Synthesis, characterization and coordination properties of bis(alkyl)selenosalen ligands

Article abstract of DOI:10.1039/c1dt10114e

New bis (alkyl) selenosalen podand ligands having Se2N2 donor sites have been synthesized by the condensation of unsymmetrical o-formylphenyl alkyl selenide (1-3) with ethylenediamine. The reaction of bis(alkyl)selenosalen podands with Pd(II) and Pt(II) afforded selenoether-selenolate coordination complexes 7-10via cleavage of one of the two Se-C(alkyl) bonds of bis(alkyl)selenosalen podands upon complexation. DFT calculations revealed that the cleavage of Se-C(alkyl) bonds occurred possibly via S_N2 mechanism instead of a sequence of oxidative addition and reductive elimination reactions. The spectral data and elemental analyses confirmed the formation of selenoether-selenolate complexes. The structures of the podands N,N′-bis[(2-methylseleno)phenylmethylene]-1,2-ethanediamine (4), N,N′-bis[(2-decylseleno)phenylmethylene]-1,2-ethanediamine (5) and the selenoether-selenolate complex 8 have been determined by single crystal X-ray diffraction analysis. The crystal structure of 5 showed Se...H interaction with a ladder like 3D supramolecular arrangement via interdigitation of long alkyl chains. Comparison of crystal packing of podands 4 and 5 indicates that the alkyl chain length has significant impact on the crystal packing. The platinum selenolate complex 8 shows a square planar arrangement around the Pt centre, where the Se atoms in the selenolate and the selenoether have nearly equal Pt-Se bond length.

Full text of DOI:10.1039/c1dt10114e

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PAPER
Synthesis, characterization and coordination properties of
bis(alkyl)selenosalen ligands†
Snigdha Panda,* G. Rama Krishna, C. Malla Reddy and Sanjio S. Zade*
Received 20th January 2011, Accepted 11th April 2011
DOI: 10.1039/c1dt10114e
New bis (alkyl) selenosalen podand ligands having Se2N2 donor sites have been synthesized by the
condensation of unsymmetrical o-formylphenyl alkyl selenide (1–3) with ethylenediamine. The reaction
of bis(alkyl)selenosalen podands with Pd(II) and Pt(II) afforded selenoether-selenolate coordination
complexes 7–10 via cleavage of one of the two Se–C(alkyl) bonds of bis(alkyl)selenosalen podands upon
complexation. DFT calculations revealed that the cleavage of Se–C(alkyl) bonds occurred possibly via
SN2 mechanism instead of a sequence of oxidative addition and reductive elimination reactions. The
spectral data and elemental analyses confirmed the formation of selenoether-selenolate complexes. The
structures of the podands N,N¢-bis[(2-methylseleno)phenylmethylene]-1,2-ethanediamine (4),
N,N¢-bis[(2-decylseleno)phenylmethylene]-1,2-ethanediamine (5) and the selenoether-selenolate
complex 8 have been determined by single crystal X-ray diffraction analysis. The crystal structure of 5
showed Se ◊ ◊ ◊ H interaction with a ladder like 3D supramolecular arrangement via interdigitation of
long alkyl chains. Comparison of crystal packing of podands 4 and 5 indicates that the alkyl chain
length has significant impact on the crystal packing. The platinum selenolate complex 8 shows a square
planar arrangement around the Pt centre, where the Se atoms in the selenolate and the selenoether have
nearly equal Pt–Se bond length.
complexation to HgCl2 the salen ligand afforded a monomer
Introduction
complex with four-coordinated mercury(II) having coordina-
tion with two chlorine and two tellurium atoms in the form
of telluroether. The macrocyclic ligands having Se/N donor
sites are well studied and showed some interesting properties.4
Despite the growing number of selenium containing ligands,5
there is hardly any report on acyclic selenosalen ligands to our
knowledge.
Acyclic podands have certain advantages over their cyclic ana-
logues, such as their facile synthesis, which does not require high
dilution techniques or use of a template. Moreover, complexation
and decomplexation processes are generally faster in the acyclic
systems and the pseudo-cavity formation by podand type ligands
usually has greater conformational flexibility. Among the various
acyclic podands, salen ligands are quite interesting. They are
comprised of a potentially tetradentate N2O2 donor sites usually
obtained by the condensation of amines and aldehydes.1 The
importance of salen ligands in homogeneous catalysis and organic
synthesis has unambiguously been demonstrated over the last
two decades.2 In addition incorporation of selenium/tellurium to
the salen framework would influence the complexation properties
of these ligands due to the large covalent radius and greater
polarizability of selenium/tellurium compared to oxygen and
sulfur. McWhinnie et al.3 reported synthesis and complexation
of dialkyltellurasalen ligand having N2Te2 donor sites. Upon
The cleavage of the C–Se bond has interest in organic syn-
thesis such as for synthesis of functionalized vinylchalcogenides.6
However, most of the literature reports indicate that the C–Se
bond cleavage occurred by Pd(0) and Pt(0).7,8 In fact only very
few reports on the cleavage of Se–C bond by Pt(II) and Pd(II) are
found in the literature. The cleavage of the C–Se bond generally
occurs by oxidative addition7 as well as by the nucleophilic
substitution of the incoming nucleophile at C of Se–C(alkyl).8
Though macrocyclic selenosalen ligands are known, complexation
to Pd(II) and Pt(II) does not lead to any systematic cleavage of the
Se–C bond, but rather results in the hydrolyzed product9 and Pt(IV)
metallamacrocycle7b (in the case of macrocyclic salan type ligand).
In this article we report the synthesis of bis(alkyl)selenosalen
podand ligands with varying alkyl chain length attached to the
Se atoms. Upon reaction of these podands with Pd(II) and Pt(II) a
systematic cleavage of one of the Se–C(alky) bonds, resulting in the
first selenolate-selenoether complexes is observed. This Se–C(alkyl
chain) bonds cleavage is attributed to occur via nucleophilic
substitution, which is supported by the DFT calculations.
Department of Chemical Sciences, Indian Institute of Science Education
and Research, Kolkata, PO: BCKV campus main office, Mohanpur,
741252, Nadia, West Bengal, India. E-mail: snigdha@iiserkol.ac.in, san-
jiozade@iiserkol.ac.in; Fax: +91-33-25873020
† Electronic supplementary information (ESI) available: ORTEP diagrams
of 4 and 5, calculated absolute energies and coordinates of the optimized
geometries for DFT calculation. CCDC reference numbers 808493–
808495. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c1dt10114e
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◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for 4 and 5
Results and discussion
Synthesis of ligands
4
5
The unsymmetrical10 monoselenides 1–3 were obtained by the
reaction of bis(o-formylphenyl)diselenide with NaBH4 followed by
the addition of methyl iodide, decyl bromide and dodecyl bromide,
respectively.11 The bis(o-formylphenyl)diselenide was prepared
from o-chlorobenzaldehyde following the reported procedure.12
The compounds 1–3 were obtained as viscous liquids at ambient
Se(1)–C(8)
Se(1)–C(9)
N(1)–C(2)
N(1)–C(1)
Se1 ◊ ◊ ◊ N1
C8–Se1–C9
1.907(3)
1.951(4)
1.252(4)
1.464(5)
2.803(3)
99.74(14)
1.918(2)
1.966(2)
1.270(3)
1.461(3)
2.7949(16)
100.51(8)
1
temperature. The H NMR results suggests no significant shift
for the formyl peaks of selenides 1–3 compared to the precursor
diselenides. In the 77Se NMR spectra the aldehyde precursor
showed peak at d ~309 ppm, whereas, the precursor diselenide
has a signal at d 478 ppm.12b The FT-IR analysis shows that the
n(C frequency for the 1–3 were observed at 1690 cm-1.
O)
The bis(alkyl)selenosalen podands 4–6 were obtained by the
condensation of ethylenediamine with aldehydes 1–3, respectively
(Scheme 1). The amount of solvent used in the reactions is
significantly less than that required for the preparation of the
related macrocycle.9 Podands 4–6 were obtained as white solids
and further recrystallized from CHCl3/CH3CN. The vibrational
frequencies for C N bond (n(C N)) of the podands 4–6 were
observed at 1640–1650 cm-1. The Schiff-base podands 4–6 showed
a singlet at d ~ 8.7 ppm for azomethine protons in 1H NMR spec-
trum. The 77Se NMR spectra of podands 4–6 (d ~268 ppm) showed
an upfield shift compared to that of related precursor selenides 1–
3, respectively. The podands 4–6 showed the molecular ion peaks
[M+] at 421.80, 674.50 and 730.45, respectively, as expected in the
ESI-MS spectra. Furthermore, the mass spectra clearly exhibit the
expected isotopic distribution pattern as expected for the selenium
containing compound.
Fig. 1 Crystal packing in podand 5 to show the 1-D supramolecular
ladder network formed via weak C–H ◊ ◊ ◊ Se contacts and close packing of
alkyl chains from the adjacent ladders.
In the crystal structure of compound 5, the molecules form a
supramolecular 1-D ladder network13 along the [110] plane via
C–H ◊ ◊ ◊ Se14 contacts by the aromatic ring C–H group and Se of
the adjacent translation related molecule (Fig. 1). The C–H ◊ ◊ ◊ Se
◦
˚
(d = 3.032 A; q = 135.16 ) distance is within the van der Waals
limit. The alkyl chains interdigitation in combination with C–
H ◊ ◊ ◊ Se contacts lead to the formation of a corrugated 2-D sheet
structure as shown in Fig. 1. In the third dimension, the ladders
are stacked down along the [100] direction to enhance the p ◊ ◊ ◊ p
interactions in the structure. Crystal packing has two regions; first
with decyl chain interdigitation (each chain surrounded by six
other alkyl chains) and second, the selenosalen unit (held together
with Se ◊ ◊ ◊ H and p ◊ ◊ ◊ p interactions). The structure in compound
4 (Figure S1a†) has the similar supramolecular arrangement, but
the interdigitation of alkyl chains is missing due to its shorter
length, but the methyl groups from the adjacent molecules close
pack in a similar manner.
Structures of 4 and 5
The molecular structures of compounds 4 and 5 are closely related,
however, their crystal packing is different due to the change in
the length of alkyl chain (Fig. 1 and S1†). Both the compounds
¯
crystallize in the triclinic space group P1 with one molecule in
the unit cell. The selected bond lengths and bond angles are
given in Table 1. The molecule 4 lies across the crystallographic
inversion centre in that it adapts E-configuration. The imine
groups are coplanar with the aromatic rings however, trans to
each other across the inversion centre. The intramolecular Se ◊ ◊ ◊ N
Complexation of 4–6 with Pd(II) and Pt(II)
The selenosalen ligands were further studied for their coordi-
nation properties towards Ni(II), Pd(II) and Pt(II). Reaction of
the podands 4–6 with Pd(C6H5CN)2Cl2 and PtCl2, in refluxing
methanol led to the formation of the complexes 7–10. However,
under similar reaction conditions the selenosalen ligands 4 and
5 do not coordinate to Ni(II) (metal source is NiCl2). Although
˚
(2.803(3) A) distance is significantly shorter than the sum of van
˚
˚
der Waals radii of Se (1.99 A) and N (1.53 A) atoms indicating
its considerable influence on the molecular conformation. The
Se ◊ ◊ ◊ N distance and C–Se–C angle (~ 100◦) in 4 are comparable
to that found in the related Schiff base macrocycle.9
Scheme 1 Synthesis of podand ligands 4–6 and complexes 7–10.
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many Ni(II) complexes of similar thiasalen ligands15 are known
in the literature, we observed that selenosalen ligands 4 and 5 do
not form complexes with Ni(II), whereas macrocyclic selenosalen
ligands does.9 This behavior of Ni(II) may be attributed to the
hard nature of Ni(II) and more affinity of the Ni(II) to form a
hexa-coordinate complex.5c
m/z = 512.90 [C17H17N2PdSe2] and 640.60 [C26H35N2PdSe2] which
can be assigned to [M+-PF6].
DFT calculation
Nucleophilic substitution reaction is known for the
thioether/selenoether ligands at Pd(II).8 Although there are
few of examples of oxidative addition of Pt(II) to a Se–C bond,
similar reports with Pd(II) complexes is not known. There are
two possibilities of the mechanistic pathway for the cleavage of
an alkyl group: (i) oxidative addition of Pd(II) to the Se–C(alkyl)
bond followed by reductive elimination of alkyl halide and (ii)
SN2 substitution at methyl group by halide ion where selenolate
complex act as leaving group to eliminate alkyl halide. In our
study, we have not observed the formation of alkenes as in the
case of de-t-butylation of di-t-butylthiosalen ligands.17 In case
of reaction of 5 and 6 with Pd(II)/Pt(II), we have isolated and
characterized decyl chloride and dodecyl chloride as a by-product,
respectively. We have explored both the possibility using DFT
calculations (see theoretical methods) for the formation of
complex 7·Cl. We presume the formation of complexes 11 and 12
as starting materials for the SN2 and oxidative addition/reductive
elimination pathways, respectively (Fig. 2). In complex 12, the
bis(methyl)selenosalen podand acts as a tetradentate ligand
(N2Se2), while in complex 11, it acts as a tridentate ligand
(N2Se) (by swapping one of the Se coordinating sites of the
bis(alkyl)selenosalen ligand with a chloride ligand). Calculation
indicates that the complex 12 is more stable by 5.0 kcal mol-1 than
complex 11. In SN2 reaction Pd(II) complex 7 acts as a leaving
group although generally, Pd(II) complexes are poorer leaving
group than that of Pd(0). That may be the reason that we have
not observed bisdealkylation of bis(alkyl)selenosalen ligand upon
complexation to Pd(II) and Pt(II). Whereas, oxidative addition of a
Pd(II) square planar complex to a Se–C(Me) bond converts it into
a Pd(IV) octahedral complex which further reductively eliminates
methyl chloride to afford Pd(II) complex 7·Cl. The activation
energy for SN2 type reaction is only 21.1 kcal mol-1, while, the
activation energies for the sequence of oxidative addition and
reductive elimination are 47.2 and 31.1 kcal mol-1, respectively.
Thus, DFT calculation suggests a SN2 reaction is more likely
the reaction pathway for the dealkylation of selenoether upon
complexation to Pd(II) and Pt(II).
The spectroscopic and elemental analyses of the complexes
imply the reduction or brake-down of symmetry of the complexes
compared to the parent ligands. For example, each carbon atom
of the complexes gives a separate signal in the 13C NMR spectra
1
and the H-NMR integration indicated the cleavage of one of
the alkyl chains. Additionally, the formation of the corresponding
alkyl halides was also observed in the residual filtrate. For all the
complexes, mass spectra showed the expected molecular ion peak
with correct isotopic pattern. De-t-butylation at both thioether
sulfurs was observed for di-t-butylthiosalen upon complexation
to Ni(II)16 and Cu(II) (where isobutene was obtained as a by-
product).17
Reaction of 4–5 with Pd(II)
Reaction of 4 and 5 with Pd(C6H5CN)2Cl2 in refluxing methanol
led to the formation of a deep brown color solution, which was
precipitated by the addition of NH4PF6. The complexes were
soluble in CH3CN, DMSO and acetone, however insoluble in
chlorinated solvents. The NMR spectroscopic studies show the
formation of selenolate-selenoether complexes via cleavage of one
of the alkyl chains. Reid et al. reported a similar type of Se–C
bond cleavage upon complexation to the metal ion.18 The cleavage
of the C–Se bond is more facile in podands compared to that
of the related macrocyclic Pd complexes,9 where either hydrolysis
of the C N bond occurred or a square planar macrocycle-Pd
complex was obtained. C(sp2)–Se bond activation by Pt(0) leading
to breakage of the terminal C–Se bond has been reported,19 which
occurred via an oxidative addition pathway. Here the cleavage of
the C(sp3)–Se bond rather than the C(sp2)–Se bond has occurred
via a nucleophilic substitution process which is supported by the
DFT calculation. The FT-IR spectrum of 9 indicates the presence
of PF6 counter ion {837 [n(P–F)], 557 [d(F–P–F)] cm-1}. In
-
addition the spectrum displays the characteristic n(C
stretching
N)
frequency around 1624 cm-1, which is shifted to lower value
compared with the n(C
stretching frequencies of 1647 cm-1 for
N)
the free ligands 5. The 1H NMR spectrum of the complex 7 showed
two closely spaced peaks at d 8.66 and 8.67 ppm and that of 9
showed two closely spaced singlets at d 8.69 ppm for two types
of azomethine protons. The peak at d 2.68 ppm corresponds to
Se–Me fragment in 7 (d 2.20 ppm for the precursor ligand 1,
methyl protons). For complex 9 multiplets at d 3.10–3.22 ppm
corresponds to the two protons of SeCH2 which were downfield
shifted with respect to the ligand (d 2.75 ppm) indicating that the
Se is strongly coordinating to the Pd(II) ion. The cleavage of alkyl
chain is further proved by 77Se NMR spectra, where one of the Se
atoms is covalently linked to the Pd(II) in complex 9 (d 352 ppm),
whereas the other one co-ordinates to Pd(II) as a selenoether (d
312 ppm). The observed downfield shift with respect to the peak
of the ligand in the 77Se NMR spectrum (d 268 ppm), further
indicates that both the Se atoms are co-ordinated to the Pd(II)
ion. The molecular ion peaks for 7 and 9 were not observed in
the ESI-MS spectra. The base peaks for 7 and 9 were observed at
Reaction of 4 and 6 with Pt(II)
Reaction of PtCl2 with 4 and 6 in refluxing methanol afforded
an orange colored solution. Addition of NH4PF6 led to an orange
colored precipitate. The complexes 8 and 10 are soluble in CH3CN,
DMSO and acetone, however insoluble in chlorinated solvents.
The 77Se NMR spectrum of 10 showed two peaks at d 264 and
279 ppm. The results from the spectroscopic analysis of Pt(II)
complexes 8 and 10 closely resemble with that of related Pd(II)
complexes 7 and 9.
Crystal Structure of 8
The selenolate complex crystallized in the monoclinic space group
P21/n. The crystal structure shows the square planar geometry
around the Pt(II) centre (Fig. 3). The crystal structure showed the
cleavage of one of the Se2–C bonds leading to the formation of
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Fig. 2 Calculated energy profile for SN2 and oxidative addition/reductive elimination pathways of dealkylation reaction upon complexation to Pd(II)
with 4 to afford complex 7·Cl. The energy of complex 7·Cl was considered as a reference point.
◦
˚
˚
˚
Table 2 Selected bond lengths (A) and angles ( ) for 8
A, van der Waal radii 3.3 A) are nearly same and the two Pt– N
˚
bond distances are 2.040(4) and 2.018(4) A (sum of the covalent
Pt1–Se1
Pt1–Se2
Pt1–N1
Pt1–N2
Se1–C1
Se2–C17
2.3636(6)
2.3583(6)
2.040(4)
2.018(4)
1.953(7)
1.886(5)
Se1–Pt1–Se2
Se1–Pt1–N1
Pt1–Se1–C1
N1–Pt1–N2
Se2–Pt1–N2
N1–Pt1–N2
86.48(2)
95.04(13)
103.7(2)
83.52(17)
95.00(11)
83.52(17)
˚
˚
radii 2.05 A, van der Waal radii 2.84 A). The geometry around
the selenolate Se2 is ‘V-shaped’ while that of the selenoether Se1
is pyramidal.
Conclusion
a selenoether-selenolate complex. The distances between the two
A series of bis(alkyl)selenosalen podand ligands having Se2N2
donor sites have been synthesized. The crystal structure of 5 shows
Se ◊ ◊ ◊ H interaction resulting in the ladder like supramolecular
˚
Pt–Se bonds (selenolate (Pt1–Se2), 2.3583(6) A and selenoether
˚
(Pt1–Se1), 2.3636(6) A, Table 2) (sum of the covalent radii 2.46
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used for column chromatography. The mass spectra were recorded
on a MICROMAX Q-TOF-MICRO instrument. Melting points
are reported uncorrected.
Synthesis of ligands
The compounds 1–3 were synthesized according to the reported
procedure.11
N,N¢-Bis[(2-methylseleno)-phenylmethylene]-1,2-ethanediamine
(4). A solution of ethylenediamine (0.017 g, 0.28 mmol) in
acetonitrile (10 mL) was added to a stirred solution of compound
1 (0.2 g, 0.5 mmol) in acetonitrile. The mixture was stirred
overnight and the precipitated white powder was filtered off,
washed with acetonitrile. Evaporation of the filtrate to 2 mL
afforded more crystalline compound. The mother liquor was
decanted and the crystalline compound was washed with
acetonitrile. The NMR on both the fractions showed the presence
of same compound. Yield: 0.2 g (60%). mp 115-116 ◦C; Anal.
Calcd (%) for C18H20N2Se2: C, 51.20; H, 4.77; N, 6.63. Found: C,
50.80; H, 4.50; N, 6.52. IR nmax (KBr, cm-1): 1645 (C N), 1560.
1H NMR (CDCl3): d 2.20 (s, 6H), 4.00 (s, 4H), 7.20–7.80 (m, 8H),
8.60 (s, 2H). 13C NMR (CDCl3): d 7.2, 61.6, 125.1, 128.9, 130.1,
130.9, 135.0, 135.1, 162.5. 77Se NMR (CDCl3): d 268 (s). ESI-MS:
+
421.80 (C18H20N2Se2 , 422.28).
Compounds 5–6 were analogously prepared starting from the
appropriate unsymmetrical monoselenides and amine.
-
N,N¢-Bis[(2-decylseleno)-phenylmethylene]-1,2-ethanediamine
(5). Yield: 0.18 g (43%). mp 58.3 ◦C; Anal. Calcd (%) for
C36H56N2Se2: C, 64.08; H, 8.37; N, 4.15. Found: C, 63.87; H, 8.30;
Fig. 3 ORTEP diagram of complex 8 (PF6 counteranion is omitted for
clarity). Thermal ellipsoids are drawn at 50% probability.
arrangement via interdigitation of long alkyl chains. Comparison
of crystal packing of podand 4 and 5 clearly indicates that
the alkyl chain length has played a significant impact on the
crystal packing. The reaction of bis(alkyl)selenosalen podands
with Pd(II) and Pt(II) results in the formation of selenoether-
selenolate coordination complexes 7–10 via cleavage of one of
the two Se–C(alkyl) bonds of bis(alkyl)selenosalen podands. The
plausible mechanism of cleavage Se–C bond has been studied by
DFT calculations, which revealed that the cleavage of Se–C(alkyl)
bonds occurred possibly via SN2 mechanism instead of sequence
of oxidative addition and reductive elimination reactions. Further
study on these selenosalen ligands are going on in our lab.
1
N, 4.61. H NMR (CDCl3): d 0.89 (t, 6H, CH3, J = 7 Hz), 1.25
(m, 24H), 1.33 (m, 4H), 1.63 (m, 4H), 2.70 (t, 4H, SeCH2, J =
9.5 Hz), 4.04 (s, 4H, NCH2CH2N), 7.21–7.77 (m, 8H, ArH), 8.71
(s, 2H, CH N). 13C NMR (CDCl3) d (ppm): 14.1, 22.6, 27.8, 28.0,
29.1, 29.3, 29.4, 29.5, 29.9, 31.8, 61.6, 126.2, 129.5, 130.1, 132.0,
133.6, 136.4, 162.8. 77Se NMR: d 268 (s). IR nmax (KBr, cm-1):
1647 (C N), 1560. ESI-MS: m/z 674.49 (M+, 674.76), 365.14
(C19H29N2Se+, 364.40), 325.72 (C17H26NSe+, 324.42).
N,N¢-Bis[(2-dodecylseleno)-phenylmethylene]-1,2-ethanediamine
(6). Yield: 0.19 g (43%). mp 62.5 ◦C. Anal. Calcd (%) for
C40H64N2Se2: C, 65.73; H, 8.83; N, 3.83. Found: C, 66.08; H, 8.73;
N, 4.67. 1HNMR (CDCl3): d 0.90 (t, 6H, CH3, J = 6.7 Hz), 1.25
(m, 28H), 1.33(m, 4H), 1.56 (m, 4H), 1.63 (m, 4H), 2.70 (t, 4H,
SeCH2, J = 7.4 Hz), 4.04 (s, 4H, NCH2CH2N), 7.21–7.77 (m, 8H,
ArH), 8.71 (s, 2H, CH N). 13C NMR (CDCl3): d 14.1, 22.7,
25.8, 26.3, 29.0, 29.1, 29.3, 29.5, 29.6, 29.6, 30.1, 31.9, 61.7, 125.5,
126.3, 129.6, 134.0, 134.9, 137.8, 162.5.77Se NMR (CDCl3): d 268
(s). IR nmax (KBr, cm-1): 1647 (C N), 1565. ESI-MS: m/z 730.54
(M+, 732.34), 396.73 (C21H34N2Se+, 394.18), 351.76 (C19H29NSe+,
350.39).
Experimental Section
All reagents were purchased from Aldrich/Merck and used
without further purification. AR (analytical reagent) grade THF
was passed through alumina to remove hydrogen peroxide and
for partial drying and kept over the molecular sieves. AR grade
acetonitrile was distilled from P2O5 and kept over molecular sieves.
UV-Vis spectra were recorded on a Hitachi U4100 spectropho-
tometer, with a quartz cuvette (path length, 1 cm). H and 13C
1
NMR spectra were recorded on a Bruker 500 MHz and 77Se NMR
spectra on JEOL-FT NMR-AL 400 MHz spectrophotometer
using CDCl3/CD3CN as solvent and tetramethylsilane (SiMe4)
as internal standard. Data are reported as follows: chemical shifts
in ppm (d). UV-vis studies were performed in dry acetonitrile. IR
spectra of the compounds have been recorded on a Perkin-Elmer
spectrophotometer as KBr pellets. Silica gel (60–120 mesh) was
General methodology for the preparation of complexes
A mixture of the appropriate ligand and Pd(C6H5CN)2Cl2/PtCl2
(in methanol and in equimolar amounts) was stirred for 2 h at
reflux temperature. The reaction mixture was filtered and to the
filtrate NH4PF6 was added. The product was precipitated, filtered
off and dried under vacuum.
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7. Yield: 0.07 g (45%). mp 78 ◦C (d). Anal. Calcd (%) for
C17H17F6N2PPdSe2: C, 31.00; H, 2.60; N, 4.25. Found: C, 31.07; H,
2.52; N, 4.01. 1HNMR (CD3CN): d 2.68 (s, 3H, SeCH3), 4.06 (m,
4H, NCH2CH2N), 7.40–8.00 (8H, Ar-H), 8.66 (s, 1H, CH N),
8.67 (s, 1H, CH N). 13C NMR (CD3CN): d 22.3, 63.9, 64.0,
118.2, 119.6, 125.8, 132.6, 132.8, 133.6, 134.0, 135.0, 135.5, 136.3,
139.5, 139.6, 136.8, 166.2. ESI-MS: m/z 512.90 (C17H17N2PdSe2,
513.67).
Table 3 Crystallographic data and structure refinement parameters for
compounds 4, 5 and 8
Compound
Formula
4
5
8
C18 H20 N2 Se2 C36 H56 N2 Se2 C17 H17 F6 N2 P Pt Se2
Crystal system Triclinic
Triclinic
P1
Monoclinic
P21/n
¯
¯
Space group
P1
˚
a/A
4.9264(3)
7.4097(4)
12.3868(7)
76.344(4)
88.234(4)
79.904(3)
432.55(4)
0.71073
1
4.8148(2)
7.2403(2)
24.6213(8)
96.012(2)
91.398(2)
98.086(2)
844.44(5)
0.71073
1
1.327
354
2.215
2.50–36.87
-6 £ h £ 6
-9 £ k £ 9
-31 £ l £ 30
100(2)
0.0285
0.0881
14.6757(5)
8.3057(3)
17.3588(6)
90
97.908(2)
90
2095.78(13)
0.71073
4
2.368
1392
10.303
2.37–26.33
-18 £ h £ 18
-10 £ k £ 10
-21 £ l £ 22
296(2)
0.0250
0.0794
˚
b/A
8. Yield: 0.09 g (50%). mp 208 ◦C. Anal. Calcd (%) for
C17H17F6N2PPtSe2: C, 27.32; H, 2.29; N, 3.75. Found: C, 27.07;
H, 2.49; N, 3.68. 1H NMR (CD3CN): d 2.68 (s, 3H, SeCH3), 4.10–
4.20 (m, 4H, NCH2CH2N), 7.30–8.10 (m, 8H, Ar-H), 8.97 (s, 1H,
CH N), 8.98 (s, 1H, CH N). 13C NMR (CD3CN): 24.9, 64.6,
65.7, 117.2, 125.9, 131.2, 132.9, 133.2, 133.6, 134.0, 135.0, 135.3,
136.5, 139.0, 139.5, 160.9, 162.9. ESI-MS: m/z 602.85 (M+-PF6,
603.93), 587 (C16H14N2PtSe2, 588.91), 509 (C16H16N2PtSe, 510.34),
428 (C16H16N2Pt, 431.09).
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
˚
l/A
z
rc/g cm-3
F[000]
1.621
210
4.272
2.87–30.40
-5 £ h £ 6
-9 £ k £ 9
-15 £ l £ 15
296(2)
0.0331
0.0891
m/mm-1
q/◦
Index ranges
9. Yield 0.2 g (65%). mp 76–78 ◦C (d). Anal. Calcd (%) for
C26H35F6N2PPdSe2: C, 39.79; H, 4.45; N, 3.57. Found: C, 39.37;
1
H, 4.49; N, 3.68. H NMR (CD3CN): d 0.83 (t, 3H, CH3, J =
T/K
R1
5.2 Hz), 1.17 (m, 14H), 2.15 (m, 2H), 3.10–3.22 (m, 2H, SeCH2),
4.09 (m, 4H, NCH2CH2N), 7.36–8.01 (m, 8H, ArH), 8.69 (s, 2H,
CH N). 13C NMR (CD3CN): d 14.3, 22.1, 23.2, 25.3, 29.2, 29.3,
29.8, 30.0, 32.4, 42.7, 63.8, 64.0, 125.6, 132.9, 136.1, 136.5, 139.6,
139.7, 163.7, 165.9.77Se NMR (CD3CN): 311, 352. IR nmax (KBr,
cm-1): 1624, 1585, 837, 761,557. ESI-MS: m/z = 640.60 (M+ - PF6,
641.01) lmax, nm (M-1 cm-1): 430 (3400), 349 (9500), 248 (6950).
10. Yield 0.1 g (39%). mp. 110–112 ◦C (d). Anal. Calcd (%) for
C28H39F6N2PPtSe2: C, 37.30; H, 4.36; N, 3.11. Found: C, 37.19;
wR2
Rmerge
0.0379
101
0.658
0.0313
182
0.815
0.0384
263
0.725
Parameters
GOF
reflns total
unique reflns
obsd reflns
9656
1892
1707
10775
3692
3436
52549
4589
3731
corrections method,25 and the resulting corrected energy values
were also included in addition to ZPVE and solvent corrections.
1
H, 3.74; N, 3.54. H NMR (CD3CN): d 0.83 (t, 3H, CH3, J =
5 Hz), 1.13 (m,14H), 1.60 (m, 2H), 1.90 (m, 2H), 2.14 (m, 2H),
3.06–3.13 (m, 2H), 4.18 (m, 4H, NCH2CH2N) 7.36–8.01 (m, 8H,
ArH), 8.9, 9.0 (s, 1H, azomethine). 13C NMR (CD3CN): 14.4,
23.4, 23.4, 28.7, 29.3, 29.9, 30.0, 30.1, 30.3, 32.6, 44.6, 64.7, 65.8,
115.8, 126.0, 131.5, 133.0, 133.4, 133.7, 134.2, 135.99, 136.0, 136.4,
139.2, 139.6, 161.0, 162.8.77Se NMR (CD3CN): 279, 264. IR nmax
(KBr, cm-1): 1609, 1440, 756, 557. ESI-MS: m/z 754.83 (M+-PF6,
758.10). UV-Vis lmax, nm (M-1 cm-1): 423 (4120), 264 (13570), 213
(25800).
Crystal structure determination
Crystallization
The compounds 4 and 5 were crystallized from slow evaporation
of CHCl3/CH3CN solvent mixture at room temperature. The
compound 8 was crystallized from CH3CN by slow diffusion of
ether.
X-ray crystallography
Theoretical methods
Intensity data were collected on a Bruker’s Kappa Apex II
CCD Duo diffractometer with graphite monochromatic Mo-
All calculations were performed using the B3LYP20 hybrid density
functional21 as implemented in Gaussian 03.22 The SDD23 pseudo
potential was employed for the palladium center, and the standard
6-31G(d) basis set was used for the other atoms. Transition states
were located by using the TS routine as implemented in Gaussian
03. Frequency calculations were performed at the same level for
all stationary points to differentiate them as minima or saddle
points. The energies of optimized structures were corrected using
the unscaled zero-point vibrational energies (ZPVEs). We have
corrected the gas phase values by using single-point calculations
for methanol as a solvent with the Polarized Continuum Model
(PCM) at the same level of theory.24 Gas phase optimized geome-
tries were taken for single point calculations. All complexes were
calculated as a neutral species by placing appropriate numbers
of counter ions (chloride) in close proximity of Se of selenoether
moiety in the complexes. Basis set superposition errors (BSSE)
were evaluated for each of the complexes by the counterpoise
˚
Ka radiation (0.71073 A) at the temperature of 100(2) K.
Scaling and multiscan absorption correction were employed using
SADABS.26 The structures were solved by direct methods and
all the non-hydrogen atoms were refined anisotropically while the
hydrogen atoms fixed in the predetermined positions by Shelxs-
97 and Shelxl-97 packages respectively.27 Crystal data are given
in Table 3. CCDC-808493–808495 contains the supplementary
crystallographic data for compound 4, 5 and 8.† The data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements
We (SP, SSZ and CMR) are thankful to Department of Science and
Technology (DST), India for funding this work. Additional help
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 6684–6690 | 6689
©

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from Prof. H. B. Singh, IIT Bombay for CHN analysis is gratefully
acknowledged. GRK thanks IISER Kolkata for fellowship.
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6690 | Dalton Trans., 2011, 40, 6684–6690
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©