PtII-mediated imine-nitrile coupling leading to symmetrical (1,3,5,7,9-pentaazanona-1,3,6,8-tetraenato)Pt(II) complexes containing the incorporated 1,3-diiminoisoindoline moiety

Article abstract of DOI:10.1021/ic301176b

Treatment of trans-[PtCl₂(NCR)₂] (1; R = Et (1a), Ph (1b)) with 1,3-diiminoisoindoline (2) gives access to the corresponding symmetrical (1,3,5,7,9-pentaazanona-1,3,6,8-tetraenato)Pt(II) complexes [PtCl{NH=C(R)N=C(C₆H₄)NC=NC(R)=NH}] (3). The reactions of 1 with one equivalent of 1,1,3,3-tetramethylguanidine (4), 1,3-diphenylguanidine (6), or acetone oxime (8) leads to the formation of mixed asymmetrical Pt(II) complexes trans-[PtCl₂{NH=C(R)N=C(NMe₂)₂}(NCR)] (5), [PtCl{NH=C(R)NC(NHPh)=NPh}(NCR)] (7), or trans-[PtCl₂{NH=C(Ph) ON=CMe₂}(NCPh)] (9), respectively, as a result of nucleophilic addition to one of the nitrile ligands in 1. Treatment of 5, 7, and 9 with one equivalent of 2 leads to complexes 3. The complexes were characterized by IR, ¹H, ¹³C{¹H}, and ¹⁹⁵Pt NMR (for 3) spectroscopies, ESI⁺-MS, elemental analyses, and X-ray diffraction (for 3). Complex 3a has an asymmetric unit with five independent Pt molecules of the same chemical composition and two molecules of water, resulting in a total of 40 molecules of the complex and sixteen guest water molecules per unit cell. Theoretical calculations revealed that the most plausible mechanism of formation of complexes 3 includes stepwise nucleophilic addition of 2 to one of the nitrile ligands in 1, a first cyclization upon formation of the Pt-N bond and elimination of HCl, and a second nucleophilic addition/cyclization.

Full text of DOI:10.1021/ic301176b

Article
pubs.acs.org/IC
PtII-Mediated Imine−Nitrile Coupling Leading to Symmetrical
(1,3,5,7,9-Pentaazanona-1,3,6,8-tetraenato)Pt(II) Complexes
Containing the Incorporated 1,3-Diiminoisoindoline Moiety
Jamal Lasri,*,† Maxim L. Kuznetsov,† M. Fatima C. Guedes da Silva,†,‡ and Armando J. L. Pombeiro*,†
́
†Centro de Química Estrutural, Complexo I, Instituto Superior Tec
Lisbon, Portugal
́
nico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001
‡Universidade Lusof
́
ona de Humanidades e Tecnologias, Av. Campo Grande 376, ULHT Lisbon, 1749-024, Lisbon, Portugal
S
* Supporting Information
ABSTRACT: Treatment of trans-[PtCl2(NCR)2] (1; R = Et (1a), Ph (1b)) with
1,3-diiminoisoindoline (2) gives access to the corresponding symmetrical (1,3,5,7,9-
pentaazanona-1,3,6,8-tetraenato)Pt(II) complexes [PtCl{NHC(R)NC(C6H4)-
NCNC(R)NH}] (3). The reactions of 1 with one equivalent of 1,1,3,3-
tetramethylguanidine (4), 1,3-diphenylguanidine (6), or acetone oxime (8) leads to
the formation of mixed asymmetrical Pt(II) complexes trans-[PtCl2{NHC(R)N
C(NMe2)2}(NCR)] (5), [PtCl{NHC(R)NC(NHPh)NPh}(NCR)] (7), or
trans-[PtCl2{NHC(Ph)ONCMe2}(NCPh)] (9), respectively, as a result of
nucleophilic addition to one of the nitrile ligands in 1. Treatment of 5, 7, and 9 with
one equivalent of 2 leads to complexes 3. The complexes were characterized by IR,
1H, 13C{1H}, and 195Pt NMR (for 3) spectroscopies, ESI+-MS, elemental analyses,
and X-ray diffraction (for 3). Complex 3a has an asymmetric unit with five
independent Pt molecules of the same chemical composition and two molecules of
water, resulting in a total of 40 molecules of the complex and sixteen guest water
molecules per unit cell. Theoretical calculations revealed that the most plausible
mechanism of formation of complexes 3 includes stepwise nucleophilic addition of 2
to one of the nitrile ligands in 1, a first cyclization upon formation of the Pt−N bond and elimination of HCl, and a second
nucleophilic addition/cyclization.
of triazapendienes is much less described, at least in part, because
of the low stability of triazapentadienes, in particular the
unsubstituted ones,9 which hampers direct syntheses of their
complexes. For the preparation of triazapentadiene complexes, a
direct one-pot template synthesis with nitriles has been investi-
gated when the nitrile is activated by an electron-withdrawing
group.10 A novel route to (imidoylamidine)Ni(II) complexes has
been discovered by us using oximes and Ni(II) ions in combina-
tion with nitriles,11 and this methodology has been extended
to prepare (1,3,5-triazapentadienato)Pd(II) complexes as well.12
Very recently, symmetrical and asymmetrical (alkoxy-1,3,5-
triazapentadienato)Cu(II) complexes have been also prepared by
us using a template synthesis.13
INTRODUCTION
■
Nucleophilic addition reactions on metal coordinated nitriles
have long been used to prepare a variety of useful organic
compounds.1 The formation of C−N or C−O bonds using this
methodology has been achieved using different types of
nucleophiles2,3 or 1,3-dipole reagents.4 1,3-Diiminoisoindoline,
a cyclic diimine and a potential sp2-nitrogen nucleophile, is
well-known for its use in the preparation of metallopthalo-
cyanines5 and other macrocycles, such as expanded hemi-
porphyrazine,6 and is an important ingredient in the pigment
industry. The iminoisoindoline-1-one, from which 1,3-diimi-
noisoindoline is derived, has already been studied by our group
as a nucleophile toward activated nitriles and isonitriles.7 The
iminoisoindoline-1-one can act as a nucleophile through its
imine group toward such substrates resulting in the formation
of triazapentadienato or iminocarbene complexes, respectively.
Nevertheless, 1,3-diiminoisoindoline has a potential to employ
both its imine groups for nucleophilic attacks on metal-bound
organonitriles, thus leading to symmetrical triazapentadienato-
type complexes. Unlike β-diimines, triazapentadiene bears one
additional N donor site, and DFT calculations8 indicate that
they possess an even greater ability for sequestering metal
centers than β-diimines. However, the coordination chemistry
In this work, we have studied the nucleophilic addition of a sp2-
nitrogen nucleophile, 1,3-diiminoisoindoline, to Pt(II)-bound
organonitriles like propionitrile and benzonitrile. We have thus
observed the formation of symmetrical (1,3,5,7,9-pentaazanona-
1,3,6,8-tetraenato)Pt(II) complexes 3a and 3b, respectively. These
may be regarded as extended triazapentadienato complexes as the
Received: June 2, 2012
Published: September 21, 2012
© 2012 American Chemical Society
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newly formed ligands can be viewed as two such coupled units
bearing one common nitrogen.
Pt(II) complexes by using bis(propionitrile) and bis-
(benzonitrile) as starting dinitrile Pt(II) complexes, and 1,3-
diiminoisoindoline as the reacting sp2-nitrogen nucleophile
(Scheme 1).
On attempting to obtain asymmetrical products from the
reactions with 1,3-diiminoisoindoline, this species was reacted
with the asymmetrical imine-Pt(II) complexes which have been
obtained from nucleophilic addition of 1,1,3,3-tetramethylgua-
nidine, 1,3-diphenylguanidine, or acetone oxime to one of the
nitrile ligands of Pt(II)-bound bis(nitrile). It was found that in
all cases the above complexes 3a or 3b were also formed as a
result of substitution of the starting nucleophilic fragment from the
respective complexes 5, 7, and 9 by 1,3-diiminoisoindoline 2 (see
below). Nevertheless, nitrone monocycloaddition product 11 did
not respond to such type of reaction. The plausible mechanisms of
the formation of 3 from 1,3-diiminoisoindoline 2 and bis(nitrile)-
Pt(II) complexes trans-[PtCl2(NCR)2] (1) were studied in detail
using theoretical DFT calculations.
Scheme 1
RESULTS AND DISCUSSION
■
Reactions of 1,3-Diiminoisoindoline with Symmetrical
Organonitrile Pt(II) Complexes. Following our ongoing
project on metal-mediated activation of small molecules (i.e.,
nitriles1,2,4 and isonitriles14), we have recently discovered that
iminoisoindolin-1-ones, which represent a family of stable
aromatic imines, exhibit nucleophilic properties toward metal-
bound organonitriles and isonitriles. Iminoisoindolin-1-ones
bear an endocyclic auxiliary amide functionality, which upon
deprotonation may be involved in complexation forming
relatively stable chelated metallacycles (Figure 1). Thus, the
Hence, treatment of trans-[PtCl2(NCR)2] (1) (R = Et (1a),
Ph (1b)) with one equivalent of 1,3-diiminoisoindoline
HNCC6H4C(NH)NH (2), in refluxing CH2Cl2 for 2 h,
gives access to the corresponding symmetrical (1,3,5,7,9-
pentaazanona-1,3,6,8-tetraenato)Pt(II) complexes [PtCl-
{NHC(R)NC(C6H4)NCNC(R)NH}] (3) (R= Et
(3a), Ph (3b)) in good yields (65−70%). The reactions are
accelerated by focused microwave irradiation (30 min) giving
the same products 3 in comparable yields (∼70%) (Scheme 1).
In a blank experiment, a prolonged reflux (48 h) of a mixture
of 1 equiv. of propionitrile and 2 equiv. of 1,3-diiminoisoindo-
line 2 in CH2Cl2 showed no addition to nitrile and only the
starting materials were recovered, indicating the Pt(II)-
mediated character of the coupling.
The obtained complexes 3, whose formation was monitored by
TLC, were purified by column chromatography on silica gel and
characterized by IR, 1H, 13C{1H}, and 195Pt NMR spectroscopies,
ESI+-MS, elemental analyses and also by X-ray diffraction.
The IR spectra of complexes 3 do not exhibit the typical
υ(NC) values (2350−2300 cm−1 range), while new bands
due to υ(NH) and υ(CN) are observed at ∼3255 and ∼1648
Figure 1.
reaction between iminoisoindolin-1-ones and metal-bound
organonitriles or isonitriles leads to the formation of asym-
metrical (1,3,5-triazapentadienato)[M] complexes [M = Ni(II),7a
Cu(II),7b Pd(II),7c and Pt(II)7c].
These observations on the stability of the imine (i.e.,
iminoisoindolin-1-one) and of the products of its addition to
nitriles (chelated 1,3,5-triazapentadienato species7a,b) prompted
us to widen this type of chemistry to the commercially available
1,3-diiminoisoindoline (Figure 1) (bearing two nucleophilic
sp2−N centers and one endocyclic auxiliary amine functionality,
which upon deprotonation might coordinate to the metal
forming relatively stable chelated fused metallacycles). We
employed this nucleophile for coupling with Pt(II)-bound
organonitriles.
1
cm−1, respectively. For example, in the H NMR spectrum of
complex [PtCl{NHC(Et)NC(C6H4)NCNC(Et)
NH}] (3a), the signals of the phenyl ring appear at δ 7.75
and 8.26, and the NH protons are exhibited at δ 9.77. The
13C{1H} NMR spectrum of 3a shows the characteristic signals
of the imine groups at δ 153.2 and 163.8, and the absence of
the NC resonance at ∼116 ppm confirms that the
nucleophilic addition of 1,3-diiminoisoindoline 2 occurs to
both propionitrile ligands in 1a.
X-ray Structure Crystallography. The structural parameters
for complexes 3a and 3b are given in Table 1, representative
diagrams are given in Figures 2 and 3 and selected bond
distances and angles are provided in the respective legends.
Other relevant features of the structures are given as Supporting
Information.
In the first part of this work, we report the selective synthesis
of new symmetrical (1,3,5,7,9-pentaazanona-1,3,6,8-tetraenato)-
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Table 1. Crystal Data, Experimental Parameters, and
Selected Details of the Refinement Calculations of
Compounds 3a and 3b
3a·2H2O
3b
formula
C70H84Cl5N25O2Pt5
2460.32
C22H14ClN5Pt
578.92
formula weight
crystal system
space group
a (Å)
monoclinic
C2/c
monoclinic
Cc
55.400(2)
12.4426(5)
25.4089(11)
115.2820(10)
15837.1(11)
8
13.3847(6)
23.6077(10)
6.9904(3)
120.469(2)
1903.81(14)
4
b (Å)
Figure 3. Crystal structure of complex 3b with atomic numbering
scheme (ellipsoid probability level of 50%). Selected bond distances
(Å) and angles (deg): N1−Pt1 1.948(4), N11−Pt1 1.948(4), N21−
Pt1 1.962(4), Cl1−Pt1 2.3087(16), C21−N21 1.306(7), C21−N2
1.368(6), C1−N2 1.311(6), C1−N1 1.389(6), C8−N3 1.304(6), C8−
N1 1.370(7), C11−N11 1.313(6), C11−N3 1.360(6), C8−N1−C1
110.6(4), C1−N2−C21 122.8(4), C8−N3−C11 123.6(5), C11−
N11−Pt1 128.8(4), N1−Pt1−N11 89.35(17), N1−Pt1−N21
90.10(18), N11−Pt1−N21 178.86(18), N1−Pt1−Cl1 179.25(13).
c (Å)
β (deg)
V (Å3)
Z
ρcalcd (g/cm3)
μ(Mo−Kα) (mm−1
reflns collected
reflns unique
Rint
2.064
2.020
)
9.032
7.530
50855
11008
14378
5581
0.0559
0.0349
a
b
R1, wR2 (I ≥ 2σ)
R1, wR2 (all data)
GOF on F2
R1 = Σ||Fo| − |Fc||/Σ|Fo|. wR2 = [Σ[w(Fo2 − Fc2)2]/ Σ[w(Fo )2]]1/2
0.0351, 0.0652
0.0605, 0.0704
1.006
0.0305, 0.0548
0.0400, 0.0581
is shown in Figure 2. A quaternion fit15 of the five
crystallographically independent Pt complex molecules (here-
after denoted as Pt1−Pt5) was attempted via the program
Platon AutoMolFit16 (Figure S3) which showed that they can
be related by pseudoglide planes and pseudorotation
symmetries (hydrogen atoms and water molecules were
excluded). While Pt1 and Pt2 are related by a pseudo-c glide
plane [lattice vector of (−0.547, 0.298, 1.000) with a shift of
10.586 Å], the former is related with Pt3 and Pt4 by
pseudorotation; a pseudo-b glide plane interconnect the Pt3
and Pt4 [lattice vector of (0.632, −1.000, −0.949) with a shift
of 7.462 Å]. The overall root-mean square (rms) deviations for
fittings of Pt1, Pt2, Pt3 and Pt4 range from 0.084 (for the fitting
of Pt3 and Pt4) to 0.220 Å (for the fitting of Pt1 and Pt3). The
same method for fitting the Pt5 molecule with any of the other
Pt molecules gave rms deviations in the 1.474−1.841 Å range.
The shortest Pt···Pt distances were found to be between
4.0880(4) and 4.4616(5) Å.
0.954
a
b
2
.
Multiple molecules in the asymmetric unit is a matter of
considerable debate,17−20 and the phenomena is believed to be
the result of a compromise of several factors such as, among
others, the size and shape of a molecule and intermolecular
interactions.17,21−23 In the present case, only a few hydrogen
bond interactions could be found in the structure (Table S1)
and, therefore, other features may be responsible for the high
number of metal complex molecules in the asymmetric unit of
3a. Indeed, the five independent metal complexes and the two
water molecules form unique intermolecular hydrogen bonds,
of which two represent Dwater···APt interactions with distances
of 2.849(7) and 2.950(7) Å, and one represents a DPt···Awater
contact (3.021(7) Å) which, in conjunction with contacts
between the water molecules, lead to one-dimensional (1D)
chains along the crystallographic c direction. The remaining
hydrogen bonds pertain mainly to DPt···ACl contacts in the
3.369(7)−3.514(6) Å range with typical D−H···A angles
between 157.9 and 165.6°. Some primary parameters were
selected (Supporting Information Table S2) that might have
also contributed to the uncommon number of formula units in
the structure: (i) the folding of the complex molecules, as
expressed by the distance of the Pt atom to the plane of the
phenyl ring; in only one of the Pt molecules (Pt5) the metal
atom lies on the plane of the phenyl ring, all the others lying
below that plane. (ii) The two (CC)EtCNPt torsion angles
Figure 2. Crystal structure of one of the molecules of complex 3a with
the respective atomic numbering scheme (ellipsoid probability level of
50%). Selected bond distances (Å) and angles (deg): Cl1−Pt1
2.3250(17), N11−Pt1 1.974(5), N13−Pt1 1.942(5), N15−Pt1
1.972(5), C11−N11 1.299(8), C11−N12 1.368(8), C14−N12
1.305(8), C14−N13 1.381(8), C15−N14 1.317(8), C15−N13
1.384(8), C16−N15 1.316(9), C16−N14 1.372(8); N11−C11−N12
124.2(6), N12−C14−N13 128.9(6), N14−C15−N13 128.2(6),
N15−C16−N14 125.9(7), N13−Pt1−N15 89.7(2), N13−Pt1−N11
88.9(2), N13−Pt1−Cl1 178.28(16), N15−Pt1−Cl1 91.67(17).
The geometry around the Pt ions in complexes 3a and 3b is
of square planar type, comprising two fused six-membered
metallacycles. Bond distances and angles involving equivalent
moieties in both structures do not differ noticeably, but relevant
features are described as follows.
Complex 3a has a relatively simple molecular structure, but it
forms a very complex crystal structure in the centrosymmetric
C2/c space group with five independent Pt molecules of the
same chemical composition and two molecules of water in the
asymmetric unit; therefore, a total of 40 complex molecules and
sixteen guest water molecules can be found in the unit cell
(Supporting Information Figures S1 and S2). A representative
molecular geometry of a single metal complex (the Pt1 molecule)
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(Table S2) involving the ethyl groups, since in each molecule
one of these groups is nearly in the plane of the coordination
sphere of the metal while the other is markedly twisted out of
that plane; moreover, only in Pt1 and Pt5 molecules both
torsion angles have the same sign. Additionally, the molecules
are also strongly associated through π···π interactions involv-
ing both the metallacycles and the phenyl rings, in offset
parallel displacements (Supporting Information Figure S1),
whose centroid···centroid distances range from 3.452(5) to
3.687(5) Å.
Complexes 5 are formed by nucleophilic attack of the imine
N atom to one nitrile ligand of 1, since 1,1,3,3-tetramethylgua-
nidine does not react with free NCR (R = Et, Ph) under the
coupling conditions, implying that the nitrile-guanidine
coupling is Pt(II)-mediated.
Complexes 5a and 5b have been characterized by elemental
analyses, ESI+−MS, IR, 1H, and 13C{1H} NMR spectroscopies.
The compounds give satisfactory C, H and N elemental
analyses for the proposed formulation. In the ESI+ mass spectra,
5a and 5b give the expected molecular ion [M + 1]+.
The most striking feature of the molecule of 3b is the relative
tilting of the phenyl rings, relative to the plane defined by the
coordination atoms; while for the ring (C12−C17) that angle is
of 16.79°, for the ring (C22−C27) it widens to 32.02°. Such
distortions enables C−H···π strong interactions in the 2.62−
2.99 Å range, which should play considerable role in the
formation, stabilization, and crystallization of the compound.
The shortest metal···metal distance is of 3.7717(3) Å, quite
below that found for compound 3a (see above).
Reactions of 1,3-Diiminoisoindoline with Mixed
Asymmetrical Pt(II) Complexes. In the second part of this
work, we studied the reactions of 1,3-diiminoisoindoline with
asymmetrical Pt(II) complexes derived from the above
bis(nitrile) Pt(II) compounds, expecting to obtain asym-
metrical final products. For such a purpose, we started with
1,1,3,3-tetramethylguanidine, 1,3-diphenylguanidine, acetone
oxime, and acyclic nitrone as the first reacting sp2-nitrogen
nucleophiles, and 1,3-dipole reagents, respectively.
Hence, treatment of trans-[PtCl2(NCR)2] (1) (R = Et (1a),
Ph (1b)) with one equivalent of 1,1,3,3-tetramethylguanidine
HNC(NMe2)2 (4), in refluxing CH2Cl2 for 12 h, gives access
to the corresponding asymmetrical Pt(II) complexes trans-
[PtCl2{NHC(R)NC(NMe2)2}(NCR)] (5) (R= Et (5a),
Ph (5b)), containing both N-bound monodentate 1,3-diaza-1,3-
diene and nitrile ligands, in good yields (65−67%) (Scheme 2,
reaction a).
The IR spectroscopic data additionally confirm the
nucleophilic addition of tetramethylguanidine to one NCR
ligand and rule out the possibility of displacement of nitriles by
the guanidine. Thus, comparison of the IR spectra of 5a and 5b
with those of the starting complexes shows the presence of
intense stretching bands υ(CN) at ∼1636 cm−1. In addition,
the bands because of υ(NH) and υ(NC) are observed
at ∼3445 and ∼2228 cm−1, respectively.
In the 1H NMR spectra of 5a and 5b, the signal of the proton
from the imino group CNH (δ 6.61 and 6.13),24 is shifted
upfield compared to those observed in NMR spectra of other
Pt imine complexes (δ 8−9).2a−c In the latter, the hydrogen
bonding involving the imine CNH proton was unambigu-
ously recognized, while in our case the position of the signal at
such a high field gives indirect evidence that the proton of the
CNH group is not involved in the hydrogen bonding in
solution.24 The 13C{1H} NMR spectra show the signals of the
CN bonds in the 163.3−178.3 ppm range, which
corresponds to the characteristic CN resonances in Pt
imine complexes.2,4,24 Moreover, the NC resonances are
observed at 120.3 and 115.8 ppm, for 5a and 5b, respectively.
Treatment of the asymmetrical Pt(II) complexes trans-
[PtCl2{NHC(R)NC(NMe2)2}(NCR)] (5) (R= Et (5a),
Ph (5b)) with one equivalent of 1,3-diiminoisoindoline HN
CC6H4C(NH)NH (2), in refluxing CH2Cl2 for 2 h, gives
access to the corresponding above-mentioned symmetrical
(1,3,5,7,9-pentaazanona-1,3,6,8-tetraenato) Pt(II) complexes
[PtCl{NHC(R)NC(C6H4)NCNC(R)NH}] (3)
(R= Et (3a), Ph (3b)) in good yields (65−70%), respectively,
as a result of displacement of the tetramethylguanidine moiety
(in complex 5) by 1,3-diiminoisoindoline 2 and elimination of
HCl with attack at the nitrile ligand (Scheme 2, reaction a′).
Treatment of trans-[PtCl2(NCR)2] (1) (R = Et (1a), Ph
(1b)) with one equivalent of 1,3-diphenylguanidine HN
C(NHPh)2 (6), in refluxing CH2Cl2 for 12 h, resulted in
formation of the known25 complexes [PtCl{NHC(R)NC-
(NHPh)NPh}(NCR)] (7) (R= Et (7a), Ph (7b))
(containing both bidentate 1,3,5-triazapentadienato and nitrile
ligands), which were isolated in 50 and 60% yields, respectively
(Scheme 2, reaction b). Complexes 7a−7b are formed as
products of the nucleophilic addition of 1,3-diphenylguanidine
to one nitrile carbon atom, followed by ring closure of the
formed 1,3,5-triazapentadienato ligand and elimination of HCl.
Treatment of the asymmetrical bidentate (1,3,5-triazapenta-
dienate)Pt(II) complexes [PtCl{NHC(R)NC(NHPh)
NPh}(NCR)] (7) (R= Et (7a), Ph (7b)) with one equiv of
1,3-diiminoisoindoline 2, in refluxing CH2Cl2 for 2 h, gives
access to the corresponding above-mentioned symmetrical
(1,3,5,7,9-pentaazanona-1,3,6,8-tetraenato)Pt(II) complexes
[PtCl{NHC(R)NC(C6H4)NCNC(R)NH}] (3)
(R= Et (3a), Ph (3b)) in good yields (65−70%), respectively,
as a result of displacement of diphenylguanidine moiety
Scheme 2
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Scheme 3. Two Possible Pathways of the Formation of 3c from 1c and 2
(in complex 7) by 1,3-diiminoisoindoline 2 and elimination of
HCl with attack at the ligated nitrile (Scheme 2, reaction b′).
On the other hand, treatment of trans-[PtCl2(NCPh)2] (1b)
with the acetone oxime HO-NCMe2 (8), in refluxing
CH2Cl2 for 2 h, gives access to the known2a,b monoimine
trans-[PtCl2{NHC(Ph)ONCMe2}(NCPh)] (9) complex
in moderate yield (∼55%) (Scheme 2, reaction c).
υ(NC) at 2287 cm−1 that is identical to that of the starting
complex 1b (2286 cm−1). The NC stretching vibration
(1634 cm−1) is also comparable with those of the corres-
4j
ponding bis-imine2a−c or bis-oxadiazoline complexes. The H
1
and 13C{1H} NMR spectra of 11 show that the compound
1
contains both an oxadiazoline and a nitrile ligand. In the H
NMR spectrum, the N−CH−N resonance is detected at 6.41
ppm, and, in the 13C{1H} NMR spectrum, the N−CH−N
resonance appears at 91.9 ppm, while the NC signal occurs at
116.3 ppm.
Similarly, treatment of 9 with one equivalent of 1,3-
diiminoisoindoline 2, in refluxing CH2Cl2 for 2 h, leads to
the corresponding above symmetrical complex [PtCl{NH
C(Ph)NC(C6H4)NCNC(Ph)NH}] (3b) in good yield
(∼68%), as a result of displacement of acetone oxime moiety
(in complex 9) by 1,3-diiminoisoindoline 2 and elimination of
HCl with attack at the ligated NCPh (Scheme 2, reaction c′).
On the other hand, in the reaction of trans-[PtCl2(NCPh)2]
Once the first cycloaddition has taken place, the second
nitrile ligand still present in the molecule exhibits a lower
reactivity because of the different electronic properties of the
oxadiazoline in trans-position, in comparison with the nitrile in
1b. On the other hand, no reaction between the mono-
oxadiazoline complex 11 and the 1,3-diiminoisoindoline 2 has
been observed, and only the starting material was recovered
(Scheme 2, reaction d′). Refluxing the reaction mixture for a
prolonged time (24 h) affords a number of uncharacterized
products.
−
(1b) with one equivalent of the acyclic nitrone O+N(Me)
C(H)(C6H2Me3-2,4,6) (10), the system was refluxed in
CH2Cl2 for 12 h, to give the mono-oxadiazoline complex
trans-[PtCl2{NC(Ph)ON(Me)C(H)(C6H2Me3-2,4,6)}-
(NCPh)] (11) as the exclusive product (∼67% yield) (Scheme 2,
reaction d).
Theoretical Mechanistic Studies. In this part, the plaus-
ible mechanisms of the formation of complexes 3 (methyl
derivative 3c) are discussed. Taking into account the previous
experimental1b,2f,26 and theoretical27 data on the reactions of
addition of various protic nucleophiles (H2O, ROH, NH3,
RNH2, RR′NH, NR2OH, RR′CNOH, etc.) to metal-bound
Complex 11 has been characterized by elemental analysis,
ESI+-MS, IR, 1H, and 13C{1H} NMR spectroscopies. The
compound gives satisfactory C, H and N elemental analysis for
the proposed formulation. In the ESI+ mass spectrum, 11 gives
the expected molecular ion [M+1]+. Its IR spectrum exhibits
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Scheme 4. Concerted Mechanism of the Nucleophilic Addition of 2-NH2 to 1c by the NH2 Group
nitriles, it seems to be a good assumption that the reaction
starts with the nucleophilic addition (NA) of 1,3-diiminoisoin-
doline 2 to one of the nitrile ligands of complex trans-
[PtCl2(NCR)2] to give imino-complexes I−III followed by the
first cyclization to IV (with HCl elimination) and then by the
second nucleophilic addition/cyclization affording the final
product 3 (Scheme 3, Pathway A). Alternatively, the
coordination of the 1,3-diiminoisoindoline 2 to the Pt atom
accompanied by the elimination of HCl may occur on the first
step, and then two consecutive NAs of imino groups to the
nitrile ligands should afford the final product 3 (Scheme 3,
Pathway B). However, the calculations indicate that the
Pathway B is much less favorable than the Pathway A (see
Supporting Information for details).
Tautomeric Equilibrium of 2. 1,3-Diiminoisoindoline 2 may
exist in two possible tautomeric forms, that is, diimino form
2-NH and imino-amino form 2-NH2 (Scheme 3), which can
convert to each other upon an intramolecular H-transfer. Such
tautomeric equilibrium was proved for related amidines HN
C(R)−NHR′ ⇄ H2N−C(R)NR′ by a series of chemical and
physicochemical experiments.28 Our calculations indicate that
both forms 2-NH and 2-NH2 have very similar stabilities in
both gas phase and solution, the symmetrical form 2-NH being
only by 0.5 kcal/mol more stable in CH2Cl2 solution than
2-NH2. Hence, the mechanisms of reaction of both 2-NH and
2-NH2 forms with trans-[PtCl2(NCMe)2] (1c) are discussed in
the following sections.
Taking into account that there is a significant amount of water
in nondried CH2Cl2 used in the experimental part (see
Experimental Section), H2O was considered as solvent−
H-transfer promoter in TSs.
Type b transition state of the concerted mechanism, TS1,
was found for the nucleophilic addition of 2-NH2 to 1c by the
NH2 group (Scheme 4). The activation barrier in CH2Cl2
solution calculated for this route is 41.1 kcal/mol (in terms of
ΔG⧧s ) being unacceptably high for an effective realization of this
route. This value is even higher than the activation energy
estimated previously for the diphenylamine addition to 1c (32.8
kcal/mol27c). Structurally similar transition states (TS2 and
TS3) were also found for the reactions of 2-NH and 2-NH2 (by
NH-group) with 1c. However, the analysis of the nature of
these TSs indicates that they correspond to the associative
stepwise rather than concerted mechanism (see the next section
and also Supporting Information for more detailed discussion).
Thus, the concerted mechanism of the formation of products
I−III may be ruled out.
Associative Mechanism. The associative mechanism in-
volves the addition of nucleophile to the nitrile carbon atom
followed by the proton transfer to the nitrile nitrogen atom via
one-step H-shift or via deprotonation/protonation steps
(Schemes 5 and 6). This mechanism was found for the NAs
of 2-NH and 2-NH2 (by NH group) to 1c and it starts with the
formation of TS4 and TS5, respectively, leading to
intermediates INT1 and INT2, each of them having two
isomers with different position of substituents and the lone
electron pair relative to the CN bond. The activation
energies of the formation of INT1a and INT2b are very similar
(ΔG⧧s are 20.0 and 19.3 kcal/mol, respectively), and those of
the formation of INT1b and INT2a are only slightly higher
(ΔGs‡ are 22.9 and 22.6 kcal/mol, respectively). The
intermediates INT1a, INT2a, and INT2b have similar
thermodynamic stabilities (ΔGs values of formation are in the
range of 11.8−12.5 kcal/mol), whereas INT1b is by 4.8−
5.5 kcal/mol less stable.
Nucleophilic Addition of 2 to Coordinated Nitrile.
Concerted Mechanism. For the NAs to metal-coordinated
nitriles, three general types of the mechanisms are usually
considered, that is, concerted, dissociative, and associative. The
first one combines the formation of a new CN bond and the H-
transfer from the imino (amino) nitrogen to the nitrile nitrogen
in a single step, and it includes the generation of one cyclic
transition state (TS) (Scheme 4). This transition state may be
4-membered (type a, Chart 1) or 6-membered (type b, Chart 1).
In contrast, no intermediate of the INT1 or INT2 type was
found for the NA of 2-NH2 by the NH2 group. All attempts to
locate it resulted in a decomposition of initial structures and
moving the trans-[PtCl2(NCMe)2] and 2-NH2 molecules away
from each other. Thus, the associative stepwise mechanism for
the addition of 2-NH2 by amino-group can be excluded.
The generated intermediates INT1a and INT2a can be
transformed to the nucleophilic addition products E-I and
E-III, respectively, via transition states TS2 and TS3 of the type
b (Chart 1). The calculated activation barrier of the reaction
INT1a → TS2 → E-I is 7.3 kcal/mol while that of the reaction
INT2a → TS3 → E-III is only 1.0 kcal/mol.
Alternatively, the INT1 → I, INT1 → II, INT2 → II, and
INT2 → III transformations could occur in a stepwise manner
via the sequential deprotonation/protonation steps. The
deprotonation of INT1 or INT2 by water molecule in
CH2Cl2 solution (Schemes 5 and 6, B = H2O) is very
Chart 1
In the latter case, a solvent molecule participates in the
formation of TS and plays the role of the H-transfer promoter.
Previous theoretical studies of NAs of NH3 and amines to trans-
[PtCl2(NCMe)2] (1c)27c showed that the solvent (water)-
assisted mechanism via the 6-membered TS is much more
energetically favorable than the pathway via the 4-membered
TS due to a higher stability of 6-membered cyclic structures,
and namely this route is discussed in the present work.
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Scheme 5. Stepwise Associative Mechanisms of the Nucleophilic Addition of 2-NH to 1c
Scheme 6. Stepwise Associative Mechanisms of the Nucleophilic Addition of 2-NH2 to 1c
endoergonic (by 40.1−54.5 kcal/mol, Table S4). However, if 2
plays the role of base (Schemes 5 and 6, B = 2-NH) the
deprotoation energies appear to be significantly lower (4.2−
18.5 kcal/mol, Tables 2 and S4). The lowest ΔGs values of
deprotonation were found for the reactions INT1b + 2-NH →
INTb-H + 2H+ (4.2 kcal/mol), INT1b + 2-NH → INT1b-H +
2H+ (6.8 kcal/mol), and INT1a + 2-NH → INT1a-H + 2H+
(7.5 kcal/mol), all of these processes being quite competitive
with the INT1a → TS2 → E-I route (ΔG⧧s = 7.3 kcal/mol).
Dissociative Mechanism. The dissociative mechanism in-
cludes the initial deprotonation of the nucleophile (by a solvent
molecule or autoionization), subsequent addition of the deproto-
nated fragment to the nitrile carbon atom and protonation of the
nitrile nitrogen atom (Scheme 7). However, as was found previously
for the nucleophilic addition of oximes27a and amines,27b,c this
mechanism is more energetically demanding compared to the
concerted or associative pathways. Indeed, the calculated ΔGs values
of the reactions 2-NH + B → 2-NH-H + HB+, 2-NH2 + B → 2-
NH2-Ha + HB+, and 2-NH2 + B → 2-NH2-Hb + HB+ in CH2Cl2
solution with B = H2O are 84.8, 70.1, and 98.8 kcal/mol,
respectively, and those with B = 2-NH are 48.9, 34.1, and 62.8 kcal/
mol, correspondingly. Additionally, in accord with the experimental
kinetic studies of the NA of hydroxylamines R2NOH to Pt(II) and
Pt(IV) nitrile complexes,29 the activation entropy of these processes
has a clearly negative value (−9.8 2.4 cal/mol·K and −11.2 5.5
cal/mol·K, respectively) indicating that the mechanism is of
associative or concerted type.
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Table 2. Calculated Energetic Characteristics (in kcal/mol)
of the Reactions Discussed in the Text
Scheme 7. Stepwise Dissociative Mechanism of the
Nucleophilic Addition of 2 to 1c (Relative Gibbs Free
Energies in Solution Are Indicated in Parentheses in
kcal/mol)
reaction
ΔH⧧s ΔG⧧s ΔHs ΔGs
2-NH → 2-NH2
0.7
0.5
1c + 2-NH2 → E-II
via TS1 23.5 41.1 −14.9 −4.8
1c + 2-NH → INT1a
1c + 2-NH → INT1b
1c + 2-NH2 → INT2a
1c + 2-NH2 → INT2b
INT1a → E-I
via TS4a 10.1 20.0
via TS4b 13.1 22.9
via TS5a 13.9 22.6
via TS5b 9.5 19.3
1.6
6.9
3.6
1.8
11.8
17.3
12.5
11.9
via TS2 −0.7
via TS3 −8.0
7.3 −17.3 −16.9
1.0 −21.8 −21.3
INT2a → E-III
INT1a + 2-NH → INT1a-H + 2H+
INT1b + 2-NH → INTb-H + 2H+
INT1b + 2-NH → INT1b-H + 2H+
INT2b + 2-NH → INTb-H + 2H+
INT1a-H + 2H+ → E-I + 2-NH
INT1b-H + 2H+ → Z-I + 2-NH
INTb-H + 2H+ → Z-II + 2-NH
2-NH + 2-NH → 2-NH-H + 2H+
2-NH2 + 2-NH → 2-NH2-Ha + 2H+
2-NH2 + 2-NH → 2-NH2-Hb + 2H+
INT1a → E-II
8.0
5.2
6.7
9.6
7.5
4.2
6.8
9.0
−25.3 −24.4
−29.5 −29.5
−27.0 −25.8
49.6
33.8
63.0
48.9
34.1
62.8
via TS7 −1.6 −1.3 −15.8 −16.0
via TS8a 10.8 19.3 −1.5 −0.9
via TS8b 11.1 19.1 −1.0 −1.0
via TS9a 6.4 13.8 −1.8 −3.2
E-II → E-I
Z-II → Z-I
Scheme 8. Mechanisms of the Nucleophilic Addition of
2-NH to 1c Involving the Central NH Group (Gibbs Free
Energies Relative to Reactants 1c + 2-NH are Indicated
in Parentheses in kcal/mol)
E-I → E-III
Z-I → Z-III
via TS9b 11.4 19.5
via TS10 24.8 26.5
via TS11 26.5 27.8
via TS12 13.3 16.2
3.7
7.8
6.8
4.1
2.5
2.5
1.5
0.0
Z-I → IV
Z-II → IV
Z-III → IV
IV → V
via TS13 5.7
8.3 −6.0 −3.0
9.8 9.6
−34.2 −33.9
V + 2-NH → V−H + 2H+
V-H + 2H+ → 3c + 2-NH
Mechanisms Involving the Central NH Group. The
presence of the central imino group in the 2-NH form of the
nucleophile opens the possibility of other routes which involve
directly this imino group (Scheme 8). The first such route
might be a direct one-step addition of 2-NH to 1c via TS6
including the simultaneous formation of the CN bond and
H-transfer from the central NH group of 2-NH to the nitrile
nitrogen. However, a search of the potential energy surface for
TS6 showed that there is no transition state of this type. The
second possibility is the stepwise mechanism which starts with
the formation of INT1a (via TS4a) and followed by the
H-transfer via TS7 to give the NA product E-II [route (1)].
The rate limiting step of this mechanism is the first step
(ΔG⧧s = 20.0 kcal/mol, Table 2) while the second step is
barrierless in terms of ΔGs (ΔG⧧s = −1.3 kcal/mol).
routes 1−3 and thus it may effectively operate concurrently.
The second step of the route 4 is rate limiting: the energy of
the deprotonated complex INTb-H relative to 1c + 2-NH is
21.5 kcal/mol vs the energy of TS5b of 19.8 kcal/mol. The
activation barriers of the routes 1−4 (20.0 and 21.5 kcal/mol)
are close to the experimentally determined Gibbs free energy of
activation for the NA of hydroxylamine HON(p-CH2C6H4Cl)2
to the Pt(II) complex [PtCl3(NCEt)]− (20.6 kcal/mol).29,30
Nucleophilic Addition Products. The NA products E/Z-I−
E/Z-III (Schemes 5 and 6) have rather similar thermodynamic
stabilities, the ΔGs values of their formation from 1c and 2-NH
being in the range of (−2.9)−(−8.3) kcal/mol. The isomers
E-III and Z-I are the most stable ones followed by E-I, Z-II,
E-II, and Z-III. Note that according to the experimental X-ray
data, both E- and Z-configurations are known for the products
of nucleophilic addition of various amines and imines to
nitriles.24,31 As discussed above, the isomers E-I, E-II, and Z-II
are directly accessible upon the reaction of 2 with 1c. How-
ever all isomers I−III are in equilibrium with each other via
(1)
2‐NH + 1c → TS4a → INT1a → TS7 → E‐II
(2)
2‐NH + 1c → TS4a → INT1a → TS2 → E‐I
2‐NH + 1c → TS4a → INT1a(+ 2) → INT1a‐H(+ 2H+) → E‐I
(3)
2‐NH2 + 1c → TS5b → INT2b(+ 2) → INTb‐H(+ 2H+) → Z‐II
(4)
The analysis of the energy profiles of all pathways discussed
above indicates that three of the most favorable routes, that is,
1−3, have the same rate limiting step (formation of INT1a)
and, hence, the same overall activation barrier of 20.0 kcal/mol.
The lowest-energy route leading to the formation of a Z-isomer
(Z-II) [route 4] requires only 1.5 kcal/mol higher energy than
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water-assisted H-transfers involving TS8a,b and TS9a,b
(Scheme 5). The activation barriers of the E-II → E-I,
Z-II → Z-I, E-I → E-III, and Z-I → Z-III transformations are
19.3, 19.1, 13.8, and 19.5 kcal/mol.
Scheme 10. Most Plausible Mechanisms of the Second
Cyclization/Nucleophilic Addition Step
First Cyclization. The Z-isomers of the NA products formed
at the first stage can undergo cyclization to give intermediate IV
(Scheme 9). Transition states were found for the cyclizations of
a
Scheme 9. Mechanisms of the First Cyclization Step
FINAL REMARKS
■
The results of the experimental part of this work can be summarized
under three perspectives. First, the reaction between two trans-
ligated RCN species (in 1) and 1,3-diiminoisoindoline (2) leads to
the formation of symmetrical (1,3,5,7,9-pentaazanona-1,3,6,8-
tetraenato)Pt(II) complexes (3), and the system represents a
novel reactivity mode which has never been reported for any nitrile
at a Pt metal center. The developed synthetic method operates
under mild conditions, affords pure (1,3,5,7,9-pentaazanona-1,3,6,8-
tetraenato)Pt(II) complexes in good yields, and, in contrast to the
preparation of asymmetrical (1,3,5-triazapentadienato)Ni(II) com-
plexes,7a does not require the addition of a base. The reactions are
accelerated by focused microwave irradiation giving the same
products in comparable yields.
Second, the asymmetrical imine-Pt(II) complexes obtained
by nucleophilic additions to one nitrile ligand of the starting
dinitrile Pt(II) compounds react with 1,3-diiminoisoindoline to
give the same final (1,3,5,7,9-pentaazanona-1,3,6,8-tetraenato)-
Pt(II) complexes 3.
Third, the obtained products 3 can be viewed as fused
tetracyclic chelates and represent a novel type of symmetrical
pentaazanonatetraene complexes and themselves, bearing two
potential coordinating metallacycle-imine groups, can be used
as metallaligands, leading to heteronuclear complexes with
different molecular architectures. Work focusing on the latter
topic is underway in our laboratory.
a
Gibbs free energies relative to Z-I are indicated in parentheses in
kcal/mol.
all three complexes Z-I−Z-III (TS10−TS12). TS10 and TS12
correspond to the concerted formation of the Pt−N bond and
elimination of the HCl molecule whereas TS11 is associated
with the elimination of the Cl− ion which, on the next step,
abstracts the proton from the N atom. The activation barrier of
the reaction Z-III → TS12 → IV is rather low (16.2 kcal/mol)
but those of the reactions Z-I → TS10 → IV and Z-II → TS11 →
IVH+ (+ Cl−) → IV + (HCl) are significantly higher (26.5 and
27.8 kcal/mol, respectively). Thus, two latter processes are not
favorable. Complex IV whose formation is by 2.9 kcal/mol
exoergonic relative to the initial reactants 2-NH and 1c is the
precursor for the second cyclization.
Second Nucleophilic Addition/Cyclization. For the last
stage of the formation of 3c, several plausible mechanisms have
been examined (see Supporting Information for details). The
calculations indicated that the most favorable mechanism of
this stage includes the formation of the bicyclic structure V via
TS13 and proton migration in a stepwise manner V (+ 2) →
V−H (+ 2H+) → 3c (Scheme 10). The activation barrier of the
first step of this route is 8.3 kcal/mol and the energy of
deprotonation of V is only 9.6 kcal/mol.
Theoretical mechanistic studies of the formation of 3 from 1
and 2 reveal that the most plausible pathway of this process
includes the stepwise nucleophilic addition of 2 (in imino-
amino form 2-NH2) to one of the nitrile ligands of 1, a first
cyclization accompanying the formation of the Pt−N bond and
elimination of HCl, and a second stepwise nucleophilic
addition/cyclization. The rate limiting step of the whole
process is the first nucleophilic addition, and the calculated
apparent Gibbs free energy of activation is 21.5 kcal/mol.
EXPERIMENTAL SECTION
Material and Instrumentation. Solvents and reagents were
obtained from commercial sources (Aldrich) and used as received. For
TLC, Merck Silica gel 60F254 plates have been used. C, H, and N
■
In summary, the most plausible mechanism of the formation
of 3c from 1c and 2 is depicted in Scheme 11, the energy
profile is shown in Figure 4. The first nucleophilic addition step
of this process is the rate-limiting one and the apparent Gibbs
free energy of activation was calculated to be 21.5 kcal/mol, a
value quite comparable with the experimental one obtained for
the reaction of HON(p-CH2C6H4Cl)2 with [PtCl3(NCEt)]−
(20.6 kcal/mol).29
elemental analyses were carried out by the Microanalytical Service of
1
the Instituto Superior Tec
́
nico. H and 13C{1H} spectra (in CDCl3)
were measured on Bruker Avance II 300 and 400 MHz (UltraShield
Magnet) spectrometers at ambient temperature. 1H and 13C{1H}
chemical shifts (δ) are expressed in ppm relative to Si(Me)4, and 195Pt
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Scheme 11. Most Plausible Mechanism of the Reaction between 2 and 1c Leading to 3c
Figure 4. Energy profile of the most plausible mechanism of the reaction between 2 and 1c leading to 3c.
chemical shifts are relative to Na2[PtCl6] (by using aqueous K2[PtCl4],
δ = −1630 ppm, as a standard). J values are in Hz. Infrared spectra
(4000−400 cm−1) were recorded on a Bio-Rad FTS 3000MX
instrument in KBr pellets and the wavenumbers are in cm−1.
Electrospray 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 solutions 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 temperature
was maintained at 350 °C and dinitrogen was used as nebulizer gas at a
pressure of 35 psi. Scanning was performed from m/z = 50 to 1500.
The microwave irradiation experiments were undertaken in a focused
microwave CEM Discover reactor (10 mL, 13 mm diameter, 300 W
maximum power), which is fitted with a rotational system and an IR
detector of temperature.
Reactions of the Organonitrile Pt(II) Complexes trans-
[PtCl2(NCR)2] [R = Et (1a), Ph (1b)] with 1,3-Diiminoisoindoline
(2). By the Conventional Method. A solution of 1a (200 mg, 0.532
mmol) or 1b (200 mg, 0.423 mmol) in CH2Cl2 (4 mL) was added at
room temperature to 1,3-diiminoisoindoline (2) (1 equiv), and the
mixture was refluxed for 2 h whereupon the solvent was removed in
vacuo. The crude residue was purified by column chromatography on
silica (CH2Cl2 as the eluent), followed by evaporation of the solvent in
vacuo to give the final 3a or 3b products.
Crystals of 3a and 3b suitable for X-ray analysis were obtained by
slow evaporation of a chloroform solution.
Complex 3a. Method i, 65% yield; method ii, 68% yield. TLC on
SiO2: Rf = 0.81 (eluent CH2Cl2). IR (cm−1): 3255 (NH), 1648 (C
N). 1H NMR (CDCl3), δ: 1.47 (t, JHH 7.5 Hz, 6H, CH3CH2), 2.82 (q,
JHH 7.5 Hz, 4H, CH3CH2), 7.75 (dd, JHH 3.0 and 5.4 Hz, 2H,
CHaromatic), 8.26 (dd, JHH 3.0 and 5.4 Hz, 2H, CHaromatic), 9.77 (s, br,
2H, NH). 13C{1H} NMR (CDCl3), δ: 11.0 (CH3), 35.1 (CH2), 123.2,
132.1, 137.9 (Caromatic), 153.2 and 163.8 (CN). 195Pt NMR
(CDCl3), δ: −2233. ESI+-MS, m/z: 486.2 [M + 1]+. Anal. Calcd for
C14H16N5ClPt (484.84): C, 34.68; H, 3.33; N, 14.44. Found: C, 34.74;
H, 3.25; N, 14.33.
Complex 3b. Method i, 70% yield; method ii, 69% yield. TLC on
SiO2: Rf = 0.83 (eluent CH2Cl2). IR (cm−1): 3454 (NH), 1641 (C
N). 1H NMR (CDCl3), δ: 7.56−7.60 (m, 4H, CHaromatic), 7.68 (t, JHH
7.6 Hz, 2H, CHaromatic), 7.80 (q, JHH 2.8 Hz, 2H, CHaromatic), 8.27−8.30
(m, 4H, CHaromatic), 8.38 (q, JHH 2.8 Hz, 2H, CHaromatic), 10.38 (s, br,
2H, NH). 13C{1H} NMR (CDCl3), δ: 123.4, 127.5, 129.2, 131.6,
132.2, 136.7, 138.1 (Caromatic), 153.8 and 156.3 (CN). 195Pt NMR
(CDCl3), δ: −2163. ESI+-MS, m/z: 581.3 [M + 1]+. Anal. Calcd for
C22H16N5ClPt (580.93): C, 45.49; H, 2.78; N, 12.06. Found: C, 45.68;
H, 2.55; N, 12.21.
Reactions of the Organonitrile Pt(II) Complexes trans-
[PtCl2(NCR)2] [R = Et (1a), Ph (1b)] with 1,1,3,3-Tetramethylgua-
nidine (4). A solution of 1a (200 mg, 0.532 mmol) or 1b (200 mg,
0.423 mmol) in CH2Cl2 (4 mL) was added at room temperature to
1,1,3,3-tetramethylguanidine (4) (1 equiv), and the mixture was
refluxed for 12 h whereupon the solvent was removed in vacuo. The
crude residue was purified by column chromatography on silica
(acetone as the eluent), followed by evaporation of the solvent in
vacuo to give the final 5a or 5b products.
By Focused Microwave Irradiation. In this method, identical
amounts of the reagents described above were added to a cylindrical
Pyrex tube, which was then placed in the focused microwave reactor.
The system was left under irradiation (100 W) for 30 min at 60 °C.
After evaporation of the solvent in vacuo to dryness, the crude residue
was purified as indicated in the By the Conventional Method section.
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Complex 5a. Yield: 65%. TLC on SiO2: Rf = 0.67 (eluent acetone).
IR (cm−1): 3442 (NH), 2229 (NC), 1637 (CN). 1H NMR
(CDCl3), δ: 1.12−1.39 (m, 6H, CH3CH2), 2.83−2.88 (m, 4H,
CH3CH2), 2.97 (s, 6H, CH3N), 3.06 (s, 6H, CH3N), 6.61 (s, br, 1H,
NH). 13C{1H} NMR (CDCl3), δ: 9.5, 9.6, 12.1, and 13.3 (CH3CH2),
29.1, 29.3, 29.9, and 30.8 (CH2CH3), 39.9, 40.1, 40.2, and 40.3
(C(NMe2)2), 119.1 and 120.3 (NC), 163.3, 164.2, 175.1, and 178.3
(CN). ESI+-MS, m/z: 491.9 [M + 1]+. Anal. Calcd for
C11H23N5Cl2Pt (491.3): C, 26.89; H, 4.72; N, 14.25. Found: C,
26.75; H, 4.55; N, 14.43.
Complex 5b. Yield: 67%. TLC on SiO2: Rf = 0.69 (eluent acetone).
IR (cm−1): 3449 (NH), 2227 (NC), 1635 (CN). 1H NMR
(CDCl3), δ: 3.14 (s, 12H, CH3N), 6.13 (s, br, 1H, NH), 7.36−7.42
(m, 3H, CHaromatic), 7.49−7.52 (m, 2H, CHaromatic), 7.57−7.72 (m, 5H,
CHaromatic). 13C{1H} NMR (CDCl3), δ: 40.4 (Me groups), 110.4
(Cipso, NCPh), 115.8 (NC), 126.8, 128.4, 129.2, 130.5, 133.3,
134.3, and 138.2 (Caromatic), 163.6 and 170.1 (CN). ESI+-MS, m/z:
587.9 [M + 1]+. Anal. Calcd for C19H23N5Cl2Pt (587.4): C, 38.85; H,
3.95; N, 11.92. Found: C, 38.66; H, 3.65; N, 11.73.
X-ray Structure Determinations. The X-ray quality single
crystals of complexes 3a and 3b were immersed in cryo-oil, mounted
in a Nylon loop and measured at a temperature of 150 K. Intensity
data were collected using a Bruker AXS-KAPPA APEX II
diffractometer with graphite monochromated Mo−Kα (λ 0.71073)
radiation. Data were collected using omega scans of 0.5° per frame and
full sphere of data were obtained. Cell parameters were retrieved using
Bruker SMART software and refined using Bruker SAINT32 on all the
observed reflections. Absorption corrections were applied using
SADABS.32 Structures were solved by direct methods by using the
SHELXS−97 package33 and refined with SHELXL−97.33 Calculations
were performed using the WinGX System−Version 1.80.03.34 All
hydrogen atoms were inserted in calculated positions. Least square
refinements with anisotropic thermal motion parameters for all the
non-hydrogen atoms and isotropic for the remaining atoms were
employed. CCDC 884882 and 884883 contain the supplementary
crystallographic data for 3a and 3b, respectively. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Center via www.ccdc.cam.ac.uk/data_request/cif.
Computational Details. The full geometry optimization of all
structures and transition states (TS) has been carried out at the DFT/
HF hybrid level of theory using Becke’s three-parameter hybrid
exchange functional in combination with the gradient-corrected
correlation functional of Lee, Yang and Parr (B3LYP)35,36 with the
help of the Gaussian-0337 program package. No symmetry operations
have been applied. The geometry optimization was carried out using a
quasi-relativistic Stuttgart pseudopotential that described 60 core
electrons and the appropriate contracted basis set (8s7p6d)/
[6s5p3d]38 for the Pt atom and the 6-31G(d) basis set for other
atoms. Then, single-point calculations were performed on the basis of
the equilibrium geometries found using the 6-311+G(d,p) basis set for
nonmetal atoms. The Hessian matrix was calculated analytically for the
optimized structures in order to prove the location of correct minima
(no imaginary frequencies) or saddle points (only one negative
frequency), and to estimate the thermodynamic parameters, the latter
being calculated at 25 °C. The nature of all transition states was
investigated by the analysis of vectors associated with the imaginary
frequency and, in some cases, by the calculations of the intrinsic
reaction coordinates (IRC) using the Gonzalez-Schlegel method.39,40
Total energies corrected for solvent effects (Es) were estimated at
the single-point calculations on the basis of gas-phase geometries at the
CPCM-B3LYP/6-311+G(d,p)//gas-B3LYP/6-31G(d) level of theory
using the polarizable continuum model in the CPCM version41,42 with
CH2Cl2 as solvent. The UAKS model was applied for the molecular
cavity. The entropic term in CH2Cl2 solution (Ss) was calculated
according to the procedure described by Wertz43 and Cooper and
Ziegler44 using eqs 1−4
Reactions of the Organonitrile Pt(II) Complexes trans-
[PtCl2(NCR)2] [R = Et (1a), Ph (1b)] with 1,3-Diphenylguanidine
(6). A solution of 1a (200 mg, 0.532 mmol) or 1b (200 mg, 0.423
mmol) in CH2Cl2 (4 mL) was added at room temperature to 1,3-
diphenylguanidine 6 (1 equiv), and the mixture was refluxed for 12 h
whereupon the solvent was removed in vacuo. The crude residue was
purified by column chromatography on silica (CH2Cl2 or CH2Cl2/
Et2O as the eluent, respectively), followed by evaporation of the
solvent in vacuo to give the final 7a or 7b products. All the analytical
data are identical to those already reported.25a
Reaction of the Organonitrile Pt(II) Complex trans-[PtCl2(NCPh)2]
(1b) with Acetone Oxime (8). A solution of 1b (200 mg, 0.423 mmol)
in CH2Cl2 (4 mL) was added at room temperature to acetone oxime 8
(30.9 mg, 0.423 mmol), and the mixture was refluxed for 2 h
whereupon the solvent was removed in vacuo. The crude residue was
purified by column chromatography on silica (CH2Cl2 as the eluent),
followed by evaporation of the solvent in vacuo to give the final
product 9. All the analytical data are identical to those already
reported.2a,b
Reaction of the Organonitrile Pt(II) Complex trans-[PtCl2(NCPh)2]
(1b) with the Acyclic Nitrone −O+N(Me)C(H)(2,4,6-Me3C6H4) (10).
A solution of 1b (200 mg, 0.423 mmol) in CH2Cl2 (4 mL) was added
at room temperature to acyclic nitrone 10 (74.9 mg, 0.423 mmol), and
the mixture was refluxed for 12 h whereupon the solvent was removed
in vacuo. The crude residue was purified by column chromatography
on silica (CH2Cl2 as the eluent), followed by evaporation of the
solvent in vacuo to give the final product 11.
Complex 11. Yield: 67%. TLC on SiO2: Rf = 0.56 (eluent CH2Cl2).
IR (cm−1): 2287 (NC), 1634 (CN). 1H NMR (CDCl3), δ: 2.32,
2.49, and 2.82 (three s, 3H each, CH3Ph), 3.09 (s, 3H, CH3N), 6.41 (s,
1H, N−CH−N), 6.96 (d, JHH 8.1 Hz, 2H, CHaromatic), 7.48−7.72 (m,
8H, CHaromatic), 9.00 (d, JHH 8.1 Hz, 2H, CHaromatic). 13C{1H} NMR
(CDCl3), δ: 20.1, 20.9, and 21.1 (CH3Ph), 47.4 (CH3N), 91.9 (N−
CH−N), 109.8 (Cipso, NCPh), 116.3 (NC), 122.2, 128.2, 128.5,
129.1, 129.5, 130.3, 131.6, 133.4, 133.7, 134.6, 137.9, 139.3, and 140.3
(Caromatic), 163.7 (C(O)N). ESI+-MS, m/z: 650.6 [M + 1]+. Anal.
Calcd for C25H25N3Cl2OPt (649.5): C, 46.23; H, 3.88; N, 6.47.
Found: C, 46.34; H, 3.69; N, 6.56.
ΔS1 = R ln Vms ,liq/Vm,gas
(1)
s
°
ΔS2 = R ln Vm/Vm,liq
(2)
(3)
Sliq − (Sgas + R ln Vms ,liq/Vm,gas
)
,s
,s
°
°
α =
Sgas + R ln Vms ,liq/Vm,gas
,s
°
Ss = Sg + ΔSsol = Sg + [ΔS1 + α(Sg + ΔS1) + ΔS2]
Reaction of the Pt(II) Complexes trans-[PtCl2{NHC(R)N
C(NMe2)2}(NCR)] [R = Et (5a), Ph (5b)], [PtCl{NHC(R)NC-
(NHPh)NPh}(NCR)] [R = Et (7a), Ph (7b)] and trans-[PtCl2{NH
C(Ph)ONCMe2}(NCPh)] (9) with 1,3-Diiminoisoindoline (2). A
solution of 5a (200 mg, 0.407 mmol) or 5b (200 mg, 0.340 mmol) or
7a (200 mg, 0.363 mmol) or 7b (200 mg, 0.309 mmol) or 9 (200 mg,
0.367 mmol) in CH2Cl2 (4 mL) was added at room temperature to
1,3-diiminoisoindoline 2 (1 equiv), and the mixture was refluxed for
2 h whereupon the solvent was removed in vacuo. The crude residue
was purified by column chromatography on silica (CH2Cl2 as the
eluent), followed by evaporation of the solvent in vacuo to give the
final 3a or 3b products.
= Sg + [(−11.80 cal/mol·K) − 0.21(Sg − 11.80 cal/mol·K)
+ 5.45 cal/mol·K]
(4)
where Sg = gas-phase entropy of solute, ΔSsol = solvation entropy, S°liq,s,
Sg°a,ss, and Vms ,liq = standard entropies and molar volume of the solvent in
liquid or gas phases (173.84 and 270.28 J/mol·K and 64.15 mL/mol,
respectively, for CH2Cl2), Vm,gas = molar volume of the ideal gas at
25 °C (24450 mL/mol), V°m = molar volume of the solution cor-
responding to the standard conditions (1000 mL/mol). The enthalpies
and Gibbs free energies in solution (Hs and Gs) were estimated using
10784
dx.doi.org/10.1021/ic301176b | Inorg. Chem. 2012, 51, 10774−10786

Inorganic Chemistry
Article
the expressions 5 and 6
Haukka, M.; Wagner., G.; Pombeiro, A. J. L. J. Chem. Soc., Dalton
Trans. 2001, 560. (l) Kuznetsov, M. L.; Kukushkin, V. Yu.; Pombeiro,
A. J. L. J. Org. Chem. 2010, 75, 1474.
Hs = Es(6‐311+G(d, p)) − Eg(6‐311+G(d, p))
+ Hg(6‐31G(d))
́ ́
(3) (a) Vicente, J.; Abad, J. A.; Lopez-Saez, M. J.; Jones, P. G. Angew.
(5)
(6)
Chem., Int. Ed. 2005, 44, 6001. (b) Vicente, J.; Chicote, M. T.; Beswick,
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(c) Vicente, J.; Chicote, M. T.; Lagunas, M. C.; Jones, P. G. Inorg. Chem.
Gs = Hs − TSs
where Es, Eg, and Hg are the total energies in solution and in gas phase
and gas-phase enthalpy calculated at the corresponding level.
1995, 34, 5441. (d) Vicente, J.; Chicote, M. T.; Fernan
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Guedes da Silva, M. F. C.; Smolenski, P.; Kopylovich, M. N.; Frausto
́
dez-Baeza, J.;
ASSOCIATED CONTENT
* Supporting Information
́
■
́
́
S
da Silva, J. J. R.; Pombeiro, A. J. L. J. Organomet. Chem. 2011, 696,
3513. (c) Fernandes, R. R.; Lasri, J.; Guedes da Silva, M. F. C.; Palavra,
X-ray crystallographic data for complexes 3a and 3b in CIF format,
X-ray structure, hydrogen bond distances and angles, and selected
bonding parameter of complex 3a, discussion of the mechanistic
details of the nucleophilic addition of 2 to 1, and tables with
calculated energies and atomic coordinates. This material is
available free of charge via the Internet at http://pubs.acs.org.
A. M. F.; da Silva, J. A. L.; Frausto da Silva, J. J. R.; Pombeiro, A. J. L.
́
Adv. Synth. Catal. 2011, 353, 1153. (d) Lasri, J.; Guedes da Silva, M. F.
C.; Kopylovich, M. N.; Mukhopadhyay, B. G.; Pombeiro, A. J. L. Eur. J.
Inorg. Chem. 2009, 5541. (e) Lasri, J.; Guedes da Silva, M. F. C.;
Kopylovich, M. N.; Mukhopadhyay, S.; Januar
Pombeiro, A. J. L. Dalton Trans. 2009, 2210. (f) Mukhopadhyay, S.;
Mukhopadhyay, B. G.; Guedes da Silva, M. F. C.; Lasri, J.; Januario
Charmier, M. A.; Pombeiro, A. J. L. Inorg. Chem. 2008, 47, 11334.
(g) Mukhopadhyay, S.; Lasri, J.; Guedes da Silva, M. F. C.; Januario
Charmier, M. A.; Pombeiro, A. J. L. Polyhedron. 2008, 27, 2883. (h) Lasri,
J.; Kopylovich, M. N.; Guedes da Silva, M. F. C.; Januario Charmier, M.
A.; Pombeiro, A. J. L. Chem.Eur. J. 2008, 14, 9312. (i) Mukhopadhyay,
S.; Lasri, J.; Januario Charmier, M. A.; Guedes da Silva, M. F. C.;
Pombeiro, A. J. L. Dalton Trans. 2007, 5297. (j) Lasri, J.; Januario
́
io Charmier, M. A.;
AUTHOR INFORMATION
Corresponding Author
*E-mails: jamal.lasri@ist.utl.pt (J.L.); pombeiro@ist.utl.pt
(A.J.L.P.).
́
■
́
́
Notes
The authors declare no competing financial interest.
́
́
ACKNOWLEDGMENTS
This work has been partially supported by the Fundaca
■
Charmier, M. A.; Haukka, M.; Pombeiro, A. J. L. J. Org. Chem. 2007, 72,
̧
o para a
̃
750. (k) Bokach, N. A.; Krokhin, A. A.; Nazarov, A. A.; Kukushkin, V. Yu.;
Cien
̂
cia e a Tecnologia (FCT), Portugal, and its PEst-OE/
Haukka, M.; Frausto da Silva, J. J. R.; Pombeiro, A. J. L. Eur. J. Inorg.
́
Chem. 2005, 3042. (l) Bokach, N. A.; Kukushkin, V. Yu.; Haukka, M.;
QUI/UI0100/2011 project. J.L. and M.L.K express gratitude to
the FCT and the Instituto Superior Tecnico (IST) for their
research contracts (Ciencia 2007 program). The authors
Pombeiro, A. J. L. Eur. J. Inorg. Chem. 2005, 845. (m) Januar
M. A.; Haukka, M.; Pombeiro, A. J. L. Dalton Trans. 2004, 2741.
(n) Januario Charmier, M. A.; Kukushkin, V. Yu.; Pombeiro, A. J. L.
́
io Charmier,
́
̂
́
gratefully acknowledge the Portuguese NMR Network (IST-
UTL Center) for access to the NMR facility.
Dalton Trans. 2003, 2540. (o) Kuznetsov, M. L.; Kukushkin, V. Yu.;
Haukka, M.; Pombeiro, A. J. L. Inorg. Chim. Acta 2003, 356, 85.
(p) Wagner, G.; Haukka, M.; Frausto da Silva, J. J. R.; Pombeiro, A. J. L.;
́
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