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1H NMR analysis clearly showed the formation of coupling product
3aa over the same time period. These results suggest that the
“transmetallation first” catalytic cycle is the most plausible
mechanism when cationic PPh3AuNTf2 is used as catalyst.
7
8
DOI: 10.1039/C6CC05078F
Catal., 2015, 357, 2622.
For selected recent reviews on visible light photoredox
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,
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2013,
4
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4
, 561.
9
For review on cooperative photoredox catalysis, see: X.
Lang, J. Zhao and X. Chen, Chem. Soc. Rev., 2016, 45, 3026.
10 For an elegant alternative; photoredox using only Au
catalysts with blue LEDs by Hashmi and Barriault: (a) L.
Huang, M. Rudolph, F. Rominger and A. S. K. Hashmi,
Angew. Chem. Int. Ed., 2016, 55, 4808; (b) G. Revol, T.
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Chem. Int. Ed., 2013, 52, 13342; (c) L. Huang, F. Rominger,
Figure 2 31P NMR monitoring of PPh3AuCl‐catalysed reaction (plot
PPh3AuNTf2‐catalysed reaction (plot
C) and
D
)
In conclusion, we have developed the first application of
dual gold/photoredox catalysis for C(sp2)‐C(sp2) coupling.
Successful cross‐coupling was found to significantly depend on
the amount of water added. While studies have shown that
M. Rudolph and A. S. K. Hashmi, Chem. Commun., 2016; 52
,
6435; (d) J. Xie, S. Shi, T. Zhang, N. Mehrkens, M. Rudolph
and A. S. K. Hashmi, Angew. Chem. Int. Ed., 2015, 54, 6046.
11 Although it is known with ligand‐ and base‐assisted redox
gold‐catalysis (mechanistically distinct from photoredox):
(a) R. Cai, M. Lu, E. Y. Aguilera, Y. Xi, N. G. Akhmedov, J. L.
Petersen, H. Chen and X. Shi, Angew. Chem. Int. Ed., 2015,
54, 8772. See also Pd‐catalysis review: H. Bonin, E. Fouquet
and F.‐X. Felpin, Adv. Synth. Catal., 2011, 353, 3063.
oxidation of Au(I) to Au(III) species
V is the first step in several
dual gold/photoredox catalysed reactions, our mechanistic
studies reveal that the mechanistic sequence is in fact highly
catalyst dependent. Cationic PPh3AuNTf2 actually undergoes
transmetallation with arylboronic acid prior to oxidation of
Au(I) to Au(III), whereas neutral PPh3AuCl undergoes the
expected “oxidation first” pathway.
We thank the Leverhulme Trust (RPG‐2014‐345) for
funding. Mass spectrometry data was acquired at the EPSRC
UK National Mass Spectrometry Facility at Swansea University.
12 During the preparation of this manuscript, Barriault
disclosed
coupling to alkylate heterocycles: T. McCallum and L.
Barriault, Chem. Sci., 2016, , 4757.
a
photoredox gold catalysed C(sp3)‐C(sp2)
7
13 G. Barker, S. Webster, D. G. Johnson, R. Curley, M.
Andrews, P. C. Young, S. A. Macgregor and A.‐L. Lee, J. Org.
Chem., 2015, 80, 9807.
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15 See also: M. D. Levin and F. D. Toste, Angew. Chem. Int.
Ed., 2014, 53, 6211.
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