PdII-promoted single-pot template transformations of benzonitriles, cyanoguanidine and sodium dicyanamide with the formation of symmetrical and asymmetrical (1,3,5-Triazapentadienate)palladium(II) complexes

Article abstract of DOI:10.1002/ejic.201000898

Treatment of benzonitriles 4-XC₆H₄CN (1) [X = H (1a), F (1b), Cl (1c), Br (1d), I (1e)] with an excess of 2-butanone oxime (Me)(Et)C=NOH (as a reagent and solvent) in the presence of PdCl₂ at 100 °C for 12 h affords the symmetrical cationic 2,4-diaryl-1,3,5- triazapentadiene (Htap) palladium(II) complexes [Pd(Htap)₂]Cl ₂ (2') [Htap = HN=C(4-XC₆H₄)NHC(4-XC ₆H₄)=NH]. Recrystallization of 2' from MeOH/CHCl ₃ with two equivalents of n-propylamine gives the corresponding neutral triazapentadienate (tap) complexes [Pd(tap)₂] (2) [tap = HN=C(4-XC₆H₄)NC(4-XC₆H₄)=NH; X = H (2a), F (2b), Cl (2c), Br (2d), I (2e)] in good yields. When cyanoguanidine, HN=C(NH₂)N(H)C=N (3), or sodium dicyanamide NaN(C=N)₂ (5) are treated with an excess of primary alcohols, ROH [R = Me, Et, nPr, nBu or (CH₂)₂OMe] in the presence of PdCl₂, while being heated for 12 h, the corresponding asymmetrical 2-amino-4-alkoxy-1,3,5- triazapentadienate-Pd^II complexes [Pd{HN=C(NH₂)NC(OR)=NH} ₂] (4) [R = Me (4a), Et (4b), nPr (4c), nBu (4d)] or the symmetrical 2,4-dialkoxy-1,3,5-triazapentadienate-Pd^II complexes [Pd{HN=C(OR)NC(OR)=NH}₂] (6) [R = Me (6a), Et (6b), nPr (6c), (CH₂)₂OMe (6d)], respectively, are formed and isolated as a mixture of isomers in good yields. All these compounds have been characterized by IR, ¹H and ¹³C NMR spectroscopy, ESI-MS, elemental analyses and, in the case of 2c, by XRD. Symmetrical and asymmetrical 1,3,5-triazapentadienate-Pd^II complexes have been synthesized by the template transformations of benzonitriles, cyanoguanidine and sodium dicyanamide bound to Pd^II centers. Copyright

Full text of DOI:10.1002/ejic.201000898

FULL PAPER
DOI: 10.1002/ejic.201000898
PdII-Promoted Single-Pot Template Transformations of Benzonitriles,
Cyanoguanidine and Sodium Dicyanamide with the Formation of Symmetrical
and Asymmetrical (1,3,5-Triazapentadienate)palladium(II) Complexes
Maximilian N. Kopylovich,[a] Jamal Lasri,[a] M. Fátima C. Guedes da Silva,[a,b] and
Armando J. L. Pombeiro*[a]
Keywords: Palladium / N ligands / Template synthesis
Treatment of benzonitriles 4-XC6H4CN (1) [X = H (1a), F (1b),
Cl (1c), Br (1d), I (1e)] with an excess of 2-butanone oxime
(Me)(Et)C=NOH (as a reagent and solvent) in the presence
of PdCl2 at 100 °C for 12 h affords the symmetrical cationic
2,4-diaryl-1,3,5-triazapentadiene (Htap) palladium(II) com-
plexes [Pd(Htap)2]Cl2 (2Ј) [Htap = HN=C(4-XC6H4)NHC(4-
XC6H4)=NH]. Recrystallization of 2Ј from MeOH/CHCl3 with
two equivalents of n-propylamine gives the corresponding
neutral triazapentadienate (tap) complexes [Pd(tap)2] (2) [tap
= HN=C(4-XC6H4)NC(4-XC6H4)=NH; X = H (2a), F (2b), Cl
(2c), Br (2d), I (2e)] in good yields. When cyanoguanidine,
alcohols, ROH [R = Me, Et, nPr, nBu or (CH2)2OMe] in the
presence of PdCl2, while being heated for 12 h, the corre-
sponding asymmetrical 2-amino-4-alkoxy-1,3,5-triazapen-
tadienate-PdII complexes [Pd{HN=C(NH2)NC(OR)=NH}2] (4)
[R = Me (4a), Et (4b), nPr (4c), nBu (4d)] or the symmetri-
cal 2,4-dialkoxy-1,3,5-triazapentadienate-PdII complexes
[Pd{HN=C(OR)NC(OR)=NH}2] (6) [R = Me (6a), Et (6b), nPr
(6c), (CH2)2OMe (6d)], respectively, are formed and isolated
as a mixture of isomers in good yields. All these compounds
have been characterized by IR, 1H and 13C NMR spec-
troscopy, ESI-MS, elemental analyses and, in the case of 2c,
by XRD.
HN=C(NH2)N(H)CϵN
(3), or
sodium dicyanamide
NaN(CϵN)2 (5) are treated with an excess of primary
Previously, some tap-PdII complexes were synthesized by
the reaction of pre-prepared tap with metal ion
sources.[3,5,6,12] These pre-prepared tap ligands usually con-
tain N1,N3 nitrogen atoms connected to bulky groups, e.g.
phenyls, and can be synthesized by the reaction of primary
amines, RNH2, with the fluorinated imine C3F7-CF=N-
Introduction
Palladium complexes containing an imino (C=N) ligand
moiety are known to be good catalysts for many organic
syntheses, in particular C–C cross-coupling or carboxyl-
ation reactions.[1,2] Lately one class of such imino ligands,
viz. 1,3,5-triazapentadienates N(H)=C(R)-N-C(RЈ)=N(H)
(tap), has attracted increasing attention.[3–20] These com-
pounds are triaza isoelectronic analogues of the well known
and widely used O,O-β-diketonates R-C(=O)-CH-C(=O)-
R, and usually coordinate to a metal ion as chelating N,N-
bidentate ligands, forming stable complexes with a square
planar core.[3–20] On the other hand, it was noted[9] that
these ligands resemble bis(pyrazolyl)borates, another im-
portant class of ligands. Thus, tap can also potentially im-
pact areas in which O,O-β-diketonates or bis(pyrazolyl)bo-
rates find application, such as in organic synthesis, catalysis,
the preparation of optical recording materials, enzyme inhi-
bition, analytical chemistry, etc.[21,22]
[6]
C4F9 or by the Ley and Muller method[23] where amidine
is treated with an N-imidoyl chloride.[3–5,12] Another route
to tap-Pd complexes involves template transformations of
cyanopyridines[10,16] through lithium amidinate, which is
[10]
produced in situ from LiN(SiMe3)2 or via an oxime-me-
diated process.[16] In the latter case, the synthesized com-
plexes were shown[16] to display catalytic activity towards
Suzuki–Miyaura and Heck cross-coupling reactions.
A further synthetic path to tap ligands proceeds via nu-
cleophilic addition of alcohols to dicyanamides or cyano-
guanidines that are coordinated to a metal center.[17–20] Un-
til now only copper, nickel and platinum ions have been
studied in these transformation reactions and no data on
palladium(II)-mediated transformations have been re-
ported, irrespective of the potential ability of PdII to form
tap complexes[3,5,6,10,12,16] and its expected behavioural simi-
larity to that of PtII in promoting nucleophilic addition re-
actions with substrates containing the CϵN group, namely
organonitriles.[24–27]
[a] Centro de Química Estrutural, Complexo I, Instituto Superior
Técnico, TU Lisbon,
Av. Rovisco Pais, 1049-001 Lisbon, Portugal
E-mail: pombeiro@ist.utl.pt
http://cqe.ist.utl.pt/research/group5.php
[b] Universidade Lusófona de Humanidades e Tecnologias,
Av. Campo Grande n° 376, ULHT Lisbon, 1749-024 Lisbon,
Portugal
Thus, one can conclude that the template conversions of
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000898.
CϵN-containing reagents to tap ligands bound to PdII cen-
Eur. J. Inorg. Chem. 2011, 377–383
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377

M. N. Kopylovich, J. Lasri, M. F. C. Guedes da Silva, A. J. L. Pombeiro
FULL PAPER
ters deserve to be explored further as a convenient route to
new tap-palladium(II) complexes. In the current study we
have extended the family of triazapentadienate-palladium
complexes by applying the template oxime-mediated trans-
formation of benzonitriles, and the nucleophilic addition of
alcohols to cyanoguanidine and dicyanamide.
Results and Discussion
Conversion of Benzonitriles to 2,4-Diaryl-1,3,5-triaza-
pentadienate Ligands Mediated by the Palladium(II)/
2-Butanone Oxime System
Recently, we performed an easy and convenient template
synthesis of tap complexes in good yields from nitriles that
was mediated by oximes.[7,11,16] Initially, this procedure in-
volved an NiII metal center, and liquid nitriles in a high
excess since they acted also as solvents,[7] but a route with
solid nitriles (in particular, cyanopyridine) was developed
with a liquid oxime used as a solvent,[11] and the synthetic
procedure was extended to involve other metal centers (in
particular, PdII).[16] This route is attractive due to its sim-
plicity and the low cost of the reagents, further it does not
Scheme 1.
1
need special precautions and proceeds in air and in solvents pear in the δ = 7–8 ppm range in the H NMR spectra,
and reagents that have not been predried. Thus, we have with the corresponding 13C NMR resonances at δ = 120–
now tested a similar strategy for the synthesis of related 2,4- 140 ppm, while the C=N carbon atom is observed at ca.
diaryl-1,3,5-triazapentadienate-PdII complexes.
160–170 ppm. The monoprotonated molecular ions [M +
The reactions of the unsubstituted benzonitrile 4- H]+ are observed with the expected isotopic patterns in the
XC6H4CN (1) [X = H (1a)], and of those containing an ESI-MS spectra (see Exp. Sect.).
electron-withdrawing substituent at the para-position [X =
Yellow crystals of 2c suitable for XRD analysis were ob-
F (1b), Cl (1c), Br (1d), I (1e)], with palladium(II) chloride tained upon recrystallization by slow evaporation of a
(PdCl2) and 2-butanone oxime [(Me)(Et)C=NOH] for 12 h MeOH/CHCl3 solution of 2c, in the presence of 2 equiv. of
at 100 °C, lead to the formation of the cationic 1,3,5-triaza- nPrNH2. In the structure of 2c the metal cation is located
pentadiene palladium(II) complexes [Pd(Htap)2]Cl2 (2Ј) on a crystallographic inversion center and two uninegatively
that were isolated as yellow powders from the reaction mix- charged para-chlorophenyl tap ligands act as N,N-bidentate
ture (Scheme 1, reaction 1), in a similar manner to the pyr- chelating agents and occupy the four coordination sites of
idine-containing nitriles we reported earlier.[16] In contrast, the central PdII ion, which has a slightly distorted square-
if acetone is used as solvent in the presence of 4 equiv. of planar geometry (Figure 1). The N–Pd–N bite angles
2-butanone oxime, only a palladium(II)-oxime complex is [87.80(5) and 92.20(5)°] and the Pd–N bond distances
recovered after refluxing the reaction mixture for 1 d (see [1.9783(13) and 1.9849(13) Å] are close to those observed
Exp. Sect.). Recrystallization of 2Ј from MeOH/CHCl3 with in PdII bis-1,3,5-triazapentadienes. The negative charges on
2 equiv. of n-propylamine leads to the deprotonation of the the tap ligands are delocalized over each N1C2N3C1N2
central nitrogen atom in the PdN(H)=CN(H)- fragment that feature a delocalized π-system, which is indi-
C=N(H) metallacycles to give the corresponding neutral cated by the C(sp2)=N character[28] of the N1–C2 and N2–
1,3,5-triazapentadienate compounds [Pd{HN=C(4-XC6H4)- C1 [1.305(2) and 1.3055(19) Å, respectively] bonds, as well
NC(4-XC6H4)=NH}2] (2) [X = H (2a), F (2b), Cl (2c), Br as by the N3–C1 and N3–C2 distances [1.3504(19) and
(2d), I (2e)] (Scheme 1, reaction 2). Since these complexes 1.3547(19) Å, respectively] that are characteristic of planar
are more soluble in organic solvents than 2Ј and more con- C(sp2)–N(sp2) groups.[28] The metallacycle cores are almost
venient for characterization, we focused our attention on planar, but the Cl1- and Cl2-phenyl arms are twisted by
their isolation and full characterization.
All complexes 2a–2e were characterized by IR, H and distortions were found in related PdII complexes.[16]
13C NMR spectroscopy, ESI-MS, elemental analyses (C, H,
The molecules of 2c are linked together by means of N–
33.84 and 10.94°, respectively, from the core plane. Similar
1
N) and, in the case of 2c, by XRD. The IR spectra of 2a– H–O connections with the intercalated methanol molecules
2e show no ν(CϵN) bands, while the characteristic ν(NH) (Figure 1), which operate both as H-acceptors and H-do-
and ν(C=N) bands are observed at ca. 3200 and ca. nors, and are involved in medium strong intermolecular hy-
1
1600 cm–1, respectively. The H and 13C NMR spectra dis- drogen bonds (see legend of Figure 1). The methanol mole-
play the expected resonances at the usual chemical shifts cules are further involved in other hydrogen bond interac-
for the expected functional groups, e.g. the phenyl rings ap- tions, e.g. C22–H22···O10 [d(H···A) 2.51 Å, Є(DH···A)
378
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Iminopalladium(II) Complexes
or of the metal(II) salt, thus indicating that these reagents
have an essential role in the process, which conceivably in-
volves the complete hydrolysis of the nitrile to ammonia
and a carboxylic acid, followed by the metal(II)-mediated
reaction of the ammonia with the nitrile to yield an amidine
that then couples with the cyano group of a nitrile ligand
to give the tap complex.[7,11,13,16,29–33]
It is noteworthy that reactions of aliphatic liquid nitriles,
such as acetonitrile or propionitrile, in excess (also playing
the role of solvent) with PdCl2 and 4 equiv. of acetone ox-
ime and 2-butanone oxime were attempted, but in all cases
only oxime-palladium(II) complexes of the type [PdCl2(ox-
ime)2] were isolated. The identity of these products was con-
firmed by IR, NMR and elemental analysis, and by com-
parison of their analytical data with those of the oxime-PdII
complexes prepared independently by a known[16] modified
procedure (see Exp. Sect. for details).
Figure 1. Crystal structure of complex 2c, with atomic numbering
scheme, showing the strongest hydrogen bonding interactions. Se-
lected bond lengths [Å] and angles [°]: Pd1–N1 1.9849(13), Pd1–N2
1.9783(13), N1–C2 1.305(2), N2–C1 1.3055(19), N3–C1 1.3504(19),
N3–C2 1.3547(19), N1–Pd1–N2 87.80(5), Pd1–N1–C2 128.14(11).
Selected torsion angles [°]: N2–C1–C11–C16 37.7(2), N1–C2–C21–
C22 13.4(2). Selected hydrogen bonds [d(H···A), Є(DHA)]: N1–
H1···O10 2.53(2) Å, 143.4(18)°, N2–H2···O10 2.14(2) Å, 162.1(18)°;
O10–H10···N3 2.16(3) Å, 161(2)°. Symmetry codes: (i) 2 – x, 1 –
y, –z; (ii) –1 + x, y, z; (iii) 1 + x, y, z; (iv) 1 – x, 1 – y, –z.
Conversion of Cyanoguanidine to 2-Amino-4-alkoxy-1,3,5-
triazapentadienate Ligands Mediated by Palladium(II)/
Primary Alcohol Systems
For the preparation of asymmetrical 2-amino-4-alkoxy-
172°]. Intermolecular contacts between the chloride ions 1,3,5-triazapentadienate-PdII complexes, a modified one-
and aromatic hydrogen atoms were also detected; as a result pot template synthesis that was reported for the methanol–
of Cl1···H26 interactions the molecules are held together to cyanoguanidine integration at PtII,[19] NiII and CuII[20] cen-
form 1D hydrogen-bonded molecular chains, and by means ters was employed. Thus, treatment of PdCl2 with 2 equiv.
of Cl2···H12 interactions the structure is extended in the of 3 in an aliphatic primary alcohol ROH (R = Me, Et, nPr,
second dimension (Figure S1). Furthermore, π···π stacking nBu) suspension, under reflux or by heating at 100 °C (in
interactions between the C21–C26 phenyl rings and the the case of n-butanol) for 12 h, leads to the formation of
metallacycles contribute to the formation of a supramolec- palladium(II)-1,3,5-triazapentadiene chlorides [Pd(Htap)2]-
ular network structure (Figure S2); the centroid–centroid Cl2 (4Ј) (Scheme 2, reaction 1). These compounds were then
distances of 3.835 and 4.109 Å are within the normal range deprotonated by n-propylamine to give the corresponding
for such interactions.
PdII complexes 4a–4d (Scheme 2, reaction 2). Like but-
The mechanism of the transformation of an aromatic ni- anone oxime in the synthetic procedure described above,
trile into a ligated tap was not studied in detail, but we the neat alcohol plays a dual function by acting as both
noticed that it does not proceed in the absence of the oxime solvent and reactant.
Scheme 2.
Eur. J. Inorg. Chem. 2011, 377–383
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379

M. N. Kopylovich, J. Lasri, M. F. C. Guedes da Silva, A. J. L. Pombeiro
FULL PAPER
Compounds 4a–4d were isolated, as pale yellow solids in
good yields (73–78%), from the reaction medium by evapo-
ration of the solvent. The reaction was successfully con-
ducted with aliphatic linear alcohols at a temperature nor-
mally determined by the boiling point of the alcohol. In
contrast, no reaction was observed when secondary
alcohols such as racemic 2-butanol or tert-butyl alcohol
were used, probably due to their bulkiness that sterically
hinders the nucleophilic attack of the alcohol towards the
cyano moiety in 3. We also attempted to use 3 as a nucleo-
phile due to its amino and imino moieties, but treatment
with PdCl2 (0.5 equiv.) and an excess of benzonitrile or pro-
pionitrile at 100 °C for 3 d, did not lead to the formation
of any new species and only the starting materials were re-
covered from the reaction mixture.
Scheme 3.
ESI-MS spectra display peaks corresponding to the [M +
H]+ ions. The IR bands at 3331–3376 and 1608–1633 cm–1
prove that the N–H and C=N groups have been formed,
and agree with the data for related tap-PdII complexes.[10]
1
Complexes 4a–4d were characterized by IR, H and 13C
NMR spectroscopy, ESI-MS and elemental analyses, which
all gave data that were consistent with the proposed formu-
lations for these compounds. The ESI-MS spectra contain
[M]+ or [M + H]+ signals that are the most intense peaks
and have characteristic isotopic distribution. The IR spectra
of 4a–4d show no ν(CϵN) bands and display one or two
strong vibrational bands for the C=N imine moieties within
the 1600–1700 cm–1 range, which is typical for tap-PdII
complexes,[10,16] while the ν(N–H) vibrations emerge in the
1
The H and 13C NMR spectra of 6a–6d show, in almost
all cases, more than one set of signals conceivably due the
presence of different isomers in solution. For example, in
1
the H NMR spectrum of complex 6a, the protons of the
methoxy group (OCH3) appear as a multiplet within the δ
= 3.66–3.75 ppm range, while the 13C NMR spectrum
shows five signals in the δ = 54.9–55.7 ppm range for the
methoxy carbon (OCH3) and also five signals in the δ =
160.9–162.0 ppm range due to the imino group (C=NH).
Possibly due to the presence, in solution, of complexes 6a–
6d in different isomeric forms, all attempts to prepare single
crystals of these compounds suitable for XRD analysis
failed.
1
3300–3400 cm–1 range. The H and 13C NMR spectra of
these complexes show more than one set of signals, most
probably due the presence of different isomers. For exam-
1
ple, the H NMR spectrum of complex 4a displays three
resonances at δ = 3.99, 4.01 and 4.04 ppm that are assigned
to the protons of the methoxy groups (OCH3), while the
13C NMR spectrum exhibits three signals at δ = 55.2, 55.6
and 55.9 ppm for the methoxy carbon (OCH3) and five sig-
nals in the δ = 152–154 ppm range related to the imino
groups (C=NH). Possibly due to the presence of different
isomeric forms, the preparation of single crystals of 4a–4d
suitable for XRD analysis was not successful.
Final Remarks
We synthesized, via a single-pot template transformation
method, new symmetrical tap-PdII complexes 2a–2e and
6a–6d containing aryl and alkoxy substituents, respectively,
as well as asymmetrical tap-PdII complexes 4a–4d that bear
amino and alkoxy substituents. The frameworks of the tap-
PdII azametallacycles are conveniently provided by arene-
carbonitriles (assisted by an oxime in the case of complexes
2a–2e), cyanoguanidine or dicyanamide (assisted by
alcohols in the cases of 4a–4d and 6a–6d, which also behave
as the sources for the alkoxy substituents). The reactions
proceed via a metal-promoted nucleophilic addition of a
protic nucleophile (an oxime or an alcohol) to the cyano
substrates coordinated to PdII.
The proposed syntheses are attractive due to their sim-
plicity; they do not require special precautions and proceed
in air with solvents and reagents that do not need to be
predried. In a further extension to this work, an investiga-
tion into the application of the newly synthesized tap-PdII
complexes as catalysts for (microwave-assisted) C–C cross-
coupling reactions is currently underway in our laboratory.
Conversion of Sodium Dicyanamide to 2,4-Dialkoxy-1,3,5-
triazapentadienate Ligands
The reaction of PdCl2 with 2 equiv. of 5 in neat ROH (R
= Me, Et, nPr, (CH2)2OMe), under reflux conditions or by
heating at 100 °C (in the case of 2-methoxyethanol) for
12 h, furnishes the symmetrical palladium(II) complexes
6a–6d (Scheme 3). At the end of reactions the formed com-
plex (which usually has a yellow color with an intensity that
is dependent on the R substituent) is soluble in the reaction
mixture, while a colorless precipitate of sodium chloride
(NaCl) is formed. NaCl is partly soluble in the solvent used,
but the soluble portion can be removed by evaporation of
the solvent, and washing the resulting residue several times
with water. The complexes 6a–6d are insoluble in water, and
are then recrystallized from an acetone/water (10:1) mixture
to give the pure compounds.
Experimental Section
1
Complexes 6a–6d were characterized by IR, H and 13C
Materials and Instrumentation: Solvents and reagents were ob-
NMR spectroscopy, ESI-MS and elemental analyses. The tained from commercial sources (Aldrich) and used as received. C,
380 Eur. J. Inorg. Chem. 2011, 377–383
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Iminopalladium(II) Complexes
H and N elemental analyses were carried out by the Microanalyti-
cal Service of the Instituto Superior Técnico. Attempts were made
to measure the melting points of the compounds with a Kofler
Table, but the complexes underwent decomposition upon heating
(the approximate temperatures at which decomposition started are
given below). 1H and 13C spectra (in CDCl3, CDCl3/CD3OD or
[D6]DMSO) were measured at ambient temperature on Bruker Av-
ance II 300 and 400 MHz (UltraShieldTM Magnet) spectrometers,
and chemical shifts (δ) are expressed in ppm with respect to Me4Si
(1H, 400.130 MHz; 13C, 100.613 MHz), while J values are in Hz.
Infrared spectra (4000-400 cm–1) were recorded with KBr pellets
on a Bio-Rad FTS 3000MX instrument and the wavenumbers are
in cm–1. Positive-ion FAB mass spectra were obtained on a Trio
2000 instrument by bombarding 3-nitrobenzyl alcohol (NBA) ma-
trixes of the samples with 8 keV (ca 1.28ϫ1015 J) Xe atoms. Elec-
trospray mass spectra were carried out with an ion-trap instrument
(Varian 500-MS LC Ion Trap Mass Spectrometer) equipped with
an electrospray (ESI) ion source. The compounds in methanol were
continuously introduced into the mass spectrometer source with a
syringe pump at a flow rate of 10 μL/min. The drying gas tempera-
ture was maintained at 350 °C and dinitrogen at 35 psi was the
nebulizer gas; scanning was performed from m/z = 50 to m/z =
1500.
4.00 mmol of the corresponding oxime in acetone for 12 h. Thus,
the identity of the oxime-palladium(II) complexes was confirmed
by IR and NMR spectroscopy, elemental analysis, and by compari-
son of the analytical data with those of the independently synthe-
sized known compounds.
[Pd{HN=C(C6H5)NC(C6H5)=NH}2] (2a): Yield 80% (440 mg)
based on PdCl2. Decomp. temp. Ͼ 250 °C. C28H24N6Pd (550):
calcd. C 61.04, H 4.39, N 15.25; found C 61.33, H 4.22, N 15.55.
ESI-MS: m/z (%) = 551 [M + H]+. IR: ν = 3299 (NH), 1641 and
˜
1673 (C=N) cm–1. 1H NMR (300 MHz, CDCl3): δ = 7.45–7.55 (m,
12 H, CHaromatic), 7.83 (d, JHH = 8.4 Hz, 8 H, CHaromatic) ppm.
13C{1H} NMR (400 MHz, CDCl3): δ = 127.3, 128.5, 132.0, 133.3
(Caromatic), 169.4 (C=NH) ppm.
[Pd{HN=C(4-FC6H4)NC(4-FC6H4)=NH}2] (2b): Yield 68%
(423 mg) based on PdCl2. Decomp. temp. Ͼ 280 °C. C28H20F4N6Pd
(622): calcd. C 53.99, H 3.24, N 13.49; found C 53.77, H 3.54, N
13.57. ESI-MS: m/z (%) = 623 [M + H]+. IR: ν = 3179 and 3377
˜
(NH), 1606, 1622 and 1662 (C=N) cm–1. 1H NMR (300 MHz,
CDCl3): δ = 7.12–7.16 (m, 8 H, CHaromatic), 7.84–7.87 (m, 8 H,
CHaromatic) ppm. 13C{1H} NMR (400 MHz, CDCl3): δ = 115.7,
129.8, 163.8, 166.3 (Caromatic), 168.4 (C=NH) ppm.
[Pd{HN=C(4-ClC6H4)NC(4-ClC6H4)=NH}2] (2c): Yield 64%
Reactions of Benzonitrile Derivatives 4-XC6H4CN 1 [X = H (1a), F
(1b), Cl (1c), Br (1d), I (1e)] with PdCl2 Mediated by 2-Butanone
(440 mg) based on PdCl2. Decomp. temp.
Ͼ
290 °C.
C28H20Cl4N6Pd (688): calcd. C 48.83, H 2.93, N 12.20; found C
Oxime with Formation of Symmetrical (2,4-Diaryl-1,3,5-Triaza- 48.57, H 2.86, N 11.96. FAB+-MS (m-NBA): m/z (%) = 689 [M +
pentadienate)palladium(II) Complexes 2a–2e: PdCl2 (177 mg, H]+. IR: ν = 3269 (NH), 1590 (C=N) cm–1. H NMR [300 MHz,
1
˜
1.00 mmol) was stirred in 2-butanone oxime (5 mL) for 5 min, CDCl3(90%), CD3OD(10%)]: δ = 7.32 (d, JHH = 8.5 Hz, 8 H,
whereupon the corresponding benzonitrile derivative 4-XC6H4CN
1 [X = H (1a), F (1b), Cl (1c), Br (1d), I (1e)] (6.00 mmol) was
added, and the reaction mixture was heated at 100 °C for 12 h.
Homogenization of the mixture was observed within ca. 30 min,
giving a yellow-brown solution. A yellow powder began to form
after ca. 1 h and after 12 h the reaction mixture was filtered, and
the residue washed with three 15 mL portions of acetone and dried
in vacuo at room temperature to give [Pd(Htap)2]Cl2 2Ј.
Recrystallization of 2Ј from a hot methanol/chloroform (1:1) solu-
tion, with addition of nPrNH2 (2.00 equiv. to 2Ј), gave a yellow
crystalline precipitate of the corresponding [Pd(tap)2] (2) complex.
CHaromatic), 7.87 (d, JHH = 8.5 Hz, 8 H, CHaromatic) ppm. 13C{1H}
NMR [400 MHz, CDCl3(90%), CD3OD(10%)]: δ = 128.3, 128.6,
135.9, 137.4 (Caromatic), 161.4 (C=NH) ppm.
[Pd{HN=C(4-BrC6H4)NC(4-BrC6H4)=NH}2] (2d): Yield 65%
(563 mg) based on PdCl2. Decomp. temp.
Ͼ
280 °C.
C28H20Br4N6Pd (866): calcd. C 38.81, H 2.33, N 9.70; found C
39.01, H 2.54, N 9.81. ESI-MS: m/z (%) = 867 [M + H]+. IR: ν =
˜
1597 and 1647 (C=N) cm–1. 1H NMR (300 MHz, CD3OD): δ =
7.58 (d, JHH = 8.6 Hz, 8 H, CHaromatic), 7.65 (d, JHH = 8.6 Hz, 8
H, CHaromatic) ppm. 13C{1H} NMR (400 MHz, CD3OD): δ =
129.1, 130.4, 132.4, 133.4 (Caromatic), 169.0 (C=NH) ppm.
For the reactions attempted with liquid alkanenitriles, PdCl2
(1.00 mmol) was stirred in acetonitrile or propionitrile (5 mL) for
5 min, whereupon acetone oxime Me2C=NOH (case A) or 2-but-
anone oxime (Me)(Et)C=NOH (case B) (4.00 mmol) was added.
The reaction mixture was kept under reflux by heating the solution
in an oil bath for 1 d. In all the cases, the reaction mixture homoge-
nizes after ca. 1 h after the addition of the oxime, giving a yellow
[Pd{HN=C(4-IC6H4)NC(4-IC6H4)=NH}2] (2e): Yield 67%
(706 mg) based on PdCl2. Decomp. temp. Ͼ 270 °C. C28H20I4N6Pd
(1054): calcd. C 31.89, H 1.91, N 7.97; found C 32.11, H 2.23, N
8.05. ESI-MS: m/z (%) = 1055 [M + H]+. IR: ν = 3179 and 3365
˜
1
(NH), 1622 and 1661 (C=N) cm–1. H NMR (300 MHz, CDCl3):
δ = 7.55 (d, JHH = 8.4 Hz, 8 H, CHaromatic), 7.82 (d, JHH = 8.4 Hz,
8 H, CHaromatic) ppm. 13C{1H} NMR (400 MHz, CDCl3): δ =
128.9, 133.1, 137.9, 138.5 (Caromatic), 168.5 (C=NH) ppm.
solution, whereupon
a yellow precipitate of [PdCl2(acetone
oxime)2] starts to form (for case A) or the reaction mixture stays
homogeneous (for case B). The yellow powder of [PdCl2(acetone
oxime)2] (for case A) was removed from solution by filtration,
washed with three 5 mL portions of acetone and dried in vacuo at
room temperature. For case B, after 24 h the solvent (nitrile) was
removed from the reaction mixture under vacuum, the residue was
washed with three 5 mL portions of diethyl ether and dried in
vacuo at room temperature. Oxime-palladium(II) complexes were
recovered as the only product when acetone was the solvent and
the corresponding oxime was added in a 4 equiv. amount (with
1.00 equiv. of PdCl2 and 4 equiv. of benzonitrile). In this case the
reaction mixture was refluxed for 1 d, whereupon the solvent was
removed under vacuum. The residue was washed several times with
diethyl ether to remove the starting materials and by-products. As
described by us earlier,[16] palladium(II)-oxime complexes can also
be prepared independently by refluxing PdCl2 (2.00 mmol) with
[PdCl2(HON=CMe2)2]:. C6H14Cl2N2O2Pd (323.5): calcd. C 22.28,
H 4.36, N 8.66; found C 21.99, H 4.20, N 8.62. IR: ν = 3425 (OH),
˜
1650 and 1622 (C=N–OH) cm–1.
[PdCl2(HON=C(Me)(Et))2]: C8H18Cl2N2O2Pd (351.6): calcd. C
27.33, H 5.16, N 7.97; found C 27.45, H 5.23, N 8.03. IR: ν = 3191
˜
(OH), 1666 (C=N–OH) cm–1. 1H NMR (300 MHz, CDCl3): δ =
1.31 (t, JHH = 7.5 Hz, 3 H, CH2CH3), 2.07 (s, 3 H, CH3), 3.05
(m, JHH = 7.5 Hz, 2 H, CH2CH3) ppm. 13C{1H} NMR (400 MHz,
CDCl3): δ = 11.0 (CH2CH3), 16.43 (CH3), 31.9 (CH2CH3), 168.1
(C=NOH) ppm.
Reactions of Cyanoguanidine HN=C(NH2)N(H)CϵN (3) with
PdCl2 and Aliphatic Alcohols ROH (R = Me, Et, nPr, nBu) with
the Formation of Asymmetrical (2-Amino-4-alkoxy-1,3,5-triaza-
pentadienate)palladium(II) Complexes 4a–4d: PdCl2 (177 mg,
Eur. J. Inorg. Chem. 2011, 377–383
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
381

M. N. Kopylovich, J. Lasri, M. F. C. Guedes da Silva, A. J. L. Pombeiro
FULL PAPER
1.00 mmol) and 3 (168 mg, 2.00 mmol) were added to the corre-
sponding alcohol ROH (R = Me, Et, nPr or nBu) (5 mL) and the
reaction mixture was refluxed or heated at 100 °C (in the case of
n-butanol) for 12 h (homogenization of the reaction mixture was
observed within ca. 1 h, giving a yellow solution). The solvent was
then removed in vacuo, and the residue washed with three 10 mL
portions of diethyl ether and then dried in air to give [Pd(Htap)2]-
Cl2 (4Ј). Recrystallization of 4Ј from a methanol/chloroform (1:1)
solution, with the addition of nPrNH2 (2.00 equiv. to 4Ј) gave the
yellow palladium(II) complexes [Pd(tap)2] 4a–4d. Compounds 4a–
4d were isolated as mixtures of isomers (see NMR spectroscopic
data) and all attempts to obtain single crystals suitable for XRD
analysis failed.
portions of water (to remove the NaCl), and the remaining residue
was crystallized from an acetone-water (10:1) mixture to give the
corresponding symmetrical palladium(II) complexes 6a–6d, which
were isolated as mixtures of isomers (see NMR spectroscopic data).
All attempts to obtain single crystals suitable for XRD analysis
failed.
[Pd{HN=C(OMe)NC(OMe)=NH}2] (6a): Yield 80% (293 mg)
based on PdCl2. Decomp. temp. Ͼ 250 °C. C8H16N6O4Pd (366):
calcd. C 26.20, H 4.40, N 22.92; found C 26.45, H 4.81, N 23.12.
ESI-MS: m/z (%) = 367 [M + H]+. IR: ν = 3359 (NH), 1613 (C=N)
˜
1
cm–1. H NMR (300 MHz, [D6]DMSO): δ = 3.66–3.75 (m, 12 H,
CH3) ppm. 13C{1H} NMR (400 MHz, [D6]DMSO): δ = 54.9, 55.0,
55.1, 55.6, 55.7 (CH3), 160.9, 161.1, 161.3, 161.6, 162.0 (C=NH)
ppm.
[Pd{HN=C(NH2)NC(OMe)=NH}2] (4a): Yield 75% (252 mg)
based on PdCl2. Decomp. temp. Ͼ 120 °C. C6H14N8O2Pd (336):
calcd. C 21.41, H 4.19, N 33.29; found C 21.76, H 4.27, N 33.36.
[Pd{HN=C(OEt)NC(OEt)=NH}2] (6b): Yield 79% (333 mg) based
on PdCl2. Decomp. temp. Ͼ 230 °C. C12H24N6O4Pd (422): calcd.
C 34.09, H 5.72, N 19.88; found C 34.23, H 5.99, N 20.07. ESI-
ESI-MS: m/z (%) = 337 [M + H]+. IR: ν = 3401 (NH), 1558, 1668
˜
and 1686 (C=N) cm–1. 1H NMR (300 MHz, CD3OD): δ = 3.99,
4.01, 4.04 (3 s, 6 H, CH3) ppm. 13C{1H} NMR (400 MHz,
CD3OD): δ = 55.2, 55.6, 55.9 (CH3), 152.4, 152.7, 154.1, 154.4,
154.6 (C=NH) ppm.
MS: m/z (%) = 423 [M + H]+. IR: ν = 3371 (NH), 1610 (C=N)
˜
1
cm–1. H NMR (300 MHz, [D6]DMSO): δ = 1.19–1.24 (m, 12 H,
CH3), 4.12–4.24 (m, 8 H, CH2) ppm. 13C{1H} NMR (400 MHz,
[D6]DMSO): δ = 15.0, 15.1 (CH3), 64.1, 64.2 (CH2), 160.8, 161.1
(C=NH) ppm.
[Pd{HN=C(NH2)NC(OEt)=NH}2] (4b): Yield 77% (280 mg) based
on PdCl2. Decomp. temp. Ͼ 110 °C. C8H18N8O2Pd (364): calcd. C
26.35, H 4.97, N 30.72; found C 26.66, H 5.13, N 31.05. ESI-MS:
[Pd{HN=C(OPr)NC(OPr)=NH}2] (6c): Yield 81% (387 mg) based
on PdCl2. Decomp. temp. Ͼ 230 °C. C16H32N6O4Pd (478): calcd.
C 40.13, H 6.74, N 17.55; found C 40.34, H 6.88, N 17.69. ESI-
m/z (%) = 365 [M + H]+. IR: ν = 3321 (NH), 1549 and 1689 (C=N)
˜
cm–1. 1H NMR (300 MHz, CD3OD): δ = 1.40–1.46 (m, 6 H, CH3),
4
H, CH2) ppm. 13C{1H} NMR (400 MHz,
MS: m/z (%) = 479 [M + H]+. IR: ν = 3376 (NH), 1608 and 1633
4.28–4.46 (m,
˜
1
(C=N) cm–1. H NMR (300 MHz, [D6]DMSO): δ = 0.87–0.93 (m,
CD3OD): δ = 12.7, 12.8, 12.9, 12.9 (CH3), 65.3, 65.8, 66.1, 66.2
(CH2), 152.4, 152.7, 152.8, 153.4, 153.7, 153.8, 154.2, 154.5
(C=NH) ppm.
12 H, CH3), 1.57–1.65 (m, 8 H, CH3CH2), 4.02–4.18 (m, 8 H,
OCH2) ppm. 13C{1H} NMR (400 MHz, [D6]DMSO): δ = 10.4,
10.6, 10.7 (CH3), 21.9, 22.4, 22.5 (CH3CH2), 69.1, 69.7, 69.8, 70.0
(OCH2), 160.9, 161.3 (C=NH) ppm.
[Pd{HN=C(NH2)NC(OPr)=NH}2] (4c): Yield 73% (286 mg) based
on PdCl2. Decomp. temp. Ͼ 100 °C. C10H22N8O2Pd (392): calcd.
C 30.58, H 5.65, N 28.53; found C 30.67, H 5.95, N 28.77. ESI-
[Pd{HN=C(O(CH2)2OMe)NC(O(CH2)2OMe)=NH}2] (6d): Yield
MS: m/z (%) = 393 [M + H]+. IR: ν = 3328 (NH), 1552 and 1689
˜
83% (450 mg) based on PdCl2. Decomp. temp.
Ͼ 200 °C.
(C=N) cm–1. 1H NMR (300 MHz, CD3OD): δ = 0.91–1.07 (m, 6
H, CH3), 1.51–1.85 (m, 4 H, CH3CH2), 4.19–4.36 (m, 4 H, OCH2)
ppm. 13C{1H} NMR (400 MHz, CD3OD): δ = 8.95, 8.99, 9.02,
9.05, 9.22 (CH3), 21.3, 21.4, 21.5, 25.3 (CH2), 63.3, 70.7, 71.2, 71.4,
71.5, 71.6 (OCH2), 152.4, 152.7, 152.8, 153.3, 153.5, 153.8, 153.9,
154.3, 154.6 (C=NH) ppm.
C16H32N6O8Pd (542): calcd. C 35.40, H 5.94, N 15.48; found C
35.67, H 5.89, N 15.77. ESI-MS: m/z (%) = 543 [M + H]+. IR: ν
˜
= 3331 (NH), 1615 (C=N) cm–1. 1H NMR (300 MHz, [D6]DMSO):
δ = 3.26–3.27 (m, 12 H, CH3), 3.53 (br. s, 8 H, CH3OCH2), 4.21
and 4.27 (2 br. s, 8 H, OCH2) ppm. 13C{1H} NMR (400 MHz, [D6]
DMSO): δ = 58.5 (OCH3), 66.6 (CH3OCH2), 70.7 (OCH2), 160.5
(C=NH) ppm.
[Pd{HN=C(NH2)NC(OBu)=NH}2] (4d): Yield 78% (328 mg) based
on PdCl2. Decomp. temp. Ͼ 100 °C. C12H26N8O2Pd (420): calcd.
C 34.25, H 6.23, N 26.63; found C 34.37, H 6.55, N 26.87. ESI-
X-ray Structure Determination: Single crystals of 2c were obtained
as indicated above. Intensity data were collected on a Bruker AXS-
KAPPA APEX II diffractometer with graphite monochromated
Mo-Kα (λ 0.71073) radiation. Data were collected at 150 K with
omega scans at 0.5° steps and full sphere of data was obtained.
Cell parameters were retrieved with the Bruker SMART software
and refined against all the observed reflections with the Bruker
SAINT[34] program. An absorption correction was applied with
SADABS.[34] The structure was solved by direct methods with the
SHELXS–97 package[35] and refined with SHELXL–97.[36] Calcu-
lations were performed with WinGX software (version 1.80.03).[37]
All hydrogen atoms were inserted into the model at calculated posi-
tions, except for H1 and H2 and the methanol hydrogen atom H10
that were located from the difference Fourier maps. Least square
refinement, with anisotropic thermal parameters for all the non–
hydrogen atoms and isotropic parameters for the hydrogen atoms,
gave R1 = 0.0196 [IϾ2σ(I)] and R1 = 0.0207 (all data). The maxi-
mum and minimum peaks in the final difference electron-density
map are of 0.435 and –0.553 eÅ–3. Crystallographic data are listed
in Table 1.
MS: m/z (%) = 421 [M + H]+. IR: ν = 3428 (NH), 1550 and 1682
˜
(C=N) cm–1. 1H NMR [300 MHz, CDCl3(90%), CD3OD(10%)]: δ
= 0.80–0.88 (m, 6 H, CH3), 1.26–1.35 (m, 4 H, CH3CH2), 1.39–
1.65 (m, 4 H, OCH2CH2), 4.22 (br. s, 4 H, OCH2) ppm. 13C{1H}
NMR [400 MHz, CDCl3(90%), CD3OD(10%)]: δ = 13.2, 13.3,
13.4, 13.5, 13.6 (CH3), 18.5, 18.6, 18.6, 18.7, 19.2 (CH3CH2), 29.8,
30.0, 30.1, 31.7, 34.4 (OCH2CH2), 62.0, 62.1, 65.2, 70.1, 70.3
(OCH2), 152.2, 152.9, 153.8, 154.2 (C=NH) ppm.
Reactions of Sodium Dicyanamide NaN(CϵN)2 (5) with PdCl2 and
Aliphatic Alcohols ROH [R=Me, Et, Pr, (CH2)2OMe] with the For-
mation of Symmetrical (2,4-Dialkoxy-1,3,5-triazapentadienate)pal-
ladium(II) Complexes 6a–6d: PdCl2 (177 mg, 1.00 mmol) and 5
(178 mg, 2.00 mmol) were added to the corresponding alcohol
ROH [R = Me, Et, nPr or (CH2)2OMe] (5 mL) and the reaction
mixture was refluxed or heated at 100 °C (in the case of 2-methoxy-
ethanol) for 12 h (homogenization of the reaction mixture was ob-
served within ca. 1–2 h, giving a yellow solution). The solvent was
then removed in vacuo, and the residue washed with three 10 mL
382
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 377–383

Iminopalladium(II) Complexes
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Table 1. Crystallographic data for 2c (at 150 K).
2c
Empirical formula
Formula weight
C28H20Cl4N6Pd, 2(CH4O)
752.78
Crystal system
Space group
triclinic
P1
¯
a [Å]
b [Å]
c [Å]
α [°]
7.0242(2)
10.7629(2)
11.0018(3)
79.901(1)
75.572(3)
76.778(2)
777.956(36)
1
β [°]
γ [°]
V [Å3]
Z
ρcalc [gcm–3]
μ(Mo-Kα) [mm–1]
F (000)
1.607
0.979
380
Rint
0.0200
10016/3436
1.093
Reflections collected/unique
Goodness of fit on F2
R1 [IϾ2σ(I)]
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CCDC-790158 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
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Supporting Information (see also the footnote on the first page of
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structure of 2c.
Acknowledgments
This work has been partially supported by the Portuguese
Fundação para a Ciência e a Tecnologia (FCT) and Fundo
Europeu de Desenvolvimento Regional (FEDER) (PPCDT pro-
gram). M. N. K. and J. L. express gratitude to the FCT and the
Instituto Superior Técnico (IST) for their research contracts
(CIÊNCIA 2007 program). The authors gratefully acknowledge
Dr. Maria Cândida Vaz for the direction of the elemental analysis
service, Dr. Conceição Oliveira (IST) for the direction of the ESI-
MS analysis and the Portuguese NMR Network for providing ac-
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Received: August 23, 2010
Published Online: December 9, 2010
Eur. J. Inorg. Chem. 2011, 377–383
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