Gold and palladium hetero-bis-NHC complexes: Characterizations, correlations, and ligand redistributions

Article abstract of DOI:10.1021/om400313r

A series of new Au(I) hetero-bis-NHC complexes [Au(ⁱPr ₂-bimy)(NHC)]X (X = BF₄, PF₆, 2-6) and the hetero-tetrakis-NHC complex [Au₂(ⁱPr₂-bimy) ₂(μ-ditz)](BF₄)₂ (7) have been synthesized using the Au(I) acetato complex [Au(O₂CCH₃)( ⁱPr₂-bimy)] (C) as a basic metal precursor ( ⁱPr₂-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene, ditz = 1,2,4-triazolidine-3,5-diylidene). The Au(III) hetero-bis-NHC complex trans-[AuCl₂(ⁱPr₂-bimy)(Bn₂-bimy)] BF₄ (12; Bn₂-bimy = 1,3-dibenzylbenzimidazolin-2-ylidene) and the hetero-tetrakis-NHC complex all-trans-[Au₂Cl ₄(ⁱPr₂-bimy)₂(μ-ditz)](BF ₄)₂ (13) were obtained by oxidation of their corresponding Au(I) hetero-NHC precursors. For all Au(I) hetero-NHC complexes, the ¹³C carbene signals of the constant ⁱPr₂-bimy ligand are found to be highly correlated with those in Pd(II) analogues of the type trans-[PdBr₂(ⁱPr₂-bimy)(NHC)], which could be applied to detect the σ-donating ability of the trans-standing NHC. In addition, an interesting ligand redistribution process was observed for some of the Au(I) hetero-bis-NHC complexes.

Full text of DOI:10.1021/om400313r

Article
pubs.acs.org/Organometallics
Gold and Palladium Hetero-Bis-NHC Complexes: Characterizations,
Correlations, and Ligand Redistributions
Shuai Guo, Haresh Sivaram, Dan Yuan, and Han Vinh Huynh*
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Republic of Singapore
S
* Supporting Information
ABSTRACT: A series of new Au(I) hetero-bis-NHC complexes
[Au(iPr2-bimy)(NHC)]X (X = BF4, PF6, 2−6) and the hetero-tetrakis-
NHC complex [Au2(iPr2-bimy)2(μ-ditz)](BF4)2 (7) have been synthe-
sized using the Au(I) acetato complex [Au(O2CCH3)(iPr2-bimy)] (C) as
a basic metal precursor (iPr2-bimy = 1,3-diisopropylbenzimidazolin-2-
ylidene, ditz = 1,2,4-triazolidine-3,5-diylidene). The Au(III) hetero-bis-
NHC complex trans-[AuCl2(iPr2-bimy)(Bn2-bimy)]BF4 (12; Bn2-bimy =
1,3-dibenzylbenzimidazolin-2-ylidene) and the hetero-tetrakis-NHC
complex all-trans-[Au2Cl4(iPr2-bimy)2(μ-ditz)](BF4)2 (13) were obtained
by oxidation of their corresponding Au(I) hetero-NHC precursors. For all
Au(I) hetero-NHC complexes, the 13C carbene signals of the constant
iPr2-bimy ligand are found to be highly correlated with those in Pd(II)
analogues of the type trans-[PdBr2(iPr2-bimy)(NHC)], which could be
applied to detect the σ-donating ability of the trans-standing NHC. In addition, an interesting ligand redistribution process was
observed for some of the Au(I) hetero-bis-NHC complexes.
and characterized. Finally, a ligand redistribution process of
Au(I) hetero-NHC complexes was observed in some cases and
studied in detail.
INTRODUCTION
■
N-heterocyclic carbene (NHC) complexes of Au(I) have
received increased interest due to their catalytic,1 luminescent,2
and biological properties.3 In addition, they have also found
applications in the building of metallosupramolecular archi-
tectures.4 A wide range of Au(I) homo-bis-NHC complexes
have been previously reported,2a,5 while Au(I) hetero-bis-NHC
complexes,6 which contain two different NHCs, have been
given less attention. In addition, most compounds reported are
limited to imidazolin-2-ylidene ligands,6a,b and an extension to
other types of carbenes is highly desirable. As a contribution to
the new area of gold heterocarbene chemistry, we herein report
different routes to a series of Au(I) hetero-bis-NHC complexes
of the type [Au(iPr2-bimy)(NHC)]BF4 (I; Figure 1) bearing
the fixed spectator iPr2-bimy (iPr2-bimy = 1,3-diisopropylbenzi-
midazolin-2-ylidene) and various types of additional NHC
ligands. Furthermore, the Janus-type 1,2,4-triazolidine-3,5-
diylidene ligand has also been included in this study, which
forms a new digold hetero-tetrakis-NHC complex [Au2(iPr2-
bimy)2(μ-ditz)](BF4)2 (II; Figure 1).
RESULTS AND DISCUSSION
■
Syntheses of Au(I) Hetero-NHC Complexes. Homo-bis-
NHC Au(I) complexes of the general formula [Au(NHC)2]Y
(Y = noncoordinating anion) can be obtained by reacting the
mono-NHC precursor [AuX(NHC)] (X = halido ligand) with
the respective azolium salts and a base.2a
Thus, this method was utilized in our initial attempts to
synthesize hetero-bis-NHC complexes of the type [Au(NHC)-
(NHC’)]Y bearing two different NHC ligands. Hence, the
previously reported indazolin-3-ylidene complex A8 was treated
i
−
with the benzimidazolium salt Pr2-bimy·H+BF4 (a) and
K2CO3, cleanly affording the hetero-bis-NHC complex [Au-
(iPr2-bimy)(Indy)]BF4 (1) in a yield of 76% (Indy = 6,7,8,9-
tetrahydropyridazino[1,2-a]indazolin-3-ylidene; Scheme 1).
On the other hand, the known mono-NHC complex B9 gave
product mixtures containing the desired hetero-bis-NHC
complex as well as non-negligible amounts of two homo-bis-
NHC complexes when treated in the same manner with
triazolium (b) or benzimidazolium salts (c), as indicated by 1H
NMR spectroscopy (Scheme 2). It should be noted that such
an observation was previously reported by Lin et al.10
It was previously found that the iPr2-bimy spectator could be
employed as a highly sensitive 13C NMR spectroscopic probe
to determine the net donating ability of a second trans-standing
NHC ligand in complexes of the type trans-[PdBr2(iPr2-
bimy)(NHC)]7 (III; Figure 1). As a potential extension of this
An alternative approach to Au(I) hetero-bis-NHC complexes
by in situ deprotonation of azolium salts using the basic
methodology to other metal−NHC systems, a comparison and
13
correlation of the
C
(iPr2-bimy) NMR data between
carbene
Pd(II) complexes III and Au(I) complexes I/II is reported as
well. For this purpose, three new hetero-bis-carbene complexes,
trans-[PdBr2(iPr2-bimy)(NHC)] (1′, 4′, 8′), were synthesized
Received: April 12, 2013
© XXXX American Chemical Society
A
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Figure 1. Au(I) and Pd(II) hetero-NHC complexes.
solid form, it is not very stable under aerobic conditions, as
evidenced by the observation of purple gold upon exposure to
air overnight. However, when fully dried, this complex can be
kept under an inert atmosphere for at least 2 weeks.
Scheme 1. Synthesis of Hetero-Bis-Carbene Complex
[Au(iPr2-bimy)(Indy)]BF4 (1)
The 1H NMR spectrum of complex C shows a characteristic
multiplet at 5.45 ppm due to the isopropyl C−H protons. 13C
NMR spectroscopy further supports the formation of C by a
carbenoid signal at 170.2 ppm, which is shifted upfield in
comparison to that in its chlorido precursor B (cf. 175.8 ppm).
This upfield shift is attributed to the decreased σ-donating
ability of the acetato compared to that of the chlorido coligand,
which in turn results in a more Lewis acidic Au(I) center.12
Furthermore, its ESI mass spectrum shows a dominant peak at
m/z 601 arising from the cationic [Au(iPr2-bimy)2]+ species. It
should be noted that such Au(I) bis-NHC cations are typically
observed in the ESI mass spectra of Au(I) mono-NHC
complexes.8
Scheme 2. Attempts To Prepare Au(I) Hetero-Bis-NHC
Complexes
The identity of complex C was unambiguously confirmed by
X-ray diffraction. Suitable single crystals were obtained by
layering a concentrated solution of C in CH2Cl2 with hexane
and storing at 4 °C. Selected crystallographic data are given in
Table 1, and the molecular structure depicted in Figure 2
confirms the linear coordination geometry of the Au(I) center
with both iPr2-bimy and acetato ligands bound in a
monodentate fashion. The Au−C bond length falls in the
hydroxo complex [Au(OH)(IPr)] (IPr = 1,3-bis(2,6-
diisopropylphenyl)imidazolin-2-ylidene) was reported by
Nolan and co-workers.6b However, preparation of the
analogous complex [Au(OH)(iPr2-bimy)] following the
reported methods11 was to no avail. Instead, decomposition
was observed, as indicated by deposition of purple gold on the
6c,9
i
range typically observed for Au(I) Pr2-bimy complexes.
The potential use of acetato complex C as a basic metal
precursor for the preparation of Au(I) hetero-NHC complexes
was subsequently examined by treatment with a range of
azolium salts (b−f) with the noncoordinating anions BF4− and
i
glass surface of the flask. The Pr2-bimy ligand is probably not
sufficiently bulky to stabilize the highly active Au−hydroxo
moiety, in contrast to the case for the IPr or SIPr (SIPr = 1,3-
bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene) ligands in
the reported analogues.11
As a suitable alternative, we opted for mixed NHC−acetato
Au(I) complexes. Such complexes have been known for some
time, but their potential use as basic metal precursors to hetero-
bis-NHC complexes has not been studied. The chlorido
complex [AuCl(iPr2-bimy)] (B) was thus treated with 1
equiv of AgO2CCH3 in CH2Cl2 following a reported method,12
which affords the acetato complex [Au(O2CCH3)(iPr2-bimy)]
(C) in a 75% yield (Scheme 3). Complex C is readily soluble in
halogenated solvents, acetone, DMF, and DMSO but insoluble
in nonpolar solvents such as diethyl ether and hexane. Even in
−
PF6 (Scheme 4). Under the optimal conditions shown in
Table 2, all desired Au(I) hetero-bis-NHC complexes 2−6
could be obtained in high yields.
Notably, elevated temperatures were required to facilitate the
formation of complexes 5 and 6 incorporating the highly bulky
IPr ligand. However, several attempts to synthesize indazolin-3-
−
ylidene complex 1 by treating C with IndyH+BF4 were
unsuccessful, due to the lower acidity of the indazolium salt. In
addition to monodentate NHC ligands, we extended the
methodology to the synthesis of digold complexes bearing the
Janus-type dicarbene ligand ditz (ditz = 1,2,4- trimethyltriazo-
lidine-3,5-diylidene), which bears two carbene donors in a
single five-membered ring.13 Very recently, Peris et al. reported
one heterobimetallic Au−Ir triazolidinediylidene complex,13b
while to the best of our knowledge, digold ditz complexes are
still unknown. Indeed, the reaction of C with the dicationic salt
Scheme 3. Synthesis of Au(I) Acetato Complex
[Au(O2CCH3)(iPr2-bimy)] (C)
ditz·(H+BF4 )2 (g) in a 2:1 ratio afforded the Au(I)
−
heterotetrakis-NHC complex 7 in a moderate yield. Alter-
natively, complex 7 can be synthesized via a Ag−carbene
transfer route13a involving the chlorido complex B as a
precursor (Scheme 5).
All Au(I) hetero-bis-NHC complexes 1−6 and the
heterotetrakis-NHC complex 7 are readily soluble in common
B
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Table 1. Selected X-ray Crystallographic Data for Complexes C, 1, 2, 6, 9, 12, and 13·3CH2Cl2
C
1
2
6
formula
fw
C15H21AuN2O2
C24H30AuBF4N4
C29H33AuBF4N5
C40H54AuF6N4P
932.81
458.30
658.30
735.38
cryst size (mm)
temp (K)
cryst syst
space group
a (Å)
0.54 × 0.16x 0.16
223(2)
0.36 × 0.20 × 0.16
100(2)
0.60 × 0.26 × 0.60
100(2)
0.31 × 0.23 × 0.18
100(2)
monoclinic
monoclinic
monoclinic
monoclinic
Pc
P21/m
P21/c
P21/n
9.4713(15)
10.3775(10)
11.3640(17)
9.6056(4)
13.1707(6)
16.2740(8)
90
b (Å)
7.4385(12)
13.4807(13)
13.907(2)
c (Å)
10.8863(17)
17.2073(16)
18.598(3)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
90
90
90
91.231(4)
98.989(3)
90.016(4)
95.7720(10)
90
90
90
90
766.8(2)
2377.7(4)
2939.3(8)
2048.43(16)
2
2
4
4
Dc (g cm−3
μ (mm−1
)
1.985
1.839
1.662
1.512
)
9.596
6.239
5.058
3.690
θ range (deg)
2.15−27.47
1882
1.93−27.48
5436
1.83−27.50
6756
1.99−27.48
7951
no. of unique data
max, min transmission
final R indices (I > 2σ(I))
R indices (all data)
goodness of fit on F2
0.3921, 0.1722
0.4305, 0.3274
R1 = 0.0365, wR2 = 0.0731
R1 = 0.0507, wR2 = 0.0776
1.014
2253.4290, 0.1513
R1 = 0.0380, wR2 = 0.0926
R1 = 0.0430, wR2 = 0.0952
1.044
0.5564, 0.3942
R1 = 0.0345, wR2 = 0.0887
R1 = 0.0327, wR2 = 0.0673
R1 = 0.0376, wR2 = 0.0911
R1 = 0.0356, wR2 = 0.0685
1.075
0.960
peak/hole (e Å−3
)
2.249/−2.057
1.939/−0.827
3.607/−2.200
1.460/−0.655
9
12
13
formula
fw
C42H36AuBF4N4
880.52
C34H36AuBCl2F4N4
855.34
C31H45Au2B2Cl4F8N7·3CH2Cl2
1394.94
cryst size (mm)
temp (K)
cryst syst
space group
a (Å)
0.50 × 0.20 × 0.12
100(2)
0.24 × 0.19 × 0.11
100(2)
0.20 × 0.18 × 0.16
100(2)
triclinic
triclinic
orthorhombic
P1
̅
8.3264(3)
P1
̅
Pccn
10.4294(4)
11.4264(5)
14.3320(6)
89.6620(10)
84.8510(10)
79.5560(10)
1672.78(12)
2
20.517(2)
b (Å)
10.9307(4)
11.1756(5)
68.5800(10)
86.5110(10)
67.9390(10)
874.11(6)
23.027(2)
c (Å)
20.4338(19)
α (deg)
β (deg)
γ (deg)
V (Å3)
90
90
90
9654.1(16)
Z
1
8
Dc (g cm−3
)
1.673
1.698
1.919
μ (mm−1
)
4.267
4.610
6.579
θ range (deg)
2.16−25.00
4009
1.81−27.50°
7666
1.66−27.50
11072
no. of unique data
max, min transmission
final R indices (I > 2σ(I))
R indices (all data)
goodness of fit on F2
0.6749, 0.4824
R1 = 0.0179, wR2 = 0.0445
R1 = 0.0179, wR2 = 0.0445
1.045
0.6310, 0.4041
R1 = 0.0523, wR2 =0.1093
R1 = 0.0308, wR2 = 0.0634
1.046
0.4191, 0.3529
R1 = 0.0523, wR2 = 0.1093
R1 = 0.0878, wR2 = 0.1207
1.029
peak/hole (e Å−3
)
1.030 /−0.999
1.365/−1.078
1.990/−1.172
organic solvents, with the exception of diethyl ether and
hexane.
NMR Spectroscopic Analyses of Au(I) Complexes. All
octahydropyridazino[1,2-a]indazolin-11-ylidene) was included
as well for comparison.
The isopropyl C−H protons of complexes 1−8 exclusively
give only one multiplet, indicating a free rotation of Au−Ccarbene
bonds. Notably, these signals ranging from 4.36 to 5.42 ppm
are at significantly higher field than those (cf. 5.34−6.44 ppm)
in their previously reported Pd counterparts of the type trans-
[PdBr2(iPr2-bimy)(NHC)].7a This suggests the absence of C−
H···M anagostic (or preagostic) interactions, which are typically
complexes (1−7) were subjected to multinuclear NMR
spectroscopy in CDCl3. Due to their very good solubilities,
13
resolution of the
C
signals could be accomplished with
carbene
less than 100 scans. The isopropyl C−H signals in the common
iPr2-bimy spectator and the carbenoid resonance in all Au(I)
hetero-NHC complexes described here are summarized in
Table 3. The recently reported pyrazole-derived NHC complex
[Au(iPr2-bimy)(FPyr)]PF6 (8)6c (Fpyr = 1,2,3,4,6,7,8,9-
14
i
observed for Pr2-bimy complexes of group 10 metals. It was
also noted that the nature of the noncoordinating counteranion
1
has little effect on the H and 13C NMR spectra (cf. Table 3,
C
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complexes 5 and 6). However, a pronounced counteranion
effect (BF4 vs PF6) on the NMR spectra has been observed in a
study involving NH,NR-substituted Ni(II) NHC complexes.15
1
In addition, the H NMR spectrum of the heterotetrakis-NHC
complex 7 shows two singlets at 4.31 and 4.13 ppm in a 2:1
integral ratio for the three N-methyl groups of the diylidene
ligand, which indicates a 2-fold symmetry of this molecule.
As expected, the 13C NMR spectra of 1−8 all display two
carbenoid resonances in the downfield regions, which fall in a
wide range from 182.4 to 214.8 ppm. Baker and co-workers
13
have reported a correlation of the
C
signal in neutral
carbene
[AuX(NHC)] complexes with the donating ability of the
anionic ligand X.12 Interestingly, it was found that the constant
iPr2-bimy ligand in complexes 1−8 could be employed as a 13
C
Figure 2. Molecular structure of C showing 50% probability ellipsoids.
Hydrogen atoms and disordered atoms are omitted for clarity. Selected
bond lengths (Å) and angles (deg): Au1−C1 = 1.988(8); N1−C1−N2
= 108.5(7). Bond lengths and angles related to the acetato ligand are
not given, due to the disorder in the crystal.
NMR spectroscopic probe to determine the donor strength of
the trans-standing second NHC, whereby stronger donating
ligands would lead to a more downfield shift (Figure 3). Among
the NHCs investigated herein, the weakest triazolidinediylidene
(ditz)13a,c ligand in complex 7 leads to the most upfield Pr2-
i
bimy carbenoid signal, while the strongest pyrazole-derived
ligand (FPyr) in complex 8 gives rise to the most downfield
iPr2-bimy carbene signal. Remarkably, these 13C NMR values
nicely correlate with those found in their Pd(II) counterparts
(vide infra).
Scheme 4. Synthesis of Au(I) Hetero-Bis-NHC Complexes
2−6
Ligand Redistribution of Au(I) Hetero-NHC Com-
plexes. During the synthesis of complexes 2−4 and 7 it was
observed that prolonging the reaction time beyond the
tabulated value (Table 2) generally favored ligand redistrib-
ution processes, which are irreversible and led to the generation
of homo-bis-NHC complexes as side products. This process
Table 2. Optimal Conditions for Synthesis of Complexes 2−6
a
A.T. = ambient temperature.
D
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Scheme 5. Synthesis of Au(I) Hetero-Tetrakis-NHC Complex 7
Table 3. Selected NMR Spectroscopic Data for Complexes
1−8 of the Type [Au(iPr2-bimy)(NHC)]X (X = BF4/PF6)
b
c
c
δH1
δC1
δC2
a
complex
(ppm)
(ppm)
(ppm)
[Au(iPr2-bimy)(Indy)]BF4 (1)
[Au(iPr2-bimy)(Bn2-tazy)]BF4 (2)
[Au(iPr2-bimy)(Bn2-bimy)]BF4 (3)
[Au(iPr2-bimy)(Bn-btzy)]BF4 (4)
[Au(iPr2-bimy)(IPr)]BF4 (5)
5.42
5.08
5.18
5.25
4.36
4.36
5.31
5.33
190.8
186.6
187.6
186.2
186.7
186.7
185.6
192.5
182.4
186.7
191.5
214.8
187.3
187.3
189.4
179.6
[Au(iPr2-bimy)(IPr)]PF6 (6)
[Au2(iPr2-bimy)2(μ-ditz)](BF4)2 (7)
[Au(iPr2-bimy)(FPyr)]PF6 (8)6c
a
i
Abbreviations: Pr2-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene;
Indy = 6,7,8,9-tetrahydropyridazino[1,2-a]indazolin-3-ylidene; Bn2-
tazy = 1,4-dibenzyl-1,2,4-triazolin-5-ylidene; Bn2-bimy = 1,3-diben-
zyl-benzimidazolin-2-ylidene; Bn-btzy = 3-benzylbenzothiazolin-2-
ylidene; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene;
ditz = 1,2,4-triazolidine-3,5-diylidene; Fpyr = 1,2,3,4,6,7,8,9-
Figure 4. Time-dependent 1H NMR spectra showing the ligand
redistribution of complex 3 in CDCl3..
b
octahydropyridazino[1,2-a]indazolin-11-ylidene. δH1 refers to the
c
isopropyl C−H signals in the constant iPr2-bimy ligands. δC1 refers to
the carbenoid signal of the spectator ligand iPr2-bimy, and δC2 refers to
the carbenoid signal of the NHC trans to the Pr2-bimy ligand. 13C
i
While initially only signals due to the hetero-bis-NHC
complex 3 are present, new signals due to the homoleptic bis-
carbene complexes 9 and 10 (Scheme 6) start evolving with
NMR spectra were measured in CDCl3 and internally referenced to
the solvent signal at 77.7 ppm relative to TMS.
i
time. In addition, signals due to the azolium salts Pr2-
−
−
can be monitored by 1H NMR spectroscopy and is
demonstrated for complex 3 as a representative in Figure 4.
bimy·H+BF4 (a) and Bn2-bimy·H+BF4 (c) are also observed
with time, supposedly due to hydrolysis of free carbenes, which
Figure 3. Donor abilities of NHCs on the 13C NMR scale.
E
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Scheme 6. Ligand Redistribution of Hetero-Bis-NHC Complex 3
Scheme 7. Ligand Redistribution of the Hetero-Tetrakis-NHC Complex 7
Figure 5. Molecular structures of 1, 2, 6, and 9 showing 50% probability ellipsoids. Hydrogen atoms and counteranions are omitted for clarity.
Selected bond lengths (Å) and angles (deg) are as follows. Complex 1: Au1−C14 = 2.025(5), Au1−C1 = 2.035(5); C14−Au1−C1 = 178.51(19),
N2−C1−N1 = 107.2(4), N3−C14−C15 = 104.8(4). Complex 2: Au1−C14 = 1.995(4), Au1−C1 = 2.021(4); C14−Au1−C1 = 176.93(15), N2−
C1−N1 = 107.2(3), N4−C14−N3 = 101.8(3). Complex 6: Au1−C14 1.996(5), Au1−C1 2.015(5); C14−Au1−C1 176.1(2), N2−C1−N1
107.8(5), N4−C14−N3 103.9(4). Complex 9: Au1−C1 = 2.022(2); C1−Au1−C1A = 180.00(13), N1−C1−N2 = 106.59(17).
may point to a dissociative pathway. Interestingly, signals of the
mono-carbene complexes [AuCl(Bn2-bimy)] and [AuCl(iPr2-
bimy)] (B) are also present. The last two are formed by capture
of chlorido ligands present in the chlorinated solvent.
insoluble in common organic solvents, thus hampering further
characterization. This supposedly polymeric/oligomeric com-
plex 11 (Scheme 7) further decomposes to purple gold upon
prolonged standing.
Notably, the rearrangement for the dinuclear complex 7
bearing a triazolidine-3,5-diylidene bridge is markedly faster
than that for mononuclear hetero-bis-NHC analogues. Within 1
h, a white precipitate formed from its CDCl3 solution that was
Similar ligand redistribution processes in solution have been
observed for complexes of the type [Au(X)(NHC)] (X =
anionic ligand) and [Au(NHC)(PPh3)]CF3SO3.6a,16 However,
to the best of our knowledge, these are the first reports on the
F
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Scheme 8. Synthesis of Au(III) Hetero-NHC Complexes 12 and 13
ligand redistribution of Au(I) hetero-bis- or hetero-tetrakis-
NHC complexes. The process is likely to be triggered by the
presence of two or more different carbene ligands with different
donating abilities and trans influences, resulting in Au−Ccarbene
bonds of different strengths. The thermodynamically stable
rearrangement products, on the other hand, are homoleptic
complexes with only one type of Au−Ccarbene bond of the same
strength, rendering them more stable than their kinetically
controlled heteroleptic counterparts. The presence of azolium
salts as hydrolysis products of free NHCs may point to a
dissociative rearrangement pathway involving de- and recoordi-
nation of carbene ligands (Figure 4). However, the nature of
this redistribution process remains to be explored in the future.
Finally, it should be noted that the redistribution process is
slow in comparison to the time required for the acquisition of
angles close to 180°. The two carbene planes are twisted by
angles of 8.43° (1), 43.97° (2), and 10.74° (6), respectively.
The Au−C(iPr2-bimy) bond lengths of 2.015(5)−2.035(5) Å
are comparable to those in Au(I) homo-bis-iPr2-bimy
complexes.9 The N-dipp substituents of the IPr ligand in 6
are oriented perpendicularly to the imidazole-based carbene
ring, which is typically observed in Au−IPr complexes.6b On
the other hand, the molecular structure of 9 reveals an Au(I)
center coordinated by two Bn2-bimy ligands in a linear
arrangement. The two carbene ligands are related to each
other by a crystallographic inversion center and are thus
coplanar, with their benzyl substituents pointing to opposite
directions to reduce the steric hindrance. It should finally be
noted that no aurophilic17 interactions were observed in any of
the molecular structures, probably due to the steric bulk of the
NHC ligands.
Syntheses and Characterization of Au(III) Hetero-NHC
Complexes. As discussed above, complexes 3 and 7 readily
undergo ligand redistribution in solution upon standing, which
hampers their crystallization. To provide a more conclusive
evidence for their formation, they were subjected to oxidative
addition using a slight excess of PhICl2 in an attempt to form
their Au(III) derivatives (Scheme 8).
13C NMR spectra and thus poses no problem in the detection
13
of the respective
C
carbene
signals for all Au(I) hetero-carbene
complexes described here.
Interestingly, for complexes 1, 5, 6, and 8, such ligand
redistributions were not observed. The nonclassical indazole-
derived carbene (Indy) in 1 and pyrazole-derived carbene
(FPyr) in 8 are known to be the strongest carbene donors
studied here (Figure 3).7a The increased electron density in
these two complexes may result in stronger Au−carbene bonds
due to enhanced π back-donation, which are non-negligible in
d10 complexes, hindering further ligand redistribution.
For complexes 5 and 6, electronic factors certainly do not
play a major role, since these complexes contain the very bulky
IPr ligand. Apparently, the formation of the cationic [Au-
(IPr)2]+ species is disfavored due to steric factors, and the
hetero-bis-NHC complexes remain stable.
X-ray Diffraction Study of Au(I) Complexes. Single
crystals of the hetero-bis-NHC complexes 1, 2, and 6 suitable
for X-ray diffraction analyses were obtained by slow
evaporation of concentrated CH2Cl2/hexane solutions. On
the other hand, attempted crystallization of the hetero-bis-
NHC complex [Au(iPr2-bimy)(Bn2-bimy)]BF4 (3) from a
concentrated CH2Cl2/hexane solution afforded crystals of the
homoleptic bis-NHC complex [Au(Bn2-bimy)2]BF4 (9; Bn2-
bimy = 1,3-dibenzylbenzimidazolin-2-ylidene) due to the
aforementioned redistribution processes (vide supra).
Indeed, these reactions gave the respective hetero-bis-NHC
and hetero-tetrakis-NHC complexes trans-[AuCl2(iPr2-bimy)-
(Bn2-bimy)]BF4 (12) and all-trans-[Au2Cl4(iPr2-bimy)2(μ-
ditz)](BF4)2 (13) in good yields (Scheme 8). They are soluble
in CH2Cl2 and DMSO but less soluble in CHCl3 and insoluble
in nonpolar solvents such as diethyl ether and hexane. In their
ESI mass spectra, base peaks were found at m/z 769 and 526
arising from the cationic and dicationic species [12 − BF4]+ and
[13 − 2BF4]2+, respectively. Their 1H NMR spectra recorded in
i
CD2Cl2 show the isopropyl C−H protons of the Pr2-bimy
ligand as a multiplet at 4.49 (12) and 5.38 ppm (13),
suggesting rotational freedom of the Au−C(iPr2-bimy) bonds
despite the coordination of the additional two chlorido
13
coligands. Notably, all
C
NMR signals of complexes
carbene
12 and 13 found at 153.4−168.6 ppm show significant upfield
shifts (ΔδC = 20.7−32.1 ppm) in comparison to those in their
respective Au(I) precursor complexes 3 and 7.
The formation of complexes 12 and 13 was unambiguously
confirmed by X-ray diffraction studies of single crystals
obtained by slow evaporation of concentrated solutions of 12
and 13 in CH2Cl2/hexane. The molecular structures are
In the molecular structures of 1, 2, and 6 depicted in Figure
i
5, the Pr2-bimy and the second carbene ligand adopt a linear
arrangement about the gold(I) center with C−Au−C bond
G
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depicted in Figure 6. In complex 12, the Au(III) center adopts
a square-planar coordination geometry with the two different
respectively. The Au−Ccarbene bond lengths of 2.042(3) and
2.046(3) Å are in good agreement with those found in other
chlorido AuIII−NHC complexes.18
Notably, and unlike the case for their Au(I) precursors 3 and
7, Au(III) complexes 12 and 13 are much more stable, and no
ligand redistributions in CH2Cl2 solutions were observed even
on standing for a couple of days. The increased Lewis acidity of
Au(III) versus Au(I) would probably lead to stronger AuIII−
NHC bonds, stabilizing the Au(III) hetero-NHC complexes
and thus hampering the ligand redistribution process.
Palladium Hetero-NHC Complexes. Previously, we
evaluated the donating abilities of various types of NHCs by
13
comparing the
C
(iPr2-bimy) chemical shifts in hetero-
carbene
bis-NHC complexes of the type trans-[PdBr2(iPr2-bimy)-
(NHC)].7,13a With the aim of a more detailed comparison
with all analogous Au(I) hetero-NHC complexes described
above, the three new Pd(II) hetero-bis-NHC complexes trans-
[PdBr2(iPr2-bimy)(FPyr)] (1′), trans-[PdBr2(iPr2-bimy)(Bn-
btzy)] (4′), and trans-[PdBr2(iPr2-bimy)(Indy)] (8′) were
synthesized, following a straightforward Ag−carbene transfer
protocol (Scheme 9).7 Complexes 1′ and 8′ could be afforded
by a one-pot bridge-cleavage reaction involving the dimeric
complex [PdBr2(iPr2-bimy)]2 (D), Ag2O, and the correspond-
ing azolium salts. However, in the case of the 3-
benzylbenzothiazolin-2-ylidene complex trans-[PdBr2(iPr2-
bimy)(Bn-btzy)] (4′), this transmetalation approach was
unsuccessful and instead led to ring opening of the
benzothiazolium salt. Thus, the “inverse” bridge-cleavage
reaction of the previously reported dimeric complex
Figure 6. Molecular structures of 12 and 13 showing 50% probability
ellipsoids. Hydrogen atoms and counteranions are omitted for clarity.
Selected bond lengths (Å) and angles (deg) are as follows. Complex
12: Au1−C1 = 2.042(3), Au1−C14 = 2.046(3), Au1−Cl1 =
2.2745(8), Au1−Cl2 = 2.2790(8); C1−Au1−C14 = 175.78(12),
C1−Au1−Cl1 = 87.17(9), C14−Au1−Cl1 = 90.41(9), C1−Au1−Cl2
= 92.36(9), C14−Au1−Cl2, = 90.11(9), Cl1−Au1−Cl2 = 178.97(3).
Complex 13: Au1−C1 = 2.031(8), Au1−C14 = 2.056(7), Au1−Cl2 =
2.277(2), Au1−Cl1 = 2.280(2), Au2−C19 = 2.030(9), Au2−C15 =
2.061(8), Au2−Cl4 = 2.281(2), Au2−Cl3 = 2.283(2); C1−Au1−C14
= 177.2(3), C1−Au1−Cl2 = 89.9(2), C14−Au1−Cl2 = 91.2(2), C1−
Au1−Cl1 = 89.5(2), C14−Au1−Cl1 = 89.4(2), Cl2−Au1−Cl1 =
177.62(8), C19−Au2−C15 = 175.8(3), C19−Au2−Cl4 = 89.7(3),
C15−Au2−Cl4 = 94.1(2), C19−Au2−Cl3 = 87.6(2), C15−Au2−Cl3
= 88.6(2), Cl4−Au2−Cl3 = 177.27(8).
[PdBr2(Bn-btzy)]2 (E)19 using the benzimidazolium salt Pr2-
i
bimy·H+Br− was attempted, which gave the desired complex 4′
in a good yield.
Complexes 1′, 4′, and 8′ were isolated in good yields as
yellow solids, which are soluble in most organic solvents with
the exception of nonpolar solvents such as diethyl ether and
hexane. In all three cases, their formation was supported by ESI
mass spectra, where a base peak corresponding to the [M −
Br]+ fragment was observed. In contrast to the aforementioned
Au(I) analogues 1, 4, and 8, the 1H NMR spectra of 1′, 4′, and
i
8′ all display two multiplets due to the two inequivalent Pr2-
bimy isopropyl C−H protons, suggesting a hindered rotation of
Pd−Ccarbene bonds.
In their 13C NMR spectra, two carbene signals are observed,
i
benzimidazolin-2-ylidene ligands and two chlorido ligands in a
trans arrangement. The C1−Au−C14 and Cl1−Au−Cl2 bonds
are almost linear with angles of 175.78(12) and 178.97(3)°,
as expected. The Pr2-bimy carbenoid 13C signals are found at
181.4 (1′), 176.4 (4′), and 184.0 ppm (8′), respectively. In
comparison to the donor strengths of other carbene ligands
Scheme 9. Synthesis of Pd(II) Hetero-Bis-NHC Complexes 1′, 4′, and 8′
H
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Figure 7. Donor abilities of NHCs on the 13C NMR scale.
Table 4. Selected NMR Data of Au(I) Hetero-NHC Complexes 1−8 and Pd(II) Analogues 1′−8′
a
b
Measured in CDCl3 and internally referenced to the solvent residual signal at 77.7 ppm relative to TMS. Values are from a previous study.6c,7a,13a
previously determined on the Pd(II) 13C NMR spectroscopic
scale7 (Figure 7), pyrazole-derived FPyr in 1′ and indazole-
derived Indy in 8′ prove to be stronger donors than the classical
NHC ligands iv and v (Figure 7). The donor ability of the
alicyclic FPyr ligand is even stronger than that of 1,2-
diethylpyrazolin-3-ylidene (i), which could be rationalized by
the greater +I effect of two alicyclic moieties in FPyr versus
only two ethyl substituents in i (Figure 7). In addition, the
donating ability of the alicyclic indazolin-3-ylidene (Indy) falls
in the range between those of its diethyl analogue ii and 1,2,3-
triazolin-5-ylidene iii (Figure 7). Finally, the benzothiazole-
derived ligand Bn-btzy in 4′ turns out to a be relatively weaker
fall in a narrower region in comparison to those in Pd(II)
analogues, which may suggest a reduced resolution of the Au(I)
system with respect to a donor strength evaluation of trans-
standing NHC ligands.
Donating capacities of NHC ligands are also known to be
evaluated by Tolman’s electronic parameter (TEP), and the
correlation of TEP values between different metal systems
(Ni(0), Ir(I), Rh(I)) has been established.20 To examine how
13
our
C
carbene
(iPr2-bimy) based electronic parameter correlates
between Pd(II) and Au(I) systems described in this work, the
data sets in Table 4 were subjected to linear regression, and the
resulting graphical presentation is shown in Figure 8. Notably,
the regression coefficient R2 = 0.98 was obtained, which clearly
donor comparable to the 1,2,4-triazolin-5-ylidene vi.
13
(iPr2-bimy) Signals.
carbene
indicates a very good linear correlation between the
Au(I)/Pd(II) Correlation of
C
13
C
(iPr2-bimy) values of these two metal systems. This
The Pr2-bimy carbenoid NMR signals in both [Au(iPr2-
bimy)(NHC)]BF4/PF6 and trans-[PdBr2(iPr2-bimy)(NHC)]
hetero-NHC complexes were found to be good indicators of
the donor strengths of the trans-standing NHC ligands,
whereby stronger donating ligands would lead to a greater
i
carbene
further supports that Pr2-bimy carbenoid signals in [Au(iPr2-
bimy)(NHC)]BF4/PF6 and trans-[PdBr2(iPr2-bimy)(NHC)]
could both reliably be employed as an electronic parameter
for NHC ligands. Interconversion between the Au(I) and
Pd(II) systems can be easily achieved by applying eq 1, where
[Pd] and [Au] are the 13Ccarbene(iPr2-bimy) chemical shift values
in ppm.
i
i
downfield shift. A direct comparison between the Pr2-bimy
carbenoid signals in Au(I) complexes 1−8 and their Pd(II)
analogues 1′−8′ is summarized in Table 4. Notably, the
13
C
signals of iPr2-bimy in the Au(I) systems are generally
carbene
[Pd] = 1.19[Au] − 45.0
(1)
more downfield (ΔδC ≈ 10 ppm) in comparison to those in
their corresponding Pd(II) analogues (Table 4), which again
The introduction of Au(I) as an alternative metal center
increases the versatility of future complex probe syntheses,
which broadens the scope of our 13C NMR based electronic
reflects a more Lewis acidic metal center in the latter. In
13
addition, the
C
(iPr2-bimy) values in Au(I) complexes
carbene
I
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[Au(iPr2-bimy)(Indy)]BF4 (1). K2CO3 (29 mg, 0.2 mmol) was
added to a solution of the chlorido complex A (42 mg, 0.1 mmol) and
1,3-diisopropylbenzimidazolium tetrafluoroborate (a; 30 mg, 0.1
mmol) in acetone (30 mL). The reaction mixture was stirred for 24
h at ambient temperature, and the solvent of the reaction mixture was
then removed under vacuum. The residue was suspended in CH2Cl2
(15 mL) and subsequently filtered over Celite. The solvent of the
filtrate was then removed under vacuum. The residue was washed with
ethyl acetate (3 × 10 mL) and dried under vacuum, affording the
1
product as an off-white powder (52 mg, 0.08 mmol, 76%). H NMR
(500 MHz, CDCl3): δ 7.99 (d, 1 H, Ar-H), 7.70 (dd, 2 H, Ar-H), 7.68
(d, 1 H, Ar-H), 7.57 (d, 1 H, Ar-H), 7.43 (dd, 2 H, Ar-H), 7.36 (t, 1 H,
Ar-H), 5.42 (m, 2 H, CH(CH3)2, 3J(H,H) = 6.90 Hz), 4.85 (br t, 2 H,
NCH2), 4.37 (br t, 2 H, NCH2), 2.37 (br m, 4 H, CH2), 1.87 (d, 12 H,
CH(CH3)2, 3J(H,H) = 6.90 Hz). 13C{1H} NMR (125.76 MHz,
CDCl3): δ 190.8 (s, NCN), 182.4 (s, NCC), 141.7, 133.3, 132.9, 131.1,
127.3, 125.1, 124.1, 113.6, 110.6 (s, Ar-C), 54.3 (s, CH(CH3)2), 54.0,
48.0 (s, NCH2), 23.3 (s, CH(CH3)2), 22.4, 21.3 (s, NCH2). 19F NMR
(282.40 MHz, CDCl3): δ −77.88 (s, 10BF4), −77.94 (s, 11BF4). MS
(ESI): m/z 571 [M − BF4]+. Anal. Calcd for C24H30N4AuBF4: C,
43.79; H, 4.59; N, 8.51. Found: C, 43.88; H, 4.42; N, 8.47%.
13
Figure 8. Correlation of the
C
(iPr2-bimy) NMR values of
carbene
[Au(iPr2-bimy)(NHC)]BF4/PF6 and trans-[PdBr2(iPr2-bimy)(NHC)]
complexes.
[Au(O2CCH3)(iPr2-bimy)] (C). CH2Cl2 (10 mL) was added to a
mixture of complex B (43.5 mg, 0.1 mmol) and silver acetate (20 mg,
0.12 mmol). The reaction mixture was stirred for 1 h while it was
shielded from light and subsequently filtered through Celite. Removal
of the solvent from the filtrate under vacuum yielded the product as a
parameter. Finally, it should be noted that the solubility of
Au(I) hetero-NHC complexes in CDCl3 is significantly better
than that of their Pd(II) congeners. This advantage will allow a
much faster detection of the iPr2-bimy 13C NMR signals, which
can generally be accomplished in less than 100 scans.
1
white powder (34.3 mg, 0.075 mmol, 75%). H NMR (300 MHz,
CDCl3): δ 7.64−7.61 (m, 2 H, Ar-H), 7.36−7.33 (m, 2 H, Ar-H), 5.45
CONCLUSION
(m, 2 H, CH(CH3)2, 3J(H,H) = 6.9 Hz), 2.09 (s, CH3COO), 1.75 (d,
■
3
12 H, CH(CH3)2, J(H,H) = 6.9 Hz). 13C{1H} NMR (75.47 MHz,
We have reported the synthesis of the Au(I) acetato
benzimidazolin-2-ylidene complex [Au(O2CCH3)(iPr2-bimy)]
(C), which represents a new versatile precursor to a wide range
of Au(I) hetero-bis-NHC complexes (2−6) as well as one
hetero-tetrakis-NHC complex (7). The constant 1,3-diisopro-
pylbenzimidazolin-2-ylidene ligand (iPr2-bimy) in complexes of
the type [Au(iPr2-bimy)(NHC)]BF4/PF6 (1−8) was found to
be a useful spectroscopic probe to determine the donating
abilities of trans-standing NHC ligands. Some of the Au(I)
hetero-NHC complexes were found to undergo ligand
redistributions, which depend on the donor strength and
CDCl3): δ 178.0 (s, CH3COO), 170.2 (s, NCN), 133.1, 125.5, 124.4,
113.5 (s, Ar-C), 54.8 (s, CH(CH3)2), 24.3 (s, CH3COO), 22.3 (s,
CH(CH3)2). MS (ESI): m/z 601 [M − CH3COO + L]+. Anal. Calcd
for C15H21AuN2O2: C, 39.31; H, 4.62; N, 6.11. Found: C, 39.14; H,
4.35; N, 6.06.
General Procedure for [Au(iPr2-bimy)(NHC)]X (X = BF4/PF6,
2−7). Complex C (46 mg, 0.1 mmol) and the chosen azolium salt
NHC·H+X− (b−f; 0.1 mmol) were mixed in the chosen solvent (10
mL), and the reaction mixture was stirred at the temperature and time
indicated in Table 2. The reaction mixture was filtered via Celite, and
the filtrate was concentrated under vacuum. Hexane was added, and
the resulting white precipitate was collected and dried under vacuum,
affording the product as a white solid.
bulkiness of the incorporated NHC ligands. A very good linear
correlation was found between the
13
C
carbene
(iPr2-bimy) NMR
[Au(iPr2-bimy)(Bn2-tazy)]BF4 (2). The general procedure afforded 2
signals of the Au(I) complexes and their respective Pd(II)
analogues trans-[PdBr2(iPr2-bimy)(NHC)]. This allows the
determination of our 13C NMR based electronic parameter for
a wider range of NHC ligands. Research in our laboratories is
underway to broaden the scope of this new electronic
parameter as well as to study its limitations.
1
as a white solid (59 mg, 0.08 mmol, 80%). H NMR (300 MHz,
CDCl3): δ 8.61 (s, 1 H, NCHN), 7.69−7.65 (m, 2 H, Ar-H), 7.43−
7.40 (m, 2 H, Ar-H), 7.33 (br, m, 10 H, Ar-H), 5.57 (s, 4 H, CH2Ph),
5.08 (m, 2 H, CH(CH3)2, 3J(H,H) = 6.9 Hz), 1.65 (d, 12 H,
CH(CH3)2, 3J(H,H) = 6.9 Hz). 13C{1H} NMR (75.47 MHz, CDCl3):
δ 186.6 (s, NCN-iPr2-bimy), 186.6 (s, NCN-Bn2-bimy), 145.0, 135.7,
135.5, 133.1, 129.75, 129.66, 129.3, 128.4, 128.2, 125.3, 113.9 (s, Ar-
C), 57.7 (s, CH2Ph), 53.0 (s, CH(CH3)2), 22.9 (s, CH(CH3)2). 19F
NMR (282.4 MHz, CDCl3): δ −76.33 (s, 10BF4), −76.39 (s, 11BF4).
MS (ESI): m/z 648 [M − BF4]+. Anal. Calcd for C29H33AuBF4N5: C,
47.36; H, 4.52; N, 9.52. Found: C, 47.44; H, 4.74; N, 9.20.
EXPERIMENTAL SECTION
■
General Considerations. Unless otherwise stated, all manipu-
lations were carried out without taking precautions to exclude air and
moisture. All chemicals and solvents were used as received without
further purification if not mentioned otherwise. Complexes A,8 B,9
D,14a and 86c and the salt g13a were synthesized as previously reported.
Complex E was synthesized via a modified procedure.19 1H, 13C, and
19F NMR spectra were recorded on Bruker ACF 300 and Bruker AMX
500 spectrometers, and the chemical shifts (δ) were internally
referenced to the residual solvent signals relative to [Si(CH3)4] (1H,
13C) or externally to CF3CO2H (19F). ESI mass spectra were measured
using a Finnigan MAT LCQ spectrometer. Elemental analyses were
done on an Elementar Vario Micro Cube elemental analyzer at the
Department of Chemistry, National University of Singapore.
General Procedure for Synthesis of Mono-NHC·H+X− (X =
BF4, PF6). All carbene precursor salts (a−f) were obtained by anion
exchange of the corresponding NHC·H+Br−/Cl− with excess NaBF4 in
CH3CN or KPF6 in H2O. NHC·H+Br−/Cl− were synthesized
according to reported methods.7a,14
[Au(iPr2-bimy)(Bn2-bimy)]BF4 (3). The general procedure afforded 3
1
as a white solid (64 mg, 0.082 mmol, 82%). H NMR (300 MHz,
CDCl3): δ 7.66−7.63 (m, 2 H, Ar-H), 7.55−7.52 (m, 2 H, Ar-H),
7.41−7.31 (m, 14 H, Ar-H), 5.89 (s, 4 H, CH2Ph), 5.14 (m, 2 H,
3
3J(H,H) = 6.9 Hz, CH(CH3)2), 1.64 (d, 12 H, J(H,H) = 6.9 Hz,
CH(CH3)2). 13C{1H} NMR (75.47 MHz, CDCl3): δ 191.5 (s, NCN-
Bn2-bimy), 187.6 (s, NCN-iPr2-bimy), 135.8, 134.2, 133.0, 129.7,
129.0, 127.2, 126.0, 125.2, 113.7, 112.9 (s, Ar-C), 54.4, 52.6 (s, CH2Ph
and CH(CH3)2), 22.9 (s, CH(CH3)2). 19F NMR (282.4 MHz,
CDCl3): δ −76.87 (s, 10BF4), −76.92 (s, 11BF4). MS (ESI): m/z 697
[M − BF4]+. Anal. Calcd for C34H36AuBF4N4: C, 52.06; H, 4.63; N,
7.14. Found: C, 52.31; H, 4.42; N, 7.03.
[Au(Bn-btay)(iPr2-bimy)]PF6 (4). The general procedure afforded 4
1
as a white solid (58 mg, 0.076 mmol, 76%). H NMR (500 MHz,
CDCl3): δ 7.69−7.30 (m, 13 H, Ar-H), 6.21 (s, 2 H, CH2Ph), 5.25 (s,
J
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2 H, CH(CH3)2, 3J(H,H) = 6.9 Hz), 1.74 (d, 12 H, CH(CH3)2,
3J(H,H) = 6.9 Hz). 13C{1H} NMR (125.76 MHz, CDCl3): δ 214.8 (s,
NCS), 186.2 (s, NCN), 143.7, 134.5, 133.2, 131.3, 130.4, 129.9, 129.4,
127.7, 127.1, 125.3, 123.7, 116.9, 113.9, 113.8 (s, Ar-C), 59.4 (s,
CH2Ph), 54.7 (s, CH(CH3)2), 23.0 (s, CH(CH3)2). 19F NMR (282.4
MHz, CDCl3): δ −75.92 (s, 10BF4), −75.97 (s, 11BF4). MS (ESI): m/z
624 [M − PF6]+. Anal. Calcd for C27H29AuBF4N3S: C, 45.59; H, 4.11;
N, 5.91. Found: C, 45.61; H, 4.31; N, 6.04.
6 H, NCH3), 4.59 (s, 3 H, NCH3), 1.87 (CH(CH3)2, d, 12 H, 3J(H,H)
= 6.5 Hz). 13C{1H} NMR (75.47 MHz, CD2Cl2): δ 168.6 (s, NCHN,
ditz), 153.4 (s, NCHN, Pr2-bimy), 133.4, 125.8, 114.9 (s, Ar-C), 56.4
(s, CH(CH3)2), 41.6 (s, NCH3), 39.8 (s, NCH3), 21.3 (s, CH(CH3)2).
19F NMR (300 MHz, CD2Cl2): δ −76.75 (s, 10BF4), −76.80 (s, 11BF4).
MS (ESI): m/z 1138 [M − BF4]+, 526 [M − 2BF4]2+. Anal. Calcd for
C31H45Au2B2Cl4F8N7: C, 30.39; H, 3.70; N, 8.00. Found: C, 30.18; H,
3.87; N, 7.82.
i
[PdBr2(Indy)(iPr2-bimy)] (1′). Dimeric complex D (105 mg, 0.11
mmol) and Indy·H+Br− (57 mg, 0.23 mmol) were suspended in
CH2Cl2 (25 mL). Ag2O (36 mg, 0.16 mmol) was added to the
mixture, and the resulting suspension was stirred for 12 h while it was
shielded from light. The reaction mixture was then filtered over Celite,
and the solvent of the filtrate was removed under vacuum, yielding the
crude product. The crude product was redissolved in a minimal
volume of CHCl3, and the solution was filtered over Celite. A large
excess of diethyl ether was added to the filtrate to precipitate the
product. The precipitate was collected and dried under vacuum,
yielding the product as a pale orange powder (125 mg, 0.20 mmol,
87%). 1H NMR (500 MHz, CDCl3): δ 8.54 (d, 1 H, Ar-H), 7.54−7.64
(m, 3 H, Ar-H), 7.36 (t, 1 H, Ar-H), 7.27 (d, 1 H, Ar-H), 7.23 (dd, 2
H, Ar-H), 6.47 (br m, 1 H, NCH), 6.23 (br m, 1 H, NCH), 5.08 (br t,
2 H, NCH2), 4.01 (br t, 2 H, NCH2), 2.25 (br m, 4 H, CH2), 1.93 (br
d, 6 H, CH3), 1.87 (br d, 6 H, CH3). 13C{1H} NMR (125.8 MHz,
CDCl3): δ 181.4 (s, Ccarbene (iPr2-bimy)), 179.6 (s, Ccarbene (Indy)),
142.9, 134.5, 134.3, 131.9, 131.6, 130.5, 123.3, 122.5, 113.2, 109.6 (s,
Ar-C), 54.3 (s, NCH), 53.1, 48.4 (s, NCH2), 23.3, 22.1 (s, CH2), 21.9
(s, CH3). MS (ESI): m/z 561 [M − Br]+. Anal. Calcd for
C24H30N4PdBr2: C, 44.99; H, 4.72; N, 8.74. Found: C, 45.00; H,
4.93; N, 8.57.
[Au(IPr)(iPr2-bimy)]BF4 (5). The general procedure afforded the
1
product as a white solid (77 mg, 0.088 mmol, 88%). H NMR (500
MHz, CDCl3): δ 7.64−7.27 (m, 12 H, Ar-H), 4.36 (m, 2 H,
3
3
CH(CH3)2, J(H,H) = 6.9 Hz), 2.56 (m, 4 H, CH(CH3)2, J(H,H) =
6.9 Hz), 1.27−1.24 (d, 36 H, CH(CH3)2, 3J(H,H) = 6.9 Hz). 13C{1H}
NMR (125.76 MHz, CDCl3): δ 187.3 (s, NCN−IPr), 186.7 (s,
NCN-iPr2-bimy), 146.6, 134.5, 133.0, 131.6, 125.4, 125.2, 125.0, 113.5
(s, Ar-C), 53.9 (s, CH(CH3)2-iPr2-bimy), 29.5 (s, CH(CH3)2-IPr),
25.2, 24.8, 22.6 (s, CH(CH3)2). 19F NMR (282.37 Hz, CDCl3): δ
−77.90 (s, 10BF4), −77.94 (s, 11BF4). MS (ESI): m/z 788 [M − BF4]+.
Anal. Calcd for C40H54AuBF4N4: C, 54.93; H, 6.22; N, 6.41. Found: C,
54.90; H, 6.13; N, 6.25.
[Au(IPr)(iPr2-bimy)]PF6 (6). The general procedure afforded the
1
product as a white solid (80 mg, 0.086 mmol, 86%). H NMR (300
MHz, CDCl3): δ 7.64−7.27 (m, 12 H, Ar-H), 4.36 (m, 2 H,
3
3
CH(CH3)2, J(H,H) = 6.9 Hz), 2.57 (m, 4 H, CH(CH3)2, J(H,H) =
6.9 Hz), 1.27 (d, 24 H, CH(CH3)2, 3J(H,H) = 6.9 Hz), 1.26 (d, 12 H,
CH(CH3)2, 3J(H,H) = 6.9 Hz). 13C{1H} NMR (75.47 MHz, CDCl3):
δ 187.3 (s, NCN−IPr), 186.7(s, NCN-iPr2-bimy), 146.5, 134.5, 133.0,
131.6, 125.3, 125.1, 125.0, 113.5 (s, Ar-C), 53.9 (s, CH(CH3)2-iPr2-
bimy), 29.4 (s, CH(CH3)2-IPr), 25.1, 24.8, 22.6 (s, CH(CH3)2). 31P
2
NMR (121.49 MHz, CDCl3): δ −143.7 (sept, J(P,F) = 712.4 Hz).
[PdBr2(Bn-btay)(iPr2-bimy)] (4′). The precursor salt iPr2-
bimy·H+Br− (16 mg, 0.06 mmol) and Ag2O (7 mg, 0.03 mmol)
were suspended in CH2Cl2 (5 mL) and stirred for 3 h. The resulting
mixture was filtered into a CH2Cl2 solution of dimeric complex E (28
mg, 0.03 mmol) and stirred for 1 h. The suspension was filtered over
Celite, and the solvent of the filtrate was removed under vacuum. The
product was obtained as a yellow solid after recrystallization from
CH2Cl2/toluene (32 mg, 0.05 mmol, 82%). 1H NMR (300 MHz,
CDCl3): δ 7.85−7.83 (m, 1 H, Ar-H), 7.65−7.59 (m, 5 H, Ar-H),
7.43−7.34 (m, 5 H, Ar-H), 7.21−7.18 (m, 2 H, Ar-H), 6.54 (s, 2 H,
NCH2), 6.05 (m, 2 H, CH(CH3)2, 3J(H, H) = 7.1 Hz), 1.71 (d, 12 H,
CH(CH3)2, 3J(H, H) = 7.1 Hz). 13C{1H} NMR (75.48 MHz, CDCl3):
δ 217.7 (s, NCS), 176.4 (s, NCN-iPr2-bimy), 144.3, 137.2, 135.0,
134.3, 129.7, 128.9, 128.1, 127.3, 125.6, 122.8, 122.7, 115.3, 113.3 (s,
Ar-C), 59.1 (s, NCH), 54.6 (s, NCH2), 21.6 (s, CH3). MS (ESI): m/z
614 [M − Br]+. Anal. Calcd for C27H29Br2N3PdS: C, 46.74; H, 4.21;
N, 6.06. Found: C, 46.39; H, 4.55; N, 5.66.
2
19F NMR (282.37 Hz, CDCl3): δ 2.395 (d, J(P,F) = 712.4 Hz). MS
(ESI): m/z 788 [M − PF6]+. Anal. Calcd for C40H54AuF6N4P: C,
51.50; H, 5.83; N, 6.01. Found: C, 51.74; H, 5.57; N, 5.55.
[Au(iPr2-bimy)]2(μ-ditz)(BF4)2 (7). The general procedure followed
by flash column chromatography (ethyl acetate) afforded 7 as a white
solid (52 mg, 0.048 mmol, 48%). Complex 7 could be alternatively
1
synthesized via Ag−carbene transfer method in a yield of 56%. H
NMR (500 MHz, CDCl3): δ 7.68−7.66 (m, 4 H, Ar-H), 7.39−7.37
(m, 4 H, Ar-H), 5.31 (m, 4 H, CH(CH3)2, 3J(H,H) = 7.0 Hz), 4.31 (s,
6 H, NCH3), 4.13 (s, 3 H, NCH3), 1.75 (d, 24 H, 3J(H,H) = 7.0 Hz).
13C{1H} NMR (125.76 MHz, CDCl3): δ 189.4 (s, NCHN, ditz), 185.6
(s, NCHN, iPr2-bimy), 133.0, 125.1, 113.7 (s, Ar-C), 54.5 (s,
CH(CH3)2), 40.5 (s, NCH3), 38.6 (s, NCH3), 22.9 (s, CH(CH3)2).
19F NMR (282.37 Hz, CDCl3): δ −77.30 (s, 10BF4), −77.35 (s, 11BF4).
MS (ESI): m/z 455 [M − 2BF4]2+, 996 [M − BF4]+. Elemental
analyses were not available due to fast decomposition.
[AuCl2(Bn2-bimy)(iPr2-bimy)]BF4 (12). Complex 3 (78 mg, 0.1
mmol) and PhICl2 (30 mg, 0.11 mmol) were mixed, and CH2Cl2 (10
mL) was added. The reaction mixture was stirred at ambient
temperature overnight while it was shielded from light. All volatiles
were removed under vacuum, and the residue was washed with diethyl
ether (3 × 5 mL), yielding an off-white solid (75 mg, 0.87 mmol,
[PdBr2(FPyr)(iPr2-bimy)] (8′). Dimeric complex D (99 mg, 0.11
mmol) and FPyr·H+Br− (54 mg, 0.21 mmol) were suspended in
CH2Cl2 (20 mL). Ag2O (29 mg, 0.13 mmol) was added to the
mixture, and the resulting suspension was stirred for 12 h while it was
shielded from light. The reaction mixture was then filtered over Celite,
and the solvent of the filtrate was removed under vacuum, yielding the
crude product. Recrystallization of the crude product from a solution
in CH2Cl2 layered with toluene produced a yellow crystalline product
(113 mg, 0.18 mmol, 83%). 1H NMR (500 MHz, CDCl3): δ 7.52 (dd,
2 H, Ar-H), 7.16 (dd, 2 H, Ar-H), 6.31 (m, 1 H, NCH, 3J(H,H) = 6.95
1
87%). H NMR (300 MHz, CD2Cl2): δ 7.72−7.71 (m, 4 H, Ar-H),
7.61−7.60 (m, 2 H, Ar-H), 7.48−7.46 (m, 8 H, Ar-H), 7.32−7.29 (m,
4 H, Ar-H), 6.03 (s, 4 H, CH2Ph), 4.49 (m, 2 H, CH(CH3)2, 3J(H,H)
3
= 6.9 Hz), 1.53 (d, 12 H, CH(CH3)2, J(H,H) = 6.9 Hz). 13C{1H}
3
NMR (75.47 MHz, CD2Cl2): δ 165.3 (s, NCN, Bn2-bimy), 158.7 (s,
NCN, iPr2-bimy), 134.5, 134.0, 133.0, 129.8, 129.3, 127.0, 126.7, 125.6
(s, Ar-C), 55.4 (s, CH2Ph), 51.3 (s, CH(CH3)2), 21.1 (s, CH(CH3)2).
19F NMR (282.4 MHz, CD2Cl2) δ −77.52 (s, 10BF4), −77.57 (s,
11BF4). MS (ESI): m/z 769 [M − BF4]+. Anal. Calcd for
C34H36AuBF4N4: C, 47.74; H, 4.24; N, 6.55. Found: C, 47.66; H,
4.19; N, 6.68.
Hz), 6.13 (m, 1 H, NCH, J(H,H) = 6.95 Hz), 4.75 (t, 2 H, NCH2,
3J(H,H) = 5.70 Hz), 3.84 (t, 2 H, NCH2, 3J(H,H) = 5.65 Hz), 2.93 (t,
2 H, CH2, 3J(H,H) = 5.65 Hz), 2.43 (t, 2 H, CH2, 3J(H,H) = 6.30 Hz),
2.14 (m, 2 H, CH2), 2.08 (m, 2 H, CH2), 1.84 (d, 6 H, CH3, 3J(H,H)
3
= 6.95 Hz), 1.81 (d, 6 H, CH3, J(H,H) = 6.95 Hz) (signals due to
another two CH2 groups of the FPyr ligand were overlapped with the
i
signals due to the CH3 groups of the Pr2-bimy ligand, in the 1.75−
[AuCl2(iPr2-bimy)]2(μ-ditz)(BF4)2 (13). This complex was synthe-
sized in analogy to the procedure for complex 12, with the exception
of decreasing the reaction temperature to 0 °C. Fractional
1.85 ppm region). 13C{1H} NMR (125.8 MHz, CDCl3): δ 184.0 (s,
Ccarbene (iPr2-bimy)), 171.4 (s, Ccarbene (FPyr)), 142.5 (s, NCCH2),
134.6 (s, Ar-C), 134.3 (s, Ar-C), 125.2 (s, NCcarbeneCCH2), 122.3 (s,
Ar-C), 113.0 (s, Ar-C), 54.1 (s, NCH), 53.9 (s, NCH), 51.2 (s,
NCH2), 46.0 (s, NCH2), 23.6, 23.1, 22.8, 22.7, 22.03, 21.99, 21.7, 21.4
(s, CH2 and CH3). MS (ESI): m/z 565 [M − Br]+. Anal. Calcd for
1
crystallization afforded 13 as an off-white solid in a yield of 81%. H
NMR (500 MHz, CD2Cl2): δ 7.86−7.85 (Ar-H, m, 4H), 7.54−7.52
(Ar-H, m, 4 H), 5.38 (CH(CH3)2, m, 4 H, 3J(H,H) = 6.5 Hz), 4.60 (s,
K
dx.doi.org/10.1021/om400313r | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
C24H34N4PdBr2·0.2C7H8: C, 46.00; H, 5.41; N, 8.45. Found: C, 45.77;
H, 5.08; N, 8.50.
(d) Hartinger, C. G.; Metzler-Nolte, N.; Dyson, P. J. Organometallics
2012, 31, 5677.
X-ray Diffraction Studies. X-ray data were collected with a
Bruker AXS SMART APEX diffractometer, using Mo Kα radiation
with the SMART suite of programs.21 Data were processed and
corrected for Lorentz and polarization effects with SAINT22 and for
absorption effects with SADABS.23 Structural solution and refinement
were carried out with the SHELXTL suite of programs.24 The
structure was solved by direct methods to locate the heavy atoms,
followed by difference maps for the light, non-hydrogen atoms. All
hydrogen atoms were placed at calculated positions. All non-hydrogen
atoms were generally given anisotropic displacement parameters in the
final model.
(4) (a) Hahn, F. E.; Radloff, C.; Pape, T.; Hepp, A. Chem. Eur. J.
2008, 14, 10900. (b) Radloff, C.; Weigand, J. J.; Hahn, F. E. Dalton
Trans. 2009, 9392. (c) Rit, A.; Pape, T.; Hahn, F. E. J. Am. Chem. Soc.
2010, 132, 4572. (d) Rit, A.; Pape, T.; Hepp, A.; Hahn, F. E.
Organometallics 2011, 30, 334.
(5) For more recently reported examples, see: (a) Cure, J.; Poteau,
R.; Gerber, I. C.; Gornitzka, H.; Hemmert, C. Organometallics 2012,
31, 619. (b) Wimberg, J.; Meyer, S.; Dechert, S.; Meyer, F.
Organometallics 2012, 31, 5025. (c) Liu, W.; Bensdorf, K.; Proetto,
M.; Hagenbach, A.; Abram, U.; Gust, R. J. Med. Chem. 2012, 55, 3713.
(d) Kunz, P. C.; Wetzel, C.; Kogel, S.; Kassack, M. U.; Spingler, B.
̈
Dalton Trans. 2011, 40, 35.
(6) (a) Raubenheimer, H. G.; Lindeque, L.; Cronje, S. J. Organomet.
Chem. 1996, 511, 177. (b) Gaillard, S.; Nun, P.; Slawin, A. M. Z.;
Nolan, S. P. Organometallics 2010, 29, 5402. (c) Sivaram, H.; Tan, J.;
Huynh, H. V. Organometallics 2012, 31, 5875.
(7) (a) Huynh, H. V.; Han, Y.; Jothibasu, R.; Yang, J. A.
Organometallics 2009, 28, 5395. (b) Yuan, D.; Huynh, H. V.
Organometallics 2012, 31, 405.
ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files giving crystallographic data for C, 1, 2, 6, 9, 12, and
13·3CH2Cl2. This material is available free of charge via the
Internet at http://pubs.acs.org.
(8) Sivaram, H.; Jothibasu, R.; Huynh, H. V. Organometallics 2012,
31, 1195.
(9) Jothibasu, R.; Huynh, H. V.; Koh, L. L. J. Organomet. Chem. 2008,
AUTHOR INFORMATION
■
Corresponding Author
*E-mail for H.V.H.: chmhhv@nus.edu.sg.
Notes
693, 374.
(10) Wang, H. M. J.; Chen, C. Y. L.; Lin, I. J. B. Organometallics
1999, 18, 1216.
(11) (a) Gaillard, S.; Slawin, A. M. Z.; Nolan, S. P. Chem. Commun.
The authors declare no competing financial interest.
2010, 46, 2742. (b) Gom
Nolan, S. P. Dalton Trans. 2012, 41, 5461.
(12) Baker, M. V.; Barnard, P. J.; Brayshaw, S. K.; Hickey, J. L.;
Skelton, B. W.; White, A. H. Dalton Trans. 2005, 37.
(13) (a) Guo, S.; Huynh, H. V. Organometallics 2012, 31, 4565.
(b) Sabater, S.; Mata, J. A.; Peris, E. Chem. Eur. J. 2012, 18, 6380.
(c) Mas-Marza, E.; Mata, J. A.; Peris, E. Angew. Chem., Int. Ed. 2007,
46, 3729. (d) Guerret, O.; Sole, S.; Gornitzka, H.; Teichert, M.;
Trinquier, G.; Bertrand, G. J. Am. Chem. Soc. 1997, 119, 6668.
(14) (a) Huynh, H. V.; Han, Y.; Ho, J. H. H.; Tan, G. K.
Organometallics 2006, 25, 3267. (b) Han, Y.; Huynh, H. V.; Koh, L. L.
J. Organomet. Chem. 2007, 692, 3606. (c) Han, Y.; Huynh, H. V.; Tan,
G. K. Organometallics 2007, 26, 6447. (d) Huynh, H. V.; Wong, L. R.;
Ng, P. S. Organometallics 2008, 27, 2231.
́ ́ ́
ez-Suarez, A.; Ramon, R. S.; Slawin, A. M. Z.;
ACKNOWLEDGMENTS
■
We thank the National University of Singapore and the
Singapore Ministry of Education for financial support (WBS R-
143-000-483-112). Technical assistance from the staff at the
CMMAC of our department is appreciated. In particular, we
thank Ms. Geok Kheng Tan, Ms. Hong Yimian, and Prof. Lip
Lin Koh for determining the X-ray molecular structures.
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dx.doi.org/10.1021/om400313r | Organometallics XXXX, XXX, XXX−XXX