Contrasting reactivity of fluoropyridines at palladium and platinum: C-F oxidative addition at palladium, P-C and C-F activation at platinum

Article abstract of DOI:10.1021/om049448p

The divergent behavior of palladium(0) and platinum(0) is revealed in the reactivity of [M(PR₃)₂] (M = Pd or Pt; R = Cy or ⁱPr) toward pentafluoropyridine and 2,3,5,6-tetrafluoropyridine. The palladium complexes react with pentafluoropyridine at 100 °C to yield the fluoride complexes trans-[Pd(F)(4-C₅NF₄)(PR ₃)₂]. They do not react with 2,3,5,6-tetrafluorapyridine. The reaction of platinum(0) complexes [Pt(PR₃)₂] with pentafluoropyridine in THF at ambient temperature yields trans-[Pt(R)4-C ₅NF₄)(PR₃)(PFR₂)] complexes, whereas the reaction of [Pt(PCy₃)₂] with 2,3,5,6- tetrafluoropyridine results in C-H activation to form cis-[Pt(H)(4-C ₅NF₄)(PCy₃)₂]; this complex may be converted to the trans isomer by photolysis. The cis-hydride also forms during the reaction of [Pt(PCy₃)₂] with C₅NF ₅ in hexane. These reactions also contrast with earlier studies of the reactivity of the same substrates toward {Ni(PEt₃)₂}, which yield [Ni(F)(2-C₅NF₅)(PEt₃)₂] with pentafluoropyridine and [Ni(F)-(2-C₅NF₄H)(PEt ₃)₂] with tetrafluoropyridine. Thus palladium has different regioselectivity from nickel and is the least reactive. Platinum is capable of both C-F and C-H activation and is alone in the triad in undergoing rearrangement to the alkyl complex with the fluorophosphine ligand. Mechanisms for the rearrangement are proposed. The platinum dihydride complex trans-[Pt(H)₂(PR₃)₂] reacts with pentafluoropyridine at room temperature, yielding a 1:1:1 mixture of trans-[PtH(FHF)(PR₃)₂], trans-[Pt(H)(4-C ₅NF₄)(PR₃)₂], and trans-[Pt(R)(4-C₅NF₄)(PR₃)(PFR₂)]. Crystal structures are reported for trans-[Pd(F)(4-C₅NF ₄)-(PCy₃)₂]-H₂O-C₆H ₆, trans-[Pd(F)(4-C₅NF₄)(PⁱPr ₃)₂], trans-[Pt(C₆H₁₁)(4-C ₅NF₄)(PCy₃)(PFCy₂)]-CH ₂Cl₂, and cis-[Pt(H)(4-C₅NF₄) (PCy₃)₂].

Full text of DOI:10.1021/om049448p

6140
Organometallics 2004, 23, 6140-6149
Contrasting Reactivity of Fluoropyridines at Palladium
and Platinum: C-F Oxidative Addition at Palladium,
P-C and C-F Activation at Platinum†
Naseralla A. Jasim,§ Robin N. Perutz,*,§ Adrian C. Whitwood,§ Thomas Braun,*,‡
Joseph Izundu,‡ Beate Neumann,‡ Sascha Rothfeld,‡ and Hans-Georg Stammler‡
Department of Chemistry, University of York, Heslington, York, YO10 5DD, U.K., and
Fakulta¨t fu¨r Chemie, Universita¨t Bielefeld, Postfach 100131, 33501 Bielefeld, Germany
Received July 22, 2004
The divergent behavior of palladium(0) and platinum(0) is revealed in the reactivity of
i
[M(PR3)2] (M ) Pd or Pt; R ) Cy or Pr) toward pentafluoropyridine and 2,3,5,6-
tetrafluoropyridine. The palladium complexes react with pentafluoropyridine at 100 °C to
yield the fluoride complexes trans-[Pd(F)(4-C5NF4)(PR3)2]. They do not react with 2,3,5,6-
tetrafluoropyridine. The reaction of platinum(0) complexes [Pt(PR3)2] with pentafluoro-
pyridine in THF at ambient temperature yields trans-[Pt(R)(4-C5NF4)(PR3)(PFR2)] complexes,
whereas the reaction of [Pt(PCy3)2] with 2,3,5,6-tetrafluoropyridine results in C-H activation
to form cis-[Pt(H)(4-C5NF4)(PCy3)2]; this complex may be converted to the trans isomer by
photolysis. The cis-hydride also forms during the reaction of [Pt(PCy3)2] with C5NF5 in hexane.
These reactions also contrast with earlier studies of the reactivity of the same substrates
toward {Ni(PEt3)2}, which yield [Ni(F)(2-C5NF5)(PEt3)2] with pentafluoropyridine and [Ni(F)-
(2-C5NF4H)(PEt3)2] with tetrafluoropyridine. Thus palladium has different regioselectivity
from nickel and is the least reactive. Platinum is capable of both C-F and C-H activation
and is alone in the triad in undergoing rearrangement to the alkyl complex with the
fluorophosphine ligand. Mechanisms for the rearrangement are proposed. The platinum
dihydride complex trans-[Pt(H)2(PR3)2] reacts with pentafluoropyridine at room temperature,
yielding a 1:1:1 mixture of trans-[PtH(FHF)(PR3)2], trans-[Pt(H)(4-C5NF4)(PR3)2], and trans-
[Pt(R)(4-C5NF4)(PR3)(PFR2)]. Crystal structures are reported for trans-[Pd(F)(4-C5NF4)-
(PCy3)2]‚H2O‚C6H6, trans-[Pd(F)(4-C5NF4)(PiPr3)2], trans-[Pt(C6H11)(4-C5NF4)(PCy3)(PFCy2)]‚
CH2Cl2, and cis-[Pt(H)(4-C5NF4)(PCy3)2].
Introduction
tions of fluoroaromatics via C-F activation at a transi-
tion metal center. We achieved the functionalization of
heteroaromatic molecules within the coordination sphere
of nickel2-5,7,8 and showed that these routes yield
fluorinated heterocycles that are otherwise not acces-
sible. A key feature is the unusual regio- and chemose-
lectivity of the attack by nickel at the heterocycle.2,3,7,8
Thus, [Ni(COD)2] (COD ) 1,5-cyclo-octadiene) reacts
In the past decade, the selective activation of aromatic
C-F bonds has developed from a curiosity to a well-
recognized process.1 Recently, the focus has been on
stoichiometric2-7 and catalytic2,8-10 derivatization reac-
† Dedicated to Professor Helmut Werner on the occasion of his 70th
birthday.
* To whom correspondence should be addressed. E-mail: rnp1@
york.ac.uk; thomas.braun@uni-bielefeld.de.
(7) Sladek, M. I.; Braun, T.; Neumann B.; Stammler, H.-G. J. Chem.
Soc., Dalton Trans. 2002, 297.
(8) Braun, T.; Perutz, R. N.; Sladek, M. I. Chem. Commun. 2001,
2254.
§ University of York.
‡ Universita¨t Bielefeld.
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(b) Kiplinger, J. L.; Richmond, T. G.; Osterberg, C. E. Chem. Rev. 1994,
94, 373. (c) Murphy, E. F.; Murugavel, R.; Roesky, H. W. Chem. Rev.
1997, 97, 3425. (d) Mazurek, U.; Schwarz, H. Chem. Commun. 2003,
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35, 1095. (b) Kiso, Y.; Tamao, K.; Kumada, M. J. Organomet. Chem.
1973, 50, C12. (c) Gsto¨ttmayr, C. W. K.; Weskamp, T.; Herrmann, W.
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R. J.; Grushin, V. V. Organometallics 1999, 18, 294. (d) Yang, H.; Gao,
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10.1021/om049448p CCC: $27.50 © 2004 American Chemical Society
Publication on Web 11/16/2004

Reactivity of Fluoropyridines at Pd and Pt
Organometallics, Vol. 23, No. 26, 2004 6141
Table 1. NMR Data for Palladium Complexes 1a and 1b at 300 K in C6D6; δ (J/Hz)
complex
1H
31P{1H}
19F
13C{1H}
1a
0.74-2.10 (m)
30.3 (d, JPF ) 14.1)
-322 (s, br, 1 F) PdF
-115.7 (m, 2 F)
-99.4 (m, 2 F)
-323 (s, br, 1 F) PdF
-115.0 (m, 2 F)
-97.7 (m, 2 F)
1b
1.08 (dd, JHH ) 7, JPH
14, 18 H), 1.97 (m, 6 H)
)
39.1 (d, JPF ) 16.0)
19.7 (m, CH3), 23.7 (vtt, apparent
JCP ) 24.8, JCF ) 9.7, CH), 143.1
(ddd, JCF ) 256.8, 24.8, 12.4, CF), 144.3
(m, ipso-C), 144.7 (dm, JCF ) 230.7, CF).
Scheme 1. Reactivity of [Ni(COD)2] toward
Pentafluoropyridine and 2,3,5,6-Tetrafluoro-
pyridine in the Presence of Triethylphosphine
postulated. Reaction of trans-[Pt(H)2(PCy3)2] with pen-
tafluorobenzene yields trans-[Pt(H)(C6F5)(PCy3)2],14 while
reaction with hexafluorobenzene in the presence of
[NMe4]F yields a mixture of the latter and trans-[Pt(H)-
(FHF)(PCy3)2].15 There is no direct information about
formation of palladium phosphine fluorides by C-F
activation,16 but there are some examples of catalytic
cross-coupling reactions of fluoroaromatics with pal-
ladium catalysts.9 For instance, [Pd(PPh3)4] catalyzes
the coupling of arylboronic acids to 2-fluoronitrobenzene
to form the corresponding biphenyl; the authors postu-
lated formation of a palladium aryl fluoride via a SNAr
mechanism.9f
In this paper, we report the C-F activation of
fluorinated pyridines at Pd(0) and Pt(0). We show that
the selectivity of the reactions is distinct from the
corresponding reactions at nickel with respect to both
the position of activation and the comparative reactivity
of C-H and C-F bonds within the same molecule. The
reactions at palladium lead to direct C-F oxidative
addition and allow us to determine the molecular
structure of two palladium fluoride complexes. However,
the reactions at platinum afford unexpected complexes
bearing a fluorophosphine ligand and a platinum alkyl
bond.
Results
with pentafluoropyridine in the presence of trieth-
ylphosphine to form trans-[Ni(F)(2-C5NF4)(PEt3)2]. This
selective insertion of the {Ni(PEt3)2} moiety into a C-F
bond at the 2-position forms the basis of the metal-
mediated synthesis of new pyridines.2,3,8 Another im-
portant feature of the reactions at nickel is the selec-
tivity for C-F over C-H bonds within the fluoropyridine
substrates. For instance, 2,3,5,6-tetrafluoropyridine and
2,3,4,5-tetrafluoropyridine both undergo C-F activation
exclusively (Scheme 1).2,3c Carbon-fluorine bond activa-
tion also acts as a source of transition metal fluoride
complexes that can otherwise be demanding to synthe-
size2,11 and are applied increasingly in catalysis and as
starting materials for synthesis.1,8,12
Previous work on C-F activation at phosphine com-
plexes of platinum is limited. Hofmann et al.11 have
shown that the {Pt(tBu2PCH2PtBu2)} moiety can acti-
vate the C-F bond of C6F6 to form [Pt(F)(C6F5)-
(tBu2PCH2PtBu2)]. Hintermann et al. showed that trans-
[Pt(H)2(PCy3)2] reacts with 4-RC6F4CN (R ) H, F, CN,
and OCH3) to give the C-F activated product trans-
[Pt(H){C6F3R(CN)}(PCy3)2].13 An electron transfer reac-
tion involving the formation of a caged radical pair was
1. C-F Activation of Pentafluoropyridine at
Palladium. Treatment of the palladium(0) complex
[Pd(PCy3)2] with excess pentafluoropyridine in toluene
at 100 °C yields a single product 1a, which was
characterized by its 19F and 31P NMR spectra (Table 1).
The 19F NMR spectrum shows two multiplets at δ -99.4
and -115.7, which indicate the presence of the tetra-
fluoropyridyl ligand with the palladium in the 4-posi-
tion. A broad signal at δ -322 is characteristic of a
fluoride ligand coordinated at the metal center.17-21 The
31P NMR spectrum exhibits a doublet at δ 30.3 with a
coupling constant JPF of 14.1 Hz to the metal-bound
fluorine. Product 1a is therefore readily assigned as the
product of C-F oxidative addition at the 4-position of
(13) Hintermann, S.; Pregosin, P. S.; Ru¨gger, H.; Clark, H. C. J.
Organomet. Chem. 1992, 435, 225.
(14) Fornies, J.; Green, M.; Spencer, J. L.; Stone, F. G. A. J. Chem.
Soc., Dalton Trans. 1977, 1006.
(15) Jasim, N.; Perutz, R. N. J. Am. Chem. Soc. 2000, 122, 8685.
(16) Grushin, V. V. Chem. Eur. J. 2002, 8, 1006.
(17) Fraser, S. L.; Antipin, M. Y.; Khroustalyov, V. N.; Grushin, V.
V. J. Am. Chem. Soc. 1997, 119, 4769.
(18) Pilon, M. C.; Grushin, V. V. Organometallics 1998, 17, 1774.
(19) Marshall, W. J.; Thorn, D. L.; Grushin, V. V. Organometallics
1998, 17, 5427.
(11) Hofmann, P.; Unfried, G. Chem. Ber. 1992, 125, 659.
(12) (a) Doherty, N. M.; Hoffman, N. W. Chem. Rev. 1991, 91, 553.
(b) Pagenkopf, B. L.; Carreira, E. M. Chem. Eur. J. 1999, 5, 3437. (c)
Noveski, D.; Braun, T.; Schulte, M.; Neumann, B.; Stammler, H.-G.
Dalton Trans. 2003, 4075.
(20) Grushin, V. V.; Marshall, W. J. Angew. Chem., Int. Ed. 2002,
41, 4476.
(21) Roe, D. C.; Marshall, W. J.; Davidson, F.; Soper, P. D.; Grushin,
V. V. Organometallics 2000, 19, 4575.

6142 Organometallics, Vol. 23, No. 26, 2004
Jasim et al.
Figure 1. ORTEP diagram of 1a‚H2O‚C6H6 (1a′) (el-
lipsoids at 50% probability level, hydrogens and solvent
omitted).
Figure 2. ORTEP diagram of 1b (ellipsoids at 50%
Scheme 2. C-F Oxidative Addition of
Pentafluoropyridine at Palladium
probability level, hydrogens omitted).
Table 2. Selected Bond Lengths (Å) and Angles
(deg) of 1a‚H2O‚C6H6 (1a′) with the Estimated
Standard Deviations in Parentheses
bond
length
bond
length
Pd-C(19)
Pd-F(1)
1.986(4)
2.041(3)
2.3369(7)
1.295(7)
1.291(8)
1.376(7)
1.378(8)
C(20)-C(21)
C(22)-C(23)
F(2)-C(20)
F(3)-C(21)
F(4)-C(22)
F(5)-C(23)
F(1)‚‚‚O(1)
1.379(7)
1.393(8)
1.422(5)
1.342(7)
1.349(6)
1.357(6)
2.601(6)
Pd-P(1)
N(1)-C(21)
N(1)-C(22)
C(19)-C(20)
C(19)-C(23)
bonds
angle
bonds
angle
pentafluoropyridine,
trans-[Pd(F)(4-C5NF4)(PCy3)2]
C(19)-Pd-P(1)
F(1)-Pd-P(1)
C(19)-Pd-F(1)
P(1)-Pd-P(1a)
C(20)-C(19)-Pd 125.6(3)
C(23)-C(19)-Pd 122.0(4)
93.04(3)
87.21(3)
176.38(16) N(1)-C(21)-C(20)
170.30(3)
C(20)-C(19)-C(23) 112.4(5)
C(19)-C(20)-C(21) 122.0(5)
(Scheme 2). This product may also be formed by reflux-
ing in THF. The regioselectivity of reaction may be
contrasted with the corresponding reaction of {Ni(PEt3)2}
(Scheme 1). We note that [Pd(PCy3)2] does not react with
excess 2,3,5,6-tetrafluoropyridine in toluene at 100 °C.
The C-F activation product 1a can be obtained in
better yield starting from [PdMe2(tmeda)] (tmeda )
tetramethylethylenediamine), pentafluoropyridine, and
PCy3 (Scheme 2). The complex [PdMe2(tmeda)] also
proved to be a useful starting material for the synthesis
of the PiPr3 analogue, trans-[Pd(F)(4-C5NF4)(PiPr3)2]
(1b). The 19F and 31P NMR data for 1b resemble those
found for 1a.
2. Molecular Structures of trans-[Pd(F)(4-C5NF4)-
(PCy3)2]‚H2O‚C6H6 (1a′) and trans-[Pd(F)(4-C5NF4)-
(PiPr3)2] (1b). The colorless complex 1a′ was crystal-
lized from a solution of 1a in wet benzene at 20 °C, while
colorless crystals of 1b were obtained from a hexane
solution at -80 °C. The structures were determined by
X-ray diffraction at low temperature (Figures 1, 2).
Selected bond lengths and angles are summarized in
Tables 2 and 3. The molecular structures show the
expected trans disposition of the phosphine ligands with
approximately square-planar coordination at palladium.
The torsion angle between the plane defined by the
tetrafluoropyridyl ring in 1b and the coordination plane
of palladium is 96.5°. The palladium-fluorine distances
in 1a′ and 1b are 2.041(3) and 2.0158(16) Å, respec-
tively. The latter represents the shortest Pd-F separa-
tion found in palladium fluoride complexes according
124.7(5)
115.0(5)
124.7(5)
C(22)-N(1)-C(21)
N(1)-C(22)-C(23)
C(19)-C(23)-C(22) 121.3(6)
Table 3. Selected Bond Lengths (Å) and Angles
(deg) of 1b with the Estimated Standard
Deviations in Parentheses
bond
length
bond
length
Pd-C(19)
Pd-F(1)
Pd-P(1)
Pd-P(2)
N(1)-C(21)
N(1)-C(22)
C(19)-C(20)
1.988(3)
2.0158(16)
2.3479(6)
2.3310(6)
1.314(4)
1.322(4)
1.392(4)
C(19)-C(23)
C(20)-C(21)
C(22)-C(23)
F(2)-C(20)
F(3)-C(21)
F(4)-C(22)
F(5)-C(23)
1.385(4)
1.376(4)
1.378(4)
1.360(3)
1.350(3)
1.346(3)
1.354(3)
bonds
angle
bonds
angle
C(19)-Pd-P(1)
F(1)-Pd-P(1)
C(19)-Pd-F(1)
P(1)-Pd-P(2)
C(20)-C(19)-Pd 120.7(2)
C(23)-C(19)-Pd 126.6(2)
97.08(7) C(20)-C(19)-C(23) 112.8(2)
82.52(5) C(19)-C(20)-C(21) 121.8(3)
177.02(9) N(1)-C(21)-C(20)
168.94(2) C(22)-N(1)-C(21)
124.3(3)
114.9(2)
124.5(3)
N(1)-C(22)-C(23)
C(19)-C(23)-C(22) 121.6(3)
to CSD.17,19-22 A recent example of particular relevance
is [Pd(F)2(dippp)] (dippp ) bis(diisopropylphosphino)-
propane) with Pd-F bond lengths of 2.065(3) Å.23
(22) (a) CSD version 5.25 (November 2003). (b) Allen, F. H. Acta
Crystallogr. 2002, B58, 380.
(23) Yhav, A.; Goldberg, I.; Vigalok, A. J. Am. Chem. Soc. 2003, 125,
13634.

Reactivity of Fluoropyridines at Pd and Pt
Organometallics, Vol. 23, No. 26, 2004 6143
Table 4. NMR Data for Platinum Complexes 2 and 3 at 300 K, δ, J/Hz
complex
1H
31P{H}
19F
195Pt
2a
1.2-2.0 (m)
18.5 (dd, JPtP ) 2716, JPP ) 428,
JPF ) 37) PCy3
-176.2 (ddt, JPF ) 910, JPtF ) 372,
JPF ) 36, JPF ) 17) PF
-4405
CD2Cl2
181.0 (dd, JPtP ) 3710, JPF ) 910,
JPP ) 428) PCy2F
-117.8 (m, JPtF ) 181) Fortho
-93.3 (m) Fmeta
2b
CD2Cl2
0.95 (m) P(CHMe2)3
0.98 (m) PF(CHMe2)2
29.8 (dd, JPtP ) 2745, JPP ) 430,
JPF ) 36) PiPr3
-179 (ddt, JPF ) 914, JPtF ) 365,
JPF ) 37, JFF ) 17) PF
-116.8 (m, JPtF ) 180) Fortho
-4550
188 (dd JPtP ) 3808, JPF ) 914,
JPP ) 430) PiPr2F
1.75 (d J ) 7.6, JPtH ) 43)
PtCHMe2
1.80 (m) PF(CHMe2)2
2.0 (m) P(CHMe2)3
2.25 (m) PtCHMe2
-8.35 (tm, JHF ) 11, JPtH
703)
-98.7 (m) Fmeta
3-trans
C6D6
)
36.7 (s, JPtP ) 2732)
-118.3 (dm, JPtF ) 259, JHF ) 11) Fortho
-100.4 (m) Fmeta
-120.5 (m, JPtF ) 366) Fortho
3-cis
C6D6
-7.05 (ddt JHPtrans ) 167.5,
JHPcis ) 26.0, JHF ) 4.4,
JPtH ) 885)
26.4 (dd, JPtP ) 2073, JPP ) 13,
JPF ) 10) Ptrans to H
30.6 (m, JPtP ) 2574) Ptrans to C
-100.3 (td, JPF ) 26, JFF ) 6, JPtF )
48) Fmeta
i
Notably, trans-[Pt(F)(Ph)(PPh3)2], the nearest crystal-
lographically characterized platinum fluoride analogue
of 1b, exhibits a substantially longer metal-fluorine
bond (2.117(3) Å).24 The short distances in 1a′ and 1b
may indicate a less pronounced Pd-F dπ-pπ filled/filled
repulsion,25-27 perhaps due to delocalization of electron
density from filled metal d-orbitals into a π*-orbital of
the aromatic system. The Pd-C(19) bond length of
1.986(4) Å in 1a′ and 1.988(3) Å in 1b are comparable
to other Pd-C distances with a fluoro ligand in the
position trans to an aryl ligand.17,18,20 The Pd-C separa-
tion in trans-[PdBr(4-C5NH4)(PEt3)2] of 2.030(17) Å is
in a similar range.28
The structure of compound 1a′ reveals short inter-
molecular F‚‚‚O contacts from a water of crystallization
to the fluoride ligand [F(1)‚‚‚O(1): 2.602 Å]. The hydro-
gen atoms at the oxygen were located in the difference
Fourier map, but were not refined. They were fixed with
an O-H bond length of 0.84 Å and a displacement
parameter of 1.2 times that of O(1). This results in an
estimate of the H(1a)‚‚‚F(1) distance of 1.76 Å, a value
well below the sum of the van der Waals radii of 2.67
Å.20 For comparison, we identified intramolecular
F‚‚‚C contacts of 2.87 Å in [(η5-C5H5)Ir(C2H4)(η2-C6F6)].29
The general principles of hydrogen bonding to halide
ligands are summarized in Brammer’s review.30
3. Reactions of Pt(0) Complexes with Penta-
fluoropyridine. Reaction of [Pt(PiPr3)2] with pen-
tafluoropyridine in THF at room temperature produced
a white precipitate that was recrystallized from THF-
hexane to yield complex 2b. An analogous complex (2a)
was prepared from [Pt(PCy3)2]. Complexes 2a and 2b
were identified initially by NMR spectroscopy (Table 4);
their characterization is best illustrated by the Pr
complex because of its higher solubility and its distinct
isopropyl resonances.
The 31P NMR spectrum of 2b shows two resonances,
a doublet of doublets at δ 29.8 (JPtP ) 2745, JPP ) 430,
and JPF ) 36 Hz) and a second resonance at δ 188 (dd,
JPtP ) 3808, JPP ) 430, and JPF ) 914 Hz). The coupling
of 914 Hz is close to that found in the literature for a
fluorine directly bonded to phosphorus.31 The large
value of JPP demonstrates the presence of inequivalent
mutually trans phosphorus nuclei. Thus the complex
contains one PiPr3 group and one PFiPr2 group.
The 19F NMR spectrum of 2b shows three resonances.
A second-order multiplet with platinum satellites at δ
-116.8 (JPtF ) 180 Hz) is assigned to the fluorine ortho
to the platinum nucleus of a tetrafluoropyridyl ligand,
and a multiplet at δ -98.7, which was not coupled to
platinum, is assigned to the fluorine meta to the
platinum center. These two resonances are consistent
with a tetrafluoropyridyl group bound to the metal at
the 4-position, as in 1a and 1b. The third resonance is
a doublet of doublets of triplets with platinum satellites
at δ -179.3 (JPtF ) 365, JPF ) 914, JPF(far) ) 36, and
JFF ) 17 Hz) corresponding to the fluorine of the PFiPr2
group. No resonance was observed in the 19F NMR
spectra for fluorine directly bonded to platinum.
1
The H NMR spectrum of 2b shows a multiplet at δ
0.95, a doublet with conspicuous platinum satellites at
δ 1.75, a broad multiplet at δ 2.0, and a multiplet at δ
2.25. The resonance at δ 2.25 collapses to a doublet with
platinum satellites when the resonance at δ 1.75 is
selectively decoupled. Phosphorus correlation experi-
ments show no coupling with these two proton reso-
nances when the delay is appropriate to a two-bond
P-H coupling. These spectra provide direct evidence for
a platinum-bound isopropyl group with resonances at
δ 2.25 Pt(CHMe2) and 1.75 Pt(CHMe2) for the isopropyl
directly attached to platinum. The resonance at δ 2.0
is coupled to the resonance at δ 0.95, with both
resonances showing a correlation with a 31P resonance
at δ 29.8 consistent with isopropyl groups bound to
(24) Nilsson, P.; Plamper, F.; Wendt, O. F. Organometallics 2003,
22, 5235.
(25) Caulton, K. G. New J. Chem. 1994, 18, 25.
(26) Flemming, J. P.; Pilon, M. C.; Borbulevitch, O. Y.; Antipin, M.
Y.; Grushin, V. V. Inorg. Chim. Acta 1998, 280, 87.
(27) (a) Mezzetti, A.; Becker, C. Helv. Chim. Acta, 2002, 85, 2686.
(b) Becker, C.; Kieltsch, I.; Broggini, D.; Mezzetti, A. Inorg. Chem. 2003,
42, 8417.
(28) Isobe, K.; Kai, E.; Nakamura, Y.; Kinoshita, K.; Nakatsu, K. J.
Am. Chem. Soc. 1980, 102, 2475.
(29) Bell, T. W.; Helliwell, M.; Partridge, M. G.; Perutz, R. N.
Organometallics 1992, 11, 1911.
(31) Blum, O.; Frolow, F.; Milstein, D. J. Chem. Soc., Chem.
Commun. 1991, 258.
(30) Brammer, L. Dalton Trans. 2003, 3145.

6144 Organometallics, Vol. 23, No. 26, 2004
Jasim et al.
Figure 3. Chemical shifts and coupling constants (Hz) of
trans-[Pt(4-C5NF4)(CHMe2)(PiPr3)(PFiPr2)], 2b.
Figure 4. ORTEP diagram of 2a‚CH2Cl2 (ellipsoids at 50%
probability level, hydrogens and solvent omitted).
Scheme 3. Reactions of Pentafluoropyridine and
2,3,5,6-Tetrafluoropyridine at Pt(0)
resonance with a doublet of doublets of triplets splitting
at δ -7.05 (JPtH ) 885, JPHtrans ) 167.5, JPHcis ) 26.0,
and JHF ) 4.4 Hz, Table 4). This resonance collapses to
a triplet with 31P decoupling, leaving the 19F coupling
unaffected. The 31P NMR spectrum shows two reso-
nances, a doublet of doublets at δ 26.4 (JPtP ) 2073, JPP
) 13, JPF )10 Hz) and a multiplet at δ 30.6 (JPtP ) 2574
1
Hz). The H-31P correlation shows that the 31P reso-
nances are coupled to the hydride resonance. The 19F
NMR spectrum shows two resonances each with plati-
num satellites at δ -100.3 (td, JPtF ) 48, JPF ) 26, JFF
) 6 Hz, F meta to Pt) and at δ -120.5 (m, JPtF ) 366
Hz, F ortho to Pt). This complex exhibits a characteristic
ν(Pt-H) vibration at 2054 cm-1 in the IR spectrum. The
spectroscopic data indicate that the C-H bond of
tetrafluoropyridine has been activated so that 3-cis may
be identified as cis-[Pt(H)(4-C5F4N)(PCy3)2] (Scheme 3).
The same hydride complex, 3-cis, was obtained from
the reaction of [Pt(PCy3)2] with pentafluoropyridine
using hexane as the solvent. It can be isolated from this
reaction but in lower yield than from the reaction of
[Pt(PCy3)2] with tetrafluoropyridine. This reaction pro-
ceeds more slowly than the conversion to 2b in THF.
To find the source of the hydride in the complex, the
reaction was repeated in dry [2H12]-cyclohexane and in
C6F6 as solvents, but the hydride complex still formed.
We deduce that one of the C-H bonds of a PCy3 ligand
acts as the source of the hydride ligand, but the
byproducts have not been identified.
Photolysis of a solution of 3-cis in C6D6 (broad band
λ > 290 nm, 2 h) caused complete conversion of 3-cis to
the corresponding trans isomer 3-trans (see below for
characterization). The isomerization also takes place
thermally at 80 °C. Attempts to replace the hydride
ligand by halides via reaction with Et3N‚3HF, HCl, or
HBr resulted instead in displacement of the tetrafluo-
ropyridyl group, yielding trans-Pt(H)(X)(PCy3)2 (X ) F,
Cl, Br)15 whether starting with 3-cis or 3-trans.
5. Molecular Structures of trans-[Pt(C6H11)(4-
C5NF4)(PCy3)(PFCy2)]‚CH2Cl2 (2a‚CH2Cl2) and cis-
[Pt(H)(4-C5NF4)(PCy3)2] (3-cis). Complex 2a‚CH2Cl2
was crystallized by slow evaporation from a dichlo-
romethane solution to form colorless crystals and char-
acterized by X-ray crystallography (Figure 4, Table 5).
The bond angles at platinum are close to the ideal of
phosphorus. Further evidence for a metal alkyl group
comes from the 13C{1H} spectrum which exhibits a
resonance at δ 19.2 (s) with prominent platinum satel-
lites (JPtC ) 18 Hz).
The {1H-195Pt} HMQC correlation (Supporting In-
formation) reveals a 195Pt resonance at δ -4550 with
passive couplings to two 31P nuclei as well as two ortho
19F nuclei. This resonance is strongly correlated to the
proton resonances of the isopropyl group bound directly
to platinum, and there is also correlation to other
isopropyl protons. The multinuclear NMR spectra,
therefore, establish the identity of 2b as trans-[Pt(4-
C5NF4)(CHMe2)(PiPr3)(PFiPr2)] (Figure 3, Scheme 3).
The 19F and 31P NMR spectra of the product of
reaction of [Pt(PCy3)2] with pentafluoropyridine are very
similar to those of 2b and consistent with an assignment
as trans-[Pt(C6H11)(4-C5NF4)(PCy3)(PFCy2)], 2a. NMR
data for this complex are listed in Table 4. We also
investigated the same reaction at 235 K in THF-d8 in
order to detect possible intermediates, but the only
product observed was 2a. The reaction of [Pt(PCy3)2]
with pentafluoropyridine in hexane, however, takes a
different course as described below.
4. Reaction of [Pt(PCy3)2] with 2,3,5,6-Tetra-
fluoropyridine. A solution of [Pt(PCy3)2] in hexane was
reacted overnight with 2,3,5,6-tetrafluoropyridine (2
equiv) at room temperature, yielding colorless crystals
of 3-cis. The 1H NMR spectrum of 3-cis shows a hydride

Reactivity of Fluoropyridines at Pd and Pt
Organometallics, Vol. 23, No. 26, 2004 6145
Table 5. Selected Bond Lengths (Å) and Angles
(deg) of trans-Pt(Cy)(C5NF4)(PCy3)(PFCy2),
2a‚CH2Cl2, with the Estimated Standard
Deviations in Parentheses
bond
length
bond
length
Pt-P(1)
2.3527(8)
2.2567(8)
2.139(3)
2.100(3)
1.597(2)
1.310(5)
1.317(5)
1.361(3)
1.348(4)
1.358(4)
1.344(4)
C(37)-(38)
C(38)-(39)
C(37)-(41)
C(40)-C(41)
C(31)-C(32)
C(31)-C(36)
C(32)-C(33)
C(33)-C(34)
C(34)-C(35)
C(35)-C(36)
1.392(4)
1.379(4)
1.393(5)
1.373(4)
1.536(4)
1.541(5)
1.538(4)
1.519(5)
1.529(5)
1.533(5)
Pt-P(2)
Pt-C(31)
Pt-C(37)
P(2)-F(5)
N-C(39)
N-C(40)
F(1)-C(41)
F(3)-C(39)
F(4)-C(38)
F(2)-C(40)
bonds
angle
bonds
angle
C(31)-Pt-P(1)
C(31)-Pt-P(2)
C(37)-Pt-P(1)
C(37)-Pt-P(2)
P(1)-Pt-P(2)
88.57(8)
92.64(8)
91.88(8)
87.48(8)
177.31(10)
F(5)-P(2)-C(19)
F(5)-P(2)-C(25)
F(5)-P(2)-Pt
C(38)-C(37)-Pt
C(41)-C(37)-Pt
98.32(13)
97.75(14)
116.34(8)
126.0(2)
122.8(2)
square planar coordination. The tetrafluoropyridyl ring
is approximately perpendicular to the platinum coordi-
nation plane with a torsion angle of 82.7(1)°. The plane
formed by the central four carbon atoms of the cyclo-
hexyl group, C(32), C(33), C(35), and C(36), lies perpen-
dicular to the platinum coordination plane with a
torsion angle of 86.4(2)°. The P-F bond lies in the plane
of the platinum center; its length (1.597(2) Å) lies within
3σ of that found in [Ir(C6F5)(PEt3)2(PEt2F)] (IrP-F )
1.630(12) Å).31 The Pt-C(31) (cyclohexyl) bond length
is 2.139(3) Å, while the Pt-C(37) (tetrafluoropyridyl)
is shorter, 2.100(3) Å. The Pt-PCy2F distance (2.2567(8)
Å) is shorter than the Pt-PCy3 distance (2.3527(8) Å)
as in [Ir(C6F5)(PEt3)2(PEt2F)].31
Colorless crystals of 3-cis were grown from hexane.
Its crystal structure reveals a distorted square planar
coordination geometry at platinum (Figure 5, Table 6).
The P(1)-Pt-P(2) angle was 106.96(3)°, while the C(3)-
Pt-P(1) angle was 96.39(9)°. The tetrafluoropyridyl
carbon C(3) lies approximately trans to P(2), but the
angle C(3)-Pt-P(2) is 155.35(9)°. The Pt-P(1) bond
(2.3686(8) Å) is longer than the Pt-P(2) bond (2.2904(9)
Å), indicating that the hydride has a stronger trans
influence than the tetrafluoropyridyl ligand. The Pt-C
bond length is 2.058(3) Å, appreciably shorter than the
corresponding bond of complex 2a (2.100(3) Å), presum-
ably as a result of the different trans ligand. The hydride
was located leading to a Pt-H bond length of 1.68(5)
Å. The platinum lies out of the plane of P(1), P(2), and
C(3) by 0.124(1) Å. The pyridyl ring lies exactly per-
pendicular to the best Pt coordination plane defined by
Pt, P(1), P(2), and C(3).
Figure 5. ORTEP diagram of 3-cis (ellipsoids at 50%
probability level, hydrogens omitted except for hydride).
Top: General view. Bottom: View showing distortion of
platinum coordination plane with cyclohexyl groups re-
moved.
Table 6. Selected Bond Lengths (Å) and Angles
(deg) of cis-[PtH(C5NF4)(PCy3)2], 3-cis, with the
Estimated Standard Deviations in Parentheses
bond
length
bond
length
Pt-P(2)
Pt-P(1)
Pt-C(3)
Pt-H(3)
N-C(5)
N-C(1)
F(1)-C(1)
2.2904(9)
2.3686(8)
2.058(3)
1.68(5)
1.303(5)
1.317(5)
1.345(4)
F(2)-C(2)
F(3)-C(4)
F(4)-C(5)
C(1)-C(2)
C(4)-C(5)
C(3)-C(4)
C(3)-C(2)
1.357(4)
1.354(4)
1.351(4)
1.375(5)
1.378(5)
1.378(4)
1.383(5)
bonds
angle
bonds
angle
C(3)-Pt-P(1)
C(3)-Pt-P(2)
P(1)-Pt-P(2)
96.39(9)
155.35(9)
106.96(3)
C(3)-Pt-H(3)
P(1)-Pt-H(3)
P(2)-Pt-H(3)
81.5(17)
75.8(17)
175.4(15)
shows a broad resonance at δ 11.2 for the acidic proton
and a hydride as a doublet of triplets with platinum
satellites at δ -27. The NMR and IR spectra of this
product are identical to the published spectra.15
6. Reaction of trans-[Pt(H)2(PCy3)2] with Pen-
tafluoropyridine. Since platinum C-F activation
chemistry is not limited to Pt(0) complexes,13,32 we
decided to compare the reactivity of trans-[Pt(H)2-
(PCy3)2] toward pentafluoropyridine with the Pt(0)
reaction. The platinum dihydride complex reacts with
pentafluoropyridine in THF at room temperature to give
a 1:1:1 mixture of trans-[Pt(H)(FHF)(PCy3)2], 3-trans,
and 2a (Scheme 4). The presence of trans-[Pt(H)(FHF)-
The second product, 3-trans, was characterized by
NMR spectroscopy. The 1H NMR spectrum shows a
hydride resonance at δ -8.35 as a multiplet with
platinum satellites. The 1H{31P} NMR spectrum ap-
pears as a triplet with platinum satellites due to a
hydride coupled to two ortho fluorines (JPtH ) 703, JHF
) 11 Hz). The 31P NMR spectrum shows a singlet with
platinum satellites at δ 36.7 (JPtP ) 2732 Hz), indicating
that the complex adopts a trans geometry. The 19F NMR
spectrum shows two resonances for 3-trans: the signal
at δ -118.3 with a clear hydride coupling and platinum
1
(PCy3)2] is revealed by the H NMR spectrum, which
(32) Clark, H. C.; Tsang, W. S. J. Am. Chem. Soc. 1967, 89, 529.

6146 Organometallics, Vol. 23, No. 26, 2004
Jasim et al.
Scheme 4. Reaction of Pentafluoropyridine with
Transfer of electron density from metal d-orbitals into
a π*-orbital of the aromatic system can diminish the
pπ-dπ filled/filled repulsion shortening the Pd-F
bond.19,25-27 Consequently, removal of electron density
by hydrogen bonds can result in a reduction in the
donating properties of the fluorine ligand and a slight
elongation of the Pd-F bond in 1a′ compared to 1b. An
alternative view is that the hydrogen bond diminishes
the polar character of the metal-fluorine bond, result-
ing in an elongation of the bond according to the
principles of Pauling electronegativity.27,38 Coordination
of HF to a fluoro ligand also leads to an elongation of
the metal-fluorine bond.4,21 It has been observed previ-
ously that coordination of water to a fluoride ligand
facilitates dissociation of fluoride.39
trans-[Pt(H)2(PCy3)2]
satellites is assigned to the fluorines ortho to platinum
(dm JPtF ) 259, JHF ) 11 Hz). The resonance at δ -100.4
(m) is assigned to the fluorines meta to platinum. The
reaction of trans-[Pt(H)2(PiPr3)2] with pentafluoropyri-
dine gave products analogous to the tricyclohexylphos-
phine complex with a very similar distribution.
The multinuclear NMR spectra provide conclusive
evidence that Pt0 complexes also activate the C-F bond
of pentafluoropyridine at the 4-position at room tem-
perature. In a remarkable rearrangement, the fluoride
attacks one of the phosphorus atoms and an alkyl group
migrates from phosphorus to platinum to give the
complexes trans-[Pt(R)(4-C5NF4)(PR3)(PFR2)] 2a (R )
Discussion
i
Cy) and 2b (R ) Pr) (Scheme 3). Since the product is
The C-F activation of pentafluoropyridine at [Pd-
(PCy3)2] yielding trans-[Pd(F)(4-C5NF4)(PCy3)2] (2) is
shown in Scheme 2. Complex 1a and its PiPr3 analogue
1b can also be prepared by treatment of [PdMe2(tmeda)]
with pentafluoropyridine in the presence of the ap-
propriate phosphine. It is reasonable that the formation
of the 14-electron compounds [Pd(PCy3)2] and [Pd-
(PiPr3)2] precedes the activation step in this case.33,34
This assumption was confirmed by monitoring the
reactions by 31P NMR spectroscopy.
The insertion of the metal into the C-F bond proceeds
selectively at the 4-position of the heterocycle. This
selectivity contrasts with the comparable reaction at
{Ni(PEt3)2}, which yields a metal tetrafluoropyridyl
derivative with the metal in the 2-position.2,35 Further-
more, C-F activation at Ni occurs very rapidly at room
temperature, whereas the reaction at Pd is slower and
needs more drastic reaction conditions. Our experiments
do not distinguish concerted from ionic mechanisms of
oxidative addition. Although C-F oxidative addition at
palladium has been assumed in order to explain cross-
coupling reactions,9 this is the first direct observation
of such a reaction.
formed immediately, even at low temperature, it is hard
to establish the mechanism. There are three relevant
examples of P-C cleavage in the literature. In the first
example, [Pt(dppe)(trans-stilbene)] reacts with PHMes2
to give [Pt(Mes)(dppe)(PHMes)] as the thermodynamic
product.40 In the second, [Ir(PEt3)3Me] reacts with
hexafluorobenzene to give [Ir(C6F5)(PEt3)2(PEt2F)]; the
authors postulated a radical-ion-pair mechanism for this
reaction.31 Third, Grushin and Marshall showed very
recently that [Rh(F)(PPh3)3] disproportionates at 80 °C
to form trans-[Rh(F)(PPh2F)(PPh3)2] and trans-[Rh-
(PPh2C6H4)(PPh3)2]; the authors postulate that [Rh(F)-
(PPh3)3] rearranges initially to trans-[Rh(Ph)(PPh2F)-
(PPh3)2].41 The reaction that we have observed at
platinum is consistent with formation of a platinum
fluoride analogous to palladium complex 1a, followed
by rearrangement as postulated by Grushin and Mar-
shall for their rhodium fluoride complex. Grushin also
considered related reactions when studying the thermal
decomposition of trans-[Pd(F)(Ar)(PPh3)2].16
We were unable to detect any intermediates in the
reaction of [Pt(PCy3)2] with pentafluoropyridine in THF,
even at low temperatures. Grushin’s rearrangement at
rhodium fluoride strongly suggests, however, that plati-
num analogues of 1a/b act as intermediates. Three
possible mechanisms are shown in Scheme 5, the first
involving a phosphorus(V) cation and a platinum(0)
anion (mechanism a, see ref 16). The second combines
the cation and anion into a metallophosphorane as
either an intermediate or transition state (mechanism
b).41,42 The third involves formation of a platinum(IV)
The molecular structures of 1b and an H2O adduct
of 1a (1a′) have been determined by X-ray diffraction.
Complex 1b exhibits the shortest known Pd-F distance
for a molecular complex, and according to CSD, 1a′ is
the first example of a structure of a water adduct of a
transition metal fluoro complex.22,36 It is conceivable
that the short Pd-F distances in 1a′ and 1b might
result from a push/pull interaction induced by the
π-acceptor properties of the fluoroaryl ligand.3,28,37
(37) Sladek, M. I.; Braun, T.; Neumann, B.; Stammler H.-G. New
J. Chem. 2003, 313.
(33) (a) Krause, J.; Cestaric, G.; Haak, K.-J.; Seevogel, K.; Storm,
W.; Po¨rschke, K.-R. J. Am. Chem. Soc. 1999, 121, 9807. (b) Reid, S.
M.; Mague, J. T.; Fink, M. J. J. Am. Chem. Soc. 2001, 123, 4081.
(34) de Graaf, W.; Boersma, J.; Smeets, W. J. J.; Spek, A. L.; van
Koten, G. Organometallics 1989, 8, 2907.
(38) Moigno, D.; Kiefer, W.; Callejas-Gaspar, B.; Gil-Rubio, J.;
Werner, H. New J. Chem. 2001, 25, 1389.
(39) (a) Veltheer, P.; Burger, P.; Bergman, R. G. J. Am. Chem. Soc.
1995, 117, 12478. (b) Branan, D. M.; Hoffman, N, W.; McElroy, E. A.;
Miller, N. C.; Ramage, D. L.; Schott, A. F.; Young, S. H. Inorg. Chem.
1987, 26, 2915.
(35) Cronin, L.; Higgitt, C. L.; Karch, R.; Perutz, R. N. Organome-
tallics 1997, 16, 4920.
(36) The complex originally identified as [W(F)(H)2(H2O)(PMe3)4]F
with a hydrogen bond between H2O and F, was later shown to contain
coordinated FHF and was reformulated as [W(F)(H)2(FHF)(PMe3)4]:
Murphy, V. J.; Rabinovich, D.; Hascall, T.; Klooster, W. T.; Koetzle, T.
F.; Parkin, G. J. Am. Chem. Soc. 1998, 120, 4372.
(40) Kourkine, I. V.; Sargent, M. D.; Glueck, D. S. Organometallics
1998, 17, 125.
(41) Grushin, V. V.; Marshall, W. J. J. Am. Chem. Soc., 2004, 126,
3068.
(42) Macgregor, S. A.; Neave, G. W. Organometallics 2004, 23, 891.

Reactivity of Fluoropyridines at Pd and Pt
Organometallics, Vol. 23, No. 26, 2004 6147
Scheme 5. Proposed Mechanisms of Formation of 2a and 2b
phosphide complex that is attacked by fluoride (mech-
anism c). At this stage we cannot distinguish these
mechanisms. The first and third pathways of Scheme 5
postulate ionic intermediates that should be favored by
the polarity of THF compared to hexane. Attempts to
test the mechanism by converting 3-cis or 3-trans to
fluoride complexes displaced the tetrafluoropyridyl ligand
instead of the hydride.
Comparison with Milstein’s reaction of [IrMe(PEt3)3]
to form [Ir(C6F5)(PEt3)2(PEt2F)] leads to a radical mech-
anism31 for formation of 2a/b in which the [Pt(PR3)2]+
cation is attacked by free fluoride released from penta-
fluoropyridine anion. We note that several steps would
be required before the complex recovered a closed-shell
configuration.
The reaction of [Pt(PCy3)2] with 2,3,5,6-tetrafluoro-
pyridine is likely to be a conventional C-H activation.
The platinum reaction gives a cis-product as expected
for concerted oxidative addition. The reaction of
[Pt(PCy3)2] with pentafluoropyridine in hexane results
in slow conversion to the same hydride as formed with
tetrafluoropyridine, but in lower yield. Since a control
reaction of PCy3 and C5NF5 in THF at room tempera-
ture yielded 2,3,5,6-tetrafluoropyridine,43 the unex-
pected reaction of [Pt(PCy3)2] in hexane may go via
intermediate formation of tetrafluoropyridine.
Comparison of the platinum(0) and platinum(II)
systems shows that C-F activation of Pt(0) with penta-
fluoropyridine was faster and more selective than with
Pt(II). The cis-hydride complex was detected in the Pt(0)
reactions, but only trans products were detected with
Pt(II).
Insight into the origin of the very different behavior
of zerovalent Ni and Pt toward pentafluoropyridine and
tetrafluoropyridine can be obtained by reference to
recent calculations on reactions of [M(H2PCH2CH2PH2)]
(M ) Ni, Pt) with benzene and hexafluorobenzene.44
These calculations showed that C-F activation is
exothermic for both metals, while C-H activation is
energetically favorable only for platinum. The metal-
fluorine bond is found to be substantially weaker for Pt
because of increased pπ-dπ repulsions, and the barrier
to C-F activation is higher for Pt. The barrier to C-H
activation at Pt is far lower than for C-F activation.
The present work suggests that the same principles
apply to the reactions of heteroaromatics at [M(PR3)2]
under investigation in the present study. The recent
structure of trans-[Pt(F)(Ph)(PPh3)2] is consistent with
these calculations.24
Conclusions
C-F activation is possible in both palladium and
platinum systems, but the behavior of the two metals
is very different. Neither metal behaves similarly to
{Ni(PEt3)2}.
i
1. [Pt(PR
3)2] (R ) Pr, Cy) can activate the C-F bond
of C
5NF5 in THF to yield trans-[Pt(4-C5NF4)(R)(PR3)-
(PFR
2)] as a single product at room temperature. This
reaction can be considered as a combination of C-F and
P-C activation.The reaction takes a different course in
hexane, giving cis-[Pt(4-C5NF4)(H)(PCy3)2]. In contrast,
[Pd(PR
[Pd(F)(4-C
3)2] reacts at 100 °C in toluene to form trans-
5NF4)(PCy3)2], providing a new route to pal-
ladium fluoride complexes and an example of C-F
(43) The control reaction of PCy3 with pentafluoropyridine also
yielded three 31P NMR product resonances at δ -33.7, 30.0, and -26.3
and a 19F NMR resonance at δ -58.5, d, J ) 736 Hz. The same
resonances were detected in the spectra after reaction of [Pt(PCy3)2]
with C5NF5.
oxidative addition. These reactions are all regioselective
(44) McGrady, J. E.; Perutz, R. N.; Reinhold, M. J. Am. Chem. Soc.
2004, 126, 5268.

6148 Organometallics, Vol. 23, No. 26, 2004
Table 7. Crystallographic Data for 1a′, 1b, 2a‚CH2Cl2, and 3-cis
Jasim et al.
1a′
1b
2a‚CH2Cl2
3-cis
color, habit
cryst dimens/mm3
empirical formula
diffractometer
monochromator
fw
colorless plate
colorless plate
0.15 × 0.14 × 0.05
C23H42F5NP2Pd
Nonius Kappa CCD
graphite
colorless plate
0.30 × 0.10 × 0.05
C42H68Cl2F5NP2Pt
Bruker Smart CCD
graphite
colorless plate
0.20 × 0.12 × 0.04
0.23 × 0.13 × 0.03
C41H67F4NP2Pt
Bruker Smart CCD
graphite
C
47H74F5NOP2Pd
Bruker Smart CCD
graphite
718.77
595.92
1009.90
906.99
temp/K
193(2)
100(2)
0.71073
monoclinic
P21
8.7100(2)
115(2)
0.71073
monoclinic
P21/c
19.5509(10)
9.6008(5)
115(2)
wavelength/Å
cryst syst
0.71073
0.71073
orthorhombic
Pmn21
monoclinic
P21/c
space group
unit cell dimens a/Å
b/Å
14.0615(8)
17.1605(9)
9.5865(5)
9.5184(5)
19.6473(9)
21.8841(11)
100.9810(10)
4017.6(3)
4
13.0340(4)
12.0380(2)
95.9540(15)
1359.26(6)
2
c/Å
23.0223(11)
94.2310(10)
4309.6(4)
â/deg
volume/Å3
Z
2313.2(2)
2
4
density(calcd)/Mg m-3
1.339
1.456
1.557
1.499
µ/mm-1
0.525
0.846
3.506
3.620
F(000)
984
616
2056
1856
θ range/deg
index ranges
1.87 to 26.99
-17 e he 11,
-20 e ke 21,
-12 e le 12
13 420
3.04 to 27.50
-11 e he 11,
-16 e ke 16,
-15 e le 15
24 473
1.04 to 30.01
-20 e he 27,
-13 e ke 13,
-32 e le 32
33 814
2.16 to 27.54
-12 eh e 10,
-25 ek e 25,
-28 e le 28
27 404
no. of reflns collected
no. of indep reflns
R(int)
5158
5957
12 354
9246
0.0304
0.058
0.0269
0.0392
completeness to θ
absorption correction
max./min. transmn
no. of data/restraints/params
structure soln
99.6% to 26.99°
multiscan
99.6% to 27.50°
multiscan
0.884 and 0.960
5957/1/301
direct methods
full-matrix least-
squares on F2
SHELXTL PLUS,
SHELX-97
riding
98.2% to 30.01°
multiscan
99.6% to 30.01°
multiscan
0.835 and 1.000
5158/5/324
direct methods
full-matrix least-
squares on F2
SHELXTL PLUS,
SHELX-9749,50
riding + diff
1.009
R1 ) 0.0353
wR2 ) 0.0778
on 4479 reflections
R1 ) 0.0460,
wR2 ) 0.0821
0.828 & -0.330
245385
0.839 and 0.663
12 354/0/478
direct methods
full-matrix least-
squares on F2
SHELXS-97,
SHELXL-97
riding
9246/0/446
direct methods
full-matrix least-
squares on F2
SHELXS-97,
SHELXL-97
riding + diff
1.007
refinement method
programs
H atoms
goodness-of-fit on F2
final R indices [I>2σ(I)]
1.039
1.038
R1 ) 0.0259,
wR2 ) 0.0551
on 5617 reflections
R1 ) 0.0294,
wR2 ) 0.0568
0.432 & -0.424
245386
R1 ) 0.0311,
wR2 ) 0.0789
on 10590 reflections
R1 ) 0.0390,
wR2 ) 0.0827
3.428 & -2.233
245387
R1 ) 0.0298,
wR2 ) 0.0672
on 7622 reflections
R1 ) 0.0418,
wR2 ) 0.0714
2.875 & -0.992
245388
R indices (all data)
max. diff peak & hole/e Å-3
CCDC ref number
with oxygen levels below 10 ppm. All solvents were purified
and dried by conventional methods and distilled under argon
before use. Benzene-d6 was dried by stirring over potassium
for attack at the 4-position of pentafluoropyridine (typi-
cal of nucleophilic attack), unlike {Ni(PEt3)2}, which is
selective for attack at the 2-position.
2. [Pt(PR3)2] reacts via C-H activation with 2,3,5,6-
C5NHF4 at room temperature to form cis-[Pt(4-C5F4N)-
(H)(PCy3)2]. The latter is converted to the trans isomer
on UV irradiation. In contrast, [Pd(PR3)2] does not react
with 2,3,5,6-C5NHF4 at 100 °C.
3. trans-[Pt(H)2(PCy3)2] can activate the C-F bonds
of C5NF5 at room temperature to yield three com-
pounds: trans-[Pt(H)(FHF)(PCy3)2], trans-[Pt(4-C5NF4)-
(H)(PCy3)2], and trans-[Pt(4-C5NF4)(Cy)(PCy3)(PFCy2)].
4. Once again, C-F activation has proved to be a
useful source of metal fluoride complexes. Our mecha-
nistic interpretation carries the implication that plati-
num fluoride complexes behave very differently from
palladium fluoride complexes because the Pt-F bond
is weaker and longer than the Pd-F bond.44 Moreover,
the platinum complexes are susceptible to a rearrange-
ment similar to that observed by Grushin and Marshall
at rhodium.41
45
and then distilled under vacuum. The complexes [Pd(PCy3)]2
and [PdMe2(tmeda)]34 and [Pt(PR3)2]46 (R ) Cy, iPr) were
synthesized by published methods. The phosphines, PCy3 and
PiPr3, were either purchased from Strem or synthesized
according to the literature.47,48
The NMR spectra were recorded on Bruker DRX 500 or
AMX500 spectrometers (1H 500.13, 31P 202.46. 19F 407.4, 13C
125.78, 195Pt 107.52 MHz). The 1H NMR chemical shifts were
referenced to residual C6D5H at δ 7.15. The 13C{1H} spectra
were referenced to C6D6 at δ 128.0. The 31P{1H} NMR spectra
are reported downfield of an external solution of H3PO4 (85%).
The 19F NMR spectra were referenced to external C6F6 at δ
-162.9. The 195Pt spectra were referenced relative to the
absolute frequency of 86.024 MHz as δ 0.The infrared spectra
were recorded on Bruker Vector 22 or Mattson Research Series
spectrometers. Mass spectra were recorded on a VG Autospec
instrument and are listed for 196Pt. Elemental analyses were
(45) Yoshida, T.; Otsuka, S. Inorg. Synth. 1990, 28, 113.
(46) Yoshida, T.; Otsuka, S. Inorg. Synth. 1979, 19, 101.
(47) Issleib, K.; Brack, A. Z. Anorg. Allg. Chem. 1954, 277, 258.
(48) Ho¨hn, A., Ph.D. Thesis, University of Wu¨rzburg, 1986.
(49) SHELXTL-PLUS; Siemens Analytical X-Ray Instruments
Inc.: Madison, WI, 1990.
Experimental Section
1. General Procedures. Most of the synthetic work was
carried out on a Schlenk line or in a glovebox (under N2 or Ar)
(50) Sheldrick, G. M. SHELX-97, Program for Crystal Structure
Refinement; University of Go¨ttingen, 1997.

Reactivity of Fluoropyridines at Pd and Pt
Organometallics, Vol. 23, No. 26, 2004 6149
performed by Elemental Microanalysis Ltd, Devon, UK, or in
house (Bielefeld).
Reaction of [Pt(PCy3)2] with Pentafluoropyridine in
Hexane. A 2-fold excess of pentafluoropyridine (0.17 g, 1.01
mmol) was added to a hexane solution of [Pt(PCy3)2] (0.4 g,
0.53 mmol). The solvent was decanted and the mixture was
left to stand overnight at room temperature to give a colorless
crystal precipitate of 3-cis. The precipitate was recrystallized
from a layered solution of THF-hexane at -20 °C overnight
to give 25% (0.12 g, 0.132 mmol) yield.
2. Syntheses. trans-[PdF(4-C5NF4)(PCy3)2] (1a).
(a) [Pd(PCy3)2] (48 mg, 0.07 mmol) was dissolved in toluene
(10 mL), giving a yellow solution. After addition of penta-
fluoropyridine (9 µL, 0.8 mmol) the reaction mixture was
stirred for 6 h at 100 °C, and the volatiles were removed under
vacuum. The remaining colorless solid was washed with
hexane (5 mL), giving a colorless powder (yield 18 mg, 30%).
(b) [PdMe2(tmeda)] (221 mg, 0.88 mmol) and PCy3 (509 mg,
1.94 mmol) were dissolved in toluene (20 mL). After stirring
the reaction mixture for 1 h at room temperature, penta-
fluoropyridine (193 µL, 1.76 mmol) was added. The reaction
mixture was stirred for another 15 min, after which the
resulting light yellow solution was heated to 90 °C. The
reaction temperature was maintained for 4 h, during which
the solution turned to dark orange. The solution was then
cooled and filtered from a gray residue through a cannula, and
the volatiles were removed from the toluene filtrate in the
vacuum, giving a dark red residue. This residue was washed
with hexane (10 mL), resulting in a colorless powder. The gray
residue was suspended in toluene (10 mL) and the suspension
filtered. Evaporation of the solvent under vacuum yields a
colorless substance. Both colorless powders consisted of com-
pound 1a and were combined (yield 368 mg, 50%). Anal. Calcd
for C41H66F5NP2Pd: C, 58.89; H, 7.95; N 1.67. Found: C, 59.07;
H, 7.78; N, 1.51. IR (KBr, cm-1): 1615 (s), 1586 (w), 1497 (w),
1443 (s), 1424 (s), 1409 (s), 1352 (w), 1325 (vw), 1298 (w), 1268
(m), 1199 (s), 1174 (m), 1128 (m), 1112 (m), 1048 (w), 1005
(m), 922 (s), 888 (m), 849 (m), 823 (s), 733 (s), 695 (m), 533
(w), 524 (m), 512 (m), 493 (w), 468 (m), 401 (w), 393 (w).
trans-[PdF(4-C5NF4)(PiPr3)2] (1b). [PdMe2(tmeda)] (163
mg, 0.65 mmol) was dissolved in toluene (10 mL). The solution
was cooled to -20 °C, and PiPr3 was added (280 µL, 1.47
mmol). After stirring the reaction mixture for 1 h at -20 °C,
pentafluoropyridine (160 µL, 1.56 mmol) was added at -10
°C. The reaction mixture was stirred for another 15 min at
-10 °C, after which the resulting light yellow solution was
heated to 90 °C. The reaction temperature was maintained
for 4 h, during which the solution turned to dark orange. The
solution was then cooled and filtered through a cannula, and
the volatiles were removed from the filtrate in the vacuum.
The resulting light orange residue was washed with hexane
(10 mL) at -60 °C, giving a colorless powder (yield 310 mg,
80%). Anal. Calcd for C23H42F5NP2Pd: C, 46.36; H, 6.94; N
2.24. Found: C, 46.31; H, 7.10; N, 2.24. IR (KBr, cm-1): 1617
(s), 1591 (m), 1554 (m), 1451 (s), 1425 (s), 1389 (s), 1369 (m),
1245 (m), 1200 (s), 1091 (m), 1962 (m), 1036 (m), 921 (s), 883
(m), 824 (m), 731 (w), 693 (w), 660 (s), 619 (w), 527 (s), 458 (s).
trans-[Pt(4-C5NF4)(C6H11)(PCy3)(PFCy2)] (2a). The
method was identical to that for 2b (see below) and gave a
70% yield of 2a. The 13C{1H} spectrum exhibited a resonance
at δ 32.0 with prominent platinum satellites (JPtC ) 59 Hz).
Anal. Calcd for C41H66F5NP2Pt: C, 53.24; H, 7.19; N, 1.51.
Found: C, 52.31; H, 7.19; N, 1.51. MS (EI) (m/z): 924.4 (M+,
8%), 905.4 (M+ - F, 22%), 841 (M+ - C6H11, 100%).
cis-[Pt(H)(4-C5NF4)(PCy3)2] (3-cis).
A
solution of
[Pt(PCy3)2] (0.2 g, 0.26 mmol) in hexane was reacted with
2,3,5,6-tetrafluoropyridine (0.08 g, 0.53 mmol) under argon;
colorless crystals were formed overnight at room temperature
(yield 0.18 g, 77%). Anal. Calcd for C41H66F5NP2Pt: C, 54.29;
H, 7.45; N, 1.54. Found: C, 54.30; H, 7.70; N, 1.58. MS (EI)
(m/z): 905.4 (M+ - H, 2%), 755.4 (29%, Pt(PCy3)2+).
Isomerization of 3-cis to 3-trans. Two identical NMR
samples of 3-cis were prepared in NMR tubes containing 3-cis
(ca. 5 mg) in C6D6, and the reactions were followed by NMR
spectroscopy. The first one was irradiated for 2 h (broad band
irradiation with Philips HPK 125 W mercury arc, λ > 290 nm),
causing complete conversion of 3-cis to the corresponding trans
isomer 3-trans. The second sample was heated at ∼80 °C,
giving the following conversions of 3-cis to 3-trans determined
by the integration ratio of the hydride resonances: after 2 h
integration Hcis/Htrans ) 1:0.2, after 6 h 1:0.4, after heating
overnight 1:0.9.
Reaction of cis-[Pt(H)2(PCy3)2] with Pentafluoropyri-
dine. [Pt(H)2(PCy3)2] (0.5 g, 0.66 mmol) was dissolved in THF
(15 mL), and C5NF5 (0.2 g, 1.18 mmol) was added to the
solution. The reaction mixture was stirred for 1 h. The solvent
was removed under vacuum. The residue was extracted with
benzene and recrystallized from THF-hexane at -30 °C to
yield a mixture of (1:1:1) three products (0.34 g).
Crystal Structures. Crystallographic data for 1a′, 1b, 2a,
and 3-cis are listed in Table 7.
Methods for 1a′. Hydrogen atoms at O(1) were located in
the difference Fourier map, but could not be refined isotropi-
cally. They were fixed with a bond length of 0.84 Å and a
displacement parameter of 1.2 times that of O(1). The Flack
parameter of 0.13(3) indicates racemic twinning.
Methods for 3-cis. The hydride was located on a difference
map after all non-hydrogen atoms had been located and riding
hydrogen atoms included.
Acknowledgment. We acknowledge the Deutsche
Forschungsgemeinschaft (grants BR-2065/1-3 and BR-
2065/1-4) for financial support. T.B. also thanks Profes-
sor P. Jutzi for his generous and continuing support.
We are indebted to Dr. S. A. Macgregor (Heriot-Watt)
for suggesting the metallophosphorane mechanism to
us. We also appreciated productive discussions with
Professor R. Jackson (Sheffield) and Dr. S. B. Duckett
(York).
Supporting Information Available: Figure S1 (2D {195Pt-
1H} correlation spectrum), Figure S2-S9 (ORTEP diagrams
and packing diagrams of 1a′, 1b, 2a and 3-cis), and tables of
atomic coordinates, anisotropic displacement parameters, and
bond distances and angles for 1a′, 1b, 2a, and 3-cis. Crystal-
lographic data are also available in cif format. This material
is available free of charge via the Internet at http://pubs.acs.org.
trans-[Pt(4-C5NF4)(CHMe2)(PiPr3)(PFiPr2)] (2b). Penta-
fluoropyridine (0.131 g, 0.78 mmol) was added to a solution of
[Pt(PiPr3)2] (0.2 g, 0.39 mmol) in THF. The mixture was stirred
for 1 h at room temperature to yield a white precipitate. The
precipitate was recrystallized from a layered solution of THF-
hexane at -20 °C overnight to give 2b (yield 0.21 g, 80%). The
complex was not obtained analytically pure, since it was not
stable under vacuum.
OM049448P