Synthesis and structural studies of binuclear platinum(II) complexes with a novel phosphorus-nitrogen-phosphorus ligand

Article abstract of DOI:10.1021/ic020668+

The new pyridinediphosphinite ligand PONOP (1) was synthesized in one step from 2,6-pyridinedimethanol and diphenylchlorophosphane. Reaction of 1 with PtCl₂(PhCN)₂ led to the neutral homobimetallic complex [Pt₂Cl₄(PONOP)₂] (2), where the benzonitriles have been substituted by the phosphorus atoms of 1. The X-ray structure of 2 revealed a metallamacrocycle where the pyridines remained free. Addition of 2 equiv of [Cu(MeCN)₄](BF₄) to 2 led to CuCl and to the binuclear dicationic complex [Pt₂Cl₂(PONOP)₂](BF₄)₂ (3), where chloro ligands have been substituted by pyridine groups. Conversely, reaction of 3 with chloride anions gave back complex 2. Solid-state (X-ray) and solution (NMR) studies indicated that after the transformation of 2 into 3, the platinum centers were brought much closer and the pyridinediphosphinite ligand was stiffened. The methylene NMR protons of 3 were strongly deshielded, and the corresponding proton-phosphorus coupling constants followed a Karplus-type relationship.

Full text of DOI:10.1021/ic020668+

Inorg. Chem. 2003, 42, 2902−2907
Synthesis and Structural Studies of Binuclear Platinum(II) Complexes
with a Novel Phosphorus−Nitrogen−Phosphorus Ligand†
Laurent Barloy,‡ Gre´gory Malaise´,‡ Shailesh Ramdeehul,‡ Claire Newton,‡ John A. Osborn,*,‡,§ and
Nathalie Kyritsakas|
Laboratoire de Chimie des Me´taux de Transition et de Catalyse, UMR 7513 CNRS, and
SerVice Commun des Rayons X, Faculte´ de Chimie, Institut Le Bel, UniVersite´ Louis Pasteur,
4 rue Blaise Pascal, 67070 Strasbourg Cedex, France
Received November 12, 2002
The new pyridinediphosphinite ligand PONOP (1) was synthesized in one step from 2,6-pyridinedimethanol and
diphenylchlorophosphane. Reaction of 1 with PtCl2(PhCN)2 led to the neutral homobimetallic complex [Pt2Cl4-
(PONOP)2] (2), where the benzonitriles have been substituted by the phosphorus atoms of 1. The X-ray structure
of 2 revealed a metallamacrocycle where the pyridines remained free. Addition of 2 equiv of [Cu(MeCN)4](BF ) to
4
2 led to CuCl and to the binuclear dicationic complex [Pt2Cl2(PONOP)2](BF ) (3), where chloro ligands have been
4 2
substituted by pyridine groups. Conversely, reaction of 3 with chloride anions gave back complex 2. Solid-state
(X-ray) and solution (NMR) studies indicated that after the transformation of 2 into 3, the platinum centers were
brought much closer and the pyridinediphosphinite ligand was stiffened. The methylene NMR protons of 3 were
strongly deshielded, and the corresponding proton−phosphorus coupling constants followed a Karplus-type relationship.
Introduction
that the chain length or the bulkiness of the substituents on
phosphorus were of prime importance.3a-d
Polydentate ligands have been widely used in the field of
inorganic and organometallic chemistry. They coordinate
metallic ions either as chelates, yielding monometallic
complexes, or as bridges, yielding polynuclear (especially
dinuclear) complexes. With transition metals, the former
complexes have encountered great success, e.g. in homoge-
neous catalysis.1 The latter have also found extremely diverse
applications in the fields of redox chemistry, catalysis, cluster
chemistry, self-assembly, encapsulation, or biomimetic chem-
istry.2 Several reports have appeared in the literature
concerning the structural and electronic factors that govern
the formation of monomers or dimers upon coordination of
metallic complexes.3 With diphosphines, it was elucidated
We have recently investigated the coordination chemistry
of various achiral trifunctional ligands, such as terpyridines,
triphosphines, or pyridinediphosphines, with transition metals
such as palladium4 or ruthenium.5 In our hands, these ligands
have led to mononuclear complexes, coordinating the metal
in either a bidentate or a tridentate meridional mode. Chiral,
C2-symmetric tridentate ligands have also been devised and
(2) (a) Balch, A. L. Progr. Inorg. Chem. 1994, 41, 239-329. (b)
Steinhagen, H.; Helmchen, G. Angew. Chem., Int. Ed. Engl. 1996,
35, 2339-2342. (c) Olenyuk, B.; Fechtenko¨tter, A.; Stang, P. J. J.
Chem. Soc., Dalton Trans. 1998, 1707-1728. (d) Bosnich, B. Inorg.
Chem. 1999, 38, 2554-2562. (e) Lindner, E.; Veigel, R.; Ortner, K.;
Nachtigal, C.; Steimann, M. Eur. J. Inorg. Chem. 2000, 959-969. (f)
Holliday, B. J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2001, 40, 2022-
2043.
(3) (a) Pryde, A.; Shaw, B. L.; Weeks, B. J. Chem. Soc., Dalton Trans.
1976, 322-327. (b) Al-Salem, N. A.; Empsall, H. D.; Markham, R.;
Shaw, B. L.; Weeks, B. J. Chem. Soc., Dalton Trans. 1979, 1972-
1982. (c) Hill, W. E.; Minahan, D. M. A.; Taylor, J. G.; McAuliffe,
C. A. J. Am. Chem. Soc. 1982, 104, 6001-6005. (d) Manojlovic-
Muir, L.; Muir, K. W.; Frew, A. A.; Ling, S. S. M.; Thomson, M. A.;
Puddephatt, R. J. Organometallics 1984, 3, 1637-1645. (e) van der
Boom, M. E.; Gozin, M.; Ben-David, Y.; Shimon, L. J. W.; Frolow,
F.; Kraatz, H.-B.; Milstein, D. Inorg. Chem. 1996, 35, 5, 7068-7073.
(f) Casares, J. A.; Espinet, P.; Soulantica, K.; Pascual, I.; Orpen A.
G. Inorg. Chem. 1997, 36, 5251-5256. (g) Hii, K. K.; Thornton-Pett,
M.; Jutand, A.; Tooze, R. P. Organometallics 1999, 18, 1887-1896.
† Dedicated to the memory of Jacky Kress.
‡ Laboratoire de Chimie des Me´taux de Transition et de Catalyse.
§ Deceased April 23, 2000. Please address further correspondence to L.
Barloy (Fax: + 33 390-241329. E-mail: barloy@chimie.u-strasbg.fr).
| Service Commun des Rayons X.
(1) For example, see: (a) Kagan, H. B. in ComprehensiVe Organometallic
Chemistry; Wilkinson, G., Stone, F. G. A. Eds.; Pergamon: Oxford,
1982; Vol 8. (b) Brunner, H. Angew. Chem., Int. Ed. Engl. 1983, 22,
897-907. (c) Knowles, W. S. Acc. Chem. Res. 1983, 16, 106-112.
(d) Whitesell, J. K. Chem. ReV. 1989, 89, 1581-1590. (e) Noyori, R.
Asymmetric Catalysis in Organic Synthesis; Wiley: New York, 1994.
2902 Inorganic Chemistry, Vol. 42, No. 9, 2003
10.1021/ic020668+ CCC: $25.00 © 2003 American Chemical Society
Published on Web 04/05/2003

Pt(II) Complexes with a NoWel P-N-P Ligand
evaporated to dryness, and the resulting thick oil was extracted five
times with 25 mL of pentane. Evaporation of the pentane solutions
to dryness led to 1 as a colorless oil (1.52 g, 42% yield). It could
be further purified by distillation through a short path elbow (bp
150 °C/0.01 mmHg). Anal. Calcd for C31H27NO2P2: C, 73.37; H,
5.36; N, 2.76. Found: C, 73.25; H, 5.18; N, 2.57. MS (FAB+, NBA
matrix): m/z 508 ([M + 1]+, 10%), 306 ([M - OPPh2]+, 65%),
230 ([M + 1 - OPPh2 - Ph]+, 10%), 201 (OPPh2+, 100%). IR
(cm-1): 1576, 1592 (pyridine). 31P{1H} NMR (121.5 MHz,
applied to asymmetric homogeneous catalysis by transition
metal complexes.6 Their interest lies in the fact that if the
ligand is coordinated in a tridentate meridional geometry,
the quadrant effect is enhanced in octahedral catalytic
intermediates, and the substrate undergoes a close interaction
with the chiral substituents of the ligand.
As part of our project on the design and application of
trifunctional ligands, we report hereafter the synthesis of the
pyridinediphosphinite 1 as a novel mixed-P,N-donor ligand
and the study of its complexation behavior toward plati-
num(II).
1
CDCl3): δ 116.7 (s). H NMR (300 MHz, CDCl3) δ 4.95 (d, 4H,
3JHP ) 9.3 Hz, CH2), 7.2-7.7 (m, 23H, Har).
Synthesis of Compound 2. A solution of 1 (1.00 g, 1.97 mmol)
in 30 mL of dichloromethane was slowly added at room temperature
to a solution of PtCl2(PhCN)2 (0.930 g, 1.97 mmol) in 50 mL of
dichloromethane. The yellow solution was stirred at room temper-
ature for 1.5 h and filtered. After concentration of the solution to
ca. 50 mL and slow addition of pentane, complex 2 precipitated as
a white powder (1.04 g, 68% yield). It could be recrystallized from
dichloromethane/pentane. Anal. Calcd for C62H54Cl4N2O4P4Pt2: C,
48.14; H, 3.52; N, 1.81. Found: C, 48.01; H, 3.35; N, 1.84. IR
(cm-1): 295, 318 (Pt-Cl), 1576, 1594 (pyridine). 31P{1H} NMR
(121.5 MHz, CD2Cl2): δ 84.7 (s, 1JPPt ) 4201 Hz). 1H NMR (300
Experimental Section
General Procedures. All experiments were carried out under a
nitrogen or argon atmosphere, using a vacuum line or Vacuum
Atmospheres glovebox equipped with a Dri-Train HE-493 inert gas
purifier. Pentane and THF were distilled over sodium and ben-
zophenone, toluene over sodium, and dichloromethane over calcium
hydride under nitrogen immediately before use. 2,6-Bis(hydroxy-
methyl)pyridine (Aldrich) and n-butyllithium (Fluka, 1.6 M solution
in hexanes) were used as received. Diphenylchlorophosphane (95%
min., Strem) was distilled at 170 °C under reduced pressure and
3
MHz, CD2Cl2) δ 4.85 (d, 8H, JHP ) 6.1 Hz, CH2), 6.84 (d, 4H,
3JHH ) 7.8 Hz, Hpyridine meta), 7.34-7.80 (m, 42H, Har).
7
stored under argon. PtCl2(PhCN)2 and [Cu(MeCN)4](BF4)8 were
Synthesis of Compound 3. A solution of [Cu(MeCN)4](BF4)
(45 mg, 0.143 mmol) in 3 mL dichloromethane was added dropwise
at room temperature to a white suspension of 2 (0.11 g, 0.071 mmol)
in 10 mL dichloromethane. After addition of half of the copper (I)
solution, the mixture became clear, and then progressively turned
back to a white, cloudy suspension until the end of the addition.
After stirring at RT for 3 h, the suspension was filtered on Celite.
After concentration of the solution and slow addition of pentane,
complex 2 precipitated as a white powder (82 mg, 70% yield). It
could be recrystallized from dichloromethane/pentane. Anal. Calcd
for C62H54B2Cl2F8N2O4P4Pt2: C, 45.14; H, 3.30; N, 1.70; Cl 4.30;
F, 9.21. Found: C, 44.96; H, 3.21; N, 1.83; Cl 4.20; F, 8.78. MS
(FAB+, NBA matrix): m/z 1475.0 ([M - 2BF4]+, 13%), 738.0
([M - 2BF4]2+, 100%), 702.0 (Pt(1), M+, 21%). IR (cm-1): 307
(Pt-Cl), 1575, 1610 (pyridine). 31P{1H} NMR (202.5 MHz,
prepared following reported procedures. The NMR spectra were
recorded at room temperature (unless otherwise indicated) on Bruker
spectrometers. 1H NMR spectra were recorded at 300.16 MHz (AC-
300 instrument) or 500.13 MHz (ARX-500) and referenced to
SiMe4. 31P{1H} (broadband decoupled) were recorded at 121.51
MHz (AC-300) or 202.46 MHz (ARX-500) and referenced to 85%
aqueous H3PO4; for compound 3, the numbering of the phosphorus
atoms refers to the crystallographic structure (Figure 2). The
assignments given are supported by 2D NMR analysis performed
1
on the ARX-500 spectrometer (COSY, H-31P HMQC). FT-IR
spectra were recorded on a Perkin-Elmer 1600 series spectrometer
on KBr pellets. FAB MS spectra and elemental analyses were
carried out by the corresponding facilities at the Fe´de´ration de
Recherche de Chimie, Universite´ Louis Pasteur, Strasbourg.
2
1
Synthesis of 2,6-Bis[(diphenylphosphinyl)oxymethyl]pyridine
(1). A solution of n-BuLi in hexanes (9.44 mL, 15.1 mmol) was
added dropwise at -78 °C to 2,6-bis(hydroxymethyl)pyridine (1.00
g, 7.19 mmol) partly dissolved in 200 mL of THF, leading to a
purple solution. The solution was stirred at -78 °C for 30 min,
and the temperature was raised to 0 °C. PPh2Cl (2.80 mL, 15.1
mmol) was slowly added to the solution via syringe, after which
the solution turned pale yellow. Stirring was maintained at 0 °C
for 30 min and then at room temperature for 3 h. The solution was
DMSO-d6): δ 86.3 (d, 2P, JPP ) 14 Hz, JPPt ) 3870 Hz, P2),
2
1
1
90.0 (d, 2P, JPP ) 14 Hz, JPPt ) 3760 Hz, P1). H NMR (500
MHz, DMSO-d6) δ 5.69 (dd, 2H, 2JHH ) 13.9 Hz, 3JHP ) 31.5 Hz,
H4), 6.28 (d, 2H, JHH ) 14.1 Hz, H2), 6.67 (dd, 2H, JHH ) 13.7
Hz, 3JHP ) 6.7 Hz, H3), 7.28 (dd, 2H, 2JHH ) 14.2 Hz, 3JHP ) 7.5
Hz, H1), 6.70-8.30 (m, 46H, Har).
2
2
Collection of the X-ray Data and Structure Determination
for 2 and 3. The crystal data of 2 were collected on a CAD4-
MACH3 diffractometer and those of 3 on a Kappa CCD diffrac-
tometer, using monochromated Mo KR radiation (λ ) 0.71073 Å).
Details of data collection parameters and refinements results are
listed in Table 1. The structures were solved using direct methods.
Hydrogen atoms were introduced as fixed contributors at calculated
positions (C-H ) 0.95 Å, B(H) ) 1.3 Beqv)), except for the
solvent molecules. Final difference maps revealed no significant
maxima. All calculations were done using the Nonius OpenMoleN
package.9 Neutral atom scattering factor coefficients and anomalous
dispersion coefficients were taken from a standard source.10
(4) (a) Ramdeehul, S.; Barloy, L.; Osborn, J. A.; De Cian, A.; Fischer, J.
Organometallics 1996, 15, 5442-5444. (b) Barloy, L.; Ramdeehul,
S.; Osborn, J. A.; Carlotti, C.; Taulelle, F.; De Cian, A.; Fischer, J.
Eur. J. Inorg. Chem. 2000, 2523-2532. (c) Barloy, L.; Gauvin, R.
M.; Osborn, J. A.; Sizun, C.; Graff, R.; Kyritsakas, N. Eur. J. Inorg.
Chem. 2001, 1699-1707.
(5) (a) Barloy, L.; Ku, S. Y.; Osborn, J. A.; De Cian, A.; Fischer, J.
Polyhedron 1997, 16, 291-295. (b) Rahmouni, N.; Osborn, J. A.; De
Cian, A.; Fischer, J.; Ezzamarty, A. Organometallics 1998, 17, 2470-
2476.
(6) (a) Sablong, R.; Newton, C.; Dierkes, P.; Osborn, J. A. Tetrahedron
Lett. 1996, 37, 4933-4936. (b) Bellemin-Laponnaz, S.; Coleman, K.
S.; Dierkes, P.; Masson, J.-P.; Osborn, J. A. Eur. J. Inorg. Chem. 2000,
1645-1649.
(7) Uchiyama, T.; Toshiyasu, Y.; Nakamura, Y.; Miwa, T.; Kawaguchi,
S. Bull. Chem. Soc. Jpn. 1981, 54, 181-185.
(8) Kubas, G. J. Inorg. Synth. 1979, 19, 90-92.
(9) OpenMoleN, InteractiVe Structure Solution; Nonius B. V., Delft, The
Netherlands, 1997.
(10) Cromer D. T., Waber J. T., International Tables for X-ray Crystal-
lography; The Kynoch Press: Birmingham, 1974; Vol. IV (a) Table
2.2b; (b) Table 2.3.1.
Inorganic Chemistry, Vol. 42, No. 9, 2003 2903

Barloy et al.
Table 1. Summary of the Crystal and Refinement Data for Compounds
2 and 3
compound
formula
mol wt
space group
a (Å)
2‚2CH2Cl2
C64H58Cl8N2O4P4Pt2
1716.89
P121/n1
11.311(3)
3‚4CH3NO2‚C6H6
C72H72B2Cl2F8N6O12P4Pt2
1972.00
P1h
11.412(1)
12.815(1)
13.718(1)
87.01(6)
82.71(6)
79.45(6)
1955.4(5)
1
b (Å)
c (Å)
15.927(4)
19.080(5)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
105.81(2)
3307(1)
2
1.72
D
calc (g cm-3
)
1.67
wavelength (Å)
0.71073
4.693
294
0.031
0.036
0.71073
3.805
173
0.026
0.045
µ (mm-1
)
Figure 1. Ortep drawing of [Pt2Cl4(PONOP)2] (2) showing 50% prob-
ability thermal ellipsoids. Hydrogen atoms and solvent molecules are omitted
for clarity.
temp (K)
Ra
Rw
b
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(Fo - Fc)2/∑w(Fo)2]1/2
.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Compound 2
Scheme 1
Pt-Cl1
Pt-Cl2
P1-O1
2.348(2)
2.346(2)
1.615(4)
Pt-P1
Pt-P2
P2-O2′
2.219(2)
2.226(2)
1.602(4)
Cl1-Pt-Cl2
Cl1-Pt-P1
Cl1-Pt-P2
Cl2-Pt-P1
Cl2-Pt-P2
88.24(7)
177.67(7)
86.31(6)
89.89(6)
173.96(6)
P1-Pt-P2
95.62(6)
111.18(6)
111.68(6)
121.7(4)
123.2(4)
Pt-P1-O1
Pt-P2-O2′
P1-O1-C13
P2-O2′-C19′
to use high-dilution conditions to synthesize similar diplat-
inamacrocycles,2e this precaution was not necessary in our
case.
Single crystals of complex 2 were obtained by cooling a
saturated CH2Cl2 solution to -20 °C. The X-ray structure
of 2 is shown in Figure 1, and the corresponding bond lengths
and angles are given in Table 2. Complex 2 consists of a
neutral bimetallic molecule where PONOP acts as a bridging
ligand between both platinum centers, forming a large 20-
membered diplatinamacrocycle. Each platinum is coordinated
by two chloro ligands, which point outside the macrocycle,
and two phosphorus atoms in a cis geometry. It seems highly
probable that the cis,cis isomer is the thermodynamic product,
by comparison with analogous platinum complexes.3c,13
Interestingly, the reaction product 2 had the same configu-
ration whether the reagent was cis- or trans-Pt(PhCN)2Cl2.
The pyridines remain uncoordinated, which is consistent
with the stronger affinity of late transition metals toward
phosphorus rather than nitrogen.3g,4b The molecule is cen-
trosymmetric, an inversion center being present between the
pyridines. The planes of the pyridine moieties are parallel
and separated by 3.58(1) Å; their dipolar moments are
antiparallel. No π-stacking is involved, as long as the
pyridines are not positioned one above the other. The
platinum-donor atom bond distances are in good agreement
with the crystallographic data of cis-[(phosphinite)PtCl2]
complexes reported in the literature.11 The Pt-Cl bond
lengths [2.348(2) and 2.346(2) Å] are long, in connection
with the strong trans influence of the P donor atom.14 On
the contrary, the moderate trans influence of the chloro ligand
Results and Discussion
The ligand 2,6-bis[(diphenylphosphinyl)oxymethyl]pyridine
(1) (abbreviated PONOP) has been easily synthesized in one
step with 42% yield from 2,6-bis(hydroxymethyl)pyridine.
The alcohol functions were first deprotonated with n-
butyllithium, and the resulting bis-alkoxide reacted with 2
equiv diphenylchlorophosphane, yielding 1 and lithium
chloride (Scheme 1). Both phosphorus atoms are equivalent;
the chemical shift of their 31P NMR signal (116.7 ppm) lies
in the normal range for a phosphinite.11 The methylene signal
1
on the H NMR spectrum is a doublet at 4.99 ppm with a
proton-phosphorus coupling constant that also falls in the
expected range (9.4 Hz).12
PONOP (1) was converted into the dimeric macrocyclic
complex [Pt2Cl4(µ-PONOP)2] (2) in 68% yield, by reaction
with 1 equiv of Pt(PhCN)2Cl2 in methylene chloride at room
temperature, resulting from the substitution of the labile
benzonitrile ligands by the phosphinites (Scheme 1). The
reaction proceeded cleanly without formation of any mon-
omeric or polymeric material; although Lindner et al. had
(11) Atherton, M. J.; Fawcett, J.; Hill, A. P.; Holloway, J. H.; Hope, E.
G.; Russell, D. R.; Saunders G. C.; Stead, R. M. J. J. Chem. Soc.,
Dalton Trans. 1997, 1137-1147.
(12) Smith, D. J. H. in ComprehensiVe Organic Chemistry; Barton, D. H.
R., Ollis, W. D., Eds.; Pergamon: Oxford, 1979; Vol 2, p 1125.
(13) Armstrong, S. K.; Cross, R. J.; Farrugia, L. J.; Nichols, D. A.; Perry
A. Eur. J. Inorg. Chem. 2002, 141-151.
2904 Inorganic Chemistry, Vol. 42, No. 9, 2003

Pt(II) Complexes with a NoWel P-N-P Ligand
Scheme 2
is at the origin of the rather short Pt-P bond lengths [2.219-
(2) and 2.226(2) Å]. The P1-Pt-P2 angle is larger [95.62-
(6)°] and the Cl1-Pt-Cl2 smaller [88.24(7)°] than the ideal
90°, probably because of mutual steric repulsions of the
phenyl rings borne by each phosphorus atom. The size of
the 20-membered metallacycle is such that the platinum
atoms are located far one from the other, with an intermetallic
distance of 11.543(1) Å.
metallic guest in 2. Precedents exist in the literature of similar
strategies involving metallamacrocycles, which lead to
trinuclear complexes.2a,e,19 We first tried to coordinate a third
dichloroplatinum(II) fragment by the pyridines by allowing
2 equiv of ligand 1 to react with 3 equiv of Pt(PhCN)2Cl2;
yet we were not successful, as this led only to complex 2.
We then chose copper(I) as guest, as bis-coordinate com-
plexes of this metal ion have been reported with ortho-
substituted pyridines.20
However, treatment of complex 2 with excess (2 equiv)
[Cu(MeCN)4](BF4) in CH2Cl2 did not lead to inclusion of
the CuI atom. Instead, CuI removed one chloride atom from
the coordination sphere of each platinum center, the vacant
coordination site being occupied by a pyridine (vide infra).
This led to the dicationic platinum dimer [Pt2Cl2(PONOP)2]-
(BF4)2 (3) in 70% yield and to CuCl (Scheme 2). We
observed by 1H NMR that 2 was completely converted into
the dication [Pt2Cl2(PONOP)2]2+ even if only 1.2 equiv of
[Cu(MeCN)4]+ was used. A possible explanation is that CuCl
can remove a second chloro ligand to yield the [CuCl2]-
anion.21 This hypothesis also allows us to understand why
the reaction mixture, which was at the beginning a white
suspension of 2, became a clear colorless solution after 1
equiv of CuI was added to 2 (see Experimental Section):
the intermediate species was probably the soluble compound
[Pt2Cl2(PONOP)2](CuCl2)(BF4). The addition of the second
equivalent of CuI then led to 3 and precipitation of CuCl,
which resulted from the comproportionation reaction 1.
IR spectroscopy provides confirmation of the structural
features provided by the X-ray diffraction analysis. The
presence of two νPt-Cl signals at 295 and 318 cm-1 in the IR
spectrum of 2 is characteristic of a cis,cis complex.15 The
pyridine ring vibrations16 at 1576 and 1592 cm-1 are
unchanged in comparison with the spectrum of the free ligand
1, which confirms that the pyridines are uncoordinated.
Upon coordination of the phosphorus atoms of 1 to
platinum, the 31P NMR signal is shifted to lower frequency
at 84.7 ppm, as shown on the spectrum of 2. This upfield
1
shift, as well as the large value of JPPt (4201 Hz), is
indicative of a cis coordination,11 in agreement with our
X-ray data. Further confirmation is provided by the 1H NMR
spectrum, because in a trans coordination mode a virtual
triplet would have been expected for the methylene signal.17
Instead, it appears as a doublet; we note that the value of
3JHP (6.1 Hz) is reduced in comparison with that of the free
ligand 1. The 20-membered metallamacrocycle is flexible
enough so that all methylene protons are chemically equiva-
lent at 298 K.
The coordination behavior of PONOP toward PtII sharply
contrasts with that of the closely related ligand 2,6-(diphen-
ylphosphinomethyl)pyridine (PNP):18 the reaction of Pt-
(PhCN)2Cl2 with PNP leads to the mononuclear species
[Pt(PNP)Cl]Cl, where the ligand is tridentate. The chelate
effect of PNP may explain this, as long as two five-
membered metallacycles exist in this latter complex. By
contrast with PNP, ligand PONOP has longer “arms”, which
reduces the chelate effect and favors a bridging coordination
as in 2.
CuCl2- + Cu+ f 2CuClV
(1)
We also observed that zinc(II) triflate could abstract some
chloro ligands from 2 and convert it into [Pt2Cl2(PONOP)2]2+
like copper(I) did; a white precipitate formed, which was
very probably ZnCl2.
The interconversion of 2 into 3 is reversible: addition of
2 equiv of PPh4Cl to compound 3 in DMSO at room
temperature gave back compound 2. This can be interpreted
in terms of competition between Cl- and the pyridine moiety
for coordination of platinum, which is in favor of Cl- in our
case. On the contrary, 3 is stable in DMSO, as shown by
At this stage, our purpose was to take advantage of the
pyridines in the cavity of the macrocycle to encapsulate a
(14) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. ReV. 1973,
10, 335-422.
(19) (a) Huang, Y., Drake, R. J., Stephan, D. W. Inorg. Chem. 1993, 32,
3022-3028. (b) Hiraki, K.; Khono, S.; Onishi, M.; Kuwahara, T.;
Michita, Y. Inorg. Chim. Acta 1996, 245, 243-249.
(20) Sorrell, T. N.; Jameson, D. L. J. Am. Chem. Soc. 1983, 105, 6013-
6018.
(21) Hathaway, B. J. In ComprehensiVe Coordination Chemistry; Wilkinson,
G., Gillard, R. D., McCleverty, J. A., Eds.; Pergamon: Oxford, 1987;
Vol 5, p 584.
(15) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coor-
dination Compounds, 4th ed.; Wiley: New York, 1986; p 326.
(16) Dahlhoff, W. V.; Nelson, S. M. J. Chem. Soc. (A) 1971, 2184-2190.
(17) Verkade, J. G.; McCarley, R. E.; Hendricker, D. G.; King R. W. Inorg.
Chem. 1965, 4, 228-231.
(18) Vasapollo, G.; Nobile, C. F.; Sacco, A. J. Organomet. Chem. 1985,
296, 435-441.
Inorganic Chemistry, Vol. 42, No. 9, 2003 2905

Barloy et al.
connection with the strong trans influence of the phosphinite,
the Pt-N bond distance is rather long [2.142(3) Å]. The P1-
Pt-P2 bond angle has increased from 95.62(6)° (in complex
2) to 100.77(3)°, which is probably related to steric interac-
tions between phenyl groups. Figure 2 indicates clearly that
these phenyls are π-stacked, with their planes nearly parallel
and about 3.3 Å apart.
One “arm” of ligand PONOP is bridging between the
platinum atoms, whereas the other one makes a six-
membered chelate ring in a boat conformation. The Pt-P1-
O1 bond angle, which belongs to this constrained ring, is
smaller than the Pt-P2-O2′ angle [106.46(3)° vs 110.24-
(3)°]. The pyridine ring is tilted with respect to the coordina-
tion plane, with a C14-N1-Pt-P1 torsion angle of 57.95-
(7)°. The Cl atom lies 0.4620(3) Å out of the mean plane
defined by Pt, N1, P1, and P2, 4.8434(3) Å away from Pt′
and roughly on its z axis. Both platinum-chloride vectors
of complex 3 are antiparallel. The 12-membered diplati-
namacrocycle appears almost planar; its atoms display
maximal deviations of 0.2 Å from its mean plane. Espinet
et al. have reported a palladium binuclear complex, the solid-
state structure of which shows a very similar, highly puckered
macrocycle.3f
Figure 2. Ortep drawing of [Pt2Cl2(PONOP)2](BF4)2 (3) showing 50%
probability thermal ellipsoids. Hydrogen atoms, BF4 anions, and solvent
molecules are omitted for clarity.
-
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Compound 3
Pt-Cl
Pt-N1
P1-O1
2.3561(9)
2.139(3)
1.609(2)
Pt-P1
Pt-P2
P2-O2′
2.2260(9)
2.2520(9)
1.611(3)
Cl-Pt-P1
Cl-Pt-N1
Cl-Pt-P2
N1-Pt-P1
N1-Pt-P2
P1-Pt-P2
168.63(7)
87.93(8)
86.10(7)
85.78(8)
172.75(8)
100.77(7)
Pt-P1-O1
106.46(3)
110.24(3)
119.54(8)
120.52(7)
120.7(2)
Pt-P2-O2′
Pt-N1-C14
Pt-N1-C15
P1-O1-C13
P2-O2′-C19′
The 31P NMR spectrum of 3 exhibits two doublets at 86.3
and 90.0 ppm, representative of an AB system; the small
P-P coupling constant (14 Hz) is characteristic of phos-
phorus donor atoms located in a cis position. Both values of
JPtP are significantly smaller than in complex 2 (3870 and
3760 Hz).
123.94(7)
our NMR analyses; therefore, DMSO does not compete with
the pyridine moiety of 1 as a ligand.
Compound 3 is colorless, air-stable, soluble in ni-
tromethane or DMSO, and moderately soluble in dichlo-
romethane or acetone. In comparison with 2, modifications
in the region of the pyridine vibrations (1550-1650 cm-1)
are observed on the IR spectrum of 3. In particular, a new
high-frequency band characteristic of a coordinated pyridine
appears at 1610 cm-1.16
The transformation of 2 into 3 is followed by a general
splitting of the H NMR signals, in connection with a loss
1
of symmetry. In particular, the methylene doublet is split
into four distinct signals, three of them being observable at
low frequency as one doublet (6.28 ppm) and two doublets
of doublets (5.69 and 6.67 ppm). A 2D COSY spectrum of
3 allowed us to detect the fourth one at 7.28 ppm among
the aromatic signals, and to identify the methylene protons
as two pairs of geminally coupled diastereotopic protons.
Single crystals of compound 3 were obtained by slow
diffusion of toluene into a saturated CD3NO2 solution, and
its molecular structure was established by an X-ray diffrac-
tion study (Figure 2). Selected bond distances and angles
are listed in Table 3. The structure of 3 consists of a dinuclear
dicationic complex with unbound tetrafluoroborate anions.
Like 2, 3 displays a crystallographic symmetry center. The
X-ray analysis of 3 reveals a drastic change of the tridimen-
sional structure in comparison with that of 2. Coordination
of the pyridines onto the platinum centers has induced a
double folding of the dimer, with a sharp decrease of the
Pt‚‚‚Pt nonbonding distance to 5.3087(1) Å. Each platinum
is also coordinated by one chloro ligand, which now points
inside the cavity, and two phosphorus atoms in a classical
distorted square-planar geometry. The phosphorus atoms
remain in the cis position as they were in complex 2; the
coordination of pyridine induces therefore no cis-trans
isomerization.
2
The measured gem JHH coupling constants are normal (ca.
14 Hz), whereas 3JHP ranges between extreme values (from
0 up to 31.5 Hz). Applying the extension of the Karplus
relationship to H-C-O-P systems,22 we found a good
3
correlation between the values of JHP and the H-C-O-P
dihedral angles estimated from calculated positions of the
protons in the X-ray structure of 3. This allowed us to assign
the four methylene signals as indicated in Scheme 2. Indeed,
(1) the coupling of H2 with phosphorus is not detectable, in
agreement with a dihedral angle close to 90° (exactly -83°);
(2) a large value of JHP (31.5 Hz) is associated with a nearly
straight angle (-167°) for H4; and (3) intermediate and close
values of both JHP and H-C-O-P angles are found for H1
and H3 (respectively 7.5 Hz/41° and 6.7 Hz/-43°).
In comparison with 2, the methylene protons of PONOP
in 3 are strongly deshielded (0.84 ppm < ∆δ < 2.43 ppm).
The Pt-P1 and Pt-Cl bond lengths [respectively 2.2268-
(9) and 2.3555(9) Å] are almost unchanged in comparison
with 2, but Pt-P2 (in trans position with regard to the
pyridine) is slightly longer [2.2529(9) Å] than Pt-P1. In
(22) Bentrude, W. G.; Setzer, W. N. In Phosphorus-31 NMR Spectroscopy
in Stereochemical Analysis; Verkade, J. G., Quin, L. D., Eds.; VCH:
Deerfield Beach, 1987; Vol. 8, pp 365-389.
2906 Inorganic Chemistry, Vol. 42, No. 9, 2003

Pt(II) Complexes with a NoWel P-N-P Ligand
This probably results from their position relative to the
anisotropic cones of the aromatic groups in the molecule.
Furthermore, the most deshielded methylene protons, viz.
H1 and H2, lie inside the cavity created by the diplatinacycle
and are therefore in a pseudoaxial position with respect to
the platinum centers. The shortest interatomic H‚‚‚Pt dis-
tances estimated from crystallographic data are 3.00 Å (H1)
and 2.88 Å (H2). Such downfield NMR shifts of protons
associated with close H‚‚‚M contacts in d8 metal complexes
have been reported23 and interpreted in terms of paramagnetic
anisotropy of the metal, hydrogen bonding, weakly agostic
interaction, or repulsive interaction.23a,24
ligand that competes reversibly with chloride; this hemilabile
behavior of PONOP is reminiscent of similar systems
reported by Mirkin et al.2f Copper(I) can play the role of a
chloride-abstracting agent; Braunstein et al. have reported
the similar behavior of [Cu(MeCN)4]+, which could break a
Pd-Cl bond.25 We note that, on the contrary, a tetranuclear
Ru2-Cu2 complex has been prepared from [Cu(MeCN)4]+
and a ruthenium carbonyl chloro complex without any
abstraction of the chloro ligands.26
The reversible interconversion of 2 into 3 is accompanied
by a folding of the complex. This folding results in a marked
shortening of the intermetallic distance and a significant
stiffening of PONOP, as shown by NMR and X-ray studies.
We plan to take advantage of this rigidity in asymmetric
catalysis using chiral derivatives of this ligand,6a with
platinum or other platinum metals.
1
The H NMR spectrum of 3 in DMSO-d6 undergoes no
modification up to 386 K; thus, the molecule is not fluxional
in this temperature range. The close agreement between the
NMR and X-ray data suggests that the tridimensional
structure of 3 is roughly the same in solution and in the solid
state. In particular, no conformational equilibrium involving
the methylene groups is taking place. Consequently, the
transformation of 2 into 3 is followed by a marked rigidi-
fication of ligand 1 within the binuclear complex.
Acknowledgment. We thank Michel Pfeffer for critical
reading of the manuscript, Roland Graff for 2D NMR
analysis, and Maurice Coppe and Marie-The´re`se Youinou
for experimental assistance. Financial support of the Centre
National de la Recherche Scientifique is gratefully acknowl-
edged. We are grateful to one of the referees for valuable
suggestions.
Concluding Remarks
The work presented here provides a new insight into the
coordination chemistry of P-N-P-type ligands. We found
that by contrast with 2,6-(diphenylphosphinomethyl)pyridine,
the coordination reaction of the pyridinediphosphinite PONOP
on platinum(II) leads cleanly to a binuclear metallamacro-
cyclic complex. The central pyridine behaves as a hemilabile
Supporting Information Available: NMR data of 3, and X-ray
crystallographic files in CIF format for the crystal structures of 2
and 3. This material is available free of charge via the Internet at
http://www.pubs.acs.org.
IC020668+
(23) (a) Lagunas, M.-C.; Gossage, R. A.; Smeets, W. J. J.; Spek, A. L.;
van Koten, G. Eur. J. Inorg. Chem. 1998, 163-168. (b) Dieleman,
C. B.; Marsol, C.; Matt, D.; Kyritsakas, N.; Harriman, A.; Kintzinger,
J.-P. J. Chem. Soc., Dalton Trans. 1999, 4139-4148.
(24) Hambley, T. W. Inorg. Chem. 1998, 37, 3767-3774 and cited
references.
(25) Braunstein, P.; Luke, M. A.; Tiripicchio, A.; Tiripicchio Camellini,
M. Angew. Chem., Int. Ed. Engl. 1987, 26, 768-770.
(26) Ziessel, R.; Matt, D.; Toupet, L. J. Chem. Soc., Chem. Commun. 1995,
2033-2035.
Inorganic Chemistry, Vol. 42, No. 9, 2003 2907