Reactivity of dipyridyl ditellurides with (diphosphine)Pt0 and 2-pyridyltellurolates with (diphosphine)PtCl2 and isolation of different structural motifs of platinum(II) complexes

Article abstract of DOI:10.1021/om2010589

Oxidative addition reaction of dipyridyl ditellurides to [Pt ₂(dppm)₃] gave two types of complexes, [Pt{2-Te-C ₅H₃(3-R)N}₂(dppm)] (1) and [Pt{PPh ₂C(TeC₅H₃(3-R)N)₂PPh ₂}₂] (2) (R = H or Me), in ～65 and ～20% yield, respectively. Both these complexes are also formed in the substitution reaction between [PtCl₂(dppm)] and NaTeC₅H₃(3-R)N. Treatment of [Pt(dppe)₂] with dipyridyl ditellurides yielded an oxidative addition product, [Pt{2-Te-C₅H₃(3-R)N} ₂ (dppe)] (3) (R = H or Me), exclusively. In a substitution reaction of [PtCl₂(dppe)] with NaTeC₅H₃(3-Me)N a complex of composition Pt{TeC₅H₃(3-Me)N}(dppe)Cl (4) wasformed. The reaction between either [Pt(dppp)₂] and Te₂(C ₅H₃(3-Me)N)₂or [PtCl₂(dppp)] and NaTeC₅H₃(3-R)N afforded a mixture of [Pt{2-Te-C ₅H₃(3-Me)N}₂(dppp)] (5) and [Pt ₃Te₂(dppp)₃]²⁺ (6), which were separated by column chromatography. All the complexes were characterized by elemental analyses and NMR (¹H, ³¹P, ¹⁹⁵Pt) spectroscopy. The molecular structures of [Pt{PPh₂C(TeC ₅H₄N)₂PPh₂}₂] and [Pt₂{TeC₅H₃(3-Me)N}₂(dppe) ₂][BPh₄]₂ were established by single-crystal X-ray diffraction analyses. The bonding, charge transfer, and geometry of compounds [Pt{2-Te-C₅H₃(3-R)N}₂(dppm)] (1), [Pt{PPh₂C(TeC₅H₃(3-R)N)₂PPh ₂}₂] (2), and [Pt₃Te₂(dppp) ₃]²⁺ (6) have been analyzed through relativistic density functional calculations.

Full text of DOI:10.1021/om2010589

Article
pubs.acs.org/Organometallics
Reactivity of Dipyridyl Ditellurides with (Diphosphine)Pt0 and
2-Pyridyltellurolates with (Diphosphine)PtCl2 and Isolation of
Different Structural Motifs of Platinum(II) Complexes
Rohit Singh Chauhan,† G. Kedarnath,*,† Amey Wadawale,† Arnold L. Rheingold,‡ Alvaro Munoz-Castro,§
̃
Ramiro Arratia-Perez,§ and Vimal K. Jain*,†
†Chemistry Division, Bhabha Atomic Research Centre, Mumbai-400 085, India
‡Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0358, United States
§Departamento de Ciencias Quimicas, Universidad Andres Bello, Avenida Republica 275, Santiago, Chile
S
* Supporting Information
ABSTRACT: Oxidative addition reaction of dipyridyl ditellurides to
[Pt2(dppm)3] gave two types of complexes, [Pt{2-Te-C5H3(3-R)N}2(dppm)]
(1) and [Pt{PPh2C(TeC5H3(3-R)N)2PPh2}2] (2) (R = H or Me), in ∼65
and ∼20% yield, respectively. Both these complexes are also formed in
the substitution reaction between [PtCl2(dppm)] and NaTeC5H3(3-R)N.
Treatment of [Pt(dppe)2] with dipyridyl ditellurides yielded an oxidative
addition product, [Pt{2-Te-C5H3(3-R)N}2 (dppe)] (3) (R = H or Me),
exclusively. In a substitution reaction of [PtCl2(dppe)] with NaTeC5H3
(3-Me)N a complex of composition Pt{TeC5H3(3-Me)N}(dppe)Cl (4) was
formed. The reaction between either [Pt(dppp)2] and Te2(C5H3(3-Me)N)2
or [PtCl2(dppp)] and NaTeC5H3(3-R)N afforded a mixture of [Pt{2-Te-
C5H3(3-Me)N}2(dppp)] (5) and [Pt3Te2(dppp)3]2+ (6), which were sepa-
rated by column chromatography. All the complexes were characterized
by elemental analyses and NMR (1H, 31P, 195Pt) spectroscopy. The molecular structures of [Pt{PPh2C(TeC5H4N)2PPh2}2] and
[Pt2{TeC5H3(3-Me)N}2(dppe)2][BPh4]2 were established by single-crystal X-ray diffraction analyses. The bonding, charge
transfer, and geometry of compounds [Pt{2-Te-C5H3(3-R)N}2(dppm)] (1), [Pt{PPh2C(TeC5H3(3-R)N)2PPh2}2] (2), and
[Pt3Te2(dppp)3]2+ (6) have been analyzed through relativistic density functional calculations.
organic synthesis12 and materials science.13 These reactions
with Pd(0) species, in general, afford binuclear complexes (e.g.,
[Pd2(ER)2(μ-ER)2(PR′3)2]), whereas the corresponding plati-
INTRODUCTION
■
Oxidative addition reactions of E−X (E = heteroatom, X = H,1
C,2 or heteroatom3,4) to zerovalent group 10 metal complexes
have attracted considerable attention for quite some time.5 The
num(0) derivatives yield mononuclear complexes (e.g., [Pt-
(ER)2(PR′3)2] (E = S or Se)).9 In contrast, oxidative addition
remarkable reactivity of Ni0 and Pd0 has been used in synthetic
reactions of diorgano ditellurides with Pd(0) and Pt(0) are
chemistry, as their reactions, in general, give high product yield
often more complex, yielding several products.14,15 Some of
these products, e.g., [Pd6Te4(TePh)4(PPh3)6] and [Pt3Te2(Th)-
(PPh3)5]Cl,14 are formed by competitive cleavage of Te−Te and
Te−C bonds. The distinct reactivity of tellurium ligands may
be attributed to comparable bond energies of Te−Te and
Te−C bonds and increased metallic character of Te from lighter
chalcogens (S or Se). Recent theoretical calculations by
Morokuma et al. on oxidative addition of an E−E bond to
Pd(0) and Pt(0) have revealed that the M−TeR bond energy is
the lowest in [Pt(ER)2(PR′3)2] (E = S, Se or Te) complexes
and the Pt−ER bond is stronger than the Pd−ER linkage.9 It has
also been shown that the transition state involving activation
of RE−ER by M0(PR3)2 species requires deformation in the P−
M−P angle.9
with great selectivity under mild conditions.6 Not only are these
complexes used as precursors, but several of them are envisaged
as active species in catalytic reactions. The corresponding
platinum(0) complexes, on the other hand, due to their superior
stability, provide an opportunity to understand the mechanistic
details and learn about the nature of complexes involved in such
reactions.7
Oxidative addition reaction of diorgano-disulfides and -diselenides
to zerovalent group 10 metals is of much current interest.4,8−10
The reaction has been employed for the synthesis of vinyl-
sulfides and vinylselenides by E−E addition to CC bonds of
acetylenic hydrocarbons.4,11 Such addition reactions proceed
in a regio- and stereoselective manner with almost 100% atom
efficiency.4 During oxidative addition reactions, the chalcogen−
chalcogen bond is reductively cleaved with concomitant
formation of two metal−chalcogenolate bonds under relatively
mild conditions. The resulting complexes find application in
Received: November 1, 2011
Published: February 21, 2012
© 2012 American Chemical Society
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Article
Pyridyl tellurolates are hemilabile ligands and can bind metal
atoms in different ways, viz., through a tellurium atom, through
a nitrogen atom, or in a bidentate mode (Te∩N; chelating or
bridging). Unlike simple tellurolate ligands (e.g., PhTe−), the
presence of both hard (N) and soft (Te) atoms in the pyridyl
tellurolate ligand may contribute to the reactivity and overall
stability of the resulting complexes. Recently we have reported
the formation of a serendipitous product, [Pt(Te)(TeAr)2(PPh3)]
(Ar = C5H4N and C5H3(Me)N), containing bare Te0 co-
ordinated to platinum(II), together with the expected products,
[Pt(TeAr)2(PPh3)2], in the reactions of [Pt(PPh3)4] with dipyridyl
ditellurides.15 We have now chosen platinum(0) complexes con-
taining chelating diphosphines with varying degree of P−M−P
angles and studied their oxidative addition reactions with dipyridyl
ditellurides (I). Depending on the nature of the diphosphine
ligand, different products could be isolated. The results of this
work are reported herein.
Table 1. Crystallographic and Structural Determination Data
for [Pt{PPh2C(TeC5H4N)2PPh2}2]·2CH2Cl2 (2a·2CH2Cl2)
and [Pt2{TeC5H3(3-Me)N}2(dppe)2]·[BPh4]2 (4b)
2a·2CH2Cl2
4b
chemical formula
fw
C60H48N2P4PtTe2·2CH2Cl2 C112H100B2N2P4Pt2Te2
1541.03
2264.82
cryst size (mm3)
0.30 × 0.30 × 0.20
monoclinic
298
0.32 × 0.25 × 0.10
monoclinic
100
cryst syst
temperature (K)
space group
unit cell dimensions
a (Å)
P21/n
C2/c
19.740(4)
13.033(2)
11.766(2)
90.618(15)
3026.7(10)
1.691
30.256(4)
16.828(2)
22.048(5)
123.007(2)
9414(3)
b (Å)
c (Å)
β (deg)
volume (Å3)
ρcalcd (g cm−3
)
1.598
Z
2
4
μ (mm−1)/F(000)
3.585/1496
−25 ≤ h ≤ 25
0 ≤ k ≤ 16
−15 ≤ l ≤ 8
2.54 to 27.50
3.695/4464
−36 ≤ h ≤ 36
−20 ≤ k ≤ 20
−21 ≤ l ≤ 26
2.90 to 25.44
limiting indices
θ for data collection
EXPERIMENTAL SECTION
(deg)
■
The compounds [PtCl2(P∩P)] (P∩P = dppm, dppe, dppp),16
[Pt2(dppm)3],17 [Pt(P∩P)2] (P∩P = dppe, dppp),18 (C5H4N)2Te2, and
(3-MeC5H3N)2Te219 were prepared according to literature methods.
Tertiary phosphines were procured from Strem Chemicals. All reac-
tions were carried out under an argon/nitrogen atmosphere in dry and
distilled analytical grade solvents 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. Chemical
no. of reflns collected
6934
8487
no. of independent reflns 4975
6503
data/restraints/params
final R1, wR2 indices
R1, wR2 (all data)
6934/1/340
8487/0/560
0.0287/0.0599
0.0475/0.0666
1.017
0.0514/0.1267
0.0857/0.1478
1.040
goodness of fit on F2
[Pt{PPh2C(TeC5H4N)2PPh2}2] (2a) (yield 32 mg, 21%, mp
48 °C). Anal. Calcd for C60H48N2P4PtTe2: C, 52.55; H,
3.53; N, 2.04. Found: C, 52.19; H, 3.65; N, 2.35. H
1
shifts are relative to internal chloroform (δ 7.26) for H, external 85%
H3PO4 for 31P, and Na2PtCl6 in D2O for 195Pt. Elemental analyses were
carried out on a Thermo Fischer Flash EA1112 CHNS analyzer. The con-
ductivity measurements were carried out on a EUTECH-CON 1500 con-
ductivity meter.
1
NMR (CDCl3) δ: 7.02 (dd, C5H4N); 7.04−7.74 (m, Ph);
8.04 (d, 7 Hz, C5H4N); 8.45 (d, 1.8 Hz, C5H4N).
31P{1H} NMR (CDCl3) δ: −29.3 (1J(Pt−P) = 1909 Hz).
(ii) To a dichloromethane solution (14 cm3) of [PtCl2(dppm)]
(110 mg, 0.17 mmol) was added a methanol−benzene solu-
tion (10 cm3) of Na(2-Te-C5H4N) [freshly prepared from
(C5H4N)2Te2 (72 mg, 0.17 mmol) in benzene and NaBH4
(13.4 mg, 0.35 mmol) in methanol]. The mixture was stirred
for 5 h, whereupon a clear orange solution was obtained. The
solvents were evaporated under vacuum. The residue was
washed thoroughly with hexane followed by diethyl ether. The
product was extracted with dichloromethane, filtered, and
passed through a Florisil column. The resulting solution was
concentrated (5 cm3) under vacuum, and hexane (0.5 cm3) was
added, which on refrigeration at −5 °C afforded two different
products, viz., orange crystals of [Pt{PPh2C(TeC5H4N)2PPh2}2]
(2a) [(yield 104 mg, 45%, mp 48 °C) Anal. Calcd for
C60H48N2P4PtTe2·CH2Cl2: C, 50.31; H, 3.46; N, 1.92. Found:
C, 49.78; H, 3.52; N, 1.56. 1H NMR (CDCl3) δ: 6.82 (d,
C5H4N), 7.05 (m, Ph), 7.40 (dd, C5H4N 2H), 7.68 (br, Ph),
8.04 (m, Ph + C5H4N 2H), 8.46 (d, C5H4N). 31P{1H} NMR
(CDCl3) δ: −29.3 (1J(Pt−P) = 1909 Hz)], and a yellow
powder, [Pt(2-Te-C5H4N)2(dppm)] (1a) [(yield 46 mg, 25%; mp
163 °C (dec)) Anal. Calcd for C35H30N2P2PtTe2: C, 42.42; H,
Intensity data for [Pt{PPh2C(TeC5H4N)2PPh2}2]·2CH2Cl2
(2a·2CH2Cl2) and [Pt2{μ-TeC5H3(3-Me)N}2(dppe)2]·[BPh4]2
(4b) were measured on Rigaku AFC 7S and Bruker Apex-II CCD
diffractometers, respectively, with Mo Kα radiation so that θmax = 27.5°.
The structures were solved by direct methods,20 and refinement21 was
on F2 using data that had been corrected for absorption effects with an
empirical procedure. Non-hydrogen atoms were modeled with aniso-
tropic displacement parameters, with hydrogen atoms in their calculated
positions. Molecular structures were drawn using ORTEP.22 Crystallo-
graphic and structural determination data are listed in Table 1.
(i)
Syntheses of Complexes. [Pt(2-Te-C5H4N)2(dppm)] (1a)
and [Pt{PPh2C(TeC5H4N)2PPh2}2] (2a). To a toluene solution
(10 cm3) of (C5H4N)2Te2 (98 mg, 0.24 mmol) was
added a solution (30 cm3) of [Pt2(dppm)3] (175 mg,
0.11 mmol) in the same solvent with stirring, which con-
tinued for 4 h at room temperature. The supernatant
was decanted, and the orange precipitate was washed
thoroughly with hexane and diethyl ether and dried
under vacuum to afford a yellow powder, [Pt(2-Te-
C5H4N)2(dppm)] (1a) [(yield 75 mg, 67%; mp 163 °C
(dec)) Anal. Calcd for C35H30N2P2PtTe2: C, 42.42; H,
1
3.05; N, 2.82. Found: C, 42.17; H, 3.23; N, 2.52. H
1
3.05; N, 2.82. Found: C, 42.58; H, 3.08; N, 3.42. H NMR
NMR (CDCl3) δ: 4.40 (t, 2J(P−H) = 10 Hz, 3J(Pt−H) =
53 Hz); 6.57 (d); 6.76 (dt, 1.8 Hz d, 7.5 Hz (t)
(C5H4N)); 7.09−7.79 (m, Ph); 8.04 (d, 7.8 Hz, C5H4N);
8.46 (dd, 1, 4 Hz, C5H4N). 31P{1H} NMR (CDCl3)
δ: −53.0 (1J(Pt−P) = 2547 Hz)]. The supernatant was
passed through a Florisil column, and the filtrate was
dried under reduced pressure to give an orange powder,
(CDCl3) δ: 4.40 (m, dppm −PCH2), 7.05 (d, 7.8 Hz, C5H4N),
7.13−7.80 (m, Ph), 8.45 (d, C5H4N 2H). 31P{1H} NMR
(CDCl3) δ: −53.0 (1J(Pt−P) = 2552 Hz)], which were separated
manually.
(i)
[Pt{2-Te-C5H3(3-Me)N}2(dppm)] (1b) and [Pt{PPh2C-
(TeC5H3(3-Me)N)2PPh2}2] (2b). Prepared similarly to the
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Article
above method (i) and recrystallized from benzene−hexane, which
Pt{TeC5H3(3-Me)N}(dppe)Cl (4a). To a benzene suspension
(13 cm3) of [PtCl2(dppe)] (110 mg, 0.17 mmol) was added a
methanolic solution (8 cm3) of Na{2-Te-C5H3(3-Me)N}
[freshly prepared from {C5H3(3-Me)N}2Te2 (74 mg, 0.17 mmol)
in benzene and NaBH4 (13.7 mg, 0.36 mmol)]. The mixture
was stirred for 3 h, whereupon a clear orange solution was
obtained. The solvents were evaporated under vacuum. The
residue was washed thoroughly with hexane followed by diethyl
ether. The product was extracted with acetone, filtered, and
passed through a Florisil column. To the resulting solution was
added hexane to yield an orange powder of Pt{TeC5H3
(3-Me)N}(dppe)Cl (4a) (yield 104 mg, 74%, mp 193 °C (dec)).
Anal. Calcd for C64H60N2Cl2P4Pt2Te2: C, 45.28; H, 3.56; N, 1.65.
Found: C, 45.68; H, 3.62; N, 1.91. Conductivity measurements
(μS cm2 mol−1): 3.0 (CHCl3), 70.6 (CH3CN), 83.3 (CH3OH).
1H NMR (CDCl3) δ: 2.09 (s, Me), 2.86 (br, dppe −CH2), 6.70
(m, C5H3(3-Me)N), 7.00 (m), 7.36 −7.87 (m, Ph), 8.24 (d,
C5H3(3-Me)N). 31P{1H} NMR (CDCl3) δ: 41.9 [1J(Pt−P) =
2940 Hz], 36.7 [1J(Pt−P) = 3267 Hz].
afforded an orange powder, [Pt{PPh2C(TeC5H3(3-Me)N)2-
PPh2}2] (2b) [(yield 24 mg, 18%; mp 110 °C (dec)) Anal.
Calcd for C62H52N2P4PtTe2: C, 53.21; H, 3.74; N, 2.00. Found:
C, 53.10; H, 3.78; N, 1.97. 31P{1H} NMR (CDCl3) δ: −25.1
(1J(Pt−P) = 1903 Hz)], and a yellow powder, [Pt{2-Te-
C5H3(3-Me)N}2(dppm)] (1b) [(yield 39 mg, 62%; mp 170 °C
(dec)) Anal. Calcd for C37H34N2P2PtTe2: C, 43.61; H, 3.36; N,
2.75. Found: C, 43.89; H, 3.34; N, 2.64. 31P{1H} NMR
1
(CDCl3) δ: −51.9 [ J(Pt−P) = 2615 Hz].
(ii) Prepared in a similar fashion adopting method (ii), and the
crude product was extracted with benzene and recrystallized
from a benzene−hexane mixture to afford an orange powder,
[Pt{PPh2C(TeC5H3(3-Me)N)2PPh2}2] (2b) [(yield 22%; mp
110 °C (dec)) Anal. Calcd for C62H52N2P4PtTe2: C, 53.21; H,
1
3.74; N, 2.00. Found: C, 52.80; H, 3.43; N 1.71. H NMR
(CDCl3) δ: 2.44 (s, Me), 7.06 (d, C5H3N 2H), 7.18(m, Ph),
7.30 (d, C5H3N 2H), 7.36 (q, Ph), 7.49(m, Ph), 7.65(dd,
C5H3N 2H), 7.69(br, Ph), 8.31(d, C5H3N 2H). 31P{1H} NMR
(CDCl3) δ: −25.6 (1J(Pt−P) = 1913 Hz)], and the benzene-
insoluble part of the crude product, which was extracted in
dichloromethane and recrystallized from a dichloromethane−
diethyl ether mixture to give a yellow powder, [Pt{2-Te-C5H3-
(3-Me)N}2(dppm)] (1b) (yield 58%; mp 170 °C (dec)). Anal.
Calcd for C37H34N2P2PtTe2: C, 43.61; H, 3.36; N, 2.75. Found: C,
43.52; H, 3.68; N, 2.42. 1H NMR (CDCl3) δ: 2.44 (s, Me), 3.16
(d, dppm −PCH2), 6.92 (dd, C5H3N 2H), 7.28 (br, Ph), 7.43 (d,
C5H3N 2H), 7.71 (br, Ph), 7.93 (dd, C5H3N 2H), 8.25 (d, C5H3N
To prepare good-quality crystals, a larger anion, Ph4B−, was used. Thus
during the reaction, an acetone solution of NaBPh4 (113 mg,
0.33 mmol) was added to the reaction mixture and stirred for 2 h. The
whole solution was centrifuged for 10 min. The supernatant was
decanted and dried under vacuum to afford an orange powder, which
was recrystallized from an acetone−diethyl ether mixture to yield
orange crystals of [Pt2{TeC5H3(3-Me)N}2(dppe)2](BPh4)2 (4b)
(yield 80 mg, mp 205 °C (dec)). Characterization data are consistent
with the reported ones.23
1
2H). 31P{1H} NMR (CDCl3) δ: −51.9 [ J(Pt−P) = 2632 Hz].
(i)
[Pt{2-Te-C5H3(3-Me)N}2(dppp)] (5) and [Pt3Te2(dppp)3]Cl2
(6a). To an acetone solution (15 cm3) of [PtCl2(dppp)]
(97 mg, 0.14 mmol) was added a methanolic solution (12 cm3)
of Na{2-Te-C5H3(3-Me)N} [freshly prepared from {C5H3
(3-Me)N}2Te2 (69 mg, 0.16 mmol) in benzene and NaBH4
(11.8 mg, 0.31 mmol)]. The mixture was stirred for 4 h, where-
upon a clear orange solution was obtained. The solvents were
evaporated under vacuum. The residue was washed thoroughly
with hexane followed by diethyl ether and dried under reduced
pressure. The crude product was purified by column chromato-
graphy (neutral and active aluminum oxide), eluting with a
benzene−diethyl ether mixture, from which a yellow powder
was obtained, [Pt{2-Te-C5H3(3-Me)N}2(dppp)] (5) (yield
58 mg, 39%, mp 147 °C (dec)). Anal. Calcd for C39H38N2P2PtTe2:
C, 44.74; H, 3.66 N, 2.67. Found: C, 44.36; H, 3.96 N, 2.54. 1H
NMR (CDCl3) δ: 1.86 (s, Me); 2.52 (br); 3.04−3.15 (m) CH2;
6.45−7.79 (m, Ph + C5H3N). 31P{1H} NMR (CDCl3) δ: −10.3
(1J(Pt−P) = 2740 Hz). After separation of 5, the column was
run using a benzene−chloroform mixture (4:1 v/v), giving an
orange powder of [Pt3Te2(dppp)3]Cl2 (6a) (yield 107 mg,
35%, mp 169 °C). Anal. Calcd for C81H78Cl2P6Pt3Te2: C,
45.28; H, 3.66. Found: C, 45.26; H, 3.96. To this was added a
solution of AgSO3CF3 (73 mg, 28 mmol) with stirring, which
continued for 1 h at room temperature. The contents were
centrifuged for 5 min. The supernatant was decanted, filtered,
and dried under vacuum to afford a brown powder, which was
recrystallized from a chloroform−diethyl ether mixture to yield
yellowish-brown crystals of [Pt3Te2(dppp)3](SO3CF3)2 (6b)
(mp 152 °C). Anal. Calcd for C83H78S2F6O6P6Pt3Te2: C, 41.96;
195Pt{1H} NMR (CDCl3) δ: −4712 (1J(Pt−P) = 2650 Hz).
(i)
[Pt(2-Te-C5H4N)2(dppe)] (3a). To a benzene solution (12 cm3)
of (C5H4N)2Te2 (54 mg, 0.13 mmol) was added a solution
(30 cm3) of [Pt(dppe)2] (125 mg, 0.13 mmol) in the same
solvent with stirring, which continued for 3 h at room tem-
perature. The solvent was evaporated under vacuum, and the
residue was washed thoroughly with hexane followed by diethyl
ether to remove liberated dppe. The residue was recrystal-
lized from a benzene−hexane mixture to afford a yellow
powder (yield 86 mg, 68%, mp 178 °C (dec)). Anal. Calcd
for C36H32N2P2PtTe2: C, 43.03; H, 3.21; N, 2.79. Found: C,
43.51; H, 3.07; N 2.96. 31P{1H} NMR (CDCl3) δ: 46.1
[1J(Pt−P) = 2894 Hz].
(ii) To a benzene suspension (15 cm3) of [PtCl2(dppe)] (100 mg,
0.15 mmol) was added a methanolic solution (12 cm3) of
Na(2-Te-C5H4N) [freshly prepared from (C5H4N)2Te2 (62 mg,
0.15 mmol) in benzene and NaBH4 (13 mg, 0.34 mmol) in
methanol]. The mixture was stirred for 3 h, whereupon a clear
orange solution was obtained. The solvents were evaporated
under vacuum. The residue was washed thoroughly with hexane
followed by diethyl ether. The product was extracted with
acetone and passed through a Florisil column. To the resulting
solution was added hexane to precipitate the title complex as an
orange powder (yield 98 mg, 65%, mp 178 °C (dec)). Anal.
Calcd for C36H32N2P2PtTe2·CH2Cl2: C, 40.78; H, 3.14; N,
1
2.57. Found: C, 41.20; H, 3.29; N, 2.30. H NMR (CDCl3)
δ: 2.10 (m, dppe 6H), 6.63 (d, C5H4N 2H), 6.72 (t, C5H4N),
7.30−7.35 (m, Ph), 7.84 (d, 3.6 Hz, C5H4N). 31P{1H} NMR
(CDCl3) δ: 46.1 [1J(Pt−P) = 2887 Hz]. 195Pt{1H} NMR
(CDCl3) δ: −5346 [1J(Pt−P) = 2914 Hz].
1
H, 3.30; S, 2.69. Found: C, 42.34; H, 3.21; S, 2.41. H NMR
(CDCl3) δ: 2.94 (br, dppp −CH2), 7.11−7.63 (m, Ph).
31P{1H} NMR (CDCl3) δ: −13.6 [1J(Pt−P) = 2965 Hz].
[Pt{2-Te-C5H3(3-Me)N}2(dppe)] (3b). To a benzene solution (10 cm3)
of {C5H3(3-Me)N}2Te2 (48 mg, 0.11 mmol) was added a solution
(30 cm3) of [Pt(dppe)2] (110 mg, 0.11 mmol) in the same solvent
with stirring, which continued for 4 h at room temperature. The sol-
vent was evaporated under vacuum, and the residue was washed thoroughly
with hexane followed by diethyl ether to remove liberated dppe. The
residue was recrystallized from a benzene−hexane mixture to afford a
yellow powder (yield 81 mg, 71%, mp 185 °C (dec)). The character-
ization data are consistent with the literature values.23
(ii) To a benzene solution (10 cm3) of {C5H3(3-Me)N}2Te2
(48 mg, 0.11 mmol) was added a solution (30 cm3) of [Pt(dppp)2]
(102 mg, 0.10 mmol) in the same solvent with stirring, which
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
dppp. The residue was extracted with benzene, filtered, and
passed through a Florisil column to give a yellow powder,
[Pt{2-Te-C5H3(3-Me)N}2(dppp)] (5) [(yield 44 mg, 42%, mp
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Scheme 1
Scheme 2
147 °C) Anal. Calcd for C39H38N2P2PtTe2: C, 44.74; H,
yield (Scheme 1). The substitution reaction between
[PtCl2(dppm)] and NaTeC5H3(3-R)N, prepared in situ by
reductive cleavage of the Te−Te bond in the corresponding
ditellurides by methanolic NaBH4, also gave 1 and 2 (Scheme 2).
The 31P NMR spectra of 1 displayed a single resonance at δ ≈
−52 ppm with a 195Pt−31P coupling of ∼2600 Hz indicative of a
tellurolate ligand trans to the phosphine ligand.23−25 The 195Pt
NMR spectrum of 1b exhibited a triplet at δ −4712 ppm with a
1J(Pt−P) of 2650 Hz due to coupling with two equivalent
phosphorus nuclei. The 31P NMR spectra of 2 exhibited signals
at −29.3 (2a) and −25.1 (2b) ppm with a 195Pt−31P coupling of
∼1900 Hz. The resonance is considerably deshielded with respect
to the signal for 1. The magnitude of 1J(Pt−P) suggests that the
strong trans-influencing phosphine ligands are mutually trans,
3.66 N, 2.67. Found: C, 44.73; H, 3.59 N, 2.45. 31P{1H} NMR
(CDCl3) δ: −10.3 (1J(Pt−P) = 2740 Hz)], and a benzene-
insoluble part, which was extracted with chloroform to afford
an orange powder of [Pt3Te2(dppp)3]Cl2 (6a) (yield 81 mg,
38%, mp 152 °C). Anal. Calcd for C81H78Cl2P6Pt3Te2: C, 45.28;
H, 3.66. Found: C, 44.98; H, 3.43. 31P{1H} NMR (CDCl3)
δ: −13.6 [1J(Pt−P) = 2970 Hz].
RESULTS AND DISCUSSION
■
Treatment of [Pt2(dppm)3] with (3-RC5H3N)2Te2 (R = H or
Me) in toluene at room temperature gave an oxidative addition
product, [Pt{2-TeC5H3(3-R)N}2(dppm)] (1) (R = H (1a) and
Me (1b)), in ∼65% yield as a yellow powder together with an
orange crystalline product identified as [Pt{PPh2C(TeC5H3-
(3-R)N)2PPh2}2] (2) (R = H (2a) and Me (2b)) in ∼20%
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which is further confirmed by an X-ray structural analysis of 2a
(see later).
complexes. It is likely that, in solution, a monomeric species
containing a chelating tellurolate ligand may form (eq 1).
The strong trans influence of the phosphine ligand may weaken
the Pt−Te−Pt bridge. Such a mononuclear species would show
two 31P NMR resonances with different 1J(Pt−P) coupling con-
stants, one due to a Ph2P group trans to nitrogen (1J(Pt−P) =
3267 Hz) and another for that trans to the tellurolate ligand
(1J(Pt−P) = 2940 Hz).
The reaction of [Pt(dppp)2] with (3-RC5H3N)2Te2 in benzene,
in addition to oxidative addition product [Pt{2-Te-C5H3(3-Me)-
N}2(dppe)] (5), gave an ionic trinuclear complex, [Pt3Te2-
(dppp)3]Cl2 (6a). Similarly, a substitution reaction of [PtCl2-
(dppp)] with NaTeC5H3(3-Me)N gave a mixture of 5 and 6a,
which were separated by column chromatography. Treatment of
6a with AgOTf gave the corresponding OTf complex [Pt3Te2-
(dppp)3][OTf]2 (6b). Formation of similar tellurido-bridged
The formation of 2 in these reactions is rather intriguing, as
the methylene carbon is attacked by the TeC5H3(3-R)N moiety
and is also deprotonated. Deprotonation of the methylene
proton in dppm and related ligands R2PCH2L (L = SMe, NHR,
PR2, etc.) is well documented in literature.26 For instance,
reactions of [MIr(CO)3(dppm)2] (M = Ir or Rh) with CH2I2
or CH2(I)CN did not yield the expected oxidative addition
product; instead products formed by deprotonation of one of
the dppm ligands, [MIr(CO)2(μ-I)(μ-CO)(Ph2PCHPPh2)dppm)],
are isolated.27 The reactions of [Pt2(μ-OH)2(dppm)2]2+ with
LiN(SiMe3)2 in THF deprotonates the dppm ligand rather
than the bridging OH to give [Pt2(μ-OH)2(Ph2PCHPPh2)2].28
Similarly, in amido-bridged complexes, [Pt2(μ-NHR)2(dppm)2]2+,
deprotonation of dppm by LiN(SiMe3)2 proceeds via the amido
group.29 Double deprotonation of the dppm ligand has also
been reported in the literature.30 For example, reaction of
[Ru(CNR)2(dppm)2]2+ with [AuCl(PPh3)2] in the presence of
KOH affords [Ru(CNR)2{PPh2C(AuPPh3)2PPh2}2]2+.30b In
the present study, double deprotonation of the dppm ligand appears
to be elicited by strong nucleophilicity of the pyridyltellurolate
ligand in both the oxidative addition and substitution reactions.
During the oxidative addition reaction, the activated dite-
llurides by the platinum center attack the dppm ligand to give
Ph2PCHTeArPPh2 and ArTeH (Ar = pyridyl group). The former
on oxidative addition to platinum (0) may give “Ph2PCTeArPPh2”
species. In the case of the substitution reaction, the tellurolate ion
attacks the chelating dppm to give “Ph2PCHTeArPPh2PtCl2”,
which in the presence of base generates “Ph2PCTeArPPh2Pt”.
The reaction of [Pt(dppe)2] with (3-RC5H3N)2Te2 gave ex-
clusively an oxidative addition product, [Pt{2-Te-C5H3(3-R)N}2-
(dppe)] (3) (R = H (3a), Me (3b)), in ∼70% yield. Alter-
natively, 3 could be obtained by the reaction of [PtCl2(dppe)]
with two equivalents of NaTeC5H3(3-R)N as described earlier
by us.23 This reaction in the case of 3-methyltellurolate ligand
gave a complex of composition Pt{TeC5H3(3-Me)N}(dppe)Cl
(4a). The latter complex is a nonelectrolyte in chloroform
(3.0 μS cm2 mol−1), while it is a 1:1 elelctrolyte in methanol
(83.3 μS cm2 mol−1) and acetonitrile (70.6 μS cm2 mol−1).
This suggests that the complex exists as a monomeric neutral
species with a monodentate tellurolate ligand in chloroform,
while in methanol and acetonitrile it adopts an ionic structure
with a chelating tellurolate ligand and chloride as counteranion.
During the preparation of 4a, addition of NaBPh4 to the reac-
tion flask resulted in the formation of BPh4 salt [Pt2{TeC5H3
(3-Me)N}2(dppe)2](BPh4)2 (4b). The 31P NMR data of 3b and
4b are in agreement with those reported earlier.23 The magni-
tude of 1J(Pt−P) in 3 is consistent with mononuclear cis tellurolate
complexes.31,32 It is interesting to note that 4b is a centro-
symmetric dimer stabilized by Te bridges (see later, X-ray
crystallography), and the 31P NMR spectrum showed two signals
Figure 1. Crystal structure of [Pt{PPh2C(TeC5H4N)2PPh2}2]·2CH2Cl2
(2a·2CH2Cl2) with atomic numbering scheme. The ellipsoids are drawn
at 50% probability.
1
with different J(Pt−P) values. A similar 31P NMR pattern has
been reported for [Pt2(μ-SeCH2CH2NMe2)2(dppe)2]2+.33 Ini-
tially, in the absence of X-ray structural analysis,23,33 asymmetric
Pt−E (E = Se or Te) bridges have been suggested for these
Figure 2. Crystal structure of [Pt2{TeC5H3(3-Me)N}2(dppe)2]·(BPh4)2
(4b) with atomic numbering scheme. The ellipsoids are drawn at 50%
probability.
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trinuclear platinum complex [Pt3(μ-Te)2(Th)(PPh3)5]Cl has been
reported by oxidative addition reaction of Th2Te2 to [Pt(PPh3)4]
in dichloromethane.14
X-ray Crystallography. The molecular structures of
[Pt{Ph2PC(TeC5H4N)PPh3}2] (2a) and [Pt2{μ-TeC5H3(3-Me)-
N}2(dppe)2][BPh4]2 (4b), established by X-ray diffraction
analysis, are shown in Figures 1 and 2. Selected interatomic
parameters are summarized in Tables 2 and 3. The platinum
atom in 2a adopts a distorted square-planar configuration
defined by a “P4” coordination core. The chelate P1−Pt1−P2
angle is acute (70.66°); as a consequence, the adjacent angles
are opened up. The Pt−P distances are similar (2.31−2.33 Å)
and are slightly longer than those reported for [PtSe4(dppe)]
(2.24 Å),36 [Pt3(μ-Stol)4(dppm)2][CF3SO3]2 (2.25 Å),24
and [Pt{o-C6H4(PPh2)2}(PhCCPh)] (2.26 Å).37 The Te−C
distances are as expected.23,38 Various angles involving the
C-1 carbon vary between 100.5° and 131.1°, indicative of a
trigonal (allylic-type) configuration.
Compound 4b is a centrosymmetric dimer comprised of two
distorted square-planar platinum atoms that are held together
by tellurolato bridges. Coordination around each platinum is
defined by a P2Te2 donor set from a chelating dppe ligand and
two tellurolate ligands. The Pt−P and Pt−Te distances are as
expected.2,15,17 The four-membered Pt2Te2 ring is planar with
C5H3(3-Me)N groups adopting an anti configuration.
The 31P NMR spectrum of 5 exhibited a singlet at
1
δ −10.3 ppm with a J(Pt−P) of 2744 Hz, while the spectrum
of 6b showed a resonance at lower frequency (δ −13.6 ppm)
with a 1J(Pt−P) of 2965 Hz. The NMR data are consistent with
the reported values.34 The chemical structure of 6b was con-
firmed by X-ray structural analysis. There are two independent
tellurido-bridged (Pt−Te = 2.62 Å (av); Pt−Te bond distance in
35
[Pt3(μ-Te)2(PEt3)6]2+ and [Pt3(μ-Te)2(Th)(PPh3)5]Cl14 is
2.604 and 2.630 Å, respectively) cations in the crystal; one
molecule has a 2-fold symmetry, while the other has a 3-fold
symmetry. However, due to disorder in the OTF counterions,
the structure is not described here (Supporting Information).
Table 2. Selected Bond Lengths (Å) and Angles (deg) of
[Pt{PPh2C(TeC5H4N)2PPh2]·2CH2Cl2 (2a·2CH2Cl2)
Pt1−P1
Pt1−P2
Te1−C1
P2−Pt1−P2′
P2−Pt1−P1′
P2−Pt1−P1
C1−Te1−C2
C1−P2−Pt1
C25−P2−Pt1
2.3292(17)
2.3116(18)
2.059(7)
180.00(9)
109.34(6)
70.66(6)
99.3(3)
Te1−C2
P1−C1
P2−C1
C19−P2−Pt1
P1−C1−P2
P1−C1−Te1
P2−C1−Te1
N1−C2−Te1
2.144(8)
1.742(8)
1.750(7)
115.8(2)
100.5(4)
131.1(4)
127.6(4)
121.9(7)
Theoretical Calculations. The bonding, charge transfer,
and geometry of compounds [Pt{2-Te-C5H3(3-R)N}2(dppm)]
(1), [Pt{PPh2C(TeC5H3(3-R)N)2PPh2}2] (2), and [Pt3Te2-
(dppp)3]2+ (6) have been analyzed through relativistic density
functional calculations.39 The formation of products 1 and 2
shows a clear preference for 1. These systems differ by the
substitution of the dppm ligand with a (3-RC5H3N)Te moiety,
which leads to changes in the ligand-to-metal charge transfer.
In order to characterize the latter point, we performed a
detailed charge analysis employing the Hirshfeld partition-
ing schemes of the electron density, focusing on the charge
distribution between the dppm and {PPh2C(TeC5H3(3-
R)N)2PPh2} ligands in systems 1 and 2, respectively. The
calculations characterize a more efficient charge donation
toward the Pt center for 1 (0.37 e), in comparison to 2, which
shows an almost negligible donation (0.08 e). These results
suggest that a stronger bond is formed between Pt and dppm
ligand in compound 1, accounting for the described preference
(see text).
94.6(3)
117.8(3)
Table 3. Selected Bond Lengths (Å) and Angles (deg) of
[Pt2{TeC5H3(3-Me)N}2(dppe)2]·[BPh4]2 (4b)
Pt(1)−P(1)
Pt(1)−Te(1)
Pt(1)−Te(1)#1
P(1)−Pt(1)−Te(1)
P(1)−Pt(1)−Te(1)#1 95.87(3)
2.2555(11) Pt(2)−P(2)
2.2523(11)
2.6318(4)
2.168(5)
2.6382(4)
2.6383(4)
168.98(3)
Pt(2)−Te(1)
Te(1)−C(75)
P(2)−Pt(2)−Te(1)
173.36(3)
85.064(19)
Te(1)#1−Pt(2)−
Te(1)
Te(1)−Pt(1)−Te(1)
#1
84.806(19) C(75)−Te(1)−Pt(2) 94.09(12)
P(2)#1−Pt(2)−P(2)
85.72(6) C(75)−Te(1)−Pt(1) 90.65(12)
The formation of system 6, which exhibits a [Pt3(dppp)3]6+
core stabilized by a [Te2]4− fragment as ligand, participates in
the making of the Pt−Te bond that results from the direct 5d-
Pt−5p-Te interaction. The molecular orbital diagram in Figure 3
P(2)#1−Pt(2)−Te(1) 173.36(3)
Pt(2)−Te(1)−Pt(1)
N(1)−C(75)−Te(1)
95.066(16)
114.6(3)
#1
P(2)−Pt(2)−Te(1)#1 94.99(3)
P(2)#1−Pt(2)−Te(1) 95.00(3)
Figure 3. Molecular orbital diagram describing the core fragment interaction and [Te2]4− in compound 6.
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denotes the contribution from the [Te2]4− toward the elec-
tronic structure of [Pt3Te2(dppp)3]2+, which arises mainly
from the σ, π, π*, and σ* 5p-Te combinations. The HOMO
(Figure 4) is formed mainly by a 5d−5p bonding interaction
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ASSOCIATED CONTENT
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■
Corresponding Author
*E-mail: kedar@barc.gov.in; jainvk@barc.gov.in.
Notes
The authors declare no competing financial interest.
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One of the authors (R.S.C.) is grateful to DAE for the award of
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(39) Geometry optimizations and charge analyses calculations were
done employing the ADF2010 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 potentials, through ZORA.
1750
dx.doi.org/10.1021/om2010589 | Organometallics 2012, 31, 1743−1750