2-(Dimethylamino)ethaneselenolates of palladium(II): Synthesis, structure, spectroscopy and transformation into palladium selenide

Article abstract of DOI:10.1039/b008310k

Bis[2-(dimethylamino)ethyl] diselenide was prepared by the reaction of Na₂Se₂ with ClCH₂CH₂NMe₂. 2-(Dimethyl-amino)ethaneselenolate complexes of palladium(II) of the type [PdCl(SeCH₂CH₂NMe₂)]₃ 1, [PdCl(SeCH₂CH₂NMe₂)(PR₃)] 2, [Pd₂Cl₃(SeCH₂CH₂NMe₂)(PR ₃)₂] 3 and [Pd(SeCH₂CH₂NMe₂)2(PPh₃)₂ ] 4 have been synthesized and characterized by elemental analysis, IR and NMR (¹H, ³¹P, ⁷⁷Se) spectroscopy. The structures of orange 1 and of violet (λ_max = 514 nm) 2c have been established by single crystal X-ray diffraction analyses. The trimer 1 contains a six-membered Pd₃Se₃ ring in twist conformation. The thermal behaviour of three complexes, yielding Pd₁₇Se₁₅ has been investigated.

Full text of DOI:10.1039/b008310k

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2-(Dimethylamino)ethaneselenolates of palladium(II): synthesis,
structure, spectroscopy and transformation into palladium selenide
Sandip Dey,a Vimal K. Jain,*a Satyajeet Chaudhury,b Axel Knoedler,c Falk Lissnerc and
Wolfgang Kaimc
a Novel Materials and Structural Chemistry Division, Bhabha Atomic Research Centre
(B.A.R.C.), Mumbai 400085, India. E-mail: jainvk@apsara.barc.ernet.in
b Fuel Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India
c Institut für Anorganische Chemie, Universitüt Stuttgart, Pfaffenwaldring 55,
D-70569 Stuttgart, Germany
Received 16th October 2000, Accepted 14th December 2000
First published as an Advance Article on the web 8th February 2001
Bis[2-(dimethylamino)ethyl] diselenide was prepared by the reaction of Na2Se2 with ClCH2CH2NMe2. 2-(Dimethyl-
amino)ethaneselenolate complexes of palladium() of the type [PdCl(SeCH2CH2NMe2)]3 1, [PdCl(SeCH2CH2NMe2)-
(PR3)] 2, [Pd2Cl3(SeCH2CH2NMe2)(PR3)2] 3 and [Pd(SeCH2CH2NMe2)2(PPh3)2] 4 have been synthesized and
characterized by elemental analysis, IR and NMR (1H, 31P, 77Se) spectroscopy. The structures of orange 1 and of
violet (λmax = 514 nm) 2c have been established by single crystal X-ray diffraction analyses. The trimer 1 contains a
six-membered Pd3Se3 ring in twist conformation. The thermal behaviour of three complexes, yielding Pd17Se15 has
been investigated.
Melting points were determined in capillary tubes and are
Introduction
uncorrected. Elemental analyses were carried out by the
The continuing drive to scale down dimensions of electronic
Analytical Chemistry Division of B.A.R.C. 1H, 13C-{1H},
devices has necessitated the introduction of new classes of
31P-{1H} and 77Se-{1H} NMR spectra were recorded on a Bruker
growth techniques (cf. MOCVD, plasma CVD, etc.) which
DPX-300 NMR spectrometer operating at 300, 75.47, 121.49
employ molecular precursors rather than the elements for the
and 57.24 MHz, respectively. Chemical shifts are relative to the
synthesis of solid state inorganic materials.1 Accordingly,
1
internal chloroform peak at δ 7.26 for H and δ 77.0 for 13C,
research in the design and development of molecular precursor
external 85% H3PO4 for 31P, and Me2Se for 77Se. A 90Њ pulse was
chemistry has accelerated in recent years.2
used in each case. The IR spectra were recorded as Nujol mulls
between CsI plates on a Bomen MB-102 FT-IR spectrometer,
Platinum group metal chalcogenides (MxEy; M = Pd or
Pt; E = S, Se or Te) find several applications in catalysis3 and
UV/Vis absorption spectra on a Bruins Instruments Omega 10
in the electronic industry.4–6 Platinum group metal chalco-
spectrophotometer. Cyclic voltammetry was carried out at
genolates have an attractive potential to serve as precursors
100 mV sϪ1 scan rate in dichloromethane–0.1 M Bu4NPF6
for the synthesis of such chalcogenides.7,8 Their chemistry is
using a three-electrode configuration (glassy carbon electrode,
dominated by thiolate complexes9 which in most cases have
platinum counter electrode, Ag–AgCl reference) and a PAR 273
been isolated as polymeric, non-volatile, insoluble or sparingly
potentiostat and function generator. The ferrocene–ferro-
soluble complexes. To suppress polymerization, sterically
cenium couple served as internal reference. FAB mass spectra
demanding chalcogenolate ligands10 or strongly coordinating
were recorded on a JEOL SX 102/DA-6000 mass spectrometer
neutral ligands such as tertiary phosphines11,12 have been
at CDRI, Lucknow, India. Thermogravimetric analysis (TGA)
employed. In an alternative approach, internally functionalized
was carried out on a Setaram 92-16-18 instrument calibrated
ligands, which not only yield low nuclearity complexes but
with CaC2O4ؒH2O. The TG curves were recorded at a heating
also enhance complex stability, have been used as demonstrated
rate of 3 ЊC minϪ1 under a flow of argon. X-Ray powder
for compounds with 3-dimethylamino-1-propanethiolate,13
diffraction was measured using Cu-Kα radiation. SEM photo-
graphs were taken on a JEOL JSM-T330A instrument.
2-selenopyridinates14,15 and phosphorus–sulfur donor ligands.16
With the current interest in selenium containing inorganic
materials17 and in pursuance of our program on the molecular
Preparations
design of platinum group precursors, we have now synthesized
(Me2NCH2CH2Se)2 and investigated the chemistry of its
palladium complexes.
Bis[2-(dimethylamino)ethyl] diselenide (Me2NCH2CH2Se)2.
Finely powdered grey selenium (14.2 g, 179.8 mmol) and
sodium metal (4.2 g, 182.6 mmol) were charged in liquid
ammonia (250 cm3) at Ϫ78 ЊC. The brownish red solution of
sodium diselenide was stirred for 2 h and ammonia evaporated
at room temperature. The brown mass of Na2Se2 was dried
under vacuum and dissolved in DMF (250 cm3), then stirred for
4 h. Freshly dried and distilled Me2NCH2CH2Cl (19.4 g, 180.3
mmol) [from Me2NCH2CH2ClؒHCl by neutralising with aq.
NaOH, extracting with diethyl ether, drying over CaCl2 and
distilling at 107–108 ЊC] was added dropwise. The mixture
was stirred for 1 h at 70 ЊC. After cooling to room temperature
the reaction was quenched with water (250 cm3), followed by
Experimental
All reactions were carried out under nitrogen using con-
ventional Schlenk techniques. Solvents were dried by standard
methods with subsequent distillation under nitrogen. Grey
selenium (NFC, Hyderabad, India), tertiary phosphines (Strem
Chemicals, USA) and Me2NCH2CH2ClؒHCl were obtained
from commercial sources. The complexes Na2PdCl4, [PdCl2-
(PPh3)2], [Pd2Cl2(µ-Cl)2(PR3)2] (PR3 = PMe2Ph, PMePh2 or
PPh3) were prepared according to literature methods.18–20
DOI: 10.1039/b008310k
J. Chem. Soc., Dalton Trans., 2001, 723–728
This journal is © The Royal Society of Chemistry 2001
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hexane (250 cm3). The organic layer was separated and the
aqueous layer extracted with hexane (3 × 100 cm3). The com-
bined extracts were dried over CaCl2. After evaporation of the
solvent the red liquid was distilled in vacuo (118–124 ЊC, 0.1
point, analyses and other data were consistent with the product
obtained in method (a).
[PdCl(SeCH2CH2NMe2)(P(C6H4Me-p)3)] 2d. As described
for complex 2c in method (a). The pink product was recrystal-
lized from dichloromethane–acetone. Yield 75%. mp 222 ЊC.
Calc. for C25H31ClNPdSeP: C, 50.3; H, 5.2; N, 2.3. Found: C,
1
mmHg) to give an orange-red liquid (19.6 g, 72%). H NMR
(CDCl3): δ 2.26 (s, 6H, NMe2); 2.63 (t, J 7.1, 2H, SeCH2) and
3.05 (t, J 7.1 Hz, 2H, NCH2). 13C-{1H} NMR (CDCl3): δ 28.3
(s, 1J(77Se–31C) 73 Hz, SeCH2); 45.0 (s, NMe2) and 60.3 (s,
NCH2). 77Se-{1H} NMR (CDCl3): δ 293.3.
1
50.1; H, 5.6; N, 2.1%. H NMR (CDCl3): δ 2.35 (s, C6H4Me);
2.51 (br, s, SeCH2); 2.74 (br, s, NMe2); 3.18 (br, s, NCH2) and
7.18 (br), 7.61 (br) (C6H4). 31P-{1H} NMR (CDCl3): δ 27.5.
77Se-{1H} NMR (CDCl3): δ 354.4.
[PdCl(SeCH2CH2NMe2)]3 1. To a methanolic solution (25
cm3) of (Me2NCH2CH2Se)2 (917 mg, 3.03 mmol) was added
a methanolic solution (25 cm3) of Na2[PdCl4] (891 mg, 3.03
mmol) at room temperature whereupon a yellow precipitate
formed. The mixture was stirred for 3 h. The precipitate was
washed thoroughly with water, ethanol, diethyl ether and
hexane and dried in vacuo (yield: 718 mg, 81%). It was recrystal-
lized from dichloromethane as orange microcrystals (682 mg,
95%). mp 216 ЊC (decomp.). Calc. for C4H10ClNPdSe: C, 16.4;
[PdCl(SeCH2CH2NMe2)(PPh2C5H4N-2)] 2e. As described for
complex 2c in method (a). The violet-brown product was
recrystallized from dichloromethane–acetone. Yield 72%.
mp 217 ЊC. Calc. for C21H24ClN2PdSeP: C, 45.3; H, 4.3; N, 5.0.
1
Found: C, 45.1; H, 4.4; N, 5.2%. H NMR (CDCl3): δ 2.53 (t,
J 6.1, SeCH2); 2.78, 2.79 (each s, NMe2); 3.22 (t, J 5.7, NCH2);
7.28–7.46 (m), 7.71–7.85 (m) (Ph ϩ 2H py); 8.41 (t, J 7, 1 H py)
and 8.73 (dd, J 0.8, 1.7 Hz, 1 H, py). 31P-{1H} NMR (CDCl3):
δ 28.2.
1
H, 3.4; N, 4.8. Found: C, 15.9; H, 3.4; N, 4.7%. H NMR
(CDCl3): δ 2.82 (br, s, NMe2 ϩ SeCH2) and 3.06 (br, s, NCH2).
IR (Nujol): 303 cmϪ1. UV/Vis (CH2Cl2): λmax 274, 293 and 385
(sh) nm. FAB-MS: m/z 879, 845 and 736.
[Pd2Cl3(SeCH2CH2NMe2)(PMePh2)2] 3a. To a dichloro-
methane solution (20 cm3) of [Pd2Cl2(µ-Cl)2(PMePh2)2] (30 mg,
0.04 mmol) solid [PdCl(SeCH2CH2NMe2)(PMePh2)] (55 mg,
0.08 mmol) was added and the mixture stirred for 4 h. The
solvent was evaporated in vacuo. The residue was recrystallized
from dichloromethane–hexane. Yield 74%. mp 123 ЊC. Calc. for
C30H36Cl3NPd2SeP2: C, 41.4; H, 4.2; N, 1.6. Found: C, 41.2; H,
4.2; N, 1.3%. 1H NMR (CDCl3): δ 1.94–3.59 (complex pattern,
NMe2, PMe, NCH2/SeCH2) and 6.83–7.72 (br m, Ph). 31P-{1H}
NMR (CDCl3): δ 7.7, 16.4 and 17.6.
[PdCl(SeCH2CH2NMe2)(PMe2Ph)]
2a.
A
dichloro-
methane solution (20 cm3) of [Pd2Cl2(µ-Cl)2(PMe2Ph)2] (184
mg, 0.29 mmol) was added to a freshly prepared methanolic
solution of NaSeCH2CH2NMe2 (prepared from (Me2NCH2-
CH2Se)2 (90 mg, 0.29 mmol) and NaBH4 (23 mg, 0.60 mmol))
with stirring at room temperature. After 3 h the solvents were
evaporated in vacuo. The brown residue was extracted with
dichloromethane (3 × 8 cm3), the solution passed through a
Florisil column and the solvent removed in vacuo. The residue
was recrystallized from dichloromethane–acetone. Yield 113
mg (45%). mp 175 ЊC. Calc. for C12H21ClNPdSeP: C, 33.4; H,
4.9; N, 3.2. Found: C, 32.0; H, 4.8; N, 2.7%. 1H NMR (CDCl3):
[Pd2Cl3(SeCH2CH2NMe2)(PPh3)2] 3b. Method (a). As
described for complex 3a. The yellow solid was recrystallized
from acetone. Yield 75%. mp 168 ЊC. Calc. for C40H40Cl3-
NPd2SeP2: C, 48.3; H, 4.1; N, 1.4. Found: C, 46.8; H, 3.7; N,
2
δ 1.85 (d, J(P–H) 11.5, PMe2), 2.55 (t, J 6.2, SeCH2); 2.63,
2.64 (each s, NMe2); 3.04 (t, J 5.8 Hz, NCH2) and 7.40 (m),
1
0.9%. H NMR (CDCl3): δ 2.16 (s, NMe2); 2.83 (br, NCH2/
7.64–7.71 (m) [Ph]. 31P-{1H} NMR (CDCl3): δ 2.6.
SeCH2) and 7.35–7.89 (m, Ph). 31P-{1H} NMR (CDCl3): δ 21.7,
23.7 and 27.6.
[PdCl(SeCH2CH2NMe2)(PMePh2)] 2b. Prepared analo-
gously to complex 2a by using [Pd2Cl2(µ-Cl)2(PMePh2)2] (202
mg, 0.27 mmol) and NaSeCH2CH2NMe2 (prepared from
(Me2NCH2CH2Se)2 (80 mg, 0.27 mmol) and NaBH4 (21 mg,
0.55 mmol)) as starting materials. The compound was recrystal-
lized from a dichloromethane–acetone mixture. Yield 148 mg
(40%). mp 194 ЊC. Calc. for C17H23ClNPdSeP: C, 41.4; H, 4.7;
Method (b). As described for complex 2a by using [Pd2Cl2-
(µ-Cl)2(PPh3)2] (204 mg, 0.23 mmol), NaSeCH2CH2NMe2 (pre-
pared from (Me2NCH2CH2Se)2 (36 mg, 0.12 mmol) and NaBH4
(9.1 mg, 0.24 mmol)) as starting materials. The NMR spectra
and other data of the product were consistent with those of the
sample obtained in method (a).
1
N, 2.8. Found: C, 40.9; H, 4.7; N, 2.6%. H NMR (CDCl3):
[Pd(SeCH2CH2NMe2)2(PPh3)2] 4. To a methanolic solution
(8 cm3) of NaSeCH2CH2NMe2 (prepared from (Me2NCH2-
CH2Se)2 (144 mg, 0.48 mmol) and NaBH4 (35.8 mg, 0.96
mmol)) was added a suspension of [PdCl2(PPh3)2] (334 mg, 0.48
mmol) in 25 cm3 toluene and the reactants were stirred for 3 h.
The solvents were evaporated in vacuo and the residue was
extracted with acetone. The extracts were concentrated and the
solid recrystallized from acetone–hexane (267 mg, 60%). Owing
to PPh3 dissociation, analyses varied from sample to sample.
Typical analysis: Calc. for C44H50N2PdSe2P2: C, 56.7; H, 5.4; N,
3.0; found C, 53.3; H, 4.9; N, 4.4%. mp 145 ЊC. 1H NMR
complicated due to mixture of products. 31P-{1H} NMR
(acetone-d6): δ Ϫ4.9 (PPh3); 26.8, 32.0 and 35.8. When treated
with CCl4–CHCl3 [PdCl(SeCH2CH2NMe2)(PPh3)] was formed
exclusively. This also formed in some preparations but is
insoluble in acetone and can be separated easily.
2
δ 2.22 (d, J(P–H) 11.4, PMe); 2.52 (t, 6.2 Hz, SeCH2); 2.71,
2.72 (each s, NMe2); 3.13 (t, J 5.9 Hz, NCH2) and 7.36–7.46
(m), 7.62–7.69 (m) [Ph]. 31P-{1H} NMR (CDCl3): δ 16.7.
[PdCl(SeCH2CH2NMe2)(PPh3)] 2c. Method (a). To
a
dichloromethane suspension (30 cm3) of [PdCl(SeCH2CH2-
NMe2)]3 (412 mg, 1.40 mmol) solid PPh3 (372 mg, 1.41 mmol)
was added and the mixture stirred for 1 h under nitrogen. The
pinkish solution was dried in vacuo, the solid washed with
hexane and recrystallized from dichloromethane–acetone to
yield violet crystals (710 mg, 91%). mp 212 ЊC. Calc. for
C22H25ClNPdSeP: C, 47.6; H, 4.5; N, 2.5. Found: C, 46.8; H,
4.7; N, 2.4%. 1H NMR (CDCl3): δ 2.52 (t, J 6.1, SeCH2); 2.76,
2.77 (each s, NMe2); 3.21 (t, J 5.7 Hz, NCH2) and 7.36–7.47
(m), 7.72–7.79 (m) [Ph]. 31P-{1H} NMR (CDCl3): δ 29.5.
77Se-{1H} NMR (CDCl3): δ 364.6. UV/Vis (CH2Cl2): λmax(ε) 344
(1980) and 514 nm (80) (MϪ1 cmϪ1). FAB-MS: m/z 555, 520 and
447.
Crystallography
Method (b). As described for complex 2a by using [Pd2Cl2-
(µ-Cl)2(PPh3)2] (230 mg, 0.26 mmol), NaSeCH2CH2NMe2
(prepared from (Me2NCH2CH2Se)2 (79 mg, 0.26 mmol) and
NaBH4 (19.9 mg, 0.53 mmol)) as starting materials. Melting
X-Ray data of an orange single crystal of [PdCl(SeCH2CH2-
NMe2)]3 1 were collected on a Stoe IPDS diffractometer (at
room temperature) using graphite monochromated Mo-Kα
radiation. Unit cell parameters were determined from 5000
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J. Chem. Soc., Dalton Trans., 2001, 723–728

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reflections. The intensity data were corrected for Lorentz
polarization and absorption effects.21 X-Ray data of a violet
crystal of [PdCl(SeCH2CH2NMe2)(PPh3)] 2c were collected at
173(2) K on a Siemens P3 diffractometer using graphite mono-
chromated Mo-Kα radiation (λ = 0.71073 Å), employing the
ω–2θ scan technique. The unit cell parameters (Table 1) were
determined from 25 reflections measured by a random search
routine. The intensity data were corrected for Lorentz polariz-
ation and absorption effects. The structure was solved using
direct methods. The non-hydrogen atoms were refined aniso-
tropically.
orbital (HOMO) at the selenolate center to the lowest
unoccupied (LUMO) situated at the PPh3 ligand. Cyclic
voltammetry in CH2Cl2 confirmed that there is a high-lying
HOMO (oxidation at ϩ0.55 V) and a rather low-lying LUMO
(Ϫ2.04 V; all peak potentials for irreversible processes vs. the
ferrocene–ferrocenium couple).
When compounds 2 are treated with [Pd2Cl2(µ-Cl)2(PPh3)2]
a new series of dinuclear complexes with the composition
[(R3P)Cl2Pd(SeCH2CH2NMe2)PdCl(PR3)]
3 (PR3 = PMePh2
(3a) or PPh3 (3b)) is isolated. Complex 3b can also be prepared
by reaction of [Pd2Cl2(µ-Cl)2(PPh3)2] with one equivalent of
NaSeCH2CH2NMe2. The 31P NMR spectra of complexes 3
display three resonances. The most deshielded signal may be
attributed to the phosphine bound to the palladium atom
which connects with the chelating selenolate group. The other
two resonances, lower in intensities, can be assigned to the
phosphine attached to the PdCl2 fragment. Recently we have
reported similar dinuclear palladium/platinum complexes
containing 2-selenopyridine.15
CCDC reference number 186/2302.
See http://www.rsc.org/suppdata/dt/b0/b008310k/ for crystal-
lographic files in .cif format.
Results and discussion
Synthesis and spectroscopic data
When a methanolic solution of Na2[PdCl4] was treated with
(Me2NCH2CH2Se)2, a yellow, insoluble product formed initially
which on recrystallization from dichloromethane afforded
orange microcrystals of empirical composition [PdCl(SeCH2-
CH2NMe2)]n 1 (eqn. 1). The IR spectrum of 1 exhibits a ν(Pd–
Cl) band at 303 cmϪ1. The 1H NMR spectrum in CDCl3 shows
broad resonances due to NMe2, SeCH2 and NCH2 protons,
indicative of fluxional behaviour. The analogous palladium
complex with 3-dimethylamino-1-propanethiolate is dimeric
22
([PdCl(SCH2CH2NMe2)]2
) while 2-sulfanylnicotinic acid
forms a trimer.23 A trinuclear structure containing a Pt3S3 ring
has been reported for [PtBr(SCH2CH2NMe2)]3.24 The FAB
mass spectrum of 1 displayed a peak at m/z 879 suggesting that
this complex is trimeric. No signal attributable to either the
monomer (m/z 293) or the dimer (m/z 586) is observed. Other
prominent peaks were due to [M Ϫ Cl] (m/z 845) and
[M Ϫ (Cl2 ϩ CH2CH2NMe2)] (m/z 736). The trimeric structure
of 1 is confirmed by X-ray diffraction analysis (cf. below).
Reaction of complex 1 with tertiary phosphines readily
afforded violet complexes [PdCl(SeCH2CH2NMe2)(PR3)] 2.
The latter have also been synthesized by treatment of [Pd2Cl2-
(µ-Cl)2(PPh3)2] with NaSeCH2CH2NMe2 (eqn. 1). The 1H
NMR spectra of compounds 2 display characteristic peaks and
integration for various groups. The NMe2 protons are aniso-
chronous, two separate methyl signals being observed. The
NMe2 and NCH2 protons showed phosphine dependence while
the SeCH2 protons were little affected. This suggests that the
phosphine ligand is in trans position to the nitrogen atom of the
chelating selenolate ligand. This is further supported by vanish-
ingly small 2J(Se–P) coupling in the 77Se NMR spectra of these
complexes. The magnitudes of the 2J(Se–P) cis and trans coup-
lings have been reported to be ≈10 and 80 Hz, respectively.12
The 31P NMR spectra of compounds 2 show single resonances.
The FAB mass spectrum of 2c exhibits a peak at m/z 555, indi-
cating the monomeric nature of the product which is confirmed
by structural analysis. Other peaks are at m/z 520 [M Ϫ Cl] and
447 [M Ϫ (Cl ϩ CH2CH2NMe2)]. The distinct violet colour of
2c is due to a weak absorption at 514 nm (in CH2Cl2 solution).
The low molar absorption coefficient of only 80 MϪ1 cmϪ1
points to a symmetry-forbidden transition which we tentatively
identify as occurring from the highest occupied molecular
Reaction of [PdCl2(PPh3)2] with 2 equivalents of NaSeCH2-
CH2NMe2 yielded [Pd(SeCH2CH2NMe2)2(PPh3)2] 4 which dis-
sociated into [Pd(SeCH2CH2NMe2)2(PPh3)] and PPh3. Similar
behaviour is observed for analogous [M(EC5H4N)2(PPh3)2]
(M = Pd or Pt; E = S or Se) complexes.15,25 When 4 is treated
with CCl4–CHCl3 2c forms readily.
Structure of [PdCl(SeCH2CH2NMe2)]3 1
The structure of complex 1, established by single crystal X-ray
diffraction analysis (Table 1), is shown in Fig. 1, selected bond
lengths and angles are given in Table 2. The molecule contains
three distorted square planar palladium centers held together
by three bridging selenium atoms of the chelating dimethyl-
aminoethaneselenolate ligand. The resulting six-membered
Pd3Se3 ring adopts a twist conformation (Fig. 2). The coordin-
ation around each palladium atom is defined by two mutually
cis positioned selenium atoms, a nitrogen donor atom and a
terminally bonded chloride ligand. The dimethylaminoethane
selenolate ligands form “exocyclic” five-membered PdSeC2N
chelate rings, with envelope conformations.
Although the Pd–Se distances (2.367–2.419 Å) are well with-
in the expected range12,15 there are clearly two different types of
bonds. The one in the chelate ring is typically shorter (≈ 2.37 Å)
than the other kind (≈ 2.40 Å). The angles around the selenium
atoms show considerable deviation from the ideal tetrahedral
value (109.5 ЊC) and lie in the range 92.6(2)–110.18(19)Њ. The
strong trans influence of the selenolate ligand is reflected in the
Pd–Cl distances which are marginally longer (av. 2.356 Å) than
those reported in other complexes (≈ 2.30 Å).15 The Pd–Cl,
Pd–N (av. 2.136 Å), Se–C (av 1.965 Å) distances in the three
3Na2[PdCl4] ϩ ³(Me2NCH2CH2Se)2
[PdCl(SeCH2CH2NMe2)]3 1
(1)
¯
²
3PR3
[Pd2Cl2(µ-Cl)2(PPh3)2] ϩ 2NaSeCH2CH2NMe2
[PdCl(SeCH2CH2NMe2)(PR3)]
PR3 = PMe2Ph (2a)
PMePh2 (2b)
PPh3 (2c)
P(C6H4Me-p)3 (2d)
PPh2C5H4N-2 (2e)
J. Chem. Soc., Dalton Trans., 2001, 723–728
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Table 1 Crystal data and structure refinement for [PdCl(SeCH2CH2NMe2)]3 1 and [PdCl(SeCH2CH2NMe2)(PPh3)] 2c
1
2c
Chemical formula
Formula weight
C12H30Cl3N3Pd3Se3
878.82
C22H25ClNPPdSe
555.21
Crystal system, space group
a/Å
Monoclinic, P21/a
10.7805(5)
Monoclinic, P21/n
9.527(2)
b/Å
c/Å
13.1187(9)
16.6749(8)
19.827(4)
11.661(2)
β/Њ
95.899(5)
2345.8(2)
95.77(3)
2191.4(8)
V/Å3
Z
4
4
µ/mmϪ1
7.274
2.710
Refinement method
Reflections collected/unique
Data/restraints/parameters
Final R1, wR2 indices
(all data)
Full matrix least squares on F2 > 0
22492/5593
5593/0/218
Full matrix least squares on F2 > 0
7291/5997
5997/0/245
0.0478, 0.1354
0.0597, 0.1469
0.0357, 0.0938
0.0520, 0.0883
Table 2 Selected bond lengths (Å) and angles (Њ) for [PdCl(SeCH2-
CH2NMe2)]3 1
Pd(1)–Se(1)
Pd(1)–Se(2)
Pd(2)–Se(2)
Pd(2)–Se(3)
Pd(3)–Se(3)
Pd(3)–Se(1)
Pd(1)–Cl(1)
Pd(2)–Cl(2)
Pd(3)–Cl(3)
Pd(1)–N(1)
Pd(2)–N(2)
Pd(3)–N(3)
2.3783(7)
2.3982(7)
2.3672(7)
2.4115(6)
2.3709(6)
2.4199(7)
2.3455(16)
2.3673(16)
2.3540(14)
2.133(5)
Se(1)–C(1)
Se(2)–C(5)
Se(3)–C(9)
N(1)–C(2)
N(2)–C(6)
N(3)–C(10)
C(1)–C(2)
C(5)–C(6)
C(9)–C(10)
1.978(7)
1.942(7)
1.975(6)
1.444(11)
1.496(7)
1.476(7)
1.250(13)
1.507(9)
1.520(8)
2.135(4)
2.141(5)
Se(1)–Pd(1)–Se(2)
Se(1)–Pd(1)–Cl(1)
Se(1)–Pd(1)–N(1)
Pd(1)–Se(1)–Pd(3)
Pd(1)–Se(2)–Pd(2)
Cl(1)–Pd(1)–Se(2)
Cl(1)–Pd(1)–N(1)
91.45(2)
177.41(5)
88.19(15)
102.41(2)
107.00(2)
86.86(5)
N(1)–Pd(1)–Se(2)
Pd(3)–Se(1)–C(1)
Pd(1)–Se(1)–C(1)
Pd(1)–N(1)–C(2)
Se(1)–C(1)–C(2)
N(1)–C(2)–C(1)
178.94(15)
99.8(2)
92.6(2)
110.0(5)
115.8(6)
130.2(8)
Fig. 1 Molecular structure of [PdCl(SeCH2CH2NMe2)]3 1 with
atomic numbering scheme.
93.46(16)
Se(2)–Pd(2)–Se(3)
Se(2)–Pd(2)–Cl(2)
Se(2)–Pd(2)–N(2)
Pd(2)–Se(3)–Pd(3)
Cl(2)–Pd(2)–Se(3)
Cl(2)–Pd(2)–N(2)
84.16(2)
178.98(5)
86.88(13)
94.89(2)
96.23(4)
92.81(13)
N(2)–Pd(2)–Se(3)
Pd(2)–Se(2)–C(5)
Pd(1)–Se(2)–C(5)
Pd(2)–N(2)–C(6)
Se(2)–C(5)–C(6)
N(2)–C(6)–C(5)
169.91(13)
92.9(2)
107.0(2)
112.6(3)
105.8(5)
112.3(4)
Se(3)–Pd(3)–Se(1)
Se(3)–Pd(3)–Cl(3)
Se(3)–Pd(3)–N(3)
Cl(3)–Pd(3)–Se(1)
Cl(3)–Pd(3)–N(3)
N(3)–Pd(3)–Se(1)
90.92(2)
174.15(4)
87.28(12)
89.39(5)
92.66(13)
176.85(13)
Pd(3)–Se(3)–C(9)
Pd(2)–Se(3)–C(9)
Pd(3)–N(3)–C(10) 111.6(4)
Se(3)–C(9)–C(10)
N(3)–C(10)–C(9)
94.45(17)
110.18(19)
104.8(4)
112.6(5)
Fig. 2 Conformation of the six-membered Pd3Se3 ring of [PdCl-
(SeCH2CH2NMe2)]3 1.
“PdCl(SeCH2CH2NMe2)” fragments are comparable, however
various angles in each fragment differ slightly.
the Pd–Se distance (2.371 Å) is slightly shorter than the values
reported for [Pd(SePh)2(dppe)] (Pd–Se 2.444(1), 2.480(1) Å)12
and [(PPr3)Cl2Pd(µ-SeC5H4N)PdCl(PPr3)] (Pd–Se 2.508, 2.421
Å).15 The five-membered chelate ring (Pd–Se–C–C–N) exists in
a puckered conformation with the carbon atoms [C(19) and
C(20)] lying on opposite sides of the mean plane. The geometry
around the nitrogen atom is distorted tetrahedral (106.6–
114.8Њ).
Structure of [PdCl(SeCH2CH2NMe2)(PPh3)] 2c
An ORTEP plot26 with the atomic numbering scheme of
[PdCl(SeCH2CH2NMe2)(PPh3)] 2c is shown in Fig. 3; selected
bond lengths and angles are summarized in Table 3. The geom-
etry around the palladium center is essentially square planar
with the atoms P, Cl, Se, N, defining the coordination sphere.
The phosphine ligand is trans to the nitrogen atom while the
chloride is trans to the Se atom of the chelating ligand. The
trans influence of various ligands is reflected in the Pd–X
distances. Thus, Pd–N [2.160(3) Å] and Pd–Cl [2.382(1) Å] are
slightly longer owing to the strong trans influence of PPh3 and
Se when compared to those in [Pd2Cl2(µ-Me2pz)2(PMe2Ph)2]
(Pd–Clav 2.30, Pd–N 2.03–2.08 Å)27 and [(PPr3)Cl2Pd(µ-SeC5-
H4N)PdCl(PPr3)] (Pd–Clav 2.30, Pd–N 2.10 Å).15 Consequently,
Thermal studies
Thermogravimetric analyses of [Pd(SeCH2CH2NMe2)Cl]3
1
(Fig. 4) and [PdCl(SeCH2CH2NMe2)(PPh3)] 2c were carried out
under a flowing argon atmosphere. The TG curve of 1 showed
two closely spaced steps of decomposition (284 ЊC), leading to
formation of Pd17Se15 as inferred from the calculated mass loss.
The XRD pattern of the product and the elemental analyses
[Found: C 3.9, Pd 59.0, Se 41.0 ( 2%), H and N not detected
726
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View Article Online
Table 3 Selected bond distances (Å) and bond angles (Њ) for [PdCl-
(SeCH2CH2NMe2)(PPh3)] 2c
Pd–N
Pd–P
Pd–Se
Pd–Cl
Se–C(19)
2.160(3)
N–C(20)
N–C(21)
N–C(22)
C(19)–C(20)
P–C(av.)
1.500(5)
1.484(5)
1.489(6)
1.514(6)
1.826
2.2554(11)
2.3710(6)
2.3823(10)
1.963(4)
N–Pd–P
173.13(10)
87.33(9)
88.95(3)
91.82(9)
91.31(4)
174.29(3)
95.71(13)
C(21)–N–C(22)
C(21)–N–C(20)
C(22)–N–C(20)
C(21)–N–Pd
C(22)–N–Pd
C(20)–N–Pd
107.9(4)
106.6(3)
109.6(3)
114.8(3)
106.6(3)
111.3(2)
111.1(3)
109.1(3)
N–Pd–Se
P–Pd–Se
N–Pd–Cl
P–Pd–Cl
Se–Pd–Cl
Pd–Se–C(19)
N–C(20)–C(19)
Se–C(19)–C(20)
Fig. 5 SEM picture of Pd17Se15 obtained from [PdCl(SeCH2CH2-
NMe2)]3 1.
obtained from TG, indicating formation of the same product in
each case. The XRD pattern of these products has been inter-
preted in terms of a cubic structure with the lattice parameter
10.584(1) Å. The X-ray diffraction patterns are in compliance
with patterns reported for the standard compound.28 The
surface morphology of these products was studied by the SEM
technique. The scanning electron micrographs (Fig. 5) of
Pd17Se15 taken at different resolutions showed large aggregates
of microcrystals.
Acknowledgements
We thank Drs J. P. Mittal and P. Raj for encouragement of
this work. We are also grateful to Dr P. K. Mathur, Head,
Analytical Chemistry Division for providing microanalyses of
the complexes. Support for this work from the BMBF (project
IND 99/060), the DFG and the FCI (Frankfurt am Main) is
gratefully acknowledged.
Fig. 3 Molecular structure of [PdCl(SeCH2CH2NMe2)(PPh3)] 2c with
atomic numbering scheme.
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