Preparation and Catalytic Activity of Novel σ,π-Dual Gold(I) Acetylide Complexes

Article abstract of DOI:10.1002/ejoc.201901623

Synthesis, characterisation and catalytic activity of a series of novel σ,π-dual gold(I) acetylide complexes are presented. σ,π-Dual gold(I) complexes based on the JohnPhos ligand or the bridging chiral MeO-BIPHEP ligand were generated from terminal alkyn

Full text of DOI:10.1002/ejoc.201901623

A Journal of
Accepted Article
Title: Preparation and catalytic activity of novel σ,π-dual gold(I)
acetylide complexes
Authors: Huey-San Melanie Siah and Anne Fiksdahl
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10.1002/ejoc.201901623
European Journal of Organic Chemistry
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Preparation and catalytic activity of novel-dual gold(I)
acetylide complexes
Huey-San Melanie Siah[a] and Anne Fiksdahl*[a]
Abstract: Synthesis, characterisation and catalytic activity of a series
The structures of digold complex II and -dual gold complex III
of novel-dual gold(I) acetylide complexes are presented. -Dual
gold(I) complexes based on the JohnPhos ligand or the bridging chiral
MeO-BIPHEP ligand were generated from terminal alkynes in the
presence of an organic base. The catalytic activity of the complexes
was explored in a range of gold(I)-catalysed reactions of propargylic
alcohol derivatives and their catalytic and enantioselective potential
were compared to corresponding monogold(I) phosphane and chiral
digold(I) diphosphane species.
(Figure 1b) have recently been reported. The catalytic ability of
digold complex II has been tested in one reaction,[4] while the
catalytic potential of bridged -dual gold complexes has not
been explored so far. In contrast to chiral bridged -dual gold
complexes, such as complex Vb (Figure 1c), chiral digold
complex IV and similar complexes have been applied in
enantioselective reactions.[5] Bridged chiral -dual gold
acetylide complexes can be generated from chiral digold
complexes and alkynes and may have potential to give different
catalytic activity, including enantioselectivity.
Introduction
-Dual gold(I) acetylide complexes, mainly based on NHC
ligands, have been reported to be active catalytic species in
organic transformations, and there is a growing interest for use of
such complexes.[1] Investigations of isolated -dual gold
catalysts show different catalytic activity or regioselectivity when
compared to monogold complexes.[1a, 2] The Fiksdahl group has
previously identified dual gold complexes as the catalytically
active species in electrophilic trifluoromethylation of terminal
alkynes (Figure 1).[3] It was proposed that the JohnPhos -dual-
Au(I) complex Ib (Figure 1a) promoted alkyne-CF3 product
formation in a catalytic manner by transfer of a [LAu]+ fragment
from the -dual-Au complex to the alkyne substrate, activating
for trifluoromethylation.
The aim of the present study was to acquire more knowledge on
the synthesis and properties, as well as the catalytic ability, of new
-dual gold complexes. We also wanted to observe whether the
two closer gold atoms in chiral -dual gold(I) acetylide
complexes would provide different regioselectivity or
enantioselectivity from the corresponding monogold JohnPhos
phosphane complex VI and the chiral digold diphosphane
complex IV (Scheme 1a,b). We hereby present further studies on
synthesis and characterisation of novel dual gold(I)
complexes. Their catalytic activity in different gold(I)-catalysed
propargyl reaction is discussed, as well.
Figure 1. a) -Dual gold(I) acetylide complex Ib, reported by the Fiksdahl
group.[3] Structures of b) digold and dual gold complexes[4] (II, III) and c) chiral
digold and dual gold complexes (IV, Vb).
[a]
H.-S. M. Siah and prof. dr. A. Fiksdahl
Department of Chemistry, Norwegian University of Science and
Technology, Hoegskoleveien, NO-7491 Trondheim, Norway
E-mail: anne.fiksdahl@ntnu.no
Homepage: https://www.ntnu.edu/gold/
Supporting information for this article is given via a link at the end of
the document.
1
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Results and Discussion
The electron-deficient alkyne 1a initially failed to give a dual gold
complex via the direct method (Scheme 1a), as only the gold-
acetylide was formed. However, an indirect method (Scheme 1c),
via the gold-acetylide intermediate VIII (generated from alkyne 1a
and sodium hydride, and chloride replacement of the JohnPhos
gold(I) chloride species VII) and final-coordination of a second
cationic gold unit VI, gave excellent yield of the desired JohnPhos
dual gold complex Ia (96% over two steps).
Synthesis of JohnPhos and MeO-BIPHEP dual gold
complexes I and V
In order to probe the catalytic activity in reactions of propargylic
alcohol derivatives, a series of -dual gold(I) complexes, with
coordinated JohnPhos ligand or the bridging chiral MeO-BIPHEP
ligand were synthesised from a range of alkynes, including a
chiral alkyne (Scheme 1a-c).
The formation of dual gold complex from the most electron-
deficient alkyne 1e was not successful with any of the methods,
as only gold-acetylide was obtained, with no further coordination
of a second gold unit. This demonstrates how the nature of the
alkyne may favor either dual gold complex or gold-acetylide
formation.
(R)-MeO-BIPHEP bridged dual gold complexes V
In initial studies, digold complexes, such as (R)-MeO-BIPHEP-
digold IV (Scheme 1b), were generated in situ[5e] from five chiral
diphosphane ligands ((R)-BINAP, (R,R)-DIOP, (R)-Phanephos,
(R)-MeO-BIPHEP and (S)-iPr-MeOBIPHEP) by complexation
with gold chloride (Me2S-Au(I)Cl) and counterion exchange, as
shown by NMR (Figure 2). The digold complexes were identified
1
by H and 31P NMR. Synthesis of the target bridged dual gold
complexes from the digold complexes and alkyne 1b gave
products with varied purity and stability (NMR, MS). However, the
stable bridged (R)-MeO-BIPHEP-dual gold complex Vb was
successfully obtained from digold species IV and alkyne 1b.
Thus, mixing the digold species IV with the appropriate electron-
rich or electron deficient arylalkyne (1a, 1b and 1g) (1:1 ratio
IV:alkyne) in the presence of diisopropylethylamine, afforded the
(R)-MeO-BIPHEP bridged dual gold complexes Va, Vb and Vg in
high yields in a single step (84-87%, Scheme 1b). The dual gold
complexes were characterised and identified by NMR (1H, 19F, 13C,
31P) and HRMS.
NMR studies
The dual gold(I) complex Ib has previously been studied by the
Fiksdahl group.[3] The crystal structure (XRD, Figure 1a)
confirmed the -coordination of the gold units in the solid state,
while NMR data indicated that the gold units are interchangeable
in solution, as both alkyne 13C NMR signals were recorded as
triplets (13C-31P coupling). Only a single set of proton signals and
a single phosphorous signal from the gold ligand was seen in 1H
and 31P NMR, in accordance with previous reports.[6] Similar NMR
observations were made for complexes Ia, Ic, Id, If and Va, Vb,
Vg in the present study.
Scheme 1. Preparation of a) JohnPhos dual gold complexes and b) chiral MeO-
BIPHEP -dual gold complexes. c) Indirect preparation method. Yields
calculated from amount of gold complex used.
JohnPhos dual gold complexes I
The complexes were prepared from aryl alkynes (1b, 1c and 1d)
and the chiral alkylalkyne 1f by a procedure based on our
previous
experience
from
trifluoromethylation
studies
(Scheme 1a).[3] By mixing the JohnPhos-Au(I) cationic species VI
with the appropriate alkyne (1b, 1c, 1d, 1f; 1:1 or 2:1 ratio) in the
presence of diisopropylethylamine, the dual gold complexes Ib, Ic,
Id and If were obtained in moderate to high yields (40-78%) in a
single step. The most electron-rich alkyne 1d, required excess of
the Au(I) source (2:1 ratio VI:1d), as only the gold-acetylide was
formed using a 1:1 ratio. A similar 2:1 ratio of VI:alkyne 1c
improved the yield of the dual gold complex Ic (from 61% to 78%).
2
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Figure 2. 1H and 31P NMR studies of a) the (R)-MeO-BIPHEP ligand through b) complexation with gold chloride, c) counter-ion exchange (IV) and d) formation of
dual gold complex Vb with e) alkyne 1b.
Table 1. Gold(I)-catalysed propargyl test reactions; a) cyclopropanation,[7a] b)
The generation of the (R)-MeO-BIPHEP dual gold complex Vb
cyclopentenylation[7b] and c) tandem cyclisation reactions[7c] with known
(Figure 2a-e) from the diphosphane ligand (a) by complexation
with gold chloride to give the digold complex (b), subsequent
exchange with a non-coordinating anion (c) and by final formation
of the target dual gold complex Vb (d) of alkyne 1b (e), was clearly
followed by 1H and 31P NMR studies. The methoxy 1H NMR signal
from the MeO-BIPHEP ligand showed a significant shielding
effect by ligand coordination to give the digold complex. Smaller
changes were also observed by further transformation into the
dual gold complex Vb. The effect on the aromatic ligand protons,
particularly in biphenyl ortho and para positions, was noticeable
all through the process a)-d) to give the target dual gold
complex Vb. Also, coordination is shown by distinct 1H NMR
patterns of alkyne 1b, as the methoxy signal and the aromatic H-3
protons experience a deshielding effect and move to higher shift
values. As expected, the terminal alkyne proton disappears by
complexation. The changes in the phosphorous environment
were also seen by 31P NMR. In particular, a characteristic
monogold complex VI and dual gold complexes I.
Entry
Complex
Temp.
Time
Yield
Ratio
5a : 5b
2 : 1
8 : 1
8 : 1
9 : 1
8 : 1
8 : 1
6a : 6b
1 : 0
1 : 2
1 : 1
1 : 2.4
0 : 1
1 : 3
7a : 7b
60 : 40
55 : 45
57 : 43
56 : 44
55 : 45
56 : 44
a) Cyclopropanationa 2+4a:
1
2
3
4
5
6
VI
Ia
Ib
Ic
Id
If
r.t.
r.t.
40 °C
40 °C
r.t.
30 min
24 h
4 h
24 h
2 h
98%
89%
97%
91%
94%
99%
deshielding effect was observed as a large change to a higher 31
P
NMR shift value (from −15 ppm to 24 ppm) by initial ligand
coordination to AuCl to give the digold complex. Smaller
deshielding effects were also observed throughout the next steps
towards the final dual complex Vb.
r.t.
24 h
b) Cyclopentenylationb 3+4b:
VI[7b]
Ia
Ib
r.t.
r.t.
r.t.
r.t.
15 min
2 h
24 h
2 h
61%
66%
36%
68%
19%
7
8
9
Reactivity of JohnPhos dual gold complexes I in reactions of
propargylic alcohol derivatives
10
Ic
11
12
Id
If
40 °C
r.t.
24 h
24 h
66%
Based on our previous studies,[7] the catalytic activity of the
synthesised JohnPhos dual-gold complexes I was tested in three
gold(I)-catalysed propargyl ester and acetal reactions. The results
from a) cyclopropanation,[7a] b) cyclopentenylation[7b] and c)
tandem cyclisation[7c] were compared with our results obtained
with JohnPhos monogold(I)-complex VI previously[7b, 7c] or in the
current study (Table 1a-c).
c) Tandem cyclisationc 3+4c:
13
14
15
16
17
18
VI[7c]
Ia
Ib
Ic
Id
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
15 min
15 min
2 h
1 h
1 h
54%
48%
55%
61%
31%
57%
If
24 h
Reaction conditions: a) propargyl ester 2 (1 equiv.) and alkene 4a (4 equiv.) in
CH2Cl2 (c ≈ 50 mM) with gold catalyst (5 mol%); b) propargyl acetal 3 (1 equiv.)
and alkene 4b (3 equiv.) in CH2Cl2 (c ≈ 80 mM) with gold catalyst (5 mol%). c)
propargyl acetal 3 (1 equiv.) and alkene 4c (3 equiv.) in CH2Cl2 (c ≈ 80 mM) with
gold catalyst (5 mol%).
3
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The five dual gold complexes I gave excellent yields in
cyclopropanation of propargyl ester 2 with styrene 4a (89-99% of
5, Table 1a, entries 2-6), low to good yields for the
cyclopentenylation of propargyl acetal 3 with 1-vinylpyrrolidin-2-
one 4b (19-68% of 6, Table 1b, entries 8-12), and moderate yields
for the tandem cyclisation reaction between propargyl acetal 3
with vinyl acetate 4c (31-61% of 7, Table 1c, entries 14-18). In all
reactions, more than one of the new dual gold complexes gave
higher yields than JohnPhos monogold complex VI (entries
1,7,13). In addition, higher cis-diastereoselectivity was obtained
in cyclopropanation with all dual gold complexes (up to 80% de,
gold-acetylide (Scheme 2) to regenerate the -dual gold
complex.
Cyclopentenylation, catalysed by the dual gold complexes I, with
electron-withdrawing or bulky ligands, gives mainly enol ether
product 6b (up to 100% of total 6, entries 8-12). The reaction may
be rationalised by cleavage of the bulky gold unit from the most
accessible 4-position of the substrate to regenerate the -dual
gold complex (Scheme 3). The exclusive formation of isomer 6a
with the less bulky monogold (JohnPhos) complex VI (entry 7)
may be enabled by formation of a stabilised conjugated system in
product 6a by rearrangement into the more crowded Au-benzylic
intermediate.
entries 2-6, Table 1a).
A
regioselectivity shift for
cyclopentenylation into the other enol ether product 6b (up to
100%, entry 11, Table 1b) was observed, as well. The selective
formation of the trans isomer was in accordance with previous
studies.[7b]
No significant change in stereoselectivity was apparent for the
tandem cyclisation reaction, as the smaller and more flexible
acetyl group may not interfere with the incoming -gold-acetylide
(Scheme 4) to the same extent as the more rigid and bulky phenyl
group in the cyclopropanation reaction above (Scheme 2).
The preferences for other isomers may generally be explained by
the cyclisation deauration step, where the stereo- or
regioselectivity is determined by transfer of the substrate-
connected gold unit back to the-gold-acetylide to regenerate the
-dual gold complex (Schemes 2-4). In the deauration step,
favouring cis-cyclopropanation (Table 1a, entries 2-6), the bulky
departing gold unit may prefer cis relation to the rigid phenyl ring
in the substrate, to enable approach and coordination of the -
All reactions using dual gold complexes I required longer times or
higher temperatures than the commercially available monogold
complex VI. The lower reactivity may be caused by the necessary
transfer of the-bonded gold unit from the dual gold complex to
the propargyl substrates, to act as
(Schemes 2-4).
a catalytic species
Scheme 2. Proposed mechanism of dual gold-catalysed cyclopropanation (Table 1a) of propargyl ester 2 and styrene, 4a.
Scheme 3. Proposed mechanism of dual gold-catalysed cyclopentenylation (Table 1b) of propargyl acetal 3 and vinyl amide 4b.
Scheme 4. Proposed mechanism of the cyclopropanation step of dual gold-catalysed tandem cyclisation (Table 1c) of propargyl acetal 3 and vinyl acetate, 4c.
4
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The electronic and steric properties of the substituents on alkynes
1b-f affect the reactivity of the dual gold complexes, but the trend
is not clear, as the overall reactivity is influenced by at least two
opposing factors. The initial step, where the catalytic active gold
unit is disconnected from the dual gold-acetylide complex and
transferred to the propargyl substrate (Schemes 2-4), would likely
require an energy barrier crossing. Electron-rich (e.g. complex Id,
entries 11 and 17) or sterically non-hindered gold-acetylides may
deactivate for initial disconnection and transfer of the -bonded
gold unit, but would, in contrast, activate for final deauration to
regenerate the -dual gold complex by re-connection to the -
gold-acetylide.
Fair yields of products
5
(61-76%) were obtained in
cyclopropanation of propargyl ester 2 and alkene 4a in the
presence of (R)-MeO-BIPHEP complexes
(Table 2).[7a]
V
Reaction times with digold complex IV and dual gold complexes
V, were longer compared to the monogold complex VI (Table 2,
entries 1, 2, 7, 9 and 10), as also seen for dual gold complexes I
above (Table 1a). The reaction times to give full conversion
increased with increasing electron-density of the acetylide
(entries 7, 9 and 10; 2 h to 24 h at r.t.), which indicates that the
rate-determining step in this reaction is the disconnection of the
-bound gold unit from the -dual gold complex.
The digold and bridged dual gold complexes V give exclusive cis
diastereomer formation at r.t. (entries 2, 7, 9, 10), as seen for
complexes I, likely for the same deauration reason as discussed
above (Scheme 2). The enantioselectivity of the reactions was
positively affected by temperature reduction. All the tested chiral
The chiral dual gold complex If, based on the chiral MeO-
camphorylalkyne 1f, did not induce any enantioselectivity in
cyclopropanation or cyclopentenylation reactions (HPLC, GLC),
probably due to the long distance between the chiral acetylide unit
and the propargyl substrate in the stereogenerating deauration
step. The proposed mechanisms (Schemes 2-4) are supported by
results from our earlier trifluoromethylation study where the dual
gold complex was the sole gold species observed.[3]
(R)-MeO-BIPHEP complexes IV and
V gave substantial
enantioselectivity (65% ee of cis-5a with digold complex IV, entry
2; and up to 52% ee cis-5a with dual gold complexes V, entries 5,
8, 10). The lower enantioselectivity obtained with dual gold
complexes than the digold complex IV, may be explained by a
conceivable gem-digold intermediate,[1b, 9] which is possible for
monogold complex VI and digold complex IV, but not for the
bridged dual gold complexes V (Figure 3a).
Reactivity of chiral (R)-MeO-BIPHEP dual-gold complexes V
in reactions of propargylic alcohol derivatives
8]
Based on our previous studies,[7c, the catalytic activity and
stereoselectivity of chiral dual gold complexes V were tested in
gold(I)-catalysed reactions of propargylic alcohol derivatives
(Tables 2-5 and Scheme 5). The results were compared with our
corresponding results with digold complex IV and JohnPhos
monogold-complex VI.[7c, 8]
The cyclopentenylation reaction of propargyl ester 2 and
sulfonamide 4d[8] with bridged dual gold complexes V (Table 3a,
entries 5-9) gave selectively the vinyl acetate product 8 (up to
67%). In contrast to cyclopropanation results (Table 2), the
bridged dual gold complexes V gave higher enantioselectivity (42-
46% ee of 8 at r.t.; entries 4-9) than the digold complex IV (<16%
ee, entries 2 and 3).
Table 2. Gold(I)-catalysed propargyl cyclopropanation with monogold (VI)
digold (IV) and dual gold complexes (V).
An explanation for the higher enantioselectivity of the dual gold
complexes in cyclopentenylation reactions, may be seen in the
cyclisation step, which determines the enantioselectivity (Figure
3b). As a larger ring is formed, the gold centers are less directly
involved. Therefore, the effect of a possible gem-digold complex
on the enantioselectivity of the reaction is reduced, and the
selectivity is likely mainly dependent on the bulkiness of the
overall gold complex.
eeb
5a; cis
-
65%
-
eeb
5b; trans
Entry
[Au]
Temp.
Time
Yield
5a:5b
1
2
3
VI
IV
r.t.
r.t.
−40 °C
−40 °C
to 10 °C
−20 °C
0 °C
r.t.
0-4 °C
r.t.
15 min
2 h
6 h
98%
58%
0%
2:1
1:0
-
-
-
-
4
18 h
40%
14:1
43%
35%
Va
5
6
7
8
9
24 h
3 h
2 h
24 h
6 h
24 h
4 h
40%
66%
36%
56%
76%
40%
61%
6:1
3:1
1:0
11:1
1:0
1:0
1:0
52%
50%
38%
51%
40%
44%
40%
15%
10%
-
20%
Vg
Vb
-
-
-
10
11
r.t.
40 °C
a) The reactions were performed with propargyl ester 2 (1 equiv.) and alkene
4a (4 equiv.) in CH2Cl2 (c ≈ 50 mM) together with gold catalyst (5 mol%); b) % ee
determined by HPLC (Chiralpak AD Column 5:95 2-propanol:hexane,
0.8 mL/min).
Figure 3. Possible gold-intermediates with digold complex IV and dual gold complexes V in the deauration step of the a) cyclopropanation reaction (Scheme 2) and
b) cyclopentenylation reactions (Scheme 3).
5
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The slow gold-catalysed [2+5] cycloaddition of propargyl acetal 3
and imine 4e[11] afforded benzazepine product 10 less efficiently
with di-/dual gold complexes IV and V (17-42% in 42 h, Table 4,
entries 2-5) than monogold catalyst VI (60%, entry 1). The yields
improved (from 25% to 42%, entries 3-5) with increased acetylide
electron density (from 4-CF3 to 4-OMe). Low enantioselectivity
(up to 9% ee) was observed with dual gold complex Va.
Table 3. Gold(I)-catalysed propargyl cyclopentenylation with gold complexes
IV, VI and Va
Table 4. Gold(I)-catalysed [2+5]-cycloaddition of propargyl acetal 3 and imine
4e.a
Entry
Complex
Solvent
DCM
DCM
DCM
DCM
DCM
Time
30 min
42 h
42 h
42 h
Yield
60%
17%
25%
27%
42%
eeb
-
9%
9%
8%
2%
1
2
3
4
5
VI
IV
Va
Vg
Vb
Temp.
Product
yield
Entry
Au (I)
Alkene
Time
42 h
eec
a) The reactions were performed with propargyl acetal 3 (1 equiv.) and imine 4e
(1.5 equiv.) in CH2Cl2 or CH3CN (c ≈ 50 mM) together with gold catalyst (5
mol%); b) % ee determined by HPLC (Chiralpak AD Column 10:90 2-
propanol:hexane, 0.8 mL/min).
a) Propargyl acetate 2:
8:
1
2
3
4
5
6
7
8
9
VI
IV
4d
4d
4d
4d
4d
4d
4d
4d
4d
r.t.
r.t.
40 °C
r.t.
40 °C
r.t.
40 °C
r.t.
40 °C
15 min
5 h
3 h
5 h
2 h
72 h
24 h
3 h
64%
58%b
40%b
19%
38%b
18%b
29%
67%b
32%b
6a:
-
9%
16%
42%
36%
46%
44%
44%
39%
Va
Vg
Vb
Gold-catalysed reactions of non-terminal propargyl esters were
also tested (Scheme 5, Table 5). Only dual gold complex Va was
sufficiently active to generate product 12 (14%) with some
enantioselectivity (20% ee), but the reaction was slow and
challenging, due to substrate and product instability. Fast
cycloisomerisation of propargyl ester 11[12] took place with
monogold complex VI (5 min, 42%).
3 h
b) Propargyl acetal 3:
10
11
12
VI
IV,Va,Vb
Vg
4b
4b
4b
r.t.
r.t.
r.t.
15 min
48 h
48 h
61%
-
-
5-24%b
31%
9:
54%
26%
33%
30%
55%
14%
c) Propargyl acetal 3:
13
14
15
16
17
VI
IV
Va
Vg
Vb
4d
4d
4d
4d
4d
r.t.
r.t.
r.t.
r.t.
r.t.
15 min
48 h
48 h
48 h
24 h
-
32%
32%
36%
38%
Scheme 5. Gold(I)-catalysed cycloisomerisation of 1,3-enyne propargyl ester
11.
a) The reactions were performed with propargyl ester 2 (1 equiv.) and alkene
4d (2 equiv.) in CH2Cl2 (c ≈ 17 mM); or acetal 3 (1 equiv.) and alkene 4b or 4d
(3 equiv.) in CH2Cl2 (c ≈ 80 mM) in the presence of gold catalyst (5 mol%); b)
yield calculated by NMR from product mixture; c) % ee of products 6, 8 and 9
determined by HPLC (Chiralpak AD Column 10:90 2-propanol:hexane, 0.8
mL/min for product 8; 1.0 mL/min for products 6a/6b; 0.5 mL/min for 9).
Non-terminal propargyl ester 13 was subjected to gold-catalysed
acetate migration[13] to afford allene product 14. The outcome of
the reaction is in accordance with previous reports on selective
allene formation with Au(I)-phosphine, whereas indene products
were generated with Au(I) NHC complexes.[14] Monogold complex
VI readily afforded high yield of allene product 14 (70%, 30 min,
Table 5, entry 1). Similar yields were only obtained by very slow
reactions in the presence of digold complex IV or the dual gold
complex Va (65-75%, 7 days, Table 5, entries 2 and 3). No
enantioselectivity was observed (HPLC). Only trace amounts of
indene product 15[15] were formed by separate gold-catalysed
cyclisation of isolated allene 14 with complexes IV and V.
Corresponding cyclopentenylation reactions of the more reactive
propargyl acetal 3 with vinyl amide 4b[7b] (Table 3b, entries 10-12)
were studied, as well. However, the di-/dual gold complexes IV
and V performed poorly, and only low yields of product 6a, were
estimated from complex product mixtures (NMR; 5-31% yield in
48 h). Analysis of isolated enol ether 6a (31%) indicated low
enantioselectivity (14% ee, entry 12).
The reaction was further studied by replacing the electron
deficient vinyl amide 4b with the moderately deactivated vinyl
sulfonamide 4d[10] (Table 3c, entries 13-17).[7b] The effect was
apparent, and higher yields and greater enantiomeric excess of
the enol ether product 9 were obtained for the dual gold
complexes V (33-55% yield of 9, 32-38% ee), relative to the digold
complex IV (26% yield of 9, 32% ee), as discussed above (Table
3a and Figure 3b). Highest yield (55% of product 9, entry 17),
comparable to monogold complex VI (54%, entry 13), was
obtained with the dual gold complex Vb with electron-rich
acetylide (4-OMe-C6H4). This result may imply that the catalytic
efficiency is controlled by regeneration step of the -dual gold
complex in the final deauration.
6
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10.1002/ejoc.201901623
European Journal of Organic Chemistry
FULL PAPER
rationalised by bulkiness or proximity effects in the deauration and
product formation step.
Table 5. Gold(I)-catalysed generation of allene by rearrangement of propargyl
ester 13.
The dual gold(I) complexes I and V appear to be less catalytically
active than the monogold JohnPhos complex VI. However, the
resulting selectivity may be useful in certain reactions to obtain
specific target products, as hereby demonstrated for enantio-,
diastereo- and regioselective reactions. To the best of our
knowledge, the catalytic activity of bridged dual gold(I) complexes
has not previously been studied. Thus, the present work
contributes to new understanding of the synthesis, properties and
catalytic potential of dual gold(I) complexes, including
enantioselective chiral bridged dual gold(I) species.
Conversion
13
amount
Yield
14
Entry
Complex
Time
of 13 to 14
(NMR)
-
93%
82%
eec
1
2
3
4
5
VI
IV
Va
Vg
Vb
30 min
7 d
7 d
7 d
7 d
20 mg
6.0 mg
6.0 mg
6.0 mg
6.0 mg
70%
65%b
75%b
-
-
0%
0%
-
20%
7%
-
-
a) The reactions were performed with propargyl ester 13 (1 equiv.) in CH2Cl2
(c ≈ 50 mM) together with gold catalyst (5 mol%); b) isolated with starting
material; yield calculated from NMR; c) % ee determined by HPLC (Chiralpak
AD Column 2:98 2-propanol:hexane, 0.8 mL/min).
Experimental Section
General: Commercial grade reagents were used as received. Dry solvents
were collected from a solvent-purification system. All reactions were
monitored by thin-layer chromatography (TLC) using silica gel 60 F254
(0.25-mm thickness) or by 1H-NMR. Flash chromatography was carried
out using silica gel 60 (0.040-0.063 mm). High Throughput Flash
Purification (HPFP) was performed on pre-packed cartridges. 1H and 13C
NMR spectra were recorded using a 400 or 600 MHz spectrometer.
Chemical shifts are reported in ppm () relative to d-CDCl3 or d-DCM.
Coupling constants (J) are reported in Hertz (Hz). The attributions of the
chemical shifts were determined using COSY, HSQC and HMBC NMR
experiments and cis/trans isomers by NOESY experiments. Accurate
mass determination in either positive or negative mode was performed with
a “Synapt G2-S” Q-TOF instrument from Waters. Samples were ionised
with an ASAP probe, and no chromatographic separation was used before
the mass analysis. IR spectra were obtained using a Bruker Alpha FT-IR
spectrometer using OPUS V7 software to analyse the spectra.
Compounds 1a-1e, 1g, 4a, 4b and 4c were used as received from Sigma-
Aldrich. Propargyl acetates 2,[7a] 11[12] and 13[14a], propargyl acetal 3[7c] and
imine 4e[16] were synthesised from known procedures. Products 5a, 5b, 6a,
Conclusions
A series of new -dual gold(I)-acetylide complexes were
prepared by gold coordination of selected ligands and a range of
alkynes, and characterised (1H, 19F, 13C, 31P NMR; HRMS). The
catalytic activity of the JohnPhos dual-gold complexes I and the
bridged chiral MeO-BIPHEP dual-gold complexes V was tested in
several reactions of propargylic alcohol derivatives. The results
from the dual gold(I)-catalysed reactions (cyclopropanation,
cyclopentenylation, tandem cyclisation, selective allene
generation and cycloisomerisation of propargyl 1,3-enyne) were
compared with corresponding results based on the monogold(I)
phosphane (JohnPhos) complex VI as well as the chiral digold(I)
diphosphane complex IX.
The JohnPhos dual gold complexes I gave excellent yields and
high cis-diastereoselectivity in cyclopropanation (89-99% yield;
up to 80% de). Electron-rich dual gold complexes afforded higher
yields than the monogold(I) JohnPhos complex VI in propargyl
cyclopentenylation and tandem cyclisation. The catalytic activity
of bridged chiral dual gold(I) MeO-BIPHEP complexes V was
demonstrated, as well. Both digold and bridged dual gold
complexes IV and V afforded cis-diastereoselective (>99% de)
and enantioselective (up to 65% ee) cyclopropanations. Higher
yields (up to 76%) were obtained with dual gold V than digold IV
complexes. The chiral dual gold complexes V were also
catalytically active in cyclopentenylation reactions (up to 67%
product yields) and were more enantioselective (up to 46% ee)
than the chiral digold complex IV (<16% ee). Dual gold complexes
V were not promising for tandem cyclisation, the allene generation
reaction or the cycloisomerisation reaction, as very slow
conversion of propargyl substrates were observed.
8, 11, 13]
7a, 7b, 9, 10, 14, 15a and 15b are reported in literature.[7,
Compound 4d is a known compound that has been previously synthesised
in the Fiksdahl group, but not fully characterised. Missing spectroscopic
data is included here for posterity. Compounds 1f, 6b, 8 and 12 are novel
and are fully characterised here. Test reactions were carried out following
literature procedures with any variations in conditions specified in the text.
Complex IV (and the other chiral digold complexes) were generated
following a literature procedure[5e] to obtain the dichloride salt and
subsequent reaction with silver hexafluoroantimonate and filtration gave
the required complex in situ. The syntheses of complexes I and V are
described below.
Preparation of (1R,2S,4R)-2-ethynyl-2-methoxy-1,7,7-
trimethylbicyclo[2.2.1]heptane (1f)
Compound 1f was synthesised from (1R,2S)-2-ethynyl-1,7,7-
trimethylbicyclo[2.2.1]heptan-2-ol through a known procedure.[17] (1R,4R)-
1,7,7-trimethylbicyclo[2.2.1]heptan-2-one (541.9 mg, 3.56 mmol) was
added to a solution of ethynylmagnesium bromide in THF (0.5 M, 10.0 mL,
5.00 mmol). The reaction mixture was heated under reflux for 24 h. After
cooling to room temperature, the solution was quenched by the addition of
H2O (1 mL). The crude mixture was concentrated until most of the THF
was removed. The residue was dissolved in Et2O (25 mL) and sat. aq.
NH4Cl (25 mL) was added. The phases were separated, and the aqueous
layer was extracted with Et2O (3 × 25 mL). The combined organic phases
were washed with brine (25 mL) and dried over Na2SO4. After filtration and
removal of the solvents in vacuo the crude product was purified by column
The present study demonstrates that dual gold complexes have
different catalytic potential than the monogold VI or digold IV
complexes in a variety of reactions of propargylic alcohol
derivatives. The chiral dual gold(I) complexes
V exhibit
comparable catalytic activity and similar or higher
enantioselectivity than the corresponding digold species IV in
selected reactions. Mechanistic explanations are proposed for the
differing regio- or stereoselective outcome of some reactions,
chromatography (gradient pentane
- 1:30 EtOAc:pentane - 1:4
EtOAc:pentane to give 201.9 mg of a colourless wax (ca. 60% pure
(1R,2S)-2-ethynyl-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ol). This product
was dissolved in DMF (2 mL), cooled to 0 °C and sodium hydride (47.0 mg,
7
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10.1002/ejoc.201901623
European Journal of Organic Chemistry
FULL PAPER
1,96 mmol) was added slowly. After stirring for 30 min at the same
temperature, iodomethane (100 µl, 1.61 mmol) was added. The solution
was warmed to r.t. and the DMF was extracted with ether (10 mL) and
water (5 mL). The ether phase was washed with water (2 x 10 mL) and the
combined aqueous washes were extracted with ether (4 x 10 mL). The
combined ether extracts were concentrated in vacuo and the crude oil was
chromatographed (1:10 Et2O:pentane) to give (1R,2S,4R)-2-ethynyl-2-
methoxy-1,7,7-trimethylbicyclo[2.2.1]heptane as a colourless volatile wax
(60.4 mg, 9% yield over two steps). 1H NMR (400 MHz, CDCl3): δ ppm
3.25 (s, 3H, OCH3), 2.40 (s, 1H, ≡CH), 2.28-2.23 (m, 1H, CH3OCCH2),
2.02-1.95 (m, 1H, CCH2CH2), 1.74-1.72 (m, 1H, CH2CHCH2), 1.69-1.64 (m,
1H, CHCH2CH2), 1.51 (d, 1H, J = 13.2 Hz, (CH3OCCH2), 1.47-1.39 (m, 1H,
CCH2CH2), 1.14-1.08 (m, 1H, CHCH2CH2), 0.96 (s, 3H, CH3, bridge), 0.90 (s,
3H, CH3), 0.85 (s, 3H, CH3, bridge); 13C NMR (100 MHz, CDCl3): δ ppm 85.0
(≡C), 83.7 (OC), 72.7 (≡CH), 54.0 (CCH3), 50.2 (OCH3), 48.1 (C(CH3)2),
45.5 (CH2CHCH2), 42.9 (CH3OCCH2), 32.6 (CCH2CH2), 26.9 (CHCH2CH2),
21.2 (CH3, bridge), 20.9 (CH3, bridge), 10.6 (CH3); IR (neat, cm-1) 3306, 2949,
2823, 1451, 1120, 1086, 1057, 1034, 645, 623; HRMS (ASAP+) calcd for
C16H20NO2 [M+H] 258.1494, found 258.1490.
3-Phenyl-3a,5,6,7-tetrahydro-4H-inden-1-yl acetate (12)
The reactions were performed with propargyl ester 11 (1 equiv.) in CH2Cl2
(c ≈ 20 mM) together with gold catalyst (5 mol%) for the required time at
the required temperature. The crude mixture was purified using silica
chromatography (1:50 EtOAc:pentane) to give product 12 as a yellow oil.
12: 1H NMR (400 MHz, CDCl3): δ ppm 7.39-7.38 (m, 2H, CHAr), 7.32-7-30
(m, 2H, CHAr), 7.19-7.16 (m, 1H, CHAr), 6.65 (s, 1H, =CH), 3.13 (dd, J =
12.7/5.8 Hz, 1H, CH), 2.70-2.66 (m, 1H, =CCH2), 2.40-2.36 (m, 1H,
CHCH2), 2.23 (s, 3H, COCH3), 2.09 (td, J = 13.4/5.4 Hz, 1H, =CCH2), 1.96-
1.92 (m, 1H, =CCH2CH2), 1.82-1.79 (m, 1H, CHCH2CH2), 1.48 (qt, J
=13.4/3.3 Hz, 1H, CHCH2CH2), 1.28-1.16 (m, 1H, =CCH2CH2), 0.90 (qd, J
= 12.8/3.2 Hz, 1H, CHCH2); 13C NMR (100 MHz, CDCl3): δ ppm 169.0
(C=O), 147.9 (CCAr), 142.1 (=CO), 135.0 (CAr), 132.6 (OC=C), 128.5
(CHAr), 126.7 (CHAr), 125.6 (CHAr), 123.8 (=CH), 48.5 (CH), 33.2 CHCH2),
28.4 (=CCH2CH2), 25.6 (CHCH2CH2), 24.4 (=CCH2), 20.8 (COCH3); IR
(neat, cm-1) 2931, 2852, 1753, 1652, 1492, 1444, 1368, 1352, 1211, 1169,
1148, 1015, 889, 757, 693; HRMS (ES+) calcd for C15H17O [(M+H2O-
HOCOCH3)+H]+ 213.1279, found 213.1276. The mass of the product was
not observed. However, the product is unstable and previous work has
identified it only by deacetylation.[18] It is proposed that in the conditions in
the MS instrument the compound undergoes deacetylation to give the
mass given above.
N,4-Dimethyl-N-vinylbenzenesulfonamide (4d)
1H NMR (400 MHz, CDCl3): δ ppm 7.62 (d, 2H, J = 8.3 Hz, CHAr), 7.28 (d,
2H, J = 7.9 Hz, CHAr), 6.98 (dd, 1H, J = 15.6/9.0 Hz, =CH), 4.31 (dd, 1H, J
= 9.0/1.2 Hz, =CH2), 4.16 (dd, 1H, J = 15.5/1.0 Hz, =CH2), 2.84 (s, 3H,
NCH3), 2.40 (s, 3H, PhCH3); 13C NMR (100 MHz, CDCl3): δ 143.8 (CH3CAr),
134.8 (SCAr), 133.8 (=CH), 129.7 (CHAr), 127.0 (CHAr), 93.1 (=CH2), 31.2
(NCH3), 21.5 (PhCH3); HRMS (ASAP+) calcd for C10H14NO2S [M+H]
212.0745, found 212.0745.
Preparation of gold complexes I and V
Complex Ia (CF3)
Method
B:
Chloro[(1,1′-biphenyl-2-yl)di-tert-butylphosphine]gold(I)
(41.5 mg, 1 eq) and alkyne 1a (21.1 mg, 2 eq) were dissolved in dry DCM
(5 mL) and NaH (21.1 mg, 11 eq) was added. The reaction mixture was
stirred until complete conversion of the gold complex as analysed by TLC
(2-7 days). The mixture was filtered through Celite and evaporated to give
the gold-acetylide VIII as a colourless powder. The gold-acetylide (20.7
1-((1S,2R)-3-Methoxy-2-phenylcyclopent-3-en-1-yl)pyrrolidin-2-one
(6b)
Compound 6b was synthesised from a literature procedure[7b] using
propargyl acetal 3 (1 equiv.) and alkene 4b (3 equiv.) in CH2Cl2 (c ≈ 80
mM) together with gold catalyst (5 mol%) for the required time at the
required temperature. The crude mixture was purified using silica
chromatography (2% MeOH/DCM) to give products 6a and 6b as yellow
oils. 6b: 1H NMR (400 MHz, CDCl3): δ ppm 7.29-7.26 (m, 2H, CHAr), 7.21-
7.17 (m, 1H, CHAr), 7.16-7.14 (m, 2H, CHAr), 4.68-4.64 (m, 2H, =CH and
NCH), 3.71 (br d, 1H, J = 4.3 Hz, PhCH), 3.59 (s, 3H, OCH3), 3.46-3.34
(m, 2H, NCH2), 2.70 (dtt, 1H, J = 15.5/8.1/1.9 Hz, =CHCH2), 2.37-2.33 (m,
2H, COCH2), 2.27-2.21 (m, 1H, =CHCH2), 2.04-1.96 (m, 2H, NCH2CH2);
13C NMR (100 MHz, CDCl3): δ ppm 174.5 (CO), 159.6 (C=), 140.4 (CAr),
128.6 (2C, CHAr), 127.6 (1C, CHAr), 126.9 (CHAr), 93.5 (=CH), 57.7 (NCH),
56.8 (OCH3), 53.8 (PhCH), 43.7 (NCH2), 31.43 and 31.40 (overlapping, 2C,
OCCH2 and =CHCH2), 18.2 (NCH2CH2); IR (neat, cm-1) 2933, 2855, 1676,
1645, 1419, 1284, 1250, 1231, 1161, 1024, 754, 699, 628; HRMS
(ASAP+) calcd for C16H20NO2 [M+H] 258.1494, found 258.1490.
mg,
1 eq) and (acetonitrile)[(2-biphenyl)di-tert-butylphosphine]gold(I)
hexafluoroantimonate (23.5 mg, 1 eq) were dissolved in DCM (0.5 mL) and
stirred for 30 min. The mixture was evaporated to give complex Ia as a
colourless solid (96% over two steps).
1H NMR (400 MHz, CDCl3): δ ppm 7.89-7.84 (m, 2H, CHAr, ligand), 7.68 (d,
2H, J = 8.0 Hz, CHAr, acetylide), 7.57-7.51 (m, 6H, 4xCHAr, ligand and 2xCHAr,
acetylide), 7.30-7.27 (m, 6H, CHAr, ligand), 7.25-7.22 (m, 2H, CHAr, ligand), 7.11-
7.09 (m, 4H, CHAr, ligand), 1.42 (d, 36H, J = 16.0Hz, t-Bu); 13C NMR (100
MHz, CDCl3): δ ppm 149.1 (d, J = 13.8 Hz, CAr, ligand), 142.7 (d, J = 6.7 Hz,
CAr, ligand), 133.8 (d, J = 1.8 Hz, CHAr, ligand), 133.3 (d, J = 7.7 Hz, CHAr, ligand),
132.6 (CHAr, acetylide), 131.5 (q, J = 33.1 Hz, CCF3), 131.2 (br s, CHAr, ligand),
129.4 (s, CHAr, ligand), 129.1 (CHAr, ligand), 128.0 (CAr, acetylide), 127.6 (d, J =
6.9 Hz, CHAr, ligand), 125.7 (q, J = 3.5 Hz, CHAr, acetylide), 125.1 (CAr, ligand),
124.9 (d, J = 12.9 Hz, CAr, ligand), 124.7 (t, J = 80.2 Hz, AuC), 123.5 (q, J =
272.2 Hz, CF3), 113.0 (t, J = 12.7 Hz, AuCC), 38.1 (d, J = 24.4 Hz, PC),
31.0 (d, J = 5.8 Hz, PC(CH3)3); 19F NMR (376 MHz, CDCl3): δ ppm −62.9;
31P NMR (162 MHz, CDCl3): δ ppm 62.57; IR (neat, cm-1) 2956, 2900, 2869,
1465, 1320, 1168, 1125, 1065, 755, 801, 654, 525, 495, 477; HRMS (ES+)
calcd for C49H59F3P2Au2 [M+H]+ 1160.3375, found 1160.3376.
(4S,5R)-4-((N,4-Dimethylphenyl)sulfonamido)-5-(4-
methoxyphenyl)cyclopent-1-en-1-yl acetate (8)
Compound 8 was synthesised from a literature procedure[8] using
propargyl ester 2 (1 equiv.) and alkene 4d (2 equiv.) in CH2Cl2 (c ≈ 17 mM)
together with gold catalyst (5 mol%) for the required time at the required
temperature. The crude mixture was purified using silica chromatography
(1:10 – 1:4 EtOAc:pentane) to give product 8 as a colourless oil.
8: 1H NMR (600 MHz, CDCl3): δ ppm 7.45-7.44 (m, 2H, CHAr, Ts), 7.13 (d,
J =8.2 Hz, 2H, CHAr, Ts), 6.87-6.74 (m, 2H, CHAr), 6.76-6.74 (m, 2H, CHAr),
5.48-5.47 (m, 1H, =CH), 4.56 (dt, J = 8.5/4.6 Hz, 1H, NCH), 3.80-3.79 (m,
overlapping, 1H, ArCH), 3.78 (s, 3H, OCH3), 2.88 (s, 3H, NCH3), 2.61 (ddt,
J = 17.0/8.6/2.4 Hz, 1H, CH2), 2.38 (s, 3H, ArCH3), 2.15 (dm, J =17.0 Hz,
1H, CH2), 1.90 (s, 3H, COCH3); 13C NMR (150 MHz, CDCl3): δ ppm 168.4
(C=O), 158.7 (CArOCH3), 150.2 (=C), 142.9 (CArCH3), 136.7 (SC), 131.7
(CArCH), 129.5 (CHAr, Ts), 128.6 (CHAr), 127.1 (CHAr, Ts), 114.0 (CHAr),
112.8 (=CH), 63.4 (NCH), 55.2 (OCH3), 51.9 (ArCH), 31.2 (CH2), 29.1
(NCH3), 21.5 (ArCH3), 20.7 (COCH3); IR (neat, cm-1) 2929, 2837, 1753,
1511, 1337, 1244, 1203, 1178, 1155, 1088, 1032, 969, 814, 654, 569, 549;
HRMS (ES+) calcd for C22H25NO5NaS [M+Na]+ 438.1351, found 438.1353.
Complex Ib (OMe)
Method
A:
(Acetonitrile)[(2-biphenyl)di-tert-butylphosphine]gold(I)
hexafluoroantimonate (43.8 mg, 1 eq) and DIPEA (10 µL, 1.0 eq) were
mixed in DCM (1 mL), then alkyne 1b (8.8 mg, 1.2 eq) in DCM (1 mL) was
added. After stirring for 5 min, the mixture was filtered through Celite and
precipitated with pentane to give complex Ib as a colourless solid (23.6 mg,
74%). The 1H NMR spectrum was in accordance with reported literature.[3]
Complex Ic (MeO/Me)
Method
A
(1
eq
alkyne):
(Acetonitrile)[(2-biphenyl)di-tert-
butylphosphine]gold(I) hexafluoroantimonate (40.8 mg, 1 eq) and DIPEA
(10 µL, 1.1 eq) were mixed in DCM (0.5 mL), then alkyne 1c (7.8 mg, 1.0
eq) in DCM (0.5 mL) was added. After stirring for 5 min, 2 mL DCM was
added and the mixture was washed with water (5 x 2 mL), the organic
phase dried over Na2SO4, filtered and evaporated. The resulting powder
was dissolved in ca. 0.25 mL DCM and 4 mL pentane added carefully and
8
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10.1002/ejoc.201901623
European Journal of Organic Chemistry
FULL PAPER
placed in the freezer overnight. The crystals were washed with pentane (5
x 1 mL) and dried in vacuo to give complex Ic as a colourless solid (22.0
mg, 61%).
CH3OCCH2), 1.85-1.76 (m, 3H, CCH2CH2 and CH2CHCH2 and
CHCH2CH2), 1.49 (d, 1H, J = 13.6 Hz, CH3OCCH2), 1.42 (dd, 37H, J =
15.5/11.3 Hz, t-Bu and CCH2CH2), 1.26-1.22 (m, 1H, CHCH2CH2), 0.950
(s, 3H, CH3), 0.946 (s, 3H, CH3), 0.88 (s, 3H, CH3); 13C NMR (150 MHz,
CDCl3): δ ppm 149.1 (d, J = 13.8 Hz, CAr), 133.8 (br s, CHAr), 133.4 (d, J =
7.5 Hz, CHAr), 132.1 (t, J = 11.8 Hz, AuCC), 131.2 (br s, CHAr), 129.4 (d, J
= 5.4 Hz, CHAr), 129.3 (CHAr), 129.0 (CHAr), 127.8 (CHAr), 127.5 (d, J = 7.1
Hz, CHAr), 124.6 (d, J = 44.7 Hz, PCAr), 117.0 (t, J = 68.7 Hz, AuC), 85.0
(OC), 55.1 (CCH3), 50.1 (OCH3), 48.6 (C(CH3)2), 45.4 (CH2CHCH2), 44.0
(CH3OCCH2), 38.4 (dd, 24.4/24.4 Hz, PC(CH3)3), 32.8 (CCH2CH2), 31.0
(dd, J = 20.0/6.8 Hz, PC(CH3)3), 27.1 (C), 21.3 (CH3), 20.8 (CH3), 11.7
(CH3); 31P NMR (162 MHz, CDCl3): δ ppm 61.95; IR (neat, cm-1) 2950,
2900, 1471, 1391, 1369, 1170, 1084, 755, 702, 655, 526, 475; HRMS (ESI)
calcd for C52H71OP2Au2 [M]+ 1167.4311, found 1167.4329.
Method
A
(0.5 eq alkyne):
(Acetonitrile)[(2-biphenyl)di-tert-
butylphosphine]gold(I) hexafluoroantimonate (20.0 mg, 1 eq) and DIPEA
(5 µL, 1.1 eq) were mixed in DCM (1.0 mL), then alkyne 1c (3.8 mg, 1.0
eq) in DCM (1.0 mL) was added. was added. After stirring for 5 min, 2 mL
DCM was added and the mixture was washed with water (5 x 2 mL), the
organic phase dried over Na2SO4, filtered and evaporated. The resulting
powder was dissolved in ca. 0.25 mL DCM and 4 mL pentane added
carefully and placed in the freezer overnight. The crystals were washed
with pentane (5 x 1 mL) and dried in vacuo to give complex Ic as a
colourless solid (13.8 mg, 78%).
1H NMR (400 MHz, CDCl3): δ ppm 7.88-7.84 (m, 2H, CHAr, ligand), 7.53-7.50
(m, 4H, CHAr, ligand), 7.38 (d, J = 8.3 Hz, CHAr, acetylide), 7.28-7.19 (m, 8H,
CHAr, ligand), 7.08-7.05 (m, 4H, CHAr, ligand), 6.81-6.77 (m, 2H, CHAr, acetylide,
ortho to OMe), 3.86 (s, 3H, OCH3), 2.45 (s, 3H, CH3), 1.39 (d, J = 15.6 Hz, t-
Bu); 13C NMR (150 MHz, CDCl3): δ ppm 161.5 (COCH3), 149.3 (d, J = 13.9
Hz, CAr, ligand), 144.5 (CH3CAr, acetylide), 142.3 (d, J = 7.4 Hz, CAr, ligand), 136.0
(CHAr, acetylide, meta to OMe), 133.9 (br s, CHAr, ligand), 133.3 (d, J = 8.0 Hz, CHAr,
ligand), 131.1 (CHAr, ligand), 129.3 (CHAr, ligand), 129.0 (CHAr, ligand), 128.0 (CHAr,
ligand), 127.4 (d, J = 7.5 Hz, CHAr, ligand), 125.2 (d, C, J = 44.3 Hz, CAr, ligand),
123.7 (t, J = 69.3 Hz, AuC), 123.5 (t, J = 10.8 Hz, AuCC), 115.3 (CHAr,
acetylide, ortho to OMe), 112.1 (CAr, acetylide, ortho to OMe), 111.8 (CHAr, acetylide), 55.5
(OCH3), 38.1 (d, J = 24.7 Hz, PC), 31.0 (d, J = 7.5 Hz, PCC), 21.4 (CH3);
31P NMR (162 MHz, CDCl3): δ ppm 62.31; IR (neat, cm-1) 2954, 2898, 2865,
2018, 1603, 1561, 1466, 1366, 1295, 1247, 754, 733, 699, 656, 525, 498;
HRMS (ES+) calcd for C50H63OP2Au2 [M]+ 1135.3685, found 1135.3696.
General procedure for synthesis of Complexes V
A
solution
of
(R)-(6,6'-dimethoxy-[1,1'-biphenyl]-2,2'-
diyl)bis(diphenylphosphine) (9.9 mg, 0.017 mmol) in DCM (1 mL) was
added to chloro(dimethylsulfide)gold (10 mg, 0.034 mmol) in DCM (1 mL).
The resulting solution was stirred for 5-10 min then silver
hexafluoroantimonate (11.7 mg, 0,034 mmol) was added and the mixture
filtered. A mixture of N-ethyl-N-isopropylpropan-2-amine (5 µl, 0.029
mmol) and alkyne 1a, 1b or 1g (0.017 mmol) in a small amount of DCM
was added. The mixture was stirred for 5-10 min then washed with water
5x1mL, dried over Na2SO4, filtered and evaporated. The residue was
washed with pentane (3 x 1 mL) to give the required gold complex. The
complexes tended to retain a small amount of pentane and where
necessary, the yield was calculated from 1H NMR.
Complex Id (diOMe)
Complex Va (BIPHEP-CF3)
Method
A:
(Acetonitrile)[(2-biphenyl)di-tert-butylphosphine]gold(I)
Complex Va was synthesised according to the general procedure above
using alkyne 1a (2.9 mg, 1.0 eq) to give the desired complex as a yellow
solid (20.5 mg, 87%). 1H NMR (600 MHz, CD2Cl2): δ ppm 7.75 (d, 2H, CHAr,
acetylide), 7.60-7.56 (m, 4H, 2xCHAr, ligand, Ph, 2xCHAr, acetylide), 7.54-7.51 (m,
4H, CHAr, ligand, Ph), 7.37-7.27 (m, 6H, CHAr, ligand, Ph), 7.29 (dt, 2H, J = 8.1/2.1
Hz, CHAr, ligand), 7.20-7.17 (m, 4H, CHAr, ligand, Ph), 7.13 (dd, 4H, J = 13.3/7.5
Hz, CHAr, ligand, Ph), 6.93 (dd, 2H, J = 9.8/8.1 Hz, CHAr, ligand), 6.61 (d, 2H, J
= 8.4 Hz, CHAr, ligand), 2.91 (s, 6H, OCH3); 13C NMR (150 MHz, CD2Cl2): δ
ppm 159.4-159.3 (m, 2C, COCH3, ligand), 136.1-136.0 (m, 4C, CHAr, ligand, Ph),
134.7-134.6 (m, 4C, CHAr, ligand, Ph), 133.4 (s, (m, 2C, CHAr, acetylide), 133.3
(m, 2C, CHAr, ligand, Ph), 132.5 (m, 2C, CHAr, ligand, Ph), 131.0-130.9 (m, 2C,
CHAr, ligand), 130.3 (dm, 2C, J = 62.3 Hz, PCAr, ligand), 129.75-129.68 (m, 4C,
CHAr, ligand, Ph), 129.3-129.2 (m, 4C, CHAr, ligand, Ph), 128.3 (d, 2C, J = 61.4
Hz, PCAr, Ph), 128.3-128.2 (m, 2C, PCCAr, ligand), 126.7 (q, 1C, J = 3.3 Hz,
CHCCF3), 126.2 (d, 2C, J = 63.7 Hz, PCAr, Ph),125.2 (br s, 2C, PCCHAr,
ligand), 123.9 (q, 1C, J = 272.8 Hz, CF3), 123.8 (1C, CAr, acetylide), 117.6 (only
HMBC, AuCC), 114.7 (s, 2C, CHAr, ligand), missing, AuC and CCF3; 19F NMR
(376 MHz, CD2Cl2): δ ppm −63.34; 31P NMR (162 MHz, CDCl3): δ ppm
29.29; IR (neat, cm-1) 3056, 2936, 2837, 1567, 1460, 1435, 1156, 1123,
1097, 1064, 1043, 845, 743, 691, 654, 500; HRMS (ES+) calcd for
C47H36O2F3P2Au2 [M+] 1145.1474, found 1145.1473.
hexafluoroantimonate (40.5 mg, 1 eq) and DIPEA (10 µL, 1.1 eq) were
mixed in DCM (1 mL), then alkyne 1d (4.2 mg, 0.5 eq) in DCM (1 mL) was
added. After stirring for 5 min, 2 mL DCM was added and the mixture was
washed with water (5 x 2 mL), the organic phase dried over Na2SO4,
filtered and evaporated. The resulting powder was dissolved in ca. 0.25
mL DCM and 4 mL pentane added carefully and placed in the freezer
overnight. The crystals were washed with pentane (5 x 1 mL) and dried in
vacuo to give complex Id as a colourless powder (32.5 mg, 45%).
1H NMR (600 MHz, CDCl3): δ ppm 7.87-7.85 (m, 2H, CHAr, ligand), 7.54-7.51
(m, 4H, CHAr, ligand), 7.36-7.30 (m, 6H, CHAr, ligand), 7.24-7.21 (m, 2H, CHAr,
ligand), 7.11 (dd, 1H, J = 8.3/1.9 Hz, CHAr, acetylide), 7.09-7.07 (m, 4H, CHAr,
ligand), 6.94 (dd, 1H, J = 8.4/1.5 Hz, CHAr, acetylide), 6.89 (d, 1H, J = 1.8 Hz,
CHAr, acetylide), 3.95 (s, 3H, OCH3), 3.93 (s, 3H, OCH3), 1.39 (d, 36H, J =
15.7 Hz, t-Bu); 13C NMR (150 MHz, CDCl3): δ ppm 151.3 (CAr, acetylide),
149.2 (d, J = 14.0 Hz, CAr, ligand), 148.6 (CAr, acetylide), 142.6 (d, J = 6.8 Hz,
CAr, ligand), 133.9 (br s, CHAr, ligand), 133.3 (d, J = 7.7 Hz, CHAr, ligand), 131.1
(br s, CHAr, ligand), 129.3 CHAr, ligand), 129.0 CHAr, ligand), 128.0 (CHAr, ligand),
127.5 (d, J = 7.5 Hz, CHAr, ligand), 127.3 (CHAr, acetylide), 125.2 (d, J = 44.8 Hz,
PCAr), 124.6 (t, J = 68.5 Hz, AuC), 118.2 (t, J = 11.4 Hz, AuCC), 115.3
(CHAr, acetylide), 112.5 (CAr, acetylide), 111.2 (CHAr, acetylide), 56.1 (2xOCH3), 38.0
(d, J = 22.7, C(CH3)3), 31.0 (d, J = 7.0 Hz, PC(CH3)3); 31P NMR (162 MHz,
CDCl3): δ ppm 62.35; IR (neat, cm-1) 2947, 2899, 2865, 2017, 1592, 1508,
1463, 1263, 1136,1023, 753, 699, 655, 525; HRMS (ESI) calcd for
C50H63O2P2Au2 [M]+ 1151.3634, found 1151.3649.
Complex Vb (BIPHEP-OMe)
Complex Vb was synthesised according to the general procedure above
using alkyne 1b (2.3 mg, 1.0 eq) to give the desired complex as a yellow
1
solid (19.4 mg, 85%). H NMR (600 MHz, CD2Cl2): δ ppm 7.58-7.52 (m,
Complex If (camphorOMe)
6H, CHAr, ligand), 7.40-7.37 (m, 2H, CHAr, acetylide), 7.34-7.31 (m, 4H, CHAr,
ligand), 7.29 (td, 2H, J = 8.3/2.5 Hz, CHAr, ligand), 7.28-7.23 (m, 2H, CHAr, ligand),
7.17-7.11 (m, 8H, CHAr, ligand), 7.03-7.01 (m, 2H, CHAr, acetylide), 6.97 (dd, 2H,
J = 10.5/7.9 Hz, CHAr, ligand), 6.57 (d, 2H, J = 8.5 Hz, CHAr, ligand), 3.95 (s,
3H, OCH3, acetylide), 2.87 (s, 6H, OCH3, ligand); 13C NMR (150 MHz, CD2Cl2):
δ ppm 163.3 (s, 1C, COCH3, acetylide), 159.3-159.2 (m, 2C, COCH3, ligand),
136.2-136.1 (m, 4C, CHAr, ligand, Ph), 135.8 (s, 2C, CHAr, acetylide), 134.8-134.7
(m, 4C, CHAr, ligand, Ph), 133.0 (s, 2C, CHAr, ligand, Ph), 132.1 (s, 2C, CHAr, ligand,
Ph), 130.81-130.74 (m, 2C, CHAr, ligand, Ar), 130.7 (dm, 2C, J = 63.1 Hz, PCAr),
129.44-129.37 (m, 4C, CHAr, ligand, Ph), 129.07-128.99 (m, 4C, CHAr, ligand, Ph),
128.4 (dm, 2C, J = 61.5 Hz, PCPh), 128.2-128.1 (m, 2C, PCC), 126.3 (dm,
2C, J = 63.2 Hz, PCPh), 125.2 (br s, 2C, CHAr, ligand, Ar), 119.5 (t, J = 72.2
Method
A:
(Acetonitrile)[(2-biphenyl)di-tert-butylphosphine]gold(I)
hexafluoroantimonate (21.2 mg, 1 eq) and DIPEA (10 µL, 2.1 eq) were
mixed in DCM (0.5 mL), then alkyne 1f (5.0 mg, 0.9 eq) in DCM (0.5 mL)
added. After 10 min stirring, the mixture was washed with water (5 x 1 mL),
the organic phase dried over Na2SO4, filtered and precipitated with
pentane. The solvents were evaporated and the resulting powder was
washed with pentane and dried in vacuo to give complex If as a colourless
powder (15.5 mg, 40%).
1H NMR (400 MHz, CDCl3): δ ppm 7.90-7.86 (m, 2H, CHAr, ligand), 7.54-7.52
(m, 4H, CHAr, ligand), 7.35-7.26 (m, 6H, CHAr, ligand), 7.22-7.18 (m, 2H, CHAr,
ligand), 7.13-7.08 (m, 4H, CHAr, ligand), 3.23 (s, OCH3), 2.37-2.32 (m, 1H,
9
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10.1002/ejoc.201901623
European Journal of Organic Chemistry
FULL PAPER
Hz, AuC), 115.4 (s, 2C, CHAr, acetylide), 114.4 (s, 2C, CHAr, ligand, Ar), 110.9 (s,
1C, C≡CC), 56.3 (s, 1C, OCH3, acetylide), 55.2 (s, 2C, OCH3, ligand), AuCC not
visible; 31P NMR (162 MHz, CD2Cl2): δ ppm 29.42; IR (neat, cm-1) 3053,
2936, 2837, 1998, 1597, 1435, 1255, 1167, 1156, 1086, 1042, 1025, 836,
785, 743, 653, 500; HRMS (ES+) calcd for C47H39O3P2Au2 [M+] 1107.1705,
found 1107.1721.
References
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Complex Vg (BIPHEP-H)
[2]
Complex Vg was synthesised according to the general procedure above
using alkyne 1g (1.7 mg, 1.0 eq) to give the desired complex as a yellow
1
solid (18.8 mg, 84%). H NMR (600 MHz, CD2Cl2): δ ppm 7.64-7.61 (m,
1H, CHAr, acetylide), 7.59-7.50 (m, 9H, 2xCHAr, acetylide and 7xCHAr, ligand, Ph),
7.44-7.43 (m, 2H, CHAr, acetylide), 7.34-7.32 (m, 4H, CHAr, ligand, Ph), 7.30-7.28
(m, 4H, 2xCHAr, ligand and 2xCHAr, ligand, Ph), 7.16-7.12 (m, 7H, CHAr, ligand, Ph),
6.97 (dd, 2H, J = 10.8/8.0 Hz, CHAr, ligand), 6.58 (d, 2H, J = 8.3 Hz, CHAr,
ligand), 2.88 (s, 6H, OCH3); 13C NMR (150 MHz, CD2Cl2): δ ppm 159.3-159.2
(m, 2C, COCH3, ligand), 136.2-136.1 (m, 4C, CHAr, ligand, Ph), 134.8-134.7 (m,
4C, CHAr, ligand, Ph), 133.4 (s, 2C, CHAr, acetylide), 133.1 (s, 2C, CHAr,ligand, Ph),
132.4 (s, 2C, CHAr,ligand, Ph), 132.2 (s, 1C, CHAr, acetylide), 130.9-130.8 (m, 2C,
CHAr, ligand), 130.5 (dm, 2C, J = 62.7 Hz, PCAr), 129.8 (s, 2C, CHAr, acetylide),
129.53-129.47 (m, 4C, CHAr, ligand, Ph), 129.07-128.99 (m, 4C, CHAr, ligand, Ph),
128.3 (dm, 2C, J = 61.4 Hz, PCPh), 128.3-128.2 (m, 2H, PCC), 126.3 (dm,
2C, J = 63.2 Hz, PCPh),125.2 (br s, 2C, CHAr, ligand), 122.9 (t, J = 72.2 Hz,
AuC), 121.4 (t, J = 6.6 Hz, AuCC), 119.7 (s, CAr, acetylide), 114.5 (s, 2C,
CHAr,ligand), 55.2 (s, 2C, OCH3, ligand); 31P NMR (12xCHAr, acetylide and 7xCHAr,
Ph), 62 MHz, CDCl3): δ ppm 29.35; IR (neat, cm-1) 3053, 2935, 2836, 1567,
1460, 1434, 1264, 1155, 1086, 1042, 743, 690, 653, 501; HRMS (ES+)
calcd for C46H37O2P2Au2 [M+] 1077.1600, found 1077.1621.
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Acknowledgements
This work was partly supported by the Research Council of
Norway through the Norwegian NMR Platform, NNP
(226244/F50).
[8]
[9]
Keywords: chiral; bridged; σ,π- dual gold(I) complexes; acetylide;
propargyl; catalytic activity
[10] I. Chataigner, C. Panel, H. Gérard, S. R. Piettre, Chem.
Commun. 2007, 3288-3290.
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10
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10.1002/ejoc.201901623
European Journal of Organic Chemistry
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Entry for the Table of Contents
Layout 1:
FULL PAPER
Text for Table of Contents:
chiral bridgeddual gold(I)-
acetylide complexes *
Chiral bridged -dual gold(I)-
acetylide complexes were
synthesised, characterised, and
their catalytic activity was
investigated. Dual gold(I)-
Huey-San Melanie Siah
and Anne Fiksdahl*
catalysed reactions of propargylic
alcohol derivatives show different
catalytic potential than the
monogold or digold complexes.
Mechanistic explanations are
proposed for the differing
regioselectivity or the similar or
higher enantioselective outcome
of some reactions.
Page No. – Page No.
Preparation and catalytic activity
of novel-dual gold(I)-acetylide
complexes
*one or two words that highlight the emphasis of the paper or the field of the study
11
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