Novel reactivity mode of metal diaminocarbenes: Palladium(II)-mediated coupling between acyclic diaminocarbenes and isonitriles leading to dinuclear species

Article abstract of DOI:10.1021/om2002574

Metal-mediated coupling between equimolar amounts of cis-[PdCl ₂(CNR¹)₂] [R¹ = 2,6-Me ₂C₆H₃ (Xyl) 1, 2-Cl,6-Me-C₆H ₃2, cyclohexyl (Cy) 3] and H₂NC₅H ₃R²N [R² = H, 2-aminopyridine 4; R² = NH₂, 2,6-diaminopyridine 5] proceeds smoothly for 12 h at 20-25 °C and leads to the diaminocarbene species [PdCl{C(NHC₅H ₃R²N)=N(H)R¹}(CNR¹)]Cl (6-9). In the reaction of 2 with 5 (1:1 molar ratio), corresponding carbene 10 was detected only by high-resolution ESI⁺-MS in a mixture with other yet unidentified products. Addition of each of 6-8 to starting 1 or 2 (1:1 molar ratio) in the presence of excess solid K₂CO₃ in CHCl ₃ and heating of the reaction mixture for 12 h at 40 °C led to a novel type of dinuclear complexes, 11 (75% isolated yield) and 13 (65%). Similar dinuclear complexes 12 and 14, formed by addition of 7 or 10 to 2, were identified by high-resolution ESI⁺-MS in the mixture with other species (e.g., 7 and 10). Generation of 11-14 proceeds via a cascade reaction including addition of the amino group of a 2-aminopyridine to the metal-activated isonitrile, ring-closure, and coupling of the derived acyclic diaminocarbene complex with the yet unreacted starting material. Complexes 6-9, 11, and 13 were fully characterized by elemental analyses (C, H, N), high-resolution ESI⁺-MS, IR, and ¹H and ¹³C{¹H} NMR spectroscopies, while 10, 12, and 14 were identified by ESI⁺-MS. In addition, the structures of five complexes [6, 6a (the latter is a neutral species derived from the deprotonation of 6), 9, 11, and 13] were elucidated by single-crystal X-ray diffraction.

Full text of DOI:10.1021/om2002574

ARTICLE
pubs.acs.org/Organometallics
Novel Reactivity Mode of Metal Diaminocarbenes: Palladium(II)-
Mediated Coupling between Acyclic Diaminocarbenes and
Isonitriles Leading to Dinuclear Species
Alexander G. Tskhovrebov,† Konstantin V. Luzyanin,†,‡ Fedor M. Dolgushin,§
||
M. Fꢀatima C. Guedes da Silva,‡,^ Armando J. L. Pombeiro,*,‡ and Vadim Yu. Kukushkin*,†,
†Department of Chemistry, St.Petersburg State University, 198504 Stary Petergof, Russian Federation
‡Centro de Química Estrutural, Complexo I, Instituto Superior Tꢀecnico, TU Lisbon, Avenida Rovisco Pais, 1049-001 Lisbon, Portugal
§A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilova Street 28, 119991 Moscow,
Russian Federation
^Universidade Lusꢀofona de Humanidades e Tecnologias, ULHT Lisbon, 1749-024 Lisbon, Portugal
Institute of Macromolecular Compounds of Russian Academy of Sciences, Bolshoii Pr. 31, 199004 St.Petersburg,
Russian Federation
S Supporting Information
b
ABSTRACT: Metal-mediated coupling between equimolar amounts of
cis-[PdCl2(CNR1)2] [R1 = 2,6-Me2C6H3 (Xyl) 1, 2-Cl,6-Me-C6H3 2,
cyclohexyl (Cy) 3] and H2NC5H3R2N [R2 = H, 2-aminopyridine 4;
R2 = NH2, 2,6-diaminopyridine 5] proceeds smoothly for 12 h at
20ꢀ25 ꢀC and leads to the diaminocarbene species [PdCl-
{C(NHC5H3R2N)dN(H)R1}(CNR1)]Cl (6ꢀ9). In the reaction of
2 with 5 (1:1 molar ratio), corresponding carbene 10 was detected only
by high-resolution ESIþ-MS in a mixture with other yet unidentified
products. Addition of each of 6ꢀ8 to starting 1 or 2 (1:1 molar ratio) in
the presence of excess solid K2CO3 in CHCl3 and heating of the reaction
mixture for 12 h at 40 ꢀC led to a novel type of dinuclear complexes, 11
(75% isolated yield) and 13 (65%). Similar dinuclear complexes 12 and
14, formed by addition of 7 or 10 to 2, were identified by high-resolution
ESIþ-MS in the mixture with other species (e.g., 7 and 10). Generation of 11ꢀ14 proceeds via a cascade reaction including addition
of the amino group of a 2-aminopyridine to the metal-activated isonitrile, ring-closure, and coupling of the derived acyclic
diaminocarbene complex with the yet unreacted starting material. Complexes 6ꢀ9, 11, and 13 were fully characterized by elemental
analyses (C, H, N), high-resolution ESIþ-MS, IR, and 1H and 13C{1H} NMR spectroscopies, while 10, 12, and 14 were identified by
ESIþ-MS. In addition, the structures of five complexes [6, 6a (the latter is a neutral species derived from the deprotonation of 6), 9,
11, and 13] were elucidated by single-crystal X-ray diffraction.
’ INTRODUCTION
in excellent reviews related to the preparation2,3,5,6,11 and cata-
lytic applications10,24 of these compounds.
In the past decade, metal-aminocarbenes gained special atten-
tion in both organometallic and organic chemistry.1ꢀ6 In parti-
cular, complexes with N-heterocyclic carbenes [M](NHC)1,7ꢀ10
and, to a lesser extent so far, structurally relevant acyclic diamino-
carbene [M](ADC) species6,11ꢀ23 (Figure 1) have revolutioned
catalysis of a number of useful organic transformations.8,24 It is
therefore not surprising that the number of studies on NHCs and
ADCs dramatically increased in recent years. Most of work in this
field is devoted to the preparation of novel metal-aminocarbenes,
optimization of the electronic and steric effects of the carbenes in
their complexes, understanding the nature of the metalꢀCcarbene
bond, and, what is also very important, the application of carbene
metal species as catalysts in organic syntheses. A significant
number of publications on metal-aminocarbenes are summarized
Although metal-aminocarbenes have been prepared for a long
time [starting from pioneering works of Chugaev,25 when they
could not be recognized as such, and later by Richards26], the
reactivity modes of aminocarbene ligands are practically un-
known. A few reports in this direction27ꢀ30 [see also a review31]
indicate that the NH moieties of diaminocarbenes (and of related
aminooxycarbenes) exhibit a significant Brønsted acidity and can
be deprotonated either by action of bases or electrochemically.
Recently, within our project on the nucleophilic addition to
metal-activated substrates bearing CN triple bonds [i.e., nitriles
Received: March 24, 2011
Published: May 26, 2011
r
2011 American Chemical Society
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Figure 1. Complexes with N-heterocyclic carbene ([M](NHC)) and
acyclic diaminocarbene ([M](ADC)) ligands.
Figure 3. Different product patterns obtained from the coupling of
metal-bound isonitriles with aminopyridines.
’ RESULTS AND DISCUSSION
Generation of Diaminocarbenes via Addition of 2-Amino-
pyridines to (RNC)2PdII Species. Previously Belluco and
colleagues44ꢀ46 reported on the reaction of an isonitrile in either
the mononuclear cis-[PdCl2(CNMe)2]44,45 or halogen-bridged
46
dinuclear [PdCl2(CNPh)]2 complexes and 2-aminopyridine
(1:1 molar ratio, at room temperature, overnight), yielding mono-
nuclear acyclic diaminocarbene complexes (70ꢀ80%). These
species are derived from the addition of the amine functionality
to the CN bond of a coordinated isonitrile. It was reported46 that
the pyridine N atom remains uncoordinated (step 1, Scheme 1),
and its ligation could be achieved only by a further treatment with
NaClO4 or AgBF4 (step 2).
As an extension of these studies to various isonitrile complexes
and aminopyridines, we investigated the interplay between
cis-[PdCl2(CNR1)2] [R1 = 2,6-Me2C6H3 (Xyl) 1, 2-Cl-6-Me-
C6H3 2, cyclohexyl (Cy) 3] and two 2-aminopyridines, i.e.,
2-aminopyridine (4) and 2,6-diaminopyridine (5); combinations
of these reactants were not previously studied. Dropwise addition of
a CHCl3 solution of 4 or 5 to each of 1ꢀ3 (1:1 molar ratio) leads to
the immediate color change from pale yellow to intense lemon-
yellow (for 4) or orange (for 5), followed by the dissolution of solid
1ꢀ3. After 12 h at 20ꢀ25 ꢀC, the reaction mixture contained 6ꢀ9
(Scheme 1), which were isolated in good (60ꢀ75%) yields. When
2 was treated with 5 (1:1 molar ratio), wedetected complex10 only
by high-resolution ESIþ-MS along with a broad mixture of other yet
unidentified products. Thus, the interplay between 2 and 5 in
CHCl3 in the temperature range 20ꢀ45 ꢀC led to formation of a
dark orange, oily residue comprising a broad mixture of products
(five spots on TLC). The presence of 10 among other products
(four spots on TLC) was detected by high-resolution ESIþ-MS, but,
unfortunately, we were unable to isolate 10 as an individual species
and, consequently, characterize it by NMR and elemental analyses.
Furthermore, 3 does not react with 5 upon reflux in CHCl3. The
change of the solvent to MeNO2 and increase of the temperature to
80 ꢀC brings about decomposition of the starting materials.
We found that our systems, in contrast to those studied by the
Italian group,44,45 are more reactive, and generation of 6ꢀ10 is
accompanied by other intriguing processes disclosed in sections
given below, while in the next section we describe the identifica-
tion of 6ꢀ10.
Figure 2
and isonitriles; for our reviews see refs 11 and 32ꢀ37],
we reported the coupling of metal-bound isonitriles with sp2-N
nucleophiles, such as benzophenone imine (Figure 2, A),38
3-iminoisoindolin-1-one (B),39ꢀ41 diiminoisoindoline (C),42
and N-Ph-benzamidine (D1 and D2; two regiosiomers are
given),43 furnishing a novel type of [M](ADCs). Some of these
species are highly efficient in SuzukiꢀMiyaura42 and Sonogashira
reactions.43
We found that when the nucleophiles bear the amidine
NdCꢀN moiety, the reaction leads to aminocarbene-like species
with distinct single and double bonds in the CN2 moiety, thus
contrasting with typical diaminocarbenes, which exhibit bond
delocalization (Figure 1). As a continuation of these works, it
seemed logical to study other systems with various NdCꢀN
groups, and we turned our attention to amino- and diaminopyr-
idines as nucleophiles. These systems were previously investi-
gated by Balch et al.27 and also by Belluco et al.,44,45 who
described the coupling reactions with RNC at Pt centers, leading
to the monodentate (E, Figure 3) and chelated (F1, F2)
diaminocarbenes.44,45
Insofar as X-ray studies of complexes shown in Figure 3
were not performed, we decided to fill this gap and also to
extend the number of such complexes. To our surprise, in
addition to the findings reported in refs 27, 44, and 45 and fully
confirmed in our study, we discovered that the chelated
diaminocarbenes shown in Scheme 1 (see later) under certain
conditions could themselves behave as nucleophiles and be
involved in a cascade reaction with metal-activated isonitriles,
thus forming dinuclear complexes. In this article, we disclose
our observations and report on this novel reactivity mode of
diaminocarbene ligands.
Characterization of 6ꢀ10. Complexes 6ꢀ9 were fully char-
acterized by elemental analyses (C, H, N), IR, high-resolution
ESIþ-MS, and 1H and 13C{1H} NMR spectroscopies. Complex
10 was identified in their mixture with other species (e.g., 14, see
later) by high-resolution ESIþ-MS. The ESIþ mass spectra
of 6ꢀ10 display the molecular ion peaks [M]þ or a fragmenta-
tion corresponding to the loss of Cl from the molecular ion, viz.,
[M ꢀ Cl]þ, with the characteristic isotopic distribution.
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Scheme 1. Conventional Addition of Pyridine-2-amine-6-R2 to an Isonitrile Ligand in cis-[PdCl2(CNR1)2] and Subsequent
Ring Closure
Figure 4. View of 6 and 9 (form A) with the atomic numbering schemes. Thermal ellipsoids are drawn with 50% probability. Hydrogen labels are
omitted for simplicity.
The 1H NMR spectra of 6ꢀ9 exhibit two broad singlets in the
δ 13.5ꢀ12.1 range from the NH protons and a set of overlapped
resonances (δ 9.0ꢀ6.1) assigned to the aromatic CꢀH protons.
Two singlets corresponding to the Me groups of 6ꢀ8 emerge in
the 1H NMR in the range δ 2.5ꢀ2.2 and in the 13C{1H} NMR in
diffraction (Figure 4 and Table 1; Figure 1S and Tables 1S and
2S, Supporting Information), and the obtained data reveal both
the addition of 4 to one isonitrile ligand (while the other RNC
ligand remains intact) and coordination of the pyridine ring to
the PdII center. In the crystal structure of 9, two slightly different
independent molecules (A and B) were detected; a mean value of
both was used for a further comparison (see Supporting Infor-
mation for detailed examination of the X-ray data).
In both diaminocarbene complexes 6 and 9, the slightly
distorted square-planar geometry around the metal center is
completed with one bidentate diaminocarbene ligand, one iso-
nitrile (in the cis-position to the carbene moiety), and one chloride.
In the palladacycle, the PdꢀCcarbene distances [Pd1ꢀC6:
1.986(2) Å for 6, 1.972(2) Å for 9] are slightly longer (for 6)
or equal within 3σ to those in the related cis-[PdCl2{C-
(OMe)dN(H)Me}2] (1.953ꢀ1.972 Å)48 and cis-[PdCl2{C-
(dNHCy)NHNHC(dNHCy)}2] (1.958ꢀ1.964 Å)49 com-
plexes. The newly formed carbene ligands adopt the Z (for 6)
1
the δ 19.3ꢀ18.5 range. In the H NMR spectrum of 9, the
characteristic signals of the protons of the tertiary group from the
cyclohexyl rings emerge at 4.3 and 4.2 ppm. In the 13C{1H}
NMR spectra of 6ꢀ9, the CcarbenedNH signals were found to
resonate in the range from 188 to 172 ppm. These values are
more downfield than the values that fall in the interval of
157ꢀ159 ppm, reported for the series of chelated N-heterocyclic
carbenes, such as bis(imidazolylidene) palladium dichloride
complexes, but are upfield of the 194ꢀ227 ppm range found
for the palladium-bound monodentate acyclic diaminocarbenes
and are close to the typical values for coordinated NHCs
obtained by the [2 þ 3] cycloaddition of nitrones to coordinated
isonitriles (ca. 170 ppm).47
Each of the IR spectra of 6ꢀ9 displays one strong ν(CtN)
stretching vibration at 2239ꢀ2217 cmꢀ1. In the carbene moi-
eties, a strong band due to ν(CdN) appears between 1653 and
1568 cmꢀ1. The medium-intensity band at 3447ꢀ3323 cmꢀ1 is
characteristic of ν(NꢀH) vibrations, while a strong-intensity
or E (for 9) configuration, correspondingly, and the NCcarbeneN
moiety is roughly planar. In the latter moiety, the C6ꢀN2 and
C6ꢀN3 bond lengths [1.358(2) and 1.309(2) Å for 6, 1.337(3)
and 1.314(3) Å for 9] are nearly equal and are intermediate
between typical single and typical double bonds,50 indicating a
bond delocalization that is typical for the diaminocarbene
systems.
band due to δ(CꢀH from Ar) is displayed at 785ꢀ772 cmꢀ1
.
The cationic complexes 6 and 9 and corresponding deproto-
nated neutral complex 6a (one crystal of 6a was obtained from
the mixture with 6) were characterized by X-ray single-crystal
In 6a, the slightly distorted square-planar geometry around the
metal center is completed with one bidentate aminocarbene-derived
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ligand [Pd1ꢀC6: 1.993(2) Å], one isonitrile, and one chloride.
The aminocarbene-derived ligand (obtained via the deprotona-
tion of the original diaminocarbene species) is in the Z-config-
uration. The NCNXyl moiety is roughly planar, and the NC
bonds [C6ꢀN2 1.391(3) Å and C6ꢀN3 1.279(3) Å] are close to
a normal single and a normal double bond, correspondingly,
indicating the difference as compared to typical diaminocarbene
species 6 and 9.
excess solid K2CO3 in CHCl3 and heating of the reaction mixture
at 40 ꢀC for 12 h led to novel products 11 and 13 (Scheme 2,
Table 2), which were isolated in good (11, 75%; 13, 65%) yields.
The similar dinuclear complexes 12 and 14, formed by the
addition of 8 or 10 to 2, were identified by high-resolution
ESIþ-MS in the mixture with other species (e.g., 8 or 10,
correspondingly). We were not, however, able to isolate 12
and 14 as individual substances (in the case of 14, presumably
due to an insufficient purity of starting 10) and, consequently,
characterize them with the use of NMR and elemental analyses.
We believe that the generation of 11ꢀ14 proceeds by addition
of Belluco-type ADC complexes with two nucleophilic N centers
to both electrophilic centers (a ligated isonitrile carbon and the
metal) of the starting isonitrile complexes (Scheme 3). This
overall cascade reaction includes the addition of the amino group
of a 2-aminopyridine to the metal-activated isonitrile moiety, ring
closure, and the coupling of the derived ADC complex with the
yet unreacted starting material.
Coupling between ADCs and Isonitriles. Addition of each of
ADCs 6ꢀ8 to starting 1 or 2 (1:1 molar ratio) in the presence of
Table 1. Selected Bond Lengths [Å] and Angles [deg] for
6 and 9 (mean value of forms A and B)
6
9 (A þ B)
Pd(1)ꢀCl(1)
Pd(1)ꢀN(1)
Pd(1)ꢀC(6)
Pd(1)ꢀC(15)
N(1)ꢀC(1)
N(1)ꢀC(5)
N(2)ꢀC(5)
N(2)ꢀC(6)
N(3)ꢀC(6)
N(3)ꢀC(7)
N(4)ꢀC(15)
2.3255(4)
2.043(1)
1.986(2)
1.940(2)
1.350(2)
1.346(2)
1.379(2)
1.358(2)
1.309(2)
1.435(2)
1.147(2)
2.3755(6)
2.084(2)
1.972(2)
1.945(2)
1.360(3)
1.362(3)
1.391(3)
1.337(3)
1.314(3)
1.477(3)
1.141(3)
This process is facilitated upon addition of K2CO3, which
serves as a base, assisting deprotonation of the HN carbene
moiety and thus increasing the nucleophilic activity of the N2C
group. Complexes 11ꢀ14 are also formed in the syntheses of
6ꢀ10 without the base, but their formation is then not selective,
leading to a mixture of species (five spots on TLC), where
11ꢀ14 were generated in ca. 10ꢀ15% NMR yields.
Characterization of Dinuclear Complexes 11ꢀ14. Com-
plexes 11 and 13 were characterized by elemental (C, H, N) ana-
lyses, high-resolution ESIþ-MS, IR, and 1H and 13C{1H} NMR
spectroscopies, while 12 and 14 were detected by high-resolution
ESIþ-MS monitoring of the reaction mixtures. In addition, the
C(6)ꢀPd(1)ꢀCl(1)
C(15)ꢀPd(1)ꢀN(1)
C(6)ꢀPd(1)ꢀN(1)
N(1)ꢀPd(1)ꢀCl(1)
C(15)ꢀPd(1)ꢀCl(1)
C(15)ꢀPd(1)ꢀC(6)
C(6)ꢀN(2)ꢀC(5)
N(2)ꢀC(6)ꢀPd(1)
N(3)ꢀC(6)ꢀPd(1)
N(3)ꢀC(6)ꢀN(2)
C(6)ꢀN(3)ꢀC(7)
C(15)ꢀN(4)ꢀC(16)
N(4)ꢀC(15)ꢀPd(1)
172.33(4)
176.41(7)
170.1(1)
80.34(8)
102.96(5)
85.18(9)
91.5(1)
179.45(6)
80.53(6)
94.21(4)
86.11(5)
99.20(6)
119.7(1)
111.9(1)
133.0(1)
115.0(1)
126.4(1)
177.2(2)
170.5(1)
Scheme 2. Reaction of 1 or 2 with 6ꢀ8
119.5(2)
113.3(2)
126.8(2)
120.0(2)
127.0(2)
173.4(3)
176.0(3)
Table 2. Numbering of Complexes Given in Scheme 2
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Scheme 3. Nucleophilic Addition of the Complexed ADCs to Metal-Activated Isonitriles
structures of 11 and 13 were confirmed by single-crystal X-ray
diffraction technique.
Compounds 11 and 13 gave satisfactory elemental analyses.
The ESIþ-MS mass spectra of 11ꢀ14 display the molecular ion
(or protonated molecular ion [M þ H]þ) or a fragmentation
corresponding to the loss of Cl from the molecular ion, viz.,
[M ꢀ Cl]þ, with the characteristic isotopic distribution. The IR
spectra of 11 and 13 exhibit one strong and broad ν(CtN)
peak in the 2201ꢀ2189 cmꢀ1 range from both RNC ligands.
The characteristic IR absorptions for the starting cis-[PdCl2-
(CNR1)2] complexes, usually displayed as two overlapped
ν(CtN) stretches in the 2270ꢀ2150 cmꢀ1 interval, logically
were not observed in the dimers. In 11ꢀ14, two strong
ν(CdN) bands appear between 1663 and 1565 cmꢀ1. The
medium/strong-intensity bands in the 3082ꢀ2849 cmꢀ1 range
are characteristic of ν(CꢀH) vibrations, while a strong-inten-
sity band due to δ(CꢀH from Ar) appears in the range
The 1H NMR spectra of 11 and 13 exhibit a set of overlapped
signals in the δ 9.15ꢀ6.09 range assigned to NH2 (for 13) and
the aromatic CꢀH protons. The spectra of 11 and 13 in the
range δ 2.54ꢀ2.04 display four singlets due to the Me groups. In
the 13C NMR spectra, two overlapped signals are observed in the
194ꢀ189 ppm range for both 11 and 13, which corresponds to
the carbon resonances from CdN moieties. Signals of the Me’s
are observed as four singlets (19.7, 19.6, 18.7, 18.6 ppm) for 13
and two singlets (19.7, 19.5 ppm) and one broad overlapped
peak (18.7 ppm) for 11.
Figure 5. View of 11 with the atomic numbering scheme. Thermal
ellipsoids are drawn with 50% probability. Hydrogen labels are omitted
for simplicity.
783ꢀ776 cmꢀ1
.
(82.89 Å),55 cis-[PtCl(NH3)(NH2CH2COO)] (81.56 Å),56 and
[PtCl(PPh3)(NMe2CH2NMe2CH2)](Cl) (82.30 Å).57
Among the PdꢀC distances, Pd1ꢀC6 (in 11) and Pd1ꢀC3
(in 13) [1.988(2) Å] are slightly longer than (while Pd2ꢀC24
1.977(2) Å for 11 and Pd2ꢀC4 1.975(2) Å for 13 are equal to)
those reported for the relevant palladium complexes cis-[PdCl2-
{C(OMe)dN(H)Me}2] (1.953ꢀ1.972 Å)48 and cis-[PdCl2{C-
(dNHCy)NHNHC(dNHCy)}2] (1.958ꢀ1.964 Å).49 The fused
rings [the first C1d(N1pyrNH2)N2Xyl group repeats the one from
mononuclear 6ꢀ9, while the second C2d(N2Xyl)N3Xyl is gene-
rated during the formation of target 11ꢀ14], in both complexes,
are roughly planar.
The crystallographic data and processing parameters for 11
and 13 are summarized in Table 3S (Supporting Information),
while the corresponding plots can be found in Figure 5 and Figure
2S (Supporting Information), and bond lengths and angles are
given in Table 3 and Table 4S.
In the first moiety, the bond lengths [C6ꢀN2 1.342(3) Å and
C6ꢀN3 1.343(3) Å for 11; C3ꢀN3 1.346(3) Å and C3ꢀN5
1.320(3) Å for 13] are equal and are intermediate between the
typical double and single bonds resembling the typical diamino-
carbene structure. In the second fragment, the bond lengths
C24ꢀN3 1.458(3) Å (for 11) and C4ꢀN3 1.463(3) Å (for 13)
are single, while C24ꢀN5 1.259(3) Å (for 11) and C4ꢀN4
1.257(3) Å (for 13) are typical double bonds. All other bond
lengths in 11 and 13 are normal, and their values agree with those
reported for related palladium(II)48,49,51ꢀ53 carbene and isoni-
trile species.
In 11 and 13, both metal centers adopt a distorted square-
planar geometry. The isonitrile ligands are in cis-position to the C
atoms of {C(dNXyl)N(Xyl)CN(C5H3R2N)}; the latter forms
the dinuclear bicyclic framework. The bond lengths of the two
coordinated CN groups in each of 11 and 13 fall in the interval of
1.144ꢀ1.153 Å, typical for the common range of the CN triple
bonds in related isonitrile palladium complexes, e.g., cis-[PdCl2-
(CNR)2] [R = Cy (1.128ꢀ1.142 Å),51 But (1.108ꢀ1.149 Å),52
and Xyl (1.145ꢀ1.156 Å)53].
In the metallacycles, the angles around the Pd centers in
both 11 and 13 are within the 78.73(9)ꢀ79.36(8)ꢀ range, being
slightly smaller than those previously observed in the mono-
nuclear palladium and platinum five-membered chelates
[Pd(phen){C(dO)NPhC(dO)NPh}] (80.14 Å),54 [PdI{Ct
NC6H3(2,6-Me2)}{C(C6H4(2-NH2))dNC6H3(2,6-Me2)}]
’ FINAL REMARKS
The results from this work may be considered from at least
three perspectives. First, we discovered that metal-diaminocarbenes
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Table 3. Selected Bond Lengths [Å] and Angles [deg] for 11
positive ion mode using a m/z range of 50ꢀ3000. The capillary voltage
of the ion source was set at ꢀ4500 V (ESIþ-MS), and the capillary exit
at 70ꢀ150 V. The nebulizer gas flow was 0.4 bar, and drying gas flow
4.0 L/min. For ESI, species were dissolved in MeCN or MeOH. In the
isotopic pattern, the most intensive peak is reported. Mass calibration
for data system acquisition was achieved using CsI. Infrared spectra
(4000ꢀ400 cmꢀ1) were recorded on a Shimadzu FTIR-8400S instru-
ment in KBr pellets. 1H and 13C{1H} NMR spectra were recorded on
Bruker Avance IIþ 400 MHz (UltraShield Magnet) and Bruker Avance
IIþ 500 MHz (UltraShield Plus Magnet) spectrometers at ambient
Pd(1)ꢀCl(1)
Pd(1)ꢀN(1)
Pd(1)ꢀC(6)
Pd(1)ꢀC(15)
Pd(2)ꢀCl(2)
Pd(2)ꢀN(2)
Pd(2)ꢀC(24)
Pd(2)ꢀC(33)
N(1)ꢀC(1)
N(1)ꢀC(5)
C(1)ꢀC(2)
C(2)ꢀC(3)
C(3)ꢀC(4)
2.3469(5)
2.028(2)
1.988(2)
1.940(2)
2.4082(6)
2.054(2)
1.977(2)
1.945(2)
1.348(3)
1.351(3)
1.376(3)
1.389(3)
1.384(3)
C(4)ꢀC(5)
N(2)ꢀC(5)
N(2)ꢀC(6)
N(3)ꢀC(6)
N(3)ꢀC(7)
N(3)ꢀC(24)
N(4)ꢀC(15)
N(4)ꢀC(16)
N(5)ꢀC(24)
N(5)ꢀC(25)
N(6)ꢀC(33)
N(6)ꢀC(34)
1.390(3)
1.391(2)
1.342(3)
1.343(3)
1.446(3)
1.458(3)
1.149(3)
1.401(3)
1.259(3)
1.407(3)
1.153(3)
1.396(3)
1
temperature. H and 13C{1H} NMR chemical shifts are reported in
ppm relative to SiMe4 (1H and 13C = 0.0 ppm) with reference to the
residual solvent resonances of 7.26 ppm (1H) and 77.1 ppm (13C) for
chloroform-d.
X-ray Structure Determinations. Single-crystal X-ray diffraction
experiments for 6, 6a, 9, 11, and 13 were carried out with a Bruker
SMART APEX II diffractometer [graphite-monochromated Mo KR
radiation, λ = 0.71073 Å, ω-scan technique, T = 100 K (6, 6a, 9, 11) or
150 K (13)]. For 6, 6a, 9, and 11, the APEX II software61 was used for
collecting frames of data, indexing reflections, determination of lattice
constants, integration of intensities of reflections, and scaling and
absorption correction, and SHELXTL62 for space group and structure
determination, refinements, graphics, and structure reporting. The
structures were solved by direct methods and refined by the full-matrix
least-squares technique against F2 with the anisotropic thermal para-
meters for all non-hydrogen atoms. The hydrogen atoms of NH and
NH2 groups were located in difference Fourier synthesis and refined
isotropically; the rest of the hydrogen atoms were placed geometrically
and included in the structure factors calculation in the riding motion
approximation. For 13, cell parameters were retrieved using Bruker
SMART software and refined using Bruker SAINT61 on all the observed
reflections. Absorption corrections were applied using SADABS.63
Structures were solved by direct methods by using the SHELXS-97
package64 and refined with SHELXL-97.62 Calculations were performed
using the WinGX System, version 1.80.03.65 All hydrogens were inserted
in calculated positions. Least-square refinements with anisotropic ther-
mal motion parameters for all the non-hydrogen atoms and isotropic
for the remaining atoms were employed. The principal experimental
and crystallographic parameters are presented in Tables 1S and 3S of
Supporting Information.
C(6)ꢀPd(1)ꢀCl(1)
C(15)ꢀPd(1)ꢀN(1)
C(6)ꢀPd(1)ꢀN(1)
N(1)ꢀPd(1)ꢀCl(1)
C(15)ꢀPd(1)ꢀCl(1)
C(15)ꢀPd(1)ꢀC(6)
C(24)ꢀPd(2)ꢀCl(2)
C(33)ꢀPd(2)ꢀN(2)
C(24)ꢀPd(2)ꢀN(2)
N(2)ꢀPd(2)ꢀCl(2)
C(33)ꢀPd(2)ꢀCl(2)
C(33)ꢀPd(2)ꢀC(24)
C(1)ꢀN(1)ꢀC(5)
C(5)ꢀN(1)ꢀPd(1)
C(1)ꢀN(1)ꢀPd(1)
N(1)ꢀC(5)ꢀN(2)
N(1)ꢀC(5)ꢀC(4)
172.81(6) C(4)ꢀC(5)ꢀN(2)
177.25(8) C(6)ꢀN(2)ꢀC(5)
79.36(8) C(6)ꢀN(2)ꢀPd(2)
93.97(5) C(5)ꢀN(2)ꢀPd(2)
86.26(6) N(2)ꢀC(6)ꢀPd(1)
100.54(8) N(3)ꢀC(6)ꢀPd(1)
176.99(6) N(2)ꢀC(6)ꢀN(3)
174.60(8) C(6)ꢀN(3)ꢀC(7)
78.90(8) C(6)ꢀN(3)ꢀC(24)
101.47(5) C(7)ꢀN(3)ꢀC(24)
122.9(2)
115.0(2)
114.5(1)
130.1(1)
115.4(1)
130.5(2)
114.0(2)
125.5(2)
117.4(2)
117.0(2)
83.44(7) C(15)ꢀN(4)ꢀC(16) 175.9(2)
96.08(9) C(24)ꢀN(5)ꢀC(25) 124.1(2)
119.7(2)
113.1(1)
126.7(1)
116.1(2)
120.9(2)
N(3)ꢀC(24)ꢀPd(2)
N(5)ꢀC(24)ꢀPd(2)
N(5)ꢀC(24)ꢀN(3)
C(33)ꢀN(6)ꢀC(34) 172.0(2)
N(6)ꢀC(33)ꢀPd(2) 171.1(2)
110.5(1)
135.1(2)
114.4(2)
upon deprotonation may behave as metal-containing nucleo-
philes, and this property is clearly manifested in the observed
coupling with ligated isonitriles leading to the unreported
dimetallic species. We are currently exploring the diaminocarbeneꢀ
isonitrile integration by expanding to other types of ligated amino-
carbenes and to other electrophiles bearing multiple bonds.
Second, the observed coupling is novel for the chemistry of
coordinated isonitrile species. Indeed, previously for N-type
nucleophiles, only additions of amines/hydrazines6,11 andimines38,39
to metal-bound isonitriles were reported. Third, the newly
observed ADCꢀisonitrile coupling led to a dinuclear system
bearing two terminal cis-Cl(CNR1)[Pd] moieties, which, in turn,
are expected to be employed (via similar additions) for con-
struction of larger polymetallic species with their potential
application in materials science.
Synthetic Work. Preparation of cis-[PdCl2(R1NC)2] (R1 = 2-Cl,6-
MeC6H3) (2). A mixture of solid cis-[PdCl2(MeCN)2] (0.259 g,
1 mmol) and 2-Cl,6-Me-C6H3NC (0.303 g, 2 mmol) in CHCl3
(25 mL) was refluxed under vigorous stirring. After 1 h, the reaction
mixture was allowed to reach room temperature and then evaporated
to dryness under a stream of dinitrogen. The colorless precipitate
formed was washed with three 10 mL portions of diethyl ether and
dried in vacuo at 20ꢀ25 ꢀC (87% isolated yield). Anal. Calcd for
C16H12N2Cl4Pd: C 39.99; H 2.52; N 5.83. Found: C 40.11; H 2.53;
N 5.49. High-resolution ESIþ-MS (150 V, MeCN): found 479.8768
[M]þ, calcd for C23H24N4ClPd 479.8760. 1H NMR (CD2Cl2, δ): 7.40
(d, 2H, J3HH 6.5 Hz, H3), 7.39 (d, 2H, J3HH 7.5 Hz, H5), 7.30 (dd, 2H,
J3HH 6.5 and 7.5 Hz, H4), 2.55 (s, 6H, Me’s). 13C{1H} NMR (CD2Cl2,
δ): 144.1 (C1), 139.7 (C2), 131.8 (C6), 132.3 (C4), 129.7 (C5), 129.7
(C3), 19.2 (Me’s).
’ EXPERIMENTAL SECTION
Reaction between cis-[PdCl2(CNR1)2] (1ꢀ3) and 4 or 5 (General
Procedure). Solid 4 or 5 (0.25 mmol) was added to a solution (for 2
and 3) or a suspension (for 1) (0.25 mmol) in CHCl3 (5 mL), and the
reaction mixture was then left to stand at 20ꢀ25 ꢀC for 12 h. During the
reaction time, the color of the mixture turned from light to lemon yellow
(for 4) or orange (for 5). After 12 h, the reaction mixture was evaporated
to dryness at 40ꢀ45 ꢀC, whereupon the solid residue was dissolved in
CH2Cl2 (5 mL) and filtered off from a small amount of undissolved
material. The filtrate was evaporated to dryness at room temperature,
Materials and Instrumentation. Solvents, all isonitriles, and
pyridine-2-amine-6-R2 were obtained from commercial sources and
used as received. The complexes cis-[PdCl2(R1NC)2] (R1 = Cy and
Xyl)58ꢀ60 were prepared as previously reported. C, H, and N elemental
analyses were carried out by the Department of Organic Chemistry,
St.Petersburg State University. Electrospray ionization mass spectra
were obtained on a Bruker microTOF spectrometer equipped with
electrospray ionization (ESI) source. The instrument was operated in
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Organometallics
ARTICLE
washed with three 1 mL portions of Et2O, and dried in air at 20ꢀ25 ꢀC.
Yields were 60ꢀ75%, based on Pd.
ring), 166.6, 140.8, 136.9, 130.9, 129.3, 127.8, 127.6, 113.8, 113.4, 112.1,
111.8 (C and CH from aryls), 19.5 and 18.3 (Me’s).
9 (60% isolated yield). Anal. Calcd for C19H28N5ClPd CHCl3: C
3
6 (75% isolated yield). Anal. Calcd for C23H24N4Cl2Pd: C 51.75; H
4.53; N 10.50. Found: C 51.62; H 4.42; N 10.49. High-resolution ESIþ-
MS (150 V, MeCN): found 499.0772 [Mcat ꢀ Cl]þ, calcd for
C23H24N4ClPd 499.0818. IR (KBr, selected bands, cmꢀ1): ν(NꢀH)
40.87; H 4.97; N 11.91. Found: C 41.12; H 5.21; N 11.83; solvated
CHCl3 molecule has been detected in the NMR spectra measured in
DMSO-d6. High-resolution ESIþ-MS (70 V, MeOH): found 470.1129
[Mcat]þ, calcd for C19H28N5ClPd 470.1162. IR (KBr, selected
bands, cmꢀ1): ν(NꢀH) 3323 (m), ν(CꢀH) 3172 (m), 2933 (s), 2857
(s), ν(CtN) 2239 (s), ν(NdCcarbene, NdC) and δ(NꢀH) 1653 (s),
1624 (s), 1589 (s), 1568 (s), δ(CꢀH from the pyridine ring) 780 (s). 1H
3447 (m), ν(CꢀH) 2923 (m), ν(CtN) 2217 (s), ν(NdCcarbene
,
NdC) and δ(NꢀH) 1628 (s), 1595 (s), 1546 (s), δ(CꢀH from aryls)
774 (s). 1H NMR (CDCl3, δ): 13.32 (s, br) and 12.14 (s, br, 2H, NH’s)
9.01ꢀ8.99 (m, 1H), 7.99ꢀ7.94 (m, 1H), 7.36ꢀ7.33 (m) and 7.25ꢀ6.43
(m, 8H, aryls), 2.42 (s) and 2.19 (s, 12H, Me’s). 13C{1H} NMR (CDCl3,
δ): 187.8 (CdN from carbene C atom), 157.9 (C2 from the pyridine
ring), 147.5, 143.0, 138.2ꢀ128.0, 118.7, 111.3 (C and CH from aryls),
19.3 and 18.5 (Me’s).
NMR (DMSO-d6, δ): 8.62 (s, 2H, NHs), 7.96 (s, 2H, NH2), 7.53 (t, J3
HH
8.0 Hz, 1H, H4 from the pyridine ring), 6.71 (d, J3HH 7.5 Hz, 1H), 6.29 (d,
J3HH 8.5 Hz, 1H, H3þH5 from the pyridine ring), 4.29 (m) and 4.21 (m,
2H, CH), 1.86ꢀ1.08 (m, 20H, CH2). 13C{1H} NMR (DMSO-d6, δ):
172.2 (CdN from carbene C atom), 161.8, 152.5 (C2 þ C6 from the
pyridine ring), 141.9 (C4), 106.0 (C5), 97.6 (C3 from the pyridine ring),
55.3, 54.8 (CH from Cy’s), 31.8, 31.0, 25.1, 24.8, 24.7, 22.2 (CH2).
7 (72% isolated yield). Anal. Calcd for C23H25N5Cl2Pd: C 50.33; H
4.59; N 12.76. Found: C 50.61; H 4.87; N 12.55. High-resolution ESIþ-
MS (70 V, MeCN): found: 514.0991 [Mcat ꢀ Cl]þ, calcd for
C23H25N5ClPd 514.0927. IR (KBr, selected bands, cmꢀ1): ν(NꢀH)
3431 (s, br), ν(CꢀH) 2980, 2922 (m), ν(CtN) 2204 (s), ν-
(NdCcarbene, NdC) and δ(NꢀH) 1638, 1617 (s), 1542 (s), δ(CꢀH
from aryls) 785 (s). 1H NMR (CDCl3, δ): 7.47ꢀ7.32 (m) and
7.20ꢀ6.06 (m), (m, 12H, aryls, NH’s), 2.47 (s), 2.21 (s, 12H, Me’s).
13C{1H} NMR (CDCl3, δ): 185.5 (CdN from carbene C atom), 158.9
(C2 from the pyridine ring), 154.5 (C6 from the pyridine ring), 143.0,
134.2ꢀ127.2, 116.7, 111.3 (C and CH from aryls), 19.2 and 18.4 (Me’s).
10. High-resolution ESIþ-MS (70V, MeCN):found 553.9917 [Mcat
ꢀ
Cl]þ, calcd for C21H19N5Cl3Pd 553.9835. The reaction between 2 and 5
led to formation of a dark orange, oily residue, which was a broad mixture
of products (five spots on TLC). High-resolution ESIþ-MS showed the
presence of 10 and dinuclear 14 among the other products.
Reaction of 1 or 2 with 6ꢀ8 and 10 (General Procedure). Each of
solid 6ꢀ8 or 10 (0.25 mmol) was added to a solution (for 2) or a
suspension (for 1) (0.25 mmol) in CHCl3 (5 mL), and the reaction
mixture was stirred with an excess of K2CO3 (1.50 mmol) at 40 ꢀC for 12
h. During the reaction time, the mixture turned from colorless to lemon
yellow (for 6 and 7) or orange (for 8 and 10). After 12 h, the reaction
mixture was filtered off from the solid material and evaporated to dryness
at 40ꢀ45 ꢀC, whereupon the oily residue formed was dissolved in
CH2Cl2 (5 mL). The filtrate was evaporated to dryness at room
temperature, washed with three 1 mL portions of Et2O, and dried in
air at 20ꢀ25 ꢀC. Yields were 65ꢀ75%, based on Pd.
8 (62% isolated yield). Anal. Calcd for C21H18N4Cl4Pd: C 43.89; H
3.15; N 9.75. Found: C 44.17; H 3.38; N 9.54. High-resolution ESIþ-MS
(70 V, CH2Cl2): found 538.9531 [Mcat
ꢀ
Cl]þ, calcd for
C21H18N4Cl3Pd 538.9726. IR (KBr, selected bands, cmꢀ1): ν(NꢀH)
3445 (s, br), ν(CꢀH) 2949 (m), 2838 (m), ν(CtN) 2208 (s),
ν(NdCcarbene, NdC) and δ(NꢀH) 1639, 1620 (s), 1549 (s), δ(CꢀH
from aryls) 772 (s). 1H NMR (CDCl3, δ): 13.46 (s, br), 12.35 (s, br, 2H,
NH’s) 9.03ꢀ9.00 (m), 8.02ꢀ7.96 (m), 7.39ꢀ7.30 (m), and 7.23ꢀ6.87
(m, 10H, aryls), 2.51 (s), 2.32 (s, 6H, Me’s). 13C{1H} NMR (CDCl3,
δ): 195.3 (CdN from carbene C atom), 155.8 (C2 from the pyridine
11 (75% isolated yield). Anal. Calcd for C41H40N6Cl2Pd2: C 54.68; H
4.47; N 9.33. Found: C 54.75; H 4.56; N 9.46. High-resolution ESIþ-MS
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Organometallics
ARTICLE
(150 V, MeCN): found 902.0426 [M þ H]þ, calcd for C41H40N6Cl2Pd2
902.0955. IR (KBr, selected bands, cmꢀ1): ν(CꢀH) 3081 (m), 2919
(s), 2849 (s), ν(CtN) 2201 (s), ν(NdC) 1663 (s), 1608 (s), δ(CꢀH
from aryls) 777 (s). 1H NMR (CDCl3, δ): 9.06ꢀ8.99 (m, 1H),
7.87ꢀ7.82 (m, 1H), 7.22ꢀ6.17 (m, 14H, aryls), 2.45 (s, 6H), 2.27 (s,
6H), 2.23 (s, 6H), 2.04 (s, 6H, Me’s). 13C{1H} NMR (CDCl3, δ): 194.8
and 167.0 (CdN), 162.5, 149.5, 147.6, 146.9, 143.0, 141.8,
136.8ꢀ134.3, 129.8ꢀ126.7, 123.8, 118.5, 117.5 (C and CH from aryls),
19.7, 19.5, 18.7 (Me’s).
products (five spots on TLC). High-resolution ESIþ-MS indicated the
presence of 10 and dinuclear 14 among other species.
’ ASSOCIATED CONTENT
S
Supporting Information. This material is available free
b
of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*(A.J.L.P.) E-mail: pombeiro@ist.utl.pt. Fax: (þ351)218464455.
(V.Y.K.) E-mail: kukushkin@VK2100.spb.edu. Fax: þ7(812)-
4286939.
’ ACKNOWLEDGMENT
The Russian group thanks the Federal Targeted Program
“Scientific and Scientific-Pedagogical Personnel of the Innovative
Russia in 2009ꢀ2013” (contract no. P676 from 20/05/2010),
Russian Fund for Basic Research (grants 09-03-00065a and 11-
03-12044), and RAS Presidium Subprogram coordinated by
acad. N T. Kuznetsov. The authors acknowledge Saint-Peters-
burg State University for a research grant (2011ꢀ2013). The
Visby Program is thanked for the cooperation grant. In Portugal,
this work has been partially supported by the Fundac-~ao para a
Ci^encia e a Tecnologia (FCT), Portugal, and its PPCDT
program (FEDER funded) through the research projects
PTDC/QUI-QUI/098760/2008 and PTDC/QUI-QUI/
109846/2009. K.V.L. is grateful to both the FCT and Instituto
Superior Tꢀecnico (IST) for the research contract (Ci^encia 2008
Initiative). The authors also thank the Portuguese NMR Net-
work (ISTꢀUTL NMR Center) for providing access to the
NMR facilities.
12. High-resolution ESIþ-MS (70 V, MeCN): found 946.8987 [M ꢀ
Cl]þ, calcd for C37H28N6Cl5Pd2 946.8862. The reaction between 2 and
7 led to formation of an orange, oily residue of a broad mixture of
products. High-resolution ESIþ-MS showed the presence of 12 among
other species.
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