Cationic palladium(II) complexes of the sterically hindered bis(4-methylthiazolyl)isoindoline (4-Mebti) with neutral group XVI donor ligands

Article abstract of DOI:10.1016/j.ica.2011.02.080

A series of cationic palladium complexes [(4-Mebti)PdL]⁺ with 4-Mebti = anion of bis(4-methylthiazolylimino)isoindoline and L = neutral ligand with group 16 donor atom has been prepared from the chlorido derivative [(4-Mebti)PdCl] and NaBAr^F (BAr^F = tetrakis(3,5- bis(trifluoromethyl)phenyl)boranate) in the presence of the respective donor ligand. Crystallographic and spectroscopic analyses were achieved for species with L = SMe₂, SeMe₂, dmf, acetamide, diphenylurea, and formiate. The latter two complexes represent products from hydrolyses of phenyl isocyanate and dmf, respectively, which occur during the ligand exchange reactions. Several other O-donor ligands like thf, acetone, Me₂O, water, and others are not bound to the palladium ion, and the dinuclear μ-chlorido derivative [{(4-Mebti)Pd}₂Cl]⁺ is isolated in these cases instead. The crystallographic analyses prove the expected presence of distorted, pseudo-planar palladium chelates, and the degree of distortion correlates well with the chemical shifts observed for the proton nuclei of the terminal methyl groups in the ¹H NMR experiment.

Full text of DOI:10.1016/j.ica.2011.02.080

Inorganica Chimica Acta 374 (2011) 572–577
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Cationic palladium(II) complexes of the sterically hindered
bis(4-methylthiazolyl)isoindoline (4-Mebti) with neutral
group XVI donor ligands
⇑
Martin Bröring , Christian Kleeberg, Anne Scheja
Technische Universität Braunschweig, Institut für Anorganische und Analytische Chemie, Hagenring 30, 38106 Braunschweig, Germany
a r t i c l e i n f o
a b s t r a c t
A series of cationic palladium complexes [(4-Mebti)PdL]+ with 4-Mebti = anion of bis(4-methylthiazolyli-
mino)isoindoline and L = neutral ligand with group 16 donor atom has been prepared from the chlorido
derivative [(4-Mebti)PdCl] and NaBArF (BArF = tetrakis(3,5-bis(trifluoromethyl)phenyl)boranate) in the
presence of the respective donor ligand. Crystallographic and spectroscopic analyses were achieved for
species with L = SMe2, SeMe2, dmf, acetamide, diphenylurea, and formiate. The latter two complexes rep-
resent products from hydrolyses of phenyl isocyanate and dmf, respectively, which occur during the
ligand exchange reactions. Several other O-donor ligands like thf, acetone, Me2O, water, and others are
Article history:
Available online 13 March 2011
Dedicated to Prof. Dr. Wolfgang Kaim on the
occasion of his 60th birthday.
Keywords:
BAI ligands
Palladium
not bound to the palladium ion, and the dinuclear
l
-chlorido derivative [{(4-Mebti)Pd}2Cl]+ is isolated
in these cases instead. The crystallographic analyses prove the expected presence of distorted, pseudo-
planar palladium chelates, and the degree of distortion correlates well with the chemical shifts observed
for the proton nuclei of the terminal methyl groups in the 1H NMR experiment.
Ó 2011 Elsevier B.V. All rights reserved.
Cationic complexes
Group 16 donors
X-ray structure determination
1. Introduction
to push a (trpy)PdL compound towards dissociation into the three-
coordinate T-shaped 14 VE cation. This approach failed as the
Ligand exchange processes of square-planar palladium(II) com-
pounds and other low spin d8 complexes have always shown asso-
ciative reaction mechanisms in the cases studied so far [1]. A
general possibility to move this mechanism towards a dissociative
process and to observe a rare three-coordinate, T-shaped palla-
dium(II) compound would lie in the kinetic destabilization of the
square-planar ligand sphere. Such a scenario can be realized by
applying a suitably substituted meridional tridentate ligand to a
system accepts quite large distortions with these strongly binding
ligands, and escapes in the case of PMe3 towards a square–pyramidal
five-coordinate 18 VE complex. Applying weaker ligands resulted
in the decomposition of the sensitive tripyrrin scaffold [8]. We
have now turned to the more robust and structurally related
bis(4-methylthiazolylimino)isoindoline
(4-Mebti)
framework
[9,10], and report here a series of cationic palladium complexes with
group 16 donor ligands (O, S, Se).
palladium ion.
a,x-Dimethyltripyrrins provide for such a ligand
class and have been studied by us in the past towards this goal
[2–8]. In these ligands backbones, the terminal methyl groups
are oriented in a way that the fourth coordination site of a central
palladium atom may not be occupied in the N3 plane of the cationic
(trpy)Pd fragment without significant distortion of either the or-
ganic ligand or the coordination geometry. As illustrated in Fig. 1,
either of two forms is usually observed, the pseudo-planar form
and the helical form, depending on the shape and sterical require-
ment of the employed additional ligand. In some cases an equilib-
rium exists, and both forms are observed crystallographically [4,5].
In a foregoing study, we have used group 14 and 15 donor li-
gands (C, N, P) with a stepwise increase in steric hindrance in order
2. Experimental
2.1. General remarks
Reagents were purchased from commercial sources and used
without further purification. Solvents were dried by conventional
methods and stored under Argon. The preparation of the cationic
complexes was performed using standard Schlenk techniques.
[(4-Mebti)PdCl]
1
[11], sodium tetrakis(3,5-bis(trifluoro-
methyl)phenyl)boranate (NaBArF [12]), and dimethylselenium
[13] were prepared according to the literature methods. NMR
spectra were recorded on a Bruker Avance 300 or DRX 400 spec-
trometer, respectively. Chemical shifts (d) are given in ppm, using
the resonance of the residual solvent CD2Cl2 as internal reference
(1H NMR: 5.32 ppm, 13C NMR: 53.5 ppm). Nomenclature and
⇑
Corresponding author. Tel.: +49 (0) 531 391 5302; fax: +49 (0) 531 391 5387.
E-mail address: m.broering@tu-bs.de (M. Bröring).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.02.080

M. Bröring et al. / Inorganica Chimica Acta 374 (2011) 572–577
573
170 °C (C50H29BF24N6OPdS2 Â CH2Cl2 requires: C, 42.18; H, 2.15;
N, 5.79. Found: C, 42.13; H, 2.57; N, 6.02%). 1H NMR (CD2Cl2,
295 K): d 2.02 (br s, 3H, acetamide), 2.57 (s, 6H, 4-MeTh), 6.40–
6.71 (br s, 2H, NH2), 6.98 (s, 2H, 5-CHTh), 7.56 (s, 4H, p-CH F),
7.71–7.74 (m, 10H, b-CH + o-CHBArF), 8.02–8.04 ppm (m, 2HB,Ara
-
CH). 13C NMR (CD2Cl2, 295 K): d 19.3, 115.9, 117.9 (m, p-CHBArF),
1
123.4, 125.0 (q, JC–F = 271 Hz, CF3), 129.1 (m, m-CBArF), 133.1,
135.2, 136.6, 150.2, 154.1, 162.0 (m, BCBArF), 167.6 ppm; the
remaining signal for the acetamide could not be detected. 19F
NMR (CD2Cl2, 295 K): d À65.5 ppm.
Fig. 1. Conformational dynamics observed for palladium complexes with sterically
hindered tripyrrin ligands.
2.3.3. [(4-Mebti)Pd(dmf)]+ BArFÀ (3) and [(4-Mebti)Pd(OCHO)] (4)
A mixture of toluene and DMF (60:1) was used for the prepara-
tion. Single crystals of 3 were obtained by diffusion of n-pentane
into a dichloromethane solution at À20 °C. (15.7 mg, 54%), mp
132 °C (decomp.) (C51H31BF24N6OPdS2 requires: C, 44.36; H, 2.26;
N, 6.08. Found: C, 43.92; H, 2.41; N, 5.99%). 1H NMR (CD2Cl2,
295 K): d 2.60 (s, 6H, 4-MeTh), 2.98 (s, 3H, dmf), 3.01 (s, 3H, dmf),
6.91 (s, 2H, 5-CHTh), 7.56 (s, 4H, p-CHBArF), 7.66–7.69 (m, 2H, b-
numbering scheme for the assignment of the resonance signals is
given in Chart 1. In the case of 19F NMR spectra, CFCl3 was used
as external reference. Elemental analyses were carried out on an
Elementar Vario EL instrument. Melting points were determined
on a Büchi SMP-20 in open capillaries and are not corrected.
2.2. Single crystal X-ray structural determinations
CH), 7.73 (br s, 8H, o-CHBArF), 7.89–7.92 ppm (m, 2H,
a-CH), 8.01
Experimental details relating to the crystallographic character-
ization are summarized in Table 1. Diffraction data were collected
(s, 1H, dmf). 13C NMR (CD2Cl2, 295 K): d 19.7, 33.5, 38.2, 115.2,
1
117.4 (m, p-CHBArF), 123.0, 124.7 (q, JCÀF = 273 Hz, CF3), 128.9
using graphite monochromated Mo K
instrument at 193(2) K using -scans, or on a Stoe IPDS-II at
173(2) K using -scans. The structures were solved by direct meth-
a radiation on a Stoe IPDS-I
(m, m-CBArF), 132.6, 134.7, 136.3, 149.5, 153.7, 161.9 (m, BCBArF),
166.3, 166.8 ppm. 19F NMR (CD2Cl2, 295 K): d À62.9 ppm. If wet
THF is added to the crystallization mixture, a small deposit of crys-
tals of the formiate complex 4 forms over several days.
U
x
ods and refined against F2 by least-squares utilizing the software
packages SHELXL-97 [14], SIR-92 [15], PLATON [16], and WINGX [17]. All
non-hydrogen atoms were refined anisotropically. Hydrogen
atoms were placed in calculated positions and refined using a rid-
ing model. Selected bond lengths, distances and angles for 2–7 are
given in Table 2.
2.3.4. [(4-Mebti)Pd(OC(NHPh)2)]+ BArFÀ (5)
Wet toluene and phenylisocyanate (0.1 mL, 92 lmol) were used
for the preparation. Single crystals of 5 were obtained by diffusion
of n-pentane into a dichloromethane solution at À20 °C. (10.2 mg,
58%), mp 172 °C (decomp.) (C61H36BF24N7OPdS2 requires: C, 48.19;
H, 2.39; N, 6.45. Found: C, 47.47; H, 2.95; N, 7.27%). 1H NMR
(CD2Cl2, 295 K): d 2.61 (s, 6H, 4-MeTh), 6.84 (s, 2H, 5-CHTh), 7.10–
7.28 (m, 10H, CHPh), 7.56 (s, 4H, p-CHBArF), 7.64 (s, 2H, b-CH),
2.3. Syntheses of complexes
2.3.1. General procedure
[(4-Mebti)PdCl] 1 (10.0 mg, 21
l
mol) was dissolved in dry tolu-
a
-CH + o-CHBArF); the NH signal was not detected.
ene or dichloromethane (2 mL), and NaBArF (18.7 mg, 21
l
mol)
7.73 (m, 10H,
13C NMR (CD2Cl2, 295 K): d 19.8, 115.0, 117.5 (m, p-CHBArF),
was added in one portion. The mixture was stirred for 5 min before
the neutral ligand was added, and stirring continued for 16 h. If a
red solid has precipitated, the solvent was removed in vacuum
and the solid extracted with dry dichloromethane. After filtration
on celite the solvent was removed again, the residue washed with
pentane, and dried in vacuum. If the product remained in solution,
the reaction mixture was directly filtered and treated as described.
Purification was achieved by crystallization as detailed below for
each case.
1
122.9, 123.0, 124.7 (q, JC–F = 270 Hz, CF3), 126.5, 129.0 (m,
m-CBArF), 129.8, 132.6, 134.9, 135.9, 136.2, 149.8, 153.4, 162.0 (m,
BCBArF), 166.2; the carbonyl carbon atom was not detected. 19F
NMR (CD2Cl2, 295 K): d À65.4 ppm.
2.3.5. [(4-Mebti)Pd(SMe2)]+ BArFÀ (6)
A mixture of toluene and dimethylsulfide (25:1) was used for
the preparation. Single crystals of 6 were obtained by diffusion of
n-pentane into a dichloromethane solution at À20 °C. (18.7 mg,
65%), mp 163–166 °C (C50H30BF24N5PdS3 Â 1.86 CH2Cl2 (from the
crystallographic analysis) requires: C, 40.59; H, 2.23; N, 4.57.
Found: C, 40.62; H, 2.42; N, 4.44%). 1H NMR (CD2Cl2, 295 K): d
2.14 (s, 6H, Me2S), 2.77 (s, 6H, 4-MeTh), 7.13 (s, 2H, 5-CHTh), 7.56
(br s, 4H, p-CHBArF), 7.73 (br s, 8H, o-CHBArF), 7.76 (m, 2H, b-CH),
2.3.2. [(4-Mebti)Pd(OC(NH2)Me)]+ BArFÀ (2)
Purified acetamide (5.9 mg, 100 lmol) and dichloromethane
were used for the preparation. Single crystals of 2 were obtained
after double recrystallization from toluene/n-pentane and dichlo-
romethane/n-pentane, respectively. (14.6 mg, 51%), mp 168–
Chart 1. Nomenclature and numbering systems for the spectroscopic assignments.

574
M. Bröring et al. / Inorganica Chimica Acta 374 (2011) 572–577
Table 1
Crystallographic data and structure refinement parameters for 2–7.
Compound
Formula
2
3
4
5
6
7
C
C
18H17N6OPdS2,
32H12BF24, CH2Cl2
C19H19N6OPdS2,
C
C17H13N5O2PdS2,0.5 C29H24N7OS2Pd,
C4H8O
C18H18N5PdS3,
C
C18H18N5PdS2Se,
C32H12BF24, 1.79 CH2Cl2
32H12BF24
C
32H12BF24
32H12BF24, 1.86 CH2Cl2
Formula weight
Color/habit
Crystal system
Space group
a (Å)
1452.09
orange/block
1381.19
red/block
triclinic
526.65
red/fragment
monoclinic
P21/n
8.8497(7)
18.3119(9)
12.3881(9)
90
100.267(6)
90
1975.4(2)
4
1520.34
red/block
triclinic
1528.19
red/block
monoclinic
P21/c
13.415(2)
22.188(2)
20.856(2)
90
103.78(1)
90
6029(1)
4
1569.24
red/block
monoclinic
P21/c
13.373(1)
22.144(3)
20.873(2)
90
103.000(7)
90
6023(1)
4
triclinic
ꢀ
ꢀ
ꢀ
P1
P1
P1
13.1121(7)
14.274(2)
16.714(2)
75.31(1)
82.31(2)
68.98(2)
2821.3(7)
2
13.066(2)
13.811(4)
16.748(3)
114.26(3)
90.81(2)
90.59(3)
2755(1)
2
13.940(2)
15.362(2)
17.416(2)
105.19(1)
105.42(2)
90.25(2)
3458.8(8)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dc (g cmÀ3
)
1.709
0.622
1.665
0.540
1.769
1.181
1.461
0.439
1.698
0.702
1.727
1.25
l
(mmÀ1
)
F (0 0 0)
1440
1372
1058
1671
3401
3086
Crystal size (mm) 0.36 Â 0.27 Â 0.06
0.42 Â 0.36 Â 0.18 0.36 Â 0.24 Â 0.11
0.37 Â 0.31 Â 0.23 0.48 Â 0.32 Â 0.16
0.23 Â 0.22 Â 0.05
T (K)
193(2)
193(2)
100(2)
193(2)
193(2)
173(2)
h-range (°)
Reflections
collected
Reflections
1.86–26.14
28 128
2.07–26.02
27 118
2.01–25.41
10 088
1.97–26.01
33 864
1.81–26.11
47 361
1.81–26.04
32 330
7679
7832
2573
8621
8634
6557
[I > 2r(I)]
Data/restraints/
10 369/6/852
9994/0/919
3585/35/292
12 560/46/959
11 785/15/939
11 724/5/824
parameters
Goodness-of-fit
0.980
0.946
0.956
0.955
1.048
0.923
Final R1 [I > 2
Final wR2 (all
r
(I)] 0.0454
0.1228
0.0393
0.1038
0.0501
0.1277
0.0529
0.1453
0.0553
0.1605
0.0605
0.1320
data)
Table 2
Selected bond lengths (Å) and bond angles (°) for the palladium complexes 2–7.
2 [D@O(1)]
3 [D@O(1)]
4 [D@O(2)]
5 [D@O(1)]
6 [D@S(3)]
7 [D@Se(1)]
Pd–N(1)
Pd–N(3)
Pd–N(4)
Pd–D
2.033(3)
1.968(3)
2.038(3)
2.068(3)
4.516(8)
2.838(6)
2.811(6)
89.2(1)
166.3(1)
93.7(1)
89.7(1)
162.6(1)
91.4(1)
2.022(3)
1.968(2)
2.029(3)
2.100(2)
4.374(6)
2.926(5)
2.921(5)
90.4(1)
169.59(9)
92.0(1)
89.5(1)
156.30(9)
92.27(9)
2.026(5)
1.976(5)
2.041(5)
2.026(4)
4.73(1)
2.770(9)
2.765(9)
89.6(2)
171.8(2)
90.2(2)
90.2(2)
166.7(2)
91.9(2)
2.031(4)
1.962(3)
2.059(4)
2.047(3)
4.788(8)
2.790(6)
2.776(6)
89.9(2)
170.4(1)
89.7(2)
90.3(1)
166.2(1)
92.4(1)
2.030(4)
2.009(3)
2.017(4)
2.357(1)
4.253(8)
3.240(7)
3.197(5)
89.2(1)
163.6(2)
95.6(1)
88.6(1)
151.7(1)
94.0(1)
2.025(4)
2.010(4)
2.015(5)
2.4650(8)
4.35(1)
3.226(7)
3.283(9)
89.1(2)
164.9(2)
93.6(1)
89.3(2)
150.8(1)
95.1(1)
C(1)Á Á ÁC(16)
C(1)Á Á ÁD
C(16)Á Á ÁD
N(1)–Pd–N(3)
N(1)–Pd–N(5)
N(1)–Pd–D
N(3)–Pd–N(5)
N(3)–Pd–D
N(5)–Pd–D
8.08 (m, 2H,
a
-CH). 13C NMR (CD2Cl2, 295 K): d 19.9, 24.5, 116.4,
3. Results and discussion
1
117.6 (m, p-CHBArF), 123.4, 124.7 (q, JC–F = 271 Hz, CF3), 129.0
(m, m-CBArF), 133.2, 134.9, 136.6, 148.0, 155.2, 161.8 (m, BCBArF)),
167.9. 19F NMR (CD2Cl2, 295 K): d À62.8 ppm.
3.1. Preparation of complexes
Cationic palladium(II) complexes with the 4-Mebti ligand can
be prepared successfully by salt metathesis of the chlorido deriva-
2.3.6. [(4-Mebti)Pd(SeMe2)]+ BArFÀ (7)
Toluene and dimethylselenide (1.7
l
L, 22
l
mol) was used for
tive [(4-Mebti)PdCl] 1 with sodium tetrakis(3,5-bis(trifluoro-
the preparation. Single crystals of 7 were obtained by diffusion of
n-pentane into a dichloromethane solution at À20 °C. (20.2 mg,
68%), mp 155 °C (decomp.) (C50H30BF24N5PdS2Se requires: C,
42.38; H, 2.13; N, 4.94. Found: C, 42.06; H, 2.52; N, 4.58%). 1H
NMR (CD2Cl2, 295 K): d 2.04 (s, 6H, Me2S), 2.76 (s, 6H, 4-MeTh),
7.11 (s, 2H, 5-CHTh), 7.57 (br s, 4H, p-CHBArF), 7.75 (br s, 8H, b-
methyl)phenyl)boranate (NaBArF) [12] in the presence of
different neutral ligands and solvents. The use of the chlorido pre-
cursor 1 is recommended over the analogous and more accessible
acetato derivative [18] as the low solubility of sodium chloride ap-
pears to be the major driving force for the reaction with neutral do-
nor ligands. A similar approach has successfully been applied for a
number of cationic palladium(II) precatalysts for norbornene poly-
merization [19,20]. Scheme 1 presents an overview of successful
preparations and of unsuccessful attempts.
CH + o-CHBArF), 8.07 (m, 2H,
a
-CH). 13C NMR (CD2Cl2, 295 K): d
1
15.6, 20.7, 116.2, 117.6 (m, p-CHBArF), 123.3, 125.1 (q, JC–
F = 270 Hz, CF3), 129.3 (m, m-CBArF), 133.1, 134.9, 136.7, 148.1,
156.3, 162.0 (m, BCBArF), 167.9. 19F NMR (CD2Cl2, 295 K):
d
The outcome of the attempted ligand exchange reactions can be
divided into three classes. Hard O-donor ligands of the group
À64.4 ppm.

M. Bröring et al. / Inorganica Chimica Acta 374 (2011) 572–577
575
Scheme 1. Overview of ligand exchange reactions performed in this study.
water, alcohols, ketones, aldehydes, esters, and ethers do not form
isolable cationic chelate complexes with the (4-Mebti)Pd fragment.
Instead, the dinuclear chlorido-bridged species [{(4-Mebti)Pd}2Cl]+
BArFÀ 8 [11] forms as the only palladium-containing product dur-
ing all these attempts. The application of the particularly soft
TeMe2 donor on the other side results in the observation of many
different reaction products. Obviously, demetalation and decom-
position of the organic ligand occurs during the uncontrollable
transformation, and a simple [PdCl(TeMe2)3]+ complex has been re-
ported as the only isolated species from this mixture [21].
quite likely in view of the low tendency of DMF to hydrolyze spon-
taneously in the presence of water traces [22]. Dimethylsulfide and
dimethylselenide react smoothly to the expected products 6 and 7,
respectively. For the selenium derivative, a strict stoichiometric
control is necessary in order to avoid the massive formation of
by-products from demetalation and ligand decomposition.
All products were obtained in analytical purity after recrystalli-
zation, and were characterized by NMR spectroscopy and X-ray
diffraction.
O
amido-, S-, and Se-ligands with an intermediate hardness have
3.2. Structural and spectroscopic features
been found capable to form the desired cationic species. The use
of purified acetamide and dmf directly result in the compounds
[(4-Mebti)PdL]+ 2 and 3, respectively, while phenylisocyanate
leads to the diphenylurea complex 5 only in the presence of water
traces. It is likely that the diphenylurea ligand forms from phenyl-
isocyanate and aniline, which in turn is produced by the hydrolysis
of phenylisocyanate. Whether the formation of diphenylurea oc-
curs prior to the metathesis reaction, or is catalyzed by the (4-
Mebti)Pd fragment could not be resolved. If freshly distilled phen-
ylisocyanate is used with careful exclusion of water, the dinuclear
Single crystals have been obtained for the six compounds 2–7
by diffusion of n-pentane into dichloromethane or dichlorometh-
ane/THF (for 4) solutions at À20 °C. Except for the dmf and urea
complexes 3 and 5 all crystals contain co-crystallized dichloro-
methane or THF molecules (in the case of 4) to stabilize the crystal
lattice. Table 1 contains crystallographic data and details for the
structure solutions and refinements. Table 2 summarizes selected
molecular data of the investigated complexes.
The acetamide and dmf derivatives 2 and 3, respectively, crys-
l-chlorido derivative 8 forms exclusively. Another hydrolysis
ꢀ
tallize in the triclinic system, space group P1, with Z = 2 (Fig. 2).
product has been obtained from an attempted crystallization of
the dmf complex 3 in the presence of wet THF. Several crystals
of the neutral formiate species [(4-Mebti)PdOCHO] 4 were isolated
as the only product and could be analyzed by X-ray diffraction. As
before it is unclear whether the hydrolysis process is catalyzed by
the (4-Mebti)Pd fragment or not. A catalytic reaction, however, is
The palladium(II) ion of 2 is situated in a N3O ligand field with
one short Pd–N bond to the isoindole imido nitrogen donor
(1.968(3) Å), two longer Pd–N bonds (2.033(3) and 2.038(3) Å) to
the thiazole imino nitrogen donors, and a long Pd–O bond to the
acetamide ligand of 2.068(3) Å. The coordination geometry is basi-
cally planar with a marked, but evenly distributed distortion

576
M. Bröring et al. / Inorganica Chimica Acta 374 (2011) 572–577
Fig. 2. Molecular structures of acetamide and dmf complexes 2 and 3 (cation only).
towards a tetrahedron. This distortion can be quantified by similar
N(1)–Pd–N(5) and N(3)–Pd–O(1) angles of 166.3(1)° and
162.6(1)°, respectively, and accounts for an intermediate amount
of steric repulsion between the 4-Mebti ligand and the methyl-
and amino groups of the acetamide ligand. The amino group is ro-
tated into conjugation with the carbonyl moiety, and the C–O and
C–N bond lengths of the bound acetamide ligand of 1.264(5) Å and
1.295(6) Å, respectively, are clearly aligned as compared to the free
acetamide
(C–O:
1.242(2)/1.243(2) Å;
C–N:
1.325(2)/
1.326(2) Å)[23]. This finding accounts for a significant contribution
of a resonance structure with a C@N double bond and a partially
anionic O-donor, and therefore for an electrophilic activation of
the amide functionality in the metal complex. Another noticeable
feature of the solid state structure of 2 is the absence of hydrogen
bridges between adjacent molecular units. The reason for this
observation can be found in the interaction of the complex cation
with the BArF counterions. The aryl rings of these BArF anions are
rotated towards each other in a way as to form two juxtaposed 2
phenyl embrace (2PE) binding pockets [24–28]. One of these pock-
ets binds to the H3C–C–NH2 motif presented at the surface of the
cation and efficiently shields this potent hydrogen bridge donor
from interacting with any acceptor site.
The PdN3O coordination unit of the dmf derivative 3 displays
Pd–N bond lengths similar to the acetamide derivative 2 (Pd–
N(1): 2.022(3) Å; Pd–N(3): 1.968(2) Å; Pd–N(5): 2.029(3) Å), but
differs structurally through the elongated Pd–O(1) bond of
2.100(2) Å. In addition, the non-planar distortion of the PdN3O unit
is unevenly distributed, with a planarized PdN3 substructure
(N(1)–Pd–N(5): 169.59(9)°) and a steep N(3)–Pd–O(1) angle of
156.30(9)°. A possible explanation for these differences lies in the
sterical requirements of a significant 2PE binding of the NMe2
group of the dmf ligand of 3 by a BArF anion, which is observed
in the crystal structure. Similar to the acetamido ligand of 2, the
NMe2 group of the dmf ligand of 3 is rotated into conjugation with
the binding carbonyl, and the coordination of dmf to the cationic
(4-Mebti)Pd fragment again causes an elongation of the C–O bond
from 1.2224(6) Å in the free DMF molecule to 1.251(4) Å, and a
reduction of the C–N bond length from 1.389(5) to 1.308(4) Å
[29]. The polarization of the amide ligand thus appears stronger
for dmf than for acetamide. Consequently, the formation of the
hydrolyzed formiate complex 4 was observed upon crystallization
attempts in the presence of water. The structure of this complex
(Fig. 3) resembles largely that of the homologous acetato complex
described earlier and will not be discussed in detail [18]. Compared
to the cationic amide complexes 2 and 3, the overall planarized
geometry of the PdN3O subunit of 4 with angles N(3)–Pd–O(2) of
166.7(2)° and 171.8(2)°, and the short Pd–O(2) bond of
2.026(4) Å are the most remarkable features of the neutral formi-
ate complex.
Fig. 3. Molecular structures of formiate and diphenylurea complexes 4 and 5
(cation only).
The second hydrolysis product in this series, the diphenylurea
ꢀ
complex 5, crystallizes in the triclinic system, space group P1, with
Z = 2 (Fig. 3). Other than for the other amide derivatives 2 and 3 the
bond lengths and angles within the PdN3O subunit of the urea
compound 5 (Pd–N(1): 2.031(4) Å; Pd–N(3): 1.962(3) Å; Pd–N(5):
2.059(4) Å; Pd–O(1): 2.047(3) Å; N(3)–Pd–O(1): 166.2(1)°; N(1)–
Pd–N(5): 170.4(1)°) resemble largely those of the neutral formiate
4. The diphenylurea ligand of 5 contains activated C–O and C–N
bonds (C–O: 1.251(4) Å; C–N: 1.327(5) Å and 1.344(5) Å) as judged
by the changes found with respect to free diphenylurea (C–O:
1.233(3) Å; C–N: 1.342(5) Å and 1.363(5) Å) [30], albeit the activa-
tion appears to be smaller than for the amide ligands in 2 and 3. A
reason for the flattened structure of the PdN3O coordination unit of
5 may be found in the orientation of the phenyl groups of the urea
ligand. While one of these phenyl moieties is bound by the 2PE
pocket of the BArF anion, the other C6H5 unit is
the (4-Mebti)Pd cation with a medium stacking distance of
p-stacked onto
p–p
3.1395(3) Å (distance of the C6 centroid to the mean squares plane
Fig. 4. Molecular structures of dimethylsulfide and dimethylselenide derivatives 6
and 7 (cation only).

M. Bröring et al. / Inorganica Chimica Acta 374 (2011) 572–577
577
Table 3
group 14 and 15 donor ligands, the degree of distortion depends
mainly on the sterical requirements of the employed ligands, and
can be monitored in solution by the shift of the 1H NMR signal of
the terminal methyl group protons. Harder O-donor ligands, on
the other hand, cannot compete with the binding strength of the
Correlation of structural parameters and NMR data for the cationic [(4-Mebti)PdL]+
complexes 2, 3 and 5–7.
Complex (donor
ligand)
N(3)–Pd–D
Nterm–Pd–D
d[1H] CH3 (term)
(°)
(°)a
2 (Acetamide)
3 (dmf)
5 (Diphenylurea)
6 (Dimethylsulfide)
7 (Dimethylselenide)
162.6(1)
156.30(9)
166.2(1)
151.7(1)
150.8(1)
92.5
92.1
91.1
94.8
94.3
2.57
2.60
2.61
2.77
2.76
bridging chlorido ligand of a dinuclear l-chlorido complex, which
appears to be the common intermediate in all ligand exchange
reactions studied here. This result fits into the general expectations
from the HSAB concept and shows, that besides the sterical compo-
nent, the ligand softness must be considered in future attempts to
prepare three-coordinate palladium(II) complexes.
a
Mean value from N(1)–Pd–D and N(5)–Pd–D.
of all sp2 atoms of the 4-Mebti ligand, including the Pd atom) and
thus tears the whole urea ligand closer to the mean PdN3 plane.
The EMe2 complexes (E = S, Se) 6 and 7 crystallize isomorphous
in the monoclinic system, space group P21/c, with Z = 4. Fig. 4 illus-
trates the molecular structures of both [(4-Mebti)Pd(EMe2)]+ cat-
ions. The Pd–E bond lengths in 6 and 7 are found at 2.357(1) Å
and 2.4650(8) Å, respectively, and the difference in the bond
lengths quantitatively reflects the different vdW radii of the S
and Se atom. The C–S–C and Pd–S–C angles at the sulfur atom
are 98.3(3)°, 99.4(2)°, and 103.8(2)°, respectively, and therefore
slightly larger than the analogous C–Se–C and Pd–Se–C angles of
96.4(4)°, 96.4(2)°, and 101.0(2)°. These values proof the expected
decrease of the contribution of the E’s s-type valence orbital to
the binding interaction with increasing atomic number. The geom-
etry of the PdN3E subunit differs from the amide and urea cases de-
scribed above by an elongated N(3)–Pd bond of 2.009(3) Å (E = S)
and 2.010(4) Å (E = Se), and by significantly larger N(3)–Pd–E an-
gles of 151.7(1)° (E = S) and 150.8(1)° (E = Se). Beside the obviously
larger vdW radii of S and Se, the fact that the orientation of these
two EMe2 ligands is perpendicular to those of the O-donor ligands
in 2–5 accounts for an additional gain in LÁ Á Á4-Mebti repulsion, and
thus in a higher degree of distortion.
Acknowledgements
Funding was kindly provided by the Deutsche Forschungsgeme-
inschaft (DFG). The authors thank Nicola Biermann for his help
with the dmf derivative 3.
Appendix A. Supplementary material
CCDC Nos. 813871 (2), 813872 (3), 813870 (4), 813867 (5),
813869 (6), and 813868 (7) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.ica.2011.02.080.
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4. Conclusions
Soft Oamide-, S-, and Se-donor ligands bind well to the cationic
(4-Mebti)Pd fragment and allow for a number of crystallographi-
cally characterized distorted complexes of the pseudo-planar
geometry. As for the related palladium tripyrrin complexes with