Secondary phosphine oxide-gold(I) complexes and their first application in catalysis

Article abstract of DOI:10.1021/om500568q

A series of new secondary phosphine oxide (SPO)-gold(I) complexes have been synthesized and characterized by X-ray crystallography. Complexes exhibited dimeric structures interconnected by O-H···Cl hydrogen bonds. Their first use in homogeneous catalysis

Full text of DOI:10.1021/om500568q

Article
pubs.acs.org/Organometallics
Secondary Phosphine Oxide−Gold(I) Complexes and Their First
Application in Catalysis
Felix Schroder,† Coralie Tugny,† Elise Salanouve,† Herve Clavier,‡ Laurent Giordano,‡
́
̈
Delphine Moraleda,‡ Yves Gimbert,§ Virginie Mouries-Mansuy,† Jean-Philippe Goddard,†,⊥
̀
and Louis Fensterbank*,†
†Institut Parisien de Chimie Molec
75005 Paris, France
‡Aix Marseille Universite,
́ ́
ulaire (UMR CNRS 8232), UPMC Univ Paris 06, Sorbonne Universites, 4 place Jussieu, C. 229,
́
Centrale Marseille, CNRS, iSm2 UMR 7313, 13397, Marseille, France
§Univ Grenoble Alpes and CNRS, DCM UMR 5250, F-38000 Grenoble, France
S
* Supporting Information
ABSTRACT: A series of new secondary phosphine oxide (SPO)−gold(I) complexes have been synthesized and characterized
by X-ray crystallography. Complexes exhibited dimeric structures interconnected by O−H···Cl hydrogen bonds. Their first use in
homogeneous catalysis is reported and suggests a broad field of application in prototypical enyne cycloisomerization and
hydroxy- and methoxycyclization reactions.
solution which can be displaced in favor of the phosphinous
acid (PA) form by preferred coordination of the phosphorus
atom to a transition metal (Figure 1).11
INTRODUCTION
■
After sporadic reports in the 1980s and 1990s featuring
landmarks such as Hayashi’s asymmetric aldol reaction,1 Teles’
addition of alcohol to alkyne,2 and Hashmi’s phenol synthesis,3
homogeneous gold catalysis has emerged over the past decade
as a highly versatile synthetic methodology providing unique
opportunities in the construction of carbon−carbon or
carbon−heteroatom bonds.4 Indeed, in 2004, Echavarren,5
Furstner,6 and Toste7 disclosed enyne cycloisomerizations in
̈
the presence of gold(I) cationic complexes. It is also now well
established and consistent with Xu’s8 recent report that the
nature of the ligand coordinated to the gold center plays a
major role in the reactivity and selectivity of gold-catalyzed
reactions, as well as in the sustainability of the catalytic cycle.
While initially the ancillary ligands were phosphorus-based
ligands such as phosphites and phosphines (triphenylphos-
phine, JohnPhos, etc.), subsequently stronger σ-donor NHC
ligands and related structures have been widely used, for
instance in cycloisomerization reactions, allowing new reac-
tivity.9 Thus, there is still an important need to provide new
gold complexes, based on original ligands, to give access to
unprecedented reactivities and optimal catalytic cycles.10
As part of our ongoing efforts to develop new gold-catalyzed
cyclizations of enynes, we were interested in studying the
reactivity of secondary phosphine oxide (SPO)−gold com-
plexes. These ligands are very attractive for metal catalysis
under homogeneous conditions because they are air and
moisture stable. Moreover, a tautomeric equilibrium exists in
Figure 1. Coordination of an SPO ligand to a metal.
Thus, SPO catalysts have enjoyed great interest since the first
report by Li, who used these preligands in very efficient
palladium-catalyzed cross-coupling reactions for the formation
of C−C, C−N, and C−S bonds using unactivated aryl
chlorides.12 Since this breakthrough, novel SPO−transition-
metal complexes have been used in various other cross-
coupling13 and hydrogenation reactions.14 Furthermore, some
of us reported a formal palladium-catalyzed [2 + 1]
cycloaddition15 and more recently an unprecedented inter-
molecular tandem [2 + 1]/[3 + 2] cycloaddition sequence
catalyzed by SPO−platinum complexes.16 Note also that for a
dissymmetric SPO (R1 ≠ R2), the phosphorus atom becomes
stereogenic, thereby giving access to asymmetric catalysis.17
Received: May 28, 2014
Published: July 23, 2014
© 2014 American Chemical Society
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Particularly worthy of note, to the best of our knowledge, is
the absence of applications of SPO−gold complexes in
homogeneous catalysis. In a few publications, the Schmidbaur
group examined the coordination chemistry of SPO−gold
complexes.18 Notably, the structure of the complex [Ph2P-
(OH)AuCl]2 (2a) was confirmed by X-ray analysis.18c,d
However, no catalytic activity was reported in any of these
studies. This year, van Leeuwen used the complex [t-
Bu(naphthalen-1-yl)P(OH)AuCl]2 as a precursor for gold
nanoparticles that proved to be highly active catalysts for the
hydrogenation of substituted aldehydes.19
RESULTS AND DISCUSSION
■
SPO-Au(I) Complexes. In this context, we prepared a
library of SPO−gold(I) complexes following Schmidbaur’s
procedure by treatment of the corresponding SPOs (R1R2P-
(O)H, 1a−e)20 with (dimethyl sulfide)gold(I) chloride in
CH2Cl2 (Scheme 1). After partial evaporation of CH2Cl2, gold
Scheme 1. Preparation of SPO−Gold(I) Complexes
Figure 2. X-ray structures of complexes 2b,f.
Scheme 2. Preparation of Cationic Complex 2f
complexes were isolated by precipitation from pentane in
moderate yields of 31% for the sterically demanding bis-tert-
butyl SPO ligand 2c to excellent yields of 97% for 2b and were
fully characterized (see the Supporting Information).
Suitable crystals were obtained in order to determine the
structures of 2b−e by XRD.21 Except for 2e, which exhibited
distinct features,22 all structures 2b−d share common features
with 2a (Table 1). They are dimeric, interconnected by two
peripheral O−H···Cl hydrogen bonds, the bond lengths being
in the typical range of 2.03−2.37 Å. Interestingly, they all show
rather unusual bent P−Au−Cl angles, from 170° (2b) to 175°
(2c). As is the case for 2a, they do exhibit Au−Au interactions,
but to a weaker extent, since the Au···Au distance in 2a is 3.11
Å while it is between 3.35 and 3.75 Å in 2b−d.23 The structure
of complex 2b, shown in Figure 2, is chosen as a representative
the presence of 1 equiv of 2,4,6-trimethoxybenzonitrile in
CH2Cl2. A quantitative yield of 2f was obtained, and a single-
crystal X-ray diffraction analysis revealed a monomeric structure
featuring a P−Au−N angle of 178.30°. This confirmed our
assumption that the dimeric arrangement was responsible for
the angle deviation.
Whereas currently buried volumes are commonly used to
quantify the steric properties of phosphine and NHC ligands,
no metric for SPO ligands has been reported to date.25 Having
in hand a set of X-ray structures for the gold−SPO complexes
2a−e, we assessed the steric bulk of these ligands by calculating
the percent buried volume (%Vbur).26,27 A comparison of Vbur
values revealed a narrow range for SPO ligands 1a−e (Table 2).
As expected, tBu2P(OH) (1c; entry 5) is significantly more
sterically demanding than the other SPOs (entries 1, 3, 7, and
8). A comparison with their phosphine parents showed a
moderate difference between Ph2P(OH) and PPh3 (entry 1 vs
2), but this gap gradually increases with congeners exhibiting
greater steric hindrance around phosphorus (entry 3 vs 4 and
entry 5 vs 6).
example. In this case, crystals are triclinic with a P1 space group
̅
(Z = 1 molecular unit in the unit cell). Therefore, the O−H···
Cl length (2.207 Å) and the P−Au−Cl angle (170.68°) are
identical in the two units of the dimer. Similar P−Au−Cl angles
deviating from linearity have been found in gold complexes
bearing very bulky biarylphosphines.24 In our case, we ascribed
the values of the P−Au−Cl angles to the dimeric assembly
which would generate constraints favoring the nonlinearity. To
probe this hypothesis, we prepared cationic complex 2f
(Scheme 2) by treatment of 2b with 1 equiv of AgSbF6 in
Table 1. Characteristic Bond Lengths and Bond Angles of SPO−AuICl
gold complex
OH(1)···Cl(2) (Å)
OH(2)···Cl(1) (Å)
Au(1)···Au(2) (Å)
P(1)−Au(1)−Cl(1) (deg)
P(2)−Au(2)−Cl(2) (deg)
Ph2(OH)PAuCl (2a)
tBuPh(OH)PAuCl (2b)
tBu2(OH)PAuCl, (2c)
Cy2(OH)PAuCl (2d)
2.029
2.207
2.374
2.177
2.105
2.207
2.223
2.224
3.111
3.748
3.349
3.390
169.18
170.85
170.68
173.3(1)
175.15
170.68
175.59(9)
174.58
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Table 2. Au−P Bond Lengths and Percent Buried Volumes
(%Vbur) of SPO Ligands 1a−e
Table 3. Enyne Cycloisomerization
entry
ligand
d(Au−P) (Å)
Vbur (%)
1
2
3
4
5
6
7
8
Ph2P(OH) (1a)
PPh3
2.220
2.232
2.230
2.242
2.232
2.252
2.238
2.225
27.3
30.7
28.9
34.1
32.6
38.6
27.1
29.2
Cy2P(OH) (1d)
PCy3
tBu2P(OH) (1c)
PtBu3
PhCyP(OH) (1e)
PhtBuP(OH) (1b)
We investigated the catalytic potential of complexes 2 in the
context of enyne cycloisomerization, focusing initially on
substrate 3a (Scheme 3).28 Typical conditions involved 1
Scheme 3. Preliminary Catalytic Tests
a
b
NMR yield. Isolated yield.
equiv of AgSbF6, with respect to the gold complex, in CH2Cl2
for less than 1 h at room temperature. Full conversion of 3a was
observed with all salts 2a−e to give uniformly good yields of 4a
as a very major product (yields: 76−79%), accompanied by
minor amounts of 5a (yields: 2−6%).29 No effect of the ligand
structure was noticed in this series of reactions. Interestingly,
cationic complex 2f proved to be competent for this reaction
and gave in slightly optimized yields a mixture of 4a (86%) and
5a (8%).
We also examined the more demanding substrate 3b, which
has so far proven to be rather reluctant to cycloisomerization
under various metal-catalyzed conditions.30,31 Initial testing
under conditions similar to those before with complexes 2b−e
proved however to be much less rewarding, since moderate
yields of the corresponding product 5b were generally obtained
(see Table 3, entries 1−4).
We then decided to run the following experiment. To a
solution of 2b (0.036 mmol) in 0.6 mL of CH2Cl2 was added 1
equiv of AgSbF6 at room temperature. Some AgCl precipitated
instantaneously. After filtration over a Teflon filter, a limpid
yellow solution was obtained, to which 1 equiv of 3b was
added. This led to a new production of AgCl. 1H NMR analysis
of the crude product showed full conversion of the starting
material 3b. Thus, enyne 3b presumably intervened in the
formation of the cationic gold catalytic species. This finding was
highly reminiscent of Echavarren’s recent report dealing with
the detrimental formation of chloride-bridged digold com-
plexes,32 the latter being potentially cleaved by the addition of
more coordinating substrates.33 We thus further investigated
the possible implication of such a phenomenon in our reactions
by running the following NMR-MS coupled analyses (see the
Supporting Information). We first mixed in CD2Cl2 1 equiv of
2b with 0.25 equiv of AgSbF6. Some AgCl precipitated
a
Conditions A: 2 mol % of complex 2 and 2 mol % of AgSbF6 in
b
CH2Cl2 at room temperature for 0.5−2 h. Conditions B: 2 mol % of
complex 2 and 4 mol % of AgSbF6 in CH2Cl2 at room temperature for
4−15 h. Reaction in refluxing toluene for 40 h.
c
instantaneously, and 31P NMR showed a broad resonance at
111 ppm, presumably corresponding to 2b (δ(31P) 111 ppm)
and other cationic entities, accompanied by a minor and
sharper peak at 85 ppm (most likely a hydrate cationic Au(I)
complex34). The ESI MS spectrum at 60 V revealed a peak at
m/z 379 ascribed to the [t-BuPhP(OH)Au]+ fragment and a
peak at m/z 793 corresponding to the expected bridged
complex [t-BuPhP(OH)AuClAu(OH)P-t-BuPh]+. Charging
0.5 equiv of AgSbF6 gave no observable change in the aspect
of the 31P NMR and mass spectra. However, in the presence of
2 equiv of AgSbF6, while the 31P NMR spectrum was globally
identical, the MS spectrum showed the disappearance of the
peak at m/z 793 in favor of the peak at m/z 379, suggesting
strongly, and as observed by Echavarren,32a that an excess of
silver is needed to fully obtain the active cationic complex
(Scheme 4).
These findings drove us to try another set of conditions with
2 equiv of AgSbF6 (conditions B, see Table 1) when the
reaction was sluggish with only 1 equiv (conditions A). This
proved to be beneficial, as illustrated by yields superior to 60%
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be high-performing precatalysts for difficult cycloisomerization
reactions, which now ranks them in the short list of valuable
ligands for gold homogeneous catalysis. This study also
provided some confirming elements about the detrimental
intervention of chloride-bridged digold complexes, as recently
reported by Echavarren. Finally, an opportunity for asymmetric
gold catalysis is at hand with chiral SPO ligands.
Scheme 4. Monitoring by MS of the Formation of a Cationic
SPO−AuI Complex
recorded with precatalysts 2a,b (entries 5 and 6). Interestingly,
these yields were better than that recorded with PPh3AuSbF6
(5b; 55%).30d A series of substrates (3c−f) could also be
smoothly engaged in catalytic reactions, giving satisfactory
yields of the corresponding products (5c−f, 6, and 7) by using
the simple conditions A. Interestingly, substrate 3g, which has
to the best of our knowledge never been engaged in gold-
catalyzed reactions, provided additional information about a
putative silver salt effect. Preliminary testing under conditions A
(CH2Cl2, room temperature for 2 h) showed very little
conversion (3g:8 80:20). In contrast, in refluxing toluene for 40
h, in the presence of an equimolar mixture of 2b and AgSbF6,
significant formation of product 8 was observed (3g:8 40:60).
Strikingly, as observed with precursor 3b, conditions B, based
on a 2-fold excess of AgSbF6, resulted in the ratio 20:80 for 3g
and 8 and 73% isolated yield of 8 as the sole product.35 Thus,
the use of an SPO ligand proved particularly beneficial for the
cycloisomerization of this substrate since, in comparison, the
use of the 2 mol % PPh3AuCl−AgSbF6 mixture was poorly
productive, as demonstrated by little conversion, giving a 90:10
mixture of 3g and 8 in CH2Cl2 for 2 h at room temperature and
a 70:30 mixture of 3g and 8 in refluxing toluene for 40 h
accompanied by byproducts.
EXPERIMENTAL SECTION
■
General Information. All reactions were performed under an
argon atmosphere. All solvents were freshly distilled prior to use:
tetrahydrofuran over sodium and benzophenone and dichloromethane
over calcium hydride. Silica gel (35−70 mm) was used for column
chromatography. Thin-layer chromatography (TLC) was performed
1
on silica gel and visualized with a UV lamp (254 nm). H NMR and
13C NMR spectra were recorded at room temperature unless otherwise
required on 300 and 400 MHz spectrometers with the solvent
resonance as the internal standard (1H NMR, CDCl3 at 7.26 ppm; 13
C
NMR, CDCl3 at 77.16 ppm; 31P NMR, H3PO4 at 0 ppm). Chemical
shifts (δ) are given in parts per million (ppm), and coupling constants
(J) are given in hertz (Hz). The letters m, s, d, t, and q stand for
multiplet, singlet, doublet, triplet, and quartet, respectively. The letter
b indicates that the signal is broad. Referenced high-resolution mass
spectra were obtained at UPMC using a mass spectrometer with an
electron spray ion source (ESI) and a TOF detector. Melting points
(mp) were recorded with a melting point apparatus. IR data are
reported as characteristic bands (cm−1).
General Procedure for the Synthesis of SPO−AuCl Com-
plexes 2. To a solution of secondary phosphine oxide 1 (5.5 mmol,
1.0 equiv) in dry dichloromethane (70 mL) was added chloro-
(dimethyl sulfide)gold(I) (5.5 mmol, 1.0 equiv). The mixture was
stirred at room temperature or at reflux for 2 h in the absence of light
under an argon atmosphere. The crude mixture was concentrated
under vacuum. The resulting brown solid was dissolved in dichloro-
methane (3 mL), and pentane (30 mL) was added to precipitate the
expected complex as a white solid, which was isolated by filtration. The
latter was dissolved in dichloromethane (3 mL), and pentane was
added slowly in order to obtain a biphasic solution. Overnight
crystallization occurred to give crystals of the expected complex.
Chloro(diphenylphosphinous acid)gold(I) (2a). According to the
general procedure, using commercially available diphenylphosphine
oxide (1.11 g, 5.5 mmol) and chloro(dimethyl sulfide)gold(I) complex
(1.62 g, 5.5 mmol) at room temperature, 2a was isolated after filtration
We also looked at methoxy- and hydroxycylization
reactions36 from precursors 3a,f. The latter smoothly trans-
formed into the corresponding adducts 9a, 10, and 9b (Scheme
5).
Scheme 5. Methoxy- and Hydroxycyclization Reactions
1
(2.22 g, 93%): H NMR (400 MHz, CDCl3) δ 7.69−7.51 (m, 4H),
7.50−7.47 (m, 2H), 7.46−7.37 (m, 4H); 13C NMR (101 MHz,
CDCl3) δ 134.4 (d, J = 74.7 Hz), 132.4 (d, J = 2.0 Hz), 131.6 (d, J =
15.1 Hz), 129.1 (d, J = 12.1 Hz); 31P NMR (162 MHz, CDCl3) δ 89.9;
mp 132−133 °C; IR (neat, cm−1) 3055, 1588, 1481, 1436. The
spectral data for this compound correspond to the previously reported
data.37
( )-Chloro(tert-butylphenylphosphinous acid)gold(I) (2b). Ac-
cording to the general procedure, using ( )-tert-butylphenylphosphine
oxide (1b;38 1.0 g, 5.5 mmol) and chloro(dimethyl sulfide)gold(I)
complex (1.62 g, 5.5 mmol) at room temperature, 2b was isolated as a
1
white solid (2.23 g, 97%): H NMR (400 MHz, CDCl3) δ 7.67−7.61
(m, 2H), 7.47−7.43 (m, 1H), 7.39−7.34 (m, 2H), 1.07 (d, J = 16.0
Hz, 9H); 13C NMR (101 MHz, CDCl3) δ 132.1 (d, J = 2.0 Hz), 131.9
(d, J = 14.1 Hz), 131.4 (d, J = 61.6 Hz), 128.4 (d, J = 12.1 Hz), 35.3
(d, J = 46.5 Hz), 24.6 (d, J = 6.1 Hz); 31P NMR (162 MHz, CDCl3) δ
110.5; mp 178−179 °C; IR (neat, cm−1) 3124, 2961, 2866, 1474,
1459, 1393, 1364; HRMS (ESI+) calcd for [C10H15AuClOP + Na]+
m/z 437.0107, found 437.0124.
Chloro(dicyclohexylphosphinous acid)gold(I) (2d). According to
the general procedure, using dicyclohexylphosphine oxide (1d;38
(0.103 g, 0.48 mmol) and chloro(dimethylsulfide)gold(I) complex
(0.142 g, 0.48 mmol) at reflux, 2d was isolated as a white solid (0.095
g, 44%): 1H NMR (400 MHz, CDCl3) δ 6.74 (bs, 1H), 1.98−1.71 (m,
10H), 1.50−1.48 (m, 2H), 1.35−1.22 (m, 10H); 13C NMR (101
MHz, CDCl3) δ 38.0 (d, J = 43.4 Hz), 27.7 (d, J = (5.1 Hz), 26.7 (d, J
CONCLUSION
■
In summary, SPO ligands have been successfully coordinated to
gold(I) chloride, providing good yields of the corresponding
new complexes, which have been fully characterized. Dimeric
structures, interconnected by O−H···Cl hydrogen bonds and
featuring Au−Au interactions, have been recorded in the solid
state. Using X-ray crystallographic data, percent buried volumes
(%Vbur) have been calculated to provide the previously
undetermined steric parameter value of SPO ligands. Their
first uses in gold(I) homogeneous catalysis have been
described, suggesting a broad versatility. They have proven to
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= 2.0 Hz), 26.4 (d, J = 9.1 Hz), 26.2 (d, J = 6.1 Hz), 25.9 (d, J = 1.0
Hz); 31P NMR (162 MHz, CDCl3) δ 118.48; mp 224−225 °C; IR
(neat, cm−1) 3135, 2927, 2852; HRMS (ESI−) calcd for
[C12H23AuClOP − H]− m/z 445.7678, found 445.7670.
Author Contributions
The experiments described were performed by F.S., C.T., E.S.,
H.C., L.G., D.M., Y.G., V.M.-M., and J.-P.G. Buried volumes
were determined by H.C.. The manuscript was written by V.M.-
M. and L.F.
( )-Chloro(cyclohexylphenylphosphinous acid)gold(I) (2e). Ac-
c o r d i n g t o t h e g e n e r a l p r o c e d u r e , u s i n g
(
) -
cyclohexylphenylphosphine oxide (1e;38 0.69 g, 0.33 mmol) and
chloro(dimethyl sulfide)gold(I) (0.98 g, 0.33 mol) at room temper-
Notes
The authors declare no competing financial interest.
1
ature, 2e was isolated as a white solid (0.93 g, 64%): H NMR (400
MHz, CDCl3) δ 7.71−7.66 (m, 2H), 7.51−7.47 (m, 1H), 7.44−7.39
(m, 2H), 2.75 (bs, 1H), 1.97−1.82 (m, 2H), 1.79−1.59 (m, 4H),
1.31−1.08 (m, 5H); 13C NMR (101 MHz, CDCl3) δ 132.6 (d, J = 66.6
Hz), 132.2 (d, J = 3.0 Hz), 131.3 (d, J = 15.1 Hz), 128.8 (d, J = 12.1
Hz), 42.8 (d, J = 48.5 Hz), 26.6 (d, J = 4.0 Hz), 26.5 (d, J = 55.5 Hz),
26.0 (d, J = 2;0 Hz), 25.8 (d, J = 2.0 Hz); 31P NMR (162 MHz,
CDCl3) δ 103.5; HRMS (ESI+) calcd for [C12H21NOPAuCl + NH4]+
m/z 458.0709, found 458.0713.
ACKNOWLEDGMENTS
■
Support by the UPMC, CNRS, IUF, AMU, and Centrale
Marseille is gratefully acknowledged. We thank K. Boubekeur,
L.-M. Chamoreau, and G. Gontard (UPMC) and M. Giorgi
(Spectropole, Federation des Sciences Chimiques de Marseille)
́ ́
for the X-ray structure determinations and D. Lesage (UPMC)
for the MS analyses.
Chloro(di-tert-butylphosphinous acid)gold(I) (2c). To a solution
of di-tert-butylphosphine oxide (1c;38 0.14 g, 0.86 mmol, 1.0 equiv) in
dry dichloromethane (25 mL) was added chloro(dimethyl sulfide)-
gold(I) (0.255 g, 0.86 mmol, 1.0 equiv). The mixture was stirred at
reflux for 2 h in the absence of light under an argon atmosphere. The
crude product was concentrated under vacuum. The resulting solid
was dissolved in dichloromethane (3 mL), and pentane (30 mL) was
added to precipitate the nonreactive ClAuSMe2. After removal of the
solvent, the expected complex 2c was obtained as a white solid which
could be crystallized in a cyclohexane/CH2Cl2 mixture (20/1). 2c was
isolated after filtration (0.106 g, 31%): 1H NMR (400 MHz, CDCl3) δ
1.31 (s, 9H), 1.35 (s, 9H); 13C NMR (101 MHz, CDCl3) δ 37.9 (d, J
= 35.5 Hz), 27.5 (d, J = 7.1 Hz); 31P NMR (162 MHz, CDCl3) δ
133.1; IR (neat, cm−1) 3133, 2954, 2868, 1472, 1393, 1370; low-
resolution MS (ESI 30 V, CH2Cl2) m/z 395.1 (36), 393.1 (100).
( )(tert-Butylphenylphosphinous acid)(2,4,6-trimethoxybenzo-
nitrile)gold(I) Hexafluoroantimonate (2f). To a solution of 2b
(0.415 g, 1.0 mmol, 1.0 equiv) and 2,4,6-trimethoxybenzonitrile (0.197
g, 1.0 mmol, 1.0 equiv) in dry dichloromethane (11 mL) was added
AgSbF6 (0.351 g, 1.0 mmol, 1.0 equiv) under an argon atmosphere. A
white precipitate of AgCl appeared instantly. The mixture was stirred
in the dark for 15 min, and then it was filtered through a Teflon filter
to afford a yellow solution which was concentrated under vacuum. The
crude solid was dissolved in dichloromethane (3 mL), and pentane (3
mL) was added slowly in order to obtain a biphasic solution.
Overnight crystallization gave gray crystals of complex 2f (0.808 g, 1.0
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̈
1
mmol, quantitative): H NMR (400 MHz, CD2Cl2) δ 7.75−7.69 (m,
2H), 7.60−7.53 (m, 3H), 6.13 (s, 2H), 3.91 (s, 6H), 3.89 (s, 3H), 1.16
(d, J = 16.0 Hz, 9H); 13C NMR (101 MHz, CD2Cl2) δ 169.7, 166.6,
133.6 (d, J = 3.0 Hz), 132.3 (d, J = 15.2 Hz), 129.9 (d, J = 66.7 Hz),
129.4 (d, J = 12.1 Hz), 119.8, 91.7, 57.2, 56.9, 35.7 (d, J = 48.5 Hz),
24.5 (d, J = 7.1 Hz); 31P NMR (162 MHz, CDCl3) δ 113.6; mp 170−
171 °C; IR (neat, cm−1) 3608, 2956, 2249, 1603, 1576, 1477, 1460,
1437, 1421.02; HRMS (ESI+) calcd for [C20H26AuNO4P]+ m/z
572.1259, found 572.1272.
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(9) For a recent review on the benefits brought by NHCs in
homogenous gold catalysis, see: Gatineau, D.; Goddard, J.-P.; Mouries
̀
-
Mansuy, V.; Fensterbank, L. Isr. J. Chem. 2013, 53, 892.
(10) For representative and very recent examples of new ligands in
gold catalysis, see: (a) Fourmy, K.; Mallet-Ladeira, S.; Dechy-Cabaret,
O.; Gouygou, M. Organometallics 2013, 32, 1571. (b) Yavari, K.;
Aillard, P.; Zhang, Y.; Nuter, F.; Retailleau, P.; Voituriez, A.; Marinetti,
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ASSOCIATED CONTENT
* Supporting Information
Text, figures, and CIF files giving experimental procedures and
characterization data for all new compounds and crystallo-
graphic data for all X-ray structures. This material is available
free of charge via the Internet at http://pubs.acs.org.
■
S
Bohling, C. R. N.; Serrano-Becerra, J. M.; Hashmi, A. S. K. Angew.
̈
Chem., Int. Ed. 2013, 52, 7963. (d) Guittet, M.; et al. Angew. Chem., Int.
Ed. 2013, 52, 7213. (e) Henrion, G.; Chavas, T. E. J.; Le Goff, X.;
Gagosz, F. Angew. Chem., Int. Ed. 2013, 52, 6277. (f) Dubarle-Offner,
J.; et al. Organometallics 2013, 32, 1665. (f) Malhotra, D.; Mashuta, M.
S.; Hammond, G. B.; Xu, B. Angew. Chem. Int. Ed. 2014, 53, 4456.
(11) (a) Griffiths, J. E.; Burg, A. B. J. Am. Chem. Soc. 1960, 82, 1507.
(b) Chatt, J.; Heaton, B. T. J. Chem. Soc. A 1968, 2745. (c) Hoge, B.;
Neufeind, S.; Hettel, S.; Wiebe, W.; Thoesen, C. J. J. Organomet. Chem.
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AUTHOR INFORMATION
Corresponding Author
*E-mail for L.F.: louis.fensterbank@upmc.fr.
■
Present Address
⊥Laboratoire de Chimie Organique et Bioorganique EA4566,
́ ́
Universite de Haute-Alsace, Ecole Nationale Superieure de
Chimie de Mulhouse, 3 rue Alfred Werner, F-68093 Mulhouse
Cedex, France.
Ludwig, R.; Spannenberg, A.; Baumann, W.; Franke, R.; Borner, A.
̈
Eur. J. Org. Chem. 2010, 2733.
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Organometallics
Article
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15331. A series of catalytic tests on this NCbz analog with complexes
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CH2Cl2 at reflux for 15 h proved to be sluggish, resulting in 85% of
conversion and 30% (NMR yield) of 5b. This suggests that 3b does
not efficiently displace the nitrile ligand, resulting in a poor
coordination to the Au+ center.
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(34) Tang, Y.; Yu, B. RSC Adv. 2012, 2, 12686.
(35) A blank experiment (2 mol % of AgSbF6, 40 h in refluxing
toluene) showed no conversion.
̂
(36) (a) Genin, E.; Leseurre, L.; Toullec, P. Y.; Genet, J.-P.; Michelet,
V. Synlett 2007, 1780. (b) Nieto-Oberhuber, C.; Munoz, M. P.; Lopez,
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(18) (a) Schmidbaur, H.; Aly, A. A. M. Angew. Chem., Int. Ed. 1980,
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(38) Achard, T.; Giordano, L.; Tenaglia, A.; Gimbert, Y.; Buono, G.
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Organometallics 2010, 29, 3936.
(20) SPO ligands 1a−e were obtained from a chemical supplier or by
following literature procedures; see: Achard, T.; Giordano, L.;
Tenaglia, A.; Gimbert, Y.; Buono, G. Organometallics 2010, 29, 3936.
(21) X-ray crystal structures: 2b, CCDC 985626; 2c, CCDC 985414;
2d, CCDC 985627; 2e, CCDC 985415; 2f, 996088. See the
Supporting Information for details on the X-ray structures.
(22) An oligomeric structure is observed. Monomers are linked via
aurophilic interactions (Au···Au 3.243 Å) and hydrogen bonding (O-
H···Cl 3.121 Å). See ref 18b for a similar arrangement.
(23) The generally accepted contact limit for significant aurophilic
interactions is below 3.6 Å. See: (a) Balch, A. L.; Olmstead, M. M.;
Vickery, J. C. Inorg. Chem. 1999, 38, 3494. (b) Schmidbaur, H.; Schier,
A. Chem. Soc. Rev. 2008, 37, 1931.
(24) (a) Herrero-Gomez, E.; Nieto-Oberhuber, C.; Lopez, S.; Benet-
Buchholz, J.; Echavarren, A. M. Angew. Chem., Int. Ed. 2006, 45, 5455.
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(25) Clavier, H.; Nolan, S. P. Chem. Commun. 2010, 46, 841.
(26) (a) Poater, A.; Cosenza, B.; Correa, A.; Giudice, S.; Ragone, F.;
Scarano, V.; Cavallo, L. Eur. J. Inorg. Chem. 2009, 1759. (b) https://
www.molnac.unisa.it/OMtools/sambvca.php.
(27) All generated using SambVca with the following settings: 3.5 Å
sphere radius; crystallographically determined values for the distance
from the center of the sphere; 0.05 Å mesh spacing; hydrogens
excluded; Bondi radii scaled by 1.17.
(28) For seminal reports of PtCl2 electrophilic catalysis on related
enynes, see: (a) Chatani, N.; Furukawa, N.; Sakurai, H.; Murai, S.
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̈
2001, 123, 11863.
(29) Under identical conditions, 2 mol % of AgSbF6 alone provided a
1
84:4:12 mixture of 3a, 4a, and 5a as determined by H NMR of the
crude product.
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