Tellurium(0) as a ligand: Synthesis and characterization of 2-pyridyltellurolates of platinum(II) and structures of [Pt{2-Te-3-(R)C 5H3N}2Te(PR′3)] (R = H or Me)

Article abstract of DOI:10.1021/ic902347s

Treatment of toluene solutions of the ditellurides [Te₂{C ₅H₃N(R)-3}₂] (R = H or Me) with [Pt(PPh ₃)₄] yielded two types of complexes, [Pt{2-Te-3-(R)C ₅H₃N}₂(PPh₃)₂] (1a-d) as the major products and [Pt{2-Te-3-(R)C₅H₃N} ₂Te(PPh₃)] (2a-d) as minor products. The above complexes can also be obtained by the reaction of [PtCl₂(PR′₃) ₂] (PR′₃ = PPh₃ or PPh ₂(2-C₅H₄N)) with 2 equiv of Na(2-Te-C ₅H₃R). The complexes were characterized by elemental analyses and UV-vis, NMR (¹H and ³¹P), and (in part) XPS spectroscopy. The molecular structures of [Pt(2-Te-C₅H ₄N)₂Te(PPh₃)] (2a) and [Pt{2-Te-C ₅H₃(Me)N}₂Te(PPh₃)] (2b) were established by single crystal X-ray diffraction. Both complexes exhibit a distorted square-planar configuration at the platinum(II) centers. The two mutually trans positioned 2-pyridinetellurolate ligands [2-Te-C ₅H₃(R)N] coordinate to the central platinum atom in a monodentate fashion through the tellurium atoms. The tellurium(0) atom adopts a "bent T" configuration as it is bridging the 2-Te- C₅H ₃(R)N molecules via N-Te-N bonds (166° angle) and coordinates to Pt^II in the trans position to PPh₃. The novel bis(pyridine)tellurium(0) arrangement resembles the bis(pyridine)iodonium structure. The calculated NICS indices and ELF functions clearly show that the compounds 2a and 2b are aromatic in the region defined by the Te-C-N-Te-Pt five-membered rings.

Full text of DOI:10.1021/ic902347s

Inorg. Chem. 2010, 49, 4179–4185 4179
DOI: 10.1021/ic902347s
Tellurium(0) as a Ligand: Synthesis and Characterization of 2-Pyridyltellurolates of
Platinum(II) and Structures of [Pt{2-Te-3-(R)C5H3N}2Te(PR03)] (R = H or Me)
†
§
§
Rohit Singh Chauhan,† G. Kedarnath,*,† Amey Wadawale, Alvaro Munoz-Castro, Ramiro Arratia-Perez,
~
Vimal K. Jain,*,† and Wolfgang Kaim‡
†Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India, ‡Institut fuer Anorganische
Chemie, Universitaet Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, and §Departamento de
Ciencias Quimicas, Universidad Andres Bello, Republica 275, Santiago, Chile
Received November 27, 2009
Treatment of toluene solutions of the ditellurides [Te2{C5H3N(R)-3}2] (R = H or Me) with [Pt(PPh3)4] yielded two types
of complexes, [Pt{2-Te-3-(R)C5H3N}2(PPh3)2] (1a-d) as the major products and [Pt{2-Te-3-(R)C5H3N}2Te(PPh3)]
(2a-d) as minor products. The above complexes can also be obtained by the reaction of [PtCl2(PR03)2] (PR03 = PPh3
or PPh2(2-C5H4N)) with 2 equiv of Na(2-Te-C5H3R). The complexes were characterized by elemental analyses and
UV-vis, NMR (1H and 31P), and (in part) XPS spectroscopy. The molecular structures of [Pt(2-Te-C5H4N)2Te(PPh3)]
(2a) and [Pt{2-Te-C5H3(Me)N}2Te(PPh3)] (2b) were established by single crystal X-ray diffraction. Both complexes
exhibit a distorted square-planar configuration at the platinum(II) centers. The two mutually trans positioned
2-pyridinetellurolate ligands [2-Te-C5H3(R)N] coordinate to the central platinum atom in a monodentate fashion
through the tellurium atoms. The tellurium(0) atom adopts a “bent T” configuration as it is bridging the 2-Te- C5H3(R)N
molecules via N-Te-N bonds (166° angle) and coordinates to PtII in the trans position to PPh3. The novel
bis(pyridine)tellurium(0) arrangement resembles the bis(pyridine)iodonium structure. The calculated NICS indices
and ELF functions clearly show that the compounds 2a and 2b are aromatic in the region defined by the
Te-C-N-Te-Pt five-membered rings.
Introduction
also provides a convenient route to metal chalcogenolate
complexes which have relevance in materials science.10
Oxidative addition of diorgano-disulfides and -diselenides
to platinum(0) complexes such as [Pt(PPh3)4] or [Pt(PPh3)2-
(olefin)] yields mononuclear [Pt(ER)2(PPh3)2] as isolable
products,5,11-15 while similar reactions with palladium(0)
derivatives (e.g., [Pd(PPh3)4], Pd2(dba)3/PR03) result in the
formation of dinuclear complexes [Pd2(μ-ER)2(ER)2(PR03)2]
(E = S or Se).2,5,13,15,16 However, reactions of diorganodi-
tellurides with Pd(0) and Pt(0) complexes were shown to
be much more complex, affording several products.17 For
instance, the reaction of [Pd(PPh3)4] with Th2Te2 (Th =
2-thienyl) in dichloromethane yields a hexanuclear complex,
Oxidative addition reactions of diorganodichalcogenides
(REER) to palladium(0) and platinum(0) complexes have
been of considerable interest for quite some time.1 This
reaction finds applications in regio- and stereoselective
E-E addition to CtC bonds in organic synthesis2-9 and
*To whom correspondence should be addressed. Tel: þ91-22-25592589
(G.K.), þ91-22-25595095 (V.K.J.). Fax: þ91-22-25505151 (G.K.), þ91-22-
25505151 (V.K.J.). E-mail: kedar@barc.gov.in (G.K.), jainvk@barc.gov.in
(V.K.J.).
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r
2010 American Chemical Society
Published on Web 04/06/2010
pubs.acs.org/IC

4180 Inorganic Chemistry, Vol. 49, No. 9, 2010
Chauhan et al.
[Pd6Cl2(Te4)(TeTh)2(PPh3)6], together with several other
unidentified products.14,17 When carried out in toluene, this
reaction affords yet another hexanuclear complex, [Pd6(Te4)-
(TeTh)4(PPh3)6], while Chia and McWhinnie18 have reported
the formation of the expected dinuclear compound [Pd2(μ-
TeTh)2(TeTh)2(PPh3)2]. A similar reaction with [Pt(PPh3)4],
however, yielded [Pt3Te2(Th)(PPh3)5]Cl and [PtCl(Th)-
(PPh3)2].17,19 The complexes [Pd6Cl2(Te4)(TeTh)2(PPh3)6],
[Pd6(Te4)(TeTh)4(PPh3)6], and [Pt3Te2(Th)(PPh3)5]Cl have
tellurido bridges which are formed via cleavage of Te-C
bonds. The cleavage of Te-C bonds has also been reported in
reactions of telluro-ethers with platinum(0) compounds.20,21
Recently, we have examinedthe chemistry of palladium(II)
and platinum(II) complexes with hemilabile 2-pyridyltellur-
olate ligands (2-Te-C5H4N).22 The complexes observed
exhibited distinct structural and reactivity features which
were different from those containing more simple organotel-
lurolate ligands. It was of interest, therefore, to study oxida-
tive addition reactions of bis(2-pyridyl)ditellurides with
[Pt(PPh3)4] in the expectation of isolating new structural
motifs. The reaction gave yellow [Pt(2-Te-C5H4N)2(PPh3)2]
as described earlier,22 together with a small amount of a
crystalline serendipituous product, [Pt(2-Te-C5H4N)2Te-
(PPh3)], containing bare tellurium (Te0) coordinated to
platinum(II). The results of this work are described herein.
Table 1. Crystallographic and Structural Determination Data for [Pt(2-Te-
C5H4N)2Te(PPh3)] (2a) and [Pt{2-Te-C5H3(Me)N}2Te(PPh3)] C6H6 (2b.C6H6)
3
complex
2a
2b C6H6
3
chemical formula
formula wt.
crystal system
space group
unit cell dimensions
a (A)
C28H23N2PPtTe3
996.34
C30H27N2PPtTe3.C6H6
1102.53
triclinic
P1
monoclinic
C2/c
39.040(7)
13.261(4)
11.9426(11)
90.00
12.300(12)
15.251(8)
10.029(7)
107.38(3)
99.51(6)
b (A)
c (A)
R (deg)
β (deg)
93.850(11)
90.00
6169(2)
γ (deg)
83.25(4)
1766(2)
volume (A3)
F
calcd, g cm-3
2.146
8
2.073
2
Z
μ (mm-1)/F(000)
θ for data collection (deg)
data/restraints/params
final R1, ωR2 indices
R1, ωR2 (all data)
goodness of fit on F2
7.400/3632
2.72-27.49
7078/0/317
0.0419/0.0980
0.0874/0.1082
0.933
6.473/1024
2.52-27.50
8092/0/390
0.0562/0.1249
0.1775/0.1628
0.951
298 K so that θmax = 27.5°. The structures were solved by
direct methods,25 and refinement25 was on F2 using data that
had been corrected for absorption effects with an empirical
procedure.26 Non-hydrogen atoms were modeled with aniso-
tropic displacement parameters, hydrogen atoms in their
calculated positions. Molecular structures were drawn using
ORTEP.27 Crystallographic and structural determination
data are listed in Table 1.
Syntheses of Complexes. [Pt(2-Te-C5H4N)2(PPh3)2] (1a)
and [Pt(2-Te-C5H4N)2Te(PPh3)] (2a). Method i: To a toluene
solution (10 cm3) of (C5H4N)2Te2 (67 mg, 0.16 mmol) was added
a solution (30 cm3) of [Pt(PPh3)4] (201 mg, 0.16 mmol) in the
same solvent, with stirring being continued for 4 h at room
temperature. The solvent was evaporated in vacuo, and the
residue was washed thoroughly with hexane followed by diethyl
ether to remove liberated triphenylphosphine. The residue was
recrystallized from benzene-acetone to afford two different
products, viz., a yellow powder (1a; yield 113 mg (0.10 mmol),
62%; mp 145 °C (dec.)) and orange crystals of [Pt(2-Te-
C5H4N)2Te(PPh3)] (2a) which were separated manually (yield
24 mg (0.02 mmol), 15%; mp 138 °C (dec.)). Compound 1a,
Anal. Calcd. for C46H38N2P2PtTe2: C, 48.8; H, 3.4; N, 2.5%.
Found: C, 48.3; H, 3.3; N 2.3%. Since there is always dissocia-
tion of PPh3, the analytical values varied from sample to sample.
UV-vis (C6H5CH3), λmax: 415 nm (sh). 1H NMR (C6D6): δ 7.08
(m, Ph þ C5H4N), 7.49 (br), 7.88 (m); 7.99 (br, C5H4N). 31P{1H}
NMR (C6D6): δ 23.5 (1J(Pt-P) = 3241 Hz] (-5.39 (PPh3)
Experimental Section
The complexes [Pt(PPh3)4], [PtCl2(PPh3)2], [PtCl2(PPh2(2-
C5H4N))2],23 (C5H4N)2Te2 and (3-MeC5H3N)2Te2,24 and
diphenyl(2-pyridyl)phosphine23 were prepared according to
literature methods. All reactions were carried out under an
argon atmosphere in dry and distilled analytical grade sol-
vents at room temperature. The 1H, 31P{1H}, and 195Pt{1H}
NMR spectra were recorded on a Bruker Avance-II spectro-
meter operating at 300, 121.49, and 64.52 MHz, respectively.
Chemicalshiftsare relativetointernal chloroform (δ 7.26) for
1H, external 85% H3PO4 for 31P, and Na2PtCl6 in D2O for
195Pt. Elemental analyses were carried out on a Thermo
Finnigan Flash EA1112 CHNS analyzer. UV-vis absorp-
tion spectra were recorded on a Chemito Spectroscan UV
2600 double beam UV-vis spectrophotometer. XPS studies
were conductedin a UHV chamber (base pressure <2ꢀ 10-8
mbar) using an AVG make CLAM-2 model analyzer with a
nonmonochromatic twin Al/Mg X-ray source.
1
∼5%). 195Pt{1H} NMR (C6D6): δ -4228 (t, J(Pt-P) = 3251
Intensity data for [Pt(2-Te-C5H4N)2Te(PPh3)] (2a) and
[Pt{2-Te-C5H3(Me)N}2Te(PPh3)] (2b) were measured on a
Rigaku AFC7S diffractometer with Mo KR radiation at
Hz). Compound 2a, Anal. Calcd. for C28H23N2PPtTe3: C, 33.8;
H, 2.3; N, 2.8%. Found: C, 34.0; H, 2.4; N 2.6%. UV-vis
(C6H5CH3), λmax: 404 nm. 1H NMR (C6D6): δ 6.15 (t, 6.6 Hz,
C5H4N 2-H), 6.33 (td, 1.2 Hz (d), 6.6 Hz (t), C5H4N 2-H), 7.13
(m, C6H5), 7.48 (d, C5H4N), 8.11 (m, Ph), 8.59 (d, 6 Hz, 2-H,
C5H4N). 31P{1H} NMR (C6D6): δ 21.1 (1J(Pt-P) = 3028 Hz).
XPS (eV): 72.6 (Pt 4f7/2), 76.06 (Pt 4f5/2), 575.0 (Te 3d5/2), 585.4
(Te 3d3/2).
(18) Chia, L. Y.; McWhinnie, W. R. J. Organomet. Chem. 1978, 148, 165–
170.
(19) Oilunkaniemi, R.; Niiranen, M.; Laitinen, R. S.; Ahlgren, M.;
Pursiainen, J. Acta Chem. Scand. 1998, 52, 1068–1070.
(20) Han, L. B.; Choi, N.; Tanaka, M. J. Am. Chem. Soc. 1997, 119, 1795–
1796.
(21) Khanna, A.; Khandelwal, B. L.; Saxena, A. K.; Singh, T. P.
Polyhedron 1995, 14, 2705–2710.
(22) Dey, S.; Jain, V. K.; Singh, J.; Trehan, V.; Bhasin, K. K.; Varghese,
B. Eur. J. Inorg. Chem. 2003, 744–750.
(25) (a) Sheldrick, G. M. SHELX 97-Program for Crystal Structure
€
€
Analysis; University of Gottingen: Gottingen, Germany, 1997. (b) Sheldrick,
G. M. Acta. Crystallogr. A 2008, 64, 112–122.
(23) (a) Jain, V. K.; Jackal, V. S.; Bohra, R. J. Organomet. Chem. 1990,
389, 417–426. (b) Maisonnet, A.; Farr, J. P.; Olmstead, M. M.; Hunt, C. T.; Balch,
A. L. Inorg. Chem. 1982, 21, 3961–3967.
(26) Higashi, T. ABSCOR-Empirical Absorption Correction based on
Fourier Series Approximation; Rigaku Corporation: Matsubara, Akishima,
Japan, 1995.
(27) Johnson, C. K. ORTEP II, Report ORNL-5136; Oak Ridge National
Laboratory: Oak Ridge, TN, 1976.
€
(24) Bhasin, K. K.; Arora, V.; Klapotke, T. M.; Crawford, M. J. Eur. J.
Inorg. Chem. 2004, 4781–4788.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4181
Scheme 1
Method ii: To a dichloromethane solution (15 cm3) of
residue was washed thoroughly with hexane followed by diethy-
lether. The residue was extracted with dichloromethane, filtered,
and passed through a Florisil column. Addition of a few drops of
hexane and slow evaporation gave a yellow powder of [Pt(2-Te-
C5H4N)2(PPh2(2-C5H4N))2] (1c) (yield 103 mg (0.09 mmol),
65%; mp 118-120 °C (dec.)) and red crystals of [Pt(2-Te-
C5H4N)2Te(PPh2(2-C5H4N))] (2c), which were separated manu-
ally (yield 21 mg (0.02 mmol), 15%; mp 131 °C (dec.)). Com-
[PtCl2(PPh3)2] (150 mg, 0.19 mmol) was added a methanolic
solution (12 cm3) of Na(2-Te-C5H4N) [freshly prepared
from (C5H4N)2Te2 (80 mg, 0.19 mmol) and NaBH4 (16.4 mg,
0.22 mmol)]. The mixture was stirred for 5 h, whereupon a clear
orange solution was obtained. The solvents were evaporated
under a vacuum. The residue was washed thoroughly with
hexane followed by diethylether. The product was extracted
with benzene, was filtered, and was passed through a Florisil
column. To the resulting solution was added acetone to produce
orange crystals of 2a (yield 57 mg (0.06 mmol), 30%; Anal.
Calcd. for C28H23N2PPtTe3: C, 33.8; H, 2.3; N, 2.8%. Found: C,
34.1; H, 2.2; N 2.7%) and yellow 1a (yield 112 mg (0.10 mmol),
52%; mp 145 °C (dec.); Anal. Calcd. for C46H38N2P2PtTe2: C,
48.8; H, 3.4; N, 2.5%. Found: C, 48.2; H, 3.5; N 2.4%). The
NMR data are consistent with complexes 1a and 2a.
pound 1c, Anal. Calcd. for C44H36N4P2PtTe2 2CH2Cl2: C, 42.4;
3
H, 3.1; N, 4.2%. Found: C, 42.1; H, 3.1; N 4.1%. Compound 2c,
Anal. Calcd. for C27H22N3PPtTe3 2CH2Cl2: C, 29.8; H, 2.2; N,
3
3.6%. Found: C, 30.1; H, 2.1; N 3.6%. 1H NMR (CDCl3): δ 5.32
(CH2Cl2), 6.20-8.12 (m, C5H4N þ Ph). 31P{1H} NMR (CDCl3):
δ (1c) 23.3 (1J(Pt-P) = 3222 Hz); (3b) 10.5 (1J(Pt-P) = 3840
Hz). Compound 2c, 1H NMR (CDCl3): δ 5.31 (CH2Cl2); 6.90 (t,
6 Hz, Te-C5H4N), 7.14 (t, 6 Hz, Te-C5H4N) 7.43 (br, C6H5);
7.67 (d, 8 Hz, Te-C5H4N), 7.74 (br), 7.90 (br, C6H5); 8.39 (t),
8.72 (d, 6 Hz, Te-C5H4N), 8.81 (d, 6 Hz). 31P{1H} NMR
(CDCl3): δ 17.8 (1J(Pt-P) = 2992 Hz).
[Pt{2-Te-C5H3(Me)N}2(PPh3)2] (1b) and [Pt{2-Te-C5H3-
(Me)N}2Te(PPh3)] (2b). Method i: Preparation was done in a
similar fashion as 1a, adopting method i (above), and a 69%
yield was achieved as an orange powder (mp 171 °C dec.). Anal.
Calcd. for C48H42N2P2PtTe2: C, 49.7; H, 3.7; N, 2.4%. Found:
C, 50.3; H, 3.7; N 1.9%. UV-vis (C6H5CH3), λmax: 302, 425 nm.
1H NMR (CDCl3): δ 2.25 (s, Me); 6.97 (m, 6-H), 7.37
(m, C6H5), 7.81 (br), 8.65 (br, C5H3(Me)N). 31P{1H} NMR
[Pt{2-Te-C5H3(Me)N}2(PPh2(2-C5H4N))2] (1d) and [Pt{2-
Te-C5H3(Me)N}2Te{PPh2(2-C5H4N)}] (2d). Method i: Prepara-
tion was done in a similar fashion to that for 1c with recrystalli-
zation from benzene-acetone to obtain a yellow powder (1d;
yield 98 mg (0.08 mmol), 61%; mp 158 °C (dec.). Anal. Calcd.
for C46H40N4P2PtTe2: C, 47.6; H, 3.5; N, 4.8%. Found: C, 47.7;
H, 3.3; N 4.7%) and orange crystals of [Pt{2-Te-C5H3-
(Me)N}2Te(PPh2(2-C5H4N))] (2d), which were separated manu-
ally (yield 20 mg (0.02 mmol), 14%. Anal. Calcd. for
C29H26N3PPtTe3: C, 34.0; H, 2.6; N, 4.1%. Found: C, 33.7;
H, 2.7; N 4.0%). Compound 1d, 31P{1H} NMR (CDCl3): δ 22.2
(1J(Pt-P) = 3231 Hz). Compound 3c, 31P{1H} NMR: 5.4
(toluene-d8): δ 7.2 [1J(Pt-P) = 3768 Hz], -5.3 (PPh ). 195Pt-
3
{1H} NMR (toluene-d8): δ -4810 [d, 1J(Pt-P) 3713 Hz].
Method ii: Preparation was done in a similar fashion to that
for 1a using method ii (above), and recrystallization from
benzene-acetone afforded [Pt{2-Te-C5H3(Me)N}2(PPh3)2] (1b;
yield 126 mg (0.11 mmol), 58%) and [Pt{2-Te-C5H3(Me)N}2Te-
(PPh3)] (2b; yield: 22 mg (0.02 mmol), 12%; mp 158 °C (dec.)).
The latter was separated manually as needle-shaped orange
crystals. Anal. Calcd. for C30H27N2PPtTe3 C6H6 (2b C6H6):
1
(1J(Pt-P) = 3829 Hz). Compound 2d, H NMR (CDCl3): δ
2.26 (s, Me); 6.91 (t, 6 Hz, H-5, 2-Te-C5H3(Me)N), 7.11 (d, 7.2 Hz,
H-4, 2-Te-C5H3(Me)N); 8.67 (d, 6 Hz, H-6, 2-Te-C5H3(Me)N);
7.43 (br), 7.95 (br) [Ph-P]; 7.77 (br m), 8.56 (t, 6 Hz) [NC5H4-P].
31P {1H} NMR (CDCl3): δ 20.5 (1J(Pt-P) = 2945 Hz).
3
3
C, 39.2; H, 3.0; N, 2.5%. Found: C, 38.7; H, 2.9; N, 2.6%.
UV-vis (C6H5CH3), λmax: 398 nm. 31P{1H} NMR (CDCl3): δ
21.3 [1J(Pt-P) = 2982 Hz]. When 1b was left in CDCl3 solution
for several hours, a new species [PtCl{2-Te-C5H3(Me)N}(PPh3)]
(31P{1H} NMR: δ -0.8 ppm, 1J (Pt-P) = 3692 Hz)22 together
with a small amount of Ph3PO (29.3 ppm) was identified.
[Pt(2-Te-C5H4N)2(PPh2(2-C5H4N))2] (1c) and [Pt(2-Te-
C5H4N)2Te(PPh2(2-C5H4N))] (2c). To a dichloromethane so-
lution (20 cm3) of [PtCl2(PPh2(2-C5H4N))2] (110 mg, 0.14 mmol)
was added a methanolic solution (8 cm3) of Na(2-Te-C5H4N)
[freshly prepared from (C5H4N)2Te2 (57 mg, 0.14 mmol) and
NaBH4 (11 mg, 0.29 mmol)], and the mixture was stirred for 6 h.
The solvents were evaporated under reduced pressure. The
Results and Discussion
Synthesis and Spectroscopy. Reaction of [Pt(PPh3)4]
with (3-RC5H3N)2Te2 (R = H or Me) at room tempera-
ture afforded yellow to orange products of oxidative
addition, [Pt{2-Te-3-(R)C5H3N}2(PPh3)2] (1), together
with small amounts of crystalline material, [Pt{2-
Te-3-(R)C5H3N}2Te(PPh3)] (2) (Scheme 1). Compounds
1 can also be obtained by treatment of [PtCl2(PR3)2]

4182 Inorganic Chemistry, Vol. 49, No. 9, 2010
Chauhan et al.
with Na{2-Te-3-(R)C5H3N}, readily prepared by the
reductive cleavage of the Te-Te bond of corres-
ponding bis(pyridyl)ditellurides with NaBH4 in methanol
(Scheme 1), as described earlier by us for 1b.22 On
attempted recrystallization of the products obtained from
these reactions, compounds 1 were obtained as yellow-
orange powders, accompanied by crystalline 2. Except 1a,
all other complexes (1) dissociate in solution to give PR3
and [Pt{Te-C5H3(R)N}{η2-Te-C5H3(R)N}(PR3)] (3) as
revealed by NMR spectroscopy.
The 31P NMR spectra of 1 displayed single resonance
signals with 195Pt-31P coupling. Compounds 1 undergo
dissociation of the phosphine ligand in solution to give 3
and thus establish a dynamic equilibrium with 1. The
complexes 1a, 1c, and 1d exhibited a 31P NMR resonance
at δ ∼22 ppm with 1J ∼ 3230 Hz. The 195Pt NMR
spectrum of 1a displayed a triplet at δ = -4228 ppm
(1J(Pt-P) = 3251 Hz), indicating coordination of two
mutually trans positioned triphenylphosphine ligands.28,29
The 31P{1H} NMR spectrum of [Pt{2-Te-C5H3(Me)N}2-
(PPh3)2] consists of a single resonance at 7.2 ppm with
1J(Pt-P) = 3711 Hz. The former resonance has been
assigned to [Pt{Te-C5H3(Me)N}{η2-Te-C5H3(Me)N}-
(PPh3)] (3b). Coordination of one PPh3 ligand in 3a is further
corroborated by the 195Pt NMR spectrum, which showed a
doublet centered at -4810 ppm due to coupling with one 31P
nucleus. Several attempts to remove PPh3 from the complex
either by repeated recrystallization or by treatment with air to
convert into OPPh3 were unsuccessful. In solution, complex
1b exists as 3b, in which the PPh3 ligand is trans to the
nitrogen atom of the chelated 2-Te-C5H3(Me)N ligand. The
complexes 1c and 1d, when left in solution for a few hours,
showed signals due to 3c and 3d in their 31P NMR spectra
with 1J(Pt-P) of ∼3830 Hz. Attempts to record 125Te{1H}
NMR spectra of these complexes were thwarted due to their
reactivity in chlorinated solvents (CD2Cl2 or CDCl3) during
long NMR acquisition times.
Figure 1. Crystal structure of [Pt(2-Te-C5H4N)2Te(PPh3)] (2a) with
atomicnumberscheme. The ellipsoidswere drawn at the 50%probability.
The complexes 2, isolated in low yields as orange
crystalline solids during the synthesis of 1, exhibit one
single 31P{1H} NMR resonance at ∼20 ppm with 195Pt
satellites. The magnitude of 1J(Pt-P) (2945-3028 Hz) is
indicative of a strong trans influence of the new, formally
Te0 ligand (see below). It is also within the range expected
for platinum(II) telluride and tellurolate complexes.30 In
an attempt to differentiate between tellurolate and the
coordinated tellurium atom, XPS measurements were
carried out as 125Te{1H} NMR spectra could not be
obtained (vide supra). However, the XPS chemical shifts
for tellurium (3d5/2 and 3d3/2) in different oxidation states
appear in a narrow region. For instance, the shifts for Te
metal [573.1 (3d5/2) and 583.5 (3d3/2) eV],31 diphenyldi-
telluride [573.9 (3d5/2) and 584.3 (3d3/2) eV],31 and CdTe
[576 (3d5/2) and 586 (3d3/2) eV]32 differ only slightly and
are only of limited diagnostic value33 (cf. below). The XPS
Figure 2. Crystal structure of [Pt{2-Te-C5H3(Me)N}2Te(PPh3)] C6H6
3
(2b C6H6) with atomic number scheme. The ellipsoids were drawn at the
3
50% probability.
study of 2a exhibited signals for tellurium at 575.0 (3d5/2
and 585.4 (3d3/2) eV.
)
All complexes are colored and show absorption in their
UV-vis spectra in toluene solutions (see the Experimen-
tal Section). The bands are red-shifted with respect to the
ditelluride ligands. The highest occupied molecular orbi-
tal (HOMO) is considered to be centered on the tell-
urolate ligands, whereas the lowest unoccupied molecular
orbital (LUMO) is probably delocalized with significant
contributions from the phosphine coligand.34
X-Ray Crystallography. The molecular structures of 2a
and 2b C6H6 were established by single crystal X-ray
diffraction analyses. ORTEP drawings with the atomic
numbering scheme are shown in Figures 1 and 2, and
selected inter atomic parameters are summarized in
(28) Narayan, S.; Jain, V. K.; Varghese, B. J. Chem. Soc., Dalton Trans.
1998, 2359–2366.
(29) Dey, S.; Jain, V. K.; Knoedler, A.; Klein, A.; Kaim, W.; Zallis, S. Eur.
J. Inorg. Chem. 2001, 2965–2973.
(30) Jain, V. K.; Jain, L. Coord. Chem. Rev. 2005, 249, 3075–3197.
(31) Konno, H.; Yamamoto, Y. Bull. Chem. Soc. Jpn. 1988, 61, 2990–
2992.
3
(32) Bartolo-Perez, P.; Farias, M. H.; Castro-Rodriguez, R.; Pena, J. L.;
Caballero-Briones, F.; Cauich, W. Superficies vacio 2001, 12, 8–11.
(33) Shimanoe, K.; Sakashita, M. Jpn. J. Appl. Phys. 1992, 31, 2066–2070.
(34) Dey, S.; Jain, V. K.; Knoedler, A.; Klein, A.; Kaim, W.; Zalis, S.
Inorg. Chem. 2002, 41, 2864–2870.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4183
[Pt{2-Te-C5H3(Me)N}2Te(PPh3)].C6H6 (2b.C6H6)
Table 2. Selected Bond Lengths (A) and Angles (deg) of 2a and 2b C6H6
3
[Pt(2-Te-C5H4N)2Te(PPh3)] (2a)
exp.
calc.a
exp.
calc.a
Pt1-Te1
2.5940(7)
2.5752(6)
2.5720(7)
2.357(7)
2.297(7)
2.282(2)
2.103(9)
2.088(8)
2.659
2.631
2.638
2.386
2.373
2.298
2.119
2.119
166.3
96.4
96.6
104.2
104.4
92.4
92.5
173.4
89.4
2.588(3)
2.569(2)
2.612(3)
2.35(1)
2.32(1)
2.283(3)
2.11(2) (Te2-C25)
2.10(1)
165.4(4)
97.1(3)
97.5(3)
2.662
2.643
2.686
2.388
2.410
2.297
2.162
2.162
166.8
96.1
Pt1-Te3
Pt1-Te2
Te3-N1
Te3-N2
Pt1-P1
Te2-C24
Te1-C19
N2-Te3-N1
N2-Te3-Pt1
N1-Te3-Pt1
C24-Te2-Pt1
C19-Te1-Pt1
Te3-Pt1-Te1
Te2-Pt1-Te3
Te2-Pt1-Te1
P1-Pt1-Te2
P1-Pt1-Te3
P1-Pt1-Te1
166.1(2)
96.6(2)
96.6(2)
96.9
104.6(2)
104.6(2)
92.83(2)
92.56(2)
172.74(2)
89.29(6)
171.40(6)
86.10(6)
104.8(5) (C25-Te2-Pt1)
106.4(4)
91.59(6)
104.3
104.9
91.9
91.5
171.6
86.8
91.40(7)
173.99(4)
86.99(10)
175.56(9)
90.40(10)
171.8
86.3
173.6
90.4
a PBE/ZORAþSO calculations.
Table 2. The two structures are rather similar, involving
discrete molecules with distorted square planar environments
around the platinum(II) center and a “Te3P” coordina-
tion core. The two mutually trans 2-pyridinetellurolate
ligands are bound by the central platinum(II) atom in a
monodentate fashion through the tellurolate atoms. A
conceivable tellurone resonance structure is not sup-
ported by the structural data. For both 2a and 2b, the
nitrogen atoms of the pyridyl rings are connected to the
“bare” tellurium atom (Te3) with a N1-Te3-N2 angle of
about 166°. The deviation of the N-Te-N angle from
linearity is rather small and may be assigned to repulsion
from two nonbonding pairs of electrons. The tellurium(0)
atoms (Te3) thus adopt a “bent T” configuration. Its
geometry can be defined as distorted trigonal-bipyrami-
dal with the platinum and two lone pairs at the equatorial
positions and two pyridyl nitrogen atoms occupying the
axial sites. On the basis of the isoelectronic relationship
between Te0 and IþI, the observed novel bis(pyridine)-
tellurium(0) structural motif in 2a and 2b can be com-
pared with the well-known,35,36 theoretically studied37 and
synthetically applied38 bis(pyridine)iodonium cations.
of (C5H4)N-E-N(C5H4) from 180°36 in the present
situation. This arrangement receives additional stabiliza-
tion through coordination of all three Te atoms to the
metal in a tridentate fashion. Remarkably, all Pt-Te
distances (2.5690(19)-2.612(3) A) are similar, which
could mean that Te is gaining a significant amount of
negative charge from the lone pairs of nitrogen that leave
them positively charged. The Pt-Te bonds are slightly
longer than those reported for [PtCl(TeCH2CH2NMe2)-
(PR3)] (2.5261(5) A)34 but are comparable to those in
complexes containing tellurolate ligands trans to phos-
phine (e.g., cis-[Pt(TeTh)2(dppe)] (2.607, 2.6594(9) A),39
cis-[Pt(1,2-Te2C6H4)(PPh3)2] (2.586(1) A),40 or trans-[Pt-
(TeCOC6H4Me-4)2(PEt3)2] (2.592(1), 2.632(2) A).41 The
Pt-P distances are as expected.39,40 The slight lengthen-
ing of the Pt-Te distances may be attributed to the strong
trans influence of tellurolate. The Te-N distances
(2.297(7)-2.357(7) A) are well within the range reported
in organotellurium compounds, e.g., R2Te(N3)2 (2.180-
2.253 A),42 [{Ph2TeN3}2O] (2.397(8) A),43 or [{Ph2Te-
(NCS)}2O] (2.40(1) A).44
Density Functional Calculations. In order to gain more
insight over the charge distribution in 2a and 2b, all-
electron density functional calculations were done, em-
ploying the Hirshfeld and Voronoi deformation densities
(VDD), which are partitioning schemes for selected
0
½C5H5N- I- C5H5Nꢁþ ½C5H5N- Te- C5H5Nꢁ
In both cases, the empty 5p orbital interacts with the
pyridine lone pairs, leading to the straightened N-E-N
angle and, for 2a, to the observed XPS shift in the
direction of Te-II. The chelate-promoted coplanarity of
the bis(pyridine)element entity in 2a and 2b was noted36
and analyzed37 similarly for [C5H5N-I-C5H5N]þ. The
steric requirements by the 2-pyridyltellurolate groups are
probably responsible for the slightly increased deviation
(39) Risto, M.; Jahr, E. M.; Hannu-Kuure, M. S.; Oilumkaniemi, R.;
Laitinen, R. S. J. Organomet. Chem. 2007, 692, 2193–2204.
(40) Giolando, D. M.; Rauchfuss, T. B.; Rheingold, A. L. Inorg. Chem.
1987, 26, 1636–1638.
(41) Kato, S.; Niyomura, O.; Kawahara, Y.; Kanda, T. J. Chem. Soc.,
Dalton Trans. 1999, 1677–1686.
€
(42) (a) Klapotke, T. M.; Krumm, B.; Mayer, P.; Ruscitti, O. P. Inorg.
€
Chem. 2000, 39, 5426–5427. (b) Klapotke, T. M.; Krumm, B.; Mayer, P.;
Piotrowski, H.; Ruscitti, O. P.; Schiller, A. Inorg. Chem. 2002, 41, 1184–1193.
(35) (a) Barluenga J. Pure Appl. Chem. 1999, 71, 431–436. (b) Noronha,
L. A.; Judson, T. J. L.; Dias, J. F.; Santos, L. S.; Eberlin, M. N.; Mota, C. J. A. J.
Org. Chem. 2006, 71, 2625–2629.
€
(c) Klapotke, T. M.; Krumm, B.; Mayer, P.; Naumann, D.; Schwab, I. J. Fluorine
€
Chem. 2004, 125, 997–1005. (d) Klapotke, T. M.; Krumm, B.; Polborn, K.;
ꢀ
ꢀ
´
ꢀ
(36) Alvarez-Rua, C.; Garcıa-Granda, S.; Ballesteros, A.; Gonzalez-
Schwab, I. J. Am. Chem. Soc. 2004, 126, 14166–14175.
(43) Magnus, P.; Roe, M. B.; Lynch, V.; Hulme, C. J. Chem. Soc., Chem.
Commun. 1995, 1609–1610.
(44) Mancinelli, C. S.; Titus, D. D.; Ziolo, R. T. J. Organomet. Chem.
1977, 140, 113–125.
ꢀ
Bobes, F.; Gonzalez, J. M. Acta Crystallogr., Sect. E 2002, 58, o1381–1383.
(37) Sabin, J. R. J. Mol. Struct. 1971, 7, 407–419.
ꢀ
(38) Barluenga, J.; Gonzalez-Bobes, F.; Murguı
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a, M. C.; Ananthoju,
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S. R.; Gonzalez, J. M. Chem.;Eur. J. 2004, 10, 4206–4213.

4184 Inorganic Chemistry, Vol. 49, No. 9, 2010
Chauhan et al.
Table 3. Hirshfeld and VDD Charge Analyses for Selected Atoms and Fragments
of 2a and 2b
2a
2b
Hirshfeld
VDD
atoms
Hirshfeld
VDD
Te3
Pt1
Te1
Te2
-0.001
-0.059
-0.001
-0.005
-0.081
-0.115
-0.061
-0.060
-0.004
-0.078
-0.003
-0.007
-0.072
-0.142
-0.049
-0.047
fragments
[2-Te-py]- 1a
[2-Te-py]- 2b
PPh3
-0.034
-0.038
þ0.132
-0.008
-0.006
þ0.208
-0.041
-0.045
þ0.150
-0.017
-0.017
þ0.251
Figure 3. ELF values for the five-membered ring formed by
Te-C-N-Te-Pt.
a Refers to the fragment formed by Te1-C19-C20-C21-
C22-C23-N1 for 2a, and Te1-C19-C20-C24-C21-C22-C23-N1
for 2b. b Refers to the fragment formed by Te2-C24-C25-C26-
C27-C28-N2 for 2a, and Te2-C25-C26-C30-C27-C28-C29-N2
for 2b.
density of the system. In this sense, ELF = 1 denotes
perfect localization and 0.5 a perfect delocalization.48
Values between ∼0.0 and 0.5 indicate delocalization in
low-density regions.48 In Figure 3, the ELF values for 2b
are given for the Te-C-N-Te-Pt plane, denoting typi-
cal values for delocalization in the rings, ELF = 0.71
between Te-C- and C-N-, and values less than ELF =
0.5 between N-Te- (ELF = 0.43), Te-Pt- (ELF =
0.25), and Pt-Te- (ELF = 0.25), respectively. These
ELF values are in accord with the electronic delocaliza-
tion in the five-membered ring as suggested by the
NICS index. Compound 2a exhibits a similar aromatic
behavior.
atoms and fragments.45 The calculated data suggest that
the three tellurium atoms (Te1, Te2, and Te3) exhibit
similar charge densities. We performed a detailed analysis
focusing on the charge distribution for the Te3 and Pt1
atoms, for the fragments denoted by the 2-pyridyltellur-
olate ([2-Te-C5H4N]- and [2-Te-C5H3(Me)N]- for 2a
and 2b, respectively), and for the PPh3 ligands
(Table 3). Similar results were observed for Hirshfeld
and VDD analyses; thus, herein we focus on the former.
The Hirshfeld analysis for 2a shows that the PtII (Pt1)
atom gains about 0.132 e from the triphenylphosphine
and about 0.966 e from each 2-pyridyltellurolate ligand to
give a total charge of -0.059 in the region defined by the
Hirshfeld scheme. Similar results were obtained for 2b.
Thus, the calculations are consistent with the suggestion
that the tricoordinated tellurium(0) atoms (Te3) act as
zero-valent ligands.
Additionally, the Nuclear Independent Chemical Shift
index (NICS)46 and the Electron Localization Function
(ELF)47 including spin-orbit interaction have been eval-
uated to determine the electronic structure of the five-
membered ring constituted by the Te-C-N-Te-Pt
atoms. The values of the NICS index in the center of
the ring are -7.46 ppm and -7.55 ppm for 2a and 2b,
respectively, which indicates a similar aromatic behavior
to that of benzene (-7.89 ppm). Moreover, the values of
the ELF (η) function are conveniently defined between 0
and 1 (0 e ELF e 1), where 0.5 is the parameter for a
homogeneous electron gas at a density equal to the local
Conclusion
In an attempt to investigate the oxidative addition reaction
alternatives between bis(2-pyridyl)ditellurides and platinum-
(0) compounds, we obtained not only the expected systems of
the type [Pt{2-Te-3-(R)-C5H3N}2(PR03)2] but also the crys-
talline products [Pt{2-Te-3-(R)-C5H3N}2Te(PR03)] in which
formally zero-valent tellurium bridges two pyridine nitrogen
rings of two trans-situated Te-coordinated 2-pyridyltelluro-
lates. An all-tellurium-donor tridentate ligand is thus formed,
and the otherwise conventional, slightly distorted square-
planar coordination arrangement at platinum(II) consists
of one triarylphosphine-P and three tellurium atoms. The
little varied Pt-Te distances and the N-Te-N angles of
about 166° signify an unstrained situation, the bis(pyridine)-
tellurium(0) structural motif being isoelectronic with the well
established36,37 and synthetically useful38 bis(pyridine)-
iodonium cations. The calculated NICS indices and ELF
functions clearly show that compounds 2a and 2b are
aromatic in the region defined by the Te-C-N-Te-Pt
five-membered rings.
(45) Geometry optimizations and charge analyses calculations were done
for 2a and 2b, employing the ADF2009 code (http://www.scm.com). We
employed all-electron triple-ζ Slater basis sets plus polarization function
(STO-TZP) within the generalized gradient approximation (GGA) of
Perdew-Burke-Ernzerhof (PBE) for the exchange and correlation poten-
tials, through the ZORA Hamiltonian for the inclusion of both scalar and
spin-orbit effects. The NICS indexes were calculated by using the OPBE
functional.
CCDC numbers 754781 and 754782 for [Pt(2-Te-C5H4N)2-
Te(PPh3)] (2a) and [Pt{2-Te-C5H3(Me)N}2Te(PPh3)] C6H6
3
(2b C6H6), respectively, contain the supplementary crystal-
3
lographic data for this paper. These data can be obtained
free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html
or from the Cambridge Crystallographic Data Centre,
(46) (a) Zhan, C.-G.; Zheng, F.; Dixon, D. A. J. Am. Chem. Soc. 2002,
124, 14795–14803. (b) Kuznetsov, A. E.; Boldyrev, A. I.; Li, X.; Wang, L.-S. J.
Am. Chem. Soc. 2001, 123, 8825–8831. (c) Boldyrev, A. I.; Kuznetsov, A. E.
Inorg. Chem. 2002, 41, 532-537 and references therein.
(47) (a) Becke, A. D.; Edgecombe, K. E. J. Chem. Phys. 1990, 92, 5397–
5403. (b) Burdett, J. K.; McCormick, T. A. J. Phys. Chem. A 1998, 102, 6366–
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(48) (a) Savin, A.; Nesper, R.; Wengert, S.; Fassler, T. F. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 1808–1832. (b) Savin, A.; Jepsen, O.; Flad, J.; Andersen,
O. K.; Preuss, H.; von Schnering, H. G. Angew. Chem. 1992, 31, 187–188.
(c) Sun, Q.; Wang, Q.; Yu, J. Z.; Kumar, V.; Kawazoe, Y. Phys. Rev. B 2001, 63,
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Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4185
12 Union Road, Cambridge CB2 1EZ, U.K. [fax: þ44-1223/
supported by the Fondecyt 1070345, Millennium Nucleus
P07-006-F, UNAB-DI 09-09/I, UNAB-DI 02-09/R.
336-033; e-mail: deposit@ccdc.cam.ac.uk].
Acknowledgment. One of the authors (R.S.C.) is grate-
ful to DAE for the award of JRF. We thank Drs.
T. Mukherjee and D. Das for encouragement of this
work. The work by R.A.-P. and A.M.-C. was financially
Supporting Information Available: Crystallographic data for
Pt(Tepy)2Te(PPh3) and Pt(TepyMe)2Te(PPh3) in CIF format.
This material is available free of charge via the Internet at http://
pubs.acs.org.