Synthesis, Structure, and Reactivity of Arylfluoro Platinum(II) Complexes

Article abstract of DOI:10.1021/om030524i

Complexes of the type trans-[PtPhFL₂], where L = PPh ₃ (4), PMe₂Ph (5), were synthesized. Complex 4 was characterized by X-ray crystallography. The equilibrium constant for the substitution of the fluoride trans to phenyl in 4 by Cl^- and I ^- was determined, and the stability sequence follows the normal trend seen in "soft" metal centers: i.e., the Pt has a preference for the halide in the order I > Cl > F; the difference is, however, fairly small. The substitution kinetics follow the usual two-term rate law, and the rate constants for the solvolytic (k₁) and the direct (k ₂) reaction pathways were determined to be k₁ = (9.7 ± 2.4) × 10^-5 s^-1, k₂ = (11.7 ± 0.3) × 10^-2 M^-1 s^-1 and k ₁ = (7.1 ± 4.9) × 10^-5 s^-1, k ₂ = (23.0 ± 1.3) × 10^-2 M^-1 s ^-1 for Cl^- and I^-, respectively. Activation parameters for the solvolytic and direct pathways with Cl^- as incoming ligand are typical for associative processes and were determined to be δHDagger; = 77.8 ± 5.5 kJ mol^-1, δS ^Dagger; = -56 ± 18 J K^-1mol^-1 and δH^? = 67.6 ± 1.8 kJ mol^-1, δS? = -37 ± 6 J K^-1mol^-1, respectively. Complexes 4 and 5 react with Me₃SnPh, and within 2-15 min there is a complete conversion to products. 4 gives a single product, trans-[PtPhMe(PPh₃)₂], which was characterized by X-ray crystallography. 5 gives two products: trans-[PtPhMe(PMe₂Ph) ₂] and trans- [PtPh₂(PMe₂Ph)₂]. Steric effects on the reactivity speak in favor of an associative mechanism. The surprisingly high reactivity for the transmetalations, compared to the substitution reactions, can be explained in terms of an associative mechanism, where a strong, bridging Sn-F interaction stabilizes the transition state. Furthermore, only trans products are formed; i.e., we have an exclusive F-for-R (R = Me, Ph) substitution at these platinum fluoro complexes. Treatment of 4 with phenylacetylene in benzene at room temperature gives the alkynyl complex trans-[PtPh(CCPh)(PPh₃)₂] (8).

Full text of DOI:10.1021/om030524i

Organometallics 2003, 22, 5235-5242
5235
Syn th esis, Str u ctu r e, a n d Rea ctivity of Ar ylflu or o
P la tin u m (II) Com p lexes
Patrik Nilsson, Felix Plamper, and Ola F. Wendt*
Inorganic Chemistry, Department of Chemistry, Lund University, P.O. Box 124,
S-221 00 Lund, Sweden
Received J uly 7, 2003
Complexes of the type trans-[PtPhFL2], where L ) PPh3 (4), PMe2Ph (5), were synthesized.
Complex 4 was characterized by X-ray crystallography. The equilibrium constant for the
substitution of the fluoride trans to phenyl in 4 by Cl- and I- was determined, and the
stability sequence follows the normal trend seen in “soft” metal centers: i.e., the Pt has a
preference for the halide in the order I > Cl > F; the difference is, however, fairly small.
The substitution kinetics follow the usual two-term rate law, and the rate constants for the
solvolytic (k1) and the direct (k2) reaction pathways were determined to be k1 ) (9.7 ( 2.4)
× 10-5 s-1, k2 ) (11.7 ( 0.3) × 10-2 M-1 s-1 and k1 ) (7.1 ( 4.9) × 10-5 s-1, k2 ) (23.0 ( 1.3)
× 10-2 M-1 s-1 for Cl- and I-, respectively. Activation parameters for the solvolytic and
direct pathways with Cl- as incoming ligand are typical for associative processes and were
determined to be ∆Hq ) 77.8 ( 5.5 kJ mol-1, ∆Sq ) -56 ( 18 J K-1mol-1 and ∆Hq ) 67.6
( 1.8 kJ mol-1, ∆Sq ) -37 ( 6 J K-1mol-1, respectively. Complexes 4 and 5 react with
Me3SnPh, and within 2-15 min there is a complete conversion to products. 4 gives a single
product, trans-[PtPhMe(PPh3)2], which was characterized by X-ray crystallography. 5 gives
two products: trans-[PtPhMe(PMe2Ph)2] and trans-[PtPh2(PMe2Ph)2]. Steric effects on the
reactivity speak in favor of an associative mechanism. The surprisingly high reactivity for
the transmetalations, compared to the substitution reactions, can be explained in terms of
an associative mechanism, where a strong, bridging Sn-F interaction stabilizes the transition
state. Furthermore, only trans products are formed; i.e., we have an exclusive F-for-R (R )
Me, Ph) substitution at these platinum fluoro complexes. Treatment of 4 with phenylacetylene
in benzene at room temperature gives the alkynyl complex trans-[PtPh(CCPh)(PPh3)2] (8).
In tr od u ction
Organometallic fluoro complexes are of special inter-
est in catalysis, because likely the metal-fluoro inter-
mediate could play a crucial role in the cleavage and
formation of the strong C-F bond. Fluorocarbons are
reluctant to coordinate to metal centers and are in
general chemically inert, due to the strong C-F bond
and the high electronegativity of fluorine. Hence, orga-
nometallic fluoro complexes are rare in the literature.
It is also known that fluoride can activate organo-silicon
compounds, producing a pentacoordinated silicate, which
is another reason fluorides have received attention in
catalysis. One application is the so-called Hiyama
coupling,6 where organosilanes are used as nucleophiles
in palladium-catalyzed cross-coupling reactions. Fluo-
rides have also been used in Stille cross-couplings to
precipitate insoluble tin-fluoro compounds, thereby
effectively removing the toxic tin byproduct.7 In this
context there is still a lack of understanding of the
reactivity of late-transition-metal fluoro complexes.
Here we report the synthesis of complexes of the type
trans-[PtPhF(PR3)2]; these are among the first organo-
metallic PtII-F complexes to be reported and fully
Very few examples of late-transition-metal complexes
with covalent metal-fluorine bonds have been reported
in the literature.1 There is, however, a growing interest
in the study of these types of complexes due to their
high reactivity,2 relevance to metal-mediated C-F bond
activation,3 and potential use in catalysis.4 Their rare
abundance, compared to the analogous chloro, bromo,
and iodo complexes, stems mainly from two reasons.
First, according to the hard-soft acid-base principle,5
the bond between the “soft” low-valent late-transition-
metal center and the “hard” fluoro ligand is supposed
to be weak. Second, the difficulties in introducing the
fluoro ligand have contributed to troublesome and
sometimes low-yielding synthetic strategies.
* To whom correspondence should be addressed. E-mail:
ola.wendt@inorg.lu.se.
(1) (a) Doherty, N. M.; Hoffman, N. W. Chem. Rev. 1991, 91, 553.
(b) Grushin, V. V. Chem. Eur. J . 2002, 8, 1006-1014.
(2) (a) Vicente, J .; Gil-Rubio, J .; Bautista, D. Inorg. Chem. 2001,
40, 2636. (b) Veltheer, J . E.; Burger, P.; Bergman, R. G. J . Am. Chem.
Soc. 1995, 117, 12478.
(3) (a) Kiplinger, J . L.; Richmond, T. G.; Osterberg, C. E. Chem. Rev.
1994, 94, 373. (b) Hofmann, P; Unfried, G. Chem. Ber. 1992, 125, 659.
(4) Mezzetti, A.; Becker, C. Helv. Chim. Acta 2002, 85, 2686.
(5) (a) Leden, I.; Chatt, J . J . Chem. Soc. 1955, 2936. (b) Ahrland,
S.; Chatt, J .; Davies, N. R. Q. Rev., Chem. Soc. 1958, 12, 265. (c)
Pearson, R. G. J . Am. Chem. Soc. 1963, 85, 3533.
(6) (a) Hiyama, T.; Hatanaka, Y. Pure Appl. Chem. 1994, 66, 1471.
(b) Mateo, C.; Ferna´ndez-Rivas, C.; Echavarren, A. M.; Ca´rdenas, D.
J . Organometallics 1997, 16, 1997.
(7) Diederich, F., Stang, P. J ., Eds. Metal-Catalyzed Cross-Coupling
Reactions; Wiley-VCH: New York, 1998; Chapter 4.
10.1021/om030524i CCC: $25.00 © 2003 American Chemical Society
Publication on Web 11/11/2003

5236 Organometallics, Vol. 22, No. 25, 2003
Nilsson et al.
characterized.8 The reactivity of these complexes toward
organosilanes and organostannanes was investigated
and will be discussed together with a thorough kinetic
investigation of the nucleophilic substitution of the
fluoro ligand in trans-[PtPhF(PPh3)2]. The crystal struc-
tures of this complex and trans-[PtPhMe(PPh3)2] are
also reported.
with benzene and twice with dichloromethane. The combined
organic phases were filtered through Celite, and the solvent
was removed from the filtrate. The brownish crystals were
washed with petroleum ether and recrystallized from dichlo-
romethane and petroleum ether, giving 177 mg (0.217 mmol,
94%) of an off-white product. Anal. Calcd for C42H35FP2Pt: C,
1
61.84; H, 4.32. Found: C, 61.71; H, 4.40. H NMR (CDCl3): δ
3
6.08 (t, 2H), 6.26 (t, 1H), 6.59 (d, 2H, J Pt-H ) 50 Hz), 7.22-
7.36 (m, 18H), 7.53-7.59 (m, 12H). 31P{1H} NMR (CDCl3): δ
1
2
23.7 (d, J Pt-P ) 3269 Hz, J P-F ) 19 Hz). 19F NMR (CDCl3):
Exp er im en ta l Section
δ -107.6 (t, J Pt-F ) 399 Hz, J P-F ) 16 Hz). IR (cm-1) 416
(ν(Pt-F)).
1
2
Gen er a l P r oced u r es a n d Ma ter ia ls. All experiments
involving air-sensitive compounds were carried out using
standard high-vacuum-line or Schlenk techniques or in a
glovebox under nitrogen. Unless otherwise stated, all reagents
and solvents were of the best quality available and used as
received from Aldrich. Tetrabutylammonium chloride (J anssen
Chimica) and iodide (Merck) were recrystallized,9 dried in
vacuo, and stored under nitrogen prior to use. cis-/trans-[PtCl2-
(SMe2)2] (1) was prepared according to the method of Cox et
al.,10 and trans-[PtPhCl(SMe2)2] (2) was prepared according
to the method of Otto,11 using a modification of the procedure
developed by Kukushkin et al.12 trans-[PtPhCl(PPh3)2] (3) was
conveniently prepared from 2 by the substitution of SMe2 by
PPh3. This procedure has also been described by Otto and has
been used in the synthesis of the corresponding trans-[PtCl2-
(PPh3)2] complex.13 Using the same procedure, the correspond-
ing iodo complexes, trans-[PtPhI(L)2] (L ) PMe2Ph, PPh3),
were prepared and their NMR data were in agreement with
those in the literature.14 Elemental analyses were performed
by H. Kolbe Mikroanalytisches Laboratorium, Mu¨lheim an der
Ruhr, Germany. IR spectra were recorded as polyethylene
pellets on a Bio-Rad FTS 6000 FT-IR spectrometer. Fast atom
bombardment (FAB) mass spectroscopic data were obtained
on a J EOL SX-102 spectrometer using 3-nitrobenzyl alcohol
as matrix.
tr a n s-[P tP h F (P Me2P h )2] (5). The synthesis was per-
formed in accordance with the procedure described for complex
4. The starting compound was the corresponding iodo complex,
trans-[PtPhI(PMe2Ph)2] (6). The product was isolated as a
1
yellow oil, which resisted further purification. H NMR (CD2-
2
3
Cl2 at 298 K): δ 1.44 (t, 12H, J P-H ) 6.0 Hz, J Pt-H ) 30 Hz),
3
6.64-6.73 (m, 3H, o-, p-H, Pt-Ph), 6.95-7.05 (m, 2H, J Pt-H
) 60 Hz, m-H, Pt-Ph), 7.30-7.51 (m, 6H), 7.55-7.70 (m, 4H).
31P{1H} NMR (CD2Cl2/C6H6 at 277 K): δ 4.3 (d, J Pt-P ) 2983
1
Hz, J P-F ) 24 Hz). 19F NMR (CD2Cl2 at 298 K): δ -161 (bs).
2
MS (FAB+): m/z 548 [PtPh(PMe2Ph)2+], 686 [PtPh(PMe2Ph)3+].
tr a n s-[P tP h Me(P P h 3)2] (7). A 22.2 mg (27 µmol) portion
of complex 5 was dissolved in 10 mL of dry dichloromethane
in a Schlenk flask under nitrogen. Seven microliters of Me3-
SnPh was added, and the solution was allowed to stand
overnight before evaporation of the solvent gave the product.
It was washed with n-hexane and dried under vacuum.
Recrystallization from dichloromethane and n-pentane gave
11.8 mg (14.5 µmol, 53%) of the product. Anal. Calcd for
C
43H38P2Pt: C, 63.62; H, 4.72. Found: C, 63.47; H, 4.64. 1H
NMR (CD2Cl2): δ -0.57 (t, 3H, 2J Pt-H ) 48 Hz, 3J P-H ) 6 Hz),
3
6.23-6.29 (m, 3H, o-, p-H, Pt-Ph), 6.7-6.9 (m, 2H, J Pt-H
)
30 Hz, m-H, Pt-Ph), 7.1-7.6 (m, 30H). 31P{1H} NMR (CD2-
1
Cl2): δ 29.7 (s, J Pt-P ) 3223 Hz).
1
NMR Mea su r em en ts. H, 31P, and 19F NMR spectra were
tr a n s-[P tP h (CtCP h )(P P h 3)2] (8). A 4.3 mg (5.3 µmol)
portion of complex 4 was almost completely dissolved in
benzene in a J . Young NMR tube. Approximately 25 µL (150
µmol) of degassed phenylacetylene was added, and the reaction
mixture was left for 1 h at room temperature before the volatile
substances were removed under reduced pressure. Washing
with acetone and drying in vacuo gave a few milligrams of
white crystals. Anal. Calcd for C50H40P2Pt: C, 66.88; H, 4.49.
Found: C, 66.3; H, 4.5. 1H NMR (CD2Cl2): δ 6.17-6.31 (m,
4H, m-H, CtC-Ph/Pt-Ph), 6.62-6.66 (m 2H, p-H, CtC-Ph/
Pt-Ph), 6.82-6.85 (m, 4H, o-H, CtC-Ph/Pt-Ph), 7.22-7.34
(m, 18H, o-/p-H P-Ph), 7.54-7.56 (m, 12H, m-H, P-Ph). 31P-
recorded on a Varian Unity 300 spectrometer working at
299.79 MHz (1H). The 13C and 2D spectra were recorded on a
Bruker DRX 400 working at 100.6 MHz (13C). Chemical shifts
are given in ppm downfield from TMS using residual solvent
peaks (1H, 13C NMR) or H3PO4 (31P NMR, δ 0) and CFCl3 (19F
NMR, δ 0) as external references. The temperature was
measured using the temperature-dependent shift of the CH2
and OH protons of ethylene glycol.
tr a n s-[P tP h F (P P h 3)2] (4). A Schlenk flask was charged
with 193 mg (0.232 mmol) of complex 3 and 76.7 mg (0.605
mmol) of AgF (Merck). The flask was evacuated and refilled
with nitrogen, and approximately 30 mL of benzene was added.
After the addition of approximately 10 drops of chlorobenzene,
the flask was shaken and placed in a sonication bath in the
absence of light. After 36 h the reaction mixture was filtered
and the precipitate (residual silver) was washed three times
1
{1H} NMR (C6D6): δ 24.6 (s, J Pt-P ) 2979 Hz). 13C{1H} NMR
2
(CDCl3): δ 115.3 (t, 1C, J P-C ≈ 20 Hz, Pt-CtC), 116.1 (s,
3
1C, Pt-CtC), 128.0 (vt, 12C, J P-C ) 5 Hz, 12C, o-C, P-Ph),
1
2
130.1 (s, 6 C, p-C, P-Ph), 132.0 (vt, J P-C ) 14 Hz, J Pt-C
)
2
56 Hz, 6C, i-C, P-Ph), 135.2 (vt, J P-C ) 6 Hz, 12C, m-C,
P-Ph), 120.8, 124.4, 127.37, 127.44, 131.1, 139.9 (s, Pt-Ph/
tC-Ph), 129.8 (s, 1C, i-C, tC-Ph), 157.7 (s, J Pt-C ≈ 15 Hz,
1
(8) (a) McAvoy, J .; Moss, K. C.; Sharp, D. W. A. J . Chem. Soc. A
1965, 1376. (b) Howard, J .; Woodward, P. J . Chem. Soc., Dalton Trans.
1973, 1840. (c) Coulson, D. R. J . Am. Chem. Soc. 1976, 98, 3111. (d)
Rusell, D. R.; Mazid, M. A.; Tucker, P. A. J . Chem. Soc., Dalton Trans.
1980, 1737.
(9) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon Press: Oxford, England, 1988.
(10) Cox, E. G.; Saenger, H.; Wardlaw, W. J . Chem. Soc. 1934, 182.
(11) Otto, S. Structural and Reactivity Relationships in Platinum-
(II) and Rhodium(I) Complexes; Thesis, University of The Orange Free
State, Bloemfontein, South Africa, 1999; Chapter 3.
1C, i-C, Pt-Ph).
Rea ction of 4 a n d 5 w ith Sila n es a n d Sta n n a n es. In a
typical experiment, a J . Young NMR tube was loaded with the
platinum fluoro complex and solvent. The reaction mixture was
thermostated prior to addition of an excess of the silane or
1
the tin compound, and the reaction was monitored using H,
31P, or 19F NMR spectroscopy. In most cases the products were
not separated and isolated but characterized in situ.
(12) (a) Clark, H. C.; Dixon, K. R. J . Am. Chem. Soc. 1969, 91, 596.
(b) Kukushkin, V. Y.; Lo¨vqvist, K.; Nore´n, B.; Oskarsson, Å.; Elding,
L. I. Phosphorus, Sulfur Silicon Relat. Elem. 1992, 73, 253. (c) Kapoor,
P.; Kukushkin, V. Y.; Lo¨vqvist, K.; Oskarsson, Å. J . Organomet. Chem.
1996, 517, 71.
(13) J ohansson, M. H.; Otto, S. Acta Crystallogr. 2000, C56, e12.
(14) (a) Eaborn, C.; Kandu, K.; Pidcock, A. J . Chem. Soc., Dalton
Trans. 1981, 933. (b) Appleton, T. G.; Clark, H. C.; Manzer, L. E. J .
Organomet. Chem. 1974, 65, 275. (c) Mintcheva, N.; Nishihara, Y.;
Mori, A.; Osakada, K. J . Organomet. Chem. 2001, 629, 61.
Str u ctu r e Deter m in a tion . Crystal data and details of the
data collection are given in Table 1. The intensity data sets
for 4 and 7 were collected at 293 K with a Bruker SMART
CCD system using ω-scans and a rotating anode with Mo KR
radiation (λ ) 0.710 73 Å).15 The intensities were corrected
(15) BrukerAXS, SMART, Area Detector Control Software; Bruker
Analytical X-ray Systems, Madison, WI, 1995.

Arylfluoroplatinum(II) Complexes
Organometallics, Vol. 22, No. 25, 2003 5237
Ta ble 1. Cr ysta l Da ta a n d Deta ils of Da ta
Collection a n d Refin em en t
Sch em e 1
4
7
chem formula
Mr
cryst syst
space group
a/Å
C
42H35FP2Pt
C43H38P2Pt
811.79
monoclinic
P21/c
15.4989(12)
12.0592(9)
20.2752(15)
110.864(2)
3541.0(5)
4
1.523
4.682
1.41-31.75
34 866
10 998 (Rint
0.0662)
815.75
orthorhombic
Pbca
11.532(2)
23.943(5)
25.042(5)
90
6914(2)
8
1.567
4.186
1.63-32.07
63 546
11 202 (Rint
0.188)
exchange,21 we obtained 4 from trans-[PtPhI(PPh3)2] (9)
in good yield (cf. Scheme 1). Complex 4 was also
obtained directly from the chloro complex 3 with AgF
under sonication. This latter procedure afforded 4 in
excellent yield, and the complex was characterized by
NMR spectroscopy, elemental analysis, and X-ray crys-
tallography (vide infra).
b/Å
c/Å
â/deg
V/Å3
Z
D
calcd/g cm-3
µ/mm-1
θ range/deg
Complex 5 was successfully synthesized from the
corresponding iodo complex, 6. It was isolated as a
yellow oil, which resisted further purification and was
characterized by NMR spectroscopy.
no. of rflns collected
no. of unique rflns
)
)
no. of params
R(F)a, Rw(F2)b (I > 2σ(I))
Rw(F2) (all data)
Sc
412
416
0.0517, 0.0637
0.0767
0.969
0.0371, 0.0628
0.0724
31P NMR data in dichloromethane solvent confirm the
0.982
1
trans configuration for complexes 4 and 5 with J Pt-P
R ) ∑(|Fo| - |Fc|)/∑|Fo|. Rw ) [∑w(|Fo| - |Fc|)2/∑|Fo| ]1/2
.
c S
a
b
2
coupling constants of 3269 and 2983 Hz, respectively.
These values are larger than those of the corresponding
chloro complexes (3157 and 2868 Hz), indicating a low
demand for the Pt 6s orbital by the polar Pt-F bond.22
) [∑w(|Fo| - |Fc|)2/(m - n)]1/2
.
for Lorentz, polarization, and absorption effects using SAD-
ABS.16 In both structures the first 50 frames were collected
again at the end to check for decay; no decay was observed.
All reflections were integrated using SAINT.17 Both structures
were solved by Patterson methods and refined by full-matrix
least-squares calculations on F2 using SHELXTL 5.1.18 Non-H
atoms were refined with anisotropic displacement parameters.
Hydrogen atoms were constrained to parent sites, using a
riding model. The crystals of 4 were weak scatterers, giving
rise to a large fraction of weak reflections and thus a large
Rint value.19
1
2
The presence of J Pt-F and J F-P coupling constants in
the 31P and 19F NMR spectra confirm the presence of a
Pt-F bond in both complexes also in solution. There is
no indication of any solvolysis of 4 in dichloromethane,
chloroform, or THF. Complex 5, however, having a less
sterically hindered environment, is subject to some
dynamic behavior in dichloromethane solution. At room
2
temperature the J F-P coupling is not resolved in the
31P NMR spectrum, but when the temperature is
lowered to ca. 4 °C, the peak sharpens and splits into
the expected doublet. There is no sign of any solvolysis
product in the spectrum, thus indicating that also for 5
the solvolytic equilibrium is shifted far to the fluoro
complex. The stability to air and moisture is good for
both complexes. In solution there is no sign of decom-
position in the presence of air and moisture, and in the
pure state the compounds can be kept at ambient
temperature and under air for a very long time.
Kin etics. The kinetic experiments for the substitution
reactions were performed on
a Varian Cary 300 UV/vis
spectrophotometer. The substitutions with chloride or iodide
as nucleophile were studied in tetrahydrofuran by observing
the change in absorbance at 250 and 315 nm, respectively. All
reactions were studied under pseudo-first-order conditions
with at least a 10-fold excess of the nucleophile ((0.8-11.9) ×
10-3 mol dm-3) with respect to the complex ((2-4) × 10-5 mol
dm-3). Stock solutions of the nucleophile were prepared daily,
whereas the stock solutions of complexes 3 and 4 were stored
for 5 days at the maximum. The kinetic traces were fitted to
single exponentials using the software provided by Varian,20
resulting in observed rate constants at different concentrations
of incoming ligand. Variable-temperature experiments were
performed between 288 and 318 K. Complete data are reported
in the Supporting Information.
Single crystals of 4 suitable for X-ray diffraction were
obtained by slow evaporation of a dichloromethane solu-
tion of the complex in a pentane bath. The X-ray deter-
mination confirms the molecular structure of 4 (cf.
Figure 1). Selected bond distances and angles are given
in Table 2. The complex has a distorted-square-planar
coordination geometry with angles ranging from 85.9(1)
to 92.9(2)°; the maximum deviation from a least-squares
plane through PtP2CF is 0.045 Å. Only a few examples
of PtII-F bond distances are available in the litera-
ture.8b,8d These Pt-F bonds are trans to a tertiary
phosphine and are significantly shorter (by almost 0.1
Å) than that observed in complex 4, presumably due to
the higher trans influence of the phenyl ligand. How-
ever, the difference between the Pt-F bond in cis-
[PtF(CH(CF3)2)(PPh3)2] (2.03 Å) and that in 4 is larger
than one would expect on the basis of similar trans
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of F lu or o Com -
p lexes. Late-transition-metal fluoro complexes are
scarce in comparison to complexes of the heavier
halogens. Lately, however, a number of methods have
been developed for the synthesis of Pd-F complexes.
Applying one of these, the ultrasound promoted I/F
(16) G. M. Sheldrick, SADABS, Program for Absorption Correction;
University of Go¨ttingen, Go¨ttingen, Germany, 1996.
(17) BrukerAXS, SAINT, Integration Software; Bruker Analytical
X-ray Systems, Madison, WI, 1995.
(18) Sheldrick, G. M. SHELXTL5.1, Program for Structure Solution
and Least-Squares Refinement; University of Go¨ttingen, Go¨ttingen,
Germany, 1998.
(19) Wiess, M. S.; Hilgenfeld, R. J . Appl. Crystallogr. 1997, 30, 203.
(20) Varian Cary WinUV, Software manual; Varian Australia Pty
Ltd, 1997.
(21) Pilon, M. C.; Grushin, V. V. Organometallics 1998, 17, 1774.
(22) The complex trans-[PtPhCl(PMe2Ph)2] has also been synthe-
sized, and the NMR data were in agreement with those in the
literature: Cross, R. J .; Wardle, R. J . Chem. Soc. A 1970, 840.

5238 Organometallics, Vol. 22, No. 25, 2003
Nilsson et al.
F igu r e 2. Equilibrium absorbance as a function of iodo
concentration at [Cl-] ) 6.78 × 10-5 mol dm-3 and [3] )
1.76 × 10-5 mol dm-3. T ) 298 K.
understand the reactivity of the Pt-F bond, especially
in light of the extensive knowledge about substitution
reactions in platinum(II) complexes. Complex 4 reacts
with various anionic nucleophiles, substituting the
fluoro ligand. Thus, treatment of 4 with 1 equiv of Cl-
or I- in THF is complete in ca. 3 h, as indicated by 31P
NMR spectroscopy, and gives 3 and 9 as the sole
products of reaction 1. No intermediates were identified.
F igu r e 1. Diamond drawing with atomic numbering of
the molecular structure of complex 4. The ellipsoids denote
30% probability.
Ta ble 2. Selected Cr ysta llogr a p h ic Dista n ces (Å)
a n d An gles (d eg) w ith Estim a ted Sta n d a r d
Devia tion s
trans-[PtPhY(PPh3)2] + X- f
trans-[PtPhX(PPh3)2] + Y- (1)
4 (E ) F)
7 (E ) C7)
Distances
2.2975(14)
2.2957(13)
1.978(5)
2.117(3)
1.824(5)
1.816(5)
1.829(5)
1.815(6)
1.819(5)
1.820(5)
To our knowledge, this is the first substitution reaction
of a Pt(II) complex where F- is the leaving ligand, and
we decided to pursue a more detailed investigation of
this reaction.
Pt1-P1
Pt1-P2
Pt1-C1
Pt1-E
P1-C11
P1-C21
P1-C31
P2-C41
P2-C51
P2-C61
2.2730(10)
2.2816(10)
2.058(4)
2.226(4)
1.840(4)
1.819(4)
1.816(4)
1.815(4)
1.826(4)
1.821(4)
According to NMR measurements in THF the equi-
librium constant, Ke, for reaction 1 with Y ) F- and X
) Cl- is around 4, thus indicating that the position of
the equilibrium is to the right even at low concentra-
tions of nucleophile. In the case where Y ) F-, Cl- (the
latter included for comparative purposes) and X ) I-,
NMR measurements were of limited use because of
problems of solubility of the nucleophile in the fairly
high concentration range that was needed in the NMR
experiments (compared to UV/vis measurements). There-
fore, the equilibrium constant was determined by mea-
suring the absorbance at different chloride and iodide
concentrations for reaction 1 with Y ) Cl- and X ) I-.
Equation 2, where ꢀM (the extintion coefficient of 9 at
Angles
P1-Pt1-C1
P2-Pt1-C1
P1-Pt1-E
P2-Pt1-E
92.92(15)
92.80(15)
85.92(9)
88.34(9)
93.68(10)
90.22(10)
86.45(10)
90.04(10)
influence comparisons in Pt-Cl complexes.23 One pos-
sibility is that the π-acceptor properties of the phosphine
are more pronounced in the fluoro complex, since the
fluoride is a better π-donor.1,4 This push/pull interaction
would result in a relative strengthening of the Pt-F
bond in cis-[PtF(CH(CF3)2)(PPh3)2], giving it some π-char-
acter. The phenyl group in 4, on the other hand, is
almost perpendicular (71.5°) to the coordination plane;
thus, any π-interaction in the Pt-C bond is probably
weak. Needless to say, the limited data on Pt-F bonds
preclude any far-reaching conclusions. Tables giving
detailed crystallographic data, atomic positional param-
eters, and bond lengths and angles in the CIF format
are given in the Supporting Information.
A0[Cl-] + ꢀMKe[I-]CPt
A )
(2)
[Cl-] + Ke[I-]
the path length used) and Ke are the adjustable param-
eters, was fitted to the data. In this equation A0 is the
absorbance before reaction and CPt is the total concen-
tration of platinum: i.e., complexes 3 and 9 together.
The fit (Figure 2) gave Ke ) 11.6 ( 3.9. The stability in
the trans-[PtPhX(PPh3)2] series is thought to increase
on going down the halogen group according to conven-
tional wisdom, as expressed in, for example, the HSAB
concept.5 Lately, however, this has been shown to not
always be true in nonpolar solvents and with noninno-
cent spectator ligands. Thus, the stability in methylene
chloride of the corresponding palladium complexes,
Su b st it u t ion R ea ct ion s. Substitution reactions
seemed like a reasonable starting point when trying to
(23) The difference between
a Pt-Cl bond trans to a tertiary
phosphine and one trans to a phenyl group is approximately 0.05 Å.
See: (a) Conzelmann, W.; Koola, J . D.; Kunze, U.; Strahle, J . Inorg.
Chim. Acta 1984, 89, 147. (b) J ohansson, M. H.; Malmstro¨m, T.; Wendt,
O. F. Inorg. Chim. Acta 2001, 316, 149.

Arylfluoroplatinum(II) Complexes
Organometallics, Vol. 22, No. 25, 2003 5239
Ta ble 4. Activa tion P a r a m eter s for th e Solvolytic
(k1) a n d Dir ect (k2) P a th w a ys of Rea ction 1 w ith
Com p lex 4 a n d Ch lor id e a s En ter in g Liga n d in
THF Solven ta
∆Hq/kJ mol-1
∆Sq/J K-1 mol-1
k1 path
k2 path
77.8 ( 5.5
67.6 ( 1.8
-56 ( 18
-37 ( 6
a
A weighted linear regression has been used to obtain the most
accurate activation parameters. Each point has been given a
weighting inversely proportional to the corresponding variance.
Sch em e 2
F igu r e 3. Observed pseudo-first-order rate constants for
reaction 1 as a function of nucleophile concentration in THF
at 298 K: (O) X ) I and [4] ) 3.8 × 10-5 mol dm-3; (0) X
) Cl and [4] ) 2.1 × 10-5 mol dm-3; (9) X ) I and [3] )
1.8 × 10-5 mol dm-3
.
Ta ble 3. Ra te Con sta n ts for Rea ction 1 a t 25 °C in
THF Solven t
nucleophile
Cl-
I-
Tables of all observed rate constants as a function of
temperature and concentration are given in the Sup-
porting Information.
complex 105k1/s-1 102k2/M-1 s-1 105k1/s-1 102k2/M-1 s-1
3
4
9.0 ( 2.7
7.1 ( 4.9
12.9 ( 0.6
23.0 ( 1.3
Scheme 2 depicts the classical substitution mecha-
nism involving a solvent species (10). The rate law
derived from this scheme, using the steady-state ap-
proximation for the solvento species, results in a rate
law of the form of eq 3. The alternative explanation for
the intercept is a reversible reaction, but the equilibrium
constants allowed us to compare the intercept with a
calculated rate constant for the reverse reaction, indi-
cating that the reversible reaction can be excluded
under the experimental conditions used. On the basis
of this evaluation and the activation parameters, the
intercept and slope are interpreted as associative at-
tacks on the metal center by the solvent and nucleo-
phile, respectively.
9.7 ( 2.4
11.7 ( 0.3
trans-[PdPhX(PPh3)2], was shown to be opposite: i.e.,
the stability decreased on going down group 17.24
Likewise, trans-[Pt(SiPh3)I(PMe2Ph)2] was shown to be
less stable than the corresponding chloro and bromo
complexes in acetonitrile.25 In the present case the
conventional stability sequence is obviously followed so
that the preference for the Pt center decreases in the
order F < Cl < I. This reversed order as compared to
that for palladium is probably due to the higher solva-
tional power of THF (as compared to CH2Cl2, for
example), which will give a stronger solvation of the
smaller free halides, thus stabilizing the free halides
in the order F > Cl > I. It should be noted that the order
of stability between the various halide complexes is that
expected for a “soft” metal center, but the difference is
small.
The intrinsic reactivities of 3 and 4 (as displayed by
k1) are the same within experimental error. Thus, there
is nothing to suggest that the Pt-F is more susceptible
to solvolysis than other halides, as observed for example
for the Ir-F bond.2b On the other hand, 4 displays a
slightly higher nucleophilic discrimination than 3 as
seen from the higher k2 value. This could be explained
by the smaller size of the fluoride or the higher elec-
tronegativity giving a more electrophilic metal center,
but one should keep in mind that a factor of 2 higher
reactivity on going from chloride to iodide as an incom-
ing nucleophile speaks in favor of a very open transition
state also for 4; this is in keeping with the activation
parameters, which show that the enthalpy is the
dominating contribution to the activation barrier.
The kinetics of reaction 1 was studied using high
nucleophile concentration to ensure first-order condi-
tions and to avoid reversibility. Plots of the observed
first-order rate constant vs ligand concentration are
linear with intercepts. The usual two-term rate law, eq
3, was fitted to the data (cf. Figure 3). Values of the
rate ) (k1+ k2[X-])[Pt]
(3)
rate constants k1 and k2 are given in Table 3.
Enthalpies and entropies of activation were deter-
mined for chloride as incoming ligand by fitting the
Eyring equation to the first- and second-order rate
constants, k1 and k2, at different temperatures. These
first- and second-order rate constants were obtained as
slopes and intercepts from plots of the observed rate
constants vs concentration of chloride at different tem-
peratures. Values of ∆Hq and ∆Sq are given in Table 4.
Tr a n sm eta la tion Rea ction s. The reaction of com-
plex 4 or 5 with Me3SnPh was studied in CD2Cl2 at room
temperature by 1H and 31P NMR spectroscopy (cf.
Scheme 3). Complex 4 reacts with Me3SnPh, and within
15 min there is a complete conversion to a single
product, complex 7. It was fully characterized by NMR
spectroscopy, elemental analysis, and X-ray crystal-
1
lography. It displays a J Pt-P value of 3223 Hz, typical
(24) Flemming, J . P.; Pilon, M. C.; Borbulevitch, O. Y.; Antipin, M.
Y.; Grushin, V. V. Inorg. Chim. Acta 1998, 280, 87.
of a trans compound, and in the 1H NMR spectrum there
(25) Wendt, O. F.; Elding, L. I. Inorg. Chem. 1997, 36, 6028.
is a triplet with platinum satellites at -0.57 ppm

5240 Organometallics, Vol. 22, No. 25, 2003
Nilsson et al.
Ta ble 5. NMR Da ta for Com p ou n d s 11-15
chem shift/δ (multiplicity,
nucleus
1H
coupling const/Hz, assignt)a
3
3
11
12
0.35 (dd, 3H, J H-P ) 6.0, J H-P ) 9.0),
6.05-6.71 (m, 5H), 6.97-7.60 (m, 30H)
31P{1H} 26.4 (d, J Pt-P ) 1725, J P-P ) 10.9),
1
2
1
2
27.7 (d, J Pt-P ) 2003, J P-P ) 10.9)
1H
6.30-6.50 (m, 10H), 7.00-7.62 (m, 30H)
31P{1H} 20.8 (s, J Pt-P ) 1762)
1
2
3
13b 1H
-0.19 (t, 3H, J Pt-H ) 50, J P-H ) 6 Hz, Pt-Me),
2
3
1.22 (vt, 12H, J P-H ) 3, J Pt-H ) 42, P-Me),
6.72-6.77 (m, 2H, Pt-Ph)
31P{1H} -8.3 (s, J Pt-P ) 2898)
1
1
14
15
31P{1H} -5.5 (s, J Pt-P ) 2916)
31P{1H} -14.8 (s, J Pt-P ) 1754)
1
a
The solvent is CD2Cl2 unless stated otherwise. The assignment
is only displayed for clarification when necessary. b Not all protons
could be assigned due to interference with protons from the tin
compound.
1.978(5) Å in 4. The Pt-C(methyl) distance in 7 is
substantially longer at 2.226(4) Å. Again, this is in line
with what one would expect, and it corresponds to the
difference in s character for the two bonds; the higher
s character gives a stronger and, hence, shorter bond.
This is also manifested in the 31P NMR spectrum of 11,
F igu r e 4. Diamond drawing with atomic numbering of
the molecular structure of complex 7. The ellipsoids denote
30% probability.
1
where the J Pt-P coupling constant trans to the Pt-
C(sp3) bond is some 275 Hz higher than that trans to
the Pt-C(sp2) bond. Due to the high trans influence of
hydrocarbyl ligands, a cis disposition is usually the most
stable form, and there are not many Pt-methyl bond
distances trans to other hydrocarbyl ligands reported
in the literature. The PtII-C(methyl) distance in 7 is
the second longest reported in the literature; the only
one longer is one of the chemically equivalent Pt-C
distances in (2,2-diethyl-1,3-bis(diphenylphosphino)pro-
pane)dimethylplatinum(II), reported to be 2.258(4) Å.26
Sch em e 3
The reaction between 5 and Me3SnPh is also very
fast. Within 2 min all the starting material is consumed
and two products have formed in approximately a 9:11
molar ratio: trans-[PtPhMe(PMe2Ph)2] (13) and trans-
[PtPh2(PMe2Ph)2] (14). They were characterized by
NMR spectroscopy (cf. Table 5). After 18 h also cis-
[PtPh2(PMe2Ph)2] (15) was identified in the reaction
mixture, in addition to complexes 13 and 14. The
formation of 15 correlates with the loss of 14; i.e., what
is observed is an isomerization of 14 to 15. The cis to
trans ratio of the diphenyl complexes after 18 h was
about 5:7, whereas there was no sign of any isomeriza-
tion of 13. Over the course of several days this ratio
increased, making the cis complex the dominant species.
Complex 15 has been synthesized elsewhere,27 giving
the same NMR signature as observed here.
corresponding to the platinum methyl group. Keeping
the NMR sample at room temperature for 1 week
changed the product distribution, as seen by 31P NMR
spectroscopy. The reaction mixture now contained not
only 7 but also the analogous cis complex, 11, in
approximately the same amount. Also cis-[PtPh2(PPh3)2]
(12) was formed, though only to an extent of about 10%.
11 and 12 were characterized by 1H and 31P NMR
spectroscopy.
Single crystals of 7 suitable for X-ray diffraction were
obtained by slow evaporation of the solvent from a
reaction mixture of 4 and Me3SnPh in dichloromethane-
d2 at room temperature. The molecular structure is
given in Figure 4, and selected bond distances and
angles are given in Table 2. The complex has a distorted-
square-planar coordination geometry with the two phos-
phines in a trans arrangement. The maximum deviation
from a least-squares plane through PtP2C2 is 0.11 Å,
and the plane of the phenyl group is oriented almost
perpendicular to the coordination plane (80.9°). As
expected from the higher trans influence of the methyl
group as compared to that of the fluoride ion, the Pt-
C(phenyl) distance is 2.058(4) Å in 7 as compared to
Qualitatively it is clear that 5 is more reactive than
4, in agreement with what is observed for the simple
substitution reaction. On the basis of the fact that PMe2-
Ph is less sterically demanding than PPh3, this speaks
in favor of an associative mechanism also for the
transmetalation. Furthermore, it is clear that only trans
products are formed, regardless of substrate; i.e., we
have an exclusive F-for-R (R ) Me, Ph) substitution at
(26) Smith, D. C.; Haar, C. M.; Stevens, D. E.; Nolan, S. P.; Marshall,
W. J .; Moloy, K. G. Organometallics 2000, 19, 1427.
(27) Wendt, O. F. Platinum(II) and Palladium(II) Complexes with
Group 14 and 15 Donor Ligands. Synthesis, Structure and Substitution
Mechanisms; Thesis, Lund University, Lund, Sweden, 1997.

Arylfluoroplatinum(II) Complexes
Organometallics, Vol. 22, No. 25, 2003 5241
these platinum fluoro complexes. The formation of cis
products seems to be a consecutive process; i.e., the cis
complex forms via isomerization of the trans products
and not directly from the fluoro complexes. Also notable
is the fact that 14 isomerizes but not 13. This could be
due to a difference in kinetics, but the likely explanation
is that a trans arrangement of an sp3- and sp2-hybrid-
ized carbon is a more tolerable configuration than a
trans arrangement of two sp2 carbons. This is in line
with the trans influence sequence observed in 7.
The expected tin byproducts of these reactions were
not observed in solution using, for example, 19F NMR
spectroscopy. However, it is a well-known fact that
organotin fluorides have a propensity to polymerize and
the polymer of Ph3SnF thus formed is highly insoluble
in organic solvent, thus preventing its observation. In
a very recent paper, Me2SnPhF was characterized, and
it turns out that this compound also is highly polymeric
but also highly soluble in organic solvents.30 The
polymeric nature of Me2SnPhF gives rise to a very broad
19F NMR peak; this might be the explanation why we
failed to observe this species in solution.
In light of the high reactivity of the fluoro complexes
toward organostannanes we decided to also investigate
their reactivity toward organosilanes. Thus, complexes
4 and 5 were reacted with trimethylvinylsilane or
trimethylphenylsilane in THF or C6D6. No reaction was
observed, and neither addition of CsF(s) nor the pres-
ence of water enabled the desired transmetalation
reaction.
Rea ction w ith Acetylen es. Treatment of 4 with
degassed phenylacetylene in benzene at room temper-
ature gave the alkynyl complex trans-[PtPh(CtCPh)-
(PPh3)2] (8). It was characterized by 1D and 2D NMR
spectroscopy and elemental analysis. 13C NMR data
confirm the presence of a σ-bonded alkynyl unit, dis-
playing a triplet at δ 115.25 (2J P-C ≈ 20 Hz) and a
singlet at δ 116.06, assigned to the R- and â-carbons,
respectively. The 31P NMR spectrum displays a singlet
with Pt satellites (1J Pt-P ) 2979 Hz), unambiguously
showing 8 to be a trans complex. Platinum acetylide
complexes are well-known in the literature,31 but they
are usually synthesized from the acetylene in the
presence of base, although there is an example in the
literature of a synthesis of an acetylene complex from
phenylacetylene and a Pt alkoxide complex.32 This
suggests that the coordinated fluoride has considerable
basicity (just as the alkoxide), and this is also supported
by the weak, but significant, intramolecular H-F
interaction (2.13 Å) between the fluoride and the
aromatic hydrogens H12 and H62.33
Although the intimate mechanism for the transmeta-
lation is unknown, the nonpolar nature of the Sn-C
bond speaks in favor of some type of concerted mecha-
nism. Typically in concerted reactions, the substrate
bond with the highest s character has the highest
reactivity; a classical example is the σ-bond metathesis
of C-H bonds on a Sc metal center, where the reactivity
follows the hybridization of the carbon atom.28
In light of this, one would expect the Sn-Ph bond to
be the most reactive in the Me3SnPh substrate, and this
is almost always observed in, for example, palladium-
catalyzed Stille couplings.7 However, there are examples
where the tin-alkyl bond is more reactive than a tin-
aryl bond; in the work by Eaborn, Pidcock, and co-
workers on the reactivity of platinum metal centers
toward organotin reagents it was shown that, with
sterically demanding substrates or ancillary ligands,
Sn-Me bonds are favored over Sn-aryl bonds.29 Our
results also follow along these lines. When the first step
of the reactions depicted in Scheme 2 is considered, it
is clear that products 7 and 13 are formed via trans-
metalation over the Sn-Me bond. To form product 14,
the transmetalation also occurs over the Sn-Ph bond.
The differences in the reaction patterns can be rational-
ized in terms of steric effects. Obviously, the steric
demand of the PMe2Ph ligand is less than that of the
PPh3 ligand, thus facilitating the transmetalation over
both the Sn-Me bond and the Sn-Ph bond.
In the simple substitutions the reactivity of the
fluoride is not substantially different from that of a
chloride. In the transmetalation reaction the picture is
quite different. We know from the literature and from
experiments of our own that chlorobis(phosphine)-
platinum(II) complexes are virtually unreactive toward
organotin reagents.29 The high, or in some cases very
high, reactivity of the present fluoro complexes was
therefore somewhat surprising, especially in light of the
results from the substitution reactions. The transmeta-
lations are clearly driven by something other than an
extremely weak Pt-F bond; we suggest that this is the
presence of a strong Sn-F bond in the products. The
transmetalations are, however, not only thermodynami-
cally favored but they are also faster than the substitu-
tions by a factor of 10-100. To understand the high
reactivity, it is necessary to invoke some stabilizing
property of the associative transition state, most likely
a fairly strong Sn-F interaction: i.e., the fluoride
probably acts as a bridging ligand in the transmetala-
tion transition state.
A C-F reductive elimination from 4 was also at-
tempted. A benzene solution of 4 in the presence of an
excess of diphenylacetylene was heated to approxi-
mately 75 °C for 48 h, but no reaction was observed.
Con clu sion s
We have prepared two platinum fluoride complexes
of the type trans-PtPhF(PR3)2 and tested their reactiv-
ity. Our investigations of simple substitution reactions
show that the Pt-F bond behaves in a manner similar
to that for other Pt-X bonds. In THF solution it is
thermodynamically slightly less stable and kinetically
about as labile as a Pt-Cl bond. In the transmetalation
reaction with Me3SnPh the reactivities of the Pt-F
complexes are very high, especially in comparison to
(30) Beckmann, J .; Horn, D.; J urkschat, K.; Rosche, F.; Schu¨rmann,
M.; Zachwieja, U.; Dakternieks, D.; Duthie, A.; Lim, A. E. K. Eur. J .
Inorg. Chem. 2003, 164.
(31) Kowalski, M. H.; Arif, A. M.; Stang, P. J . Organometallics 1988,
7, 1227.
(32) Kim, Y.-J .; Osakada, K.; Yamamoto, A. J . Organomet. Chem.
1993, 452, 247.
(28) Thomson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J .; Nolan,
M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J . E. J . Am. Chem.
Soc. 1987, 109, 203.
(29) Eaborn, C.; Odell, K. J .; Pidcock, A. J . Chem. Soc., Dalton Trans.
1979, 758.
(33) Osterberg, C. E.; King, M. A.; Arif, A. M.; Richmond, T. G.
Angew. Chem., Int. Ed. Engl. 1990, 29, 888.

5242 Organometallics, Vol. 22, No. 25, 2003
Nilsson et al.
those of the corresponding Pt-Cl complexes. Our ex-
planation for this high reactivity is that the reaction
takes place in an associative fashion and that the
fluoride stabilizes the transition state through a strong
Sn-F binding interaction.
tion, and the Royal Physiographic Society in Lund is
gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Tables giving de-
tailed crystallographic data, atomic positional parameters, and
bond lengths and angles and all observed rate constants as a
function of temperature and concentration; X-ray data are also
available as CIF files. This material is available free of charge
via the Internet at http://pubs.acs.org.
Ack n ow led gm en t. We thank Prof. A˙ ke Oskarsson
for his help with the X-ray crystallography. We also
thank Ms. J ohanna Fors for experimental assistance
with the kinetic measurements. Financial support from
the Swedish Research Council, the Crafoord Founda-
OM030524I