Photoinitiated oxidative addition of CF3I to gold(I) and facile aryl-CF3 reductive elimination

Article abstract of DOI:10.1021/ja503974x

Herein we report the mechanism of oxidative addition of CF₃I to Au(I), and remarkably fast C_aryl-CF₃ bond reductive elimination from Au(III) cations. CF₃I undergoes a fast, formal oxidative addition to R₃PAuR' (R = Cy, R' = 3,5-F₂-C ₆H₄, 4-F-C₆H₄, C₆H ₅, 4-Me-C₆H₄, 4-MeO-C₆H₄, Me; R = Ph, R' = 4-F-C₆H₄, 4-Me-C₆H ₄). When R' = aryl, complexes of the type R₃PAu(aryl) (CF₃)I can be isolated and characterized. Mechanistic studies suggest that near-ultraviolet light (λ_max = 313 nm) photoinitiates a radical chain reaction by exciting CF₃I. Complexes supported by PPh₃ undergo reversible phosphine dissociation at 110 °C to generate a three-coordinate intermediate that undergoes slow reductive elimination. These processes are quantitative and heavily favor C _aryl-I reductive elimination over C_aryl-CF₃ reductive elimination. Silver-mediated halide abstraction from all complexes of the type R₃PAu(aryl)(CF₃)I results in quantitative formation of Ar-CF₃ in less than 1 min at temperatures as low as -10 °C.

Full text of DOI:10.1021/ja503974x

Article
pubs.acs.org/JACS
Photoinitiated Oxidative Addition of CF3I to Gold(I) and Facile Aryl-
CF3 Reductive Elimination
Matthew S. Winston, William J. Wolf, and F. Dean Toste*
Department of Chemistry, University of California, Berkeley, California 94720, United States
S
* Supporting Information
ABSTRACT: Herein we report the mechanism of oxidative
addition of CF3I to Au(I), and remarkably fast Caryl−CF3 bond
reductive elimination from Au(III) cations. CF3I undergoes a
fast, formal oxidative addition to R3PAuR′ (R = Cy, R′ = 3,5-
F2-C6H4, 4-F-C6H4, C6H5, 4-Me-C6H4, 4-MeO-C6H4, Me; R =
Ph, R′ = 4-F-C6H4, 4-Me-C6H4). When R′ = aryl, complexes of
the type R3PAu(aryl)(CF3)I can be isolated and characterized.
Mechanistic studies suggest that near-ultraviolet light (λmax
=
313 nm) photoinitiates a radical chain reaction by exciting
CF3I. Complexes supported by PPh3 undergo reversible phosphine dissociation at 110 °C to generate a three-coordinate
intermediate that undergoes slow reductive elimination. These processes are quantitative and heavily favor Caryl−I reductive
elimination over Caryl−CF3 reductive elimination. Silver-mediated halide abstraction from all complexes of the type
R3PAu(aryl)(CF3)I results in quantitative formation of Ar−CF3 in less than 1 min at temperatures as low as −10 °C.
To access complexes of the type R3PAu(aryl)(CF3)I, we
were drawn to Puddephatt’s report of the oxidative addition of
CF3I to Me3PAuMe to afford cis/trans mixtures of
Me3PAuMe2(CF3) and Me3PAuI.14 In one case, Me3PAu(Me)-
(CF3)I was obtained exclusively, but its preparation could not
be reproduced by the authors. Because reaction times varied
from 5 min to 1 day, and rates dramatically slowed in the
presence of galvinoxyl, the authors concluded that a free-radical
INTRODUCTION
■
Reports of organogold complexes undergoing redox processes
are typically limited to slow oxidative additions and reductive
eliminations.1,2 However, organogold complexes are not
necessarily unreactive; we recently showed that diaryl Au(III)
complexes undergo remarkably fast aryl−aryl reductive
elimination at temperatures as low as −50 °C.3 These recent
findings from our group, as well those established by Vicente,4
Hashmi,5 and Lloyd-Jones,6 suggest that the barrier for
challenging reductive eliminations might be substantially
diminished at Au(III). Caryl−CF3 bond reductive elimination
is typically a slow process requiring elevated temperatures and
long reaction times, due to ground state stabilization afforded
by exceptionally strong bonding between transition metals and
CF3 ligands.7 For instance, (dppbz)Pd(2-Me-C6H4)(CF3)
(dppbz = 1,2-bis(diphenylphosphino)benzene) is stable at
130 °C for 3 days,8 while (dppp)Pd(Ph)(CF3) (dppp = 1,3-
diphenylphosphinopropane) and (dppe)Pd(Ph)(CF3) (dppe =
1,2-diphenylphosphinoethane) yield only 10% PhCF3 after 3
days at 145 °C.9 Reductive eliminations at temperatures
between 50 and 80 °C can be achieved at Pd(II) by employing
bulky ligands, such as Xantphos10 and Brettphos.11 Notably,
while aryl-CF3 reductive eliminations from Pd(IV) often
require similarly high temperatures,12a Sanford has shown
that they can occur at temperatures as low as 23 °C over 1 h.12b
Despite advances in catalytic trifluoromethylation, Caryl−CF3
reductive elimination still remains a challenging step. Given the
importance of trifluoromethylated arenes in pharmaceuticals
and agrochemicals,13 we were prompted to investigate
potentially low-barrier Caryl−CF3 bond reductive elimination
at Au(III).
•
chain mechanism was operative, with CF3 as the propagating
species.
RESULTS AND DISCUSSION
■
Prior investigations by our group revealed that oxidation of
Ph3PAu(4-F-C6H4) rapidly generates 4,4′-difluorobiphenyl
through a mechanism involving aryl group transfer.3 However,
the use of the bulkier PCy3 prevents transfer of the arene
ligand, instead resulting in clean, rapid oxidation of Cy3PAu(4-
F-C6H4) (1a) to the isolable Au(III) complex cis-(Cy3P)Au(4-
F-C6H4)Cl2 (2) (eq 1).15 Therefore, we began our inves-
tigations of Au(I) oxidation by CF3I using 1a, with the
fluorinated arene ligand also providing a convenient 19F NMR
handle. Treatment of 1a in CD2Cl2 with CF3I (25 equiv)
afforded the product of formal CF3I oxidative addition 3a in 1 h
in good yield (eq 2 and Table 1). Both the CF3 and PCy3
Received: April 21, 2014
Published: May 16, 2014
© 2014 American Chemical Society
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fragmentation of valerophenone as a standard.18 The oxidative
addition of CF3I to 1a was complete after 20 s of irradiation by
a Hg vapor lamp (2 mM aq. K2CrO4 optical filter;
transmittance λmax = 313 nm), while the fragmentation of
valerophenone (Φ = 1) took place over 24 h under identical
conditions. This rate difference, in addition to the ability of
ambient light to bring the reaction to full conversion over
variable reaction times (between 15 min and 1 h), supports a
radical chain reaction as the mechanism of Au(I) oxidation by
CF3I.
The reaction of excess CF3I and 1a is also fast in THF, but
the conversion is never greater than 65% (52% yield of 3a),
even when irradiated by a Hg vapor lamp for 1 h (vida infra).
Notably, an excess of fluoroform (HCF3) is generated in THF,
regardless of the light source (only DCF3 is formed when THF-
d8 is used). GC-MS analysis of reaction mixtures reveals several
products of THF oxidation, likely formed by H• abstraction by
•CF3.
Table 1. Photoinitiated Oxidative Addition of CF3I to
Electronically Diverse Au(I) Aryl Complexes 1a−1f, 11a,
and 11b
Au(I) reactant
PR3
Ar
product
yield (%)
1a
PCy3
PCy3
PCy3
PCy3
PCy3
PCy3
PPh3
PPh3
4-F-C6H4
3a
64
44
59
38
44
NR
71
63
1b
1c
3,5-F2-C6H3
C6H5
3b
3c
Several control experiments, using HCF3 production relative
to a standard as a probe to detect •CF3 generation, support the
involvement of Au(I) during the initiation of the chain reaction.
The UV absorption of CF3I is centered at 270 nm but tails
beyond 350 nm.19 When irradiated at 313 nm, CF3I undergoes
fast, reversible C−I bond homolysis. However, in the absence of
1a, only negligible amounts of HCF3 are observed when THF
solutions of CF3I are irradiated for 30 min, indicating that
carbon/iodine radical recombination is substantially faster than
H• abstraction from THF. Similarly insignificant quantities of
HCF3 are observed when 20 equiv (relative to CF3I) of the H•
donors 1,4-cyclohexadiene, 9,10-dihydroanthracene, or triphe-
nylmethane are added (Figure 2A). Additionally, Cy3PAu(2-
(CH2CHCH2)C6H4) (4), containing a pendent olefin to
1d
1e
4-Me-C6H4
4-MeO-C6H4
2-Me-C6H4
4-F-C6H4
3d
3e
1f
−
12a
11a
11b
4-Me-C6H4
12b
ligands (doublet at δ = −24.5 and quartet at δ = 25.6 in the 19
F
and 31P NMR spectra, respectively) provide diagnostic NMR
signals (Table 2). The substantial coupling (3JP−F = 63 Hz)
between fluorine and phosphorus are characteristic of a trans
relationship between the CF3 and phosphine ligands.14 X-ray
analysis of crystals of 3a confirmed this stereochemical
relationship around the square planar Au(III) (Figure 1A);
other than the homoleptic anion [Au(CF3)4]−,16 complex 3a
contains a rare example of a crystallographically characterized
Au(III)−CF3 bond. Complex 3a is not only stable to air and
water but can be purified by column chromatography as well.
Mechanism of Oxidative Addition of CF3I. The reaction
of 1a and CF3I represents a rare oxidation of Au(I) to Au(III)
that directly installs potentially reactive Au(III)−carbon
bonds.1 During our attempts to monitor the oxidative addition
by 19F NMR, we found that no reaction occurred when the
reaction mixture was placed inside the dark NMR spectrometer.
However, when the reaction mixture was exposed to ambient
fluorescent light for 5 min, the formation of 3a was detected
(∼20%). Given the reliance of numerous methods on CF3I as a
trifluoromethyl source,17 we investigated its photochemical
reactivity. Actinometry experiments were carried out to
determine the overall quantum yield, using the Norrish II
•
either capture a putative Au(II) intermediate and/or CF3, is
fully consumed upon irradiation in the presence of excess CF3I
(Figure 2B). This oxidation affords multiple Au(III) products
•
of indiscriminate CF3 addition to the terminal olefin and gold
atom (and HCF3 when THF is used as solvent) (see SI).
Because 2-allylbromobenzene (5) does not react with CF3I
when irradiated under similar conditions (no HCF3 is observed
after 5 min, and less than 2% after 30 min), we conclude that
the Au(I) aryl complex is necessary for chain initiation. These
results are also consistent with an initiation mechanism
•
involving [CF3I]•−, which generates iodide and CF3 following
C−I bond homolysis.
We envisioned two possible initiation mechanisms for
•
generating CF3 as a propagating species from [CF3I]•− in a
chain reaction: (1) initial photoexcitation of 6 followed by
electron transfer to CF3I, or (2) initial photoexcitation of CF3I
followed by electron transfer from 6 (Scheme 1).
Table 2. 31P{1H} and 19F NMR Data for Complexes 3a−3e, 12a, and 12b
complex
PR3
Ar
δ
31P{1H} (ppm)
δ
19F (ppm)
3
3
3a
PCy3
PCy3
PCy3
PCy3
PCy3
PPh3
PPh3
4-F-C6H4
3,5-F2-C6H3
C6H5
25.6 (q, JP−F = 63 Hz)
−24.5 (d, JP−F = 63 Hz)
3
3
3b
26.1 (q, JP−F = 63 Hz)
−22.0 (d, JP−F = 64 Hz)
3
3
3c
25.5 (q, JP−F = 62 Hz)
−22.7 (d, JP−F = 62 Hz)
3
3
3d
3e
4-Me-C6H4
4-MeO-C6H4
4-F-C6H4
4-Me-C6H4
25.5 (q, JP−F = 62 Hz)
−23.6 (d, JP−F = 62 Hz)
3
3
23.3 (q, JP−F = 63 Hz)
−20.6 (d, JP−F = 64 Hz)
3
3
12a
12b
20.0 (q, JP−F = 68 Hz)
−21.0 (d, JP−F = 68 Hz)
3
3
20.4 (q, JP−F = 67 Hz)
−21.3 (d, JP−F = 67 Hz)
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Figure 1. (A−F) Thermal ellipsoid representations of 3a−3d, 12a, and 12b at the 50% probability level. Hydrogens have been omitted for clarity.
Atoms are color-coded: gray (carbon), yellow (fluorine), gold (gold), purple (iodine), orange (phosphorus). See Supporting Information (SI) for
bond lengths and angles.
Scheme 1. Possible Initiation Mechanisms Involving
Photoexcitation of Either Au(I) Complex 6 (Mechanism 1)
or CF3I (Mechanism 2)
Figure 2. Control experiments to assess involvement of Au(I) in the
initiation of the radical chain mechanism. (A) Irradiation of CF3I
solutions containing H• donors to detect CF3H in the absence of gold.
(B) Radical trapping using an olefin with and without a pendant gold
center.
fluorimetry samples under vacuum, fluorescence is restored to
the same intensity prior to introduction of the gas, indicating
that consumption of Au(I) has not occurred.
Surprisingly, fluorescence quenching by the Au(III) complex
3a is more than 2 orders of magnitude more effective (KSV
=
Au(I) aryl complexes are well-known chromophores, and
their photophysical properties have been investigated pre-
viously.20 While 1a absorbs weakly above 310 nm (the cutoff
for many laboratory fluorescent lamps19), excitation at 320 nm
(ε = 37 M−1 cm−1) results in a weak, broad luminescence from
340 to 460 nm, classified as fluorescence based on the lifetime
of excited species 1a* (<10 ns, quantum yield of fluorescence =
0.03).21 Despite the short lifetime of 1a*, CF3I effectively
quenches its fluorescence (Stern−Volmer quenching constant
KSV = 30 M−1, Figure 3). Although this energy transfer could
conceivably generate •CF3 and initiate a chain reaction
(mechanism 1, Scheme 1), when CF3I is removed from
4270 M−1) than quenching by CF3I (Figure 3). If propagating
species terminate frequently, some critical concentration of
Au(III) product exists that may impede productive energy
transfer from an excited species, halting reinitiation of the chain
reaction.
In light of Puddephatt’s report, Au(I) alkyl complexes, such
as Me3PAuMe, clearly react with CF3I.14 However, there is no
mention of the dependence of light on this process, although if
the reaction is photoinitiated, mechanism 1 would seem
especially unlikely given the absence of a chromophoric aryl
ligand in Puddephatt’s examples. To test this hypothesis, we
irradiated Cy3PAuMe (9) in the presence of CF3I (Scheme 2).
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unreactive toward CF3I, oxidation of 11a cannot be initiated by
small amounts of dissociated PPh3 (we cannot disprove the
analogous mechanism for PCy3-supported complex 1a.)
Complex 12a was characterized by X-ray crystallography and
shown to be isostructural to 3a (Figure 1B).
Figure 3. Stern−Volmer plots of fluorescence quenching of 1a by
different concentrations of CF3I (blue boxes) and Au(III) complex 3a
(blue triangles) in CH2Cl2. Concentrations of Au(III) are in mol/L
and CF3I concentrations are in mmol/L.
On the basis of these results, we propose that while
photoexcited [CF3I]* undergoes rapid C−I bond homolysis
and recombination, it also oxidizes Au(I) aryl and alkyl
complexes by accepting electrons into a low-lying SOMO to
generate radical anion [CF3I]•− (mechanism 2, Scheme 1).
Homolysis of the C−I bond of [CF3I]•− generates iodide and
•CF3, which oxidizes (R3P)AuR′ (6) to Au(II) intermediate 7.
Iodine atom abstraction of CF3I by 7 affords Au(III) complex 8
Scheme 2. Photochemical Oxidative Addition of CF3I to 9 in
CD2Cl2 and Spontaneous Reductive Elimination of CH3I
•
and regenerates •CF3. In THF, oxidation of 6 by CF3 is
competitive with solvent H• abstraction to make HCF3 and
terminate the radical chain. At sufficiently high concentrations,
the Au(III) product (8) quenches [CF3I]* before it can
reinitiate the radical chain reaction.
While 9 does not absorb above 300 nm (see SI), the reaction is
quantitative in CD2Cl2 when irradiated with ambient light, and
does not proceed in the dark. The oxidized product is
unobservable, eliminating CH3I to generate Cy3PAuCF3 at
room temperature.22,23 In THF, the reaction generates excess
HCF in THF3, presumably also from solvent H• abstraction by
•CF3.
Promisingly, the photoinitiated oxidative addition of CF3I is
general for electronically diverse complexes of the type
Cy3PAu(aryl) (Tables 1 and 2). The resulting Au(III) products
(see Figure 1 for their crystallographic analyses) can be purified
by chromatography on silica. Complex 1b (aryl = 3,5-F2-C6H3),
which is more electron-deficient than 1a (aryl = 4-F-C6H4),
reacts smoothly with CF3I to afford 3b. While complexes with
more electron-rich ligands such as 1c (aryl = C6H5) and 1d
(aryl = 4-Me-C6H4) also react with CF3I to afford 3c and 3d,
respectively, the most electron-rich complex 1e (aryl = 4-MeO-
C6H4) decomposes to Au nano particles and several CF3-
containing Au(III) complexes in solution and solid state (no
products of Caryl−I or Caryl−CF3 reductive elimination can be
detected). Au(III) product 3e is detectable, however, and its
decomposition can be slowed substantially by addition of
MeCN upon concentration of the reaction, allowing its
solution-state characterization. The mechanism of decomposi-
tion has not yet been identified, although we speculate that the
electron-rich arene may encourage PCy3 dissociation at room
temperature and subsequent aryl group transfer.
•
If initiation mechanism 2 is operative, then CF3 could be
generated by irradiating CF3I solutions containing electron
donors other than Au(I), such as phosphines (Scheme 3).24
Scheme 3. Photochemical Oxidation of Trialkylphosphines
by CF3I
Indeed, irradiation of PMe3 or PCy3 in the presence of CF3I
2
results in formation of [Me3P-CF3]I (10a, JP−F = 63 Hz) or
The complex 1f (aryl = 2-Me-C6H4) does not react with
CF3I at all, suggesting that CF3I oxidative addition is sensitive
to the sterics of the aryl ligand and that relaxation of [CF3I]* is
faster than oxidation of the metal center to initiate the radical
chain. Unsurprisingly, no HCF3 is observed when 1f is
irradiated in THF for 20 min.
[Cy3P-CF3]I (10b, 2JP−F = 42 Hz);25 neither reaction proceeds
in the dark. Consistent with quenching of [CF3I]* by Au(III),
the oxidation of PCy3 in THF stalls at roughly 45% conversion
(by 31P NMR) in the presence of 25 mol % Au(III) complex
3a.
PPh3 does not react with CF3I (eq 3), presumably due to its
lower oxidation potential relative to PMe3 and PCy3. When
PCy3 and PPh3 are irradiated together with CF3I, only PCy3 is
consumed, suggesting that PPh3 neither initiates the chain nor
Reductive Elimination from Au(III) Complexes. We
next probed Caryl−CF3 reductive eliminations from Au(III). To
our surprise, 12a undergoes quantitative Caryl−I reductive
elimination in toluene-d8 at 110 °C to afford 4-fluoroiodo-
benzene and Ph3PAuCF3 over 20 min (Scheme 4).22 No 4-
fluoro(trifluoromethyl)benzene is observed by 19F NMR or
GC. This process is highly sensitive to free phosphine, stalling
completely in the presence of PPh3 (0.1 or 1.0 equiv) at 110 °C
for 12 h. Treatment of 12a with PPh3-d15 at room temperature
•
reacts with CF3 during propagation. Contrary to our initial
hypothesis that bulky phosphine ligands prevent aryl group
transfer upon Au(I) oxidation, we found that Ph3PAu(4-F-
C6H4) (11a) undergoes quantitative photoinitiated reaction
with CF3I in CD2Cl2 to generate 12a (eq 4). Since PPh3 is
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Scheme 4. Behavior of Au(III) Complex 12a and 12b in the
Presence of Free PPh3 and at Elevated Temperatures
reductive elimination due to slower dimer dissociation and/or a
dimer−monomer equilibrium that more favors the dimer, based
on the smaller cone angle and weaker σ-donation of PPh3
relative to PCy3.
CONCLUSION
■
These results reported herein support the oxidative addition of
CF3I to Au(I) via a photoinitiated chain reaction. The reactions
are fast at room temperature for both Au(I) aryl and alkyl
complexes. Aryl-CF3 reductive elimination is typically a high-
barrier process but occurs in seconds at room temperature from
a Au(III) cation. The Au(I)aryl species may be regenerated via
one of the numerous transmetalation strategies available
involving carbon nucleophiles.27 For instance, excess (4-F-
C6H4)SnMe3 (10 equiv) undergoes fast, quantitative trans-
metalation with [Cy3PAu]SbF6 at room temperature to afford
1a, thereby closing a hypothetical catalytic cycle based on the
three elementary steps shown in Scheme 5. Silver-free halide
results in immediate formation of 12a-d15, presumably via an
associative process.2a−c
More electron-rich aryl ligands, such as 4-methylphenyl
(12b), do not significantly affect the relative rates of Caryl−I and
Caryl−CF3 reductive elimination (Scheme 4). At 110 °C,
complex 12b undergoes mostly Caryl−I reductive elimination
within 10 min to afford 4-methyliodobenzene.26 Both Caryl−I
and Caryl−CF3 reductive eliminations are also completely
inhibited in the presence of PPh3 (0.1 or 1.0 equiv), while
PPh3-d15 reacts immediately at room temperature to afford 12b-
d15, also via associative ligand exchange. These observations are
consistent with a mechanism involving highly reversible PPh3
dissociation from 12a and 12b, followed by slow Caryl−I
reductive elimination from 13a or 13b, respectively.
Scheme 5. Oxidation of 1a, Aryl-CF3 Reductive Elimination,
and Regeneration of 1a Supports the Feasibility of a Mild,
Catalytic Trifluoromethylation
Clearly, the behaviors of 12a and 12b are similar to
Au(III)alkyl complexes studied by Kochi, which not only
reductively eliminate Calkyl−Calkyl bonds between 70 and 100
°C via a dissociative mechanism but also undergo associative
ligand exchange at ambient temperature with excess phosphi-
ne.2a−c Unsurprisingly, analogous PCy3-stabilized complexes 3a
and 3d are stable at 110 °C for at least 12 h, presumably due to
the greater σ-donating ability of PCy3 relative to PPh3.
Phosphine exchange with excess P(n-Bu)3, PBn3, or PCy3
does not occur even at these temperatures, precluding not
only the lower-barrier associative exchange mechanism
observed with the PPh3-supported systems (attributed to the
larger cone angle of PCy3 relative to PPh3), but also PCy3
dissociation to form a three-coordinate complex.
Because Caryl−I reductive elimination is significantly faster
than Caryl−CF3 reductive elimination, a cycle for gold-catalyzed
trifluoromethylation must necessarily involve iodide abstraction
from the Au(III) product of CF3I oxidative addition. Despite
the apparent kinetic stabilities of the Au(III) complexes 3a−3e,
12a, and 12b, they all undergo quantitative Caryl−CF3 reductive
elimination in less than 1 min upon treatment with AgSbF6 at
room temperature.
To consider the effects of the phosphine ligand on the silver-
mediated Caryl−CF3 reductive elimination of Au(III), we used
variable-temperature NMR to follow the reductive elimination
from 3a and 12a in the presence of AgSbF6. PCy3-substituted
complex 3a undergoes very fast (quantitative conversion in less
than 1 min) Caryl−CF3 reductive elimination at −10 °C, while
the analogous PPh3-stabilized 12a reacts similarly fast at room
temperature (eq 5). At lower temperatures, several bridging
species (most likely dimers) are observed by 19F NMR upon
halide abstraction in both cases. If Caryl−CF3 bond reductive
elimination can only occur from a monomeric three-coordinate
intermediate, then 12a might be expected to undergo slower
abstraction from Au(III) complexes could conceivably enable a
practical and mild cycle for gold-catalyzed trifluoromethylation
of aryl nucleophiles, although deleterious reactions between
starting material and metalloradical intermediates and •CF3
must be mitigated, as well as competitive aryl−aryl homocou-
pling.
While we initially set out to probe Caryl−CF3 reductive
elimination at Au(III), we also explored the oxidative addition
of CF3I to Au(I), a process with potential implications beyond
gold chemistry. The possibility of photoinitiated oxidation of
transition metals or main group elements by CF3I should not
be discounted in methods employing this reagent as a
trifluoromethyl source, particularly since ambient fluorescent
laboratory lighting is sufficient to initiate a chain in the presence
of a suitable reductant. The results presented also suggest that
substrate photoexcitation may provide a low-barrier avenue to
kinetically challenging oxidative additions by Au(I), providing
access to potentially reactive Au(III) complexes.28
ASSOCIATED CONTENT
* Supporting Information
Experimental details, characterization data, and crystallographic
information (cif). This material is available free of charge via
the Internet at http://pubs.acs.org.
■
S
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Chem. 2010, 131, 98. (c) Ye, Y.; Sanford, M. S. J. Am. Chem. Soc. 2012,
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(18) Wagner, P. J.; Kemppainer, A. E. J. Am. Chem. Soc. 1972, 94,
AUTHOR INFORMATION
Corresponding Author
E-mail: fdtoste@berkeley.edu
Notes
■
7495.
(19) Nyden, M. R. Photodegradation of CF3I. In Fire Suppression
System Performance of Alternative Agents in Aircraft Engine and Dry Bay
Laboratory Simulations; Gann, R. G., Ed.; National Institute of
Standards and Technology: Washington, D.C., 1995; pp 77−95.
(20) For some recent examples, see: (a) Partyka, D. V.; Zeller, M.;
Hunter, A. D.; Gray, T. G. Angew. Chem., Int. Ed. 2006, 45, 8188.
(b) Partyka, D. V.; Esswein, A. J.; Zeller, M.; Hunter, A. D.; Gray, T.
G. Organometallics 2007, 26, 3279. (c) Vogt, R. A.; Gray, T. G.;
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge Professor Robert G. Bergman for
helpful discussions, David Tatum and Professor Kenneth N.
Raymond for use of fluorimetry equipment, Professor Felix
Fischer for access to a Hanovia lamp, and Mercedes Taylor and
the Chemistry 208 course at UC-Berkeley for assistance with
the X-ray structure of 3b. This work was generously funded by
the NIHGMS (RO1 GM073932), an NIH fellowship to M. S.
W. (F32 GM103238-02), and an NSF fellowship to W.J.W.
(DGE 1106400).
Crespo-Hernan
(d) Visbal, R.; Ospino, I.; Lop
Gimeno, M. C. J. Am. Chem. Soc. 2013, 135, 4712. (e) Crespo, O.;
Díez-Gil, C.; Jones, P. G.; Laguna, A.; Ospino, I.; Tapias, J.;
Villacampa, M. D.; Visbal, R. Dalton Trans. 2013, 42, 8298.
́
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(21) The excited state lifetime of 1a* is shorter than the lower limit
of detection of our fluorimeter (<10 ns).
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7782
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