Reactivity of 2-chalcogenopyridines with palladium-phosphine complexes: Isolation of different complexes depending on the nature of chalcogen atom and phosphine ligand

Article abstract of DOI:10.1039/c2dt30535f

Reactions of either Pd(0) phosphine complexes with dipyridyldichalcogenides or [PdCl₂(P^∩P)] (P^∩P = dppe, dppp) with pyridylchalcogenolate ions have been examined and a variety of Pd(ii) complexes have been isolated and characterized. Oxidative addition of {SeC ₅H₃(3-R)N}₂ (R = H or Me) to [Pd(P ^∩P)₂] (P^∩P = dppe, dppp) gave either a mononuclear complex, [Pd{2-Se-C₅H₃(3-R)N} ₂(P^∩P)] (for P^∩P/R: dppe/H or Me; dppp/H) or a cationic binuclear complex, [Pd₂{μ-SeC ₅H₃(3-Me)N}₂(dppp)₂]²⁺ (4b) (R = Me) whereas reactions involving the tellurium analogue exclusively afforded trinuclear complexes, [Pd₃(μ-Te)₂(P ^∩P)₃]Cl₂ (P^∩P = dppe (2) or dppp (6)). The latter was also obtained in the substitution reaction between [PdCl₂(P^∩P)] and NaTeC₅H₃(3-R)N. The substitution reactions between [PdCl₂(dppe)] and Pb{EC ₅H₃(3-R)N}₂ yielded mononuclear complexes, [Pd{2-E-C₅H₃(3-R)N}₂(dppe)] (1a-1e) (E = S, Se or Te) while in the case of [PdCl₂(dppp)], the reactions resulted in the formation of mono-, bi- and tri- nuclear complexes depending on the nature of the chalcogen atom (E = S, Se or Te) and the substituent on the pyridyl ring (R = H or Me). Treatment of dipyridyl ditellurides, {TeC₅H ₃(3-R)N}₂ (R = H or Me), with [Pd(PPh₃) ₄] gave expected tellurolate complexes, [Pd{2-TeC₅H ₃(3-R)N}₂(PPh₃)₂] (7a, 7b) which on prolonged standing in CDCl₃ solution gave green crystals of [PdCl{2-Te(Cl)₂C₅H₃(3-Me)N}(PPh₃)] (9). The molecular structures of {TeC₅H₃(3-Me)N} ₂, [Pd₂{μ-TeC₅H₃(3-Me)N} ₂(dppp)₂]Cl₂·3H₂O (5·3H₂O), [Pd₃(μ-Te)₂(dppp) ₃]Cl₂·3CHCl₃ (6·3CHCl ₃) and [PdCl{2-Te(Cl)₂C₅H₃(3-Me)N} (PPh₃)] (9) were established by single crystal X-ray diffraction analyses. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c2dt30535f

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Reactivity of 2-chalcogenopyridines with palladium–
phosphine complexes: isolation of different complexes
depending on the nature of chalcogen atom and
phosphine ligand†
Cite this: Dalton Trans., 2013, 42, 259
Rohit Singh Chauhan,a G. Kedarnath,*a Amey Wadawale,a Alexandra M. Z. Slawinb
and Vimal K. Jain*a
Reactions of either Pd(0) phosphine complexes with dipyridyldichalcogenides or [PdCl2(P∩P)] (P∩P =
dppe, dppp) with pyridylchalcogenolate ions have been examined and a variety of Pd(II) complexes have
been isolated and characterized. Oxidative addition of {SeC5H3(3-R)N}2 (R = H or Me) to [Pd(P∩P)2] (P∩P =
dppe, dppp) gave either a mononuclear complex, [Pd{2-Se-C5H3(3-R)N}2(P∩P)] (for P∩P/R: dppe/H or Me;
dppp/H) or a cationic binuclear complex, [Pd2{μ-SeC5H3(3-Me)N}2(dppp)2]2+ (4b) (R = Me) whereas reac-
tions involving the tellurium analogue exclusively afforded trinuclear complexes, [Pd3(μ-Te)2(P∩P)3]Cl2
(P∩P = dppe (2) or dppp (6)). The latter was also obtained in the substitution reaction between
[PdCl2(P∩P)] and NaTeC5H3(3-R)N. The substitution reactions between [PdCl2(dppe)] and Pb{EC5H3(3-R)-
N}2 yielded mononuclear complexes, [Pd{2-E-C5H3(3-R)N}2(dppe)] (1a–1e) (E = S, Se or Te) while in the
case of [PdCl2(dppp)], the reactions resulted in the formation of mono-, bi- and tri- nuclear complexes
depending on the nature of the chalcogen atom (E = S, Se or Te) and the substituent on the pyridyl ring
(R = H or Me). Treatment of dipyridyl ditellurides, {TeC5H3(3-R)N}2 (R = H or Me), with [Pd(PPh3)4] gave
expected tellurolate complexes, [Pd{2-TeC5H3(3-R)N}2(PPh3)2] (7a, 7b) which on prolonged standing in
CDCl3 solution gave green crystals of [PdCl{2-Te(Cl)2C5H3(3-Me)N}(PPh3)] (9). The molecular structures of
{TeC5H3(3-Me)N}2, [Pd2{μ-TeC5H3(3-Me)N}2(dppp)2]Cl2·3H2O (5·3H2O), [Pd3(μ-Te)2(dppp)3]Cl2·3CHCl3
(6·3CHCl3) and [PdCl{2-Te(Cl)2C5H3(3-Me)N}(PPh3)] (9) were established by single crystal X-ray diffraction
analyses.
Received 6th March 2012,
Accepted 2nd October 2012
DOI: 10.1039/c2dt30535f
www.rsc.org/dalton
Oxidative addition reactions of RE–ER (E = S or Se) with
platinum(0) precursors, [Pt(PPh3)4] or [Pt(PPh3)2(olefin)],
Introduction
Oxidative addition reactions of diorgano-disulfides and -disele- afford
mononuclear
platinum
chalcogenolates,
[Pt-
nides to zero-valent Group-10 metal complexes have received (ER)2(PR3)2],11–16 whereas similar reactions with palladium(0)
considerable attention recently.1–5 The remarkable reactivity of complexes, in general, yield binuclear derivatives,
Ni0 and Pd0 complexes has been exploited in regio- and stereo- [Pd2(μ-ER)2(ER)2(PR′3)2] (E = S or Se).7,13,15–17 In contrast
selective E–E addition to CuC bonds in organic synthesis.3,6–8 similar reactions of diorgano ditellurides with palladium(0)
The reaction also provides a convenient route for the synthesis and platinum(0) species are often more complex yielding
of metal chalcogenolate complexes which find applications in several products which seem to be formed by competitive clea-
organic synthesis9 and materials science.10
vage of Te–Te and Te–C bonds.14,18,19 Recently we have
isolated a serendipitous product, [Pt(Te){Te-C5H3(R)N}2(PPh3)]
containing bare Te0 coordinated to platinum from such
reactions.19
aChemistry Division, Bhabha Atomic Research Centre, Mumbai-400 085, India.
E-mail: kedar@barc.gov.in, jainvk@barc.gov.in; Fax: +91-22-25505151;
Tel: +91-22-25595095
Recently Morokuma et al.1 have investigated factors control-
ling the oxidative addition of E–E (E = S, Se, Te) to M(0) phos-
phine derivatives (M = Pd or Pt) by using density functional
approach. It has been reported that the transition state invol-
ving activation of RE–ER by “M0(PR3)2” species requires defor-
mation in the P–M–P angle.
bSchool of Chemistry, University of St. Andrews, St. Andrews, KY16 9ST Fife, UK.
E-mail: amzs@st-andrews.ac.uk
†CCDC 864902, 864901, 864905 and 864904 for {TeC5H3(3-Me)N}2,
[Pd2{μ-TeC5H3(3-Me)N}2(dppp)2]Cl2·3H2O
(5·3H2O),
[Pd3(μ-Te)2(dppp)3]-
Cl2·3CHCl3 (6·3CHCl3) and [PdCl{2-Te(Cl)2C5H3(3-Me)N}(PPh3)] (9). For crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c2dt30535f
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Dalton Trans., 2013, 42, 259–269 | 259

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With the above perspective we have chosen palladium(0) electrons, this is in close agreement with three molecules of
phosphine complexes with varying degree of P–Pd–P angles CHCl3) and large disorder in the positions and distribution of
(chelating diphosphines and PPh3) and studied their reactions solvent CHCl3 molecules and chloride anions. In order to
with dipyridyldichalcogenides. Substitution reactions of minimize these, SQUEEZE29,30 function was applied followed
[PdCl2(P∩P)] with pyridylchalcogenolate ions have also been by application of geometrical restraints (DFIX, DELU, SIMU,
examined to find the nature of products formed in such reac- ISOR, EADP) to the disordered moieties, which significantly
tions and also compare them with those obtained from oxi- improved the displacement parameters.
dative addition reactions. The results of this work are
described herein.
In case of [Pd2{TeC5H3(3-Me)N}2(dppp)2]Cl2 (5·3H2O), H
atoms on solvate water molecules could neither be located nor
positioned appropriately. In case of [PdCl{2-Te(Cl)2C5H3(3-Me)-
N}(PPh3)] (9), SIMU restraints have been applied to the aro-
matic carbon atoms.
Experimental
Molecular structures were drawn using ORTEP.31 Crystallo-
The compounds [Pd2Cl2(μ-Cl2)(PPh3)2],20 [PdCl2(P∩P)] [P∩P = graphic and structural determination data are listed in
dppe (1,2-bis(diphenylphosphino)ethane), dppp (1,3-bis(diphe- Table 1.
nylphosphino)propane)],21 Pd(PPh3)4,22 [Pd(P∩P)2] (P∩P = dppe,
dppp),23 (SeC5H4N)2, {SeC5H3(3-Me)N}2, (TeC5H4N)2 and
Syntheses of complexes
24
{TeC5H3(3-Me)N}2
and Pb(SC5H4N)2,25 Pb(SeC5H4N)2, [Pb-
REACTIONS INVOLVING 1,2-BIS(DIPHENYLPHOSPHINO)ETHANE PALLADIUM
PRECURSORS
{SeC5H3(3-Me)N}2]26 were prepared according to literature
methods. Tertiary phosphines were procured from Strem
[Pd(2-SC5H4N)2(dppe)] (1a). This was prepared from
a
Chemicals. All reactions were carried out under an argon/nitro- method different from earlier report.32 To a benzene suspen-
gen atmosphere in dry and distilled analytical grade solvents sion of [PdCl2(dppe)] (180 mg, 0.31 mmol) was added a
at room temperature. The 1H, 31P{1H}, 77Se{1H}, 125Te{1H} dichloromethane solution of [Pb(SC5H4N)2] (140 mg,
NMR spectra were recorded on a Bruker Avance-II spectrometer 0.32 mmol) with stirring which continued for 3 h at room
operating at 300, 121.49, 57.23, 94.77 MHz, respectively. temperature where upon an orange turbid solution was
Chemical shifts are relative to internal chloroform (δ 7.26) for formed. The latter was centrifuged and passed through Celite
1H, external 85% H3PO4 for 31P, external Ph2Se2 (δ 463 ppm and the filtrate was concentrated under reduced pressure. The
relative to Me2Se) in CDCl3 for 77Se{1H} and external [Te(dtc)2] residue was extracted with dichloromethane, filtered and
in CDCl3 (δ 440 ppm relative to Me2Te; dtc = N,N-diethyldithio- passed through a Florisil column. Hexane was added to the
carbamate) for 125Te{1H} NMR spectra. Elemental analyses resulting solution to give an orange powder (yield 147 mg,
were carried out on a Thermo Fischer Flash EA1112 CHNS 65% m.p. 181 °C (dec.)). Anal. calcd for C36H32N2P2PdS2: C,
analyzer.
59.62; H, 4.45, N; 3.86, S, 8.84%. Found: C, 59.91; H, 4.38 N;
Intensity data for {TeC5H3(3-Me)N}2 and [Pd2{TeC5H3(3-Me)- 3.51, S, 8.82%. 1H NMR (CDCl3) δ: 2.87 (m, –PCH2), 6.77 (t),
N}2(dppp)2]Cl2 (5·3H2O) (slow evaporation of benzene–hexane 6.94 (d, 8.1 Hz, C5H4N), 7.10 (t, 7.8 Hz, Ph), 7.47 (m, C5H4N),
solution of 5 gave red crystals which entrapped water from 7.81 (m, Ph), 8.45 (br, C5H4N); 31P{1H} NMR (CDCl3) δ:
atmospheric moisture), were collected on a Rigaku MM007 RA 59.5 ppm.
equipped with a Mercury CCD, while for [Pd3(μ-Te)2(dppp)3]Cl2
[Pd(2-SeC5H4N)2(dppe)] (1b). (i) To a benzene solution
(6·3CHCl3) on a Oxford diffraction Xcalibur S and for [PdCl- (10 cm3) of (SeC5H4N)2 (62 mg, 0.20 mmol), a solution
{2-Te(Cl)2C5H3(3-Me)N}(PPh3)] (9) were on a Rigaku AFC 7S (30 cm3) of [Pd(dppe)2] (175 mg, 0.19 mmol) in the same
diffractometer using MoKα radiation at 298 K so that θmax
=
solvent was added with stirring which continued for 4 h at
27.5°. The structures were solved by direct methods27 and room temperature. The orange solution was concentrated to
refinement28 was on F2 using data that had been corrected for 5 cm3 under reduced pressure and on addition of diethyl ether
absorption effects with an empirical procedure. Non-hydrogen (20 cm3) a yellow precipitate was formed which was washed
atoms were modelled with anisotropic displacement para- thoroughly with diethyl ether. The residue was recrystallized
meters, hydrogen atoms in their calculated positions.
from acetone to afford yellow crystals of the title compound
In the case of {TeC5H3(3-Me)N}2, very small prism-shaped (yield 110 mg, 69%; m.p. 175 °C (dec.)). Anal calcd for
red crystals were obtained, from which the best possible C36H32N2P2PdSe2: C, 52.80; H, 3.93; N, 3.42%. Found: C, 52.70;
crystal (size ∼ 0.1 × 0.1 × 0.03 mm) was isolated with a very H, 3.94; N, 3.24%. 1H NMR (CDCl3) δ: 2.61–2.68 (m, CH2,
thin needle and data were collected. Hence number of dppe), 7.10–7.56 (m, Ph), 7.81 (m), 8.45 (d, C5H4N), 8.55 (d,
observed reflections were low leading to slightly distorted C5H4N); 31P{1H} NMR (CDCl3) δ: 54.6 ppm.
atomic displacement parameters (ADPs) of some of the atoms.
Geometrical restraints like ISOR were used to improve the 0.23 mmol) was added a suspension of [PdCl2(dppe)] (130 mg,
ADPs. 0.23 mmol) in the same solvent with stirring which continued
(ii) To a benzene suspension of Pb(SeC5H4N)2 (122 mg,
In case of [Pd3(μ-Te)2(dppp)3]Cl2 (6·3CHCl3), after initial for 6 h at room temperature affording an orange turbid solu-
solution and refinement cycles the structure showed presence tion. The latter was centrifuged and passed through Celite and
of large solvent accessible void (541 Å3, at 0.5, 0.5, 1.0 with 178 the filtrate was concentrated under reduced pressure. The
260 | Dalton Trans., 2013, 42, 259–269
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Table 1 Crystallographic and structural determination data for {TeC5H3(3-Me)N}2, [Pd2{μ-TeC5H3(3-Me)N}2(dppp)2]Cl2·3H2O (5·3H2O), [Pd3(μ-Te)2(dppp)3]Cl2·3CHCl3
(6·3CHCl3) and [PdCl{2-Te(Cl)2C5H3(3-Me)N}(PPh3)] (9)
[Pd2{μ-TeC5H3(3-Me)N}2-
[Pd3(μ-Te)2(dppp)3]-
[PdCl{2-Te(Cl)2C5H3-
(3-Me)N}(PPh3)]
Complex
{TeC5H3(3-Me)N}2
12H12N2Te2
(dppp)2]Cl2·3H2O
Cl2·3CHCl3
Chemical formula
C
C66H64
C81H78Cl2P6Pd3
C24H21Cl3NPPdTe
Cl2N2P4Pd2Te2·3H2O
1602.2
0.10 × 0.10 × 0.02
Triclinic
Te2·3CHCl3
2240.85
0.33 × 0.26 × 0.21
Triclinic
Formula wt.
439.4
694.74
Crystal size (mm3)
0.10 × 0.10 × 0.03
Triclinic
93(2)
0.5 × 0.15 × 0.15
Monoclinic
298(2)
Crystal system
Temperature (K)
Space group
93(2)
150(2)
ˉ
P1
ˉ
ˉ
P1
P1
P21/a
Unit cell dimensions
a (Å)
b (Å)
c (Å)
α (°)
β (°)
6.804(2)
7.5995 (14)
7.7209(4)
63.64(3)
66.90(3)
86.84(4)
325.58 (12)
1
11.934(6)
13.083(7)
13.460(7)
114.084(2)
99.385(4)
111.686(5)
1656.3(15)
1
14.2448(4)
18.8456(6)
18.9875(5)
81.392(2)
83.613(2)
69.894(3)
4722.9(2)
2
17.000(14)
10.775(4)
15.631(15)
—
115.51(6)
—
2584(3)
4
1.786
γ (°)
Volume (Å3)
Z
ρcalcd, g cm−3
2.241
4.455/202
1998
1.606
1.629/794
16 863
1.563
1.609/2191
57 477
μ (mm−1)/F(000)
2.209/1344
7091
5940/1494
No of reflections collected
No of independent reflection/no. of observed
reflections with I > 2σ(I)
Data/restraints/parameters
Final R1, wR2 indices
R1, wR2 (all data)
1126/1085
6038/4541
31 378/10 308
1126/12/73
0.0339/0.0977
0.0427/0.1449
6038/0/365
0.0657/0.1577
0.0945/0.1727
31 237/112/1024
0.0841/0.2253
0.2159/0.2544
5940/132/240
0.0720/0.0929
0.3597/0.1452
residue was extracted with benzene, filtered, and passed for C38H36N2P2PdTe2: C, 48.33; H, 3.84; N, 2.96%. Found: C,
through a Florisil column. Hexane was added to the resulting 48.88; H, 3.72; N 2.48%. 1H NMR (CDCl3) δ: 2.28 (br, PCH2),
solution to give a yellow powder (yield 102 mg, 55%, m. 2.42 (s, Me), 6.99 (m, C5H3(3-Me)N), 7.29–7.48 (m, Ph), 8.21 (d,
p. 175 °C (dec.)). Anal. calcd for C36H32N2P2PdSe2: C, 52.80; H, 4.5 Hz, C5H3(3-Me)N); 31P{1H} NMR (CDCl3) δ: 52.8 ppm.
3.93; N, 3.42%. Found: C, 53.08; H, 3.92; N 3.48%. 31P{1H}
NMR (CDCl3) δ: 54.9 ppm.
[Pd3(μ-Te)2(dppe)3]Cl2 (2). (i) To a toluene solution (10 cm3)
of (TeC5H4N)2 (80 mg, 0.19 mmol), a solution (30 cm3) of [Pd-
[Pd{2-SeC5H3(3-Me)N}2(dppe)] (1c). (i) Prepared in a similar
fashion as 1b adopting method (i) in 68% yield as a yellow
(dppe)2] (175 mg, 0.19 mmol) in the same solvent was added
with stirring which continued for 4 h at room temperature
whereupon an orange precipitate formed. The supernatant was
powder. Anal. calcd for C38H36N2P2PdSe2: C, 53.89; H, 4.28; N,
1
3.31%. Found: C, 53.48; H, 4.08; N, 3.22%. H NMR (CDCl3) δ:
decanted and the precipitate was washed with hexane followed
2.16 (s, Me), 2.78 (m, dppe), 6.67 (m), 7.00–7.51 (m, Ph), 7.87
by diethyl ether. The residue was extracted from dichloro-
methane and after drying under vacuum and recrystallization
from acetone–dichloromethane mixture gave red crystals of 2
(yield 91 mg, 77%; m.p. 193 °C (dec.)). Anal calcd for
(m, C5H3(3-Me)N), 8.29 (d, 4.5 Hz, C5H3(3-Me)N); 31P{1H} NMR
(CDCl3) δ: 54.5 (br) ppm.
(ii) Prepared similar to 1b using method (ii), and recrystal-
lized from dichloromethnae–hexane (yield 139 mg, 63%).
C78H72Cl2P6Pd3Te2: C, 50.89; H, 3.94%. Found: C, 50.70; H,
3.46%. 1H NMR (CDCl3) δ: 2.30 (m, –PCH2), 6.86 (t, 8.1 Hz),
Anal. calcd for C38H36N2P2PdSe2: C, 53.89; H, 4.28; N, 3.31%.
Found: C, 53.97; H, 4.53; N, 3.76%. 31P{1H} NMR (CDCl3) δ:
7.14 (m), 7.43 (br), 7.68 (m); 31P{1H} NMR (CDCl3) δ: 46.1 ppm.
(ii) Similarly the reaction of {TeC5H3(3-Me)N}2 (79 mg,
0.18 mmol) with [Pd(dppe)2] (168 mg, 0.19 mmol) and after
extraction from CH2Cl2 gave [Pd3(μ-Te)2(dppe)3]Cl2 (2) which
was recrystallized from acetone dichloromethane to afford red
crystals (yield 78 mg, 69%; m.p. 193 °C (dec.)). Anal. calcd for
C78H72Cl2P6Pd3Te2: C, 50.89; H, 3.94%. Found: C, 51.20; H,
4.10%. 1H NMR (CDCl3) δ: 2.44–2.62 (m, –PCH2), 7.15–7.90 (m,
Ph); 31P{1H} NMR (CDCl3) δ: 46.2 ppm.
54.8 ppm.
[Pd(2-TeC5H4N)2(dppe)] (1d). Prepared similar to 1b (method
ii) using [PdCl2(dppe)] (126 mg, 0.22 mmol) and Pb(TeC5H4N)2
(135 mg, 0.22 mmol) benzene–methanol mixture in 67%
(134 mg) yield, (m.p. 189 °C (dec)). Anal. calcd for
C36H32N2P2PdTe2: C, 47.23; H, 3.52; N, 3.06%. Found: C, 47.69;
H, 3.38; N 3.48%. 1H NMR (CDCl3) δ: 2.46 (m, –PCH2), 6.52
(br), 6.65 (t, C5H4N), 6.87 (br), 7.17–7.90 (m, Ph), 8.03 (d, 7.8
Hz, C5H4N), 8.45 (br, C5H4N); 31P{1H} NMR (CDCl3) δ:
51.1 ppm.
(iii) To a benzene suspension (15 cm3) of [PdCl2(dppe)]
(250 mg, 0.43 mmol) was added a methanol–benzene solution
[Pd{2-TeC5H3(3-Me)N}2(dppe)] (1e). Prepared similar to 1b (10 cm3) of NaTeC5H4N [prepared from (TeC5H4N)2 (180 mg,
(method ii) using [PdCl2(dppe)] (116 mg, 0.20 mmol) and Pb- 0.43 mmol) in benzene and NaBH4 (33 mg, 0.87 mmol) in
{TeC5H3(3-Me)N}2 (130 mg, 0.20 mmol) in benzene–methanol methanol]. The mixture was stirred for 3 h, whereupon a clear
mixture in 70% (134 mg) yield (m.p. 181 °C (dec.)). Anal. calcd red solution was obtained. The solvents were evaporated under
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reduced pressure. The residue was washed with hexane fol- C, 54.03; H, 4.25; N, 1.96%. Found: C, 54.09; H, 4.23; N 1.84%.
lowed by diethyl ether. The product was extracted with 1H NMR (CDCl3) δ: 2.46 (m, –PCH2), 2.51 (br, –CH2), 6.11 (t,
acetone-dichloromethane and passed through
a Florisil C5H4N), 6.26 (br, C5H4N), 6.46 (t, 6 Hz, C5H4N), 6.80–7.90 (m,
column which on slow evaporation gave red crystals of Ph), 8.44 (dd, 6 Hz, 1 Hz, C5H4N); 31P{1H} NMR (CDCl3) δ:
[Pd3(μ-Te)2(dppe)3]Cl2 (2) (yield 210 mg, 79%; m.p. 193 °C 15.5, −0.9; 77Se{1H} NMR (CDCl3) δ: 160 ppm. Even on pro-
(dec.)). Anal. calcd for C78H72Cl2P6Pd3Te2: C, 50.89; H, 3.94%. longed stirring (16 h) of the reactants, both (3b and 4a) pro-
Found: C, 51.20; H, 3.86%. 1H NMR (acetone-d6) δ: 2.71 (br, ducts were formed.
PCH2), 7.15 (br, Ph), 7.33 (t, 13.5 Hz, Ph), 7.51 (q), 7.70 (m);
[Pd2(μ-2-SeC5H3(3-Me)N)2(dppp)2]Cl2 (4b). (i) To a benzene
31P{1H} NMR (acetone-d6) δ: 46.7; 125Te{1H} NMR (acetone-d6) solution (10 cm3) of {SeC5H3(3-Me)N}2 (58 mg, 0.17 mmol) a
δ: 195 ppm. Similarly the reaction between [PdCl2(dppe)] solution (15 cm3) of [Pd(dppp)2] (150 mg, 0.16 mmol) in the
(250 mg, 0.43 mmol) and Na{2-Te-C5H3(3-Me)N}[from same solvent was added with stirring which continued for 5 h
{TeC5H3(3-Me)N}2 (195 mg, 0.44 mmol) in benzene and NaBH4 at room temperature. The contents were concentrated under
(35 mg, 0.92 mmol) in methanol], after processing and recrys- reduced pressure and diethyl ether (15 ml) was added to pre-
tallization, afforded red crystals of 2 (yield 194 mg, 73%; cipitate a yellow powder. The residue was extracted with
m.p. 193 °C (dec.)). Anal. calcd for C78H72Cl2P6Pd3Te2: C, dichloromethane which on drying under vacuum afforded an
1
50.89; H, 3.94%. Found: C, 51.32; H, 3.68. H NMR (acetone- orange powder (yield 61 mg, 52%, m.p. 153 °C (dec.)). Anal.
d6) δ: 2.71 (br, –PCH2), 7.11–7.55 (m, Ph); 31P{1H} NMR calcd for C66H64Cl2N2P4Pd2Se2: C, 54.63; H, 4.45; N, 1.93%.
1
(acetone-d6) δ: 46.7 ppm.
Found: C, 54.79; H, 4.33; N 2.14%. H NMR (CDCl3) δ: 2.01 (s,
REACTIONS INVOLVING 1,3-BIS(DIPHENYLPHOSPHINO)PROPANE PALLADIUM Me), 3.19 (br, PCH2), 6.19 (br, C5H3(3-Me)N), 6.38 (t, 5.4 Hz,
PRECURSORS
C5H3(3-Me)N), 7.40 (br, Ph), 7.72 (m, Ph), 8.29 (d, 4.5 Hz,
C5H3(3-Me)N); 31P{1H} NMR (CDCl3) δ: 15.4, −1.2; 77Se{1H}
NMR (CDCl3) δ: 132 ppm.
[Pd(2-SC5H4N)2(dppp)] (3a). Prepared in a manner similar to
1a using [PdCl2(dppp)] (100 mg, 0.17 mmol) and Pb(SC5H4N)2
(75 mg, 0.18 mmol) in 58% (72 mg) yield as orange crystalline
solid, m.p. 137 °C (dec.). Anal. calcd for C37H34N2P2PdS2: C,
60.12; H, 4.63, N; 3.78, S, 8.67%. Found: C, 59.91; H, 4.38 N;
3.51, S, 8.82%. 1H NMR (CDCl3) δ: 2.48 (m, CH2), 3.20–3.35
(br, PCH2), 6.03 (t, 12.3 Hz, C5H4N), 6.38 (t, 12.9 Hz, C5H4N),
6.72–7.76 (m, Ph + C5H4N), 7.93 (br, C5H4N); 31P{1H} NMR
(CDCl3) δ: 7.1 ppm.
(ii) To
a benzene suspension of Pb{SeC5H3(3-Me)N}2
(57 mg, 0.10 mmol) was added a suspension of [PdCl2(dppp)]
(60 mg, 0.10 mmol) in the same solvent with stirring which
continued for 6 h at room temperature. The orange turbid sol-
ution was centrifuged and passed through Celite and the
solvent was evaporated under reduced pressure. The orange
residue was washed with diethyl ether. The product was
[Pd(2-SeC5H4N)2(dppp)] (3b). (i) Prepared similar to 1b extracted with dichloromethane, filtered, and passed through
(method i) using (SeC5H4N)2 (30 mg, 0.096 mmol) and [Pd- a Florisil column. To the resulting solution hexane was added
(dppp)2] (80 mg, 0.086 mmol) in benzene as a brown powder, to afford a brown powder (yield 50 mg, 68%, m.p. 153 °C
(yield 48 mg, 67%; m.p. 146 °C (dec.)). Anal. calcd for (dec.)). Anal. calcd for C66H64Cl2N2P4Pd2Se2: C, 54.63; H, 4.45;
1
C37H34N2P2PdSe2: C, 53.35; H, 4.11; N, 3.36%. Found: C, 52.85; N, 1.93%. Found: C, 54.88; H, 4.53; N 1.76%. H NMR (CDCl3)
H, 3.98; N, 3.75%. 1H NMR (CDCl3) δ: 2.76 (m, PCH2), 3.45 (m, δ: 1.99 (s, Me), 2.21 (br, CH2), 3.22 (t, –PCH2), 6.21 (br, C5H4N),
CH2), 6.38 (br, C5H4N), 7.00–7.73 (m, Ph + C5H4N), 8.37 (d, 6.39 (t, 6.5 Hz, C5H4N), 7.13–7.73 (m, Ph), 8.30 (d, 4.5 Hz,
4.2 Hz, C5H4N, H-6); 31P{1H} NMR (CDCl3) δ: 3.9; 77Se{1H} C5H4N); 31P{1H} NMR (CDCl3) δ: 15.6, −1.2 ppm.
NMR (CDCl3) δ: 308 ppm.
[Pd(2-TeC5H4N)2(dppp)] (3c). To a benzene suspension of Pb-
(ii) To a benzene suspension of Pb(SeC5H4N)2 (83 mg, (TeC5H4N)2 (64 mg, 0.10 mmol) was added a suspension of
0.16 mmol) was added a suspension of [PdCl2(dppp)] (90 mg, [PdCl2(dppp)] (60 mg, 0.10 mmol) in the same solvent with
0.15 mmol) in the same solvent with stirring which continued stirring which continued for 6 h at room temperature where-
for 6 h at room temperature whereupon a turbid orange solu- upon a turbid red solution was obtained. The contents were
tion formed. The latter was centrifuged and passed through centrifuged and passed through Celite and the solvent was
Celite and the solvent was evaporated under reduced pressure. reduced under vacuum. The residue was washed with hexane
The residue was washed with diethyl ether. The product was and diethyl ether. The product was extracted with benzene, fil-
extracted with benzene, filtered and passed through a Florisil tered and passed through a Florisil column. To the resulting
column and the resulting solution on addition of hexane pro- solution, hexane was added to obtain red crystals (yield 52 mg,
duced an orange powder, [Pd(2-Se-C5H4N)2(dppp) (3b) (yield 55%, m.p. 173 °C (dec.)). Anal. calcd for C37H34N2P2PdTe2: C,
41 mg, 32%, m.p. 146 °C (dec.)). Anal calcd for 47.77; H, 3.68; N, 3.01%. Found: C, 47.98; H, 3.72; N 3.48%.
C37H34N2P2PdSe2: C, 53.35; H, 4.11; N, 3.36%. Found: C, 53.21; 1H NMR (CDCl3) δ: 2.28 (m, –PCH2), 3.76 (br, dppp –CH2), 6.68
H, 4.56; N, 3.01%. 1H NMR (CDCl3) δ: 2.49 (m, –PCH2), 2.83 (br, Ph), 6.86 (m, C5H4N), 7.04 (br, Ph + C5H4N), 7.39 (m, Ph),
(br, –CH2), 7.05–7.71 (m, C5H4N + Ph); 31P{1H} NMR (CDCl3) δ: 7.23 (m, ph) 7.79 (br, Ph), 8.01 (d, 7.8 Hz C5H4N), 8.48 (dd,
3.9 ppm. The benzene insoluble part was extracted with 4.5 Hz, 3.9 Hz, C5H4N); 31P{1H} NMR (CDCl3) δ: −4.6 ppm.
dichloromethane and precipitated by addition of hexane as a
[Pd2{μ-2-TeC5H3(3-Me)N}2(dppp)2]Cl2 (5). To a benzene sus-
brown powder, [Pd2(μ-Se-C5H4N)2(dppp)2]Cl2 (4a) (yield 54 mg, pension of Pb{TeC5H3(3-Me)N}2 (91 mg, 0.14 mmol) was
50%, m.p. 159 °C (dec.)). Anal. calcd for C64H60Cl2N2P4Pd2Se2: added a suspension of [PdCl2(dppp)] (80 mg, 0.14 mmol) in
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the same solvent with stirring which continued for 5 h at room
temperature to give a turbid red solution. The contents were
centrifuged for 10 minutes and the supernatant was passed
through Celite. The solvent was removed under reduced
pressure. The residue was washed with hexane and diethyl
ether. The product was extracted with benzene, filtered and
passed through a Florisil column. To the resulting solution,
hexane was added to afford red crystals (yield 61 mg, 58%, m.p.
REACTION INVOLVING TRIPHENYLPHOSPHINE PALLADIUM COMPLEXES
[Pd(2-TeC5H4N)2(PPh3)2] (7a). (i) To benzene solution
a
(10 cm3) of (TeC5H4N)2 (52 mg, 0.13 mmol), a solution
(30 cm3) of [Pd(PPh3)4] (140 mg, 0.12 mmol) in the same
solvent was added with stirring which continued for 4 h at
room temperature. The solvent was evaporated under vacuum
and the residue was washed thoroughly with diethyl ether to
remove liberated triphenylphosphine. The residue was recrys-
tallized from acetone to afford a brown powder (yield 84 mg,
67% m.p. 137 °C (dec.)). Anal. calcd for C46H38N2P2PdTe2: C,
53.00; H, 3.67, N; 2.69%. Found: C, 52.84; H, 3.69; N; 2.56%.
1H NMR (acetone-d6) δ: 7.46 (d, C5H4N), 7.56 (dd, Ph),
7.60–7.69 (m, Ph), 8.09 (d, C5H4N), 8.45 (br, C5H4N); 31P{1H}
NMR (acetone-d6) δ: 28.4 ppm.
179 °C (dec.)). Anal. calcd for
C66H64N2Cl2P4Pd2Te2: C,
51.20; H, 4.17; N, 1.81%. Found: C, 51.88; H, 4.38; N 2.10%.
1H NMR (CDCl3) δ: 2.34 (s, Me), 3.18 (br, dppp, –CH2), 6.13 (t,
C5H3(3-Me)N), 6.60 (br, C5H3(3-Me)N), 7.04–7.80 (m, Ph), 8.45
(d, C5H3(3-Me)N); 31P{1H} NMR (CDCl3) δ: −9.6 ppm. The
benzene insoluble part (yield 14 mg, 20%) was extracted with
dichloromethane which on concentration gave an orange
powder identified as [Pd3(μ-Te)2(dppp)3]Cl2 (6) 31P{1H} NMR
(CDCl3) δ: −11.0 ppm.
[Pd{2-TeC5H3(3-Me)N}2(PPh3)2]
(7b). [Pd{2-TeC5H3(3-Me)-
N}2(PPh3)2] was prepared by the reaction between {TeC5H3(3-
Me)N}2 (77 mg, 0.18 mmol) and [Pd(PPh3)4] (193 mg,
0.17 mmol) in benzene similar to 7a. (yield 111 mg, 62%
m.p. 164 °C (dec.)). Anal. calcd for C48H42N2P2PdTe2: C, 53.85;
[Pd3(μ-Te)2(dppp)3]Cl2 (6). (i) To a toluene solution (10 cm3)
of (TeC5H4N)2 (42 mg, 0.10 mmol), a solution (30 cm3) of [Pd-
(dppp)2] (90 mg, 0.096 mmol) in the same solvent was added
with stirring which continued for 4 h at room temperature. An
orange precipitate formed during the reaction was filtered and
washed thoroughly with diethyl ether. The precipitate was
extracted with dichloromethane which on slow evaporation
gave orange crystals of 6 (yield 45 mg, 73%; m.p. 212 °C
(dec.)). Anal. calcd for C81H78Cl2P6Pd3Te2: C, 51.67; H, 4.17%.
Found: C, 51.54; H, 4.04%. 1H NMR (CDCl3) 3.08 (br, dppp
–CH2), 7.16 (br); 31P{1H} NMR (CDCl3) δ: −11.0 ppm. Similarly
the reaction between {TeC5H3(3-Me)N}2 (43 mg, 0.10 mmol)
and [Pd(dppp)2] (85 mg, 0.09 mmol) in toluene gave 6 in 72%
yield (m.p. 212 °C (dec.)). Anal. calcd for C81H78Cl2P6Pd3Te2:
C, 51.67; H, 4.17%. Found: C, 51.43; H, 4.23%. 1H NMR
(CDCl3) 3.12 (br, dppp –CH2), 7.18 (br), 7.47–7.81 (m); 31P{1H}
NMR (CDCl3) δ: −11.0 ppm.
1
H, 3.95, N; 2.62%. Found: C, 53.99; H, 4.08 N; 2.65%. H NMR
(CDCl3) δ: 2.47 (s, Me), 7.05 (br, C5H3(3-Me)N), 7.35 (br,
C5H3(3-Me)N), 7.46–7.71 (m, Ph), 8.30 (br, C5H3(3-Me)N); 31P
{1H} NMR (CDCl3) δ: 29.4 ppm.
[PdCl{2-Te(Cl)2C5H3(3-Me)N}(PPh3)] (9). When a CDCl3 solu-
tion of 7b was left for a few hours, it turned greenish and after
processing, green crystals of the title complex were manually
separated (m.p. 110 °C). Anal. calcd for C24H21NCl3PPdTe: C,
41.49; H, 3.04, N; 2.01%. Found: C, 41.83; H, 3.45; N; 1.87%.
1H NMR (CDCl3) 2.51 (s, Me), 7.43 (m, Ph + C5H3(3-Me)N), 7.83
(m, Ph), 8.83(d, C5H3(3-Me)N); 31P{1H} NMR (CDCl3) δ:
27.8 ppm. Similarly when the complex [PdCl{2-Te-C5H3(3-Me)-
N}(PPh3)] (8), (Anal calcd for C24H21NClPPdTe: C, 46.20; H,
3.39, N; 2.25%. Found: C, 45.92; H, 3.38; N; 2.76%. 1H NMR
(CDCl3) 2.07 (s, Me), 6.84 (t, C5H3(3-Me)N) 7.28 (d, C5H3(3-Me)-
N), 7.46–7.67 (m, Ph), 7.89 (d, C5H3(3-Me)N); 31P{1H} NMR
(CDCl3) δ: 29.04 ppm), prepared according to reported
method33 and left in CDCl3 solution for a few days turned dark
green, depositing green crystals of 9 in the NMR tube. 31P{1H}
NMR (CDCl3) δ: 28.0 ppm.
(ii) To a benzene suspension (15 cm3) of [PdCl2(dppp)]
(125 mg, 0.21 mmol) was added a methanol–benzene solution
(10 cm3) of NaTeC5H4N [prepared from (TeC5H4N)2 (90 mg,
0.22 mmol) in benzene and NaBH4 (16.9 mg, 0.45 mmol) in
methanol]. The mixture was stirred for 3 h, whereupon a clear
red solution was obtained. The solvents were evaporated under
reduced pressure. The residue was washed with hexane fol-
lowed by diethyl ether. The product was extracted with
dichloromethane and passed through a Florisil column. The
Results and discussion
resulting solution on slow evaporation gave orange-red crystals Reactions of 2-chalcogenopyridine ligands with palladium(0)
of 6 (yield 86 mg, 65%; m.p. 212 °C (dec.)). Anal. calcd for and palladium(II) precursors afforded a variety of complexes
C81H78Cl2P6Pd3Te2: C, 51.67; H, 4.17%. Found: C, 51.34; H, depending on the nature of chalcogen atom, palladium precur-
1
3.9%. H NMR (CDCl3) 2.39 (m, PCH2), 3.11 (br, dppp, –CH2), sor and the reaction conditions (Schemes 1–5). The treatment
7.18 (br), 7.45 (br), 7.81 (q); 31P{1H} NMR (CDCl3) δ: −11.0; of [PdCl2(dppe)] with lead 2-pyridinechalcogenolates gave
125Te{1H} NMR (CDCl3) δ: −497 ppm. Similarly, reaction of mononuclear palladium complexes, [Pd{EC5H3(3-R)N}2(dppe)]
[PdCl2(dppp)] (115 mg, 0.19 mmol) with NaTeC5H3(3-Me)N (E = S, Se, Te) (1) as yellow-to-orange powder (Scheme 1).
[prepared from {TeC5H3(3-Me)N}2 (90 mg, 0.21 mmol) Similar substitution reactions between [PdCl2(dppe)] and
in benzene and NaBH4 (16.9 mg, 0.45 mmol) in methanol] NaTeC5H3(3-R)N, prepared by reductive cleavage of Te–Te bond
gave orange-red crystals in 83% (101 mg) yield (m.p. 212 °C of dipyridylditellurides by NaBH4 in methanol, gave an orange
(dec.)). Anal. calcd for C81H78Cl2P6Pd3Te2: C, 51.67; H, 4.17%. precipitate which on extraction with dichloromethane afforded
Found: C, 51.28; H, 3.87%. 31P{1H} NMR (CDCl3) δ:
−11.0 ppm.
a
tellurido-bridged trinuclear
palladium(II)
complex,
[Pd3(μ-Te)2(dppe)3]Cl2 (2) (Scheme 2) as a red crystalline solid
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Scheme 1 Reactions of [PdCl 2(dppe)] with lead 2-pyridine chalcogenolates.
Scheme 2 Reactions of [PdCl2(P∩P)] and Pd(P∩P)2 (P∩P = dppe or dppp) with sodium 2-pyridyl tellurolates and dipyridyl ditellurides, respectively.
which was isolated in good yield. Similarly, 2 was formed
The reactions of 2-seleno/telluoro-pyridines with “Pd-
when a palladium(0) precursor, [Pd(dppe)2], was treated with (dppp)” species were markedly different from those involving
dipyridylditellurides in benzene followed by extraction with “Pd(dppe)” species as described above. The reaction of Pb-
dichloromethane (Scheme 2). Morley and co-workers have (SC5H4N)2 with [PdCl2(dppp)] gave expected mononuclear
reported the formation of the platinum analogue of 2 by an complex, [Pd(2-SC5H4N)2(dppp)] (3a) as described earlier in
oxidative addition reaction of tellurium powder with Pt(dppe)2 the literature.32 However the reaction of [PdCl2(dppp)] with Pb-
followed by extraction with dichloromethane at room (SeC5H4N)2 afforded
a
(3b)
mixture of mononuclear, [Pd(2-
temperature.34 Interestingly, the corresponding reaction of SeC5H4N)2(dppp)]
and binuclear, [Pd2(μ-2-
dipyridyldiselenides with [Pd(dppe)2] afford oxidative addition SeC5H4N)2(dppp)2]Cl2 (4a) complexes (Scheme 4) even on pro-
products, [Pd{SeC5H3(3-R)N}2(dppe)] (R = H (1b); Me (1c)) longed stirring of the reactants at room temperature. In con-
(Scheme 3).
trast, the similar reaction with Pb{SeC5H3(3-Me)N}2 gave
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Scheme 3 Oxidative addition reactions of Pd(dppe)2 with dipyridyl diselenides.
Scheme 4 Reactions of [Pd(dppp)2] and [PdCl2(dppp)] with dipyridyl diselenides and lead 2-pyridine selenolates, respectively.
Scheme 5 Reactions of triphenylphosphine palladium precursors with 2-telluropyridines.
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exclusively
a
dimeric complex, [Pd2(μ-2-SeC5H3(3-Me)- (eqn (1)). Similar behaviour has been observed for the analo-
N)2(dppp)2]Cl2 (4b). Interestingly, treatment of (SeC5H4N)2 gous platinum derivatives.40 For mononuclear complex two 31
P
with [Pd(dppp)2] yielded mononuclear complex, [Pd(2- NMR resonances would be expected, one due to phosphorus
SeC5H4N)2(dppp)] (3b) while {SeC5H3(3-Me)N}2 gave the binuc- trans to the chalcogen atom and another trans to the nitrogen
lear complex 4b (Scheme 4). The complexes 4a and 4b appear atom.
to be formed either by partial substitution of one chloride
from PdCl2(dppp) with a selenolate ligand or by nucleophilic
attack of CH2Cl2 on the bis substituted products. We attribute
the former route for the formation of 4a and 4b as the 31P
NMR spectrum of a CDCl3 solution of 3b remained unchanged
for several hours. The reaction of [PdCl2(dppp)] with [Pb-
(TeC5H4N)2] yielded [Pd(2-TeC5H4N)2(dppp)] (3c) which slowly
converted to a dimeric species in halogenated solvents,
ð1Þ
[Pd2(μ-2-TeC5H4N)2(dppp)2]Cl2
[PdCl2(dppp)] with Pb{TeC5H3(3-Me)N}2, on the other hand,
gave mixture of products from which the dimeric
(5a).
The
reaction
of
Treatment of [Pd(PPh3)4] with dipyridyl ditellurides readily
gave oxidative addition products, trans-[Pd{2-TeC5H3(3-R)-
N}2(PPh3)2] (7) (R = H (7a) or Me (7b)) (Scheme 5). It is note-
worthy that the similar reaction with [Pt(PPh3)4] with dipyridyl
ditellurides, in addition to the expected product trans-[Pd{2-
TeC5H3(3-R)N}2(PPh3)2], also gave a serendipetous complex, [Pt-
(Te){TeC5H3(3-R)N}2(PPh3)].19 The complex 7b, when left in
CDCl3 solution, afforded green crystals of a new derivative,
[PdCl{2-Te(Cl)2C5H3(3-Me)N}(PPh3)] (9) (Scheme 5) which was
structurally characterized. Recently we have described the syn-
thesis of palladium complexes of the type [PdCl(TeC5H4N)-
(PR3)].33 To assess whether such complexes also undergo
similar reactions, the complex [PdCl{TeC5H3(3-Me)N}(PPh3)]
(31P{1H} NMR δ: 29.04 ppm) was left in CDCl3 for several
hours, green crystals of 9 (31P{1H} NMR δ: 28.0 ppm) were sep-
arated. The bridging sulfido ligands in palladium and plati-
num complexes, [M2(μ-S)2(PR3)4] are known to be susceptible
to nucleophilic attack by various halogenated compounds like
CHCl3, CH2Cl2, R′X, HCl to yield [M2(μ-S)(μ-SR′)(PR3)4]X.41 In
the present case the coordinated tellurolato ion is further
oxidized in CDCl3 solution. Recently a complex, [CpFe-
(CO)2(TePhI2)], in which ‘ArTeX2’ fragment is coordinated to a
metal atom, has been isolated by a reaction between [CpFe-
(CO)2I] and PhTeI.42
a
[Pd2{μ-TeC5H3(3-Me)N}2(dppp)2]Cl2 (5b) and trimeric tellurido-
bridged complexes, [Pd3(μ-Te)2(dppp)3]Cl2 (6) could be iso-
lated. Treatment of either [PdCl2(dppp)] with NaTeC5H3(3-R)N
(Scheme 2) or [Pd(dppp)2] with {TeC5H3(3-Me)N}2 (Scheme 2)
invariably lead to the formation of 6. Since the isolation of
[Pt3(μ-S)2(PMe2Ph)6]2+ cluster by Chatt and Mingos in 1970,35
considerable work has been reported on chalcogenido-bridged
trinuclear clusters36 with predominance of the sulfido-bridged
derivatives.37 However, there are only a few reports describing
tellurido-bridged derivatives which are often isolated in poor
yields.38,39 In our preparations 6 have been isolated in fairly
good yield.
The formation of Te–C bond cleaved products (2 and 6) and
5 is rather intriguing. It appears that initially bis tellurolate
complexes, “[Pd{TeC5H3(3-R)N}2(P∩P)]” are formed in both the
reactions, viz. (i) oxidative addition of {TeC5H3(3-R)N}2 to [Pd-
(P∩P)2] and (ii) substitution reaction between [PdCl2(P∩P)] and
NaTeC5H3(3-R)N. When the bis products are dissolved/
extracted in halogenated solvents (CDCl3 or CH2Cl2), nucleo-
philic attack at coordinated tellurolate ligand takes place
giving products like 2 and 6. Nucleophilic attack at coordi-
nated selenolate and tellurolate ligand is documented in the
literature.33
The 31P NMR spectra of [Pd{EC5H3(3-R)N}2(P∩P)] (P∩P =
X-ray crystallography
dppe, dppp) exhibited single resonances. The chalcogen The molecular structures of {TeC5H3(3-Me)N}2, [Pd2{μ-
dependence on the 31P NMR chemical shift is evident. With a TeC5H3(3-Me)N}2(dppp)2]Cl2·3H2O
(5·3H2O),
[Pd3(μ-
given diphosphine ligand, the 31P NMR resonance is progress- Te)2(dppp)3]Cl2·3CHCl3 (6·3CHCl3) and [PdCl{2-Te(Cl)2-
ively shielded, e.g. [Pd(EC5H4N)2(dppe)] (δ 31P NMR = 59.5 (E = C5H3(3-Me)N}(PPh3)] (9), established by X-ray diffraction ana-
S); 54.6 (E = Se) and 51.5 (E = Te) ppm). The nuclearity of the lyses are shown in Fig. 1–4. Selected interatomic parameters
complex also influenced the 31P NMR chemical shifts which are summarized in Tables 2–4.
are shielded with increasing nuclearity of the complex, e.g. [Pd-
The molecular structure of {TeC5H3(3-Me)N}2 is shown in
(2-TeC5H4N)2(dppp)] (δ 31P = −4.6 ppm); [Pd2{μ-2-TeC5H3(3- Fig. 1. The Te–Te bond length (2.7199(17) Å) is slightly longer
Me)N}2(dppp)2]2+ (δ 31P = −9.6 ppm) and [Pd3(μ-Te)2(dppp)3]2+ than that in dipyridylditellurides, viz. bis(2-pyridyl)ditelluride
(δ 31P = −11.0 ppm).
(2.68(6) Å),24 bis(2,5-dibromo-3-pyridyl)ditelluride (2.68(15)
The complexes [Pd2{μ-2-SeC5H3(3-R)N}2(dppp)2]2+ showed Å)24 and bis(2,5-dibromo-6-methyl-3-pyridyl)ditelluride (2.69(11)
two 31P NMR signals in solution whereas corresponding telluro- Å),24 but shorter than for bis(8-dimethylaminonaphthyl)ditel-
lates displayed a single resonance at −9.6 ppm. For the latter luride (2.765(1) Å).43,44 There are intramolecular secondary
a dimeric structure has been established by X-ray crystallogra- Te⋯N interactions (3.015 Å) (cf. sums of covalent and van der
phy (see later). It is likely that the selenolate complexes are Waals radii of Te and N are 2.15 and 3.61 Å, respectively)
monomeric in solution containing chelating pyridyl selenolate which are absent in other dipyridylditellurides.24 Because of
266 | Dalton Trans., 2013, 42, 259–269
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Fig. 3 ORTEP diagram of [Pd3(μ-Te)2(dppp)3]Cl2·3CHCl3 (6·3CHCl3) with atomic
number scheme. (phenyl groups attached to phosphorus are omitted for clarity
so the solvent molecules). The ellipsoids were drawn at the 25% probability.
Fig. 1 ORTEP diagram of {TeC5H3(3-Me)N}2 with atomic number scheme. The
ellipsoids were drawn at the 50% probability. [Interatomic parameters: bond
lengths (Å): Te1–C1, 2.136(11); Te1–Te1i, 2.7199(17); bond/torsion angles (°),
C1–Te1–Te1i, 87.7(3), N2–C1–Te1, 115.7(8), C6–C1–Te1, 120.1(8), Te1i–Te1–C1–
N2, 0.0(8), Te1i–Te1–C1–C6, 177.8(8), C1–Te1–Te1i–C1i, 180].
Fig. 4 ORTEP diagram of [PdCl{2-Te(Cl)2C5H3(3-Me)N}(PPh3)] (9) with atomic
number scheme. The ellipsoids were drawn at the 25% probability.
Fig. 2 ORTEP diagram of [Pd2{μ-TeC5H3(3-Me)N}2(dppp)2]Cl2·3H2O (5b·3H2O)
with atomic number scheme. The ellipsoids were drawn at the 25% probability.
Solvated water molecules are omitted for clarity.
Table 2 Selected bond lengths (Å) and angles (°) of [Pd2{TeC5H3(3-Me)-
N}2(dppp)2]Cl2·3H2O (5·3H2O)
Pd1–Te1
Pd1–Te1′
Pd1–P1
Pd1–P2
Te1–C1
P1–C8
2.6299(15)
2.6391(17)
2.282(2)
2.294(2)
2.148(8)
1.811(8)
P1–C11
P1–C17
P2–C10
P2–C23
P2–C29
Pd1–Pd1′
1.800(8)
1.820(6)
1.824(7)
1.817(8)
1.830(8)
3.888
these secondary Te⋯N interactions the two pyridyl rings and
Te–Te linkage are coplanar with C–Te–Te–C torsion angle of
180° (in case of bis(2-pyridyl)ditellurides the C–Te–Te–C
torsion angle is 86.3(2)°24). The existence of Te⋯N interactions
may also contribute to the lengthening of Te–Te bond.43 The
Te–C distances (2.136(11) Å) are similar to those reported in
diorgano ditellurides.
P1–Pd1–Te1
P2–Pd1–Te1
P1′–Pd1–Te1
P2′–Pd1–Te1
P1–Pd1–P2
Te1–Pd1–Te1′
C1–Te1–Pd1
C1–Te1–Pd1′
91.20(5)
167.01(6)
172.79(5)
90.54(5)
95.32(7)
83.89(2)
95.5(2)
Pd1–Te1–Pd1′
C8–P1–Pd1
C11–P1–Pd1
C17–P1–Pd1
C10–P2–Pd1
C23–P2–Pd1
C29–P2–Pd1
96.11(2)
116.0(2)
114.1(2)
109.3(2)
117.8(2)
116.5(2)
106.7(3)
The cationic complexes, [Pd2(μ-TeC5H4N)2(dppp)2]2+ and
[Pd2{μ-TeC5H3(3-Me)N}2(dppp)2]2+ are isostructural and both
contain two tellurolato-bridges. The complexes are centrosym-
metric dimers formed by two distorted square planar
85.7(2)
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triangle (Pd1–Pd2, 3.507 Å, Pd1–Pd3, 3.539 Å and Pd2–Pd3,
3.354 Å). The Te⋯Te separation (3.326 Å) can be compared
Table 3 Selected bond lengths (Å) and angles (°) of [Pd3Te2(dppp)3]Cl2·3CHCl3
(6·3CHCl3)
with [Pd2(μ-Te)2(dppe)2] (Te⋯Te
=
3.319(1) Å)49 and
Pd1–Te1
Pd1–Te2
Pd2–Te1
Pd2–Te2
Pd3–Te1
Pd3–Te2
2.6052(9)
Pd1–P1
Pd1–P2
Pd2–P3
Pd2–P4
Pd3–P5
Pd3–P6
2.290(2)
2.299(3)
2.292(3)
2.293(3)
2.281(3)
2.299(3)
[Pt3(μ-Te)2(dppe)3][BPh4]2 (Te⋯Te = 3.432(1) Å).38 The Pd–P23
2.6030(11)
2.6020(10)
2.6046(10)
2.6040(11)
2.6026(10)
and Pd–Te49,50 distances are as expected.
Various interatomic parameters involving the palladium
atom in [PdCl{2-Te(Cl)2C5H3(3-Me)N}(PPh3)] differ slightly
from its precursor, [PdCl{2-TeC5H3(3-Me)N}(PPh3)].33 The
metal square-plane defined by “TeNPCl” donor atoms forms
an angle of 2° with the four membered chelate ring
(“PdTeCN”) which lies at an angle of 7.36° with the planar pyri-
dine ring. The geometry around tellurium atom is distorted tri-
gonal bipyramidal in which one of the equatorial sites is
occupied by the stereochemically active lone pair of electrons.
The chloride atoms lie at the axial position forming Cl–Te–Cl
angle of 173.04(16)° which is comparable to the X–Te–X angle
observed in R2TeX2 (X = Cl, Br, I).51–53 The Te–C distance is
well in agreement with the value reported in literature for orga-
notellurium compounds, e.g. (napthyl)(MesCOCH2)TeCl2
(Te–C = 2.121(3) Å).51
P1–Pd1–Te1
P1–Pd1–Te2
P1–Pd1–P2
P2–Pd1–Te1
P2–Pd1–Te2
Te2–Pd1–Te1
P3–Pd2–Te1
P3–Pd2–Te2
P3–Pd2–P4
P4–Pd2–Te1
P4–Pd2–Te2
171.28(9)
92.15(8)
96.19(10)
92.33(7)
171.55(7)
79.38(3)
92.11(8)
171.52(8)
96.14(10)
171.71(8)
92.34(7)
P5–Pd3–Te1
P5–Pd3–Te2
P5–Pd3–P6
94.81(8)
174.03(9)
91.99(11)
173.01(9)
93.76(8)
79.41(3)
84.69(3)
85.60(3)
84.68(3)
85.67(3)
80.22(3)
80.20(3)
P6–Pd3–Te1
P6–Pd3–Te2
Te2–Pd3–Te1
Pd2–Te1–Pd1
Pd3–Te1–Pd1
Pd2–Te2–Pd1
Pd3–Te2–Pd1
Pd2–Te1–Pd3
Pd3–Te2–Pd2
Table 4 Selected bond lengths (Å) and angles (°) of [PdCl{2-Te(Cl)2C5H3(3-Me)-
N}(PPh3)] (9)
Te1–Pd1
Pd1–N1
Pd1–P1
Pd1–Cl1
2.540(2)
2.108(11)
2.241(5)
2.322(4)
Te1–Cl2
Te1–Cl3
Te1–C1
2.536(5)
2.508(5)
2.120(13)
Conclusions
The reactions of 2-chalcogenpyridines with palladium phos-
phine precursors yield a variety of complexes depending on
the nature of the phosphine ligand and the chalcogen atom.
The reactivity of tellurium ligands is markedly different from
those of sulfur/selenium ligands. The tellurium ligands also
undergo Te–C bond cleavage leading to the formation of tellur-
ido-bridged derivatives. The coordinated tellurolate ligand are
much more susceptible to oxidation as observed in case of
[PdCl{2-Te(Cl)2C5H3(3-Me)N}(PPh3)].
N1–Pd1–P1
N1–Pd1–C11
P1–Pd1–C11
N1–Pd1–Te1
P1–Pd1–Te1
Cl1–Pd1–Te1
C5–N1–Pd1
C1–N1–Pd1
172.4(4)
95.7(4)
91.17(15)
73.8(4)
99.35(12)
169.48(12)
134.2(12)
106.5(9)
Cl2–Te1–Pd1
Cl3–Te1–Pd1
C1–Te1–Pd1
Cl3–Te1–Cl2
C1–Te1–Cl2
C1–Te1–Cl3
90.14(14)
90.07(13)
73.6(5)
173.04(16)
88.6(4)
84.8(4)
palladium atoms each coordinated to chelated dppp ligand
and two bridging tellurolate groups. Due to a poor R factor for
the former complex, structural data is not reported here. The
Pd–P distances are well in agreement with the reported
values.45,46 The Pd–Te distances (∼2.63 Å) are longer than
those reported for palladium complexes containing non-brid-
ging tellurolate ligands, e.g. [PdCl(TeCH2CH2CH2NMe2)(PR3)]
(PR3 = PPr3 (Pd–Te = 2.5095(8) Å); PMePh2 (Pd–Te = 2.5156(6)
Å),47 [PdCl{2-TeC5H3(3-Me)N}(PPh3)] (Pd–Te = 2.5606(8) Å),33
but similar to those in other bridging systems, e.g. [PdCl-
(μ-TeCH2CH2CH2NMe2)]2 (Pd–Te(av) = 2.54 Å),48 tellurolate
ligands. The observed distances can however be compared
with the [Pd(TePh)2(dppe)] (2.6361(9) Å) a complex containing
tellurolate ligand trans to the strong trans influencing phos-
phine ligand.45 The four-membered Pd2Te2 ring is planar with
C5H3(3-Me)N groups adopting an anti configuration. The geo-
metry around the bridging tellurolate is pseudo-tetrahedral as
indicated by the bond angles at tellurium.
Acknowledgements
One of the authors (RSC) is grateful to DAE for the award of
SRF. We thank Dr T. Mukherjee and Dr D. Das for encourage-
ment of this work.
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