Structural variation in [PdX2{RE(CH2)nNMe2}] (E = Se, Te; X = Cl, OAc) complexes: Experimental results, computational analysis, and catalytic activity in Suzuki coupling reactions

Article abstract of DOI:10.1002/ejic.201402943

A series of chalcogenoether ligands RE(CH₂)_nNMe₂ (1) [E = Se or Te; R = Ph, o-tol (o-tol = ortho-tolyl), Mes (Mes = 2,4,6-trimethylphenyl); n = 2 or 3] and their palladium complexes [PdX₂{RE(CH₂)

Full text of DOI:10.1002/ejic.201402943

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DOI:10.1002/ejic.201402943
Structural Variation in [PdX2{RE(CH2)nNMe2}] (E = Se,
Te; X = Cl, OAc) Complexes: Experimental Results,
Computational Analysis, and Catalytic Activity in Suzuki
Coupling Reactions
Dilip K. Paluru,[a] Sandip Dey,*[a] Amey Wadawale,[a]
Dilip K. Maity,[b,c] Nattamai Bhuvanesh,[d] and Vimal K. Jain*[a]
Keywords: Palladium / Cross-coupling / C–C coupling / Chalcogens / Density functional calculations
A series of chalcogenoether ligands RE(CH2)nNMe2 (1) [E =
Se or Te; R = Ph, o-tol (o-tol = ortho-tolyl), Mes (Mes = 2,4,6-
trimethylphenyl); n = 2 or 3] and their palladium complexes
[PdX2{RE(CH2)nNMe2}]m [X = Cl (2) or OAc (3); m = 1, 2]
were synthesized. Complexes [PdCl2(RECH2CH2NMe2)]
[R/E = Ph/Se (2a), Mes/Se (2b), Mes/Te (2c)] were isolated as
monomers. Complexes [PdCl2(RECH2CH2CH2NMe2)]m [R/E
= Ph/Se (2d), Ph/Te (2e), o-tol/Te (2f)] exist in one monomeric
and two dimeric forms in solution; their ratio depends on E
and R as revealed by NMR spectroscopic data. Crystal struc-
tures of monomeric 2a, 2b, 3b, 2d, 2f, and dimeric 2e were
established. Compounds 2a, 2d, 2e, and 2f were also investi-
gated by means of density functional theory (DFT)-based
quantum chemical calculations to understand structural vari-
ation. The complexes that contained acetate or chalco-
genoether ligands with n = 3 showed higher catalytic activity
than other derivatives in Suzuki C–C cross-coupling reac-
tions.
ligands can bind weakly and reversibly to the metal center.
The electronic differences, differing trans influence, and the
variable chemical reactivity of two different donor atoms of
these hybrid ligands, in addition to substituents on them,
influence the overall activity and the selectivity of a reac-
tion.[4] Accordingly palladium complexes that contain hy-
brid ligands derived from various combinations of donor
atoms, such as (P,O),[5] (P,S),[4c,6,7] (P,N),[1a,8] (N,O),[9]
(N,S),[10] (N,Se),[11] and so forth have been synthesized and
several of them are effective catalysts in a number of C–C
bond-formation reactions. Hemilabile ligands have an ad-
vantage as they can protect one or more coordination sites
that are formed during the catalytic reaction and are also
capable of stabilizing the active catalytic species/reactive in-
termediates.[4,12]
Palladium complexes with hemilabile phosphane ligands
have been used for quite some time as catalysts in various
coupling reactions,[13–16] but their air and moisture sensitiv-
ity has often posed difficulty in handling.[8a] Thus there is
an enduring interest in developing phosphane-free, inexpen-
sive, efficient catalyst systems. Sulfur-based ligands, despite
their rich transition-metal chemistry, remained dormant as
they are often considered catalyst poisons. Of late, palla-
dium complexes derived from both a chalcogenolate group
(RE–; E = S or Se)[4c,17] and chalcogenoether ligands[11]
have been successfully used in C–C coupling reactions.
Scant attention has been paid to palladium complexes with
tellurium ligands in catalysis, possibly due to the lack of
availability of suitable ligands and also the markedly dif-
Introduction
Among various transition-metal complexes, palladium
complexes have played a pivotal role in metal-catalyzed or-
ganic transformations and have emerged as the most versa-
tile catalytic systems.[1] They can catalyze a wide variety of
reactions that range from carbon–carbon to carbon–hetero-
atom bond formations.[1–3] Catalyst design has remained of
paramount importance for understanding various catalytic
processes as well as for improving the activity of catalyst
systems. Accordingly, catalysts derived from phosphane as
well as non-phosphane ligands have been designed and ex-
tensively utilized for a variety of synthetic transformations.
More recently, metal complexes that contain hemilabile hy-
brid ligands that consist of one strong (soft) donor in com-
bination with a weak (hard) donor have shown great poten-
tial in catalytic reactions.[4] The hard donor atom in these
[a] Chemistry Division, Bhabha Atomic Research Centre,
Mumbai 400 085, India
E-mail: dsandip@barc.gov.in
jainvk@barc.gov.in
www.barc.gov.in
[b] Theoretical Chemistry Section, Bhabha Atomic Research
Centre,
Mumbai 400 085, India
[c] Homi Bhabha National Institute, Training School Complex,
Mumbai 400 094, India
[d] Department of Chemistry, Texas A&M University,
PO Box 30012, College Station,
Texas 77842-3012, USA
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201402943.
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ferent reactivity pattern of tellurium ligands with respect to sponding diaryl ditelluride, whereas the converse is true for
the lighter congeners (S or Se).
analogous selenoethers.
To pursue our interest in the chemistry of platinum-
group metals with selenium and tellurium ligands,[18–20] we
have synthesized palladium complexes with dimethyl-
aminoalkyl chalcogenoether RE(CH2)nNMe2 (E = Se and
Te) ligands that contain neutral donor atoms, namely, a
chalcogen and nitrogen, and evaluated their catalytic ac-
tivity in Suzuki C–C coupling reactions. The results of this
work are reported herein.
Synthesis and Spectroscopy of Palladium Complexes
Treatment of [PdCl2(PhCN)2] or [Pd(OAc)2]3 with
chalcogenoethers gave complexes of the composition
[PdX2{RE(CH2)nNMe2}]m (X = Cl or OAc; E = Se or Te)
(Schemes 2 and 3) as yellow to orange-red to red crystalline
solids. The chloride complexes are sparingly soluble in
chloroform, acetone, benzene, and ether, but moderately
soluble in dichloromethane. Recrystallization from di-
chloromethane resulted in low yields of chloride complexes.
The acetato complexes are lighter in color than the corre-
sponding chloro derivatives. The telluroether complexes are
darker in color than the analogous selenoether derivatives.
The telluroether complexes 2e and 2f decompose at 325 and
305 °C, respectively; thermogravimetric analysis (TGA)
suggests the formation of Pd3Te2 (Figures S13 and S14 in
the Supporting Information). It is worth noting that the
reaction of palladium acetate trimer with mesityl chalco-
genoethers MesECH2CH2NMe2 yields a coordination com-
plex rather than the cyclopalladated derivatives.[22] It has
been demonstrated that the proton of the 2-methyl of the
mesityl group forms short contacts (anagostic interaction)
with the palladium atom before undergoing cyclopallad-
ation.[22] In the present case ligands are chelated without
any interactions between the aryl ring and the metal center.
For instance, the mesityl ring in 3b is almost perpendicular
to the metal coordination plane and there is hardly any
Pd···H (methyl) interaction. As a result, metalation is not
facilitated.
Results and Discussion
Synthesis of Ligands
Aryl chalcogenoethers, RE(CH2)nNMe2, were synthe-
sized by a nucleophilic substitution reaction of sodium aryl
chalcogenolate with freshly distilled dimethylaminoalkyl
chloride (Scheme 1). Yellow selenoethers and red telluro-
ethers were isolated as oils after silica-gel column
chromatography. The selenoethers can be stored at room
temperature for several months, whereas telluroethers were
stored in the refrigerator at approximately 5 °C due to de-
composition at room temperature.
Scheme 1. Syntheses of aryl chalcogenoether ligands.
1
The H and 13C{1H} NMR spectra of these compounds
displayed the expected resonances and peak multiplicities.
The 13C NMR spectra exhibited a resonance due to CH2Se
and CH2Te carbon at approximately δ = 25 ppm and in the
region of δ = 4.7–9.2 ppm, respectively. The resonances in
telluroethers are influenced by the substituents, whereas the
corresponding resonance for the selenoethers are barely in-
fluenced. These resonances were flanked by 77Se/125Te cou-
1
plings. The observed magnitude of J(77Se,13C) (ca. 63 Hz)
for selenoethers is in accordance with the values reported
for selenoethers.[21] The 77Se/125Te{1H} NMR spectra dis-
played single resonances that are influenced by the nature
of the substituents. The 77Se NMR spectroscopic resonance
is deshielded by δ = 15 ppm upon increasing the alkyl chain
length from (CH2)2 to (CH2)3 (Table S1 in the Supporting
Information). Shielding of the resonances is noted on re-
placing the phenyl with a methyl-substituted aryl ring (o-
Scheme 2. Syntheses of palladium chloride complexes.
All these complexes were characterized by elemental
tol or Mes) (o-tol = ortho-tolyl; Mes = 2,4,6-trimeth- analyses, NMR (1H, 13C, 77Se, 125Te) and UV/Vis spec-
ylphenyl) within a series. The 125Te NMR spectroscopic sig- troscopy, and in several cases by single-crystal X-ray dif-
nal of telluroethers is deshielded with respect to the corre- fraction analyses. The chloride complexes 2a–2c derived
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ing a comparatively less hindered rotation of the Te–C(Mes)
bond than the Se–C(Mes) bond at room temperature (Fig-
ure S4 in the Supporting Information). The longer Pd–Te
bond keeps the two ortho methyl groups away from the vi-
cinity of other groups in complex 2c, hence free rotation
occurs at room temperature. By contrast, in both acetato
complexes [Pd(OAc)2(MesECH2CH2NMe2)] (E = Se (3b),
Te (3c)), the broad singlets at δ = 3.09 and 3.01 ppm for
Se and Te derivatives, respectively, for 2,6-Me groups also
indicate the hindered rotation of the E–C(Mes) bond.
Scheme 3. Syntheses of palladium acetato complexes.
from RECH2CH2NMe2 ligands invariably exist as a dis-
crete monomeric species with chelating chalcogenoether li-
gands. In contrast, complexes 2d–2f, which contain
RECH2CH2CH2NMe2, exist as one monomeric and two
different dimeric species in solution; however, in the solid
state only one species could be obtained by crystallization.
The 1H NMR spectra of 2a–2c at room temperature
showed a complex ABXY spin system for the CH2 groups
of the ligand (Figure S2 in the Supporting Information).
The 13C{1H} NMR spectra displayed a single set of peaks,
except for the NMe2 groups for which two singlets were
observed. The 77Se{1H} (Figure S3 in the Supporting Infor-
mation) and 125Te{1H} NMR spectra also showed sharp
Figure 1. Variable-temperature 400 MHz 1H NMR spectra of
[PdCl2(MesSeCH2CH2NMe2)]n (2b) in CD2Cl2.
Complexes 2d–2f, derived from RECH2CH2CH2NMe2
singlets that indicated only one isomer in solution. The and [PdCl2(PhCN)2] exhibited three sets of resonances (see
1
1
complex pattern of H spectra at room temperature can be Figures S5–S12 in the Supporting Information) in H, 13C,
explained by the chiral center generated at chalcogen atom and 77Se/ 125Te NMR spectra (Figures 2 and 3), thus clearly
after complexation. The CH2 group attached to this chalco- indicating the existence of three species in solution. By com-
gen atom become diastereotopic (and also the NMe2 groups paring the 1H NMR spectroscopic peaks of analogous
are anisochronous) in the absence of any interconversion monomers 2a–2c in which the ligands adopt a chelating
process. Variable-temperature NMR spectra of 2a (Fig- mode, the sharp singlets for NMe2 groups of monomers
ure S1) were determined in [D6]DMSO. Upon increasing have been assigned in the deshielded range relative to the
the temperature, the separation between two doublet of dimers of 2d–2f (see Figures S8 and S10), and the corre-
triplets for the SeCH2 group, two doublet of doublet of sponding integration ratio has been used for the calculation
doublets for the NCH2 group, and two singlets for the of their relative ratio. A minor product (ca. 4%) was ob-
1
NMe2 group begin decreasing and broadening. At 358 K, served in H and 125Te (δ = 566 ppm) NMR spectra, which
two peaks for NMe2 groups coalesce and become a broad might be due to the oligomeric/trimeric form of 2e.
singlet at 368 K. The rate constant calculated for the in-
terconversion of the two isomers is 59.5 s–1, and the acti- lating monomeric structure, whereas a dimeric structure
vation energy barrier is 18.2 kcalmol–1.
was observed for the analogous 2e (see later). It is likely
The X-ray structural analysis of 2d and 2f revealed a che-
The 2,6-methyl groups of the Mes part of [PdCl2(Mes- that both monomeric (Scheme 2, I) and dimeric structures
SeCH2CH2NMe2)] (2b) displayed a very broad peak in the (Scheme 2, II and III) can form in solution and their rela-
1
range δ = 2.9–3.2 ppm in the H NMR spectrum at room tive concentration is influenced by the nature of the ligand.
temperature. Upon lowering the temperature to 253 K, two The inversion at the chiral Se or Te centers in both the
broad singlets appeared at δ = 3.46 and 2.53 ppm for the dimeric structures would generate invertomers that are dia-
two ortho-methyl groups of the Mes group owing to the steroisomers. For example, the crystallographically charac-
slow rotation of Se–C(Mes) bond (Figure 1). The 3,5-aryl terized dimer (2e) is the meso form (out–out) (II) in which
protons of the Mes group, which showed a sharp singlet at the two aryl groups are outwardly oriented with respect to
δ = 7.04 ppm at ambient temperature, split into two broad the metallo ring and away from the chloride groups. The
singlets at 243 K. In the case of analogous Te complex 2c, inversion at one or two Se/Te centers of II can lead to un-
a sharp singlet was observed at δ = 3.03 ppm, thus indicat- stable invertomers IV (dl: out–in) or V (meso: in–in) (see
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small peaks at δ = 414, 426 and 339, 361 ppm in addition
to the major peaks at δ = 442 and 345 ppm assigned to 3a
and 3b, respectively. On the basis of the previous discussion
and theoretical calculations (see below), as the ligand of
two carbon spacer length RECH2CH2NMe2 is unable to
form bridged dimeric structures, the small peaks in the pres-
ent case might be due to acetato-bridged oligomeric com-
plexes of 3a and 3b as minor products; no attempt was
made to isolate either one. Even after repeated recrystalli-
zation these minor products could not be removed. As a
result the yields of these acetato complexes are low.
The absorption spectra of all the yellow to orange com-
plexes in CH2Cl2 displayed a characteristic broad and weak
band at 400–409 nm in the visible region. Variation of the
chalcogen center or the chain length hardly affects the
wavelength at the absorption maxima, thus indicating that
the highest-occupied orbitals are not formed from any sig-
nificant orbital contribution from the chalcogen atom. The
charge-transfer transitions from the selenolato or tellurol-
ato centers to unoccupied orbitals that involve mainly the
phosphane coligands (LLCT) for the PtII compounds and
more delocalized MOs for the PdII analogues has been ob-
served in [MCl(EʝN)(PR3)] (M = Pd, Pt; EʝN = 2-
C5H4N,[27] ECH2CH2NMe2[19]). In the case of non-phos-
phane complexes [PdCl(SeCH2CH2CH2NMe2)]2,[28] the
long-wavelength transitions have been assigned as charge-
transfer transitions from the selenolato centers to unoccu-
pied metal orbitals [ligand-to-metal charge transfer
(LMCT)]. In the present case, the observed absorption is
assigned to the charge-transfer transition from the bonding
orbital of Pd to the antibonding (π*) orbital of the phenyl
ring of the ligand [metal-to-ligand charge transfer (MLCT)]
and is also supported by time-dependent (TD) DFT calcu-
lations (see below).
Figure 2.
77Se{1H}
NMR
spectrum
of
[PdCl2(PhSeCH2CH2CH2NMe2)]n (2d).
Figure 3. 125Te{1H} NMR spectrum of [PdCl2(PhTeCH2CH2CH2-
NMe2)]n (2e).
Scheme S1 in the Supporting Information) in which the aryl
groups occupy a position inside the metallo ring and very
close to the chloride groups, which is sterically unfavorable.
This is justified by theoretical modeling; the gradual inver-
X-ray Crystallography
Molecular structures of [PdCl2(PhSeCH2CH2NMe2)]·
sion at the Se/Te center finally leads to an unstable species 0.5CH2Cl2 (2a·0.5CH2Cl2), [PdX2(MesSeCH2CH2NMe2)]
before forming IV or V. The two dl forms IV and VI are [X = Cl (2b), OAc (3b)], [PdCl2(PhSeCH2CH2CH2NMe2)]
identical by rotation. The pyramidal inversion at the sulfur, (2d), [PdCl2(PhTeCH2CH2CH2NMe2)]2 (2e), and [PdCl2-
selenium, and tellurium center in mononuclear complexes (o-tolTeCH2CH2CH2NMe2)] (2f) have been established by
trans-[MX2(ER2)] (M = Pd, Pt; X = Cl, Br; R = Et,[23] single-crystal X-ray analyses. ORTEP drawing with atomic
CH2SiMe3[24]) and trans-[MX2{RE(CH2)3ER}] (X = Cl, numbering schemes are shown in Figures 4, 5, 6, 7, and 8,
Me; R = Me,[25] Ph[26]) has been reported to generate in- as well as Figures S15 and S16 of the Supporting Infor-
vertomers. For selenoether complex 2d, the monomeric mation, whereas selected interatomic parameters are given
form predominates, whereas for telluroether ligands, all in Tables 1, 2, 3, and 4.
three structural forms of 2e and 2f exist with nearly equal
These complexes, except for 2e, are discrete monomers
probability. It is clear that the complexes of the ligand that with chelating chalcogenoether ligands. The 2e is a dimer
possess longer chains and larger Te atoms generate more with a bridging chalcogenoether ligand. The coordination
dimeric forms than monomers in solution.
environment around the distorted square-planar palladium
The 77Se and 125Te NMR spectroscopic resonances for atom is defined by E, N, and two anionic ligands (Cl or
the complexes are considerably deshielded from the respec- OAc). The latter in monomeric complexes are cis disposed,
tive signals for the corresponding free ligands. The deshield- whereas in 2e the chloride ligands occupy trans positions.
ing is more pronounced in telluroether complexes than the There are two distinctly different Pd–Cl distances (ca. 2.30
analogous selenoether derivatives. In the case of acetato and ca. 2.33 Å) in mononuclear complexes, with the Pd–Cl
complexes 3a and 3b, the 77Se NMR spectra displayed two bond trans to the chalcogen atom being marginally longer
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Figure 7. Molecular structure of [PdCl2(o-tolTeCH2CH2CH2-
NMe2)] (2f) ellipsoids drawn at 50% probability. Hydrogen atoms
are omitted for clarity.
Figure 4. Molecular structure of [PdCl2(MesSeCH2CH2NMe2)]
(2b) ellipsoids drawn at 50% probability. Hydrogen atoms are omit-
ted for clarity.
Figure 8. Molecular structure of [Pd(OAc)2(MesSeCH2CH2NMe2)]·
1.5(H2O) (3b·1.5H2O) ellipsoids drawn at 50% probability. Two
molecules of a and b are associated through intermolecular
hydrogen bonds. Hydrogen atoms in the ligands have been omitted
for clarity.
Figure 5. Molecular structure of [PdCl2(PhSeCH2CH2CH2NMe2)]
(2d) ellipsoids drawn at 50% probability. Hydrogen atoms are omit-
ted for clarity.
Table 1. Selected interatomic parameters (bonds [Å], angles [°]) of
[PdCl2(RSeCH2CH2NMe2)] (R = Ph, Mes).
2a·0.5CH2Cl2
2b
Pd1–Se1
Pd1–Cl1
Pd1–Cl2
Pd1–N1
Se1–C1
Se1–C5
N1–Pd1–Se1
N1–Pd1–Cl1
N1–Pd1–Cl2
Cl2–Pd1–Cl1
Se1–Pd1–Cl1
Se1–Pd1–Cl2
Pd1–Se1–C5
Pd1–Se1–C1
C1–Se1–C5
2.3611(11)
2.287(2)
2.326(2)
2.083(6)
1.941(8)
1.945(7)
89.06(19)
175.36(19)
92.95(19)
91.53(8)
86.59(6)
174.45(6)
105.0(2)
94.6(2)
2.3914(6)
2.3085(7)
2.3383(7)
2.0882(19)
1.962(2)
1.957(2)
89.30(5)
176.91(5)
90.77(5)
91.13(2)
88.55(2)
173.583(17)
113.12(6)
92.60(7)
Figure 6. Molecular structure of [PdCl2(PhTeCH2CH2CH2NMe2)]2
(2e) ellipsoids drawn at 50% probability. Hydrogen atoms are omit-
ted for clarity.
99.1(3)
97.73(10)
than the one trans to nitrogen. This difference is due to the parable to complexes of the composition [Pd(OAc){E(CH2)n-
difference in the trans influence of chalcogen and the chlor- NMe2}]m (n = 2 or 3; m = 3 or 2; E = S, Se, or Te).[17a,28b]
ide ligand. The observed distances are in good agreement The Pd–N distance in 2e, however, is much longer
with the values reported in palladium complexes.[7,22a,29] (2.210 Å). This is in accordance with the distances reported
The Pd–O and Pd–N (2.067–2.121 Å) distances are com- in compounds that contain a nitrogen atom trans to strong
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Table 2. Selected interatomic parameters (bonds [Å], angles [°]) of gated either by replacing a phenyl group by mesityl with n
[Pd(OAc)2(MesSeCH2CH2NMe2)].
= 2 {e.g., 2a [2.3611(11) Å] and 2b [2.3914(6) Å]} or in-
creasing the alkyl chain length {e.g., 2a and 2d [Pd–Se =
2.3938(11) Å]}. A similar elongation of the Pd–Se bond is
noted for selenolato complexes [PdCl(SeCH2CH2-
3b·1.5(H2O)
3b
molecule a
molecule b
Pd1–Se1
Pd1–O1
Pd1–O3
Pd1–N1
Se1–C1
Se1–C5
Se1–Pd1–N1
N1–Pd1–O1
N1–Pd1–O3
O1–Pd1–O3
O3–Pd1–Se1
Se1–Pd1–O1
Pd1–Se1–C5
Pd1–Se1–C1
C1–Se1–C5
2.3582(4)
2.0365(18)
2.0197(19)
2.067(2)
1.965(3)
1.942(3)
2.3595(5)
2.006(2)
2.0469(19)
2.067(2)
1.957(3)
1.929(3)
87.32(6)
174.70(8)
89.15(8)
86.96(8)
175.82(6)
96.70(6)
114.88(8)
94.03(8)
103.77(11)
2.3730(3)
2.0460(13)
2.0087(14)
2.0714(16)
1.972(2)
1.9447(18)
88.71(5)
89.23(6)
174.33(6)
85.60(6)
[34]
NMe2)]3 and [PdCl(SeCH2CH2CH2NMe2)]2.[28a]
The binuclear complex 2e forms a 12-membered macro-
cyclic ring; the two phenyl groups lie on the opposite side
of the ring, thus leading to an anti conformation, which is
actually a meso invertomer (III: out–out). The Pd–N bond
[2.210(13) Å] is elongated relative to the chelated complex
[PdCl2(o-tol–TeCH2CH2CH2NMe2)] [2.111(5) Å], whereas
in similar dinuclear complexes of a trans-“PdCl2TeN” coor-
dination environment, comparatively shorter Pd–N dis-
tances [2.097(4), 2.101(4) Å] are observed in which the ni-
trogen donor atom is a part of the pyridyl group.[35] Dinu-
clear and trinuclear complexes [PdCl2(μ-6-MepyCH2EPh-
N,E)]n (E = S, n = 3; E = Se, n = 2) of trans-“PdCl2EN”
geometry have also been reported to form a macrocyclic
ring.[36]
87.97(6)
88.47(8)
174.44(8)
86.18(8)
97.28(6)
175.17(5)
115.13(8)
93.61(9)
96.06(4)
171.40(4)
114.74(6)
94.49(6)
99.23(12)
97.96(8)
Table 3. Selected interatomic parameters (bonds [Å], angles [°]) of
[PdCl2(RECH2CH2CH2NMe2)]n (RE = PhSe, o-tolTe).
The acetato complex 3b could be crystallized with and
without a water molecule (Figure 8 and Figure S16 in the
Supporting Information). There is a slight variation in vari-
ous interatomic parameters in the two structures. In the hy-
drated molecule the Pd1–O3 bond is slightly elongated
(0.011 Å), whereas the Se1–Pd1–O1 angle is opened up
(3.77°) relative to the values of the structure without a water
molecule. The O3 oxygen in fact is hydrogen bonded to the
lattice water molecule. There are two independent molecules
in the crystal lattice (Figure 8) of the hydrated complex that
differ slightly in their interatomic parameters.
2d
2f
Pd1–E1
Pd1–Cl1
Pd1–Cl2
Pd1–N1
E1–C3
E1–C6
N1–Pd1–E1
N1–Pd1–Cl1
N1–Pd1–Cl2
Cl2–Pd1–Cl1
Cl1–Pd1–E1
E1–Pd1–Cl2
Pd1–E1–C6
Pd1–E1–C3
C3–E1–C6
2.3938(11)
2.298(2)
2.313(3)
2.121(7)
1.935(9)
1.943(8)
96.2(2)
2.5395(8)
2.3161(18)
2.353(2)
2.111(5)
2.136(7)
2.135(7)
100.17(16)
176.14(18)
90.68(16)
88.86(8)
172.2(2)
91.4(3)
89.34(12)
83.25(8)
172.18(9)
101.8(2)
108.7(3)
101.2(4)
80.54(6)
168.62(6)
99.65(19)
104.6(2)
Theoretical Calculations
94.0(3)
To assess the factors responsible for structural variation
of palladium complexes with the nature of ligand, DFT cal-
Table 4. Selected bond lengths [Å] and angles [°] of culations were performed. Minimum-energy equilibrium
[PdCl2(PhTeCH2CH2CH2NMe2)]2 (2e).
structures were obtained in each of these monomers and
Pd1–Te1i
Pd1–N1
Pd1–Cl1
2.5321(15)
2.210(13)
2.310(4)
Pd1–Cl2
Te1–C3
Te1–C6
2.297(4)
2.144(14)
2.118(13)
dimers of palladium complexes with different possible input
structures based on different spatial orientations of the
groups. Optimization of the structures were carried out by
applying the BP86 functional, which is known to work well
for Pd-based complexes with mixed atomic basis functions
for the metal and other atoms. The final optimized struc-
tures of monomer and dimer units are shown in Figure 9
and Figure S17 in the Supporting Information. The largest
discrepancies occur for the Pd–Te and Pd–N bonds, which
were calculated with distances that are too long by about
0.12 and 0.10 Å, respectively, whereas the Pd–Se bond
lengths were calculated to be 0.07 Å higher than the experi-
Cl1–Pd1–Cl2
Cl1–Pd1–N1
Cl1–Pd1–Te1i
Cl2–Pd1–N1
Cl2–Pd1–Te1i
173.24(16)
93.9(4)
82.27(12)
92.1(4)
N1–Pd1–Te1i
Pd1–Te1i–C3i
Pd1–Te1i–C6i
C3i–Te1i–C6i
176.1(4)
108.6(4)
98.6(3)
93.3(5)
91.73(11)
trans-influencing ligands (e.g., [PdI(SeC6H4CH2NMe2-2)-
(PPh3)] [Pd–N
=
2.1958(18) Å];[30] [Pd2(μ-Sepy)2(Me2-
NCH2C6H4-C,N)2] [Pd–N = 2.189(8) Å][31]. The Pd–Se (ca.
2.37 Å) and Pd–Te (ca. 2.53 Å) bond lengths are in confor-
mity with the values reported for palladium chalco-
genoether complexes, such as [Pd2(μ-Cl)2{MesSeC6H2-
Table 5. Comparison of DFT-calculated bond lengths with experi-
mental data for [PdCl2{RE(CH2)nNMe2}]m.
(Me2)CH2}2]
[Pd–Se
=
2.3438(8) Å],[22a]
[PdCl-
{OC6H4C(Ph)=NCH2CH2SePh}] [Pd–Se = 2.3575(6) Å],[32]
2a-I (E = Se) 2d-I (E = Se) 2f-I (E = Te)
2e-II (E = Te)
calcd.
exp. calcd. exp. calcd. exp. calcd.
exp.
[PdCl2{TeMe(C4H3O)}2] [Pd–Te
=
2.530(1) Å],[33] and
[Pd2(μ-Cl)2Cl2(TeMes2)2] [Pd–Te = 2.5068(13) Å].[22b] The
Pd–E
Pd–N
2.43
2.18
2.36
2.08
2.45 2.39 2.66
2.19 2.12 2.17
2.54
2.12
2.65
2.22
2.53
2.21
Pd–Se bond in [PdCl2{RSe(CH2)nNMe2}] is slightly elon-
Eur. J. Inorg. Chem. 0000, 0–0
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Table 6. Stabilization energy of monomer and dimer complexes of PdCl2 with RE(CH2)nNMe2 (E = Se, Te) units [kcalmol–1] at the
current DFT level.
RE(CH2)nNMe2
PhSe(CH2)2NMe2
PhSe(CH2)3NMe2
PhTe(CH2)3NMe2
o-tolTe(CH2)3NMe2
Monomer
Dimer
77.3 (2a-I)
does not form (2a-II)
79.4 (2d-I)
24.8 (2d-II)
77.0 (2e-I)
31.4 (2e-II)
22.7 (2e-III)
77.7 (2f-I)
28.4 (2f-II)
19.6 (2f-III)
mental values (Table 5). With the present rigid all-electron perimentally determined crystal structure of 2e-II, even
basis set applied for Pd and Te, these observed differences though 2e-II and 2e-III remain in a 1:1 ratio in solution as
in bond lengths are understandable. In a good comparison, determined by NMR spectroscopic data.
the monomer unit of the selenoether complex with three –
Excited-state calculations were also carried out to predict
CH2– groups (2d-I) is slightly more stable (2.1 kcalmol–1; UV/Vis absorption peaks of the four monomer units of Pd
Table 6) than the corresponding complex with two –CH2– complexes. The optical absorption peaks of 2a, 2d, 2e, and
groups (2a-I). The monomer units of telluroether complexes 2f are calculated at 382, 385, 386, and 395 nm, respectively,
that contain phenyl and o-tolyl have comparable stability. with low oscillator strength and are in close agreement with
The structure of the dimer unit of PdCl2 with PhSe(CH2)2- the observed band at 400–409 nm for the complexes of vari-
NMe2 (2a-II) could not be obtained on optimization, which ous groups. To find out the origin of these electronic transi-
might be due to the instability of the complex, thus firmly tion bands, calculated MOs of these complexes are also vis-
supporting the experimental data as observed in NMR ualized. Excited-state calculations based on time-dependent
spectra. All the monomers (2a-I, 2d-I, 2e-I, and 2f-I) are density functional theory suggest that the experimental op-
more stable than the corresponding dimers. The relative sta- tical absorption peak at 405 nm for complex 2a-I is due to
bility of the dimer unit of PdCl2 with PhSe(CH2)3NMe2 electronic transition from MO 97 (HOMO–2) to MO 100
(2d-II) relative to the monomer unit was calculated to be (LUMO). Figure 10 depicts the plot of the two MOs sug-
24.8 kcalmol–1.
gesting the charge-transfer transition predominantly from
metal bonding orbital (dxy) to antibonding (π*) orbital of
phenyl ring of the ligand (MLCT). The low molar extinc-
tion coefficient of only 1500 m–1 cm–1 points to a symmetry-
forbidden transition.
Figure 10. Plot of MOs 97 (HOMO–2) and 100 (LUMO) for the
palladium selenoether complex 2a-I with a contour cut off of
0.1 a.u. Plot of MO 97 indicates that the MO is contributed by
metal dxy orbital and lone pairs of two Cl atoms. Plot of MO 100
points out that it is constructed mainly by phenyl π* orbitals.
Figure 9. Optimized structures of monomer units of
[PdCl2{PhSe(CH2)2NMe2}] (2a) and monomer and dimer units of
[PdCl2{PhTe(CH2)3NMe2}] (2e) calculated by applying the density
functional theory and adopting all-electron basis functions.
Suzuki C–C Coupling Reactions
To assess whether the chalcogenoether complexes of pal-
ladium can be employed as the catalyst in C–C bond forma-
Minimum-energy dimeric structures of symmetric as well tion, their suitability as a catalyst in Suzuki C–C coupling
as asymmetric telluroether complexes from the correspond- reactions was studied. The reaction conditions were initially
ing monomer units (2e-I and 2f-I) are calculated (Figure 9 optimized with respect to solvent and base in the coupling
and Figure S17 in the Supporting Information). Symmetric of 4-iodotoluene with phenylboronic acid using 0.1 mol-%
dimeric structures (2e-II and 2f-II) are predicted to be more of [Pd(OAc)2(MesSeCH2CH2NMe2)] as
a
catalyst
stable by approximately 9 kcalmol–1 over asymmetric struc- (Tables S4–S6 in the Supporting Information). 1,4-Dioxane
tures (2e-III and 2f-III), which is in agreement with the ex- was the preferred solvent among the solvents DMF, tolu-
Eur. J. Inorg. Chem. 0000, 0–0
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Table 7. Suzuki C–C cross-coupling reaction.[a]
Entry
no.
R
X
Base
“Pd” complex
Yield[b]
[%]
TON
[mol-%]
1
2
3
4
5
6
7
8
4-CH3
4-CH3
4-CH3
4-CH3
4-CH3
2-CHO
2-CHO
4-NO2
4-CH3
2-CHO
4-CH3
4-CH3
2-CHO
I
I
I
I
Na2CO3
K2CO3
[PdCl2(PhSeCH2CH2NMe2)]
0.1
0.1
0.1
0.1
0.01
0.1
0.01
0.1
0.1
0.1
0.1
0.1
0.1
59
62
62
94
94
80
21
95
88
65
76
94
72
590
620
620
940
9400
800
2100
950
880
650
760
940
720
[PdCl2(MesSeCH2CH2NMe2)]
[PdCl2(PhSeCH2CH2CH2NMe2)]
[PdCl2(PhSeCH2CH2CH2NMe2)]
[PdCl2(PhSeCH2CH2CH2NMe2)]
[PdCl2(PhSeCH2CH2CH2NMe2)]
[PdCl2(PhSeCH2CH2CH2NMe2)]
[PdCl2(PhSeCH2CH2CH2NMe2)]
[PdCl2(PhTeCH2CH2CH2NMe2)]
[Pd(OAc)2(PhSeCH2CH2NMe2)]
[Pd(OAc)2(MesSeCH2CH2NMe2)]
[Pd(OAc)2(MesSeCH2CH2NMe2)]
[Pd(OAc)2(MesSeCH2CH2NMe2)]
Na2CO3
Bu4NOH
Bu4NOH
Bu4NOH
Bu4NOH
Bu4NOH
Na2CO3
K2CO3
I
Br
Br
Br
I
Br
I
9
10
11
[c]12
[c]13
K2CO3
Bu4NOH
Bu4NOH
I
Br
[a] Reaction conditions: aryl halide (1 mmol), phenylboronic acid (1.3 mmol), base (2 mmol), dioxane (2 mL). [b] Isolated yield. [c] When
refluxed in methanol the yields were 88% (entry 12) and 80% (entry 13).
ene, and methanol. The use of inorganic bases K2CO3 and crystallization only one form is preferentially crystallized
Na2CO3 led to the comparable yields (76%), whereas the out. DFT calculations support the existence of all the iso-
organic base Bu4NOH gave a higher yield (94%) of biaryls. meric forms. The observed coordination pattern of the lat-
By using the optimized conditions, the catalytic activity of ter ligand, a system comparable to R2PCH2CH2CH2PR2
the complexes was evaluated in the coupling reaction of aryl (dppp), is clearly distinct from chelating bis-phosphanes.
halides and phenylboronic acid (Table 7). Moderate to The flexibility of chalcogenoether ligands aids in improving
quantitative yields of desired products were obtained within the catalytic activity in C–C Suzuki coupling reactions.
six hours in the presence of 0.1 mol-% of Pd complexes in
cases of 4-iodotoluene and arylbromides activated by CHO
and NO2 groups. A comparative study on the complexes
showed that complexes of the acetato ligand (entries 2 and
Experimental Section
General Methods: All reactions were carried out in Schlenk flasks
under a nitrogen atmosphere. The compounds Me2NCH2CH2Cl·
HCl, Me2NCH2CH2CH2Cl·HCl, arylboronic acids, aryl halides,
and other reagents were procured from commercial sources. The
compounds Ph2Se2, Mes2Se2, Ph2Te2, o-tol2Te2, Mes2Te2, and
palladium precursors Na2PdCl4, [PdCl2(PhCN)2], and [Pd(OAc)2]3
(see references S1, S2, and S3, respectively, in the Supporting Infor-
mation) were prepared according to the literature methods.
11) performed better than the corresponding chloro ana-
logues. This is possibly due to the formation of more active
catalytic species in the case of the more labile acetato ligand
capable of facile ligand displacement during the catalysis
reaction.[17c] Enhancement of the catalytic activity was ob-
served on increasing the chain length from strongly chelat-
ing CH2CH2 to flexible CH2CH2CH2 in the ligand (entries
6 and 13). However, a significant improvement in activity
was noted on replacing selenium by tellurium (entries 3 and
9).
Melting points were determined in capillary tubes and are uncor-
rected. Elemental analyses were carried out on a Carlo–Erba EA-
1110 CHN-S instrument. 1H, 13C{1H}, 77Se{1H}, and 125Te{1H}
NMR spectra were recorded on a Bruker Ascend TM-400 NMR
spectrometer operating at 400, 100.61, 76.31, and 126.24 MHz,
respectively. Chemical shifts are relative to the internal chloroform
peak (δ = 7.26 ppm for 1H and δ = 77.0 ppm for 13C{1H}) and
external Ph2Se2 (δ = 463 ppm relative to Me2Se) for 77Se{1H} and
Ph2Te2 (δ = 421 ppm relative to Me2Te) for 125Te{1H}. TG curves
were obtained at a heating rate of 10 °Cmin–1 under flowing argon
on a Setaram Setsys evolution-1750 instrument.
Conclusion
A series of palladium complexes with dimethylamino-
alkyl chalcogenoether ligands have been isolated and char-
acterized. The color of these complexes arises from the
charge-transfer transition from the palladium dxy orbital to
the antibonding π* orbital of the aryl ring. The complexes
with the five-membered chelate ring formed by
Me2NCH2CH2ER exist exclusively in monomeric form
both in the solid state and in solution. The complexes de-
rived from ligands Me2NCH2CH2CH2ER, capable of form-
ing six-membered chelates, tend to exist both as monomeric
Preparation of Ligands: Synthesis of chalcogenoether ligands
(Scheme 1) PhSeCH2CH2NMe2 (1a),[37] MesSeCH2CH2NMe2 (1b)
(Mes
=
2,4,6-trimethylphenyl), MesTeCH2CH2NMe2 (1c),
PhSeCH2CH2CH2NMe2 (1d), MesSeCH2CH2CH2NMe2 (1e),
PhTeCH2CH2CH2NMe2 (1f), and o-tolTeCH2CH2CH2NMe2 (1g)
(o-tol = ortho-tolyl) together with their characterization data are
chelates and in two dimeric forms in solution and on given in the Supporting Information.
Eur. J. Inorg. Chem. 0000, 0–0
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Synthesis of Complexes
NMe2), 7.38–7.55 (m, 3 H, 3,4-H, Ph), 7.85–7.92, 7.92–7.98, 8.28–
8.38 (m, 2 H, 2-H, Ph) (in 64:23:13 ratio) ppm. 13C{1H} NMR
(CDCl3): δ = 25.3, 27.2, 27.5 (s, 7:2:1 ratio, –CH2–), 30.9, 31.7, 31.8
(s, in 6:2:1 ratio, SeCH2), 52.4, 53.9 (each s), 52.5, 52.6 (each s),
52.65, 52.70 (each s) (in 12:5:3 ratio, NMe2), 64.16, 64.20, 64.93 (s,
in 3:2:10 ratio, NCH2), 127.0, 127.3 (s, i to Se), 129.7, 129.9, 130.2
(s, in 1:2:7 ratio, m to Se), 130.1, 130.3, 130.6 (s, in 6:2:3 ratio, p to
Se), 132.55, 132.62, 133.22 (s, in 1:2:5 ratio, o to Se) ppm. 77Se{1H}
NMR (CDCl3): δ = 339, 344, 348 ppm (2:1:6 ratio).
[PdCl2(PhSeCH2CH2NMe2)] (2a): [PdCl2(PhCN)2] (152 mg,
0.396 mmol) in acetone (10 mL) was added to a solution of
PhSeCH2CH2NMe2 (203 mg, 0.891 mmol) in toluene (10 mL). The
red solution was stirred at room temperature for 4 h. The solvents
were removed under vacuum and the residue was washed thor-
oughly with diethyl ether followed by hexanes. The product was
extracted with dichloromethane (5ϫ10 mL), passed through Ce-
lite, concentrated to 15 mL, which on slow evaporation at room
temperature gave orange-red crystals of 2a (103 mg, 0.254 mmol,
64%), m.p. 200 °C (decomp.). C10H15Cl2NPdSe (405.50): calcd. C
29.62, H 3.73, N 3.45; found C 29.21, H 3.60, N 3.30. UV/Vis
(CH2Cl2): λmax (ε in m–1 cm–1) = 239 (40900), 316 (7300), 405 (1500)
[PdCl2(PhTeCH2CH2CH2NMe2)] (2e): Complex 2e was prepared
in a manner similar to that of 2a by using PhTeCH2CH2CH2NMe2
(298 mg, 1.024 mmol) in benzene/acetone (5 mL; 1:1 v/v) and
[PdCl2(PhCN)2] (350 mg, 0.912 mmol) in acetone (20 mL).
Recrystallization from dichloromethane yielded red crystals
of 2e (150 mg, 0.160 mmol, 35%), m.p. 120 °C (decomp.).
C11H17Cl2NPdTe (468.17): calcd. C 28.21, H 3.66, N 2.99; found
C 27.93, H 3.67, N 2.81. UV/Vis (MeOH): λmax (ε in m–1 cm–1) =
1
2
3
nm. H NMR (CDCl3): δ = 2.71, 3.18 (dt, JH,H = 13.2 Hz, JH,H
= 4 Hz, 2 H, AAЈBBЈ pattern, SeCH2), 2.88, 2.97 (each s, 6 H,
NMe2), 2.96, 3.35 (ddd, 2JH,H = 13.2 Hz, JH,H = 11.6 Hz, JH,H
=
3
3
3.6 Hz, 2 H, AAЈBBЈ pattern, NCH2), 7.46–7.55 (m, 3 H, Ph),
8.19–8.26 (m,
H, Ph) ppm. 77Se{1H} NMR ([D6]-
DMSO): δ = 474 ppm.
1
2
332 (5400), 405 (1600) nm. H NMR (CDCl3): δ = 2.13–2.61 (m,
2 H, –CH2–), 2.17, 2.46; 2.48, 2.57; 2.64, 2.69; 2.83, 3.04 (each s, 6
H, NMe2) (in 1:10:10:6 ratio), 2.61–3.79 (m, 4 H, TeCH2, NCH2),
7.32–7.49 (m, 3 H, 3,4-H, Ph), 7.89–7.99; 8.23–8.29 (m, 2 H, 2-H,
Ph) (in 7:2 ratio) ppm. 13C{1H} NMR (CDCl3): δ = 16.7, 17.8,
17.8 (s, in 1:2:2 ratio, –CH2–), 26.5, 27.5, 27.9 (s, in 1:2:2 ratio,
TeCH2), 50.4, 50.8; 51.4, 51.9; 52.6, 54.0 (s, in 2:2:1 ratio, NMe2),
64.16, 64.25, 68.61 (s, in 2:2:1 ratio, NCH2), 115.23, 115.29, 118.48,
(s, in 2:2:1 ratio, i to Te), 129.76, 129.88, 130.48 (s, in 2:2:1 m to
Te), 130.29, 130.37, 130.42 (s, in 1:2:2 ratio, 1 H, p to Te), 136.6,
136.9 (s, in 5:4 ratio, 2 H, o to Te) ppm. 125Te{1H} NMR (CDCl3):
δ = 607, 643, 680 (s, 1:2:2 ratio) ppm. A small peak (Ͻ5%) at δ =
566 ppm. TG: weight loss 40% corresponds to the formation of
Pd3Te2 (calcd. weight loss 40.8%).
[PdCl2(MesSeCH2CH2NMe2)] (2b): Complex 2b was prepared
similarly to that of 2a by using MesSeCH2CH2NMe2 (109 mg,
0.403 mmol) and [PdCl2(PhCN)2] (141 mg, 0.377 mmol) in di-
chloromethane (15 mL). Recrystallization from dichloromethane
yielded orange crystals of 2b (70 mg, 0.156 mmol, 43%), m.p.
195 °C (decomp.). C13H21Cl2NPdSe (447.58): calcd. C 34.88, H
4.73, N 3.13; found C 34.71, H 4.61, N 2.98. UV/Vis (CH2Cl2):
λmax (ε in m–1 cm–1) = 405 (1100), 313 (6960), 268 (13300), 237
(27100) nm. 1H NMR (CD2Cl2): δ = 2.30 (s, 3 H, 4-Me, Mes),
2.68–2.75 (m), 2.89–3.29 (br. m, 10 H, SeCH2CH2, 2,6-Me of Mes),
2.88, 2.89 (each s, 6 H, NMe2), 7.00 (s, 2 H, 3,5-H, Mes) ppm.
13C{1H} NMR (CD2Cl2): δ = 21.2 (s, 4-Me, Mes), 25.3 (br. s, 2,6-
1
Me, Mes), 30.8 (s, JSe,C = 47.5 Hz, SeCH2), 52.1, 53.1 (each s,
[PdCl2(o-tolTeCH2CH2CH2NMe2)] (2f): Complex 2f was prepared
in a way similar to complex 2e by using o-tolTeCH2CH2CH2NMe2
(177 mg, 0.576 mmol) in methanol (5 mL) and [PdCl2(PhCN)2]
(202 mg, 0.526 mmol) in benzene/acetone (20 mL). Red crystals
(107 mg, 0.222 mmol, 42%) were obtained by recrystallization from
dichloromethane, m.p. 136 °C (decomp.). C12H19Cl2NPdTe
(482.19): calcd. C 29.89, H 3.97, N 2.90; found C 29.23, H 3.72, N
2.71. UV/Vis (MeOH): λmax (ε in m–1 cm–1) = 328 (3800), 409 (1000)
nm. 1H NMR (CD2Cl2): δ = 2.24–2.49, 2.51–2.77, 2.83–3.12, 3.48–
3.76 (m, 6 H, TeCH2CH2CH2), 2.50, 2.56; 2.63, 2.66; 2.91, 2.95 (s,
6 H, 6:7:8 ratio, NMe2), 2.61, 2.62, 2.63 (s, 3 H, tolCH3), 7.21–7.49
NMe2), 67.8 (s, NCH2), 123.5 (s, 1-C, Mes), 131.3 (s, 3,5-C, Mes),
141.5 (s, 2,6-C, Mes), 142.4 (s, 4-C, Mes) ppm. 77Se{1H} NMR
(CD2Cl2): δ = 361 (s) ppm.
[PdCl2(MesTeCH2CH2NMe2)] (2c): Complex 2c was prepared in a
manner similar to that of 2b by using a methanolic solution (5 mL)
of MesTeCH2CH2NMe2 (99 mg, 0.310 mmol) and [PdCl2(PhCN)2]
(108 mg, 0.282 mmol) in benzene (20 mL). Recrystallization from
dichloromethane yielded orange crystals of 2c (70 mg, 0.141 mmol,
50%), m.p. 180 °C (decomp.). C13H21Cl2NPdTe (496.22): calcd. C
31.46, H 4.27, N 2.82; found C 31.88, H 4.13, N 2.60. 1H NMR
3
4
2
(m, 3 H, 3,4,5-H, Ph), 8.12; 8.20; 8.97 (dd, JH,H = 7.6 Hz, JH,H
= 1.2 Hz, 1 H, 7:8:9 ratio, 2-H, Ph) ppm. 13C{1H} NMR (CD2Cl2):
δ = 15.8, 17.0, 17.3 (s, 5:2:4 ratio, TeCH2), 26.03, 26.09, 26.87 (s,
2:2:3 ratio, tolCH3), 26.09, 27.87, 28.09 (s, 5:3:3 ratio, -CH2-), 50.9,
51.1; 51.6, 51.9; 52.9, 53.9 (s, 3:3:5 ratio, NMe2), 64.6, 64.7, 69.8
(s, 4:3:5 ratio, NCH2), 118.75, 118.83. 121.90 (s, 4:4:5 ratio, i to Te)
ppm. 125Te{1H} NMR (CD2Cl2): δ = 560, 572, 588 (ca. 1:1:1 ratio)
ppm. TG weight loss corresponds to the formation of Pd3Te2
(found 38; calcd. for Pd3Te2 39.7%).
(CD2Cl2): δ = 2.34 (s, 3 H, 4-Me, Mes), 2.48, 4.00 (ddd, JH,H
=
3
15.6, JH,H = 4.4 Hz, 2 H, AAЈBBЈ pattern, TeCH2), 2.85, 3.23
(ddd, 2JH,H = 13.4 Hz, 3JH,H = 4 Hz, 2 H, AAЈBBЈ pattern, NCH2),
2.85, 2.88 (each s, 6 H, NMe2), 3.04 (s, 6 H, 2,6-Me, Mes), 7.08 (2
H, 3,5-H, Mes) ppm. 13C{1H} NMR(CD2Cl2): δ = 12.1 (s, 4-Me,
Mes), 20.3 (s, 2,6-Me, Mes), 28.0 (s, TeCH2), 51.2 (s, NMe2), 70.5
(s, NCH2), 129.6 (s, 3,5-C, Mes), 142.7 (s, 2,6-C, Mes) ppm. An-
other peak corresponds to the NMe2 group merged with the sol-
vent peak. The peaks for 1-C and 4-C of Mes could not be detected
from spectral noise. 125Te{1H} NMR(CD2Cl2): δ = 643 (s) ppm.
[Pd(OAc)2(PhSeCH2CH2NMe2)] (3a): A solution of [Pd(OAc)2]3
[PdCl2(PhSeCH2CH2CH2NMe2)] (2d): Complex 2d was prepared (130 mg, 0.193 mmol) in toluene/acetone (25 mL, 3:2 v/v) was
similarly to 2a by using PhSeCH2CH2CH2NMe2 (147 mg,
0.607 mmol) and [PdCl2(PhCN)2] (210 mg, 0.548 mmol) in di-
added to a solution of Me2NCH2CH2SePh (263 mg, 1.150 mmol)
in toluene (5 mL). The contents were stirred at 60 °C for 4 h. The
chloromethane (20 mL). Recrystallization from dichloromethane solution was passed through a Florosil column to remove any insol-
yielded orange-red crystals of 2d (86 mg, 0.205 mmol, 37%), m.p.
140 °C (decomp.). C11H17Cl2NPdSe (419.53): calcd. C 31.49, H
uble solid particles. To the clear solution, a few drops of hexane
were added whereupon the title complex was precipitated. The lat-
4.08, N 3.34; found C 31.44, H 4.24, N 3.16. UV/Vis (CH2Cl2): ter was filtered, extracted with toluene (3ϫ10 mL), concentrated
λmax (ε in m–1 cm–1) = 240 (20200), 264 (16700), 306 (8300), 400
(1900) nm. H NMR (CDCl3): δ = 2.05–2.70, 2.89–3.48, 3.70–3.91
to 5 mL, and a few drops of diethyl ether were added and kept
overnight at –5 °C. The recrystallized product was thoroughly
1
(m, 6 H, SeCH2CH2CH2), 2.65, 2.66, 2.85, 3.01 (each s, 6 H, washed with diethyl ether and hexane, and was extracted with benz-
Eur. J. Inorg. Chem. 0000, 0–0
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ene (3ϫ10 mL), concentrated to 5 mL, and a few drops of hexane
(2ϫ10 mL), dried with anhydrous Na2SO4, filtered, and the sol-
were added and on cooling gave a sticky orange-red solid (107 mg,
vent was removed under reduced pressure. The residue was charac-
0.236 mmol, 32%). C14H21NO4PdSe (452.68): calcd. C 37.20, H terized by 1H and 13C{1H} NMR spectra. In the case of a poor
1
4.68, N 3.09; found C 37.81, H 4.98, N 2.87. H NMR (CDCl3): δ yield of the product or its contamination with other impurities, the
= 1.87 (s, 3 H, OAc, trans to N), 2.11 (s, 3 H, OAc, trans to Se),
product was subjected to chromatography on a silica-gel column.
2
3
2.42 (dt, JH,H = 13.2 Hz, JH,H = 4 Hz, AAЈBBЈ pattern, 2 H,
SeCH2, another peak of same pattern merged in the base of NMe2
peak at δ = 2.71 ppm), 2.55, 2.67; 2.61, 2.73; (s, 6 H, 1:7 ratio,
NMe2), 2.82 (ddd, 2JH,H = 13.2 Hz, 3JH,H = 11.8 Hz, 3JH,H = 4 Hz,
AAЈBBЈ pattern, 2 H, NCH2, another peak of same pattern merged
in the base of NMe2 peak at δ = 2.61 ppm) ppm; 13C{1H} NMR
(CDCl3): δ = 21.6 (s, COCH3, trans to N), 23.8 (s, COCH3, trans
to Se), 30.8 (s, 1JSe,C = 45.3 Hz, SeCH2), 31.3 (s, SeCH2) (6:1 ratio),
47.2, 49.8; 48.8, 51.1; 50.2, 52.1 (s, 1:5:34 ratio, NMe2), 64.9, 65.6
(s, 1:6 ratio, NCH2), 125.7 (s, i to Se), 128.6, 129.9, 130.0, 130.5,
130.9 (s, m and p to Se), 133.5, 133.9, 134.9 (s, in 37:6:1 ratio, o to
Se), 177.4 (s, –COCH3), 178.2 (br. s, –COCH3) ppm. 77Se{1H}
NMR (CDCl3): δ = 414, 426, 442 (each s, in ca. 5:1:28 ratio) ppm.
DFT Calculations: Full geometry optimization of Se and Te com-
plexes of palladium 2a, 2d, 2e, and 2f has been carried out by apply-
ing a DFT functional, namely, BP86. The BP86 is a generalized
gradient approximation (GGA) functional that combines Becke’s
1988 exchange functional with Perdew’s 1986 correlation func-
tional. Gaussian-type atomic basis functions, 6-31G(d,p) for H, C,
N, Cl, and Se atoms were considered for all the calculations. How-
ever, for Te and Pd atoms, all-electron basis sets 3-21G were applied
as more flexible all-electron basis functions are not available in the
literature for these two atoms. The quasi-Newton–Raphson-based
algorithm was applied to carry out geometry optimization to locate
the minimum energy structure in each case. All these calculations
were carried out by applying GAMESS suit of ab initio pro-
grams.[38]
[Pd(OAc)2(MesSeCH2CH2NMe2)] (3b): A solution of [Pd(OAc)2]3
(140 mg, 0.208 mmol) in toluene/acetone (25 mL, 3:2 v/v) was
added to a solution of MesSeCH2CH2NMe2 (178 mg, 0.659 mmol)
in toluene (5 mL). The yellow precipitate was heated at 65 °C for
1 h. After allowing it to cool to room temperature, solvents were
removed under vacuum, washed thoroughly with hexane and di-
ethyl ether, extracted with toluene (8ϫ10 mL), concentrated to
30 mL and which on slow evaporation at room temperature gave
pale yellow crystals of 3b (100 mg, 0.202 mmol, 32%), m.p. 165 °C
(decomp.). C17H27NO4PdSe (494.76): calcd. C 41.27, H 5.50, N
2.83; found C 41.46, H 5.40, N 2.67. UV/Vis (CH2Cl2): λmax (ε in
CCDC-1010153 (for 2a·0.5CH2Cl2), 1010154 (for 2b), 1010155 (for
2d), 1010156 (for 2e), 1010157 (for 2f), 1010158 (for 3b·1.5H2O), and
-1010159 (for 3b) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
Supporting Information (see footnote on the first page of this arti-
cle): It contains details of general procedures of the experiments;
crystallographic and structure-refinement data of all complexes;
optimization of reaction parameters of Suzuki reactions; NMR
spectra; ORTEP diagrams; optimized structures calculated by ap-
plying DFT; and single-crystal X-ray diffraction studies.
m
–1 cm–1) = 268 (13300), 311 (7310), 402 (1640) nm. IR (KBr): ν =
˜
1594, 1618 cm–1. H NMR (CDCl3): δ = 1.76 (s, 3 H, OAc, trans
to N), 2.09 (s, 3 H, OAc, trans to Se), 2.26 (s, 3 H, 4-Me, Mes),
2.33–2.42, 2.59–2.80 (m, 4 H, SeCH2CH2), 2.69, 2.71 (each s, 6 H,
NMe2), 2.97–3.28 (br., 6 H, 2,6-Me, Mes), 6.95 (s, 2 H, 3,5-H, Mes)
ppm. 13C{1H} NMR (CDCl3): δ = 21.0 (s, 4-Me, Mes), 21.5 (s,
COCH3, trans to N), 23.8 (br. s, 2,6-Me, Mes), 24.6 (s, COCH3,
1
Acknowledgments
1
trans to Se), 29.64 (s, JSe,C = 42.4 Hz, SeCH2), 51.4, 51.6 (each s,
One of the authors (D. K. P.) is thankful to the Department of
Atomic Energy (DAE) for the award of a Senior Research Fellow-
ship (SRF).
NMe2), 66.3 (s, NCH2), 126.4 (s, 1-C, Mes), 130.6 (s, 3,5-C, Mes),
140.1 (s, 2,6-C, Mes), 140.6 (s, 4-Me, Mes), 177.7 (s,
-COCH3), 178.4 (br. s, -COCH3) ppm. 77Se{1H} NMR (CDCl3): δ
= 339, 345, 361 (each s, in ca. 1:10:2 ratio) ppm.
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Coupling Reaction
General Procedure for Suzuki Cross-Coupling Reaction of Aryl Hal-
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dioxane (3 mL), aryl halide (1.0 mmol), arylboronic acid
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Received: October 1, 2014
Published Online: ᭿
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FULL PAPER
Seleno- and Telluroether as Ligands
D. K. Paluru, S. Dey,* A. Wadawale,
D. K. Maity, N. Bhuvanesh,
V. K. Jain* ...................................... 1–12
Structural Variation in [PdX2{RE(CH2)
nNMe2}] (E = Se, Te; X = Cl, OAc) Com-
plexes: Experimental Results, Compu-
tational Analysis, and Catalytic Activity in
Suzuki Coupling Reactions
Keywords: Palladium / Cross-coupling / C–
C coupling / Chalcogens / Density func-
tional calculations
Complexes [PdX2{RE(CH2)nNMe2}]m (X
= Cl, OAc) exist in one monomeric and two
dimeric forms in solution depending on E
and n. Molecular structures were estab-
lished by X-ray structural analyses and
supported by DFT calculations. These
complexes act as catalyst in Suzuki cou-
pling reactions.
Eur. J. Inorg. Chem. 0000, 0–0
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim