Bulky acyclic aminooxycarbene ligands

Article abstract of DOI:10.1021/om200602k

A series of sterically demanding acyclic aminooxycarbenes (AAOCs) were prepared in good yields from chloroiminium salts and alkoxysilanes via the TMS-Cl elimination pathway. The steric profiles of bulky AAOCs were determined by X-ray crystallographic stud

Full text of DOI:10.1021/om200602k

ARTICLE
pubs.acs.org/Organometallics
Bulky Acyclic Aminooxycarbene Ligands
Hwimin Seo, David R. Snead, Khalil A. Abboud, and Sukwon Hong*
Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville, Florida 32611-7200, United States
S Supporting Information
b
ABSTRACT: A series of sterically demanding acyclic aminoox-
ycarbenes (AAOCs) were prepared in good yields from chlor-
oiminium salts and alkoxysilanes via the TMS-Cl elimination
pathway. The steric profiles of bulky AAOCs were determined
by X-ray crystallographic studies of the Au(I) complexes. The
percent buried volume values (%VBur) of the AAOC ligands
range from 35.8% to 47.9%. Acyclic aminooxycarbenes maintain
coplanarity around the carbene center, in sharp contrast to the
similarly bulky acyclic diaminocarbenes that show significant distortion from the coplanarity. The Au(I) complexes of AAOCs
exhibited high efficiency in the hydroamination of alkenyl ureas. Bulkier AAOCꢀAu(I) complexes displayed faster reaction rates
and higher conversions. The reaction rate, yield, and stereoselectivity observed with the AAOCꢀAu(I) catalyst were better than
those with acyclic diaminocarbene Au catalysts and comparable to the best results reported to date.
’ INTRODUCTION
Although N-heterocyclic diaminocarbenes (NHCs) have
emerged as an important class of ligands in catalysis,1 their N,
O-congeners, cyclic aminooxycarbenes (CAOCs), have not
been frequently encountered as ancillary ligands despite having
a different electronic profile (Figure 1).2,3 The structural variety
of CAOCs is rather limited because both bonds of oxygen are
incorporated in the heterocyclic core. Furthermore, CAOCs
are less bulky than NHCs, because an oxygen lone pair in
Figure 1. Steric profiles of diaminocarbenes and aminooxycarbenes.
AAOCꢀAu(I) complexes and their remarkable efficiency in the
CAOCs does not exert the same level of steric protection as the
intramolecular hydroamination of alkenyl ureas.
flanking N substituents in NHCs. Considering that steric
tuning of NHC ligands is often critical in the optimization
process and that, generally, NHC ligands bearing bulky N
substituents effectively promote a wide variety of reactions,4
the inherent lack of such possibilities could be a serious
limitation in the potential development of CAOCs as useful
ligands. We envisioned that acyclic aminooxycarbenes (AAOCs),
in contrast, could impose the steric bulk if the nitrogen sub-
stituents are large enough to position the oxygen substit-
uent toward the metal center in the preferred conformation
(Figure 1c).
Typically, AAOCꢀmetal complexes have been prepared from
addition of alcohols to metalꢀisocyanide complexes5 or addition
of amines to metalꢀCO complexes.6 However, these methods
cannot be used to make AAOCs featuring bulky substituents on
both oxygen and nitrogen atoms.7 The free carbenes of sterically
demanding AAOCs were developed by the research group of
Alder8 and Bertrand,9 although no catalytic activity was reported.
To the best of our knowledge, examples of AAOCꢀmetal
catalyzed reactions are rare.10 In the pursuit of acyclic amino-
carbeneꢀmetal catalysts,11 we recently developed highly bulky
acyclic diaminocarbenes (ADCs) displaying unique ligand prop-
erties in gold catalysis.11a Herein, we report the synthesis of bulky
’ RESULTS AND DISCUSSION
Alkoxyiminium salts (1aꢀ1e) were prepared from alkoxysi-
lanes and chloroiminiums, following the TMS-Cl elimination
protocol that was effective in the synthesis of analogous for-
mamidinium salts11a (Scheme 1). Corresponding gold(I) com-
plexes (2aꢀ2e) were then synthesized by deprotonation of the
alkoxyiminium salts, followed by metalation with Me2S AuCl.
3
The three-dimensional structure of AAOCꢀAuCl complexes
12
(2aꢀ2e) was characterized by X-ray crystallography, and the %
buried volume (%VBur
)
was calculated to compare steric
properties of newly prepared AAOC ligands (Figure 2).13 To
our delight, the AAOC ligands in 2d and 2e are highly sterically
demanding as the oxygen substituent is oriented proximal to the
metal, and their %VBur values (44.7%/47.9% and 45.8%) are
comparable to those of other known bulky diaminocarbenes,
such as IPr14 (45.6%) or the Ph2Ad2-ADC in 2f (45.7%).11a The
X-ray data also revealed unique structural features of AAOC
Received: July 7, 2011
Published: October 06, 2011
r
2011 American Chemical Society
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Scheme 1. Synthesis of AAOCꢀAu(I) Complexes
Figure 2. X-ray structures of acyclic aminocarbeneꢀgold(I) complexes. a%VBur values are calculated using X-ray crystallographic data. bTwo
conformationally similar structures found in the crystal unit cell (see the Supporting Information for details).
Table 1. Selected Bond Lengths [Å], Angles [°], and Torsion Angles [°] for 2aꢀ2e
ꢀ
bond lengths [Å]
2a
2b
2c
2d
2e
NꢀCcarbene
OꢀCcarbene
AuꢀCcarbene
AuꢀCl
1.317(2)
1.331(2)
2.007(2)
2.2910(5)
1.330(2)
1.325(2)
1.996(2)
2.2834(6)
1.336(5)
1.336(4)
2.005(4)
2.287(1)
1.328(2), 1.314(2)
1.345(2), 1.345(2)
1.983(2), 1.990(2)
2.2883(6), 2.2768(4)
1.319(2)
1.353(2)
1.996(1)
2.2820(4)
bond angles [deg]
2a
2b
2c
2d
2e
NꢀCcarbeneꢀO
Ccarbeneꢀ AuꢀCl
111.5(2)
112.5(2)
110.7(3)
176.3(1)
110.7(2), 11.6(2)
110.9(1)
173.45(5)
178.39(5)
175.13(5), 177.63(6)
178.41(4)
torsion angles [deg]
2a
2b
2c
2d
2e
CꢀNꢀCcarbeneꢀO
2.2(3)
1.3(2)
6.3(4)
1.2(2), 3.4(2)
5.6(2)
ligands distinct from the ADCs. In AAOCs, the R1 position of
the N substituent (which is distal from the metal and proximal
to the oxygen lone pair) seems to accommodate steric bulk better
than the R2 position. For example, 2b prefers the adamantyl
group at the R1 position (away from the metal), whereas related
ADCꢀAuCl 2f has the adamantyl group toward the metal center.
It is interesting to note that, in 2cꢀ2e, the R1 position is
preferentially taken by ortho-disubstituted phenyl rings (2,6-
diisopropylphenyl or 2,6-dimethylphenyl) over bulky alkyl
groups, such as isopropyl, cyclohexyl, or adamantyl. In addition,
AAOCꢀAuCl (2aꢀ2e) displayed a relatively small dihedral
angle of CꢀNꢀCꢀO (ranging from 1.2° to 6.3°), in sharp
contrast to ADCꢀAuCl (2f),11a showing significant distortion
from coplanarity (CꢀNꢀCꢀN dihedral angle: 41.0°) (Table 1).
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Figure 3. Variable-temperature 1H NMR of AAOCꢀAu(I) complexes.15
heating. The new signals were from the conformational isomer
(2b0) of 2b. Heating of 2b at 45 °C for 24 h led the ratio of 2b and
2b0 to be 2.5:1. The equilibrium between 2b and 2b0 seems to be
reached very slowly at low temperatures, but becomes quicker as
the temperature increased. 2b0 was separated from 2b, and
heating 2b0 at 90 °C yielded an approximately 2:1 ratio of 2b
and 2b0 (Figure 3b). No additional peaks appeared when 2c and
2e were heated to 90 °C, and the chemical shifts remained within
0.2 ppm (Figure 3c,d). Potentially, bulky nitrogen substituents
block rotation about the CcarbeneꢀN bond.
Recently, ADCs have attracted attention from the synthetic
community as alternative ligands in Au catalysis.11a,16 New
AAOCꢀAu(I) complexes (2aꢀ2e) were tested in Au-catalyzed
intramolecular hydroamination of alkenyl ureas since sterically
demanding diaminocarbene ligands showed high rates of re-
action.11a,17 Figure 4 illustrates that a similar trend was observed
with AAOCs. Thus, faster rates and higher conversions were
displayed by the bulkier AAOCs (2e > 2d > 2a), and it is important
to note that highly bulky AAOCꢀAu catalysts (2d and 2e)
exhibited much higher reactivity than the analogous ADCꢀAu
catalyst 2f. Furthermore, less bulky AAOCs (2aꢀ2c) also
showed noticeable conversions at room temperature,18 whereas
the use of diaminocarbenes (NHCs and ADCs) of similar steric
demand (%VBur less than 40%) resulted in negligible product
formation under the same conditions.11a
Figure 4. Reaction profile of Au(I)-catalyzed hydroamination.
AAOCs seem to maintain coplanarity around the carbene
carbon, owing to the fact that there is much less steric interaction
between R1 and the oxygen lone pair (or R3). The conforma-
tional stability of the AAOCꢀAu(I) complexes was investigated
through collection of variable-temperature NMR (VT-NMR)
spectra of 2b, 2c, and 2e (Figure 3). The proton peaks of 2b were
unchanged until 40 °C. At 45 °C, new signals appeared, and as
the temperature increased, the size of the new peaks increased
(Figure 3a). A 2:1 ratio of the old to new signals was reached at
90 °C, and this relationship was maintained even after 1 h of
The optimized AAOCꢀAu catalyst 2e is effective for catalytic
hydroamination of various alkenyl ureas (Table 2). Methanol was
disclosed to be a better solvent for the reaction with 3a as it was for
IPrꢀAu catalyzed hydroamination reactions (entry 1 vs 2).17b
With gem-dialkyl substitution, the reaction proceeded smoothly
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Table 2. Hydroamination of Alkenyl Ureas Catalyzed by
from the metal. Importantly, one of the most sterically demand-
ing AAOCꢀAu(I) catalysts (2e) exhibited high efficiency in
intramolecular hydroamination of various alkenyl ureas. The reac-
tion rate, yield, and stereoselectivity observed with AAOCꢀAu(I)
catalysts were better than those with acyclic diaminocarbene
(ADC) Au catalysts and comparable to the best results reported
to date. To the best of our knowledge, this report represents the
first effective example of aminooxycarbene ligands used in Au
catalysis. More detailed investigation on the electronic nature of
AAOCs and further applications of AAOC ligands in catalysis are
ongoing in our laboratory.
AAOCꢀAu(I)a
’ EXPERIMENTAL SECTION
General. All reactions were conducted in flame-dried glassware
under an inert atmosphere of dry argon. THF, CH2Cl2, and toluene
were purified under a positive pressure of dry nitrogen by a Meyer
Solvent Dispensing System prior to use. 1,4-Dioxane was dried over Na/
benzophenone and was distilled. All the other chemicals used were
purchased from Sigma-Aldrich Co., Acros Organics, and Strem Chemi-
cals Inc. and were used as received without further purification. NMR
spectra were recorded using a Mercury-300 FT-NMR, operating at
300 MHz for 1H NMR and at 75.4 MHz for 13C NMR. All chemical shifts
for 1H and 13C NMR spectroscopy were referenced to residual signals
from CDCl3 (1H) 7.27 ppm and (13C) 77.23 ppm. High-resolution mass
spectra were recorded on a Finnigan MAT95Q Hybrid Sector spectro-
meter or an Agilent 6210 TOF-LC/MS.
1-Adamantanoxy-N,N-dimethylmethanaminium Chloride
(1a). Oxalyl chloride (0.85 mL, 10 mmol) was added dropwise to a
toluene (15 mL) solution of diisopropylformamide (0.818 g, 6.33 mmol)
at ꢀ78 °C. The solution was stirred for 2 h at room temperature before
evaporating all the volatiles in vacuo. CH2Cl2 (10 mL) was added to
the dry mixture, and then 1-adamantyloxytrimethylsilane (1.46 g, 6.51
mmol) was added at ꢀ78 °C. After stirring for 3 h at room temperature,
the solution was concentrated to 3 mL. The concentrated solution was
dropped into vigorously stirred hexanes (20 mL). Washing the pre-
cipitated solid with additional hexanes (60 mL) gave 1a as a white solid
(1.34 g, 71%). 1H NMR (300 MHz, CDCl3): δ 10.22 (s, 1H), 5.20ꢀ4.98
(m, 1H), 3.92ꢀ3.77 (m, 1H), 2.31 (br s, 3H), 2.27ꢀ2.18 (m, 6H),
1.79ꢀ1.53 (m, 6H), 1.39 (d, J = 6.8 Hz, 6H), 1.38 (d, J = 6.8 Hz, 6H).
13C NMR (75 MHz, CDCl3): δ 165.4, 93.4, 56.9, 49.5, 42.0, 35.2, 31.7,
20.7, 20.0. HRMS-ESI (m/z): [M ꢀ Cl]+ calcd for C17H30NO,
264.2327; found, 264.2322.
1-Adamantanoxy-N-(1-adamantyl)-N-phenylmethanami-
nium Chloride (1b). With the same method used in the synthesis of
1a, 1b (73%) was obtained as a white solid from N-(1-adamantyl)-N-
phenylformamide and 1-adamantyloxytrimethylsilane. 1H NMR (300 MHz,
CDCl3): δ 9.75 (s, 1H), 7.56ꢀ7.42 (m, 3H), 7.16ꢀ7.06 (m, 2H),
2.32ꢀ2.10 (m, 19H), 1.78ꢀ1.53 (m, 11H). 13C NMR (75 MHz,
CDCl3): δ 165.9, 133.7, 130.2, 129.8, 127.4, 94.9, 66.7, 41.8, 41.6,
35.3, 35.2, 31.8, 30.1. HRMS-ESI (m/z): [M ꢀ Cl]+ calcd for
C27H36NO, 390.2791; found, 390.2787.
1-Adamantanoxy-N-(2,6-diisopropylphenyl)-N-isopropyl-
methanaminium Chloride (1c). With the same method used in
the synthesis of 1a, 1c (55%) was obtained as a white solid from
N-(2,6-diisopropylphenyl)-N-isopropylformamide and 1-adamantyloxytri-
methylsilane. 1H NMR (300 MHz, CDCl3): δ 11.39 (s, 1H),
7.52ꢀ7.36 (m, 1H), 7.33ꢀ7.19 (m, 2H), 5.01ꢀ4.88 (m, 1H),
2.77ꢀ2.61 (m, 2H), 2.31ꢀ2.22 (m, 9H), 1.79ꢀ1.58 (m, 6H), 1.54 (d,
J = 6.8 Hz, 6H), 1.29 (d, J = 6.8 Hz, 6H), 1.11 (d, J = 6.8 Hz, 6H). 13C
NMR (75 MHz, CDCl3): δ 169.4, 144.5, 131.0, 130.0, 125.2, 94.7, 60.3,
42.1, 35.1, 31.8, 29.3, 25.7, 23.3, 22.4. HRMS-ESI (m/z): [M ꢀ Cl]+
calcd for C26H40NO, 382.3110; found, 382.3108.
a 0.05 M conc. [LAuCl] and AgOTf were stirred for 30 min before
addition of 3. b Isolated yield. c Determined by 1H NMR. d Dioxane used
as a solvent. e Methanol used as a solvent. f Conversion determined by 1H
NMR. The combined yields of the recovered substrates and the products
were 98% (entries 6, 7, 9) and 97% (entry 10).
at room temperature to afford five-membered pyrrolidines
(entries 2, 3, and 5) and a six-membered piperidine product
(entry 4). The reaction also tolerates more challenging sub-
strates, including a 2,2-disubstituted alkene substrate (entry 3).
Less reactive substrates without gem-dialkyl substituents af-
forded better yields at higher reaction temperatures and catalysts
loading in 1,4-dioxane rather than in methanol (entries 8, 10). It
is noteworthy that AAOCꢀAu catalyst 2e exhibited a better yield
and improved cis-selectivity compared with ADCꢀAu catalyst
2f for the formation of 2,3,3,5-tetrasubstituted pyrrolidine 4d
(entry 5 vs 6) and 3,5-disubstituted pyrrolidine 4e (entry 7 vs 8).
These results are also comparable to those obtained by IPrAuCl,
the best gold catalyst for hydroamination of alkenyl ureas known
to date.19
’ CONCLUSION
Sterically demanding acyclic aminooxycarbenes (AAOCs)
and their gold complexes were prepared. X-ray crystallographic
studies revealed unique structural features of these bulky AAOC
ligands, including coplanarity around the carbene center and the
preferential placement of the bulky nitrogen substituent away
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2,6-Diisopropylphenoxy-N-cyclohexyl-N-(2,6-diisopropyl-
phenyl)methanaminium Chloride (1d). With the same method
used in the synthesis of 1a, 1d (42%) was obtained as a white solid from
N-(2,6-diisopropylphenyl)-N-cyclohexylformamide and 2,6-diisopro-
HRMS-ESI (m/z): [M + Na]+ calcd for C31H45AuClNNaO, 702.2753;
found, 702.2747.
[N-(1-Adamantyl-N-(2,6-dimethylphenyl)-O-(2,6-diisopro-
pylphenyl)aminooxycarbene]gold(I) Chloride (2e). With the
same method used in the synthesis of 2a, 2e (81%) was obtained as an
1
pylphenyloxytrimethylsilane. H NMR (300 MHz, CDCl3): δ 10.26
1
(s, 1H), 7.56ꢀ7.48 (m, 1H), 7.40ꢀ7.34 (m, 2H), 7.33ꢀ7.27 (m, 1H),
7.22ꢀ7.14 (m, 2H), 4.25ꢀ4.12 (m, 1H), 3.13ꢀ3.00 (m, 2 H),
2.92ꢀ2.79 (m, 2 H), 2.48ꢀ2.36 (m, 2H), 2.01ꢀ1.89 (m, 2H),
1.87ꢀ1.64 (m, 3H), 1.46ꢀ1.17 (m, 27H). 13C NMR (75 MHz, CDCl3):
δ 169.0, 149.2, 144.5, 138.7, 131.4, 129.1, 125.8, 125.4, 123.6, 68.1, 32.3,
29.4, 27.5, 25.7, 25.0, 24.8, 23.0. HRMS-APCI (m/z): [M ꢀ Cl]+ calcd for
C31H46NO, 448.3574; found, 448.3580.
off-white solid. H NMR (300 MHz, CDCl3): δ 7.22ꢀ6.96 (m, 6H),
3.01ꢀ2.85 (m, 2H), 2.64 (br s, 6H), 2.39 (s, 6H), 2.18 (br s, 3H),
1.77ꢀ1.61 (m, 6H), 1.35 (d, J = 6.8 Hz, 6H), 0.94 (d, J = 7.1 Hz, 6H).
13C NMR (75 MHz, CDCl3): δ 214.7, 152.3, 139.9, 139.0, 134.0, 129.0,
128.4, 127.6, 124.4, 66.4, 44.1, 36.0, 30.8, 27.4, 24.0, 23.0, 20.6. HRMS-
ESI (m/z): [M + Na]+ calcd for C31H41AuClNNaO, 698.2440; found,
698.2442.
Au(I)-Catalyzed Intramolecular Hydroamination of Alke-
nyl Ureas. Reactions for Figure 4. A mixture of a goldꢀchloride
complex (5.0 μmol) and AgOTf (5.0 μmol) in 1,4-dioxane (2.0 mL) was
stirred for 30 min before adding N-(2,2-Diphenyl-4-pentenyl)-N0-phe-
nylurea (3a)17b (0.100 mmol). After stirring the reaction mixture for a
specified time at room temperature, an aliquot (0.3 mL) of the reaction
solution was taken and filtered through a short pad of silica gel. The pad
was rinsed with EtOAc. After evaporation of the solvent in vacuo, the
conversion was calculated by 1H NMR comparing the integration of the
reactant (3a) and the product (4a).17b
2,6-Diisopropylphenoxy-N-(1-adamantyl)-N-(2,6-dimethyl-
phenyl)methanaminium Chloride (1e). With the same method
used in the synthesis of 1a, 1e (68%) was obtained as a white solid from
N-(2,6-dimethylphenyl)-N-(1-adamantyl)formamide and 2,6-diisopro-
pylphenyloxytrimethylsilane. 1H NMR (300 MHz, CDCl3): δ 11.84 (s,
1H), 7.34ꢀ7.19 (m, 4H), 7.18ꢀ7.07 (m, 2H), 3.01ꢀ2.70 (m, 2H), 2.43
(s, 12H), 2.24 (br s, 3H), 1.89ꢀ1.77 (m, 3H), 1.69ꢀ1.57 (m, 3H), 1.21
(d, J = 6.7 Hz, 12H). 13C NMR (75 MHz, CDCl3): δ 172.5, 149.3, 138.5,
133.9, 133.4, 130.2, 129.9, 129.1, 124.8, 70.0, 42.4, 35.1, 30.8, 27.8, 23.4,
20.0. HRMS-ESI (m/z): [M ꢀ Cl]+ calcd for C31H42NO, 444.3266;
found, 444.3276.
Reactions for Table 2. A mixture of a goldꢀchloride complex (5 or
10 mol %) and AgOTf (5 or 10 mol %) in 1,4-dioxane (2.0 mL) or MeOH
(2.0 mL) was stirred for 30 min before adding 317b (0.100 mmol). After
stirring the reaction mixture for a specified time at a specified temperature,
the solvent was evaporated. Short column chromatography (silica gel, 3:1
hexane/EtOAc) gave the desired product or a mixture of the reactant and
the product. For reactions that were not completed, conversion was
calculatedby1HNMRcomparing the integration of therecoveredreactant
and the product.17b The regioselectivity was calculated by 1H NMR.17b
Variable-Temperature 1H NMR. VT-NMR for 2b and 2b0. 1H
NMR spectra of 2b dissolved in toluene-d8 were measured at 30, 40, 45,
50, 60, 70, 80, and 90 °C, 5 min after reaching the desired temperature.
The same sample was heated at 90 °C for 1 h, and the 1H NMR spectrum
was measured again. Another fresh sample of 2b in toluene-d8 was
prepared and heated at 45 °C for 24 h. 1H NMR spectrum of the sample
was measured. 2b0 was separated from the first NMR sample by column
[N-Diisopropyl-O-(1-adamantyl)aminooxycarbene]gold-
(I) Chloride (2a). To a suspension of 1a (60.2 mg, 0.201 mmol) in
THF (2 mL) was added LiHMDS (1.0 M solution in THF) (0.22 mL,
0.22 mmol) at ꢀ78 °C. After stirring the reaction mixture at the same
temperature for 15 min, Me2S AuCl (64.8 mg, 0.220 mmol) was added .
3
The mixture was stirred at 0 °C for 1 h. Column chromatography (silica
gel, 5:1 hexanes/EtOAc) gave 2a (65.1 mg, 32.4%) as an off-white solid.
1H NMR (300 MHz, CDCl3): δ 5.62ꢀ5.44 (m, 1H), 3.73ꢀ3.54 (m, 1
H), 2.56ꢀ2.40 (m, 4H), 2.35ꢀ2.20 (br s, 2H), 1.81ꢀ1.64 (br s, 5H),
1.63ꢀ1.47 (br s, 3H), 1.38 (d, J = 6.8 Hz, 6H), 1.28 (d, J = 6.8 Hz, 6H),
0.96ꢀ0.75 (m, 1H). 13C NMR (75 MHz, CDCl3): δ 203.2, 86.0, 48.9,
43.5, 36.0, 31.4, 29.9, 21.1, 20.6. HRMS-DIP-CI (m/z): [M + H]+ calcd
for C17H30AuClNO, 496.1682; found, 496.1666.
[N-(1-Adamantyl)-N-phenyl-O-(1-adamantyl)aminooxy-
carbene]gold(I) Chloride (2b). With the same method used in the
synthesis of 2a, 2b (61%) was obtained as an off-white solid. 1H NMR
(300 MHz, CDCl3): δ 7.45ꢀ7.28 (m, 3H), 7.20ꢀ7.02 (m, 2H), 2.55 (d,
J = 2.8 Hz, 6H), 2.27 (br s, 3H), 2.07 (s, 9 H), 1.70 (br s, 6H), 1.62 (br s,
6H). 13C NMR (75 MHz, CDCl3): δ 207.8, 143.7, 129.7, 129.2, 128.9,
87.8, 65.0, 43.3, 41.6, 36.2, 36.0, 31.4, 30.4. HRMS-DIP-CI (m/z):
[M ꢀ Cl]+ calcd for C27H35AuNO, 586.2384; found, 586.2365.
[N-(2,6-Diisopropylphenyl)-N-isopropyl-O-(1-adamantyl)-
aminooxycarbene]gold(I) Chloride (2c). With the same method
used in the synthesis of 2a, 2c (68%) was obtained as an off-white solid.
1H NMR (300 MHz, CDCl3): δ 7.34ꢀ7.22 (m, 1H), 7.17 (d, J = 7.9 Hz,
2H), 5.16ꢀ5.02 (m, 1H), 2.76ꢀ2.63 (m, 2H), 2.27 (br s, 6H), 2.16 (br s,
3H), 1.60 (br s, 6H), 1.35 (dd, J = 0.9, 6.7 Hz, 6H), 1.25 (d, J = 6.7 Hz,
6H), 1.11 (d, J = 6.7 Hz, 6H). 13C NMR (75 MHz, CDCl3): δ 207.3,
144.6, 134.6, 129.2, 124.4, 86.8, 59.8, 43.3, 35.9, 31.3, 29.1, 25.9, 23.8,
22.9. HRMS-ESI (m/z): [M + Na]+ calcd for C26H39AuClNNaO,
636.2283; found, 636.2275.
1
chromatography (silica gel, 5:1 hexanes/EtOAc). The H NMR spec-
trum of 2b0 was measured at 30 and 90 °C with the same scheme for the
first sample.
1
VT-NMR for 2c and 2e. The H NMR spectra of 2c and 2e were
measured at 30, 50, 70, and 90 °C, 5 min after reaching the desired
temperature.
’ ASSOCIATED CONTENT
S
Supporting Information. Detailed synthetic procedures,
b
analytical data for new compounds, and X-ray crystallogrphic
data for 2a (CCDC 825024), 2b (CCDC 825025), 2c (CCDC
825026), 2d (CCDC 825027), and 2e (CCDC 825028). This
material is available free of charge via the Internet at http://pubs.
acs.org.
[N-Cyclohexyl-N-(2,6-diisopropylphenyl)-O-(2,6-diisopro-
pylphenyl)aminooxycarbene]gold(I) Chloride (2d). With the
same method used in the synthesis of 2a, 2d (72%) was obtained as an
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: sukwon@ufl.edu.
1
off-white solid. H NMR (300 MHz, CDCl3): δ 7.44ꢀ7.33 (m, 1H),
7.32ꢀ7.18 (m, 3H), 7.17ꢀ7.05 (m, 2H), 3.72ꢀ3.58 (m, 1H),
3.12ꢀ3.00 (m, 2H), 2.94ꢀ2.81 (m, 2H), 2.67ꢀ2.51 (m, 2H),
2.48ꢀ2.34 (m, 2H), 1.99ꢀ1.78 (m, 2H), 1.65 (br s, 1H), 1.45 (d, J =
6.8 Hz, 6H), 1.38ꢀ1.15 (m, 15H), 1.05 (d, J = 6.8 Hz, 6H). 13C NMR
(75 MHz, CDCl3): δ 214.5, 152.1, 143.9, 140.4, 137.8, 129.7, 127.9,
125.4, 125.1, 69.8, 34.5, 29.7, 26.8, 26.6, 26.2, 25.4, 25.1, 24.7, 24.6.
’ ACKNOWLEDGMENT
We thank the James & Esther King Biomedical Research
Program and the Florida Department of Health (08KN-04) for
support of this research.
5729
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Organometallics
ARTICLE
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