The interaction between heteroditopic pyridine-nitrogen NHC with novel sulfur NHC ligands in palladium(0) derivatives: Synthesis and structural characterization of a bis-carbene palladium(0) olefin complex and formation in solution of an alkene-alkyne mixed intermediate as a consequence of the ligands hemilability

Article abstract of DOI:10.1016/j.ica.2012.04.018

We have synthesized a new class of heteroditopic chelating ligands bearing the phenylthiomethyl group and variously substituted imidazole derivatives and the corresponding complexes [Pd(η²-ma)(R-NHC-CH₂-SPh) (ma = maleic anhydride; R = methyl, mesityl, di-i-propylphenyl). We have compared their chemical characteristics and reactivity with those of similar palladium(0) complexes bearing the R-NHC-CH₂-Py ligands. The hemilability of the above-mentioned moieties is apparent when their palladium derivatives react with an excess of the same or different heteroditopic ligands. In these cases, we obtained complexes bearing maleic anhydride and two mono-coordinated heteroditopic ligands bound to the same metal center. However, at variance with the generally accepted opinion, precipitation of AgBr does not warrant the quantitative formation of the bis-heteroditopic Pd(0) derivative and in some cases, a reaction involving a heterogeneous equilibrium is observed. The reaction of the palladium(0) carbene-sulfur or carbene-nitrogen complexes with the alkyne dimethyl-2-butynedioate (dmbd) to give palladacyclometallate derivatives is not always warranted and formation of the intermediate [Pd(η²-ma)(η²-dmdb)(κ¹-Mes-NHC- CH₂-SPh)] is detected only in one case. Finally, we have carried out a diffractometric study on the solid-state structures of two derivatives and in particular we describe the configurations of the complex [Pd(η²- ma)(κ¹-Me-NHC-CH₂-SPh)₂] and of [Pd(η²-ma)(Me-NHC-CH₂-SPh)].

Full text of DOI:10.1016/j.ica.2012.04.018

Inorganica Chimica Acta 390 (2012) 105–118
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Inorganica Chimica Acta
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The interaction between heteroditopic pyridine–nitrogen NHC with novel sulfur
NHC ligands in palladium(0) derivatives: Synthesis and structural characterization
of a bis-carbene palladium(0) olefin complex and formation in solution
of an alkene–alkyne mixed intermediate as a consequence of the ligands
hemilability
a
a
a
b
Luciano Canovese a, , Fabiano Visentin , Carlo Levi , Claudio Santo , Valerio Bertolasi
⇑
a Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari, Venice, Italy
b Dipartimento di Chimica e Centro di Strutturistica Diffrattometrica, Università di Ferrara, Ferrara, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
We have synthesized a new class of heteroditopic chelating ligands bearing the phenylthiomethyl group
and variously substituted imidazole derivatives and the corresponding complexes [Pd(
2-ma)(R-NHC-
CH2-SPh) (ma = maleic anhydride; R = methyl, mesityl, di-i-propylphenyl). We have compared their
chemical characteristics and reactivity with those of similar palladium(0) complexes bearing the R-
NHC-CH2-Py ligands.
Received 14 February 2012
Received in revised form 4 April 2012
Accepted 10 April 2012
g
Available online 21 April 2012
The hemilability of the above-mentioned moieties is apparent when their palladium derivatives react
with an excess of the same or different heteroditopic ligands. In these cases, we obtained complexes bear-
ing maleic anhydride and two mono-coordinated heteroditopic ligands bound to the same metal center.
However, at variance with the generally accepted opinion, precipitation of AgBr does not warrant the
quantitative formation of the bis-heteroditopic Pd(0) derivative and in some cases, a reaction involving
a heterogeneous equilibrium is observed.
Keywords:
Palladium(0) carbene derivatives
Hetroditopic C–S, C–N carbene ligands
X-ray crystal structures
The reaction of the palladium(0) carbene–sulfur or carbene–nitrogen complexes with the alkyne
dimethyl-2-butynedioate (dmbd) to give palladacyclometallate derivatives is not always warranted
and formation of the intermediate [Pd(
one case.
g g j
2-ma)( 2-dmdb)( 1-Mes-NHC-CH2-SPh)] is detected only in
Finally, we have carried out a diffractometric study on the solid-state structures of two derivatives and
in particular we describe the configurations of the complex [Pd(
2-ma)( 1-Me-NHC-CH2-SPh)2] and of
[Pd(
2-ma)(Me-NHC-CH2-SPh)].
g
j
g
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
tant role as well, since it will restore the starting substrates by
re-coordinating the site made vacant as a consequence of the cat-
alytic activity of the complexes [2].
Catalysts should be simultaneously characterized by a remark-
able stability, a high reactivity and finally by selectivity toward the
formation of the reaction products. These peculiarities which
somehow might be considered chemically in conflict should all
be present when metal complexes bearing hemilabile ligands [1]
are used as catalysts. As a matter of fact, the introduction of a labile
terminus into chelating ligands should promote the activation of a
specific geometric site while the stability and the electronic
requirements of the related complexes should be warranted by
the pivot, which is the strong coordinating part of the ligands.
The dangling wing bearing the labile nucleophile plays an impor-
Several classes of complexes of different metals and hemilabile
ligands with a number of different scaffolds, different pivots and
labile donors were synthesized and recently reviewed [2,3]. Fur-
thermore, after the seminal article by Arduengo [4] a novel class
of the performing donor ligands NHC was available for the chem-
ists’ community and hence several new heteroditopic and hemila-
bile NHC-E (E = P, N, O) ligands soon appeared in the literature [5].
Owing to our interest on chelating ligands bearing thioetheric sul-
fur [6] and the scarcity of heteroditopic NHC-S spectator ligands in
the literature [7], we have synthesized some phenyl-thiomethyl-
carbene (R-NHC-CH2-SPh) (R = methyl, mesityl, di-i-propylphenyl)
derivatives and the corresponding low valent palladium complexes
and have compared their chemical characteristics and reactivity
⇑
Corresponding author.
E-mail address: cano@unive.it (L. Canovese).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.04.018

106
L. Canovese et al. / Inorganica Chimica Acta 390 (2012) 105–118
with those of the more studied R-NHC-CH2-Py palladium(0) com-
pounds [8].
represents a very efficient synthetic approach to palladium(0) car-
bene complexes [5e,5j,7e,11b,11c,12]. Thus, we have synthesized
the silver(I) NHC substrates according to the method reported in
the literature [5g,5h] and described in Scheme 2.
Moreover, we have carried out a diffractometric study on the
solid state structures of two olefin complexes and in particular
we describe the configuration of a complex bearing maleic anhy-
dride, Mes-NHC-CH2-Py and Me-NHC-CH2-SPh ligands coordinated
to the same metal center.
The disappearance of the solid Ag2O marks the reaction pro-
gress, whereas the 1H and 13C NMR spectra of the products confirm
the formation of the title complexes. In particular, the acid imi-
dazolium proton is no more detectable in the NMR spectra of the
silver derivatives and the coordinated imidazole carbon resonates
at about 180 ppm. Remarkably, the methylene groups CH2-Py or
CH2-S resonate as singlets thanks to the monocoordination of the
R-NHC-CH2-Py or R-NHC-CH2-SPh and the consequent free rotation
of the dangling uncoordinated wing bearing the thioether or pyri-
dine fragment.
2. Result and discussion
2.1. Synthesis of imidazolium bromide derivatives
The synthesis of the N-methylimidazolium (1a and 2a) and
N-arylimidazolium salts (1b, 1c, 2b and 2c) was easily achieved
in good yield (70–94%) by reacting 1-(2,4,6-trimethylphenyl)
imidazole, 1-(2,6-di-i-propylphenyl)imidazole [9] or commercial
1-methylimidazole with an almost equimolecular amount of chlo-
romethylphenylthioether or chloromethylpyridine in anhydrous
acetonitrile in the presence of KBr, according to the literature
procedure (Scheme 1): [10].
The formation of the imidazolium salts was easily detected by
1H and 13C NMR technique owing to the very low field resonance
of the acid imidazole proton between 10.0 and 10.5 and of the
imidazole carbon between 136 and 139 ppm. Notably, compounds
2b and 2c which are known were synthesized by means of a
slightly different procedure from that reported in the literature
[11] (see Section 4).
2.3. Synthesis of [Pd(g
2-ol)(NHC)] complexes
Taking advantage of the lability of COD, Cavell and co-workers
proposed the reaction between [Pd(
2-ma)(COD)] and free mono-
g
dentate NHC ligands for the synthesis of some novel palladium(0)
carbene derivatives [12]. However, such a direct approach is not
possible with our carbene ligands since they are not available as
free species. Therefore, we have reacted the same palladium(0)
precursor with the silver derivatives R-NHC-CH2-PyAgBr or R-
NHC-CH2-SPhAgBr. In order to minimize the decomposition of
[Pd(g
2-ma)(COD)], we have carried out the reaction by mixing
the reactants at 253 K. The gradual temperature increase to
273 K promotes the reaction progress and the separation of the
heteroditopic palladium(0) carbene complexes upon filtration of
AgBr (Scheme 3).
2.2. R-NHC-CH2-SPh and R-NHC-CH2-Py silver(I) complexes
The transmetalation protocol with silver(I) NHC derivatives
represents an advantageous and general synthetic procedure for
the obtainment of transition metal carbene substrates [5g,5h,11].
As a matter of fact, the stability of silver carbene complexes does
not require particular precautions and the synthesis of the
corresponding transition metal carbene substrates has usually a
remarkable yield. In particular, the transmetalation between
silver(I) NHC derivatives and palladium(0) olefin precursors
However, a limitation of such a method is represented by the
fact that the ensuing carbene derivatives can only bear maleic
anhydride (ma) or tetracyanoethene (tcne) since low valent palla-
dium COD complexes with other, even slightly less stabilizing ole-
fins are unstable and immediately decompose. The alternative
approach to obtaining palladium(0) olefin complexes of the type
[Pd(g2-ol)(L-L0)] (ol = ma, fn, tcne; L-L0 = NHC-Nitrogen) proposed
by Elsevier and co-workers, consisting in the reaction between
Scheme 1. Synthetic methodology for the preparation of compounds 1a–1c and 2a–2c.

L. Canovese et al. / Inorganica Chimica Acta 390 (2012) 105–118
107
Scheme 2. Synthetic methodology for the preparation of compounds 3a–3c and 4a–4c.
Scheme 3. Synthetic methodology for the preparation of compounds 5a–5c and 6a, 6b.
the complexes [Pd(
g
2-ol)(t-BuDAB)] (ol = ma, fn, tcne, t-BuDAB =
can be carried out at RT. However, addition of R-NHC-CH2-SPh-
AgBr to a solution of pyridylthioether palladium(0) derivatives
leads to the formation of an equilibrium mixture of differently
substituted species. This fact seems to suggest that the chelating li-
gands R-NHC-CH2-SPh are less efficient than R-NHC-CH2-Py in dis-
placing the pyridylthioether fragment.
The formation of the heteroditopic carbene olefin complexes
can be clearly deduced from their 1H and 13C NMR spectra. In par-
ticular, the olefin protons and carbons resonate at higher fields
N,N0-di-t-butyl-1,4-diaza-1,3-butadiene) and the silver carbene
derivatives NHC-NMe2AgBr [5g], NHC-pyridylAgBr, NHC-pic-
olylAgBr (ol = ma) [11c] and NHC-pyrimidylAgBr (ol = ma) [13b],
suggested to us an alternative protocol. Thus, we have reacted
the NHC silver(I) derivatives with complexes of the type
[Pd(g
2-ol)(MeN-SPh)] (ol = ma, nq, tmetc; MeN–SPh = 2-methyl-
6-sulfanylmethyl-pyridine) [14], the spectator ligand of which is
displaced very easily by several nucleophiles [14b]. Thus, we were
able to obtain the complexes of type [Pd(
(ol = nq, tmetc) (Scheme 4):
g
2-ol)(R-NHC-CH2-Py)]
than those of the uncoordinated ma (
respectively).
D
d ꢀ3–4 and ꢀ100 ppm,
Apparently, the complex [Pd(
g
2-ol)(MeN-SPh)] is more stable
In the low temperature (253 K) 1H NMR spectra of the com-
than [Pd(
g
2-ma)(COD)], thus the exchange reaction based on it
plexes bearing ma and R-NHC-CH2-SPh (5a–5c), the olefin protons

108
L. Canovese et al. / Inorganica Chimica Acta 390 (2012) 105–118
Scheme 4. Synthetic methodology for the preparation of compounds 7a–7c and 8a–8c.
always resonate as two doublets as a consequence of the asymme-
try of the spectator ligands. Consistently, at the same temperature
the olefin carbons show up as two separated signals.
At RT the olefin protons coalesce into two broad singlets. Such a
phenomenon was often attributed to an apparent olefin rotation
consisting in the de-coordination of the thioether wing followed
by ligand rotation about the Pd–C bond and re-coordination at
the opposite side (T-shape–Y-shape–T-shape mechanism). How-
ever, an alternative associative way triggered by the free electron
pair on the sp3 sulfur, cannot be ruled out [15].
Despite their diasterotopic nature at RT the CH2–S protons res-
onate as a broad singlet. This not unprecedented phenomenon is
probably due to inversion of the sulfur absolute configuration
due to fast exchange between the coordinated and the uncoordi-
nated doublet of sp3 sulfur [6a and refs. therein]. At low tempera-
ture (223 K), the broad singlet of complex 5c only splits into an AB
system.
derivatives by reacting the Pd(II) cyclo-octadiene substrates
[Pd(COD)(R)Cl], [Pd(COD)Cl2] or [Pd(NCMe)4](BF4)2 with the silver
complexes of heteroditopic carbene–pyridine, carbene–imine or
carbene–thioether respectively. Moreover, palladium(0) com-
plexes bearing two monocoordinating carbene and maleic anhy-
dride or tetracyanoethene have appeared so far in the literature
[12,18]. However, attempts to synthesize complexes bearing two
different heteroditopic carbenes simultaneously coordinated to
low valent palladium were never carried out.
Therefore, we have reacted the palladium(0) derivative 5a with
the silver(I) complex 4b in CH2Cl2 at RT. The ensuing fast reaction
yields quantitatively the complex 9 represented in Chart 1. The
structure of complex 9 in solution is deduced from its NMR spectra
and confirmed by a diffractometric study. In particular, the con-
comitant coordination of both carbenes is testified by the presence
of two distinct carbene carbon signals at 189.2 and 189.3 ppm in
the 13C NMR spectrum whereas the coordination of maleic anhy-
dride is confirmed by the presence of two doublets of the olefin
protons at 3.27 and 3.33 ppm in the 1H NMR spectrum. Curiously,
the CH2–Py and CH2–S protons resonate as two AB systems
although the sulfur and nitrogen are not bound to the metal center.
This is probably due to the crowded molecular structure which
hampers every rearrangement of the ligands, as can also be de-
duced from the hindered rotation of the mesityl ring about the
C–N bond. As already stated, the mono-crystal diffractometric
study of complex 9 confirms the proposed structure ( vide post,
Fig. 5a).
The 1H NMR spectra of the complexes 5b and 5c at 253 K dis-
play the net separation of the signals ascribable to the ortho methyl
protons of the mesityl and di-i-propylphenyl fragments, indicating
that the rotation of those groups about their bond with the imidaz-
ole nitrogen is hampered.
In agreement with previous findings [11c] the carbenic carbons
signal that is observed between 188.1 and 192.5 ppm exhibits a
low field shift as compared to that of the Ag(I) complexes.
Finally, it is noteworthy that the resolved solid state structure of
complex 5b confirms the observation reported above (vide post).
Also in the case of the complexes bearing R-NHC-CH2-Py and
naphthoquinone (7a–7c) the olefin protons are detected as broad
singlet in the RT 1H NMR spectra. However, this signal splits into
two separated signals at 253 K.
Owing to the ring inversion of the chelating ligand (olefin
apparent rotation) the CH2-Py protons which are detected as an
AB system at 253 K broaden at RT [11c].
The OCH3 protons of the tetramethylethene tetracarboxylate
derivatives (8a–8c) are detected at RT as two singlets. Probably,
due to the steric hindrance in the complexes no olefin apparent
rotation is operative in these cases.
2.4. Synthesis of bis-carbene palladium(0) olefin complexes
Taking advantage of the hemilability of these heteroditopic
ligands, we have explored the possibility of introducing another
carbene into the molecular scaffold of the palladium(0) olefin
derivatives. Mc Guiness and Cavell [8a], Frøseth [16] and Fliedel
and Braunstein [17] have obtained trans or cis bis-carbene
Chart 1. Topological representation of the complexes 9 and 10 bearing the two
monocoordinated ditopic carbenes and the olefin ma coordinated to palladium.

L. Canovese et al. / Inorganica Chimica Acta 390 (2012) 105–118
109
In order to verify the general validity of such a protocol we have
reacted palladium(0) and silver(I) complexes bearing the same car-
bene ligand. Thus, we have studied the reaction of the complex 5a in
CD2Cl2 with an equimolecular amount of the silver derivative 3a by
1H NMR at 298 K. Again, we have observed the fast and quantitative
formation in solution of a new compound which was identified as
complex 10 and isolated by addition of diethyl ether (Chart 1).
Surprisingly, the reaction between complexes 6b and 4b is not
quantitative and is better represented by an equilibrium involving
the incomplete displacement of the pyridine nitrogen of the coor-
dinated ligand Mes-NHC-Py by the carbene carbon of the same li-
gand despite the commonly accepted idea that precipitation of
insoluble AgBr should in any case drive this kind of reactions to
completion. As a consequence, the contemporary presence in solu-
tion of 6b, 4b and 11 is clearly observed in the ensuing NMR
spectrum whereas solid AgBr is detected as a cloudy suspension
(Chart 2; Fig. 1).
Addition to the solution of further amounts of 4b confirms the
equilibrium nature of the reaction which can be easily driven to
completion by addition of three equivalent of the silver derivative.
Similar equilibrium distributions can also be detected in the
case of the reaction between complexes 6a with 4a and 6a with
4b (or 6b with 4a). It is apparent that the equilibrium position
for these reactions is essentially determined by the insolubility of
AgBr which dissolves in CH2Cl2 in an almost negligible extent,
12. The presence of four distinct OCH3 signals at 3.40, 3.42, 3.68
and 3.73 ppm and of the displaced maleic anhydride at about
7 ppm testifies the formation of the metallacyclopentadienyl deriv-
ative (Fig 2). Consistently, the carbene carbon signal shifts from
188.1 ppm of the starting complex 6a to 180.5 ppm (see Section 4).
On the contrary, when complexes 5a, 5b and 6b react with
dmbd, an extensive decomposition with concomitant formation of
metallic palladium was observed. In order to explain such a differ-
ent behavior we resorted to an NMR study of the reaction between
5b and the alkyne dmbd at low temperature (CD2Cl2; 253 K). The
formation of a new organometallic species was immediately ob-
served. The detailed investigation of its 1H NMR spectrum strongly
suggests that the derivative [Pd(g g j
2-ma)( 2-dmdb)( 1-Mes-NHC-
CH2-SPh)] (13) bearing ma, dmbd and the monocoordinate car-
bene bound to palladium(0) is formed (Chart 3).
As a matter of fact, the olefin protons of the
g
2-coordinated
ma resonate as a couple of doublets at 4.02 and 4.51 ppm
(JHH = 4.5 Hz), whereas the coordinated dmbd displays two singlets
ascribable to the methyl protons of the non-equivalent methoxy
fragments at 3.70 and 3.96 ppm, respectively. Interestingly, owing
to the asymmetry of the intermediate, the CH2-S protons resonate
as an AB system irrespective of the fact that the sulfur remains
uncoordinated. This is probably due to the crowded molecular
structure of 13 which hampers the free rotation of the wing bear-
ing the thioether fragment, as was observed in the case of complex
9, the open structure of which was unambiguously determined.
Moreover, no uncoordinated ma is detectable in solution and the
methyl groups of the mesityl fragment resonate as three distinct
singlets since the free rotation of the latter is also hampered by ste-
ric hindrance (Fig. 3).
The HMQC spectrum confirms such an interpretation (see Sup-
plementary material, Fig. 1SI); in particular, the coordination of the
olefin ma is evident thanks to the cross-peaks between the olefin
carbons (61.8, 62.8 ppm) and the olefin protons (4.02, 4.51 ppm)
and to the signal resonance at lower field than that of the corre-
sponding starting olefin complex.
and by the efficiency of the carbene as strong
r-donor. These
two concomitant phenomena support the widespread idea that
these reactions are always quantitative. We have however shown
that the chelating effect can efficiently contrast the reaction pro-
gress, and when two R-NHC-CH2-Py carbene ligands are involved
at the same time, the reaction is not completely shifted to the right.
At variance, these reactions are quantitative when at least one
heteroditopic R-NHC-CH2-SPh carbene is involved. Evidently, the
coordinative capability of the phenyl substituted sulfur appears
to be less effective than that of the pyridine nitrogen, [6].
Further confirmation comes from the presence of the olefin car-
bonyl carbon resonances at 168.4 and 168.7 ppm, the signal of the
coordinated carbene carbon at 180.9 ppm and those of the non-
equivalent esteric carbons of the coordinated dmbd fragment at
159.8 and 160.8 ppm, respectively.
In some respect the compound 13 reminds similar species bear-
ing two olefins and one NHC ligand coordinated to palladium, the
existence of which was hitherto hypothesized by Cavell [19].
Moreover, beside the clear evidence displayed by the NMR spectra
2.5. Reaction of thepalladium(0) carbene derivatives with dimethyl-2-
butynedioate (dmbd)
We have also studied the attack of the activated alkyne
dimethyl-2-butynedioate (dmbd) on the complexes [Pd(g
2-ma)
(R-NHC-CH2-Py)] and [Pd(g
2-ma)(R-NHC-CH2-SPh)]. As can be
deduced from the 1H and 13C NMR spectra, the complex 6a reacts
at RT with dmbd in CD2Cl2 giving quantitatively the palladium(II)
cyclopentadienyl derivative [Pd(Me-NHC-CH2-Py)(C4(COOMe)4)]
Chart 2. Equilibrium reaction between complexes 6b and 4b yielding complex 11.

110
L. Canovese et al. / Inorganica Chimica Acta 390 (2012) 105–118
Fig. 1. Selected intervals of the 1H NMR spectra at 298 K of CD2Cl2 solution of: (a) complex 6b; [6b] = 1.5 ꢁ 10ꢂ2 M; (b) complex 4b; [4b] = 1.5 ꢁ 10ꢂ2 M; (c) product 11 (d)
from the equilibrium reaction between equimolecular amounts of complexes 4b and 6b (see Chart 2 and text).
Fig. 2. Selected intervals of the 1H NMR spectra at 298 K of CD2Cl2 solution of: (a) complex 6a; [6a] = 1.5 ꢁ 10ꢂ2 M; (b) complex 12; [12] = 1.5 ꢁ 10ꢂ2 M. (top insert)
topological representation of complex 12.
a theoretical investigation confirms the existence of a similar
structure [20] (Chart 3b).
upon increasing the temperature. Interestingly, the decomposition
of complex 5a promotes the formation of the examethylmellitate
derivative as can be deduced from the intense signal at 3.87 ppm
ascribable to its eighteen protons [21]. The progress of the reaction
yielding the palladacyclometallate product is probably controlled
by small differences in the steric and electronic demands among
the investigated complexes and in our case only the complex 6a ful-
fills those steric requirements.
Remarkably, a palladium(0) complex bearing one olefin and one
alkyne coordinated was hypothesised as a possible intermediate in
the case of the attack of an alkyne to an olefin derivative bearing a
pyridylthioether as spectator ligand, but in that case its presence in
solution was not detectable [21a]. The stability of such an interme-
diate might probably be traced back to the donor nature of carbene
and consequently to the high electron density on the Pd center
which can be consequently easily shared between the two electron
withdrawing unsaturated molecules.
2.6. Crystal structure determination
Increasing the temperature of the solution induces a general
decomposition with formation of metallic palladium and several
unidentified species.
Similar behavior is detectable in the case of complexes 5a and 6b
whereas, as already stated, only the complex 6a yields the pallada-
cyclopentadiene derivative [Pd(Me-NHC-CH2-Py)(C4(COOMe)4)]
ORTEP [22] views of complexes 5b and 9 are shown in Figs. 4a and
5a. A selection of bond distances and angles is given in Table 1. In
complex 5b the palladium is bonded to a dissymmetric NHC biden-
tate ligand through the carbene carbon and the sulfur atom of the
methylthiophenyl N-substituent and
double bond of maleic anhydride. In complex 9 the palladium is
g
2-coordinated to the C@C

L. Canovese et al. / Inorganica Chimica Acta 390 (2012) 105–118
111
bonds in the bis-carbene derivative 9 are lengthened with respect
to those of the Pd–Ccarbene complex 5b and of those of the chelate
heteroditopic complexes described elsewhere [5g,11c,13b] but
compare well with those of the similar complexes described in
Ref. [18]. This fact is probably due to the increased electronic charge
on the metal center. The C1@C2 alkene bond lengths of 1.430(4)
and 1.444(4) Å, for structures 5b and 9, respectively, are about
0.1 Å longer than in the free alkene and are consistent with p-back
bonding from Pd(0). The maleic anhydride rings are almost perpen-
dicular to the basal coordination plane forming angles of 82.43(7)°
with the Pd1, C1, C2, C5, S1 mean coordination plane of complex 5b
and of 79.5(8)° with the Pd1, C1, C2, C5, C16 mean coordination
plane of 9 (Figs. 4b and 5b).
In the crystals the molecules are held together by means of C–
H. . .O hydrogen bonds involving the oxygens of maleic anhydride
as acceptors (Table 2).
3. Conclusion
We have synthesized new thioether derivatives of imidazolium
salts 1a–1c, the corresponding silver bromide derivatives 3a–3c
and the palladium(0) complexes 5a–5c. We have compared the
chemical characteristics and reactivity of the latter with those of
complexes 6a and 6b bearing the carbene–pyridine R-NHC-CH2-
Py fragments as spectator ligands and resolved the solid state
structure of complex 5b.
Taking advantage of the hemilability of the above mentioned li-
gands we were able to obtain complexes with two mono-coordi-
nated heteroditopic ligands and maleic anhydride concomitantly
bound to the metal (complexes 9–11) by adding one more equiva-
lent of the silver carbenic precursor. From the NMR spectra of the
reaction solutions it was clear that, despite the precipitation of
AgBr an equilibrium mixture is often obtained in these cases. The
structure of complex 9 bearing two different heteroditopic carb-
enes and an olefin concomitantly coordinated to a palladium(0)
center, was determined by means of a diffractometric study. More-
over, in the attempt to obtain palladacyclometallate derivatives
bearing R-NHC-CH2-SPh or R-NHC-CH2-Py as ancillary ligands we
have reacted complexes 5a, 5b, 6a and 6b with the alkyne di-
methyl-2-butynedioate. The expected complex was obtained only
in the case of 6a, whereas complexes 5a, 5b and 6b undergo mas-
sive decomposition at RT. In the latter cases, the formation of an
intermediate bearing ma, dmbd and the monodentate heteroditop-
ic carbene coordinated to the same metal center was shown by
means of low temperature NMR spectra.
4. Experimental
4.1. Materials
Chart 3. (a) Topological representation of the complex 13 bearing the monocoor-
dinated ditopic carbene, the olefin ma and the alkyne dmbd coordinated and (b)
structure of the complex 13 theoretically determined (see text).
All solvents were purified by standard procedures and distilled
under argon immediately before use. 1D- and 2D-NMR spectra
were recorded using a Bruker 300 Avance spectrometer. Chemical
shifts (ppm) are given related to TMS (1H and 13C NMR). IR
spectra were recorded on a Perkin-Elmer Spectrum One spectro-
photometer.
bonded to two carbene carbons of two dissymmetric NHC ligands
and
In both structures the palladium center is trigonal planar, as ex-
pected for zero-valent complexes of the type [PdL0L00 2-alkene)].
g
2-coordinated to the C@C double bond of maleic anhydride.
(
g
All bond distances involving the Pd(0) metal are in reasonable
agreement with those in other complexes of Pd(0) with maleic
anhydride [18,23]. In complex 5b the Pd1–C2 length (2.125(3) Å)
is considerably longer than the corresponding Pd1–C1
(2.060(3) Å) owing to the trans influence exerted by the carbene
carbon of the ligand on the coordinated olefin, whereas the Pd–ole-
fin distances in the case of complex 9 are similar in agreement with
the findings of Lee et al. [18]. Remarkably, the Pd1–C5 and Pd1–C16
4.2. Computational details
Theoretical calculations were performed with the GAUSSIAN 09
[20] package using the functional hybrid meta-GGA M06 [20c]
and the Def2-TZVP basis set [20b]. The geometry optimization
was performed without any symmetry constraint, followed by ana-
lytical frequency calculation to confirm that a minimum had been
reached.

112
L. Canovese et al. / Inorganica Chimica Acta 390 (2012) 105–118
Fig. 3. Selected intervals of the 1H NMR spectra at 298 K of a CD2Cl2 solution of: (a) complex 5b; [5a] = 1.5 ꢁ 10ꢂ2 M and (b) compound 13.
Table 1
Selected bond distances and angles (Å and degrees).
5b
9
Distances
Pd1–C5
Pd1–S1
Pd1–C16
Pd1–C1
Pd1–C2
C1–C2
C5–N1
C5–N2
C16–N3
C16–N4
2.040(3)
2.4157(8)
2.067(3)
2.061(2)
2.101(3)
2.121(3)
1.444(4)
1.354(4)
1.357(4)
1.366(3)
1.362(3)
2.060(3)
2.125(3)
1.430(4)
1.359(3)
1.355(3)
Angles
C5–Pd1–S1
C5–Pd1–C16
C5–Pd1–C1
C5–Pd1–C2
S1–Pd1–C1
S1–Pd1–C2
C16–Pd1–C1
C16–Pd1–C2
C1–Pd1–C2
82.5(1)
98.6(1)
108.1(1)
147.9(1)
116.2(1)
155.5(1)
161.1(1)
121.7(1)
152.8(1)
113.4(1)
40.0(1)
39.9(1)
Dihedral Angles
Pd1,C1,C2,C5,S1 ^
C1,C2,C3,C4,O2
Pd1,C1,C2,C5,C16^
C1,C2,C3,C4,O2
82.43(7)
Fig. 4. (a) An ORTEP view of complex 5b showing the thermal ellipsoids at 30%
probability level. (b) The orientation of
the Pd coordination plane in complex 5b.
79.54(8)
g
2-maleic anhydride moiety with respect to
4.3. Crystal structure determinations
Crystallographic data (excluding structure factors) have been
deposited at the Cambridge Crystallographic Data center and allo-
cated the deposition numbers CCDC 848987 and CCDC 848988.
These data can be obtained free of charge via www.ccdc.cam.a-
c.uk/conts/retrieving.html or on application to CCDC, Union Road,
Cambridge, CB2 1EZ, UK (fax: +44 1223-336033, e-mail:
deposit@ccdc.cam.ac.uk).
The crystal data of compounds 5b and 9 were collected at room
temperature using a Nonius Kappa CCD diffractometer with graph-
ite monochromated Mo Ka radiation. The data sets were integrated
with the Denzo-SMN package [24] and corrected for Lorentz, polar-
ization and absorption effects (SORTAV). [25] The structures were
solved by direct methods using SIR97 [26] system of programs
and refined using full-matrix least-squares with all non-hydrogen
atoms anisotropically and hydrogens included on calculated posi-
tions, riding on their carrier atoms.
All calculations were performed using SHELXL-97 [27] and PARST
[28] implemented in WINGX [29] system of programs. The crystal
data are given in Table 1SI.
4.4. Synthesis of the precursors
The palladium precursors Pd2(DBA)3ꢃCH3Cl, [30] [Pd(
g
2-ma)-
COD], [31] [(2-methyl-6-(phenylthiomethyl)pyridine)palladium(0)
(naphthoquinone)] [23a] and [(2-methyl-6-(phenylthiomethyl)

L. Canovese et al. / Inorganica Chimica Acta 390 (2012) 105–118
113
Table 2
ene}silver bromide (4b) {[1-(2-pyridyl)methylene-3-(2,6-diisopro
pylphenyl)]imidazolyl-2-ene}silver bromide (4c) were prepared
following literature procedures [11c].
Hydrogen bond parameters (Å and degrees).
A–Hꢃ ꢃ ꢃB
A–H
Aꢃ ꢃ ꢃB
Symm. Op.
Hꢃ ꢃ ꢃB
A–Hꢃ ꢃ ꢃB
5b
4.7. [1-(Phenylthio)methylene-3-methyl]imidazolium bromide (1a)
C6–H6ꢃ ꢃ ꢃO3
0.93
3.167(4)
3/2 ꢂ x, y ꢂ 1/2,
z ꢂ 1/2
2.24
172
C16–H16Aꢃ ꢃ ꢃO1
C22–H22ꢃ ꢃ ꢃO2
C19–H19ꢃ ꢃ ꢃO2
0.96
0.93
0.93
3.449(5)
3.409(4)
3.527(3)
x ꢂ 1/2, 3/2 ꢂ y, z
x, y ꢂ 1.z
2.58
2.52
2.65
151
159
158
To a solution of 0.93 g (13.8 mmol) of N-methyl-imidazole in
anhydrous MeCN (40 ml), 2 g (12.6 mmol) of chloro-methyl-phe-
nyl-sulfide and 1.65 g (13.9 mmol) of KBr were added under inert
atmosphere (Ar).The resulting suspension was stirred for 48 h,
treated with 60 ml of CH2Cl2 and filtered on a Celite filter. The clear
solution was dried under vacuum and the residue was re-dissolved
in CH2Cl2 (2–3 ml) and re-precipitated with diethylether as a sticky
white solid. 2.68 g (yield 94%) of the title dry product were ob-
tained upon decantation and evaporation of the solvent.
1H NMR (CDCl3, T = 298 K, ppm) d: 3.99 (s, 3H, NCH3), 6.28 (s,
2H, SCH2), 5.86 (s, 2H, m-mesityl), 7.33 (m, 3H, SPh), 7.40 (t,
J = 1.8 Hz, 1H, CH@CH Im), 7.44 (m, 2H, SPh), 7.51 (t, J = 1.7 Hz,
1H, CH@CH Im), 9.99 (bs, 1H, NCHN). 13C {1H} NMR (CDCl3,
T = 298 K, ppm) d: 36.8 (CH3, NCH3), 53.4 (CH2, SCH2), 121.7 (CH,
CH@CH Im), 123.8 (CH, CH@CH Im), 128.8 (CH, SPh–CH), 129.7
(CH, SPh–CH), 130.4 (C, SPh–C), 132.2 (CH, CPh–CH), 136.5 (CH,
NCHN). Anal. Calc. for C11H13BrN2S: C, 46.32; H, 4.59; N, 9.82.
Found: C, 46.21; H, 4.62; N, 9.90%.
2 ꢂ x, 2 ꢂ y,
z ꢂ 1/2
9
C31–H31ꢃ ꢃ ꢃO3
0.93
0.93
0.97
3.364(5)
3.258(3)
3.439(3)
1/2 + x, 1/2 ꢂ y,
z ꢂ 1/2
2.48
2.40
2.55
159
153
152
C17–H17ꢃ ꢃ ꢃO3
C28–H28Bꢃ ꢃ ꢃO1
1/2 ꢂ x, y ꢂ
1/2, 1/2 ꢂ z
ꢂx, ꢂy, ꢂz
The following derivatives were prepared in a similar way using
the appropriate reactants.
4.8. [1-(Phenylthio)methylene-3-mesityl]imidazolium bromide (1b)
White micro crystals: Yield 77%. 1H NMR (CDCl3, T = 298 K,
ppm) d: 1.87 (s, 6H, o-mesityl-CH3), 2,33 (s, 3H, p-mesityl-CH3),
6.28 (s, 2H, SCH2), 6.95 (s, 2H, m-mesityl-H), 7.04 (t, J = 1.8 Hz,
1H, CH@CH Im), 7.35 (m, 3H, SPh), 7.62 (m, 2H, SPh), 7.69 (t,
J = 1.7 Hz, 1H, CH@CH Im), 10.22 (bs, 1H, NCHN).
13C {1H} NMR (CDCl3, T = 298 K, ppm) d: 17.3 (CH3, o-mesityl-
CH3), 20.9 (CH3, p-mesityl-CH3), 53.4 (CH2, SCH2), 121.7 (CH,
CH@CH Im), 122.8 (CH, CH@CH Im), 129.0 (CH, SPh–CH), 129.5
(C, SPh–C), 129.6 (CH, SPh–CH), 129.7 (CH, m-mesityl-CH), 130.2
(C, o-mesityl-C), 132.7 (CH, SPh–CH), 134.0 (C, SPh–C), 138.4 (CH,
NCHN), 141.4 (C, p-mesityl-C). Anal. Calc. for C19H21BrN2S: C,
58.61; H, 5.44; N, 7.19. Found: C, 58.59; H, 5.47; N, 7.12%.
Fig. 5. (a) An ORTEP view of complex 9 showing the thermal ellipsoids at 30%
probability level. (b) The orientation of
2-maleic anhydride moiety with respect to
the Pd coordination plane in complex 9.
g
4.9. [1-(Phenylthio)methyl-3-(2,6-di-i-propylphenyl)]imidazolium
bromide (1c)
White micro crystals: Yield 68%. 1HNMR (CD2Cl2, T = 298 K,
ppm) d: 1.06 (d, J = 6.8 Hz, 6H, iPr-CH3), 1.13 (d, J = 6.8 Hz, 6H,
iPr–CH3), 2.01 (sept, J = 6.8 Hz, 2H, iPr–CH), 6.42 (s, 2H, SCH2),
7.07 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.26 (d, J = 7.9 Hz, 2H, m-aryl-
H), 7.30–7.40 (m, 3H, SPh), 7.50 (t, J = 7.9 Hz, 2H, p-aryl-H), 7.65–
7.68 (m, 2H, SPh), 7.89 (d, J = 1.8 Hz, 1H, CH@CH Im), 10.37 (bm,
1H, NCHN). 13C {1H} NMR (CD2Cl2, T = 298 K, ppm) d: 23.8 (CH3,
iPr–CH3), 22.9 (CH3, iPr–CH3), 28.4 (CH, iPr–CH), 53.6 (CH2, SCH2),
122.0 (CH, CH@CH Im), 124.2 (CH, CH@CH Im), 124.5 (CH, m-
aryl-CH), 128.8 (CH, SPh–CH), 129.6 (CH, SPh–CH), 129.7 (C, i-
aryl-C), 129.8 (C, SPh–C), 131.7 (CH, p-aryl-CH), 132.3 (CH, SPh–
CH), 138.2 (CH, NCHN), 128.7 (C, o-aryl-C). Anal. Calc. for
pyridine)palladium(0)(tetramethyl ethene tetracarboxylate)] [23e]
were synthesized according to published procedures.
4.5. Synthesis of the N-arylimidazoles
The syntheses of the N-mesityl-imidazole and N-2,6-diisopro-
pylphenyl-imidazole were carried out according to the optimized
published procedure. [9] The nucleophilic attack of the appropriate
arylamine to oxalaldehyde in MeOH at RT was followed by the
cyclization reaction of the cheto-imino derivatives in the presence
of ammonium chloride, formaldehyde and phosphoric acid. The
reaction products were extracted in diethylether and re-crystal-
lized. The N-methyl-imidazole was a commercial product and used
as purchased.
C22H27BrN2S: C, 61.25; H, 6.31; N, 6.49. Found: C, 61.31; H, 6.28;
N, 6.53%.
4.10. [1-(2-Pyridyl)methylene-3-methyl]imidazolium bromide (2a)
4.6. Synthesis of the N-arylimidazolium salts
To an anhydrous MeCN solution (70 ml) of 3 g (23.5 mmol) of 2-
chloromethylpyridine (obtained by neutralization with Na2CO3 of
the corresponding hydrochloride), 4.13 g (34.5 mmol) of KBr and
2.1 ml (25.5 mmol) of N-methylimidazole were added under inert
[1-(2-Pyridyl)methylene-3-mesityl]imidazolium bromide (2b),
[1-(2-pyridyl)methylene-3-(2,6-di-i-propylphenyl)]imidazolium
bromide (2c) {[1-(2-pyridyl)methylene-3-mesetyl]imidazolyl-2-

114
L. Canovese et al. / Inorganica Chimica Acta 390 (2012) 105–118
atmosphere (Ar). The red-orange mixture was stirred for 48 h and
the solvent reduced to 3–4 ml under vacuum. An equivalent volume
of CH2Cl2 (70 ml) was then added and the resulting suspension was
filtered on a Celite filter. The clear solution was evaporated to dry-
ness and the reddish sticky residue was re-dissolved in CH2Cl2
(15 ml) and precipitated with diethylether (40 ml). 5.08 g (yield
87%) of red hygroscopic micro crystals were obtained.
119.9 (CH, CH@CH Im), 124.1 (CH o-Ph), 124.7 (CH, CH@CH Im),
129.2 (CH, p-DiPP), 129.8 (CH, m-Ph), 130.5 (CH, p-Ph), 133.5 (C,
i-DiPP), 145.4 (C, o-DiPP-C), 183.6 (C, NHC). Anal. Calc. for
C22H26AgBrN2S: C, 49.09; H, 4.87; N, 5.20. Found: C, 49.18; H,
4.75; N, 5.29%.
4.14. {[1-(2-Pyridyl)methylene-3-methyl]imidazolyl-2-ene}silver
1H NMR (CDCl3, T = 298 K, ppm) d: 4.06 (s, 3H, NCH3) 5.76 (s, 2H,
NCH2), 7.27 (d, J = 1,6 Hz, 1H, CH@CH Im), 7.30 (m, 1H, 5-Pyr), 7.63
(d, J = 1,6 Hz, 1H, CH@CH Im), 7.77 (td, J = 7.4, 1.6 Hz, 1H, 4-Pyr),
7.84 (d, J = 7.4 Hz, 1H, 3-Pyr), 8.55 (d, J = 4.9 Hz, 1H, 6 Pyr), 10.71
(bs, 1H, NCHN). 13C {1H} NMR (CDCl3, T = 298 K, ppm) d: 36.6
(CH3, NCH3), 53.7 (CH2, NCH2), 122.7 (CH, 5-Py), 123.3 (CH, CH@CH
Im), 123.6 (CH, CH@CH Im), 123.8 (CH, 3-Py), 137.3 (CH, 4-Py),
137.5 (CH, NHC), 149.7 (CH, 6-Py), 152.3 (C, 2-Py). Anal. Calc. for
bromide (4a)
White microcrystals: Yield 71%. 1H NMR (CDCl3, T = 298 K, ppm)
d: 3.87 (d, J = 0.7 Hz, 3H, NCH3), 5.44 (s, 2H, NCH2), 7.00 (d,
J = 1.8 Hz, 1H, CH@CH Im), 7.18 (d, J = 1.8 Hz, 1H, CH@CH Im),
7.24 (dd, J = 7.6, 4.9 Hz, 1H, 5-Pyr), 7.39 (d, J = 7.6 Hz, 1H, 3-Pyr),
7.69 (td, J = 7.6, 1.6 Hz, 1H, 4-Pyr), 8.56 (d, J = 4.9 Hz, 1H, 6-Pyr).
13C {1H} NMR (CDCl3, T = 253 K, ppm) d: 39.2 (CH3, NCH3), 57.4
(CH2, NCH2), 122.3 (CH, CH@CH Im), 122.7 (CH, CH@CH Im),
123.1 (CH, 5-Pyr), 123.8 (CH, 3-Pyr), 137.8 (CH, 4-Pyr), 150.3 (CH,
6-Pyr), 155.0 (C, 2-Pyr), 182.4 (C, NCN). Anal. Calc. for
C10H12BrN3: C, 47.26; H, 4.76; N, 16.54. Found: C, 47.19; H, 4.73;
N, 16.59%.
4.11. {[1-(Phenylthio)methylene-3-methyl]imidazolyl-2-ene}silver
C10H11AgBrN3: C, 33.27; H, 3.07; N, 11.64. Found: C, 33.35; H,
bromide (3a)
3.21; N, 11.51%.
To a solution of 0.322 g (1.13 mmol) of [Me-NHC-CH2-SPh]Br in
anhydrous CH2Cl2 (20 ml) under inert atmosphere (Ar) 0.144 g
(0.621 mmol) of Ag2O was added. The mixture was stirred in the
dark for 12 h and filtered on a Celite filter. The clear solution was
evaporated to small volume under vacuum and the title product
was precipitated by addition of diethylether filtered on gouch
and washed with diethylether and pentane. 0.378 g (yield 85%)
of the complex as a whitish solid was obtained. 1H NMR (CD2Cl2,
T = 298 K, ppm) d: 3.76 (s, 3H, NCH3), 5.42 (s, 2H, SCH2), 7.00 (d,
J = 1.8 Hz, 1H, CH@CH Im), 7.11 (d, J = 1.8 Hz, 1H, CH@CH Im),
7.38 (m, 5H, SPh). 13C {1H} NMR (CDCl3, T = 253 K, ppm) d: 38.7
(CH3, NCH3). 56.2 (CH2, SCH2), 120.4 (CH, CH@CH Im), 122.6 (CH,
CH@CH Im), 129.7 (CH, SPh–CH), 129.0 (CH, SPh–CH), 130.9 (C,
SPh–C), 133.3 (CH, SPh–CH), 182.2 (C, NCN). Anal. Calc. for
4.15. {[1-(Phenylthio)methylene-3-mesityl]imidazolyl-2-
ene}palladium(0) (maleic anhydride) (5b)
To the yellowish solution of 0.05 g (0.16 mmol) of [Pd(g
2-ma)
(COD)] under inert atmosphere (Ar) in 15 ml of anhydrous CH2Cl2
at 253 K (liquid N2/acetone) 0.0793 g (0.16 mmol) of the silver(I)
complex (3b) dissolved in 10 ml of anhydrous CH2Cl2 previously
cooled at 253 K was added in two successive aliquots (5 ml each).
The resulting brownish mixture was stirred for 1 h and the bath
temperature was gradually increased to 270 K. The precipitated
AgBr and traces of metallic palladium were removed by Millipore
filtration and the resulting yellow solution evaporated to dryness.
Addition of diethylether (20 ml) induced the precipitation of
0.0675 g (yield 83%) of the title complex which was filtered off,
washed with diethylether and stored at 253 K.
C11H12AgBrN2S: C, 33.70; H, 3.09; N, 7.15. Found: C, 33.73; H,
2.99; N, 7.21%.
1H NMR (CD2Cl2, T = 298 K, ppm) d: 2.00 (s, 6H, o-mesityl-CH3),
2.43 (s, 3H, p-mesityl CH3), 3.55 (bs, 2H, CH@CH ma), 5.32 (s, 2H,
SCH2), 7.04 (d, J = 1.9 Hz, 1H, CH@CH Im), 7.09 (s, 2H, m-mesityl-
H), 7.27 (d, J = 1.9 Hz, 1H, CH@CH Im), 7.41 (m, 3H, SPh), 7.65 (m,
2H, SPh). 1H NMR (CD2Cl2, T = 253 K, ppm) d: 1.95 (s, 3H, o-mesi-
tyl-CH3), 2.00 (s, 3H, o-mesityl-CH3), 2.40 (s, 3H, p-mesityl CH3),
3.40 (d, J = 3.3 Hz 1H, CH@CH ma), 3.62 (d, J = 3.3 Hz, 1H, CH@CH
ma), 5.30 (bs, 2H, SCH2), 7.01 (s, 1H, m-mesityl-H), 7.04 (d,
J = 1.9, 1H, CH@CH Im), 7.14 (s, 1H, m-mesityl-H), 7.26 (d, J = 1.9,
1H, CH@CH Im), 7.40 (m, 3H, SPh), 7.64 (m, 2H, SPh). 13C {1H}
NMR (CD2Cl2, T = 253 K, ppm) d: 17.5 (CH3, o-mesityl-CH3), 17.8
(CH3, p-mesityl-CH3), 21.0 (CH3, o-mesityl-CH3), 42.4 (CH, CH@CH
ma), 47.1 (CH, CH@CH ma), 59.9 (CH2, SCH2), 118.8 (CH, CH@CH
Im), 123.6 (CH, CH@CH Im), 128.2 (CH, m-mesityl-CH), 129.2
(CH, m-mesityl-CH), 129.5 (CH, SPh-CH), 130.0 (CH, SPh-CH),
131.7 (C, SPh-C), 132.7 (CH, SPh-CH), 134.4 (C, o-mesityl-C),
135.6 (C, o-mesityl-C), 136.4 (C, i-mesityl-C)), 138.7 (C, p-mesi-
tyl-C), 173.0 (C, C@O ma), 173.2 (C, C@O ma), 190.3 (C, NCN), IR
The following derivatives were prepared in a similar way using
the appropriate reactants.
4.12. {[1-(Phenylthio)methylene-3-mesityl]imidazolyl-2-ene}silver
bromide (3b)
Light brown microcrystals: Yield 83%. 1H NMR (CDCl3, T = 298 K,
ppm) d: 1.80 (s, 6H, o-mesityl CH3), 2.31 (s, 3H, p-mesityl CH3),
5.51 (s, 2H, SCH2), 6.91 (m, 3H, CH@CH Im, m-mesityl-H), 7.34
(m, 3H, SPh), 7.37 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.45 (m, 2H,
SPh), 13C {1H} NMR (CDCl3, T = 298 K, ppm) d: 17.5 (CH3, o-mesi-
tyl-CH3), 20.9 (CH3, p-mesityl-CH3), 56.4 (CH2, SCH2), 120.2 (CH,
CH@CH Im), 123.4 (CH, CH@CH Im), 129.2 (CH, m-mesityl-CH),
129.3 (C, o-mesityl-C), 129.8 (CH, SPh–CH), 130.01 (C, SPh–C),
133.8 (CH, SPh–CH), 134.4 (CH, SPh–CH), 134.9 (C, i-mesityl-C),
139.5 (C, p-mesityl-C), 183.1 (C, NCN). Anal. Calc. for
C19H20AgBrN2S: C, 45.99; H, 4.06; N, 5.65. Found: C, 46.03; H,
4.11; N, 5.67%.
(KBr pellet, cmꢂ1
) mCO: 1791, 1724. Anal. Calc. for C24H24N2O2PdS:
C, 56.42; H, 4.73; N, 5.48. Found: C, 56.31; H, 4.83; N, 5.36%.
The following derivatives were prepared in a similar way using
the appropriate reactants.
4.13. {[1-(Phenylthio)methylene-3-(2,6-di-i-
propylphenyl)]imidazolyl-2-ene}silver bromide (3c)
White microcrystals: Yield 92%. 1H NMR (300 MHz, CDCl3) d:
1.06 (d, J = 6.9 Hz, 6H, iPr-CH3), 1.11 (t, J = 6.8 Hz, 6H, iPr-CH3),
2.12 (sept, J = 6.8 Hz, 2H, iPr-CH), 5.54 (s, 2H, CH2-S), 6.95 (s, 1H,
CH@CH Im), 7.19 (d, J = 7.8 Hz, 2H, CH o-Ph), 7.33–7.38 (m, 3H,
CH mesityl), 7.39–7.43 (m, 2H, CH@CH Im, CH p-Ph), 7.44–7.50
(m, 2H, CH m-Ph). 13C NMR (75 MHz, CDCl3) d: 24.2 (CH3, iPr–
CH3), 24.3 (CH3, iPr–CH3), 28.0 (CH, iPr–CH), 56.3 (CH2, CH2–S),
4.16. {[1-(Phenylthio)methylene-3-metyl]imidazolyl-2-
ene}palladium(0) (maleic anhydride) (5a)
Yellow microcrystals: yield 70%. 1H NMR (CD2Cl2, T = 298 K,
ppm) d: 3.92 (s, 3H, NCH3), 3.95 (bs, 2H, CH@CH ma), 5.18 (s, 2H,
SCH2), 7.09 (bm, 2H, CH@CH Im), 7.41 (m, 3H, SPh), 7.61 (m, 2H,
SPh). 1H NMR (CD2Cl2, T = 253 K, ppm) d: 3.82 (bs, 1H, CH@CH

L. Canovese et al. / Inorganica Chimica Acta 390 (2012) 105–118
115
ma), 3.90 (s, 3H, NCH3), 4.47 (bs, 1H, CH@CH ma), 5.17 (s, 2H,
SCH2), 7.10 (bs, 2H, CH@CH Im), 7.39 (m, 3H, SPh), 7.59 (m, 2H,
SPh). 13C {1H} NMR (CDCl3, T = 253 K, ppm) d: 39.0 (CH3, NCH3),
42.0 (CH, CH@CH ma), 47.6 (CH, CH@CH ma), 59.2 (CH2, SCH2),
118.4 (CH, CH@CH Im), 123.4 (CH, CH@CH Im), 129.6 (CH, SPh–
CH), 129.9 (CH, SPh–CH), 131.7 (C, SPh–C), 132.7 (CH, SPh–CH),
172.7 (C, C@O ma), 172.8 (C, C@O ma), 188.1 (C, NCN), IR (KBr pel-
CH3), 2.40 (s, 3H, p-mesityl-CH3), 3.12 (bs, 1H, CH@CH ma), 3.31
(bs, 1H, CH@CH ma), 5.13, 5.43 (AB system, J = 14.8 Hz, 1H,
NCH2), 6.94 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.03 (m, 2H, m-mes-
iyl-H), 7.26 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.39 (ddd, J = 7.6, 5.3,
1.7 Hz, 1H, 5-Pyr), 7.56 (d, J = 7.6 Hz, 1H, 5-Pyr), 7.89 (td, J = 7.6,
1.7 Hz, 1H, 4-Pyr), 8.96 (dd, J = 1.0, 5.3 Hz, 1H, 6-Pyr), IR (KBr pellet,
cmꢂ1
) mCO: 1785, 1715. Anal. Calc. for C23H23N3O2Pd: C, 57.57; H,
let, cmꢂ1
)
m
CO: 1785, 1719. Anal. Calc. for C16H16N2O2PdS: C, 47.24;
4.83; N, 8.76. Found: C, 57.42; H, 4.95; N, 8.64%.
H, 3.96; N, 6.89. Found: C, 47.36; H, 3.83; N, 6.73%.
4.20. {[1-(2-Pyridyl)methylene-3-mesityl]imidazolyl-2-
4.17. {[1-(Phenylthio)methylene-3-(2,6-di-i-
ene}palladium(0)(naphthoquinone) (7b)
propylphenyl)]imidazolyl-2-ene}palladium(0) (maleic anhydride) (5c)
To a solution of [2-methyl-6-(phenylthiomethyl)pyridine]palla-
dium(0)(naphthoquinone) (0.050 g, 0.10 mmol) in dichloromethane
Yellow microcrystals: yield 92%. 1H NMR (CD2Cl2, T = 298 K,
ppm) d: 1.10 (d, J = 6.9 Hz, 6H, iPr–CH3), 1.23 (d, J = 6.9 Hz, 6H,
iPr–CH3), 2.47 (bm, 2H, iPr–CH), 3.61 (bs, 2H, CH@CH ma), 5.33
(s, 2H, SCH2), 7.10 (d, J = 1.9 Hz, 1H, CH@CH Im), 7.27 (d, J
= 1.9 Hz, 1H, CH@CH Im), 7.36 (d, J = 7.7 Hz, 2H, m-aryl-H), 7.43
(m, 3H, SPh–CH), 7.56 (t, J = 7.7 Hz, 1H, p-aryl-H,), 7.64 (m, 2H,
SPh–CH). 13C {1H} NMR (CDCl3, T = 298 K, ppm) d: 23.2 (CH3,iPr–
CH3), 24.7 (CH3, iPr–CH3), 28.4 (CH3, iPr–CH), 59.1 (CH2, SCH2),
118.2 (CH, CH@CH Im), 124.8 (CH, CH@CH Im), 124.0 (CH, m-
aryl-CH), 129.6 (CH, SPh–CH), 129.8 (CH, p-aryl-CH), 129.9 (CH,
SPh–CH), 131.54 (C, SPh–C), 132.0 (CH, SPh–CH), 135.9 (C, i-aryl-
C), 144.9 (C, o-aryl-C), 192.5 (C, NCN). 1H NMR (CD2Cl2, T = 253 K,
ppm) d: 1.07 (bs, 6H, iPr–CH3), 1.18 (bd, J = 6.5 Hz, 3H, iPr–CH3),
1.26 (bd, J = 7.4 Hz, 3H, iPr–CH3), 2.28 (bm, 1H, iPr–CH), 2.50
(bm, 1H, iPr–CH), 3.58 (bd, J = 3.1 Hz, 1H, CH ma), 3.77 (bd,
J = 3.1 Hz, 1H, CH ma), 5.24 (d, J = 12.1 Hz, 1H, CH2S), 5.31 (d,
J = 12.6 Hz, 1H, CH2S), 7.07 (d, J = 1.7 Hz, 1H CH@CH Im), 7.26 (d,
J = 1.8 Hz, 1H CH@CH Im), 7.32–7.41 (m, 5H, CH Ph, DiPPh), 7.55–
7.62 (m, 3H, CH Ph, DiPPh). 13C NMR (CD2Cl2, T = 253 K, ppm) d:
23.2 (CH3, iPr–CH3), 23.5 (CH3, iPr–CH3), 24.8 (CH3, iPr–CH3), 25.0
(CH3, iPr–CH3), 28.3 (CH, i Pr–CH), 28.4 (CH, i Pr–CH), 43.3 (CH,
Ma), 47.9 (CH, Ma), 59.5 (CH2, CH2S), 118.6 (CH, CH@CH Im),
123.5 (CH, CH@CH Im), 124.5 (CH, m-DiPP),124.8 (CH, m-DiPP),
129.7 (CH, o-Ph–C), 130.0 (CH, p-DiPP), 130.1 (CH, p-Ph–C), 131.4
(C, i-Ph),132.5 (CH, m-Ph–C), 135.8 (C, i-DiPP), 144.5 (C, o-DiPP–
C), 145.3 (C, o-DiPP–C), 171.2 (CO, Ma), 173.7 (CO, Ma), 191.3 (C,
(10 ml) was added
a solution of {[1-(2-pyridyl)methylene-3-
mesityl]imidazolyl-2-ene}silver bromide (4b) (0.046 g,0.10 mmol)
in 10 ml in the same solvent. Immediate precipitation of silver
bromide was observed. After a half hour the reaction mixture
was filtered through Celite and concentrated to a small volume
at reduced pressure. The slow addition of diethylether gave the
precipitation of the product as microcrystalline red–orange solid
(0.044 g, 82%).
1H NMR (CD2Cl2 T = 253 K, ppm) d: 1.46 (s, 3H, o-mesityl-CH3),
1.99 (s, 3H, o-mesityl-CH3), 2.47 (s, 3H, p-mesityl-CH3), 4.18, 4.36
(AB system, J = 6.7 Hz, 2H, CH@CH nq), 5.04, 5.24 (AB system,
J = 14.6 Hz, 2H, NCH2), 6.76 (d, J = 1.8 Hz, 1H, CH@CH Im), 6.87
(bs, 1H, m-mesityl-H), 7.07 (bs, 1H, m-mesityl-H), 7.21 (d,
J = 1.8 Hz, 1H, CH@CH Im), 7.33–7.50 (m, 5H, 3-Pyr, 5-Pyr, CH-
nq), 7.84 (td, J = 7.7, 1.7 Hz, 1H, 4-Pyr), 7.92 (d, J = 7.4 Hz, 1H, CH-
nq), 8.47 (d, J = 4.5 Hz, 1H, 6-Pyr),
13C NMR (CD2Cl2, T = 253 K, ppm) d: 17.3 (CH3, o-mesityl), 18.0
(CH3, o-mesityl), 21.4 (CH3, p-mesityl), 55.5 (CH2–Py), 58.7 (CH@CH
nq), 65.5 (CH@CH nq), 121.1 (CH@CH Im), 122.0 (CH@CH Im), 123.6
(CH, 3-Py), 124.0 (CH, 5-Py), 125.3 (CH, Nq), 125.5 (CH, Nq), 128.8
(CH, m-mesityl), 129.4 (C, p-mesityl), 130.6 (CH, m-mesityl), 134.9
(C, o-mesityl), 135.2 (CH, Nq), 135.4 (C, o-mesityl), 135.8 (CH, Nq),
137.5 (C, i-mesityl), 138.1 (CH, 4-Py), 138.5 (C, Nq), 150.7 (CH, 6-
Py), 152.3 (C, 2-Py), 174.1 (CO), 183.8 (CO), 187.0 (C, NHC). IR
(KBr pellet, cmꢂ1
)mCO: 1790, 1720. Anal. Calc. for C28H25N3O2Pd: C,
62.06; H, 4.65; N, 7.75. Found: C, 62.14; H, 4.51; N, 7.88%.
The following derivatives were prepared in a similar way using
the appropriate silver complex.
NHC). IR (KBr pellet, cmꢂ1
)
mCO: 1790, 1720. Anal. Calc. for
C27H30N2O2PdS: C, 58.64; H, 5.47; N, 5.07. Found: C, 58.77; H,
5.59; N, 5.21%.
4.18. {[1-(2-Pyridyl)methylene-3-methyl]imidazolyl-2-
4.21. {[1-(2-Pyridyl)methylene-3-metyl]imidazolyl-2-
ene}palladium(0) (maleic anhydride) (6a)
ene}palladium(0)(naphthoquinone) (7a)
Yellow microcrystals: yield 95%. 1H NMR (CD2Cl2, T = 298 K,
ppm) d: 3.58 (d, J = 3.2 Hz, 1H, CH@CH ma), 3.76 (s, 3H, NCH3),),
4.13 (d, J = 3.2 Hz, 1H, CH@CH ma), 4.98, 5.22 (AB system, 1H,
J = 14.4 Hz, SCH2), 6.95 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.07 (d,
J = 1.8 Hz, 1H, CH@CH Im), 7.42 (ddd, J = 7.6, 5.3, 1.7 Hz, 1H, 5-
Pyr), 7.51 (d, J = 7.6 Hz, 1H, 3-Pyr), 7.87 (td, J = 7.6, 1.7 Hz, 1H, 4-
Pyr), 8.88 (dd, J = 5.3, 0.9 Hz, 1H, 6-Pyr), 13C {1H} NMR (CD2Cl2,
T = 298 K, ppm) d: 37.7 (CH3, N CH3), 40.1 (CH, CH@CH ma), 41.3
(CH, CH@CH ma), 55.3 (CH2, NCH2), 120.7 (CH, CH@CH Im), 120.8
(CH, CH@CH Im), 124.4 (CH, 3-Pyr), 124.7 (CH, 5-Pyr), 138.4 (CH,
4-Pyr), 153.1 (CH, 6-Pyr), 153.2 (C, 2-Pyr), 174.0 (C, C@O ma),
Red-orange microcrystals: yield 64%. 1H NMR (CD2Cl2 T = 253 K,
ppm) d: 3.54 (s, 3H, NCH3), 4.88, 4.54 (AB system, J = 6.7 Hz, 2H,
CH@CH nq), 4.89, 5.17 (AB system, J = 14.5 Hz, 2H, NCH2), 6.83
(d, J = 1.7 Hz, 1H, CH@CH Im), 7.02 (d, J = 1.7 Hz, 1H, CH@CH Im),
7.43–7.53 (m, 4H, 3-Pyr, 5-Pyr, CH-nq), 7.81 (td, J = 7.6, 1.6 Hz,
1H, 4-Pyr), 8.01–8.04 (m, 2H, CH-nq), 8.08–8.11 (m, 2H, CH-nq),
8.39 (d, J = 5.1 Hz, 1H, 6-Pyr), 13C {1H} NMR (CDCl3, T = 298 K,
ppm) d: 37.0 (CH3, NCH3), 55.3 (CH2, NCH2), 61.0 (CH, CH@CH
nq), 63.8 (CH, CH@CH nq), 120.4 (CH, CH@CH Im), 121.4 (CH,
CH@CH Im), 123.8 (CH, 5-Pyr), 124.0 (CH, CH-nq) 125.3 (CH, 3-
Pyr), 130.3 (CH, CH-nq), 130.8 (CH, CH-nq), 137.9 (CH, 4-Pyr),
149.6 (CH, 2-Pyr), 150.9 (CH, 6-Pyr), 180.8(C, CO),188.7 (C, NCN).
186.0 (C, NCN). IR (KBr pellet, cmꢂ1
) mCO: 1779, 1714. Anal. Calc.
for C15H15N3O2Pd: C, 47.95; H, 4.02; N, 11.18. Found: C, 47.84; H,
IR (KBr pellet, cmꢂ1
) mCO: 1633. Anal. Calc. for C20H17N3O2Pd: C,
4.18; N, 11.01%.
54.87; H, 3.91; N, 9.60. Found: C, 54.72; H, 3.79; N, 9.74%.
4.19. {[1-(2-Pyridyl)methylene-3-mesityl]imidazolyl-2-
4.22. {[1-(2-Pyridyl)methylene-3-(2,6-di-i-propylphenyl)]imidazolyl-
ene}palladium(0) (maleic anhydride) (6b)
2-ene}palladium(0) (naphthoquinone) (7c)
Yellow microcrystals: yield 95%. 1H NMR (CD2Cl2, T = 298 K,
ppm) d: 1.94 (bs, 3H, o-mesityl-CH3), 2.07 (bs, 3H, o-mesityl-
Red-orange microcrystals, yield 68%. 1H NMR (CD2Cl2, T = 253 K,
ppm) d: 0.20 (d, J = 6.8 Hz, 3H, iPr–CH3), 0.75 (d, J = 6.8 Hz, 3H,

116
L. Canovese et al. / Inorganica Chimica Acta 390 (2012) 105–118
iPr–CH3), 1.10 (d, J = 6.8 Hz, 3H, iPr–CH3), 1.50 (d, J = 6.8 Hz, 3H,
iPr–CH3), 1.54 (sept, J = 6.8 Hz, 1H, iPr–CH), 2.60 (sept, J = 6.8 Hz,
1H, iPr–CH), 4.42, 4.46 (AB system, J = 6.8 Hz, 2H, CH@CH nq),
5.42, 5.02 (AB system, J = 14.4 Hz, 2H, NCH2), 6.84 (d, J = 1.7 Hz,
1H, CH@CH Im), 6.98 (d, J = 7.7 Hz, 2H, m-aryl-H), 7.19 (d,
J = 1.7 Hz, 1H, CH@CH Im), 7.31–7.49 (m, 6H, m-aryl-H, 3-pyr, 5-
Pyr, CH-nq), 7.59 (t, J = 7.8 Hz, 1H, p-aryl-H), 7.81 (td, J = 7.6,
1.5 Hz, 1H, 4-Pyr), 8.02 (d, J = 6.9 Hz, 1H, CH-nq), 8.37 (d,
J = 4.4 Hz, 1H, 6-Pyr), 13C {1H} NMR (CD2Cl2, T = 253 K, ppm) d:
22.2 (CH3, iPr–CH3), 22.7 (CH3, iPr–CH3), 22.2 (CH3, iPr–CH3), 24.0
(CH3, iPr–CH3), 27.8 (CH, iPr–CH), 28.6 (CH, iPr–CH), 55.6 (CH2,
NCH2), 57.2 (CH, CH@CH nq), 64.2 (CH, CH@CH nq), 120.8 (CH,
CH@CH Im), 123.1 (CH, CH@CH Im), 123.9 (CH, m-aryl-CH), 124.0
(CH, CH-nq) 125.4 (CH, 3-Pyr), 125.9 (CH, 5-pyr), 129.4 (CH,
p-aryl-CH), 130.0 (CH, CH-nq), 130.8 (CH, CH-nq), 135.1 (C,
i-aryl-C), 135.5 (C, C-nq), 137.2 (C, C-nq), 138.0 (CH, 4-Pyr), 144.9
(C, o-aryl-C), 145.2 (C, o-aryl-C), 150.1 (C, 6-Pyr), 152.2 (CH, 2-
Pyr), 176.7 (C, C@O), 185.4 (C, C@O), 189.1 (C, NCN). IR (KBr pellet,
Pyr), 153.4 (C, 2-Pyr), 155.7 (CH, 6-Pyr), 170.5 (C, C@O), 171.1 (C,
C@O), 185.2 (C, NCN). IR (KBr pellet, cmꢂ1
CO: 1707, 1681. Anal.
Calc. for C20H23N3O8Pd: C, 44.50; H, 4.29; N, 7.78. Found: C,
)
m
44.63; H, 4.37; N, 7.65%.
4.25. {[1-(2-Pyridyl)methylene-3-(2,6-di-i-propylphenyl)]imidazolyl-
2-ene}palladium(0)(tetramethyl ethene tetracarboxylate) (8c)
Yellow microcrystals: yield 71%. 1H NMR (CD2Cl2, T = 298 K,
ppm) d: 1.01 (d, J = 6.8 Hz, 6H, iPr–CH3), 1.31 (d, J = 6.8 Hz, 6H,
iPr–CH3), 2.43 (bm, 2H, iPr–CH), 3.21 (bs, 6H, OCH3), 3.45 (s, 6H,
OCH3), 5.34 (s, 2H, NCH2), 6.83 (d, J = 1.6 Hz, 1H, CH@CH Im),
7.21 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.22 (d, J = 7.7 Hz, 2H, m-aryl-
H), 7.37 (m, 2H, p-aryl-H, 5-Pyr), 7.48 (d, J = 7.7 Hz, 1H, 3-Pyr),
7.85 (td, J = 7.6, 1.5 Hz, 1H, 4-Pyr), 9.48 (d, J = 4.4 Hz, 1H, 6-Pyr),
13C {1H} NMR (CD2Cl2, T = 298 K, ppm) d: 23.4 (CH3, iPr–CH3),
24.7 (CH3, iPr–CH3), 28.2 (CH, iPr–CH), 51.3 (CH3, OCH3), 51.5
(CH3, OCH3), 55.8 (CH2, NCH2), 120.2 (CH, CH@CH Im), 123.3 (CH,
CH@CH Im), 123.7 (CH, 3-Pyr), 123.7(CH, m-aryl-CH), 124.1 (CH,
5-Pyr), 129.1 (CH, p-aryl-CH), 135.5 (C, i-aryl-C), 137.5 (CH, 4-
Pyr), 146.0 (C, o-aryl-C), 153.5 (C, 2-Pyr), 155.3 (CH, 6-Pyr), 170.3
cmꢂ1
) mCO: 1641. Anal. Calc. for C31H31N3O2Pd: C, 63.75; H, 5.35; N,
7.20. Found: C, 63.88; H, 5.49; N, 7.07%.
4.23. {[1-(2-Pyridyl)methylene-3-mesityl]imidazolyl-2-
(C, C@O), 170.8 (C, C@O), 191.1 (C, NCN). mCO: 1729, 1699, 1680.
ene}palladium(0)(tetramethyl ethene tetracarboxylate) (8b)
Anal. Calc. for C31H37N3O8Pd: C, 54.27; H, 5.44; N, 6.12. Found:
C, 54.38; H, 5.38; N, 6.19%.
To a solution of [2-methyl-6-(phenylthiomethyl)pyridine]palla-
dium(0)(tetramethyl
ethene
tetracarboxylate)
(0.050 g,
0.09 mmol) in dichloromethane (10 ml) was added a solution of
{[1-(2-pyridyl)methylene-3-mesetyl]imidazolyl-2-ene}silver bro-
mide (4b) (0.040 g, 0.09 mmol) in 10 ml of the same solvent.
Immediate precipitation of silver bromide was observed. After a
half hour the reaction mixture was filtered through a pad of Celite
and concentrated to a small volume at reduced pressure. The slow
addition of diethyl ether gave the precipitation of the product as
microcrystalline yellow solid (0.041 g, 74%). 1H NMR (CD2Cl2,
T = 298 K, ppm) d: 2.01 (s, 6H, o-mesityl-CH3), 2.34 (s, 3H, p-mesi-
tyl-CH3), 3.29 (s, 6H, OCH3), 3.49 (s, 6H, OCH3), 5.29 (s, 2H, NCH2),
6.77 (d, J = 1.8 Hz, 1H, CH@CH Im), 6.95 (s, 2H, m-mesityl-H), 7.25
(d, J = 1.8 Hz, 1H, CH@CH Im), 7.40 (ddd, J = 7.6, 4.3, 1.3 Hz, 1H, 5-
Pyr), 7.52 (d, J = 7.6 Hz, 1H, 3-Pyr), 7.84 (td, J = 7.6, 1.7 Hz, 1H, 4-
Pyr), 9.60 (d, J = 4.3 Hz, 1H, 6-Pyr), 13C {1H} NMR (CD2Cl2,
T = 298 K, ppm) d: 17.4 (CH3, o-mesityl-CH3), 20.6 (CH3, p-mesi-
tyl-CH3), 51.1 (CH3, OCH3), 55.6 (CH2, NCH2), 120.8 (CH, CH@CH
Im), 121.6 (CH, CH@CH Im), 123.7 (CH, 3-Pyr), 124.1 (CH, 5-Pyr),
128.6 (CH, m-mesityl-CH), 135.3 (C, o-mesityl-C), 135.9 (C, i-mesi-
tyl-C), 137.8 (CH, 4-Pyr), 137.9 (C, p-mesityl-C), 153.4 (C, 2-Pyr),
155.3 (CH, 6-Pyr), 170.5 (C, C@O), 170.6 (C, C@O), 188.6 (C, NCN).
4.26. {j -
1-C-[1-(Phenylthio)methylene-3-metyl]imidazolyl-2-ene}{j1
C-[1-(2-pyridyl)methylene-3-mesityl]imidazolyl-2-
ene}palladium(0)(maleic anhydride) (9)
To a solution of {[1-(2-pyridyl)methylene-3-mesityl]imidazo-
lyl-2-ene}palladium(0)(maleic anydride) (6b) (0.064 g,
0.133 mmol) in dichloromethane (10 ml) was added a solution of
{[1-(phenylthio)methylene-3-metyl]imidazolyl-2-ene}silver bro-
mide (2a) (0.052 g, 0.133 mmol) in 10 ml of the same solvent.
Immediate precipitation of silver bromide was observed. After a
half hour the reaction mixture was filtered through a Millipore fil-
ter yielding a clear solution. Reduction to small volume (ꢀ3 ml)
and addition of diethylether gave the products as microcrystalline
yellow solid after cooling to 0 °C (0.062 g, 67%). The same product
was obtained starting from {[1-(2-pyridyl)methylene-3-mesi-
tyl]imidazolyl-2-ene}silver bromide (4b) and {[1-(phenyl-
thio)methylene-3-metyl]imidazolyl-2-ene} (5a). 1H NMR (CD2Cl2,
T = 298 K, ppm) d: 1.62 (s, 3H, p-mesityl-CH3), 1.85 (s, 3H, o-mesi-
tyl-CH3), 2.34 (s, 3H, o-mesityl-CH3), 2.89 (s, 3H, NCH3), 3.29, 3.37
(AB system, J = 3.7 Hz, 2H, CH@CH ma) 4.81, 5.06 (AB system,
J = 14.1 Hz, 2H, CH2–Pyr), 5.59, 5.84 (AB system, J = 15.5 Hz, 2H,
SCH2) 6.7 (d, J = 1.9 Hz, 1H, CH@CH Im), 6.81 (d, J = 1.9 Hz, 1H,
CH@CH Im), 6.83 (s, 1H, m-mesityl-H), 6.87 (d, J = 1.9 Hz, 1H,
CH@CH Im), 6.95 (s, 1H, m-mesityl-H), 7.25 (d, J = 1.9 Hz, 1H,
CH@CH Im), 7.27–7.34 (m, 6H, S-Ph 5Pyr) 7.41 (d, J = 7.9 Hz, 1H,
3-Pyr), 7.79 (td, J = 7.7, 1.9 Hz, 1H, 4-Pyr), 8.63 (d, J = 4.0 Hz, 1H,
6-Pyr). 13C {1H} NMR (CD2Cl2, T = 298 K, ppm) d: 16.7 (CH3, p-mesi-
tyl-CH3), 16.8 (CH3, p-mesityl-CH3), 20.57 (CH3, o-mesityl-CH3),
36.4 (CH3, NCH3), 38.2 (CH, CH@CH ma), 38.7 (CH, CH@CH ma),
54.1 (CH2, CH2-Pyr), 56.5 (CH2, SCH2), 119.1 (CH, CH@CH Im),
121.3 (CH, 5-Pyr), 121.9 (CH, CH@CH Im), 122.4 (CH, CH@CH Im),
122.8 (CH, 3-Pyr), 123.0 (CH, CH@CH Im), 128.3 (CH, m-mesityl),
128.8 (CH, p-Ph), 129.1 (C, p-mesityl-C), 129.2 (CH, o-Ph), 131.6
(C, i-Ph), 133.4 (CH, m-Ph), 136.0 (C, o-mesityl-C), 136.2 (C, o-mesi-
tyl-C), 137.1 (CH, 4-Pyr), 138.4 (C, i-mesityl-C), 149.4 (CH, 6-Pyr),
156.5 (C, 2-Pyr), 174.0 (C, C@O), 174.4 (C, C@O), 189.2 (C, NCN),
IR (KBr pellet, cmꢂ1
28H23N3O8Pd: C, 52.22; H, 4.85; N, 6.53. Found: C, 52.08; H,
) mCO = 1724, 1682. Anal. Calc. for
C
4.71; N, 6.41%.
The following derivatives were prepared in a similar way using
the appropriate silver complex.
4.24. {[1-(2-Pyridyl)methylene-3-metyl]imidazolyl-2-
ene}palladium(0)(tetramethyl ethene tetracarboxylate) (8a)
Yellow microcrystals: yield 64%. 1H NMR (CD2Cl2, T = 298 K,
ppm) d: 3.60 (s, 6H, OCH3), 3.63 (s, 6H, OCH3), 3.76 (s, 3H, NCH3),
5.12 (s, 2H, NCH2), 6.92 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.06 (d,
J = 1.8 Hz, 1H, CH@CH Im), 7.41 (ddd, J = 7.6, 4.6, 1.0 Hz, 1H, 5-
Pyr), 7.47 (d, J = 7.6 Hz, 1H, 3-Pyr), 7.84 (td, J = 7.6, 1.6 Hz, 1H, 4-
Pyr), 9.63 (d, J = 4.6 Hz, 1H, 6-Pyr), 13C {1H} NMR (CD2Cl2,
T = 298 K, ppm) d: 37.4 (CH3, NCH3), 51.3 (CH3, OCH3), 51.5 (CH3,
OCH3), 55.2 (CH2, NCH2), 120.6 (CH, CH@CH Im), 120.9 (CH,
CH@CH Im), 124.0 (CH, 5-Pyr), 124.4 (CH, 3-Pyr), 138.1 (CH, 4-
189.3 (C, NCN). IR (KBr pellet, cmꢂ1
) mCO: 1765, 1704. Anal. Calc.
for C42H43N5O2PdS: C, 63.99; H, 5.50; N, 8.88. Found: C, 63.89; H,
5.58; N, 8.81%.

L. Canovese et al. / Inorganica Chimica Acta 390 (2012) 105–118
1-C-[1-(phenylthio)methylene-3-metyl]imidazolyl-2-ene}2
Konstantinovski, D. Milstein, Inorg. Chem. 49 (2010) 1615;
4.27. Bis-{j
117
(e) J.L. van der Vlugt, E.A. Pidko, D. Vogt, M. Lutz, A.L. Spek, Inorg. Chem. 48
(2009) 7513;
palladium(0)(maleic anhydride) (10)
(f) J.I. van der Vlugt, M.A. Siegler, M. Janssen, D. Vogt, A.L. Spek,
Organometallics 28 (2009) 7025;
(g) R. Lindner, B. van der Bosch, M. Lutz, J.N.H. Reek, J.I. van der Vlugt,
Organometallics 30 (2011) 499;
To a solution of {[1-(phenylthio)methylene-3-metyl]imidazo-
lyl-2-ene}palladium(0)(maleic
anhydride)
(5a)
(0.025 g,
0.061 mmol) in dichloromethane (10 ml) was added a solution of
{[1-(phenylthio)methylene-3-metyl]imidazolyl-2-ene} silver bro-
mide (2a) (0.024 g,0.061 mmol) in 10 ml of the same solvent.
Immediate precipitation of silver bromide was observed. After a
half hour the reaction mixture was filtered through a Millipore fil-
ter yielding a clear solution. Reduction to small volume (ꢀ3 mL)
and addition of diethylether gave the product as microcrystalline
yellow solids after cooling to 0 °C. (0.031 g, 82%). 1H NMR (CD2Cl2,
T = 298 K, ppm) d: 3.54 (s, 2H, HC@CH ma), 3.69 (s, 6H, NCH3), 5.46,
5.33 (AB system, J = 14.3 Hz, 2H, SCH2), 6.90 (bs, 4H, HC@CH Im),
7.32–7.40 (m, 10H, SPh-CH). 13C {1H} NMR (CD2Cl2, T = 298 K,
ppm) d: 37.9 (CH3, NCH3), 38.7 (CH, CH@CH ma), 55.0 (CH2,
NCH2), 120.1 (CH, CH@CH Im), 122.4 (CH, CH@CH Im), 127.9 (CH,
SPh-CH), 129.2 (CH, SPh-CH), 131.7 (CH, SPh-CH), 174.2 (C, C@O),
188.9 (C, NCN). Anal. Calc. for C43H44N4O2PdS2: C, 63.03; H, 5.41;
N, 6.84. Found: C, 63.01; H, 5.48; N, 6.79%.
(h) M.T. Whited, R.H. Grubbs, Acc. Chem. Res. 42 (2009) 1607;
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Gebbink, K.J. Szabó, Chem. Eur. J. 14 (2008) 4800;
(j) I. Moreno, R. San Martin, B. Inés, M.T. Herrero, E. Dominguez, Curr. Org.
Chem. 13 (2009) 878;
(k) D.M. Spasyuk, D. Zargarian, A. van der Est, Organometallics 28 (2009) 6531;
(l) S. Bonnet, J. Li, M.A. Siegler, L.S. von Chrzanowski, A.L. Spek, G. van Koten,
R.J.M. Klein Gebbink, Chem. Eur. J. 15 (2009) 3340;
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Organometallics 29 (2010) 2248;
(p) B.-S. Zang, W. Wang, D.D. Shao, X.-D. Hao, J.-F. Gong, M.-P. Song,
Organometallics 29 (2010) 2579;
(q) M.A. Siegler, M. Lutz, A.L. Spek, R.J.M. Klein Gebbink, G. van Koten, Adv.
Synth. Catal. 352 (2010) 2474.
[4] A.J. Arduengo, Acc. Chem. Res. 32 (1999) 913. and refs. therein.
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4.28. Equilibrium reactions between silver(I)- and palladium(0)-NHC
derivatives
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To a 1.5 ꢁ 10ꢂ2 M solution in CD2Cl2 of palladium(0)NHC com-
plexes 6a or 6b, equimolecular amounts of the silver derivatives 4a
or 4b were added at RT and the 1H NMR spectra of the ensuing
reaction mixtures were recorded.
4.29. Reaction between palladium(0)NHC derivatives and dmbd
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To a 1.5 ꢁ 10ꢂ2 M CD2Cl2 solution of palladium(0)NHC of com-
plexes 5a, 5b, 6a or 6b a stoichiometric amount of dmbd ([com-
plex]: [dmbd] ꢄ 1:2) was added at 253 K and the 1H NMR spectra
of the ensuing reaction mixtures were recorded. In the RT 1H and
13C NMR spectra in CDCl3 of the reaction mixture between 6a
and dmbd the formation of species 12 was observed. 1H NMR
(CDCl3, T = 298 K, ppm) d: 3.40 (s, 3H, OCH3), 3.42 (s, 3H, OCH3),
3.68(s, 3H, OCH3), 3.72 (s, 3H, NCH3), 3.73 (s, 3H, OCH3), 5.07
(bd, 1H, NCH2), 5.83 (bd, 1H, NCH2), 6.78 (d, J = 1.5 Hz, 1H, CH@CH
Im), 7.08 (d, J = 1.5 Hz, 1H, CH@CH Im), 7.33 (ddd, J = 7.7, 5.4,
1.0 Hz, 1H, 5-Pyr), 7.56 (d, J = 7.7 Hz, 1H, 3-Pyr), 7.84 (td, J = 7.7,
1.7 Hz, 1H, 4-Pyr), 8.66 (d, J = 5.4 Hz, 1H, 6-Pyr), 13C {1H} NMR
(CDCl3, T = 298 K, ppm) d: 37.4 (CH3, NCH3), 50.3 (CH3, OCH3),
50.9 (CH3, OCH3), 51.2 (CH3, OCH3), 51.2 (CH3, OCH3), 56.5 (CH2,
NCH2), 121.3 (CH, CH@CH Im), 121.4 (CH, CH@CH Im), 124.1 (CH,
5-Pyr), 124.7 (CH, 3-Pyr), 138.5 (CH, 4-Pyr), 141.1 (C, C@C), 148.4
(C, C@C), 152.7 (C, 6-Pyr), 154.1 (CH, 2-Pyr), 164.3 (C, C@O),
166.1 (C, C@O), 175.1 (C, C@O), 175.7 (C, C@O), 177.5 (C, C@C),
180.5 (C, NCN). Anal. Calc. for C22H23N3O8Pd: C, 46.86; H, 4.11; N,
7.45. Found: C, 46.53; H, 4.05; N, 7.38%.
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Appendix A. Supplementary material
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