Cyclopalladation of telluro ether ligands: Synthesis, reactivity and structural characterization

Article abstract of DOI:10.1039/c4dt02200a

Treatment of [PdCl₂(PhCN)₂] with diaryl telluride in 1:2 molar ratio gave mononuclear palladium complexes, trans-[PdCl₂(TeR₂)₂] (1) (R = Mes (1a) (Mes = 2,4,6-trimethylphenyl), Ph (1b), o-tol (1c) (o-tol = ortho-tolyl)). Reaction of [PdCl₂(TeMes₂)₂] with one equivalent of [PdCl₂(PhCN)₂] or Na₂PdCl₄ with TeRR′ afforded chloro-bridged binuclear complexes, [Pd₂(μ-Cl)₂Cl₂(TeRR′)₂] (2) (R/R′ = Mes/Mes (2a); Mes/Ph (2b); Ph/Ph (2c)). A toluene-methanol solution of trans-[PdCl₂(TeMes₂)₂] on refluxing for 30 minutes yielded a binuclear cyclopalladated complex, [Pd₂(μ-Cl)₂{CH₂C₆H₂(4,6-Me₂)TeMes)}₂] (3). When the refluxing was prolonged, a mononuclear complex cis-[PdCl₂{MesTeCH₂C₆H₂(4,6-Me₂)TeMes}] (4) was isolated. Treatment of palladium acetate with TeMes₂ afforded an acetato-bridged analogue of 3, [Pd₂(μ-OAc)₂{CH₂C₆H₂(4,6-Me₂)TeMes}₂] (5a) together with a very minor component, a tetranuclear complex, [Pd(μ-OAc)(μ-TeMes)]₄ (6). This reaction with unsymmetrical tellurides, MesTeR, also gave cyclopalladated complexes [Pd₂(μ-OAc)₂{CH₂C₆H₂(4,6-Me₂)TeR}₂] (R = o-tol (5b) and Ph (5c)) in which 2-methyl of the mesityl group of the telluride was exclusively metallated. The complex trans-[PdCl₂(TeMes₂)₂] on refluxing in xylene gave palladium telluride, Pd₇Te₃. These complexes were characterized by elemental analyses, IR and NMR (¹H, ¹³C and ¹²⁵Te) spectroscopy. The molecular structures of trans-[PdCl₂(TeMes₂)₂] (1a), [Pd₂(μ-Cl)₂Cl₂(TeMes₂)₂]·2acetone (2a·2acetone), cis-[PdCl₂{MesTeCH₂C₆H₂(4,6-Me₂)TeMes}] (4), [Pd₂(μ-OAc)₂{CH₂C₆H₂(4,6-Me₂)TeMes)}₂]·toluene (5a·toluene), [Pd₂(μ-OAc)₂{CH₂C₆H₂(4,6-Me₂)Tetol-o}₂] (5b) and [Pd(μ-OAc)(μ-TeMes)]₄ (6) were established by single crystal X-ray diffraction analyses. The mononuclear complex 1a was isolated in two polymorphic forms each with the trans configuration. This journal is

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Cyclopalladation of telluro ether ligands:
synthesis, reactivity and structural
characterization†
Cite this: Dalton Trans., 2014, 43,
16056
Siddhartha Kolay,a Mukesh Kumar,b Amey Wadawale,a Dasarathi Dasa and
Vimal K. Jain*a
Treatment of [PdCl2(PhCN)2] with diaryl telluride in 1 : 2 molar ratio gave mononuclear palladium com-
plexes, trans-[PdCl2(TeR2)2] (1) (R = Mes (1a) (Mes = 2,4,6-trimethylphenyl), Ph (1b), o-tol (1c) (o-tol =
ortho-tolyl)). Reaction of [PdCl2(TeMes2)2] with one equivalent of [PdCl2(PhCN)2] or Na2PdCl4 with TeRR’
afforded chloro-bridged binuclear complexes, [Pd2(µ-Cl)2Cl2(TeRR’)2] (2) (R/R’ = Mes/Mes (2a); Mes/Ph
(2b); Ph/Ph (2c)). A toluene–methanol solution of trans-[PdCl2(TeMes2)2] on refluxing for 30 minutes
yielded a binuclear cyclopalladated complex, [Pd2(µ-Cl)2{CH2C6H2(4,6-Me2)TeMes)}2] (3). When the
refluxing was prolonged, a mononuclear complex cis-[PdCl2{MesTeCH2C6H2(4,6-Me2)TeMes}] (4) was
isolated. Treatment of palladium acetate with TeMes2 afforded an acetato-bridged analogue of 3, [Pd2(µ-
OAc)2{CH2C6H2(4,6-Me2)TeMes}2] (5a) together with a very minor component, a tetranuclear complex,
[Pd(µ-OAc)(µ-TeMes)]4 (6). This reaction with unsymmetrical tellurides, MesTeR, also gave cyclopalladated
complexes [Pd2(µ-OAc)2{CH2C6H2(4,6-Me2)TeR}2] (R = o-tol (5b) and Ph (5c)) in which 2-methyl of the
mesityl group of the telluride was exclusively metallated. The complex trans-[PdCl2(TeMes2)2] on refluxing
in xylene gave palladium telluride, Pd7Te3. These complexes were characterized by elemental analyses, IR
and NMR (1H, 13C and 125Te) spectroscopy. The molecular structures of trans-[PdCl2(TeMes2)2] (1a),
[Pd2(µ-Cl)2Cl2(TeMes2)2]·2acetone (2a·2acetone), cis-[PdCl2{MesTeCH2C6H2(4,6-Me2)TeMes}] (4), [Pd2-
(µ-OAc)2{CH2C6H2(4,6-Me2)TeMes)}2]·toluene (5a·toluene), [Pd2(µ-OAc)2{CH2C6H2(4,6-Me2)Tetol-o}2]
(5b) and [Pd(µ-OAc)(μ-TeMes)]4 (6) were established by single crystal X-ray diffraction analyses. The
mononuclear complex 1a was isolated in two polymorphic forms each with the trans configuration.
Received 21st July 2014,
Accepted 28th August 2014
DOI: 10.1039/c4dt02200a
www.rsc.org/dalton
pounds have remained in the forefront ever since their initial
isolation in the mid-1960s by Cope and Siekman.2 The growing
Introduction
The chemistry of organopalladium compounds has witnessed interest in these compounds may be attributed to their appli-
a rapid growth in the last half century owing to the ease of syn- cations in organic synthesis,3,4 catalysis5–8 (e.g. [Pd2(µ-OAc)2-
thesis, their rich reaction chemistry and wide applications in {o-tol2PC6H4CH2-o}2] (o-tol = ortho-tolyl) by Herrmann and co-
diverse areas. Among them cyclopalladated compounds or pal- workers) and materials science.9,10 These compounds are also
ladacycles represent an interesting family of most popular encountered as reaction intermediates in palladium catalyzed
and well investigated organopalladium derivatives.1 These com- organic transformations.8,11 Their unique metallomesogenic,12
photo-physical13 and antitumor14 properties have provided
further impetus to the progress in this area.
Over a period, a myriad of internally functionalized organic
compounds containing the neutral donor atom (e.g. N, P, As,
aChemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400085,
India. E-mail: jainvk@barc.gov.in; Fax: +91 22 2550 5151; Tel: +91 22 2559 5095
bSolid State Physics Division, Bhabha Atomic Research Centre, Trombay,
O, S) have been utilized for cyclopalladation reactions
Mumbai-400085, India
†Electronic supplementary information (ESI) available. CCDC 996454–996460
(Scheme 1) leading to the formation of, in general, a four elec-
tron C-anionic donor ligand (C∩Y).1,8 Initially these organic
for trans-[PdCl2(TeMes2)2]·2CH3CN (1a·2CH3CN) (996459), trans-[PdCl2(Te-
Mes2)2]·toluene
(1a·toluene)
(996458),
[Pd2(µ-Cl)2Cl2(TeMes2)2]·2acetone
molecules coordinate to the metal centre through a neutral
donor atom and it is believed that the C–H bond of the organic
fragment is activated when it falls within the metal coordi-
nation plane.3,8 Thus the reactions with compounds containing
lighter hetero-atoms are quite facile while the heavier hetero-
(2a·2acetone) (996455), cis-[PdCl2{MesTeCH2C6H2(4,6-Me2)TeMes}] (4) (996460),
[Pd2(µ-OAc)2{CH2C6H2(4,6-Me2)TeMes}2]·toluene (5a·toluene) (996457), [Pd2(µ-
OAc)2{CH2C6H2(4,6-Me2)Tetol-o}2] (5b) (996456) and [Pd(µ-OAc)(µ-TeMes)]4 (6)
(996454). For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c4dt02200a
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In the light of the above, we have examined reactions of
common palladium precursors ([PdCl2(PhCN)2], Na2PdCl4,
[Pd(OAc)2]3) used in cyclopalladation reactions with diorgano-
tellurides and isolated a whole range of novel complexes by
subtle variation in the reaction conditions. The complexes
include simple coordination complexes, trans-[PdCl2(TeR2)2];
intermediate binuclear complexes with intramolecular C–H⋯Pd
interactions, [Pd2(µ-Cl)2Cl2(TeMes2)2] (Mes = 2,4,6-trimethyl-
pheny), cyclopalladated complexes, [Pd2(µ-X)2{CH2C6H2(4,6-
Me2)TeR}2] (X = Cl, OAc; R = Mes, o-tol (o-tol = ortho-tolyl), Ph),
complexes formed by Te–C bond cleavage, cis-[PdCl2{Mes-
TeCH2C6H2(4,6-Me2)TeMes}], [Pd(µ-OAc)(µ-TeMes)]4 to even-
tually palladium telluride as the decomposition product. The
results of this exploration are described herein.
Scheme 1 Cyclopalladation of organic ligands.
atom containing compounds show little tendency to metalate.
For instance, the effect of the size of the hetero-atom on metal-
lation is evident in the reactions of Me2ECH2Ph (E = N, P, As,
Sb). Both dimethyl benzylamine and dimethyl benzylphosphine
(E = N, P)15,16 are metallated readily while dimethyl benzylarsine
affords [PdX2(PhCH2AsMe2)2], (X = Cl, Br, I).17
Cyclopalladation of a wide variety of organic compounds
containing nitrogen and phosphorus as neutral donor atoms
has been extensively investigated.1,8 Among group 16 donors,
metallation of oxygen18 and sulfur (thioethers, thioketones,
etc.)6,19 compounds is well documented. However, with heavier
chalcogen compounds, metallation of only a few organo-
selenium ligands (ButSeCH2Ph7 and Mes2Se20) has been
described recently, whereas there is hardly any report on
metallation of tellurium ligands. Such a limited exploration
with heavier chalcogen compounds may possibly be attributed
to either the formation of coordination complexes,
[PdX2(ER2)2] (E = Se or Te), cleavage of the E–C bond or even
complete decomposition of the complexes under metallation
conditions. In a recent attempt by Singh and co-workers to
metalate di-o-tolyltelluride cleavage of the Te–C bond
occurred.21 They isolated [Pd(OAc)2{o-tolTe)2O}] (o-tol = ortho-
tolyl) and [o-tol2Pd3(µ-OAc)4{Te(o-tol)2}2] formed by cleavage of
the Te–C bond of o-tol2Te, rather than a metalated complex.21
Interestingly the metalated compounds with heavier chalcogen
ligands show a higher catalytic activity than the lighter chalco-
gen compounds, e.g. [Pd(µ-OAc)(ButECH2C6H4)]2 (E = S or Se).7
Results and discussion
Synthesis
Syntheses of various palladium complexes are depicted in
Schemes 2 and 3. Treatment of [PdCl2(PhCN)2] with diaryl tell-
uride in a 1 : 2 molar ratio in toluene at room temperature gave
mononuclear palladium complexes, trans-[PdCl2(TeR2)2] (1)
(R = Mes (1a) (Mes = 2,4,6-trimethylphenyl, Ph (1b), o-tol (1c)
(o-tol = ortho-tolyl)) as orange crystalline solids. The latter (R =
Mes) when treated with one equivalent of [PdCl2(PhCN)2] in a
toluene–acetonitrile mixture at room temperature afforded a
chloro-bridged binuclear complex, [Pd2(µ-Cl)2Cl2(TeMes2)2]
(2a). The complex 2a can also be prepared by the reaction of
Na2PdCl4 with TeMes2 at room temperature in 79% yield. This
reaction can be extended to prepare analogues of 2a by
employing MesTePh and Ph2Te.
When
a
toluene–methanol solution of trans-[PdCl2-
(TeMes2)2] (1a) was refluxed for ∼30 minutes, a cyclopalladated
binuclear complex, [Pd2(µ-Cl)2{CH2C6H2(4, 6-Me2)TeMes}2] (3)
Scheme 2 Synthetic routes for palladium telluro ether complexes.
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Scheme 3 Synthesis of acetato bridged cyclopalladated telluro ether complexes.
was isolated as an orange powder in 75% yield. When refluxing Mes2Te due to steric crowding of two bulky mesityl rings, one
was prolonged for two hours a mononuclear complex cis- of the ortho C–H bond falls into the coordination plane of pal-
[PdCl2{MesTeCH2C6H2(Me2-4,6)TeMes}] (4) was isolated. The ladium as is evidenced in the molecular structure of 2a (see
latter was also formed when a toluene–methanol solution of later, Fig. 3(b)) leading to metallation with the generation of
either trans-[PdCl2(TeMes2)2] or a 1 : 1 mixture of Na2PdCl4 and HCl as a by-product. On the other hand, with [Pd(OAc)2]3, in
TeMes2 was refluxed for 2 h. The complex 4 appears to be the reaction medium via the η2-bridging mode OAc− give a
formed by a nucleophilic attack of a tellurolate ion (MesTe−), cyclic transition state by coordinating palladium with one
generated by the Te–C bond cleavage,22,23 on methylene oxygen and at the same time bringing one of the ortho C–H
carbon of the cyclopalladated complex 3. The formation of a bond of the methyl group of mesityl into close proximity of
tellurolate ion from a telluro ether ligand has been noted pre- palladium using other oxygen atoms through C–H⋯O inter-
viously24 and also in the present study (see later, e.g. isolation action and leads to activation of the C–H bond with the gene-
of 6). Attempts to prepare similar cyclopalladated complexes ration of HOAc as the by-product. HOAc being a weak
with o-tolTeMes, o-tol2Te and Ph2Te were unsuccessful. The conjugate of OAc− also makes the metallation energetically
solution of 1a on prolonged refluxing (2 h) either in xylene or more feasible than strong acid; HCl is generated in the case of
2-ethoxy ethanol gave black powder which was identified as Na2PdCl4 and has a strong interference with the formed M–C
Pd7Te3 from powder X-ray diffraction pattern (JCPDS File no. bond than HOAc.
43-1294) (ESI†). The product formed in 2-ethoxy ethanol was
however contaminated with elemental tellurium. Recently, a
telluro ether complex of palladium, [PdCl{C6H5(2-HOC6H4)-
Spectroscopy
CHNH(CH2)3TeC6H4OMe-4}], was used for the preparation of
Pd3Te2 nanoparticles.25
The IR spectra of acetato-bridged metallated complexes
showed absorptions at 1615, 1558 (5a)/1566 (5b) cm−1 attribu-
table to bridging acetate groups. The 1H NMR spectra dis-
played expected resonances. The methyl groups (at 2- and
6-positions) of the coordinated mesityl telluride were
Treatment of palladium acetate with TeMes2 in toluene at
room temperature afforded an acetato-bridged analogue of 3,
[Pd2(µ-OAc)2{CH2C6H2(4,6-Me2)TeMes}2] (5a) as a yellow crys-
talline solid together with a very minor component, a tetra-
nuclear complex, [Pd(µ-OAc)(µ-TeMes)]4 (6) (Scheme 3). This
reaction with unsymmetrical telluro ether ligands, MesTeR
1
deshielded in the H NMR spectra while they were shielded in
the 13C NMR spectra with reference to the corresponding free
ligands. The cyclopalladated complexes showed a distinct AB
pattern for the Pd–CH2 protons at a chemical shift signifi-
cantly downfield from that of the mesityl methyl groups
(3.38 ppm, br, 2H (3); 3.36 ppm, 2H, ΔνAB = 71 Hz, JAB = 13 Hz
(5a); 3.09 ppm, 2H, ΔνAB = 24.6 Hz, JAB = 12.7 Hz (5b)). Similar
anisotropic behavior was also noted for analogous selenium
complex, [Pd2(µ-Cl)2{CH2C6H2(4,6-Me2)SeMes}2].20 The CH2
protons in 4 were also anisotropic and appeared as an AX
pattern at 3.55 ppm with significantly large chemical shift
difference (2H, ΔνAX = 169 Hz, JAX = 11 Hz).
(R
= o-tol, Ph) also yielded cyclopalladated complexes
[Pd2(µ-OAc)2{CH2C6H2(4,6-Me2)TeR}2] (R = o-tol (5b) and Ph
(5c)) in which 2-methyl of the mesityl group of the telluro
ether ligand was exclusively metallated.
Cyclopalladation using telluro ether ligands containing at
least one mesityl group was quite facile when [Pd(OAc)2]3 was
used as the palladating agent, whereas the same took place
with Na2PdCl4 or [PdCl2(PhCN)2] only in the case of Mes2Te.
This could be due to the fact that in the latter case only with
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The 125Te{1H} NMR spectra of these complexes displayed a Crystallography
single resonance which appeared at higher frequency with
Molecular structures of trans-[PdCl2(TeMes2)2] (1a), [Pd2-
(µ-Cl)2Cl2(TeMes2)2]·2acetone (2a·2acetone), cis-[PdCl2{Mes-
TeCH2C6H2(4,6-Me2)TeMes}] (4), [Pd2(µ-OAc)2{CH2C6H2(4,6-
Me2)TeMes}2]·toluene (5a·toluene), [Pd2(µ-OAc)2{CH2C6H2(4,6-
Me2)Tetol-o}2] (5b) and [Pd(µ-OAc)(µ-TeMes)]4 (6) were estab-
lished by single crystal X-ray diffraction analyses and are
shown in Fig. 1–7. Selected inter-atomic parameters are sum-
marized in Tables 1–7. The palladium atom in all these com-
plexes acquires a distorted square planar configuration. The
Pd–Te distances (2.47–2.59 Å) are well within the range
reported for palladium-telluro ether complexes, [PdCl{OC9H6C-
(Me) = NCH2CH2TeC6H4OMe-4}] (Pd–Te = 2.5025(7) Å),26
[PdCl2{4-BrC3H2N2CH2CH2TeC6H4OMe-4}] (Pd–Te = 2.512(6)
Å),27 [Pd(TePh)2(dppe)] (Pd–Te = 2.5871–2.6704(8) Å28 and
[tol2Pd3(μ-OAc)4(Tetol2-o)2] (Pd–Te = 2.5054(5) Å).21 The Pd–C
distances (∼2.0 Å) are in accord with the values reported for
cyclopalladated complexes such as [Pd2(μ-Cl)2{CH2C6H2(4,6-
Me2)SeMes}2] (Pd–C = ∼2.03 Å)20 and [Pd(OCH-C4H3N)(Bzq)]
(Bzq = 7,8-benzoquinolyl) (Pd–C = 1.993(3) Å).29 The Te–C
respect to the free ligand (TeMes2, 125Te δ = 260.8 ppm,
Te(o-tol)2, 125Te δ = 499.3 ppm, TePh2, 125Te δ = 693.4 ppm,
MesTe(o-tol) 125Te
δ = δ =
336.8 ppm, MesTePh 125Te
427.2 ppm). The 125Te NMR resonance was progressively
deshielded from mononuclear (1a) (δ 489.1 ppm) to cyclopalla-
dated derivative 3 (δ 644.0 ppm) through the binuclear 2a
(δ 575.0 ppm). Such a large deshielding (69 ppm) from binuc-
lear complex 2a to cyclopalladated complex 3 has also been
noted by our group in the corresponding mesityl seleno ether
derivatives (deshielded by 86 ppm in 77Se resonance).20 The
effect of the bridging ligand as well as the nature of the R
group on Te is also evident in cyclopalladated complexes.
There is shielding of ∼90 ppm of the 125Te NMR resonance on
replacing the bridging chloride in 3 (δ 644.0 ppm) by the
acetate group (5a) (δ 554.1 ppm). Replacement of the mesityl
group on Te in 5a by ortho-tolyl or phenyl groups results in suc-
cessive deshielding of the resonance (5b, 592.2 ppm; 5c,
690.4 ppm). Such changes could be attributed to the electron
releasing methyl groups in the aryl ring which consequently
increases electron density at the tellurium.
Fig. 1 (a) ORTEP diagram of trans-[PdCl2(TeMes2)2]·2MeCN (1a·2MeCN)
(25% probability). Hydrogen atoms are omitted for clarity, (b) view per-
pendicular to the Pd1 square plane, (c) optical microscope image of
1a·2MeCN crystallized from acetonitrile-diethyl ether.
Fig. 2 ORTEP diagram of trans-[PdCl2(TeMes2)2]·toluene (1a·toluene)
(25% probability). Hydrogen atoms are omitted for clarity, (b) view per-
pendicular to the Pd1 square plane, (c) optical microscope image of
1a·toluene crystallized from a toluene–hexane mixture.
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Fig. 5 ORTEP diagram of [Pd2(μ-OAc)2{CH2C6H2(4,6-Me2)TeMes}2]·
toluene (5a·toluene) (25% probability). Hydrogen atoms and toluene
molecule are omitted for clarity.
Fig. 3 ORTEP
diagram
of
[Pd2(μ-Cl)2Cl2(TeMes2)2]·2acetone
(2·2acetone) (25% probability). Hydrogen atoms and solvent molecules
are omitted for clarity, (b) intramolecular interactions.
Fig. 6 ORTEP diagram of [Pd2(μ-OAc)2{CH2C6H2(4,6-Me2)Tetol-o}2]
(5b) (25% probability). Hydrogen atoms are omitted for clarity.
isolated from acetonitrile–diethyl ether (monoclinic form,
Fig. 1) and toluene–hexane (triclinic form, Fig. 2) mixture,
respectively. The triclinic form described here also differs from
the one reported earlier.32 The two polymorphs essentially
differ slightly in the inter-atomic parameters as well as in the
relative orientation of the mesityl groups on tellurium. The
Te–Pd–Te angle in the triclinic form is significantly reduced
(∼164°) from the ideal value of 180° while in the monoclinic
form it is 180°. The Pd–Te–C angles in the monoclinic form
are smaller than the triclinic form. The C–Te–C angle (∼100°
in the triclinic form and 102.5° in the monoclinic form) are as
observed in Mes2Te (101.0(1)°).30 In the monoclinic form the
Fig. 4 ORTEP diagram of cis-[PdCl2{MesTeCH2C6H2(4,6-Me2)TeMes}]
(4) (25% probability). Hydrogen atoms are omitted for clarity.
(∼ 2.14 Å) bond distances are in conformity with the range mesityl rings (C1–C9) and (C1i–C9i) are coplanar and are
reported in organotellurium compounds (e.g. Mes2Te (Te–C = almost perpendicular (85.60°) to the Pd square plane
2.140(3) Å),30 Te{C5H3(Me-3)N}2 (Te–C = 2.136(1) Å)23 and (Cl1Te1Pd1Te1iCl1i), while the other mesityl rings (C10–C18)
[Cd(TeMes)2]∞ (Te–C = 2.164(12) Å).31
and (C10i–C18i) lie in plane parallel to each other which are
The mononuclear complex, [PdCl2(TeMes2)2] (1a) was iso- nearly perpendicular to the Pd square plane (77.80°). The two
lated in a trans configuration and showed polymorphism mesityl rings attached to the tellurium atom lie at an angle of
depending on the crystallization solvents. The two poly- 80.04°. There are weak secondary interactions between the
morphs, viz rectangular block and needle shaped crystals were chloride and the hydrogen atoms of the acetonitrile molecule
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Table 3 Selected bond lengths (Å) and bond angles (°) for
[Pd2(μ-Cl)2Cl2(TeMes2)2]·2acetone (2·2acetone)
Cl1–Pd1
Cl1–Pd1i
Cl2–Pd1
2.310(4)
2.403(4)
2.290(4)
C1–Te1
2.156(13)
2.119(14)
2.5067(13)
3.421
C10–Te1
Pd1–Te1
Pd1–Pd1i
Cl1–Pd1–Cl1i
Cl1–Pd1–Te1
Cl1i–Pd1–Te1
Cl1–Pd1–Cl2
Cl1i–Pd1–Cl2
86.96(13)
96.25(10)
174.08(12)
177.78(17)
93.14(13)
Cl2–Pd1–Te1
Pd1–Te1–C1
C1–Te1–C10
Pd1–Te1–C10
Pd1–Cl1–Pd1i
83.47(11)
108.4(3)
97.6(5)
111.0(4)
93.04(13)
Table 4 Selected bond lengths (Å) and bond angles (°) for cis-
[PdCl2{MesTeCH2C6H2(4,6-Me2)TeMes}] (4)
Pd1–Te1
Pd1–Te2
Pd1–Cl1
Pd1–Cl2
2.5402(3)
2.5137(3)
2.3419(10)
2.3389(9)
C1–Te1
2.151(4)
2.135(4)
2.166(4)
2.133(3)
C10–Te1
C16–Te2
C19–Te2
Cl1–Pd1–Te1
Cl1–Pd1–Te2
Cl1–Pd1–Cl2
Cl2–Pd1–Te1
Cl2–Pd1–Te2
Te2–Pd1–Te1
85.97(3)
172.31(3)
93.85(4)
177.01(3)
85.30(3)
95.278(11)
C1–Te1–Pd1
C10–Te1–Pd1
C10–Te1–C1
C16–Te2–Pd1
C19–Te2–Pd1
C19–Te2–C16
110.96(10)
97.38(9)
100.76(14)
105.18(9)
113.44(9)
94.41(13)
Table 5 Selected bond lengths (Å) and bond angles (°) for
[Pd2(μ-OAc)2{CH2C6H2(4,6-Me2)TeMes}2]·toluene (5a·toluene)
Fig. 7 (a) ORTEP diagram of [Pd(μ-OAc)(μ-TeMes)]4 (6) (25% prob-
ability). Hydrogen atoms are omitted for clarity. (b and c) Orientations of
atomic planes within the molecule.
Pd1–O1
Pd1–O3
Pd1–C7
Pd1–Te1
Te1–C1
2.108(7)
2.238(7)
2.027(9)
2.4706(10)
2.133(10)
2.140(11)
3.0831(10)
Pd2–O2
Pd2–O3
Pd2–C27
Pd2–Te2
Te2–C19
Te2–C28
2.097(7)
2.272(8)
1.999(10)
2.4845(9)
2.090(10)
2.152(9)
Table 1 Selected bond lengths (Å) and bond angles (°) for monoclinic
form of trans-[PdCl2(TeMes2)2]·2MeCN (1a·2MeCN)
Te1–C10
Pd1⋯Pd2
Pd1–Cl1
Pd1–Te1
2.3006(14)
2.5817(3)
Te1–C1
Te1–C10
2.130(5)
2.137(5)
O1–Pd1–C7
O3–Pd1–O1
Te1–Pd1–O1
Te1–Pd1–O3
O3–Pd1–C7
Te1–Pd1–C7
Pd1–Te1–C1
Pd1–Te1–C10
Pd1–C7–C2
Pd1–O1–C37
Pd1–O3–C39
86.5(4)
87.6(3)
172.29(19)
98.8(2)
173.9(4)
86.9(3)
O2–Pd2–C27
O3–Pd2–O2
86.9(3)
89.4(3)
173.0(2)
97.0(2)
175.7(3)
86.8(3)
Cl1–Pd1–Cl1i
Cl1–Pd1–Te1
Cl1–Pd1–Te1i
Cl1i–Pd1–Te1
Cl1i–Pd1–Te1i
180.00(11)
83.78(4)
96.22(4)
96.22(4)
83.78(4)
C1–Te1–Pd1
C10–Te1–Pd1
C1–Te1–C10
Te1–Pd1–Te1i
110.36(13)
106.71(13)
102.5(2)
Te2–Pd2–O2
Te2–Pd2–O3
O3–Pd2–C27
Te2–Pd2–C27
Pd2–Te2–C19
Pd2–Te2–C28
Pd2–C27–C20
Pd2–O2–C37
Pd2–O3–C39
Pd2–O3–Pd1
180.000(15)
94.0(3)
93.7(3)
107.4(3)
122.2(7)
124.9(7)
130.4(11)
105.8(3)
122.9(7)
129.4(7)
116.7(13)
86.3(3)
Table 2 Selected bond lengths (Å) and bond angles (°) for triclinic form
of trans-[PdCl2(TeMes2)2]·toluene (1a·toluene)
Pd1–Cl1
Pd1–Cl2
Pd1–Te1
Pd1–Te2
2.290(2)
2.292(2)
2.5951(6)
2.5908(6)
Te1–C1
2.149(6)
2.137(6)
2.143(8)
2.126(8)
Te1–C10
Te2–C19
Te2–C28
mesityl rings are completely different. The mesityl rings
(C10–C18) and (C29–C36) are syn to the Pd square plane.
The binuclear complex, [Pd2(µ-Cl)2Cl2(TeMes2)2] (2a) (Fig. 3)
crystallizes with two molecules of acetone and comprises of a
rectangular planar four-membered chloro-bridged “Pd2(µ-Cl)2”
core; a configuration usually observed for the chloro-bridged
complexes1 with neutral monodentate group 16 ligands, e.g.
[Pd2(µ-Cl)2Cl2(SeMes2)2].20 Two telluro ether ligands are
mutually trans, forming a sym–trans dimeric structure. The
Cl1–Pd1–Cl2
Cl1–Pd1–Te1
Cl1–Pd1–Te2
Cl2–Pd1–Te1
Cl2–Pd1–Te2
Te2–Pd1–Te1
177.61(10)
83.86(5)
95.50(5)
95.78(6)
84.19(6)
163.97(3)
C1–Te1–Pd1
C10–Te1–C1
C10–Te1–Pd1
C19–Te2–Pd1
C28–Te2–C19
C28–Te2–Pd1
109.92(17)
100.2(3)
113.57(18)
112.0(2)
100.2(3)
114.2(2)
(Cl1⋯C25 = 2.719 Å) as well as the nitrogen and hydrogen terminal Pd–Cl distances are marginally shorter (2.290(4) Å)
(sp2 (2.691 Å) and the sp3 (2.718 Å)) atom of the nearby mole- than the bridging Pd–Cl distances (2.310(4), 2.403(4) Å). The
cule (ESI†). In the triclinic form the arrangement of the Pd–Te distance is shorter than the one noted for the mono-
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between the terminal chloride and the hydrogen atom (H17A)
of the ortho methyl group (Cl2⋯H17A–C17 = 2.925 Å).
Table 6 Selected bond lengths (Å) and bond angles (°) for
[Pd2(μ-OAc)2{CH2C6H2(4,6-Me)2Tetol-o}2] (5b)
The complex cis-[PdCl2{MesTeCH2C6H2(Me2-4,6)TeMes}] (4)
(Fig. 4) is a discrete monomer in which coordination around
palladium is defined by two cis chlorides and a chelating
telluro ether ligand. The Pd–Te and Pd–Cl distances are
slightly shorter and longer, respectively, than 1a owing to weak
trans influencing chloride ligand trans to Te. The Pd–Te dis-
tances are well in agreement with the reported cis configured
complexes such as cis-[PdCl2{MeTe(C4H3E)}2] (E = O (Pd–Te =
Te1–Pd1
C7–Pd1
O1–Pd1
O4–Pd1
C1–Te1
C10–Te1
O1–C33
O2–C33
2.4979(13)
1.980(15)
2.142(10)
2.103(11)
2.120(13)
2.122(12)
1.261(15)
1.225(16)
Te2–Pd2
C23–Pd2
O2–Pd2
O3–Pd2
C17–Te2
C26–Te2
O3–C35
O4–C35
Pd1⋯Pd2
2.4926(13)
2.007(14)
2.097(10)
2.164(10)
2.104(12)
2.152(13)
1.248(18)
1.246(18)
2.8677(14)
2.530 Å);
S (Pd–Te =
∼2.54 Å))34 and cis-[PdCl2{meso-
O1–Pd1–O4
O1–Pd1–C7
O1–Pd1–Te1
O4–Pd1–C7
O4–Pd1–Te1
C7–Pd1–Te1
Pd1–Te1–C1
Pd1–Te1–C10
Pd1–O1–C33
Pd1–O4–C35
C1–Te1–C10
91.7(4)
177.6(5)
94.2(3)
89.7(5)
173.9(3)
84.4(4)
92.4(4)
106.6(3)
123.3(9)
124.2(9)
99.6(5)
O2–Pd2–O3
O2–Pd2–C23
O2–Pd2–Te2
O3–Pd2–C23
O3–Pd2–Te2
C23–Pd2–Te2
Pd2–Te2–C17
Pd2–Te2–C26
Pd2–O2–C33
Pd2–O3–C35
C17–Te2–C26
91.5(4)
87.1(5)
168.5(3)
178.4(5)
95.1(3)
86.2(4)
93.3(3)
100.9(3)
128.0(9)
124.7(10)
98.1(5)
(TeC6H4OMe-4)2CH2}] (Pd–Te = 2.518, 2.526 Å).35 The six-
membered “PdTeCCCTe” ring is puckered. The Cl1 lies slightly
(0.391 Å) out of the Pd1 mean square plane.
The molecular structure of [Pd2(µ-OAc)2{CH2C6H2(4,6-Me2)-
TeMes}2] (5a) (Fig. 5) is unique and distinctly different from
bis acetato-bridged binuclear palladium complexes, [Pd2-
(µ-OAc)2X2Y2] reported thus far.1 The molecule adopts a sym–
cis configuration in which tellurium atoms are trans to the ani-
sobidentate acetate group. The Pd–Te distances are shorter
than the one observed for mono- and bi-nuclear complexes
described above and also from those found in [Pd3(o-tol)2-
(μ-OAc)4{Te(o-tol)2}2] (Pd–Te = 2.5054(5) Å).21 The Pd⋯Pd sep-
aration is longer than those reported in acetate-bridged binuc-
lear complexes but is significantly shorter than the sum of the
van der Waal radii (3.08 Å vs. 3.26 Å, respectively).1 In 5a two
palladium atoms are held together by two different types of
bridging acetate groups; one acting in an anisobidentate
fashion while the other bridges through only one oxygen atom,
so as to give a six-membered “Pd(µ-OAc)(µ-O)Pd” ring rather
than an eight-membered boat shaped “Pd2(µ-OAc)2” ring
usually observed. The second acetate group (O3–C39–C40–O4)
is almost coplanar with Pd1 but almost perpendicular to Pd2
square planes. The distances between the O4 and Te1 and Te2
are 3.447 and 2.989 Å, respectively. The latter (O4–Te2) is sig-
nificantly shorter than the sum of the van der Waal radii of
Table 7 Selected bond lengths (Å) and bond angles (°) of [Pd(μ-OAc)-
(μ-TeMes)]4 (6)
Pd1–O1
Pd1–O3
2.130(5)
2.104(5)
2.5404(7)
2.5448(6)
2.149(7)
2.154(7)
2.130(5)
2.104(5)
2.5404(7)
2.5448(6)
2.9474(7)
3.695
Pd2–O2
Pd2–O4
2.117(5)
2.100(5)
2.5299(6)
2.5374(7)
2.154(7)
2.149(7)
2.117(5)
2.100(5)
2.5374(7)
2.5299(6)
2.9474(7)
3.695
Pd1–Te1
Pd1–Te2i
Te1–C1
Pd2–Te2
Pd2–Te1i
Te2–C10
Te1i–C1i
Pd2i–O2i
Pd2i–O4i
Pd2i–Te1
Pd2i–Te2i
Pd2i–Pd1i
Pd2–Pd1i
Te2i–C10i
Pd1i–O1i
Pd1i–O3i
Pd1i–Te1i
Pd1i–Te2
Pd1⋯Pd2
Pd1⋯Pd2i
O1–Pd1–O3
87.7(2)
O2–Pd2–O4
88.3(2)
O1–Pd1–Te1
O1–Pd1–Te2i
O3–Pd1–Te1
O3–Pd1–Te2i
Te1–Pd1–Te2i
Pd1–Te1–C1
Pd1–Te2i–C10i
Pd1–Te1–Pd2
Pd1–Te2i–Pd2i
O1i–Pd1i–O3i
O1i–Pd1i–Te2
O1i–Pd1i–Te1i
O3i–Pd1i–Te2
O3i–Pd1i–Te1i
Te2–Pd1i–Te1i
176.59(15)
96.00(15)
94.85(19)
175.54(17)
81.347(19)
102.82(17)
106.78(18)
93.40(2)
93.47(2)
87.7(2)
96.00(15)
176.59(15)
175.54(17)
94.85(19)
81.347(19)
O2–Pd2–Te2
O2–Pd2–Te1i
O4–Pd2–Te2
O4–Pd2–Te1i
Te2–Pd2–Te1i
Pd2–Te2–C10
Pd2–Te1i–C1i
Pd2–Te2–Pd1i
Pd2–Te1i–Pd1i
O2i–Pd2i–O4i
O2i–Pd2i–Te1
O2i–Pd2i–Te2i
O4i–Pd2i–Te1
O4i–Pd2i–Te2i
Te1–Pd2i–Te2i
177.60(15)
96.20(16)
93.78(17)
175.42(18) oxygen and tellurium (3.58 Å) indicating a short secondary
81.694(19)
103.63(17)
107.59(18)
93.47(2)
93.40(2)
Te2⋯O4 interaction. Also the O4 is placed almost equidistant
to neighbouring methyl groups in the unit cell (O4⋯H36C–
C36 = 2.440 Å; O4⋯H16C–C16 = 2.663 Å; O4⋯H9B–C9 =
2.591 Å (adjacent molecule). Both Te1 and Te2 atoms are
nearly coplanar with the bridging acetate group.
In contrast to 5a, the complex, [Pd2(μ-OAc)2{CH2C6H2(4,6-
Me2)Tetol-o}2] (5b) (Fig. 6) adopts an usual acetate bridged
structure with short Pd⋯Pd distance 2.8677(14) Å and boat
shaped eight-membered “Pd2(µ-OAc)2” ring. The two tellurium
ligands are mutually trans. Methyl of tolyl rings and oxygen
atoms show short contacts (C16–H16A⋯O1 = 2.749 Å and C32–
88.3(2)
96.20(16)
93.78(17)
175.42(18)
93.78(17)
81.694(19)
nuclear complex, 1a. This may be attributed to the weak trans H32A⋯O3 = 2.763 Å). The O2–Pd2 (2.097 Å) and O4–Pd1
influencing effect of the chloro ligand trans to it. The C–Te–C (2.104 Å) (trans to the Te atom) distances are shorter than the
angle (97.64°) is also reduced significantly from the mono- O1–Pd1 (2.142 Å) and O3–Pd2 (2.164 Å) (trans to methylene
nuclear complex. The Pd⋯H17A–C17 distance (2.377 Å), which groups).
is significantly shorter than the sum of their van der Waal
The complex [Pd(µ-OAc)(µ-TeMes)]4 (6) is a tetramer and
radii (2.83 Å), and the C17–H17⋯Pd1 angle (171.19°) corres- adopts a paddle-wheel geometry. Two pairs of orthogonal
pond to an anagostic interaction between palladium and the acetate groups and two pairs of mesityl tellurolate ligands hold
ortho-methyl hydrogen atom.33 There is also a short contact two different pairs of palladium atoms. The molecule contains
16062 | Dalton Trans., 2014, 43, 16056–16065
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two almost rectangular planes formed by Pd1–Pd2–Pd1i–Pd2i δ: 20.9, 27.2 (Me), 118.8 (Te–C), 129.3 (3,5-CH), 139.9, 143.6.
(Pd2–Pd1–Pd2i = 93.17°, Pd1–Pd2–Pd1i = 86.83; Pd1–Pd2i = 125Te{1H} NMR (CDCl3) δ: 489.1 ppm.
3.696 Å, Pd1–Pd2 = 2.947 Å) and Te1–Te2–Te1i–Te2i (Te2–Te1–
trans-[PdCl2(TePh2)2] (1b). Prepared similar to 1a and iso-
Te2i = 89.42, Te1–Te2–Te1i = 90.58, Te1–Te2 = 3.314 Å, Te1– lated as an orange-red crystalline solid in 74% yield; m.
Te2i = 4.009 Å) which are nearly perpendicular (89.90°). The p. 160 °C (dec). Anal calcd for C24H20Cl2PdTe2: C, 38.90; H,
geometry around each palladium atom is defined by two 2.72%. Found: C, 38.71; H, 2.70%. 1H NMR (CDCl3)
oxygen atoms from two different acetate groups and two tellur- δ: 7.29–7.44 (m), 7.81 (d, 7.2 Hz) (Ph). 13C{1H} NMR (CDCl3) δ:
olate ligands. The four palladium atoms form a rectangular 117.9 (C–Te), 129.7, 130.0, 137.0. 125Te{1H} NMR (CDCl3)
plane with short Pd⋯Pd distances (bridged by two acetate δ: 749.8 ppm.
groups) varying in the range 2.947–3.695 Å, which lie well
[PdCl2{Te(o-tol)2}2] (1c). Prepared similar to 1a and isolated
within the range reported in iso-structural chalcogenolate in 58% yield; m.p. 195 °C (dec). Anal calcd for C28H28Cl2PdTe2:
complexes, [Pd(µ-OAc)(µ-ER)]n (ER = SePh, Pd⋯Pd = 2.864(18) C, 42.19; H, 3.54%. Found: C, 42.40; H, 3.17%. 1H NMR
Å;36 ER = o-tolSe, Pd⋯Pd = 2.8805(8) Å;21 ER = SEt, Pd⋯Pd = (CDCl3) δ: 2.54 (s, Me), 7.10 (t, 7.2 Hz) 7.25 (d) 7.34 (t, 7.2 Hz),
3.036, 3.194 Å37). The structures of palladium acetate com- 7.84 (d, 7.2 Hz) (o-tol). 13C{1H} NMR (CDCl3) δ: 25.5 (Me),
plexes of the composition [Pd(µ-OAc)(µ-ER)]n are influenced by 119.8 (C–Te), 127.4, 130.2, 130.3, 138.4, 142.4 (o-tol). 125Te{1H}
the nature of R groups and ranges from bi-nuclear to tetra- NMR (CDCl3) δ: 637 ppm.
nuclear. For example, [Pd(OAc)(ECH2CH2CH2NMe2)]2·H2O (E =
[PdCl2(MesTetol-o)2] (1d). Prepared similar to 1a and iso-
S or Se)38 and [Pd(OAc)(SCH2CH2NMe2)]3·3H2O39 are di- and lated in 62% yield; m.p. 183–184 °C (dec). Anal calcd for
trimeric, respectively, with terminal monodentate acetate C32H36Cl2PdTe2: C, 45.05; H, 4.25%. Found: C, 45.52; H,
1
groups and chelating bridging chalcogenolate ligands. In con- 4.00%. H NMR (CDCl3) δ: 2.31, 2.46, 2.76 (each s, Me), 7.01
trast complexes with chalcogenolate ligands without internal (s), 7.15–7.25 (m).
functionalized organic group yield tetrameric derivatives.
[Pd2(µ-Cl)2Cl2(TeMes2)2] (2a). (i) To a methanolic solution
(5 cm3) of Na2PdCl4 (102 mg, 0.35 mmol), a toluene solution
(25 cm3) of Mes2Te (131 mg, 0.36 mmol) was added with stir-
ring at room temperature. The contents were stirred for 3 h at
room temperature whereupon a dark-red precipitate formed
which was filtered and washed with toluene. The precipitate
was extracted with acetone. The volume of the solvent was
reduced to 5 ml and hexane (1 ml) was added which on
cooling at −5 °C for several hours gave red needle shaped crys-
tals (150 mg, 79% yield), m.p. 178 °C (dec). Anal calcd for
C36H44Cl4Pd2Te2: C, 39.79; H, 4.08%. Found: C, 39.71; H,
4.07%. 1H NMR (CDCl3) δ: 2.24 (s, 1Me); 2.65 (s, 2Me), 6.88
(s, 2H). 13C{1H} NMR (CDCl3) δ: 20.9, 26.8 (Me), 116.8
(C–Te), 130.1 (3,5-CH), 141.0, 143.3. 125Te{1H} NMR (CDCl3)
δ: 575.0 ppm.
(ii) To a toluene–acetonitrile (1 : 1) solution of trans-
[PdCl2(TeMes2)2] (1a) (100 mg, 0.11 mmol), PdCl2(PhCN)2
(42 mg, 0.11 mmol) was added with stirring at room tempera-
ture, which was continued for 5 h. The red precipitate formed
during the reaction was filtered and washed with toluene and
was processed similar to (i) and isolated in 71% yield. The
NMR data were consistent with the above preparation.
Experimental section
Solvents were dried and distilled under a nitrogen atmosphere
prior to use according to the literature method.40 All the reac-
tions were carried out in an argon atmosphere. Diaryl tellur-
ides, RTeR′ were prepared by the reaction of RTeBr, obtained
in situ by bromination of diaryl ditellurides (R2Te2) with
bromine in THF with an appropriate aryl magnesium bromide
43
(R′MgBr) (ESI†).41 [PdCl2(PhCN)2]42 and [Pd(OAc)2]3
were
prepared according to literature methods. Elemental analyses
were carried out on a Carlo-Erba-1110 CHNS micro-analyzer.
Melting points were determined in capillary tubes and are
uncorrected. 1H, 13C{1H} and 125Te{1H} NMR spectra were
recorded on a Bruker Avance-II 300 NMR spectrometer operat-
ing at 300.1, 75.5 and 94.7 MHz, respectively. The chemical
shifts are relative to an internal chloroform peak (δ 7.26 for 1H
and 77.0 ppm for 13C) and external Me2Te for 125Te (secondary
reference Ph2Te2, δ 421 ppm in C6D6).
Synthesis
[Pd2(µ-Cl)2Cl2{Te(Ph)Mes}2] (2b). This was prepared similar
trans-[PdCl2(TeMes2)2] (1a). To
a toluene solution of to 2a method (i) and isolated as a brown crystalline solid from
[PdCl2(PhCN)2] (300 mg, 0.78 mmol), a solution of Mes2Te a acetone–hexane mixture at −5 °C in 74% yield; m.p. 174 °C
(572 mg, 1.56 mmol) was added at room temperature with (dec). Anal calcd for C30H32Cl4Pd2Te2: C, 35.95; H, 3.22%.
1
stirring which continued for 4 h whereupon an orange-red Found: C, 35.86; H, 3.22%. H NMR (CDCl3) δ: 2.34 (s, 1Me),
precipitate formed. The latter was filtered and washed with 2.81 (s, 2Me), 7.04 (s, 3,5-CH, Mes), 7.19–7.44 (m, Ph).
hexane and diethyl ether, and extracted with acetonitrile. The 125Te{1H} NMR (CDCl3) δ: 704.0 ppm.
concentrated acetonitrile solution (∼2 ml) containing few
[Pd2(µ-Cl)2Cl2(TePh2)2] (2c). This was prepared in a manner
drops of diethyl ether on slow evaporation at room tempera- similar to (2a) employing both methods (i) and modified (ii)
ture gave orange-red rectangular shaped crystals (550 mg, 77% under refluxing in toluene and was isolated as an orange-red
yield); m.p. 178 °C (dec). Anal calcd for C36H44Cl2PdTe2: C, crystalline solid from acetonitrile–diethyl ether mixture at
1
47.55; H, 4.88%. Found: C, 47.37; H, 4.86%. H NMR (CDCl3) room temperature in 66–73% yield, m.p. 142 °C (dec). Anal
δ: 2.23, 2.58 (s, Me); 6.86 (s, 3,5-CH). 13C{1H} NMR (CDCl3) calcd for C24H20Cl4Pd2Te2: C, 31.39; H, 2.19%. Found:
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Dalton Transactions
1
C, 31.32; H, 2.19%. H NMR (CDCl3) δ: 7.38 (t, 7.5 Hz), 7.49 (t, products. The solution was concentrated to 5 ml and precipi-
7.2 Hz), 7.78 (d, 7.2 Hz). 125Te{1H} NMR (CDCl3) δ: 823.5 ppm.
tated by adding petroleum ether. The precipitate was filtered
[Pd2(µ-Cl)2{CH2C6H2(4,6-Me2)TeMes}2] (3). A toluene– out and washed with a small portion of petroleum ether and
methanol (5 : 1 v/v; 50 cm3) solution of trans-[PdCl2(TeMes2)2] then recrystallized from a toluene–hexane mixture (1 : 1, v/v) at
(1a) (100 mg, 0.11 mmol) was refluxed for 30 min with stirring room temperature to afford two different types of crystals, viz
under an argon atmosphere whereupon an orange-red solution yellow rectangular blocks (260 mg, 55% yield), m.
faded to orange color. The solvents were evaporated under p. 138–139 °C (dec) and a few red needle shaped crystals. The
vacuum and the residue was washed with petroleum ether, two were separated manually. The yellow crystals were charac-
and then extracted with toluene. The solvent was reduced to terized as the title complex (5a) while the red crystals could be
2 ml under vacuum, on addition of hexane (5 ml) the title characterized by single crystal X-ray diffraction analysis as a
complex precipitated out as an orange powder (42 mg, 75%), tetra-nuclear complex [Pd(µ-OAc)(μ-TeMes)]4 (6). Anal calcd for
m.p. 164–169 °C (dec.). Anal calcd for C36H42Cl2Pd2Te2: C, (5a) C40H48O4Pd2Te2: C, 45.29; H, 4.56%. Found: C, 44.00; H,
1
42.66; H, 4.18%. Found: C, 42.52; H, 4.17%. H NMR (CDCl3) 4.31%. 1H NMR (CDCl3, 400 MHz) δ: 1.95–2.53 (overlapping
δ: 2.04 (s, 1Me), 2.25 (s, 1Me), 2.53 (s, 2Me), 3.38 (br, CH2), singlets due to methyl groups of mesityl and acetate groups),
6.94 (s, 1H), 6.78 (s, 1H), 6.87 (s, 2H) (CH, Mes). 13C{1H} NMR 3.36 (AB pattern, CH2 metallated, ΔνAB = 71 Hz, JAB = 13 Hz),
(CDCl3) δ: 20.9, 21.0, 22.9, 25.7, 27.2 (1Me), 29.7 (CH2, metal- 6.43, 6.60, 6.64, 6.77, 6.81, 6.86 (each br s of 3,5-CH of
lated), 127.4, 128.8 (3/5-CH of metallated), 129.1 (3,5-CH non- mesityl). 125Te{1H} NMR (CDCl3) δ: 554.1 ppm.
metallated), 140.3, 140.8, 141.2, 143.9 (quaternary carbons).
[Pd2(µ-OAc)2{CH2C6H2(4,6-Me)2Tetol-o}2]
similar to 5a and isolated as orange crystals from acetonitrile–
(5b). Prepared
125Te{1H} NMR (CDCl3) δ: 644.0 ppm.
Complex 3 could also be obtained when a toluene–metha- diethyl ether at −5 °C in 63% yield, m.p. 140 °C (dec). Anal
nol solution of [Pd2(µ-Cl)2Cl2(TeMes2)2] was refluxed for calcd for C36H40O4Pd2Te2: C, 43.04; H, 4.01%. Found: C, 43.05;
30 min (125Te{1H} NMR (CDCl3) δ: 644.0 ppm).
cis-[PdCl2{MesTeCH2C6H2(4,6-Me2)TeMes}]
H, 3.84%. 1H NMR (CDCl3) δ: 1.88 (s, OAc), 2.04, 2.14, 2.29
(each s, 1Me), 3.09 (AB pattern, CH2 metallated, ΔνAB = 24.6
(4). (i)
A
toluene–methanol solution of 3 was refluxed for 2 h and the Hz, JAB = 12.7 Hz), 6.60 (s, 3,5-CH, Mes), 6.70–6.91 (m), 7.18
colour of the solution darkened from orange to dark red. The (br) (o-tol). 13C{1H} NMR (CDCl3) δ: 21.2, 22.2, 23.4, 24.0, 24.2,
solvents were evaporated under vacuum and the residue was (for Me, CH2), 118.9 (C–Te), 126.6, 127.2, 128.7, 128.9, 130.4,
washed with petroleum ether and extracted with toluene. The 132.6, 140.6, 141.0, 142.2, 179.8 (CvO);125Te{1H} NMR (CDCl3)
solvent was reduced to 2 ml and a few drops of hexane were δ: 592.2 ppm.
added which on slow evaporation afforded dark-red crystals,
[Pd2(µ-OAc)2{CH2C6H2(4,6-Me2)TePh}2]
(5c). Prepared
m.p. 185 °C (dec). Anal calcd for C27H32Cl2PdTe2: C, 41.10; H, similar to 5a as a red powder in 45% yield, m.p. 147 °C (dec).
4.09%. Found, C, 41.20; H, 3.96%. 1H NMR (CDCl3) δ: 2.02, The complex tends to decompose and hence gave variable ana-
2.22, 2.27, 2.50 (each s, 1Me), 2.47, 2.63 (br, s, each 2Me, 2,6- lysis. 125Te{1H} NMR (CDCl3) δ: 690.4 ppm.
Me of Mes), 3.55 (AX pattern, CH2 metallated, ΔνAX = 169 Hz,
X-ray crystallography
JAX = 11 Hz), 6.25, 6.83 (each s, 1H, 3,5-CH, metallated), 6.93
(s, 3,5-CH, Mes). 13C{1H} NMR (CDCl3) δ: 20.5, 20.8, 25.3, 26.5
(1Me), 27.5, 28.5 (br, 2Me), 117.0, 117.6 (C–Te), 129.0, 129.2,
130.4, 130.9, 140.6, 140.9, 141.1, 142.3, 142.7, 144.3 ppm.
125Te{1H} NMR (CDCl3) δ: 428.2 ppm.
(ii) A toluene–methanol solution of trans-[PdCl2(TeMes2)2]
(150 mg, 0.16 mmol) was refluxed for 2 h which resulted in a
dark-red solution. After processing in a similar way gave red
crystals (45 mg, 35%). The NMR data were consistent with the
product obtained in the above preparation.
(iii) To a methanolic solution of Na2PdCl4 (200 mg,
0.68 mmol), a toluene solution of TeMes2 (254 mg, 0.69 mmol)
was added with stirring and the whole mixture was refluxed
for 2 h. The solvents were evaporated under reduced pressure
and the residue was washed with petroleum ether. The residue
was extracted with toluene and recrystallized similarly as above
(125 mg, 23%). Analytical and NMR data were consistent to the
product obtained through (i).
Single crystal X-ray data on trans-[PdCl2(TeMes2)2] (1a), [Pd2-
(µ-Cl)2Cl2(TeMes2)2]·2acetone (2a·2 acetone), cis-[PdCl2{Mes-
TeCH2C6H2(4,6-Me2)TeMes}] (4), [Pd2(µ-OAc)2{CH2C6H2(4,6-
Me2)TeMes}2]·toluene (5a·toluene), [Pd2(µ-OAc)2{CH2C6H2(4,6-
Me2)Tetol-o}2] (5b) and [Pd(µ-OAc)(μ-TeMes)]4 (6) were col-
lected on an Agilent SuperNova or Bruker APEX-II CCD
diffractometer. Crystallographic data, together with data collec-
tion and refinement details are given in Tables S1 and S2 of
ESI.† All the data were corrected for Lorentz and polarization
effects. The structures were solved by direct methods44 and
expanded using the Fourier technique.45 Hydrogen atoms were
added to the parent atom with idealized geometry and refined
isotropically. Molecular structures were drawn using ORTEP.46
Conclusion
[Pd2(µ-OAc)2{CH2C6H2(4,6-Me2)TeMes}2] (5a). To a toluene In summary we have isolated a number of complexes formed
solution of palladium acetate (200 mg, 0.30 mmol) a toluene in the reactions of telluro ethers with palladium precursors.
solution of Mes2Te (328 mg, 0.89 mmol) was added with stir- By subtle variation in reaction conditions a variety of com-
ring at room temperature which continued for 1 h. The solu- plexes, such as addition complexes (e.g. trans-[PdCl2-
tion was passed through Celite to remove any decomposition (TeMes2)2]), complexes showing secondary Pd⋯H interactions
16064 | Dalton Trans., 2014, 43, 16056–16065
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(e.g. [Pd2(µ-Cl)2Cl2(TeMes2)2]), cyclometallated complexes (e.g. 23 R. S. Chauhan, G. Kedarnath, A. Wadawale, A. M. Z. Slawin
[Pd2(µ-OAc)2{CH2C6H2(4,6-Me2)TeMes}2]), complexes formed and V. K. Jain, Dalton Trans., 2013, 42, 259–269.
by Te–C bond cleavage (e.g. [Pd(µ-OAc)(µ-TeMes)]4) and finally 24 L. B. Han, N. Choi and M. Tanaka, J. Am. Chem. Soc., 1997,
leading to palladium telluride (Pd7Te3), have been isolated and 119, 1795–1796.
structurally characterized. The cyclopalladation of telluroether 25 G. K. Rao, A. Kumar, M. P. Singh and A. K. Singh, J. Organo-
ligands via benzyl C–H bond activation has also been demon-
met. Chem., 2014, 749, 1–6.
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26 A. Kumar, M. Agarwal and A. K. Singh, J. Organomet.
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27 K. N. Sharma, H. Joshi, A. K. Sharma, O. Prakash and
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28 M. Risto, E. M. Jahr, M. S. Hannu-Kuure, R. Oilunkaninemi
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