Gold(I) chloride complexes of polyphosphine ligands with electron-rich arene spacer: Gold-arene interactions

Article abstract of DOI:10.1021/om201276w

The reactions of Au(tht)Cl (tht = tetrahydrothiophene) with the electron-rich-arene-spacer-containing polyphosphine ligands N,N′- bis((diphenylphosphino)methyl)benzene-1,4-diamine (Dpba), N,N′- bis((diphenylphosphino)methyl)naphthalene-1,5-diamine (Dpna), N,N,N′,N′- tetrakis((diphenylphosphino)methyl)benzene-1,4-diamine (Pbaa), N,N,N′,N′-tetrakis((diphenylphosphino)methyl)naphthalene-1, 5-diamine (Pnaa), and N,N,N′,N′-tetrakis((diphenylphosphino)methyl) biphenyl-4,4′-diamine (Pbbaa) lead to [Dpba(AuCl)₂] (1), [Dpna(AuCl)₂] (2), [Pnaa(AuCl)₄] (3), [Pbbaa(AuCl) ₄ (4). and [Pbaa(AuCl)₄] (5), which are characterized by ¹H and ³¹P NMR, IR, elemental analysis, and X-ray crystal structure analysis. These complexes exhibit weak Au-arene interactions with the electron-rich arene spacer, while the Au-arene interactions are modified by a combination of electronic and steric effects from the ligands. Different from monomeric complexes 1, 2, 3, and 4, complex 5 in the solid state exhibits a centrosymmetric trimeric unit that is constructed by intermolecular Au???Au interactions between the central molecule and the two symmetry-related terminal molecules and in which the conformation of the central molecule is different from that of the two symmetric terminal molecules. On the basis of the Kochi's geometric criteria and the crystal structural parameters relating to Au-arene interactions, the Au???C_arene contacts in 3 and 4 feature nearly η²-arene interactions, while the Au???C_arene contacts in 5 can be described as η¹-arene interactions, and the Au???C _arene contacts in 1 and 2 are very weak due to intermolecular N-H???Cl interactions.

Full text of DOI:10.1021/om201276w

Article
pubs.acs.org/Organometallics
Gold(I) Chloride Complexes of Polyphosphine Ligands with Electron-
Rich Arene Spacer: Gold−Arene Interactions
Qing-Ling Ni, Xuan-Feng Jiang, Ting-Hong Huang, Xiu-Jian Wang,* Liu-Cheng Gui, and Kun-Guo Yang
Key Laboratory for the Chemistry and Molecular Engineering of Medicinal Resources (Ministry of Education of China), School of
Chemistry and Chemical Engineering, Guangxi Normal University, Guilin 541004, People's Republic of China
S
* Supporting Information
ABSTRACT: The reactions of Au(tht)Cl (tht = tetrahydrothio-
phene) with the electron-rich-arene-spacer-containing polyphosphine
ligands N,N′-bis((diphenylphosphino)methyl)benzene-1,4-diamine
(Dpba), N,N′-bis((diphenylphosphino)methyl)naphthalene-1,5-dia-
mine (Dpna), N,N,N′,N′- tetrakis((diphenylphosphino)methyl)-
b e n z e n e - 1 , 4 - d i a m i n e ( P b a a ) , N , N , N ′ , N ′ - t e t r a k i s -
((diphenylphosphino)methyl)naphthalene-1,5-diamine (Pnaa), and
N,N,N′,N′-tetrakis((diphenylphosphino)methyl)biphenyl-4,4′-diamine
(Pbbaa) lead to [Dpba(AuCl)2] (1), [Dpna(AuCl)2] (2), [Pnaa(AuCl)4] (3), [Pbbaa(AuCl)4 (4). and [Pbaa(AuCl)4] (5),
which are characterized by 1H and 31P NMR, IR, elemental analysis, and X-ray crystal structure analysis. These complexes exhibit
weak Au−arene interactions with the electron-rich arene spacer, while the Au−arene interactions are modified by a combination
of electronic and steric effects from the ligands. Different from monomeric complexes 1, 2, 3, and 4, complex 5 in the solid state
exhibits a centrosymmetric trimeric unit that is constructed by intermolecular Au···Au interactions between the central molecule
and the two symmetry-related terminal molecules and in which the conformation of the central molecule is different from that of
the two symmetric terminal molecules. On the basis of the Kochi’s geometric criteria and the crystal structural parameters
relating to Au−arene interactions, the Au···Carene contacts in 3 and 4 feature nearly η2-arene interactions, while the Au···Carene
contacts in 5 can be described as η1-arene interactions, and the Au···Carene contacts in 1 and 2 are very weak due to intermolecular
N−H···Cl interactions.
terminal phenyl ring, which is placed above or aside the Au
atom (Scheme 1). Such weak Au···π interactions might provide
INTRODUCTION
■
Gold catalysis is one of the most active areas of research in
organic synthesis.1,2 Some gold complexes are proved to be
effective in the activation of alkynes, alkenes, allenes, and even
arenes,3,4 associated with π-coordination with low η2-hapticity
(or, in special cases, η1 and η3). However, only a few π-
complexes could be isolated due to dissociation in air and
moisture. In many catalytic processes, organo-gold halides are
catalyst precursors and a silver salt as a cocatalyst, giving rise to
cationic active gold species in the catalytic system.5 However,
the Ag+ could lead to unwanted side reactions due to the
practical deficiency regarding the light sensitivity, the easy
reduction to metallic silver, and the coorperative effects of Au−
Ag metallophilic interactions, leading to some limitations for
effective catalysis.6 Therefore, the development of silver-free
gold catalysts is advantageous. Sterically hindered ligands such
as phosphines, bulky N-heterocyclic carbenes, and triazadienyl
have been demonstrated to be particularly useful to develop
highly active and selective gold catalysts, by strengthening the
stability of gold cations.7 The excellent and extensively
researched supporting ligand is bulky dialky(2-biphenylyl)-
phosphine,8 whose gold complexes exhibit effective catalysis for
cross-coupling reaction, cycloaddition reaction, or gold-
catalyzed transformation of unsaturated hydrocarbons. In
neutral AuCl and gold cationic complexes with bulky
biphenylphosphines, the gold atom weakly interacts with the
Scheme 1
additional stabilization to the transition states or intermediates
in the reactions of biphenylphosphine gold complexes with
alkynes, allenes, or alkenes, which were isolated as crystalline
compounds and proved to be stable toward air and moisture.
Moreover, their cationic complexes can make catalytic
transformations possible under silver-free conditions. The
introduction of an electron-donating group (e.g., alkoxy) into
the terminal phen is well documented to increase the electron
density in the biphenyl backbone and stabilize intermediate
complexes due to the reinforcement of the weak interactions
between the metal and the arene ring. Similar weak interactions
between Au and an anthracene ring were also found by Zhang’s
Received: December 23, 2011
Published: March 2, 2012
© 2012 American Chemical Society
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Article
group in the ditertiary phosphine anthracene-based gold
complex.9 These ligand-unsupported Au···π interactions (the
Au···Carene distance is in the range of 2.95−3.38 Å) are
distinguished from the ligand-supported Au···π interactions
(the distance is less than 2.50 Å), which were investigated by
Schmidbaur.1e To understand the nature of these weak
interactions better in the Au-catalytic system and to pursue
new highly reactive and selective catalysts, we endeavored to
develop some new functionally semirigid phosphine ligands,
N,N′-bis((diphenylphosphino)methyl)benzene-1,4-diamine
(Dpba), N,N′-bis((diphenylphosphino)methyl)naphthalene-
1,5-diamine (Dpna) N,N,N′,N′-tetrakis((diphenylphosphino)-
methyl)benzene-1,4-diamine (Pbaa), N,N,N′,N′-tetrakis-
((diphenylphosphino)methyl)naphthalene-1,5-diamine (Pnaa),
and N,N,N′,N′-tetrakis((diphenylphosphino)methyl)biphenyl-
4,4′-diamine (Pbbaa), involving an arene diamine moiety of
which the lone electron pairs on the nitrogen atoms donate to
the arene ring featuring an electron-rich arene spacer10 that is
presumably favorable for the donation of π-electrons to the Au
center. These ligands were exploited to construct Cu−P
complexes in which electron-rich arene rings are involved in
π···π and C−H···π interactions. Changing the size of the central
arene to tune its electron density can modify the Au−arene
interactions. By the reaction of Au(tht)Cl (tht = tetrahy-
drothiophene) with these polyphosphine ligands, complexes
[Dpba(AuCl)2] (1), [Dpna(AuCl)2] (2), [Pnaa(AuCl)4] (3),
[Pbbaa(AuCl)4] (4), and [Pbaa(AuCl)4] (5) are afforded.
Ligands and their Au complexes are enumerated in Chart 1.
synthesis and structures of these AuCl complexes and try to
understand the electronic and steric control of the semirigid
ligands over the Au···π interactions.
EXPERIMENTAL SECTION
■
General Procedures. All chemicals were of reagent grade and
were used as received without further purification. IR spectra were
recorded as KBr pellets on a Perkin-Elmer FT-IR spectrometer in the
range 4000−450 cm−1. Elemental analyses were performed with a
Carlo ERBA 1106 analyzer. 1H and 31P{1H} spectra were recorded on
a Bruker Avance DMX400 spectrometer at 400.13 MHz. Phosphine
ligands were synthesized according to ref 11.
Synthesis. 1·0.5(CH2Cl2). A mixture of [AuCl(THT)]
(0.0320 g, 0.1 mmol) and Dpba (0.0260 g, 0.05 mmol) in 5
mL of CH2Cl2 was stirred at room temperature for 2 h. The
resulting yellow solution was diffused by diethyl ether in a 0 °C
refrigerator. Four days later, yellow block crystals were afforded.
Yield: 50%. Anal. Calcd for C32.5H31N2P2Cl3Au2: C, 38.54; H,
3.06; N, 2.77. Found: C, 38.26; H, 3.15; N, 3.04; IR (cm−1):
3349 (s), 1619 (m), 1517 (vs), 1482 (s), 12435 (s), 1252 (s),
1
1105 (s), 743 (s), 619 (s), 518 (s). H NMR (400 MHz,
DMSO): δ 7.56−7.81 (m, 20H, P-C6H5), 6.61(s, 4H, N-C6H4-
N), 5.46 (s, 2H, NH), 4.50 (s, 4H, P-CH2-N). 31P{1H} NMR
(DMSO): 22.11.
2. A mixture of [AuCl(THT)] (0.0320 g, 0.1 mmol) and Dpna
(0.0270 g, 0.05 mmol) in 7 mL of CH2Cl2/DMF mixed solvent
(volume ratio of 2:5) was stirred at room temperature for 2 h. The
resulting scarlet solution was diffused by diethyl ether in a 0 °C
refrigerator. Four days later, pink crystals were afforded. Yield: 40%.
Anal. Calcd for C36H32N2P2Cl2Au2: C, 42.39; H, 3.14; N, 2.75. Found:
C, 42.53; H, 3.44; N, 2.58; IR (cm−1): 3336 (vs), 1636 (m), 1536 (s),
1436 (s), 1107 (s), 747 (s), 691 (s). 1H NMR (400 MHz, DMSO): δ
7.79−7.56 (m, 20H, P-C6H5), 7.23−6.95 (m, 6H, N-C10H6-N), 6.50
(s, 2H, NH), 4.79−4.78 (d, 4H, P-CH2-N). 31P{1H} NMR (DMSO):
δ 21.01.
Chart 1
3·2(CH2Cl2). After the mixture of [AuCl(THT)] (0.0320 g, 0.1
mmol) and Pnaa (0.0240 g, 0.025 mmol) in 5 mL of CH3CN was
stirred at room temperature for 1 h, the resulting white deposit was
filtered and dissolved in 6 mL of DMF/CH2Cl2 (volume ratio of 1:1).
The white solution was diffused by diethyl ether in a 0 °C refrigerator.
Seven days later, colorless prism crystals were afforded. Yield: 35%.
Anal. Calcd for C64H58N2P4Cl8Au4: C, 37.46; H, 2.83; N, 1.37. Found:
C, 37.71; H, 2.60; N, 1.52; IR (cm−1): 1608 (m), 1498 (s), 1435 (s),
1
1198 (m), 1104 (s), 864(s), 747 (s), 691 (s), 519 (s). H NMR (400
MHz, DMSO): δ 7.54−7.37 (m, 40H, P-C6H5), 7.13−6.64(m, 6H, N-
C10H6-N), 5.09−4.85 (m, 8H, P-CH2-N). 31P{1H} NMR (CDCl3): δ
18.35.
4. After the mixture of [AuCl(THT)] (0.0320 g, 0.1 mmol) and
Pbbaa (0.0240 g, 0.025 mmol) in 5 mL of CH3CN was stirred at room
temperature for 1 h, the resulting white deposit was filtered and
dissolved in 8 mL of CH2Cl2/toluene (volume ratio of 1:1). This
solution was diffused by diethyl ether in a 0 °C refrigerator. Half a
month later, colorless plate crystals were afforded. Yield: 21%. Anal.
Calcd for C64H56N2P4Cl4Au4: C, 40.29; H, 2.94; N, 1.47. Found: C,
40.45; H, 3.24; N, 1.62; IR (cm−1): 1589 (m), 1482 (s), 1435 (s),
Complexes 1 and 2 are dinuclear complexes supported by
diphosphines Dpba and Dpna, respectively, while 3, 4, and 5
are tetranuclear based on tetraphosphine Pnaa, Pbbaa, and
Pbaa, respectively. In the solid state of 5, three molecules of
[Pbaa(AuCl)4] are linked by significant aurophilic interactions
into a trimeric unit in which two different conformations of
[Pbaa(AuCl)4] are exhibited (Scheme 2). Here we detail the
1
1102 (s), 863 (s), 742 (s), 690 (s), 522 (s). H NMR (400 MHz,
CDCl3): δ 7.49−7.39 (m, 40H, P-C6H5), 7.16−6.71(m, 8H, N-C6H4-
C6H4-N), 4.77 (s, 8H, P-CH2-N). 31P{1H} NMR (CDCl3): δ 17.06.
5·(CH2Cl2)·0.5(Et2O). A mixture of [AuCl(THT)] (0.0320 g, 0.1
mmol) and Pbaa (0.0230 g, 0.025 mmol) in 7 mL of CH2Cl2 was
stirred at room temperature for 2 h. The resulting colorless solution
was diffused by diethyl ether in a 0 °C refrigerator. Four days later,
colorless needle crystals were afforded. Yield: 50%. Anal. Calcd for
C60H56.5N2OP4Cl6Au4: C, 37.00; H, 2.90; N, 1.44. Found: C, 37.35; H,
2.89; N, 1.25; IR (cm−1): 1635 (m), 1512 (s), 1435 (s), 1102 (vs), 868
(m), 745 (s), 691 (s), 513 (s). 1H NMR (400 MHz, DMSO): δ 7.75−
7.49 (m, 40H, P-C6H5), 6.56(s, 4H, N-C6H4-N), 4.78 (s, 8H, P-CH2-
N). 31P{1H} NMR (DMSO): δ 18.96.
Scheme 2
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Organometallics
Article
Table 1. Crystallographic Data for Complexes 1−5
1
2
3
4
5
formula
fw
C
32.5H31N2P2Cl3Au2
C36H32N2P2Cl2Au2
1019.41
monoclinic
P21/n
C64H58N2P4Cl8Au4
2050.47
C64H56N2P4Cl4Au4
1906.65
monoclinic
P21/c
C58H52N2P4Cl4Au4
1830.56
1011.82
monoclinic
C2/c
cryst syst
space group
a (Å)
triclinic
triclinic
P1
̅
P1
̅
28.201(6)
11.827(3)
10.764(2)
90
9.6892(4)
14.2541(5)
12.3140(5)
90
9.8229(18)
11.518(2)
15.667(3)
69.607(3)
82.607(3)
72.291(3)
1582.2(5)
1
17.476(3)
11.628(2)
17.143(3)
90
15.4246(6)
16.2064(5)
20.1659(7)
83.8890(10)
85.1360(10)
74.7730(10)
4827.9(3)
3
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
106.932(5)
90
105.922(4)
90
117.887(3)
90
3434.5(13)
4
1635.45(11)
2
3079.1(10)
2
μ(Mo Kα)
0.8885
0.9251
0.9726
0.9818
0.9389
(cm−1
)
T (K)
153
293
110
110
153
−3
ρcalc (g cm
λ (Å)
)
1.957
0.71073
2.070
0.71073
2.152
0.71073
2.056
0.71073
1.889
0.71073
index ranges
−33 ≤ h ≤ 33, −13 ≤ k ≤ −11 ≤ h ≤ 11, −16 ≤ k ≤ −11 ≤ h ≤ 11, −13 ≤ k ≤ −21 ≤ h ≤ 21, −8 ≤ k ≤ −18 ≤ h ≤ 18, −19 ≤ k ≤
14, −12 ≤ l ≤ 12
16, −14 ≤ l ≤ 11
13, −18 ≤ l ≤ 18
14, −20 ≤ l ≤ 21
18, −23≤l ≤ 23
indep reflectns 3015 (0.1422)
(Rint)
2836 (0.0383)
5493 (0.0263)
6635 (0.0545)
16671 (0.0692)
obsd reflectns
1969
195
2064
4548
4913
11 281
[I > 2σ(I)]
params
199
370
316
973
goodness-of-fit 1.075
R [I > 2σ(I)] 0.0773
Rw [I > 2σ(I)] 0.1904
0.932
0.0315
0.0744
0.0467
0.0785
1.095
0.0295
0.0878
0.0407
0.0940
1.021
0.0433
0.1051
0.0712
0.1244
1.139
0.0591
0.1512
0.0895
0.1874
R (all data)
Rw (all data)
0.1151
0.2274
X-ray Crystallography. Reflection intensity data for these five
complexes were collected on a Oxford “Xcalibur, Sapphire3, Gemini
Ultra” diffractometer with graphite-monochromated Mo Kα radiation
(l = 0.71073 Å) using the ω technique. All the structures were solved
by direct methods and refined with the full-matrix least-squares on F2
using SHELXTL. Anisotropic thermal parameters were used in the last
cycles of refinement for the non-hydrogen atoms. All hydrogen atoms
were introduced into the last cycle of the refinement from geometrical
calculations and refined by using a riding model. During the structure
refinement of 5, the unidentified and badly disordered solvent
molecules (probably CH2Cl2 and diethyl ether) were removed with
the Squeeze option in PLATON. Crystal and structure refinement
data are summarized in Table 1. The selected geometric parameters
are shown in Table 2.
RESULTS AND DISCUSSION
■
The structures of these five complexes were determined by X-
ray single-crystal diffraction analysis. In these five complexes,
each phosphine group is coordinated with one AuCl. As
expected, the overall geometry about each gold(I) center is
essentially linear, exhibiting the two-coordinated Au unit P−
Au−Cl. The Au−P and Au−Cl bond lengths are unremarkable,
falling within the range of bond lengths for crystallographically
characterized phosphine-ligated gold(I) chlorides.12 The P−
Au−Cl bond angles range from 169° to 179°. The geometry
about each P is tetrahedral, as expected. Dpba in 1 takes as a cis-
coordination mode, while Dpna in 2 performs as a trans-
coordination mode, to bridge two AuCl units (Figures 1 and 2).
The P−Au−Cl units in 1 and 2 lie on each side of the central
arene spacers with the shortest Au···Carene distances of 3.46 Å
(Au1−C1) in 1 and 3.55 Å (Au1−C1) in 2. These Au···C
Table 2. Selected Geometric Parameters Related to Au−
Arene Interactions (Å and deg)
a
b
complex
Au−P
Au−Cl
Au−Ar
P−Au−Cl dihedral angle
1 (Au1)
2 (Au1)
3 (Au2)
4 (Au1)
5
2.22(4)
2.22(2)
2.23(1)
2.23(2)
2.28(5)
2.29(2)
2.30(2)
2.30(2)
3.56
3.55
3.20
3.35
178.2(2)
177.2(1)
177.2(1)
178.3(1)
75.1
66.0
Au2
2.23(4)
2.24(4)
2.23(4)
2.29(4)
2.29(3)
2.30(4)
3.42
3.17
3.07
175.0(1)
176.6(2)
175.4(1)
73.7
72.1
77.9
Au5
Au6
a
Shortest distance between Au and the plane of the central arene.
Dihedral angle between the plane of the central arene and the P−
b
Figure 1. Molecular structure of 1, showing the very weak Au···Carene
contact.
Au−Cl over or below the central arene.
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Pbaa are the same as syn−anti:syn−anti (Scheme 2a). The two
Ph2PCH2 units tethered to the same N atom take a syn−anti
conformation to coordinate to AuCl, producing one P−Au−Cl
unit located above or below the arene spacer and another P−
Au−Cl unit stretched away from the arene spacer. The overall
structure can be described as being that of two symmetry-
related P−Au−Cl units located above and below the plane of
arene spacer, respectively, while the other two symmetry-
related P−Au−Cl units are stretched out from the two termini
of the arene spacer, respectively. This geometric conformation
is attributed to a combination of electronic and steric properties
of the ligand. The P−Au−Cl units above or below the central
arene plane in 3 and 4 are tilted to the corresponding central
arene planes by approximately 75.1° and 66.0°, respectively,
possibly due to the π···chloride repulsion. The most significant
feature of these structures is the interactions between Au and
the C atoms of the central arene ring. The distances of Au2−
C2 (3.20 Å/Cipso) and Au2−C3 (3.30 Å/Cortho) in 3, and Au1−
C1(3.35 Å/Cipso) and Au1−C2 (3.37 Å/Cortho) in 4, are
comparable with those of Au−Carene in biphenylphosphine
AuCl complexes (the average distance of Au−Carene = 3.15 Å).
Moreover, the Au−Carene distances in 3 are slightly shorter than
those in 4, which may correspond to the higher electron density
of the anthrance ring that enhances the Au−Carene interactions
in 3. The asymmetric unit of 5 contains one and a half
crystallographically independent molecules of [Pbaa(AuCl)4];
these are generated symmetrically into a centrosymmetric
trimeric unit in which molecules are aggregated through strong
intermolecular aurophilic interactions (Figure 5). The inversion
Figure 2. Molecular structure of 2, showing the Au···Carene contact.
distances are well above the sum of the van der Waals radii
(3.36 Å) of carbon and gold,13 showing atypical, weak
Au···πarene interactions. In 1, neighboring molecules are bridged
to each other via two intermolecular N−H···Cl interactions into
a one-dimensional chain (Figure S1). But in 2, each molecule
performs as a four-linker to bridge four neighboring molecules
via N−H···Cl contacts, resulting in a two-dimensional structure
along the ab plane (Figure S2). Due to the N−H···Cl contacts,
the P−Au−Cl units deviate significantly from the central arene
plane, resulting in very weak Au···Carene contacts. In order to
eliminate the influence of N−H···Cl on the Au−arene
interaction and increase the electronic and steric control over
the Au···arene interactions, ligands Pnaa, Pbbaa, and Pbaa, in
which the hydrogens on the N atoms are substituted
completely by Ph2PCH2 units, are applied to build complexes
3, 4, and 5, respectively. Both 3 and 4 are centrosymmetric with
the inversion center located at the center of the arene spacer
(Figures 3 and 4), while the coordination modes of Pnaa and
Figure 5. Structure of a trimer in 5, showing Au···Au interactions.
Phenyl groups are deleted for clarity.
Figure 3. Molecular structure of 3, showing the Au···Carene
interactions.
center is located at the centroid of the arene spacer in the
central molecule. In this trimeric unit, Pbaa adopts two different
geometric conformations, syn−anti:syn−anti and syn−syn:anti−
anti (Scheme 2), to link AuCl units. In the central molecule,
Pbaa performs as a syn−anti:syn−anti mode, like that in 3 and 4
to bridge four AuCl molecules (Figure 6a). The P2−Au2−Cl2
and its symmetry-related units are located above and below the
central arene plane, respectively, with the tilt angle between
P2−Au2−Cl2 and the arene plane of 73.8°. The shortest and
second shortest atom−atom distances from the Au2 center to
Carene are 3.43 (Cipso) and 3.52 Å (Cortho), respectively. These
values are a little longer than those in 3 and 4, but comparable
with those in 1 and 2. However, in the two symmetry-related
terminal molecules, Pbaa performs as a syn−syn:anti−anti
Figure 4. Molecular structure of 4, showing the Au···Carene
interactions.
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Article
two van der Waals radii (3.80 Å).14 All five complexes exhibit
only one 31P singlet. The chemical shifts of 31P in 1 and 2 are
approximate, while those in 3, 4, and 5 are also similar. The
feature of one 31P singlet shows that these polyphosphine Au
complexes are flexible in solution, and the behavior of 5 in
DMSO solution is similar to 3 and 4, presenting only one
flexible monomer.
In these complexes, gold(I) can interact weakly with the
electron-rich central arene ring. Concerning the structural
feature of Au−Carene interactions, the P−Au−Cl units in 1 and
2 are located on each side of the central arene spacers due to
N−H···Cl interactions, but the P−Au−Cl units related to the
Au···Carene interactions in 3, 4, and 5 are above and below the
central arene planes. The shortest Au···C distances in 1, 2, and
the central molecules of 5 (3.43−3.55 Å) are well above the
sum of the van der Waals radii (3.36 Å) of carbon and gold,
significantly deviated from the typical Au···C interaction.
Nevertheless, the corresponding values in 3, 4, and the
terminal molecules of 5 are in the range 3.07−3.35 Å,
exhibiting common Au···C interactions, but distinguished
from the ligand-supported Au−C interactions (below 2.5
Å).1e,3b It is noteworthy that the distance of Au−Cipso is shorter
than that of Au−Cortho in 3 and 4 due to the ipso position
corresponding to the highest electron density. Of course, the
steric effect is also ignored for the Au−Carene interactions. Due
to the steric congestion, both the shortest and the second
shortest Au−Carene distances in the central molecule of 5 are
beyond the sum of the van der Waals radii (3.36 Å) of carbon
and gold, while the Au−Cortho contacts in the terminal
molecules are remarkably shorter than the Au−Cipso values.
For a further evaluation of these Au−arene interactions, Kochi’s
geometric criteria15 for the gold−arene plane in 3−5 are shown
in Table 3. The β and D values are within 30 3° and 3.1 0.2
Å, respectively. The hapticity values of 3 and 4 are 1.79 and
1.94, respectively, while the d1 and d2 are approximate and
within the sum of the van der Waals radii, featuring nearly η2-
arene interactions. However in 5, the hapticity parameters
related to Au5 and Au6 are 1.56 and 1.59, respectively, showing
that the coordination of Au to arene could be intermediate
between η1 and η2, but the strikingly inequivalent d1 and d2
values show that these Au−C arene interactions are highly
asymmetric and should be described as η1-arene interactions.
The structural features related to Au2 show a very weak η2-
Figure 6. Geometries of the central (a) and terminal (b) molecules in
the trimer, showing Au···π interactions. Phenyl groups are deleted for
clarity.
conformation in which two PPh2CH2 units bound to one N
atom link two AuCl molecules by the syn−syn coordination
mode, which supports the intramolecular Au···Au interaction
between Au3 and Au4 (3.10 Å) (Figure 6b),14 while the other
two Ph2PCH2 moieties appended to another N atom take an
anti−anti mode to link two AuCl, leading to these two P−Au−
Cl units locating above and below the central arene plane (P5−
Au5−Cl5, P6−Au6−Cl6), which are involved in intramolecular
Au···C interactions. The shortest and second shortest distances
from Au to C atoms are 3.18 (Au5−C34) and 3.52 Å (Au5−
C33) relative to Au5, and 3.07 (Au6−C32) and 3.59 Å (Au6−
C31) relative to Au6, featuring a highly asymmetric
coordination mode of Au···C, which could be described as
either a η1 or a distorted η2 bond. The intermolecular Au···Au
interactions between Au5 and Au1 (3.36 Å) and their
symmetry-related atoms lead to the aggregation between the
central and terminal molecules into a trimeric unit.
Furthermore, these trimeric units are extended into a one-
dimensinal chain by interunit, weak Au···Au interactions
between Au6 and its symmetric atoms (3.51 Å) from
neighboring trimeric units (Figure 7). The Au···Au distances
Figure 7. One-dimensional chain constructed by trimers through
Au···Au interactions. Phenyl groups are deleted for clarity.
(3.18 and 3.36 Å) within the trimeric unit are longer than those
between the units (3.51 Å), while they are all below the sum of
a
Table 3. Structural Parameters of 3−5 Relating to Au−Arene Interactions
complex
D [Å]
β [deg]
Δ [Å]
d1
d2
ηx
3
3.128
3.256
27.6
28.4
1.635
1.761
3.201
3.347
3.295
3.372
1.79
1.94
4
5
Au2
Au5
Au6
3.376
3.100
2.946
16.8
33.8
37.4
1.019
2.076
2.253
3.416
3.169
3.069
3.509
3.524
3.591
1.71
1.56
1.59
a
Kochi criteria for hapticity ηx, x = 1 + 2(d12 − D2)1/2/[(d12 − D2)1/2 + (d22 − D2)1/2]; d1 and d2 are the nearest and second-nearest Au−C distances;
D is the distance between Au and the mean plane of the central arene. β is the angle between the normal vector of the arene ring and the vector
passing through the centroid to the gold atom. Δ is the distance from Au to the ring normal vector passing through the centroid of the arene ring.
2347
dx.doi.org/10.1021/om201276w | Organometallics 2012, 31, 2343−2348

Organometallics
Article
(7) (a) Nolan, S. P. Acc. Chem. Res. 2011, 44, 91. (b) Amijs, C. H. M.;
Lopez-Carrillo, V.; Raducan, M.; Perez-Galan, P.; Ferrer, C.;
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Echavarren, A. M. J. Org. Chem. 2008, 73, 7721. (c) Li, G.; Zhang,
L. Angew. Chem., Int. Ed. 2007, 46, 5156. (d) Partyka, D. V.; Robilotto,
T. J.; Updegraff, J. B. III; Zeller, M.; Hunter, A. D.; Gray, T. G.
Organometallics 2009, 28, 795. (e) Flores, J. A.; Rasika Dias, H. V.
Inorg. Chem. 2008, 47, 4448.
arene interactions between Au and arene. All Δ values are more
than 1.33 Å, showing that the projection sites of Au are located
outside the central arene planes. So these Au−C interactions
are side-on, which is also observed in Au−biphenylphosphines
complexes.
ASSOCIATED CONTENT
́ ́ ́
(8) (a) Perez-Galan, P.; Delpont, N.; Herrero-Gomez, E.; Maseras,
■
F.; Echavarren, A. M. Chem.Eur. J. 2010, 16, 5324. (b) Walker, S.
D.; Barder, T. E.; Martinelli, J. R.; Buchwald, S. L. Angew. Chem., Int.
Ed. 2004, 43, 1871. (c) Partyka, D. V.; Robilotto, T. J.; Zeller, M.;
Hunter, A. D.; Gray, T. G. Organometallics 2008, 27, 28. (d) Barder, T.
E. J. Am. Chem. Soc. 2006, 128, 898. (e) Christmann, U.; Pantazis, D.
A.; Benet-Buchholz, J.; McGrady, J. E.; Maseras, F.; Vilar, R. J. Am.
Chem. Soc. 2006, 128, 6376.
S
* Supporting Information
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: wang1_xj@yahoo.com.cn.
(9) (a) Xu, F.-B.; Li, Q.-S.; Wu, L.-Z.; Leng, X.-B.; Li, Z.-C.; Zeng, X.-
S.; Chow, Y. L.; Zhang, Z.-Z. Organometallics 2003, 22, 633. (b) Li, Q.-
S.; Wan, C.-Q.; Zou, R.-Y.; Xu, F.-B.; Song, H.-B.; Wan, X.-J.; Zhang,
Z.-Z. Inorg. Chem. 2006, 45, 1888.
Notes
The authors declare no competing financial interest.
(10) Hou, R.; Huang, T.-H.; Wang, X.-J.; Jiang, X.-F.; Ni, Q.-L.; Gui,
L.-C.; Fan, Y.-J.; Tan, Y.-L. Dalton Trans. 2011, 40, 7551.
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ACKNOWLEDGMENTS
■
This work is financially sponsored by the National Natural
Foundation of China (No. 20863001), the Natural Foundation
o f G u a n g x i P r o v i n c e ( 2 0 1 1 G X N S F A 0 1 8 0 4 1 ,
2010GXNSFF013001), and the Programme for Excellent
Talents in Guangxi Higher Education Institution.
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Edition), http://www.webelements.com. (b) Bondi, A. J. Phys. Chem.
1964, 68, 441. (c) Tiekink, E. R. T.; Zukerman-Schpector, J.
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