
a reaction that requires a reduction potential so negative that
even the well-known and strongly reducing Ir(2-phenylpyr-
idine)3 photosensitizer cannot catalyze it. Our study thus
provides the proof-of-concept for the use of chelating isocya-
0
The photophysical and photochemical properties of Mo
complexes with monodentate arylisocyanide ligands were
[
15]
3
first explored nearly 40 years ago. Some MLCT lumines-
cence was indeed observed, but these complexes become
substitutionally labile upon photoexcitation, thus making
[15,16]
0
them unsuitable for most applications.
Recently, W
complexes with monodentate arylisocyanides were found to
0
3
0
nides to obtain Mo complexes with long-lived MLCT excited
states that are applicable to unusually challenging photoredox
chemistry.
be strong emitters and photoreductants, but as a 5d metal, W
is inherently more inert to substitution than the 4d metal
0
[17]
Mo . We hypothesized that by using chelating arylisocya-
nides rather than monodentate ligands, it might be possible to
2
+
0
3
R
(
u(bpy)3 is the prototype of a very large class of metal
obtain robust Mo complexes with long-lived MLCT excited
complexes with long-lived metal-to-ligand charge transfer
MLCT) excited states, which comprises many examples
based on the precious metals Ru , Os , Re , and Ir .
Aside from such d metal diimines, many Pt and Au
complexes have favorable luminescence properties, but
emissive complexes made from earth-abundant metals are
more difficult to obtain. Notable exceptions are complexes
based on Zn or Cu , but their MLCT excited states usually
undergo strong geometrical distortion, and nonradiative
relaxation to the ground state is rapid.
states and high reducing power.
3
[1]
[18]
Except for a series of older studies,
there has been
II [2]
II [3]
I [4]
III [5]
surprisingly little prior work on chelating isocyanide ligands,
6
II
I/III
[19]
particularly with regard to luminescent metal complexes.
[6]
We prepared the new 2,2’’-diisocyano-3,5,3’’,5’’-tetramethyl-
1,1’:3’,1’’-terphenyl (CNAr NC) ligand and reacted it with
3
[
7]
Mo(THF) Cl4 in the presence of Na/Hg to obtain the
2
II
I [8]
Mo(CNAr NC) complex shown in Figure 1 (pages S2–S5 in
3
3
[9]
the Supporting Information). X-ray diffraction on single
crystals revealed MoÀC distances of 2.051(5) and 2.056(4) ꢁ,
Many of the above-mentioned metal complexes have
found applications, for example, as triplet harvesters in
as well as C-Mo-C bite angles between 82.9(2) and 94.2(4)8
(pages S6–S7 in the Supporting Information). In each ligand,
there are torsion angles of 51.2(7) and 55.8(7)8 between the
central benzene ring and the two flanking aryls. trans-
[
10]
organic light emitting diodes (OLEDs),
in dye-sensitized solar cells (DSSCs),
photosensitizers
or sensitizers of
[
11]
electron- and energy-transfer processes in artificial and
[
12]
biological systems.
In recent years, photoredox catalysis
[
13]
II
has received much attention in organic synthesis, with Ru
and Ir complexes playing a particularly prominent role.
Furthermore, Ru(bpy)3 and related complexes are now
frequently used for the production of solar fuels, for example,
in the light-driven reduction of CO or H O.
III
2
+
[
14]
However,
2
2
ruthenium is a precious metal with a natural abundance of
À3
approximately 10 ppm in the earthꢀs crust, and even though
[*] L. A. Bꢀldt, Dr. X. Guo, Dr. A. Prescimone, Prof. Dr. O. S. Wenger
Department of Chemistry, University of Basel
St. Johanns-Ring 19 and Spitalstrasse 51, 4056 Basel (Switzerland)
E-mail: oliver.wenger@unibas.ch
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under http://dx.doi.org/10.
Figure 1. Molecular (a) and crystallographic (b) structures of the
Mo(CNAr NC) complex; thermal ellipsoids are drawn at the 50%
3
3
[29]
1002/anie.201605571.
probability level. Hydrogen atoms are omitted for clarity.
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1
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Standing isocyanobenzene units are nearly orthogonal to each
another. The methyl substituents help shield the metal center
from the environment and thus presumably contribute to the
overall stability of the complex. The CꢀN stretch frequency in
Mo(CNAr NC) in THF is strongly quenched upon addition
3 3
of ACP (page S14 in the Supporting Information), and
a Stern–Volmer plot (Figure 3a) yields a quenching constant
9
À1 À1
of (3.1 Æ 0.4) ꢂ 10 m s , which is near the diffusion limit.
À1
À1
the complex is n˜ = 1939 cm , compared to n˜ = 2113 cm in
the free ligand, thus indicating substantial p backbonding
[
20]
(
page S8 in the Supporting Information).
0
In cyclic voltammetry, the Mo center is oxidized rever-
sibly to Mo at a potential (E ) of À0.40 V vs. Fc /Fc in THF
page S9 in the Supporting Information), which is in line with
a prior report of Mo complexes with monodentate isocyanide
ligands.
The UV/Vis absorption spectrum of Mo(CNAr NC) in
I
0
+
(
0
[
15a]
3
3
THF (Figure 2a) exhibits a broad band between l = 350 and
Figure 3. Stern–Volmer plot based on luminescence lifetimes
À5
(
ldet =615 nm) of ca. 10 m Mo(CNAr NC) in deaerated THF at 208C
3
3
in presence of increasing concentrations of acetophenone (ACP).
À5
b) Transient absorption of ca. 10 m Mo(CNAr NC) in the absence
3
3
(black) and presence (gray) of 34 mm ACP. Excitation and detection
was as described above. The disappearance of the bleach between 400
À
and 520 nm is caused by formation of the ACP radical anion (ACP );
see text and pages S14–S16 in the Supporting Information.
The transient absorption data in Figure 3b are fully compat-
ible with the formation of ACP and Mo(CNAr NC) (see
3 3
pages S14–S16 in the Supporting Information for further
details).
Figure 2. a) UV/Vis absorption spectrum of Mo(CNAr NC) in THF at
À
+
3
3
2
08C. b) Luminescence spectra in different solvents at 208C
(lexc =500 nm).
To assess the potential applicability of Mo(CNAr NC) as
3
3
l = 560 nm, which is reminiscent of the MLCT absorption of
a photoredox catalyst, we attempted to perform a rearrange-
ment of an acyl cyclopropane (1) to a 2,3-dihydrofuran (2;
Scheme 1), a reaction related to vinylcyclopropane-cyclo-
pentene rearrangements that are important for organic
2
+
Ru(bpy)3 . At shorter wavelengths, there are ligand-based
absorptions. The photoluminescence band maximum is blue-
shifted when going from THF to toluene to n-hexane
[
22]
(
Figure 2b), as expected for MLCT emission. The lumines-
cence lifetime (t) increases from 74 Æ 7 (THF) to 166 Æ 17
toluene) to 225 Æ 23 ns (n-hexane) in deaerated solutions at
08C (page S11 in the Supporting Information), and in
synthesis.
2,3-Dihydrofurans play key roles as structural
(
2
parallel there is an increase of the luminescence quantum
yield (f) from 0.6 Æ 0.1 to 2.3 Æ 0.2 to 4.5 Æ 0.4% (page S11 in
the Supporting Information). In frozen matrices at 77 K, there
is a strong rigidochromic effect and emission decays are
biexponential with lifetimes in the ms region (pages S12–S13
in the Supporting Information). From the 77 K emission
spectra, we estimate an energy (E ) of 2.2 eV for the emissive
Scheme 1. Rearrangement of acyl cyclopropane (1) to 2,3-dihydrofuran
2) accomplished in 84% yield through photoirradiation
(lexc =455 nm) of 5% Mo(CNAr NC) in dry [D ]benzene (TON=17).
(
3
3
6
0
0
3
MLCT state. The transient absorption spectra of the long-
3
lived MLCT excited state of Mo(CNAr NC) in various
elements of biologically active compounds such as aflatox-
3
3
3
solvents are very similar to the spectrum of the MLCT state
of Ru(bpy)3 (page S10 in the Supporting Information).
in B , and they are considered very useful synthetic inter-
1
2
+
[23]
mediates. We used the reaction in Scheme 1 as a benchmark
+
Given a potential of À0.40 V vs. Fc /Fc in the electronic
for the utility of our complex. Thermally, the conversion of
ground state and an energy (E ) of 2.2 eV for the emissive
1 into 2 is very difficult to perform because very harsh
0
0
[
24]
excited state (see above), a potential of around À2.6 V vs.
conditions or activating groups are necessary.
+
0
I
Fc /Fc can be expected for oxidation of Mo to Mo in the
When irradiating a mixture of substrate 1 and 5%
Mo(CNAr NC) in dry [D ]benzene with a blue LED at l =
3
long-lived MLCT state. In order to test this estimate of the
3
3
6
excited-state redox potential, the possibility of photoinduced
electron transfer with acetophenone (ACP) was explored.
455 nm in an evacuated sealed NMR tube, product 2 is
formed in 84% yield (at room temperature). When attempt-
ing to perform the same reaction with the well-known
À
The redox potential for the ACP/ACP couple in THF is
+
[21]
3
À2.5 V vs. Fc /Fc,
and hence MLCT-excited Mo-
Ir(ppy) (ppy = 2-phenylpyridine) photosensitizer, no conver-
3
(
CNAr NC) should be thermodynamically competent for
the reduction of ACP to ACP . Indeed the luminescence of
sion is observed. We attribute this to the very negative
potential required for one-electron reduction of 1, which is
3
3
À
2
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Angewandte
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[
13c,17a,28]
necessary to initiate pericyclic rearrangement through a dir-
adical mechanism. This potential can reasonably be assumed
Ir(ppy)3,
thus making it one of the most potent
visible-light absorbing photoreductants known to date. The
application potential of Mo complexes with chelating
isocyanides for photoredox catalysis was illustrated in this
study by using the example of a pericyclic rearrangement,
which is a very challenging benchmark reaction because its
initiation requires exceptionally strong reductants. The
+
0
to be similar to that of acetophenone (À2.5 V vs. Fc /Fc), and
0
our Mo complex has sufficient reducing power (À2.6 V vs.
+
Fc /Fc) to undergo photoinduced electron transfer with
nearly diffusion-limited kinetics (see above). By contrast,
the Ir(ppy) photosensitizer has an excited-state reduction
3
+
[13c]
potential of only À2.1 V vs. Fc /Fc
and is therefore unable
Mo(CNAr NC)3 complex is able to act as a robust and
efficient photoredox sensitizer for this reaction, clearly out-
3
to reduce 1 efficiently.
The proposed reaction mechanism for the conversion of
performing the widely used Ir(ppy) complex.
3
1
into 2 with Mo(CNAr NC) is shown in Scheme 2. Initially
In conclusion, our study provides a proof-of-concept for
3
3
[25]
0
only the trans isomer of 1 is present.
between photoexcited Mo(CNAr NC) and trans-1 produces
radical intermediate A which can be oxidized to diradical B
Electron transfer
the use of chelating isocyanides to obtain Mo complexes with
3
long-lived MLCT excited states, which emit visible light and
3
3
À,
are applicable to unusually challenging photoredox chemistry.
Acknowledgements
This research was supported by the Swiss National Science
Foundation through grant number 200021_156063/1 and
through the NCCR Molecular Systems Engineering.
Keywords: electron transfer · isocyanide ligands ·
luminescence · photocatalysis · photochemistry
[
[
1] a) C. R. Bock, T. J. Meyer, D. G. Whitten, J. Am. Chem. Soc.
974, 96, 4710 – 4712; b) R. Bensasson, C. Salet, V. Balzani, J.
1
Am. Chem. Soc. 1976, 98, 3722 – 3724.
2] a) A. Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser, A.
Von Zelewsky, Coord. Chem. Rev. 1988, 84, 85 – 277; b) J. K.
McCusker, Acc. Chem. Res. 2003, 36, 876 – 887; c) J. England,
C. C. Scarborough, T. Weyhermꢃller, S. Sproules, K. Wieghardt,
Eur. J. Inorg. Chem. 2012, 4605 – 4621.
Scheme 2. Proposed reaction mechanism for the conversion of 1 into
0
2
. Mo * denotes the photoexcited Mo(CNAr NC) complex.
3
3
[
3] J.-P. Sauvage, J.-P. Collin, J.-C. Chambron, S. Guillerez, C.
Coudret, V. Balzani, F. Barigelletti, L. De Cola, L. Flamigni,
Chem. Rev. 1994, 94, 993 – 1019.
+
[26]
by Mo(CNAr NC)3 in the electronic ground state. B can
3
then either undergo intramolecular reaction to form product
[
4] a) K. S. Schanze, D. B. MacQueen, T. A. Perkins, L. A. Cabana,
Coord. Chem. Rev. 1993, 122, 63 – 89; b) D. J. Stufkens, A. Vlcek,
Coord. Chem. Rev. 1998, 177, 127 – 179.
2
or it can revert to substrate 1, thereby producing a mixture
of cis and trans isomers. Both diastereomers can then re-enter
0
[5] a) M. S. Lowry, S. Bernhard, Chem. Eur. J. 2006, 12, 7970 – 7977;
b) J. Li, P. I. Djurovich, B. D. Alleyne, M. Yousufuddin, N. N. Ho,
J. C. Thomas, J. C. Peters, R. Bau, M. E. Thompson, Inorg.
Chem. 2005, 44, 1713 – 1727; c) K. N. Swanick, S. Ladouceur, E.
Zysman-Colman, Z. F. Ding, Angew. Chem. Int. Ed. 2012, 51,
11079 – 11082; Angew. Chem. 2012, 124, 11241 – 11244; d) R. D.
Costa, E. Orti, H. J. Bolink, F. Monti, G. Accorsi, N. Armaroli,
Angew. Chem. Int. Ed. 2012, 51, 8178 – 8211; Angew. Chem. 2012,
124, 8300 – 8334.
the catalysis cycle with photoexcited Mo complex until
conversion to 2 is complete. In principle, this can be
[
27]
considered an electron-catalyzed reaction.
Owing to the ability of diradical B to undergo forward and
backward reactions, the irradiation time to achieve complete
conversion to 2 is relatively long, at approximately 80 hours.
This is evidently an inherent property of the model reaction
0
investigated here and is clearly not a shortcoming of the Mo
[
6] a) M. Hissler, J. E. McGarrah, W. B. Connick, D. K. Geiger, S. D.
sensitizer. We were able to follow the isomerization of 1 and
conversion to 2 as a function of irradiation time by NMR
spectroscopy (page S17 in the Supporting Information). The
overall yield of 2 is 84%, which corresponds to a TON of 17,
which is close to the theoretical limit of 20 at a catalyst loading
of 5%.
Cummings, R. Eisenberg, Coord. Chem. Rev. 2000, 208, 115 –
137; b) V. W. W. Yam, Acc. Chem. Res. 2002, 35, 555 – 563;
c) T. T. Zou, C. T. Lum, C. N. Lok, J. J. Zhang, C. M. Che, Chem.
Soc. Rev. 2015, 44, 8786 – 8801; d) F. N. Castellano, I. E. Pomest-
chenko, E. Shikhova, F. Hua, M. L. Muro, N. Rajapakse, Coord.
Chem. Rev. 2006, 250, 1819 – 1828; e) M. A. Malwitz, S. H. Lim,
R. L. White-Morris, D. M. Pham, M. M. Olmstead, A. L. Balch,
J. Am. Chem. Soc. 2012, 134, 10885 – 10893; f) M. J. Irwin, J. J.
Vittal, R. J. Puddephatt, Organometallics 1997, 16, 3541 – 3547.
In summary, we have synthesized and characterized the
0
first homoleptic Mo complex with bidendate isocyanide
ligands. Photoexcited Mo(CNAr NC) has roughly 1.3 V
3
3
[7] a) S. Otto, M. Grabolle, C. Fçrster, C. Kreitner, U. Resch-
Genger, K. Heinze, Angew. Chem. Int. Ed. 2015, 54, 11572 –
11576; Angew. Chem. 2015, 127, 11735 – 11739; b) A. Vogler, H.
3
2+ [1a,2a,13c]
more reducing power than MLCT-excited Ru(bpy)3
,
and it is about 0.5 V more reducing than photoexcited
Angew. Chem. Int. Ed. 2016, 55, 1 – 5
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Angewandte
Communications
Chemie
Kunkely, Transition Metal and Rare Earth Compounds: Excited
States, Transition, Interactions I, Vol. 213, Springer, Berlin, 2001,
pp. 143 – 182; c) A. J. Lees, Chem. Rev. 1987, 87, 711 – 743.
8] a) G. Cheng, G. K. M. So, W. P. To, Y. Chen, C. C. Kwok, C. S.
Ma, X. G. Guan, X. Chang, W. M. Kwok, C. M. Che, Chem. Sci.
Windle, M. W. George, R. N. Perutz, P. A. Summers, X. Z. Sun,
A. C. Whitwood, Chem. Sci. 2015, 6, 6847 – 6864; i) H. Takeda,
O. Ishitani, Coord. Chem. Rev. 2010, 254, 346 – 354; j) J. H.
Alstrum-Acevedo, M. K. Brennaman, T. J. Meyer, Inorg. Chem.
2005, 44, 6802 – 6827; k) C. Herrero, A. Quaranta, S. El Ghach-
touli, B. Vauzeilles, W. Leibl, A. Aukauloo, Phys. Chem. Chem.
Phys. 2014, 16, 12067 – 12072.
[
[
2015, 6, 4623 – 4635; b) D. G. Cuttell, S. M. Kuang, P. E. Fanwick,
D. R. McMillin, R. A. Walton, J. Am. Chem. Soc. 2002, 124, 6 – 7.
9] L. X. Chen, G. B. Shaw, I. Novozhilova, T. Liu, G. Jennings, K.
Attenkofer, G. J. Meyer, P. Coppens, J. Am. Chem. Soc. 2003,
[15] a) K. R. Mann, H. B. Gray, J. Am. Chem. Soc. 1977, 99, 306 – 307;
b) K. R. Mann, M. Cimolino, G. L. Geoffroy, G. S. Hammond,
A. A. Orio, G. Albertin, H. B. Gray, Inorg. Chim. Acta 1976, 16,
97 – 101.
[16] L. E. Shaw, C. H. Langford, Coord. Chem. Rev. 2002, 230, 165 –
169.
125, 7022 – 7034.
[
10] a) A. Tsuboyama, H. Iwawaki, M. Furugori, T. Mukaide, J.
Kamatani, S. Igawa, T. Moriyama, S. Miura, T. Takiguchi, S.
Okada, M. Hoshino, K. Ueno, J. Am. Chem. Soc. 2003, 125,
1
2971 – 12979; b) H. Yersin, A. F. Rausch, R. Czerwieniec, T.
[17] a) W. Sattler, M. E. Ener, J. D. Blakemore, A. A. Rachford, P. J.
LaBeaume, J. W. Thackeray, J. F. Cameron, J. R. Winkler, H. B.
Gray, J. Am. Chem. Soc. 2013, 135, 10614 – 10617; b) W. Sattler,
L. M. Henling, J. R. Winkler, H. B. Gray, J. Am. Chem. Soc.
2015, 137, 1198 – 1205; c) H. Kvapilovꢅ, W. Sattler, A. Sattler,
I. V. Sazanovich, I. P. Clark, M. Towrie, H. B. Gray, S. Zalis, A.
Vlcek, Inorg. Chem. 2015, 54, 8518 – 8528.
[18] a) F. E. Hahn, Angew. Chem. Int. Ed. Engl. 1993, 32, 650 – 665;
Angew. Chem. 1993, 105, 681 – 696; b) F. E. Hahn, M. Tamm,
Angew. Chem. Int. Ed. Engl. 1991, 30, 203 – 205; Angew. Chem.
1991, 103, 213 – 215; c) D. T. Plummer, G. A. Kraus, R. J.
Angelici, Inorg. Chem. 1983, 22, 3492 – 3497; d) M. L. Winzen-
burg, J. A. Kargol, R. J. Angelici, J. Organomet. Chem. 1983, 249,
415 – 428.
[19] F. Monti, A. Baschieri, E. Matteucci, A. Mazzanti, L. Sambri, A.
Barbieri, N. Armaroli, Faraday Discuss. 2015, 185, 233 – 248.
[20] a) G. W. Margulieux, N. Weidemann, D. C. Lacy, C. E. Moore,
A. L. Rheingold, J. S. Figueroa, J. Am. Chem. Soc. 2010, 132,
5033 – 5035; b) C. C. Mokhtarzadeh, G. W. Margulieux, A. E.
Carpenter, N. Weidemann, C. E. Moore, A. L. Rheingold, J. S.
Figueroa, Inorg. Chem. 2015, 54, 5579 – 5587.
Hofbeck, T. Fischer, Coord. Chem. Rev. 2011, 255, 2622 – 2652.
11] A. Hagfeldt, G. Boschloo, L. C. Sun, L. Kloo, H. Pettersson,
Chem. Rev. 2010, 110, 6595 – 6663.
[
[
12] a) B. Geiss, C. Lambert, Chem. Commun. 2009, 1670 – 1672;
b) A. Magnuson, M. Anderlund, O. Johansson, P. Lindblad, R.
Lomoth, T. Polivka, S. Ott, K. Stensjç, S. Styring, V. Sundstrçm,
L. Hammarstrçm, Acc. Chem. Res. 2009, 42, 1899 – 1909; c) J. R.
Winkler, H. B. Gray, Chem. Rev. 1992, 92, 369 – 379; d) L.
De Cola, P. Belser, Coord. Chem. Rev. 1998, 177, 301 – 346;
e) D. G. Brown, N. Sanguantrakun, B. Schulze, U. S. Schubert,
C. P. Berlinguette, J. Am. Chem. Soc. 2012, 134, 12354 – 12357;
f) A. J. Howarth, M. B. Majewski, M. O. Wolf, Coord. Chem.
Rev. 2015, 282, 139 – 149; g) M. Goez, C. Kerzig, R. Naumann,
Angew. Chem. Int. Ed. 2014, 53, 9914 – 9916; Angew. Chem.
2
014, 126, 10072 – 10074.
[
13] a) J. Svoboda, B. Kçnig, Chem. Rev. 2006, 106, 5413 – 5430;
b) J. M. R. Narayanam, C. R. J. Stephenson, Chem. Soc. Rev.
2011, 40, 102 – 113; c) C. K. Prier, D. A. Rankic, D. W. C.
MacMillan, Chem. Rev. 2013, 113, 5322 – 5363; d) T. P. Yoon,
M. A. Ischay, J. N. Du, Nat. Chem. 2010, 2, 527 – 532; e) T. Bach,
J. P. Hehn, Angew. Chem. Int. Ed. 2011, 50, 1000 – 1045; Angew.
Chem. 2011, 123, 1032 – 1077; f) D. B. Bagal, G. Kachkovskyi, M.
Knorn, T. Rawner, B. M. Bhanage, O. Reiser, Angew. Chem. Int.
Ed. 2015, 54, 6999 – 7002; Angew. Chem. 2015, 127, 7105 – 7108;
g) H. H. Huo, X. D. Shen, C. Y. Wang, L. L. Zhang, P. Rose,
L. A. Chen, K. Harms, M. Marsch, G. Hilt, E. Meggers, Nature
[21] P. J. Wagner, R. J. Truman, A. E. Puchalski, R. Wake, J. Am.
Chem. Soc. 1986, 108, 7727 – 7738.
[22] a) J. E. Baldwin, Chem. Rev. 2003, 103, 1197 – 1212; b) M. Rubin,
M. Rubina, V. Gevorgyan, Chem. Rev. 2007, 107, 3117 – 3179.
[23] a) S. Son, G. C. Fu, J. Am. Chem. Soc. 2007, 129, 1046 – 1047;
b) T. G. Kilroy, T. P. OꢀSullivan, P. J. Guiry, Eur. J. Org. Chem.
2005, 4929 – 4949.
2
014, 515, 100 – 103; h) K. T. Tarantino, P. Liu, R. R. Knowles, J.
Am. Chem. Soc. 2013, 135, 10022 – 10025; i) O. Gutierrez, J. C.
Tellis, D. N. Primer, G. A. Molander, M. C. Kozlowski, J. Am.
Chem. Soc. 2015, 137, 4896 – 4899; j) A. C. Bissember, R. J.
Lundgren, S. E. Creutz, J. C. Peters, G. C. Fu, Angew. Chem. Int.
Ed. 2013, 52, 5129 – 5133; Angew. Chem. 2013, 125, 5233 – 5237.
14] a) J. L. Dempsey, B. S. Brunschwig, J. R. Winkler, H. B. Gray,
Acc. Chem. Res. 2009, 42, 1995 – 2004; b) M. G. Pfeffer, B.
Schꢄfer, G. Smolentsev, J. Uhlig, E. Nazarenko, J. Guthmꢃller, C.
Kuhnt, M. Wachtler, B. Dietzek, V. Sundstrçm, S. Rau, Angew.
Chem. Int. Ed. 2015, 54, 5044 – 5048; Angew. Chem. 2015, 127,
[24] a) C. L. Wilson, J. Am. Chem. Soc. 1947, 69, 3002 – 3004; b) R. K.
Bowman, J. S. Johnson, Org. Lett. 2006, 8, 573 – 576; c) V. K.
Yadav, R. Balamurugan, Org. Lett. 2001, 3, 2717 – 2719.
[25] K. Miyazawa, T. Koike, M. Akita, Chem. Eur. J. 2015, 21, 11677 –
11680.
À
[
[26] The oxidation potential of A is estimated to be lower than
+
À0.8 V vs. Fc /Fc, given the reported values for related enolates:
M. Schmittel, M. Lal, R. Lal, M. Rçck, A. Langels, Z.
Rappoport, A. Basheer, J. Schlirf, H. J. Deiseroth, U. Florke,
G. Gescheidt, Tetrahedron 2009, 65, 10842 – 10855.
5
132 – 5136; c) D. J. Boston, C. D. Xu, D. W. Armstrong, F. M.
[27] A. Studer, D. P. Curran, Nat. Chem. 2014, 6, 765 – 773.
[28] K. A. King, P. J. Spellane, R. J. Watts, J. Am. Chem. Soc. 1985,
107, 1431 – 1432.
[29] CCDC 1446591 contains the supplementary crystallographic
data for this paper. These data are provided free of charge by
The Cambridge Crystallographic Data Centre.
MacDonnell, J. Am. Chem. Soc. 2013, 135, 16252 – 16255; d) A.
Fihri, V. Artero, M. Razavet, C. Baffert, W. Leibl, M. Fontecave,
Angew. Chem. Int. Ed. 2008, 47, 564 – 567; Angew. Chem. 2008,
1
20, 574 – 577; e) E. Reisner, D. J. Powell, C. Cavazza, J. C.
Fontecilla-Camps, F. A. Armstrong, J. Am. Chem. Soc. 2009, 131,
8457 – 18466; f) J. F. Hull, Y. Himeda, W. H. Wang, B. Hashi-
1
guchi, R. Periana, D. J. Szalda, J. T. Muckerman, E. Fujita, Nat.
Chem. 2012, 4, 383 – 388; g) S. Kato, J. U. Jung, T. Suenobu, S.
Fukuzumi, Energy Environ. Sci. 2013, 6, 3756 – 3764; h) C. D.
Received: June 8, 2016
Published online: && &&, &&&&
4
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 5
These are not the final page numbers!

Angewandte
Communications
Chemie
Communications
Photoredox Catalysis
0
A homoleptic Mo complex with chelating
isocyanide ligands was investigated. This
chemically robust complex exhibits long-
L. A. Bꢁldt, X. Guo, A. Prescimone,
3
O. S. Wenger*
&&&& — &&&&
lived MLCT luminescence, and it is a far
stronger photoreductant than d metal
6
A Molybdenum(0) Isocyanide Analogue
of Ru(2,2’-Bipyridine)3 : A Strong
Reductant for Photoredox Catalysis
diimines made from precious metals. The
utility of this complex as a photoredox
sensitizer is demonstrated by its suc-
cessful application in the rearrangement
of an acyl cyclopropane to a 2,3-dihydro-
furan.
2
+
Angew. Chem. Int. Ed. 2016, 55, 1 – 5
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!