Bis(4-methylthiazolyl)isoindoline (4-mebti) complexes of palladium: Cationic [PdII(4-Mebti)L]+ species with a L = neutral group XIV or group XV donor ligand

Article abstract of DOI:10.1002/zaac.201100211

Ligand exchange has been studied on the chlorido palladium(II) complex of the bis(4-methylthiazolylimino)isoindoline ligand, [Pd(4-Mebti)Cl], with a number of neutral group XIV and group XV donor ligands in the presence of the sodium salt of tetrakis[3,5-bis(trifluoromethyl)phenyl]borate NaB(Ar ^F)₄. Seven new cationic compounds with L = PMe ₃, tBuNH₂, PhNH₂, py, 2,6-Me₂py, MeCN and MeNC were obtained as B(Ar^F)₄^- salts, and were characterized by analytic, spectroscopic and crystallographic means. Further attempts to observe ligand exchange reactions with either the softer AsMe₃ or SbMe₃ donor ligands or with different carbenes were unsuccessful and led to decomposed material or to mixtures of different compounds. Most of the crystallographically characterized complexes have been found to reside in a pseudoplanar conformation regardless of the size or cone angle of the external donor ligand. The derivatives carrying an sp ²-type donor atom (L = py, 2,6-Me₂py), however, adopt helical forms in the solid state. ¹H NMR and UV/Vis spectroscopic data suggest that this helicity is also present in solution. The expected chirality, however, could not be observed due to the lack of diastereotopic ligand protons. Copyright

Full text of DOI:10.1002/zaac.201100211

ARTICLE
DOI: 10.1002/zaac.201100211
Bis(4-methylthiazolyl)isoindoline (4-Mebti) Complexes of Palladium:
Cationic [PdII(4-Mebti)L]+ Species with a L = Neutral Group XIV or Group
XV Donor Ligand
Martin Bröring*[a] and Christian Kleeberg[a]
In Memory of Professor Kurt Dehnicke
Keywords: BAI ligands; Palladium; Cationic complexes; Group 14 donors; Group 15 donors
Abstract. Ligand exchange has been studied on the chlorido palla- led to decomposed material or to mixtures of different compounds.
dium(II) complex of the bis(4-methylthiazolylimino)isoindoline li- Most of the crystallographically characterized complexes have been
gand, [Pd(4-Mebti)Cl], with a number of neutral group XIV and group found to reside in a pseudoplanar conformation regardless of the size
XV donor ligands in the presence of the sodium salt of tetrakis[3,5- or cone angle of the external donor ligand. The derivatives carrying
bis(trifluoromethyl)phenyl]borate NaB(ArF)4. Seven new cationic an sp2-type donor atom (L = py, 2,6-Me2py), however, adopt helical
1
compounds with L = PMe3, tBuNH2, PhNH2, py, 2,6-Me2py, MeCN forms in the solid state. H NMR and UV/Vis spectroscopic data sug-
and MeNC were obtained as B(ArF)4– salts, and were characterized by gest that this helicity is also present in solution. The expected chirality,
analytic, spectroscopic and crystallographic means. Further attempts to however, could not be observed due to the lack of diastereotopic ligand
observe ligand exchange reactions with either the softer AsMe3 or protons.
SbMe3 donor ligands or with different carbenes were unsuccessful and
palladium[3] two different conformational states have been ob-
served, denoted “pseudoplanar” and “helical”, as shown in Fig-
ure 1. Neutral as well as anionic co-ligands, L and X, respec-
tively, possess the ability to distort the complex in either of the
Introduction
Palladium(II) complexes with N donor chelate ligands have
received much attention over the last decades. Cationic N do-
nor chelate complexes and organometallics of divalent palla-
two forms, and in one case an equilibrium between the two
dium have found many uses in academic as well as in applied
conformers has been observed. α,ω-Me2bpi ligands (bpi =
chemistry. Prominent examples are found in the polymeriza-
bis(pyridylimino)isoindoline[4]), on the other hand, are bound
tion or oligomerization of alkenes[1] and in alkene/CO copoly-
by palladium(II) in a strained manner only, if further alkyl
merization reactions,[2] which are successfully catalyzed by ac-
groups block intramolecular reactions.[5] Otherwise the N,N,N
tivated palladium complexes with diimine or other N,N chelate
coordination of the chelate ligand is observed in short-lived
ligands, and which yield a plethora of functional polymers with
kinetic products. Within several minutes, and in particular in
specialized and commercially interesting properties.
the presence of additional palladium acetate, these intermedi-
A N,N,N ligand with a planar and conjugated backbone in
ates form thermodynamically stable products by rotation of
combination with steric encumbrance at the fourth position of
a square may be considered to provide for a steric situation
around a palladium(II) ion incompatible with an overall flat
complex structure. In the course of our investigations on
strained palladium compounds with such meridional tridentate
one of the pyridine rings and C(sp2)–H activation.[6] This proc-
ess does not occur for α,ω-Me2bti ligands (bti
=
bis(thiazolylimino)isoindoline[7]), which have so far been ob-
served to form exclusively pseudoplanar structures with ani-
ligands we have discovered, that the steric influence of α,ω- onic and with neutral co-ligands. C(sp3)–H activation and S
situated methyl groups leads to non-planar distortion modes
and/or an increased reactivity, depending on the chelate ligand
used. For α,ω-dimethyltri pyrrin (trpy) complexes of
coordination can, however, be enforced if sterically more de-
manding tert-butyl groups are introduced.[8] Figure 1 summari-
zes these different findings with the closely related trpy, bpi
and bti systems. We have now extended our study and investi-
gated cationic 4-Mebti complexes of palladium(II) with group
XIV and group XV donor co-ligands (4-Mebti = bis(4-methyl-
thiazolylimino)isoindoline), and we describe here the prepara-
tion as well as the solid state and solution structures of seven
new complexes.
* Prof. Dr. M. Bröring
Fax: +49-531-3915387
E-Mail: m.broering@tu-bs.de
[a] Institut für Anorganische und Analytische Chemie
Technische Universität Braunschweig
Hagenring 30
38106 Braunschweig, Germany
Z. Anorg. Allg. Chem. 2011, 637, 1769–1776
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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M. Bröring, C. Kleeberg
ARTICLE
treatment with an excess of PMe3 does not result in the forma-
tion of a pentacoordinate palladium(II) complex similar to the
[(trpy)Pd(PMe3)2]+-species observed earlier.[3c],[d],[e] All iso-
lated products 2–8 thus display the typical flat, tetracoordinate
structure expected for palladium(II) complexes with a 4d8 con-
figuration, and could be analyzed and characterized spectro-
scopically by optical and magnetic resonance methods.
Scheme 1 summarizes the outcome of the study.
Figure 1. Schematic presentation of the behaviour of strained palla-
dium(II) complexes with structurally-related N,N,N chelate ligands.
Scheme 1. Overview of ligand exchange reactions performed in this
study.
Results and Discussion
The preparation of cationic palladium(II) complexes with the
4-Mebti ligand can be carried out by a two-step procedure as
Single crystals for X-ray crystallographic investigations have
described in the foregoing study.[7b] Starting from the chlorido been obtained at –20 °C from the seven substances 2–8 by the
complex [Pd(4-Mebti)Cl] (1)[9] (Scheme 1) the anion is par- diffusion method, with 7 crystallizing in two different systems
tially exchanged by treatment with NaB(ArF)4 (sodium salt of from toluene/n-pentane (7) and from dichloromethane/n-pen-
tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) in either dichlo- tane (7'). The B(ArF)4 anions present in the crystal lattices
–
romethane or toluene solution for five minutes. Subsequently, show occasional disorder with respect to the rotation of the
this reaction mixture is treated with the donor ligand of choice. CF3 groups. These positions have been treated with restraints
The amount of co-ligand and the choice of solvent are used to and refined in reasonable split-atom models. Crystallographic
optimize the conditions in each case. Successful preparations data and selected molecular parameters are summarized in Ta-
were achieved with most of the small N donor ligands, and ble 1, Table 2, and Table 3, respectively.
with the strong-field ligands PMe3 and MeNC. Attempts with
The PMe3 complex 2 crystallizes free of solvent in the space
¯
the larger and softer ligands NMe3, PEt3, tBuPH2, AsMe3 and group P1 with Z = 2. The molecular structure of the cation
SbMe3 were unsuccessful und led to decomposed material, pal- of 2 reveals the expected pseudoplanar conformation of the
ladium metal deposition and/or product mixtures. The use of coordination unit (Figure 2), with characteristic angles N1–
carbon donor ligands, i.e. of CO and of different carbenes or Pd–N5 of 164.63(9)° and N3–Pd–P of 142.69(6)°. These an-
carbene precursors (1-n-butyl-3-methyl-imidazolin-2-ylidene, gles are the steepest found in the whole series and reflect the
bis(4-methylphenyl)diazomethane ((4-MeC6H4)2CN2), and di- steric repulsion and the large van der Waals radius of the third
azomethane (CH2N2)) results either in the formation of the di- row phosphorus atom. The displacement of the N,N,N,P coor-
nuclear complex 9[9] (Scheme 1), or in untraceable product dination environment of the palladium atom from a planar ar-
mixtures. This result is in contrast to the successful preparation rangement is also reflected in an enlarged Pd–N3 bond length
of palladium(II) diarylcarbene complexes with the tripyrrin li- of 2.036(2) Å, whereas the Pd–P bond shows no particular
gand which we reported about some years ago. In addition, elongation. This observation is unique in the series of cationic
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Z. Anorg. Allg. Chem. 2011, 1769–1776

Bis(4-methylthiazolyl)isoindoline (4-Mebti) Complexes of Palladium
Table 1. Selected crystallographic data for [Pd(4-Mebti)L][B(ArF)4] complexes 2–5.
L
PMe3
2
tBuNH2
3
PhNH2
4
py
5
Compound
Formula
C51H33BF24N5PPdS2
1384.12
C52H35BF24N6PdS2
1381.23
P21/c
C54H31BF24N6PdS2
1401.22
C53H29BF24N6PdS2
1397.19
Mr /g·mol–1
Space group
a /Å
¯
P1
¯
P1
¯
P1
13.400(2)
14.435(2)
14.721(2)
73.72(2)
86.04(2)
88.65(2)
2726.6(7)
2
12.5785(9)
18.991(1)
23.321(2)
90.00
13.294(2)
13.803(2)
16.505(2)
67.13(1)
87.45(1)
88.55(2)
2787.7(6)
2
16.764(2)
19.582(3)
20.554(3)
71.55(1)
69.25(1)
77.21(1)
5940(1)
4
b /Å
c /Å
α /°
β /°
97.655(9)
90.00
γ /°
V /Å3
5521.3(6)
4
Z
dcalcd. /g·cm–3
Cryst. size /mm
μ /mm–1
1.686
1.662
1.669
1.530
0.40 × 0.32 × 0.23
0.571
0.19 × 0.15 × 0.13
0.536
0.19 × 0.19 × 0.14
0.530
0.33 × 0.30 × 0.17
0.501
2θ limits /°
measured
independent
observeda)
parameters/ restraints
R1b) all data
wR2c)
4.1–51.9
26997
3.9–52.22
43452
4–50
3.5–50
24190
45264
9964
10851
9240
20769
7847
6090
5327
16042
855/0
893/0
881/0
1683/78
0.0682
0.0470
0.0870
0.0857
0.0850
0.0854
0.0774
0.1392
max./ min. peak /e·Å–3
0.602 / –0.522
0.550 / –0.579
0.954 / –0.548
2 2 2 2
1.019 / –1.295
a) Observation criterion: I > 2σ(I). b) R1 = Σ||Fo|–|Fc||/Σ|Fo|. c) wR2 = {Σ[w(Fo –Fc ) ]/Σ[w(Fo ) ]}1/2
.
2
Table 2. Selected crystallographic data for [Pd(4-Mebti)L][B(ArF)4] complexes 6–8.
L
2,6-Me2py
6
MeCNa)
7
MeCNb)
7'
MeNC
8
Compound
Formula
C55H33BF24N6PdS2
1415.24
C2/c
C50H27BF24N6PdS2
1349.11
C51H29BCl2F24N6PdS2
1434.07
C51H29BCl2F24N6PdS2
1434.07
Mr /g·mol–1
Space group
a /Å
¯
P1
¯
P1
¯
P1
26.257(3)
36.732(3)
15.963(1)
90
12.94(1)
15.68(2)
17.85(1)
96.5(2)
106.6(1)
108.7(1)
3202(6)
2
10.019(1)
14.511(2)
20.615(2)
104.90(1)
103.47(1)
90.89(2)
2807.8(6)
2
10.021(1)
14.527(2)
20.684(2)
105.17(1)
103.63(1)
90.86(2)
2814.8(6)
2
b /Å
c /Å
α /°
β /°
114.61(1)
90
γ /°
V /Å3
13997(2)
8
Z
dcalcd. /g·cm–3
Cryst. size /mm
μ /mm–1
1.343
1.401
1.696
1.650
0.43 × 0.32 × 0.07
0.430
0.29 × 0.15 × 0.04
0.465
0.33 × 0.24 × 0.21
0.621
0.47 × 0.31 × 0.11
0.608
2θ limits /°
measured
independent
observedc)
parameters/ restraints
R1d) all data
wR2e)
4–51.66
66208
3.54–52.1
31672
4.02–52.08
27773
4.04–52.16
27967
12790
11708
10250
10322
8624
7149
7275
7129
919/0
788/0
843/0
899/6
0.0715
0.0801
0.0687
0.0661
0.1129
0.1122
0.1148
0.0952
max./ min. peak /e·Å–3
0.479 / –0.338
0.760 / –0.402
0.941 / –0.568
0.813 / –0.618
a) From toluene. b) From dichloromethane. c) Observation criterion: I > 2σ(I). d) R1 = Σ||Fo|–|Fc||/Σ|Fo|. e) wR2 = {Σ[w(Fo –Fc ) ]/Σ[w(Fo ) ]}1/2
.
2
2 2
2 2
[Pd(4-Mebti)L]+ species from this and the foregoing study.[7b] cations, Pd–P bond lengths of 2.314(1) Å and 2.3122(7) Å
In all other cases the bond to the central nitrogen donor atom were observed, compared to 2.3087(8) Å for 2, and the Pd–N
is the shortest metal-N donor bond due to the localization of bond lengths to the central and the peripheral nitrogen atoms
negative charge at the N3 position of the deprotonated 4-Mebti are 2.053(2) Å/ 2.079(2) Å and 2.020 Å/ 2.043 Å (mean val-
ligand. The situation is very similar to the findings earlier re- ues) for the tripyrrin complexes, and 2.036(2) Å and 2.018 Å
ported on related palladium tripyrrin chelates,[3c],[e] although (mean value) for the bti derivative 2, respectively. These data
the tripyrrin ligand is more capable of delocalizing the negative show that steric interactions govern the structure of these palla-
charge than the bti ligand. For two [(α,ω-Me2trpy)Pd(PMe3)] dium chelates, rather than electronic ones.
Z. Anorg. Allg. Chem. 2011, 1769–1776
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M. Bröring, C. Kleeberg
ARTICLE
Table 3. Selected bond lengths, distances /Å and angles /° for [Pd(4-Mebti)L][B(ArF)4] complexes 2–8.
L
PMe3
2
tBuNH2
3
PhNH2
4
py
5
2,6-Me2py
6
MeCNa)
7
MeCNb)
7'
MeNC
8
Compound
cation I
2.066(3)
1.973(3)
2.061(3)
2.023(3)
88.5(1)
cation II
2.048(3)
1.969(3)
2.056(3)
2.031(3)
88.1(1)
Pd–N1
2.026(2)
2.036(2)
2.010(2)
2.3087(8)
88.75(9)
164.63(9)
97.19(6)
88.40(9)
142.69(6)
94.21(6)
4.327(6)
3.503(4)
3.403(4)
2.029(3)
1.988(3)
2.031(3)
2.097(3)
89.0(1)
2.028(3)
1.974(3)
2.034(4)
2.107(3)
89.2(1)
2.056(3)
1.969(3)
2.054(3)
2.064(3)
87.0(1)
2.041(5)
1.961(4)
2.046(4)
2.026(5)
88.6(2)
2.044(3)
1.969(3)
2.055(3)
2.040(3)
89.1(1)
2.038(3)
2.000(3)
2.057(3)
1.969(4)
88.6(1)
Pd–N3
Pd–N5
Pd–Dc)
N1–Pd–N3
N1–Pd–N5
N1–Pd–Dc)
N3–Pd–N5
N3–Pd–Dc)
N5–Pd–Dc)
C1···C16
C1···Dc)
164.9(1)
96.6(1)
168.3(2)
89.8(1)
175.8(1)
92.2(1)
174.8(1)
91.2(1)
174.3(1)
93.7(1)
167.1(1)
92.8(2)
166.6(1)
91.8(1)
166.5(1)
92.4(1)
89.4(1)
89.8(1)
87.3(1)
87.5(1)
87.3(1)
90.3(2)
89.6(1)
89.4(1)
152.5(1)
91.7(1)
157.3(2)
95.6(1)
177.3(1)
92.0(1)
179.0(1)
93.3(1)
179.2(1)
92.0(1)
158.1(1)
93.0(2)
159.2(1)
94.2(1)
159.3(1)
94.2(1)
4.423(5)
3.216(5)
3.065(5)
4.561(7)
2.981(6)
3.027(7)
5.941(7)
2.973(6)
2.975(6)
5.964(8)
2.975(7)
2.995(7)
5.966(6)
2.982(5)
2.985(5)
4.53(1)
4.557(7)
2.955(6)
2.930(5)
4.607(6)
2.966(6)
2.925(5)
2.966(8)
2.932(8)
C16···Dc)
a) From toluene. b) From dichloromethane. c) D = P1 for 2; D = N6 for 3–7; D = C17 for 8.
Figure 2. Molecular structure of the [Pd(4-Mebti)(PMe3)]+ cation of 2.
Two primary amines, tert-butylamine and aniline, were suc-
cessfully coordinated to the [Pd(4-Mebti)]+ fragment to yield
the amine complexes 3 and 4. Both compounds crystallize free
of solvent molecules and were analyzed in the space group
¯
P21/c with Z = 4 (3), and P1 with Z = 2 (4). Both amine
Figure 3. Molecular structures of the [Pd(4-Mebti)(tBuNH2)]+ cation
of 3 (bottom) and of the [Pd(4-Mebti)(PhNH2)]+ cation of 4 (top).
derivatives reside in the pseudoplanar conformation as de-
picted in Figure 3, and show the expected short central and
long peripheral Pd–N bond lengths within the [Pd(4-Mebti)]+
complex fragment (Table 3). The situation resembles the find-
ings made earlier on a tert-butylamine complex of a (α,ω-
Me2trpy)Pd fragment,[3c] with the marked difference, that the
polarized NH protons of 3 and 4 show weak hydrogen bonding
Weak hydrogen bonding to a fluorine atom of the B(ArF)4 anion is
–
indicated in both cases.
The compounds 5 and 6 with the N heterocyclic co-ligands
to fluorine atoms of the B(ArF)4– counterions. Such a behavior pyridine (py) and lutidine (2,6-Me2py) crystallized in the space
¯
has not been observed so far within this class of palladium group P1 with Z = 4, and C2/c with Z = 8, respectively, as
chelates. In all earlier instances,[3c,7b] the potential H-bridge solvates. Due to severe disorder these solvent molecules were
donors of the palladium bound ligands have been isolated by removed using the SQUEEZE command in PLATON.[10] Two
encapsulation in non-polar confinements, which were build up crystallographically independent cations with very similar
either by the aryl rings of the anion, or by the co-ligand and structural parameters have been observed in the unit cell of the
ligand terminal methyl groups. The N–H···F hydrogen bonds py derivative 5 (Table 3), of which only cation I is described
found in 3 and 4 are, however, very weak as can be estimated further in detail. Figure 4 illustrates the molecular structures
from the rather long N···F distances of about 3.23 Å and of the two complexes 5 and 6, which are the first ever observed
3.20 Å, respectively.
4-Mebti species residing in the helical conformation.
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Bis(4-methylthiazolyl)isoindoline (4-Mebti) Complexes of Palladium
ligand, as compared to the methine subunits of tripyrrins. As
before, steric arguments appear more important for the descrip-
tion of the structural features of these systems than do elec-
tronic ones.
In solution, the cationic species 5 and 6 appear to retain the
helical conformation. 1H NMR spectroscopic measurements
reveal resonance signals for the terminal methyl group protons
of 5 and 6 at 1.02 and 1.08 ppm, respectively, whereas for
the pseudoplanar derivatives typical values between 2.6 and
2.9 ppm are observed. The high-field shift of the former sig-
nals may be explained by the deshielding influence of the pyri-
dine ring current if the pyridine moiety is located right inbe-
tween the two methyl groups. In addition, the distorted ligand
π-system of the helical conformation should induce a red-shift
in the lowest energy absorption of the optical spectra. Such a
shift of about 37 and 51 nm is in fact observed for 5 and 6,
respectively. In contrast, the optical absorption spectra of the
pseudoplanar 2, 3, 4, 7, and 8 are almost indistinguishable and
consist of broad and rather unstructured bands with maxima of
447–451 nm. The question, whether a racemization process
transforms the two different helical enantiomers into each
other in solution, could not be answered unambiguously,
mainly due to the lack of diastereotopic protons at the 4-Mebti
ligand.
Figure 4. Molecular structures of one of the crystallographically inde-
pendent forms of the [Pd(4-Mebti)(py)]+ cation of 5 (top) and of the
[Pd(4-Mebti)(2,6-Me2py)]+ cation of 6 (bottom).
The derivatives 7 and 8 with the isomeric acetonitrile and
methylisocyanide co-ligands crystallize as solvates in the space
The metrics of the PdN4 coordination subunits of 5 and 6
deviate characteristically from those of the pseudoplanar deriv-
atives. The Pd–N bonds to the peripheral N1 and N5 donor
atoms are slightly elongated by about 0.02 Å, and the N3–Pd–
N6 and N1–Pd–N5 angles are close to 180° with deviations of
less than 6°. The helical conformation of the 4-Mebti ligand
resembles much the ruffling conformation observed in many
porphyrinoid macrocycles and leads to an increase of the ac-
cessible space between the terminal methyl groups. Therefore,
the distance between these methyl group carbon atoms C1 and
C16, as well as the angle between the mean-square planes of
the juxtaposed C3NS heterofivering moieties are meaningful
measures for the degree of helicity in these compounds. For 5
and 6, C1···C16 distances of 5.941(7) Å and 5.966(6) Å, and
a rotational twist of about 51° and 55° are observed, respec-
tively. Apparently these data are very similar and do not reflect
the significant increase in steric bulk by the introduction of the
2,6-situated methyl groups in the pyridine co-ligand upon go-
ing from 5 to 6. These methyl groups are obviously directed
away from the [Pd(4-Mebti)]+ complex fragment and point into
“free space”, so that no significant changes in the intramolecu-
lar metrics are necessary to host the lutidine moiety.
¯
group P1 with Z = 2. The solvent molecules in crystals of 7
obtained from a toluene solution are highly disordered and
were removed, as before, using the SQUEEZE command in
PLATON.[10] From dichloromethane solutions, isomorphic
crystals of 7' and 8 grew with one molecule of dichlorometh-
ane per formula unit. The molecular structures of cationic
[Pd(4-Mebti)L]+ complexes 7, 7' and 8 are of very similar
shape. Figure 5 illustrates these results.
Figure 5. Molecular structures of the [Pd(4-Mebti)(MeCN)]+ cation of
7 (top; left side: crystallized from toluene, right side: crystallized from
dichloromethane) and of the isomeric [Pd(4-Mebti)(MeNC)]+ cation of
8 (bottom).
An interesting comparison can be made to two examples of
earlier described helical (trpy)Pd compounds. The degree of
helical distortion of (trpy)Pd species with the bis(4-
methylphenyl)carbene[3d] and the thiocyanate[7b] co-ligand is
quantified by slightly longer C1···C16 distances of 6.34(1) Å
From an electronic point of view, the axes N3–Pd–N6–C17–
and 6.05(1) Å, as well as by larger rotational twists of the C4N C18 for 7, 7' and N3–Pd–C17–N6–C18 for 8 should be linear,
heterofivering moieties of 76° and 71°, respectively. These val- or almost linear. In fact, the intramolecular strain imposed by
ues account for a more flexible ligand backbone of the trpy the presence of the terminal methyl groups of the 4-Mebti li-
ligand, which contrasts the larger degree of electronic π-conju- gand leads to deviations from this idealized linearity which can
gation between the different heterocyclic substructures, but be analyzed as tilting and bending distortions, i.e. deviation of
may be explained by the smaller imino bridges of the 4-Mebti the N3–Pd–N6/C17 and of the Pd–N6/C17–C17/N6 angles
Z. Anorg. Allg. Chem. 2011, 1769–1776
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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1773

M. Bröring, C. Kleeberg
ARTICLE
strument. Melting points were determined with a Büchi SMP-20 in
open capillaries and are not corrected.
from 180°. The analyses show an almost identical tilting of
21.9°, 20.8° and 20.7°, but a variation of the bending of 17.3°,
14.3° and 11.8°, respectively, for 7, 7' and 8. In addition, the
shape of the MeCN and the MeNC ligands is not perfectly
linear but deviates from 180° by 1.6° (7), 3.0° (7') and 3.1°
(8). A comparison can be made with an analogous complex
[Pd(trpy)(MeNC)]+ for which a tilting of 20.9°, a bending of
13.3°, and a deviation from methylisocyanide linearity of 3.1°
has been reported.[7b]
Whereas a differentiation between the MeCN and MeNC li-
gands by the bond angles discussed above is not successful, a
bond lengths analysis provides clear evidence. The stronger C
donor atom of the MeNC ligand binds more tightly to the pal-
ladium atom of the [Pd(4-Mebti)]+ fragment then the nitrogen
atom of the acetonitrile ligand. In addition, the Pd–N3 bond
Figure 6. Nomenclature and numbering systems for the spectroscopic
assignments.
trans to this interaction is elongated by the stronger trans influ- Preparation of Cationic Complexes – General Procedure: [Pd(4-
Mebti)Cl] (1) (10.0 mg, 21 μmol) was dissolved in dry toluene or di-
chloromethane (2 mL), and NaB(ArF)4 (18.7 mg, 21 μmol) 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 vacuo and the solid extracted
with dry dichloromethane. After filtration through celite the solvent
was removed again, the residue washed with pentane, and dried in
vacuo. 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.
ence of the isocyanide (Table 3). A similar trend has been ob-
served before within a series of tetracoordinate [(trpy)CoL]+
chelates.[11]
Conclusions
We described the interaction of the cationic [Pd(4-Mebti)]+
complex fragment with several group XIV and group XV do-
nor ligands. Formation and successful isolation of the product
complexes [Pd(4-Mebti)L][B(ArF)4] was achieved for several
medium size and small N donor ligands as well as for the small
strong field ligands PMe3 and MeNC. Larger N donor ligands,
larger group XV homologues and different carbene type li-
gands on the other hand did not result in isolable products.
Seven new complexes were crystallographically characterized
and emphasized the known preference of the [Pd(4-Mebti)]+
complex fragment to reside in a pseudoplanar conformation.
In the cases of pyridine and 2,6-lutidine co-ligands the first 4-
Mebti complexes of palladium with helical conformation were
observed. This conformation is present in the solid state as
well as in solution and could be detected by optical and NMR
spectroscopy.
[Pd(4-Mebti)(PMe3)][B(ArF)4] (2): PMe3 (13 mg, 168 μmol) and di-
chloromethane were used for the preparation. Single crystals of 2 were
obtained after crystallization from dichloromethane/n-pentane at
–20 °C. Yield: 18.4 mg (13 μmol, 63 %). 1H NMR (400 MHz,
CD2Cl2): δ = 8.10–8.05 (m, 2 H, α-CH), 7.76–7.72 (m, 10 H, β-CH,
o-CHB(ArF)4), 7.56 (s, 4 H, p-CHB(ArF)4), 7.11 (s, 2 H, 5-CHTh), 2.77
2
(s, 6 H, 4-MeTh), 1.37 (d, JPH = 11.5 Hz, 9 H, P(CH3)3). 13C NMR
(100.6 MHz, CD2Cl2): δ = 168.7, 161.8 (m, BCB(ArF)4), 156.6, 148.5,
1
137.3, 134.9, 132.9, 129.5–128.4 (m, m-CB(ArF)4), 124.9 (q, JCF
=
270.9 Hz, CF3), 123.2 (oCB(ArF)4), 117.6 (pCB(ArF)4), 114.9, 21.0, 17.1
(d, JPC = 29.2 Hz, P(CH3)3). 19F NMR (188 MHz, CD2Cl2): δ =
1
–61.34. 31P NMR (81 MHz, CD2Cl2): δ = –18.13. UV/Vis (CH2Cl2):
λmax = 230, 250, 302, 368, 451 nm. HRMS (ESI, MeOH): m/z
520.0011; calcd. for [C19H21N5PPdS2]+: 520.0005.
[Pd(4-Mebti)(tBuNH2)][B(ArF)4] (3): tert-Butylamin (3.4 μL, 32
μmol) and toluene were used for the preparation. Single crystals of 3
were obtained after crystallization from dichloromethane/n-pentane
at –20 °C. Yield: 17.7 mg (13 μmol, 61 %). calcd. (%) for
C52H35N6S2PdBF24: C 45.22, H 2.55, N 6.08; found: C 44.95, H 2.56,
N 6.03. 1H NMR (300 MHz, CD2Cl2): δ = 8.07–8.05 (m, 2 H, α-CH),
7.73 (br.s, 10 H, β-CH, o-CHB(ArF)4), 7.56 (br.s, 4 H, p-CHB(ArF)4), 7.14
(s, 2 H, 5-CHTh), 3.05 (br.s, 2 H, NH2), 2.75 (s, 6 H, 4-MeTh), 1.21 (s,
9 H, C(CH3)3). 13C NMR (75 MHz, CD2Cl2): δ = 168.0, 162.2 (m,
BCB(ArF)4), 155.3, 146.8, 136.7, 134.9, 133.0, 129.6–128.3 (m,
Experimental Section
Materials and Methods: 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.
[Pd(4-Mebti)Cl] 1,[9] sodium tetrakis(3,5-bis(trifluoromethyl)phe-
nyl)borate (NaB(ArF)4[12]), trimethylphosphane and triethylphosphane
(PMe3 and PEt3[13]), trimethylstibane (SbMe3[14,15]), methylisocyanide
(MeNC[16]), diazomethane (CH2N2[17]), and bis(4-methylphenyl)dia-
zomethane ((4-MeC6H4)2CN2[18]) were prepared according to literature
methods. NMR spectra were recorded with a Bruker Avance 300 or
DRX 400 spectrometer, respectively. Chemical shifts (δ) are given in
ppm, using the resonance of the residual solvent CD2Cl2 as internal
1
m-CB(ArF)4), 124.4 (q, JCF = 272.2 Hz, CF3), 122.9 (oCB(ArF)4), 117.5
(pCB(ArF)4), 117.1, 57.7, 30.7, 20.0. 19F NMR (188 MHz, CD2Cl2):
δ = –65.33. UV/Vis (CH2Cl2): λmax = 230, 244, 298, 366, 388, 450
nm.
reference (1H NMR: 5.32 ppm, 13C NMR: 53.5 ppm). Nomenclature [Pd(4-Mebti)(PhNH2)][B(ArF)4] (4): Aniline (2.0 μL, 22 μmol) and
and numbering scheme for the assignment of the resonance signals is toluene were used for the preparation. Single crystals of 4 were ob-
given in Figure 6. In the case of 19F and 31P NMR spectra, CFCl3 tained after crystallization from dichloromethane/n-pentane at –20 °C.
and phosphoric acid were used as external references, respectively. Yield: 18.8 mg (13 μmol, 64 %). calcd. (%) for C54H31N6S2PdBF24: C
Elemental analyses were carried out with an Elementar Vario EL in- 46.29, H 2.23, N 6.00; found: C 46.19, H 2.30, N 6.47. 1H NMR
1774
www.zaac.wiley-vch.de
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2011, 1769–1776

Bis(4-methylthiazolyl)isoindoline (4-Mebti) Complexes of Palladium
(400 MHz, CD2Cl2): δ = 8.00 (br.s, 2 H, α-CH), 7.73 (br.s, 10 H, CF3), 123.4 (oCB(ArF)4), 119.0 (CN-CH3), 117.6 (p-CB(ArF)4), 115.4,
β-CH, oCHB(ArF)4), 7.57 (br.s, 4 H, p-CHB(ArF)4), 7.24–7.03 (m, 7 H, 30.8 (CN-CH3), 22.0 (4-MeTh). 19F NMR (282 MHz, C6D6): δ =
CHPh, 5-CHTh), 4.84 (br.s, 2 H, NH2), 2.84 (s, 6 H, 4-MeTh). 13C NMR –62.82. UV/Vis (CH2Cl2): λmax = 243, 281, 295, 368, 390, 421, 447
(100 MHz, CD2Cl2): δ = 167.6, 162.1 (m, BCB(ArF)4), 154.7, 148.8, nm. HRMS (ESI, MeOH): m/z 484.9832; calcd. for [C18H15N6PdS2]+:
136.5, 134.9, 132.9, 130.5, 129.5–128.5 (m, m-CB(ArF)4), 124.7 (q, 484.9829.
1JCF = 272.5 Hz, CF3), 123.2 (oCB(ArF)4), 120.6, 117.6 (p-CB(ArF)4),
116.9, 116.7, 19.5; no signal was detected for the quarternary ipso-
CPh. 19F NMR (188 MHz, CD2Cl2): δ = –65.37. UV/Vis (CH2Cl2):
λmax = 216, 242, 298, 366, 450 nm.
Collection and Reduction of X-ray Data: Intensity data were col-
lected at 130(2) K (5 and 6) or at 193(2) K, using a Stoe IPDS-1 X-ray
diffractometer (Stoe IPDS-2 for 5). Graphite monochromated Mo-Kα
radiation (0.71073 Å) was used. The structures were solved by direct
methods with SIR-92[19] or with SHELXS-97 (6).[20] Refinements were
carried out by full-matrix least-squares techniques against F2 using
SHELXL-97.[20] All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were assigned to idealized positions if not stated oth-
erwise. Selected crystal data are given in Table 1 and Table 2. Crystal-
lographic data (excluding structure factors) for the structures reported
in this paper have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication no. CCDC-818999,
-819000, -819001, -819002, -819003, -819004, -819005, -819006.
Copies of the data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax: +44-1223-
336-033; E-Mail: deposit@ccdc.cam.ac.uk].
[Pd(4-Mebti)(py)][B(ArF)4] (5): Pyridine (2.5 μL, 32 μmol) and tolu-
ene were used for the preparation. Single crystals of 5 were obtained
after crystallization from dichloromethane/n-pentane at –20 °C. Yield:
23.8 mg (17 μmol, 81 %). calcd. (%) for C53H29N6S2F24BPd: C 45.89,
H 2.11, N 6.06; found: C 45.63, H 2.55, N 5.95. 1H NMR (300 MHz,
CD2Cl2): δ = 8.69–8.67 (m, 2 H, o-CHPy) 8.02 (t, J = 6.8 Hz, 1 H,
p-CHPy), 7.93–7.89 (m, 2 H, α-CH), 7.72 (br.s, 10 H, β-CH,
o-CHB(ArF)4), 7.65–7.63 (m, 2 H, m-CHPy), 7.52 (s, 4 H, p-CHB(ArF)4),
6.82 (s, 2 H, 5-CHTh), 1.02 (s, 6 H, 4-MeTh). 13C NMR (100 MHz,
CD2Cl2): δ = 170.1, 162.2 (m, BCB(ArF)4), 153.6, 149.0, 141.6, 136.4,
1
134.9, 132.7, 129.7–128.4 (m, m-CB(ArF)4), 128.1, 124.9 (q, JCF
=
273.1 Hz, CF3), 123.5 (oCB(ArF)4), 122.9, 117.6 (p-CB(ArF)4), 116.1,
17.5. 19F NMR (282 MHz, CD2Cl2): δ = –62.83. UV/Vis (CH2Cl2):
λmax = 229, 301, 387, 487 nm.
Acknowledgement
[Pd(4-Mebti)(2,6-Me2py)] [B(ArF)4] (6): 2,6-Lutidine (14.8 mg, 139
μmol) and toluene were used for the preparation. Single crystals of
6 grew upon crystallization from toluene/n-pentane at –20 °C. Yield:
12.1 mg (9 μmol, 41 %). calcd. (%) for C55H33N6S2F24BPd: C 46.68,
Support for this research by the Deutsche Forschungsgemeinschaft is
gratefully acknowledged. The authors thank Anne Scheja and Nicola
Biermann for their help, and Dr. Thomas Linder for a sample of 1-n-
butyl-3-methylimidazolin-2-ylidene.
1
H 2.35, N 5.94; found: C 46.26, H 2.57, N 5.81. H NMR (400 MHz,
CD2Cl2): δ = 8.00–7.99 (m, 2 H, α-CHTh), 7.85 (t, J = 8.0 Hz, 1 H,
p-CHPy), 7.72 (br.s, 10 H, β-CH, o-CHB(ArF)4), 7.55 (s, 4 H,
p-CHB(ArF)4), 7.37 (d, J = 8.0 Hz, 2 H, m-CHPy), 6.83 (s, 2 H, 5-CHTh),
3.04 (s, 6 H, o-MePy), 1.08 (s, 6 H, 4-MeTh). 13C NMR (100 MHz,
CD2Cl2): δ = 170.2, 162.1 (m, BCB(ArF)4), 161.8, 153.9, 149.1, 141.8,
136.3, 134.9, 132.8, 129.6–128.5 (m, m-CB(ArF)4), 125.7, 124.7 (q,
1JCF = 273.2 Hz, CF3), 123.5 (oCB(ArF)4), 117.5 (p-CB(ArF)4), 116.3,
26.6, 16.9. 19F NMR (188 MHz, CD2Cl2): δ = –62.84. UV/Vis
(CH2Cl2): λmax = 230, 241, 299, 393, 501 nm.
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[Pd(4-Mebti)(MeCN)][B(ArF)4] (7): A toluene/acetonitrile mixture
(2:1) was used for the preparation. Single crystals of 7 were obtained
after crystallization from toluene/n-pentane (7), or from dichlorometh-
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5-CHTh), 3.58 (s, 3 H, CN-Me), 2.68 (s, 6 H, 4-MeTh). 13C NMR
(75 MHz, C6D6): δ = 168.0, 161.9 (m, BCB(ArF)4), 154.2, 149.1, 136.6,
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M. Bröring, C. Kleeberg
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Received: May 6, 2011
Published Online: June 30, 2011
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Z. Anorg. Allg. Chem. 2011, 1769–1776