Reactivity of 1,3-bis(2-pyridyl)benzene, NCHN, with gold(III) chlorides: Salts, adducts and cyclometalated pincer derivatives. Crystal and molecular structures of [HNCHN][AuCl4], [Au(NCN)Cl][PF6] and [Au(NCN)Cl(PPh3)2][PF6]

Article abstract of DOI:10.1039/b822842f

The reaction of 1,3-bis(2-pyridyl)benzene, NCHN, with H[AuCl₄] has been studied under different conditions. Mono- ([NCHNH][AuCl₄]) and di-protonated salts ([HNCHNH][AuCl₄]₂), as well as an adduct, [(NCHN)(AuCl₃)₂], have been isolated. Very rare cyclometalated pincer derivatives, [Au(NCN)Cl]⁺ have been obtained as different salts, either by transmetallation from the corresponding mercury(ii) derivative, [Hg(NCN)Cl], or by direct C-H activation. The structures in the solid state of [NCHNH][AuCl₄] and [Au(NCN)Cl][PF₆] have been solved by X-ray diffraction. Reaction of the pincer derivatives with PPh₃, dppm (bis(diphenylphosphino)methane) and dppe (1,2-bis(diphenylphosphino)ethane) occurs with displacement of the coordinated nitrogen atoms to afford [Au(NCN)(Cl)(PPh₃)₂]⁺, [Au(NCN)(Cl)(dppm)₂]⁺ and [Au(NCN)(Cl)(dppe)] ⁺, respectively. The X-ray structure of [Au(NCN)(Cl)(PPh ₃)₂][PF₆] confirms that the ligand NCN is only σ-carbon bonded and the PPh₃ molecules are in a trans-arrangement. The pattern of the ³¹P{¹H}NMR spectrum of [Au(NCN)(Cl)(dppm)₂]⁺, a pair of "triplets", deserves comments: the spectrum is not of the A₂X₂ type but a case of a deceptively simple AA'XX' spin system.

Full text of DOI:10.1039/b822842f

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PAPER
www.rsc.org/dalton | Dalton Transactions
Reactivity of 1,3-bis(2-pyridyl)benzene, NŸCHŸN, with gold(III) chlorides:
salts, adducts and cyclometalated pincer derivatives. Crystal and molecular
structures of [HNŸCHŸN][AuCl4], [Au(NŸCŸN)Cl][PF6] and
[Au(NŸCŸN)Cl(PPh3)2][PF6]†
Sergio Stoccoro,*a Giuseppe Alesso,a Maria Agostina Cinellu,a Giovanni Minghetti,a Antonio Zucca,a
Mario Manassero*b and Carlo Manasserob
Received 19th December 2008, Accepted 16th February 2009
First published as an Advance Article on the web 13th March 2009
DOI: 10.1039/b822842f
The reaction of 1,3-bis(2-pyridyl)benzene, NŸCHŸN, with H[AuCl4] has been studied under different
conditions. Mono- ([NŸCHŸNH][AuCl4]) and di-protonated salts ([HNŸCHŸNH][AuCl4]2), as well as an
adduct, [(NŸCHŸN)(AuCl3)2], have been isolated. Very rare cyclometalated pincer derivatives,
[Au(NŸCŸN)Cl]+ have been obtained as different salts, either by transmetallation from the
corresponding mercury(II) derivative, [Hg(NŸCŸN)Cl], or by direct C–H activation. The structures in
the solid state of [NŸCHŸNH][AuCl4] and [Au(NŸCŸN)Cl][PF6] have been solved by X-ray diffraction.
Reaction of the pincer derivatives with PPh3, dppm (bis(diphenylphosphino)methane) and dppe
(1,2-bis(diphenylphosphino)ethane) occurs with displacement of the coordinated nitrogen atoms to
afford [Au(NŸCŸN)(Cl)(PPh3)2]+, [Au(NŸCŸN)(Cl)(dppm)2]+ and [Au(NŸCŸN)(Cl)(dppe)]+, respectively.
The X-ray structure of [Au(NŸCŸN)(Cl)(PPh3)2][PF6] confirms that the ligand NŸCŸN is only s-carbon
1
bonded and the PPh3 molecules are in a trans-arrangement. The pattern of the 31P{ H}NMR spectrum
of [Au(NŸCŸN)(Cl)(dppm)2]+, a pair of “triplets”, deserves comments: the spectrum is not of the A2X2
type but a case of a deceptively simple AA‘XX’ spin system.
are rare.5 Noteworthy is the structurally characterized complex
Introduction
[Au{C6H3(CH2NMe2}Cl]2[Hg2Cl6].5a
Organometallic complexes with pincer ligands1 are attracting
We have previously reported on the reactivity of Pd(II) and
much attention in catalysis2 and material science.1e,1f,3 In the aro-
matic pincer ligands containing two meta-positioned substituents
bearing N, O, P, or S donors, coordination to a metal centre can
enhance the reactivity of a Caryl–H bond, favouring metalation.
With ligands capable of trans coordination, the outcome of the
reaction is a metallacycle, mostly with five or six-membered rings,
where the metal ion is locked up by a tridentate monoanionic
six-electron ligand. Most of the stable pincer complexes are
square planar complexes of the d8 metal ions: the coordination
mode with trans positioned donors forces the aryl ring of
the ligand into a conformation essentially coplanar with the
coordination plane of the metal centre. Among the molecules
potentially able to act as pincers, a number of NŸCŸN systems
have been considered in the last 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 the isoelectronic Au(III) ion
Pt(II) with 1,3-bis(2-pyridyl)benzene, NŸCHŸN, and analogous
ligands with substituted pyridines: the new pincer species have
also been investigated for their catalytic activity in the Heck
reaction and other C–C bond formations.4f,6 Following these
previous reports, here we describe the reactivity of 1,3-bis(2-
pyridyl)benzene, NŸCHŸN, with gold(III), an ion for which we
are not aware of any similar chemistry. Indeed in the course of
the present study we have observed that the reaction of gold(III)
chlorides with this molecule is complex and different species
can form: salts, adducts and metalated pincer derivatives. As
is the case for other late transition metals, the synthesis of the
latter species is not straightforward. Nevertheless, under precise
conditions, metalation by direct activation of a C–H bond of
the ligand was achieved, albeit in moderate yields. As often
reported, somewhat better yields were obtainedbytransmetalation
of the corresponding mercury(II) derivative, [Hg(NŸCŸN)Cl].4f
All the new species have been characterized analytically and by
NMR spectroscopy. The X-ray structures of the pincer species
[Au(NŸCŸN)Cl)][PF6], of the outcome of its reaction with PPh3,
[Au(NŸCŸN)Cl)(PPh3)2][PF6], as well as of the monoprotonated
ligand, [HNŸCHŸN][AuCl4], are also reported.
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, Uni-
versita’di Milano, Centro CNR, I-20133, Milano, Italy. E-mail:mario.
manassero@unimi.it
Results and discussion
The ligand, 1,3-bis(2-pyridyl)benzene, throughout this paper indi-
cated as NŸCHŸN, was best prepared by co-cyclotrimerization of
† CCDC reference numbers 713741–713743. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b822842f
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1,3-dicyanobenzene with acetylene, in the presence of Bo¨nnemann
catalyst, according to literature procedure.7 After purification, it
1
was extensively characterized by H NMR spectra, registered in
several solvents (see Experimental section).
The main goal of the present study was to synthesize pincer
gold(III) derivatives [Au(NŸCŸN)X]+[A]- (X = coordinating anion,
[A]- = not coordinating anion) and to compare them with the
corresponding, but neutral, palladium(II) and platinum(II) species,
previously reported and found to be, at least in the case of
palladium, catalysts of high activity in the Heck reaction.4f,6
To achieve direct C–H activation in this type of molecules by d8
late transition metal ions is not an easy task; in addition, in gold(III)
chemistry with nitrogen heterocycles, the pattern of the reaction is
usually complex and strongly dependent on the exact experimental
conditions. Several species are often formed, sometimes poorly
soluble, and their separation and identification can be a tiresome
matter.
In the present case we observed first that direct reaction of
H[AuCl4]·3H2O with [NŸCHŸN], in mild conditions (diethyl ether,
room temperature) affords, in almost quantitative yield, a salt of
the diprotonated ligand, [HNŸCHŸNH][AuCl4]2, 1. Compound 1 is
a pale yellow solid that was characterized by CHN analysis and 1H
NMR spectroscopy. The NMR spectra show one set of resonances
with a significant difference respect to the free ligand as for the
H6¢, H6¢¢ protons of the pyridine rings that are ca. 0.5 ppm shifted
downfield (acetone-d6). The shift is comparable to that observed
for 2-phenylpyridine, d 8.68, vs. d 9.15 upon protonation.8
The outcome of the same reaction, carried out in ace-
tonitrile at reflux for five days is the monoprotonated salt,
[HNŸCHŸN][AuCl4], 2, that was characterized, inter alia, by
X-ray diffraction analysis.
Fig. 1 ORTEP view of the cation in compound 2. Ellipsoids are drawn
at the 30% probability level.
◦
170.0 , N(2) ◊ ◊ ◊ N(1)a 2.67◦0(4) A, H(1) ◊ ◊ ◊ N(1) –C(7) 128.6◦,
H(1) ◊ ◊ ◊ N(1)a–C(11)a 111.1 . Obviously, each cation is hydrogen
bonded to a neighbouring one, so that cations of 2 in the crystal
can be seen as forming an infinite monodimensional chain. In the
a
a
˚
˚
anion the shortest intermolecular Au–Au distance is 5.483(1) A.
In addition to the [AuCl4]- salts of the mono and diprotonated
ligand, 2 and 1, also an adduct, [(NŸCHŸN)(AuCl3)2], 3, can
be isolated as a yellow solid. Compound 3 is frequently ob-
served in solution when more species are simultaneously present.
Compound 3 is best obtained on treating the diprotonated salt
[HNŸCHŸNH][AuCl4]2, 1, with the stoichiometric amount of
NaHCO3 in THF. The 1H NMR spectrum, registered in acetone-
d6, gives evidence for a symmetric species. Complex 3 is soluble
but unstable in DMSO.
1
On the whole, the H NMR spectra of compounds 1–3 give
clear-cut evidence for all the protons of the aryl ring, ruling out
metalation (see Scheme 1).
The 1H NMR spectrum shows also in this case one set of
resonances indicating exchange of the hydrogen between the
nitrogen atoms on the NMR time scale. The spectrum is similar
but clearly distinct from that of the diprotonated species 1: in
particular the H6¢, H6¢¢ resonance is less deshielded than in 1, ca.
0.3 ppm, with respect to the ligand.
Crystals of X-ray quality were obtained by slow evaporation
of an acetone solution at room temperature. The structure of 2
consists of the packing of [HNŸCHŸN] cations and [AuCl4]- anions
in the molar ratio 1 : 1 in the monoclinic space group Pc. An
ORTEP9 view of the cation is shown in Fig. 1.
All bond lengths and angles in monomeric cations and anions
are as usual. Instead, different cations are linked by very strong
hydrogen bonds between nitrogen atoms of neighbouring moieties:
so, if we mark as a the molecule generated by symmetry operation
Scheme 1 Synthesis of compounds 1–3.
As previously mentioned direct C–H activation is not easy and
is usually accomplished under definite experimental conditions
whose settlement often requires tiresome experiences. Many
1
x, -1 + y, - z, we find the following hydrogen bond parameters:
2
a
a
˚
˚
N(2)–H(1) 0.970 A, H(1) ◊ ◊ ◊ N(1) 1.709 A, N(2)–H(1) ◊ ◊ ◊ N(1)
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alternative strategies have been reported: among them transmeta-
lation of the corresponding mercury(II) derivative is traditional in
the synthesis of late-transition metal pincers.
The synthesis of the mercury derivative of 1,3-bis(2-
pyridyl)benzene, [Hg(NŸCŸN)Cl], has been previously described.4f
Reaction with H[AuCl4] in ethanol, in the presence of NaHCO3,
gives the gold pincer in excellent yield as a mercury salt, likely
[Hg2Cl6]2-, eqn (1):
NaHCO
3
H[AuCl4 ]◊3H2O + [Hg(N^C^N)Cl] ææææÆ
-NaCl
(1)
1/2[Au(N^C^N)Cl]2[Hg2Cl6 ] (4a)
The NMR spectrum provides evidence for a non-symmetric
species. In particular two resonances at d 9.26 and d 9.76 can
be assigned to H6¢¢ (protonated ring) and H6¢ (coordinated ring)
protons respectively. C(4) metalation has also been reported in
platinum chemistry of analogous systems.4c
In the attempt to get simple and soluble salts of the pincer
gold(III) complex the reaction between H[AuCl4] and the ligand
was carried out in the presence of excess hexafluorophosphate
or tetrafluoborate salts. Compound 4b was still obtained: direct
exchange of the anion, eqn (3), failed:
Attempts to achieve direct C–H activation by reaction of
NŸCHŸN with H[AuCl4] (1 : 1) were carried out in acetic acid
at reflux (ca. 120 ◦C) in the presence of a base. The reaction
was partially successful: the pincer derivative, a yellow solid, was
obtained as the [AuCl4]- salt, [(Au(NŸCŸN)Cl][AuCl4], 4b, eqn (2);
yields are moderate even using the correct ratio 1 : 2. Compound
4b is soluble in DMSO, poorly soluble in most organic solvents.
CH COOH, NaHCO
3
3
[Au(N^C^N)Cl][AuCl4 ] + K[PF ] Æ
H[AuCl4 ]◊3H2O + N^CH^N æææææææÆ
6
reflux
(3)
(2)
[Au(N^C^N)Cl][PF ] (4d) + K[AuCl4 ]
[Au(N^C^N)Cl][AuCl4 ] (4b)
6
Nevertheless anion metathesis was achieved by a two step
procedure: reaction of 4b with [NBu4]Cl in dichloromethane gives
[(Au(NŸCŸN)Cl][Cl], 4c, and [NBu4][AuCl4] (eqn (4)) which were
isolated and characterized. Addition of an excess of K[PF6] to
an acetone solution of 4c allows the isolation of the soluble
[Au(NŸCŸN)Cl][PF6], 4d (eqn (5)).
[Au(N^C^N]Cl][AuCl4 ] (4b) + [NBu4 ]Cl Æ
(4)
[Au(N^C^N)Cl][Cl] (4c) + [NBu4 ][AuCl4 ]
[Au(N^C^N)Cl][Cl] (4c) + K[PF ] Æ
6
(5)
[Au(N^C^N)Cl][PF ] (4d) + KCl
6
Exchange of [PF6]- for [Hg2Cl6]2- can also be accomplished
in compound 4a: yield is almost quantitative. On the whole the
transmetalation path gives the best yields and reduces the reaction
time.
All the complexes 4a–d were characterized by elemental analysis
(CHN) and 1H NMR spectra (see Table 1). Most diagnostic is the
lack of the H2 proton of the aryl ring. The other resonances were
assigned by comparison with the spectrum of the ligand and by
selective H–H decoupling. As shown in Table 1, at least in DMSO
the chemical shifts are not affected by the counter ion.
Complex 4b was collected from the reaction medium after
seven days at reflux: monitoring the reaction over this time
by 1H NMR, species such as [HNŸCHŸNH][AuCl4]2, 1, and
[(NŸCHŸN)(AuCl3)2], 3, were identified as by-products. Further-
more under this thermally promoted activation, C(2) metalation is
not completely selective: in addition to complex 4b, we isolated a
minor product which on the basis of the analytical (CHN) values
and 1H NMR spectra we tentatively describe as compound 5.
Table 1 1H NMR data of NŸCHŸN and [(Au(NŸCŸN)Cl][X] in DMSO-d6
H2
H5
H4, H6
H3¢, H3¢¢
H4¢, H4¢¢
H5¢, H5¢¢
H6¢, H6¢¢
NŸCHŸN
8.82
7.61
7.70
7.72
7.72
7.72
8.07
7.99
8.01
8.03
8.01
8.14
8.47
8.49
8.50
8.48
7.91
8.52
8.52
8.53
8.52
7.39
7.86
7.87
7.87
7.86
8.71
9.13
9.16
9.17
9.17
4a, X = 1 [Hg2Cl6]
2
4b, X = [AuCl4]
4c, X = Cl
4d, X = [PF6]
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ogous pincer compound [Pd(NŸCŸN)Cl].4f In this complex Pd–Cl
˚
Table 2 Selected Distances (A) and Angles (deg) in the cation of 4d with
Estimated Standard Deviations (Esd’s) on the last figure in parentheses
˚
˚
˚
2.427(1) A, Pd–N(1) 2.065(1) A, Pd–N(2) 2.063(1) A, and Pd–C(2)
˚
1.910(2) A. A comparison with the Au–ligand distances reported
Au–Cl
Au–N(2)
2.360(1)
2.032(5)
99.2(1)
179.7(2)
80.5(2)
115.1(4)
114.8(4)
114.8(5)
Au–N(1)
Au–C(2)
2.019(5)
1.950(5)
99.6(1)
161.2(2)
80.7(2)
124.7(4)
124.6(4)
114.3(5)
in Table 2 shows that in three cases [Cl, N(1) and N(2)] the distances
involving gold are shorter, whereas in one case [C(2)] the opposite
occurs, so that no definite conclusion can be drawn on the relative
length of the covalent radius of Au(III) with respect to that of
Pd(II). The Pd–ligand bond lengths in [Pd(NŸCŸN)Cl] are very
similar to those found in the analogous platinum pincer compound
[Pt(NŸCŸN)Cl].4c The present Au–Cl distance is elongated by the
trans influence of the C(2) carbon atom and is statistically identical
with that found in [AuCl2(pop-C1,N)]10 where Au–Cl (trans-C) =
Cl–Au–N(1)
Cl–Au–C(2)
N(1)–Au–C(2)
Au–N(1)–C(7)
Au–N(2)–C(12)
C(2)–C(1)–C(7)
Cl–Au–N(2)
N(1)–Au–N(2)
N(2)–Au–C(2)
Au–N(1)–C(11)
Au–N(2)–C(16)
C(2)–C(3)–C(12)
A single crystal of 4d suitable for X-ray diffraction was grown
by slow evaporation of an acetone solution at room temperature.
The structure of 4d consists of the packing of [Au(NŸCŸN)Cl]+
cations and [PF6]- anions in the molar ratio 1 : 1 with no unusual
van der Waals contacts. An ORTEP9 view of the cation is shown
in Fig. 2. Selected bond parameters of the cation are reported in
Table 2.
˚
2.369(5) A. It is also very similar to that found in compound
11
˚
6 (see later), Au–Cl(1) = 2.375(1) A. In [Au(PPh3)Cl3] the
˚
Au–Cl bond trans to phosphine is 2.347(2) A long, the two Au–Cl
˚
bonds not trans-influenced show a length of 2.283 A (mean value).
The present Au–C(2) bond [1.950(5) A] is shortened by the fact
˚
that it is the central bond of a bicyclic moiety formed by a
tridentate ligand. In similar arrangements marked shortenings of
the central bond are normal,12 for instance Au–C = 1.96(2) A in
˚
[AuCl{C6H3(CH2NMe2)2-2,6}]+.5a Typical Au(III)–C bonds when
the carbon atom is not confined in a cycle are much longer, as for
˚
instance Au–C(2) 2.052(2) A in compound 6 (see later), Au–C(1)
1
10
˚
˚
2.06(1) A in [AuCl(pap-C ,N)(PPh3)][BF4] and 2.033(5) A in
[Au(C6H4N NPh-2)Cl2(PPh3)].
13
=
Reactivity of [Au(NŸCŸN)Cl][PF6], 4d
Aspects of the reactivity of gold(III) cyclometalated derivatives
with nitrogen donors have been reported for bidendate CŸN5a,10,14
and tridentate ligands with CŸNŸN14b,14l,15 and CŸNŸC16 sequence
of atoms: reports mostly concern reactions not involving complete
removal of the cyclometaled ligands but rather displacement of
the nitrogen atoms or of halides by neutral ligands, typically
PR3. As previously mentioned, as yet gold(III) NŸCŸN pincer
species are very few and their reactivity almost completely
unexplored.
Fig. 2 ORTEP view of the cation in compound 4d. Ellipsoids as in
Fig. 1.
The Au atom displays a square-planar coordination with a very
slight square-pyramidal distortion, maximum distances from the
We first observed that attempts to obtain solvento species
from the [(Au(NŸCŸN)Cl]+ cations, e.g. 4d, by displacement of
the chloride were unsuccessful, despite it being trans to a carbon
atom: with poorly coordinating solvents we were unable to isolate
a definite species also in the presence of a silver salt. Even with
acetonitrile, a coordinating solvent traditionally employed to trap
unsaturated species, substitution of the chloride was not achieved:
compound 4d was recovered after treatment with Ag[PF6] in
acetonitrile at reflux.
Different behaviours were observed in reactions of (CŸN)-
cycloaurated gold(III) halide complexes with tertiary phosphines,
a reaction often taken as indicative of the reactivity of these gold
species: both replacement of the halide or cleavage of Au–N bonds
can occur whereas the Au–C bond is usually unaffected. The
hard nature of the nitrogen donors favours the gold(III) species
towards reduction to gold(I), whereas easy substitution of the
phosphine for the coordinated nitrogen(s) indicates relatively weak
Au–N bonds.17 In our case the reaction of complex 4d with PPh3
occurs with cleavage of the Au–N bonds to give the bis adduct
[Au(NŸCŸN)(PPh3)2Cl][PF6], 6, regardless of the stoichiometric
ratio used, eqn (6):
˚
best plane being +0.004(1) and -0.001(5) A for atoms Au and
N(1), respectively. Bond lengths involving gold in the cation of
4d can be compared with the corresponding Au–ligand distances
found in the cation [AuCl{C6H3(CH2NMe2)2-2,6}]+,5a which is the
only structurally characterized Au(III) NŸCŸN pincer compound.
However in [AuCl{C6H3(CH2NMe2)2-2,6}]+, the N atoms are
hybridized sp3 and bear two methyl groups each. As a result, the
Au–Cl and Au–C bond lengths are almost identical with those of
˚
the present cation (Au–Cl 2.360(1) and Au–C 1.950(5) A here,
+
˚
˚
2.369(6) A and 1.96(2) A in [AuCl{C6H3(CH2NMe2)2-2,6}] ),
whereas the two Au–N bond lengths in the two compounds are
˚
very different; thus, Au–N(1) 2.11(2) and Au–N(2) 2.12(1) A in
[AuCl{C6H3(CH2NMe2)2-2,6}]+ (note the high esd’s), Au–N(1)
˚
2.019(5) and Au–N(2) 2.032(5) A here. The lengthening of the Au–
N distances in [AuCl{C6H3(CH2NMe2)2-2,6}]+, can be attributed
partly to the different hybridization of the nitrogen atoms, and
partly to the steric hindrance of the bulky methyl groups.
We may compare also the present Au–ligand bond lengths
with the Pd–ligand distances found in the neutral, strictly anal-
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◦
˚
non-bonding distances between Au and N(1) and Au and N(2) are
Table 3 Selected distances (A) and angles ( ) in the cation of 6 with
estimated standard deviations (esd’s) on the last figure in parentheses
˚
2.929(2) and 2.876(2) A, respectively. The Au–P distances, Au–P(1)
˚
2.363(1) and Au–P(2) 2.384(1) A, are elongated by the mutual
Au–Cl(1)
Au–P(2)
Cl(1)–Au–P(1)
Cl(1)–Au–C(2)
P(1)–Au–C(2)
2.375(1)
2.384(1)
90.5(1)
176.3(1)
87.8(1)
Au–P(1)
Au–C(2)
Cl(1)–Au–P(2)
P(1)–Au–P(2)
P(2)–Au–C(2)
2.363(1)
2.052(2)
90.4(1)
176.3(1)
91.5(1)
trans influence of the phosphorus atoms. Similar distances can be
found in [AuCl(pap-C1)(PEt3)2]Cl,10 where the trans ligands are
˚
triethylphosphines: Au–P(1) 2.365(3), Au–P(2) 2.361(3) A. When
the phosphine is not trans to a trans influencing atom, typical
Au(III)–P distances are shorter, see for instance Au–P 2.329(2) A
in [Au(PPh3)Cl3]11 and Au–P 2.314(6) A in [Au(PPh3)Br2Cl].18 The
present Au–Cl(1) bond length, 2.375(1) A, is very similar to the
one found in compound 4d (see above) (both are elongated by
the trans C atom), and the Au–C(2) distance, 2.052(2) A, has
already been discussed above in comparison to that found in 4d,
˚
˚
acetone
[Au(N^C^N)Cl][PF ] (4d) + 2PPh3 æææÆ
6
˚
(6)
[Au(N^C^N)(PPh3)2Cl][PF ] (6)
6
˚
Formation of a mono adduct was never observed while mon-
itoring the reaction at room temperature (31P NMR). According
˚
1.950(5) A.
1
to the H NMR spectrum, compound 6 maintains its original
Reaction of 4d with [Ph2PCH2]2, dppe, gives complex 7, eqn (7):
arrangement with the chlorine opposite to the carbon atom. One
resonance is observed for the H6¢, H6¢¢ protons of the pyridine
rings, significantly shifted to higher field (d 7.89) compared to d
9.17 in 4d. In the 31P spectrum the only one resonance, d 32.57,
further supports the trans arrangement of the phosphines.
Crystals of compound 6 of X-ray quality were obtained by slow
evaporation of a dichloromethane solution at room temperature.
The X-ray structure confirms the cleavage of the Au–N bonds: the
NŸCŸN ligand is now bonded only through the aromatic carbon
atom.
The structure of 6·CH2Cl2 consists of the packing of
[Au(NŸCŸN)(PPh3)2Cl]+ cations, [PF6]- anions and CH2Cl2
molecules in the molar ratio 1 : 1 : 1 with no unusual van der Waals
contacts.
An ORTEP9 view of the cation is shown in Fig. 3. Selected bond
lengths and angles of the cation are reported in Table 3.
acetone
[Au(N^C^N)Cl][PF ] (4d) + dppe æææÆ
6
(7)
[Au(N^C^N)(dppe)Cl][PF ] (7)
6
In the 31P{ H} NMR spectrum (CD2Cl2) two resonances, d
1
3
3
46.47 (d, JPP = 11.8 Hz) and d 55.86 (d, JPP = 11.8 Hz), are
consistent with a chelating behaviour of the phosphine ligand. In
1
the H NMR spectrum the methylenic protons are observed as
two sets of multiplets (d 2.62–2.84, m + m overlapping; d 3.04–
3.26, m + m overlapping) each integrating for two protons. In the
aromatic region, four systems at d 6.83 (d, 3JHH = 7.5 Hz, 2H) d
6.88 (d, 3JHH = 7.5 Hz, 2H), d 8.07 (d, 3JHH = 7.5 Hz, 2H) and d
8.12 (d, 3JHH = 7.5 Hz, 2H) can be assigned to the ortho protons
of the phenyl rings of dppe. 1H–1H NOESY experiments indicate
contacts between the resonances at d 8.07, d 8.12 and multiplets
at d 2.62–2.84 and between those at d 6.83, d 6.88 and multiplets
at d 3.04–3.26.
Though in the absence of a X-ray structure of compound
7, the experimental evidence supports displacement of the ni-
trogen atoms from the coordination sphere of the metal. It
is noteworthy that the chelating behaviour displayed by the
bidentate dppe entails isomerization from a trans to a cis C–Au–Cl
arrangement.
Fig. 3 ORTEP view of the cation in compound 6·CH2Cl2. Ellipsoids as
in Fig. 1.
The reaction between 4d and [Ph2PCH2PPh2], dppm, was
initially monitored by NMR spectroscopy that provides evidence
for a symmetric species: an adduct was isolated as a white
solid, soluble in most organic solvents (dichloromethane, ace-
tone, acetonitrile) but thermally rather unstable: gentle heating
causes decomposition and free ligand, NŸCHŸN, is released. The
behaviour of dppm is reminiscent of that of PPh3: elemental
The Au atom displays a square-planar coordination with a
tetrahedral distortion, maximum distances from the best plane
˚
being +0.072(2) and -0.071(1) A for atoms C(2) and P(1),
respectively. The C(1)–C(6) phenyl ring is strictly planar and forms
a dihedral angle with the metal best plane of 85.9(1)◦. The distance
˚
of Au from the C(1)–C(6) best plane is only of 0.027(1) A. The
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analyses (CHN), support a bis adduct, [Au(NŸCŸN)(Cl)(dppm)2]-
[PF6], 8.
the corresponding mercury(II) derivative, [Hg(NŸCŸN)Cl], or by
direct C–H activation with H[AuCl4] as the metal source. The
structure in the solid state of [Au(NŸCŸN)Cl][PF6] has been
solved by X-ray diffraction. Reactions of this pincer compound
with phosphines in acetone at room temperature produced
compounds in which the pincer ligand NŸCŸN behaves as a
C monodentate ligand and the square-planar coordination of
gold(III) is completed by the phosphines and a chloride ligand.
The X-ray structure of the complex with two PPh3 confirms the
cleavage of the Au–N bonds and the NŸCŸN ligand bonded only
through the aromatic carbon atom. Attempts to remove the halide
were unexpectedly unsuccessful even in the presence of silver
salts.
The syntheses and reactivity studies of other pincer NŸCŸN
gold(III) complexes are in progress. Application of the various
species to some catalytic reactions is under investigation.
1
The 31P{ H} NMR spectrum of the complex consists of two
equally intense sets of resonances, both “triplets”, at d 28.15
and d -25.83 (Fig. 4) corresponding to coordinated and non-
1
coordinated phosphorus atoms, respectively, in line with two h -
Experimental section
dppm coordinated in a trans disposition. The pair of “triplets” may
be interpreted as a “deceptively simple” example of an AA‘XX’
spin system15d,19 corresponding to the static structure of complex 8
shown above, and are due to (i) the trans 2J(P–P) (usually >300 Hz
in d8 square planar systems20) >> 6J(PX–PX¢), (ii) the inner lines of
the AB subspectra are very close so that they cannot be resolved,
and (iii) the outer lines lie below the limit of detection. In our
General
The ligand NŸCHŸN7 and the corresponding mercury(II) deriva-
tive, [Hg(NŸCŸN)Cl],4f were prepared as previously described.
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.
Elemental analyses were performed with a Perkin-Elmer el-
emental analyzer 240B by Mr Antonello Canu (Dipartimento
di Chimica, Universita` degli Studi di Sassari, Italy). 1H and
2
case J(PA–PA¢) should be very large (ca. 400–500 Hz)20 whereas
6J(PX–PX¢) should be approximately zero.
1
The trans arrangement of the two h -dppm implies that the two
pairs of chemically equivalent phosphorus centres are magneti-
cally not equivalent. In this case several of the twelve lines of the
AA‘XX’ system collapse or have low intensity.21 Simulation of this
AA‘XX’ system is possible but does not give a unique solution.22
In our case, the distance of the outer lines in the “triplet” is N =
|JAX + JAX¢| = 50.3 Hz, unfortunately not all the other coupling
constants can be obtained from the spectrum as not enough lines
are available.
◦
1
31P{ H} NMR spectra were recorded at room temperature (20 C)
with a Varian VXR 300 spectrometer operating at 300.0 and
121.4 MHz respectively. Chemical shifts are given in ppm relatively
to internal TMS (1H) and external H3PO4 (31P). 2D-COSY and
NOESY spectra were performed by means of standard pulse
sequences.
Syntheses
Conclusion
The ligand 1,3-bis(2-pyridyl)benzene (NŸCHŸN). The ligand
1,3-bis(2-pyridyl)benzene (NŸCHŸN) was prepared from 1,3-
dicyanobenzene and acetylene, in the presence of a cobalt catalyst
according to a literature procedure (see ref. 7).
In conclusion we have obtained very rare cyclometalated pin-
cer derivatives, [Au(NŸCŸN)Cl]+, of 1,3-bis(2-pyridyl)benzene,
NŸCHŸN, as different salts, either by transmetallation from
1
Fig. 4 Region of 31P{ H}NMR spectrum (121.4 MHz) of complex 8 in deuterated acetone showing the ‘deceptively simple’ triplets of the AA‘XX’ spin
system with N = |JAX + JAX’| = 50.3 Hz.
3472 | Dalton Trans., 2009, 3467–3477
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4
3
8.91 (td, 1H, JHH = 1.7 Hz, H2); 8.95 (td, 2H, JHH = 8.0 Hz,
4JHH = 1.7 Hz, H4¢, H4¢¢); 9.24 (ddd, 2H, 3JHH = 5.9 Hz, 1.7 Hz,
0.7 Hz H6¢, H6¢¢).
Synthesis of [NŸCHŸNH][AuCl4] (2). A solution of NŸCHŸN
(232.1 mg, 1.00 mmol) in 30 cm3 of acetonitrile was added under
vigorous stirring to 393.8 mg (1.00 mmol) of H[AuCl4]·3H2O and
heated for 5 days at reflux. The solution was evaporated under
vacuum to give a yellow solid. After treatment with 5 cm3 of
diethyl ether the solid was filtered off, washed with diethyl ether
and dried under vacuum to give compound 2. Yield 429.0 mg,
1H NMR (300 MHz, CD2Cl2, 296 K): d 7.30 (ddd, 2H, JHH
=
7.4 Hz, 4.8 Hz, 1.1 Hz, H5¢, H5¢¢); 7.62 (t, 1H, 3JHH = 7.8 Hz, H5);
7.81 (ddd, 2H, JHH = 8.0 Hz, 7.4 Hz, 1.9 Hz, H4¢, H4¢¢); 7.90 (ddd,
◦
75%; mp 177–179 C; (Found: C 33.48; H 2.45; N 4.85%. Calc.
for C16H13AuCl4N2: C 33.59; H 2.29; N 4.90%).
2H, JHH = 8.0 Hz, 1.1 Hz, 0.9 Hz H3¢, H3¢¢); 8.12 (dd, 2H, 3JHH
=
1H NMR (300.0 MHz, DMSO-d6, 296 K): d 7.66 (m, 2H, H5¢,
H5¢¢); 7.76 (t, 1H, 3JHH = 8.1 Hz, H5); 8.21(dd, 2H, 3JHH = 7.8 Hz,
4JHH = 1.8 Hz, H4, H6); 8.27 (m, 4H, H4¢, H4¢¢, H3¢, H3¢¢); 8.74
(s, 1H, H2); 8.81 (dm, 2H, 3JHH = 5.1 Hz, H6¢, H6¢¢).
4
7.8 Hz, JHH = 1.7 Hz, H4, H6); 8.75 (ddd, 2H, JHH = 4.8 Hz,
1.9 Hz, 0.9 Hz, H6¢, H6¢¢); 8.78 (t, 1H, 4JHH = 1.7 Hz, H2).
1H NMR (300 MHz, CDCl3, 296 K): d 7.25 (ddd, 2H, JHH
=
3
7.4 Hz, 4.8 Hz, 1.1 Hz, H5¢, H5¢¢); 7.60 (t, 1H, JHH = 7.8 Hz,
H5); 7.77 (ddd, 2H, JHH = 8.0 Hz, 7.4 Hz, 1.8 Hz, H4¢, H4¢¢); 7.85
(ddd, 2H, JHH = 8.0 Hz, 1.1 Hz, 0.9 Hz, H3¢, H3¢¢); 8.07 (dd, 2H,
3JHH = 7.8 Hz, 4JHH = 1.9 Hz, H4, H6); 8.63 (t, 1H, 4JHH = 1.9 Hz,
H2); 8.72 (ddd, 2H, JHH = 4.8 Hz, 1.8 Hz, 0.9 Hz, H6¢, H6¢¢).
1H NMR (300.0 MHz, acetone-d6, 296 K): d 7.90 (t, 1H, 3JHH
=
7.8 Hz, H5); 7.95 (t, 2H, 3JHH = 6.0 Hz, H5¢, H5¢¢); 8.35 (dd, 2H,
3JHH = 7.8 Hz, 4JHH = 1.8 Hz, H4, H6); 8.49 (d, 2H, 3JHH = 8.1 Hz,
4JHH = 1.2 Hz H3¢, H3¢¢); 8.55 (td, 2H, 3JHH = 7.2 Hz, H4¢, H4¢¢);
8.86 (s, 1H, H2); 9.02 (d, 2H, 3JHH = 5.1 Hz, H6¢, H6¢¢).
1H NMR (300 MHz, acetone-d6, 296 K): d 7.35 (ddd, 2H, JHH
=
7.5 Hz, 4.8 Hz, 1.1 Hz, H5¢, H5¢¢); 7.60 (t, 1H, 3JHH = 7.8 Hz, H5);
7.90 (ddd, 2H, JHH = 8.0 Hz, 7.5 Hz, 1.7 Hz, H4¢, H4¢¢); 8.04 (ddd,
Synthesis of [(AuCl3)2(NŸCHŸN)] (3). 168.0 mg (2.00 mmol)
of NaHCO3 were added under vigorous stirring to a suspension
of 911.8 mg (1.00 mmol) of compound 1 in 30 cm3 of THF
and left 24 h to react at room temperature. The corresponding
solution was evaporated and the crude solid was recrystallized
from acetone/diethyl ether to give a yellow solid that was filtered
off and dried under vacuum: compound 3. Yield 486.6 mg, 58%;
mp 208–210 ◦C; (Found: C 23.16; H 1.18; N 3.02%. Calc. for
C16H12Au2Cl6N2: C 22.91; H 1.44; N 3.34%).
2H, JHH = 8.0 Hz, 1.1 Hz, 0.9 Hz, H3¢, H3¢¢); 8.19 (dd, 2H, 3JHH
=
4
7.8 Hz, JHH = 1.9 Hz, H4, H6); 8.71 (ddd, 2H, JHH = 4.8 Hz,
1.7 Hz, 1.1 Hz, H6¢, H6¢¢); 8.91 (t, 1H, 4JHH = 1.9 Hz, H2).
1H NMR (300 MHz, DMSO-d6, 296 K): d 7.39 (ddd, 2H, JHH
=
3
7.4 Hz, 4.8 Hz, 1.1 Hz, H5¢, H5¢¢); 7.61 (td, 1H, JHH = 7.7 Hz,
4JHH = 1.8 Hz, H5); 7.91 (ddd, 2H, JHH = 7.8 Hz, JHH = 7.4 Hz,
JHH = 1.7 Hz, H4¢, H4¢¢); 8.07 (dm, 2H, 3JHH = 7.7 Hz, H4, H6);
8.14 (ddd, 2H, JHH = 7.8 Hz, 1.1 Hz, 0.9 Hz, H3¢, H3¢¢); 8.71 (ddd,
2H, JHH = 4.8 Hz, 1.7 Hz, 0.9 Hz, H6¢, H6¢¢); 8.82 (t, 1H, 4JHH
1.8 Hz, H2).
=
=
1H NMR (300.0 MHz, DMSO-d6, 296 K): d 7.50 (tm, 2H,
3JHH = 6.1 Hz, H5¢, H5¢¢); 7.68 (t, 1H, 3JHH = 7.9 Hz, H5); 8.04
(tm, 2H, 3JHH = 7.7 Hz, H4¢, H4¢¢); 8.16 (dm, 2H, 3JHH = 7.8 Hz,
H3¢, H3¢¢); 8.17 (dd, 2H, 3JHH = 7.8 Hz, 4JHH = 1.8 Hz, H4, H6);
8.75 (dm, 2H, 3JHH = 4.8 Hz, H6¢, H6¢¢); 8.78 (t, 1H, 4JHH = 1.8 Hz,
H2).
1H NMR (300 MHz, CD3CN, 296 K): d 7.34 (ddd, 2H, JHH
3
7.4 Hz, 4.7 Hz, 1.1 Hz, H5¢, H5¢¢); 7.62 (t, 1H, JHH = 7.7 Hz,
H5); 7.87 (ddd, 2H, JHH = 8.1 Hz, 7.4 Hz, 1.9 Hz, H4¢, H4¢¢); 7.97
(ddd, 2H, 3JHH = 8.1 Hz, 1.1 Hz, 0.9 Hz, H3¢, H3¢¢); 8.12 (dd, 2H,
4
3
3JHH = 7.7 Hz, JHH = 1.8 Hz, H4, H6); 8.71 (dm, 2H, JHH
=
1H NMR (300.0 MHz, acetone-d6, 296 K): d 7.78 (m, 2H, H5¢,
H5¢¢); 7.81 (t, 1H, 3JHH = 7.8 Hz, H5); 8.29 (dd, 2H, 3JHH = 7.8 Hz,
4JHH = 1.8 Hz, H4, H6); 8.35 (d, broad, 4H, JHH = 3.9 Hz, H4,
4.7 Hz, H6¢, H6¢¢); 8.91 (t, 1H, 4JHH = 1.8 Hz, H2).
Synthesis of [NHŸCHŸNH][AuCl4]2 (1). A solution of 232.3 mg
(1.00 mmol) of NŸCHŸN in 30 cm3 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 cm3) and let to react for 30 min.
The precipitate which formed was filtered off, washed with diethyl
ether and dried under vacuum to give compound 1 as a pale yellow
solid. Yield 884.5 mg, 97%; mp 201–204 ◦C; (Found: C 20.91; H
1.26; N 2.94%. Calc. for C16H14Au2Cl8N2: C 21.07; H 1.55; N
3.07%).
3
H4¢¢, H3¢, H3¢¢); 8.83 (t, 1H, JHH = 1.8 Hz, H2); 8.93 (dm, 2H,
3JHH = 5.1 Hz, H6¢, H6¢¢).
Synthesis of [Au(NŸCŸN)Cl]2[Hg2Cl6] (4a). A mixture of
[Hg(NŸCŸN)Cl] (467.3 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 cm3) was let under stirring for 5 h.
The formation of abundant white precipitate could be observed.
Afterwards, the precipitate was filtered off, washed with diethyl
ether and dried in vacuum to give 4a.
1H NMR (300.0 MHz, DMSO-d6, 296 K): d 7.71 (tm, 2H,
3JHH = 6.1 Hz, H5¢, H5¢¢); 7.79 (t, 1H, 3JHH = 7.8 Hz, H5); 8.23
3
(d, 2H, JHH = 7.8 Hz, H4, H6); 8.31 (m, 4H, H4¢, H4¢¢, H3¢,
Yield 703.6 mg, 91%; mp >250 ◦C; (Found: C, 24.62; H, 1.39; N,
3.41%. Calc. for C16H11AuCl4HgN2: C, 24.94; H, 1.44; N, 3.64%).
H3¢¢); 8.73 (s, 1H, H2); 8.84 (dd, 2H, 3JHH = 5.4 Hz, 4JHH = 0.9 Hz
H6¢, H6¢¢).
1H-NMR (300.0 MHz, DMSO-d6, 296 K): d 7.70 (t, 1H, 3JHH
=
3
1H-NMR (300.0 MHz, acetone-d6, 296 K): 8.11 (td, 1H, 3JHH
=
7.7 Hz, H5); 7.86 (t, broad, 2H, JHH = 6.3 Hz, H5¢, H5¢¢); 7.99
(d, 2H, 3JHH = 7.7 Hz, H4, H6); 8.47 (d, broad, 3JHH = 7.4 Hz 4H,
H3¢, H3¢¢); 8.52 (dd, 2H, 3JHH = 7.9 Hz, 7.4 Hz, H4¢, H4¢¢); 9.13
(d, 2H, 3JHH = 5.6 Hz, H6¢, H6¢¢).
8.0 Hz, 5JHH = 0.6 Hz, H5); 8.32 (ddd, 2H, JHH = 7.7 Hz, 5.9 Hz;
3
4
1.2 Hz, H5¢, H5¢¢); 8.47 (dd, 2H, JHH = 8.0 Hz, JHH = 2.0 Hz,
H4, H6); 8.74 (dt, 2H, 3JHH = 8.0 Hz, 4JHH = 1.2 Hz, H3¢, H3¢¢);
This journal is
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©

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1H NMR (300.0 MHz, DMSO-d6, 296 K): d 7.72 (t, 1H, 3JHH
=
7.8 Hz, H5); 7.86 (t, 2H, 3JHH = 6.3 Hz, H5¢, H5¢¢); 8.01 (d, 2H,
3JHH = 7.8 Hz, H4, H6); 8.48 (m, 2H, H3¢, H3¢¢); 8.52 (m, 2H,
3
H4¢, H4¢¢); 9.17 (d, 2H, JHH = 5.5 Hz, H6¢, H6¢¢). 31P NMR
-
(121.4 MHz, DMSO-d6, 296 K): d -143.13 (sept, PF6 ).
1H NMR (300.0 MHz, acetone-d6, 296 K): d 7.81 (t, 1H, 3JHH
=
3
3
7.8 Hz, H5); 7.99 (ddd, 2H, JHH = 7.5 Hz, JHH = 6.0 Hz, H5¢,
H5¢¢); 8.06 (d, 2H, 3JHH = 7.8 Hz, H4, H6); 8.51(dd, 2H, 3JHH
=
7.5 Hz, H3¢, H3¢¢); 8.62 (td, 2H, 3JHH = 7.8, 4JHH = 1.5 Hz, H4¢,
H4¢¢); 9.34 (d, 2H, JHH = 6.0 Hz, H6¢, H6¢¢). 31P NMR (121.4 MHz,
-
acetone-d6, 296 K): d -143.43 (sept, PF6 ).
1H NMR (300.0 MHz, CD3CN, 296 K): d 7.63–7.77 (m, 5H,
3
H5, H5¢, H5¢¢, H4, H6); 8.15 (dd, 2H, JHH = 8.1 Hz, JHH
=
Synthesis of [Au(NŸCŸN)Cl][AuCl4] (4b).
0.9 Hz, H3¢, H3¢¢); 8.38 (td, 2H, 3JHH = 7.9, 4JHH = 1.6 Hz, H4¢,
H4¢¢); 9.18 (dd, 2H, 3JHH = 5.9 Hz, JHH = 1.0 Hz H6¢, H6¢¢). 31
P
Method a. To a solution of H[AuCl4]·3H2O (808.2 mg,
2.05 mmol) in 30 cm3 of freshly distilled acetic acid were added
238.3 mg (1.03 mmol) of NŸCHŸN and an excess of NaHCO3
(428.3 mg, 5.10 mmol) under stirring. Immediately a yellow
precipitate was formed which dissolved as soon as the reflux
started. The precipitate obtained after 7 days of reaction was
filtered off, washed with acetone, diethyl ether and dried under
vacuum to give 4b, as a yellow solid. Yield 350,2 mg, 41%;
mp > 250 ◦C (Found: C 24.35; H 1.49; N 3.52%. Calc. for
C16H11Au2Cl5N2: C 23.95; H 1.38; N 3.49%).
-
NMR (121.4 MHz, CD3CN, 296 K): d -143.33 (sept, PF6 ).
Synthesis of [Au(NHŸC4ŸN)Cl2][AuCl4] (5). Compound 5 was
isolated from the mother liquor of the synthesis of 4b (method
b). The solution was evaporated to dryness and 15 cm3 of acetone
were added to residue. After filtration, the yellow solution was
evaporated to small volume and diethyl ether was added. The
precipitate obtained was filtered off, washed with diethyl ether
and dried in vacuum to give 5 as a yellow solid.
Method b. To a suspension of 2, [NHŸCHŸNH][AuCl4]2
(911.8 mg, 1.00 mmol) in 30 cm3 of freshly distilled acetic acid
was added NaHCO3 (206.3 mg, 3.1 mmol). The suspension was
Yield 35.4 mg; mp 230–231 ◦C (dec.) (Found: C 22.91; H 1.44;
N 3.34%. Calc. for C16H12Au2Cl6N2: C 22.95; H 1.31; N 2.89%).
1H NMR (300.0 MHz, acetone-d6, 296 K): d 7.94 (m, 1H, H5¢);
◦
3
4
kept one week under stirring at 120 C. The hot suspension was
8.11 (dd, 1H, JHH = 8.4 Hz, JHH = 2.4 Hz, H6); 8.26 (d, 1H,
3JHH = 8.4 Hz, H5); 8.34 (ddd, 1H, JHH = 7.4 Hz, 1.2 Hz, H5¢¢);
quickly filtered, and the solid washed with acetone and dried
under vacuum to give 4b as a yellow solid. Yield 453.5 mg,
57%; mp > 250 ◦C (Found: C 24.23; H 1.48; N 3.58%; Calc.
for C16H11Au2Cl5N2: C 23.95; H 1.38; N 3.49%).
4
8.57 (m, 2H, H3¢+H4¢); 8.75 (d, 1H, JHH = 2.4 Hz, H2); 8.79
(dm, 1H, 3JHH = 8.1 Hz, H3¢¢); 8.98 (td, 1H, 3JHH = 8.1 Hz, 4JHH
=
1.8 Hz, H4¢¢); 9.26 (dm, 1H, 3JHH = 5.7 Hz, H6¢¢); 9.76 (dd, 1H,
3JHH = 6.2 Hz, 4JHH = 1.1 Hz, H6¢).
1H NMR (300.0 MHz, DMSO-d6, 296 K): d 7.72 (t, 1H, 3JHH
=
3
4
7.8 Hz, H5); 7.87 (td, 2H, JHH = 6.9 Hz, JHH = 2.1 Hz, H5¢,
3
H5¢¢); 8.01 (d, 2H, JHH = 7.8 Hz, H4, H6); 8.49 (d, broad, 2H,
3
4
3JHH = 7.8 Hz, H3¢, H3¢¢); 8.52 (dd, 2H, JHH = 8.1 Hz, JHH
=
1.2 Hz, H4¢, H4¢¢); 9.16 (d, 2H, 3JHH = 5.8 Hz, H6¢, H6¢¢).
Synthesis of [Au(NŸCŸN)Cl]Cl (4c). Tetra(n-butyl)ammonium
chloride (833.7 mg, 3.00 mmol) was added under stirring to
a suspension of 4b, (802.5 mg, 1.00 mmol) in 50 cm3 of
dichloromethane. The suspension was left two hours under stirring
at room temperature. The colour of the solution turns yellow and
the solid white. The solid was collected and dried to give 4c, white.
Yield 486.2 mg, 97%; mp >250 ◦C.
1H NMR (300.0 MHz, DMSO-d6, 296 K): d 7.72 (t, 1H, 3JHH
7.8 Hz, H5); 7.87 (ddd, 2H, JHH = 8.7 Hz, 6.2 Hz, 2.7 Hz, H5¢,
=
Synthesis of [Au(NŸCŸN)(PPh3)2Cl][PF6] (6). An excess of
PPh3 (65.6 mg, 0.25 mmol) was added to a suspension of 4d
(60.9 mg, 0.10 mmol) in 20 cm3 of acetone and let under stirring
for 15 min. Afterwards, the solvent was evaporated and diethyl
ether (15 cm3) was added. The solid was filtered off, washed with
diethyl ether and dried to give 6 as a white solid. Yield 110.3 mg,
3
3
H5¢¢); 8.03 (d, 2H, JHH = 7.8 Hz, H4, H6); 8.50 (d, 2H, JHH
=
3
4
6.9 Hz, H3¢, H3¢¢); 8.53 (td, JHH = 7.8 Hz, JHH = 1.5 Hz, H4¢,
H4¢¢); 9.17 (d, 2H, 3JHH = 6.2 Hz, H6¢, H6¢¢).
Synthesis of [Au(NŸCŸN)Cl][PF6] (4d). K[PF6] (220.8 mg,
1.2 mmol) was added to a suspension of 4c (499 mg, 1.00 mmol)
in 100 cm3 of acetone. The suspension was left under stirring
at room temperature overnight. After filtration the solution was
evaporated to dryness and 15 cm3 of water were added to the
residue. The white solid was filtered off, washed with diethyl ether
and dried in vacuum to give 4d. Yield 264.8 mg, 44%; mp >250 ◦C
(Found: C 31.79; H 1.37; N 4.61%, Calc. for C16H11AuClF6N2P:
C 31.57; H 1.82; N 4.60%).
◦
97%; mp 180 C (dec.) (Found: C 55.13; H 3.47; N 2.51%, Calc.
for C52H41AuClF6N2P3: C 55.11; H 3.65; N 2.47%).
1H NMR (300.0 MHz, CD2Cl2, 296 K): d 6.88 (dm, 2H, 3JHH
7.8 Hz, H3¢, H3¢¢); 6.96–7.48 (m, 24H + 5H, Ho, Hm PPh3, H4,
=
H5, H6, H5¢, H5¢¢); 7.53 (t, broad, 6H, Hp PPh3); 7.68 (td, 2H,
4
3JHH = 7.8 Hz, JHH = 1.8 Hz, H4¢, H4¢¢); 7.89 (dm, 2H, 3JHH
=
4.5 Hz, H6¢, H6¢¢). 31P NMR (121.4 MHz, CD2Cl2, 296 K): d -
143.31 (sept, PF6 ); 32.57 (s, 2P, PPh3). Crystals of X-ray quality
-
3474 | Dalton Trans., 2009, 3467–3477
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The Royal Society of Chemistry 2009
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2
2
were obtained by slow evaporation of a dichloromethane solution
at room temperature.
1P, JPP = 11.8 Hz, P1 dppe-cis C); 55.86 (d, 1P, JPP = 11.8 Hz,
P2 dppe-cis Cl).
1H NMR (300.0 MHz, CD3CN, 296 K, d 2.67–2.80 (m + m,
overlapping, 1H + 1H, P1–CH1H1¢-CH2H2¢–P2); 3.08–3.26 (m +
m, overlapping 1H + 1H, P1-CH1H1¢–C H2H2¢-P2); 6.82 (d, 2H,
Synthesis of [Au(NŸCŸN)(dppe)Cl][PF6] (7). An excess of
[Ph2PCH2]2, (dppe), (99.6 mg, 0.25 mmol) was added to a
suspension of 4d, (60.9 mg, 0.10 mmol) in 20 cm3 of acetone
and let under stirring for 15 min. Afterwards the solvent was
evaporated and diethyl ether (15 cm3) was added. The solid was
collected, washed with diethyl ether and dried to give 7 as a
white solid. Yield 74,1 mg, 74%; mp 183 ◦C (Found: C 50.07;
H 3.45; N 2.53%, Calc. for C42H35AuClF6N2P3: C 50.09; H 3.50;
N 2.78%).
3JHH = 7.5 Hz, ortho-Hdppe(P1)); 6.86 (d, 2H, 3JHH = 7.5 Hz ortho-
3
Hdppe(P1)); 7.06 and 7.07 (t, 2H, J = 7.8 Hz, meta-Hdppe(P1)
+
3
t, 2H, J = 7.8 Hz, meta-Hdppe(P1), overlapping); 7.23 (tm, 2H,
3JHH = 7.2 Hz, H5¢, H5¢¢); 7.31 (t, 1H, JHH = 7.5 Hz, H5); 7.43 (tm,
3
2H, para-Hdppe(P1)); 7.53 (d +d, overlapping, 1H + 1H, JHH
=
3
7.8 Hz, JHH = 7.5 Hz, H4, H6); 7.68–7.82 (m, 8H, H4¢, H4¢¢,
para-Hdppe(P2), meta-Hdppe(P2)); 7.86–7.90 (m, 4H, H3¢, H3¢¢,H6¢,
H6¢¢); 8.03 and 8.08 (d + d, 2H + 2H, JHH = 7.5 Hz, ortho-
Hdppe(P2)). 31P NMR (121.4 MHz, CD3CN, 296 K): d -143.49
1H NMR (300.0 MHz, CD2Cl2, 296 K): d 2.62–2.84 (m + dm,
overlapping, 1H + 1H, P1–CH1H1¢-CH2H2¢–P2); 3.04–3.26 (m +
m, overlapping 1H + 1H, P1-CH1H1¢–C H2H2¢-P2); 6.83 (d, 2H,
(sept, 1P, PF6 ); 48.25 (d, 1P, 2JPP = 11.4 Hz, P1dppe-cis C); 57.15
-
(d, 1P, 2JPP = 11.4 Hz, P2dppe-cis Cl).
3JHH = 7.5 Hz, ortho-Hdppe(P1)); 6.88 (d, 2H, 3JHH = 7.5 Hz ortho-
3
Hdppe(P1)); 7.07 and 7.09 (t, 2H, J = 7.8 Hz, meta-Hdppe(P1)
+
3
t, 2H, J = 7.8 Hz, meta-Hdppe(P1), overlapping); 7.21 (tm, 2H,
3JHH = 7.2 Hz, H5¢, H5¢¢); 7.35 (t, 1H, 3JHH = 7.5 Hz, H5); 7.44 (tm,
broad, 2H, 3JHH = 7.5, para-Hdppe(P1)); 7.56 (d + d, overlapping,
Synthesis of [Au(NŸCŸN)(g1-dppm)2Cl][PF6] (8). An excess
of [Ph2P]2CH2 (dppm) (96.1 mg, 0.25 mmol) was added to a
suspension of 4d (60.9 mg, 0.10 mmol) in 20 cm3 of acetone and let
under stirring for 15 min. Afterwards the solvent was evaporated
and diethyl ether (15 cm3) was added. The solid was collected,
washed with diethyl ether and dried to give 8 as a white solid.
Yield 115,7 mg, 84%; mp 130–131 ◦C (Found: C 57.30; H 3.88; N
2.19%, Calc. for C66H55AuClF6N2P5: C 57.55; H 4.02; N 2.03%).
3JHH = 7.5 Hz, JHH = 7.2 Hz, H4, H6); 7.66–7.84 (m, 10H,
3
H4¢, H4¢¢, H6, H6¢, para-Hdppe(P2), meta-Hdppe(P2)); 7.92 (d, 2H,
3JHH = 7.8 Hz, H6, H6¢); 8.07 (d, 2H, JHH = 7.5 Hz, ortho-
3
Hdppe(P2)); 8.12 (d, 2H, 3JHH = 7.5 Hz, ortho-Hdppe(P2)). 31P NMR
-
(121.4 MHz, CD2Cl2, 296 K): d -143.31 (sept, 1P, PF6 ); 46.47 (d,
Table 4 Crystallographic data
Compound
2
4d
6·CH2Cl2
Formula
M
C16H13AuCl4N2
572.05
Yellow
Monoclinic
Pc
9.3686(6)
12.3340(8)
7.6777(5)
90
96.130(1)
90
882.10(10)
2
540
2.154
150
0.33 ¥ 0.45 ¥ 0.51
89.43
0.593–1.000
w
0.30
C16H11AuClF6N2P
608.66
Yellow
Monoclinic
P21/c
5.8260(5)
13.4747(12)
21.3305(19)
90
93.960(1)
90
1670.5(3)
4
1144
2.420
150
0.02 ¥ 0.02 ¥ 0.31
91.12
0.320–1.000
w
0.50
C53H43AuCl3F6N2P3
1218.19
Colourless
Orthorhombic
P212121
14.8738(9)
16.5750(10)
19.6092(12)
90
90
90
4834.3(5)
4
2416
1.674
115
0.41 ¥ 0.43 ¥ 0.50
33.63
0.668–1.000
w
0.50
Colour
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
U/A
Z
3
˚
F(000)
Dc/g cm-3
T/K
Crystal dimensions/mm
m(Mo-Ka)/cm-1
Min. and max. transmiss. factors
Scan mode
Frame width/◦
Time per frame/s
No. of frames
10
5400
10
1260
10
1440
Detector–sample distance/cm
6.00
3–28
Full sphere
24432, 4630
0.0192
0.031, 0.045
0.018
4554
206
1.036
6.00
3–27
Full sphere
17779, 4319
0.0558
0.070, 0.077
0.040
3099
260
0.960
6.00
3–27
Full sphere
58803, 12496
0.0346
0.034, 0.043
0.021
11393
613
0.949
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
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 = 0.03 for 2 and 0.02 for 4d and for 6. CH2Cl2.
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View Article Online
1H NMR (300.0 MHz, CD2Cl2, 296 K, d 3.43 (t, 4H, P - CH2P,
2JPH = 5.0 Hz); 7.00–7.38 (m, 47H) 7.59 (td, 2H, H4¢, H4¢¢); 8.29
(m + m, 2H, H6¢, H6¢¢);
References
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-
PF6 ); AA‘XX’ spin system dA 28.15; dX -26.51, N = |JAX
+
J
AX¢| = 50.3 Hz.
X-Ray data collections and structure determinations
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[Au(NŸCŸN)(PPh3)2Cl][PF6], 6.
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Crystal data are summarised in Table 4. The diffraction
experiments were carried out on a Bruker APEX II CCD area-
detector diffractometer, at 150 K for 2 and 4d, and at 115 K for
6·CH2Cl2, using Mo-Ka radiation (l = 0.71073) with a graphite
crystal monochromator in the incident beam. No crystal decay
was observed, so that no time-decay correction was needed. The
collected frames were processed with the software SAINT,23 and
an empirical absorption correction was applied (SADABS)24 to
the collected reflections. The calculations were performed using
the Personal Structure Determination Package25 and the physical
constants tabulated therein.26 The structures were solved by direct
methods (SHELXS)27 and refined by full-matrix least-squares
ꢀ
using all reflections and minimising the function w(Fo - kFc )2
2
2
(refinement on F2). In 4d the PF6 anion is partially disordered,
-
with atoms P, F1 and F2 (in trans position) ordered, and the other
four F atoms split into pairs having occupancy factors (refined)
of 0.80 and 0.20, respectively. The F atoms with occupancy
0.20 were refined with isotropic thermal parameters, whereas
all the other non-hydrogen atoms were refined with anisotropic
thermal factors. All the hydrogen atoms were placed in their ideal
˚
positions (C–H or N–H = 0.97 A), with the thermal parameter U
1.10 times that of the atom to which they are attached, and not
refined. For noncentrosymmetric compound 2 full refinement of
the correct structure model led to R2 = 0.031 and R2w= 0.045, full
refinement of the inverted structure led to R2 = 0.089 and R2w=
0.169. For chiral 6·CH2Cl2 full refinement of the correct structure
enantiomorph led to R2 = 0.034 and R2w= 0.043, full refinement
13 J. Vicente, M. D. Bermudez, J. Escribano, M. P. Carrello and P. G.
Jones, J. Chem. Soc., Dalton Trans., 1990, 3083–3089.
of the wrong one led to R2 = 0.107 and R2w= 0.180. In the final
-3
˚
˚
Fourier maps the maximum residuals were 1.34(15) e A at 0.79 A
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-3
˚
˚
˚
from Au, 4.29(68) e A at 0.96 A from Au, and 2.10(25) e A at
˚
1.01 A from Au, for 2, 4d, and 6·CH2Cl2, respectively.
CCDC reference numbers 713741–713743. For crystallographic
data in CIF or other electronic format see DOI: 10.1039/b822842f
Acknowledgements
We are grateful to the Ministero dell’Istruzione, Universita` e della
Ricerca (MIUR) and the Universita` degli Studi di Sassari for
financial support (PRIN Project). G.A. is grateful for a grant from
RAS (Regione Autonoma Sardegna), Project Master and Back
(MAB 4.2 A2005–44). We wish to thank Prof. Roberto Gobetto
(Universita` di Torino) and Dr. Heinz Ru¨egger of Laboratorium
fu¨r Anorganische Chemie (ETH of Zu¨rich) for helpful discussions
about 31P NMR spectra. We also thank Johnson Matthey for a
generous loan of H[AuCl4]·3H2O.
3476 | Dalton Trans., 2009, 3467–3477
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The Royal Society of Chemistry 2009
©

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©