Rapid intermolecular carbon-fluorine bond activation of pentafluoropyridine at nickel(0): Comparative reactivity of fluorinated arene and fluorinated pyridine derivatives

Article abstract of DOI:10.1021/om9705160

Reaction of hexafluorobenzene with Ni(COD)₂ (COD = 1,5,-cyclooctadiene) in the presence of triethylphosphine or with Ni(PEt₃)₄ at room temperature results in very slow formation of trans-Ni(PEt₃)₂(C₆F₅)F (1). The X-ray crystal structure reveals a molecular complex with approximately square-planar coordination at nickel, a Ni-F distance of 1.836(5) ? and a Ni-C distance of 1.878(7) ?. Analogous reactions with pentafluoropyridine and 2,3,5,6-tetrafluoropyridine proceed much faster. Both reactions yield C-F activation products analogous to 1 in which a single regioisomer is dominant. The crystal structure of trans-Ni(PEt₃)₂(C₅HF₃N)F (3) shows that the trifluoropyridyl ligand is metalated at the 2-position. The Ni-F and Ni-C distances are 1.856(2) and 1.869(4) ?, respectively. In the structures of both 1 and 3, the plane of the aryl ring is perpendicular to the nickel coordination plane. These structures provide the first values of nickel-fluorine distances at square-planar Ni(II). The reaction of Ni(COD)₂ with PEt₃ and 3,5-dichloro-2,4,6-trifluoropyridine yields exclusively trans-Ni(PEt₃)₂(C₅ClF₃N)Cl (4), the product of C-Cl activation with the metal at the 3-position of the ring. The corresponding reaction with 2,3,4,5,6,-pentafluorostyrene results in rapid formation of the alkene coordination product, Ni(PEt₃)₂(η²-CH₂=CHC ₆F₅) (6). The crystal structure of 6 shows the typical trigonal Ni(0) geometry with the coordinated atoms almost perfectly coplanar with the nickel. The Ni-C distances average 1.960(6) ?; the P-Ni-P angle is 115.0(1)°. Reaction with pentafluorobenzene and methoxypentafluorobenzene yield C-F activation products very slowly with little regioselectivity. The studies reported in this paper demonstrate that intermolecular C-F activation of a fluoroaromatic can take place rapidly and in good yield at a first row transition metal through the suitable choice of substrate.

Full text of DOI:10.1021/om9705160

4920
Organometallics 1997, 16, 4920-4928
Ra p id In ter m olecu la r Ca r bon -F lu or in e Bon d Activa tion
of P en ta flu or op yr id in e a t Nick el(0): Com p a r a tive
Rea ctivity of F lu or in a ted Ar en e a n d F lu or in a ted
P yr id in e Der iva tives
Leroy Cronin, Catherine L. Higgitt, Ralf Karch, and Robin N. Perutz*
Department of Chemistry, University of York, Heslington, York YO1 5DD, U.K.
Received J une 19, 1997X
Reaction of hexafluorobenzene with Ni(COD)2 (COD ) 1,5,-cyclooctadiene) in the presence
of triethylphosphine or with Ni(PEt3)4 at room temperature results in very slow formation
of trans-Ni(PEt3)2(C6F5)F (1). The X-ray crystal structure reveals a molecular complex with
approximately square-planar coordination at nickel, a Ni-F distance of 1.836(5) Å and a
Ni-C distance of 1.878(7) Å. Analogous reactions with pentafluoropyridine and 2,3,5,6-
tetrafluoropyridine proceed much faster. Both reactions yield C-F activation products
analogous to 1 in which a single regioisomer is dominant. The crystal structure of trans-
Ni(PEt3)2(C5HF3N)F (3) shows that the trifluoropyridyl ligand is metalated at the 2-position.
The Ni-F and Ni-C distances are 1.856(2) and 1.869(4) Å, respectively. In the structures
of both 1 and 3, the plane of the aryl ring is perpendicular to the nickel coordination plane.
These structures provide the first values of nickel-fluorine distances at square-planar Ni(II).
The reaction of Ni(COD)2 with PEt3 and 3,5-dichloro-2,4,6-trifluoropyridine yields exclusively
trans-Ni(PEt3)2(C5ClF3N)Cl (4), the product of C-Cl activation with the metal at the
3-position of the ring. The corresponding reaction with 2,3,4,5,6,-pentafluorostyrene results
in rapid formation of the alkene coordination product, Ni(PEt3)2(η2-CH2dCHC6F5) (6). The
crystal structure of 6 shows the typical trigonal Ni(0) geometry with the coordinated atoms
almost perfectly coplanar with the nickel. The Ni-C distances average 1.960(6) Å; the
P-Ni-P angle is 115.0(1)°. Reaction with pentafluorobenzene and methoxypentafluoroben-
zene yield C-F activation products very slowly with little regioselectivity. The studies
reported in this paper demonstrate that intermolecular C-F activation of a fluoroaromatic
can take place rapidly and in good yield at a first row transition metal through the suitable
choice of substrate.
In tr od u ction
thermal C-F oxidative addition to form complexes of
the type M(C6F5)F (e.g., Pt(But PCH2PBut )(C6F5)F);7,12
2
2
Interest in carbon-fluorine activation by transition
metals has been increasing rapidly with the discovery
of several systems capable of activating C-F bonds both
intramolecularly and intermolecularly. Recent discov-
eries, summarized in two thorough reviews,1,2 include
systems capable of breaking the C-F bonds of perfluo-
roarenes and perfluoroalkanes. Catalytic C-F activa-
tion has also become a reality.3,4 Industrial interest in
functionalized fluorine compounds and polymers5 sug-
gests that it is timely to turn to the study of function-
alized organofluorine compounds.
At this stage, we recognize several classes of reaction
of hexafluorobenzene with transition metal complexes:
(i) Nucleophilic substitution of fluoride at C6F6 by
anionic complexes (e.g., with [Fe(η5-C5H5)(CO)2]-;6 (ii)
Coordination of C6F6 to transition metals in η2, η4, and
η6 modes (e.g., Rh(η5-C5H5)(PMe3)(η2-C6F6), Ir(η5-C5H5)-
(η4-C6F6), or W(η6-C6F6)2);7-11 (iii) Photochemical or
(v) Photochemical or thermal reaction with metal dihy-
dride complexes to form products of the type M(C6F5)H
liberating HF (e.g., Ru(dmpe)2(C6F5)H);7,13,14 (vi) Com-
bination of intermolecular C-F with intramolecular
C-H activation to yield products of the type M(C6F5)
and liberate HF (e.g., with Re(η5-C5Me5)(CO)3);15,16 (vii)
Electron transfer from transition metal complexes to
C6F6 (e.g., with Cr(η6-C6H6)2).17
The reactivity adjusts to the presence of a substituent
other than fluorine on the aromatic ring in different
ways according to the transition metal system. For
(7) Belt, S. T.; Helliwell, M.; J ones, W. D.; Partridge, M. G.; Perutz,
R. N. J . Am. Chem. Soc. 1993, 115, 7685.
(8) Bell, T. W.; Helliwell, M.; Partridge, M. G.; Perutz, R. N.
Organometallics 1992, 11, 1911.
(9) Higgitt, C. L.; Klahn, A. H.; Moore, M. H.; Oelckers, B.; Partridge,
M. G.; Perutz, R. N. J . Chem. Soc., Dalton Trans. 1997, 1269.
(10) Barker, J . J .; Orpen, A. G.; Seeley, A. J .; Timms, P. L. J . Chem.
Soc., Dalton Trans. 1993, 3097.
(11) Martin, A.; Orpen, A. G.; Seeley, A. J .; Timms, P. L. J . Chem.
Soc., Dalton Trans. 1994, 2251.
(12) Hofmann, P.; Unfried, G. Chem. Ber. 1992, 125, 659.
(13) Whittlesey, M. K.; Perutz, R. N.; Moore, M. H. J . Chem. Soc.,
Chem. Commun. 1996, 787.
(14) Whittlesey, M. K.; Perutz, R. N.; Greener, B.; Moore, M. H.
Chem. Commun. 1997, 187.
(15) Klahn, A. H.; Moore M. H.; Perutz, R. N. J . Chem. Soc., Chem.
Commun. 1992, 1699.
(16) Ballhorn, M.; Partridge, M. G.; Perutz, R. N.; Whittlesey, M.
K. J . Chem. Soc., Chem. Commun. 1996, 961.
(17) Aspley, C.; Higgitt, C. L.; Long, C.; Perutz, R. N. Unpublished
results.
X Abstract published in Advance ACS Abstracts, October 1, 1997.
(1) Kiplinger, J . L.; Richmond, T. G.; Osterberg, C. E. Chem. Rev.
1994, 94, 373.
(2) Burdeniuc, J .; J edlicka, B.; Crabtree, R. H. Chem. Ber./ Recl.
1997, 130, 145.
(3) Aizenberg, M.; Milstein, D. Science 1994, 265, 359. Aizenberg,
M.; Milstein, D. J . Am. Chem. Soc. 1995, 117, 8674.
(4) Kiplinger, J . L.; Richmond, T. G. J . Chem. Soc., Chem. Commun.
1996, 1115; J . Am. Chem. Soc. 1996, 118, 1805.
(5) Clark, J . H.; Wails, B.; Bastock, T. W. Aromatic Fluorination;
CRC Press: Boca Raton, FL, 1996.
(6) King, R. B.; Binette, M. B. J . Organomet. Chem. 1964, 2, 38.
S0276-7333(97)00516-5 CCC: $14.00 © 1997 American Chemical Society

Fluorinated Arene and Pyridine Derivatives
Organometallics, Vol. 16, No. 22, 1997 4921
Sch em e 1. Rea ction s of Ni(COD)2 w ith F lu or oa r en es, F lu or op yr id in es, a n d Tr ieth ylp h osp h in e
instance, hexafluorobenzene undergoes C-F oxidative
addition at the Rh(η5-C5Me5)(PMe3) fragment,7 but
pentafluorobenzene undergoes only C-H bond activa-
tion.18 In contrast, Ru(dmpe)2H2 yields products of C-F
bond activation with both hexafluorobenzene and pen-
tafluorobenzene:13 i.e., Rh(η5-C5Me5)(PMe3) is selective
for C-H over C-F activation, while Ru(dmpe)2H2 is
selective for C-F over C-H insertion. The presence of
a methoxy substituent is also influential. With hexaflu-
orobenzene, Rh(η5-C5H5)(PMe3)(C2H4) reacts photochem-
ically to form Rh(η5-C5H5)(PMe3)(η2-C6F6) but the C-F
oxidative-addition product is observed only in low-
temperature matrices.7 In contrast, the corresponding
reaction with C6F5OMe yields Rh(η5-C5H5)(PMe3)(η2-
C6F5OMe), which converts to the metallacycle Rh(η5-
Among the reactions reported by Fahey and Mahan
was that with hexafluorobenzene, probably the first
report of C-F oxidative addition.19 However, the reac-
tion was slow with a yield of only 7%, and characteriza-
tion of the product as trans-Ni(PEt3)2(C6F5)F was lim-
ited to elemental analysis and IR spectroscopy. This
result contrasted with early work by Stone et al. which
showed Ni(0) reacting with perfluoroalkenes to form
either Ni(η2-perfluoroalkene) complexes or Ni(II) met-
allacycles.21 Since then, three other relevant C-F
activation reactions have been reported at nickel.
Firstly, Ni(COD)2 reacts with (C6F5)CHdNC6H4(NMe2)
to form a C-F activated product.22 Secondly, Ni(dtbpe)-
(η2-C6H6) (dtbpe ) tBu2PCH2CH2PtBu2) reacts with C6F6
to form Ni(dtbpe)(η2-C6F6).23a This isolable complex
reacts over days at room temperature to form Ni(dtbpe)-
(C6F5)F. The formation of the oxidative-addition prod-
uct provides direct evidence for the thermal conversion
of an (η2-C6F6) complex to the pentafluorophenyl fluo-
ride. Thirdly, Ni(bpy)Et2 has been shown to react with
C6F6 to give Ni(bpy)(C6F5)2.23b Evidence for precoordi-
nation of electron-withdrawing arenes to Ni(bpy)Et2 was
obtained in low-temperature experiments.
C5H5)(PMe3)(C6F4OCH2) with liberation of HF.16
A
methoxy substituent, however, has little effect on the
reactivity of Ru(dmpe)2H2.13
In 1977, Fahey and Mahan reported that carbon-
halogen oxidative addition occurred on reaction of
haloaromatics with Ni(COD)2 (COD ) 1, 5-cyclooctadi-
ene) in the presence of PEt3, yielding products of the
type trans-Ni(PEt3)2(aryl)X (X ) halogen).19 The initial
reaction with PEt3 was reported to yield Ni(COD)-
(PEt3)2, which subsequently reacted with the haloarene.
Isolated Ni(PEt3)4 was sometimes used as a more
reactive precursor: Ni(PEt3)4 (colorless) is at equilibri-
um in solution with Ni(PEt3)3 (purple) with an equilib-
In this paper, we report the full characterization of
the product of the reaction of Ni(COD)2 with PEt3 and
C6F6, confirming its identity as trans-Ni(PEt3)2(C6F5)F.
We also investigate the reactivity of Ni(0) complexes
toward three different functionalized analogues of hexa-
fluorobenzene: C6F5(CHdCH2), C6F5OMe, and C6F5H.
Most importantly, we show that the corresponding
reaction with fluorinated pyridines is orders of magni-
tude more rapid and is selective for C-F over C-H
oxidative addition.
rium constant of ca. 10-2
. Later, Tsou and Kochi
showed that the reactions of Ni(PEt3)4 with haloarenes
also yield paramagnetic Ni(I) complexes, Ni(X)(PEt3)3,
as competing products, and that the ratio of the Ni(I) to
the Ni(II) product is affected by the halogen (Cl, Br, I),
the solvent polarity, and the aryl group.20 They showed
that the kinetically active species is Ni(PEt3)3 and
argued that both types of product are formed via a
common intermediate identified as a tight ion pair,
{Ni(PEt3)3+‚ArX-}.
(21) Cundy, C. S.; Green, M.; Stone, F. G. A. J . Chem. Soc. A 1970,
1647.
(22) Osterberg, C. E.; Richmond, T. G. In Inorganic Fluorine
Chemistry toward the 21st Century; Thrasher J . S., Strauss, S. H., Eds.;
ACS Symposium Series 555; American Chemical Society: Washington,
DC, 1994; pp 392-404.
(23) (a) Bach, I.; Po¨rschke, K.-R.; Goddard, R.; Kopiske, C.; Kru¨ger,
C.; Rufinska, A.; Seevogel, K. Organometallics 1996, 15, 4959. (b)
Yamamoto, T.; Abla, M. J . Organomet. Chem. 1997, 535, 209.
(18) Selmeczy, A. D.; J ones, W. D.; Partridge, M. G.; Perutz, R. N.
Organometallics 1994, 12, 522.
(19) Fahey, D. R.; Mahan, J . E. J . Am. Chem. Soc. 1977, 99, 2501.
(20) Tsou, T. T.; Kochi, J . R. J . Am. Chem. Soc. 1979, 101, 6319.

4922 Organometallics, Vol. 16, No. 22, 1997
Ta ble 1. NMR Da ta a t 298 Ka
Cronin et al.
complex
1H
31P{1H}
19F
13C{1H}
1 (C6D6)
0.97 (m, 18H, CH3),
1.08 (m, 12H, CH2)
12.24 (d, J PF ) 46)
-390.33 (tt, J PF ) 48, J FF ) 9, NiF), 7.78 (s, CH3), 13.3 (td,
-163.75 (tm, J ) 21, 2F, Fmeta),
-161.05 (t, J ) 20, 1F, Fpara),
J PC ) 20,e J FC ) 5, CH2),
113.6 (m, Cipso),b
-115.39 (d, J ) 32, 2F, Fortho
)
135.9 (dm, J ) 255, CF),
147.0 (dm, J ) 240, CF)
6.91 (s, CH3), 12.6 (td,
J PC ) 12,e J FC ) 3, CH2),
129.8 (dm, J ) 199, CF),
143.5 (dm, J ) 266, CF),
146.6 (dm, J ) 228, CF),
148.7 (dm, J ) 231, CF),
2a (THF-d8) 1.29 (m, 18H, CH3),
1.46 (m, 12H, CH2)
14.19 (d, J PF ) 47)
-371.35 (td, J PF ) 47, J FF ) 6,
1F, NiF), -173.38 (m, 1F, F5),
-150.75 (m, 1F, F4),
-131.33 (t, J ) 27, 1F, F3),
-84.70 (m, 1F, F6)
163.6 (m, Cipso
)
2b, 2c
(THF-d8)
3a (THF-d8) 1.28 (m, 18H, CH3),
1.44 (m, 12H, CH2),
6.98 (m, 1H, CH)
13.55 (d, J PF ) 48)
13.62 (d, J PF ) 49)
9.89 (d, J PF ) 48)
-368.54 (t, J ) 48, NiF),
-368.26 (t, J ) 50, NiF)
-370.31 (t, J ) 48, NiF),
-152.83 (dm, J ) 31, 1F, CF),
-111.25 (d, J ) 31, 1F, CF),
-92.23 (td, J ) 32, 8, 1F, CF)
8.05 (s, CH3), 13.78 (t,
J PC ) 11,e CH2),
109.5 (dd, J ) 31, 18, CH),
140.2 (dm, J ) 253, CF),
147.5 (dm, J ) 217, CF),
160.4 (dm, J ) 234, CF),
160.5 (m, Cipso
)
3b (THF-d8)
4 (C6D6)
9.34 (d, J PF ) 49)
15.4 (s)
-367.16 (t, J ) 45, NiF)
-82.35 (m, 1F, CF), -75.22 (m,
1F, CF), -47.97 (m, 1F, CF)
0.88 (m, 18H, CH3),
1.14 (m, 12H, CH2)
7.88 (s, CH3), 14.3 (t,
J PC ) 13,e CH2),
100.5 (m, Cipso),
111.5 (m, CCl),
157.0 (dm, J ) 248, CF),
161.6 (dm, J ) 228, CF),
169.2 (dm, J ) 222, CF)
5 (C6D6)
1.07 (m, 18H, CH3),
1.32 (m, 12H, CH2)
14.97 (s)
-162.89 (m, 2F, Fmeta),
-160.38 (t, J ) 20, 1F, Fpara),
-114.53 (m, 2F, Fortho
)
6d (THF-d8) 1.03 (dt, J PH ) 14.5,
J HH ) 7.6, 9H, CH3),
1.19 (dt, J PH ) 14.4,
J HH ) 7.5, 9H, CH3),
1.39 (ps-septet, J ) 7.2,
3H, CH2), 1.54 (ps-septet,
J ) 7.2, 3H, CH2),
1.74 (ps-quin, J ) 7.4,
7H, CH2 and Hγ or Hâ),
2.20 (m, 1H, Hâ or Hγ),
3.28 (ps-septet, J HH ) 11,
1H, HR)
15.29 (d, J PP ) 37),
19.65 (dd, J PP ) 37,
J PF ≈ 5)
-173.2 (tm, J ) 21, 2F, Fortho),
8.64 (d, J ) 1, CH3), 8.85 (s, CH3),
18.8 (dd, J ) 18, 3, CH2),
19.6 (dd, J ) 18, 3, CH2),
34.6 (dm, J ) 21, CHdCH2),
37.4 (d, J ) 18, CHdCH2),
126.2 (m, Cipso), 135.5 (dm,
J ) 244, CF),
-169.83 (tm, J ) 22, 2F, Fmeta),
-149.02 (m, CF, 1F, Fpara
)
138.7 (dm, J ) 245, CF),
144.1 (dm, J ) 241, CF)
7a (THF-d8)
7b (THF-d8)
7c (THF-d8)
8a (C6D6)
8b (C6D6)
9 (C6D6)
13.6 (d, J PF ) 46)
13.1 (d, J PF ) 46)
c
13.32 (d, J PF ) 46)
13.01 (d, J PF ) 46)
6.28 (d, J PF ) 45)
-385.38 (tt, J FP ) 46, J FF ) 9, NiF)
-385.65 (tt, J FP ) 46, J FF ) 9, NiF)
-389.43 (tt, J FP ) 46, J PF ) 9, NiF)
-389.03 (t, J FP ) 45, NiF)
-389.49 (t, J FP ) 45, NiF)
-388.03 (s, br, NiF),
-164.08 (tm, J ) 20, 2F, Fmeta),
-161.77 (t, J ) 19, 1F, Fpara),
-115.30 (d, J ) 27, 2F, Fortho
)
a
b
d
Reported in ppm (δ) and J values in Hertz. One CF resonance is masked by solvent. c Obscured. 1H{31P} spectrum of 6: 1.02 (t,
J ) 7.4), 1.19 (dt, J ) 7.5, 2.6), 1.39 (ps-sextet, J ) 7.2), 1.54 (ps-sextet, J ) 7.2), 1.74 (q, J ) 7.4), 2.20 (d, J ) 12), 3.28 (t, J ) 11).
e Virtual coupling.
Resu lts
fluorine nucleus. The 19F NMR spectrum shows a
triplet of triplets at δ -390.33 characteristic of the metal
fluoride, with coupling to both phosphorus nuclei (J PF
) 48 Hz) and the two ortho fluorine nuclei of the Ni-
(C6F5) group (4J FF ) 9 Hz). Three further resonances
at δ -163.75, -161.05, and -115.39 reveal the presence
of the C6F5 group. The trans geometry is indicated by
the equivalence of the 31P nuclei and the characteristic
virtual coupling pattern in the 13C resonance for the CH2
groups. The structure of 1 was also determined crys-
tallographically (see below). The complex can be handled
without decomposition in a glovebox but decomposes
over a few hours under vacuum.
Rea ction w ith Hexa flu or oben zen e. Nickel tetra-
kis(triethylphosphine) was isolated from the reaction of
Ni(1,5-cyclooctadiene)2 with PEt3.24 Reaction of Ni-
(PEt3)4 with C6F6 (20% excess) in hexane solution at
room temperature for 4 weeks yielded trans-Ni(PEt3)2-
(C6F5)F (1) (Scheme 1), which was crystallized at -20
°C. The isolated yield of 48% (c.f. 7% previously)19 was
limited principally by the extreme solubility of the
product. The structure of the product was determined
definitively by multinuclear NMR spectroscopy (Table
1). The 31P{1H} NMR spectrum shows a doublet at δ
12.24 (J PF ) 46 Hz), indicative of coupling to a single
The same product was obtained by addition of PEt3
(5 equiv) and C6F6 (1.3 equiv) to Ni(COD)2 in hexane
(24) Ittel, S. D. Inorg Synth. 1974, 17, 117.

Fluorinated Arene and Pyridine Derivatives
Organometallics, Vol. 16, No. 22, 1997 4923
Ta ble 2. P r in cip a l Bon d Len gth s (Å) a n d An gles
(d eg) of tr a n s-Ni(P Et3)2(C6F 5)F , 1
Ni(1)-F(1)
Ni(1)-C(1)
Ni(1)-P(1)
Ni(1)-P(2)
F(2)-C(2)
F(3)-C(3)
F(4)-C(4)
1.836(5)
1.878(7)
2.199(3)
2.201(3)
1.358(8)
1.347(9)
1.358(9)
F(5)-C(5)
F(6)-C(6)
C(1)-C(2)
C(1)-C(6)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
1.355(10)
1.339(9)
1.375(10)
1.409(10)
1.370(11)
1.381(12)
1.339(13)
1.354(11)
F(1)-Ni(1)-C(1)
F(1)-Ni(1)-P(1)
C(1)-Ni(1)-P(1)
F(1)-Ni(1)-P(2)
C(1)-Ni(1)-P(2)
P(1)-Ni(1)-P(2)
C(9)-P(1)-Ni(1)
C(7)-P(1)-Ni(1)
C(11)-P(1)-Ni(1)
C(13)-P(2)-Ni(1)
C(17)-P(2)-Ni(1)
C(15)-P(2)-Ni(1)
C(2)-C(1)-C(6)
C(2)-C(1)-Ni(1)
C(6)-C(1)-Ni(1)
177.4(3)
87.7(2)
92.8(2)
85.6(2)
94.2(2)
171.52(11)
115.1(6)
121.0(4)
109.1(8)
111.7(4)
120.2(3)
109.5(3)
112.4(7)
124.8(6)
122.8(6)
F(2)-C(2)-C(3)
F(2)-C(2)-C(1)
C(3)-C(2)-C(1)
F(3)-C(3)-C(2)
F(3)-C(3)-C(4)
C(2)-C(3)-C(4)
C(5)-C(4)-F(4)
C(5)-C(4)-C(3)
F(4)-C(4)-C(3)
C(4)-C(5)-C(6)
C(4)-C(5)-F(5)
C(6)-C(5)-F(5)
F(6)-C(6)-C(5)
F(6)-C(6)-C(1)
C(5)-C(6)-C(1)
117.4(8)
117.4(7)
125.1(8)
121.1(9)
120.0(8)
118.8(8)
122.5(9)
118.8(8)
118.7(9)
121.2(8)
117.9(8)
120.9(9)
117.2(7)
119.1(7)
123.6(8)
F igu r e 1. Molecular structure of 1, trans-Ni(PEt3)2-
(C6F5)F: ORTEP26 plot with 30% probability thermal ellips-
oids. The hydrogen atoms have been omitted for clarity.
lower quartile of Ni-(η1-aryl) distances, as would be
anticipated with a C6F5 group,28 but is almost identical
to that for Ni(PPh2Me)2(C6F5)Br (1.880(4) Å). The
dihedral angle between the plane of the aryl ring and
the nickel coordination plane is 89.2(2)°. For compari-
son, a search of CSD for related Ni(phosphine)2(aryl)X
(X ) halide) complexes revealed a range of dihedral
angles from 84° to 101°.27 Two of the ethyl groups on
P(1) show very large thermal ellipsoids, but alternative
solutions in which the occupancy was split over several
positions proved unsatisfactory. There are no close
intermolecular contacts.
Rea ction w ith P en ta flu or op yr id in e. Addition of
PEt3 to Ni(COD)2 suspended in hexane generated the
characteristic cloudy purple-red color of Ni(PEt3)3.
Subsequent addition of pentafluoropyridine (30% excess)
resulted in a change in color to yellow-orange after 3
min. The three products, isolated after 2 h reaction at
room temperature, were readily assigned as fluoride
complexes on the basis of characteristic 19F resonances
at ca. δ -370 and were present in a ratio of 85:12:3
(Table 1). The dominant product (2a ) is assigned as the
2-pyridyl isomer of trans-Ni(PEt3)2(C5F4N)F on the basis
of the four multiplets of equal integration in the 19F
NMR spectrum for the fluoroaromatic region and a
doublet coupling of 6 Hz between the fluoride at δ -371
and the multiplet at δ -131 (Scheme 1, Table 1). The
assignments of the remaining 19F resonances were
completed on the basis of selective 19F-19F decoupling
experiments and chemical shift data for free pentafluo-
robenzene. Activation of the C-F bond adjacent to the
metal is consistent with the crystallographic data on the
product of the reaction with tetrafluoropyridine (see
below). The minor resonances are tentatively assigned
as the 3-pyridyl and 4-pyridyl isomers (2b,c). The 31P
resonances of 2 show some exchange broadening in the
presence of excess PEt3.
without isolating Ni(PEt3)4. The reaction may be moni-
tored by following the decrease in the 31P resonance of
Ni(PEt3)2(COD) at δ 18 relative to that of residual Et3-
PO at δ 46. The resonances of Ni(PEt3)4/Ni(PEt3)3 (δ
ca. 3 to 4) and of PEt3 (δ -19) are broadened by
exchange23,25 and are unsuitable for monitoring the
reaction, although the former sharpens on cooling.
After 4 weeks, NMR spectra showed that all precursor
complexes were consumed and converted to 1, leaving
only excess PEt3 and a trace amount of Et3PO. At-
tempts to use higher temperatures or different solvents
(35 and 45 °C in C6D6 or 35 °C in THF-d8) failed to speed
up the reaction. Addition of an excess of hexafluoroben-
zene (2-10-fold) was also attempted without success.
Under these conditions the reaction yielded, in addition
to 1, three difluorophosphoranes, PR3F2 (R ) Et, CH2-
FCH2, etc.), characterized by triplets in the 31P NMR
spectrum at ca. δ -12 to -20 with J PF ) 550-650 Hz
and corresponding doublet resonances around δ -40 in
the 19F NMR spectrum. These species were also formed
in other reactions with excess fluoroarenes discussed
in this paper (see Experimental Section), but their full
identification will not be pursued here.
Cr ysta l Str u ctu r e of tr a n s-Ni(P Et3)2(C6F 5)F (1).
Complex 1 was crystallized from hexane at -20 °C. The
crystal structure (ORTEP diagram26 in Figure 1, Table
2) shows the expected trans disposition of the phosphine
ligands with approximately square-planar coordination
at nickel (F(1), C(1), P(1), and P(2) form a plane with
rms deviation of 0.069 Å and Ni(1) lies out of the plane
by 0.027 Å). Angles between adjacent ligands at nickel
vary from 85.6(2)° to 94.2(2)°. The most important
parameter is the nickel-fluorine distance of 1.836(5) Å,
since there are no measurements of other Ni-F dis-
tances at four-coordinate Ni(II) according to CSD.27 The
nickel-carbon distance of 1.878(7) Å lies within the
Rea ction w ith 2,3,5,6-Tetr a flu or op yr id in e. The
reaction with 2,3,5,6-tetrafluoropyridine was designed
(25) Cundy, C. S. J . Organomet. Chem. 1974, 69, 305.
(26) J ohnson, C. K. ORTEP. Report ORNL-5138; Oak Ridge, Na-
tional Laboratory: Oak Ridge, TN, 1976.
(27) Fletcher, D. A.; McMeeking, R. F.; Parkin, D. J . J . Chem. Inf.
Comput. Sci. 1996, 36, 746.
(28) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G.; Taylor, R. J . Chem. Soc., Dalton Trans. 1989, S1. Churchill, M.
R.; Kaira, K. L.; Veidis, V. Inorg. Chem. 1973, 12, 1656.

4924 Organometallics, Vol. 16, No. 22, 1997
Cronin et al.
cent ligands at nickel vary from 86.5(1)° to 91.1(1)°. The
Ni-C distance at 1.869(4) Å and Ni-F distances at
1.856(2) Å differ little from those in 1. The coordination
plane is better defined than in 1, with a rms deviation
of 0.047 Å and the Ni atom 0.009 Å from the plane. The
aryl ring and nickel coordination planes are again
almost orthogonal (dihedral angle 86.8(1)°). There is a
significant intermolecular contact between the fluoride
F(1) on one molecule and the C(4)-H(4) group of the
pyridine ring on the adjacent molecule (r(F‚‚‚C) ) 3.007-
(4) Å). The riding model gives an estimate of the H‚‚‚F
distance of 2.08(4) Å and the F‚‚‚H-C angle of 174(1)°.
Rea ction w ith 3,5-Dich lor o-2,4,6-tr iflu or op yr i-
d in e. The reaction with 3,5-dichloro-2,4,6-trifluoropyr-
idine was designed to test the selectivity for C-Cl
compared to C-F bond activation. It was conducted as
for the reaction with pentafluoropyridine. A single
product was formed in 85% yield, characterized as the
product of C-Cl activation, trans-Ni(PEt3)2(5-chloro-
2,4,6-trifluoropyrid-3-yl)Cl (4) (Scheme 1, Table 1).
Reaction with Ch lor open taflu or oben zen e. The re-
action with chloropentafluorobenzene had already been
demonstrated by Fahey and Mahan to yield the product
of C-Cl and not C-F bond activation.19 We repeated
it in order to obtain high-quality NMR and IR data of
the product, trans-Ni(PEt3)2(C6F5)Cl (5, Table 1).
F igu r e 2. Molecular structure of 3a , trans-Ni(PEt3)2(C5-
HF3N)F (C5HF3N ) 2,5,6-trifluoropyrid-2-yl): ORTEP26
plot with 30% probability thermal ellipsoids. The hydrogen
atoms, with the exception of H(4), have been omitted for
clarity.
Ta ble 3. P r in cip a l Bon d Len gth s (Å) a n d An gles
Rea ction w ith P en ta flu or ostyr en e. The reaction
with pentafluorostyrene was carried out in order to test
whether C-F bond activation might be assisted by
precoordination of the alkene moiety in the same way
as we surmised that the nitrogen atom assists with the
reaction of pentafluoropyridine. The reaction yielded
completely different spectra from those described above.
The 1H spectrum showed resonances for two of the
alkene protons at δ 2.20 and 3.28, providing immediate
evidence for alkene coordination (Table 1, the third
alkene proton was obscured by a CH2 resonance of the
PEt3 ligand). Two sets of resonances were found for the
CH3 and two for the CH2 groups of the phosphine in
the 1H and 13C{1H} spectra (coupling constants were
identified with the aid of a 1H{31P} spectrum). They
showed coupling to a single 31P nucleus, unlike the
virtual coupling pattern observed in the 13C{1H} spectra
of complexes 1-5. The 31P{1H} spectrum exhibited two
mutually coupled doublets (J PP ) 37 Hz), one of which
showed a small coupling to a single 19F nucleus (ca. 5
Hz). The 19F spectrum revealed three resonances in the
aromatic region and none elsewhere. The product could
be identified readily as the Ni(0) complex Ni(PEt3)2(η2-
CH2dCHC6F5) (6) (Scheme 1) and was also character-
ized crystallographically. In the presence of excess
PEt3, the two 31P resonances coalesced to a single broad
peak at ca. δ 18 and the peak due to free PEt3 was also
broadened, providing direct evidence for intermolecular
exchange of the PEt3 ligands with free phosphine.
(d eg) of tr a n s-Ni(P Et3)2(C5HF 3N)F , 3a
Ni(1)-F(1)
Ni(1)-C(2)
Ni(1)-P(2)
Ni(1)-P(1)
F(6)-C(6)
F(5)-C(5)
F(3)-C(3)
1.856(2)
1.869(4)
2.191(3)
2.198(3)
1.356(5)
1.365(4)
1.361(4)
F(3)-C(3)
N(1)-C(6)
N(1)-C(2)
C(2)-C(3)
C(6)-C(5)
C(5)-C(4)
C(4)-C(3)
1.361(4)
1.301(5)
1.360(5)
1.391(5)
1.368(5)
1.353(5)
1.376(5)
F(1)-Ni(1)-C(2)
F(1)-Ni(1)-P(2)
C(2)-Ni(1)-P(2)
F(1)-Ni(1)-P(1)
C(2)-Ni(1)-P(1)
P(2)-Ni(1)-P(1)
C(9)-P(1)-Ni(1)
C(7)-P(1)-Ni(1)
176.58(12) N(1)-C(2)-C(3)
92.10(9) N(1)-C(2)-Ni(1) 122.0(3)
90.45(12) C(3)-C(2)-Ni(1)
86.46(9) N(1)-C(6)-F(6)
91.10(12) N(1)-C(6)-C(5)
115.9(3)
121.9(3)
116.8(4)
124.9(4)
118.4(4)
120.9(3)
119.1(4)
120.0(4)
115.6(3)
117.7(3)
117.4(3)
124.8(3)
176.70(4)
110.9(2)
119.9(2)
F(6)-C(6)-C(5)
C(4)-C(5)-F(5)
C(4)-C(5)-C(6)
F(5)-C(5)-C(6)
C(5)-C(4)-C(3)
F(3)-C(3)-C(4)
F(3)-C(3)-C(2)
C(4)-C(3)-C(2)
C(11)-P(1)-Ni(1) 110.1(2)
C(15)-P(2)-Ni(1) 111.9(2)
C(13)-P(2)-Ni(1) 115.1(2)
C(17)-P(2)-Ni(1) 114.9(2)
C(6)-N(1)-C(2)
119.7(3)
to test the preference for C-H compared to C-F
activation. It was conducted as for the reaction with
pentafluoropyridine and generated two fluoride com-
plexes, with one formed in a far higher yield than the
other (100:1). These products were identified as isomers
of trans-Ni(PEt3)2(C5HF3N)F (3). The doublet of dou-
blets pattern for the 13C resonance of the pyridyl-CH
group provides evidence that the major isomer is meta-
lated at the 2-position of the ring (3a ). The minor
isomer is metalated at the 3-position (3b) (Scheme 1,
Table 1). This conclusion is confirmed crystallographi-
cally (see below).
Cr ysta l Str u ctu r e of tr a n s-Ni(P Et3)2(3,5,6-tr iflu -
or op yr id -2-yl)F (3a ). Complex 3a was crystallized
from hexane at -20 °C. The crystal structure of 3a
(Figure 2, Table 3) closely resembles that of 1, but is
free of any signs of incipient disorder. The trifluoro-
pyridyl ligand is metalated at the 2-position with the
hydrogen at the 4-position. The angles between adja-
Cr ysta l Str u ctu r e of Ni(P Et3)2(η2-CH2dCHC6F 5)
(6). Complex 6 was crystallized from hexane at -20
°C. The structure (Figure 3, Table 4) shows a charac-
teristic trigonal-planar Ni(0) geometry. The dihedral
angle between the planes NiC(1)C(2) and NiP(1)P(2) is
only 2.1(3)°, smaller than in many comparable com-
plexes.29-33 The Ni-C distances average 1.960(6) Å.
(29) Scott, F.; Kru¨ger, C.; Betz, P. J . Organomet. Chem. 1990, 387,
113.

Fluorinated Arene and Pyridine Derivatives
Organometallics, Vol. 16, No. 22, 1997 4925
an NMR scale with Ni(COD)2, 5 equiv of PEt3, and 5
equiv of C6F5H in THF-d8. The reaction proceeded very
slowly, as for hexafluorobenzene, reaching ca. 85%
conversion after 20 days at 35 °C. Three nickel fluoride
complexes (7a -c) were formed with 19F resonances at
ca. δ -385 in a ratio of 7:2:1 (see Table 1). These species
are tentatively identified as the ortho, meta, and para
isomers of trans-Ni(PEt3)2(C6F4H)F, though we cannot
distinguish the individual isomers. In addition to the
nickel complexes and phosphoranes (see above), a
considerable amount of p-C6F4H2 is formed (identified
by NMR and gc/ms). A similar NMR experiment with
pentafluoromethoxybenzene yielded two nickel fluoride
complexes in approximately equal proportions, with
traces of a third species. These species are provisionally
assigned as isomers of trans-Ni(PEt3)2(C6F4OMe)F (8a,b).
Rea ction w ith Hexa flu or oben zen e in th e P r es-
en ce of oth er P h osp h in es. The effect of changing the
phosphine on the reaction of Ni(PR3)2(COD) and Ni-
(PR3)4/Ni(PR3)3 with hexafluorobenzene was examined.
Of the phosphines, PMe3, Me2PCH2CH2PMe2, PMePh2,
and PnBu3, only the last proved to give a reaction.
When monitored by NMR, the reaction with PnBu3 gave
strong evidence for the formation of trans-Ni(PnBu3)2-
(C6F5)F (9) with complete conversion after ca. 12 days
(Table 1); pentafluorobenzene was also formed. How-
ever, 9 was not isolated. A control experiment with Ni-
(COD)2 and C6F6, but without phosphine, led to decom-
position.
F igu r e 3. Molecular structure of 6, Ni(PEt3)2(η2-
CH2dCHC6F5): ORTEP26 plot with 30% probability ther-
mal ellipsoids. The hydrogen atoms have been omitted for
clarity.
Ta ble 4. P r in cip a l Bon d Len gth s (Å) a n d An gles
(d eg) of Ni(P Et3)2(η2-CH2dCHC6F 5), 6
Ni(1)-C(1)
Ni(1)-C(2)
Ni(1)-P(1)
Ni(1)-P(2)
F(4)-C(4)
F(5)-C(5)
F(6)-C(6)
F(7)-C(7)
1.934(7)
1.985(6)
2.161(3)
2.171(2)
1.363(6)
1.347(6)
1.354(6)
1.347(6)
F(8)-C(8)
C(3)-C(8)
C(3)-C(4)
C(3)-C(2)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-C(8)
C(2)-C(1)
1.360(6)
1.397(7)
1.403(7)
1.468(7)
1.362(8)
1.370(8)
1.367(8)
1.365(7)
1.420(8)
Discu ssion
Rea ctivity. The reactions of the Ni(0) complexes
with hexafluorobenzene, pentafluoropyridine and re-
lated compounds, and pentafluorostyrene are summa-
rized in Scheme 1. These reactions confirm the conclu-
sions of Fahey and Mahan19 concerning the product of
the reaction with C6F6. The reactions of Ni(0) complexes
with fluoropyridines demonstrate that intermolecular
C-F activation of a fluoroaromatic can take place
rapidly, and in good yield, at a first row transition metal
through suitable choice of the substrate. Of particular
note is the contrast between the very slow reaction with
hexafluorobenzene and the rapid reactions with the
other substrates. The nitrogen atom of the pentafluo-
ropyridine accelerates the reaction and makes it regi-
oselective. Even though pentafluoropyridine is not a
Lewis base,34 it is probable that it can act as a weak
π-acceptor ligand when bound through nitrogen and
that the nickel center attacks at nitrogen initially. The
reactions of fluoropyridines at Ni(0) are selective for
C-F over C-H activation, and for C-Cl over C-F
activation. The alkene group of pentafluorostyrene,
however, binds strongly to Ni(0) in the η2-mode and
prevents C-F insertion. A methoxy substituent, as in
pentafluoranisole, appears to have little influence on
C-F activation, neither accelerating the reaction nor
directing its selectivity. The effects of substituents are
substantially different from other C-F activation reac-
tions which we have studied (see Introduction). Thus,
a methoxy group enhances photochemical C-F activa-
tion at Rh(η5-C5H5)(PMe3)7 but a pyridyl nitrogen does
not.35 However, a ring carbon-hydrogen bond is pho-
C(1)-Ni(1)-C(2)
C(1)-Ni(1)-P(1)
C(2)-Ni(1)-P(1)
C(1)-Ni(1)-P(2)
C(2)-Ni(1)-P(2)
P(1)-Ni(1)-P(2)
C(11)-P(1)-Ni(1)
C(13)-P(1)-Ni(1)
C(9)-P(1)-Ni(1)
C(17)-P(2)-Ni(1)
C(15)-P(2)-Ni(1)
C(19)-P(2)-Ni(1)
C(8)-C(3)-C(4)
C(8)-C(3)-C(2)
C(4)-C(3)-C(2)
C(5)-C(4)-F(4)
C(5)-C(4)-C(3)
42.5(2)
99.0(2)
F(4)-C(4)-C(3)
F(5)-C(5)-C(4)
F(5)-C(5)-C(6)
C(4)-C(5)-C(6)
F(6)-C(6)-C(7)
F(6)-C(6)-C(5)
C(7)-C(6)-C(5)
F(7)-C(7)-C(8)
F(7)-C(7)-C(6)
C(8)-C(7)-C(6)
F(8)-C(8)-C(7)
F(8)-C(8)-C(3)
C(7)-C(8)-C(3)
C(1)-C(2)-C(3)
C(1)-C(2)-Ni(1)
C(3)-C(2)-Ni(1)
C(2)-C(1)-Ni(1)
118.6(5)
120.9(5)
119.4(5)
119.7(5)
120.6(5)
120.5(5)
118.9(5)
119.9(5)
119.9(5)
120.2(5)
116.7(5)
119.1(5)
124.1(5)
124.9(5)
66.8(3)
141.4(2)
146.0(2)
103.6(2)
114.97(11)
112.8(2)
120.0(2)
115.3(2)
112.6(2)
115.1(2)
119.3(2)
112.5(5)
126.0(5)
121.5(5)
116.8(5)
124.6(5)
115.1(4)
70.7(3)
The P(1)-Ni-P(2) angle is 115.0(1)°, again closer to the
ideal angle of 120° than in many analogues because of
the lack of steric constraints. The plane of the C6F5
group is almost orthogonal to the Ni-C(1)-C(2) plane
(dihedral angle ) 86.9(2)°).
Rea ction w ith P en ta flu or oben zen e a n d P en ta -
flu or om eth oxyben zen e. The reaction with pentaflu-
orobenzene was investigated in order to establish
whether the nickel system is selective for C-F or C-H
bond activation. The reaction was conducted only on
(30) J arvis, A. P.; Haddleton, D. M.; Segal, J . A.; McCamley, A. J .
Chem. Soc., Dalton Trans. 1995, 2033.
(31) Dreissig, W.; Dietrich, H. Acta. Crystallogr., Sect. B 1981, 37,
931.
(32) Stanger, A.; Boese, R. J . Organomet. Chem. 1992, 430, 235.
(33) Brauer, D. J .; Kru¨ger, C. Inorg. Chem. 1977, 16, 884; J .
Organomet. Chem. 1974, 77, 423.
(34) Burdon, J .; Gilman, D. J .; Patrick, C. R.; Stacey, M.; Tatlow, J .
C. Nature 1960, 186, 231. Banks, R. E.; Burgess, J . E.; Cheng, W. M.;
Haszeldine, R. N. J . Chem. Soc. 1965, 575.
(35) Perutz, R. N.; Whitlesey, M. K. Unpublished observations.

4926 Organometallics, Vol. 16, No. 22, 1997
Cronin et al.
toactivated in preference to a C-F bond at Rh(η5-C5H5)-
(PMe3).18 The thermal reactions of Ru(dmpe)2H2 are
closer to the nickel reactions in selectivity for C-F over
C-H bonds, but in that case the regioselective influence
of a ring hydrogen or methoxy group is very strong.13
Selectivity for C-F over C-H activation is also observed
in the chelate-assisted reactions of Ni(COD)2 with
partially fluorinated Schiff bases.36 At platinum, the
selectivity in intramolecular C-F activation can go a
stage further and overcome competition from C-Cl
bonds.37,38
The reaction of Ni(PEt3)2(COD) with C6F6 is clearly
related to the conversion of Ni(dtbpe)(η2-C6F6) to Ni-
(dtbpe)(C6F5)F.23a However, we have neither observed
Ni(PEt3)2(η2-C6F6) nor cis-Ni(PEt3)2(C6F5)F in our NMR
investigations of the reaction of Ni(PEt3)2(COD) with
C6F6. We are now carrying out mechanistic studies of
this reaction and the reaction with pentafluoropyridine.
Sp ectr a a n d Str u ctu r e of Nick el F lu or id e Com -
p lexes. Since there is little information on nickel
fluoride complexes and considerable interest in the com-
bination of fluoride with phosphine and carbon ligands,39
we use this section to point out the key structural and
spectroscopic features of the trans-Ni(PR3)2(RF)F com-
plexes. The structure of 3a provides a more reliable
determination of the Ni-F bond length (1.856(2) Å) than
that obtained from 1. For comparison, the mean value
of the Ni-O distance in four-coordinate Ni(II) aryloxy
complexes is 1.865 Å.28 A palladium analogue of 1
containing a phenyl group has been described very
recently, Pd(PPh3)2(Ph)F, with a Pd-F bond length
2.085(3) Å.40 The 19F NMR resonances for the nickel-
bound fluorine in 1-4 and 7, 8 lie in the range from δ
-390 to -367 with J PF between 45 and 50 Hz.
fundamental Ni-F stretching mode is assigned to the
stronger of the bands: 535 cm-1 for 1 and 530 cm-1 for
2. The weaker bands at 486 cm-1 for 1 and 501 cm-1
for 2 may arise from a combination mode which is in
Fermi resonance with the fundamental. The assign-
ment for 3 is complicated by ligand modes in the same
region.
Con clu sion s
This paper reports the reactions of Ni(COD)2 in the
presence of PEt3 with hexafluorobenzene and with
analogues containing other functional groups. The
prototypical reaction with C6F6 yields trans-Ni(PEt3)2-
(C6F5)F (1), but is very slow. The analogous reaction
of pentafluoropyridine proceeds far more rapidly and
yields one regioisomer of trans-Ni(PEt3)2(C5F4N)F (2a )
selectively. A similar reaction occurs with 2,3,5,6-
tetrafluoropyridine, generating trans-Ni(PEt3)2(C5HF3N)F
(3). The structures of 1 and 3a provide the first values
for Ni-F distances at square-planar Ni (II) of 1.836(5)
and 1.856(2) Å, respectively. The reaction with penta-
fluorostyrene yields Ni(PEt3)2(η2-CH2dCHC6F5) (6), a
complex with trigonal-planar geometry at nickel.
Exp er im en ta l Section
Gen er a l Meth od s. Most of the synthetic work was carried
out in an argon-filled glovebox with oxygen levels below 10
ppm. Some of the preparations were, however, carried out on
a Schlenk line. All solvents (AR grade) were dried over sodium
benzophenone ketyl and distilled under argon before use.
Benzene-d6 and THF-d8 (Goss Scientific Instruments) were
dried by stirring over potassium and then transferring under
vacuum into NMR tubes fitted with Young’s stopcocks. Fluo-
roarenes and fluoropyridines were obtained from Aldrich,
except for pentafluoropyridine, pentafluorostyrene, and pen-
tafluoroanisole which were obtained from Fluorochem Ltd. The
fluoroaromatics were dried over molecular sieves (4 Å). Ni-
(COD)2 (Strem Chemicals) was used as received. The NMR
spectra were recorded with Bruker MSL 300 or AMX 500
spectrometers. Selective 19F-19F decoupling experiments were
The IR spectra provide sufficient information to
identify the Ni-F stretching modes. Nakamoto41 lists
the ν(MF) region as 750-500 cm-1 and ν(MCl) region
as 400-200 cm-1. The values of ν(NiCl) decrease in the
order NiCl2 triatomic > trans-Ni(PR3)2Cl2 > cis-Ni(PR3)2-
Cl2 > tetrahedral Ni(PR3)2Cl2 > octahedral trans-
Ni(py)4Cl2.41 Further assistance in identification of the
bands is provided by values of νas(NiX2) for NiF2 and
NiF2(CO) in matrices (779 and 713 cm-1, respectively,
for 58Ni) and NiCl2 and NiCl2CO (520 and 469 cm-1).42
The value of νas(NiCl2) in trans-NiCl2(PEt3)2 is quoted43
as 403 cm-1, while Fahey and Mahan list ν(NiCl) in 5
1
carried out on a Bruker DRX 400 spectrometer. The H NMR
chemical shifts were referenced to residual C6D5H at δ 7.15
or THF-d7 at δ 1.8. The 13C{1H} spectra were referenced to
C6D6 at δ 128.0 and THF at δ at 26.7. The 19F NMR spectra
were referenced either to internal C6F6 at δ -162.9 or to
external CFCl3 at δ 0, and the 31P{1H} NMR spectra were
referenced externally to H3PO4 at δ 0. Infrared spectra were
recorded on a Mattson-Unicam RS spectrometer fitted with a
CsI beamsplitter. NMR data are listed in Table 1.
as 373 cm-1 19
We have recorded IR spectra for com-
.
tr a n s-Ni(P Et3)2(C6F 5)(F ) (1). Ni(COD)2 (160 mg, 0.58
mmol) was suspended in hexane (1.5 cm3), and PEt3 (309 mg,
2.62 mmol) was added. After the mixture had been stirred at
25 °C for 1 h, the solution was cooled to -78 °C. A white solid
precipitated. The supernatant was removed with a cannula.
The white solid Ni(PEt3)4 was dissolved in hexane (4 cm3), and
C6F6 (130 mg, 0.70 mmol) was added. The solution was stirred
for 4 weeks at 25 °C. The reaction was monitored by 31P{1H}
NMR spectroscopy. After filtration through a cannula, the
yellow solution was concentrated under vacuum to 1 cm3 and
a yellow solid crystallized at -20 °C overnight. The super-
natant was removed with a pipette, and the remaining yellow
solid was dried rapidly under vacuum. The complex is very
soluble in THF, benzene, and hexane. It decomposes when
left under vacuum for several hours. Yield: 0.13 g (0.28 mmol,
48%). Anal. Calcd for C18H30F6NiP2: C, 44.94; H, 6.29.
Found: C, 44.89; H, 6.36.
plexes 1-6 (see Experimental Section) and compared
them with the spectra of C6F5Cl and C6F5I. The value
of ν(NiCl) in 5 has been confirmed. The chloride com-
plexes 4 and 5 show no bands between 430 and 600
cm-1. In contrast, the fluoride complexes, 1 and 2, each
exhibit two bands between 480 and 540 cm-1
. The
(36) Osterberg, C. E. Ph.D. Thesis, University of Utah, 1990 (cited
in ref 1).
(37) Crespo, M.; Martinez, M.; Sales, J . J . Chem. Soc., Chem
Commun. 1992, 823.
(38) Crespo, M.; Martinez, M.; de Pablo, E. J . Chem. Soc., Dalton
Trans. 1997, 1231.
(39) Doherty, N. M.; Hoffmann, N. W. Chem. Rev. 1991, 91, 553.
Veltheer, J . E.; Burger, P.; Bergman, R. G. J . Am. Chem. Soc. 1995,
117, 12478.
(40) Fraser, S. L.; Antipin, M. Y.; Hhroustalyov, V. N.; Grushin, V.
V. J . Am. Chem. Soc. 1997, 119, 4769.
(41) Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 4th ed.; Wiley: New York, 1986.
(42) Van Leirsburg, D. A.; De Kock, C. W. J . Phys. Chem. 1974, 78,
134.
IR (C6D6, cm-1): 1496 (s), 1448 (s), 1434 (m), 1416 (w). IR
(Nujol, cm-1): 1495 (vs), 1446 (m), 1434 (s), 1416 (m), 1276
(w), 1251 (w), 1053 (s), 1034 (s), 1003 (w), 947 (vs), 789 (m),
764 (s), 733 (m), 535 (m), 486 (w), 351 (vw). MS (EI, m/z,
(43) Shobatke, K.; Nakamoto, K. J . Am. Chem. Soc. 1970, 9, 3332.

Fluorinated Arene and Pyridine Derivatives
Organometallics, Vol. 16, No. 22, 1997 4927
relative intensity): 628 (5, [(C6F5)2Ni(PEt3)2]+), 480 (1.5, [M]+),
294 (44, [Ni(PEt3)2]+), 285 (100, [Et3P(C6F5)]+), 118 (58,
[PEt3]+).
764 (s), 722 (s), 635 (w), 425 (vw), 351 (m), 233 (m). MS (EI,
m/z, relative intensity): 497 (0.1, [M]+), 332 (0.6), 284 (100),
153 (40, [ClPEt3]+), 118 (37, [PEt3]+).
tr a n s-Ni(P Et3)2(C5F 4N)(F ) (2). Ni(COD)2 (117 mg, 0.42
mmol) was suspended in hexane (1 cm3), and PEt3 (226 mg,
1.91 mmol) was added. The cloudy red-purple solution was
stirred for 15 min at 25 °C, and C5F5N (92 mg, 0.55 mmol)
was added. Within 3 min the color of the solution changed to
yellow-orange. After 2 h of stirring at 25 °C, the volatiles were
removed under vacuum. The orange oily residue was dissolved
in hexane (10 cm3) and filtered through a cannula, and the
tr a n s-Ni(P Et3)2(C6F 5)(Cl) (5). Ni(COD)2 (110 mg, 0.4
mmol) was suspended in hexane (1.5 cm3), and PEt3 (240 mg,
2 mmol) was added, yielding a red solution. A white solid,
Ni(PEt3)4, was precipitated by cooling the tube to -78 °C. The
red supernatant was removed with a cannula filter. The white
solid was dissolved in hexane (4 cm3) to form a wine-colored
solution, and C6F5Cl (120 mg, 0.60 mmol) was added. The
solution turned yellow immediately and was left to stir for 2
h. The solvent and excess PEt3 were removed under vacuum.
Hexane (10 cm3) was added to the residue, and any undissolved
material was removed by filtration. The solvent was removed
from the filtrate under vacuum and hexane (1 cm3) was added.
The sample was left to crystallize overnight at -20 °C, yielding
yellow 5.
resulting yellow solution was concentrated to ca. 1 cm3.
A
yellow solid was crystallized at -78 °C overnight. Yield: 96
mg (0.21 mmol, 49%). Anal. Calcd for C17H30F5NNiP2: C,
44.00; H, 6.52; N, 3.02. Found: C, 43.84; H, 6.44; N, 2.93.
IR (THF-d8, cm-1): 1617 (vw), 1597 (vw), 1481 (s), 1474 (m),
1462 (w), 1405 (vs), 1386 (m), 1289 (vw), 1248 (vw), 994 (s).
IR (nujol, cm-1): 1619 (vw), 1583 (w), 1482 (s), 1418 (m), 1406
(vs), 1386 (m), 1288 (vw), 1247 (vw), 1208 (vw), 1088 (m), 1035
(s), 994 (s), 811 (m), 764 (m), 734 (m), 711 (vw), 679 (vw), 633
(vw), 530 (w), 501 (vw), 433 (w), 414 (vw), 375 (vw), 348 (m),
330 (m). MS (EI, m/z, relative intensity): 463 (0.5, [M]+), 444
(1.5, [M - F]+), 431 (3), 413 (1), 268 (80, [Et3P(C5F4N)]+), 118
(100, [PEt3]+).
tr a n s-Ni(P Et3)2(C5F 3HN)(F ) (3) (C5F 3HN ) 3,5,6-Tr iflu -
or op yr id -2-yl). Ni(COD)2 (189 mg, 0.69 mmol) was sus-
pended in hexane (5 cm3). After addition of PEt3 (366 mg, 3.10
mmol), the resulting cloudy, purple-red solution was stirred
for another 15 min before adding 2,3,5,6-tetrafluoropyridine
(136 mg, 0.90 mmol). Within 10 min the color of the solution
changed to orange-yellow. After 3 h of stirring at 25 °C, the
volatiles were removed under vacuum and the remaining
yellow, oily residue was dissolved in hexane (8 cm3) and filtered
through a cannula. The solution was concentrated to ca. 2
cm3, and a yellow powder precipitated at 0 °C. The yellow
solid was recrystallized twice from hexane (2 cm3) at -20 °C
and dried under vacuum. The complex is very soluble in THF
and benzene and soluble in hexane. Yield: 0.19 g (0.43 mmol,
63%). Anal. Calcd for C17H31F4NNiP2: C, 45.77; H, 7.00; N,
3.14. Found: C, 45.77; H, 6.99; N, 3.13.
IR (Nujol, cm-1): 1602 (m), 1586 (w), 1559 (m), 1425 (s),
1410 (m), 1256 (w), 1239 (w), 1220 (m), 1174 (m), 1147 (m),
1035 (m), 1002 (m), 962 (w), 808 (s), 764 (m), 730 (m), 705
(m), 625 (m), 567 (m), 503 (m), 473 (m), 415 (w), 374 (w), 364
(m), 331 (w), 314 (w), 291 (w), 282 (w). MS (EI, m/z, relative
intensity): 445 (0.5, [M]+), 426 (1, [M - F]+), 377 (2), 294 (2),
264 (7, [(C5F3HN)2]+), 250 (65, [Et3P(C5F3HN)]+), 118 (100,
[PEt3]+).
tr a n s-Ni(P Et3)2(C5F 3ClN)(Cl) (4) (C5F 3ClN ) 2,4,6-tr i-
flu or o-5-ch lor op yr id -3-yl). Ni(COD)2 (234 mg, 0.85 mmol)
was suspended in hexane (6 cm3). After addition of PEt3 (452
mg, 3.82 mmol), the resulting cloudy, purple-red solution was
stirred for 15 min at 25 °C before 2,4,6-trifluoro-3,5-dichloro-
pyridine (223 mg, 1.10 mmol) was added. The resulting red-
brown solution was stirred for another hour at 25 °C. The
volatiles were removed under vacuum. The remaining red-
brown, oily solid was dissolved in toluene (8 cm3), and the
solution was filtered through a cannula. The solvent was
removed under vacuum, and the remaining solid was dissolved
in hexane (5 cm3). An orange solid was crystallized at -20
°C overnight. Further precipitation of product was achieved
by stirring the solution at -78 °C. After removing the
supernatant with a pipette, the resulting orange solid was
dried under vacuum. A yellow-orange powder was ob-
tained, which is soluble in hexane and very soluble in benzene
and THF. Yield: 0.36 g (0.73 mmol, 85%). Anal. Calcd for
IR (Nujol, cm-1): 1623 (w), 1596 (w), 1547 (w), 1497 (vs),
1449 (vs), 1436 (s), 1415 (m), 1362 (w), 1350 (w), 1275 (w),
1254 (w), 1102 (w), 1054 (m), 1044 (sh), 1035 (s), 1003 (w),
951 (vs), 786 (m), 757 (m), 725 (m), 713 (w), 627 (w), 421 (w),
374 (w), 338 (w), 232 (w).
Ni(P Et3)2(η2-CH2dCHC6F 5) (6). Ni(COD)2 (131 mg, 0.48
mmol) was suspended in hexane (6 cm3). After addition of PEt3
(255 mg, 2.16 mmol), the cloudy red-purple solution was stirred
for 15 min at 25 °C. On addition of CH2dCHC6F5 (121 mg,
0.62 mmol), the color of the solution immediately changed to
orange. The solution was stirred for another 2 h, and the
volatiles were removed under vacuum. The orange oily residue
was dissolved in hexane (6 cm3), filtered through a cannula,
and concentrated to ca. 1 cm3. By storing the solution at -78
°C overnight, orange-red crystals were obtained. The super-
natant was removed with a pipette, and the resulting solid
was dried under vacuum. The complex was very soluble in
hexane, benzene, and THF. Yield: 0.13 g (0.27 mmol, 57%).
Anal. Calcd for C20H33F5NiP2: C, 49.11; H, 6.80. Found: C,
48.23; H, 7.06.
IR (THF-d8, cm-1): 1508 (vs), 1492 (s), 1455 (w), 1424 (vw),
1376 (vw). IR (Nujol, cm-1): 1505 (vs), 1493 (vs), 1417 (w),
1203 (w), 1063 (m), 1035 (w), 966 (s), 917 (m), 762 (m), 707
(w), 621 (w), 559 (vw), 474 (vw), 415 (vw). MS (EI, m/z, relative
intensity): 412 (0.5), 294 (0.8, [Ni(PEt3)2]+), 194 (24, [(C6F5)-
CHdCH2]+), 118 (100, [PEt3]+). The parent ion was not
observed.
Rea ction s of Ni(P Et3)4 or Ni(P Et3)2(COD) w ith C6F 5H.
Ni(COD)2 (21 mg, 0.08 mmol) was suspended in THF-d8 (2
cm3), and PEt3 (45 mg, 0.38 mmol) was added, giving a red-
purple solution. Pentafluorobenzene (67 mg, 0.40 mmol) was
added, and the subsequent reaction was monitored by 31P{1H}
and 19F NMR spectroscopy. The 31P NMR spectrum shows the
formation of the three nickel fluoride isomers (7a -c) and three
phosphoranes. According to the 19F NMR spectrum, the main
product of the reaction is p-C6F4H2. Further NMR resonances
could not be assigned. After 18 days (ca. 80% conversion) the
reaction was interrupted and the volatiles were collected and
investigated in a GC/MS experiment. The GC/MS showed a
strong signal for p-C6F4H2 and two weak signals for o- and
m-C6F4H2. A very weak signal for one isomer of C6F3H3 was
also detected.
Rea ction of Ni(P Et3)4 or Ni(Et3)2(COD) w ith C6F 5-
(OCH3). Ni(COD)2 (24 mg, 0.09 mmol) was suspended in C6D6
(ca. 1.5 cm3), and PEt3 (52 mg, 0.44 mmol) was added. To the
red-purple solution, C6F5OMe (23 mg, 0.12 mmol) was added.
The reaction was monitored by 31P{1H} and 19F NMR spec-
troscopy. After 2 weeks the reaction was nearly complete and
was stopped. The NMR spectra showed the continuous
formation of the nickel fluoride species 8a and 8b.
C
17H30Cl2F3NNiP2: C, 41.08; H, 6.08; N, 2.82. Found: C,
Rea ction s of Ni(P n Bu 3)4 or Ni(P n Bu 3)2(COD) w ith C6F 6.
Ni(COD)2 (28 mg, 0.10 mmol) was suspended in C6D6 (1.5 cm3).
On addition of PnBu3 (67 mg, 0.33 mmol), a red-purple solution
was formed, to which 2 equiv of C6F6 was added. The reaction
was monitored by 31P{1H} and 19F NMR spectroscopy. The
41.10; H, 6.13; N, 2.75.
IR (C6D6, cm-1): 1570 (w), 1554 (m), 1459 (w), 1420 (w), 1406
(s), 1385 (m), 1371 (w), 1336 (w), 1330 (m). IR (Nujol, cm-1):
1590 (w), 1571 (m), 1555 (m), 1418 (m), 1402 (s), 1385 (m),
1370 (m), 1326 (m), 1252 (w), 1098 (w), 1034 (s), 1017 (vs),

4928 Organometallics, Vol. 16, No. 22, 1997
Ta ble 5. Cr ysta l Str u ctu r e Da ta for Com p lexes 1, 3a , a n d 6
Cronin et al.
1
3a
6
empirical formula
Mr
C18H30F6NiP2
481.09
C17H31F4NNiP2
446.10
C20H33F5NiP2
489.14
dimens mm3
color, habit
cryst syst
space group
lattice params
a, Å
0.6 × 0.5 × 0.4
yellow block
orthorhombic
P212121
0.6 × 0.3 × 0.2
yellow needle
monoclinic
P21/c
0.6 × 0.3 × 0.3
yellow block
triclinic
P1h
9.406(6)
9.447(5)
26.62(2)
90
90
90
2365(3)
4
11.91(2)
12.571(8)
15.582(3)
90
99.29(4)
90
2303(4)
4
1.287
10.260(9)
14.994(12)
8.151(14)
97.59(10)
106.86(12)
90.44(7)
1188(3)
2
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
D
calcd, g cm-3
1.351
10.00
1000
1.367
9.93
512
µ (Mo KR),a cm-1
F(000)
10.13
936
transmission coeff
temp, K
0.93-1.00
296(3)
0.91-1.00
296(3)
0.84-1.00
296(3)
scan type
ω
ω-2θ
ω-2θ
scan width, deg
2θ range, deg
no. of reflns measd
no. of indep reflns
Rint
1.05 + 0.3 tan θ
1.05 + 0.3 tan θ
5.16-50.08 (+h, +k, l)
4575
1.31 + 0.3 tan θ
5.08-49.98 (+h, k, l)
3438
5.28-50.00 (+h, +k, + l)
2484
2400
4049
0.0224
2865
4047/232
17.44
3140
0.0351
2442
3140/268
11.72
no. of obs reflns (I > 2σ(I))
data/param
1763
2398/249
9.63
refln/param ratio
residuals
R(Fo)b
wR(Fo
0.0534
0.1543
1.03
0.42
- 0.33
0.0436
0.1241
1.01
0.39
- 0.30
0.0459
0.1337
1.06
0.57
- 0.56
2
c
)
goodness of fit
max diff peak, e Å-3
min diff peak,d e Å-3
a
b
2
2
λ ) 0.710 73 Å. R ) ∑|Fo| - |Fc|/∑|Fo| for observed reflections having Fo > 2σ(Fo2). c wR ) [∑w(Fo - Fc2)2/∑w(Fo2)2]1/2 for all data.
d
There was no shift/esd in the last cycle of refinement.
31P{1H} NMR resonance of the starting material at δ 11.65
had disappeared after 10-12 days. Product resonances were
observed for the nickel fluoride complex (9), pentafluoroben-
zene, and two phosphoranes.
all structures using a riding model with isotropic temperature
factors 1.2 times that of their carrier atoms (1.5 times for
methyl groups). Bond lengths and angles are given in Tables
2-4, crystallographic details are summarized in Table 5, and
ORTEP26 representations are shown in Figures 1-3. Full
details of atomic coordinates, anisotropic temperature factors,
and other details of the refinement are given in the Supporting
Information.
Diflu or op h osp h or a n es. Difluorophosphoranes were ob-
served by NMR spectroscopy in reactions of fluoroarenes and
fluoropyridines with Ni(0) complexes in the presence of excess
phosphine. The formation of the difluorophosphoranes ap-
peared to be catalyzed by the nickel complexes, but this aspect
was not pursued. The reaction with C6F6 yielded difluoro-
phosphoranes A, B, C, and D. The reaction with pentafluo-
ropyridine yielded A and C, together with two further diflu-
orophosphoranes E and F . The reaction with C6F5H yielded
A, B, and C. NMR data for A-F : 31P{1H} NMR: -16.64 (t,
A, J ) 642 Hz), -12.35 (t, B, J ) 589 Hz), -19.97 (t, C, J )
575 Hz), D obscured,-27.15 (t, E, J ) 598 Hz), F obscured.
19F NMR: -37.7 (d, A, J ) 642 Hz), -37.0 (d sept, B, J )
589, 11 Hz), -40.1 (d, C, J ) 571 Hz), -39.45 (d, D, J ) 642
Hz), -42.95 (d quin, E, J ) 597, 12 Hz), -42.01 (d, F , J ) 578
Hz).
X-r a y Cr ysta llogr a p h ic Stu d ies of Com p ou n d s 1, 3a ,
a n d 6. Crystals of compounds 1, 3a , and 6 were grown at
-20 °C from hexane (see above). The resulting crystals were
mounted in Lindemann tubes in a glovebox and sealed with
epoxy cement. X-ray data were collected on a Rigaku AFC6S
diffractometer. Cell constants and an orientation matrix for
the data collection were obtained from a least-squares refine-
ment of the positions of 20 automatically centered reflections.
Equivalent reflections were merged, and data were corrected
for Lorentz and polarization factors. The structures of com-
pounds 1, 3a , and 6 were solved using direct methods with
SHELXS86 and expanded using Fourier techniques with
DIRDIF.44 Full-matrix least-squares refinement on F2 was
carried out with SHELXL 93.45 All non-hydrogen atoms were
refined anisotropically. The hydrogen atoms were refined on
Ack n ow led gm en t. Our thanks go to Dr. M. G.
Partridge and Dr. S. N. Heaton for their preliminary
studies, to Dr. S. B. Duckett for assistance with decou-
pling experiments, and to Dr. T. Braun for helpful
discussions. We would like to acknowledge the Euro-
pean Commission and EPSRC for financial support.
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray
crystallographic data, data collection, structure solution, and
refinement, atomic coordinates, bond lengths and angles,
anisotropic displacement parameters, hydrogen coordinates,
and least-squares planes and packing and ORTEP diagrams
of 1, 3a , and 6 (29 pages). Ordering information is given on
any current masthead page.
OM9705160
(44) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, G.;
Garcia-Granda, W. P.; Gould, R. O.; Smits, J . M. M.; Smykalla, C. The
DIRDIF Program System. Technical Report of the Crystallographic
Laboratory; University of Nijmegen: Nijmegen, The Netherlands,
1992.
(45) Sheldrick, G. M. In Crystallographic Computing 3; Sheldrick,
G. M. Kru¨ger, C. Goddard, R., Eds.; Oxford University Press: Oxford,
U.K., 1985; pp 175-189. Sheldrick, G. M. SHELXL 93, Program for
Crystal Structure Refinement; University of Go¨ttingen: Go¨ttingen,
Germany, 1993.