Palladium(II) and platinum(II) complexes of β-functionalized ethyl selenolates: Effect of substitution on synthesis, reactivity, spectroscopy, structures and thermal behavior

Article abstract of DOI:10.1016/j.jorganchem.2009.08.005

Sodium ethylselenolates with functional groups X (where X = -OH, -COOH, -COOMe and -COOEt) at β-carbon were prepared in situ by reductive cleavage of corresponding diselenide with NaBH₄ either in methanol or aqueous ammonia. Treatment of these

Full text of DOI:10.1016/j.jorganchem.2009.08.005

Journal of Organometallic Chemistry 694 (2009) 3892–3901
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Journal of Organometallic Chemistry
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Palladium(II) and platinum(II) complexes of b-functionalized ethyl selenolates:
Effect of substitution on synthesis, reactivity, spectroscopy, structures and
thermal behavior
b
b
Liladhar B. Kumbhare a, Amey P. Wadawale a, Vimal K. Jain a, , Siddharth Kolay , Munirathinam Nethaji
*
a Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India
b Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 June 2009
Received in revised form 3 August 2009
Accepted 4 August 2009
Available online 8 August 2009
Sodium ethylselenolates with functional groups X (where X = –OH, –COOH, –COOMe and –COOEt) at
b-carbon were prepared in situ by reductive cleavage of corresponding diselenide with NaBH4 either in
methanol or aqueous ammonia. Treatment of these selenolates with [M2Cl2(
l
–Cl)2(PR0 )2] (M = Pd or
3
Pt; PR03 = PMePh2, PnPr3) in different stoichiometry yielded various bi- and tri-nuclear complexes. The
homoleptic hexanuclear complexes [Pd(l–SeCH2CH2X)2]6 (X = OH, COOH, COOEt), were obtained by
reacting Na2PdCl4 with NaSeCH2CH2X. All these complexes have been fully characterized. Molecular
structures of ethylselenolates containing hydroxyl and carboxylic acid groups revealed solid state
associated structures through inter-molecular hydrogen bond interactions. Trinuclear complex,
Keywords:
Palladium
Platinum
b-Substituted ethylselenolate
X-ray structures
NMR spectroscopy
[Pd3Cl2(l–SeCH2CH2COOH)4(PnPr3)2] (3a), was disposed in a boat form unlike chair conformation
observed for the corresponding methylester complex. The effect of b-functionality in ethylselenolate
ligands towards reactivity, structures and thermal properties of palladium and platinum complexes
has been extensively studied.
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
gands usually employ a neutral donor, like O, N, P, etc. and often
serve as hemilabile ligands, finding relevance in homogeneous
The chemistry of platinum group metal chalcogenolate com-
plexes has been an active area of research for the past several dec-
ades [1–3] and has been dominated by complexes containing M–SR
linkages. The varied applications in several areas such as catalysis
[4–9], enzymatic models in biological systems, in cancer chemo-
therapy [10,11] and more recently as molecular precursors for me-
tal chalcogenides, MxEy (M = Pd or Pt; E = S, Se, and Te) [12–14]
have been a motivating factor for the sustained interest in these
complexes.
catalysis [6,19]. The chemistry of internally functionalized protic li-
gands, particularly with heavier chalcogen atoms, is rather scanty.
The presence of protic groups may result in hydrogen bonding con-
sequently forming self assembled metal–organic-frameworks
showing different topologies. The design of metal–organic-frame-
works utilizing the self assembly of molecules which contain com-
plementary hydrogen bonding groups (e.g., trans-[PdCl2(nicotinic
acid)2] [20]) has been well documented [20–24]. In the above per-
spective and in pursuance of our work on palladium and platinum
chalcogenolates, we have examined the reactions of b-functional-
ized ethylselenolates with palladium and platinum complexes. Re-
sults of this work are described herein.
The chemistry of metal chalcogenolates, keeping other factors
unchanged (like metal and/or chalcogen atoms, auxiliary ligands
on metal), is greatly influenced by the nature of R group attached
to chalcogen. Thus various structural motifs have been identified
when R group is changed from simple alkyl/aryl to bulky aryl
(e.g., (2,4,6-C6H2R3)E) [15] to internally functionalized R groups
(e.g., 2-pyE, E = S, Se, Te) [16–18]. For instance, reactions of
2. Results and discussion
2.1. Synthesis and spectroscopy
[M2Cl2(
complexes, [M2Cl2(
l
–Cl)2(PR0 )2] with NaEPh in 1:2 molar ratio yield binuclear
3
–EPh)2(PR0 )2] whereas reactions with NaEpy
3
77Se{1H} NMR chemical shift for sodium ethylselenolates,
NaSeCH2CH2X with various b-substitutions were in the order
X = OH (ꢀ224 ppm) < COOH (ꢀ153 ppm) < COOEt (ꢀ148 ppm) <
COOMe (ꢀ123 ppm). These values suggest that selenium site of
hydroxyl derivative is the most electron rich. The diselenides fol-
lowed the same order of chemical shift values as above, although,
l
under similar conditions give mononuclear complexes,
[MCl(Epy)(PR03)] (E = Se or Te) [17,18]. Internally functionalized li-
* Corresponding author. Tel.: +91 22 2559 5095; fax: +91 22 2550 5151.
E-mail address: jainvk@barc.gov.in (V.K. Jain).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.08.005

L.B. Kumbhare et al. / Journal of Organometallic Chemistry 694 (2009) 3892–3901
3893
[PdCl2(PnPr3)2]
selenium resonance is significantly deshielded as compared to that
2NaSeR
NaSeR
of the corresponding selenolate [25].
Complexes, [M2Cl2(
l
–SeR)2(PR0 )2] (1), [M2Cl2(
l
–Cl)(
l
–SeR)-
[Pd(SeR)2(PnPr3)2]
1/2 [Pd2(μ SeR)2(PnPr3)4].2Cl
(5)
3
(PR0 )2] (2) and [Pd2(SeR)2(
l
–SeR)2(PnPr3)2] (4) were isolated as
(6)
3
yellow to orange-red crystalline solids by treatment of
2xPnPr3
(1-2x)RSe
[M2Cl2(
l
–Cl)2(PR0 )2] (M = Pd or Pt; R = Se(CH2)2OH, Se(CH2)2-
3
(1/2-x)[Pd2(μ SeR)2(PnPr3)4]2+
(5')
COOH, Se(CH2)2COOMe, Se(CH2)2COOEt; PR0 = PMe2Ph, PnPr3)
+
x [Pd2(SeR)2(μ SeR)2(PnPr3)2]
(4)
3
with sodium selenolates in 1:2, 1:1 and 1:4 stoichiometry, respec-
tively. The 1H and 31P NMR spectra revealed that 1 exists either as
sym-cis or a mixture of sym-cis and -trans isomers with the pre-
dominance of the former which is appearing at lower frequencies.
The sym-trans isomer when left in solution for several days, could
convert into the sym-cis forms. The 77Se and 195Pt NMR spectra of 1
for acid and ester derivatives exhibited similar patterns and were
as expected [26]. 77Se NMR spectra were comprised of two sets
of resonances for cis and one set of signals for trans isomer
whereas, 195Pt NMR spectra exhibited one set of resonances for
each isomer with phosphorus-selenium/platinum couplings. How-
ever, the complexes containing HOCH2CH2Seꢀ (1a–1c), two sets of
resonances in 77Se and 195Pt NMR spectra of the trans isomer were
observed suggesting that both the metal as well as bridging selen-
olates are magnetically nonequivalent in the trans isomer. The 77Se
signal showed pronounced metal (Pd or Pt) and phosphine depen-
dence. The magnitude of various couplings, 1J(195Pt–31P),
where x < 1/2; R = CH2CH2COOMe, CH2CH2OH
Scheme 2.
(Scheme 2). This transformation was monitored by time dependent
31P NMR spectroscopy. For a given ligand, the formation of 4
against 50 was hastened by purging air into a CDCl3 solution, as
conversion of phosphine to phosphine oxide drives formation of
50 in forward direction (Fig. 1). Comparison of rate of formation
of 50 from 6 for hydroxyl and methyl ester functionalities clearly
demonstrates the effect of b-substitution (Fig. 2). The concentra-
tion of [Pd2(
pared to ([Pd2(
l
–SeCH2CH2OH)2(PnPr3)4]2+ (50b) grew faster as com-
–SeCH2CH2COOMe)2(PnPr3)4]2+ (50a) which is
l
attributed to the fact that higher nucleophilic hydroxyl selenolate
must act as a poor leaving group. Therefore the conversion of 6
to 50b slows down while the growth of 4b is accelerated as com-
pared to that in the case of methyl ester derivative. The diminished
growth rate for 4b at longer standing time may be due to the for-
mation of an insoluble complex having analytical data correspond-
2J(77Se–31P)cis/trans 2J(195Pt–195Pt), 1J(195Pt–77Se) for 1 are in accor-
,
dance with the reported values for organochalcogenolate bridged
complexes [26,27–31]. The 31P and 77Se NMR spectra of 2 displayed
single resonances indicating the formation of sym-cis isomer
exclusively.
ing to [Pd(
l
–SeCH2CH2OH)2]n. This can be further supported by
During the preparation of 1, trinuclear [Pd3Cl2(l–SeR)4(PnPr3)2]
(3) and binuclear tetrakis(selenolato) complex (4) were also
formed, the latter two complexes could be separated from 1 by
recrystallization. When the reaction of [Pd2Cl2(l–Cl)2(PnPr3)2]
6a
4a
40 min
60
40
20
0
B
C
D
nPrPO
80 min
120 min
160 min
200 min
-40
with more than 2.8 mol of NaSeCH2CH2X was carried out, several
binuclear complexes along with major product 1 (Scheme 1) were
formed which could be identified by 31P NMR spectroscopy.
5a
0
40
20
-20
Intensities of 31P NMR peaks suggest that 3 and [Pd2(
l–SeR)2-
(ppm)
δ
(PnPr3)4]ꢁ2Cl (5) were formed in appreciable quantity in the case
of complexes containing –SeCH2CH2COOR (R = H or Me) whereas
hydroxyl derivative furnished 3 as a minor product. As is evident
from 31P NMR spectra, complex 4 was the major product for the
latter, while it was the minor product for the former selenolates
(Supplementary, Fig. 1). These observations could be explained
with the fact that –SeCH2CH2OH is a stronger ligand in comparison
of –SeCH2CH2COOR (R = H or Me) as supported by 77Se chemical
shifts. Thus the higher nucleophilic hydroxyl ligand replaces termi-
0
100
200
Time (min)
300
400
Fig. 1. Time trace of 31P NMR intensity (the complexes containing SeCH2CH2-
COOMe) with reference to 6a for (B) 4a, (D) 5a when air was bubbled into the CDCl3
solution; (C) 4a without air bubbling. Inset 31P NMR spectra for the conversion of
4a– 5a at different time when the air bubbled into the CDCl3 solution.
nal chloride from [Pd2Cl2(l–Cl)2(PnPr3)2] with an ease leading to
the substantial formation of 4.
The complexes, 4 and [Pd2(
l
–SeR)2(PnPr3)4]2+ (50) (50 was
traced by 31P NMR spectroscopy without isolating it and hence
its counter ion could not be ascertained) could also be obtained
by transformation of [Pd(SeR)2(PnPr3)2] (6) in CDCl3 solution
3
A
B
C
D
2 [Pd2Cl2(μ SeR)2(PnPr3)2] + NaSeR/ 2NaSeR
(1)
2
[Pd3Cl2(μ SeR)4(PnPr3)2] + [Pd2(μ SeR)2(PnPr3)4].2Cl/ [Pd(SeR)2(PnPr3)2]
(5)
(6)
(3)
1
0
PnPr3
dimerization
[Pd2(SeR)2(μ SeR)2(PnPr3)2]
(4)
[Pd2Cl2(μ Cl)2(PnPr3)2] + 4 NaSeR'
0
50
100
Time (h)
R = CH2CH2COOMe; CH2CH2COOH; CH2CH2OH
Scheme 1.
Fig. 2. Time traces of 31P NMR signal intensities with reference to 6b for (A) 4a, (B)
4b (C) 5b (D) 5a in CDCl3.

3894
L.B. Kumbhare et al. / Journal of Organometallic Chemistry 694 (2009) 3892–3901
increasing intensity of tripropylphosphine oxide signal in 31P NMR
spectra.
Table 2
Selected bond lengths (Å) and bond angles (°) for [Pd2Cl2(l–Cl)(l–SeCH2CH2OH)(P-
MePh2)2]ꢁCHCl3 (2a) and [Pd2Cl2(
l
–Cl)(
l
–SeCH2CH2COOH)(PnPr3)2] (2b).
The homoleptic complexes, [Pd(l–SeCH2CH2X)2]6 (7), could be
2a
2b
synthesized by the reaction of Na2PdCl4 with NaSeR. The yield of
complexes depends upon their solubility in organic solvents. Ester
derivatives being more soluble were obtained in the highest yield.
The 77Se and 13C NMR spectra of 7 showed two sets of resonances
for bridging selenolates, indicating existence of two different dis-
positions of selenolates with respect to hexagonal ring, one was
within the ring plane and another being parallel to the ring axis.
This was further confirmed by X-ray crystallography in which
two slightly different Pd–Se bond distances have been observed
(see later). Earlier, the existence of other oligomeric forms in solu-
tion was proposed for [Pd(SeCH2CH2COOMe)2]6 [26] based on the
observation of two 77Se NMR signals. Since the relative ratio of
intensities of two sets in the 77Se and 13C NMR spectra does not
vary by changing the ligand, existence of other oligomeric species
in the solution may be ruled out.
Pd1–Se1
Pd1–Cl3
Pd1–P1
Pd1–Cl1
Pd2–Se1
Pd2–Cl3
Pd2–P2
Pd2–Cl2
Se1–C28
O1–C27
Pd1–Pd2
2.375(2)
Cl1–Pd1
Cl1–Pd2
Cl2–Pd1
Cl3–Pd2
P1–Pd1
P2–Pd2
Pd1–Se1
Pd2–Se1
C19–Se1
O2–C21
C21–O1
Pd1–Pd2
2.413(2)
2.431(4)
2.230(4)
2.347(4)
2.392(2)
2.428(3)
2.227(4)
2.336(4)
2.015(14)
1.428(18)
3.270(2)
2.419(2)
2.334(2)
2.329(2)
2.233(2)
2.233(2)
2.393(1)
2.386(1)
1.975(9)
1.294(11)
1.209(11)
3.212(1)
Pd1–Se1–Pd2
Pd1–Cl3–Pd2
Se1–Pd1–Cl3
Se1–Pd2–Cl3
Se1–Pd1–P1
Cl3–Pd1–Cl1
Se1–Pd1–Cl1
P1–Pd1–Cl1
P1–Pd1–Cl3
Se1–Pd2–P2
Cl3–Pd2–Cl2
Se1–Pd2–Cl2
P2–Pd2–Cl3
Pd1–Se1–C28
Pd2–Se1–C28
P2–Pd2–Cl2
86.61(7)
P1–Pd1–Cl2
P1–Pd1–Se1
Cl2–Pd1–Se1
P1–Pd1–Cl1
Cl2–Pd1–Cl1
Se1–Pd1–Cl1
P2–Pd2–Cl3
P2–Pd2–Se1
Cl3–Pd2–Se1
P2–Pd2–Cl1
Cl3–Pd2–Cl1
Se1–Pd2–Cl1
C19–Se1–Pd2
C19–Se1–Pd1
Pd2–Se1–Pd1
Pd1–Cl1–Pd2
88.69(9)
93.77(6)
175.84(8)
177.27(8)
92.50(8)
84.91(5)
88.38(9)
94.03(6)
174.94(8)
177.29(9)
92.87(9)
84.92(5)
100.9(2)
102.5(3)
84.44(3)
83.33(6)
84.60(11)
85.69(10)
85.39(10)
92.56(11)
92.78(13)
177.15(10)
89.01(14)
178.03(14)
89.92(11)
93.16(14)
174.99(11)
175.28(13)
99.5(6)
2.2. Crystal structures
Molecular structures of [Pd2Cl2(
(1b), [Pd2Cl2( –SeCH2CH2COOH)2(PMePh2)2] (1e), [Pd2Cl2(
Cl)( –SeCH2CH2OH)(PMePh2)2] (2a), [Pd2Cl2( –Cl)( –SeCH2CH2-
COOH)(PnPr3)2] (2b), [Pd3Cl2( –SeCH2CH2COOH)4(PnPr3)2] (3a)
and [Pd( –SeCH2CH2OH)2]6 (7a) have been established unambigu-
l–SeCH2CH2OH)2(PMePh2)2]
l
l–
l
l
l
l
l
100.3(5)
91.46(14)
ously by X-ray crystallography. Selected bond lengths and angles
are given in Tables 1–4. Figs. 3–8 (A), show ORTEP drawings with
crystallographic numbering schemes and (B) show line diagram
depicting short contacts and H-bondings (Supplementary Table
1) which are discussed on case by case basis. The C–Se distances
in all these complexes lie in the region 1.955(9)–2.015(14) Å and
Table 3
Selected bond lengths (Å) and bond angles (°) for [Pd3Cl2(
COOH)4(PnPr3)2] (3a).
l
–SeCH2CH2-
P1–Pd2
Cl1–Pd2
Pd1–Se2
Pd1–Se1
Pd2–Se2
Pd2–Se1
Pd1–Pd2
P1–Pd2–Cl1
P1–Pd2–Se1
Cl1–Pd2–Se2
Se2–Pd2–Se1
P1–Pd2–Se2
Cl1–Pd2–Se1
Pd2–Se1–Pd1
Pd2–Se2–Pd1
Se1–Pd1–Se2
2.278(3)
2.344(3)
2.426(1)
2.433(1)
2.484(1)
2.402(1)
3.176(1)
89.15(12)
93.84(9)
95.40(8)
81.63(5)
175.45(9)
175.32(9)
82.12(4)
80.58(4)
82.21(4)
C1–Se1
C4–Se2
C3–O1
C3–O2
C6–O3
C6–O4
1.966(10)
1.967(9)
1.227(13)
1.228(14)
1.144(17)
1.241(17)
Table 1
Selected bond lengths (Å) and bond angles (°) for [Pd2Cl2(l–SeCH2CH2OH)2(P-
MePh2)2] (1b) and [Pd2Cl2(
l
–SeCH2CH2COOH)2(PMePh2)2] (1e).
1b
1e
Pd1–P1
Pd1–P2
2.282(1)
2.291(1)
2.396(1)
2.474(1)
2.386(1)
2.482(1)
2.348(1)
2.346(1)
1.976(4)
1.967(5)
1.245(7)
1.408(7)
3.317(1)
P1–Pd1
P2–Pd2
Pd1–Se2
Pd1–Se1
Pd2–Se2
Pd2–Se1
Cl1–Pd1
Cl2–Pd2
C1–Se1
C4–Se2
C3–O1
C3–O2
C6–O3
C6–O4
Pd1–Pd2
P1–Pd1–Cl1
P1–Pd1–Se2
Cl1–Pd1–Se2
P1–Pd1–Se1
Cl1–Pd1–Se1
Se2–Pd1–Se1
P2–Pd2–Cl2
P2–Pd2–Se2
Cl2–Pd2–Se2
P2–Pd2–Se1
Cl2–Pd2–Se1
Se2–Pd2–Se1
C1–Se1–Pd1
C1–Se1–Pd2
Pd1–Se1–Pd2
C4–Se2–Pd2
C4–Se2–Pd1
Pd2–Se2–Pd1
2.281(3)
2.290(3)
2.472(1)
2.403(1)
2.463(1)
2.402(1)
2.362(3)
2.383(3)
1.995(10)
1.990(9)
1.242(13)
1.318(12)
1.222(12)
1.317(12)
3.401(1)
90.37(11)
174.71(9)
94.76(8)
94.00(9)
174.36(9)
80.97(5)
90.86(10)
173.64(8)
94.10(7)
93.96(8)
175.04(8)
81.17(5)
99.1(3)
Se2a–Pd1–Se1
Se2–Pd1–Se1a
Se1–Pd1–Se1a
Se2–Pd1–Se2a
C1–Se1–Pd2
Pd1–Se1–C1
C4–Se2–Pd2
Pd1–Se2–C4
Pd2–Pd1–Pd2a
97.51(4)
97.51(4)
169.65(7)
176.99(7)
102.3(3)
105.9(3)
109.5(3)
109.0(3)
110.10(5)
Pd1–Se2
Pd1–Se1
Pd2–Se2
Pd2–Se1
Cl1–Pd1
Cl2–Pd2
C14–Se1
C16–Se2
C15–O1
C17–O2
Pd1–Pd2
a
Denotes symmetrical moiety with respect to centre of inversion.
are well within the range reported for the bridging organoseleno-
late ligands [31,32]. The Pd–Pd separations in all these complexes
range between 3.176(1) and 3.401(1) Å which are significantly too
long to account for any Pd–Pd bonding.
P1–Pd1–Cl1
P1–Pd1–Se2
Cl1–Pd1–Se2
P1–Pd1–Se1
Cl1–Pd1–Se1
Se2–Pd1–Se1
P2–Pd2–Cl2
P2–Pd2–Se2
Cl2–Pd2–Se2
P2–Pd2–Se1
Cl2–Pd2–Se1
Se2–Pd2–Se1
C14-Se1–Pd1
C14–Se1–Pd2
Pd1–Se1–Pd2
C16–Se2–Pd2
C16–Se2–Pd1
Pd2–Se2–Pd1
88.42(4)
93.30(3)
173.16(4)
175.11(3)
96.44(3)
81.81(2)
88.89(4)
95.09(3)
170.87(3)
171.78(3)
95.27(4)
81.84(2)
107.06(15)
108.67(16)
84.05(2)
The complexes 1b and 1e comprise of two distorted square pla-
nar palladium atoms bridged together by two selenolato groups.
The molecules adopt a sym-cis configuration with non-planar
four-membered Pd2Se2 rings in which SeR ligands are exocyclic
exhibiting an anti conformation. The Pd–Se distances trans to phos-
phine are longer (by ꢂ0.1 Å) than those trans to chloride owing to
the strong trans influence of the phosphine ligands. The two Pd–Se
distances are well within the range reported for palladium seleno-
late complexes [14,32,33]. The Pd–P and Pd–Cl distances are as ex-
pected [32,34]. The Se–Pd–Se angles (ꢂ81°), similar in two
molecules, are significantly smaller than the ideal value of 90° indi-
cating strain in the four-membered Pd2Se2 ring. Although the
102.3(3)
90.10(5)
107.6(3)
108.6(3)
87.10(5)
103.77(16)
106.02(15)
87.86(2)

L.B. Kumbhare et al. / Journal of Organometallic Chemistry 694 (2009) 3892–3901
3895
Table 4
The core at the metal centres of 2a and 2b are isomorphous. The
dimeric molecules have two distorted square planar palladium
atoms sharing bridging chloride and selenolate ligands, forming a
non-planar, four-membered ‘‘Pd2SeCl” ring. The molecules adopt
a sym-cis configuration with phosphine ligands trans to bridging
chloride. The Pd–Se distances for the two complexes are similar
and are comparable with other selenolato-bridged palladium
derivatives [14,33]. The Pd–Cl(bridging) distances are longer (by
ꢂ0.1 Å) than the corresponding values for Pd–Cl(terminal) although
these distances are within the range reported for chloro-bridged
binuclear palladium complexes [35,36]. The Se–Pd–Cl angles
(ꢂ85°) are all similar in two complexes which have opened up
slightly from Se–Pd–Se angles in bis(selenolato)-bridged com-
plexes, 1b and 1e (ꢂ81°). The hydroxyl group of bridging seleno-
late ligands in binuclear complexes 1b and 2a show interaction
with the terminal chloride (Clꢁ ꢁ ꢁO = 3.037(7) Å for 1b and
3.096(1) Å for 2a) of the inversion related molecules resulting in
dimeric molecular assemblies. The carboxylic acid groups of bridg-
ing selenolate ligands in 1e and 2b of centrosymmetrically related
Selected bond lengths (Å) and bond angles (°) for [Pd(
l
–SeCH2CH2OH)2]6 (7a).
Pd1–Se2
Pd1–Se5i
Pd1–Se6
Pd1i–Se5
Pd2–Se1
Pd2–Se2
Pd2–Se3
Pd2–Se4
Pd3–Se3
Pd3–Se4
Pd3–Se5
2.446(1)
2.442(1)
2.439(1)
2.442(1)
2.441(1)
2.449(1)
2.430(1)
2.448(1)
2.440(1)
2.446(1)
2.426(1)
Pd3–Se6
2.445(1)
Pd1–Pd2
Pd2–Pd3
Pd3–Pd1i
Se1–C1
Se2i–C3
Se3–C5
Se4–C7
Se5–C9
Se6–C11
3.186(1)
3.263(1)
3.227(1)
1.955(9)
1.970(8)
1.978(8)
1.972(8)
1.960(8)
1.987(9)
Se1–Pd1–Se2
Se1–Pd1–Se5i
Se1–Pd1–Se6i
Se5i–Pd1–Se2
Se6i–Pd1–Se2
Se6i–Pd1–Se5i
Se1–Pd2–Se2
Se1–Pd2–Se4
Se3–Pd2–Se1
Se3–Pd2–Se2
Se3–Pd2–Se4
Se4–Pd2–Se2
81.92(4)
179.33(4)
96.77(4)
98.73(4)
175.36(4)
82.60(4)
81.55(4)
178.81(4)
96.83(4)
173.73(4)
83.57(4)
97.93(4)
Se3–Pd3–Se4
Se3–Pd3–Se6
Se5–Pd3–Se3
Se5–Pd3–Se4
Se5–Pd3–Se6
Se6–Pd3–Se4
Pd1–Se1–Pd2
Pd1–Se2–Pd2
Pd2–Se3–Pd3
Pd3–Se4–Pd2
Pd3–Se5–Pd1i
Pd1i–Se6–Pd3
83.38(4)
174.14(4)
97.06(4)
178.18(4)
82.79(4)
96.95(4)
81.79(3)
81.20(4)
84.15(4)
83.63(4)
83.02(4)
82.70(4)
molecules
showed
hydrogen
bonding
interactions
(Oꢁ ꢁ ꢁO = 2.613(15) and 2.636(13) Å for 1e and 2.696(5) Å for 2b).
In the former selenolate groups are intermolecularly hydrogen
bonded to inversion related molecules to form an infinite poly-
meric chain of binuclear Pd complexes.
i
Denotes symmetrical moiety with respect to centre of inversion.
The structure of 3a consists of three square planar palladium
atoms sharing four bridging selenolato groups. The molecule has
a boat shape (Scheme 3) and represents the first example of such
a conformation for complexes having ‘‘M3(
stance, complexes, [Pd3Cl2( –SHx)4(PMe3)2] [37], [Pt3(
Stol)4(dppm)2][CF3SO3]2 [38], [Pd3( –SMes)4(
3–C4H7)2] [33],
[Pd3Cl2( –SeCH2CH2COOMe)4(PnPr3)2] [26] have a zigzag shape.
l–ER)4” core. For in-
l
l–
l
g
l
Thus the boat conformation in 3a may be attributed to the stabil-
ization due to hydrogen bonding. The central palladium atom (Pd1)
in 3a is surrounded by Se4 core with essentially similar Pd–Se dis-
tances. The coordination environment around terminal palladium
atoms is defined by two bridging selenolates, a chloride and a
phosphine ligand. The central palladium atom is at the inversion
centre of the molecule. The Pd–Pd distances (3.176 (1) Å) are smal-
ler than those reported for [Pd3Cl2(l–SeCH2CH2COOMe)4(PnPr3)2]
[26]. The various bond lengths and angles in ‘‘PdClPdSe2” fragment
are similar to the one observed for 1b and 1e. The R groups on
bridging Se atoms in ‘‘Pd(SeR)2” fragment adopt an anti configura-
tion. Each molecule has a series of OHꢁ ꢁ ꢁO@C contacts (Fig. 7B) viz.
O2ꢁ ꢁ ꢁO4 = 2.642(1), O1ꢁ ꢁ ꢁO3 = 2.655(1) and O4ꢁ ꢁ ꢁO4 = 2.998(1) (Å)
with its neighbours leading to a supramolecular aggregation. The
carboxylic acid groups of bridging selenolate of one side of mole-
cule a interacts with the carboxylic acid groups of another mole-
cule b while the carboxylic acid group on other side of the
molecule a coordinates with –COOH group of molecule c. Typical
Oꢁ ꢁ ꢁO distances in carboxylic acid derivatives have been reported
to be 2.637(3) Å [19].
The homoleptic complex 7a is hexameric comprising of a cen-
trosymmetric Pd6Se12 hexagon in which each square planar palla-
dium atoms has a PdSe4 core. The two adjacent palladium atoms
are held together by two selenolato bridges. The palladium coordi-
nation planes are inclined to each other by 64.35°, 56.55° and
59.10° (coordination planes of Pd1 and Pd2, Pd2 and Pd3, and
Pd1 and Pd3, respectively) resulting into a Pd6Se12 hexagon. As a
consequence of formation of hexagon, the Se–Pd–Se angles around
each palladium atom are split into acute (ꢂ82°, within the ring
plane) and obtuse (ꢂ98°, parallel to the ring axis) sets. In
‘‘Pd2(SeCH2CH2OH)2” fragment, the Pd–Se distances originating
from one of the bridging selenolate groups are slightly longer than
the other bridging ligand, although all the Pd–Se distances
(2.430(1)–2.448(1) Å) lie within the range reported for selenolate
complexes [14,32,33,36]. The overall structure is isomorphous to
Fig. 3. (A) ORTEP diagram of cis-[Pd2Cl2(l–SeCH2CH2OH)2(PMePh2)2] (1b) (ellipsoids
drawn with 50% probability); (B) line diagram showing short contacts (hydrogen
atoms are omitted for clarity).
Pd(1)–Se(2)–Pd(2) (bridging selenolate trans to phosphine) are
essentially similar in both the complexes, the angle Pd(1)–Se(1)–
Pd(2) (bridging selenolate trans to chloride) are significantly differ-
ent (84.05 (2)° for 1b and 90.10 (5)° for 1e).

3896
L.B. Kumbhare et al. / Journal of Organometallic Chemistry 694 (2009) 3892–3901
Fig. 4. (A) ORTEP diagram of cis-[Pd2Cl2(
l
–SeCH2CH2COOH)2(PMePh2)2] (1e) (ellipsoids drawn with 25% probability); (B) line diagram showing H-bridges (hydrogen atoms are
omitted for clarity).
[Pd(
l
–SeCH2CH2X)2]6 (X = NMe2 [36], COOMe [26]) and [Pd(SR)2]6
were characterized by powder XRD which were consistent with
the formation of Pd17Se15. The broadening of XRD pattern in case
of 1a (Supplementary, Fig. 3) suggests the formation of nanoparti-
cles which may be favoured by low decomposition temperature.
Decomposition byproducts of 1a were analyzed by Q-MS coupled
with TG. Mass spectra displayed oxygen bearing fragments (Sup-
plementary, Fig. 4) at around 119 °C suggesting fragmentation of
selenolate moiety. At 169 °C hydrocarbon fragments of relatively
higher intensities were observed due to fragmentation of phos-
phine groups as well as some secondary fragmentation. Major frag-
ments obtained from 1a were H2O, C2H4, C2H3 and C2H2.
(R = nPr [39,40], CH2COOMe [41]). There are several intermolecular
OHꢁ ꢁ ꢁO hydrogen bonding contacts (O2ꢁ ꢁ ꢁO5 = 2.730(12),
O2ꢁ ꢁ ꢁO6 = 2.717(10), O3ꢁ ꢁ ꢁO4 = 2.559(15), O3ꢁ ꢁ ꢁO5 = 2.706(16),
O1ꢁ ꢁ ꢁO6 = 2.716(12), O1ꢁ ꢁ ꢁO4 = 2.686(15) Å). Each OH group is
hydrogen bonded to its nearest oxygen atom of neighbouring mol-
ecule. Such interactions lead to the formation of a 3D array of hex-
americ Pd6Se12 core. Packing of 7a (Fig. 8B) shows extensive
network of intermolecular hydrogen bonds with channel down
the a-axis of diameters 7.542 and 6.887 Å.
2.3. Thermal studies
3. Experimental
TG curves for 1a, 1g and [Pd2Cl2(l–SeCH2CH2COOMe)2(PnPr3)2]
(Supplementary, Fig. 3) showed weight loss of 58.2 (Calc. 58.6)% at
202 °C, 64.1 (Calc. 63.5)% at 265 °C and 62.7 (Calc. 62.4)% at 248 °C,
respectively (parentheses indicate weight loss corresponding to
the formation of Pd17Se15). The observed weight loss indicates that
these complexes, irrespective of b-substitution on ethylselenolate,
decompose to Pd17Se15. However, b-substitution did influence the
decomposition temperature. The complex 1a decomposed at much
lower temperature (202 °C) as compared to those derived from –
SeCH2CH2COOR (R = Me, Et). To prepare sufficient quantities of
palladium selenide, complexes were pyrolyzed in a furnace at the
corresponding decomposition temperature. The residues obtained
3.1. Materials and methods
The complexes, Na2PdCl4 and [M2Cl2(
l
–Cl)2(PR0 )2] (M = Pd, Pt;
3
PR0 = PMePh2, PnPr3) and the ethyldiselenide (–SeCH2CH2COOMe)2
3
were prepared according to literature methods [26,42]. All the
reactions were carried out under an argon atmosphere in dry and
distilled solvents. Microanalyses were carried out on a Carlo Erba
EA-1110 CHN-O instrument. 1H and proton decoupled 13C, 31P,
77Se and 195Pt NMR spectra were recorded in CDCl3 on a Bruker
Avance-II 300 MHz NMR spectrometer, operating at 300, 75.47,
121.49, 57.24 and 64.52 MHz, respectively. Chemical shifts (in

L.B. Kumbhare et al. / Journal of Organometallic Chemistry 694 (2009) 3892–3901
3897
Fig. 6. (A) ORTEP diagram of cis-[Pd2Cl2(
l–Cl)(
l–SeCH2CH2COOH)(PnPr3)2] (2b)
(ellipsoids drawn with 50% probability); (B) line diagram showing H-bridges
(hydrogen atoms are omitted for clarity).
Fig. 5. (A) ORTEP diagram of cis-[Pd2Cl2(l–Cl)(l–SeCH2CH2OH)(PMePh2)2]ꢁCHCl3
(2a) (ellipsoids drawn with 50% probability); (B) line diagram showing short
contacts (hydrogen atoms are omitted for clarity).
3,30-Diselenodipropionic acid, (–SeCH2CH2COOH)2 was pre-
pared from aqueous sodium diselenide and 2-bromopropionic acid
[45]. Anal. Calc. for C6H10O4Se2: C, 23.7; H, 3.3. Found: C, 23.6; H,
3.4%. 1H NMR (acetone-d6): d 2.79 (t, 7.0 Hz, 4H, SeCH2); 3.11 (t,
6.8 Hz, 4H, COOCH2); 4.26 (br, 2H, COOH). 13C NMR (acetone-d6):
d 23.4 [1J(77Se–13C) = 74 Hz], CH2–Se), 35.2 (CH2–O), 172.8 (COOH).
77Se NMR (acetone-d6): d 325. Mass spectral data (m/e): 304 [M+],
287 [M–OH].
(–SeCH2CH2COOEt)2 was synthesized by esterification of
(–SeCH2CH2COOH)2 with dry ethanol in the presence of concen-
trated sulfuric acid. Anal. Calc. for C10H18O4Se2: C, 33.3; H, 5.0.
Found: C, 33.1; H, 4.7%. 1H NMR (CDCl3): d 1.23 (t, 7.2 Hz, 6H,
OCH2CH3); 2.78 (t, 7.1 Hz, 4H, SeCH2); 3.06 (t, 7.2 Hz, 4H, COOCH2);
4.12 (q, 7.2 Hz, 4H, OCH2). 13C NMR (CDCl3): d 14.2 (OCH2CH3);
23.3 [1J(77Se–13C) = 75 Hz, CH2Se]; 35.9 (CH2CO), 60.7 (OCH2),
172.1 (COO). 77Se NMR (CDCl3): d 324.
ppm) are relative to TMS for 1H and 13C and external 85% H3PO4 for
31P, Me2Se for 77Se (secondary reference Ph2Se2, d 463 ppm) and
Na2PtCl6 in D2O for 195Pt. For the time dependent 31P NMR studies,
freshly prepared [Pd(SeCH2CH2COOMe)2(PnPr3)2] (6a) (25 mg) in
6 mL of CDCl3 was taken in a NMR tube. The spectra were recorded
at a time interval, the first spectrum was designated as zero time
spectrum. To the above solution, air was introduced intermittently
for 30 min using a bubbler. The same procedure was repeated
for 6b. Mass spectra were recorded on a Waters Q-Tof micro
(YA-105) time of flight mass spectrometer. TG curves with mass
spectra were obtained under an argon atmosphere with a heating
rate of 10 °C/min on SETARAM Setsys evolution-1750 TG analyzer
coupled with ‘Quadstar 32-bit quadruple mass spectrometer’. Pal-
ladium selenides were obtained under a flow of argon by heating
each of the complexes, (1a, 1g and [Pd2Cl2(l–SeCH2CH2COO-
Me)2(PnPr3)2]) in a glass tube housed in a furnace. Temperature
of the furnace was set at 10 °C above the respective decomposition
temperature obtained from TG curve.
3.3. Synthesis of palladium(II) and platinum(II) complexes
3.3.1. [Pd2Cl2(l–SeCH2CH2OH)2(PnPr3)2] (1a)
3.2. Preparation of ligands
To a freshly prepared methanolic solution of NaSeCH2CH2OH
(prepared in situ by the reaction of (–SeCH2CH2OH)2 (119 mg,
0.48 mmol) with NaBH4 (36 mg, 0.96 mmol) in anhydrous metha-
Bis(2-hydroxyethyl)diselenide, (–SeCH2CH2OH)2 was synthe-
sized by acid hydrolysis of corresponding potassium selenosulfate
which was prepared by reacting aqueous potassium selenosulfate
with ethanolic 1-bromoethanol [43,44]. The yellow oil obtained
from this reaction was purified by column chromatography using
5% methanol in CHCl3. Yield = 45%. Anal. Calc. for C4H10O2Se2: C,
19.4; H, 4.1. Found: C, 19.2; H, 4.0%. 1H NMR (CDCl3): d 2.64 (s,
2H, OH); 3.11 (t, 7.7 Hz, 4H, SeCH2); 3.92 (t, 7.7 Hz, 4H, OCH2).
13C NMR (CDCl3): d 32.6 [C–Se; 1J(77Se–13C) = 75 Hz], 61.8 (C–O).
77Se NMR (CDCl3): d 259.
nol),
a
dichloromethane solution of [Pd2Cl2(l
–Cl)2(PnPr3)2]
(308 mg, 0.46 mmol) was added with vigorous stirring which con-
tinued for 1 h. The resulting orange solution was evaporated under
vacuum and the residue was extracted with dichloromethane and
filtered. The filtrate was reduced to 5 mL and layered by a mixture
of ethylacetate and hexane. The solution on cooling in a freezer
gave orange crystalline solid of the title complex (200 mg, 64%).
m.p. 108–110 °C. 1H NMR (CDCl3): d 1.07 (t), 1.63 (m), 1.86 (m)
[PnPr3]; 2.89 (t), 3.32 (m) (each OCH2); 3.94 (SeCH2); 4.14 (br,

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L.B. Kumbhare et al. / Journal of Organometallic Chemistry 694 (2009) 3892–3901
Fig. 7. (A) ORTEP diagram of trans-[Pd3Cl2(
l
–SeCH2CH2COOH)4(PnPr3)2] (3a) (ellipsoids drawn with 25% probability); (B) line diagram showing H-bridges (hydrogen atoms are
omitted for clarity).
Fig. 8. (A) ORTEP diagram of [Pd(l–SeCH2CH2OH)2]6 (7a) (ellipsoids drawn with 50% probability); (B) line diagram showing H-bridges (hydrogen atoms are omitted for clarity).
CO2Me
3.3.2. [Pd2Cl2(l–SeCH2CH2OH)2(PMePh2)2] (1b)
CO2H
HO2C
Prepared similar to 1a in 55% yield. m.p. 163–165 °C. 1H NMR
(CDCl3): d 2.10, 2.14 (each d, 2J(31P–1H) = 12 Hz, PMe); 3.14, 3.24,
3.48, 3.78 (br, SeCH2CH2 from cis and trans isomers); 4.05 (br,
OH); 7.33–7.71 (m, PPh2). 31P{1H} NMR (CDCl3): d 8.7 (cis isomer),
10.1 (trans isomer). 77Se{1H} NMR CDCl3: d ꢀ15 (SeR trans to Cl);
ꢀ67 [t, 2J(77Se–31P) = 139 Hz], SeR trans to PMePh2] [cis isomer].
ꢀ217 (d, 146 Hz); ꢀ227 (d, 146 Hz) [trans isomer]. Anal. Calc. for
C30H36Cl2O2P2Pd2Se2: C, 38.6; H, 3.9. Found: C, 38.7; H, 3.8%.
CO2Me
MeO2C
CO2H
CO2H
MeO2C
boat
chair
Scheme 3. Schematic representation of conformations for trinuclear palladium
complex.
3.3.3. [Pt2Cl2(-SeCH2CH2OH)2(PnPr3)2] (1c)
Title complex was prepared analogous to 1a. m.p. 133–135 °C.
1H NMR (CDCl3): d 1.05 (t), 1.60 (br) [PnPr3]; 2.70 (t, trans isomer);
2.93 (t, cis isomer); 3.36 (br), 3.51 (br) (trans isomer) [each OCH2].
3.84 (t, cis isomer); 4.03 (t, trans isomer) [each SeCH2]; 4.20 (br,
OH). 31P{1H} NMR (CDCl3): d 0.5 [s, cis isomer, 1J(195Pt –31P) =
3132 Hz]; 0.9 [s, trans isomer, 1J(195Pt–31P) = 3066 Hz]. 77Se{1H}
OH). 31P {1H} NMR (CDCl3: d 13.6 (s, cis); 14.2 (s, trans). 77Se {1H}
NMR (CDCl3):
d
ꢀ74 (SeR trans to Cl); ꢀ92 [t,
2J(77Se–31P) = 133 Hz), SeR trans to PnPr3] [cis isomer]. ꢀ315 (d,
139 Hz); ꢀ397 (d, 148 Hz) [trans isomer]. Anal. Calc. for
C22H52Cl2O2P2Pd2Se2: C, 31.0; H, 6.1. Found: C, 31.1; H, 6.1%.

L.B. Kumbhare et al. / Journal of Organometallic Chemistry 694 (2009) 3892–3901
3899
NMR (CDCl3): d ꢀ127 (br); ꢀ167 [1J(195Pt–77Se) = 244 Hz)] [cis iso-
mer]. ꢀ296 (d, 145 Hz); ꢀ315 (d, 130 Hz) [trans isomer]. 195Pt NMR
(CDCl3): d ꢀ4058 [1J(195Pt–31P) = 3136 Hz; 2J(195Pt–195Pt) = 925 Hz]
[cis isomer]. ꢀ3840 [d, 1J(195Ptꢀ31P) = 3053 Hz]; ꢀ3918 [d,
2 H, SeCH2); 7.30–7.80 [m, Ph]. 31P{1H} NMR (CDCl3): d 22.5. Anal.
Calc. for C28H21Cl3OP2Pd2Se: C, 39.9; H, 3.7. Found: C, 39.7; H, 3.6%.
3.3.9. [Pd2Cl2(
Prepared analogous to complex 1d from [Pd2Cl2(
(375 mg, 0.56 mmol) and NaSeCH2CH2COOH (prepared from
NaBH4 (21 mg, 0.60 mmol), (–SeCH2CH2COOH)2 (83 mg,
l–Cl)(l–SeCH2CH2COOH)(PnPr3)2] (2b)
1J(195Pt–31P) = 3053 Hz]
[trans
isomer].
Anal.
Calc.
for
l–Cl)2(PnPr3)2]
C22H52Cl2O2P2Pt2Se2: C, 25.7; H, 5.1. Found: C, 25.6; H, 4.8%.
0.30 mmol), ammonia solution (0.2 ml of 25%), conc. H2SO4
(0.05 ml) in water) in 1:1 molar ratio and the resulting complex
was recrystallized from chloroform (yield 65%). m.p. 200–202 °C.
1H NMR (CDCl3): d 1.07–1.11 (m), 1.78 (br) [PnPr3]; 2.90, 3.01,
3.17, 3.36 (each t, SeCH2CH2). 31P{1H} NMR (CDCl3): d 32.2.
77Se{1H} NMR (CDCl3): d 35. Anal. Calc. for C21H47Cl3O2P2Pd2Se:
3.3.4. [Pd2Cl2(
To a mixture of (–SeCH2CH2COOH)2 (100 mg, 0.33 mmol) and
NaBH4 (37 mg, 0.99 mmol), ammonia solution (600 L of 25%) in
distilled water (2 cm3) was added and the whole was stirred under
an argon atmosphere. To this concentrated sulfuric acid (150 L)
was added followed by addition of an acetone solution of
[Pd2Cl2( –Cl)2(PnPr3)2] (210 mg, 0.31 mmol). The reaction mixture
l–SeCH2CH2COOH)2(PnPr3)2] (1d)
l
l
C, 31.9; H, 6.0. Found: C, 32.3; H, 5.9%. When [Pd2Cl2(l–
l
Cl)2(PnPr3)2] was treated with NaSeCH2CH2COOH in methanol in
order to prepare diselenido complex (1d), complex 2b was ob-
tained instead, due to incomplete cleavage of diselenide by meth-
anolic NaBH4.
was stirred for 1 h at room temperature. The solvents were evapo-
rated under vacuum and the residue was washed with water, dried
under vacuum and extracted with dichloromethane and filtered.
The filtrate was concentrated to 5 mL and layered with hexane–
acetone mixture, which on refrigeration afforded orange crystals
of the title complex (yield 60%). m.p. 135 °C. 1H NMR (CDCl3): d
1.08 (t), 1.61 (br), 1.88 (br) [PnPr3]; 2.81, 2.87 (br, SeCH2), 3.14,
3.20 (br, CH2, syn and anti), 4.77 (br, OH). 31P{1H} NMR (acetone-
d6): d 13.8 (cis isomer)14.5 (trans isomer). 77Se{1H} NMR (ace-
tone-d6): d ꢀ51 (SeR trans to Cl); ꢀ70 [(t, 2J(77Se–31P) = 137 Hz,
trans to PnPr3] [cis isomer]. Anal. Calc. for C24H52Cl2O4P2Pd2Se2:
C, 31.7; H, 5.8. Found: C, 31.6; H, 5.6%.
3.3.10. [Pd3Cl2(l–SeCH2CH2COOH)4(PnPr3)2] (3a)
This was isolated as a byproduct from 1d during recrystalliza-
tion in poor yield (ꢂ8%). m.p. 200 °C. 1H NMR (CDCl3): d 1.08,
1.62, 1.87 [PnPr3]; 2.20, 2.88 (SeCH2CH2); 3.11 (t, COOH). 31P{1H}
NMR (CDCl3): d 14.0 (cis isomer),15.7 (trans isomer). 77Se {1H}
NMR (CDCl3): d ꢀ52 [d, 2J(77Se–31P) = 135 Hz, SeR trans to PR3];
ꢀ96 (SeR trans to Cl) [cis isomer]. Anal. Calc. for
C30H62Cl2O8P2Pd3Se4: C, 27.3; H, 4.7. Found: C, 27.6; H, 4.6%.
3.3.5. [Pd2Cl2(l-SeCH2CH2COOH)2(PMePh2)2] (1e)
3.3.11. [Pd2(SeCH2CH2OH)2(
This complex was prepared in
[Pd2(SeCH2CH2COOMe)2( –SeCH2CH2COOMe)2(PnPr3)2] (4a) [26].
31P{1H} NMR (CDCl3): d 7.9, 9.0.
l
–SeCH2CH2OH)2(PnPr3)2] (4b)
Prepared similar to 1d (yield 54%). m.p. 185 °C. 1H NMR (CDCl3):
d 2.10, 2.20 (each d, PMe); 2.45, 2.88, 3.13, 3.18, 3.44 (each t,
SeCH2CH2); 7.30–7.85 (m, PPh2). 31P{1H} NMR (acetone-d6): d 8.6
(cis isomer), 10.3 (trans isomer). 77Se{1H} NMR (acetone-d6): d
ꢀ24 (SeR trans to Cl); ꢀ35 [t, 1J(77P–77Se) = 141 Hz, SeR trans to
PMePh2] [cis isomer]. Anal. Calc. for C32H36Cl2O4P2Pd2Se2: C, 38.9;
H, 3.7. Found: C, 38.7; H, 4.0%.
a
manner similar to
l
3.3.12. [Pd2(l–SeCH2CH2COOMe)2(PnPr3)4]Cl2 (5a)
Dichloromethane solution of [PdCl2(PnPr3)2] (220 mg,
0.44 mmol) was reacted with a methanolic solution of NaS-
eCH2CH2COOMe (prepared in situ by the reaction of (–SeCH2CH2-
COOMe)2 (74 mg, 0.22 mmol) with NaBH4 (18 mg, 0.48 mmol) in
anhydrous methanol), stirred for 15 min, filtered and dried under
vacuum. 1H NMR (CDCl3): d 0.95 (t), 1.46 (m), 1.85 (m) [PnPr3];
2.49–2.59 (m, SeCH2CH2); 3.58 (s, OMe). 31P{1H} NMR (CDCl3): d
3.3.6. [Pt2Cl2(l–SeCH2CH2COOH)2(PnPr3)2] (1f)
Prepared similar to 1d (yield 50%). m.p. 192–194 °C. 1H NMR
(CDCl3): d 1.07 (t), 1.60 (br), 1.85 (br) [PnPr3]; 2.77, 2.92, 3.24, 3.34
(each br, SeCH2CH2); 4.33 (br, COOH). 31P {1H} NMR (acetone-d6):
d ꢀ1.0 [1J(195Pt–31P) = 3168 Hz; 2J(195Pt–195Pt) = 916 Hz) (cis iso-
mer). 77Se{1H} NMR (acetone-d6): d ꢀ92 (1J(195Pt–77Se) = 153 Hz);
ꢀ131 [1J(195Pt–77Se) = 252 Hz [cis isomer]. 195Pt{1H} NMR
(acetone-d6): d ꢀ4059 (d, 1J(195Pt–31P) = 3174 Hz; 2J(195Pt–195Pt) =
924 Hz] [cis isomer]. Anal. Calc. for C24H52Cl2O4P2Pt2Se2: C, 26.5; H,
4.8. Found: C, 26.3; H, 4.6%.
4.6. 77Se{1H} NMR (CDCl3):
d
ꢀ31. Similarly [Pd2(
l–SeCH2-
CH2OH)2(PnPr3)4]Cl2 (5b) was prepared. 31P{1H} NMR (CDCl3): d 4.8.
3.3.13. [Pd(SeCH2CH2COOMe)2(PnPr3)2] (6a)
Prepared analogous to 5a, from [PdCl2(PnPr3)2] (110 mg,
0.22 mmol), (–SeCH2CH2COOMe)2 (81 mg, 0.24 mmol) and NaBH4
(20 mg, 0.53 mmol). 1H NMR (CDCl3): d 0.95 (t), 1.42 (br), 2.0
(br) [PnPr3]; 2.50, 2.56 (each br, SeCH2CH2); 3.59 (s, OMe).
31P{1H} NMR (CDCl3): d 0.9. 77Se{1H} NMR (CDCl3): d ꢀ73. Similarly
[Pd(SeCH2CH2OH)2(PnPr3)2] (6b) was prepared. 31P{1H} NMR
(CDCl3): d 0.5. 77Se{1H} NMR (CDCl3): d ꢀ154.
3.3.7. [Pd2Cl2(l–SeCH2CH2COOEt)2(PnPr3)2] (1g)
Prepared similar to 1a (yield 65%). m.p. 100–101 °C. 1H NMR
(CDCl3): d 1.08 (t), 1.60 (br), 1.82–1.91 (m) [PnPr3];1.23, 1.28 (each
t, 7 Hz, CH2Me); 2.78, 2.86 (SeCH2); 3.04 (t), 3.23 (br) (CH2CO);
4.12, 4.15 (each q, OCH2). 31P{1H} NMR (CDCl3): d 12.8 (s, cis iso-
mer); 13.2 (4%, trans isomer). 77Se{1H} NMR (CDCl3): d ꢀ62
[2J(77Se–31P) = 134 Hz, trans to PPr3]; ꢀ70 (trans to Cl) [cis isomer];
ꢀ257 [d, 2J(77Se–31P) = 152 Hz, ꢂ5%] [trans isomer]. Anal. Calc. for
C28H60Cl2O4P2Pd2Se2: C, 34.9; H, 6.3. Found: C, 34.8; H, 6.5%.
3.3.14. [Pd(l–SeCH2CH2OH)2]6 (7a)
A methanolic solution of Na2PdCl4 (390 mg, 1.33 mmol) was
added to a solution of NaSeCH2CH2OH [prepared from NaBH4
(100 mg, 2.63 mmol) and (–SeCH2CH2OH)2 (329 mg, 1.33 mmol)
in methanol] and stirred for 3 h under an argon atmosphere,
whereupon a brown precipitate formed. The precipitate was fil-
tered and extracted with ethanol. The solution was passed through
cellite and concentrated under vacuum. The solution on slow evap-
oration afforded deep red crystals of the title complex (yield 40%).
m.p. 258–260 °C. 13C{1H} NMR (dmso-d6): d 29.1, 26.3 (each s,
SeCH2), 62.0, 65.0 (each s, OCH2). 77Se{1H} NMR (dmso-d6): d
ꢀ68, ꢀ207. Anal. Calc. for C24H60O8Pd6Se12: C, 13.5; H, 2.8. Found:
C, 13.9; H, 2.6%.
3.3.8. [Pd2Cl2(
Prepared in a similar manner to 1a by the reaction between
[Pd2Cl2( –Cl)2(PMePh2)2] (264 mg, 0.35 mmol) and NaS-
l–Cl)(l–SeCH2CH2OH)(PMePh2)2] (2a)
l
eCH2CH2OH [prepared in situ from (–SeCH2CH2OH)2 (90 mg,
0.36 mmol) with NaBH4 (28 mg, 0.73 mmol) in absolute methanol]
and recrystallized from dichloromethane-hexane as a yellow crys-
talline solid (yield, 200 mg, 68%). m.p. 206–207 °C. 1H NMR
(CDCl3): d 2.07 (t, 2 H, OCH2); 2.23 [d, 12 Hz, 6H, PMe]; 3.64 (br,

3900
L.B. Kumbhare et al. / Journal of Organometallic Chemistry 694 (2009) 3892–3901
Table 5
Crystal data and structure refinement details of [Pd2Cl2(l–SeCH2CH2OH)2(PMePh2)2] (1b), [Pd2Cl2(l–SeCH2CH2COOH)2(PMePh2)2] (1e), [Pd2Cl2(l–Cl)(l–SeCH2CH2OH)2(P-
MePh2)2]ꢁCHCl3](2a), [Pd2Cl2(
l
–Cl)(
l–SeCH2CH2COOH)(PnPr3)2] (2b), [Pd3Cl2(
l–SeCH2CH2OH)4(PnPr3)2] (3a) and [Pd(
l–SeCH2CH2OH)2]6 (7a).
1b
1e
2aꢁCHCl3 2b
3a
7a
Chemical formula
Formula weight
Crystal size (mm3)
Crystal system
Space group
C30H36Cl2O2P2Pd2Se2 C32H36Cl2O4P2Pd2Se2 C29H32Cl6OP2Pd2Se C21H47Cl3O2P2Pd2Se 0.5(C30H62Cl2O8P2Pd3Se4) C24H60O12Pd6Se12
932.15
988.17
962.95
791.64
659.34
2126.64
0.37 ꢃ 0.32 ꢃ 0.29
0.30 ꢃ 0.10 ꢃ 0.10
0.10 ꢃ 0.10 ꢃ 0.10
Monoclinic
P21/c
0.43 ꢃ 0.32 ꢃ 0.30
Monoclinic
P21/n
0.3 ꢃ 0.15 ꢃ 0.15
Monoclinic
C2/c
0.20 ꢃ 0.20 ꢃ 0.20
Triclinic
Triclinic
Triclinic
ꢀ
ꢀ
ꢀ
P1
P1
P1
Unit cell dimensions
a (Å)
b (Å)
c (Å)
11.273(2)
11.578(3)
14.635(3)
93.593(4)
109.687(3)
107.917(3)
1681.6(6)/2
3.514/912
2.50–27.50
ꢀ15 6 h 6 15
ꢀ14 6 k 6 14
ꢀ19 6 l 6 18
19723/7851
11.723(3)
13.600(4)
13.888(9)
107.90(3)
13.070(6)
21.646(12)
12.991(5)
13.2798(13)
18.5511(18)
14.5042(14)
16.700(5)
21.393(8)
14.978(4)
11.0797(14)
11.1000(12)
11.4471(15)
103.950(9)
104.609(10)
101.020(9)
1273.7 (3)/1
10.692/984
2.98–27.51
ꢀ8 6 l 6 14
ꢀ14 6 h 6 14
ꢀ14 6 k 6 14
7045/ 5843
a
(Å)
b (Å)
(Å)
Volume (Å3)/Z
(mmꢀ1)/F (0 0 0)
98.07(3)
103.04(3)
112.273(2)
115.52(2)
c
110.920(18)
1888.5(14)/2
3.139/968
2.63–27.49
ꢀ15 6 h 6 15
ꢀ16 6 k 6 17
ꢀ18 6 l 6 10
10346/8625
3581(3)/4
3306.6(6)/4
2.543/1584
2.35–27.00
ꢀ17 6 h 6 17
ꢀ23 6 k 6 24
ꢀ19 6 l 6 17
28369/7748
4829(3)/8
l
2.581/1888
2.68–27.53
ꢀ9 6 h 6 16
0 6 k 6 28
ꢀ16 6 l 6 16
9836/8199
4.335/2576
2.60–27.49
ꢀ12 6 h 6 21
0 6 k 6 27
ꢀ19 6 l 6 17
6614/5548
h Range (°)
Limiting indices
Number of reflections/
unique
Number of data/
restraints/parameters
7851/0/365
8625/0/399
8199/0/370
7748/0/287
5548/0/222
5843/0/250
Final R1[I > 2
R1, R2 (all data)
Goodness of fit on F2
r
(I)],
x
R2
0.0363, 0.0563
0.0811, 0.0887
1.022
0.0582, 0.2307
0.0959, 0.1339
0.936
0.0711, 0.1515
0.2662, 0.2130
0.949
0.0451, 0.0763
0.0937, 0.0892
1.000
0.0549, 0.0990
0.2119, 0.1357
0.924
0.0417, 0.0823
0.1065, 0.0988
1.000
x
Measurement temperature = 298(2) K; X-ray wavelength = 0.71073 Å.
3.3.15. [Pd(
l
–SeCH2CH2COOH)2]6 (7b)
perature for conversion of [Pd2Cl2(SeR)2(PnPr3)2] to Pd17Se15 is
lower, conversion of [Pd(SeR)2(PnPr3)2] to [Pd2(SeR)2( –SeR)2-
(PnPr3)2] is faster. However, tendency to form trinuclear species is
subdued for hydroxyl ligand compared to that of acid and ester
derivatives. Presence of hydrogen bonding in solid state structures
plays important role in stabilizing uncommon boat conformation.
Prepared similar to 7a in aqueous medium (yield 40%). m.p.
260–262 °C. 13C{1H} NMR (dmso-d6): d 18.2, 20.8 (each s, SeCH2);
36.2, 39.0 (each s, –CH2–); 172.7 (s, COOH). 77Se{1H} NMR
(dmso-d6): d –34, –171. Anal. Calc. for C36H60O24Pd6Se12: C, 17.5;
H, 2.5. Found: C, 18.0; H, 2.5%.
l
3.3.16. [Pd(l–SeCH2CH2COOEt)2]6 (7c)
Acknowledgements
Prepared similar to 7a in methanol (yield 65%). m.p. 104–106 °C.
13C{1H} NMR (CDCl3): d 14.2 (s, CH3); 17.9, 20.7 (each s, SeCH2);
36.4, 39.3 (each s, –CH2–); 60.5, 60.7 (each s, OCH2), 171.4
(s, C@O). 77Se{1H} NMR (CDCl3): d ꢀ36, ꢀ175. Anal. Calc. for
C60H108O24Pd6Se12: C, 25.7; H, 3.9. Found: C, 26.0; H, 3.6%.
Authors thank Drs T. Mukherjee and D. Das for encouragement
of this work. We are thankful to the Chemistry Department, IIT
Bombay, Mumbai for providing microanalysis and mass spectra
of the complexes.
3.4. X-ray crystallography
Appendix A. Supplementary data
Unit cell parameters and intensity data for 1b and 2b were col-
CCDC 710910, 710911, 710912, 710913, 715043, and 715044
contain the supplementary crystallographic data for these
lected on a Bruker Smart Apex CCD diffractometer using Mo K
a
radiation (k = 0.71073 Å) employing the scan technique. The
x
compounds ([Pd(
CH2OH)(PMePh2)2CHCl3]), ([Pd3Cl2(
([Pd2Cl2( –SeCH2CH2COOH)2(PMePh2)2]), ([Pd2Cl2(
OH)2(PMePh2)2]), ([Pd2Cl2( –Cl)( –SeCH2CH2COOH)(PnPr3)2]).
l
–SeCH2CH2OH)2]6), ([Pd2Cl2(
–SeCH2CH2COOH)4(PnPr3)2]),
–SeCH2CH2-
l–Cl)(l–SeCH2-
intensity data were corrected for Lorentz, polarization and absorp-
tion effects. The structures were solved and refined with SHELX pro-
gram [46], non-hydrogen atoms were refined anisotropically.
Intensity data for 1e, 2a, 3a and 7a were collected on a Rigaku
l
l
l
l
l
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2009.08.005.
AFC7S diffractometer fitted with Mo
Ka radiation so that
hmax = 27.5 Å. The structures were solved by direct methods [47]
and refinement was on F2 [46] using data which were corrected
for absorption correction effects employing an empirical procedure
[48,49]. The non-hydrogen atoms were refined with anisotropic
displacement parameters and fitted with hydrogen atoms in their
calculated positions. Molecular structures were drawn using ORTEP
[50]. Crystallographic data and structural refinement details are gi-
ven in Table 5.
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