Gold(III) six-membered NCN pincer complexes: Synthesis, structure, reactivity and theoretical calculations

Article abstract of DOI:10.1039/c0dt00705f

The first six-membered gold(III) NCN pincer complex was obtained in good yield, under very mild conditions, by transmetalation of [Hg(κC-NCN)Cl] (NCHN = 1,3-bis(pyridin-2-ylmethyl)benzene, HL¹) with Na[AuCl ₄]. The X-ray crystal structure of [Au(NCN)Cl][PF₆] showed that the fused six-membered metallacycles each exist in a strongly puckered boat conformation. As shown by the ¹H NMR spectra in various solvents, the same structure is also retained in solution: no inversion of the six-membered metallacycles is observed in DMSO up to 95 °C. This correlates well with a reaction barrier of 17.5 kcal/mole, as determined by quantum chemical calculations. The reactivity of the present pincer complex is compared to that of the analogous 1,3-bis(2-pyridyl)benzene, HL², derivative, which has five-membered fused metallacycles. Sharp differences are found in the reactions with phosphines, such as PPh₃ and dppe (1,2-bis- diphenylphosphino-ethane), and with silver salts. Theoretical calculations were carried out on the two pincer complexes in order to try to understand these differences, and we found that the gold-chlorine bond is significantly stronger in the case of the complex containing five-membered metallacyclic rings. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/c0dt00705f

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PAPER
www.rsc.org/dalton | Dalton Transactions
Gold(III) six-membered NŸCŸN pincer complexes: synthesis, structure,
reactivity and theoretical calculations†
Giuseppe Alesso,*a Maria Agostina Cinellu,a Sergio Stoccoro,*a Antonio Zucca,a Giovanni Minghetti,a
Carlo Manassero,b Silvia Rizzato,b Ole Swangc and Manik Kumer Ghoshc
Received 22nd June 2010, Accepted 9th August 2010
DOI: 10.1039/c0dt00705f
The first six-membered gold(III) NŸCŸN pincer complex was obtained in good yield, under very mild
conditions, by transmetalation of [Hg(kC-NŸCŸN)Cl] (NŸCHŸN = 1,3-bis(pyridin-2-ylmethyl)benzene,
HL1) with Na[AuCl4]. The X-ray crystal structure of [Au(NŸCŸN)Cl][PF6] showed that the fused
six-membered metallacycles each exist in a strongly puckered boat conformation. As shown by the 1H
NMR spectra in various solvents, the same structure is also retained in solution: no inversion of the
six-membered metallacycles is observed in DMSO up to 95 ◦C. This correlates well with a reaction
barrier of 17.5 kcal/mole, as determined by quantum chemical calculations. The reactivity of the
present pincer complex is compared to that of the analogous 1,3-bis(2-pyridyl)benzene, HL2, derivative,
which has five-membered fused metallacycles. Sharp differences are found in the reactions with
phosphines, such as PPh3 and dppe (1,2-bis-diphenylphosphino-ethane), and with silver salts.
Theoretical calculations were carried out on the two pincer complexes in order to try to understand
these differences, and we found that the gold–chlorine bond is significantly stronger in the case of the
complex containing five-membered metallacyclic rings.
the isoelectronic Au(III) ion are rare: the only examples reported
Introduction
so far are [Au{C6H3(CH2NMe2)2}Cl]2[Hg2Cl6],5 and the 1,3-bis(2-
EŸCŸE-pincer metal complexes (E = donor atoms, C = anionic or
pyridyl)benzene derivative [Au{C6H3(C5H4N)2}Cl][PF6].6 Both
carbenic carbon atom) are a particular type of cyclometalate, the
complexes, which feature five-membered metallacycles, have been
structurally characterized.5a,6 Aspects of the reactivity of the latter
compound were also investigated.6
first examples of which, a series of phosphorus based (E = P) pincer
derivatives, were reported in the late 1970s by Moulton and Shaw.1
The great surge of interest stirred up by these organometallic
compounds is witnessed by the huge number of publications.2,3
Such an interest stems from the unusual physical and chemical
properties of this variegated class of compounds, granted by
the strong M–C s bond, supported by two E–M dative bonds
to the heteroatoms on the pendant arms of the central moiety,
typically an anionic aryl ring. The ease with which steric and
electronic properties of the complexed metal centres can be
modulated, enables their use in a wide range of environments.
Applications encompass different fields, such as catalysis and
organic synthesis,2a–i bioorganometallic chemistry,2j and materials
science.2c,d,k
Following these previous reports, here we describe the synthe-
sis of 1,3-bis(pyridin-2-ylmethyl)benzene, HL1, (Fig. 1) and its
reactions with gold(III) salts. Significant differences of chemical
behaviour with respect to the previously studied analogous ligand
1,3-bis(2-pyridyl)benzene, HL2, are pointed out.
Amongthemolecules potentiallyableto act as pincers, a number
of NŸCŸN systems have been considered in the last few years: many
derivatives of the late transition metals, in particular of the nickel
triad, Ni(II), Pd(II) and Pt(II), have been synthesized, and their
properties thoroughly investigated.4 In spite of the widespread
interest in these d8 square planar complexes, studies relevant to
Fig. 1 NŸCHŸN pincer ligands HL1 and HL2.
3
The X-ray structures of the pincer complex [Au(h -
NŸCŸN)Cl][PF6], featuring six-membered fused metallacycles, and
a salt of the ligand, [HNŸCHŸNH][AuCl4]Cl, are reported and
show a very interesting supramolecular organization, as well as
that of the mercury(II) intermediate [Hg(kC-NŸCŸN)Cl]. Reactiv-
ity studies of the new gold(III) pincer complex have been carried
out, mainly with phosphines and silver salts, which indicated re-
markable differences from the homologous HL2 derivative, which
has five-membered fused metallacycles. Theoretical calculations
aDipartimento di Chimica, Universita` degli Studi di Sassari, Via Vienna 2,
I-07100, Sassari, Italy. E-mail: stoccoro@uniss.it
bDipartimento di Chimica Strutturale e Stereochimica Inorganica e Facolta`
di Farmacia, Universita` di Milano, I-20133, Milano, Italy
cSINTEF Materials and Chemistry, Department of Hydrocarbon Process
Chemistry, P. O. Box 124 Blindern, N-0314, Oslo, Norway
† Electronic supplementary information (ESI) available: Additional data.
CCDC reference numbers 781488–781490. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c0dt00705f
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Fig. 2 Pincer complexes [Au(NŸCŸN)Cl]+.
have been carried out on the two pincer complexes, in order to
rationalize the observed differences.
rings, with a significant downfield shift of ca. 0.6 ppm (acetone-d6)
with respect to the free ligand.
In the attempt to obtain crystals of X-ray quality by slow evapo-
ration of an acetone solution, at room temperature, rearrangement
occurred to give crystals of 1[AuCl4]Cl, resulting from formal loss
of one equivalent of AuCl3. An ORTEP view of the cation is shown
in Fig. 3.9
Results and discussion
The new ligand, 1,3-bis(pyridin-2-ylmethyl)benzene, HL1, was
prepared by co-cyclotrimerization of 1,3-phenylenediacetonitrile
with acetylene, in the presence of Bo¨nnemann catalyst, according
to literature procedures.7 After purification, it was extensively
1
characterized by H NMR spectra, recorded in several solvents
(see Experimental).
The main goal of the present study was to synthesize a
six-membered pincer complex [Au(NŸCŸN)Cl]+, and to com-
pare its reactivity, especially towards common phosphinic lig-
ands and silver salts, with that of the corresponding 1,3-bis(2-
pyridyl)benzene (HL2) derivative having five-membered fused
metallacycles (Fig. 2).
Previous studies on palladium(II) pincer complexes
[Pd(NŸCŸN)Cl] (NŸCHŸN = 1,3-bis(2-pyridyl)benzene (HL2),
1,3-bis(2-pyridyloxy)benzene), have shown that insertion of an O
spacer between the central benzenic ring and the pyridinic rings,
while reducing the bond angle strain imposed by the presence of
two five-membered fused metallacycles, had remarkably positive
effects on the catalytic activity.4h
In the various methods developed for the preparation of
metal pincer complexes, the direct cyclometalation protocol via
C–H activation is particularly attractive, since it does not require
prefunctionalization of the pincer ligands in order to achieve
regioselective metalation. However, a survey of the literature shows
that the direct cyclometalation of tridentate NŸCHŸN ligands
often fails to afford the expected pincer complexes (especially in the
case of palladium).8 The reduced tendency for direct C2 metalation
with NŸCHŸN ligands may be explained by the relatively low bond
strength of the M–N bonds, with respect to that of both M–P
and M–S bonds.2c Nevertheless, most NŸCŸN pincer complexes,
including gold(III) derivatives,5,6 could be successfully synthesized
through a transmetalation route.
As previously observed in the case of HL2, the reaction of
H[AuCl4]·3H2O with HL1 under mild conditions (diethyl ether,
room temperature) affords, in almost quantitative yield, a salt of
the protonated ligand, in the present case [HNŸCHŸNH][AuCl4]2
(1[AuCl4]2). This is a pale yellow solid that was characterized by
CHN analysis and 1H NMR spectroscopy. The 1H NMR spectrum
shows one set of resonances for the H6¢, H6¢¢ protons of the pyridine
Fig. 3 ORTEP view of cation 12+ in compound 1[AuCl4]Cl. Ellipsoids are
drawn at the 20% probability level. Cation 12+ lies on a crystallographic
two-fold axis, passing through atoms C(2) and C(5).
As in the case of the HL2 derivative [HNŸCHŸN][AuCl4],
attempts to convert the salt into the pincer derivative were unsuc-
cessful: in CH3CN, at reflux, the salt was quantitatively recovered.
The same result was obtained in acetic acid, also in the presence
of a base (NaHCO3), while forcing the experimental conditions
at reflux resulted in the formation of metallic gold. At variance
with the pincer complex of HL2, which could be also obtained
from direct reaction of the ligand with [AuCl4]-, the only way
to obtain the HL1 gold pincer compound was a transmetalation
reaction between the corresponding organomercury derivative and
[AuCl4]-. This method of synthesis has been used previously to
prepare other aryl gold(III) complexes.10 The mercury derivative
[Hg(kC-NŸCŸN)Cl], 2, was obtained, as a colourless crystalline
solid, following the classical procedure of synthesis (eqn (1)):
10294 | Dalton Trans., 2010, 39, 10293–10304
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the NMR time-scale up to room temperature, as shown by the
AB pattern displayed by the CH2 resonances in the complex (dA
4.94; dB 4.46; JAB = 15.2 Hz); in the free ligand, as well as in the
C-bound Hg(II) derivative, the signals of the CH2 protons appear
as two singlets at d 4.05 and d 4.16, respectively. Exchange of Cl- or
[PF6]- for [Hg2Cl6]2-, leading to a more soluble salt of 3+, allowed
us to obtain a more complete characterization in solution.13
A
1H NOE difference experiment was performed in acetone, which
showed contacts between HB protons and H4–H6, H3¢–H3¢¢ and of
course HA protons, while HA protons showed contacts only with
HB protons. Notably, in this solvent the H4, H5 and H6 protons
are casually isochronous, and give rise to a narrow singlet (see
Experimental), while the CH2 protons display an AB system again,
(1)
The 1H NMR spectrum shows the lack of the H2 proton.
Furthermore it turns out that the resonances of the protons of
the pyridine moieties are not very shifted in comparison with
those of the free ligand: most likely this is due to the nitrogen
atoms not being involved in the coordination of the metal ion.
This is also supported by the resonance of the methylenic protons,
that appears as a narrow singlet (this issue will be analyzed more
deeply afterwards), and confirmed by X-ray diffraction of a single
crystal of 2. The molecular structure of 2 is depicted in Fig. 4, with
principal bond parameters in the caption.11
1
with dA 4.96, dB 4.61, and JAB = 15.7 Hz. On the whole, the H
NMR spectra suggest for cation 3+ the structure as shown in Fig. 5.
Fig. 5 Proposed structure for 3+ with numbering scheme and NOE
contacts.
In fact, in the six-membered metallacycles having a boat
conformation, the HA protons occupy pseudo axial positions,
lying respectively above and below the coordination plane, so that
they can exhibit NOE effect only with the geminal proton HB.
On turn, the HB protons, being in pseudo equatorial positions,
can show NOE effects with neighbouring protons. Variable-
temperature studies showed that these protons are not involved
in a dynamic process: indeed, a sharp AB pattern is observed
up to 95 ◦C in a DMSO-d6 solution of 3[PF6], indicating that
interconversion between the left- and right-handed twisted forms
(A, B in Scheme 1) does not occur.
Fig. 4 ORTEP view of compound 2. Ellipsoids as in Fig. 1. Principal
bond and non-bond parameters are: Hg–Cl 2.308(2), Hg–C(2) 2.066(7),
˚
Hg ◊ ◊ ◊ N(1) 2.730(7), Hg ◊ ◊ ◊ N(2) 2.820(9) A, Cl–Hg–C(2) 173.6(2),
N(1) ◊ ◊ ◊ Hg ◊ ◊ ◊ N(2) 108.2(2)◦.
Reaction of the mercury derivative 2, with H[AuCl4] in ethanol,
in the presence of NaHCO3, or directly with Na[AuCl4], gives the
gold pincer in excellent yield as a mercury salt, likely [Hg2Cl6]2-
(eqn (2)):
NaHCO
3
H[AuCl4 ]⋅3H2O +[Hg(kC-N^C^N)Cl] ⎯⎯⎯⎯→
-NaCl
2
(2)
1/ 2[Au(N^C^N)Cl]2[Hg2Cl6 ]
(3) [Hg Cl ]
6
2
2
Compound (3)2[Hg2Cl6] was characterized by elemental analysis
and spectroscopic methods. The 1H NMR spectrum, registered in
DMSO-d6, the only solvent in which the compound is soluble,
shows in the aromatic region five resonances, not well resolved,
which were completely assigned by comparison with those of the
ligand, and by selective H–H decoupling. The strong deshielding
of the H6¢, H6¢¢ protons (d 9.21 vs. d 8.46 in the free ligand), usually
observed when a chlorine is in proximity of the pyridine ring,
supports the NŸCŸN pincer-like coordination of the ligand.12 The
spectrum also suggests a boat conformation of the six-membered
cyclometalated rings. No rapid inversion of the boats occurs on
Scheme 1 Left- (A) and right-handed (B) twisted forms of 3+; bottom
figures represent the Newman-projections along the Au–C bonds.
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Using quantum chemical calculations, a transition state (TS)
search was carried out for the interconversion reaction. The TS
structure is shown in Fig. 6. This TS connects the two forms of
3+ as shown by Intrinsic Reaction Coordinate (IRC) calculations.
We note that both methylene groups are on the same side of the
Au–N–N–C plane in the TS. The computed activation energy for
the transformation is 17.5 kcal mol-1, which is in line with our
failure to observe interconversion at 95 ◦C.
bond lengths and angles are listed in Table 1, together with
+
corresponding bond parameters of the five membered pincer 3¢ .6
In 3+ the metal atom displays a square planar environment with
a slight tetrahedral distortion, maximum displacements from the
˚
least-squares plane being +0.027(3) and -0.025(4) A for atoms
N(1) and C(2), respectively. The three aromatic rings are all strictly
planar, and for the sake of simplicity we will call the ring of
N(1) ring 1, that of C(2) ring 2, and that of N(2) ring 3. Thus,
the dihedral angles formed by the metal best plane and these
rings are 136.7(1), 40.7(2), and 43.0(1)◦ for rings 1, 2, and 3,
respectively. Other important dihedral angles are: ring 2–ring 1
123.9(1)◦, ring 2–ring 3 56.5(1)◦, and ring 1–ring 3 93.7(1)◦. It
is peculiar of this cation that the moiety formed by ring 1 plus
Au and C(7), and that formed by ring 2 plus C(13) (but not Au)
show a high degree of planarity, maximum distances from the
˚
best plane, in the first case, being +0.011(4) and -0.010(4) A for
atoms C(8) and C(7), respectively. In the second case, maximum
˚
displacements are +0.023(3) and -0.025(4) A for atoms N(2) and
C(13), respectively. The metal atom is out of this second best plane
˚
by 0.144(1) A, probably because of packing effects: the calculated
gas-phase geometry gives a value of zero. Corresponding moieties
in similar NŸNŸC cyclometalated derivatives are definitely non
planar, as found, for example, in [Au(NŸNŸC)Cl]+ (NŸNŸC =
N2C10H7(CMe2C6H4)-6, i.e. deprotonated 6-(1,1-dimethylbenzyl)-
2,2¢-bipyridine).14 Bond parameters of 3+ can be compared with
+
those of the five-membered pincer 3¢ (see Table 1). At variance
Fig. 6 ORTEP view of the calculated structure of the transition state
of 3+.
with 3+, this cation, which is totally planar, displays a certain
degree of bond angle strain around the metal center. It follows that,
with the only exception of the Cl–Au–C(2) angles, corresponding
bond angles in the two cations are very different (see Table 1),
whereas the main difference between the bond lengths of the
A single crystal of 3[PF6] suitable for X-ray diffraction was
grown by slow evaporation of an acetone solution at room
temperature.
˚
two cations concerns the Au–C(2) distance, 2.014(4) A here, and
Gratifyingly, the calculated geometries are in excellent agree-
ment with the experimental ones and with each other. [Au(L1)Cl]+
(3+) and the corresponding five-membered ring pincer [Au(L2)Cl]+
+
˚
1.950(5) A in 3¢ . This is not surprising, because a shortening of
the metal–ligand central bond in planar bicyclo moieties is found
as a rule. The other corresponding bond lengths are very similar in
the two compounds. Analogous structural differences have been
found between five- and six-membered NŸCŸN pincer complexes
of palladium(II); notably, the reduced bond angle strain around
the metal center, featured by the six-membered pincer complex,
resulted in a higher catalytic activity of the complex compared to
+
(3¢ ) are calculated to have C2 and C2v symmetries, respectively.
In the following description, experimental values are used, unless
otherwise mentioned. The structure consists of the packing of 3+
cations and [PF6]- anions in the molar ratio 1 : 1, in the monoclinic
space group P21/n, with no unusual van der Waals contacts. An
ORTEP view of the cation is shown in Fig. 7, and its principal
+
Fig. 7 ORTEP view of cations [Au(L1)Cl]+ (3+) (left) and [Au(L2)Cl]+(3¢ ) (right, ref. 6). Ellipsoids are drawn at the 30% probability level.
10296 | Dalton Trans., 2010, 39, 10293–10304
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◦
+
+
Table 1 Selected bond distances (A) and angles ( ) for 3 (this work) 3¢ (ref. 6), and the TS for interconversion between the two isomers on 3+ (this
work). The first values in each column are experimental ones, with Estimated Standard Deviations (Esd’s) on the last figure in parentheses, while the
values in square brackets and in braces are calculated at the B3LYP/cc-pVTZ and MP2/cc-pVDZ level of theories, respectively
˚
+
Parameter
3+
3¢
TSa
Au–Cl
Au–N(1)
Au–N(2)
Au–C(2)
N(1)–C(8)
N(1)–C(7)
N(1)–C(12)
N(1)–C(11)
N(2)–C(14)
N(2)–C(12)
N(2)–C(18)
N(2)–C(16)
2.386(1) [2.390]{2.343}
2.027(3) [2.066]{2.019}
2.031(3) [2.066]{2.019}
2.014(4) [2.044]{2.004}
1.350(6) [1.351]{1.363}
2.360(1) [2.367]{2.334}
2.019(5) [2.065]{2.029}
2.032(5) [2.065]{2.029}
1.950(5) [1.966]{1.944}
[2.415]{2.367}
[2.102]{2.055}
[2.102]{2.055}
[2.080]{2.047}
[1.346]{1.357}
1.385(8) [1.374]{1.384}
1.345(8) [1.338]{1.353}
1.377 (1.374) [1.384]
1.340(6) [1.348]{1.360}
1.362(4) [1.351]{1.363}
1.349(5) [1.348]{1.360}
[1.354]{1.366}
(1.346) [1.357]
[1.354]{1.366}
1.346(8) [1.338]{1.353}
Cl–Au–N(1)
Cl–Au–N(2)
Cl–Au–C(2)
91.7(1) [91.5]{92.1}
92.1(1) [91.5]{92.1}
179.2(1) [180.0]{180.0}
175.8(1) [177.0]{175.8}
88.2(1) [88.5]{87.9}
88.1(1) [88.5]{87.9}
121.2(3) [120.8]{120.2}
99.2(1) [99.7]{98.8}
99.6(1) [99.7]{98.8}
179.7(2) [180.0]{180.0}
161.2(1) [160.7]{162.4}
80.5(2) [80.3]{81.2}
80.7(2) [80.3]{81.2}
[89.8]{90.0}
[89.8]{90.0}
[166.2]{166.0}
[158.4]{157.2}
[92.8]{92.8}
[92.8]{92.8}
[125.4]{126.1}
N(1)–Au–N(2)
N(1)–Au–C(2)
N(2)–Au–C(2)
Au–N(1)–C(8)
Au–N(1)–C(7)
Au–N(1)–C(12)
Au–N(1)–C(11)
Au–N(2)–C(14)
Au–N(2)–C(12)
Au–N(2)–C(18)
Au–N(2)–C(16)
115.1(4) [114.0]{114.5}
124.7(4) [124.7]{123.9}
114.8(4) [114.0]{114.5}
124.6(4) [124.7]{123.9}
117.5(3) [118.5]{118.3}
120.9(3) [120.8]{120.2}
118.8(2) [118.5]{118.3}
[114.4]{113.1}
[125.4]{126.1}
[114.4]{113.1}
a Numbering scheme as in 3+.
that of the corresponding five-membered analogue.4h We note that
the computed distances corresponding to the coupling involving
typically PR3, while complete removal of the cyclometalated
ligands was never observed.17 In the previous study concerning the
five-membered pincer 3¢[PF6] we showed that reaction with PPh3
occurs with cleveage of the Au–N bonds to give the bis-phosphine
derivative [Au(kC-NŸCŸN)(PPh3)2Cl][PF6], regardless of the sto-
ichiometric ratio used.6 Interestingly, a different behaviour was
observed in reactions of the present pincer complex 3[PF6] with
tertiary phosphines. Regardless of the stoichiometric ratio used,
reaction with PPh3 occurs without cleavage of the Au–N bonds to
give [Au(NŸCŸN)(PPh3)Cl][PF6], 4[PF6], likely a pentacoordinated
species (eqn (3)):
B
˚
the H protons (see Fig. 5) are 2.38 and 2.32 A for the central and
pyridine rings, respectively.
+
At variance with [Au(L2)Cl]+, 3¢ , that can be obtained either
by transmetalation from the corresponding mercury(II) derivative
or by direct cycloauration, [Au(L1)Cl]+ could be obtained only
by transmetallation. The opposite trend was instead observed
in the C–H activation of phenyl rings of 6-substituted 2,2¢-
bipyridines to give NŸNŸC cycloaurated complexes. Indeed, the
cyclometallation of 6-phenyl-2,2¢-bipyridine, which affords a five-
membered metallacycle, requires use of mercury(II) intermediates
or silver salts and high temperature,15 while formation of six-
membered metallacycles can be easily accomplished by direct C–
H activation, as shown by the cyclometalation of 6-benzyl-2,2¢-
bipyridines.14 The high tendency of gold(III) to give six-membered
metallacycles by direct C–H activation, was clearly demonstrated
by Nonoyama and coworkers in the cycloauration of 3-phenyl-6-
p-toluidinopyridazine, as this ligand can give both five- and six-
membered metallacycles.16
PPh
3
ꢀꢀꢀꢀꢁ
[Au(N^C^N)Cl][PF ]
[Au(N^C^N)(PPh )Cl][PF ]
3 6
ꢂꢀꢀꢀꢀ
(3)
6
-PPh
3
3[PF
]
4[PF ]
6
6
As suggested by the NMR data (see below), in complex 4[PF6]
the donor atoms of the pincer system retain coordination to the
metal centre. The reaction with PPh3 in CD3CN was monitored
1
at room temperature by H and 31P NMR: after the addition of
1 equivalent of phosphine a mixture of 4+ and 3+ (ca. 6 : 1 molar
ratio) and free PPh3 (dP -4.12) was observed, whereas the presence
of a bis-phosphine adduct, analogous to [Au(kC-L2)(PPh3)2Cl]+,
was definitely ruled out. Complete conversion of 3+ to 4+ was
achieved on addition of an excess of PPh3, while removal of excess
PPh3 from the mixture promoted the reverse reaction. Indeed, the
1H and 31P NMR spectra of isolated 4[PF6] (in CD3CN) showed
a 1 : 3 : 1 mixture of 3+, 4+ and free PPh3. Any attempt to grow
crystals of 4[PF6] suitable for X-ray analysis was unsuccessful;
nevertheless, the structure of 4+ was confidently inferred by its
spectroscopic data. In the 1H NMR spectrum only one resonance
Reactivity of [Au(NŸCŸN)Cl][PF6], 3[PF6]
As previously mentioned gold(III) NŸCŸN pincer derivatives are
very few and their reactivity is almost completely unexplored. On
the contrary the reactivity of gold(III) cyclometalated derivatives
with bidendate CŸN and tridentate CŸNŸN and CŸNŸC ligands
has been reported by several groups: most reactions involve
displacement of the nitrogen atoms or of halides by neutral ligands,
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is observed for the H6¢, H6¢¢ protons of the pyridine rings, very
slightly shifted to higher field (d 9.07, CD3CN) compared to d 9.28
(same solvent) in 3+. Also shifted to higher field, in this case more
significantly, are the resonances of the methylenic protons: d 3.90
and 3.97 compared to d 4.39 and 4.77 in 3+, becoming a very tight
AB spin system.
As previously mentioned phosphines are also able to displace
a bound halide from cycloaurated Au(III) halide complexes to the
outer coordination sphere where it can be easily exchanged with
another counter ion. Assuming this could be our case, complex
4[PF6] was treated with an excess of K[PF6] in acetone. As no
exchange was observed we suggest that cation 4+ retains its original
arrangement with the chlorine trans to the carbon atom and the
two pyridinic moieties coordinated to the metal centre, with the
PPh3 occupying a fifth coordination position. The large high
field shift of the CH2 protons strongly suggests a square based
pyramidal geometry for this cation, with the phosphine in the
apical position. The 31P NMR spectrum of 4[PF6] showing only
one resonance for the coordinated phosphine (d 26.83) is a further
evidence of this arrangement.18 The reversibility of reaction 3
indicates that the phosphine ligand is not kinetically inert, likely
due to steric hindrance of the methylenic groups and to the low
stability of 5-coordinated species.
Fig. 8 Proposed structure for 52+
.
Displacement of the chloride ligand from 3[PF6] was easily
accomplished by reaction with silver salts. Reaction with AgOTf
in acetone or dichloromethane, at room temperature, led to for-
mation of the aquo complex [Au(NŸCŸN)(H2O)][PF6][OTf]·nH2O,
6[PF6][OTf]·nH2O (n = 0, 1). In the 1H NMR spectrum (CD2Cl2)
a broad signal accounts for a coordinated water molecule in rapid
exchange with the water molecules H-bonded to the solvent (n =
0) or to the crystallization water (n = 1). In the first case (n =
0), the chemical shift of the coordinated water is d 6.65 while
the peak of the water molecules H-bonded to CD2Cl2 (usually
at 1.6) is not present. In the second case (n = 1), the chemical
shift of the scrambling water molecules is d 3.90; notably, in this
case the resonances of the HA and H6¢–H6¢¢ protons which face the
coordinated H2O molecule – respectively at d 5.05 (4.74 in 3+) and
d 9.15 (9.36 in 3+) – are also broadened, while the signal of the
HB protons appears as a sharp “doublet”. In the former case the
resonance of HA is only slightly broadened while H6¢–H6¢¢ are sharp
signals. In both cases the other resonances are slightly shifted at
low field with respect to 3+. The 19F NMR spectrum confirms
Under the same experimental conditions reaction of 3[PF6] with
[Ph2PCH2]2, dppe, gave a complex that, on the basis of micro-
analytical data, was formulated as [Au(NŸCŸN)(dppe)][Cl][PF6],
5[Cl][PF6] (eqn (4)):
[Au(N^C^N)Cl][PF ] ⎯d⎯ppe⎯→ [Au(N^C^N)(dppe)][Cl][PF ]
6
6
(4)
3[PF
]
5[Cl][PF ]
6
6
The presence of the chloride ligand as a counter ion, in the
outer coordination sphere, is proven by the metathesis reaction
with K[PF6], which occurs quickly and quantitatively in acetone
at room temperature to give compound 5[PF6]2 (eqn (5)):
the presence of PF6 and OTf as counterions (d -50.65 d, JFP
710.9 Hz, d -57.37 s, respectively).
=
K[PF
]
6
[Au(N^C^N)(dppe)][Cl][PF ] ⎯⎯⎯→ [Au(N^C^N)(dppe)][PF ]2
6
6
-KCl
5[Cl][PF
]
5[PF ]
6 2
6
Reaction of 3[PF6] with AcOAg afforded the acetato complex
[Au(NŸCŸN)(OAc)][PF6], 7[PF6], in good yield. It exhibits the
na(COO) and ns(COO) at 1620 and 1315 cm-1, respectively, in
accordance with an acetato group trans to a carbon atom.20 The
1H NMR spectrum in CD3COCD3 shows the resonance of the
methyl protons at d 1.95 with the correct integral ratio; also for
this compound an AB pattern is displayed by the CH2 protons (dA
4.84; dB 4.64; JAB = 15.8 Hz). Complexes 6[PF6][OTf] and 7[PF6]
could be both valuable starting materials for the obtainment of
other gold(III) derivatives and catalytic precursors.
As shown by the reaction with dppe and with silver salts
displacement of the chloride ligand from the present pincer
complex [Au(L1)Cl][PF6] is easily accomplished contrary to what
is observed for the pincer complex [Au(L2)Cl][PF6], whose chloride
is neither displaced by phosphines nor by silver salts.6 The latter
behaviour being quite unexpected, considering that the chloride
ion is trans to a carbon atom, we deemed it of interest to shed
light on the nature of the Au–Cl bond in these pincer complexes
by quantum chemical calculations. Reaction energies for the
following reaction were computed:
(5)
The proposed structure for 52+ rests on NMR spectroscopic
evidence. In the 31P{ H} NMR spectrum (CD2Cl2) two resonances
1
at d 55.26 and d 56.54, indicative of a very similar chemical
environment, are consistent with the classical chelating behaviour
of dppe. In the 1H NMR spectrum (CD2Cl2) two sets of multiplets
at d 2.84–3.06 and d 3.36–3.60 have been assigned to the
methylenic protons of the chelating diphosphine ligand. The
presence in the spectrum of an AB system relative to the methylenic
protons of the pincer ligand proves that the pyridinic moieties have
not been displaced by the dppe. At variance with 4+, the H6¢/H6¢¢
resonances are now strongly shifted to high field (d 8.00) compared
to d 9.36 in 3+, a common effect observed when a phosphine ligand
is present in the coordination sphere of square planar complexes of
d8 late transition metals. We thus propose a trigonal bipyramidal
geometry for cation 52+ (Fig. 8) with the equatorial positions
occupied by the metalated carbon and the phosphorus atoms and
the nitrogen atoms in the axial ones.
In the attempt to obtain crystals of 5[PF6]2 suitable for X-ray
analysis we obtained instead the well known gold(I) derivative
[Au(dppe)2][PF6].19
[Au(Lx)Cl]+ → [Au(Lx)]2+ + Cl-, x = 1,2
10298 | Dalton Trans., 2010, 39, 10293–10304
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©

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For obvious reasons of electrostatic origin, the reaction energies
themselves were strongly endothermic (in the order of 200–
250 kcal mol-1) for these model reactions. The interesting aspect
here is the difference between the two complexes: at the three
employed levels of theory, the chlorine abstraction demanded from
12.5 to 13.1 kcal/mole less energy for 3+, containing six-membered
to give the ligand as a brown oil. Column chromatography on
silica gel 60, using benzene/acetone (10 : 1) as eluent, gave 15.10 g
(0.058 mol, 92%) of NŸCHŸN as light green oil.
+
rings, than for 3¢ with its five-membered rings. We infer that the
difference in reactivity between the two complexes has its roots in
different Au–Cl bond strengths.
Conclusion
A new NŸCŸN gold(III) pincer complex, featuring six-membered
NŸC metallacycles, was synthesized and structurally character-
ized. Its structural and reactivity features were compared to those
of a previously studied pincer complex having five-membered NŸC
metallacycles. Profound differences were found between the two
complexes in the reactions with phosphines and with silver salts.
Contrary to what was observed with the five-membered pincer
complex, reaction of the present complex with phosphines, both
mono and bidentate, occurred without cleavage of the Au–N bonds
leading to uncommon pentacoordinated phosphine adducts. An
unprecedented dicationic aquo complex and an acetato complex
were obtained by reaction with AgTOf and AgOAc, respectively,
while no reaction with silver salts had been observed in the case of
the five-membered pincer complex. Theoretical calculations shed
some light into this unexpected behaviour, as heterolytic cleavage
of the gold-chlorine bond in the six-membered ring complex
demanded significantly less energy.
1H NMR (CDCl3): d 4.12 (s, 4H, CH2); 7.07–7.12 (m, 6H,
H4, H6, H3¢, H3¢¢, H5¢, H5¢¢); 7.18 (s br, 1H, H2); 7.20 (dd partially
overlapped with CHCl3, 1H, JHH (av.) = 7.2 Hz, H5); 7.56 (td, 2H,
JHH = 7.5 Hz, 1.8 Hz, H4¢, H4¢¢); 8.53 (ddd, 2H, JHH = 4.5 Hz, 1.8 Hz,
0.9 Hz, H6¢, H6¢¢); (CD2Cl2): d 4.11 (s, 4H, CH2); 7.11–7.21 (m, 6H,
H4, H6, H3¢, H3¢¢, H5¢, H5¢¢); 7.20 (s br, 1H, H2); 7.24 (dd, 1H, JHH
=
6.7 Hz, H5); 7.61 (td, 2H, JHH = 7.6 Hz, 1.9 Hz, H4¢, H4¢¢); 8.52
(ddd, 2H, JHH = 4.7 Hz, 1.6 Hz, 0.8 Hz, H6¢, H6¢¢); (acetone-d6): d
4.07 (s, 4H, CH2); 7.11–7.17 (m, 6H, H4, H6, H3¢, H3¢¢, H5¢, H5¢¢);
7.20 (dd partially overlapped, 1H, JHH(av) = 7.1 Hz, H5); 7.27 (s
br., 1H, H2); 7.64 (td, 2H, JHH = 7.8 Hz, 2.0 Hz, H4¢, H4¢¢); 8.47
(ddd, 2H, JHH = 4.8 Hz, 1.8 Hz, 0.9 Hz, H6¢, H6¢¢); (DMSO-d6): d
4.05 (s, 4H, CH2); 7.08 (d, 2H, JHH = 8.4 Hz, H4, H6); 7.17–7.21
(m, 4H, H2, H5, H5¢, H5¢¢); 7.25 (d, 2H, JHH = 7.8 Hz, H3¢, H3¢¢);
7.68 (td, 2H, JHH = 7.8 Hz, 2.0 Hz, H4¢, H4¢¢); 8.46 (ddd, 2H, JHH
=
Experimental
4.8 Hz, 1.8 Hz, 0.9 Hz, H6¢, H6¢¢); (CD3CN): d 4.06 (s, 4H, CH2);
7.10 (d, 2H, JHH = 8.1 Hz, H4, H6); 7.15 (ddd, 2H, JHH = 8.1 Hz,
General
H5¢, H5¢¢); 7.19–7.24 (m, 4H, H2, H5, H3¢, H3¢¢); 7.64 (td, 2H, JHH
=
H[AuCl4]·3H2O was obtained from Johnson Matthey. All the sol-
vents were purified before use according to standard procedures.
All the reactions were performed in air.
7.6 Hz, 2.0 Hz, H4¢, H4¢¢); 8.47 (ddd, 2H, JHH = 4.8 Hz, 1.8 Hz,
0.9 Hz, H6¢, H6¢¢).
Elemental analyses were performed with a Perkin-Elmer ele-
mental analyzer 240B by Mr. Antonello Canu (Dipartimento di
Chimica, Universita` degli Studi di Sassari, Italy). Infrared spectra
Synthesis of [NHŸCHŸNH][AuCl4]2, 1[AuCl4]2. A solution of
NŸCHŸN (260.3 mg; 1.00 mmol) in 30 mL of diethyl ether was
added under vigorous stirring to a solution of HAuCl4·3H2O
(787.7 mg, 2.00 mmol) in the same solvent (50 mL) and let
to react for 30 min. The precipitate which formed was filtered
off, washed with diethyl ether and dried under vacuum to give
compoun◦d 1[AuCl4]2 as a pale yellow solid. Yield 892.9 mg, 95%;
m.p. 155 C (dec.); (Found: C 23.44; H 1.82; N 2.85%. Calc. for
were recorded with a FT-IR Jasco 480P using Nujol mulls. 1H, 19
F
and 31P{ H} NMR spectra were recorded at room temperature
(20 ◦C) with a Varian VXR 300 spectrometer operating at 300.0,
282.2 and121.4 MHzrespectively. Chemicalshifts are giveninppm
relatively to internal TMS (1H), external trifluoroacetic acid TFA
(19F) and external H3PO4 (31P). 2D-COSY and NOESY spectra
were performed by means of standard pulse sequences.
1
1
C18H18Au2Cl8N2: C 23.00; H 1.93; N 2.98%). H NMR (DMSO-
d6): d 4.16 (s, 4H, CH2); 7.15 (d, 2H, JHH = 7.8 Hz, H4, H6); 7.25 (s,
1H, H2); 7.26 (t, 1H, JHH = 7.5 Hz, H5); 7.47 (t, 2H, JHH = 7.8 Hz,
Syntheses
H5¢, H5¢¢); 7.49 (d, 2H, JHH = 7.5 Hz, H3¢, H3¢¢); 8.00 (td, 2H, JHH
=
The ligand 1,3-bis(pyridin-2-ylmethyl)benzene (NŸCHŸN), HL1.
7.8 Hz, 1.8 Hz, H4¢, H4¢¢); 8.60 (d, 2H, JHH = 4.8 Hz, H6¢, H6¢¢);
(acetone-d6): d 4.72 (s, 4H, CH2); 7.43–7.52 (m, 3H, H4, H6, H5);
7.64 (s, 1H, H2); 8.11 (d, 2H, JHH = 8.1 Hz, H3¢, H3¢¢); 8.17 (tm, 2H,
A solution of 1,3-phenylenediacetonitrile (10.00 g, 0.063 mol)
5
and [(h -cyclopentadienyl)cobalt-1,5-cyclooctadiene] (500 mg,
2.153 mmol) in degassed anhydrous toluene (100 mL) was
introduced by suction, into a 0.2 L autoclave, evacuated from
the air (0.133 mbar). The reaction vessel was pressurized to 13 bar
with acetylene and then rocked and heated to 120 ◦C for 20 h. After
cooling and release of residual gas, the solvent was evaporated and
the brown residue treated with aqueous solutions of HCl (5%)
and NaOH (5%), then extracted with Et2O, and dried on Na2SO4
J
HH(av) = 6.9 Hz, H5¢, H5¢¢); 8.76 (td, 2H, JHH = 7.8 Hz, 1.5 Hz, H4¢,
H4¢¢); 9.04 (dd, 2H, JHH = 6.1 Hz, 0.9 Hz, H6¢, H6¢¢).
By slow evaporation, at room temperature, of an acetone
solution of compound 1[AuCl4]2, crystals suitable for X-ray
diffraction were grown. The resolved structure showed that one
of the two [AuCl4]- anions had been replaced by Cl- leading to
1[AuCl4]Cl.
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Synthesis of [Hg(jC-NŸCŸN)Cl], 2. A mixture of NŸCHŸN
(260.3 mg, 1.00 mmol) and mercury(II) acetate (318.5 mg,
1.00 mmol) in absolute ethanol (20 mL) was heated for 24 h at
reflux, under stirring. Afterwards a solution of lithium chloride
(94 mg, 2.22 mmol) in methanol (15 mL) was added and the
mixture gently heated for 15 min. The solution was poured into
distilled water (100 mL): the white precipitate which formed
was filtered off, washed with water, ice-cold methanol and dried
under vacuum to give compound 2. Yield 381.4 mg, 77%; m.p.
132 ◦C. (Found: C, 43.60; H, 2.91; N, 5.53%. Anal. Calc. for
Yield 495.6 mg, 94%; m.p. 188–190 ◦C (dec.); (Found: C 40.41;
H 2.75; N 5.14%. Anal. Calcd. for C18H15AuCl2N2: C 41.01; H
2.87; N 5.31%). 1H NMR (DMSO-d6): d 4.46 (2H, JHH = 15.2 Hz,
CHAHB, AB system); 5.09 (2H, JHH = 15.2 Hz, CHAHB, AB
system); 7.23–7.27 (m, 3H, H4, H5, H6), 7.78 (t, 2H, JHH = 7.5 Hz,
H5¢, H5¢¢); 8.09 (d, 2H, JHH = 7.5 Hz, H3¢, H3¢¢); 8.35 (t, 2H, JHH
7.5 Hz, H4¢, H4¢¢); 9.28 (d, 2H, JHH = 6.0 Hz, H6¢, H6¢¢).
=
Synthesis of [Au(NŸCŸN)Cl][PF6], 3[PF6].
Method a. K[PF6] (220.8 mg, 1.2 mmol) was added to a
suspension of 3[Cl] (527.2 mg, 1.00 mmol) in 100 mL of acetone.
The suspension was left under stirring at room temperature
overnight. After filtration the solution was evaporated to dryness
and 15 mL of water were added to the residue. The white solid
was filtered off, washed with diethyl ether and dried in vacuum to
give compound 3[PF6]. Yield 452.1 mg, 71%; m.p. 208–210 ◦C
(dec.); (Found: C 33.72; H 2.18; N 4.51%. Anal. Calcd. for
C16H11AuClF6N2P: C 33.95; H 2.37; N 4.40%.
Method b. K[PF6] (920.3 mg, 5.0 mmol) was added to a
suspension of (3)2[Hg2Cl6] (798.7 mg, 1.00 mmol) in 100 mL
of acetone. The suspension was left under stirring at room
temperature overnight. After filtration the solution was evaporated
to dryness and 15 mL of water were added to the residue. The
white solid was filtered off, washed with diethyl ether and dried in
vacuum to give 3[PF6]. Yield 346.1 mg, 54%; m.p. 208–210 ◦C
(dec.). (Found: C 33.65; H 2.41; N 4.44%. Anal. Calcd. for
C16H11AuClF6N2P: C 33.95; H 2.37; N 4.40%). 1H NMR (acetone-
d6): d 4.61 (2H, JHH = 15.6 Hz, AB system, CHAHB); 4.96 (2H,
JHH = 15.6 Hz, AB system, CHAHB); 7.34 (s, 3H, H4, H5, H6), 7.84
(t, 2H, JHH(av) = 7.0 Hz, H5¢, H5¢¢); 8.19 (d, 2H, JHH = 7.8 Hz, H3¢,
1
C18H15HgClN2: C 43.64; H 3.05; N 5.66%). H NMR (CDCl3):
d 4.10 (s, 4H, CH2); 7.12–7.25 (m, 7H, H3, H4, H5, H3¢, H3¢¢, H5¢,
H5¢¢); 7.54 (td, 2H, JHH = 7.8 Hz, 1.8 Hz, H4¢, H4¢¢); 8.53 (d, 2H,
JHH = 4.2 Hz, H6¢, H6¢¢); (DMSO-d6): d 4.10 (s, 4H, CH2); 7.11 (m,
2H, H5¢, H5¢¢); 7.24–7.27 (m, 3H, H4, H5, H6); 7.38 (d, 2H, JHH
=
7.5 Hz, H3¢, H3¢¢); 7.71 (td, 2H, JHH = 7.5 Hz, 1.5 Hz, H4¢, H4¢¢); 8.43
(d, 2H, JHH = 4.3 Hz, H6¢, H6¢¢); (acetone-d6): d 4.16 (s, 4H, CH2);
7.12 (t, 1H, JHH = 7.5 Hz, H5), 7.25 (ddd, 2H, JHH = 7.5 Hz, 4.8 Hz,
0.9 Hz, H5¢, H5¢¢); 7.34 (d, 2H JHH = 7.5 Hz, JHgH ~ 60 Hz, H4, H6);
7.40 (d br, 2H, JHH = 7.5 Hz, H3¢, H3¢¢); 7.68 (td, 2H, JHH = 7.5 Hz,
1.9 Hz, H4¢, H4¢¢); 8.49 (dm, 2H, JHH = 5.1 Hz, H6¢, H6¢¢). Crystals
of X-ray quality were obtained by slow evaporation of an acetone
solution at room temperature.
Synthesis of [Au(NŸCŸN)Cl]2[Hg2Cl6], (3)2[Hg2Cl6]. A mixture
of [Hg(kC-NŸCŸN)Cl], 2, (495.4 mg, 1.00 mmol), H[AuCl4]·3H2O
(393.8 mg, 1.00 mmol) and NaHCO3 (84.01 mg, 1.00 mmol)
in absolute ethanol (100 mL) was left for 5 h to react under
stirring. The formation of a white precipitate could be observed.
Afterwards, the precipitate was filtered off, washed with diethyl
ether and dried in vacuum to give compound (3)2[Hg2Cl6]. Yield
685.2 mg, 86%; m.p. 135–136 ◦C (dec.); (Found: C, 27.14; H, 1.57;
N, 3.43%. Anal. Calcd. for C18H15AuCl4HgN2: C, 27.07; H, 1.89;
N, 3.51%).
H3¢¢); 8.44 (td, 2H, JHH = 7.8 Hz, 1,2 Hz, H4¢, H4¢¢); 9.33 (d, 2H, JHH
=
6.0 Hz, H6¢, H6¢¢); (CD3CN): d 4.39 (2H, JHH = 15.9 Hz, CHAHB,
AB system); 4.77 (2H, JHH = 15.9 Hz, CHAHB, AB system); 7.24–
7.33 (m, 3H, H4, H5, H6); 7.66 (tm, 2H, JHH(av) = 6.8 Hz, H5¢,
H5¢¢); 7.94 (d, 2H, JHH = 4.5 Hz, H3¢, H3¢¢); 8.25 (td, 2H, JHH
=
7.7 Hz, 1,5 Hz, H4¢, H4¢¢); 9.28 (dd, 2H, JHH = 6.0 Hz, 0.9 Hz, H6¢,
H6¢¢); (CD2Cl2): d 4.35 (2H, JHH = 15.9 Hz, CHAHB, AB system);
4.74 (2H, JHH = 15.9 Hz, CHAHB, AB system); 7.29 (d, 2H, JHH
=
6.3 Hz, H4, H6); 7.36 (dd, 1H, JHH(av) = 6.3 Hz, H5), 7.66 (t, 2H,
JHH = 6.3 Hz, H5¢, H5¢¢); 7.96 (d, 2H, JHH = 7.2 Hz, H3¢, H3¢¢); 8.24
(td, 2H, JHH = 7.8 Hz, 1,5 Hz, H4¢, H4¢¢); 9.36 (d, 2H, JHH = 5.7 Hz,
H6¢, H6¢¢); (DMSO-d6): d 4.45 (d, 2H, JHH = 15.3 Hz, CHAHB, AB
system); 4.95 (d, 2H, JHH = 15.3 Hz, CHAHB, AB system); 7.20–
7.32 (m, 3H, H4, H5, H6), 7.81 (t, 2H, JHH = 7.0 Hz, H5¢, H5¢¢); 8.10
(d, 2H, JHH = 7.2 Hz, H3¢, H3¢¢); 8.37 (td, 2H, JHH = 7.5 Hz, 1.2 Hz,
H4¢, H4¢¢); 9.21 (d, 2H, JHH = 6.0 Hz, H6¢, H6¢¢). 31P NMR (acetone-
-
d6): d -143.3 (sept, JPF = 707.0 PF6 ); (CD3CN): d -143.4 (sept,
1H NMR (DMSO-d6): d 4.46 (2H, JHH = 15.2 Hz, CHAHB, AB
system); 4.94 (2H, JHH = 15.2 Hz, CHAHB, AB system); 7.22–7.32
(m, 3H, H4, H5, H6), 7.81 (t, 2H, JHH = 7.5 Hz, H5¢, H5¢¢); 8.10 (d,
2H, JHH = 7.5 Hz, H3¢, H3¢¢); 8.37 (t, 2H, JHH = 7.5 Hz, H4¢, H4¢¢);
9.21 (d, 2H, JHH = 6.3 Hz, H6¢, H6¢¢).
JPF = 707.0 PF6 ). 19F NMR (acetone-d6): d -56.01 (d, JPF = 707.7
-
PF6-); (CD3CN): d -45.55 (d, JPF = 704.9 PF6-). Crystals of X-ray
quality were obtained by slow evaporation of an acetone solution
at room temperature.
Synthesis of [Au(NŸCŸN)(PPh3)Cl][PF6], 4[PF6]. An excess of
PPh3 (65.6 mg, 0.25 mmol) was added to a solution of 3[PF6]
(63.6 mg, 0.10 mmol) in 20 mL of acetone and left under stirring
for 15 min. Afterwards, the solvent was evaporated to dryness and
diethyl ether (15 mL) added. The solid was filtered off, washed
with diethyl ether and dried under vacuum to give 4[PF6] as a
white solid. Yield 82.4 mg, 93%; m.p. 175–177 ◦C (dec.); (Found:
C 47.85; H 3.15; N 2.98%. Anal. Calcd. for C36H30AuClF6N2P2:
Synthesis
of
[Au(NŸCŸN)Cl]Cl,
3[Cl]. Tetra(n-butyl)-
ammonium chloride (833.7 mg, 3.00 mmol) was added under
stirring to a suspension of (3)2[Hg2Cl6], (798.7 mg, 1.00 mmol)
in 50 mL of dichloromethane. The suspension was left under
stirring at room temperature for two hours. The colour of the
solution turned pale green and the solid gray. This was collected
and dried under vacuum to give compound 3[Cl], as a white solid.
10300 | Dalton Trans., 2010, 39, 10293–10304
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The Royal Society of Chemistry 2010
©

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3
C 48.10; H 3.36; N 3.12%. 1H NMR (CD2Cl2): d 3.82 (2H, JHH
=
(d, 2H, JHH = 7.2 Hz, H6¢, H6¢¢); (CD3CN): d 2.82–3.02 (m+m,
14.2 Hz, CHAHB, AB system); 3.97 (2H, JHH = 14.4 Hz, CHAHB,
overlapping, 1H+1H, PA-CHAHA¢-CHBHB¢-PB); 3.36–3.60 (m+m,
AB system); 6.92 (d, 2H, JHH = 7.2 Hz. H4, H6); 7.08 (t, 1H, JHH
7.4 Hz, H5); 7.50 (t, 2H, JHH = 7.4 Hz, H5¢, H5¢¢); 7.64 (d, 2H, JHH
7.4 Hz, H3¢, H3¢¢); 7.38–7.68 (m, 15H, PPh3), 7.87 (td, 2H, JHH
=
=
=
overlapping 1H+1H, PA-CHAHA¢ -CHBHB¢-PB); 3.73 (2H, JHH
=
14.7 Hz, CHAHB, AB system); 4.05 (2H, JHH = 14.7 Hz, CHAHB,
AB system); 6.76 (d, 1H, overlapping, 3JHH = 7.3 Hz, H4); 6.78 (d,
overlapping, 1H, 3JHH = 7.3 Hz, H6); 6.94–7.10 (m, 1H+2H+2H,
H5, H3¢, H3¢¢, H5¢, H5¢¢); 7.34–7.41 (m, 2H+2H, Hp Ph dppe); 7.53–
7.67 (m, 4H+4H+2H+2H, Hm dppePA, Hm dppePB, Ho dppePA,
Ho dppePB); 7.74 (td, 2H, J = 7.5 Hz, 1.5 Hz, H4¢, H4¢¢); 7.92–
8.02 (m, 2H+2H+2H, H6¢, H6¢¢, Ho dppePA, Ho dppePB). 31P NMR
7.4 Hz, 1,5 Hz, H4¢, H4¢¢); 9.06 (dm, 2H, JHH = 5.1 Hz, H6¢, H6¢¢);
(acetone-d6): d 4.07 (2H, JHH = 14.3 Hz, CHAHB, AB system); 4.10
(2H, JHH = 14.3 Hz, CHAHB, AB system); 6.98–7.08 (m, 3H, H4,
H5, H6); 7.48–7.72 (m, 19H, H3¢, H3¢¢, H5¢, H5¢¢ + PPh3), 7.98 (td,
2H, JHH = 7.5 Hz, 1,5 Hz, H4¢, H4¢¢); 9.24 (d, 2H, JHH = 5.1 Hz, H6¢,
H6¢¢); (CD3CN): d 3.90 (2H, JHH = 14.6 Hz, CHAHB, AB system);
-
(acetone-d6): d -143.39 (sept, 1P, PF6 ); 53.63 (d, 1P, JPP = 7.0 Hz,
PA); 54.20 (d, 1P, JPP = 7.0 Hz, PB); (CD2Cl2): d -143.16 (sept, 1P,
PF6 ); 55.26 (d, 1P, JPP = 7.0 Hz, PA); 56.54 (d, 1P, JPP = 7.0 Hz, PB);
(CD3CN): d -143.51 (sept, 1P, PF6 ); 55.85 (d, 1P, JPP = 7.0 Hz,
3.97 (2H, JHH = 14.6 Hz, CHAHB, AB system); 6.89 (d, 2H, JHH
=
7.2 Hz, H4, H6); 7.10 (ddd, 1H, JHH(av) = 7.2 Hz, H5); 7.36–7.66
(m, 19H, H3¢, H3¢¢, H5¢, H5¢¢ + PPh3); 7.89 (td, 2H, JHH = 7.5 Hz,
1,5 Hz, H4¢, H4¢¢); 9.07 (d, 2H, JHH = 5.4 Hz, H6¢, H6¢¢). 31P NMR
-
-
PA); 56.54 (d, 1P, JPP = 7.0 Hz, PB).
-
(CD2Cl2): d -143.34 (sept, PF6 ); 26.34 (PPh3); (acetone-d6): d
-
-143.13 (sept, PF6 ); 26.84 (PPh3); (CD3CN): d -143.52 (sept,
Synthesis of [Au(NŸCŸN)(dppe)][PF6]2, 5[PF6]2. K[PF6]
(18.4 mg, 0.1 mmol) was added to a suspension of compound
5[Cl][PF6] (103.5 mg, 0.1 mmol) in 30 mL of acetone. The
suspension was left under stirring at room temperature for 4 h.
The solution was concentrated to small volume and 15 mL of
water were added. The white precipitate obtained was filtered
off, washed with ice-cold methanol and diethyl ether, then
dried in vacuo to give compound 5[PF6]2. Yield 99.2 mg, 87%;
m.p. 185–186 ◦C. (Found: C 46.27; H 3.03; N 2.48%. Anal.
Calcd. for C44H39AuF12N2P4: C 46.17; H 3.43 N 2.45%). 1H
NMR (CD3CN): d 2.86–3.03 (m + m, overlapping, 1H + 1H,
PA-CHAHA¢-CHBHB¢-PB); 3.52–3.70 (m + m, overlapping 1H +
1H, PA-CHAHA-CHBHB¢-PB); 3.89 (2H, JHH = 14.6 Hz, CHAHB,
AB system); 3.96 (2H, JHH = 14.6 Hz, CHAHB, AB system);
6.97–6.98 (m, 3H, H4, H5, H6); 7.29 (t, 2H, JHH = 6.9 Hz, H5¢, H5¢¢);
7.43–7.57 (m, overlapping, 2H + 2H + 2H, H3¢, H3¢¢, Hp dppePA,
Hp dppePB); 7.58–7.82 (m, 4H+4H+4H+4H+2H, Hm dppePA,
-
PF6 ); 26.83 (PPh3).
Synthesis of [Au(NŸCŸN)(dppe)][Cl][PF6], 5[Cl][PF6]. An ex-
cess of [Ph2PCH2]2, (dppe), (99.6 mg, 0.25 mmol) was added to
a solution of 3[PF6] (63.6 mg, 0.10 mmol) in 20 mL of acetone
and left under stirring for 15 min. Afterwards, the solvent was
evaporated to dryness and diethyl ether (15 mL) added. The solid
was collected, washed with diethyl ether and dried under vacuum
to give 5[Cl][PF6] as a white solid. Yield 90.2 mg, 87%; m.p. 143–
145 ◦C; (Found: C 51.39; H 3.16; N 2.57%. Anal. Calcd. for
C44H41AuClF6N2P3: C 50.95; H 3.98; N 2.70%.
Hm dppePB, H◦ dppePA, H◦ dppePB, H4¢, H4¢¢); 8.60 (d, 2H, 3JHH
=
5.4 Hz, H6¢, H6¢¢). 31P NMR (CD3CN): d -143.51 (sept, 1P, PF6 );
-
48.22 (d, 1P, JPP = 4.0 Hz, PA) and 55.07 (d, 1P, 2JPP = 4.0 Hz, PB).
Synthesis of [Au(NŸCŸN)(H2O)][OTf][PF6], 6[OTf][PF6]·nH2O.
(a) n = 0: solid Ag(OTf) (38.5 mg, 0.15 mmol) was added to a solu-
tion of 3[PF6] (63.6 mg, 0.10 mmol) in dichloromethane (20 mL).
The mixture was stirred in the dark for 1 h at room temperature;
then the silver chloride was removed by filtration and the solution
evaporated to dryness. The crude product was recrystallized from
dichloromethane/n-pentane to give 6[OTf][PF6] as a white solid.
Yield 50.0 mg, 65%; (Found: C 29.45; H 2.21; N 3.50%. Anal.
1H NMR (acetone-d6): d 3.15–3.33 (m+m, overlapping,
1H+1H, PA-CHAHA¢-CHBHB¢-PB); 3.79 (2H, JHH = 14.9 Hz,
CHAHB, AB system); 3.83–4.05 (m+m, overlapping 1H+1H, PA-
CHAHA¢-CHBHB¢-PB); 4.09 (2H, JHH = 14.9 Hz, CHAHB, AB
3
1
system); 6.80 (d, 1H, overlapping, JHH = 7.5 Hz, H4); 6.82 (d,
Calcd. for C19H17AuF9N2O4PS: C 29.70; H 2.23; N 3.65%. H
overlapping, 1H, JHH = 7.5 Hz, H6); 6.98 (t, 1H, JHH = 7.5 Hz,
H5); 7.02–7.08 (m, 4H, H3¢, H3¢¢, H5¢, H5¢¢); 7.43–7.49 (m, 2H+2H,
Hp Ph dppe); 7.55 (td, 2H, J = 7.5 Hz, 1.5 Hz, H4¢, H4¢¢); 7.66–
NMR (CD2Cl2): d 4.31 (2H, JHH = 15.9 Hz, AB system, CHAHB);
5.04 (br, JHH = 16.2 Hz, 2H, AB system, CHAHB); 6.67 (br, 2H,
H2O); 7.21 (d, 1H, JHH = 7.2 Hz, H4, H6); 7.33 (dd, 1H, JHH(av) =
3
3
7.70 (m, 4H+4H+2H+2H, Hm + Ho Ph dppe); 8.03 (d, 2H, 3JHH
=
7.4 Hz, H5); 7.70 (t, 2H, JHH = 6.6 Hz, H5¢, H5¢¢); 7.93 (d, 2H, JHH
=
5.4 Hz, H6¢, H6¢¢); 8.08–8.16 (m, 2H + 2H, H◦ Ph dppe); (CD2Cl2):
d 2.84–3.06 (m+m, overlapping, 1H+1H, PA-CHAHA¢-CHBHB¢-
PB); 3.36–3.60 (m+m, overlapping 1H+1H, PA-CHAHA¢ -CHBHB¢-
PB); 3.75 (2H, JHH = 14.9 Hz, CHAHB, AB system); 4.04 (2H,
JHH = 14.9 Hz, CHAHB, AB system); 6.87 (d, 1H, overlapping,
3JHH = 7.4 Hz, H4); 6.88 (d, overlapping, 1H, 3JHH = 7.4 Hz, H6);
7.00–7.09 (m, 1H+2H+2H, H5, H3¢, H3¢¢, H5¢, H5¢¢); 7.33–7.40 (m,
2H+2H, Hp Ph dppe); 7.49–7.70 (m, 4H+4H+2H+2H+2H, Hm +
Ho Ph dppe, H4¢, H4¢¢); 7.93–7.97 (m, 2H+2H, Ho Ph dppe); 8.00
7.8 Hz, H3¢, H3¢¢); 8.23 (td, 2H, JHH = 7.5 Hz, 1.2 Hz, H4¢, H4¢¢); 9.15
(d, 2H, JHH = 5.7 Hz, H6¢, H6¢¢); 19F NMR (acetone-d6): d -50.65
-
(d, JPF = 710.9 PF6-); -57.37 (s, CF3SO3 ).
(b) n = 1: The same reaction carried out in acetone afforded
6[OTf][PF6]·H2O. 1H NMR (CD2Cl2): d 3.90 (br, 4H, H2O); 4.30
(2H, JHH = 15.9 Hz, AB system, CHAHB); 5.05 (br, 2H, AB system,
CHAHB); 7.21 (d, 1H, JHH = 7.5 Hz, H4, H6); 7.33 (dd, 1H, JHH(av) =
7.4 Hz, H5); 7.70 (t, 2H, JHH = 6.4 Hz, H5¢, H5¢¢); 7.94 (d, 2H, JHH
=
7.5 Hz, H3¢, H3¢¢); 8.23 (td, 2H, JHH = 7.5 Hz, 1.2 Hz, H4¢, H4¢¢); 9.15
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The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 10293–10304 | 10301
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(br, 2H, H6¢, H6¢¢). 19F NMR (acetone-d6): d -50.63 (d, JPF = 711.1
diffractometer, at 296 K for 1[AuCl4]Cl and 2, and at 150 K for
3[PF6], using Mo-Ka radiation (l = 0.71073) with a graphite
crystal monochromator in the incident beam. The crystal of
3[PF6] gave an excellent diffraction, whereas for the other two
crystals the diffraction was poor (actually bad for 1[AuCl4]Cl). No
crystal decay was observed, so that no time-decay correction was
needed. The collected frames were processed with the software
SAINT,21 and an empirical absorption correction was applied
(SADABS)22 to the collected reflections. The calculations were
performed using the Personal Structure Determination Package23
and the physical constants tabulated therein.24 The structures were
solved by direct methods (SHELXS)25 and refined by full-matrix
-
PF6-); -57.44 (s, CF3SO3 , OTf).
Synthesis of [Au(NŸCŸN)(OAc)][PF6], 7[PF6]. Solid Ag(OAc)
(25.0 mg, 0.15 mmol) was added to a solution of 3[PF6] (63.6 mg,
0.10 mmol) in 20 mL of acetone. The mixture was stirred in
the dark for 24 h at room temperature; then the silver chloride
was removed by filtration and the solution concentrated to small
volume. Addition of diethyl ether (15 mL) afforded a white
precipitate which was filtered off, washed with diethyl ether and
dried in vacuo to give 7[PF6] as a white solid. Yield 38.2 mg, 58%;
m.p. 160–162 ◦C (dec.); (Found: C 36.15; H 2.21; N 4.23%. Anal.
Calcd. for C20H18AuClF6N2O2P: C 36.38; H 2.75; N 4.24%. IR(nmax
least-squares, using all reflections and minimising the function
1
(Nujol)/cm-1): 1620m; 1610m; 1315m. H NMR (acetone-d6): d
ꢀ
w(Fo - kFc )2 (refinement on F2). In 1[AuCl4]Cl, cation 12+ lies
on a crystallographic two-fold axis, with atoms C(2) and C(5)
lying on the axis. The non hydrogen atoms of this cation (C
and N atoms) had to be refined with isotropic thermal factors.
Hydrogen atoms H(9), bonded to C(2), and H(10), bonded to
C(5), were detected in the final Fourier maps, and not refined.
The overall crystallographic results for 1[AuCl4]Cl are very poor,
but they are nevertheless sufficient to show that in its packing
an extremely interesting supramolecular structure is present, that
deserves to be described. This is done exhaustively, by means
of both verbal descriptions and relevant drawings, in the ESI.†
2
2
1.95 (s, 3H,CH3COO); d 4.64 (2H, JHH = 15.8 Hz, AB system,
CHAHB); 4.84 (2H, JHH = 15.8 Hz, AB system, CHAHB); 7.33 (s,
3H, H4, H5, H6), 7.89 (t, 2H, JHH(av) = 6.5 Hz, H5¢, H5¢¢); 8.22 (d,
2H, JHH = 7.8 Hz, H3¢, H3¢¢); 8.46 (td, 2H, JHH = 7.8 Hz, 1.6 Hz,
H4¢, H4¢¢); 9.00 (dd, 2H, JHH = 6.0 Hz, 0.9 Hz, H6¢, H6¢¢). 31P NMR
-
(acetone-d6): d -143.16 (sept, PF6 ).
X-Ray data collection and structure determination†
Crystal data are summarised in Table 2. The diffraction experi-
ments were carried out on a Bruker APEX II CCD area-detector
Table 2 Crystallographic data
Compound
1[AuCl4]Cl
2
3[PF6]
Formula
M
C18H18AuCl5N2
636.59
Yellow
Orthorhombic
Abm2
4.5498(4)
26.3130(26)
18.0718(18)
90
C18H15ClHgN2
495.38
Colourless
Monoclinic
C2/c
15.1595(12)
15.3382(12)
15.9166(13)
90
116.039(1)
90
3325.2(5)
8
1872
1.979
296
C18H15AuClF6N2P
636.72
Pale yellow
Monoclinic
P21/n
9.5120(4)
11.9014(4)
17.2639(7)
90
101.343(2)
90
1916.2(1)
4
1208
2.207
150
Colour
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
90
90
3
˚
U/A
2163.5(19)
4
1216
1.954
296
0.71073
0.05 ¥ 0.15 ¥ 0.22
74.17
0.366–1.000
w
0.45
Z
F(000)
Dc/g cm-3
T/K
l (Mo-Ka)
0.71073
0.14 ¥ 0.27 ¥ 0.41
94.15
0.461–1.000
w
0.50
0.71073
0.21 ¥ 0.23 ¥ 0.45
79.49
0.391–1.000
w
0.40
Crystal dimensions/mm
m(Mo-Ka)/cm-1
Min. and max. transmiss. factors
Scan mode
Frame width/◦
Time per frame/s
No. of frames
25
2760
6.00
3.00–25.00
Full sphere
16 357; 2344
0.0673
0.095, 0.132
0.056
20
3240
6.00
3.00–28.00
Full sphere
46 165; 4637
0.0442
0.081, 0.128
0.043
10
750
6.00
3.00–27.00
Full sphere
10 043; 4289
0.0215
0.042, 0.060
0.026
Detector-sample distance/cm
q-range/◦
Reciprocal space explored
No. of reflections (total; independent)
Rint
Final R2 and R2w indicesa (F2, all reflections)
Conventional R1 index [I > 2s(I)]
Reflections with I > 2s(I)
No. of variables
1377
68
0.962
2230
199
1.016
3658
262
1.014
Goodness of fitb
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
a R2 = [ (|Fo - kFc2|)/ Fo2], R2w = [ w(Fo - kFc2)2/ w(Fo2)2]1/2
.
[
w(Fo - kFc2)2/(No - Nv)]1/2, where w = 4Fo2/s(Fo2)2, s(Fo2) = [s (Fo2) +
2
2
b
2
2
(pFo2)2]1/2, No is the number of observations, Nv the number of variables, and p = 0.02 for 3¢[PF6], = 0.03 for 1[AuCl4]Cl, and = 0.04 for 2.
10302 | Dalton Trans., 2010, 39, 10293–10304
This journal is
The Royal Society of Chemistry 2010
©

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In the three compounds, all the other non-hydrogen atoms were
refined with anisotropic thermal parameters, and all the other
hydrogen atoms were placed in their ideal positions (C–H or N–
References
1 C. J. Moulton and B. L. Shaw, J. Chem. Soc., Dalton Trans., 1976,
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˚
H = 0.97 A), with the thermal parameter U being 1.10 times that
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centrosymmetric 1[AuCl4]Cl, both the inverted structure models
were fully refined: final R2 and R2w indices were 0.095 and 0.132
for the correct one, and 0.109 and 0.151 for the other. In the
-3
˚
final Fourier maps the maximum residuals were 3.57(1.34) e A
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˚
˚
˚
at 0.97 A from Au, 2.19(1.01) e A at 0.28 A from Hg, and
1.48(26) e A at 0.53 A from Au, for 1[AuCl4]Cl, 2, and 3[PF6],
-3
˚
˚
respectively. Minimum peaks (holes), in the same order, were
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˚
-2.27(1.34), -2.19(1.01), and -1.14(26) e A .
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9 For information on the interesting packing of 1[AuCl4]Cl, see the
Experimental Section and ESI.
All quantum chemical calculations were carried out using the
Gaussian03 program system.26 The equilibrium and transi-
tion structures were computed using gradient-corrected density
functional theory (DFT) with the Becke three-parameter ex-
change functional27 and the Lee–Yang–Parr correlation functional
(B3LYP).28 For gold, a multielectron adjusted quasirelativistic
effective core potential covering 60 electrons ([Kr]4d104f14) and
an (8s7p6d/[6s5p3d]-GTO valence basis set (31111, 22111, 411,
21) were used.29 To further improve the quality of basis set, f-
type polarization functions in a (21) contraction were added.30
All non-metal atoms (C, H, Cl, and N) were described with
the Dunning correlation consistent cc-pVDZ and cc-pVTZ basis
sets.31 Geometries of all stationary points were calculated at the
B3LYP/cc-pVTZ and MP2/cc-pVDZ32 levels.
The transition state for the inversion between the left- and right-
handed twisted forms of 3+ was scrutinized by performing Intrinsic
Reaction Coordinate (IRC) calculations using the Gonzalez-
Schlegel second-order method.33 The reaction path leading down
from the transition structure in both directions on the potential
energy surface (PES) was thus studied to ensure that the transition
states connected the desired reactant and product. Further, the
normal modes corresponding to the imaginary frequencies of
the transition state structures were examined with molecular
visualization to verify that the nuclear motion tends to deform the
transition state structure along the pertinent reaction coordinate.
To characterize all stationary points, the Hessian (matrix of
energy second derivatives) was calculated and diagonalized at
each stationary point which also yielded zero-point energy (ZPE)
corrections.
10 (a) J. Vicente, M. T. Chicote, M. D. Bermudez, M. J. Sanchez-Santano,
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1986, 310, 401–409; (b) J. Vicente, M. T. Chicote, A. Arcas, M. Artigao
and R. Jimenez, J. Organomet. Chem., 1983, 247, 123–129.
Acknowledgements
11 More parameters are given in Table S2 in the ESI.
12 P. K. Byers and A. J. Canty, Organometallics, 1990, 9, 210.
13 Notably, the chemical shifts of the pincer complexes 3[X] are not
affected by the counter-ion: see Table S3 in the ESI.
14 M. A. Cinellu, A. Zucca, S. Stoccoro, G. Minghetti, M. Manassero and
M. Sansoni, J. Chem. Soc., Dalton Trans., 1996, 4217–4225.
15 E. C. Constable, R. P. G. Henney, T. A. Leese and D. A. Tocher, J. Chem.
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16 M. Nonoyama, K. Nakajima and K. Nonoyama, Polyhedron, 2001, 20,
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17 The syntheses and reactivity studies of these gold(III) cyclometallated
complexes have been recently reviewed: W. Henderson, Adv. Organomet.
Chem, 2006, 54, 207–265.
We are grateful to the Ministero dell’Istruzione, Universita` e
della Ricerca (MIUR) and the Universita` degli Studi di Sassari
for financial support of this research (PRIN Project). G. A.
gratefully acknowledges the Regione Autonoma della Sardegna
(RAS) for a Master & Back fellowship. We also thank Johnson
Matthey for a generous loan of H[AuCl4]·3H2O, while M. K. G. is
similarly grateful for a postdoctoral scholarship from the Research
Council of Norway under the GASSMAKS program, project
no. 185513/I30. Finally, thanks are due to the NOTUR project
(http://www.notur.com, project No. NN2147K) for a generous
grant of computing time.
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