[2.2]Paracyclophanediyldiphosphane complexes of gold

Article abstract of DOI:10.1002/ejic.201200751

We have prepared digold(I) complexes with the rigid-backbone diphosphane ligands PhanePhos, xyl-PhanePhos, and Ph₂-GemPhos. All complexes were characterized by single-crystal X-ray diffraction, NMR, IR, Raman, and photoluminescence (PL) spectro

Full text of DOI:10.1002/ejic.201200751

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DOI: 10.1002/ejic.201200751
[2.2]Paracyclophanediyldiphosphane Complexes of Gold
Christian Sarcher,[a] Anja Lühl,[a] Florian C. Falk,[b] Sergei Lebedkin,[c] Michael Kühn,[d]
Cong Wang,[d] Jan Paradies,*[b] Manfred M. Kappes,*[c,d] Wim Klopper,*[c,d] and
Peter W. Roesky*[a]
Keywords: Aurophilicity / Homogeneous catalysis / Ligand design / Gold / Luminescence
We have prepared digold(I) complexes with the rigid-back-
bone diphosphane ligands PhanePhos, xyl-PhanePhos, and
Ph2-GemPhos. All complexes were characterized by single-
crystal X-ray diffraction, NMR, IR, Raman, and photolumi-
nescence (PL) spectroscopy. [PhanePhos(AuCl)2] and [Gem-
Phos(AuCl)2] show a very similar ligand scaffold, but dif-
ferent (aurophilic vs. nonaurophilic) intramolecular Au–Au
distances. Absorption and PL spectra of both compounds are
quite similar. Theoretical investigations reveal that the ex-
cited states are of different character (i.e., influenced by the
Au–Au contacts). The respective transition energies, how-
ever, lie close to each other, thus resulting in similar experi-
mental spectra. The gold atoms appear to produce a signifi-
cant heavy-atom effect in the electronic relaxation dynamics.
Thus, [PhanePhos(AuCl)2] and [GemPhos(AuCl)2] both show
bright-green millisecond-long phosphorescence at low tem-
peratures, although the latter is quenched at ambient tem-
perature. [PhanePhos(AuCl)2] and [GemPhos(AuCl)2] were
also used as catalysts in the intra- and intermolecular hydro-
amination of alkynes. Good to quantitative conversions on a
reasonable time scale were observed. The overall perform-
ance of these catalysts in the studied reactions was similar,
showing that Au–Au contacts do not have a major influence
on the catalytic performance.
ysis has recently increased dramatically. This is mirrored by
a significant number of reviews dealing with various topics
of gold chemistry.[1,2]
Introduction
Although gold has fascinated mankind due to its mone-
tary worth and its many uses in art for thousands of years,
the chemistry of gold, by comparison, has only been investi-
gated for a relatively short period of time.[1] Besides reports
on the synthesis and theoretical investigations of gold com-
pounds, the number of publications dealing with the appli-
cation of gold and gold compounds in materials and sur-
face sciences and in homogeneous and heterogeneous catal-
One of the fascinating properties of molecular gold(I)
compounds is the significant attractive interaction between
linearly coordinated gold atoms. About 25 years ago the
term “aurophilicity” and “aurophilic bonding” were intro-
duced to describe this phenomenon.[2t] Intra- and intermo-
lecular aurophilic contacts, which are a result of strong rela-
tivistic contractions and low coordination numbers,[2q,3]
have been observed in the Au–Au distance range of about
2.70–3.50 Å.[2t] The energies of such Au–Au interactions lie
in the range of those of hydrogen bonds.[4] In addition to
their influence on structural properties, aurophilic interac-
tions also give rise to specific physical effects that can mani-
fest themselves, for instance, in the photophysical properties
of gold complexes.[2w]
To study the influence of Au–Au interactions on photo-
physical and catalytic properties, we have aimed in this
study to attach two gold(I) ions to a class of rigid ligand
backbones that allow systematic structural variation. To
comply with such variations of the backbone structure, the
gold(I) ions are, in turn, forced to take up positions at de-
fined distances. As the rigid backbone type, we selected a
set of [2.2]paracyclophanediyldiphosphane derivatives,
which are well-established ligands in homogeneous catalysis
as well as reagents in organic synthesis[5] and chose com-
mercially available PhanePhos and xyl-PhanePhos
[a] Institut für Anorganische Chemie, Karlsruhe Institute of
Technology (KIT),
Engesserstrasse 15, 76131 Karlsruhe, Germany
E-mail: roesky@kit.edu
Homepage: http://www.aoc.kit.edu/AK%20Roesky.php
[b] Institut für Organische Chemie, Karlsruhe Institute of
Technology (KIT),
Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany
E-mail: jan.paradies@kit.edu
Homepage: www.paradies-group.de
[c] Institut für Nanotechnologie, Karlsruhe Institute of
Technology (KIT),
Hermann-von-Helmholtz-Platz 1, 76021 Karlsruhe, Germany
E-mail: kappes@kit.edu
Homepage: http://www.int.kit.edu/611.php
[d] Institut für Physikalische Chemie, Karlsruhe Institute of
Technology (KIT),
Fritz-Haber-Weg 2, 76131 Karlsruhe, Germany
E-mail: klopper@kit.edu
Homepage: http://www.ipc.kit.edu/theochem/
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201200751.
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(Scheme 1). These enantiomerically pure ligands were first with and without short Au–Au contacts. Furthermore, we
synthesized in 1997.[6] In these ligands the phosphorus compare their catalytic reactivity in the hydroamination of
atoms are located at separations of about 5 Å, which should alkynes.
exclude an intramolecular Au–Au contact in the corre-
sponding gold complexes. Such a lack of intra- and inter-
molecular aurophilic contacts would also be expected for
the complexes in the solid state. Because no solid-state
Results and Discussion
structure was available for PhanePhos, we crystallized this
ligand and characterized it by single-crystal X-ray diffrac-
tion beforehand (Figure S1). A P–P distance of 5.014 Å was
determined. The related diphosphane Ph2-GemPhos, pre-
pared recently[7] (Scheme 1), was used as a counterpart to
the above ligands. It has two P atoms at a distance of
4.068 Å, which was expected to force coordinated Au atoms
into close proximity to each other. Indeed, using these li-
gands, we have succeeded in the preparation of digold(I)
complexes with a very similar ligand scaffold but with dis-
tinct (aurophilic vs. nonaurophilic) intramolecular Au–Au
distances, as described below.
Synthesis and Characterization
The ligands PhanePhos and xyl-PhanePhos are commer-
cially available, whereas GemPhos[7] was synthesized in four
steps from (4-[2.2]paracyclophanyl)diphenylphosphane ox-
ide[11] in an overall yield of 53%. Reaction of these phos-
phanes with [(tht)AuCl] in CH2Cl2 resulted in the desired
compounds [PhanePhos(AuCl)2] (1), [xyl-PhanePhos-
(AuCl)2] (2), and [GemPhos (AuCl)2] (3) (Scheme 2).
Scheme 1. P–P distances in [2.2]paracyclophanediyldiphosphanes
(no X-ray data is available for xyl-PhanePhos).
Although PhanePhos and xyl-PhanePhos are well-estab-
lished compounds, their gold chemistry has scarcely been
explored. In 2011, gold complexes with these ligands were
prepared in situ and used for the domino cyclization/nu-
cleophile addition reactions of enynes in the presence of
water, methanol, and electron-rich aromatic derivatives.[8]
During the preparation of this manuscript, (xyl-PhanePhos)
digold(I) was developed and used as an efficient catalyst for
the enantioselective Cope rearrangement of 1,5-dienes.[9]
We also note a recent study dealing with the photophysi-
Scheme 2. Synthesis of compounds 1–3 (THT = tetrahydrothio-
phene).
The new complexes have been characterized by standard
cal properties of constrained diaryldigold(I) compounds. By analytical/spectroscopic techniques. The 1H and 13C{1H}
using the diphosphanes DPEphos, DBFphos, and NMR spectra show the expected set of signals. In compari-
Xantphos (Scheme S1 in the Supporting Information) as ri- son to the noncoordinated ligands, a slight downfield shift
gid backbones, the photophysical properties of the corre- of the protons of the ethylene bridge of the paracyclophane
sponding dinuclear gold complexes were compared with unit was observed. Most significant are the 31P{1H} NMR
mononuclear analogues.[10] The structural differences be- spectra of the gold complexes. A downfield shift of the
tween those complexes were, however, relatively large – in 31P{1H} NMR signals by more than 30 ppm was observed
contrast to the compounds examined in this study. Besides in each case. Thus, the signal of the ligand [δ(31P) = –0.53
the structural analysis, we present the results of theoretical (PhanePhos),[6a] –2.0 (xyl-PhanePhos),[6b] and –7.78 ppm
and experimental investigations of the optical and elec- (GemPhos)[11]] is shifted to δ(31P) = 30.7 (1), 31.5 (2), and
tronic properties for the PhanePhos and GemPhos com- 29.7 ppm (3), respectively. Compounds 1 and 2 have been
plexes, which are structurally the most similar compounds prepared in situ previously, but the reported NMR spectro-
2
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[2.2]Paracyclophanediyldihosphane Complexes of Gold
scopic data are not fully consistent with our observations.[8]
The very recently reported data of compound 2 agree with
our measurements.[9]
The solid-state structures of compounds 1–3 were estab-
lished by single-crystal X-ray diffraction. None of the com-
pounds show any intermolecular aurophilic interactions.
The two chiral compounds 1 and 2 crystallize in the chiral
orthorhombic space groups P212121 and P21212, whereas
compound 3 crystallizes in the monoclinic space group
P21/n (Figures 1, 2, and 3) The Au–P distances are in the
expected range of 2.231(3)–2.237(2) Å (2), 2.228(2) Å (1),
2.241(2)–2.249(2) Å (3), and the Au–Cl distances are in the
range of 2.276(3)–2.290(3) Å (2), 2.266(2)–2.228(2) Å (1),
2.310(2)–2.312(2) Å (3). In all three structures, the gold
atoms are almost linearly coordinated, exhibiting a twofold
Figure 3. Solid-state structure of 3. Hydrogen atoms and solvent
coordination mode typical for AuI [P–Au1–Cl: 174.55(13)– molecules are omitted for clarity. Selected bond lengths [Å] and
angles [°]: Au1–P1 2.241(2), Au1–Cl1 2.312(2), Au2–P2 2.249(2),
Au2–Cl2 2.310(2), Au1–Au2 2.9764(6); P1–Au1–Cl1 177.74(7), P1–
Au1–Au2 91.58(5), P2–Au2–Cl2 171.55(7), P2–Au2–Au1 104.65(5),
Cl1–Au1–Au2 89.94(5), Cl2–Au2–Au1 83.72(5).
177.66(11)° (2), 177.58(8)–179.05(9)° (1), and 177.58(8)–
177.74(7)° (3)]. The Au–Au distances in compounds 1 and
2 clearly exclude any Au–Au contact (Figures 1 and 2). The
structure of 2 agrees with that reported in previously.[9]
In contrast, as a result of the ligand scaffold, the two
gold atoms in compound 3 are forced into close proximity,
resulting in an Au–Au distance of 2.9764(6) Å. This dis-
tance is well within the range of an intramolecular auro-
philic interaction.[2t] As seen in Figure 3, the steric strain of
compound 3 results in a strong distortion of the paracyclo-
phane backbone. The two benzene rings are bent to keep
the two metal atoms within their preferred coordination
mode. As a result of this bending, the distance between the
two P atoms of 4.605 Å is more than 0.5 Å longer than that
observed in the free ligand (4.068 Å). In contrast, the P–P
distance in compound 1 (5.170 Å) is only slightly longer
than that in the corresponding free ligand (5.014 Å). The
Cl1–Au1–Au2–Cl2 torsion angle in compound 3 is 81.34°.
Figure 1. Solid-state structure of 1. Hydrogen atoms and solvent
molecules are omitted for clarity. Selected bond lengths [Å] and
angles [°]: Au1–P1 2.228(2), Au1–Cl1 2.276(2), Au2–P2 2.228(2),
Au2–Cl2 2.266(2); P1–Au1–Cl1 177.58(8), P2–Au2–Cl2 179.05(9).
Photophysical Properties
The differing Au–Au contacts in the otherwise similar
compounds 1 and 3 correspond to the absence or presence
of an aurophilic interaction, respectively. This might be ex-
pected to lead to differing optical properties. Indeed, the
effects of such interactions, in particular on the photolumi-
nescence (PL) of gold complexes, have been well documen-
ted.[12] For instance, visible PL of polynuclear gold com-
plexes at ambient temperature has typically been correlated
with aurophilic interactions. Such PL observed for mono-
nuclear complexes has been related to short intermolecular
Au–Au contacts in the solid structure or as being due to
self-aggregation in solution.[13]
Somewhat surprising in view of the above evidence,
rather similar optical properties were found for compounds
1 and 3. Their UV/Vis absorption spectra are nearly iden-
tical both in the solid (polycrystalline) state and in dichloro-
methane solutions at ambient temperature (Figure 4). The
spectra are poorly structured, with the onset of the absorp-
tion at ca. 350 nm (ca. 3.5 eV) followed by a shoulder at ca.
Figure 2. Solid-state structure of 2. Hydrogen atoms and solvent
molecules are omitted for clarity. Shown is only one of two inde-
pendent molecules. Selected bond lengths [Å] and angles [°]: Au1–
P1 2.237(2), Au2–P2 2.247(3), Au1–Cl1 2.290(3), Au2–Cl2 2.289(3),
Au3–P3 2.234(3), Au3–Cl3 2.276(3), Au4–P4 2.231(3), Au4–Cl4
2.286(4); P1–Au1–Cl1 174.55(13), P2–Au2–Cl2 174.60(10), P3–
Au3–Cl3 177.66(11), P4–Au4–Cl4 175.5(2).
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310–330 nm. The spectra of the solutions further show a
shoulder at ca. 270 nm and an intense absorption below ca.
260 nm. (Note that solid-state absorption spectra measured
in a PTFE integrating sphere start to become “saturated”
below ca. 300 nm and cannot be quantitatively analyzed in
that region.)
Figure 5. Photoluminescence excitation (PLE) and emission (PL)
spectra (left and right panels, respectively) of 1 and 3 in the solid
state at low temperatures. The PL and PLE spectra were excited
and recorded at 300 and 500 nm, respectively. The low-temperature
PL of 1 and 3 is relatively bright and was recorded with excitation
and emission monochromator slits corresponding to 1 nm spectral
width.
Figure 4. UV/Vis absorption spectra of compounds 1 and 3 in (a)
solid (polycrystalline) state and (b) dichloromethane solution at
ambient temperature. The spectra are vertically shifted for clarity.
the solid state at temperatures below ca. 100 K. However,
in contrast to 1 and 3, the ligand emission is fluorescence
with a lifetime less than ca. 5 ns, independent of the tem-
perature (corresponding to the time resolution limit of our
apparatus). Therefore, from a simplified point of view, the
major effect of the gold atoms can be considered to be that
of an effective spin interconversion (heavy-atom effect) in
the photoexcited compounds 1 and 3. The observation of a
remarkably large heavy-atom effect of gold atoms on neigh-
boring chemical groups has already been reported.[16] This
effect is also likely to be essential for the photophysics of
the above-mentioned diaryldigold(I) complexes.[10]
The solid compounds 1 and 3, when cooled below ca.
100 K and excited in the UV region, emit bright white-
green light with λmax at 500 and 485 nm, respectively (Fig-
ure 5). The PL excitation (PLE) curves correspond well to
the absorption spectra. The PL quantum efficiency at low
temperatures likely amounts to several percent, as roughly
estimated from a comparison with other luminophors that
have been measured with the same apparatus and in the
same geometry. The emission of 1 and 3 is phosphorescence
as indicated by the long lifetimes of 9.6 and 5.1 ms, respec-
tively, at T = 17 K (see Figure S2 in the Supporting Infor-
mation). The emission intensity decreases significantly
upon increasing the temperature beyond ca. 100 K. This
correlates with faster emission decay. At ambient tempera-
Theoretical Investigations
Both density-functional-theory (DFT) and wave-
ture, the phosphorescence of 1 and 3 is essentially quenched function-based-theory (WFT) methods were used in the
(both in the solid state and in an argon-purged CH2Cl2 current study. In particular, the LDA,[17] BP86,[18] TPSS,[19]
solution).
and B3LYP[20] exchange-correlation functionals were used,
There are also some similarities between the spectra of 1 including empirical dispersion corrections as developed by
and 3 and the PhanePhos ligand (Figure S3). Cyclophanes Grimme (DFT-D2).[21] Hartree–Fock theory (HF), second-
are well known for their strong transannular interactions, order Møller–Plesset perturbation theory (MP2), spin-com-
resulting in the formation of an intramolecular excimer ponent-scaled second-order Møller–Plesset perturbation
state upon UV photoexcitation.[14] An emission peak at ca. theory (SCS-MP2),[22] and second-order coupled-cluster
370 nm observed for PhanePhos in CH2Cl2 can be attrib- theory (CC2)[23] methods were also employed. The resolu-
uted to such an excimer.[15] This peak is likely redshifted to tion-of-identity (RI)[24] approximation was used in the cal-
ca. 440 nm in the PhanePhos solid and dominates the PL culations with the non-hybrid functionals as well as in the
spectrum at ambient temperature (Figure S3). An emission MP2, SCS-MP2, and CC2 calculations. The def2 basis sets
at ca. 540 nm of the ligand in CH2Cl2 and in the solid state of Weigend and Ahlrichs[25] were used. The COSMO
at low temperatures can tentatively be ascribed to excited model[26] was applied to study solvent effects. All of the
state(s) with a significant contribution of the phosphane calculations were carried out with the Turbomole[27] pro-
moiety. Similar to 1 and 3, its intensity is especially high in gram package.
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[2.2]Paracyclophanediyldihosphane Complexes of Gold
Table 1. Selected atom–atom distances [Å] according to the experimental and computational structures of compounds 1 and 3.
Distance
X-ray
MP2[a] (gas phase)
B3LYP-D2/def2-TZVP (gas phase)
Compound 1
Au–Au
Au–Cl
Au–P
5.23
2.27/2.28
2.23
5.33
2.25
2.19
5.59
2.32
2.26
Compound 3
Au–Au
Au–Cl
Au–P
2.98
2.31
2.24/2.25
2.84
2.26
2.19
3.47
2.31/2.32
2.26
[a] Au: def2-QZVPP; P, Cl: def2-TZVPP; C: def2-TZVP; H: def2-SVP.
A comparison between the X-ray and theoretical gas-
This phenomenon is an example of a general trend in
phase structures of 1 and 3 is presented in Table 1. Both [XAuL]2 complexes, namely that the interaction energy de-
MP2 and B3LYP-D2 results show good agreement with the creases when the size of the ligand L increases.[31] In the
experimental data. The only exception is the Au–Au dis- crystal structure of [PPh3AuCl], for example, the shortest
tance in compounds 1 and 3. In compound 1, the deviations Au–Au distance is ca. 7 Å.[32] We therefore conclude that
from the X-ray value are +0.10 Å for MP2 and +0.36 Å for the very short distance between the two Au atoms in 3 is
B3LYP-D2. In compound 3, the deviations are –0.14 and more a consequence of steric constraints than of the auro-
+0.49 Å, respectively.
philic interaction. Many “metallophilic-attraction” com-
Surprisingly, at all computational levels, compound 1 is pounds contain large ligands[33] and, hence, it may be true
energetically more stable than 3, in spite of the absence of that in some cases the short metal–metal distances are due
any aurophilic (attractive) Au–Au interaction in 1 (Table 2). to steric effects.
Concerning the aurophilic interaction, it has been shown[28]
We now turn our attention to the absorption spectra.
that the SCS-MP2 approach yields results that are in good Both absorption and PLE profiles of 1 and 3, as shown in
agreement with those from the more sophisticated coupled- Figures 4 and 5, are very similar. According to our compu-
cluster singles and doubles with perturbative triples method tations, the excitations to the lowest excited states of the
[CCSD(T)]. Therefore, we are confident that the SCS-MP2 two compounds are rather different in character (in 3, the
energy of 45.5 kJmol–1 (derived from a two-point extrapo- Au atoms are involved, in 1 they are not), but the absorp-
lation scheme[29]) provides a reliable estimate of the energy tion wavelengths are nevertheless very close. Therefore, the
difference between 1 and 3.
similarity of the absorption spectra of 1 and 3 can be con-
sidered as somewhat coincidental. The theoretical results
are presented in Table 3 as well as in Figures 6 and 7.
Table 2. Energy difference [kJmol–1] between compounds 1 and 3
(i.e., E3 – E1) from different wavefunction-based methods, evalu-
ated at the MP2 geometry.[a]
Table 3. Lowest singlet vertical excitation energy (VEE) of com-
pounds 1 and 3 in the gas phase. The VEE is evaluated at the
equilibrium structure of each method. For DFT geometry optimi-
zations, the dispersion correction[21] was added. For CC2, the VEE
is evaluated at the MP2 optimized structure. Results obtained with
COSMO for the solvent CH2Cl2 are given in parentheses.
Basis set
Method
Hartree–Fock
MP2
SCS-MP2
Mixed[a]
TZVPP
QZVPP
90.3
90.7
90.6
32.2
39.8
35.7
32.7
44.7
51.3
47.9
45.5
Method
Basis set
VEE [nm]
Character
T+Q extrapolation
Compound 1
[a] Au: def2-QZVPP; P, Cl: def2-TZVPP; C: def2-TZVP; H: def2-
SVP.
TPSS
B3LYP
CC2
def2-TZVP
def2-TZVP
Mixed[a]
348
321 (322)
316 (317)
86% HOMOǞLUMO
85% HOMOǞLUMO
66% HOMOǞLUMO
According to the results reported in Table 2, the energy
difference between 1 and 3 is 90.6 kJmol–1 at the Hartree–
Fock level. This difference is reduced to 32.7 (45.5) kJmol–1
at the MP2 (SCS-MP2) level. This reduction may be inter-
preted as being due to dispersion interactions, which are
not accounted for at the Hartree–Fock level.[30] Hence, the
“aurophilic compound” 3 indeed shows a stronger attract-
ive dispersion interaction than 1, but, apparently, this is not
enough to make 3 lower in energy than 1. At the B3LYP-
Compound 3
TPSS
B3LYP
CC2
def2-TZVP
def2-TZVP
Mixed[a]
476
377 (341)
362 (329)
100% HOMOǞLUMO
98% HOMOǞLUMO
73% HOMOǞLUMO
[a] Au: def2-QZVPP; P, Cl: def2-TZVPP; C: def2-TZVP; H: def2-
SVP.
The first singlet excitation of compound 3 is a charge-
D2/TZVP level, the attractive D2 energy correction for the transfer excitation from its highest occupied molecular or-
two Au atoms is –19.2 kJ/mol for 3 and only –3.3 kJ/mol bital (HOMO) to its lowest unoccupied molecular orbital
for 1. At the same geometries, the corresponding D3 values (LUMO). Note that the HOMO of 3 is antibonding be-
with Becke–Johnson damping[21] are –8.5 and –1.8 kJ/mol, tween the two Au atoms, whereas the LUMO is an empty
respectively.
orbital of the [2.2]paracyclophane cage (Figure 6). In con-
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moments in the ground and excited states are 4.5 and 4.8 D,
respectively, with little effect on the excitation wavelength.
For the emission spectra, we have used the spin-flip
Tamm–Dancoff approximation (SF-TDA) at the LDA[17]
level, which yielded more accurate results in our previous
work[35] than the TD-DFT and ΔSCF approaches, in par-
ticular for charge-transfer states. In the present work also,
SF-TDA gives the best agreement with the experimental
phosphorescence energies (Table 4). According to the SF-
TDA result, the phosphorescence wavelengths are similar in
compounds 1 and 3 although the character of the triplet
states is again different. In compound 3 it is a state with
charge transfer from the Au atoms to the ligands, whereas
in 1 it is a local state within the [2.2]paracyclophane.
Figure 6. Hartree–Fock HOMO (left) and LUMO (right) of com-
pound 3.
Table 4. Phosphorescence energy (PE, as emission wavelength in
nm) of compounds 1 and 3, obtained at the LDA/def2-SVPD level.
The triplet geometry was optimized at the BP86-D2/def2-SVPD
level. Results obtained with COSMO for the solvent CH2Cl2 are
given in parentheses.
Figure 7. Hartree–Fock HOMO (left) and LUMO (right) of com-
pound 1.
Method
PE [nm]
1
3
TD-DFT
ΔSCF
TDA
561 (561)
549 (549)
551 (561)
541 (541)
816 (590)
588 (528)
816 (590)
517 (502)
trast to this, the first singlet excitation of compound 1 is a
local excitation within the [2.2]paracyclophane cage (Fig-
ure 7). The steric constraints in 3 give rise to a short Au–
Au distance and an antibonding Au–Au orbital that is ener-
getically located above the highest occupied molecular or-
bital of the [2.2]paracyclophane cage. In 1, with a large Au–
Au separation, this antibonding orbital level lies below the
[2.2]paracyclophane highest occupied molecular orbital (cf.
Walsh diagram in Figure 8). Hence, the steric constraints in
3 may be viewed as being responsible for the metal-to-li-
gand charge-transfer character of the excitation in 3.
SF-TDA
Catalytic Properties (Hydroamination)
A particularly interesting, yet practically unexplored is-
sue is whether (how) the aurophilic interaction can affect
the catalytic reactivity of gold complexes. To compare com-
pounds 1 and 3 in this respect, we chose the catalytic hy-
droamination as a probe reaction. The catalytic hydroamin-
ation, which is the addition of an organic amine N–H bond
to a C–C double or triple bond in one step, is attractive
for many industrial and academic applications. In classical
amine synthesis, multistep reactions are typically used,
which produce side products and a large amount of chemi-
cal waste. The hydroamination can be catalyzed by a large
number of s-, d-, and f-block metal complexes, and progress
over the last decade in this area has been reviewed exten-
sively.[36] In gold chemistry, hydroamination has been re-
ported both with AuI and AuIII compounds.[37]
Because we aimed to study first only differences in reac-
tivity of 1 and 3, we used simple substrates without func-
tional groups such as aniline, mesidine, phenylacetylene,
Figure 8. Walsh diagram for compounds 1 and 3.
Despite the different character of the excitations in 1 and ethynylcyclohexene, and 5-phenylpent-4-yn-1-amine. Based
3, the B3LYP and CC2 results are surprisingly similar. on the published reaction conditions[37m] we studied the in-
Furthermore, calculations with the COSMO model (ε = ter- and intramolecular hydroamination reaction using
9.1)[34] show that there is a considerable solvent effect (ca. 5 mol-% of 1 or 3 in combination with 10 mol-% AgBF4
37 nm) for the charge-transfer excitation in 3. In this com- (Au/Ag, 1:1) (Table 5). The unoptimized reactions, which
pound, the dipole moment in the electronic ground state proceeded regiospecifically, were monitored by 1H NMR
amounts to 11.5 D (MP2 value), whereas it is only 3.9 D in spectroscopy using ferrocene or hexamethylbenzene as in-
the excited state (CC2 value). Hence, solvent effects stabilize ternal standard. It turned out that all substrates were con-
the ground state more than the excited state, and the exci- verted at 40–60 °C reaction temperature into the corre-
tation wavelength is reduced (Table 3). For 1, the dipole sponding products in good to quantitative yields. Com-
6
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[2.2]Paracyclophanediyldihosphane Complexes of Gold
pound 3 was found to be more active for the addition of with the experimental spectra. The gold atoms appear to
mesidine and aniline to phenylacetylene (Table 5, Entries 1– produce a significant heavy-atom effect in the electronic re-
4) and cyclization of 5-phenylpent-4-yn-1-amine (Table 5, laxation; both 1 and 3 manifest bright-green millisecond-
Entries 7 and 8). It required only about half of the reaction long phosphorescence at low temperatures, although the
time as compared to that when 1 was used. In contrast, latter is quenched at ambient temperature.
for the addition of mesidine to ethynylcyclohexene, reversed
Both compounds were used as catalysts in the intra- and
reactivity was observed. This reaction was efficiently cata- intermolecular hydroamination of alkynes. Good to quanti-
lyzed at temperatures as low as 40 °C (Table 5, Entries 5 tative conversions on a reasonable time scale (ca. 2–10 h)
and 6).
were observed. As expected, the reaction rate strongly de-
pends on the substrate. However, the overall performance
of these catalysts in the studied reactions was similar. We
suggest that steric effects rather than Au–Au contacts have
an influence on the catalytic performance.
Table 5. Inter- and intramolecular hydroamination of alkynes using
compounds 1 and 3 as catalysts.[a]
Experimental Section
General: All manipulations of air-sensitive materials were per-
formed with the rigorous exclusion of oxygen and moisture in
flame-dried Schlenk-type glassware either on a dual manifold
Schlenk line, interfaced to a high-vacuum (10–3 Torr) line, or in an
argon-filled MBraun glove box. THF was distilled under nitrogen
from potassium benzophenone ketyl prior to use. Hydrocarbon sol-
vents (toluene and n-pentane) were dried using an MBraun solvent
purification system (SPS-800). All solvents for vacuum-line manip-
ulations were stored in vacuo over LiAlH4 in resealable flasks. Deu-
terated solvents were obtained from Aldrich (99 atom-% D) and
were degassed, dried, and stored in vacuo over Na/K alloy in re-
sealable flasks. NMR spectra were recorded with a Bruker Avance
II 300 MHz or a Bruker Avance II 400 MHz FT-NMR spectrome-
ter. Chemical shifts are referenced to internal solvent resonances
and are reported relative to tetramethylsilane. IR spectra were ob-
tained with a Bruker Tensor 34. Raman spectra were carried out
with a Bruker MultiRAM. Mass spectra were recorded at 70 eV
with a Finnigan MAT 8200 and a Thermo Scientific DFS. UV/Vis
spectra were obtained with a Varian Cary 50 Spectrophotometer.
Elemental analyses were carried out with an Elementar Vario EL.
[(tht)AuCl][38] (tht = tetrahydrothiophene) and Ph2-GemPhos[11]
were prepared according to modified standard procedures. UV/Vis
absorption spectra of sample solutions in dichloromethane were
obtained with a Varian Cary 500 spectrophotometer in standard
quartz cuvettes. For solid-state diffuse absorption measurements,
polycrystalline samples were finely (ca. micron-sized) dispersed/
gently ground in a thin layer of viscous polyfluoroester oil (ABCR
GmbH) between two 1 mm thick quartz plates and placed at the
center of a Labsphere integrating sphere consisting of Spectralon
PTFE material. Photoluminescence (PL) measurements were per-
[a] Reaction conditions: substrate (0.46 mmol), catalyst (5 mol-%),
AgBF4 (10 mol-%), [D8]THF (0.5 mL), 60 °C. [b] Reaction tem-
perature: 40 °C. [c] Determined by 1H NMR spectroscopic analysis;
internal standard: ferrocene or hexamethylbenzene.
Kinetic measurements were performed for the reaction
of ethynylcyclohexene with mesidine (Figure S4). Using 1
as catalyst, an approximately exponential conversion curve
was observed for the first ca. 85% of conversion. In con-
trast, complex induction-period-like kinetics were found for
3. About 18% conversion was recorded in the first hour, an
increase in the reaction rate was then observed. Practically
complete conversion was reached with both 1 and 3 after 3
and 7 h reaction time, respectively.
Conclusions
formed with
a Horiba JobinYvon Fluorolog-3 spectrometer
We have prepared new digold(I) complexes with the rigid
backbone diphosphane ligands PhanePhos (1), xyl-
PhanePhos (2), and Ph2-GemPhos (3) and characterized
them by single-crystal X-ray diffraction, NMR, IR, Raman,
and PL spectroscopy and other methods. Compounds 1
and 3 are particularly interesting, because they share a very
similar ligand scaffold but show different (aurophilic vs.
nonaurophilic) intramolecular Au–Au distances.
Somewhat unexpectedly, we have found that the absorp-
tion and PL spectra are quite similar for 1 and 3. Although
the quantum chemical calculations revealed that the excited
states are very different in character (i.e., strongly influ-
enced by the Au–Au contact), the computed excitation en-
equipped with a 450 W Xe lamp for excitation, double monochro-
mators, and a Hamamatsu R9910 photomultiplier (PMT) as detec-
tor. The same preparations in polyfluoroester oil were used for PL
measurements at temperatures varying between 293 and 17 K. For
this, quartz plates with a dispersed sample between them were
clamped on the cold finger of a closed-cycle optical cryostat (Le-
ybold). The emission spectra were corrected for the wavelength-
dependent response of the spectrometer and detector (in relative
photon flux units). PL decay traces were recorded by connecting
the PMT to an oscilloscope and using a nitrogen laser for a pulsed
excitation at 337 nm (with pulses of ca. 2 ns duration and ca. 5 μJ
energy).
[PhanePhos(AuCl)2]
(1):
Chloro(tetrahydrothiophene)gold(I)
ergies of 1 and 3 were very similar, which is in agreement (0.32 g, 1.00 mmol) was dissolved in CH2Cl2 (30 mL), and
Eur. J. Inorg. Chem. 0000, 0–0
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J. Paradies, M. M. Kappes, W. Klopper, P. W. Roesky et al.
126.5 (d), 34.3 (d), 33.8 (s) ppm. 31P{1H} NMR (161.98 MHz,
FULL PAPER
(+)-(S)-4,12-bis(diphenylphosphanyl)-[2.2]paracyclophane (0.29 g,
0.50 mmol) was added whilst stirring. The mixture was stirred at
ambient temperature for 1 h, then concentrated. The remaining res-
idue was washed with diethyl ether (3ϫ10 mL) and subsequently
dried in vacuo. The product was obtained as colorless powder.
Yield: 0.48 g (92%). C40H34Au2Cl2P2·0.5CH2Cl2 (1083.96): calcd.
C 44.88, H 3.25; found C 44.49, H 4.12. 1H NMR (400.13 MHz,
CDCl ): δ = 29.7 ppm. IR (ATR): ν = 2932 (w), 2851 (w), 1479
˜
3
(w), 1435 (m), 1394 (w), 1262 (w), 1182 (w), 1098 (m), 1026 (w),
998 (w), 914 (w), 823 (w), 802 (w), 748 (m), 692 (s), 541 (s), 527
(s), 513 (s) cm–1. Raman (solid state): ν = 701 (m), 684 (m), 618
˜
(m), 603 (w), 553 (w), 517 (w), 462 (m), 335 [s, ν(AuCl)], 284 [w,
ν(AuP)], 247 (w), 196 (s), 174 (s), 147 (s) cm–1.
3
CDCl3): δ = 7.38–7.25 (m, 16 H, Ph), 7.13 (d, JH,H = 14 Hz, 4 H,
X-ray Crystallographic Studies of 1–3: Suitable crystals were cov-
ered in mineral oil (Aldrich) and mounted onto a glass fiber. Data
were collected with a diffractometer equipped with a STOE im-
aging plate detector system IPDS2 using Mo-Kα radiation with
graphite monochromatization (λ = 0.71073 Å) at 200 K. Subse-
quent computations were carried out with an Intel Core2Quad
processor. Structure solution was performed by direct methods;
full-matrix least-squares refinement against F2 using SHELXS-97
and SHELXL-97 software.[39] CCDC-884961 (PhanePhos),
-884962 (2), -884963 (1), and -884964 (3) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
H2, H3), 7.02 (s, 2 H, H1), 6.84–6.69 (m, 4 H, Ph), 3.83 (m, 2 H,
3
3
CH2), 3.39 (t, JH,H = 12 Hz, 2 H, CH2), 3.14 (t, JH,H = 12 Hz, 2
H, CH2), 2.80 (m, 2 H, CH2) ppm. 13C{1H} NMR (100.61 MHz,
CDCl3): δ = 148.8 (d), 138.4 (d), 138.1 (d), 137.4 (m), 135.2 (d),
134.5 (d), 132.8 (d), 127.9 (d), 126.7 (d), 34.6 (d), 33.9 (s) ppm.
31P{1H} NMR (161.98 MHz, CDCl ): δ = 30.7 ppm. IR (ATR): ν
˜
3
= 2962 (w), 2923 (w), 2852 (w), 1575 (w), 1479 (w), 1435 (m), 1393
(w), 1260 (m), 1097 (vs), 1019 (s), 799 (s), 747 (s), 692 (vs), 541 (s),
512 (s) cm–1. Raman (solid state): ν = 700 (m), 683 (m), 617 (m),
˜
602 (w), 463 (m), 374 (w), 337 [s, ν(AuCl)], 285 [w, ν(AuP)], 261
(m), 248 (m), 228 (m), 196 (s), 174 (s), 149 (s) cm–1. The NMR
spectroscopic data is only partly consistent with the reported in
situ data.[8]
Crystal Data for PhanePhos·(CH2Cl2): C41H36Cl2P2; M = 661.54;
a = 10.626(2) Å, b = 16.515(3) Å, c = 10.860(2) Å, β = 115.63(3)°;
V = 1718.3(6) Å3; T = 200(2) K; space group P21; Z = 2; μ(Mo-
Kα) = 0.311 mm–1; 15209 reflections measured, 9014 independent
reflections (Rint = 0.0455). The final R1 value was 0.0446 [IϾ2σ(I)].
The final wR(F2) value was 0.1017 (all data). The goodness of fit
on F2 was 0.923.
[xyl-PhanePhos(AuCl)2] (2): Chloro(tetrahydrothiophene)gold(I)
(0.16 g, 0.50 mmol) was dissolved in CH2Cl2 (15 mL), and (+)-
(S)-4,12-bis[di(3,5-xylyl)phosphanyl]-[2.2]paracyclophane (0.17 g,
0.25 mmol) was added whilst stirring. The mixture was stirred at
ambient temperature for 2 h, then concentrated. The remaining res-
idue was washed with diethyl ether (2ϫ5 mL) and subsequently
dried in vacuo. The product was obtained as colorless powder.
Yield: 0.26 g (90%). C48H50Au2Cl2P2·CH2Cl2 (1238.64): calcd. C
47.51, H 4.23; found C 47.82, H 4.88. 1H NMR (400.13 MHz,
Crystal Data for 1: C40H34Au2Cl2P2·CH2Cl2; M = 1126.42; a =
9.99825(23) Å,
b = 18.3682(5) Å, c = 20.9049(6) Å; V =
3839.16(18) Å3; T = 150 K; space group P212121; Z = 4; μ(Mo-
Kα) = 8.05 mm–1; 96872 reflections measured, 96872 independent
reflections (Rint = 0.1206). The final R1 value was 0.0432 [IϾ2σ(I)].
The final wR(F2) value was 0.0870 (all data). The goodness of fit
on F2 was 1.047. Flack parameter = 0.016(8).
3
CDCl3): δ = 7.33–7.25 (m, 8 H, H4), 7.11 (d, JH,H = 14 Hz, 4 H,
H2, H3), 7.04 (s, 2 H, H1), 6.85–6.71 (m, 4 H, H5), 3.85 (m, 2 H,
3
3
CH2), 3.40 (t, JH,H = 12 Hz, 2 H, CH2), 3.11 (t, JH,H = 12 Hz, 2
H, CH2), 2.81 (m, 2 H, CH2), 2.50 (s, 12 H, Me), 2.25 (s, 12 H,
Me) ppm. 13C{1H} NMR (100.61 MHz, CDCl3): δ = 144.5 (d),
140.3 (d), 139.4 (d), 138.4 (d), 136.9 (m), 135.7 (m), 135.1 (d), 134.7
(d), 133.3 (m), 133.1 (d), 132.3 (s), 131.7 (s), 131.3 (d), 127.5 (d),
126.9 (d), 34.6 (d), 34.1 (s), 21.8 (s), 21.3 (s) ppm. 31P{1H} NMR
Crystal Data for 2: 4(C48H50Au2Cl2P2)·7(CH2Cl2); M = 1302.27;
orthorhombic; a = 22.332(5) Å, b = 21.128(4) Å, c = 21.265(4) Å;
V = 10034(3) Å3; T = 213(2) K; space group P21212; Z = 8; μ(Mo-
Kα) = 6.231 mm–1; 87575 reflections measured, 24008 independent
reflections (Rint = 0.1077). The final R1 value was 0.0584 [IϾ2σ(I)].
The final wR(F2) value was 0.1219 (all data). The goodness of fit
on F2 was 1.035. Flack parameter = 0.002(7).
(161.98 MHz, CDCl ): δ = 31.5 ppm. IR (ATR): ν = 2962 (w), 2919
˜
3
(w), 2857 (w), 1452 (w), 1416 (w), 1260 (m), 1087 (m), 1015 (s), 794
(vs), 690 (m), 569 (m), 522 (w), 495 (w) cm–1. Raman (solid state):
ν = 684 (s), 570 (m), 545 (s), 518 (m), 467 (w), 333 [s, ν(AuCl)], 293
˜
[m, ν(AuP)], 236 (s), 199 (s), 170 (s), 143 (s) cm–1. MS (70 eV, EI,
220 °C): m/z (%) = 1153.6 (100) [M]+, 1116.7 (97) [M – Cl]+, 920.1
(80) [M – AuCl]+, 883.0 (77) [M – AuCl2]+, 776.9 (67) [M –
AuCl2C6H3Me2]+, 650.5 (56), 574.4 (50), 532.6 (46), 442.5 (38),
429.0 (37), 355.2 (31), 293.3 (25), 165.1 (14), 149.1 (13). The NMR
spectroscopic data is only partly consistent with the reported in
situ data.[8]
Crystal Data for 3: C40H34Au2Cl2P2;
M = 1041.48; a =
11.4706(4) Å, b = 17.6843(4) Å, c = 17.3733(6) Å, β = 90.295(3)°;
V = 3524.13(20) Å3; T = 200 K; space group P21/n; Z = 4; μ(Mo-
Kα) = 8.62 mm–1; 27624 reflections measured, 27624 independent
reflections (Rint = 0.0875). The final R1 value was 0.0442 [IϾ2σ(I)].
The final wR(F2) value was 0.0833 (all data). The goodness of fit
on F2 was 0.940.
[GemPhos(AuCl)2] (3): Chloro(tetrahydrothiophene)gold(I) (0.16 g,
0.50 mmol) was dissolved in CH2Cl2 (15 mL), and 4,13-bis(diphen-
ylphosphanyl)-[2.2]paracyclophane (0.14 g, 0.25 mmol) was added
whilst stirring. The mixture was stirred at ambient temperature for
1 h, then concentrated. The remaining residue was washed with
diethyl ether (3ϫ5 mL) and subsequently dried in vacuo. The prod-
uct was obtained as a colorless powder. Yield: 0.22 g (84%).
C40H34Au2Cl2P2 (1041.50): calcd. C 46.13, H 3.29; found C 45.46,
Hydroamination Reactions: The catalyst was weighed under argon
into an NMR tube. [D8]THF (ca. 0.5 mL) was condensed into the
NMR tube, and the mixture was frozen at –196 °C. The reactant
was injected onto the solid mixture, and the whole sample was
melted and mixed just before insertion into the core of the NMR
machine (t0). The ratio between the reactant and the product was
calculated by comparison of the integrals of the corresponding sig-
nals. Ferrocene or hexamethylbenzene were used as an internal
standard for kinetic measurements.
1
H 3.44. H NMR (400.13 MHz, CDCl3): δ = 7.35–7.21 (m, 16 H,
Ph), 7.09 (d, 3JH,H = 14 Hz, 4 H, H2, H3), 7.02 (s, 2 H, H1), 6.86–
3
6.75 (m, 4 H, Ph), 3.82 (m, 2 H, CH2), 3.43 (t, JH,H = 12 Hz, 2
Intermolecular Hydroamination: The substrates were purchased
3
H, CH2), 3.08 (t, JH,H = 12 Hz, 2 H, CH2), 2.79 (m, 2 H, CH2) from Aldrich, AlfaAesar and Acros. The 1H NMR spectra of N-
ppm. 13C{1H} NMR (100.61 MHz, CDCl3): δ = 149.5 (d), 138.7 (methylbenzylidene)aniline,[40]
(d), 138.2 (d), 137.3 (m), 134.9 (d), 134.5 (d), 133.1 (d), 128.6 (d),
methylaniline,[41] and N-[1-(cyclohex-1-en-1-yl)ethylidene]-2,4,6-tri-
N-(1-phenylethylidene)-2,4,6-tri-
8
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[2.2]Paracyclophanediyldihosphane Complexes of Gold
methylaniline are in agreement withthe previously reported data.[42]
T. G. Driver, J. R. Harris, K. A. Woerpel, J. Am. Chem. Soc.
2007, 129, 3836–3837.
F. C. Falk, R. Fröhlich, J. Paradies, Chem. Commun. 2011, 47,
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A. Pradal, C.-M. Chao, M. R. Vitale, P. Y. Toullec, V. Michelet,
Tetrahedron 2011, 67, 4371–4377.
Intramolecular Hydroamination: The substrate 5-phenyl-4-pentyn-
1-amine[43] was synthesized according to literature procedures. The
1H NMR spectrum of 2-benzyl-1-pyrroline[43] is in agreement with
the previously reported data.
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Supporting Information (see footnote on the first page of this arti-
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ties, and kinetic data of the hydroamination.
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Acknowledgments
This work was supported by the Deutsche Forschungsgemeinschaft
(DFG) funded transregional collaborative research center [SFB/
TRR 88 “Cooperative effects in homo- and hetero-metallic com-
plexes (3MET)”]. C. S. thanks the Konrad-Adenauer-Stiftung for a
doctoral fellowship. J. P. and F. F. thank the Fonds der Chemischen
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Received: July 5, 2012
Published Online: ᭿
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Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: I20751
/KAP1
Date: 11-09-12 16:26:17
Pages: 11
[2.2]Paracyclophanediyldihosphane Complexes of Gold
Gold Complexes
([2.2]Paracyclophanediyldiphosphane)di-
gold(I) complexes with similar backbones
but different gold–gold intramolecular dis-
tances, which facilitate or prevent auro-
philic interactions, have been synthesized
and studied theoretically. Despite the dif-
ferences, the complexes demonstrate simi-
lar photophysical properties as well as cata-
lytic activity in the hydroamination of
alkynes.
C. Sarcher, A. Lühl, F. C. Falk,
S. Lebedkin, M. Kühn, C. Wang,
J. Paradies,* M. M. Kappes,*
W. Klopper,* P. W. Roesky* ............ 1–11
[2.2]Paracyclophanediyldiphosphane Com-
plexes of Gold
Keywords: Aurophilicity / Homogeneous
catalysis / Ligand design / Gold / Lumi-
nescence
Eur. J. Inorg. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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11