Selenated Schiff bases of 2-hydroxyacetophenone and their palladium(II) and platinum(II) complexes: Syntheses, crystal structures and applications in the Heck reaction

Article abstract of DOI:10.1016/j.poly.2007.09.027

Selenated Schiff bases 2-HO-C₆H₄C(CH₃){double bond, long}N(CH₂)_nSePh (n = 2, L¹; n = 3, L²) and their complexes with Pd(II) and Pt(II), viz [Pd(L¹-H)Cl] (1), [Pt(L¹-H)Cl] (2), [Pd(L²-H)Cl] (3) and [PtL²Cl₂] (4), have been synthesized and characterized with proton, carbon-13 and ⁷⁷Se{¹H} NMR spectra. In the ⁷⁷Se{¹H} NMR spectrum of 2 the signal at δ 387.4 ppm appears as a triplet due to ¹J(¹⁹⁵Pt-Se) coupling (2043 Hz). The single-crystal structures of L¹, L², 1 and 2 were solved. The C-Se-C bond angles in L¹ and L² have been found to be around 99°. The geometry around Pd and Pt is square planar. The Pd-Se and Pt-Se bond distances are 2.3669(11) and 2.3543(16) A?, respectively. Complexes 1 and 2 are the first examples of crystal structures of Pd and Pt complexes of a (Se, N, O^-) ligand. Complex 1 has been explored as a homogeneous catalyst for a Heck type C-C coupling reaction between methyl acrylate and p-iodonitrobenzene (yield ～80%; reaction time 14 h).

Full text of DOI:10.1016/j.poly.2007.09.027

Available online at www.sciencedirect.com
Polyhedron 27 (2008) 485–492
www.elsevier.com/locate/poly
Selenated Schiff bases of 2-hydroxyacetophenone and
their palladium(II) and platinum(II) complexes: Syntheses,
crystal structures and applications in the Heck reaction
*
Arun Kumar, Monika Agarwal, Ajai K. Singh
Department of Chemistry, Indian Institute of Technology, New Delhi 110 016, India
Received 20 August 2007; accepted 13 September 2007
Available online 14 November 2007
Abstract
Selenated Schiff bases 2-HO-C6H4C(CH3)@N(CH2)nSePh (n = 2, L1; n = 3, L2) and their complexes with Pd(II) and Pt(II), viz
[Pd(L1–H)Cl] (1), [Pt(L1–H)Cl] (2), [Pd(L2–H)Cl] (3) and [PtL2Cl2] (4), have been synthesized and characterized with proton, carbon-
1
13 and 77Se{1H} NMR spectra. In the 77Se{1H} NMR spectrum of 2 the signal at d 387.4 ppm appears as a triplet due to J(195Pt–
Se) coupling (2043 Hz). The single-crystal structures of L1, L2, 1 and 2 were solved. The C–Se–C bond angles in L1 and L2 have been
found to be around 99ꢀ. The geometry around Pd and Pt is square planar. The Pd–Se and Pt–Se bond distances are 2.3669(11) and
À
˚
2.3543(16) A, respectively. Complexes 1 and 2 are the first examples of crystal structures of Pd and Pt complexes of a (Se, N, O ) ligand.
Complex 1 has been explored as a homogeneous catalyst for a Heck type C–C coupling reaction between methyl acrylate and p-iodo-
nitrobenzene (yield ꢀ80%; reaction time 14 h).
ꢁ 2007 Elsevier Ltd. All rights reserved.
Keywords: Selenated Schiff base; Selenium ligand; Palladium; Platinum; Complex synthesis; Single-crystal structure; X-ray diffraction; Heck reaction;
Catalysis
1. Introduction
tetradentate Schiff bases have the potential for multi-elec-
tron redox catalysis [4]. Metal complexes containing
Schiff-base ligands have also been found to show mesomor-
phic behaviour [5]. Among Schiff bases, ‘Salen’ and related
derivatives have been found to be very interesting. Their
complexes with transition metals are suitable catalysts for
epoxidation reactions [6–10] and a variety of other reac-
tions like dehydrogenation plus intramolecular Diels-Alder
cycloaddition [11], enantioselective conjugate addition [12]
and ring opening polymerization [13]. However, selenated
Schiff bases of mono ketones or aldehydes have not been
studied in detail so far and recently we have reported such
tellurated derivatives [14,15]. The presence of Se as a donor
site in Schiff bases may modify significantly their known
catalytic roles. Therefore, such systems are worth explor-
ing. A wide range of selenated Schiff-base ligands may be
designed by the reaction of a selenated amine with different
aldehydes or ketones. To use this strategy we have made
Schiff bases constitute an important class of ligands,
which have very rich and extensive chemistry, reviewed
recently by Vigato and Tamburini [1]. Metal complexes
of Schiff bases have found diverse applications in addition
to interesting structural chemistry. Ruthenium complexes
containing bidentate Schiff bases have been used [2] in cat-
alyzing Kharasch addition, enol-ester synthesis, alkyne
dimerization, olefin metathesis and atom transfer radical
polymerization. Metal complexes of chiral binaphthyl
Schiff bases have been used for stereoselective organic
transformations [3]. Oxovanadium(III–V) complexes of
*
Corresponding author. Tel.: +91 011 26591379; fax: +91 011
26862037.
E-mail addresses: aksingh@chemistry.iitd.ac.in, ajai57@hotmail.com
(A.K. Singh).
0277-5387/$ - see front matter ꢁ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.09.027

486
A. Kumar et al. / Polyhedron 27 (2008) 485–492
NH2CH2CH2SePh and NH2CH2CH2CH2SePh [3], which
have been used for designing selenated Schiff bases. Thus
L1 and L2 and their complexes with Pd(II) and Pd(II), in
which a metal–selenium bond is formed, have been synthe-
sized. Selenium being a very ‘‘soft’’ donor in nature does
not coordinate with 3-d transition metal ions in their com-
mon oxidation states. The ligands L1 and L2 and their com-
plexes were characterized by NMR spectroscopy (including
77Se{1H}) and X-ray diffraction studies, when single crys-
tals were obtained. The results of these investigations are
reported in this paper. The catalytic activity of the sele-
nide–Pd(II) complexes not only rivals but may outperform
that of the corresponding phosphorus and sulfur analogues
[16,17]. Practical advantages of the selenium-based cata-
lysts for the Heck reaction have been reported as their
straightforward synthesis and high activity in the absence
of any additives as well as the enhanced stability of the sel-
enide ligands toward air oxidation [17]. Therefore, 1 was
thought to be a good candidate for exploring for the Heck
reaction. Preliminary results of these explorations are also
reported in this paper.
[77Se{1H} NMR (vs Me2Se, 25 ꢀC) d, ppm: 256.6 and
257.5, respectively].
2.1. Synthesis of L1
2-(Phenylseleno)ethylamine (1.00 g, 5.0 mmol) was stir-
red in dry ethanol (20 mL) at room temperature for
0.5 h. o-Hydroxyacetophenone (0.68 g, 5.0 mmol), dis-
solved in dry ethanol (20 mL), was mixed dropwise with
stirring. The mixture was stirred further at room tempera-
ture for 2 h. The solvent was evaporated on a rotary evap-
orator which resulted in a yellow precipitate. The
precipitate on recrystallization from chloroform–hexane
(1:1) gave yellow coloured single-crystals of L1. Yield
1.43 g (ꢀ90%); m.p. 84–85 ꢀC. KM = 0.88 cm2 molÀ1 XÀ1
.
Anal. Calc. for C16H17NOSe: C, 60.33; H, 5.34; N, 4.39.
Found: C, 60.46; H, 5.28; N, 4.46%. NMR (1H, CDCl3,
25 ꢀC, vs SiMe4) d, ppm: 2.25 (s, 3H, CH3), 3.22 (t,
J = 6.9 Hz, 2H, SeCH2), 3.81 (t, J = 6.9 Hz, 2H, H6),
6.78 (t, J = 7.2 Hz, 1H, H12), 6.94 (d, J = 8.4 Hz, 1H,
H13), 7.25–7.30, (m, 4H, H2, H1 and H11), 7.49 (d,
J = 8.4 Hz, 1H, H10), 7.52–7.55 (m, 2H, H3), 15.93 (bs,
1H, OH) (13C{1H}, CDCl3, 25 ꢀC vs SiMe4) d, ppm: 14.6
(CH3), 27.8 (SeCH2), 49.4 (C6), 117.2 (C10), 118.5 (C12),
119.3 (C8), 127.2 (C1), 128.0 (C13), 129.1 (C2), 129.2 (C4),
132.4 (C11), 133.0 (C3), 163.2 (C9), 171.8 (C7) (77Se{1H},
CDCl3, 25 ꢀC vs Me2Se) d, ppm: 282.3. IR (KBr, cmÀ1):
3484, 1607, 470, 734.
3
3
2
2
6
5
5
7
6
H3C
7
H3C
1
1
N
Se
N
Se
8
9
4
4
13
14
13
8
OH
OH
12
10
11
9
10
12
11
L2
L1
2.2. Synthesis of L2
3-(Phenylseleno)propylamine (1.07 g, 5.0 mmol) was stir-
red in dry ethanol (20 mL) at room temperature for 0.5 h. o-
Hydroxyacetophenone (0.68 g, 5.0 mmol), also dissolved in
dry ethanol (20 mL), was added to it dropwise with stirring.
The mixture was stirred further at room temperature for 2 h.
On evaporating the solvent on a rotary evaporator a yellow
precipitate of L2 was obtained, which on recrystallization
from a chloroform–hexane mixture (1:1) afforded yellow sin-
gle-crystals of L2. Yield 1.49 g (ꢀ90%); m.p. 82–83 ꢀC. Anal.
Calc. for C17H19NOSe: C, 61.40; H, 5.71; N, 4.21. Found: C,
61.45; H, 5.73; N, 4.28%. NMR (1H CDCl3, 25 ꢀC, vs SiMe4)
d, ppm: 2.15 (quintet, J = 6.6 Hz, 2H, H6), 2.29 (s, 3H, CH3),
3.06 (t, J = 6.9 Hz, 2H, SeCH2), 3.66 (t, J = 6.6 Hz, 2H, H7),
6.77 (t, J = 7.5 Hz, 1H, H13), 6.92 (d, J = 8.1 Hz, 1H, H14),
7.23–7.31 (m, 4H, H2, H1 and H12), 7.48–7.50 (m, 2H, H11
and H3), 16.40 (bs, 1H, OH) (13C{1H} CDCl3, 25 ꢀC, vs
SiMe4) d, ppm: 14.3 (CH3), 25.2 (SeCH2), 30.46 (C6), 48.4
(C7), 116.9 (C11), 118.7 (C13), 119.1 (C9), 126.8 (C1), 127.9
(C14), 129.0 (C2), 129.7 (C4), 132.4 (C12), 132.5 (C3), 164.0
(C10), 172.0 (C8) (77Se {1H}, CDCl3, 25 ꢀC, vs Me2Se) d,
ppm: 286.6. IR (KBr, cmÀ1): 1612, 461, 734.
2. Experimental
The C and H analyses were carried out with a Perkin–
Elmer 2400 Series II C, H, N analyzer. The H, 13C{1H}
1
and 77Se{1H} NMR spectra were recorded on a Bruker Spec-
trospin DPX-300 NMR spectrometer at 300.13, 75.47 and
57.24 MHz, respectively. IR spectra in the range 4000–
250 cmÀ1 were recorded on a Nicolet Protege 460 FT-IR
´
spectrometer as KBr pellets. The melting points determined
in open capillary are reported as such. The conductivity mea-
surements were carried out in CH3CN (concentration ca
1 mM) using an ORION conductivity meter model 162.
Single-crystal diffraction studies were carried out with a
Bruker AXS SMART Apex CCD diffractometer using Mo
˚
Ka (0.71073 A) radiation at 298(2) K. The software SADABS
was used for absorption correction (if needed) and SHELXTL
for space group, structure determination and refinements
[18a,18b]. All non-hydrogen atoms were refined anisotrop-
ically. Hydrogen atoms were included in idealized positions
with isotropic thermal parameters set at 1.2 times that of
the carbon atom to which they are attached. The least-
squares refinement cycles on F2 were performed until the
model converged.
2.3. Synthesis of [PdCl(L1–H)] (1)
2-(Phenylseleno)ethylamine [19] and 3-(phenylseleno)-
propylamine [19] were prepared by the reported methods
An aqueous solution (5 mL) of Na2[PdCl4] (0.294 g,
1 mmol) was mixed with a solution of L1 (0.3182 g,

A. Kumar et al. / Polyhedron 27 (2008) 485–492
487
1 mmol) prepared in acetone (10 mL) with vigorous stir-
ring. An orange precipitate of 1, obtained instantaneously,
was filtered and dried. It was recrystallized from chloro-
form–hexane (2:1) mixture. Single-crystals of 1 were
obtained from the same solvent system (a few drops of
MeOH were added additionally). Yield ca. 0.3626 g
(ꢀ79%); m.p. 159 ꢀC. KM = 7.0 cm2 molÀ1 XÀ1. Anal. Calc.
for C16H16ClNOPdSe (powder form): C, 41.83; H, 3.49; N,
3.05. Found: C, 41.68; H, 3.41; N, 3.10%. NMR (1H,
CDCl3, 25 ꢀC, vs SiMe4) d, ppm: 2.22 (s, 3H, CH3), 2.69–
2.72 (m, 1H, H5), 3.56–3.71 (m, 2H, H5 + H6), 4.48–4.53
(m, 1H, H6), 6.62 (t, J = 7.8 Hz, 1H, H12), 7.12 (d,
J = 8.7 Hz, 1H, H13), 7.23–7.38 (m, 2H, H11 and H10),
7.41–7.43 (m, 3H, H2 and H1), 8.16–8.19 (m, 2H, H3)
(13C{1H}, CDCl3, 25 ꢀC, vs SiMe4) d, ppm: 19.7 (CH3),
32.4 (SeCH2), 60.7 (@NCH2), 115.4 (C10), 121.6 (C12),
123.4 (C4), 125.7 (C8), 129.9 (C2), 130.1 (C11), 131.1 (C1),
133.4 (C13), 133.6 (C3), 164.2 (C9), 168.1 (C7). (77Se{1H}
CDCl3, 25 ꢀC vs Me2Se) d, ppm: 440.4. IR (KBr, cmÀ1):
1572, 463, 747.
C, 42.82; H, 3.99; N, 3.15%. NMR (1H, CDCl3, 25 ꢀC,
vs SiMe4) d, ppm: 2.02–2.07 (m, 2H, H6), 2.34 (s, 3H,
CH3), 2.88 (d of t, J = 4.2 Hz, 1H, H5), 3.10 (d of t,
J = 4.2 Hz, J = 11.1 Hz, 1H, H5), 3.65–3.69 (m, 2H,
H7), 6.65 (t, J = 7.8 Hz, 1H, H13), 7.10 (d, J = 8.7 Hz,
1H, H14), 7.22 (t, J = 7.5 Hz, 1H, H12), 7.33–7.44 (m,
4H, H11, H2, H1), 8.05–8.07 (m, 2H, H3) (13C{1H}
CDCl3, 25 ꢀC, vs SiMe4) d, ppm: 19.6 (CH3), 26.3
(SeCH2), 29.7 (C6), 53.4 (NCH2), 116.0 (C11), 121.8
(C13), 126.6 (C9), 129.7 (C4), 129.8 (C2), 129.8 (C12),
130.3 (C1), 133.3 (C3), 134.1 (C14), 164.6 (C10), 169.1
(C8) (77Se{1H}, 25 ꢀC, vs Me2Se) d, ppm: 293.6. IR
(KBr, cmÀ1): 1592, 468, 748.
2.6. Synthesis [PtCl(L2)] (4)
K2[PtCl4] (0.415 g, 1 mmol) was dissolved in water
(5 mL). A solution of L2 (0.332 g, 1 mmol) in acetone
(10 mL) was added with vigorous stirring. An orange
coloured precipitate of 4 was immediately obtained,
which was filtered and dried. It was recrystallized from
a chloroform–hexane (60:40) mixture. Yield ꢀ0.415 g
(ꢀ50%); m.p. 147 ꢀC. KM = 6.8 cm2 molÀ1 XÀ1. Anal.
Calc. for C17H19NOSePtCl2: C, 34.11; H, 3.18; N, 2.34.
Found: C, 33.67; H, 3.58; N, 2.43%. NMR (1H, CDCl3,
25 ꢀC, vs SiMe4) d, ppm: 2.21–2.41 (m, 5H, H6 + CH3),
3.10 (t of d, J = 3.6 Hz, J = 8.1 Hz, 1H, H5), 3.54–
3.58(m, 1H, H5), 3.65–3.66 (m, 2H, NCH2), 6.78 (t,
J = 7.2 Hz, 1H, H13), 6.91 (d, J = 8.4 Hz, 1H, H14),
7.28 (t, J = 8.1 Hz, 1H, H12), 7.34–7.42 (m, 3H, H2,
H1), 7.49 (d, J = 7.8 Hz, H11), 7.86–7.89 (m, 2H, H3),
16.28 (bs, 1H, OH); (13C{1H} CDCl3, 25 ꢀC, vs SiMe4)
d, ppm: 14.6 (CH3), 28.2 (SeCH2), 31.6 (C6) 48.7
(NCH2), 117.3 (C11), 118.5 (C13), 119.3 (C9), 128.1
(C14), 129.6 (C2), 130.2 (C1), 132.5 (C12), 132.9 (C4),
133.0 (C3), 163.4 (C10), 172.5 (C8); (77Se{1H}, 25 ꢀC, vs
Me2Se) d, ppm: 337.4, 338.5. IR (KBr, cmÀ1): 3395,
1582, 465, 739, 685.
2.4. Synthesis [PtCl(L1–H)] (2)
K2[PtCl4] (0.415 g, 1 mmol) was dissolved in water
(5 mL). A solution of L1 (0.3182 g, 1 mmol) prepared in
acetone (10 mL) was added to it with vigorous stirring.
An orange precipitate of 2 was obtained, which was
filtered and dried. The orange solid was recrystallized
from chloroform–hexane (2:1). Single-crystals of 2 were
obtained from the same solvent system. Yield ca.
0.3626 g (ꢀ79%); m.p. 162 ꢀC KM = 5.0 cm2 molÀ1 XÀ1
.
Anal. Calc. for C16H16ClNOPtSe: C, 35.10; H, 2.92; N
2.56. Found: C, 35.50; H, 2.96; N, 2.51%. NMR (1H,
CDCl3, 25 ꢀC, vs SiMe4) d, ppm: 2.14 (s, 3H, CH3), 2.55
(t of d, J = 2.7 Hz, J = 12.3 Hz, 1H, H5), 3.38 (d of t,
J = 4.2 Hz, J = 12 Hz, 1H, H5), 3.56 (d of t, J = 3.9 Hz,
12.3 Hz, 1H, H6) 4.37 (t of d, J = 2.4 Hz, J = 13.5 Hz,
1H, H6), 6.66 (t, J = 7.2 Hz, 1H, H12), 7.20 (d, J =
8.4 Hz, 1H, H13), 7.34 (t, J = 8.4 Hz, 1H, H11), 7.39–
7.42 (m, 3H, H2, H1), 7.47 (d, J = 8.4 Hz, H10), 8.10–
8.13 (m, 2H, H3) (13C{1H}, CDCl3, 25 ꢀC, vs SiMe4) d,
ppm: 20.6 (CH3), 34.2 (SeCH2), 61.9 (@NCH2), 116.4
(C10), 122.0 (C12), 123.1 (C4), 124.7 (C8), 129.5 (C2),
130.2 (C11), 130.5 (C1), 132.9 (C13), 133.1 (C3), 162.5
(C9), 163.7 (C7) (77Se{1H}, 25 ꢀC, vs Me2Se) d, ppm:
387.36. IR (KBr, cmÀ1): 1572, 465, 747.
2.7. Procedure for the homogeneous catalytic Heck reaction
with 1
A mixture of methyl acrylate (0.172 g, 2 mmol), p-iodo-
nitrobenzene (0.62 g, 2.5 mmol), Et3N (0.54 g, 3.0 mmol),
p-xylene (2.0 mL) and 1 ( 22.95 mg) was stirred for 14 h
at 140 ꢀC and cooled thereafter to room temperature. It
was treated with chloroform (40 mL) and filtered. The fil-
trate was evaporated on a rotary-evaporator to obtain
the product.
It was purified through a silica gel column using hex-
ane:ethylacetate mixture (9:1); yield 0. 33 g (ꢀ80%);
NMR (1H, CDCl3, 25 ꢀC, vs TMS) d, ppm: 3.84 (s,
3H, OCH3), 6.58 (d, J = 15.9 Hz, 1H, @CH–COOMe),
7.69 (d, 2H, J = 9 Hz, ArH, o to NO2), 7.74 (d,
J = 15.9 Hz, 1H, @CH–Ar), 8.27 (d, 2H, J = 9 Hz, Ar
H, m to NO2).
2.5. Synthesis of [PdCl(L2–H)] (3)
Na2[PdCl4] (0.294 g, 1 mmol) dissolved in water
(5 mL) and a solution of L2 (0.332 g, 1 mmol) prepared
in acetone (10 mL) were stirred together vigorously. An
orange precipitate of 3 was immediately obtained, which
was filtered and dried. It was recrystallized from a chlo-
roform–hexane (60:40) mixture. Yield ꢀ0.42 g (ꢀ90%);
m.p. 170 ꢀC. KM = 6.0 cm2 molÀ1 XÀ1 Anal. Calc. for
C17H18NOSePdCl: C, 43.12; H, 3.80; N, 2.95. Found:

488
A. Kumar et al. / Polyhedron 27 (2008) 485–492
3. Results and discussion
tiplet and deshielded by an amount <0.02 ppm. The pat-
tern of the –SeCH2 signals were found to be similar to
those of 1, but deshielded by up to 0.2 ppm only. The lower
deshielding appears to be the effect of one six membered
ring formed in the case of 3. In the proton spectrum of 4,
the OH signal was observed but shielded insignificantly
(ꢀ0.1 ppm). The signals of H6 and CH3 were found to be
overlapping but not much shifted with respect to those of
the free ligand L2. The signal of H7 was found as a multi-
plet, but unshifted with respect to that of free L2. The pro-
tons of the SeCH2 group give a multiplet deshielded by
0.5 ppm with respect to those of free L2 and a triplet of
doublets at a position similar to that of L2.
The ligands L1 and L2 and their complexes have been
synthesized by the reactions given in Scheme 1. The ligands
are stable and can be stored under ambient conditions up
to 6 months. They have good solubility in CHCl3, CH2Cl2,
CH3CN, MeOH, EtOH and acetone. In hexane both
ligands are sparingly soluble. Both ligands are non-electro-
lytes. Complexes 1–4 are stable under ambient conditions
and are soluble in CHCl3, CH2Cl2, CH3CN, EtOH, MeOH
and acetone, but insoluble in hexane. All of them are non-
ionic in nature. In the IR spectra of complexes 1–4 the
˜C@N– stretching frequency has been observed to be red
shifted by 20–35 cmÀ1 with respect to those of L1 and L2,
indicating the involvement of its nitrogen in coordination.
Elemental analyses of 1 and 2 were carried out using their
non-crystalline samples.
The 13C{1H} NMR spectra of both L1 and L2 are also
characteristic. On formation of 1 and 2 signals of carbon
atoms C2, C3, C9, C10 and C11 exhibit deshielding of up
to 12.5 ppm. The signal of C6 shows maximum deshielding
(11.3–12.5 ppm) on complexation. The deshielding of the
C1, C5, C8 and C13 signals is of the order of 3–6 ppm.
The signals of C4, C7 and C11 have been observed to be
shielded by 2–8 ppm with respect to those signals of free
L1. On formation of 3 signals of carbon atoms C1, C7,
C9, C13, C14 and CH3 exhibit deshielding between 3.0 and
7.5 ppm. Of them, the signal of C9 shows maximum desh-
ielding (7.5 ppm) on complexation. The deshielding of sig-
nals C2, C3, C5 and C10 is of the order of 0.8 –1.0 ppm. The
signals of C4, C6, C8, C11 and C12 have been observed to be
shielded (by up to 2.8 ppm) with respect to those of free L2.
On complexation of L2 with Pt(II), the signals of most of
the carbon atoms are shifted marginally (0.1–0.6 ppm),
except those of C1, C4 and C5 which are deshielded by
3.3, 3.2 and 3.0 ppm, respectively. These observations sug-
gest that in 1–3 the ligands L1 and L2 coordinate in a tri-
dentate mono-anionic mode. The bonding of L2 with
Pt(II) appears to be through N and Se only.
3.1. NMR spectra
The 1H NMR spectra of both L1 and L2 have been
found characteristic. On complexation of L1 with Pd(II)
the –CH2 groups in the –Se–CH2–CH2–N system show a
group of three signals, two correspond to a single proton
and one to two protons (one from each NCH2 + SeCH2).
Their assignments are based on the HMQC NMR spec-
trum of 1. However in the case of complex 2, the –Se–
CH2–CH2–N system shows a group of four signals, each
one corresponding to one proton. These assignments are
also in agreement with the HMQC NMR spectrum of 1.
On complexation of L1 with Pd(II)/Pt(II) one signal for
the H6 protons is deshielded by ꢀ0.60–0.70 ppm and the
other one is shielded by ꢀ0.14–0.25 ppm. Similarly, of
the two signals of H5, one shows shielding of 0.52–
0.67 ppm and the other deshielding of 0.16–0.38 ppm.
The CH3 signal shifts to upfield marginally (up to
0.1 ppm) on complexation. The H13 signal shows deshiel-
ding of the order of 0.18–0.26 ppm on the formation of 1
and 2. The deshielding of the H3 signal was found to be
between 0.58 and 0.64 ppm on complexation. In complex
3 the signal of H6 was observed as a multiplet (upfield
ꢀ0.1 ppm). The NCH2 signal was also found to be a mul-
In the 77Se{1H} NMR spectra, ligands L1 and L2 exhibit
singlets at 282.3 and 286.6 ppm, respectively, which are
deshielded (ꢀ25–29 ppm) with respect to those of the pre-
cursor selenated amines. On complexation of L1 with
Pd(II) and Pt(II), the signals in the 77Se{1H} NMR spectra
were found to be shifted downfield by 158 and 105 ppm
respectively. In the case of 2, the signal at 387.4 appears
as a triplet because of 1J(195Pt–Se) coupling (2043 Hz).
On formation of 3 and 4, the deshielding of the signals in
the 77Se NMR spectra was found only to be 6.9 and
51.3 ppm. This is probably due to formation of one six
membered ring in these cases (see Table 1).
NaBH4 / NaOH
N2 atm, r.t.
Cl-(CH2)n-NH2 . HCl
Dry C2H5OH, Reflux
H2N(CH2)nSePh
n = 2 or 3
2 PhSeNa
Ph2Se2
3.2. Crystal structures
H3C
O
Dry C2H5OH
L1 or L2
H N(CH ) SePh
+
2
2 n
The crystal structures of L1, L2, 1 and 2 were solved. The
structures of 1 and 2 are isomorphous. The molecular
structure of L1 is shown in Fig. 1 and its selected bond
lengths and angles are given in Table 2. The C–Se bond
lengths of 1.916(4) and 1.953(4) A are consistent with the
earlier reports (1.939 A) [20]. The Se–C(Ar) bond distance
OH
n = 2 or 3
H2O-Me2CO(1:2)
Na2PdCl4/K2PtCl4 + L1 or L2
[Pd/Pt(L1/L2-H)Cl]
(1-4)
˚
˚
Scheme 1.
is somewhat shorter than the Se–C(alkyl) distance, as

A. Kumar et al. / Polyhedron 27 (2008) 485–492
489
Table 1
Crystal data and structural refinements for L1, L2, 1 and 2
Compound
L1
L2
1
2
Empirical formula
Formula weight
Crystal size (mm)
Crystal system
C
318.27
0.363 · 0.217 · 0.156
monoclinic
P2(1)/n
16H17NOSe
C17H19NOSe
332.29
0.480 · 0.190 · 0.160
monoclinic
P2(1)/c
C17H17Cl4NOPdSe
578.50
0.463 · 0.215 · 0.167
monoclinic
C17 H17Cl4NOPt Se
667.16
0.363 · 0.217 · 0.156
monoclinic
Space group
P2(1)/c
P2(1)/c
Unit cell dimensions
˚
a (A)
6.8629(16)
29.966(7)
7.3948(18)
107.114(0)
1453.4(60)
4
1.454
2.575
648
16.474(3)
6.7098(11)
14.689(2)
108.084(2)
1543.5(40)
4
1.430
2.428
680
14.854(2)
17.861(3)
15.917(2)
102.150(3)
4128.3(10)
8
1.862
3.186
14.814(3)
17.863(3)
15.998(3)
101.672(4)
4145.9(13)
8
2.138
9.046
˚
b (A)
˚
c (A)
b (ꢀ)
Volume (A )
3
˚
Z
Dcalc (Mg mÀ3
Absorption coefficient (mmÀ1
F(000)
)
)
2256
2512
h Range (ꢀ)
Index ranges
1.36–25.50
À8 6 h 6 8,
À36 6 k 6 36,
À8 6 l 6 8
14406
1.30–25.00
À19 6 h 6 19,
À7 6 k 6 7,
À17 6 l 6 17
13862
1.40–25.50
À17 6 h 6 17,
À21 6 k 6 21,
À19 6 l 6 19
40756
1.40–25.50
À17 6 h 6 17,
À21 6 k 6 21,
À19 6 l 6 19
40899
Reflections collected
Independent reflections (Rint
Maximum/minimum transmission 0.671/0.515
Data/restraints/parameters
Final R indices [I > 2r(I)]
)
2701(0.1000)
2706 (0.367)
0.678/0.529
2706/0/186
R1 = 0.0412,
wR2 = 0.1183
R1 = 0.0490,
wR2 = 0.1260
0.749/À0.687
7669(0.0765)
0.580/0.442
7668/0/457
R1 = 0.0712,
wR2 = 0.1357
R1 = 0.0960,
wR2 = 0.1490
0.824/À0.606
7698(0.0946)
0.246/0.104
7690/0/453
R1 = 0.0801,
wR2 = 0.1407
R1 = 0.1028,
wR2 = 0.1521
1.235/À2.728
2701/1/174
R1 = 0.0490,
wR2 = 0.1259
R1 = 0.0626,
wR2 = 0.1411
0.761/À0.458
R indices (all data)
Largest difference peak/hole
À3
˚
(e A
)
C8
C8
Se1
C9
C7
C7
C5
C2
N1
C16
C6
N1
C3
C4
C3
C11
C10
C9
C1
C6
C11
C15
C14
C4
C10
C13
C1
C12
C5
Se1
C12
O1
C14
C15
C2
C13
O1
Fig. 1. ORTEP diagram of L1 with 50% probability ellipsoids.
C17
C16
Table 2
Selected bond lengths (A) and angles (ꢀ) of L
1
˚
Fig. 2. ORTEP diagram of L2 with 50% probability ellipsoids.
Bond length
Bond angle
˚
Se(1)–C(11)
Se(1)–C(10)
N(1)–C(7)
N(1)–C(9)
C(9)–C(10)
O(1)–C(6)
H(1)Á Á ÁN(1)
1.916(4)
1.953(4)
1.284(4)
1.455(4)
1.518(5)
1.343(4)
1.786(3)
C(11)–Se(1)–C(10)
C(7)–N(1)–C(9)
N(1)–C(7)–C(8)
N(1)–C(9)–C(10)
N(1)–C(7)–C(1)
C(12)–C(11)–Se(1)
C(16)–C(11)–Se(1)
99.1(2)
121.3(3)
122.4(3)
109.5(3)
117.6(3)
120.9(3)
120.2(3)
distances, 1.914(3) and 1.956(3) A and the C–Se–C bond
angle are consistent with those of L1 and earlier reports
[20]. In this case it is also found that the Se–C(Ar) bond
distance is shorter than the Se–C(alkyl) bond distance
(see Table 3).
The molecular structure of 1 is shown in Fig. 3 and its
selected bond distances and angles are given in Table 4. In
the asymmetric unit there are two chemically similar but
crystallographically independent molecules and two mole-
cules of chloroform solvent. The 1 is the first example of a
crystal structure of a Pd complex of a (Se, N, OÀ) ligand.
The geometry around Pd is square planar. The Pd–Se
expected. Similarly the C–Se–C bond angle of 99.1(2)ꢀ was
found as expected. Intramolecular hydrogen bonding, O–
HÁ Á ÁN, exists in the structure of L1. A perspective view
of the structure of L2 is shown in Fig. 2. It also has intra-
molecular hydrogen bonding, O–HÁ Á ÁN. The Se–C bond

490
A. Kumar et al. / Polyhedron 27 (2008) 485–492
˚
Table 3
A) [22]. The shorter Pd–Se bond in 1 may be attributed
2
˚
to the tridentate nature of ligand L1, which makes two
chelate rings and forces Se to bind with Pd(II) somewhat
strongly in comparison to those complexes in which
the selenium ligand is a monodentate one. The Pd–N,
Pd–O and Pd–Cl bond distances, 2.003(7), 1.977(6) and
Selected bond lengths (A) and angles (ꢀ) of L
Bond length
Bond angle
Se(1)–C(12)
Se(1)–C(11)
N(1)–C(7)
N(1)–C(9)
C(9)–C(10)
O(1)–C(1)
H(1)Á Á ÁN(1)
1.914(3)
1.956(3)
1.284(4)
1.458(4)
1.513(4)
1.330(3)
1.53(6)
C(12)–Se(1)–C(11)
C(7)–N(1)–C(9)
N(1)–C(7)–C(6)
N(1)–C(7)–C(8)
N(1)–C(9)–C(10)
C(17)–C(12)–Se(1)
C(13)–C(12)–Se(1)
99.5(1)
122.0(2)
117.6(2)
123.0(3)
110.7(2)
119.1(3)
121.8(3)
˚
2.305(2) A, respectively, are consistent with earlier reports
˚
˚
[Pd–N = 2.01(1) A, Pd–O = 2.03(1) A and Pd–Cl = 2.290
˚
(4) A] on a Pd(II) complex of a tridentate ligand of the
(Te, N, OÀ) type [14]. In Fig. 4 the molecular structure
of 2 is shown. In Table 4 selected bond lengths and angles
are given. In the unit cell of the crystal of 2 also there are
two almost similar molecules. One molecule of chloro-
form per molecule of 2 is also present in the lattice. The
structure of 2 is also the first example of a crystal struc-
ture of a Pt-complex of a (Se, N, OÀ) ligand. The geom-
etry around Pt is nearly square planar. The Pt–Se bond
C14
C11
C10
C13
C12
C15
C16
C9
N1
˚
length, 2.3543(16) A, is consistent with the earlier
C3
C6
C4
C5
C8
C2
reported value in the case of [CH3SeCH2CH2CH(COO-
C7
˚
O1
Me)NH2 Æ PtCl2] (2.3697(8) A) [23], but is shorter than
Pd1
those reported for cis-[Pt(SePh)2(PPh3)2] (2.4970(9),
˚
2.4604(10) A) [24] and trans-[Pt(SePh)2(2,9-dimethyl-1,
C1
10-phenanthroline)(MeOOCCH@CHCOOMe)] (2.5197,
Se1
Cl1
Fig. 3. ORTEP diagram of 1 with 50% probability ellipsoids.
˚
2.5142 A) [25]. The shorter Pt–Se bond in 2 may again
be attributed to the tridentate nature of the ligand L1,
as in the case of the Pd(II) complex mentioned above.
The absence of the trans influence may also contribute,
particularly in comparison with trans-[Pt(SePh)2(2,9-di-
methyl-1,10-phenanthroline)(MeOOCCH@CHCOOMe)].
The Pt–N and Pt–Cl bond distances, 1.988(12) and
Table 4
Selected bond lengths (A) and angles (ꢀ) of 1 and 2
˚
(1)
(2)
˚
Bond lengths (A)
Pd(1)–Se(1)
Pd(1)–Cl(1)
Pd(1)–N(1)
Pd(1)–O(1)
Se(1)–C(1)
Se(1)–C(7)
N(1)–C(8)
˚
2.306(4) A, respectively, are consistent with the earlier
2.3669(11)
2.305(2)
2.003(7)
1.977(6)
1.929(8)
1.947(9)
1.493(10)
1.309(11)
1.312(10)
Pt(1)–Se(1)
Pt(1)–Cl(1)
Pt(1)–N(1)
Pt(1)–O(1)
O(1)–C(6)
N(1)–C(7)
N(1)–C(9)
Se(1)–C(10)
Se(1)–C(11)
2.3543(16)
2.306(4)
˚
reports [23], 2.043(5) and 2.294(2), 2.322(2) A, respec-
˚
tively. The Pt–O bond length of 1.976(10) A is compara-
1.988(12)
1.976(10)
1.314(15)
1.316(18)
1.512(18)
1.95 (2)
˚
ble with earlier reports (2.034 A) [26]. On comparing
Pd/Pt–N, Pd/Pt–O, Pd/Pt–Cl and Pd/Pt–Se bond lengths
with the sum of their covalent radii 2.03/2.05, 2.01/2.03,
˚
2.27/2.29 and 2.44/2.46 A. respectively, it appears that
N(1)–C(9)
O(1)–C(11)
the observed bond distances are shorter than this sum,
except in the case of Pd/Pt–Cl where the observed values
are marginally higher. This indicates that coordination of
L1 is quite strong with Pd as well as with Pt.
1.938(14)
Bond angles (ꢀ)
O(1)–Pd(1)–N(1)
O(1)–Pd(1)–Cl(1)
N(1)–Pd(1)–Cl(1)
O(1)–Pd(1)–Se(1)
N(1)–Pd(1)–Se(1)
Cl(1)–Pd(1)–Se(1)
C(1)–Se(1)–C(7)
C(1)–Se(1)–Pd(1)
C(7)–Se(1)–Pd(1)
C(9)–N(1)–Pd(1)
C(8)–N(1)–Pd(1)
C(9)–N(1)–C(8)
C(11)–O(1)–Pd(1)
O(1)–C(11)–C(12)
O(1)–C(11)–C(16)
93.0(3)
88.3(2)
173.4(2)
176.0(2)
90.5(2)
88.40(7)
98.8(4)
104.3(2)
91.5(3)
125.3(6)
114.4(6)
119.3(7)
123.8(5)
125.8(8)
115.9(8)
O(1)–Pt(1)–N(1)
O(1)–Pt(1)–Cl(1)
N(1)–Pt(1)–Cl(1)
O(1)–Pt(1)–Se(1)
N(1)–Pt(1)–Se(1)
Cl(1)–Pt(1)–Se(1)
C(11)–Se(1)–C(10)
C(11)–Se(1)–Pt(1)
C(10)–Se(1)–Pt(1)
C(7)–N(1)–Pt(1)
C(9)–N(1)–Pt(1)
C(7)–N(1)–C(9)
C(6)–O(1)–Pt(1)
O(1)–C(6)–C(5)
O(1)–C(6)–C(1)
93.1(5)
86.7(3)
174.5(3)
175.4(3)
90.9(4)
89.6(1)
98.8(7)
107.0(5)
91.7(5)
127.2(5)
114.7(5)
117.7(1)
123.2(9)
115.7(1)
126.5(1)
C8
H8C
C14
C16
C9
C13
C7
O1
C2
C12
C10
N1
C3
C1
C15
C11
C6
C4
Pt1
Se1
C5
˚
bond length, 2.3669(11) A, is shorter than those reported
for [Pd(PEt3)2(SePh)(PO(OPh)2)] (2.518(9) A) [21] and
[Pd(Me2PCH2CH2PMe2)(Me)(SeC6H4-4-Cl)] (2.4483(8)
Cl1
Fig. 4. ORTEP diagram of 2 with 50% probability ellipsoids.
˚

A. Kumar et al. / Polyhedron 27 (2008) 485–492
491
90
80
70
60
50
40
30
20
10
0
80
79.34
77.51
69.44
60.24
47.61
32.89
18.51
9.19
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17
Time (h)
Fig. 5. Kinetic profile of the Heck reaction.
3.3. Application as a homogeneous catalyst for the Heck
reaction
pling with 195Pt were observed (1J (195Pt–Se) = 2043 Hz).
1 and 2 are the first examples of crystal structures of Pd
and Pt complexes of a (Se, N, OÀ) ligand. 1is explored
for the homogeneous catalysis of the Heck reaction
between methyl acrylate and p-iodonitrobenzene. The yield
is ꢀ80% and the reaction time is only 14 h.
1 was found to be suitable to catalyze the Heck coupling
reaction, as shown below with ꢀ80% yield.
COOMe
O2N
I
+
Acknowledgements
The authors thank the Department of Science and Tech-
nology (India) for Research Project No. SR/S1/IC-23/06.
A.K. thanks the Council of Scientific and Industrial Re-
search (India) for the award of a Junior/Senior Research
Fellowship. Authors also thank Department of Science
and Technology (India) for partial financial assistance
given to establish single crystal X-ray diffraction facility
under its FIST programme.
Pd(II) catalyst of (O, N, Se) ligand
O2N
140oC
COOMe
p-xylene, Et3N,
Using 1, the time for completion of the reaction is only
14 h, less than that of a recently reported palladium(II)
complex of a bidenate Se-ligand (20–90 h at a similar reac-
tion temperature) [17]. The kinetic profile of the above
reaction followed by proton NMR is shown in Fig. 5.
The temperature cannot be much increased beyond
140 ꢀC as the yield decreases. However at a lower temper-
ature, around 100 ꢀC, the yield goes down to 40–45%. The
reaction was carried out in the presence of Na2CO3 at
140 ꢀC and the yield was found to be only 20–25%. The tri-
alkylamines (alkyl group = Me, Et, n-Bu or t-Bu) give the
maximum yield.
Appendix A. Supplementary material
CCDC 651260, 651261, 651259 and 655400 contain the
supplementary crystallographic data for L1, L2, 1 and 2.
These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK, fax: (+44) 1223-336-033, or
e-mail: deposit@ccdc.cam.ac.uk. Supplementary data asso-
ciated with this article can be found, in the online version,
at doi:10.1016/j.poly.2007.09.027.
4. Conclusion
Selenated Schiff bases 2-OH-C6H4C(CH3)@N(CH2)n
SePh (n = 2, L1; n = 3, L2) have been designed as such spe-
cies are scantly known and explored for complexation with
Pd(II)/Pt(II). Proton, carbon-13 and selenium-77 NMR
spectra of the complexes support the coordination of L1
and L2 through Se. In the case of 2, satellites due to cou-
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