The more gold-the more enantioselective: Cyclohydroaminations of γ-allenyl sulfonamides with mono-, bis-, and trisphospholane gold(I) catalysts

Article abstract of DOI:10.1002/chem.201103140

A series of chiral mono-, di-, and trinuclear gold(I) complexes have been prepared and used as precatalysts in the asymmetric cyclohydroamination of N-protected γ-allenyl sulfonamides. The stereodirecting ligands were mono-, di-, and tridentate 2,5-diphen

Full text of DOI:10.1002/chem.201103140

FULL PAPER
DOI: 10.1002/chem.201103140
The More Gold—The More Enantioselective: Cyclohydroaminations of
g-Allenyl Sulfonamides with Mono-, ACTHNUTRGNEUGNBis-, and Trisphospholane Gold(I)
AHCTUNGTRENNCGUN atalysts
Lara-Isabel Rodrꢀguez, Torsten Roth, Julio Lloret Fillol, Hubert Wadepohl, and
Lutz H. Gade*[a]
Dedicated to Professor Peter Hofmann on the occasion of his 65th birthday
Abstract: A series of chiral mono-, di-,
and trinuclear gold(I) complexes have
been prepared and used as precatalysts
in the asymmetric cyclohydroamination
of N-protected g-allenyl sulfonamides.
The stereodirecting ligands were
mono-, di-, and tridentate 2,5-diphenyl-
phospholanes, which possessed C1, C2,
and C3 symmetry, respectively, thereby
rendering the catalytic sites in the di-
and trinuclear complexes symmetry
equivalent. The C3-symmetric trinu-
clear complex displayed the highest ac-
tivity and enantioselectivity (up to
95% ee), whilst its mono- and dinu-
clear counterparts exhibited considera-
bly lower enantioselectivities and activ-
ities. A similar trend was observed in a
series of mono-, di-, and trinuclear 2,5-
dimethylphospholane gold(I) com-
plexes. Aurophilic interactions were es-
tablished from the solid-state structures
of the trinuclear gold(I) complexes,
thereby raising the question as to
whether these secondary forces were
responsible for the different catalytic
behavior observed.
Keywords: asymmetric catalysis
·
enantioselectivity · gold · hydroami-
nation · modular ligands
Introduction
tions may be a necessary structural feature in active dinu-
clear gold(I) catalysts to impose stereoinduction on the dis-
tant coordination site. Recently, Che and co-workers investi-
gated a series of dinuclear gold(I) complexes and they pro-
posed that there was a direct relationship between the exis-
Enantioselective gold catalysis has experienced an explosive
growth over the past decade, despite some inherent limita-
tions of gold(I) catalysts in inducing stereoselectivity.
Gold(I) usually favors a twofold linear coordination,[1,2]
which places the ancillary ligand (the source of chiral induc-
tion) remote from the reactive site. To overcome this draw-
back, different strategies have been devised, such as the use
of chiral counteranions[3] or, more recently, the construction
of an encapsulating chiral pocket around the active center
of a mononuclear gold catalyst.[4] Secondary forces have
been proposed to have a remarkable effect on the confor-
mational orientation of the complex and, therefore, in the
observed catalytic properties.
For example, in 2005, Echavarren and co-workers studied
the enantioselective alkoxycyclization of enynes using chiral
monodentate and dinuclear phosphine–gold(I) complexes,[5]
the latter of which induced significantly higher enantioselec-
tivity than the former. Gagnꢀ and co-workers investigated
the cycloisomerization of eneallenes,[6] and they suggested
that conformational rigidity owing to metallophilic interac-
À
tence of Au Au interactions and the enantioselectivity of
the intermolecular hydroarylation of allenes with indoles.[7]
In a recent profound mechanistic investigation of the role
of dinuclear catalysts in gold-catalyzed oxidative heteroary-
lations of alkenes, Toste and co-workers observed that auro-
philic interactions in solution (even if absent in the solid
state) modulated the redox behavior of their catalysts.[8]
This observation provided the first quantitative indication of
the way in which two Au centers may influence each other
in elementary reaction steps of catalytic cycles. Comparable
mechanistic studies with the aim of assessing how the modi-
fication of the accessible conformational space modifies the
stereoinduction in enantioselective gold-catalyzed reactions
have not been reported.
Despite indications that dinuclear gold catalysts may dis-
play superior performance for certain reactions,[7–9] no exam-
ples of gold complexes of higher nuclearity have been stud-
ied in asymmetric catalysis to date. Nor has there been a
systematic study of the influence of catalyst nuclearity for a
specific structural type of chiral stereodirecting ligand. As
noted above, aurophilic interactions may significantly influ-
ence the activity of the catalyst, considering the fact that
they are similar in energy to hydrogen bonding and that
their use has been well-established in, for example, the as-
sembly of supramolecular structures.[10] Herein, we report
[a] Dr. L.-I. Rodrꢁguez, Dipl.-Chem. T. Roth, Dr. J. Lloret Fillol,
Prof. Dr. H. Wadepohl, Prof. Dr. L. H. Gade
Anorganisch-Chemisches Institut, Universitꢂt Heidelberg
Im Neuenheimer Feld 270, 69120 Heidelberg (Germany)
Fax : (+49)6221-54-5609
E-mail: lutz.gade@uni-hd.de
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201103140.
Chem. Eur. J. 2012, 18, 3721 – 3728
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3721

the synthesis of chiral mono-, di-, and trinuclear gold com-
plexes and a systematic study of their activities and the
enantioselectivities afforded in the asymmetric cyclohydroa-
mination of N-protected g-allenyl sulfonamides. In these di-
and trinuclear complexes, the C2- and C3-symmetric chiral li-
gands rendered the catalytic sites symmetry-equivalent.[11,12]
Results and Discussion
Synthesis and characterization of chiral phospholanomethyl-
amine ligands and their gold(I) complexes: We recently re-
ported a new class of chiral bidentate C2- and tridentate C3-
symmetric diphenylphospholane (DPP) and dimethylphos-
pholane (DMP) ligands.[13] Their corresponding RhI com-
plexes were shown to be highly enantioselective hydrogena-
tion catalysts for a range of prochiral alkenes.
Scheme 2. General synthesis of chiral mono-, di-, and trinuclear phospho-
lane gold(I) complexes.
Herein, the synthesis of several new chiral mono- and bi-
dentate ligands is reported, by following a similar procedure
as described previously, to evaluate the catalytic properties
of their corresponding gold complexes and compare them
with their trinuclear counterparts. Whereas ligands 4b, 5a,
and 5b were presented in our previous report, phospholanes
3a, 3b, and 4b were synthesized for the first time in this
work (Scheme 1).[14] All of these compounds were character-
and imines.[15c] The gold complexes reported herein were
synthesized by addition of an equimolar amount of the pre-
cursor [AuACTHNUTRGNEUG(N tht)Cl] to a solution of the corresponding chiral
phospholane ligand (Scheme 2) and were found to be highly
soluble in polar organic solvents (CH2Cl2, CHCl3, CH3CN,
acetone), with the exception of trinuclear complex 8b,
which precipitated as a pure crystalline solid from the reac-
tion mixture (CH2Cl2/CH3CN).
In all cases, the formation of the metal complexes was ac-
companied by a shift in the 31P{1H} NMR singlet by approxi-
mately 40–45 ppm relative to the respective free ligands.
The major ion peaks found in the high-resolution mass spec-
tra (ESI(+)) corresponded to [M+H]+ or to the loss of one
chloride group ([MÀCl]+), thus indicating that the ligand–
metal interactions and the nuclearity of the complexes were
maintained in solution. In all cases, the analytical data were
in accordance with the formation of neutral gold(I) species.
Single-crystal X-ray analysis of complexes 6a, 6b, 8a, and
8b corroborated the proposed solution-state structures (for
full details and representations of complexes 6a and 6b, see
the Supporting Information). All structures displayed the
expected almost-linear coordination for gold (P-Au-Cl 172–
1788). For mononuclear complexes 6a and 6b, no secondary
metallophilic interactions were found in the solid state. In-
À
terestingly, short Au Au contacts were observed in both C3-
symmetric complexes. In the crystals of DMP complex 8b,
the aurophilic interactions were intermolecular (Au–
Au 3.432 ꢄ), thereby connecting the complexes in a zigzag-
type chain (Figure 1), which may explain the observed low
solubility of compound 8b.
Scheme 1. Synthesis of monodentate, C2-bidentate, and C3-tridentate
phospholane ligands.
ized by elemental analysis and high-resolution mass spec-
trometry as well as by 1H NMR, 31P NMR, and
13C{1H} NMR spectroscopy (analysis of the COSY, DEPT-
135, HSQC, and HMBC spectra allowed the complete as-
In contrast, DPP complex 8a displayed a short intramo-
lecular Au Au interaction between two of the three gold
À
1
signment of all of the H NMR and 13C NMR resonances).
atoms (Au–Au 2.978 ꢄ) whilst the third atom was neither
engaged in inter- nor intramolecular interactions in the crys-
tal structure (Figure 2). This feature revealed that at least
two of the three gold atoms were sufficiently close to allow
for aurophilic interaction in solution, which could potential-
ly influence the catalytic properties of the system.
Only a few phospholane gold(I) complexes have been de-
scribed in the literature to date.[7,15] Notable examples in-
clude the dinuclear gold(I) complexes prepared by Corma
and co-workers using Me-DuPhos ligands, which efficiently
performed the enantioselective hydrogenation of alkenes
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Chem. Eur. J. 2012, 18, 3721 – 3728

Gold-Catalyzed Cyclohydroaminations of g-Allenyl Sulfonamides
FULL PAPER
at the lower temperatures, thus indicating the presence of
intramolecular aggregation at even-lower temperatures (see
the Supporting Information). This result indicated that the
threefold symmetry of the precatalyst was essentially pre-
served on the experimental timescale under these condi-
tions. Because the catalysis was performed at 323 K and
above (see below), the general symmetry-based argument
(see the Introduction) remained valid.
Unfortunately, all attempts to grow suitable crystals of di-
nuclear complexes 7a or 7b for X-ray diffraction failed. To
obtain insight into the structural details of the dinuclear
complexes, the N-benzyl-substituted diphospholane ligand
derivative of compound 4a and its corresponding gold com-
plex (9) were prepared by following similar procedures.
Figure 3 shows the molecular structure of complex 9, which
was characterized by an intramolecular aurophilic interac-
tion (Au–Au 3.156 ꢄ).
Figure 1. Top: Molecular structure of complex 8b, ellipsoids set at 50%
probability. H atoms and one molecule of CH2Cl2 are omitted for clarity.
Selected bond lengths [ꢄ] and angles [8]: P(1)–Au(1) 2.231(3), P(2)–
Au(2) 2.226(2), P(3)–Au(3) 2.228(2); P(1)-Au(1)-Cl(1) 172.43(9), P(2)-
Au(2)-Cl(2) 173.28(10), P(3)-Au(3)-Cl(3) 174.49(9). Bottom: Ball-and-
stick structure of complex 8b, which shows aggregation through Au···Au
contacts (3.430 ꢄ).
Figure 3. Molecular structure of complex 9, ellipsoids set at 50% proba-
bility. H atoms are omitted for clarity. Selected bond lengths [ꢄ] and
angles [8]: Au(1)–Au(2) 3.156(1), P(1)–Au(1) 2.227(2), P(2)–Au(2)
2.231(2); P(1)-Au(1)-Cl(1) 173.99(7), P(2)-Au(2)-Cl(2) 171.54(7).
Catalytic asymmetric cyclohydroamination of N-protected
g-allenyl sulfonamides: The use of allenes as reactive build-
ing blocks has emerged as a powerful tool for organic trans-
formations in fields such as natural-product synthesis, phar-
maceutical chemistry, and materials science.[16] Gold(I) com-
plexes are known to activate allene groups toward nucleo-
philic attack and have been used to promote the formation
[1c,r,17]
Figure 2. Molecular structure of complex 8a, ellipsoids set at 50% proba-
bility. H atoms and one molecule of CHCl3 are omitted for clarity. There
was a statistical 60:40 disorder of two conformers that differed in orienta-
tion of the phenyl ring in the crystal structure, of which only the major
component is shown. Selected bond lengths [ꢄ] and angles [8]: Au(1)–
Au(2) 2.9782(15), P(1)–Au(1) 2.2374(15), P(2)–Au(2) 2.2336(12), P(3)–
Au(3) 2.2246(12); P(1)-Au(1)-Cl(1) 171.75(4), P(2)-Au(2)-Cl(2)
175.26(4), P(3)-Au(3)-Cl(3) 173.91(4).
À
À
À
of new C C, C N, and C O bonds.
Enantioselective
intramolecular functionalization and isomerization of allenes
have recently been successfully performed with chiral
gold(I) complexes.[3,4a–c,6,18,19]
We chose the cyclohydroamination of g-allenyl-N-sulfona-
mides as a suitable reference reaction within this area of
gold catalysis. Our first tentative trials with the phospholane
gold(I) complexes were carried out with trinuclear C3-sym-
metric gold(I) complex 8a and a cyclic N-protected g-allenyl
tosylamide (s1) as a reference system (Scheme 3).
Similar to previous work reported by Toste and co-work-
ers,[19] silver salts as halide abstractors with non-coordinating
counterions, such as AgBF4 and AgOTf, were needed to
Nevertheless, the aurophilic attractive forces were weak,
as also observed previously for oligonuclear gold(I) com-
pounds.[10] In a low-temperature VT NMR study of com-
pound 8a, a single 31P NMR signal was observed over the
temperature range 295–200 K, albeit significantly broadened
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L. H. Gade et al.
reaction using AgOPNB was conducted at 208C instead of
508C, the loss of enantioselectivity was compensated at the
expense of reaction time (Table 1, entry 12). The weaker co-
ordinating trifluoroacetate counterion led to a slightly lower
enantiomeric excess (Table 1, entry 14).
Scheme 3. Allenes used in this study.
With the optimized system in hand, we evaluated the effi-
ciency of mono- and dinuclear complexes 6a and 7a to com-
pare their catalytic behavior to that observed for their trinu-
clear counterpart 8a (Table 2). Whilst the C3-symmetric
Table 1. Screening of experimental conditions in the asymmetric cyclo-
ACHTUNGTRENNUNG
hydroamination reaction of allene s1 with catalyst complex 8a.[a]
Table 2. Examination of the catalytic properties of complexes 6a, 7a,
and 8a in the hydroamination of allenes.[a]
Entry
Silver salt
Solvent
T
[8C]
t
ee
Entry Substrate Silver salt 6a
7a
8a
[h]
[%][b]
ee [%][b,c] ee [%][b,c] ee [%][b] t [h]
1
2
3
4
5
6
7
8
–
toluene
50
20
20
50
50
50
50
20
50
50
50
20
50
50
120[d]
0.5
0.5
48
48
48
48
120
48
48
20
48
20
rac
rac
rac
95
95
93
55
85
94
95
92
94
92
84
1
2
3
4
5
6
s1
s2
s3
AgOBz
AgOPNB
AgOBz
rac
rac
À21
36
36
22
29
33
40
95
92
94
91
91
87
48
20
48
12
24
10
AgBF4
AgOTf
–
–
–
–
AgOBz (1.0)[c]
AgOBz (0.8)[c]
AgOBz (1.2)[c]
AgOBz
AgOPNB À23
AgOBz
À15
–
AgOPNB À11
nitromethane
CH2Cl2
chlorobenzene
[a] All reactions were carried out with 5 mol% of AuI in toluene (1 mL)
at 508C. [b] Enantioselectivities determined by chiral HPLC. [c] Reaction
time: 120 h.
AgOBz
AgOBz
9
10
11
12
13
14
AgOPMB
AgOPNB
AgOPNB
AgODNB
CF3CO2Ag
toluene
–
–
–
–
complex provided high enantioselectivities (up to 95% ee),
C2-symmetric complex 7a gave moderate ee values (22–40%
ee). Surprisingly, monodentate complex 6a produced race-
mic mixtures when substrate s1 was studied. Moreover, un-
expectedly, the opposite enantiomer of the desired pyrroli-
dine was afforded to that derived from substrates s2 and s3.
We also found that complex 9, the N-benzylated analogue
of compound 7a, afforded virtually identical enantioselectiv-
ity (20% ee) for the cyclization of substrate s2, thus indicat-
ing that the catalyst performance was not significantly influ-
enced by structural variation at this position.
The electronic effect of the N-substitution of the allene
was clearly reflected in the differences in reactivity between
the substrates. Full conversion of the more-electron-with-
drawing N-substituted substrate (s3) was achieved with com-
plex 8a (reaction time: 10 h), but with a slight deterioration
of the enantiomeric excess (Table 2, entries 5 and 6). In-
creasing the reaction temperature (Table 2, entry 5) to 708C
and 1008C gave complete conversion after 18 h and 10 h, re-
spectively. Remarkably, these elevated temperatures only
led to a slight decrease in enantioselectivity (708C: 89% ee;
1008C: 82% ee). This result demonstrated the robust nature
of this trinuclear gold catalyst.
On the other hand, with the mesityl-substituted allene
(s4), longer reaction times were needed to achieve high or
full conversion with complex 8a (AgOBz: 67% conversion,
87% ee, 5 days; AgOPNB: 100% conversion, 84% ee, 48 h),
whilst less than 5% conversion was observed when the re-
lated mono- and dinuclear complexes 6a and 7a were used
instead.
Figure 4 shows the trend in enantioselectivity for the cy-
clohydroamination reaction versus the DPP gold complex
employed. To assess the scope of this approach, we carried
20
[a] All reactions were carried out with 5 mol% of AuI in 1 mL solvent.
Full conversion was always observed by H NMR spectroscopy. [b] Enan-
1
tioselectivities determined by chiral HPLC. [c] Number of equivalents
used with respect to AuI are shown in parentheses. [d] 12% yield.
provide extremely active systems; however, no enantioselec-
tivity was observed in these cases (Table 1, entries 2 and 3).
On the other hand, silver salts with more-coordinating
anions, such as silver benzoate (AgOBz), were suitable chlo-
ride-abstracting agents, thereby achieving full conversions
and high enantiomeric excesses (95% ee in both cases;
Table 1, entries 4). An equimolar amount of silver salt with
respect to gold was employed in all catalytic runs because
an excess or deficit of the AgI salt showed no gain either in
the activity or enantioselectivity (Table 1, entries 4–6), in
contrast to previous reports.[4,5,20] Toluene and chloroben-
zene were the optimal solvents, whilst the use of more-polar
solvents, such as nitromethane or CH2Cl2, led to an erosion
of the enantioselectivity (Table 1, entries 7, 8, and 9),
Next, we studied the electronic effect of the counteranion
in the silver salt; in particular, a silver salt with the electron-
donating para-methoxybenzoate counterion (AgOPMB) and
the corresponding silver salts with the electron-withdrawing
para-nitrobenzoate (AgOPNB) and 3,5-dinitrobenzoate
counterions (AgODNB). Similar activities and selectivities
to AgOBz were obtained with the electron-donating coun-
teranion silver salt AgOPMB (Table 1, entry 10). On the
other hand, the electron-withdrawing counteranion silver
salts AgOPNB and AgODNB (Table 1, entries 11 and 13)
were advantageous with respect to reaction times,[19] albeit
with a slight decrease in enantioselectivity. However, if the
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Gold-Catalyzed Cyclohydroaminations of g-Allenyl Sulfonamides
FULL PAPER
enantioselective catalysis. This result opened up the possibil-
ity of studying a series of chiral catalysts with increasing nu-
clearity from combining symmetry-equivalent sites.
Using the gold(I)-catalyzed cycloamination of g-allenyl
sulfonamides as a reference reaction allowed us to study the
influence of the nuclearity of the catalysts on their catalytic
performance. Interestingly, C3-symmetric trinuclear complex
8a surpassed its mono- and dinuclear congeners both in
terms of activity and enantioselectivity (up to 95% ee). Au-
rophilic interactions may be responsible for this intriguing
behavior.
Experimental Section
General: All manipulations were carried out under the exclusion of air
and moisture by using standard Schlenk and glove-box techniques, unless
otherwise stated. Argon 5.0, purchased from Messer Group GmbH, was
used after drying over Granusicꢃ phosphorus pentoxide (granulated).
Solvents were dried according to literature procedures[22] and stored in
glass ampules under an argon atmosphere. Et2O and n-pentane were dis-
tilled from sodium/potassium alloy, benzene and n-hexane from potassi-
um, MeOH over magnesium, CH2Cl2 and CHCl3 from calcium hydride,
and toluene from sodium. The same procedures were used to dry the
deuterated solvents. Degassed solvents were obtained by three successive
freeze–pump–thaw cycles. Triethylamine was degassed. (2S,5S)-1-Hy-
droxy-1-oxo-2,5-diphenylphospholane,[23] (2R,5R)-bis(1,1-hydroxymeth-
yl)-2,5-diphenylphospholanium chloride (1a),[13] (2R,5R)-bis(1,1-hydroxy-
methyl)-2,5-dimethylphospholanium chloride (1b),[13] bis
methylphospholanomethyl)methylamine (4b),[13] benzyl-bis
diphenylphospholanomethyl)amine (4c),[13] tris
((2R,5R)-2,5-diphenyl-
phospholanomethyl)amine (5a),[13] tris
(((2R,5R)-2,5-dimethyl-phospho-
lan-1-yl)methyl)amine (5b),[13] [Au(tht)Cl] (tht=tetrahydrothiophene),[24]
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
hydroamination substrates s1[19] and s2,[25] and silver salts AgOPNB,
AgOPMB, and AgODNB[26] were prepared according to literature proce-
dures. All other chemicals were used as received without further purifica-
tion. NMR spectra were recorded on Bruker Avance II (400 MHz) and
Bruker Avance III (600 MHz) instruments. Chemical shifts (d) are re-
ported in parts per million (ppm) and are referenced to residual proton
solvent signals or carbon resonances.[27] H3PO4 (31P) and was used as an
external standard. The following abbreviations were used: s (singlet), d
(doublet), dd (doublet of doublets), t (triplet), m (multiplet), br (broad
signal). Enantioselectivities were measured on a HPLC Agilent Technol-
Figure 4. Plot of enantioselectivity versus the nuclearity of the gold com-
plex (6a, 7a, and 8a). Halide abstractor: AgOPNB (top) and AgOBz
(bottom).
out an analogous study with DMP complexes 6b, 7b, and
8b, which contained methyl groups instead of phenyl sub-
stituents at positions 2 and 5 on the phospholane ring. As in
the case of the DPP series, chiral trinuclear complex 8b pro-
moted the reaction of substrate s2 to afford the correspond-
ing pyrrolidine with the highest enantioselectivity (AgOBz:
38% conversion, 75% ee, 120 h; AgOPNB: 100% conver-
sion, 75% ee, 72 h). However, compound 8b was less active
than compound 8a, presumably owing to its low solubility in
the reaction medium, whilst C2-symmetric complex 7b was
significantly more active than its Ph-substituted analogue
(AgOBz: 98% conversion, 34% ee, 120 h; AgOPNB: 100%
conversion, 35% ee, 48 h).[21]
ogies 1200 Series instrument using
a chiral Daicel Chiracel AD-H
column. Optical rotation data were acquired by using a PerkinElmer
Model 341 polarimeter. High-resolution mass spectra were aquired on
Bruker ApexQe hybrid 9.4 T FT-ICR (ESI) and JEOL JMS-700 magnet-
ic sector (FAB) spectrometers at the mass spectrometry facility of the In-
stitute of Organic Chemistry, the University of Heidelberg. Elemental
analysis was carried out in the Microanalysis Laboratory of the Heidel-
berg Chemistry Department.
Representative procedure for the preparation of complexes 6a, 7a, 7b,
8a, and 9: To a stirring solution of compound 3a (0.118 g, 0.40 mmol) in
CH2Cl2 (7 mL), [AuACHTNUTGRNEUNG(tht)Cl] (0.127 g, 0.40 mmol) was added under exclu-
sion of ambient light. After stirring for 10 min, the volatile compounds
were removed in vacuo. Recrystallization of the residue from CH2Cl2 and
Et2O gave compound 6a as a white microcrystalline solid. For compound
numbering, see the Supporting Information.
ChloridoACTHUNRTGNEUNG((((2S,5S)-2,5-diphenylphospholan-1-yl-kP)methyl)-N,N-dime-
thylamine)gold(I) (6a): Yield: 0.117 g (56%); 31P{1H} NMR (242.9 MHz,
CDCl3, 298 K): d=43.0 ppm (s); 1H NMR (600.1 MHz, CDCl3, 298 K):
d=7.49–7.25 (10H; ArH), 4.22–4.15 (m, 1H; H6), 3.82–3.69 (m, 1H;
H3), 2.87–2.77 (m, 1H; H2’), 2.72–2.54 (m, 2H; H4’ and H5’), 2.46 (dd,
Conclusion
A series of chiral mono, di-, and trinuclear gold(I)–phospho-
lane complexes were prepared and used in the first exam-
ples of chiral trinuclear gold(I) complexes employed in
2J(H,H)=13.9 Hz, 2J
ACTHNUGTRENNUGN ACHTUNGTRENNNUG
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3725

L. H. Gade et al.
298 K): d=139.4 (s; Cipso), 134.2 (d, 2J
G
phospholanium salt 1b (0.250 g, 1.18 mmol) was stirred in MeOH
(10 mL) for 10 min. A solution of Me2NH2Cl (0.100 g, 1.22 mmol) in
MeOH (2 mL) was then added and the mixture was stirred overnight.
31P{1H} NMR spectroscopy showed the presence of a single set of signals
that were attributed to monodentate ligand 3b. The mixture was then dis-
tilled. The amount of ligand was determined by addition of an internal
1
3
(ArC), 56.3 (d, J
N
(d, 1J(C,P)=31.0 Hz; C3), 46.8 (d, 1J
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
ACHTUNGTRENNUNG(C,P)=5.0 Hz; C4), 31.1 ppm (s, C5); HRMS (ESI(+)): m/z (%) calcd:
530.1079; found: 530.1054 (100) [M+H]+; elemental analysis calcd (%)
for C19H24NPAuCl: C 43.07, H 4.57, N 2.64; found: C 42.77, H 4.57,
N 2.63.
reference (PPh3) to a small aliquot of the distilled solution. [AuACHTUNGTRENNUNG(tht)Cl]
DichloridoACHTUNGTRENNUNG(bisACHTUNGTRENNUNG
(((2S,5S)-2,5-diphenylphospholan-1-yl-k2P)methyl)-N-
(0.133 g, 0.42 mmol) was added in situ. The volatile compounds were par-
tially removed in vacuo until precipitation of a crystalline white product
was observed, which was filtered off and washed with cold Et2O. Overall
yield: 0.093 g (13%); 31P{1H} NMR (242.9 MHz, CDCl3, 298 K): d=
36.9 ppm (s); 1H NMR (600.1 MHz, CDCl3, 298 K): d=3.00–2.88 (m, 2H;
H2), 2.64–2.55 (m, 1H; H3), 2.52 (s, 3H; H1), 2.42–2.33 (m, 1H; H6),
2.30–2.18 (m, 2H; H4/H5), 2.02–1.40 (m, 2H; H4/H5), 1.35 (dd, 3J-
methylamine)digold(I) (7a): Yield: 0.185 g (54%); 31P{1H} NMR
(242.9 MHz, CDCl3, 298 K): d=43.7 ppm (s); 1H NMR (600.1 MHz,
CDCl3, 298 K): d=7.38–7.22 (20H; ArH), 4.15–4.06 (m, 2H; H-6), 3.57–
3.48 (m, 2H; H3), 3.28 (dd, 2J(H,H)=14.2 Hz, 2J
ACTHUNTGRNENUG ACHTUNTGERN(NUGN H,P)=6.2 Hz; H2),
2.63–2.48 (m, 4H; H4 and H5), 2.33 (d, 2J
ACTHNUTRGNE(UNG H,H)=14.2 Hz, 2H; H2’),
2.27–2.11 (m, 4H; H4’ and H5’), 2.15 ppm (s, 3H; H1); 13C NMR
(H,P)=20.4 Hz, 3J
3J(H,P)=7.3 Hz; Me3); 13C{1H} NMR (150.9 MHz, CDCl3, 298 K): d=
54.6 (d, 1J(C,P)=41.9 Hz; C2), 47.6 (d, 3J(C,P)=7.0 Hz; C1), 35.6 (d, 1J-
(C,P)=34.5 Hz; C3), 35.6 (d, 2J(C,P)=1.8 Hz; C4/C5), 35.2 (d, 2J
(C,P)=
4.3 Hz; C4/C5), 35.0 (d, 1J(C,P)=37.4 Hz; C6), 20.4 (d, 2J
(C,P)=6.8 Hz;
Me6), 13.0 ppm (d, 2J
(C,P)=2.6 Hz; Me3); elemental analysis calcd (%)
for C9H20NPAuCl: C 26.65, H 4.97, N 3.45; found: C 26.19, H 4.87, N 3.32.
Trichlorido(tris
(((2S,5S)-2,5-dimethylphospholan-1-yl-k3P)methyl)-
amine)trigold(I) (8b): To a stirring solution of compound 5b (0.238 g,
0.59 mmol) in CH2Cl2/MeCN (1:1, 30 mL), [Au(tht)Cl] (0.570 g,
(H,P)=7.1 Hz; Me6), 1.25 ppm (dd, 3J
ACHUTGTNRENNUG ACHUTTGNREN(NUGN H,P)=14.5 Hz,
2
(150.9 MHz, CDCl3, 298 K): d=139.0 (s; Cipso), 133.7 (d, J
A
ipso’), 129.4–127.8 (ArC), 55.6 (dd, 1J
C2), 47.6 (d, 1J(C,P)=30.4 Hz; C3), 47.0 (d, 1J
(t, 3J(C,P)=5.5 Hz; C1), 35.6 (d, 2J
(C,P)=36.0 Hz, 3J
ACHUTGTNRENNUG CAHTUNGTRENNUNG
AHCTUNGTRENNUNG
C
A
ACHTUNGTRENNUNG
N
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
N
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
HRMS (ESI(+)): m/z (%) calcd: 964.1577; found: 964.1582 (100)
[MÀCl]+; elemental analysis calcd (%) for C35H39NP2Au2Cl2: C 42.02,
H 3.93, N 1.40; found: C 42.24, H 3.86, N 1.70.
AHCTUNGTRENNUNG
DichloridoACHTUNGTRENNUNG(bisACHTUNGTRENNUNG
(((2S,5S)-2,5-dimethylphospholan-1-yl-k2P)methyl)-N-
A
ACHTUNGTRENNUNG
methylamine)digold(I) (7b): Yield: 0.322 g (71%); 31P{1H} NMR
(242.9 MHz, CDCl3, 298 K): d=36.6 ppm (s); 1H NMR (600.1 MHz,
CDCl3, 298 K): d=3.45–3.29 (m, 4H; H2), 2.77 (s, 3H; H1), 2.69–2.60
(m, 2H; H3), 2.53–2.43 (m, 2H; H6), 2.34–2.18 (m, 4H; H4 and H5),
AHCTUNGTRENNUNG
1.78 mmol) was added in the dark. After stirring for 10 min, a white crys-
talline solid formed, which was filtered off and washed with CH2Cl2 (1ꢅ
5 mL) and Et2O (2ꢅ5 mL). Yield: 0.569 g (87%); 31P{1H} NMR
(242.9 MHz, [D6]DMSO, 298 K): d=30.1 ppm (br s); 1H NMR
(600.1 MHz, [D6]DMSO, 298 K): d=4.12–3.91 (m, 6H; H1), 2.79–2.67
(m, 6H; H2 and H5), 2.28–2.08 (m, 6H; H3 and H4), 1.73–1.62 (m, 3H;
H3’/H4’), 1.49–1.40 (m, 3H; H3’/H4’), 1.27–1.16 ppm (m, 18H; Me2 and
Me5); 13C{1H} NMR (150.9 MHz, [D6]DMSO, 298 K): d=51.0 (br s; C1),
1.60–1.50 (m, 2H; H4’), 1.49–1.40 (m, 2H; H5’), 1.31 (dd, 3J
20.6 Hz, 3J(H,P)=7.1 Hz; Me6), 1.27 ppm (dd, 3J
(H,P)=7.3 Hz; Me3); 13C{1H} NMR (150.9 MHz, CDCl3, 298 K): d=53.9
(dd, 1J(C,P)=41.1 Hz, 3J(C,P)=6.3 Hz; C2), 48.1 (t, 3J
(C,P)=6.3 Hz;
C1), 35.8 (d, 2J(C,P)=1.8 Hz; C4), 35.5 (d, 1J
(C,P)=34.0 Hz; C3), 35.3
(d, 1J(C,P)=36.3 Hz; C6), 35.3 (d, 2J(C,P)=4.7 Hz; C5), 20.5 (d, 2J-
(C,P)=6.7 Hz; Me6), 13.4 ppm (d, 2J
(C,P)=3.0 Hz; Me3); HRMS
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
35.8 (s; C3/C4), 35.5 (d; 2J
34.1 Hz; C2/C5), 34.6 (d, 1J(C,P)=35.2 Hz; C2/C5), 20.4 (d, 2J
7.0 Hz; Me2/Me5), 13.2 ppm (d, 2J
(C,P)=2.0 Hz; Me2/Me5); HRMS
(C,P)=4.8 Hz; C3/C4), 35.2 (d, 1J
ACHUTGTNRENNUG ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
(ESI(+)): m/z (%) calcd: 716.0951; found: 716.0953 (40) [MÀCl]+; ele-
mental analysis calcd (%) for C15H31NP2Au2Cl2: C 23.95, H 4.15, N 1.86;
found: C 23.65, H 4.03, N 2.02.
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
(ESI(+)): m/z (%):1136.0227 (85) (calcd: 1136.0229) [M+K]+, 1120.0490
(23) (calcd: 1120.0490) [M+Na]+, 1062.0902 (40) (calcd: 1062.0904)
[MÀCl]+; elemental analysis calcd (%) for C21H42NP3Au3Cl3: C 22.96,
H 3.85, N 1.27; found: C 22.69, H 3.83, N 1.29.
TrichloridoACHTUNGTRENNUNG(trisACHTUNGTRENNUNG
(((2S,5S)-2,5-diphenylphospholan-1-yl-k3P)methyl)-
amine)trigold(I) (8a): Yield: 0.143 g (53%); 31P{1H} NMR (242.9 MHz,
CDCl3, 298 K): d=41.1 ppm (s); 1H NMR (600.1 MHz, CDCl3, 298 K):
d=7.36–7.16 (30H; ArH), 4.13–4.06 (m, 3H; H2), 3.98–3.88 (m, 3H;
H1), 3.88–3.80 (m, 3H; H5), 2.78–2.66 (m, 3H; H4), 2.56–2.40 (m, 6H;
General procedure for the cyclohydroamination reaction: A mixture of
the gold(I) complex (0.015 mmol Au) and the corresponding silver(I) salt
(0.015 mmol) was stirred in the solvent (dry and degassed, 0.5 mL) at RT
for 10 min in the dark. Then, a solution of the g-allenyl sulfonamide
(0.3 mmol) in solvent (dry and degassed, 0.5 mL) was added and the re-
action mixture was stirred at the denoted temperature (208C or 508C).
H3 and H3’), 2.05–1.95 (m, 3H; H4’), 1.73 ppm (dd, 2J
2J
d=139.5 (d, 2J
129.5–127.8 (ArC), 54.0 (dt, 1J
(d, 1J(C,P)=31.8 Hz; C2), 46.9 (d, 1J
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
E
ACHTUNGTRENNUNG
1
The progress of the reaction was monitored by H NMR spectroscopy.
G
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG(C,P)=5.2 Hz; C4), 31.3 ppm (s; C3); HRMS (ESI(+)): m/z (%) calcd:
Upon completion, the crude mixture was loaded directly onto a silica gel
column. Purification by column chromatography on silica gel (pentane/
EtOAc=5:1) gave the cyclized product.
1434.1843; found: 1434.1853 (51) [MÀCl]+; elemental analysis calcd (%)
for C51H54NP3Au3Cl3: C 41.64, H 3.70, N 0.95; found: C 41.28, H 3.67,
N 0.98.
X-ray diffraction study: For the crystal data and details of the structure
determination, see the Supporting Information. Full shells of intensity
data were collected at low temperature (T=100 K) with a Bruker AXS
Smart 1000 CCD diffractometer (MoKa radiation, graphite monochroma-
tor, l=0.71073 ꢄ). Data were corrected for air and detector absorption,
and Lorentz and polarization effects;[28] absorption by the crystal was
treated numerically[29] (complexes 6b and 8a) or with a semiempirical
multiscan method.[29–31] The structures were solved by conventional direct
methods[32,33] (complexes 6a, 8a, and 9) or by the heavy-atom method
combined with structure expansion by direct methods applied to differ-
ence structure factors[34] (complexes 6b and 8b) and refined by full-
matrix least-squares methods based on F2 against all of the unique reflec-
tions.[33,365 All non-hydrogen atoms were given anisotropic displacement
parameters. Hydrogen atoms were placed at calculated positions and re-
fined with a riding model. Crystals of compound 8b were twinned; after
de-twinning (approx. twin fractions 0.71:0.29), refinement was carried out
against all observations involving domain 1. Adp and geometry restraints
were applied to the disordered phenyl rings in compound 8a. Owing to
severe disorder and fractional occupancy, electron density attributed to
DichloridoACHTUNGTRENNUNG(bisACHTUNGTRENNUNG
(((2S,5S)-2,5-diphenylphospholan-1-yl-k2P)methyl)-N-ben-
zylamine)digold(I) (9): The corresponding ligand for the preparation of
this complex was synthesized according to a literature procedure.[13]
Yield: 0.207 g (66%); 31P{1H} NMR (242.9 MHz, CD3Cl, 298 K): d=
43.5 ppm (s); 1H NMR (600.1 MHz, CD3Cl, 258C): d=7.37–7.10 (25H;
2
ArH), 4.28 (d, J
G
2
3.35 (m, 4H; H2 and H6), 2.57 (d, J
(m, 4H; H4 and H5), 2.15 (dd, 2J(H,H)=14.4 Hz, 2J
H2’), 2.07–1.93 ppm (m, 4H; H4’ and H5’); 13C NMR (150.9 MHz, C6D6,
298 K): d=139.6 (s; Cipso), 136.4 (s; Cipso’), 133.7 (d, 2J
(C,P)=4.9 Hz;
ipso’’), 130.3–127.8 (ArC), 61.1 (t, 3J(C,P)=6.2 Hz; C1), 52.1 (dd, 1J-
(C,P)=40.2 Hz, 3J(C,P)=6.8 Hz; C2), 47.1 (d, 1J
(C,P)=30.3 Hz; C6),
47.1 (d, 1J(C,P)=31.3 Hz; C3), 35.7 (d, 2J
(C,P)=4.8 Hz; C4/C5),
C
G
A
31.2 ppm (s; C4/C5); HRMS (FAB(+)): m/z (%) calcd: 1040.1890;
found: 1040.1847 (100) [MÀCl]+; elemental analysis calcd (%) for
C41H43Au2Cl2NP2: C 45.74, H 4.03, N 1.30; found: C 45.47, H 4.08, N 1.32.
ChloridoACHTUNGTRENNUNG((((2S,5S)-2,5-dimethylphospholan-1-yl-kP)methyl)-N,N-dime-
thylamine)gold(I) (6b): A mixture of MeONa (0.317 g, 5.87 mmol) and
3726
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 3721 – 3728

Gold-Catalyzed Cyclohydroaminations of g-Allenyl Sulfonamides
FULL PAPER
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We thank the Deutsche Forschungsgemeinschaft for their financial sup-
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