Exploring the coordination of cyclic selenoureas to gold(I)

Article abstract of DOI:10.1021/om500610w

NHC-derived selenoureas, which are useful for the quantification of NHC electronic properties, are deployed as ligands for Au(I). Surprisingly, while some compounds led to the expected [AuCl(SeUr)] species, selenoureas derived from more π-accepting NHCs u

Full text of DOI:10.1021/om500610w

Article
pubs.acs.org/Organometallics
Exploring the Coordination of Cyclic Selenoureas to Gold(I)
David J. Nelson,† Fady Nahra, Scott R. Patrick, David B. Cordes, Alexandra M. Z. Slawin,
and Steven P. Nolan*
EaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife KY16 9ST, U.K.
S
* Supporting Information
ABSTRACT: NHC-derived selenoureas, which are useful for
the quantification of NHC electronic properties, are deployed
as ligands for Au(I). Surprisingly, while some compounds led
to the expected [AuCl(SeUr)] species, selenoureas derived
from more π-accepting NHCs unexpectedly furnished crystals
of the corresponding [Au(SeUr)2][AuCl2] species, in which
ligand rearrangement had occurred.
([Se(IPrCl)] (1h)) or by deprotonation of the corresponding
INTRODUCTION
■
imidazolium salt in the presence of elemental selenium
([Se(IMes)] (1i), [Se(SIMes)] (1j)). These compounds
cover a range of 1,3-diarylimidazol-2-ylidenes, as well as an
example of a 1,3-dialkylimidazol-2-ylidene. The Tolman
electronic parameters (TEP)22 of all the corresponding
NHCs are known,20,23 and the δSe chemical shift is proposed
to allow the relative back-bonding abilities of each NHC to be
quantified; the values reported here extend the range of values
previously reported by Ganter and co-workers using this
method (Figure 1).19 Further studies into the nature of the
bonding in these compounds, and how it relates to the
selenium NMR data, are currently underway in our research
group; the typically very bulky N-aryl substituents may mean
that chemical shift anisotropy has a significant effect here.
New complexes of these selenourea species with gold were
prepared by reaction of [AuCl(SMe2)] with 1 equiv of the
selenourea compound in THF at room temperature (Scheme
1). Unfortunately, complex 2g decomposed upon workup:
during removal of the solvent, a gold mirror formed on the
inside of the vial. This suggests an important role for bulky N
substituents, which may serve to stabilize the gold complex and
prevent agglomeration. For the other examples, filtration and
removal of the solvent furnished the desired complexes in
quantitative yield. These new species were characterized by a
number of methods (see the Experimental Section), including
1H, 13C{1H}, and 77Se{1H} NMR spectroscopic analyses and
elemental analysis. These analyses were all consistent with the
monomeric gold chloride structure.
The synthesis and exploration of new motifs in organometallic
chemistry is of importance to the discovery of new, useful
complexes for catalysis, medicines, and materials. Gold
complexes have been used for a number of applications,
particularly in homogeneous catalysis1−3 but increasingly as
anticancer agents4 and as luminescent materials.5 We report
herein the synthesis of a number of new AuI complexes bearing
selenourea ligands. Selenium-based ligands have been used with
a variety of metal centers. Selenoureas (SeUr) in particular have
been used as ligands for species including iridium photo-
catalysts,6 iridium and rhodium polymerization catalysts,7
precursors to zinc selenides,8 and copper complexes of
biological relevance.9−11 The latter examples are particularly
interesting, as different coordination geometries could be
obtained: a 1:1 mixture of SeUr:[CuX] (X = Cl, Br, I) led to
tetrameric [Cu4X2(μ-X)2(μ-SeUr)4] complexes, while a 2:1
ratio allowed the isolation of trigonal-planar [CuX(SeUr)2]
species.10 In gold chemistry,12 a few examples of [AuCl-
(SeUr)2)] complexes are known,13,14 as well as cationic
[AuL(SeUr)2] complexes.15−18
We recently prepared a range of N-heterocyclic carbene
(NHC)-derived selenoureas, in order to quantify the π-back-
bonding ability of NHCs via 77Se{1H} NMR spectroscopy,
according to the method of Ganter.19 We therefore sought to
prepare a range of complexes bearing these species as ligands
and probe the changes in NMR spectra and solid-state structure
on coordination to gold(I).
Solid-State Characterization of Gold(I) Complexes.
Single crystals of 2a,c−f,i,j were prepared by slow diffusion of
hexane into a saturated solution of the complex in DCM. X-ray
analysis of these crystals revealed the expected linear two-
coordinate [AuCl(SeUr)] structure for complexes 2a,e,f,i,j
(Figure 2) but led surprisingly to [Au(SeUr)2][AuCl2]
RESULTS AND DISCUSSION
■
Synthesis of Cyclic Selenoureas and Their Gold(I)
Complexes. Several known compounds (1a−g) were
deployed: [Se(IPr)] (1a) and [Se(SIPr)] (1c) were first
reported by Ganter et al.,19 while [Se(IPrOMe)] (1b),
[Se(SIPrOMe)] (1d), [Se(IPr*)] (1e), and [Se(IPr*OMe)] (1f)
were disclosed recently.20 [Se(IiPrMe)] (1g) has been reported
previously.21 Three additional selenoureas were prepared,
either by reaction of the free carbene with elemental selenium
Received: June 9, 2014
Published: July 2, 2014
© 2014 American Chemical Society
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Figure 1. Selenourea compounds used in this study and their relative π-accepting properties quantified using δSe in acetone (red) or CDCl3 (blue).
The known range reaches 800 ppm for highly π accepting NHCs.19
Scheme 1. Synthesis of [AuCl(SeUr)] Complexes
complexes for 2c,d, which bear more π-accepting saturated
NHC derivatives (Figure 3). This result was explored further by
growing new crystals for analysis using strictly oxygen and
water free solvents, in order to rule out the possibility of
decomposition during crystallization or of water interfering
with this process. In each case, crystals appeared to grow as a
single cluster and a single morphology; analysis of multiple
crystals from selected samples furnished the same results.
However, when the crystals were redissolved in deuterated
solvents, the NMR spectra obtained were the same as the initial
NMR spectra. When 1 equiv of [AuCl(SMe2)] was exposed to
0.5 equiv each of 1c,d, the resulting mixture comprised a 1:1
mixture of the products obtained separately, yet a 1:2:1 mixture
of products would be anticipated if [L2Au][AuCl2] species were
formed in solution. This suggests either that the [Au(SeUr)2]-
[AuCl2] form is present as an impurity which crystallizes
preferentially or that interconversion between the two forms is
quite facile.
Key bond lengths and angles are recorded in Table 1.
Notably, the Au−Cipso distances (the distance between the gold
center and the aryl ring of the selenourea) is within the sum of
the van der Waals radii of the two atoms (ca. 3.36 Å),
suggesting an interaction. In some complexes (e.g., 2f), Se−H
distances of just under 3.10 Å are observed. However, H atoms
were located using the riding model; thus, there is some
uncertainty in their location. In the monomeric complexes, the
Se−Au−Cl angle deviates from 180° by ca. 5−10°. C−Se−Au
angles are all in the range of ca. 103−107°. There is no
evidence of aurophilic interactions in these crystal structures,
presumably due to the steric bulk of the NHC-derived
selenourea compounds.
A search of the Cambridge Structure Database reveals a
limited number of examples of solid-state structures of
[AuX(SeUr)] complexes. Aroz et al. reported the dinuclear
complex [{Au(C6F5)}2Mbis] (Mbis = 3,3′-methylenebis(1-
methyl-1,3-dihydro-2H-imidazole-2-selenone), based on the
Figure 2. X-ray crystal structures of complexes 2a,e,f,i,j with thermal
ellipsoids at the 50% probability level. Most H atoms are excluded for
clarity.
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selenoureas, we were intrigued about their structure in solution;
the two isomers are difficult to differentiate using standard 1D
experiments and 2D correlation techniques. We therefore
turned to diffusion-based NMR experiments to elucidate the
molecular weight of the complexes in solution (Figure 4).
Figure 3. X-ray crystal structures of complexes 2c,d with thermal
ellipsoids drawn at the 50% probability level. Most H atoms are
excluded for clarity.
1
Figure 4. Overlay of 2D H-DOSY spectra recorded for 2a (red) and
2c (blue).
Table 1. Key Bond Lengths (Å) and Angles (deg) in
Selenourea−Au(I) Species 2
These experiments revealed very similar diffusion coefficients in
chloroform-d solution for 2a,c (ca. (7.5 0.1) × 10−10 and (7.6
0.1) × 10−10 m2 s−1, respectively). Using the correlation
proposed by Morris and co-workers,26 the molecular weights of
these species can be estimated at 748 and 728, respectively,
versus 700 and 702 for the monomeric [AuCl(SeUr)]
complexes. The [Au(SeUr)2]+ fragments would be expected
to have diffusion coefficients of 6.24 × 10−10 and 6.23 × 10−10
m2 s−1. These species therefore adopt a monomeric structure in
solution.
Au−Se
Se−C
Au−Cipso
C−Se−Au
Se−Au−Cl
ab
,
2a
2c
2.361
2.398
2.379
2.353
2.354
2.360
2.360
1.867
1.871
1.862
1.865
1.870
1.870
1.868
3.093
3.142
3.144
3.191
3.247
3.184
103.40
105.59
106.61
104.38
106.94
105.82
105.38
175.46
c
c
2d
a
2e
174.47
170.93
174.07
173.32
a
2f
2i
2j
a
a
3.085
a
b
Takes the form [L-Au-Cl]. Average from two independent
c
molecules. Takes the form [L-Au-L][AuCl2].
The presence of the 77Se nuclide allows the electronic
environment of the selenium atom, and how this changes on
coordination to gold(I), to be probed.27 Coordination to the
gold(I) chloride center led to a systematic decrease in the δSe
value of typically 20−30% (Figure 5), suggestive of a less
deshielded environment. The 31P NMR chemical shift of
phosphines is known to systematically increase upon binding to
the AuCl fragment.17 A plausible explanation is that, when the
selenoureas bind to the gold(I) center, less electron density is
available to donate into the aromatic system.
Most interestingly, the propensity of the ligand to form
[Au(SeUr)2][AuCl2]-type complexes instead of [AuCl(SeUr)]
species appears to be related to the δSe chemical shift on the
77Se{1H} NMR spectrum, although the limited number of
examples here makes it difficult to propose general trends.
Selenoureas with higher δSe values (suggesting that they are
derived from more π accepting imidazol-2-ylidenes) appear to
lead to the bis-selenourea motif. This may be due to the less
electron rich selenium centers (as shown by higher δSe) binding
more strongly to a cationic gold(I) fragment than to neutral
gold(I): i.e., the former ought to be more Lewis acidic than the
latter.
coordination of two [Au(C6F5)] units to two methylene-linked
cyclic selenoureas, which is quite different from the arrange-
ments reported here.13 Fettouhi et al. and Bhabak and Mugesh
have each crystallized a cationic complex of the form
[Au(PMe3)(SeUr)]2[Cl]2 (SeUr = selenourea (3a), 1-methyl-
1,3-dihydro-2H-imidazole-2-selenone (3b)) which displayed
aurophilic interactions (with Au−Au distances of 3.04 and
3.10 Å, respectively).24,25 In both of these complexes, more
acute C−Se−Au angles are observed (97.85, 100.34, 96.78, and
101.15°, respectively) with similar slight bending of the angle
around the gold center (Se−Au−C angle of 177.49°; Se−Au−P
angles of 175.06, 172.41, and 175.98°). Notably, these two
examples feature much smaller ligands in comparison to the
bis(aryl)-substituted examples considered here. The coordina-
tion behavior of these new selenourea compounds (2) is
interesting, particularly given that each of the two motifs is
obtained under identical reaction and crystallization conditions.
Solution-State Characterization of Gold(I) Complexes.
While solid-state characterization methods suggested different
structures for gold(I) chloride complexes of different
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was passed through a pad of Celite, which was then washed with
further DCM (5 mL). The DCM was removed in vacuo, and the
residue was washed with pentane (3 × 2 mL) and dried under high
vacuum to yield the title compound as a white powder (137.7 mg,
1
3
0.257 mmol, 76%). H NMR (CDCl3, 500 MHz): δ 7.54 (t, JHH
=
7.8, 2H), 7.34 (d, 3JHH = 7.8, 4H), 2.63 (sept., 3JHH = 6.8, 4H), 1.35 (d,
3JHH = 6.8, 12H), 1.26 (d, JHH = 6.8, 12H). 13C{1H} NMR (CDCl3,
3
125 MHz): δ 162.1, 146.8, 131.4, 131.1, 124.6, 115.5, 29.6, 24.02,
24.97. 77Se{1H} NMR (CDCl3, 95 MHz): δ 173.6. 1H NMR (acetone-
d6, 400 MHz): δ 7.56 (t, 3JHH = 7.7, 2H), 7.41 (d, 3JHH = 7.7, 4H), 2.69
3
3
3
(sept., JHH = 6.9, 4H), 1.33 (d, JHH = 6.9, 12H), 1.25 (d, JHH = 6.9,
12H). 77Se{1H} NMR (acetone-d6, 76 MHz): δ 174.0. Anal. Calcd for
C27H34N2Cl2Se: C, 60.45; H, 6.39; N, 5.22. Found: C, 60.45; H, 6.29;
N, 5.30.
[Se(IMes)] (1i). IMes·HCl (1.005 g, 2.95 mmol) and KOtBu (368.9
mg, 3.29 mmol, 1.1 equiv) were suspended in dry THF (40 mL), in an
oven-dried flask, under argon. Selenium was added (769.4 mg, 9.74
mmol, 3.3 equiv). The reaction mixture was stirred overnight at room
temperature. The THF was removed in vacuo, the residue was
dissolved in DCM (20 mL), and this solution was passed through a
pad of Celite, which was then washed with further DCM (5 mL). The
DCM was removed in vacuo, and the residue was washed with pentane
(3 × 10 mL) and dried under high vacuum to yield the title compound
as a pale red powder (916.8 mg, 2.39 mmol, 81%). 1H NMR (CDCl3,
500 MHz): δ 7.02 (s, 4H), 6.97 (s, 2H), 2.35 (s, 6H), 2.13 (s, 12H).
13C{1H} NMR (CDCl3, 125 MHz): δ 157.6, 139.5, 135.5, 134.3,
129.4, 120.3, 21.3, 18.1. 77Se{1H} NMR (CDCl3, 95 MHz): δ 26.7. 1H
NMR (acetone-d6, 500 MHz): δ 7.31 (s, 2H), 7.01 (s, 4H), 2.32 (s,
6H), 2.09 (s, 12H). 77Se{1H} NMR (acetone-d6, 95 MHz): δ 34.6.
Anal. Calcd for C21H24N2Se: C, 65.79; H, 6.31; N, 7.31. Found: C,
65.65; H, 6.37; N, 7.32.
Figure 5. Plot of δSe for cyclic selenoureas bound to gold(I) versus δSe
for the unbound cyclic selenourea; annotations refer to the NHC from
which the cyclic selenourea was derived, while the dashed line has a
slope of unity and an intercept of zero.
CONCLUSIONS
■
In conclusion, we have explored the coordination chemistry of
a series of NHC-derived selenourea compounds with gold(I).
New complexes were characterized by NMR spectroscopy and
elemental analysis. X-ray crystal diffraction studies revealed two
distinct geometries: selenoureas based on more π accepting
NHC ligands led to [Au(SeUr)2][AuCl2] species, while others
led to the expected [AuCl(SeUr)] motif. However, the
complexes take the form [AuCl(SeUr)] in the solution state,
[Se(SIMes)] (1j). SIMes·HBF4 (1.198 g, 3.04 mmol) and KOtBu
(370.3 mg, 3.30 mmol, 1.1 equiv) were suspended in dry THF (40
mL), in an oven-dried flask, under argon. Selenium was then added
(739.9 mg, 9.37 mmol, 3.1 equiv). The reaction mixture was stirred
overnight at room temperature. The THF was removed in vacuo, the
residue was dissolved in DCM (20 mL), and this solution was passed
through a pad of Celite, which was then washed with further DCM (5
mL). The DCM was removed in vacuo, and the residue was washed
with pentane (3 × 10 mL) and dried under high vacuum to yield the
1
as confirmed by H DOSY NMR studies of 2a,c, yet mass
spectroscopy studies suggested that 2a,c both form [Au-
(SeUr)2]+ ions in the spectrometer.28 Further work to generate
new derivatives of these complexes and explore the catalytic
activity of selenourea−gold(I) complexes is currently underway
in our laboratories.
EXPERIMENTAL SECTION
■
1
title compound as a white powder (1.004 g, 2.60 mmol, 86%). H
Reactions were performed on the bench, under ambient conditions,
unless otherwise stated. Selenium was obtained from Strem and used
as supplied. Dry THF was obtained from an MBraun solvent
purification system. Other solvents and reagents were used as
supplied. 1H, 13C{1H}, and 77Se{1H} spectra were recorded on Bruker
Avance 400 and 500 MHz spectrometers with either BBFO or QNP
probes. Chemical shifts for 1H and 13C{1H} NMR spectra are reported
in ppm relative to SiMe4; chemical shifts for 77Se{1H} NMR spectra
are reported in ppm relative to SeMe2 and are externally referenced to
PhSeSePh (δSe 463 ppm). Coupling constants are in hertz. Signals on
the 13C{1H} and 77Se{1H} NMR spectra were singlets unless otherwise
stated. Elemental analyses were performed by the London
Metropolitan University Elemental Analysis Service. Results are
reported as an average of two analyses. Accurate mass spectroscopic
analyses were carried out by the EPSRC National Mass Spectrometry
Service Centre, Swansea, U.K., using a ThermoFisher LTQ Orbitrap
XL instrument. The synthesis and characterization of [Se(IPr)] (1a),
[Se(IPrOMe)] (1b), [Se(SIPr)] (1c), [Se(SIPrOMe)] (1d), [Se(IPr*)]
(1e), [Se(IPr*OMe)] (1f), and [Se(IiPrMe)] (1g) have been reported
previously.19−21 IMes·HCl, SIMes·HBF4 and IPrCl were prepared
according to the published procedures.29,30 Caution! Care should be
taken when handling highly toxic elemental selenium. Special measures
must also be taken for its disposal.
NMR (CDCl3, 500 MHz): δ 6.98 (s, 4H), 4.00 (s, 4H), 2.32 (s, 12H),
2.31 (s, 6H). 13C{1H} NMR (CDCl3, 125 MHz): δ 180.1, 138.6,
136.4, 135.0, 129.6, 48.8, 21.3, 18.0. 77Se{1H} NMR (CDCl3, 95
MHz): δ 109.7. 1H NMR (acetone-d6, 500 MHz): δ 6.94 (s, 4H), 4.08
(s, 4H), 2.29 (s, 12H), 2.27 (s, 6H). 77Se{1H} NMR (acetone-d6, 95
MHz): δ 113.1. Anal. Calcd for C21H26N2Se: C, 65.44; H, 6.80; N,
7.27. Found: C, 65.35; H, 6.93; N, 7.16.
General Procedure for the Synthesis of [AuCl(Se(NHC))]
Complexes. In air, a vial was charged with [Se(NHC)] (1 equiv),
[AuCl(SMe2)] (1 equiv), THF (0.15 M), and a stirring bar. The
mixture was stirred at room temperature for 2 h. The product typically
precipitated from the solution. It could be redissolved by adding
DCM, after which the solution was passed through a microfilter. The
solution was concentrated. Hexane was added, the resulting precipitate
was broken into fine particles, and the solvent was removed in vacuo.
[AuCl(Se(IPr))] (2a). The product was a pale solid (74.8 mg,
quantitative). 1H NMR (500 MHz, CDCl3): δ 7.63 (t, J = 7.7 Hz, 2H),
7.38 (d, J = 7.7 Hz, 4H), 7.21 (s, 2H), 2.42 (hept, J = 6.9 Hz, 4H),
1.37 (d, J = 6.9 Hz, 12H), 1.18 (d, J = 6.9 Hz, 12H). 13C{1H} NMR
(125 MHz, CDCl3): δ 151.2, 145.6, 132.8, 131.9, 125.3, 123.8, 29.3,
24.8, 23.5. 77Se{1H} NMR (95 MHz, CDCl3): δ 69.0. Anal. Calcd for
C27H36AuClN2Se: C, 46.33; H, 5.18; N, 4.00. Found: C, 46.19; H,
5.28; N, 4.16.
[Se(IPrCl)] (1h). In the glovebox, a solution of IPrCl (154.0 mg,
0.337 mmol) in THF (5 mL) was prepared. Outside of the glovebox,
the solution was transferred under argon via cannula into an oven-
dried flask containing selenium (75.6 mg, 0.957 mmol, 2.8 equiv). The
reaction mixture was stirred overnight. The THF was removed in
vacuo, the residue was dissolved in DCM (5 mL), and this solution
[AuCl(Se(IPrOMe))] (2b). The product was a pale solid (41.1 mg,
1
quantitative). H NMR (500 MHz, CDCl3): δ 7.16 (s, 2H), 6.88 (s,
4H), 3.93 (s, 6H), 2.46 (hept, J = 6.8, 4H), 1.39 (d, J = 6.8, 12H), 1.19
(d, J = 6.8, 12H). 13C{1H} NMR (125 MHz, CDCl3): δ 162.2, 152.0,
147.0, 125.8, 124.0, 110.8, 55.8, 29.4, 24.7, 23.4. 77Se{1H} NMR (95
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MHz, CDCl3): δ 67.9. Anal. Calcd for C29H40AuClN2O2Se: C, 45.83;
H, 5.30; N, 3.69. Found: C, 45.76; H, 5.45; N, 3.57.
Notes
The authors declare no competing financial interest.
[AuCl(Se(SIPr))] (2c). The product was a pale solid (74.9 mg,
1
quantitative). H NMR (500 MHz, CDCl3): δ 7.56 (t, J = 7.4, 2H),
ACKNOWLEDGMENTS
7.32 (d, J = 7.4, 4H), 4.15 (s, 4H), 2.90 (hept, J = 7.3, 4H), 1.45 (d, J =
7.3, 12H), 1.32 (d, J = 7.3, 12H). 13C{1H} NMR (125 MHz, CDCl3):
δ 177.4, 146.5, 133.2, 131.1, 125.5, 52.7, 29.4, 25.2, 24.5. 77Se{1H}
NMR (95 MHz, CDCl3): δ 125.8. Anal. Calcd for C27H38AuClN2Se:
C, 46.20; H, 5.46; N, 3.99. Found: C, 45.98; H, 5.53; N, 4.07.
[AuCl(Se(SIPrOMe))] (2d). The product was a pale solid (81.1 mg,
■
We thank the EPSRC and the ERC (Advanced Investigator
Award FUNCAT) for funding, Umicore for supplying auric
acid, the EPSRC National Mass Spectrometry Service Centre at
Swansea for mass spectrometry experiments, and Mrs. Melanja
Smith for assistance with NMR spectroscopy facilities.
1
quantitative). H NMR (500 MHz, CDCl3): δ 6.81 (s, 4H), 4.10 (s,
4H), 3.89 (s, 6H), 2.84 (hept, J = 6.9, 4H), 1.43 (d, J = 6.9 Hz, 12H),
1.30 (d, J = 6.9 Hz, 12H). 13C{1H} NMR (125 MHz, CDCl3): δ 178.1,
161.6, 147.9, 126.2, 111.1, 55.7, 52.7, 29.6, 25.2, 24.5. 77Se{1H} NMR
(95 MHz, CDCl3): δ 124.3. Anal. Calcd for C29H42AuClN2O2Se: C,
45.71; H, 5.56; N, 3.68. Found: C, 46.04; H, 5.59; N, 3.85.
ABBREVIATIONS
■
IMes, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; IiPrMe,
1,3-diisopropylimidazol-2-ylidene; IPr, 1,3-bis(2,6-
diisopropylphenyl)imidazol-2-ylidene; IPrCl, 1,3-bis(2,6-diiso-
propylphenyl)-4,5-dichloroimidazol-2-ylidene; IPrOMe, 1,3-bis-
(2,6-diisopropyl-4-methoxyphenyl)imidazol-2-ylidene; IPr*,
1,3-bis(2,6-diphenylmethyl-4-methylphenyl)imidazol-2-ylidene;
IPr*OMe, 1,3-bis(2,6-diphenylmethyl-4-methoxyphenyl)-
imidazol-2-ylidene; SIMes, 1,3-bis(2,4,6-trimethylphenyl)-4,5-
dihydroimidazol-2-ylidene; SIPr, 1,3-bis(2,6-diisopropylphen-
yl)-4,5-dihydroimidazol-2-ylidene; SIPrOMe, 1,3-bis(2,6-diiso-
propyl-4-methoxyphenyl)-4,5-dihydroimidazol-2-ylidene
[AuCl(Se(IPr*))] (2e). The product was a pale solid (46.8 mg,
1
quantitative). H NMR (500 MHz, CDCl3): δ 7.33−7.24 (m, 20H),
7.17−7.12 (m, 12H), 6.98 (s, 4H), 6.85−6.81 (m, 8H), 5.46 (s, 2H),
5.20 (s, 4H), 2.35 (s, 6H). 13C{1H} NMR (125 MHz, CDCl3): δ
149.1, 142.8, 142.0, 141.9, 140.9, 131.9, 131.3, 130.1, 129.3, 128.7,
128.5, 127.2, 126.9, 123.3, 52.0, 22.2. 77Se{1H} NMR (95 MHz,
CDCl3): δ 73.0. MS (ESI-Orbitrap): calcd for C69H56AuN274Se ([M −
Cl]+), 1183.3328; found, 1183.3335.
[AuCl(Se(IPr*OMe))] (2f). The product was a pale solid (41.4 mg,
1
quantitative). H NMR (500 MHz, CDCl3): δ 7.28−7.18 (m, 20H),
7.11−7.06 (m, 12H), 6.81−6.77 (m, 8H), 6.62 (s, 4H), 5.34 (s, 2H),
5.14 (s, 4H), 3.61 (s, 6H). 13C{1H} NMR (125 MHz, CDCl3): δ
161.4, 142.8, 142.5, 141.9, 130.1, 129.2, 128.7, 128.5, 127.3, 127.2,
127.0, 123.5, 116.2, 55.6, 52.2. 77Se{1H} NMR (95 MHz, CDCl3): δ
72.0. MS (ESI-Orbitrap): calcd for C69H56AuN274Se ([M − Cl]+),
1215.3226; found, 1215.3227.
REFERENCES
■
(1) (a) Hashmi, A. S. K.; Rudolph, M. Chem. Soc. Rev. 2008, 37,
1766. (b) Rudolph, M.; Hashmi, A. S. K. Chem. Soc. Rev. 2012, 41,
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[AuCl(Se(IPrCl))] (2h). The product was a pale solid (43.9 mg,
(2) Nolan, S. P. Acc. Chem. Res. 2011, 44, 91.
(3) Obradors, C.; Echavarren, A. M. Chem. Commun. 2013, 50, 16.
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1
quantitative). H NMR (500 MHz, CDCl3): δ 7.70 (t, J = 7.9, 2H),
7.41 (d, J = 7.9, 4H), 2.42 (hept, J = 6.8, 4H), 1.40 (d, J = 6.8, 12H),
1.25 (d, J = 6.8, 12H). 13C{1H} NMR (125 MHz, CDCl3): δ 151.1,
146.1, 132.7, 129.8, 125.7, 119.6, 29.7, 24.2, 24.1. 77Se{1H} NMR (95
MHz, CDCl3): δ 136.3. Anal. Calcd for C27H34AuCl3N2Se: C, 42.18;
H, 4.46; N, 3.64. Found: C, 42.08; H, 4.54; N, 3.53.
[AuCl(Se(IMes))] (2i). The product was a pale solid (83.0 mg,
1
quantitative). H NMR (500 MHz, CDCl3): δ 7.16 (s, 2H), 7.09 (s,
4H), 2.41 (s, 6H), 2.10 (s, 12H). 13C{1H} NMR (125 MHz, CDCl3):
δ 146.8, 141.5, 134.8, 132.7, 130.2, 122.9, 21.5, 18.0. 77Se{1H} NMR
(95 MHz, CDCl3): δ 22.5. Anal. Calcd for C21H24AuClN2Se: C, 40.96;
H, 3.93; N, 4.55. Found: C, 41.17; H, 3.82; N, 4.48.
[AuCl(Se(SIMes))] (2j). The product was a pale solid (82.4 mg,
1
quantitative). H NMR (500 MHz, CDCl3): δ 7.04 (s, 4H), 4.11 (s,
(11) Kimani, M. M.; Wang, H. C.; Brumaghim, J. L. Dalton Trans.
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(12) Molter, A.; Mohr, F. Coord. Chem. Rev. 2010, 254, 19.
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V. Eur. J. Inorg. Chem. 2011, 2011, 2884.
4H), 2.37 (6H), 2.29 (s, 12H). 13C{1H} NMR (125 MHz, CDCl3): δ
173.7, 140.7, 135.7, 133.1, 130.5, 50.1, 21.4, 17.8. 77Se{1H} NMR (95
MHz, CDCl3): δ 81.9. Anal. Calcd for C21H26AuClN2Se: C, 40.82; H,
4.42; N, 4.53. Found: C, 40.69; H, 4.44; N, 4.47.
(14) Bredenkamp, A.; Zeng, X.; Mohr, F. Polyhedron 2012, 33, 107.
ASSOCIATED CONTENT
* Supporting Information
(15) Jones, P. G.; Thone, C. Chem. Ber. 1991, 124, 2725.
̈
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(16) Isab, A.; Ahmad, S. Transition Met. Chem. 2006, 31, 500.
(17) Ahmad, S.; Isab, A. Transition Met. Chem. 2003, 28, 540.
(18) Isab, A.; Ahmad, S.; Arnold, A. Transition Met. Chem. 2004, 29,
S
Figures, tables, and CIF files giving NMR spectra for all new
compounds, details of DOSY NMR experiments, mass spectra
for 2a,c, and crystallographic data for complexes 2a,c−f,i,j. This
material is available free of charge via the Internet at http://
pubs.acs.org. CCDC files 994254−994260 also contain
crystallographic data for complexes 2a,c−f,i,j.
870.
(19) Liske, A.; Verlinden, K.; Buhl, H.; Schaper, K.; Ganter, C.
Organometallics 2013, 32, 5269.
(20) Nelson, D. J.; Collado, A.; Manzini, S.; Meiries, S.; Slawin, A. M.
Z.; Cordes, D. B.; Nolan, S. P. Organometallics 2014, 33, 2048.
(21) Kuhn, N.; Henkel, G.; Kratz, T. Z. Naturforsch., B 1993, 48, 973.
(22) Tolman, C. A. Chem. Rev. 1977, 77, 313.
(23) Nelson, D. J.; Nolan, S. P. Chem. Soc. Rev. 2013, 42, 6723.
(24) Fettouhi, M.; Wazeer, M. I. M.; Ahmad, S.; Isab, A. A.
Polyhedron 2004, 23, 1.
(25) Bhabak, K.; Mugesh, G. J. Chem. Sci. 2011, 123, 783.
(26) Evans, R.; Deng, Z.; Rogerson, A. K.; McLachlan, A. S.;
Richards, J. J.; Nilsson, M.; Morris, G. A. Angew. Chem., Int. Ed. 2013,
52, 3199.
AUTHOR INFORMATION
Corresponding Author
*E-mail for S.P.N.: snolan@st-andrews.ac.uk.
■
Present Address
†WestCHEM Department of Pure and Applied Chemistry,
University of Strathclyde, 295 Cathedral Street, Glasgow G1
1XL, U.K.
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dx.doi.org/10.1021/om500610w | Organometallics 2014, 33, 3640−3645

Organometallics
Article
(27) A reviewer pointed out that the steric bulk in the proximity of
the selenium atom may lead to chemical shift anisotropy; further
studies are underway in our laboratories to examine bonding in these
selenoureas and will be reported in due course.
(28) Mass spectroscopic studies were also carried out, using MALDI
and ESI techniques, but these suggested that 2a,c both adopted a
[Au(SeUr)2][AuCl2] arrangement. We believe that ionization of these
complexes in the mass spectrometer may perturb their arrangement.
See the Supporting Information for data.
(29) Bantreil, X.; Nolan, S. P. Nat. Protoc. 2011, 6, 69.
(30) Arduengo, A. J., III; Krafczyk, R.; Schmutzler, R.; Craig, H. A.;
Goerlich, J. R.; Marshall, W. J.; Unverzagt, M. Tetrahedron 1999, 55,
14523.
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