Trans Influence of Ligands on the Oxidation of Gold(I) Complexes

Article abstract of DOI:10.1021/jacs.9b09363

Gold(I) complexes are considered active species toward oxidative addition; current understanding indicates a different mechanism in contrast to other late transition metals, but a rational understanding of the reactivity profile is lacking. Herein, we propose that the accessibility of the gold(I) center to tri- or tetra-coordination is critical in the oxidative process involving a tri- or tetra-coordinate gold(I) with the oxidizing reagent as one of the ligands as an intermediate. A computational study of the geometry of (Phen)R₃PAu(I)NTf₂ complexes shows that the accessibility of such tricoordinate species shows a good correlation with the "trans influence" of phosphine ligands: the weak σ-donating phosphine ligands promote tricoordination of gold(I) complexes. The oxidative addition to the asymmetric tricoordinate (Phen)R₃PAu(I)NTf₂ complexes with alkynyl hypervalent iodine reagents was built. The kinetic profile of the oxidative addition exhibits a good relationship to the Hammett substituent parameter (ρ = 3.75, R² = 0.934), in which the gold(I) complexes bearing less σ-donating phosphine ligands increase the rate of oxidative addition. The positive ρ indicates a high sensitivity of the oxidative addition to the trans influence. The reactivity profile of oxidative addition to a linear bis(pyridine)gold(I) complex further supports that the oxidative addition to gold(I) complexes is promoted by ligands with small trans influence.

Full text of DOI:10.1021/jacs.9b09363

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Article
Trans Influence of Ligands on the Oxidation of Gold(I) Complexes
Yangyang Yang, Lukas Eberle, Florian F. Mulks, Jonas F. Wunsch, Marc
Zimmer, Frank Rominger, Matthias Rudolph, and A. Stephen K. Hashmi
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b09363 • Publication Date (Web): 26 Sep 2019
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Journal of the American Chemical Society
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Trans Influence of Ligands on the Oxidation of Gold(I) Complexes
Yangyang Yang,† Lukas Eberle,† Florian F. Mulks,† Jonas F. Wunsch,† Marc Zimmer,† Frank
Rominger,† Matthias Rudolph† and A. Stephen K. Hashmi*,†,‡
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†Organisch-Chemisches Institut, Heidelberg University, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
‡Chemistry Department, Faculty of Science, King Abdulaziz University (KAU), Jeddah 21589, Saudi Arabia
ABSTRACT: Gold(I) complexes are considered active species towards oxidative addition, and current understanding indicates a
different mechanism in contrast to other late transition metals, but a rational understanding of the reactivity profile is lacking. Herein,
we propose that the accessibility of the gold(I) center to tri- or tetra-coordination is critical in the oxidative process involving a tri- or
tetra-coordinate gold(I) with the oxidizing reagent as one of the ligands as an intermediate. A computational study of the geometry
of (Phen)R3PAu(I)NTf2 complexes shows that the accessibility of such tri-coordinate species shows a good correlation with the ‘trans
influence’ of phosphine ligands: the weak σ-donating phosphine ligands promote tri-coordination of gold(I) complexes. The oxidative
addition to the asymmetric tri-coordinate (Phen)R3PAu(I)NTf2 complexes with alkynyl hypervalent iodine reagents was built. The
kinetic profile of the oxidative addition exhibits a good relationship to the Hammett substituent parameter (ρ = 3.75, R2 = 0.934), in
which the gold(I) complexes bearing less σ-donating phosphine ligands increase the rate of oxidative addition. The positive ρ indicates
a high sensitivity of the oxidative addition to the trans influence. The reactivity profile of oxidative addition to linear
bis(pyridine)gold(I) complex further supports that the oxidative addition to gold(I) complexes are promoted by ligands with small
trans influence.
coordination of oxidizing reagents with two-coordinate gold(I)
complexes to form tri-coordinate gold(I) intermediates is
critical for both of these two strategies.
INTRODUCTION
Oxidative addition of sp2-C-X or sp-C-X bonds to gold(I)
complexes is a key step in some gold-catalyzed reactions.1 A
The rehybridization of two-coordinate linear gold(I)
molecular orbitals resembles a three-center four-electron
bond,11 resulting in a coordinate competition of the two ligands,
in which electronic density transfers competitively from lone
pairs of the ligands to the s+dz2 hybrid orbital of the gold(I)
complexes, which in general is called trans-influence.12
Analogously, rehybridization of tri-coordinate gold(I)
molecular orbitals can resembled four-center six-electron
bonds, in which three σ-donor ligands transfer electronic
density to gold(I) atom competitively. Accordingly, a strong σ-
donor ligand on the gold(I) center occupies the s+d hybrid
orbitals of gold(I) competitively, undermining the further
coordination with other weak σ-donor ligands. Identical σ-
donor ligands are expected to share the orbitals of gold(I) atom,
leading to the formation of tri-coordinate, even tetra-coordinate
gold(I) complexes.12 In fact, precedents to the synthesis of tri-
coordinate gold(I) complexes indicated that the tri-coordinate
geometry is always accessible by using comparable σ-donor
ligands.13
detailed understanding of this process would provide a
guideline for the design of new gold catalysis. However, due to
the high redox potential of Au(I)/Au(III) (1.41 V) compared to
those of Pd(0)/Pd(II) (0.91 V) or Pt(0)/Pt(II) (1.18 V)2 and the
reluctance of gold(I) to form complexes with higher
coordination numbers,3 the oxidative addition to gold(I) is
difficult to study. Indeed, only a few investigations on the
oxidative addition to gold(I) complexes have been reported in
the last years.4 Recent studies on the oxidative addition of aryl
halides to gold(I) complexes showed that electron-rich
substrates react faster than electron-poor ones,4 which is the
opposite of the trend for palladium(0) with the same d-electron
configuration.5 We rationalize this contrast by the different
coordination behavior of both metals (Figure 1a).6 The typical
linear two-coordinated gold(I) thermodynamically disfavor a
coordination of the oxidizing reagents complexes,7 as different
from palladium(0) the tri-coordinated gold(I) complexes are
much less stable.
In the last years, the oxidation of gold(I) to gold(III) was
enabled by: a) introducing bidentate ligands not allowing a
trans-chelation at the gold(I) center (Figure 1b).4 Such bidentate
ligands bend the linear gold(I) complexes,8 decreasing the
oxidative barrier because of the increased energy of the d
orbitals,9 and the pre-organized orbitals facilitate the
Considering the important role of the initial coordination of
oxidizing reagents with gold(I) complexes in the process of
oxidative addition, as well as the trans influence of ligands on
the accessibility of tri- or tetra-coordinate gold(I) complexes,
we envisioned the probability of the oxidative addition to the
gold(I) complexes enabled by weak σ-donor ligands. We now
report our results on a study of reactivity of tri-coordinate and
two-coordinate gold(I) complexes towards oxidative addition,
subsequent
coordination
to
oxidizing
agents.
b)
intramolecularizing the oxidative addition, then a pre-
coordination is not necessary, there is no significant entropic
barrier (Figure 1c).10 Overall, we think that the initial
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Journal of the American Chemical Society
showing a correlation of such reactivity to the trans influence
Page 2 of 8
Tri-coordination at gold(I). In 1976, Clegg prepared a tri-
coordinate complex, 2,2’-(bipyridyl)Ph3PAuPF6, in which the
bending of the bidentate bipyridyl ligand is highly asymmetric,
and the Au-N bond lengths are 2.406 Å and 2.166 Å
respectively.14 In 2004, Cinellu et al. synthesized another tri-
coordinate complex, bipyridyl(olefin)AuNTf2,9b which has
apparently symmetric geometry (2.092 Å of Au-N bond lengths
for both), as a result of much smaller trans influence of ethylene
than Ph3P. The trans influence of ligands on the gold(I)
complexes was correlated with the Au-Cl distance in linear L-
Au-Cl complexes.15 Now we used (Phen)R3PAuNTf2
complexes to study the trans influence of ligands on the
accessibility of tri-coordination in gold(I) complexes, in which
the tri-coordinate geometry is thermodynamically stable. A
series of (Phen)R3PAuNTf2 complexes (1) were synthesized by
simply mixing of Phen with cationic R3PAuNTf2 complexes in
CH2Cl2. Single crystal structure analyses of gold(I) complexes
showed the geometry around the metal center with an extremely
unymmetric nitrogen coordination (Figure 2a). Unfortunately,
these crystals suffered strong disordering, which originated
from the site-exchange of the nitrogen atoms in the
unsymmetric tri-coordinate gold(I) complexes (Figure 2b),
preventing a detailed quantitative discussion.16
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of ligands.
a) Process for the gold(I)-induced oxidative addtion of sp2-C-X or sp-C-X bonds
L3/X
L3
L3
R
R
X
R
X
III
I
Au
Au
AAuu
L1
L1 AuI
L2
L1
L2
oxidative
addition
L2
equilibrium
of coordination
two-coordinate gold(I) or
tri-coordinate gold(I)
L = -donor ligands
b) Bidentate ligands-enabled oxidative addition of sp2-C-X or sp-C-X bonds
_
_
I
NTf2
I
NTf2
P
9
P
P
I
III
Au
I
Au NTf2
+
Au
+
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P
P
P
20144a
Bourissou
_
_
_
NTf2
NTf2
N
X
NTf2
N
N
X
III
+
AuI
I
+
+ Au
Au
P
Ad
P
P
Ad
20171d
Ad
Ad
Ad
Ad
Bourissou
_
_
_
NTf2
NTf2
I
NTf2
I
N
N
+
III
N
N
I
I
+Au
Au
+ Au
N
N
20184d
Russell
_
_
a
_
NTf2
AuI
IIII
NTf2
NTf2
N
N
OR
N
N
III
N
I
Au
+
+
N2
N2
N1
Au
N1
+
N
Ar
Ar
20194e
Au
P
Au
P
Hashmi
c) Coordinating environment-enabled oxidative addition of sp2-C-X bond
X
X
AuI
X
III
Au
I
Au
X
PPh2
PPh2
X
PPh2
X
1a
1e
coordination
201410a
b
Bourissou
N
N
+
I
N
I
N
N
Au
X
IPr
X
Au
X
III
Au
IPr
IPr
Au
PPh3
symmetric
coordination
X
N
N
N
N
201510b
+
Ribas
d) This work: weak -donating ligands-enabled oxidative additon of sp-C-X bond
+
Au
Au
X
X
cal. G
PPh3
unsymmetric
PPh3
unsymmetric
5 kJ/mol
N
N
+
N
N
+
N
Figure 2. a) Thermal ellipsoid representations of
(Phen)Ph3PAuNTf2 and (Phen)Cy3PAuNTf2 complexes at the 50%
probability level. Hydrogens have been omitted for clarity. b)
Energy profile for the site-exchange reaction for
(Phen)Ph3PAuNTf2 computed with B97X-D3 functional and
Ahlrichs def2-TZVP basis set.
I
_
I
_
NTf2
IIII
Au
NTf2
Au
NTf2
OR
R3P
PR3
PR3
unsynmmetric
tri-coordination
Ar
Ar
IIII
Ar
NTf2
To gain further insight into ligand effects on the geometry of
such tri-coordinate (Phen)R3PAuNTf2, a computational study of
the Au-N bond lengths, one of key parameters for the tri-
coordination, was carried out using KS-DFT (B97X-D3
functional with Ahlrichs def2-TZVP basis set). Standard
effective core potentials and CPCM solvent model with DCM
was used. As we expected, the (Phen)gold(I) complexes
coordinated with arylphosphine ligands bearing electron
donating group showing weaker Au-N2 bond strength
((Phen)(p-MeO-C6H4)3PAuNTf2 1c, 2.61 Å of Au-N2 distance
vs (Phen)Ph3PAuNTf2 1a, 2.60 Å of Au-N2 distance). On the
contrary, the arylphosphine ligands bearing electron-
withdrawing groups show a shortened Au-N2 bonds ((Phen)(p-
_
_
NTf2
N
N
III
+Au
OR
N
+
I
NTf2
I
Au
Au
N
N
N
Ar
linear
two-coordination
Figure 1. a) Assumption for reactive profile of oxidative addition
involving a coordinating equilibrium and oxidative barrier. b)
Bidentate ligands-enabled oxidative addition to gold(I) complexes.
c) Coordinating environment-enabled oxidative addition. d) This
work: oxidative addition to tri-coordinate and two-coordinate
gold(I) complexes.
RESULTS AND DISCUSSION
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Å of Au-N2 distance). The mechanism of this reaction can be rationalized by two
CF3-C6H4)3PAuNTf2 1b, 2.58
1
2
3
4
5
6
7
8
Especially, (Phen)(C6F5)3PAuNTf2 1d has a significantly
shortened Au-N2 bond (2.33 Å), as a result of small trans
influence of (C6F5)3P. The molecular structure of 1d in the solid
state also displays a significantly shortened Au-N2 bond. Au-
N2 distances of these tri-coordinate gold(I) complexes (1),
bearing para-substituted phosphine ligands, exhibit a negative
proportional relationship to the Hammett substituent parameter,
supporting the σ-donor competition among ligands (Figure 3).
pathways, as shown in scheme 2. The first (pathway A) involves
a phosphine dissociation from the tri-coordinate gold(I)
complex (1a), affording a trigonal gold(I) species, which was
reported to be active for an oxidative addition. The second
pathway (B) comprises two steps of oxidative addition and one
step of reductive elimination. The first oxidative addition to the
asymmetric tri-coordinate gold(I) species 1a proceeds with
alkynyl hypervalent iodine 3a through a tetra-coordinate gold(I)
transition state I,19 affording (Phen)(alkynyl)Ph3PAuIII II. The
trigonal gold(I) complex III was formed by carbon−phosphorus
reductive elimination of gold(III) species II,20 followed by the
second oxidative addition with 3a to afford gold(III) compound
4a. Since the first step of the reaction is rate-determining, we
cannot distinguish these two pathways by a detection of
intermediates. But, the formation of alkynyl(Ph3P)+ 5a, and the
kinetics (see below) support the mechanism B. On the other
hand, the failed oxidation of Ph3P with 3a as well as the absence
of free Ph3P (detected by 31P NMR spectroscopy) in the reactive
solution excludes the mechanism A.
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Scheme 2. Proposed mechanisms for the formation of 4a
Path A
slow
3a
Ph3P
N
N
+
+
N
N
N
N
+
I
_
NTf2
_
I
I
fast
I
Au
NTf2
Au
Au
Ar
IIII
3a
NTf2
PPh3
Figure 3. Correlation between calculated Au-N2 distance of
(Phen)R3PAuNTf2 and Hammett substituent parameter.
CF3
CF3
_
+
O
I
Ar
PPh3
F3C CF3
Reactivity of tri-coordinate (Phen)R3PAuNTf2 towards
oxidative addition. Compared with linear gold(I) complexes,
the tri-coordinate geometry of (Phen)R3PAuNTf2 complexes
indicates an enhanced reactivity towards oxidation. After
screening for some oxidizing agents, an oxidative addition to
(Phen)Ph3PAuNTf2 was observed with alkynyl hypervalent
_
NTf2
O
I
III
N
N
5a
Au
Ar
4a
Path B
Ar
iodine reagents in CD2Cl2, surprisingly affording
a
3a
CF3
CF3
(Phen)alkynylgold(III) complex 4a (40% yield in 16 h, Scheme
1), along with the side-product of (p-F-C6H4)Ph3P+ 5a (31P
NMR 6.7 ppm). The NMR spectroscopy of the gold(III)
complex is consistent with the one that was synthesized by
stoichiometric oxidative addition to (Phen)(ethylene)AuNTf2,
and characterized with X-ray diffraction in our previous work
(Figure S1).4e CD3CN accelerates the reaction, leading to a yield
of 60% in 50 min. In the presence of water (0.6 equiv.) in
CD3CN, the same yield was observed, along with the
decomposition of 5a to Ph3PO and the terminal alkyne,17 as well
as 1,4-bisphenylbuta-1,3-diyne being formed by the coupling of
the terminal alkyne with the alkynylgold(III) complex (see
supporting information 4.3, SI).18 We have also confirmed that
the oxidative addition behaviour is not specific to Phen complex
1a, and the complex (2,2’-bipyridyl)Ph3PAu(I)NTf2 1e is also
competent for the oxidative addition, giving the product in 38%
NMR yield after 12 hours.
N
NTf2
+
N
N
+
I
I
_
Au
N
O
Au NTf2
PPh3
I
PPh3
slow
5a
2+
_
NTf2
Ar
CF3
CF3
_
O
N
N
III
Au
N
N
I
fast
Au
PPh3
I
III
NTf2
II
3a
+
F3C CF3
O
I
_
N
III
N
N
+
Au
NTf2
_
I
fast
N
Au
NTf2
Ar
4a
Ar
IIII
The trans influence of ligands on oxidative addition is shown
in the reactivity profile with (Phen)R3PAuNTf2 (Figure 4). The
plot of the initial NMR yields of 4 against the reaction time
showed a good linear correlation (Figure 4b), allowing the
calculation of the relative initial rate constants k (10-4 mol. L-1.
h-1) of the oxidative addition to tri-coordinate gold(I) complexes
bearing various para-substituted Ar3P ligands. Weak σ-
donating phosphine ligands are expected to speed up the
oxidative addition by promoting the coordination with Phen
ligand and oxidizing agent. Accordingly, we found that triaryl
phosphine ligands bearing electron-withdrawing substituents
are highly effective (L8, L9). Especially, in the case of the
Scheme 1. Reactivity of 1a towards oxidative addition
F3C CF3
O
N
N
Au
p-F-Ph
I
O
I
-
NTf2
CF3
CF3
3a
N
N
2.5 equiv
CD2Cl2
+
4a
+
F
Au NTf2
RT
PPh3
1a 1.0 equiv
CF3
CF3
O
Ar
PPh3
5a
I
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Journal of the American Chemical Society
Page 4 of 8
a
(Phen)(C6F5)3PAuNTf2 L10, the addition of alkynyl
hypervalent iodine reagent 3a led to an immediate colour
change, and NMR spectroscopy showed the complete
conversion of gold(I) complex 4a in 5 min, which indicates an
extremely fast oxidative addition to (Phen)(C6F5)3PAuNTf2.
Conversely, phosphine ligands bearing alkyl groups (L1, L2)
and phosphite ligands (L3, L4) are completely ineffective as a
result of increased trans-influence,21 and the oxidative addition
proceeds much slower with electron-rich aryl phosphines than
that with Ph3P (L5, L6). Additionally, the sterically more
demanding (o-Me-C6H4)3P L11 and (Mesityl)3P (k = 0) strongly
inhibit the oxidative addition, which is apparently attributed to
the crowded gold transition state. This result excludes the
mechanism A (Scheme 2), in which the steric hindrance of
phosphine ligands would be expected to promote the phosphine
dissociation, accelerating the oxidative addition. The reaction
does not proceed with pyridineAuPPh3.
R1
R1
1
2
3
4
p-F-Ph
I
O
R1
F3C CF3
CF3
O
I
N
N
CF3
N
N
2.5 equiv
CD2Cl2
Au
+
Au NTf2
RT
R1
PR3
4
1.0 equiv
PCy3
F
3
5
6
7
8
9
MeO
P
O
P
Me
P
PMe3 (CH3O)3P
3
3
Phen
+
PR3
L1
L2
L3
L5
L6
L4
k
0
0
0
0
1.7
2.46
10
11
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13
14
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19
20
21
22
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60
P
PPh3
(C6F5)3P
Cl
P
F3C
P
3
3
3
Me
L7
L8
L9
L10
L11
6.28
21.06
29.32
0.4
 2400
Cl
Cl
O
O
Ph
Ph
The effects of bidentate ligands on this oxidative reactivity
were also investigated (Figure 4a). The 2,2’-bipyridine ligand
shows a ligand effect identical to Phen. Introducing electron-
withdrawing chloride to the 4,4’-position of Phen L14 strongly
decreases the oxidative reactivity. The Cl-substituted Phen
ligand weakens its coordination with gold(I) atom, thus
increasing the oxidative barrier of the oxidative addition. Phen
ligand bearing electron-donating MeO- groups L13 is also less
effective than Phen, since the raised σ-donation of Phen ligand
prevents the coordination of oxidizing agent with gold(I) atom
in the oxidative process. These two negative effects are
illustrative of an increased reactivity of gold(I) complex bearing
Ph-substituted (Hammett substituent parameter σ = 0.009) Phen
L15 with neutral σ-donation.
PPh3
+
N
N
N
N
N
N
N
N
N
N
L13
L14
5.20
L12
L15
9.28
k
6.88
1.62
Analysis of the relative reaction rates of oxidative addition to
1a showed that electron-rich alkynyl hypervalent iodine reagent
react faster than electron-poor systems (initial rate order for 4-
R substituted 3: R = CH3 > H > NO2, k = 6.8, 6.28, 2.4
respectively; Figure 4c). This order of reactivity is expected
based on the former analysis on the oxidative addition that
involves a critical coordination. The increased reactivity of
electron-rich alkynyl hypervalent iodine reagent towards
oxidative addition to 1a could be derived from the enhanced
coordination of 3 with 1a.
c
+
Ar
I
O
F3C CF3
CF3
O
I
N
N
_
N
N
CF3
Au
2.5 equiv
CD2Cl2
+
NTf2
3
Au NTf2
Ar
RT
PPh3
1a 1.0 equiv
4
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products, 7c and 7d were stable enough for the time of the 13
C
Figure 4. Ligand effects on the oxidative addition.
1
2
3
4
5
6
7
8
NMR spectroscopy. An analysis of the relative reaction rates of
oxidative addition to 6b showed that electron-donating
substituents on the alkynyl hypervalent iodine regents
accelerate the reaction. On the other hand, the electron-poor
system (such as NO2-subsituted alkynyl hypervalent iodine
regent) slow down the reaction significantly, resulting in the
failure of the characterization of these gold(III) products.
Additionally, the relative reaction rates of oxidative addition to
bis(pyridine)gold(I) complexes bearing different substituents
were also analyzed. As expected, the electron poor
bis(pyridine)gold(I) complex react significantly faster than
electron-rich systems. Especially, in the case of 7h, the addition
of alkynyl hypervalent iodine reagent led to an immediate
colour change, and 1H NMR spectroscopy showed the complete
conversion of gold(I) complex in 4 min, which indicates an
extremely fast oxidative addition. On the other hand, the
oxidative addition to (4-dimethylaminopyridyl)2AuINTf2 failed,
as a result of high trans influence of 4-dimethylaminopyridyl
ligand.
The kinetic profile of the oxidative addition exhibits a good
relationship to the Hammett substituent parameter (Figure 5, ρ
= 3.75, R2 = 0.9344). The positive ρ value (> 1) indicates a high
sensitivity of the oxidative addition to the trans influence of
phosphine ligands. Recently, Amgoune, Bourissou, and co-
workers published a catalytic Au(I)/Au(III) arylation with
hemilabile MeDalphos ligand.3g The moderate Hammett
correlations (ρ = –1.09, R2 = 0.93) for the oxidative addition of
different para-substituted iodoarenes indicated a coordination
of iodoarenes with gold(I) catalyst in the process of the
oxidative addition, which also supports the σ-donor competition
among ligands (including bidentate ligand and iodoarenes) at
the gold(I) center.
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Scheme 3. Oxidative addition of alkynyl hypervalent iodine
reagent to linear bis(pyridine)gold(I) complex
R1
+
_
R1
I
CF3
IIII
_
NTf2
F3C
O
R2
N
N
+
Au
_
NTf2
N
3
AIuII
Au
NTf2
N
CH2Cl2
N
N
R2
R1
R1
7
6
+
+
I
I
CF3
CF3
F3C
F3C
Figure 5. Hammett plot of ln(k/k0) vs σ for oxidative addition.
N
N
O
O
AIuII
AIuII
_
NTf2
_
NTf2
Reactivity of linear bis(pyridine)gold(I) towards oxidative
addition. Based on the correlation of the trans influence of
ligands with the tri-coordinate accessibility of gold(I) complex,
as well as oxidative reactivity, we assumed that a linear two-
coordinate gold(I) complex bearing weak σ-donor ligands
might also be competent for the oxidative addition. We
synthesized a bis(p-Me-pyridine)Au(I) complex 6a by simply
mixing DMSAuCl (1 eq.), p-Me-pyridine (2 eq.) and AgNTf2
(1 eq.) in CH2Cl2, followed by filtration and crystallization.22
Treatment of bis(p-Me-pyridine)Au(I)NTf2 with 1.0 equivalent
of alkynyl hypervalent iodine reagent 3a generated smoothly a
new species in only one hour (76% NMR yield, Scheme 3). The
compound was assigned to be gold(III) complex 7a, formed by
the oxidative addition with 3a, which is consistent with the 1H
NMR spectrum. The gold(III) complex 7a is not stable enough
for 13C NMR spectroscopy and X-ray analysis. In ESI-MS
analysis, an ion was observed at m/z 871.0337, which is in
agreement with the calculated m/z value for the cationic species
7a (871.0325). This is the first experimental proof of such an
intermolecular oxidative addition to a linear gold(I) complex
coordinated to two mono-dentate ligands.
N
N
H
F
7a
7b
1h, 76% Yield
1 h, 78% Yield
+
I
+
_
CF3
F3C
I
CF3
F3C
N
O
AIuII
_
NTf2
N
O
AIuII
N
NTf2
N
CH3
H3C
7d
7c
20 min, 84% Yield
20 min, 82% Yield
+
+
I
I
CF3
F3C
CF3
F3C
N
O
N
AIuII
O
_
NTf2
_
NTf2
AIuII
N
N
CH3
S
7e
7f
30 min, 49% Yield
20 min, 90% Yield
+
O
+
I
CF3
F3C
I
CF3
F3C
N
O
_
NTf2
AIuII
N
N
O
_
NTf2
AIuII
N
Under these conditions for the efficient oxidative addition of
7a to bis(pyridine)gold(I) 6a, we explored the scope of the
reaction with respect to the alkynyl hypervalent iodine and
O
7h
7g
25 min, 83% Yield
 4 min, 78% Yield
bipyridylgold(I) components. Within
1 hour at room
temperature, full conversion to the corresponding Au(III)
complex was observed with a range of alkynyl hypervalent
iodine regents, as determined by 1H NMR spectroscopy.
Oxidative addition products 7a−h were characterized by ESI-
MS, 1H NMR and 19F NMR spectroscopy, among these
CONCLUSION
In summary, we propose that the accessibility of the gold(I)
atom to tri- or tetra-coordination is critical in the oxidative
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Page 6 of 8
enabling tools for bond disconnection via reactivity umpolung. Acc.
process that involves a tri- or tetra-coordinate gold(I)
intermediate with oxidizing agent. Computational studies for
the bond lengths and bond angles of tri-coordinate
(Phen)R3PAuNTf2 shows that the tri-coordinate accessibility
increases as trans influence of phosphine ligands decreases.
The oxidative addition to the asymmetric tri-coordinate
(Phen)R3PAu(I)NTf2 complexes with alkynyl hypervalent
iodine reagents was built. The reactivity profile of these gold(I)
complexes exhibits a good relationship to the Hammett
substituent parameter (ρ = 3.75, R2 = 0.934), in which the
gold(I) complexes bearing less σ-donating phosphine ligands
increase the rate of oxidative addition. The positive ρ indicated
a strong ligand effects for the oxidative addition. Different from
the common understanding that ligands with strong σ-donation
could increase the oxidative reactivity of gold(I) complexes by
increase the electron density on the gold center, this study
suggests that the weakened σ-donor ligands increase the
oxidative reactivity by promoting tri- or tetra-coordinate
accessibility of gold(I) complexes. It was also supported by a
facile oxidative addition of alkynyl hypervalent iodine reagent
to linear bis(pyridine)lgold(I) complex, in which the less σ-
donating pyridyl ligands increase the tri-coordinate
accessibility of gold(I) intermediate with the oxidizing agent.23
From a strategic standpoint, we anticipate that this process,
which employs weakened σ-donor ligands to enable the
oxidative addition to gold(I), would find widespread and
practical use in various disciplines of chemical science.
Chem. Res. 2018, 51, 3212. (e) Rodriguez, J.; Zeineddine, A.; Carrizo,
E. D. S.; Miqueu, K.; Saffon-Merceron, N.; Amgoune, A.; Bourissou,
D. Catalytic Au(I)/Au(III) arylation with the hemilabile MeDalphos
ligand: unusual selectivity for electronrich iodoarenes and efficient
application to indoles. Chem. Sci. 2019, 10, 7183.
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elementary organometallic reactions. Angew. Chem. Int. Ed. 2015, 54,
15022. (d) Harper, M. J.; Arthur, C. J.; Crosby, J.; Emmett, E. J.;
Falconer, R. L.; Fensham-Smith, A. J.; Gates, P. J.; Leman, T.;
Mcgrady, J. E.; Bower, J. F.; Russell, C. A. Oxidative addition,
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ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS
Publications
website.
(6) Colburn, C. B.; Hill, W. E.; McAuliffe, C. A.; Parish, R. V. 31
P
N.M.R. study of tertiary phosphine complexes of gold(I). J. Chem.
Soc., Chem. Commun. 1979, 218.
Detailed experimental procedures and compound characterization
(PDF)
X-ray diffraction data of 1a, 1d, 1e (CIF)
(7) Fürstner, A.; Davies, P. Catalytic carbophilic activation: catalysis
by platinum and gold pi acids. Angew. Chem., Int. Ed. 2007, 46, 3410.
(8) (a) Crespo, O.; Gimeno, M. C.; Laguna, A.; Jones, P. G. Two-,
three- and four-coordinate gold(I) complexes of 1,2-
bis(diphenylphosphino)-1,2-dicarba-closo-dodecaborane. J. Chem.
Soc., Dalton. Trans. 1992, 1601. (b) Cinellu, M. A.; Minghetti, G.;
Cocco, F.; Stoccoro, S.; Zucca, A.; Manassero, M.; Arca, M. Synthesis
and properties of gold alkene complexes. Crystal structure of
[Au(bipyoxyl)(η2-CH2[double bond, length as m-dash]CHPh)](PF6)
and DFT calculations on the model cation [Au(bipy)(η2-CH2[double
bond, length as m-dash]CH2)]+. Dalton Trans. 2006, 5703.
(9) Joost, M.; Estevez, L.; Mallet-Ladeira, S.; Miqueu, K.;
Amgoune, A.; Bourissou, D. Enhanced π-backdonation from gold(I):
isolation of original carbonyl and carbene complexes. Angew. Chem.,
Int. Ed. 2014, 53, 14512.
(10) (a) Guenther, J.; Mallet-Ladeira, S.; Estevez, L.; Miqueu, K.;
Amgoune, A.; Bourissou, D. Activation of aryl halides at gold(I):
practical synthesis of (P,C) cyclometalated gold(III) complexes. J. Am.
Chem. Soc. 2014, 136, 1778. (b) Serra, J.; Whiteoak, C. J.; Acuna-
Pares, F.; Font, M.; Luis, J. M.; Lloret-Fillol, J.; Ribas, X. Oxidant-free
Au(I)-catalyzed halide exchange and Csp2–O bond forming reactions.
J. Am. Chem. Soc. 2015, 137, 13389. (c) Serra, J.; Parella, T.; Ribas, X.
Au(III)-aryl intermediates in oxidant-free C–N and C–O cross-
coupling catalysis. Chem. Sci., 2017, 8, 946.
AUTHOR INFORMATION
Corresponding Author
*E-mail: hashmi@hashmi.de.
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
Y. Yang is grateful for a Ph.D. fellowship from the China
Scholarship Council (CSC) and gratefully acknowledge Richard J.
Mudd for helpful discussions. J. F. Wunsch thanks for the support
by the Hector Fellow Academy. The authors acknowledge the
support by the state of Baden-Württemberg through bwHPC.
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1
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L3
L3
L1
L3/X
R
1
2
3
4
5
6
R
X
R
X
I
I
Au
L2
Au
Au
L1
III
AAuu
L1
L2
L2
two-coordinate
gold(I)
L = -donor ligands
or
tri-coordinate
gold(I)
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