Pyridine- and 3-/6-methylpyridine-2-tellurolate complexes of palladium(II) and platinum(II)

Article abstract of DOI:10.1002/ejic.200390103

The reaction of py₂Te₂ or (3-MeC₅H₃N)₂Te₂ with Na₂PdCl₄ in methanol yields an insoluble brown complex, [PdCI(TeNC₅H₃R)]_n (R=H or Me). Several reactions of pyTe^-, (3-MeC₅H₃N)Te^-, or (6-MeC₅H₃N)Te^- with various palladium(II) and platinum(II) complexes have been carried out. Complexes of the types [MCl(Te-N)(PR3)], [Pt(Te-N)₂(dppe)], [Pt(Te-N)₂(PPh₃)₂], and [Pt₂(μ-Te-N)₂(dppe)₂] [BPh₄]₂ [M=Pd or Pt; Te-N = pyTe, (3- or 6-MeC₅H₃N)Te] have been prepared and characterized by elemental analyses, UV/Vis, IR, and NMR (¹H, ³¹p, ¹⁹⁵Pt) spectroscopy. The complexes [MCl(Te-N)(PR₃)] show irreversible oxidation and reduction by CV in DMF. The molecular structure of [PdCl{Te(3MeC₅H₃N)}(PPh₃)] (2c) has been established by single-crystal X-ray diffraction analysis. The palladium atom is bound to the chelating 3-methylpyridinetellurolate ligand, a chlorine atom and a PPh3 ligand. The pyrolysis of [PdClTe(3MeC₅H₃N)}(PR₃)] (PR₃=PEt₃ or PPh₃) at 340 °C yields PdTe. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejic.200390103

FULL PAPER
Pyridine- and 3-/6-Methylpyridine-2-tellurolate Complexes of Palladium(II
)
and Platinum(II
)
Sandip Dey,[a] Vimal K. Jain,*[a] Jaspreet Singh,[b] Veena Trehan,[b] Kuldip K. Bhasin,[b] and
Babu Varghese[c]
Keywords: Palladium / Platinum / N ligands / Tellurium / NMR spectroscopy
The reaction of py2Te2 or (3-MeC5H3N)2Te2 with Na2PdCl4
in methanol yields an insoluble brown complex,
[PdCl(TeNC5H3R)]n (R = H or Me). Several reactions of pyTe−,
(3-MeC5H3N)Te−, or (6-MeC5H3N)Te− with various palla-
dium(II) and platinum(II) complexes have been carried out.
Complexes of the types [MCl(Te−N)(PR3)], [Pt(Te−N)2(dppe)],
[Pt(Te−N)2(PPh3)2], and [Pt2(µ-Te−N)2(dppe)2][BPh4]2 [M = Pd
or Pt; Te−N = pyTe, (3- or 6-MeC5H3N)Te] have been pre-
pared and characterized by elemental analyses, UV/Vis, IR,
and NMR (1H, 31P, 195Pt) spectroscopy. The complexes
[MCl(Te−N)(PR3)] show irreversible oxidation and reduction
by CV in DMF. The molecular structure of [PdCl{Te(3-
MeC5H3N)}(PPh3)] (2c) has been established by single-crys-
tal X-ray diffraction analysis. The palladium atom is bound to
the chelating 3-methylpyridinetellurolate ligand, a chlorine
atom and
a PPh3 ligand. The pyrolysis of [PdCl{Te(3-
MeC5H3N)}(PR3)] (PR3 = PEt3 or PPh3) at 340 °C yields PdTe.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
Introduction
cently by us[11,16] and others.[17Ϫ21] In contrast, metal com-
plexes with pyridine-2-tellurolate are virtually non-existent,
although py2Te2 has been known for some time.[22,23] Pos-
sibly, a rather tedious preparation (‘‘difficult to repro-
duce’’[22]) of py2Te2, the precursor for C5H4NTeϪ, appears
to be a limiting factor for its use as a ligand.
The synthesis and characterization of metal chalcogenol-
ates continues to be an area of considerable interest. Their
emerging applications as single-source precursors for a low-
temperature preparation of solid-state chalcogenide mat-
erials has further accelerated work in this area.[1Ϫ4] The
area of metal chalcogenolates has been dominated by mole-
cules containing the MϪSR linkage.[5] In most cases, these
molecules have been isolated as non-volatile insoluble (or
sparingly soluble) polymers, thus making them inconveni-
ent precursors for the preparation of metal chalcogenides.
To suppress polymerization, several strategies have been ex-
plored. These include use of (a) a strongly coordinating li-
gand, such as tertiary phosphanes,[6,7] (b) a sterically de-
manding chalcogenolate ion,[8] (c) internally functionalized
small-bite ligands.[9Ϫ13] One of the families of the latter
class of ligands is the pyridine-2-chalcogenolate ion I. While
Group-10 metal chalcogenides (MxEy; M ϭ Pd or Pt;
E ϭ S, Se, Te) have found several applications in catalysis[24]
(PdTe supported on carbon is employed industrially) and
in the electronic industry.[25,26] Besides their wide structural
diversity[5] and relevance in catalysis,[9,27,28] platinum-group
metal chalcogenolates offer an attractive possibility of ser-
the ligand chemistry of C5H4NOϪ
has been well documented, the coordination chemistry of
the pyridine-2-selenolate ion has been explored only re-
and C5H4NSϪ
[14]
[15]
[a]
Novel Materials and Structural Chemistry Division, Bhabha ving as precursors for the synthesis of metal chalcogen-
Atomic Research Centre,
ides.[12,29] In continuation of our program on the molecular
Mumbai 400085, India
design of platinum-group metal precursors, we have now
synthesized bis(2-pyridyl) and bis(methyl-substituted 2-pyr-
idyl) ditelluride, and have investigated the chemistry of their
palladium and platinum complexes.
E-mail: jainvk@apsara.barc.ernet.in
Department of Chemistry, Panjab University,
Chandigarh 160014, India
RSIC, Indian Institute of Technology,
Chennai 600036, India
[b]
[c]
744
 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ1948/03/0204Ϫ0744 $ 20.00ϩ.50/0 Eur. J. Inorg. Chem. 2003, 744Ϫ750

Pyridine- and 3-/6-Methylpyridine-2-tellurolate Complexes of PdII and PtII
FULL PAPER
Results and Discussion
Synthesis and NMR Spectroscopic Data
A methanolic solution of Na2PdCl4 was treated with
py2Te2 or (3-MeC5H3N)2Te2 at room temperature to give a
brown insoluble product, [PdCl{Te(3-RC5H3N)}]n [R ϭ H
(1a) or Me (1b)]. The IR spectrum of 1b exhibits a band at
281 cmϪ1 which is assigned to the terminal νPdϪCl stretch-
ing. On treatment with tertiary phosphanes, the mononu-
Scheme 1
clear complexes [MCl{Te(3-MeC5H3N)}(PR3)] are ob- (PR3)2],[30] while in the reactions with pySϪ, both mono-
tained. The latter complexes and their platinum analogues and dinuclear complexes [MCl(SC5H4N)(PR3)] and
can readily be prepared by the reaction of [M2Cl2(µ- [M2Cl2(µ-SC5H4N)2(PR3)2] are formed, depending on the
Cl)2(PR3)2] with 2 equiv. of NaTe(RC5H3N) (R ϭ H, 3-Me, nature of the phosphane ligand.[31Ϫ35] In solution a dimer
Ǟ
ǟ
or 6-Me) [(Scheme 1), prepared by the cleavage of the
monomer equilibrium is established, which is shifted to
TeϪTe bond in bis(2-pyridyl) ditelluride with NaBH4 either side by subtle energetic factors. The reactions with
in
methanol].
The
reaction
exclusively
gives C5H4NSeϪ preferentially yield mononuclear complexes,
[MCl(SeC5H4N)(PR3)]. However, dinuclear species are
[MCl{Te(RC5H3N)}(PR3)] (2).
Similar reactions with pyOϪ afford 2-pyridinolate- formed in small concentration (ca. 5%) in certain cases
bridged dinuclear complexes, [M2Cl2(µ-OC5H4N)2- when trialkylphosphanes are used.[11] Clearly, as the PdϪE
1
Table 1. 31P{1H} and H NMR spectroscopic data for the 2-pyridine- and methyl-2-pyridinetellurolate complexes of palladium() and
platinum()
Complex
31P{1H} NMR (δ)
1H NMR (δ)
[PdCl{Te(3-MeC5H3N)}(PEt3)][a]
[PdCl{Te(3-MeC5H3N)}(PMePh2)][a]
[PdCl{Te(3-MeC5H3N)}(PPh3)][a]
[PdCl{Te(3-MeC5H3N)}(Ptol3)][a]
[PdCl{Te(3-MeC5H3N)}(PPh2py)][a]
[PdCl(TeC5H4N)(PMePh2)][a]
[PtCl{Te(3-MeC5H3N)}(PnPr3)][a]
33.2
17.8
29.8
27.8
30.1
17.6
Ϫ9.3
1.23 [dt, J(d) ϭ 17.4, J(t) ϭ 7.6 Hz, PCH2CH3]; 1.88 (dq), 10.6 (d),
7.6 (q, PCH2); 6.98 (m, 5-H); 7.47 (d, J ϭ 7.6 Hz, 4-H); 8.19 (br, 6-H)
2.27 (d, J ϭ 11.4 Hz, PMe); 6.99 (m, 5-H); 7.46Ϫ7.51 (m, 4-H ϩ
C6H5); 7.72Ϫ7.79 (m, C6H5); 8.29 (br, 6-H)
7.05 (m, 5-H); 7.50Ϫ7.54 (m, 4-H ϩ C6H5); 7.74Ϫ7.78 (m, C6H5);
8.45 (br, 6-H)
2.38 (s, tol-Me); 7.00 (m, 5-H); 7.30 (m, C6H4); 7.51 (d, J ϭ 7.6 Hz,
4-H); 7.64 (dd, J ϭ 8 Hz, J ϭ 11.6 Hz, C6H4); 8.42 (br, 6-H)
6.99 (m, 5-H); 7.50 (m, 4-H ϩ C6H5, C5H4N); 7.83 (br, C6H5 ϩ
C5H4N); 8.38 (br, 6-H); 8.83 (br, 6-H, pyP)
2.33 (d, J ϭ 11 Hz, PMe), 7.05 (br), 7.33Ϫ7.64 (br, m); 7.80 (br),
8.40 (br) (Ph ϩ C5H4)
1.05 (t, J ϭ 7.2 Hz, PCH2CH2Me); 1.64Ϫ1.88 (m, PCH2CH2); 7.10
3
1J(Pt-P) ϭ 3575 Hz (t, J ϭ 5.7 Hz, 5-H); 7.49 (d, J ϭ 7.5 Hz, 4-H); 8.34 [br, J(Pt-H) ϭ
41 Hz, 6-H]
3
[PtCl{Te(3-MeC5H3N)}(PMe2Ph)][b]
[PtCl{Te(3-MeC5H3N)}(PMePh2)][b]
Ϫ26.0
1.93 [d, J ϭ 11 Hz, J(Pt-H) ϭ 37 Hz, PMe2]; 2.01 (s, MeC5H3N); 6.92
1J(Pt-P) ϭ 3605 Hz (m, 5-H); 7.27 (d, J ϭ 7.1 Hz, 4-H); 7.45 (m, C6H5); 7.69Ϫ7.77
3
(m, C6H5); 8.44 [br, J(Pt-H) ϭ 37 Hz, 6-H].
3
Ϫ10.4
1.97 (s, MeC5H3N); 2.25 [d, J ϭ 11.1 Hz, J(Pt-H) ϭ 33 Hz, PMe];
1J(Pt-P) ϭ 3699 Hz 6.93 (m, 5-H); 7.27 (d, J ϭ 7 Hz, 4-H); 7.43 (m, C6H5); 7.66Ϫ7.73
3
(m, C6H5); 8.51 [br, J(Pt-H) ϭ 41 Hz, 6-H]
3
[PtCl(TeC5H4N)(PMePh2)][a]
[Pt{Te(3-MeC5H3N)}2(dppe)][b]
Ϫ2.6
2.34 [d, J ϭ 11 Hz, J(Pt-H) ϭ 36 Hz, PMe]; 6.61 (m), 7.22 (m),
1J(Pt-P) ϭ 3814 Hz 7.45 (m), 7.76 (m), 8.00 (m), 8.20 (m) (Ph ϩ C5H4)
44.8
2.08 (s, MeC5H3N); 2.02 (m, CH2CH2); 6.57 (dd, J ϭ 5 Hz, J ϭ 7 Hz,
1J(Pt-P) ϭ 2947 Hz 5-H); 6.77 (d, 7.5 Hz, 4-H); 7.27Ϫ7.37 (m, C6H5); 7.56 (d, J ϭ 5 Hz,
6-H); 7.71Ϫ7.77 (m, C6H5)
[Pt{Te(6-MeC5H3N)}2(dppe)][b]
46.8
2.05 (s, MeC5H3N); 2.09 (m, CH2CH2); 6.48 (d, J ϭ 7.4 Hz, 3-H); 6.61
1J(Pt-P) ϭ 2900 Hz (t, J ϭ 7.5 Hz, 4-H); 7.27Ϫ7.36 (m, Ph); 7.69Ϫ7.76 (m, Ph, 5-H)
[b]
[Pt2{Te(3-MeC5H3N)}2(dppe)2][BPh4]2
37.1
2.02 (s, MeC5H3N); 1.85Ϫ2.00 (m, CH2CH2); 6.55 (m, 5-H);
1J(Pt-P) ϭ 2944 Hz, 6.73Ϫ6.88 (m), 7.31 (br), 7.47Ϫ7.60 (m) [C6H5 ϩ 4-H, 6-H]
42.1
1J(Pt-P) ϭ 3259 Hz
[Pt{Te(3-MeC5H3N)}2(PPh3)2][b]
6.6
2.15 (s, MeC5H3N); 6.65 (br, 5-H); 7.10 (br, 4-H); 7.35 (m), 7.80 (m)
1J(Pt-P) ϭ 3725 Hz (C6H5); 8.20 (br, 6-H)
Ϫ4.5 (PPh3)
[a]
[b]
Recorded in [D6]acetone; methyl resonance of the 3-MeC5H3N merged in the multiplet of [D6]acetone. Recorded in CDCl3.
Eur. J. Inorg. Chem. 2003, 744Ϫ750
745

S. Dey, V. K. Jain, J. Singh, V. Trehan, K. K. Bhasin, B. Varghese
FULL PAPER
˚
˚
distance (PdϪO ഠ 2.10 A; PdϪS ഠ 2.28 A; PdϪSe ഠ 2.45 UV/Vis Spectroscopy
˚
˚
A; PdϪTe ഠ 2.55 A) increases with increasing size of the
chalcogen atom, the PdϪN interaction of these small-bite
ligands with a single metal center is facilitated.
All these complexes are deeply colored crystalline solids.
The UV/Vis spectra (Table 3) in dichloromethane show a
well-separated relatively weak broad band in the visible re-
gion, and this is responsible for the deep colors observed
for these complexes. The platinum complexes have an ab-
sorbance band at higher energies than that of the corres-
ponding palladium analogues. For both the series of com-
plexes (Pd or Pt), this band is hypsochromically shifted with
increasing donor strength of the phosphane ligand. The
DFT calculations of [MCl(TeCH2CH2NMe2)(PR3)] (M ϭ
Pd or Pt) reveal a metal-mediated charge-transfer between
coordinated ligands. The highest occupied molecular or-
bital (HOMO) is predominantly centered on the tellurolate
ligand, whereas the lowest unoccupied molecular orbital
(LUMO) is delocalized over the system, with significant
phosphane contributions. The low-energy electronic trans-
itions between the frontier orbitals give rise to the colors.[35]
The reaction of PtCl2(dppe) with 2 equiv. of NaTe(3-
MeC5H3N) yields the yellow mononuclear complex
[Pt{Te(3-MeC5H3N)}2(dppe)]. The NMR spectroscopic
data (1H, 31P, and 195Pt) are consistent with several organo-
chalcogenolates, cis-[Pt(ER)2(PϪP)].[6,7,11Ϫ13] The reaction,
performed in a 1:1 ratio in the presence of NaBPh4, gives
a cationic complex [Pt2{Te(3-MeC5H3N)}2(dppe)2][BPh4]2.
The 31P and 195Pt NMR spectra show two sets of reson-
ances and doublets of doublets, respectively; a pattern
which can be attributed to the non-equivalence of the phos-
phorus nuclei of the PϪP ligand. Similar spectral features
have been reported for [Pt2(µ-SeCH2CH2NMe2)2(dppe)2]2ϩ
[13]
for which the existence of an asymmetric MϪSe bridge
has been suggested.
Treatment of PtCl2(PPh3)2 with 2 equiv. of NaTe(3-
MeC5H3N) affords [Pt{Te(3-MeC5H3N)}2(PPh3)2]. The 31P
NMR spectrum of the complex exhibits a resonance at δ ϭ
Table 3. UV/Vis data for the 2-pyridinechalcogenolate complexes
of [MCl{E(3-MeC5H3N)}(PR3)] (M ϭ PdII and PtII; E ϭ Se, Te)
in CH2Cl2
1
6.6 ppm, with J(PtϪP) ϭ 3725 Hz, together with a signal
which is assigned to PPh3 (δ ϭ Ϫ4.5 ppm) (Table 1). A dy-
[a]
Complex
λmax [nm]
namic
equilibrium
between
free
PPh3
and
[M(EC5H4N)2(PPh3)] (M ϭ Pd or Pt; E ϭ S or Se)[11,16]
has been reported earlier.
[PdCl{Te(3-MeC5H3N)}(PEt3)] (2a)
283 (13860), 371 (3280),
567 (190)
The 1H NMR spectra of 2 show characteristic resonances
for the ligand protons. The 6-H proton signal for the (3-
MeC5H3N)Te ligand in the platinum complexes is flanked
[PdCl{Te(3-MeC5H3N)}(PMePh2)] (2b) 294 (16560), 377 (4670),
595 (240)
[PdCl{Te(3-MeC5H3N)}(PPh3)] (2c)
[PdCl{Te(3-MeC5H3N)}(Ptol3)] (2d)
[PdCl(TeC5H4N)(PMePh2)] (2f)
277 (16930), 297 (15710),
380 (4400), 614 (210)
299 (15040), 381 (4660),
609 (210)
293 (sh, 13170),
373 (4200), 570 (320)
286 (sh, 7420),
by 195Pt satellites with J(Pt-H) ഠ 40 Hz. The 31P NMR
3
spectra of these complexes display a single resonance indic-
ating the formation of only one isomer. The magnitude of
1J(195Pt-31P) in the platinum complexes suggests that the
phosphane ligand is trans to the nitrogen atom of the che-
lating 2-pyridinetellurolate ligands,[11Ϫ13] and this is con-
firmed by the X-ray structural analysis. The 195Pt NMR
spectra (Table 2) show a doublet due to coupling with the
single phosphorus nucleus. The 195Pt resonance is consider-
ably shielded relative to the signal for the corresponding 2-
pyridineselenolate complexes.[11]
[PtCl{Te(3-MeC5H3N)}(PnPr3)] (3a)
402 (1880)
[PtCl{Te(3-MeC5H3N)}(PMe2Ph)] (3b) 285 (6430), 313
(sh, 3940), 404 (1342)
[PtCl{Te(3-MeC5H3N)}(PMePh2)] (3c) 286 (sh, 8090), 316
(3950), 408 (1760)
293 (26070), 475 (89)
282 (7350), 376 (1480)
[PdCl(SeC5H4N)(PnPr3)][b]
[PtCl(SeC5H4N)(PnPr3)][b]
[a]
Wavelengths λmax at the absorbance maxima in nm, molar ex-
tinction coefficients ε in Ϫ1 cmϪ1 [b] Prepared according to ref.[11]
.
Table 2. 195Pt{1H} NMR spectra of the 2-pyridinetellurolates of
platinum()
Cyclic Voltammetry
Complex
195Pt NMR (δ)
Ϫ4347
The complexes show irreversible oxidation and reduction
in DMF/0.01  Et4NClO4 (Table 4). The lower oxidation
potential of the Pt/Te system indicates that the HOMO (Te)
is destabilized relative to that of the corresponding Pd/Te
system. Such behavior has been reported for
[MCl(TeCH2CH2NMe2)(PR3)] complexes.[35] It was diffi-
cult to oxidize the 2-pyridineselenolates [MCl-
(SeC5H4N)(PR3)] (high oxidation potential values).
[PtCl{Te(3-MeC5H3N)}(PnPr3)]
[PtCl{Te(3-MeC5H3N)}(PMe2Ph)]
[PtCl{Te(3-MeC5H3N)}(PMePh2)]
[PtCl(TeC5H4N)(PMePh2)]
[Pt{Te(3-MeC5H3N)}2(dppe)]
1
[d, J(Pt-P) ϭ 3580 Hz]
Ϫ4312
1
[d, J(Pt-P) ϭ 3634 Hz]
Ϫ4314
1
[d, J(Pt-P) ϭ 3690 Hz]
Ϫ3830
1
[d, J(Pt-P) ϭ 3820 Hz]
Ϫ5311
1
[t, J(Pt-P) ϭ 2952 Hz]
Structure of [PdCl{Te(3-MeC5H3N)}(PPh3)] (2c)
[Pt2{Te(3-MeC5H3N)}2(dppe)2]-
[BPh4]2
Ϫ4843
1
The molecular structure of [PdCl{Te(3-MeC5H3N)}
[dd, J(Pt-P) ϭ 2962 Hz]
(PPh3)] (2c) was established by single-crystal X-ray diffrac-
746
Eur. J. Inorg. Chem. 2003, 744Ϫ750

Pyridine- and 3-/6-Methylpyridine-2-tellurolate Complexes of PdII and PtII
FULL PAPER
TeCH2CH2NMe2).[12,13,35] The square plane of the palla-
dium atom (defined by the N, Cl, P, Te atoms), the four-
membered chelate ring [Pd, N, C(5), Te], and the pyridine
ring are almost coplanar, with the interplanar angles vary-
ing between 3.68 and 6.68°. The Te atom lies 0.1 A out of
the plane defined by the Pd, N, Cl, and P atoms.
Table 4. Electrochemical data
Complex
Epa (ox)[a] Epc (red)[a]
[PdCl{Te(3-MeC5H3N)}(PEt3)] (2a)
[PdCl{Te(3-MeC5H3N)}(PMePh2)] (2b) 0.40
0.46
Ϫ2.13
Ϫ1.78
˚
The various angles around the Pd atom differ signific-
antly from [PdCl(TeCH2CH2NMe2)(PR3)] (PR3 ϭ PnPr3,
PMePh2),[35] owing to the small bite of the four-membered
(3-MeC5H3N)Te moiety. The PdϪTe distanceis slightly
[PtCl{Te(3-MeC5H3N)}(PMe2Ph)] (3b)
[PtCl{Te(3-MeC5H3N)}(PMePh2)] (3c)
0.36
0.39
Ϫ2.26
Ϫ2.30
[PdCl(SeC5H4N)(PnPr3)][b]
[PtCl(SeC5H4N)(PnPr3)]
0.98
0.80
Ϫ1.98
Ϫ1.63
˚
longer [2.5606(8) A] than that observed for
Scan rate 100 mV·sϪ1, peak potentials for irreversible processes [PdCl(TeCH2CH2NMe2)(PR3)] [PR3 ϭ PnPr3 2.5095(8) and
[a]
ϩ
[b]
PMePh2 2.5156(6) A],[35] while the PdϪN distance [2.085(4)
˚
in V vs. FeCp2/FeCp2
.
Measurement in DMF/Et4NClO4.
˚
A] is shorter than that reported for [PdCl(TeCH2CH2N-
Me2)(PR3)].[35] These distances, as well as the PdϪCl,
tion analysis. The ORTEP[36] plot with the atomic num-
bering scheme is shown in Figure 1, and the selected bond
lengths and angles are given in Table 5. The molecule con-
sists of a distorted square-planar palladium atom that is
bound to the chelating 3-methyl-2-pyridinetellurolate li-
gand, a chlorine atom and a PPh3 ligand. The neutral
donors (N, P) are mutually trans, and as a consequence the
chloride ion and the Te atom adopt a trans arrangement,
a configuration that has been reported previously for
selenolate and tellurolate complexes, [MCl(EϪN)(PR3)]
PdϪP and TeϪC bond lengths are not unusual.[33Ϫ35,37Ϫ40]
Thermal Behavior
Thermogravimetric analysis of [PdCl{Te(3-MeC5H3N)}
(PPh3)] (2c) was carried out under a dynamic argon pres-
sure. The TG curve shows a one-step decomposition
(290°C), leading to the formation of PdTe as inferred from
the calculated weight loss. In order to prepare large quantit-
ies of the telluride, a substantial amount (100Ϫ350 mg) of
the complexes (2a, 2c) was heated in a furnace at 340°C for
2 h under a dynamic dry argon pressure. The weight loss
and XRD pattern (Figure 2) of the residue obtained after
decomposition in each case matches the product obtained
from TG. The XRD patterns (Figure 2) of all these samples
are in agreement with the standard pattern of PdTe[41] [ana-
lysis of the prepared PdTe: sample from 2a: C 1.8, H Ͻ 0.2,
N Ͻ 0.2; sample from 2c: C Ͻ 0.2, H Ͻ 0.2, N Ͻ 0.2
(detection limit 0.2%)]. The scanning electron micrographs
(M
ϭ
Pd or Pt; EϪN
ϭ
SeCH2CH2NMe2,
Figure 1. Molecular structure of [PdCl{Te(3-MeC5H3N)}(PPh3)]
(2c) with the atomic numbering scheme
˚
Table 5. Selected bond lengths [A] and angles [°] for [PdCl{Te(3-
MeC5H3N)}(PPh3)] (2c)
PdϪTe
PdϪN
PdϪCl
PdϪP
2.5606(8)
2.085(4)
2.3620(16)
2.2420(15)
TeϪC(5)
NϪC(1)
NϪC(5)
PϪC(av)
2.118(5)
1.337(7)
1.330(7)
1.821
NϪPdϪP
NϪPdϪCl
PϪPdϪCl
NϪPdϪTe
PϪPdϪTe
ClϪPdϪTe
173.76(13)
94.17(13)
92.07(5)
73.18(12)
100.67(4)
165.21(4)
PdϪTeϪC(5)
TeϪC(5)ϪN
TeϪC(5)ϪC(4)
C(7)ϪPϪC(13)
C(7)ϪPϪC(19)
C(13)ϪPϪC(19)
72.71(15)
106.1(4)
131.1(4)
107.1(3)
104.0(3)
103.0(3)
Figure 2. XRD pattern of PdTe obtained from [PdCl{Te(3-
MeC5H3N)}(PPh3)]
Eur. J. Inorg. Chem. 2003, 744Ϫ750
747

S. Dey, V. K. Jain, J. Singh, V. Trehan, K. K. Bhasin, B. Varghese
FULL PAPER
sumed (48Ϫ96 h). The progress of the reaction was monitored by
TLC. The nitrogen flow was stopped and the mixture was subjected
to oxidation in air. The solvent was removed under vacuum and
the crude residue was washed with water, and extracted with diethyl
ether (4 ϫ 100 mL). The extract was dried with anhydrous sodium
sulfate and the solvent removed using a rotary evaporator, leaving
the crude ditelluride. This was purified by column chromatography
(silica gel; hexane/ethyl acetate, 10:1).
Bis(3-methyl-2-pyridyl) Ditelluride {[(3-MeC5H3N)Te]2}: Yield 52%,
m.p. 125Ϫ128°C. C12H12N2Te2 (439.4): calcd.
C 32.8, H
2.7, N 6.4; found C 32.6, H 2.42, N 6.18. UV/Vis (CH2Cl2): λmax
(ε) ϭ 297 (3260), 346 (sh, 1340), 412 (510) nm. 1H NMR (CDCl3):
δ ϭ 2.41 (s, Me), 6.96 (dd, J ϭ 3.2, 5.0 Hz, 5-H), 7.25 (d, J ϭ
4.6 Hz, 4-H); 8.20 (dd, J ϭ 0.8, 3.5 Hz, 6-H) ppm. 13C{1H} NMR
(CDCl3): δ ϭ 24.4 (s, Me), 122.1 (C-4), 134.9 (C-5), 137.8 (C-2),
140.7 (C-3), 148.3 (C-6) ppm. 125Te{1H} NMR (CDCl3): δ ϭ
Ϫ382.7 ppm. IR (KBr): ν˜ ϭ 3060, 2960, 2920, 1580, 1540, 1430,
1120, 1090, 1020, 840, 780, 660, 540 cmϪ1. MS (EI): m/z (%) ϭ
440 (7.33) [M (130Te)]ϩ, 314 (14.51) [M Ϫ Te]ϩ, 216 (1.47) [M Ϫ
Figure 3. SEM picture of PdTe obtained from [PdCl{Te(3-
MeC5H3N)}(PPh3)]
(Figure 3) of PdTe obtained from 2c taken at different res-
olutions show large aggregates of microcrystals.
MeC5H3NTe], 183 (76.62) [M
Ϫ Ϫ
Te2H]ϩ, 92 (100) [M
CH3pyTe2]ϩ.
Experimental Section
Bis(6-methyl-2-pyridyl) Ditelluride: Yield 24%, m.p. 55Ϫ56°C.
C12H12N2Te2 (439.4): calcd. C 32.8, H 2.7, N 6.4; found C 32.21,
H 2.52, N 6.18. UV/Vis (CH2Cl2): λmax (ε) ϭ 292 (sh, 8110), 386
(850) nm. 1H NMR (CDCl3): δ ϭ 2.50 (s, Me), 6.85 (d, J ϭ 5.0 Hz,
3-H), 7.25 (t, J ϭ 5.0 Hz, 4-H), 7.84 (d, J ϭ 5.0 Hz, 5-H) ppm.
13C{1H} NMR (CDCl3) δ ϭ 24.2 (s, Me), 121.0 (C-4), 128.0 (C-
5), 134.9 (C-2), 137.0 (C-3), 158.9 (C-6) ppm. 125Te{1H} NMR
(CDCl3): δ ϭ Ϫ426.4 ppm. IR (KBr): ν˜ ϭ 3042, 2916, 1571, 1429,
1376, 1242, 1163, 1083, 988, 826, 781, 655, 545 cmϪ1. MS (EI):
m/z (%) ϭ 444 (5.5) [M (130Te)]ϩ, 314 (6.5) [M Ϫ Te]ϩ, 216 (0.6)
[M Ϫ MeC5H3NTe], 183 (30.9) [M Ϫ Te2H]ϩ, 92 (100) [M Ϫ
CH3pyTe2]ϩ.
General: The complexes Na2PdCl4, [PtCl2(PPh3)2], [M2Cl2(µ-
Cl)2(PR3)2] (M ϭ Pd or Pt; PR3 ϭ PEt3, PnPr3, PMe2Ph, PMePh2,
PPh3), [PtCl2(dppe)],[42] py2Te2,[43a] (3-/6-MeC5H3N)2Te2,[43b] and
the methyl-substituted 2-bromopyridines[44] were prepared accord-
ing to literature methods. The phosphanes were obtained from
Strem Chemicals (USA). All reactions were carried out under ni-
trogen, in dry and distilled analytical grade solvents. Microanalyses
were carried out in the Analytical Chemistry Division of B.A.R.C.
1H, 31P{1H}, 125Te{1H}, and 195Pt{1H} NMR spectra were re-
corded with a Bruker DPX-300 NMR spectrometer, operating at
300, 121.49, 94.86, and 64.52 MHz, respectively. Chemical shifts
are relative to the internal chloroform peak (δ ϭ 7.26 ppm) for 1H,
external 85% H3PO4 for 31P, Te(dtc)2 (dtc ϭ Et2NCS2) for 125Te,
and Na2[PtCl6] in D2O for 195Pt. A 90° pulse was used in every
case. The IR spectra were recorded as Nujol mulls between CsI
plates with a Bomen MB-102 FT-IR spectrometer. UV/Vis ab-
sorbance spectra were recorded with a JASCO V-530 spectrometer
using quartz cuvettes with a diameter of 1 cm. Cyclic voltammetry
was carried out at a scan rate of 100 mV·sϪ1 in DMF/0.01 
Et4NClO4, using a three-electrode configuration (glassy carbon
electrode, platinum counter electrode, calomel reference electrode)
and an Ecochemie potentiostat 100 with autolab software. The
ferrocene/ferrocenium couple served as the external reference. Mass
spectra were recorded with a VG-705 11-250J spectrometer at
RSIC, Panjab University, Chandigarh. Thermogravimetric analysis
(TGA) was carried out using a Setaram 92-16-18 instrument calib-
rated with CaC2O4·H2O. The TG curves were recorded at a heating
rate of 10 °C·minϪ1 under a flow of argon. X-ray powder diffrac-
tion was measured using Cu-Kα radiation. SEM photographs were
taken using a JEOL JSM-T330A instrument.
[PdCl{Te(3-MeC5H3N)}]n (1b): A methanolic solution (10 mL) of
Na2PdCl4 (342 mg, 1.16 mmol) was added to a methanolic solution
(20 mL) of (3-MeC5H3N)2Te2 (256 mg, 0.58 mmol) while stirring
at room temperature, whereupon a brown precipitate formed. Stir-
ring was continued for 3 h. The brown precipitate was filtered,
washed with methanol, water, acetone, and diethyl ether and dried
in vacuo (yield: 235 mg, 56%). Complex 1a was also prepared in a
similar manner.
[PdCl{Te(3-MeC5H3N)}(PEt3)] (2a): An acetone suspension (20
mL) of [Pd2Cl2(µ-Cl)2(PEt3)2] (108 mg, 0.18 mmol) was added to a
freshly prepared methanolic solution (5 mL) of NaTe(3-MeC5H3N)
[prepared from (3-MeC5H3N)2Te2 (82 mg, 0.19 mmol) and NaBH4
(15 mg, 0.39 mmol)], and the mixture was stirred for 4 h at room
temperature. The solvents were evaporated in vacuo and the residue
was extracted with acetone (3 ϫ 8 mL). The solution was passed
through a Florisil column. The blue solution was concentrated to
3 mL, a few drops of hexane were added, and the solution was
kept at Ϫ5°C in a freezer giving blue-violet crystals (130 mg, 74%).
Similarly, other palladium (2b, 2c, 2f) and platinum (3aϪ3d) com-
plexes were prepared. The most important data are summarized
in Table 6.
Preparations
Preparation of Bis(3- and 6-methyl-2-pyridyl) Ditelluride: Sodium
[PdCl{Te(3-MeC5H3N)}(Ptol3)] (2d): Solid Ptol3 (tol ϭ 4-MeC6H4)
borohydride (4.0 g, 108 mmol) was added slowly under a flow of (26 mg, 0.09 mmol) was added to an acetone suspension (20 mL)
nitrogen to a suspension of tellurium powder (9.65 g, 76 mmol) in
2-ethoxyethanol. The resulting colorless solution was refluxed for
30 min and then cooled to room temperature; 3- or 6-methyl-sub-
stituted 2-bromopyridine (13.07 g, 76 mmol) was added and the re-
sulting solution was refluxed until all the 2-bromopyridine was con-
of 1 (30 mg, 0.08 mmol), and the mixture was stirred for 1 h. The
green solution was dried in vacuo and the residue was washed with
hexane, diethyl ether and recrystallized from acetone/hexane to
yield green crystals (38 mg, 68%). The complexes 2c and 2e were
prepared in an analogous manner.
748
Eur. J. Inorg. Chem. 2003, 744Ϫ750

Pyridine- and 3-/6-Methylpyridine-2-tellurolate Complexes of PdII and PtII
Table 6. Physical and analytical data for 3-methyl- and 6-methyl-2-pyridinetellurolate complexes of PdII and PtII
FULL PAPER
Complex
Color
Recrystallization solvent
(yield [%])
M.p.
[°C]
Analysis: found (calcd.)
C
H
N
[PdCl(TeC5H4N)]n (1a)
brown
brown
blue-violet
blue
green
green
green
green
orange-red
red
red
brown
yellow
yellow
yellow
yellow
164 (dec.)
185 (dec.)
116
163
150
167
78
102
98
124
187
166
192
167
168
213
17.0 (17.3)
18.6 (19.9)
30.5 (30.1)
40.6 (40.7)
45.4 (46.2)
48.6 (48.7)
45.0 (44.2)
38.9 (39.5)
29.5 (29.5)
28.8 (28.6)
35.1 (35.1)
(34.0)
1.2 (1.2)
1.3 (1.7)
4.2 (4.4)
3.3 (3.4)
3.2 (3.4)
3.7 (4.1)
3.0 (3.2)
3.3 (3.1)
4.2 (4.5)
2.7 (2.9)
2.6 (2.9)
(2.7)
4.1 (4.0)
3.6 (3.9)
2.8 (2.9)
2.4 (2.5)
2.3 (2.2)
2.2 (2.1)
4.8 (4.5)
2.8 (2.6)
2.2 (2.3)
2.3 (2.4)
2.1 (2.2)
(2.2)
[PdCl{Te(3-MeC5H3N)}]n (1b)
[PdCl{Te(3-MeC5H3N)}(PEt3] (2a)
[PdCl{Te(3-MeC5H3N)}(PMePh2)] (2b)
[PdCl{Te(3-MeC5H3N)}(PPh3)] (2c)
[PdCl{Te(3-MeC5H3N)}(P(tol)3] (2d)
[PdCl{Te(3-MeC5H3N)}(PPh2py)] (2e)
[PdCl(TeC5H4N)(PMePh2)] (2f)
[PtCl{Te(3-MeC5H3N)}(PnPr3] (3a)
[PtCl{Te(3-MeC5H3N)}(PMe2Ph)] (3b)
[PtCl{Te(3-MeC5H3N)}(PMePh2)] (3c)
[PtCl(TeC5H4N)(PMePh2)] (3d)
[Pt{Te(3-MeC5H3N)}2(dppe)] (4a)
[Pt{Te(6-MeC5H3N)2(dppe)] (4b)
[Pt{Te(3-MeC5H3N)}2(PPh3)2] (5)
[Pt2{Te(3-MeC5H3N)}2(dppe)2][BPh4]2 (6)
hexane (74)
acetone/hexane (72)
acetone (76)
acetone/hexane (68)
acetone (60)
acetone/hexane (56)
hexane (66)
diethyl ether/hexane (58)
acetone (62)
acetone/hexane (52)
CH2Cl2/hexane (64)
acetone/hexane (56)
acetone/benzene (42)
acetone (60)
45.0 (44.2)
43.4 (44.2)
49.3 (49.8)
59.5 (59.4)
3.2 (3.5)
3.2 (3.5)
2.5 (3.6)
4.2 (4.4)
2.8 (2.7)
2.4 (2.7)
2.1 (2.4)
1.4 (1.2)
Table 7. Crystallographic and structure refinement details for
[PdCl{Te(3-MeC5H3N)}(PPh3)] (2c)
[Pt{Te(3-MeC5H3N)}2(dppe)] (4a): This compound was prepared
analogously to 2a by using [PtCl2(dppe)] (110 mg, 0.17 mmol) and
NaTe(3-MeC5H3N) [prepared from (3-MeC5H3N)2Te2 (73 mg,
0.17 mmol) and NaBH4 (13 mg, 0.34 mmol)]. The yellow residue
was recrystallized from a CH2Cl2/hexane mixture (yield: 109 mg,
64%). Complex 4b was prepared in a similar manner.
Empirical formula
Formula mass
Crystal size [mm]
T [K]
C24H21ClNPPdTe
623.84
0.3ϫ0.3ϫ0.2
293(2)
˚
λ [A]
0.71073
[Pt{Te(3-MeC5H3N)}2(PPh3)2] (5):
A benzene suspension of
Crystal system
Space group
monoclinic
P21/n
[PtCl2(PPh3)2] (154 mg, 0.19 mmol) was added to a freshly pre-
pared methanolic solution (5 mL) of NaTe(3-MeC5H3N) [prepared
from (3-MeC5H3N)2Te2 (85 mg, 0.19 mmol) and NaBH4 (15 mg,
0.39 mmol)], and the yellow-orange mixture was stirred for 4 h. The
solvents were evaporated in vacuo and the residue was washed
thoroughly with hexane, diethyl ether, and acetone and then ex-
tracted with benzene (3 ϫ 8 mL). The solution was passed through
a Florisil column and concentrated to 5 mL, a few drops of acetone
were added, and the solution was kept at Ϫ5°C in a freezer, giving
a yellow powder (95 mg, 42%).
Unit cell dimensions
˚
a [A]
8.607(2)
11.088(3)
24.552(5)
˚
b [A]
˚
c [A]
β [°]
98.83(2)
2315.4(9)
1.790
3
˚
V [A ]
ρcalcd. [Mg·mϪ3
]
Z
4
µ [mmϪ1
]
2.231
θ for data collection/°
Reflections collected/unique
Refinement method
2.02 to 24.96
[Pt2{Te(3-MeC5H3N)}2(dppe)2][BPh4]2 (6): An acetone suspension
(20 mL) of [PCl2(dppe)] (203 mg, 0.31 mmol) was added to a
freshly prepared methanolic solution (5 mL) of NaTe(3-MeC5H3N)
[prepared from (3-MeC5H3N)2Te2 (68 mg, 0.16 mmol) and NaBH4
(12 mg, 0.32 mmol)], while stirring. After 2 h, an acetone solution
(8 mL) of NaBPh4 (107 mg, 0.31 mmol) was added, while stirring
was continued for 3 h. The solvents were evaporated under vacuum.
The yellow residue was extracted with acetone (3 ϫ 8 mL) and
passed through a Florisil column. The solution was concentrated
to 5 mL and yellow crystals were obtained (207 mg, 60%).
4349/4059 [Rint ϭ 0.03Ϫ0.01]
Full-matrix least-squares on F2
ψ scan
4059/0/263
1.104
0.0376, 0.0955
0.0563, 0.1265
Absorption correction
Data/restraints/parameters
Goodness of fit on F2
Final R1, wR2 indices
R1, wR2 (all data)
Largest diff peak and hole [e·AϪ3] 0.944 and Ϫ1.058
˚
Crystallography: X-ray data on dark green crystals of [PdCl{Te(3-
MeC5H3N)}(PPh3)] (2c) were collected at room temperature with
an EnrafϪNonius CAD-4 diffractometer using graphite-monoch-
free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html or from
the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK [Fax: (internat.) ϩ 44-1223/336-033;
E-mail: deposit@ccdc.cam.ac.uk].
˚
romated Mo-Kα radiation (λ ϭ 0.71073 A), employing the ω-2θ
scan technique. Crystal data are given in Table 7. The unit cell
parameters were determined from 25 reflections measured by ran-
dom search routine and indexed by the method of short vectors
followed by least-squares refinement. The intensity data were cor-
rected for Lorentz polarization and absorption effects. The struc-
ture was solved using the SHELXS86[45] and refined using the
SHELXL97[46] computer programs. The non-hydrogen atoms were
refined anisotropically. CCDC-181928 contains the supplementary
crystallographic data for this paper. These data can be obtained
Acknowledgments
We thank Dr. J. P. Mittal and Dr. P. Raj for encouragement of
this work. We are grateful to Dr. M. Sudersan, Head, Analytical
Chemistry Division, for providing microanalyses of the complexes.
We are thankful to Mr. S. Nath of RC&CD and Mr. A. Satpati of
ACD for recording the UV/Vis spectra and cyclic voltammograms.
Eur. J. Inorg. Chem. 2003, 744Ϫ750
749

S. Dey, V. K. Jain, J. Singh, V. Trehan, K. K. Bhasin, B. Varghese
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