Synthesis and catalytic application of palladium imidazol(in)ium-2- dithiocarboxylate complexes

Article abstract of DOI:10.1039/c2dt31413d

The palladium(ii) dimer, [Pd(C,N-C₆H₄CH ₂NMe₂)Cl]₂ reacts with two equivalents of the NHC·CS₂ zwitterionic ligands [NHC = IPr (1,3- diisopropylimidazol-2-ylidene), ICy (1,3-dicyclohexylimidazol-2-ylidene), IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), IDip (1,3-bis(2,6- diisopropylphenyl)imidazol-2-ylidene), SIMes (1,3-bis(2,4,6-trimethylphenyl) imidazolin-2-ylidene)] in the presence of NH₄PF₆, to yield the cationic products [Pd(C,N-C₆H₄CH₂NMe ₂)(S₂C·NHC)]⁺. In a similar fashion, the compounds [Pd(C,N-bzq)(S₂C·NHC)]⁺ (bzq = benzo[h]quinolinyl, NHC = ICy, IMes, IDip) are obtained from the corresponding dimer [Pd(C,N-bzq)Cl]₂. The bis(phosphine) compounds [Pd(S ₂C·NHC)(PPh₃)₂]²⁺ (NHC = ICy, IMes, IDip, SIMes) are obtained on treatment of [PdCl₂(PPh ₃)₂] with NHC·CS₂ zwitterions in the presence of NH₄PF₆. The reaction of [PdCl ₂(dppf)] with IMes·CS₂ and NH₄PF ₆ provides the complex [Pd(S₂C·IMes)(dppf)] ²⁺. The complexes [Pd(S₂C·NHC)(PPh ₃)₂](PF₆)₂ (NHC = IMes, IDip) were active pre-catalysts (1 mol% loading) for the conversion of benzo[h]quinoline to 10-methoxybenzo[h]quinoline in the presence of PhI(OAc)₂ and methanol. The intermediacy of [Pd(C,N-bzq)(S₂C·NHC)] ⁺ was supported by the high yield of 10-methoxybenzo[h]quinoline using [Pd(C,N-bzq)(S₂C·IDip)]⁺ to promote the same reaction. Small amounts of 2,10-dimethoxybenzo[h]quinoline were also isolated from these reactions. Using [Pd(C,N-bzq)(S₂C·IDip)] ⁺ and N-chlorosuccinimide as the oxidant led to the formation of 10-chlorobenzo[h]quinoline in moderate yield from benzo[h]quinoline. The molecular structures of [Pd(S₂C·IMes)(PPh₃) ₂](PF₆)₂ and [Pd(S₂C·IMes) (dppf)](PF₆)₂ were determined crystallographically.

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PAPER
Synthesis and catalytic application of palladium imidazol(in)ium-
2-dithiocarboxylate complexes†‡
Martin J. D. Champion,a Riten Solanki,a Lionel Delaude,b Andrew J. P. Whitea and
James D. E. T. Wilton-Ely*a
Received 29th June 2012, Accepted 15th August 2012
DOI: 10.1039/c2dt31413d
The palladium(II) dimer, [Pd(C,N-C6H4CH2NMe2)Cl]2 reacts with two equivalents of the NHC·CS2
zwitterionic ligands [NHC = IPr (1,3-diisopropylimidazol-2-ylidene), ICy (1,3-dicyclohexylimidazol-2-
ylidene), IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), IDip (1,3-bis(2,6-diisopropylphenyl)-
imidazol-2-ylidene), SIMes (1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene)] in the presence of
NH4PF6, to yield the cationic products [Pd(C,N-C6H4CH2NMe2)(S2C·NHC)]+. In a similar fashion, the
compounds [Pd(C,N-bzq)(S2C·NHC)]+ (bzq = benzo[h]quinolinyl, NHC = ICy, IMes, IDip) are obtained
from the corresponding dimer [Pd(C,N-bzq)Cl]2. The bis(phosphine) compounds [Pd(S2C·NHC)-
(PPh3)2]2+ (NHC = ICy, IMes, IDip, SIMes) are obtained on treatment of [PdCl2(PPh3)2] with NHC·CS2
zwitterions in the presence of NH4PF6. The reaction of [PdCl2(dppf)] with IMes·CS2 and NH4PF6
provides the complex [Pd(S2C·IMes)(dppf)]2+. The complexes [Pd(S2C·NHC)(PPh3)2](PF6)2 (NHC =
IMes, IDip) were active pre-catalysts (1 mol% loading) for the conversion of benzo[h]quinoline to 10-
methoxybenzo[h]quinoline in the presence of PhI(OAc)2 and methanol. The intermediacy of [Pd(C,N-
bzq)(S2C·NHC)]+ was supported by the high yield of 10-methoxybenzo[h]quinoline using [Pd(C,N-bzq)-
(S2C·IDip)]+ to promote the same reaction. Small amounts of 2,10-dimethoxybenzo[h]quinoline were also
isolated from these reactions. Using [Pd(C,N-bzq)(S2C·IDip)]+ and N-chlorosuccinimide as the oxidant
led to the formation of 10-chlorobenzo[h]quinoline in moderate yield from benzo[h]quinoline. The
molecular structures of [Pd(S2C·IMes)(PPh3)2](PF6)2 and [Pd(S2C·IMes)(dppf)](PF6)2 were determined
crystallographically.
ligands which are often neglected, the dithiocarboxylates
Introduction
(RCS2−, where R is a carbon-based substituent). Due to the syn-
thetic difficulties encountered in their preparation, they have
been employed only sporadically in the preparation of sulfur
chelates.1,7
A huge number of complexes bearing 1,1-dithio ligands are
known in the literature.1–5 Amongst them, compounds with
− 1–4
dithiocarbamate (R2NCS2
)
or xanthate functional groups
− 1,2,5
N-Heterocyclic carbenes (NHCs)8,9 are another class of
ligands which have acquired a prominent position in organo-
metallic chemistry and homogeneous catalysis as robust, electron-
rich alternatives to phosphines.10,11 Archetypal examples of
NHC-based catalyst precursors include the Grubbs second gen-
eration metathesis initiator [Ru(vCHPh)Cl2(SIMes)(PCy3)]12
(SIMes is 1,3-dimesitylimidazolin-2-ylidene) and the copper(I)
compounds [CuX(NHC)] (X = halide) used extensively in
‘click’ chemistry.13 Moreover, the potential of NHCs extends
well beyond their use as monodentate carbon-bonded ligands.
This has been demonstrated in the abundance of ligand systems
in which pendant donors available for coordination have been
added to a central carbene unit. Versions with sulfur arms have
been explored in a variety of palladium-catalysed carbon–carbon
coupling reactions.14,15 Braunstein and co-workers recently
reported an interesting variation on NHC pincer complexes with
two thioether donors, which were catalytically active in Suzuki–
Miyaura cross-coupling reactions.14n Conventional 1,1-dithio
ligands are rarely found in catalysis, though some disulfur
(ROCS2
)
dominate. This is not surprising given the great
synthetic ease with which these anions are obtained from the
reaction of carbon disulfide with amines under basic conditions
or alkoxides and aryloxides, respectively. In order to expand the
potential of these ligands beyond simple alkyl or aryl substitu-
ents, we have been involved in a programme to introduce
additional functional groups on their substituents.6 More
recently, our attention has turned to another class of 1,1-dithio
aDepartment of Chemistry, Imperial College London, South Kensington
Campus, London SW7 2AZ, UK. E-mail: j.wilton-ely@imperial.ac.uk
bLaboratory of Organometallic Chemistry and Homogeneous Catalysis,
Institut de Chimie (B6a), Université de Liège, Sart-Tilman par 4000
Liège, Belgium
†Dedicated to Professor David Cole-Hamilton on the occasion of his
retirement and for his outstanding contribution to transition metal
catalysis.
‡Electronic supplementary information (ESI) available. CCDC 880366
(2) and 880367 (5). For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c2dt31413d
12386 | Dalton Trans., 2012, 41, 12386–12394
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Fig. 1 N-Heterocyclic carbene-derived dithiocarboxylate ligands used in this research.
(but not 1,1-dithio) examples are known in the field of asym-
metric catalysis.16 This is perhaps surprising given that an impor-
tant industrial process – the promotion of cross-linking in rubber
vulcanisation – involves catalysis performed by zinc dithiocarba-
mate complexes.17
to explore a catalytic reaction in which the suitability of com-
plexes bearing a range of NHC·CS2 ligands could be compared.
In this contribution, we report the synthesis and characteris-
ation of the first palladium imidazol(in)ium-2-dithiocarboxylate
complexes that extend beyond the simple homoleptic examples
reported by Borer and co-workers.20 For this purpose, five
representative NHC·CS2 zwitterions bearing alkyl or aryl groups
on their nitrogen atoms were used as ligands (Fig. 1). The
association of these ligands to ruthenium–arene complexes21 did
not lead to catalytically active species due to the strong chelate
effect and the coordinative saturation of the metal centre. From
this point of view, the 16-electron compounds described here are
more promising candidates for use in a catalytic setting, particu-
larly in terms of the tuneable steric bulk of the substituents on
their nitrogen atoms. Therefore, we have investigated their cata-
lytic potential in the oxidative C–H functionalization of benzo[h]-
quinoline.
In addition to the huge impact of N-heterocyclic carbenes8,9 as
ligands of choice for many transition metal catalysts,10,11 the
potential of these divalent carbon species to generate other
ligand systems has been explored sporadically.18 One such
avenue of investigation is the facile reaction of NHCs with the
heteroallenes COS, CS2 and RNCS to afford the corresponding
betaines NHC·C(A)S (where A = S, O, NPh).19 The dithio-
carboxylate adducts of NHCs display arguably the greatest
potential for coordination chemistry. Early work carried out
in 1986 demonstrated that 1,3-dimethylimidazolium-2-dithio-
carboxylate formed stable complexes with a number of transition
metal halides or nitrates.20 The precise structure of these com-
pounds remained unclear for many years, possibly contributing
to their relative obscurity. In 2009, ruthenium–arene complexes
bearing NHC·CS2 ligands were prepared and fully characterized
in a thorough, systematic study of the coordination chemistry of
these zwitterions.21 This initiated our interest in further exploring
the potential of NHC·C(A)S ligands for coordination to a range
of metals.22 One of us has also investigated the catalytic activity
of ruthenium–arene complexes bearing NHC·C(A)S ligands in
various reactions (olefin metathesis, atom transfer radical reac-
tions, enol ester synthesis). Stable Ru(S2C·NHC) chelates were
found to be devoid of any significant activity in these transfor-
mations,21a except under forcing conditions.21b Monodentate
Ru(SOC·NHC) compounds performed better, but this was most
likely due to their rapid dethiocarboxylation under the experi-
mental conditions adopted to generate active Ru–NHC species.23
Although metal-based catalysis has been disappointing so far,
NHC·CS2 betaines24a and their thiocarboxylate analogues24b
have recently been employed in organocatalysis.
Results and discussion
In the presence of an excess of NH4PF6, the reaction of
[PdCl2(PPh3)2] with ICy·CS2 in dichloromethane and methanol
led to the formation of [Pd(S2C·ICy)(PPh3)2](PF6)2 (1)
(Scheme 1). The dark yellow product was isolated in 64% yield
after recrystallisation. 31P NMR analysis revealed the formation
of a new compound with a singlet resonance at 32.3 ppm. The
incorporation of the zwitterionic ligand was evident from the
1H NMR spectrum with a singlet at 7.60 ppm for the imida-
zolium backbone and a multiplet at 4.53 ppm for the NCH
protons of the cyclohexyl substituents. The remaining aliphatic
protons appeared as multiplets between 1.23 and 2.07 ppm,
while further aromatic signals located between 7.39 and
7.55 ppm were assigned to triphenylphosphine. Little change
was observed in the solid-state infrared spectrum of the complex
compared to the uncoordinated ligand apart from the presence of
additional features associated with the PPh3 units. The overall
formulation of 1 was confirmed by a molecular ion in the mass
spectrum at m/z 938 and a good agreement of elemental analysis
with the calculated values.
An earlier study exploring the coordination chemistry of
NHC-derived dithiocarboxylate ligands with ruthenium(II) carbo-
nyl compounds showed that variations to the steric profile of the
NHC did not result in changes to the νCO frequency.22d This
suggests that, unlike phosphines, the steric bulk of the NHC·CS2
ligands can be varied without changing their electronic proper-
ties – a potentially useful attribute. In other 1,1-dithio ligands,
such as dithiocarbamates (R2NCS2−) and xanthates (ROCS2−),
the bulk of the substitutents (R) is too remote to affect the metal
centre. This is not the case for NHC·CS2 betaines, which have
been shown to induce the adoption of a cis-arrangement in bis-
(phosphine) systems when the NHC is bulky.25 Thus, we sought
The red mesityl derivative [Pd(S2C·IMes)(PPh3)2](PF6)2 (2)
was prepared in a similar manner to 1 in 81% yield. Recrystalli-
sation of this compound by slow diffusion of petroleum ether
into a dichloromethane solution afforded large red blocky
needles suitable for X-ray diffraction analysis (Fig. 2, see also
the following section). Likewise, the SIMes·CS2 ligand featuring
a saturated imidazolinium backbone was employed to prepare
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Scheme 1 Formation of palladium imidazol(in)ium-2-dithiocarboxylate complexes 1–13. Hexafluorophosphate counteranions are present in all
complexes.
Fig. 2 Molecular structure of [Pd(S2C·IMes)(PPh3)2](PF6)2 (2). Hydro-
Fig. 3 Molecular structure of [Pd(S2C·IMes)(dppf)](PF6)2 (5). Hydro-
gen atoms, hexafluorophosphate counteranions, and co-crystallised
gen atoms, hexafluorophosphate counteranions, and co-crystallised
solvent molecules were omitted for clarity. Selected bond distances (Å)
solvent molecules were omitted for clarity. Selected bond distances (Å)
and angles (°): Pd–P(46) 2.3099(6), Pd–P(27) 2.3202(5), Pd–S(3)
and angles (°): Pd(1)–P(50) 2.2931(6), Pd(1)–P(27) 2.3035(7), Pd(1)–
2.3340(6), Pd–S(1) 2.3724(6), S(1)–C(2) 1.683(2), C(2)–C(4) 1.452(3),
S(1) 2.3391(7), Pd(1)–S(3) 2.3681(7), S(1)–C(2) 1.685(3), C(2)–C(4)
C(2)–S(3) 1.692(2), C(4)–N(8) 1.350(3), C(4)–N(5) 1.352(3), C(6)–C(7)
1.461(3), C(2)–S(3) 1.684(3), C(4)–N(8) 1.347(3), C(4)–N(5) 1.354(3),
1.346(4), S(3)–Pd–S(1) 73.71(2), S(1)–C(2)–S(3) 113.50(12), P(27)–Pd–
P(46) 100.97(2).
C(6)–C(7) 1.345(4), S(1)–Pd(1)–S(3) 73.89(2), S(3)–C(2)–S(1) 114.25(14),
P(27)–Pd–P(50) 98.24(2).
the deep red compound [Pd(S2C·SIMes)(PPh3)2](PF6)2 (3). The
main spectroscopic difference between this product and the
IMes·CS2 derivative (2) was the presence of a singlet at
4.49 ppm in the 1H NMR spectrum corresponding to the methyl-
ene bridging units of the heterocycle. Last but not least, the most
bulky of the dithiocarboxylate betaines shown in Fig. 1,
IDip·CS2, was used to prepare [Pd(S2C·SIDip)(PPh3)2](PF6)2 (4)
in an identical fashion to compounds 1–3.
[PdCl2(dppf)] (dppf is 1,1′-bis(diphenylphosphino)ferrocene)
(Scheme 1). With its chelating diphosphine ligand in place of
two triphenylphosphine ligands, this complex would also serve
as a comparison point for the catalytic investigations to come
(vide infra). Spectral data recorded for 5 were similar to those
observed for 2 apart from the resonances associated with the
ferrocene moiety at 4.47 and 4.63 ppm in the 1H NMR spectrum.
Single crystals of this heterobimetallic compound were also
obtained and a structural study undertaken (Fig. 3 and following
section).
In order to extend the scope of our methodology, we prepared
the
compound
[Pd(S2C·IMes)(dppf)](PF6)2
(5)
from
12388 | Dalton Trans., 2012, 41, 12386–12394
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Palladium is known to undergo cyclometallation reactions
readily, often resulting in halide bridged compounds.26 These
dimers are useful precursors for the synthesis of organometallic
complexes bearing bidentate chelates.6b,d,h A representative start-
ing compound, [Pd(C,N-C6H4CH2NMe2)Cl]2, was employed to
prepare the first organopalladium examples with an NHC·CS2
ligand (Scheme 1). The dimer was treated with two equivalents
of IPr·CS2 in the presence of excess ammonium hexafluoro-
phosphate to provide an orange solid in 76% yield after work up.
Retention of the cyclometallated ligand was confirmed by the
presence of singlets at 3.06 (NMe2) and 4.14 (CH2N) ppm in the
1H NMR spectrum, while the IPr ligand gave rise to resonances
at 7.61 (CHvCH), 4.94 (exocyclic NCH) and 1.65 (CH3) ppm.
The overall formulation was confirmed as [Pd(C,N-C6H4CH2-
NMe2)(S2C·IPr)]PF6 (6) by mass spectrometry (m/z 468) and
good agreement of the elemental analysis with calculated values.
The slightly bulkier ICy derivative, [Pd(C,N-C6H4CH2NMe2)-
(S2C·ICy)]PF6 (7), was prepared in the same manner. The
spectroscopic data pertaining to the NHC·CS2 ligand for [Pd(C,
N-C6H4CH2NMe2)(S2C·IMes)]PF6 (8) and [Pd(C,N-C6H4-
CH2NMe2)(S2C·SIMes)]PF6 (9) were found to be similar to
distances recorded in this study along with some related literature
data are collected in Table 1. Multiple bond character is clearly
present in all the compounds under scrutiny with values
approaching typical CvS double bond lengths (1.67 Å) rather
than C–S single bonds (1.75 Å).27 The S–C–S bond angles of
113.50(12)° for 2 and 114.25(14)° for 5 are clearly different, but
vary relatively little in the context of related bidentate ruthenium
complexes shown in Table 1. In acyclic carbenium dithiocarboxy-
lates28 and imidazol(in)ium-2-dithiocarboxylates,29 the anionic
and cationic units usually have almost orthogonal orientations in
the crystal structures, and this conformation is largely retained
upon complexation, as exemplified by the ruthenium and gold
complexes listed in Table 1. In the structures of 2 and 5, conver-
sely, the two units are approximately coplanar, the torsion angles
about the linking C–C bond being ca. 11° and 17°, respectively.
A tendency towards orthogonality in free dithiocarboxylate
betaines is often attributed to coulombic interactions.29f In the
compounds investigated here, it is unclear whether steric or
crystal packing effects are preventing this from occurring. The
bond lengths of the N2C+ motif in 2 [1.350(3) Å, 1.352(3) Å]
and 5 [1.347(3) Å, 1.354(3) Å] are the same. They are also
shorter than typical C–N single bonds (1.47 Å),27 indicating
significant CvN double bond character due to electronic
conjugation.
those observed for
2 and 3, respectively. An example
bearing the most bulky ligand shown in Fig. 1, [Pd(C,N-
C6H4CH2NMe2)(S2C·IDip)]PF6 (10) was also synthesised in
good yield.
Catalytic studies
Structural analysis
Palladium-catalysed coupling reactions are now some of the
most useful and widely employed tools in synthetic organic
chemistry. The majority of these reactions are thought to involve
zerovalent palladium species in the catalytic cycle, even if diva-
lent pre-catalysts, such as [PdCl2(PPh3)2] are often employed.
Sanford and co-workers have shown that a range of oxidative
C–H functionalization reactions are catalysed by palladium(II)
compounds, often using palladium acetate as the pre-catalyst.30
This prompted us to use the conversion of benzo[h]quinoline
to 10-methoxybenzo[h]quinoline as a benchmark reaction to
The structures of both complex 2 and 5 are based on a distorted
square planar arrangement with cis-interligand angles in the
range 73.71(2)–100.97(2)° and 73.89–98.24(2)°, respectively. In
each case, the smallest of these angles is the S–Pd–S bite angle
of the NHC·CS2 ligand. In both structures the chelates are asym-
metric (the Pd–S bond lengths being 2.3340(6) and 2.3724(6) Å
in 2, and 2.3391(7) and 2.3681(7) Å in 5), though this asymme-
try does not extend to the C–S bonds, which range between
1.683(2) and 1.692(2) Å across the two structures. The C–S
Table 1 Bond data for various transition metal complexes featuring NHC·CS2 ligands
Complex
Reference
This work
This work
22b
C–S (Å)
S–C–S (°)
113.50(12)
114.25(14)
113.26(17)
114.7(4)
S–C–C–N (°)
12.0
[Pd(S2C·IMes)(PPh3)2]+ (2)
[Pd(S2C·IMes)(dppf)]+ (5)
[Ru(CHvCHC6H4Me-4)(S2C·ICy)(CO)(PPh3)2]+
[Ru(C(CuCPh)vCHPh)(S2C·ICy)(CO)(PPh3)2]+
[RuCl(p-cymene)(S2C·IMes)]+
[(Ph3P)Au(S2C·IMes)]+
1.683(2)
1.692(2)
1.684(3)
1.685(3)
1.685(3)
1.691(3)
1.663(7)
1.690(7)
1.680(3)
1.673(2)
1.640(3)
1.708(3)
1.6420(16)
1.7027(14)
1.639(4)
1.701(4)
1.643(4)
1.702(5)
17.4
38.5
22c
46.4
21a
112.3(2)
48.1
22a
128.26(15)a
129.63(9)a
130.1(2)a
128.3(2)a
57.4
[(Ph3P)Au(S2C·IDip)]+
22a
73.1
[(IDip)Au(S2C·IPr)]+
22a
77.0
[(IDip)Au(S2C·IMes)]+
22a
54.7
a Monodentate coordination.
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Scheme 2 Selective C–H oxidative functionalization of benzo[h]-
Scheme 3 Selective C–H oxidative chlorination of benzo[h]quinoline.
quinoline.
10-position is very high, it is not exclusive, and the dithio-
carboxylate complexes reported here are capable of forming
disubstituted products. The mechanism by which this reaction
takes place is difficult to surmise as the cyclometallation of the
substrate, which leads to the high selectivity for the 10-position
in benzo[h]quinoline, is unlikely to take place at the 2-position.
Instead, a bimetallic, intermolecular activation pathway could be
responsible for the second methoxylation.
explore the catalytic potential of the compounds prepared in this
study. Sanford reported that this transformation proceeded in
94% yield in methanol using 1.2 mol% Pd(OAc)2 and a sacrifi-
cial oxidant at 100 °C for 22 h (Scheme 2).30a When the reaction
was performed using a 1 mol% loading of [Pd(S2C·ICy)-
(PPh3)2](PF6)2 (1), the desired product was isolated in 86% yield
after column chromatography. The use of complex 2 featuring
the IMes·CS2 zwitterion resulted in a higher yield (95%), while
the more bulky IDip version (4) gave the highest conversion
(96%). Thus, changes in the steric profile of imidazolium-
2-dithiocarboxylate ligands bearing aromatic substituents on
their nitrogen atoms play only a modest role in this particular
setting.
Using N-chlorosuccinimide as oxidant in place of PhI(OAc)2,
an acetonitrile solution of benzo[h]quinoline was converted
to 10-chlorobenzo[h]quinoline in 80% yield in the presence of
1 mol% of 13 (Scheme 3). Sanford et al. reported that the
same reaction with palladium acetate was sluggish30a and this
was found to be the case in this study with the reaction
mixture being heated at 100 °C for 44 h. Under these conditions,
the yield obtained was lower than the 95% value reported
by Sanford after 3 days of reaction and in both cases column
chromatography was required to purify the product. More impor-
tantly, this result provides additional support for the active cata-
lytic species being a palladium dithiocarboxylate unit. Given the
literature precedent for the use of Pd(OAc)2 in these transform-
ations, it is possible that the acetate released from the PhI(OAc)2
sacrificial oxidant would displace the dithiocarboxylate ligand,
forming a palladium acetate complex in situ, which could then
perform the catalysis. However, the performance of [Pd(C,N-
bzq)(S2C·Dip)]PF6 (13) with N-chlorosuccinimide as oxidant
provides evidence that high catalytic activity is also main-
tained in the absence of acetate, supporting the involvement
of a Pd(S2C·NHC) species in the catalytic cycle. This is not
surprising as the NHC·CS2 adducts are very robust in both
free31 and coordinated21 forms, in contrast to the carboxylate
analogues.32
In order to ascertain whether lability of the phosphines was
important, the transformation was attempted using the diphos-
phine derivative [Pd(S2C·IMes)(dppf)](PF6)2 (5). No significant
conversion was observed, which was ascribed to the lack of labi-
lity of the dppf chelate. To further probe the nature of the active
species, the residue at the end of the catalytic transformation per-
formed with 2 was analysed and found to display characteristic
resonances for the methyl substituents of the IMes·CS2 ligand at
1
2.12 and 2.40 ppm in the H NMR spectrum, slightly shifted
from their positions in precursor 2 (2.00 and 2.31 ppm) and
quite different to those of the free ligand (2.36 and 2.38 ppm).
These signals are likely due to a solvent-stabilised complex as
the reaction is performed in air and triphenylphosphine oxide is
identified by 31P NMR spectroscopy.
Sanford and co-workers showed that the cyclometallated
benzo[h]quinolinyl complex, [Pd(C,N-bzq)(OAc)]2, was also an
active (pre)catalyst for the reaction shown in Scheme 2.30 This
observation is in line with a mechanism involving cyclometalla-
tion of benzo[h]quinoline followed by attack of methanol at the
Pd–C bond. Accordingly, the series of benzo[h]quinolinyl com-
pounds [Pd(C,N-bzq)(S2C·NHC)]PF6 (NHC = ICy 11, IMes 12,
IDip 13) was prepared (Scheme 1). Compound 13 was investi-
gated in the conversion of benzo[h]quinoline to 10-methoxy-
benzo[h]quinoline under the same conditions as used previously,
giving a 69% yield with a 1 mol% catalyst loading. Shortening
the reaction time from 22 h to 17 h led only to a minor drop of
yield from 69% to 67%. Lower catalyst loadings for the reaction
were also explored. Hence, after 22 h, a 41% yield of
10-methoxybenzo[h]quinoline was obtained with 0.1 mol% of 2.
In an unexpected development, it was discovered that a small
amount of 2,10-dimethoxybenzo[h]quinoline (3%) was also
formed in the reaction using 1 mol% of 4 under literature con-
ditions. Separation of this by-product from the main 10-methoxy-
benzo[h]quinoline product (96%) was achieved by column
chromatography. This suggests that, although selectivity for the
Conclusion
Previous to this report, the only examples of palladium com-
plexes bearing NHC·CS2 ligands were simple homoleptic com-
pounds. Thus, the organopalladium and phosphine-based
complexes described here substantially broaden this class of
compounds. Moreover, for the first time, complexes bearing
imidazol(in)ium-2-dithiocarboxylate units were shown to be
effective pre-catalysts for an important and selective transform-
ation, namely oxidative C–H functionalisation. They were
able to achieve this both at a similar level of performance
and catalyst loading to the pre-eminent examples from the
literature. These results will help dispel the notion that
1,1-dithio ligands offer little in the design of highly active cata-
lytic species.
12390 | Dalton Trans., 2012, 41, 12386–12394
This journal is © The Royal Society of Chemistry 2012

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C58H54F12N2P4PdS2 (1301.49): C 53.5, H 4.2, N 2.2%; Found
C 53.6, H 4.3, N 2.1%.
Experimental section
General comments
[Pd(S2C·SIMes)(PPh3)2](PF6)2 (3). Dark red solid (28 mg,
All experiments were carried out under aerobic conditions and
the products obtained appear indefinitely stable towards the
atmosphere, whether in solution or in the solid state. The com-
57%). IR (solid): 2938, 1608, 1560, 1383, 1288, 1192, 879, 830
1
(νPF) cm−1
.
31P NMR (CD2Cl2): 32.4 (s, PPh3) ppm. H NMR
(CD2Cl2): 2.22 (s, 12H, o-CH3), 2.37 (s, 6H, p-CH3), 4.49 (s,
4H, H2CCH2), 6.98 (s, 4H, m-C6H2), 7.12–7.16, 7.32–7.35,
7.53–7.57 (3 m, 30H, PPh3) ppm. MS (FAB +ve) m/z (abun-
dance): m/z 1157 (8) [M + PF6]+, 1012 (15) [M]+. Analysis: Cal-
culated for C58H56F12N2P4PdS2 (1303.51): C 53.4, H 4.3, N
2.2%; Found C 53.6, H 4.2, N 2.1%.
30a
plexes [Pd(C,N-C6H4CH2NMe2)Cl]2,26 [Pd(C,N-bzq)(OAc)]2
cis-[PdCl2(PPh3)2]33 and [PdCl2(dppf)]34 were prepared accor-
ding to literature. The betaines IPr·CS2, ICy·CS2, IMes·CS2,
IDip·CS2 and SIMes·CS2 were prepared using an established
procedure.31 Solvents and other reagents were used as received
from commercial suppliers. Petroleum ether refers to the fraction
boiling in the 40–60 °C range. Electrospray mass spectra were
obtained using a Micromass LCT Premier instrument. Infrared
data were obtained using a Perkin-Elmer Spectrum 100 FT-IR
spectrometer. Characteristic triphenylphosphine-associated infra-
red data are not reported. Unless otherwise indicated, NMR
spectroscopy was performed at 25 °C using a Varian Mercury
300 spectrometer. All couplings are reported in Hertz. The reso-
nance for the hexafluorophosphate anion was observed in all
cases but is omitted from the NMR data below for reasons of
brevity. Elemental analyses were provided by London Metro-
politan University.
[Pd(S2C·IDip)(PPh3)2](PF6)2 (4). Dark red-brown solid
(38 mg, 72%). IR (solid): 3161, 2969, 2931, 1543, 1437, 1395,
1218, 1187, 1164, 998, 912, 877, 829 (νPF), 745 cm−1
.
1
31P NMR (CD2Cl2): 31.5 (s, PPh3) ppm. H NMR (CD2Cl2):
1.11 (d, 12H, CH3CHCH3, JHH = 6.8 Hz), 1.23 (d, 12H,
CH3CHCH3, JHH = 6.8 Hz), 2.17 (sept, 4H, CH3CHCH3, JHH
6.6 Hz), 7.09–7.13, 7.23–7.30, 7.49–7.53 (3 m, 36H, PPh3
=
+
C6H3), 7.97 (s, 2H, HCvCH) ppm. MS (FAB +ve) m/z (abun-
dance): 1157 (8) [M + PF6]+, 1012 (15) [M]+. Analysis: Calcu-
lated for C64H68F12N2P4PdS2 (1385.65): C 55.5, H 4.8, N 2.0%;
Found C 55.6, H 4.9, N 1.9%.
Synthesis of [Pd(S2C·IMes)(dppf)](PF6)2 (5)
Synthesis of [Pd(S2C·NHC)(PPh3)2](PF6)2 complexes
[PdCl2(dppf)] (27.5 mg, 0.038 mmol) and IMes·CS2 (15.7 mg,
0.041 mmol) were dissolved in chloroform (20 mL) and metha-
nol (10 mL). NH4PF6 (25 mg, 0.153 mmol) was added and the
reaction mixture was stirred for 2 h at room temperature. The sol-
vents were then removed under reduced pressure with a rotary
evaporator and a minimum amount of dichloromethane was
added to dissolve the residue. The resulting suspension was
filtered through Celite to remove NH4Cl and excess NH4PF6.
The filtrate was concentrated to ca. 2 mL and layered with
hexane to precipitate the deep red product overnight. The final
compound was washed with hexane (10 mL) and dried. Yield:
27 mg (53%). IR (solid state): 3175, 2925, 1480, 1435, 1401,
[PdCl2(PPh3)2] (27 mg, 0.038 mmol) and a NHC·CS2 ligand
(0.042 mmol) were dissolved in chloroform (20 mL) and metha-
nol (10 mL). NH4PF6 (25 mg, 0.153 mmol) was added and
the reaction mixture was stirred for 2 h at room temperature.
The solvents were then removed under reduced pressure with a
rotary evaporator and a minimum amount of dichloromethane
was added to dissolve the residue. The resulting suspension
was filtered through Celite to remove NH4Cl and excess
NH4PF6. The filtrate was concentrated to ca. 2 mL and layered
with hexane to precipitate the product overnight. The final com-
pound was washed with hexane (10 mL) and dried.
1386, 1308, 1229, 1168, 1097, 1031, 998, 904, 825 (νPF),
[Pd(S2C·ICy)(PPh3)2](PF6)2 (1). Yellow-brown solid (32 mg,
69%). IR (solid): 3173, 2939, 2862, 1481, 1452, 1436, 1313,
1
747 cm−1
.
31P NMR (CD2Cl2): 37.2 (s, dppf) ppm. H NMR
1276, 1192, 1046, 1015, 946, 875, 828 (νPF), 780, 710 cm−1
.
(CD2Cl2): 1.98 (s, 12H, o-CH3), 2.32 (s, 6H, p-CH3), 4.47, 4.63
(2 m, 8H, C5H4), 6.92 (s, 4H, m-C6H2), 7.42–7.49, 7.63–7.67
(3 m, 20H, C6H5), 7.75 (s, 2H, HCvCH) ppm. MS (FAB +ve)
m/z (abundance): 1185 (6) [M + PF6]+, 1040 (20) [M]+. Analy-
sis: Calculated for C56H52F12FeN2P4PdS2 (1333.30): C 50.5, H
3.9, N 2.1%; Found C 50.4, H 3.9, N 2.1%.
31P NMR (CD2Cl2): 32.3 (s, PPh3) ppm. H NMR (CD2Cl2):
1.23, 1.58–1.66, 1.72, 1.84, 2.04, 2.07 (6 m, 20H, cyclohexyl),
4.53 (tt, 2H, NCH-cyclohexyl, JHH = 6.6 Hz), 7.39–7.42,
7.46–7.55 (2 m, 30H, PPh3), 7.60 (s, 2H, HCvCH) ppm.
MS (FAB +ve) m/z (abundance): 938 (4) [M]+, 676 (14)
[M − PPh3]+. Analysis: Calculated for C52H54F12N2P4PdS2
(1229.43): C 50.8, H 4.4, N 2.3%; Found C 50.8, H 4.4,
N 2.2%.
1
Synthesis of [Pd(C,N-C6H4CH2NMe2)(S2C·NHC)]PF6 complexes
[Pd(C,N-C6H4CH2NMe2)Cl]2 (20 mg, 0.036 mmol) and a
[Pd(S2C·IMes)(PPh3)2](PF6)2 (2). Red solid (40 mg, 81%).
NHC·CS2 ligand (0.072 mmol) were dissolved in dichloro-
IR (solid): 3164, 2921, 1606, 1481, 1437, 1404, 1387, 1233,
methane (20 mL) and a solution of NH4PF6 (24 mg,
1000, 905, 827 (νPF), 774, 739 cm−1
.
31P NMR (CD2Cl2): 31.4
0.147 mmol) in methanol (10 mL) was added. The reaction
mixture was stirred for 2 h at room temperature. The solvents
were removed under reduced pressure with a rotary evaporator
and a minimum amount of dichloromethane was added to dis-
solve the residue. The resulting suspension was filtered through
Celite to remove NH4Cl and excess NH4PF6. The solvent was
(s, PPh3) ppm. 1H NMR (CD2Cl2): 2.00 (s, 12H, o-CH3) 2.31 (s,
6H, p-CH3), 6.91 (s, 4H, m-C6H2), 7.18–7.22, 7.29–7.32,
7.49–7.52 (3 m, 30H, PPh3), 7.77 (s, 2H, HCvCH) ppm. MS
(FAB +ve) m/z (abundance): 1155 (6) [M + PF6]+, 1010 (13)
[M]+, 748 (23) [M − PPh3]+. Analysis: Calculated for
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 12386–12394 | 12391

View Article Online
again removed and the residue was triturated ultrasonically in
diethyl ether (10 mL) to afford the product. The final compound
was washed with diethyl ether (10 mL) and dried.
solution of NH4PF6 (41 mg, 0.252 mmol) in methanol (10 mL)
was added. The reaction mixture was stirred for 2 h at room
temperature. The solvents were removed under reduced pressure
with a rotary evaporator and the residue was dissolved in a
minimum amount of dichloromethane before filtration through
Celite and removal of the dichloromethane under vacuum (rotary
evaporator). The residue was triturated with diethyl ether
(10 mL), filtered and dried in the air.
[Pd(C,N-C6H4CH2NMe2)(S2C·IPr)]PF6 (6). Orange solid
(33 mg, 75%). IR (solid): 3067, 2917, 2849, 1515, 1453, 1425,
1366, 1202, 1073, 911, 805 (νPF), 757, 722 cm−1 1H NMR
.
(CDCl3): 1.65 (d, 12H, CH3CHCH3, JHH = 6.7 Hz), 3.06 (s, 6H,
NMe2), 4.14 (s, 2H, CH2), 4.94 (s, 2H, CH3CHCH3, JHH
=
6.4 Hz), 7.02–7.19 (m, 4H, C6H4), 7.61 (s, 2H, HCvCH) ppm.
MS (ES +ve) m/z (abundance): 468 (100) [M]+. Analysis: Calcu-
lated for C19H28F6N3PPdS2 (613.96): C 37.2, H 4.6, N 6.8%;
Found C 37.3, H 4.5, N 6.7%.
[Pd(C,N-bzq)(S2C·ICy)]PF6 (11). Brown solid (49 mg, 53%).
IR (solid state): 3654, 2932, 2858, 2079, 1739, 1622, 1566,
1450, 1403, 1325, 1199, 1143, 1058, 831 (νPF), 754, 707 cm−1
.
1H NMR (CD2Cl2): 1.30–1.49, 1.73–1.85, 1.90–2.08, 2.24–2.37
(4 m, 20H, Cy), 4.59–4.73 (m, 2H, NCH-Cy), 7.22–7.29,
7.41–7.44, 7.53–7.57, 7.77, 7.86–7.92, 8.07–8.12, 8.48–8.54,
8.86–8.89 (8 m, 10H, HCvCH + bzq) ppm; MS (FAB +ve)
m/z (abundance): 592 (19) [M]+. Calculated for C29H32-
F6N3PPdS2·OEt2 (812.22): C 48.8, H 5.2, N 5.2%; Found: C
48.8, H 4.6, N 5.7%.
[Pd(C,N-C6H4CH2NMe2)(S2C·ICy)]PF6 (7). Brown solid
(34 mg, 68%). IR (solid): 3171, 2933, 2858, 1564, 1451, 1199,
1
1053, 833 (νPF), 750, 710 cm−1. H NMR (CDCl3): 1.33–1.41,
1.71–1.74, 1.92–1.95, 2.15–2.17 (4 m, 20H, cyclohexyl), 3.02
(s, 6H, NMe2), 4.10 (s, 2H, CH2NMe2), 4.44 (m, 2H, NCH-Cy),
7.00–7.15 (m, 4H, C6H4), 7.53 (s, 2H, HCvCH) ppm. MS
(ES +ve) m/z (abundance): 548 (22) [M]+. Analysis: Calculated
for C25H36F6N3PPdS2 (694.09): C 43.3, H 5.2, N 6.1%; Found
C 43.4, H 5.2, N 5.9%.
[Pd(C,N-bzq)(S2C·IMes)]PF6 (12). Brown solid (80 mg,
78%). IR (solid state): 3668, 3158, 2931, 1608, 1556, 1483,
1452, 1405, 1326, 1228, 1118, 1053, 832 (νPF), 720, 705 cm−1
.
1H NMR (CD2Cl2): 2.25 (s, o-CH3, 6H), 2.38 (s, o-CH3, 6H),
2.46 (s, p-CH3, 6H), 6.37, 6.65, 6.95, 7.13 (4 m, 4H, m-C6H2),
7.76 (s, HCvCH, 2H), 7.22–7.27, 7.32, 7.45–7.49, 7.57–7.61,
7.85, 7.99, 8.44–8.47, 8.59–8.61 (8 m, 8H, bzq) ppm. MS (FAB
+ve) m/z (abundance): 663 (35) [M]+. Calculated for
C35H32F6N3PPdS2 (810.17): C 51.9, H 4.0, N 5.2%; Found: C
51.8, H 4.0, N 5.1%.
[Pd(C,N-C6H4CH2NMe2)(S2C·IMes)]PF6 (8). Orange solid
(32 mg, 58%). IR (solid): 3165, 2921, 1607, 1579, 1556, 1484,
1452, 1383, 1230, 1119, 1061, 1020, 831 (νPF), 742, 723 cm−1
.
1H NMR (CD2Cl2): 2.19 (s, 12H, o-CH3), 2.39 (s, 6H, p-CH3),
2.79 (s, 6H, NMe2), 3.94 (s, 2H, CH2), 6.68–6.70, 6.89–6.92,
7.01–7.04 (3 m, 4H, C6H4), 7.10 (s, 4H, C6H2), 7.61 (s, 2H,
HCvCH) ppm. MS (ES +ve) m/z (abundance): 620 (23) [M]+.
Analysis: Calculated for C31H36F6N3PPdS2 (766.15): C 48.6,
H 4.7, N, 5.5%; Found C 48.6, H 4.7, N 5.6%.
[Pd(C,N-bzq)(S2C·IDip)]PF6 (13). Brown solid (82 mg, 73%).
IR (solid state): 3169, 2966, 2930, 1571, 1554, 1465, 1404,
1389, 1368, 1325, 1213, 1106, 1061, 1024, 915, 835 (νPF), 754,
[Pd(C,N-C6H4CH2NMe2)(S2C·SIMes)]PF6 (9). Dark red solid
724 cm−1. 1H NMR (CD2Cl2): 1.35, 1.42 (2 d, 24H, CH3, JHH
=
(49 mg, 89%). IR (solid): 2922, 1609, 1561, 1453, 1287, 1212,
6.8 Hz), 2.56 (sept, 4H, CHMe2, JHH = 6.7 Hz), 7.78 (s,
HCvCH, 2H), 7.03, 7.45–7.50, 7.57–7.61, 7.70–7.74, 7.85,
8.44–8.47, 8.56–8.58 (7 m, 14H, C6H3 + bzq) ppm. MS (FAB
+ve) m/z (abundance): 748 (100) [M]+. Calculated for
C41H44F6N3PPdS2·0.25CH2Cl2 (915.56): C 54.1, H 4.9, N
4.6%; Found: C 53.8, H 5.0, N 4.5%.
1098, 1023, 831 (νPF), 741 cm−1 1H NMR (CDCl3): 2.31
.
(s, 6H, p-CH3), 2.44 (s, 12H, o-CH3), 2.79 (s, 6H, NMe2), 3.91
(s, 2H, CH2), 4.51 (s, 4H CH2CH2), 6.75–6.77, 6.87–6.90,
6.93–6.98, 7.02–7.07 (4 m, 10H, C6H4 + C6H2) ppm. MS
(ES +ve) m/z (abundance): 622 (33) [M]+. Analysis: Calculated
for C31H38F6N3PPdS2 (768.15): C 48.5, H 5.0, N 5.5%; Found
C 48.6, H 4.9, N 5.4%.
Synthesis of 10-methoxybenzo[h]quinoline
[Pd(C,N-C6H4CH2NMe2)(S2C·IDip)]PF6 (10). Dark brown
solid (47 mg, 77%). IR (solid): 3149, 2966, 2927, 2871, 1545,
Methanol (7.5 mL) was added to a mixture of benzo[h]quinoline
(151 mg, 0.843 mmol), PhI(OAc)2 (541 mg, 1.680 mmol) and
the palladium complex (1 mol%, 0.0084 mmol) in a 20 mL vial.
The vial was sealed with a screw cap lined with Teflon and the
solution was heated with stirring to 100 °C for 22 h. The solvent
was then removed with a rotary evaporator and the crude solid
was purified by column chromatography on silica gel (eluent:
3 : 2 v/v ethyl acetate–n-hexane). The desired yellow-orange
product was the last fraction eluted. All the solvents were
removed and the pale yellow product was dried under vacuum.
Spectroscopic and analytical data agreed well with the values
reported in the literature.30a Yields for the 22 h runs using cata-
lyst 1: 151 mg, 86%; 2: 167 mg, 95%; 4: 169 mg, 96%; 13:
121 mg, 69% (1 mol% in all cases). Yield for the 17 h run using
catalyst 13 (1 mol%): 118 mg, 67%. Yield for the 22 h run using
catalyst 2 (0.1 mol%): 71 mg, 40%.
1469, 1390, 1220, 1100, 1063, 1046, 1000, 833 (νPF), 801,
1
730 cm−1. H NMR (CDCl3): 1.28 (d, 12H, CH3CHCH3, JHH
=
6.8 Hz), 1.30 (d, 12H, CH3CHCH3, JHH = 6.9 Hz), 2.43 (sept,
4H, CH3CHCH3, JHH = 6.8 Hz), 2.77 (s, 6H, NMe2), 3.92 (s,
2H, CH2), 6.58–6.60, 6.91–6.97, 7.03–7.06 (3 m, 4H, C6H4),
7.34 (d, 4H, m-C6H3, JHH = 7.9 Hz), 7.59 (t, 2H, p-C6H3,
JHH = 7.8 Hz), 7.89 (s, 2H, HCvCH) ppm. MS (ES +ve)
m/z (abundance): 704 (32) [M]+. Analysis: Calculated for
C37H48F6N3PPdS2 (850.31): C 52.3, H 5.7, N 4.9%; Found C
52.5, H 5.7, N 4.8%.
Synthesis of [Pd(C,N-bzq)(S2C·NHC)]PF6 complexes
[Pd(C,N-bzq)Cl]2 (40 mg, 0.063 mmol) and a NHC·CS2 ligand
(0.126 mmol) were dissolved in dichloromethane (20 mL) and a
12392 | Dalton Trans., 2012, 41, 12386–12394
This journal is © The Royal Society of Chemistry 2012

View Article Online
Synthesis of 2,10-dimethoxybenzo[h]quinoline
diffractometer; 13 549 independent measured reflections (Rint
=
0.0289), F2 refinement,35 R1(obs) = 0.0396, wR2(all) = 0.0895,
10 406 independent observed absorption-corrected reflections
[|Fo| > 4σ(|Fo|), 2θmax = 59°], 736 parameters. CCDC 880367.
The same procedure was used as above for 10-methoxybenzo[h]-
quinoline using benzo[h]quinoline (151 mg, 0.843 mmol) with
[Pd(S2C·IDip)(PPh3)2](PF6)2 (4, 11.6 mg, 0.0084 mmol) as cata-
lyst. Using a 1 : 1 v/v ethyl acetate–n-hexane mixture, the second
eluted compound was collected. All the solvents were removed
and the yellow oil was dried under vacuum (6 mg, 3%). 169 mg
(96%) of 10-methoxybenzo[h]quinoline was also isolated.
IR (solid): 2937, 2857, 1717, 1592, 1562, 1453, 1433, 1385,
Acknowledgements
We thank Johnson Matthey Ltd for a generous loan of palladium
salts.
1317, 1260 (νCO), 1194, 1122, 1072, 1030, 964 cm−1. H NMR
1
(CDCl3): 4.15 (s, 3H, CH3), 4.28 (s, 3H, CH3), 7.33 (dd, 1H,
bzq-H, JHH = 8.0, 1.1 Hz), 7.60 (dd, 1H, bzq-H, JHH = 7.9,
1.1 Hz), 7.71 (t, 1H, bzq-H, JHH = 7.9 Hz), 7.75 (d, 1H, bzq-H,
JHH = 8.8 Hz), 7.92 (d, 1H, bzq-H, JHH = 8.8 Hz), 8.34 (d, 1H,
bzq-H, JHH = 8.2 Hz), 8.39 (d, 1H, bzq-H, JHH = 8.2 Hz) ppm.
13C NMR (CDCl3): 166.3 (s), 159.3 (s), 146.8 (s), 145.9 (s),
137.5 (s), 136.8 (s), 130.9 (s), 130.3 (s), 129.1 (s), 125.8 (s),
121.4 (s), 121.3 (s), 110.6 (s), 56.8 (s), 53.1 (s) ppm. MS (FAB)
m/z (abundance): 239 [M]+. Calculated for C15H13NO2 (239.27):
C 75.3, H 5.5, N 5.9%; Found: C 75.1, H 5.3, N 5.9%.
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Synthesis of 10-chlorobenzo[h]quinoline
Acetonitrile (7.5 mL) was added to a mixture of benzo[h]-
quinoline (159 mg, 0.887 mmol), N-chlorosuccinimide (137 mg,
1.026 mmol) and [Pd(C,N-bzq)(S2C·IDip)]PF6 (13, 8 mg,
0.0089 mmol) in a 20 mL vial. The vial was sealed with a screw
cap lined with Teflon and the solution was heated with stirring to
100 °C for 44 h. The solvent was removed with a rotary evapo-
rator and the crude solid was purified by column chromato-
graphy on silica gel (eluent: 1 : 4 v/v ethyl acetate–n-hexane).
After unreacted benzo[h]quinoline was eluted, the second
fraction was carefully collected and the solvents removed. The
colourless solid was dried under vacuum to afford the product
(152 mg, 80%). Spectroscopic and analytical data agreed well
with the values reported in the literature.30a
10 For monographs, see: (a) N-Heterocyclic Carbenes in Synthesis,
ed. S. P. Nolan, Wiley-VCH, Weinheim, 2006; (b) N-Heterocyclic Car-
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ed. F. Glorius, Springer, Berlin, 2007, vol. 21; (c) N-Heterocyclic Car-
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Int. Ed., 2008, 47, 3122–3172; (b) J. C. Y. Lin, R. T. W. Huang,
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Crystallography
Crystals of compounds 2 and 5 were grown by slow diffusion of
petroleum ether (bp 40–60 °C) into a dichloromethane solution.
Crystal data for 2. [C58H54N2P2PdS2](PF6)2·1.5(CH2Cl2),
M = 1428.82, triclinic, P1 (no. 2), a = 11.1014(4), b = 14.2330(2),
ˉ
c = 20.2200(5) Å, α = 79.2326(18), β = 82.282(2), γ =
84.242(2)°, V = 3100.90(14) Å3, Z = 2, Dc = 1.530 g cm−3
,
μ(Mo-Kα) = 0.676 mm−1, T = 173 K, orange tabular needles,
Oxford Diffraction Xcalibur 3 diffractometer; 14 425 indepen-
dent measured reflections (Rint = 0.0202), F2 refinement,35
R1(obs) = 0.0359, wR2(all) = 0.0863, 11 951 independent
observed absorption-corrected reflections [|Fo|
2θmax = 59°], 783 parameters. CCDC 880366.
> 4σ(|Fo|),
12 (a) J. Huang, E. D. Stevens, S. P. Nolan and J. L. Petersen, J. Am. Chem.
Soc., 1999, 121, 2674–2678; (b) M. Scholl, S. Ding, C. W. Lee and
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1999, 121, 9531–9538; (b) A. S. Gruber, D. Zim, G. Ebeling,
Crystal data for 5. [C56H52FeN2P2PdS2](PF6)2·CH2Cl2, M =
1416.17, monoclinic, P21/c (no. 14), a = 10.6623(3), b =
20.1267(5), c = 27.4186(6) Å, β = 96.124(2)°, V = 5850.4(3) Å3,
Z = 4, Dc = 1.608 g cm−3, μ(Mo-Kα) = 0.906 mm−1, T = 173 K,
red blocky needles, Oxford Diffraction Xcalibur
3
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