Synthesis and characterization of group 11 and 12 complexes containing a new thioether-functionalized and pyridine-based bis(phosphine) ligand, 2,6-bis[2-(diphenylphosphino)ethylsulfanylmethyl]pyridine

Article abstract of DOI:10.1039/a706543d

The new ligand 2,6-bis[2-(diphenylphosphino)ethylsulfanylmethyl]pyridine, 2,6-(Ph₂PCH₂CH₂SCH₂) ₂C₅H₃N (L¹), has been synthesized. Reaction of [Cu(MeCN)₄][CF₃SO₃] or AgNO₃ with 1 molar equivalent of L¹ gave [CuL¹][CF₃SO₃] 1 or [AgL¹][NO₃] 2, in good yield. Reaction of equimolar quantities of L¹ and Au¹, followed by precipitation with AgO₃SCF₃, gave [AuL¹][CF₃SO₃] 3. In the crystal structure of 2·H₂O, L¹ co-ordinates to Ag via a P₂S₂ donor set in a distorted tetrahedral geometry. Reaction of M(O₃SCF₃)₂ (M = Zn or Cd) with 1 molar equivalent of L¹ gave [ML¹(O₃SCF₃)₂] (M = Zn 4 or Cd 5). Crystal structure analysis of 5 showed that the molecule has symmetry 2, with all five donor atoms of L¹ and a pair of monodentate CF₃SO₃^- ligands arranged in an unusual distorted pentagonal bipyramidal co-ordination geometry about the cadmium centre. Copyright 1998 by the Royal Society of Chemistry.

Full text of DOI:10.1039/a706543d

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Synthesis and characterization of Group 11 and 12 complexes
containing a new thioether-functionalized and pyridine-based
bis(phosphine) ligand, 2,6-bis[2-(diphenylphosphino)ethyl-
sulfanylmethyl]pyridine
Shan-Ming Kuang,a Zheng-Zhi Zhang*,b and Thomas C. W. Mak*,a
a The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
b Elemento-Organic Chemistry Laboratory, Nankai University, Tianjin, China
The new ligand 2,6-bis[2-(diphenylphosphino)ethylsulfanylmethyl]pyridine, 2,6-(Ph2PCH2CH2SCH2)2C5H3N (L1),
has been synthesized. Reaction of [Cu(MeCN)4][CF3SO3] or AgNO3 with 1 molar equivalent of L1 gave
[CuL1][CF3SO3] 1 or [AgL1][NO3] 2, in good yield. Reaction of equimolar quantities of L1 and AuI, followed by
precipitation with AgO3SCF3, gave [AuL1][CF3SO3] 3. In the crystal structure of 2ؒH2O, L1 co-ordinates to Ag
via a P2S2 donor set in a distorted tetrahedral geometry. Reaction of M(O3SCF3)2 (M = Zn or Cd) with 1 molar
equivalent of L1 gave [ML1(O3SCF3)2] (M = Zn 4 or Cd 5). Crystal structure analysis of 5 showed that the molecule
has symmetry 2, with all five donor atoms of L1 and a pair of monodentate CF3SO3Ϫ ligands arranged in an
unusual distorted pentagonal bipyramidal co-ordination geometry about the cadmium centre.
Acyclic phosphine ligands are well known to form stable com-
plexes with many metal ions, whereas acyclic thioether com-
plexes tend to be less stable and often hydrolyse readily.1 As the
NS2 donor set in 2,6-bis(R-sulfanylmethyl)pyridine has been
found to be good for the stabilization of transition-metal ions,2
we reasoned that the incorporation of heteroatom donors, such
as nitrogen or sulfur, on sites within a diphosphine bridge might
result in transition-metal complexes co-ordinated by sulfur (or
nitrogen) and the phosphorus centres. We anticipated that, as
phosphines are better σ donors compared to thioethers, stabil-
ization of a mixed phosphine–thioether co-ordination complex
could be achieved by inhibiting decomplexation of the more
weakly bound thioether in solution. In this context, recent
reports by Darensbourg and co-workers3 and Reid and co-
workers4 have demonstrated the development and co-
ordination chemistry of dithiobis(phosphine) chelates. We
report here the synthesis and characterization of Group 11
and 12 complexes with a new thioether-functionalized and
pyridine-based bis(phosphine) ligand, 2,6-bis[2-(diphenylphos-
phino)ethylsulfanylmethyl]pyridine, 2,6-(Ph2PCH2CH2SCH2)2-
C5H3N (L1), which displays an unusual co-ordination mode
toward Cd2ϩ.
drofuran (thf, 50 cm3) at Ϫ78 ЊC. To this mixture, a solution of
ethylene sulfide (thiirane) (1.50 cm3, 25 mmol) in thf (20 cm3)
was added. The resulting solution was continuously stirred until
0 ЊC was reached, and a solution of 2,6-bis(chloromethyl)-
pyridine (2.20 g, 12.5 mmol) in thf (80 cm3) was then added
over a period of 3 h with the temperature maintained at 0 ЊC.
After the addition the mixture was stirred at room temperature
for 48 h. The thf was removed in vacuum and water (100 cm3)
added. The water phase was next extracted with diethyl ether
(3 × 50 cm3) and the organic phase dried with anhydrous
Na2SO4 overnight. Most of the diethyl ether was removed in
vacuum and hexane (100 cm3) was added. Cooling to Ϫ30 ЊC
for 8 h yielded a colourless solid. Recrystallization from
CH2Cl2–hexane afforded L1 as an analytically pure product,
5.30 g (71%) (Found: C, 70.24; H, 5.88; N, 2.27. C35H35NP2S
requires C, 70.56; H, 5.92; N, 2.35%), m.p. 52–53 ЊC. 1H NMR
(CDCl3): δ 7.52 (t, J = 3.5, 1 H), 7.36–7.25 (m, 20 H), 7.05 (d,
J = 2.2 Hz, 2 H), 3.73 (s, 4 H), 2.50 (m, 4 H) and 2.26 (m, 4 H).
13C-{1H} NMR (CDCl3): δ 28.73 (d, J = 20.3), 28.96 (d, J = 14.9
Hz), 38.56 (s) and 121.65–138.57 (m). 31P-{1H} NMR: δ Ϫ4.54.
FAB mass spectrum: m/z = 596; Calc. 595 for (Ph2PCH2CH2-
SCH2)2C5H3N.
[CuL1][CF3SO3] 1. To a solution containing compound L1
(0.30 g, 0.5 mmol) in CH2Cl2 (20 cm3) was added solid [Cu-
(MeCN)4][CF3SO3] (0.19 g, 0.5 mmol). The resulting solution
was stirred at room temperature for 2 h. Subsequent diffusion
of diethyl ether into the concentrated solution gave complex 1
as air-stable colourless crystals (yield 0.34 g, 84%) (Found: C,
53.21; H, 4.71; N, 1.78. C36H35CuF3NO3P2S3 requires C, 53.49;
H, 4.36; N, 1.73%). 31P-{1H} NMR: δ 34.72.
Experimental
General procedure, measurement and materials
All reactions were routinely carried out under a nitrogen
atmosphere using Schlenk techniques. The solvents were puri-
fied by standard methods. The H and 13C-{1H} NMR spectra
1
were recorded on a Bruker-300 spectrometer using SiMe4 as the
external standard and CDCl3 as solvent, 31P-{1H} NMR spec-
tra on a Bruker-500 spectrometer at 202.45 MHz using (PhO)3P
as the external standard and CDCl3 as solvent and mass spectra
on a Hewlett-Packard 5989B spectrometer. The compounds
[Cu(MeCN)4][CF3SO3]5 and M(O3SCF3)2 (M = Zn or Cd)6
were prepared by the literature procedures.
[AgL1][NO3] 2. The procedure used was similar to that above,
except that AgNO3 (0.09 g, 0.5 mmol) was employed instead of
[Cu(MeCN)4][CF3SO3]. Recrystallization of the product from
CH2Cl2–diethyl ether afforded complex 2ؒH2O as colourless
crystals. Yield: 0.29 g (76%) (Found: C, 54.99; H, 4.61; N, 3.55.
C35H35AgN2O3P2S2ؒH2O requires C, 54.86; H, 4.72; N, 3.57%).
31P-{1H} NMR: δ 43.14.
Preparations
2,6-Bis[2-(diphenylphosphino)ethylsulfanylmethyl]pyridine,
L1. A solution of LiBun in hexane (1.60 , 17.0 cm3) was added
dropwise to a solution of Ph2PH (4.65 g, 25 mmol) in tetrahy-
[AuL1][CF3SO3] 3. The complex K[AuCl4]ؒ2H2O (0.10 g, 0.25
mmol) was reduced to AuI by 2,2Ј-thiodiethanol (0.06 g, 0.5
J. Chem. Soc., Dalton Trans., 1998, Pages 317–320
317

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mmol) in methanol (20 cm3) for 30 min. Compound L1 (0.15 g,
0.25 mmol) in CH2Cl2 (10 cm3) was added and stirred for 10
min, and then AgO3SCF3 (0.26 g, 1.0 mmol) in methanol (20
cm3) was added to the mixture and stirred for 30 min. Filtration
followed by solvent removal and subsequent recrystallization
from CH2Cl2–hexane afforded complex 3 as colourless crys-
tals. Yield: 0.15 g (81%) (Found: C, 45.78; H, 3.77; N, 1.41.
C36H35AuF3NO3P2S3 requires C, 45.91; H, 3.75; N, 1.49%). 31P-
{1H} NMR: δ 42.91.
Cl
Cl
Ph2PH
LiBun
N
S
S
PPh2
PPh2
S
Ph2PLi
N
Ph2P
SLi
Scheme 1
[ZnL1][CF3SO3]2 4. To a solution containing compound L1
(0.30 g, 0.5 mmol) in CH2Cl2 (20 cm3) was added solid Zn(O3-
SCF3)2 (0.18 g, 0.5 mmol). The resulting solution was stirred at
room temperature for 2 h. Subsequent diffusion of diethyl ether
into the concentrated solution gave complex 4 as air-stable col-
ourless crystals (yield 0.40 g, 77%) (Found: C, 43.95; H, 3.67; N,
1.33. C37H35F6NO3P2S4ZnؒCH2Cl2 requires C, 43.71; H, 3.57;
N, 1.34%). 31P-{1H} NMR: δ 56.53.
[CdL1(O3SCF3)2] 5. The procedure used was similar to that
above, except that Cd(O3SCF3)2 (0.21 g, 0.5 mmol) was used
instead of Zn(O3SCF3)2. Recrystallization of the product from
CH2Cl2–hexane afforded complex 5 as colourless crystals.
Yield: 0.32 g (64%) (Found: C, 43.37; H, 3.49; N, 1.34. C37H35-
CdF6NO6P2S4 requires C, 44.16; H, 3.51; N, 1.39%). 31P-{1H}
NMR: δ 55.09.
X-Ray crystallography
Fig. 1 Perspective view of the cation in [Ag{(Ph2PCH2CH2SCH2)2-
C5H3N}][NO3]ؒH2O, 2ؒH2O. The atoms are shown as 35% thermal
ellipsoids
Intensity data for complexes 2ؒH2O and 5 were collected at
294 K in the variable ω-scan mode on a four-circle diffracto-
meter (Siemens R3m/V) using Mo-Kα radiation (λ = 0.710 73
Å, 50 kV, 25 mA; 2θmin = 3, 2θmax = 55Њ). Empirical absorption
corrections were applied by fitting a pseudo-ellipsoid to the
ψ-scan data of 25 selected strong reflections over a range of 2θ
angles.7a
Structure solution by the direct method yielded the positions
of all non-hydrogen atoms, which were refined using aniso-
tropic thermal parameters. Hydrogen atoms were all generated
geometrically (C᎐H bond lengths fixed at 0.96 Å), assigned
appropriate isotropic thermal parameters, and allowed to ride
on their parent carbon atoms. All the H atoms were held sta-
tionary and included in the structure-factor calculation in the
final stage of full-matrix least-squares refinement. All compu-
tations were performed on an IBM-compatible 486 personal
computer with the SHELTX PC, version 5.03, program
package.7b
a pair of doublets centred at δ 28.73 (J = 20.3) and 28.96
(J = 14.9 Hz). On the basis of literature data for P᎐C coupling
constants8 and the observed chemical shifts for related
phosphine-containing ligands, we assigned the first and second
doublets to the carbon atoms located in the α and β positions,
respectively, with respect to the phosphorus atom. The FAB
mass spectrum showed the molecular ion at m/z = 596, and the
31P-{1H} NMR spectrum exhibited a singlet at δ Ϫ4.54.
Reaction of [Cu(MeCN)4][CF3SO3] or AgNO3 with 1 molar
equivalent of L1 in degassed dichloromethane, followed by
precipitation with diethyl ether, gave [CuL1][CF3SO3] 1 or
[AgL1][NO3] 2, as white solids in good yield. Reaction of equi-
molar amounts of L1 and AuI, generated in situ by the reduction
of K[AuCl4] with 2,2Ј-thiodiethanol in methanol, gave a colour-
less solution at room temperature. Addition of AgO3SCF3 to
the solution precipitated [AuL1][CF3SO3] 3, as a white solid.
The 31P-{1H} NMR spectra of complexes 1 and 2 at 298 K
showed a singlet at δ 34.72 and 43.14, respectively, and no Ag᎐P
coupling was observed for 2. For complex 3 the 31P-{1H} NMR
spectrum displayed a high-frequency shift of 47.4 ppm relative
to the free phosphine. This shift is similar to those of the
complexes [Au{(Ph2PCH2CH2SCH2)2}][PF6] (49.2 ppm) and
[Au{(Ph2PCH2CH2SCH2)2CH2}][PF6] (46.1 ppm),4b both of
which involve averaged P2 co-ordination in solution. In view
of the similarity of these species, we expect that in the solid
state 3 also adopts a similar primary P2 co-ordination about
AuI and a distorted linear geometry.
Information concerning X-ray data collection and structure
refinement of all compounds is summarized in Table 1.
CCDC reference number 186/780.
Results and Discussion
The synthesis of a new thioether-functionalized and pyridine-
based bis(phosphine) ligand, namely 2,6-bis[2-(diphenylphos-
phino)ethylsulfanylmethyl]pyridine (L1), was accomplished in
two steps in good yield, as outlined in Scheme 1. Reaction of
Ph2PLi (prepared ‘in situ’ from Ph2PH and LiBun) with ethylene
sulfide at low temperature gave the lithium 2-diphenylphos-
phinoethanethiolate salt, which then reacted with 2,6-bis-
(chloromethyl)pyridine to give the designed phosphine ligand.
The structure of 2,6-(Ph2PCH2CH2SCH2)2C5H3N, L1, was
Crystals of [AgL1][NO3]ؒH2O suitable for single-crystal X-
ray study were obtained by layering a solution of the complex
in CH2Cl2 at ca. Ϫ20 ЊC with toluene. The structure of the
molecular cation with the atom numbering scheme is depicted
in Fig. 1. The co-ordination geometry around silver() may be
described as a very distorted tetrahedron with a P᎐Ag᎐P angle
of 144.4(1)Њ (Table 2), far higher than the idealized value of
109.5Њ. This is certainly caused by the repulsion between two
phenyl rings [C(26) ؒ ؒ ؒ C(36) 3.690 Å] which has the further
consequence of narrowing the S᎐Ag᎐P bond angles to 80.2(1)
and 81.3(1)Њ. A similar effect has been reported in [Ag(Ph2P-
confirmed by elemental analysis and H, 13C-{1H}, 31P-{1H}
NMR spectroscopy and FAB mass spectrometry. In the H
1
1
NMR spectrum the SCH2C5H3N methylene protons appeared
as a singlet at δ 3.73 and two groups of signals attributed to the
SCH2CP and SCCH2P methylene protons coupled with the
phosphorus atoms were observed at δ 2.50 and 2.26. In the 13C-
{1H} NMR spectrum the SCC5H3N carbon atom appeared as a
singlet at δ 38.56, whereas the SCCP carbon atoms appeared as
318
J. Chem. Soc., Dalton Trans., 1998, Pages 317–320

View Article Online
Table 1 Crystal and structural data for complexes 2ؒH2O and 5
Formula
C35H35AgN2O3P2S2ؒ C37H35CdF6NO6P2S4 5
H2O 2ؒH2O
M
783.6
1006.2
Trigonal
P3221
Crystal system
Space group
a/Å
b/Å
Orthorhombic
P212121
9.875(1)
12.585(5)
28.362(3)
3524.7(12)
4
18.072(3)
18.072(3)
12.099(2)
3425(2)
3
c/Å
U/Å3
Z
F(000)
1608
1.477
0.821
1524
1.464
0.797
Dc/g cmϪ3
µ/cmϪ1
Goodness of fit
No. unique reflections
1.22
4909 (0.027)
1.10
4876 (0.030)
(Rint
)
No. observed reflections 3183
4561
[|F | у 4σ(F)]
No. variables, p
410
0.053
0.087
263
0.049
0.052
Fig. 2 An ORTEP12 view of the [Cd{(Ph2PCH2CH2SCH2)2C5H3N}-
a
RF
2 b
(O3SCF3)2] molecule, 5. The atoms are shown as 35% thermal ellipsoids.
Note that a two-fold symmetry axis passes through the Cd, N and C(6)
atoms
RЈF
¹
a Σ(|Fo| Ϫ |Fc|)/Σ|Fo|. b {w[Σ(|Fo| Ϫ |Fc|)2]/Σ|Fo|2}².
Table 2 Selected bond lengths (Å) and angles (Њ) of complexes 2ؒH2O
and 5
coplanar O(1), S(1), N, S(1a) and O(1a) atoms at the equatorial
sites, and P(1) and P(1a) occupying the axial positions. The
seven-co-ordinate geometry observed in this complex is largely
a result of the constraints imposed by the pentadentate ligand.
Since there is no ligand-field stabilization effect in Cd2ϩ, the
stereochemistry of its complexes is in general determined by
ionic size, electrostatics, and covalent bonding energies.13
Owing to its size, Cd2ϩ commonly has a co-ordination number
of six as in CdCl2, [CdCl2(NH3)2], [CdCl(OH)], K4[CdCl4], CdI2
and Cd(OH)2.14 However, a seven-co-ordinate, distorted pen-
tagonal bipyramidal complex of Cd2ϩ containing a thioether
ligand is known, namely [Cd([15]aneS5)][ClO4]2ؒH2O ([15]-
aneS5 = 1,4,7,10,13-pentathiacyclopentadecane).15
The P(1)᎐Cd᎐S(1) and P(1)᎐Cd᎐N angles are somewhat
acute [79.9(1) and 83.4(1)Њ, respectively], while P(1)᎐Cd᎐S(1a)
and P(1)᎐Cd᎐O(1) are somewhat obtuse [95.6(1) and 97.1(1)Њ].
This distortion is attributable to the geometrical constraints
imposed by the ligand, as the ethylene bridges between S and P
atoms do not allow P(1) and P(1a) to pull away far enough from
each other. The P(1)᎐Cd᎐P(1a) angle of 166.8(1)Њ is accordingly
less than the ideal value of 180Њ.
The P᎐Cd bond length of 2.590(1) Å is close to the sum of
covalent radii for cadmium and phosphorus (1.48 ϩ 1.10 =
2.58 Å)16 and also comparable to 2.602(2) Å found in
[Cd{P(C6H11)3}2][NO3]2ؒCH2Cl2.17 The Cd᎐S bond length of
2.821(1) Å is comparable to those of [Cd([15]aneS5)][ClO4]2ؒ
H2O (Cd᎐Sav 2.76 Å)15 and significantly longer than 2.703(1) Å
in the six-co-ordinate complex [{CdL2Cl2ؒH2O}2] [L2 = 2,6-
bis(ethylsulfanylmethyl)pyridine]18 and four-co-ordinate com-
plex [Cd([16]aneS4)][ClO4]2 (Cd᎐Sav 2.65 Å) ([16]aneS4 =
1,5,9,13-tetrathiacyclohexadecane).19 It has been observed that
in mercury() thioether complexes20 the metal–sulfur bond
lengths are a function of the number of donor atoms. As the
co-ordination number of the metal centre goes up, its bonds
to sulfur are lengthened. Hence it is not surprising that the
seven-co-ordinate complex 5 has such long Cd᎐S bonds com-
pared to those of an analogous six- or four-co-ordinate
complex. The Cd᎐N bond distance of 2.695(3) Å is also longer
than 2.380(3) Å in the six-co-ordinate, dimeric complex
[{CdL2Cl2ؒH2O}2].18
2ؒH2O
Ag᎐P(1)
Ag᎐S(1)
2.455(3)
2.869(3)
Ag᎐P(2)
Ag᎐S(2)
2.448(3)
2.846(3)
P(1)᎐Ag᎐P(2)
P(1)᎐Ag᎐S(2)
S(1)᎐Ag᎐S(2)
144.4(1)
110.5(1)
142.7(1)
P(1)᎐Ag᎐S(1)
P(2)᎐Ag᎐S(1)
P(2)᎐Ag᎐S(2)
80.2(1)
111.2(1)
81.3(1)
5
Cd᎐P(1)
Cd᎐O(1)
2.590(1)
2.455(2)
Cd᎐S(1)
Cd᎐N(1)
2.821(1)
2.695(3)
P(1)᎐Cd᎐S(1)
S(1)᎐Cd᎐O(1)
S(1)᎐Cd᎐N
P(1)᎐Cd᎐P(1a)
O(1)᎐Cd᎐O(1a)
P(1)᎐Cd᎐O(1a)
79.9(1)
75.8(1)
70.1(1)
166.8(1)
69.5(2)
93.8(1)
P(1)᎐Cd᎐O(1)
P(1)᎐Cd᎐N
O(1)᎐Cd᎐N
S(1)᎐Cd᎐S(1a)
P(1)᎐Cd᎐S(1a)
S(1)᎐Cd᎐O(1a)
97.1(1)
83.4(1)
145.2(1)
140.1(1)
95.6(1)
143.7(1)
CH2CH2SEt)2][ClO4] with a P᎐Ag᎐P angle of 148.9(1)Њ.9 The
Ag(1) ؒ ؒ ؒ N(1) distance of 2.689 Å, much longer than the cor-
responding distance of 2.368(6) Å in [AgL2][PF6] [L2 = 6,9,12-
trioxa-3,15-dithia-21-azabicyclo[15.3.1]henicosa-1(21),17,19-
triene],10 indicates that the Ag ؒ ؒ ؒ N interaction is very feeble,
which is consistent with the fact that the nitrogen lone pair does
not point directly toward the silver atom (Fig. 1). The Ag᎐P
distances of 2.455(3) and 2.448(3) Å are within the expected
range for silver tertiary phosphine complexes. The Ag᎐S dis-
tances of 2.869(3) and 2.846(3) Å, which are longer than
2.694(2) Å in [Ag(Ph2PCH2CH2SEt)2][ClO4]9 and 2.589(2) Å
(average) in [Agn(PhSCH2CH2CH2SPh)2n][BF4]nؒ0.5nH2O,11
suggest that the silver ion is weakly bound to the sulfur atoms.
Reactions of M(O3SCF3)2 (M = Zn or Cd) with 1 molar
equivalent of L1 in dichloromethane at room temperature gave
a colourless solution which on addition of diethyl ether gave
[ML1(O3SCF3)2] (M = Zn 4 or Cd 5). The 31P-{1H} NMR
spectra of 4 and 5 at 298 K showed a singlet at δ 56.53 and
55.09, respectively, and no Cd᎐P coupling was observed for 5.
Diffraction-quality crystals of [CdL1(O3SCF3)2] 5 were
obtained by vapour diffusion of diethyl ether into a solution of
the complex in CH2Cl2 at room temperature. A perspective view
of the molecular structure of 5, which possesses a crystal-
lographically imposed two-fold axis passing through Cd, N and
C(6), is illustrated in Fig. 2. The co-ordination geometry about
the cadmium centre is a distorted pentagonal bipyramid, with
Acknowledgements
This work is supported by Hong Kong Research Grants
Council Earmarked Grant Ref. No. CUHK 311/94P and the
National Natural Science Foundation of China.
J. Chem. Soc., Dalton Trans., 1998, Pages 317–320
319

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9 P. D. Bernardo, M. Tolazzi and P. Zanonato, Inorg. Chim. Acta, 1994,
215, 199.
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Received 8th September 1997; Paper 7/06543D
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