Carbon-hydrogen bond oxidative addition of partially fluorinated aromatics to a Ni(PiPr3)2 synthon: The influence of steric bulk on the thermodynamics and kinetics of C-H bond activation

Article abstract of DOI:10.1021/om1008499

The reaction of (PⁱPr₃)₂NiCl₂ with the anthracene adduct (THF)₃Mg(η²-C ₁₄H₁₀) in THF provides the anthracene adduct (P ⁱPr₃)₂Ni(η

Full text of DOI:10.1021/om1008499

Organometallics 2010, 29, 6077–6091 6077
DOI: 10.1021/om1008499
Carbon-Hydrogen Bond Oxidative Addition of Partially Fluorinated
Aromatics to a Ni(PiPr3)2 Synthon: The Influence of Steric Bulk on the
Thermodynamics and Kinetics of C-H Bond Activation
Jillian A. Hatnean, Robert Beck, Jenna D. Borrelli, and Samuel A. Johnson*
Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada, N9B 3P4
Received September 1, 2010
The reaction of (PiPr3)2NiCl2 with the anthracene adduct (THF)3Mg(η2-C14H10) in THF provides
the anthracene adduct (PiPr3)2Ni(η2-C14H10). In aromatic solvents (benzene, toluene, mesitylene) a
thermal equilibrium exists between the bis(phosphine)nickel(0) anthracene adduct, (PiPr3)2Ni(η2-C14H10),
and the monophosphine solvent adduct, (PiPr3)Ni(η6-solvent). The reaction of (PiPr3)2Ni(η2-C14H10) with
1,2,4,5-C6F4H2 affords the C-H activation product trans-(PiPr3)2NiH(2,3,5,6-C6F4H). The thermody-
namic C-F activation product is not obtained even after hours of heating at 100 °C. Similar reactions with
1,2,3,5-C6F4H2 and pentafluorobenzene produce the desired C-H activation products, trans-(PiPr3)2NiH-
(2,3,4,6-C6F4H) and trans-(PiPr3)2NiH(C6F5), respectively, in >95% yield. The reaction with 1,2,3,4-
tetrafluorobenzene did not produce an observable C-H activation product. Unlike previously reported
analogous C-H activation products with Ni(PEt3)2 synthons, the bulkier Ni(PiPr3)2 moiety did
not provide observable mononuclear or dinuclear η2-fluoroarene adducts. Solutions of Ni(COD)2 with
2 equiv of triisopropylphosphine and 1,2,4,5-C6F4H2 reacted to give the 1,5-cyclooctadiene insertion
and rearrangement product, (η3-C8H13)Ni(PiPr3)(2,3,5,6-C6F4H). The same reaction with 1,2,3,5- and
1,2,3,4-C6F4H2 afforded analogous compounds, which demonstrates that C-H bond activation is
kinetically accessible at room temperature with 1,2,3,4-tetrafluorobenzene despite the presence of a single
ortho-fluorine substituent adjacent to the site of activation. The room-temperature reactions of the
C-H activation products (PiPr3)2NiH(ArF) (ArF = 2,3,5,6-C6F4H; C6F5) with 3-hexyne provided a
mixture of the alkyne adduct (PiPr3)2Ni(η2-EtCtCEt), with the liberation of ArFH, and the insertion
product (PiPr3)2Ni(CEtdCHEt)(ArF), even in the presence of excess fluorinated aromatic ArFH. The
reaction of (PiPr3)2Ni(η2-EtCtCEt) with 1,2,4,5-C6F4H2 resulted in no reaction at room temperature, but
heating at 50 °C provided the insertion product (PiPr3)2Ni(CEtdCHEt)(ArF) as the initial product,
followed by the product of reductive elimination, 1,2,4,5-C6F4H-CEtdCHEt. In contrast, the reaction of
(PEt3)2Ni(η2-EtCtCEt) with 1,2,4,5-C6F4H2 at 80 °C slowly produced (PEt3)2Ni(CEtdCHEt)(2,3,5,6-
C6F4H), but very little 1,2,4,5-C6F4H-CEtdCHEt.
Introduction
and nucleophilic reagents have been devised for the preparation
of these species,2 an alternate synthetic approach starting from
fluorinated precursors can also be envisaged.3 For example,
partially fluorinated arenes could be functionalized using transi-
tion metal catalysts capable of either C-H4-6 or C-F3,7-11
Fluorinated organics have found extensive modern use in
applications such as pharmaceuticals and agrochemicals.1
Although fluorinating strategies based on both electrophilic
*To whom correspondence should be addressed. E-mail: sjohnson@
uwindsor.ca. Fax: (519) 973-7098.
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Published on Web 10/28/2010
pubs.acs.org/Organometallics

6078 Organometallics, Vol. 29, No. 22, 2010
Hatnean et al.
bond activation. This could be a particularly efficient strategy
for the synthesis of pharmaceuticals with polyfluorinated
substituents.12 Nickel complexes have been suggested as optimal
catalysts for transformations that involve C-F activation not
only because of the low cost of nickel but because of the reduced
propensity of nickel complexes to undergo C-H bond
activation13-18 versus C-F bond activation10,11,15-23 in par-
tially fluorinated aromatics. In support of this suggested selec-
tivity, DFT calculations have predicted that C-H bond
oxidative addition of C6H6 to the (H2PCH2CH2PH2)Ni frag-
ment should be strongly thermodynamically disfavored.18 Ex-
perimentally, the selective activation of C-F bonds in partially
fluorinated benzenes by nickel complexes has been achieved only
rarely, with the use of phosphine,15,17 N-heterocyclic carbene,23
and nitrogen donor ancillary ligands,20 despite numerous exam-
ples that involve perfluorinated substrates.7,9,11,19,20,22-25 The
catalytic functionalization of aromatic C-F bonds via oxidative
addition to Ni catalysts has been almost7 entirely limited to
substrates that do not contain reactive C-H bonds.9,26
In contrast to the predictions made using DFT calcula-
tions, the reactions of the anthracene complex (PEt3)2Ni(η2-
C14H10)27 with an excess of pentafluorobenzene produced
the C-H activation product (PEt3)2NiH(C6F5) as a kinetic
product prior to C-F bond activation.17 This species was
in nearly thermoneutral equilibrium with mononuclear and
dinuclear adducts, which prevented isolation. Similar C-H
activation was observed in an analogous reaction with
1,2,4,5-tetrafluorobenzene.15 In comparison to calculated
predictions based on the oxidative addition of C6H6 to
(H2PCH2CH2PH2)Ni,18 the almost thermoneutral C-H
activation of C6F5H from the mononuclear adduct,
(PEt3)2Ni(η2-C6F5H), can be attributed partially to the
stronger nickel-carbon bonds formed, due to the fluorine
substituents,28 as well as to the improved donor properties of
phosphines bearing alkyl rather than H substituents.29 How-
ever, an additional factor that could be used to provide
further thermodynamic driving force for C-H bond oxida-
tive additions is the steric bulk of the nonchelating ancil-
lary ligand. Although complexes with the chelating ligand
H2PCH2CH2PH2 can gain no energy from cis- to trans-
isomerization upon oxidative addition, the energy for related
nickel complexes bearing nonchelating donors has been
calculated to be significant.23 It can be hypothesized that
increasingly sterically bulky nonchelating phosphines could
thermodynamically favor the C-H bond activation of even
weakly activated substrates.
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During our investigation into this hypothesis, catalytic
reactions have been reported where Ni complexes bearing
bulky secondary alkyl phosphine donors mediate C-H bond
functionalization via mechanisms that are proposed to in-
volve C-H bond oxidative addition. This includes examples
where partially fluorinated arenes undergo formal insertion
of alkynes into sp2 C-H bonds5,30 and C-H bond stannyla-
tion reactions using Bu3SnCHdCH2,4 which are shown in
Figure 1. This nickel-mediated C-H bond functionalization
methodology has also been extended to pyridines and related
derivatives;31,32 however, the proposed nickel hydride inter-
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been isolated. Could the Ni(PEt3)2 moiety have entirely
different reactivity than more sterically encumbered ana-
logues, such as PCyp3 (Cyp = cyclopentyl) or PiPr3? It is
remarkable that these catalytic systems, which operate selec-
tively at 80 °C, display no products that arise from C-F
bond activation.
Herein, we report the synthesis of a new (PiPr3)2Ni syn-
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Article
Organometallics, Vol. 29, No. 22, 2010 6079
Figure 1. Two examples of the nickel-catalyzed C-H functionalization of a partially fluorinated aromatic, proposed to occur via C-H
bond oxidative addition to nickel.
via C-H bond oxidative addition. Reactions that probe
the utility of these (PiPr3)2Ni C-H bond activation pro-
ducts in catalytic C-H bond functionalization are also
described.
Results and Discussion
It has been previously shown that that the anthracene
and phenanthrene adducts (PEt3)2Ni(η2-C14H10) serve
as (PEt3)2Ni synthons in reactions with the fluorinated
benzenes.15,17 A similar approach was taken to provide a
(PiPr3)2Ni synthon using an anthracene adduct. The reaction
Figure 2. ORTEP depiction of the solid-state molecular struc-
of (PiPr3)2NiCl2 with an excess (THF)3Mg(η2-C14H10) in
ture of 1 as determined by X-ray crystallography. Hydrogen
THF afforded the deep red, 16-electron complex 1, as shown
atoms are omitted for clarity. The 30% probability ellipsoids
˚
are shown. Selected bond lengths (A): Ni(1)-P(1), 2.2197(8);
in eq 1. Complex 1 is very soluble in nonpolar organic sol-
Ni(1)-P(2), 2.2218(8); Ni(1)-C(1), 2.041(3); Ni(1)-C(2),
vents at room temperature, such as pentane and hexamethyl-
2.003(3); C(1)-C(2), 1.427(4); C(1)-C(14), 1.459(4); C(2)-
disiloxane. Multiple recrystallizations provided 1 in 71%
C(3), 1.439(4); C(3)-C(4), 1.347(4); C(4)-C(5), 1.446(4);
yield.
C(5)-C(14), 1.435(4). Selected bond angles (deg): P(1)-Ni-
(1)-P(2), 119.07(3);C(2)-C(1)-C(14), 119.7(3); C(1)-C(2)-C(3),
117.4(3); C(2)-C(3)-C(4), 123.0(3); C(3)-C(4)-C(5), 121.1(3);
C(1)-C(5)-C(14), 119.1(3).
Complex 1 was characterized by 1H, 31P{1H}, and 13C{1H}
NMR spectroscopy. The variable-temperature 1H and
31P{1H} NMR spectra in nonaromatic solvents, such as
pentane and THF-d8, are consistent with a fluxional com-
plex. The 121.5 MHz 31P{1H} NMR experimental and
modeled spectra of 1 in THF-d8 between 233 and 298 K
are shown in Figure 3. The 298 K 31P{1H} NMR spectrum
displays a single broad resonance at δ 44.4. Below the
coalescence temperature of 273 K, the peak resolves into
Single crystals of 1 suitable for structural analysis by X-ray
crystallography were obtained from slow evaporation of a
pentane solution at -40 °C. An ORTEP depiction of the
solid-state molecular structure is shown in Figure 2. X-ray
crystallographic collection and refinement parameters are
provided in Table 1. The Ni(PiPr3)2 fragment is η2-coordi-
nated to the 1,2-position of anthracene. The geometry of the
nickel metal center is approximately planar. There is a loss of
planarity in the anthracene moiety due to back-bonding by
nickel, as confirmed by a lengthened C(1)-C(2) distance of
2
two doublets, with a JPP value of 45 Hz. These variable-
temperature NMR spectra can be modeled using the
Arrhenius equation to estimate an 18.0 kcal mol-1 activa-
3
tion energy for this process. At 298 K, the 1H NMR
spectrum displays only five resonances for the anthracene
moiety in 1, rather than 10 environments expected for a C1
symmetric complex. The protons associated with C(1),
C(2), C(3), and C(4) appear as broad singlets at δ 5.3 and
5.6 with peak widths at half-height of 35 Hz in the 300 MHz
1H NMR spectrum, whereas the remaining protons of the
anthracene moiety appear in the range δ 7.17-8.43. At 233
K, the resonances at δ 5.3 and 5.6 are resolved doublets with
a 3JHH value of 8.5 Hz. At lower temperatures these peaks
broaden, but decoalescence was not observed as low as
˚
˚
1.427(4) A, which is comparable to 1.422(4) A in the ana-
logous anthracene adducts (PCy3)2Ni(η2-C14H10)33 and (PEt3)2-
Ni(η2-C14H10).27 The C(3)-C(4) bond length of 1.347(4) A is
˚
indicative of a nearly localized double bond. The larger size
of the PiPr3 donor compared to PEt3 would be expected to
result in a larger P-Ni-P angle in complex 1 compared to
(PEt3)2Ni(η2-C14H10), due to increased steric repulsion, but
should be similar to that observed for (PCy3)2Ni(η2-C14H10).
This is confirmed in the observed angle of 119.07(3)°, which
is significantly larger than the angles of 106.4(3)° and
193 K. This suggests that unlike the 18.0 kcal mol-1 barrier
3
1
to 31P exchange, the exchange of H environments has a
n
108.9(1)° for the PEt3 and Bu3P analogues, respectively,27
much lower barrier, though the lack of a slow-exchange
spectrum preventsthe estimation of the energy barrier. The1H
environments could be exchanged by a haptotropic rear-
rangement between the 16-electron complex (PiPr3)2Ni(η2-
C14H10) and the 18-electron complex (PiPr3)2Ni(η4-C14H10).
yet comparable to the PCy3 analogue, whose angle is
118.3(1)°.33
(33) Brauer, D. J.; Krueger, C. Inorg. Chem. 1977, 16 (4), 884.

6080 Organometallics, Vol. 29, No. 22, 2010
Table 1. Crystallographic Data for Compounds 1, 3, 4, 6, and 9
Hatnean et al.
1
3
4
6
9
empirical formula
fw
cryst syst
C
32H52NiP2
C24H44F4NiP2
529.24
C24H43F4NiP2
528.23
C23H35F4NiP
477.19
C24H52NiP2
461.31
557.39
orthorhombic
16.302(3)
17.505(3)
21.845(3)
90.0
90.0
90.0
6233.8(17)
Pbca
8
1.188
0.743
173(2)
55.0
66 314
7129; 0.0903
0.80-0.75
5135
monoclinic
10.8870(9)
13.4940(11)
20.7527(13)
90.0
113.002(3)
90.0
2806.4(4)
P21/c
4
1.253
0.841
173(2)
50.0
30 635
6364; 0.0279
0.85-0.74
5407
monoclinic
13.1370(6)
11.9971(6
17.7312(8)
90.0
95.243(10)
90.0
2782.8(2)
P21/c
4
1.261
0.848
213(2)
50.0
14 391
4891; 0.022
0.84-0.70
4157
monoclinic
10.2723(12)
12.3685(14)
18.484(2)
90.0
98.796(10)
90.0
2320.9(5)
P21/c
4
1.366
0.943
173(2)
50.0
21 781
4087; 0.08
0.89-0.79
2951
monoclinic
12.8640(15)
11.5975(13)
18.859(2)
90.0
102.332(1)
90.0
2746.51(8)
C2/c
4
1.116
0.830
173(2)
55.0
14 282
3095; 0.027
0.83-0.74
2904
˚
a (A)
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (degrees)
3
V (A )
˚
space group
Z value
Dcalc (g/cm3)
μ(MoKR) (mm-1
temperature (K)
2θmax (deg)
)
total no. of reflns
no. unique reflns; Rint
transmn factors
no. with I g 2σ(I )
no. variables
336
15.3
315
17.2
393
10.6
280
10.5
130
22.3
reflns/params
R; wR2 (all data)
GOF
residual density (e /A )
0.081; 0.117
1.068
0.700; -0.280
0.049; 0.0995
1.066
0.537; -0.260
0.05; 0.111
1.029
0.499; -0.261
0.0827; 0.1278
1.038
1.205; -0.364
0.048; 0.104
1.202
0.631; -0.302
-
3
˚
50 equiv of triisopropylphosphine and heated to 333 K. Unlike
in the absence of excess phosphine, a considerable amount of 1
was observed, as expected for an equilibrium reaction. The same
experiment was performed in neat triisopropylphosphine with
a stoichiometric amount of benzene, and the formation of 2a
was completely inhibited. The addition of anthracene was also
shown to shift the equilibrium.
Figure 3. Experimental (left) and modeled (right) variable-tem-
perature 31P{1H} NMR spectra for compound 1 obtained at
121.5 MHz in THF-d8.
These processes have been examined in detail for systems
bearing different phosphine donors.34,35
When compound 1 was dissolved in aromatic solvents, an
additional peak appeared at δ 58 in the 31P{1H} NMR spectra
at room temperature, along with one equivalent of triisopro-
pylphosphine. Variable-temperature NMR spectroscopic stud-
ies were carried out using C6D6, toluene-d8, and mesitylene as
solvents and revealed a thermal equilibrium between 1 and the
solvent adduct (PiPr3)Ni(η6-solvent) complexes 2a-c, as shown
in eq 2. In all three solvents, the equilibrium strongly favored
(PiPr3)Ni(η6-solvent) at 333 K, and complex 1 was not present
in significant amounts. When these samples were cooled back
to room temperature from 333 K, the resonance associated
with 1 reappeared. At 213 K, almost no complex 2 is observed.
This temperature dependence of this equilibrium reaction is in
accordance with the anticipated entropically favored formation
of 2, due to the three product species versus two reagents,
and thus the enthalpically favored production of 1. To further
probe this equilibrium, compound 1 was dissolved in C6D6 with
1
Complexes 2a-c were further characterized by H and
13C{1H} NMR spectroscopy at 333 K. The 13C resonance of
the methine carbon of the iPr group was a doublet due to coupling
to a single 31P nucleus, further confirming the nature of this com-
pound as a monophosphine complex; the bis(phosphine) com-
plexes with chemically equivalent phosphine nuclei invariably
1
exhibit virtual triplets for these carbons. In the H NMR, the
chemical shifts for the methyl substituents for the toluene and
mesitylene adducts 2b and 2c, respectively, are almost unchanged
relative to the unbound organic, whereas the aromatic protons
were shifted significantly upfield: δ 5.9 for 2a, δ 5.6-5.8 for 2b,
and δ 5.6 for 2c. The 13C{1H} NMR spectra revealed significant
upfield shifts for the coordinated aromatic carbons between δ
89.0 and 101.2. Comparison of the 1H and 13C{1H} NMR spec-
tra for 2a observed from reaction of 1 with C6H6 species and the
deuterated complex (PiPr3)Ni(η6-C6D6), 2a-d6, further aided in
the assignment of these spectra. For example, compound 2a dis-
plays a singlet at δ 90.4, yet in the analogously deuterated com-
pound, 2a-d6, there is a 1:1:1 triplet with a 1JCD value of 26 Hz,
which is comparable to that observed for the solvent C6D6 at δ
128. Similar observations are made for 2b-d8, where the reso-
nances corresponding to η6-toluene-CD are 1:1:1 triplets found
(34) (a) Stanger, A. Organometallics 1991, 10 (8), 2979. (b) Stanger,
A.; Weismann, H. J. Organomet. Chem. 1996, 515 (1-2), 183. (c) Li, T.;
Garcia, J. J.; Brennessel, W. W.; Jones, W. D. Organometallics 2010,
29 (11), 2430. (d) Atesin, T. A.; Li, T.; Lachaize, S.; Garcia, J. J.; Jones,
W. D. Organometallics 2008, 27 (15), 3811.
(35) Stanger, A.; Vollhardt, K. P. C. Organometallics 1992, 11 (1), 317.

Article
Organometallics, Vol. 29, No. 22, 2010 6081
at δ 89.0, 89.5, and 91.9 with 1JCD values of 23.0, 20.1, and 23.0
Hz, respectively, whereas the ipso-carbon is a singlet at δ 101.8.
To probe the preference for an aromatic donor at 333 K, a
competition experiment was conducted using a stoichiometric
mixture of benzene, toluene, and mesitylene with compound 1 in
hexamethyldisiloxane. The results indicated a slight preference
for the more electron-donating mesitylene over benzene and
toluene, resulting in a final mixture composition of 2a-c of
26%, 19%, and 55%, respectively, as monitored by 1H and 31
P
NMR. This is in contrast to the electron-rich bis(phosphine)-
nickel arene adducts, which preferentially bind to electron-poor
arenes.17,24 By monitoring the concentrations of individual spe-
cies through integration over the temperature range 303 to 333 K,
van’t Hoff plots for equilibrium formation of 2a-c were con-
structed, which provided estimated enthalpy changes for this
reaction of 21.9, 21.1, and 26.4 kcal mol-1, respectively. The
3
entropy changes were determined to be 58.7, 55.1, and 73.9 cal
mol-1
3
K
-1. Although not displaying an obvious trend, these
results suggest that the favored formation of 2c versus 2a or 2b is
the result of the more favorable ΔS of reaction, rather than a
more favorable ΔH of reaction.
3
Figure 4. ORTEP depiction of the solid-state molecular struc-
ture of 3 as determined by X-ray crystallography. Hydrogen atoms,
excluding the nickel hydride, are omitted for clarity. The methyl
carbons associated with a 2-fold disorder on the isopropyl moiety
are omitted for clarity. The 30% probability ellipsoids are shown.
A few structurally related examples of LNi(η6-arene) com-
plexes, where L is a phosphine,36 N-heterocyclic carbene,37 or
silylene38 ligand, are known. The presence of an equivalent of
iPr3P in the reactions that produced 2a-c hampered the isola-
tion of these products as solids. Attempts to scavenge the excess
phosphine using Lewis acids such as BEt3, B(C6F5)3, or anhy-
drous NiCl2 caused the decomposition of 2a-c.
Synthesis and Characterization of a Stable C-H Bond
Activation Product with 1,2,4,5-Tetrafluorobenzene. The re-
action of the anthracene adduct (PiPr3)2Ni(η2-C14H10) (1) witha
slight excess of 1,2,4,5-C6F4H2 in toluene results in an immediate
color change from red to orange. Analysis of the crude solution
by NMR spectroscopy reveals that the C-H activated product,
trans-(PiPr3)2NiH(2,3,5,6-C6F4H) (3), formed over the course
of 6 h, as shown in eq 3. No C-F bond activation products or
fluoroarene adducts of (PiPr3)2Ni were observed. Complex 3
was easily isolated by removal of solvent under vacuum, extrac-
tion into pentane, removal of the insoluble anthracene byprod-
uct by filtration, and crystallization at -40 °C. Divalent nickel
hydride complexes that also contain Ni-C bonded aryl moieties
are not common and are generally not accessible via C-H bond
oxidative addition.13
˚
Selected bond lengths (A): Ni(1)-H(1), 1.40(3); Ni(1)-P(1),
2.1661(6); Ni(1)-P(2), 2.1761(6); Ni(1)-C(1), 1.934(2); F(1)-
C(2), 1.365(3); F(2)-C(3), 1.357(3); F(3)-C(5), 1.366(3); F(4)-
C(6), 1.370(3). Selected bond angles (deg): P(1)-Ni(1)-P(2),
155.98(2); C(1)-Ni(1)-H(1), 177.6(11).
has trans-disposed triisopropylphosphine ligands and the
anticipated pseudo-square-planar geometry around the
nickel metal. The tetrafluorophenyl moiety is nearly ortho-
gonal to the P-Ni-P plane. The acute P(1)-Ni(1)-P(2) angle
of 155.98(2)° is attributed to the relief of steric crowding by the
bulky triisopropylphosphine ligands; the phosphine donors
bend away from the aromatic ring and toward the smaller
hydride ligand. The electron density associated with the hydride
was located in a difference map, and its position was refined
isotropically. Although the location of hydrogen atoms in the
electron density determined by X-ray crystallography can be
erroneous, the crystallographic Ni(1)-H(1) bond distance of
22
˚
1.40(3) A is within the range expected.
The solid-state molecular structure of complex 3 was
confirmed through characterization by solution NMR spec-
troscopy and elemental analysis. The room-temperature 1H
NMR spectra in C6D6 revealed a distinctive hydride reso-
nance at δ -16.25,15,17,22,39 which was a triplet of triplets of
triplets. The hydride was modeled using the WinDNMR40
simulation program as coupling to two 31P nuclei with a
2JHP value of 68.0 Hz, two ortho-fluorines with a 4JHF value
5
of 8.7 Hz, and two meta-fluorines with a JHF of value
4.0 Hz. The experimental and modeled spectra are shown
in Figure 5. The observed coupling constants are consis-
tent with the previous spectroscopic characterization of
the unisolable species (PEt3)2NiH(2,3,5,6-C6F4H2)15 and
related nickel hydrides.39
Single crystals suitable for structural analysis of 3 by X-ray
crystallography were directly obtained from this synthesis.
An ORTEP depiction of the solid-state molecular structure
is shown in Figure 4, and X-ray crystallographic collection
and refinement parameters are included in Table 1. Complex 3
The 31P{1H} NMR spectra reveal a singlet at δ 51.5, which
is a broad doublet in the 31P NMR due to coupling to the
hydride. The 19F{1H} NMR spectra show two second-order
(36) Nickel, T.; Goddard, R.; Krueger, C.; Poeschke, K. R. Angew.
Chem. 1994, 106 (8), 908.
(37) Lee, C. H.; Laitar, D. S.; Mueller, P.; Sadighi, J. P. J. Am. Chem.
(39) Darensbourg, M. Y.; Ludwig, M.; Riordan, C. G. Inorg. Chem.
1989, 28 (9), 1630.
Soc. 2007, 129 (45), 13802.
(38) Meltzer, A.; Praesang, C.; Milsmann, C.; Driess, M. Angew.
Chem., Int. Ed. 2009, 48 (17), 3170.
(40) WinDNMR, NMR Spectrum Calculations; Hans J. Reich: Madison,
WI, 2005.

6082 Organometallics, Vol. 29, No. 22, 2010
Hatnean et al.
that C-H bond breaking was not the rate-limiting step.32
This KIE observed in the formation of 3-d1 is a much smaller
than the equilibrium isotope effect (EIE) of 2.1 observed in
the activation of 1,2,4,5-C6F4HD by the (PEt3)2Ni moiety at
room temperature. The C-H/D activation reaction with the
smaller PEt3 ancillary ligand was reversible even at 233 K,
and at this temperature the EIE increased to 3.4. The C-H
bond reductive elimination from 3 must not occur at a
significant rate at room temperature, or else a similar EIE
would be observed. The relatively low KIE observed in the
formation of 1 is suggestive of an early transition state for the
oxidative addition step, where little C-H bond-breaking has
occurred. An early transition state is also consistent with the
stability of the C-H activation product compared to the
unobserved η2-arene intermediate. In an attempt to observe
reversible oxidative addition and determine the EIE for the
species 3-d1(NiH) and 3-d1(NiD), a mixture of these com-
plexes was heated to 50 °C. The ratio of 3-d1(NiH) to 3-
d1(NiD) gradually increased to a maximum value of 1.7 after
0.5 h. This demonstrates the reversibility of the C-H oxida-
tive addition reaction at 50 °C, and sets 1.7 as the minimum
possible EIE. Unfortunately, it could not be confirmed that
this was the true EIE for this reaction, due to scrambling
reactions that generated 3 and 3-d2, (PiPr3)2NiD(2,3,5,6-
C6F4D). The 19F NMR resonances of the meta-F nuclei for
3 and 3-d2 overlap with those of 3-d1(NiD) and 3-d1(NiH),
respectively, and results in a lower than actual isotope effect,
as measured by peak integration. A value greater than 1.7 is
consistent with the previously observed equilibrium isotope
effect of 2.1 observed with PEt3 as an ancillary ligand
at room temperature; there is no obvious reason for these
systems to exhibit significantly different EIEs. By using the
KIE for the forward reaction, k1H/k1D, of 1.3 and an
estimated EIE of 2.1 at 298 K, an inverse KIE for the
reductive elimination step, k-1H/k-1D, of 0.6 can be esti-
mated, consistent with the presence of a strong C-H
bonding interaction in the transition state for oxidative
addition/reductive elimination.42 Heating a mixture of
3-d1(NiD) and 3-d1(NiH) to 50 °C with an excess of non-
deuterated 1,2,4,5-tetrafluorobenzene resulted in their
conversion to 3, with the liberation of 1,2,4,5-C6F4HD,
which demonstrates that intermolecular ring hopping of
the (PiPr3)2Ni moiety from the proposed intermediate
(PiPr3)2Ni(η2-1,2,4,5-C6F4H2) is facile, similar to poly-
fluorinated η2-arene adducts of (PEt3)2Ni.16,17,23,24 Simi-
larly, heating a solution of 3 in the presence of 1,2,4,5-
C6F4HD slowly produced 3-d1(NiD) and 3-d1(NiH). IR
spectroscopy of these complexes allowed for identification
of a nickel hydride stretching frequency at 1903 cm-1. The
ratio of reduced masses for Ni-H versus Ni-D bonds can
be used to estimate a stretching frequency for the latter of
Figure 5. Experimental (bottom) and modeled (top) hydridic
region 1H NMR spectra for compound 3 obtained at 298 K in
C6D6.
multiplets at δ -112.9 and -143.0. The 13C{1H} NMR spec-
tra display a virtual triplet for the iPr-CH resonance with a
J
CP value of 10.8 Hz. To ensure that no exchange-broadened
1
resonances for adducts were missed, low-temperature H,
19F, and 31P{1H} NMR spectra were collected, but showed
no evidence of either mononuclear or dinuclear η2-arene
adducts,17 which supports the hypothesis that the bulky
phosphine donors do thermodynamically disfavor the cis-
phosphine geometries adopted in these Ni(0) species. In
the related C-H activation product (PEt3)2NiH(C6F5),
the η2-arene complex is in equilibrium with the C-H
activation product, with the latter disfavored by only
0.8 kcal mol-1 17
.
The crude reaction mixture from the synthesis of 3 was
3
monitored by NMR spectroscopy for weeks at room tempera-
ture, and no conversion to C-F activation products was
observed. Even upon heating to 100 °C for 3 h, toluene-d8 solu-
tions of complex 3 failed to convert to the anticipated thermo-
dynamic C-F activation product18 trans-(PiPr3)2NiF(2,4,5-
C6F3H2), as monitored by 1H, 19F, and 31P{1H} NMR spectro-
scopy.15 This could imply that the C-H activation product is so
stabilized with respect to the adduct (PiPr3)2Ni(η2-1,2,4,5-
C6F4H2) that the adduct is no longer kinetically accessible; this
adduct is expected to be the common intermediate for both
concerted C-H and C-F activation,17,41 Alternatively, the
C-F bond activation barrier could simply be much higher for
the (PiPr3)2Ni moiety compared to the (PEt3)2Ni moiety.
A seriesof experiments were performed to assessthe revers-
ibility of the C-H bond activation reaction that could
form the transient adduct (PiPr3)2Ni(η2-1,2,4,5-C6F4H2).
A deuterium labeling study performed by reacting 1 with
the monodeuterated tetrafluorobenzene 1,2,4,5-C6F4HD
resulted in a mixture of (PiPr3)2NiH(2,3,5,6-C6F4D),
3-d1(NiH), and (PiPr3)2NiD(2,3,5,6-C6F4H), 3-d1(NiD),
as shown in Scheme 1. In the 19F NMR spectrum, the
meta-F nuclei of these species are separated by 0.3 ppm,
which allows for their integration and a determination of a
kinetic isotope effect (KIE) of 1.3 for the C-H bond activa-
tion step labeled with the rate constant k1; the rate constant
1359 cm-1 39
however, this region of the spectrum was
;
obscured by intense peaks attributed to stretching modes
for the other ligands.
Synthesis and Characterization of a C-H Bond Activation
Product with 1,2,3,5-Tetrafluorobenzene. The reaction of the
complex 1 with excess 1,2,3,5-C6F4H2 in toluene was complete
in 36 h. Analysis of the crude reaction mixture by 19F{1H}
NMR spectroscopy reveals trans-(PiPr3)2NiH(2,3,4,6-C6F4H)
was only slightly larger for C-H bond activation, labeled k1H
,
than the C-D bond, labeled k1D. A similar intermolecular
KIE has been observed in the catalytic functionalization of
pyridine by a nickel complex, but was interpreted as suggesting
(42) (a) Churchill, D. G.; Janak, K. E.; Wittenberg, J. S.; Parkin, G.
J. Am. Chem. Soc. 2003, 125 (5), 1403. (b) Jones, W. D. Acc. Chem. Res.
2003, 36 (2), 140. (c) Parkin, G. Acc. Chem. Res. 2009, 42 (2), 315.
(41) Braun, T.; Cronin, L.; Higgitt, C. L.; McGrady, J. E.; Perutz,
R. N.; Reinhold, M. New J. Chem. 2001, 25 (1), 19.

Article
Organometallics, Vol. 29, No. 22, 2010 6083
Scheme 1
(4) as the major product, with less than 2% of other impurities,
as shown in eq 4.
Single crystals of 4 suitable for structural analysis by X-ray
crystallography were obtained by slow evaporation of a satu-
rated hexamethyldisiloxane solution at -40 °C, and an ORTEP
depiction of the solid-state molecular structure is shown
in Figure 6. Data collection was performed at 213 K, because
the yellow crystals shattered upon further cooling. There is
disorder due to the two possible orientations of the fluorinated
aryl ring; the molecules pack with little discrimination in the
orientation of the 2,3,4,6-C6F4H moiety, presumably due to the
similar sizes of fluorine and hydrogen. An associated disorder of
one of the iPr3P ligands was also modeled. These factors limit
the reliability of some of the bond lengths, but leave no doubt as
to the connectivity of the molecule. Complex 4 has a similar
structure to that of 3, where the geometry around the nickel
center is approximately square planar. The P(1)-Ni(1)-P(2)
angle of 158.94(4)° is slightly larger than in 3, and the Ni(1)-
Figure 6. ORTEP depiction of the solid-state molecular structure of
4 as determined by X-ray crystallography. Hydrogen atoms, exclud-
ing the nickel hydride, and disorder are omitted for clarity. The 30%
˚
probability ellipsoids are shown. Selected bond lengths (A): Ni(1)-
H(1), 1.54(4); Ni(1)-P(1), 2.1719(12); Ni(1)-P(2), 2.1734(12);
Ni(1)-C(1), 1.943(4); F(1)-C(2), 1.366(6); F(2)-C(3), 1.281(8);
F(3)-C(4), 1.354(6); F(4)-C(6), 1.362(6). Selected bond angles
(deg): P(1)-Ni(1)-P(2), 158.94(4); C(1)-Ni(1)-H(1), 172.9(16).
˚
H(1) distance was found to be 1.54(4) A.
Compound 4 was also characterized by multinuclear
NMR spectroscopy. The room-temperature 1HNMRspectrum
confirms the solid-state molecular structure with a resonance
for the hydridic proton at δ -16.38 with a resolved multiplet
modeled as a triplet of doublets of doublets of doublets, as
shown in Figure 7. The largest coupling is to the two phosphorus
nuclei with a 2JHP value of 68.5 Hz, which was confirmed by 31
P
NMR spectroscopy. Additional couplings to the two nonequi-
4
valent ortho-fluorines with JHF values of 8.9 and 8.7 Hz and
coupling to a meta-fluorine with a 5JHF value of 3.5 Hz were also
confirmed by modeling this multiplet, as shown at the top of
Figure 7. The 19F{1H} NMR spectrum shows four resonances at
δ -86.1, -105.8, -144.4, and -170.3, consistent with the ob-
served connectivity. The 13C{1H} NMR spectrum displays a
virtual triplet for the iPr-CH resonance, similar to 3, with a JCP
value of 10.3 Hz.
Figure 7. Experimental (bottom) and modeled (top) hydridic re-
gion 1H NMR spectra for compound 4 obtained at 298 K in C6D6.
This C-H activated complex is modestly stable in solution at
room temperature for weeks, gradually isomerizing to the

6084 Organometallics, Vol. 29, No. 22, 2010
Hatnean et al.
thermodynamically favored C-F activated product. Unlike
compound 3, heating a toluene solution of 4 to 50 °C results
in conversion to the C-F activated compounds over the course
of many days. The mechanism through which this occurs is
currently under investigation, and the description of the C-F
activation products is beyond the scope of this paper.
The substrate 1,2,3,4-tetrafluorobenzene, which has only a
single fluorine substituent adjacent to either C-H bond, failed
to produce the C-H activation product, (PiPr3)2NiH(2,3,4,5-
C6F4H), either as an isolable product or as evidenced by NMR
spectroscopy.
Synthesis and Characterization of a C-H Bond Activation
Product of Pentafluorobenzene. As monitored by NMR
spectroscopy, pentafluorobenzene reacts with a red-colored
solution of 1 in C6D6 to provide the C-H activated complex
trans-(PiPr3)2NiH(C6F5) (5) with less than 5% of other
impurities, as shown in eq 5. Unlike complexes 3 and 4,
complex 5 could be isolated only as a viscous oil.
attempt to synthesize C-H activation products directly in a
similar manner to those reported catalytically, and without
the need for the highly reactive species 1, we employed
Ni(COD)2 (COD = 1,5-cyclooctadiene) with triisopropyl-
phosphine in an attempt to make a (PiPr3)2Ni synthon
in situ. This would be advantageous, as complex 1 is only
moderately stable at 50 °C, yet the catalysts prepared from
Ni(COD)2 and phosphines can withstand temperatures up to
80 °C for extended periods of time without decomposition.4,5
A solution of 1,2,4,5-C6F4H2 was added to a mixture of
Ni(COD)2 and 2 equiv of triisopropylphosphine in C6D6.
Initial analysis of the crude solution via 19F{1H} NMR
spectroscopy revealed not only the desired C-H activated
complex 3 as a minor product (33% of the sample) but
another species with four fluorine environments, which
was later identified as the allylic cyclooctene adduct (η3-
C8H13)Ni(PiPr3)(2,3,5,6-C6F4H), 6, as shown in eq 6. After
two days, resonances associated with 6 continued to grow in
intensity from the initial quantity of 67% to 85% of the
sample, which indicates that the insertion of 1,5-cycloocta-
diene is slower than C-H bond activation.
In the 1H NMR, the hydride resonance is apparent from
its upfield shift of δ -16.5 and is a triplet of triplets of triplets,
analogous to complex 3, with comparable coupling to two
31P nuclei with a 2JHP value of 68.0 Hz, two ortho-fluorines
with a 4JHF value of 9.9 Hz, and two meta-fluorines with a
5JHF value of 4.5 Hz. Further confirmation that this is indeed
the C-H oxidative addition product was provided by the 31P
NMR spectrum, with a broad doublet at δ 51.2, indicating
coupling to the nickel hydride with a 2JPH value of 68.0 Hz.
The 19F NMR spectrum displays three resonances at δ
-110.7, -163.2, and -164.6 for the ortho-, para-, and
meta-fluorines. The para-fluorine exhibits a triplet of triplets
with coupling to two pairs of equivalent meta- and ortho-
fluorines, whereas the 19F resonances corresponding to the
ortho- and meta-fluorines are both second-order multiplets.
A variable-temperature NMR study did not reveal any
evidence of η2-arene adducts in equilibrium with hydride 5,
and an EPR spectroscopic study did not reveal paramagnetic
impurities. Over the course of weeks at room temperature,
complex 5 converts to C-F activation products, the descrip-
tion of which are beyond the scope of this paper.
It is of interest to ascertain if complexes 2a and 2b play a role
in these C-H bond activation reactions when performed in
benzene or toluene. To further investigate the mechanism of this
reaction, complex 1 was reacted with pentafluorobenzene in the
presence of a large excess of triisopropylphosphine in toluene.
By comparison with an analogous reaction in the absence of
added triisopropylphosphine, it was determined that excess
triisopropylphosphine did not slow the rate of C-H bond
activation. This suggests that complex 2b, (PiPr3)Ni(η6-
C7H8), is not necessary for C-H bond activation.
Single crystals suitable for structural analysis of 6 by X-ray
crystallography were obtained from slow evaporation of a
cold pentane solution, and an ORTEP depiction of the solid-
state molecular structure is shown in Figure 8. X-ray crystal-
lographic collection and refinement parameters are included
in Table 1. The nickel metal resides in a pseudo-square-
planar coordination sphere, with the allylic donor occupying
two coordination sites. The allylic moiety features C(7)-
˚
C(8) and C(8)-C(9) distances of 1.394(6) and 1.410(6) A,
respectively. The eight-membered ring adopts a boat con-
formation directed away from the triisopropylphosphine
ligand. Related allylic complexes of Ni not arising from
C-H bond activation are known.43
Compound 6 has been further characterized by elemental
analysis and 1H, 31P, 19F, and 13C{1H} NMR spectroscopy.
The 19F{1H} NMR spectrum reveals fluorine resonances at δ
-114.7, -115.2, -142.8, and -143.0. The presence of four
19F environments indicates that rotation around both the
Ni-C bond of the 2,3,5,6-C6F4H moiety and about the Ni-
1
allyl moiety must be slow on the NMR time scale. The H
NMR spectra is also consistent with a C1 symmetric com-
pound. A series of overlapping doublets between δ 0.85 and
0.97 correspond to the diastereotopic protons on C(10) and
C(14), while a complicated multiplet between δ 1.15 and 1.4
accounts for the remaining diastereotopic protons on C(11),
C(12), and C(13). Three multiplets at δ 3.78, 4.02, and 4.85
belong to the allylic protons on C(7), C(8), and C(9).
Unexpected Insertion Products via Reactions of Ni(COD)2
with Fluorinated Aromatics. The nickel-catalyzed examples
of polyfluoroarene C-H bond functionalization reported to
date have both utilized combinations of secondary alkyl
phosphines with Ni(COD)2 as catalyst precursors.4,5 In an
(43) (a) Henc, B.; Jolly, P. W.; Salz, R.; Stobbe, S.; Wilke, G.; Benn,
R.; Mynott, R.; Seevogel, K.; Goddard, R.; Krueger, C. J. Organomet.
Chem. 1980, 191 (2), 449. (b) Henc, B.; Jolly, P. W.; Salz, R.; Wilke, G.;
Benn, R.; Hoffmann, E. G.; Mynott, R.; Schroth, G.; Seevogel, K.; et al.
J. Organomet. Chem. 1980, 191 (2), 425.

Article
The proposed mechanism for the synthesis of 6 is a classic
Organometallics, Vol. 29, No. 22, 2010 6085
These result from trapping the kinetically accessible hydride
species from the C-H activation of 1,2,3,4-C6F4H2 that we
had previously been unable to observe, because its formation
from 1 is thermodynamically unfavorable. These com-
chain-walking mechanism whereby oxidative addition C-H
activation of the fluoroarene to the nickel phosphine moiety
is followed by the insertion of 1,5-cyclooctadiene, as shown
in Scheme 2. A β-elimination and dissociation of 1,4-cy-
clooctadiene followed by iPr3P coordination could regener-
ate the C-H activation product 3; however, this process
would be expected to lead to at least a partial isomerization
of the extra equivalent of 1,5-cyclooctadiene present in
solution to 1,4-cyclooctadiene, which was not observed
by 1H NMR spectroscopic analysis of the reaction mixture.
This suggests that the β-elimination is rapidly followed
by reinsertion, without dissociation of 1,4-cyclooctadiene.
An additional insertion and β-elimination provides a 1,3-
cyclooctadiene complex, which then inserts again into the
Ni-H bond to provide the η3-C8H13 moiety observed in
compound 6.
1
pounds have been characterized by H, 31P, and 19F NMR
spectroscopy.
Analogous reactions were performed with 1,2,3,5- and
1,2,3,4-tetrafluorobenzene, as shown in eqs 7 and 8, re-
spectively. Immediate analysis of the crude mixture by
NMR spectroscopy for the reaction of Ni(COD)2 with
1,2,3,4-C6F4H2 revealed COD insertion products 8a,b.
The 31P{1H} NMR spectra of both product mixtures
showed two separate, yet similar resonances for this mono-
phosphine species, with both pairs in equal quantities by
integration. Similarly, the 19F{1H} NMR spectra contained
two sets of resonances for four fluorine environments. This is
attributed to hindered rotation around the Ni-aryl bond,
resulting in the diastereomers 7a,b and 8a,b for 1,2,3,5- and
1,2,3,4-tetrafluorobenzene, respectively. These reactions also
contained less than 5% C-F activation impurities.
Catalytic Transformations via Alkyne Insertion. Although
complex 1 does not react with 1,2,3,4-C6F4H2 to generate
a thermodynamically favorable C-H activation product,
the isolation of 8a,b, which arises from the trapping of a
kinetically accessible hydride, suggests that nickel catalysts
should be able to facilitate the catalytic functionalization
of C-H bonds that undergo thermodynamically disfavored
oxidative addition, provided the barrier to C-H activation
is not too high. Trapping these transient hydrides via reactions
with other small molecules, such as alkynes5 and Bu3Sn-
CHdCH2,4 should result in viable catalytic cycles. The isolable
hydrides 3, 4, and 5 provide a chance to examine their potential
reactivity.
Figure 8. ORTEP depiction of the solid-state molecular structure
of 6 as determined by X-ray crystallography. Hydrogen atoms are
omitted for clarity. The 30% probability ellipsoids are shown.
˚
Selected bond lengths (A): Ni(1)-P(1), 2.2033(12); Ni(1)-C(1),
1.921(4); Ni(1)-C(7), 2.066(4); Ni(1)-C(8), 1.967(4); Ni(1)-C(9),
2.101(5); C(7)-C(8), 1.394(6); C(8)-C(9), 1.410(6); C(9)-C(10),
1.508(6); C(7)-C(14), 1.503(6). Selected bond angles (deg): P-
(1)-Ni(1)-C(1), 105.59(12); C(7)-C(8)-C(9), 122.3(4); C(7)-
Ni(1)-C(8), 40.37(18); C(7)-Ni(1)-C(9), 72.23(18); C(1)-Ni-
(1)-C(9), 159.19(18); C(7)-Ni(1)-P(1), 165.74(14).
Scheme 2

6086 Organometallics, Vol. 29, No. 22, 2010
Hatnean et al.
Scheme 3
Surprisingly, the reaction of compound 3 with stoichio-
metric amounts of 3-hexyne failed to yield more than 3%
of the desired insertion product, (PiPr3)2Ni(CEtdCHEt)-
(2,3,5,6-C6F4H) (10). Immediate analysis of the crude reac-
tion mixture by 31P{1H} NMR spectroscopy at room tempera-
ture revealed a singlet at δ 55 as the major product, identified as
the π-coordinated 3-hexyne adduct (PiPr3)2Ni(η2-EtCtCEt)
(9), as shown in Scheme 3A. The only significant byproduct
was identified as a trace amount of the desired insertion prod-
uct 10 at δ 36 in the 31P{1H} NMR spectrum. This reaction
remains unchanged at room temperature for weeks, even in the
presence of 1,2,4,5-tetrafluorobenzene.
Compound 9 is synthesized quantitatively through the reac-
tion of 1 with 3-hexyne in pentane, as shown in Scheme 3B.
Alternatively, compound 9 can be conveniently prepared
through the reaction of Ni(COD)2, 2 equiv of triisopropyl-
phosphine, and 3-hexyne in pentane. Compound 9 has been
fully characterized by 1H, 31P(1H}, and 13C{1H} NMR spec-
troscopy. Orange-colored single crystals suitable for struc-
tural analysis of 9 by X-ray crystallography were obtained
from slow evaporation of a cold pentane solution, and an
ORTEP depiction of the solid-state molecular structure is
shown in Figure 9. X-ray crystallographic collection and
refinement parameters are included in Table 1. Compound 9
has crystallographic symmetry, where the nickel metal re-
sides on a C2 axis, in a pseudoplanar geometry with a
P(1)-Ni(1)-P(1)0 angle of 115.19(4)°. The 3-hexyne moiety
is η2-coordinated to the metal center. A longer C(3)-C(3)0
Figure 9. ORTEP depiction of the solid-state molecular structure
of 9 as determined by X-ray crystallography. Hydrogen atoms
are omitted for clarity. The 30% probability ellipsoids are shown.
˚
Selected bond lengths (A): Ni(1)-P(1), 2.1864(7); Ni(1)-C(3),
1.904(3); C(3)-C(3)0, 1.275(6). Selected bond angles (deg): P(1)-
Ni(1)-P(1)0, 115.19(4); C(3)-Ni(3)-C(3)0, 39.14(18); C(3)-Ni-
(1)-P(1), 103.38(9); C(3)0-Ni(1)-P(1), 141.12(9); C(3)0-C(3)-
C(2), 146.27(18); Ni(1)-C(3)-C(2), 143.1(2); C(1)-C(2)-C(3),
116.3(3).
appears to be kinetically accessible; heating a toluene solu-
tion of 9 and 1,2,4,5-tetrafluorobenzene to 50 °C affords
dissociation of the coordinated alkyne, allowing for the
reaction to proceed in the presence of a fluoroarene. The
room-temperature reaction of compound 1 (10 mol %) or a
mixture of Ni(COD)2 (10 mol %) and triisopropylphosphine
(10 mol %) with 1,2,4,5-C6F4H2 and 3-hexyne results in the
immediate formation of compound 9 with trace amounts of
the insertion product, compound 10, as shown in Scheme 4.
Upon heating to 50 °C, the reaction mixture converts
primarily to compound 10, which has been characterized
by 1H, 31P, and 19F NMR spectroscopy, in addition to trace
amounts of the reductively eliminated monofunctionalized
compound 1,2,4,5-C6F4H-CEtdCHEt (11). The 31P{1H}
NMR spectrum of 10 reveals a singlet at δ 39.4, which is
˚
bond length of 1.275(6) A than the expected carbon-carbon
˚
triple bond for an alkyne of 1.20 A is a result of back-bonding
from the Ni(PiPr3)2 fragment and is in agreement with
comparative values in the literature between 1.272 and
˚
1.305 A, where the longer bond length is attributed to
systems with a chelating phosphine backbone.44
Although the formation of compound 9 from 3 would
suggest that C-H bond activation of 1,2,4,5-tetrafluoroben-
zene by 9 is thermodynamically unfavorable, this product
(44) (a) Bach, M. A.; Burlakov, V. V.; Arndt, P.; Baumann, W.;
Spannenberg, A.; Rosenthal, U. Organometallics 2005, 24 (13), 3047. (b)
Bartik, T.; Happ, B.; Iglewsky, M.; Bandmann, H.; Boese, R.; Heim-
bach, P.; Hoffmann, T.; Wenschuh, E. Organometallics 1992, 11 (3),
1235. (c) Bennett, M. A.; Johnson, J. A.; Willis, A. C. Organometallics
1996, 15 (1), 68. (d) Mindiola, D. J.; Waterman, R.; Jenkins, D. M.;
Hillhouse, G. L. Inorg. Chim. Acta 2003, 345, 299. (e) Rosenthal, U.; Pulst,
S.; Arndt, P.; Baumann, W.; Tillack, A.; Kempe, R. Z. Naturforsch., B:
Chem. Sci. 1995, 50 (3), 377. (f ) Waterman, R.; Hillhouse, G. L.
Organometallics 2003, 22 (25), 5182.
1
∼20 ppm upfield from compounds 3 and 9, while the H
NMR spectrum has a broad triplet at δ 5.61 attributed to the
alkene hydrogen on the inserted alkyne fragment. The 19F
NMR spectrum displays four fluorine environments at δ

Article
Organometallics, Vol. 29, No. 22, 2010 6087
Scheme 4
-110.3, -114.7, -142.1, and -142.5 that are not in ex-
change due to hindered rotation about the Ni-C bond of the
2,3,5,6-C6F4H moiety. After 24 h at 50 °C, the reaction
mixture consists mainly of the doubly activated product
1,2,4,5-C6F4H(CEtdCHEt)2 (12), which appears as a singlet
at -143.5 in the 19F{1H} NMR spectra, with trace amounts
of the monofunctionalized product 1,2,4,5-C6F4H-CEtd
CHEt (11), which displays two fluorine resonances at
-140.5 and -143.4, and unreacted 1,2,4,5-C6F4H2. The
relative ratio of products 11 and 12 in the 19F NMR is
5:95. This suggests that the C-H bond functionalization of
11 is slightly faster than that of 1,2,4,5-tetrafluorobenzene.
The initial formation of primarily 11 rather than 12 in this
reaction rules out the possibility that this preference for 12 is
the result of 10 undergoing reductive elimination without
loss of 11 via some adduct of (PiPr3)2Ni, followed by rapid
intramolecular oxidative addition of the remaining C-H
bond activation.
The stoichiometric reaction of the pentafluorobenzene C-H
activation product 5 with 3-hexyne differs than the analogous
reaction between 3 and 3-hexyne, because it instead produces
essentially equal amounts of compound 9and the insertion prod-
uct (PiPr3)2Ni(CEtdCHEt)(C6F5) (14) upon mixing. Com-
pound 14 was characterized by 1H, 31P, and 19FNMRspectros-
copy. The 31P NMR spectrum reveals a singlet at δ 38.3,
comparable to the 31P chemical shift for compound 10, and
the 1H NMR spectrum has a triplet at δ5.25 characteristic of the
hydrogen on the inserted alkyne fragment. The 19F NMR spec-
trum contains five fluorine environments at δ -107.9, -112.5,
-162.2, -163.4, and -164.0. Heating this mixture to 50 °C
drives the reaction to complete reductive elimination of the
functionalized product C6F5-CEtdCHEt, 13, as shown in
Scheme 4. The catalytic alkenylation of 1,2,3,4-C6F4H2 and
3-hexyne with Ni(COD)2 (10 mol %) and triisopropylpho-
sphine (10 mol %) is practically quantitative in producing
1,2,3,4-C6F4H-CEtdCHEt (15), as shown in Scheme 4. How-
ever, the intermediate insertion product was not observed by
NMR spectroscopy, which reveals that reductive elimination
is more rapid for this substrate with a single fluorine adjacent
to the site of functionalization; this can be attributed to the
weaker Ni-C bond to the aryl group in this species. Unlike
1,2,3,5- and 1,2,4,5-tetrafluorobenzene, the substrate 1,2,3,4-
tetrafluorobenzene failed to produce an observable C-H
bond activation complex, (PiPr3)2NiH(2,3,4,5-C6F4H), as it
is thermodynamically unfavorable. Despite this, the transient
hydride can be trapped using an alkyne, showing that this
C-H activation product is kinetically accessible. Compound
1
15 was characterized by H and 19F NMR spectroscopy,
where there are four fluorine environments at δ -141.1,
-142.4, -156.7, and -159.2.
Surprisingly, the alkyne adduct of the less bulky adduct
(PEt3)2Ni(η2-EtCtCEt) (16), synthesized analogously to
compound 9, displayed similar reactivity.45 Heating a solution
of compound 16 (10 mol %) with 1,2,4,5-tetrafluorobenzene at
80 °C causes alkyne dissociation followed by insertion into the
C-H activation product, (PEt3)2NiH(2,3,5,6-C6F4H), which
produced observable amounts of (PEt3)2Ni(CEtdCHEt)-
(2,3,5,6-C6F4H) (17). Compound 17 was characterized by 31
P
and 19F NMR spectroscopy. The 31P{1H} NMR spectrum
revealed a singlet at δ 13.3, which is slightly upfield from the
31P resonance observed for 16 at δ26.8. The 19F NMR spectrum
displays four fluorine environments at δ -113.4, -117.4,
-142.0, and -142.3, which are not in exchange due to hindered
rotation about the Ni-C bonds, analogous to compound 10.
Heating this mixture for 3 days at 80 °C eventually produced
the monoinsertion product 11 in a modest 40% yield, which
amounts to only four catalytic turnovers; unsurprisingly,
considering the low conversion, very little of the doubly func-
tionalized product 12 was observed, as shown in Scheme 4. The
reductive elimination of the functionalized product appears to
be a slow step in the catalytic cycle for alkenylation for both the
PiPr3 and PEt3 ancillary ligands, as judged by the persistence of
the resonances associated with 10 and 17, respectively. The
alkyne adducts 9 and 16 also appear in these spectra as resting
(45) Begum, R. A.; Sharp, P. R. Organometallics 2005, 24 (11), 2670.

6088 Organometallics, Vol. 29, No. 22, 2010
Hatnean et al.
states, and thus it can be concluded that C-H bond oxidative
addition steps with 10 and 17 are also slow. It should be noted
that with PEt3 as the ancillary ligand catalysis did not occur at
a significant rate at 50 °C, but heating the reaction mixture at
80 °C for prolonged periods of time resulted in significant
decomposition and the precipitation of nickel, which results in
dramatically decreased yields as the catalyst decomposes. It
appears that the main downfall of the PEt3 ancillary ligand in
these reactions is not its propensity to undergo side reactions,
such as C-F bond activation, but rather the higher tempera-
tures required for both the oxidative addition and reductive
elimination steps that occur during catalytic alkenylation, and
the inability of PEt3 to sufficiently kinetically stabilize Ni(0)
with respect to the free metal under these conditions.
deoxygenated using a Grubbs-type column system.46 Benzene-d6
was dried by heating at reflux with Na/K alloy in a sealed vessel
under partial pressure, then trap-to-trap distilled and freeze-
pump-thaw degassed three times. Toluene-d8 was purified in an
analogous manner by heating at reflux over Na. THF-d8 was
purified in an analogous manner by heating at reflux over K. 1H,
31P{1H}, 13C{1H}, and 19F{1H} NMR spectra were recorded on a
Bruker AMX spectrometer operating at 300 or 500 MHz with
respect to proton nuclei. All chemical shifts are recorded in parts
1
per million, and all coupling constants are reported in hertz. H
NMR spectra were referenced to residual protons (C6D5H, δ 7.16;
C7D7H, δ 2.09; C4D7HO, δ 1.73) with respect to tetramethylsilane
at δ 0.00. 31P{1H} NMR spectra were referenced to external 85%
H3PO4 at δ 0.00. 13C{1H} NMR spectra were referenced relative to
solvent resonances (C6D6, δ 128.0; C7D8, δ 20.4; C4D8O, δ 25.37).
19F{1H} NMR spectra were referenced to an external sample of
80% CCl3F in CDCl3 at δ 0.0. Elemental analyses were performed
by the Center for Catalysis and Materials Research, Windsor,
Ontario. The compounds benzene-d6, toluene-d8, and THF-d8 were
purchased from Cambridge Isotope Laboratory. The compounds
anthracene, pentafluorobenzene, 1,2,3,4-, 1,2,3,5-, and 1,2,4,5-tetra-
fluorobenzene, and 3-hexyne were purchased from Aldrich and
used as received. The compound triisopropylphosphine was pur-
chased from Strem and used as received. The anthracene adduct
(THF)3Mg(η2-C14H10),35 trans-[Cl2Ni(PiPr3)2],47 the anthracene
Conclusions
This work provides the first examples of the isolation and
complete characterization of products from the oxidative
addition of aromatic C-H bonds to nickel. This was achieved
by using the sterically encumbered PiPr3 ancillary ligand to
destabilize Ni(0) complexes with cis-disposed phosphine do-
nors relative to their oxidative addition products, which have
trans-disposed donors. The anthracene adduct (PiPr3)2Ni(η2-
C14H10) provedtobeaneffective(PiPr3)2Ni synthon and reacts
with, 1,2,4,5-tetrafluorobenene, 1,2,3,5-tetrafluorobenzene,
and pentafluorobenzene via C-H bond activation, with no
evidence for mononuclear or dinuclear Ni(0) adducts. The
C-H activation product of 1,2,4,5-C6F4H2 displayed remark-
able thermal stability and did not undergo C-F bond activa-
tion even with heating to 100 °C. Deuterium labeling studies
suggest that the reaction is not rapidly reversible at room
temperature. The C-H activation products arising from
1,2,3,5-C6F4H2 and pentafluorobenzene were also isolated,
but were less thermally stable. The substrate 1,2,3,4-tetrafluor-
obenzene did not produce (PiPr3)2NiH(2,3,4,5-C6F4H) as an
isolable product. However, trapping the transient hydride from
oxidative addition of 1,2,3,4-C6F4H2 to (PiPr3)2Ni with alkyne
shows that this C-H activation product is kinetically acces-
sible, despite only a single ortho-fluorine adjacent to the
activated bond. The alkyne adduct (PiPr3)2Ni(η2-EtCtCEt)
proved to be a useful precursor in the alkenylations of C6F5H
and 1,2,3,4- and 1,2,4,5-C6F4H2 into new organofluorines.
Somewhat surprisingly, similar catalytic reactivity was ob-
served using the phosphine PEt3 as the ancillary ligand. The
alkyne adduct (PEt3)2Ni(η2-EtCtCEt) was also effective in
catalytic alkenylation at relatively high temperatures; this
(PEt3)2Ni moiety is known to provide thermodynamic C-F
bond activation products under ambient conditions,15,16 thus
highlighting the possibility of using kinetic C-H activation
products in catalysis.
adduct (PEt3)2Ni(η2-C14H10), 1,2,4,5-C6F4HD,15 and Ni(COD)2
48
were prepared by literature methods.
Synthesis of the Anthracene Adduct (PiPr3)2Ni(η2-C14H10), 1.
To a mixture of trans-[Cl2Ni(PiPr3)2] (15 g, 33 mmol) and
(THF)3Mg(η2-C14H10) (15.36 g, 37 mmol) was added slowly
200 mL of THF at -78 °C, and the solution was stirred for 1 h.
The purple solution was slowly warmed to 0 °C over 3 h, and the
color changed to brown. The mixture was stirred for an additional 2
h at 0 °C, followed by removal of the solvent. The resulting solid
was extracted into 200 mL of pentane, and MgCl2 was filtered off.
The filtrate was placed in the freezer, and over the course of 30 min
colorless crystals of the paramagnetic compound ClNi(PiPr3)2
precipitated from solution and were isolated by filtration (2.7 g,
14.5% yield). The filtrate was concentrated by 75% and placed in
the freezer. X-ray quality red crystals of the desired compound 1
precipitated from the solution overnight and were filtered and dried
under vacuum (8.96 g, 48.2% yield). Concentration of the mother
liquor yielded a second crop containing a low melting solid;
isolation of this solid was achieved through recrystallization from
hexamethyldisiloxane in the freezer (4.22 g, 23% yield). Both solids
were confirmed by NMR spectroscopy to be 1 (71% total yield).
Compound 1 is very soluble in hydrocarbon solvents; however,
when dissolved in aromatic solvents such as benzene, toluene,
and mesitylene, it provides equilibrium amounts of (PiPr3)Ni(η6-
1
solvent), 2a-c, respectively. H NMR (THF-d8, 298 K, 300.13
MHz): δ 1.18 (br, 36H, iPr-CH3); 2.04 (br, 6H, iPr-CH); 5.32 and
5.55 (br, 2H, Ni-CH, W1/2 = 35.0 Hz); 7.17, 7.41, 7.60, 7.98, and
8.43 (br, 8H, anthracene-H). 31P{1H} NMR (THF-d8, 298 K,
121.5 MHz): δ 44.4 (br, W1/2 = 18.0 Hz). 31P{1H} NMR (THF-d8,
2
233 K, 121.5 MHz): δ 40.5 and 44.3(d, JPP =45 Hz). 13C{1H}
NMR (THF-d8, 298 K, 75.5 MHz): δ 21.1 (s, iPr-CH3); 22.5 (d,
iPr-CH, 1JCP = 18 Hz); 122.7, 123.8, 126.0, 126.9, 127.2, and 128.9
(s, anthracene-CH); 132.8 and 138.1 (br, anthracene-ipso-CH).
Anal. Calcd for C32H52NiP2 (MW 557.40): C, 68.95; H, 9.40.
Found: C, 69.02; H, 9.78.
Experimental Section
General Procedures. Unless otherwise stated, all manipula-
tions were performed under an inert atmosphere of nitrogen using
either standard Schlenk techniques or an MBraun glovebox. Dry,
oxygen-free solvents were employed throughout. Anhydrous pen-
tane, toluene, and THF were purchased from Aldrich, sparged
with dinitrogen, and passed through activated alumina under a
positive pressure of nitrogen gas; toluene and hexanes were further
(PiPr3)Ni(η6-C6H6), 2a. 1H NMR (C6H6, 333 K, 300.13
i
3
MHz): δ 1.04 and 1.08 (d, 18H, Pr-CH3, JHH = 6.9 Hz);
i
1.72 (br, 3H, Pr-CH); 5.87 (s, 6H, η6-C6H6)). 31P{1H} NMR
(C6H6, 333 K, 121.5 MHz): δ 59.4 (s). 13C{1H} NMR (C6H6, 333
(47) This compound was prepared analogously to the synthesis of
Cl2Ni(PEt3)2 reported in: Stanger, A.; Vollhardt, K. P. C. Organome-
tallics 1992, 11, 317–320.
(46) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15 (5), 1518.
(48) Krysan, D. J.; Mackenzie, P. B. J. Org. Chem. 1990, 55 (13),
4229.

Article
Organometallics, Vol. 29, No. 22, 2010 6089
K, 75.5 MHz): δ 21.0 (s, iPr-CH3); 24.8 (d, iPr-CH, 1JCP = 18
Hz); 90.4 (s, η6-C6H6).
second-order m, 2F, 3,5-Ar-F). IR: νNiH = 1902.94 cm-1 (br).
Anal. Calcd for C24H44F4NiP2 (MW 529.24): C, 54.47; H, 8.38.
Found: C, 54.45; H, 8.71.
1
(PiPr3)Ni(η6-C6D6), 2a-d6. H NMR (C6D6, 333 K, 300.13
MHz): δ 1.04 and 1.08 (d, 18H, iPr-CH3, 3JHH = 6.9 Hz); 1.72
Reaction of 1 with 1,2,4,5-C6F4HD. Complex 1 (50 mg, 0.09
mmol) and 1,2,4,5-C6F4HD (14 mg, 0.09 mmol) were dissolved
in C6D6 and immediately analyzed by 19F{1H} NMR spectros-
copy. The initial reaction mixture consisted primarily of the
starting materials, but also contained the C-H bond activation
products, 3-d1(NiH) and 3-d1(NiD). Through integration of the
meta-fluorine peaks that are separated by 0.3 ppm, a kinetic
isotope effect (KIE) of 1.3 was obtained for C-H bond activa-
tion. This sample mixture was then heated to 50 °C to demon-
strate the reversibility of the C-H oxidative addition reaction,
achieving a maximum value of 1.7 for the equilibrium isotope
effect (EIE). 31P{1H} NMR (C6D6, 298 K, 121.5 MHz): δ 51.5 (s,
3-d1(NiH)); 51.8 (1:1:1 t, 3-d1(NiD), 2JPD = 10.1 Hz). 19F{1H}
NMR (C6D6, 298 K, 282.4 MHz): δ -112.9 (overlapping
AA0MM0 second-order m, 3-d1(NiH) and 3-d1(NiD), ortho-F);
-143.0 (AA0MM0 second-order m, 3-d1(NiD), meta-F); -143.3
(AA0MM0 second-order m, 3-d1(NiH), meta-F).
i
(br, 3H, Pr-CH). 31P{1H} NMR (C6D6, 333 K, 121.5 MHz):
δ 59.4 (s). 13C{1H} NMR (C6D6, 333 K, 75.5 MHz): δ 21.0
(s, iPr-CH3); 24.8 (d, iPr-CH, 1JCP=18 Hz); 90.4 (1:1:1 t, η6-
C6D6, 1JCD=26 Hz).
(PiPr3)Ni(η6-C7H8), 2b. 1H NMR (C7H8, 333 K, 300.13
i
3
MHz): δ 1.03 and 1.07 (d, 18H, Pr-CH3, JHH = 6.7 Hz);
1.69 (br, 3H, iPr-CH); 2.07 (s, 3H, η6-toluene-CH3); 5.6-5.8
(overlapping m, 5H, η6-toluene-H). 31P{1H} NMR (C7H8, 333
K, 121.5 MHz): δ 60.9 (s). 13C{1H} NMR (C7H8, 333 K, 75.5
MHz): δ 20.8 (s, η6-toluene-CH3); 20.9 (s, iPr-CH3); 22.0 (d,
1
iPr-CH, JCP=19.4 Hz); 89.0, 89.5, and 91.9 (s, η6-toluene-
CH); 101.8 (s, η6-toluene-CCH3).
1
(PiPr3)Ni(η6-C7D8), 2b-d8. H NMR (C7D8, 333 K, 300.13
MHz): δ 1.03 and 1.07 (d, 18H, iPr-CH3, 3JHH = 6.7 Hz); 1.69
(br, 3H, iPr-CH). 31P{1H} NMR (C7D8, 333 K, 121.5 MHz): δ
60.9 (s). 13C{1H} NMR (C7D8, 333 K, 75.5 MHz): δ 20.8 (m, η6-
toluene-CD3); 20.9 (s, iPr-CH3); 22.0 (d, iPr-CH, 1JCP = 19.4
Hz); 89.0, 89.5, and 91.9 (1:1:1 t, η6-toluene-CD, 1JCD = 23.0,
20.1, and 23.0 Hz); 101.8 (s, η6-toluene-CCD3).
Reaction of 3-d1(NiH) and 3-d1(NiD) with 1,2,4,5-C6F4H2. A
mixture of 3-d1(NiH) and 3-d1(NiD) was heated to 50 °C for 1 h
with an excess of nondeuterated 1,2,4,5-tetrafluorobenzene,
which resulted in their conversion to 3 with the liberation of
1,2,4,5-C6F4HD.
1
(PiPr3)Ni(η6-mesitylene), 2c. H NMR (mesitylene, 333 K,
300.13 MHz): δ 1.00 and 1.04 (d, 18H, iPr-CH3, 3JHH=6.6 Hz);
i
Synthesis of (PiPr3)2NiH(2,3,4,6-C6F4H), 4. Complex 1
(500 mg, 0.89 mmol) and 1,2,3,5-tetrafluorobenzene (150 mg,
0.99 mmol) were stirred for 36 h in toluene. The solvent was
removed in vacuo, and the resultant solid extracted with hexa-
methyldisiloxane. The precipitated anthracene was filtered, and the
dark yellow filtrate placed in the freezer. Yellow-colored X-ray
quality crystals of the desired compound precipitated from solution
and were filtered off and dried in vacuo (340 mg, 72% isolated).
Concentration of the mother liquor failed to yield a suitable second
crop. 1H NMR (C6D6, 298 K, 300.13 MHz): δ -16.38 (tddd, 1H,
Ni-H, 2JHP = 68.5 Hz, 4JHF = 8.8 Hz, 4JHF = 8.7 Hz, 5JHF = 3.5
Hz); 1.01 and 1.07 (d, 36H, iPr-CH3, 3JHH = 6.7 Hz); 1.76 (m, 6H,
iPr-CH); 6.51 (m, 1H, 5-Ar-H). 31P{1H} NMR (C6D6, 298 K,
121.5 MHz): δ51.6 (s). 31PNMR(C6D6, 298 K, 121.5 MHz): δ51.6
(br d, 2JPH = 68.5 Hz). 13C{1H} NMR (C6D6, 298 K, 75.5 MHz): δ
19.7 (s, iPr-CH3); 26.0 (AMM0 virtual t, iPr-CH, JCP = 10.3 Hz);
1.66 (br, 3H, Pr-CH), 2.03 (s, 9H, mesitylene-CH3); 5.59
(s, 3H, mesitylene-CH). 31P{1H} NMR (mesitylene, 333 K,
121.5 MHz): δ 61.3 (s). 13C{1H} NMR (mesitylene, 333 K, 75.5
i
MHz): δ 21.1 (s, Pr-CH3); 22.0 (s, mesitylene-CH3); 25.4
i
1
(d, Pr-CH, JCP =17.8 Hz); 95.0 (s, mesitylene-CH); 101.2
(s, mesitylene-CCH3).
Reaction of 1 with 50 equiv of Triisopropylphosphine. Com-
pound 1 (50 mg, 0.09 mmol) and triisopropylphosphine (719 mg,
4.5 mmol, 50 equiv) were dissolved in benzene. The solution was
heated to 333 K in a J. Young tube. The formation of 2a was
partially inhibited (20% compound 1 remained).
Reaction of 1 in Neat Triisopropylphosphine with Benzene.
Compound 1 (50 mg, 0.09 mmol) and benzene (8 mg, 0.09 mmol)
were dissolved in triisopropylphosphine. The solution was
heated to 333 K in a J. Young tube. The formation of 2a was
completely inhibited.
Competition Reaction to Determine Preference for Aromatic in
(PiPr3)Ni(η6-solvent) Complexes. Compound 1 (30 mg, 0.054
mmol) and a mixture of benzene (4.5 mg, 0.054 mmol), toluene
(5.4 mg, 0.054 mmol), and mesitylene (6.5 mg, 0.054 mmol) were
dissolved in 0.75 mL of hexamethyldisiloxane in a J. Young
tube. The reaction mixture was heated to 333 K. Final reaction
composition: 2a, 26%; 2b, 19%; 2c, 55%.
2
2
98.6 (dd, 5-Ar-C, JCF = 40.4 Hz, JCP = 19.0 Hz); 134.0 (tm,
ipso-Ar-C, 2JCF=75.4 Hz); 137.2 (dm, 6-Ar-C, 1JCF=237.9 Hz);
147.8 (dm, 2-Ar-C, 1JCF=237.9 Hz); 153.5 (dd, 4-Ar-C, 1JCF
=
225.3 Hz; 2JCF = 37.2 Hz); 160.4 (ddd, 3-Ar-C, 1JCF=225.3 Hz;
4JCF = 31.0 Hz, 2JCF=10.4 Hz). 19F{1H} NMR (C6D6, 298 K,
282.4 MHz): δ -86.1 (d, 1F, 2-Ar-F, 3JFF=13.7 Hz); -105.8 (d,
1F, 6-Ar-F, 5JFF=34.4 Hz); -144.4 (d, 1F, 4-Ar-F, 3JFF=19.7
Synthesis of (PiPr3)2NiH(2,3,5,6-C6F4H), 3. Complex 1 (500
mg, 0.89 mmol) and 1,2,4,5-tetrafluorobenzene (150 mg, 0.99
mmol) were stirred for 6 h in toluene. The solvent was removed
in vacuo, and the resultant solid extracted with pentane. The
precipitated anthracene was filtered, and the yellow filtrate
placed in the freezer. Yellow-colored X-ray quality crystals of
the desired compound precipitated from solution and were
filtered off and dried in vacuo (312 mg, 66% isolated yield).
Concentration of the mother liquor failed to yield a suitable
5
3
Hz); -170.3 (ddd, 1F, 3-Ar-F, JFF =34.4 Hz, JFF =19.7 Hz,
3JFF = 13.7 Hz). IR: νNiH = 1892.13 cm-1 (br). Anal. Calcd
for C24H44F4NiP2 (MW 529.24): C, 54.47; H, 8.38. Found: C,
53.98; H, 8.76.
Synthesis of (PiPr3)2NiH(C6F5), 5. Compound 1 (500 mg,
0.897 mmol) and excess pentafluorobenzene (200 mg, 1.2 mmol)
were stirred in toluene for 2 h. The solvent was removed in vacuo,
and the resultant oil extracted in pentane. The precipitated
anthracene was filtered, and the dark yellow filtrate placed in
the freezer. A brown-colored viscous oil was confirmed to be
compound 5 by NMR spectroscopy (94% yield by NMR) and
1
second crop. H NMR (C6D6, 298 K, 300.13 MHz): δ -16.25
(ttt, 1H, Ni-H, 2JHP = 68.0 Hz, 4JHF = 8.7 Hz, 5JHF = 4.0 Hz);
1.01 and 1.05 (d, 36H, iPr-CH3, 3JHH = 6.4 Hz); 1.76 (m, 6H,
iPr-CH), 6.65 (tt, 1H, 4-Ar-H, 3JHF = 8.9 Hz, 4JHF = 7.4 Hz).
31P{1H} NMR (C6D6, 298 K, 121.5 MHz): δ 51.5 (s). 31P NMR
1
found to contain <5% C-F activation impurties. H NMR
2
(C6D6, 298 K, 300.13 MHz): δ -16.5 (ttt, 1H, Ni-H, JHP
=
68.0 Hz, 4JHF = 9.9 Hz, 5JHF = 4.5 Hz); 0.96 and 1.01 (d, 36H,
iPr-CH3, 3JHH=7.1 Hz); 1.70 (m, 6H, iPr-CH). 31P{1H} NMR
(C6D6, 298 K, 121.5 MHz): δ 51.2 (s). 31P NMR (C6D6, 298 K,
2
(C6D6, 298 K, 121.5 MHz): δ 51.5 (br d, JPH = 68.0 Hz).
13C{1H} NMR (C6D6, 298 K, 75.5 MHz): δ 19.7 (s, iPr-CH3);
26.0 (AMM0 virtual t, iPr-CH, JCP = 10.8 Hz); 99.7 (t, 4-Ar-C,
121.5 MHz): δ 51.2 (br d, JPH = 68.0 Hz). 13C{1H} NMR
2
1
2JCF = 24.0 Hz); 145.5 (ddm, 3,5-Ar-C, JCF = 249.4 Hz,
i
(C6D6, 298 K, 75.5 MHz): δ 19.7 (s, Pr-CH3); 26.0 (AMM0
2JCF = 26.3 Hz); 146.6 (dtm, 1-Ar-C, 2JCF = 134.5 Hz, 3JCF
=
i
virtual t, Pr-CH, JCP = 11.8 Hz); 100.3 (tm, ipso-Ar-C,
13.4 Hz); 148.2 (ddm, 2,6-Ar-C, 1JCF = 214.3 Hz, 2JCF = 26.8
Hz). 19F{1H} NMR (C6D6, 298 K, 282.4 MHz): δ -112.9
(AA0MM0 second-order m, 2F, 2,6-Ar-F); -143.0 (AA0MM0
2JCF = 22.9 Hz); 136.3 (ddm, 2,6-Ar-C, JCF = 230.8 Hz,
1
2JCF = 14.7 Hz); 136.3 (dddd, 3,5-Ar-C, JCF = 226.31
1
2
2
Hz, JCF = 29.5 Hz, JCF = 9.8 Hz); 147.0 (ddm, 4-Ar-C,

6090 Organometallics, Vol. 29, No. 22, 2010
Hatnean et al.
1JCF = 218.4 Hz, 2JCF = 29.5 Hz). 19F{1H} NMR (C6D6, 298
K, 282.4 MHz): δ -110.7 (AA0MM0N second-order m, 2F, 2,6-
Ar-F); -163.2 (tt, 1F, 4-Ar-F, 3JFF=19.6 Hz, 4JFF = 2.5 Hz);
-164.6 (AA0MM0N second-order m, 2F, 3,5-Ar-F).
0.82, 0.83, 0.85, 0.89, and 0.93 (overlapping d, allyliccyclooctene-
3
i
CH2, JHH = 7.5 Hz); 1.28 and 1.39 (m, 18H, Pr-CH3); 1.83
(overlapped m, 3H, allylic cyclooctene-CH2 and iPr-CH); 3.66
(overlapped m, allylic-CH); 3.85 (overlapped quartet of doub-
lets, allylic-CH, 3JHH = 9.0 Hz, 3JHP = 4.0 Hz); 4.71 and 4.85
(apparent t, allylic-CH, 3JHF = 10.7 Hz, 3JHF =8.4Hz); 5.38 (br
qt); 6.74 (tm). 31P{1H} NMR (C6D6, 298 K, 121.5 MHz): δ 44.2
and 46.5 (m). 19F{1H} NMR (C6D6, 298 K, 282.4 MHz): δ-113.4
(ddd, 2-Ar-F, 5JFF = 36.0 Hz, 3JFF = 15.7 Hz); -113.8 (ddd,
2-Ar-F, 5JFF = 36.0 Hz, 3JFF = 15.7 Hz, 4JFP = 3.8Hz); -144.1
Reaction of 1, C6F5H, and 50 equiv of Triisopropylphosphine. A
toluene solution of 1 (20 mg, 0.036 mmol), C6F5H (6 mg, 0.036
mmol), and triisopropylphosphine (287 mg, 1.79 mmol) was
monitored by 31P{1H} and 19F{1H} NMR spectroscopy. The
rate of formation of 5 was unchanged compared to the analo-
gous reaction in the absence of added triisopropylphosphine.
Synthesis of (η3-C8H13)Ni(PiPr3)(2,3,5,6-C6F4H), 6. A mix-
ture of Ni(COD)2 (18.3 mg, 0.07 mmol), triisopropylphosphine
(21.4 mg, 0.14 mmol, 2 equiv), and 1,2,4,5-C6F4H2 (10 mg, 0.07
mmol) was dissolved in toluene and reacted overnight. The
crude mixture was placed in the freezer, whereupon yellow-
3
3
(dd, 5-Ar-F, JFF = 20.0 Hz, JFF = 15.7 Hz); -144.3 (dd,
5-Ar-F, 3JFF = 20.0 Hz, 3JFF = 16.0 Hz); -161.2 (ddd, 3-Ar-F,
3JFF = 20.0 Hz, 3JFF = 15.0 Hz, 4JFF = 2.0 Hz); -161.4 (ddd,
3-Ar-F, 3JFF = 20.0 Hz, 3JFF = 15.0 Hz, 4JFF = 2.0Hz); -167.0
(ddd, 4-Ar-F, 3JFF = 20.0 Hz, 3JFF = 20.0 Hz, 4JFF = 2.0 Hz);
1
-167.2 (ddd, 4-Ar-F, 3JFF = 20.0 Hz, 3JFF = 20.0 Hz, 4JFF
2.0 Hz).
=
colored X-ray quality crystals precipitated from solution. H
NMR (C6D6, 298 K, 300.13 MHz): δ 0.85, 0.9, 0.92, and 0.97 (d,
3
Synthesis of the 3-Hexyne Adduct (PiPr3)2Ni(η2-EtCtCEt),
9. Compound 1 (250 mg, 0.449 mmol) and 3-hexyne (37 mg,
0.449 mmol) were stirred in 5 mL of pentane for 30 min. The
precipitated anthracene was filtered, and the resultant solution
placed in the freezer. Orange-colored X-ray quality crystals
precipitated from the solution and were filtered and dried in
allylic cyclooctene-CH2, JHH = 6.0 Hz); 1.02 and 1.07 (d,
i
3
36H, Pr-CH3, JHH = 7.1 Hz); 1.15-1.4 (m, allylic cy-
i
clooctene-CH2); 1.69 (m, 6H, Pr-CH); 3.78 (overlapped m,
allylic-CH); 4.02 (qdd, allylic-CH, 3JHH = 9.0 Hz, 3JHP = 4.0
Hz, 3JHF = 1.3 Hz); 4.85 (apparent t, allylic-CH, 3JHH = 8.5
Hz); 6.54 (overlapped tt, 1H, 4-Ar-H, 3JHF = 8.9 Hz, 4JHF
=
7.4 Hz). 31P{1H} NMR (C6D6, 298 K, 121.5 MHz): δ 46.9 (s).
13C{1H} NMR (C6D6, 298 K, 75.5 MHz): δ 19.2 and 19.8 (s,
iPr-CH3); 23.2 (s), 27.6 (br), 28.4 (s), 30.4 (br), and 31.6 (s)
1
vacuo (200 mg, 96.7% yield). H NMR (C6D6, 298 K, 300.13
MHz): δ 1.22 and 1.26 (d, 36H, iPr-CH3, 3JHH = 7.3 Hz); 1.42
3
i
(t, 6H, hexyne-CH3, JHH = 7.3 Hz); 2.07 (m, 6H, Pr-CH);
i
1
3
4
(allylic cyclooctene-CH2) 26.0 (d, Pr-CH, JCP = 18.5 Hz);
68.9 (br), 75.9 (d, 2JCP = 20.6 Hz), and 108.3 (br) (allylic-CH);
100.2 (tm, 4-Ar-C, 2JCF = 23.8 Hz); 140.1 (m, 1-Ar-C); 145.1
2.88 (qd, 4H, hexyne-CH2, JHH = 7.3 Hz, JHP = 2.5 Hz).
31P{1H} NMR (C6D6, 298 K, 121.5 MHz): δ 54.8 (s). 13C{1H}
NMR (C6D6, 298 K, 75.5 MHz): δ 16.2 (s, hexyne-CH3); 20.4
1
2
i
3
(s, Pr-CH3); 23.1 (AMM0 virtual t, hexyne-CH, JCP = 7.0
(ddm, 2,6-Ar-C, JCF = 228.7 Hz, JCF = 25.4 Hz); 148.1
(ddm, 3,5-Ar-C, 1JCF = 224.5 Hz, 2JCF = 25.4 Hz). 19F{1H}
NMR (C6D6, 298 K, 282.4 MHz): δ -114.7 (ddd, Ar-F,
i
Hz); 26.6 (AMM0 virtual t, Pr-CH, JCP = 7.5 Hz); 81.1 (br,
hexyne-C). Anal. Calcd for C24H52NiP2 (MW 461.31): C,
62.49; H, 11.36. Found: C, 62.31; H, 11.59.
3
4
5JFF = 33.8 Hz, JFF = 16.5 Hz, JFF = 3.5 Hz); -115.2
(ddt, Ar-F, 5JFF = 33.8 Hz, 3JFF = 16.5 Hz, 4JFF = 3.5 Hz);
Alternate Synthesis of 9. Ni(COD)2 (200 mg, 0.727 mmol)
and 3-hexyne (60 mg, 0.727 mmol) were stirred in 5 mL of
pentane for 30 min. The orange-colored solution was placed
in the freezer. Orange-colored crystals precipitated from
the solution and were filtered and dried in vacuo (319 mg,
95.2% yield).
5
3
-142.9 (dd, Ar-F, JFF = 29.0 Hz, JFF = 16.7 Hz); -143.0
(dd, Ar-F, 5JFF = 29.0 Hz, 3JFF = 16.7 Hz). Anal. Calcd for
C23H35F4NiP (MW 477.18): C, 57.89; H, 7.39. Found: C, 58.34;
H, 7.47.
Synthesis of (η3-C8H13)Ni(PiPr3)(2,3,4,6-C6F4H), 7. A mix-
ture of Ni(COD)2 (300 mg, 1.09 mmol), triisopropylphosphine
(349.6 mg, 2.18 mmol, 2 equiv), and 1,2,3,5-C6F4H2 (163.7 mg, 1.09
mmol) was dissolved in 10 mL of toluene and stirred overnight. The
crude reaction mixture was analyzed by NMR spectroscopy and
contains two diastereomers, 7a and 7b, which could not be sepa-
rated in addition to C-F activation impurities (<5%). 1H NMR
(C6D6, 298 K, 300.13 MHz): δ 0.87, 0.91, 0.93, and 0.98 (over-
Reaction of 3 with 3-Hexyne. Compound 3 (25 mg, 0.05 mmol)
and 3-hexyne (4 mg, 0.05 mmol) were dissolved in C6D6, and the
orange-colored solution was immediately analyzed by NMR
spectroscopy. The crude NMR spectra revealed the major
product to be compound 9 (>95%) with trace impurities
attributed to a mixture of compound 3 and the alkyne insertion
product, (PiPr3)2Ni(CEtdCHEt)(2,3,5,6-C6F4H) (10).
Characterization of (PiPr3)2Ni(CEtdCHEt)(2,3,5,6-C6F4H),
10. 1H NMR (C6D6, 298 K, 300.13 MHz): δ 0.87 and 1.39 (t, 6H,
Et-CH3, 3JHH = 7.8 Hz); 2.15 (dq, 2H, Et-CH2, 3JHH = 7.8 Hz,
3JHH = 7.3 Hz); 2.45 (m, 2H, Et-CH2, 3JHH = 7.8 Hz); 5.61 (br,
3
lapping d, allylic cyclooctene-CH2, JHH =7.2 Hz); 1.05 (br m,
18H, iPr-CH3, 3JHH=7.1 Hz); 1.15-1.4 (m, allylic cyclooctene-
i
CH2); 1.75 (overlapped m, 3H, Pr-CH); 3.75 (overlapped m,
allylic-CH); 4.05 (overlapped pentet of doublets, allylic-CH,
3JHH=9.0 Hz, 3JHP = 3.6 Hz); 4.86 (overlapped dd, allylic-CH,
3JHF = 10.7 Hz, 3JHF = 8.4 Hz); 6.47 and 6.53 (overlapped ddddd,
3
4
H, CH); 6.30 (tt, 1H, 4-Ar-H, JHF = 9.2, JHF = 6.2 Hz).
31P{1H} NMR (C6D6, 298 K, 121.5 MHz): δ 39.4 (s). 19F{1H}
NMR (C6D6, 298 K, 282.4 MHz): δ -110.3 (ddd, 1F, 2-Ar-F,
3JFF = 36.3 Hz, 5JFF = 16.9 Hz, 4JFF = 4.9 Hz); -114.7 (ddd,
1F, 6-Ar-F, 3JFF = 34.7 Hz, 5JFF = 17.2 Hz, 4JFF = 4.9 Hz);
5-Ar-H, 5JHF=19.4 Hz, 3JHF = 10.3 Hz, 3JHF=10.3 Hz, 4JHF
=
4.8 Hz, 5JHP=2.4 Hz). 31P{1H} NMR (C6D6, 298 K, 121.5 MHz): δ
45.3 and 45.6 (m). 19F{1H} NMR (C6D6, 298 K, 282.4 MHz): δ
-88.2 (dd, 6-Ar-F, 4JFF=13 Hz, 4JFF=3.2 Hz); -88.6 (dt, 6-Ar-
F, 4JFF=13 Hz, 4JFF=4.0 Hz); -107.3 (dt, 2-Ar-F, 5JFF=33.0 Hz,
4JFF=3.0 Hz); -108.1 (dm, 2-Ar-F, 5JFF=33.0 Hz, 4JFF=3.0 Hz);
-143.8 (dt, 4-Ar-F, 3JFF=16.0 Hz, 4JFF=2.0 Hz); -143.9 (dt,
3
5
-142.1 (dd, 1F, 3-Ar-F, JFF = 34.0 Hz, JFF = 16.7 Hz),
-142.5 (dd, 1F, 3-Ar-F, 3JFF = 36.3 Hz, 5JFF = 16.9 Hz).
Synthesis of (E)-1,2,4,5-Tetrafluoro-3-(hex-3-en-3-yl)benzene,
11. A solution of 1,2,4,5-C6F4H2 (55 mg, 0.36 mmol) and
3-hexyne (30 mg, 0.36 mmol) was added to a mixture of Ni-
(COD)2 (10 mg, 0.036 mmol) and triisopropylphosphine (11.6
mg, 0.73 mmol, 2 equiv) in C6D6. The reaction mixture was
heated to 50 °C for 24 h. The products were determined by NMR
spectroscopic analysis to be a mixture of compound 11 (3%
yield by NMR) and the doubly activated product 1,2,4,5-tetra-
fluoro-3,6-di((E-hexen-3-yl)benzene (12) (95% yield by NMR
spectroscopy). 1H NMR (C6D6, 298 K, 300.13 MHz): δ 0.79 and
0.85 (t, 6H, Et-CH3, 3JHH = 7.8 Hz); 1.81 (dq, 2H, Et-CH2,
3
4
4-Ar-F, JFF =16.0 Hz, JFF =2.0 Hz); -169.8 (ddd, 3-Ar-F,
3
3
5JFF = 20.0 Hz, JFF =12.9 Hz, JFF = 12.9 Hz); -169.9 (ddd,
3-Ar-F, 5JFF=20.0 Hz, 3JFF = 12.9 Hz, 3JFF=12.9 Hz).
Synthesis of (η3-C8H13)Ni(PiPr3)(2,3,4,5-C6F4H), 8. A mix-
ture of Ni(COD)2 (500 mg, 1.82 mmol), triisopropylphosphine
(582.6 mg, 3.64 mmol, 2 equiv), and 1,2,3,4-C6F4H2 (272.8 mg,
1.82 mmol) was dissolved in 10 mL of toluene and stirred for
48 h. The crude reaction mixture was analyzed by NMR
spectroscopy and contains two diastereomers, 8a and 8b, which
could not be separated in addition to C-F activation impurities
3JHH = 7.8 Hz, 3JHH = 7.3 Hz); 2.08 (q, 2H, Et-CH2, 3JHH
7.8 Hz); 5.30 (t, H, CH, 3JHH = 7.3 Hz); 6.51 (tt, 1H, 4-Ar-H,
=
1
(<5%). H NMR (C6D6, 298 K, 300.13 MHz): δ 0.79, 0.80,

Article
Organometallics, Vol. 29, No. 22, 2010 6091
4
3
4
3JHF = 9.2, JHF = 6.2 Hz). 19F{1H} NMR (C6D6, 298 K,
282.4 MHz): δ -140.5 (AA0MM0 second-order m, 2F, 2,6-
Ar-F); -143.4 (AA0MM0 second-order m, 2F, 3,5-Ar-F).
1,2,4,5-Tetrafluoro-3,6-di((E-hexen-3-yl)benzene, 12. 1H NMR
(C6D6, 298 K, 300.13 MHz): δ 0.85 and 1.10 (t, 6H, Et-CH3,
2.92 (qd, 4H, hexyne-CH2, JHH = 7.3 Hz, JHP = 2.5 Hz).
31P{1H} NMR (C6D6, 298 K, 121.5 MHz): δ 26.8 (s).
Reaction of 16 with 1,2,4,5-C6F4H2. 1,2,4,5-Tetrafluoroben-
zene was added to a solution of 16 (10 mol %) in C6D6. The
orange-colored solution was heated for 3 days at 80 °C and then
analyzed by NMR spectroscopy. The crude NMR spectra
revealed a mixture of compound 16, compound 11 (40% yield
by NMR), and compound 12 (5% yield by NMR). The only
other significant impurity was attributed to the alkyne insertion
product before reductive elimination, 17.
Characterization of (PEt3)2Ni(CEtdCHEt)(2,3,5,6-C6F4H),
17. 31P{1H} NMR (C6D6, 298 K, 121.5 MHz): δ 13.3 (s). 19F{1H}
NMR (C6D6, 298 K, 282.4 MHz): δ -113.4 (ddd, 1F, 2-Ar-F,
3JFF = 36.7 Hz, 5JFF = 17.3 Hz, 4JFF = 4.3 Hz); -117.4 (ddd, 1F,
6-Ar-F, 3JFF = 36 Hz, 5JFF = 17.3 Hz, 4JFF = 4.3 Hz); -142.0
(dd, 1F, 3-Ar-F, 3JFF =35.0Hz, 5JFF = 17.2 Hz), -142.3 (dd, 1F,
3-Ar-F, 3JFF = 36.0 Hz, 5JFF = 17.2 Hz).
3JHH = 7.8 Hz); 1.91 (dq, 2H, Et-CH2, 3JHH = 7.8 Hz, 3JHH
=
7.3 Hz); 2.32 (q, 2H, Et-CH2, 3JHH = 7.8 Hz); 5.41 (t, H, CH,
3JHH = 7.3 Hz). 19F{1H} NMR (C6D6, 298 K, 282.4 MHz): δ
-143.5 (s, 4F, 2,3,5,6-Ar-F).
Synthesis of (E)-1,2,3,4,5-Pentafluoro-6-(hex-3-en-3-yl)benzene,
13. A C6D6 solution of compound 1 (25 mg, 0.045 mmol),
C6F5H (76 mg, 0.45 mmol), and 3-hexyne (37 mg, 0.45 mmol)
was immediately analyzed by NMR spectroscopy to be a mixture 9
and the 3-hexyne insertion product 14. The mixture was heated to
50 °C for 3 days, yielding the monoinsertion product 13 (97% yield
by NMR). 1H NMR (C6D6, 298 K, 300.13 MHz): δ 0.84 and 0.93
(t, 6H, Et-CH3, 3JHH = 7.1 Hz); 1.91 (dq, 2H, Et-CH2, 3JHH
=
7.7 Hz, 3JHH = 7.4 Hz); 2.13 (q, 2H, Et-CH2, 3JHH = 7.4 Hz); 5.25
(t, H, CH, 3JHH = 7.7 Hz). 19F{1H} NMR (C6D6, 298 K, 282.4
MHz): δ -142.7 (AA0MM0X second-order m, 2F, 2,6-Ar-F);
X-ray Crystallography. The X-ray structures were obtained
at low temperatures, with the crystals covered in Paratone
and placed rapidly into the cold N2 stream of the Kryo-Flex
low-temperature device. The data were collected using the
SMART49 software on a Bruker APEX CCD diffractometer
using a graphite monochromator with Mo KR radiation (λ =
3
-157.5 (t, 2F, 4-Ar-F, JFF = 21.0 Hz,); -163.1 (AA0MM0X
second-order m, 2F, 3,5-Ar-F).
Characterization of (PiPr3)2Ni(CEtdCHEt)(C6F5), 14. 1H
NMR (C6D6, 298 K, 300.13 MHz): δ0.75 and 1.41 (t, 6H, Et-CH3,
˚
0.71073 A). A hemisphere of data was collected using a counting
3JHH = 7.4 Hz); 2.27 (dq, 2H, Et-CH2, 3JHH = 7.7 Hz, 3JHH
=
time of 10-30 s per frame. Details of crystal data, data collec-
tion, and structure refinement are listed in Table 1. Data
reductions were performed using the SAINT50 software, and
the data were corrected for absorption using SADABS.51 The
structures were solved by direct methods using SIR9752 and
refined by full-matrix least-squares on F2 with anisotropic
displacement parameters for the non-H atoms using SHELX-
9753 and the WinGX54 software package, and thermal ellipsoid
plots were produced using ORTEP32.55
7.4 Hz); 2.49 (m, 2H, Et-CH2, 3JHH = 7.4 Hz); 5.25 (t, H, CH,
3JHH = 7.7 Hz). 31P{1H} NMR (C6D6, 298 K, 121.5 MHz): δ 38.3
(s). 19F{1H} NMR (C6D6, 298 K, 282.4 MHz): δ-107.9 (dddd, 1F,
2-Ar-F, 3JFF = 38.6 Hz, 5JFF = 12.0 Hz, 4JFF = 8.6 Hz, 4JFF
=
3.0 Hz); -112.5 (dddd, 1F, 6-Ar-F, 3JFF = 36.7 Hz, 5JFF = 12.0
4
4
Hz, JFF = 8.6 Hz, JFF = 3.0 Hz); -162.2 (tm, 1F, 4-Ar-F,
3JFF = 20.0 Hz), -163.4 (dddd, 1F, 3-Ar-F, JFF = 37.5 Hz,
3
5JFF = 20.7 Hz, 4JFF = 12.2 Hz, 4JFF = 4.8 Hz); -164.0 (dddd,
1F, 5-Ar-F, 3JFF = 37.5 Hz, 5JFF = 20.7 Hz, JFF = 12.2 Hz,
4
4JFF = 4.8 Hz).
Acknowledgment is made to the Natural Sciences and
Engineering Research Council (NSERC) of Canada for a
discovery grant for S.A.J. and a postgraduate scholarship
for J.A.H., and to the donors of the American Chemical
Society Petroleum Research Fund for partial support of
this research.
Synthesis of (E)-1,2,3,4-Tetrafluoro-5-(hex-3-en-3-yl)benzene,
15. A solution of 1,2,3,4-C6F4H2 (55 mg, 0.36 mmol) and
3-hexyne (30 mg, 0.36 mmol) was added to a mixture of Ni(COD)2
(10 mg, 0.036 mmol) and triisopropylphosphine (11.6 mg, 0.73
mmol, 2 equiv) in C6D6. The reaction mixture was heated to 50 °C
1
for 48 h (99% yield by NMR). H NMR (C6D6, 298 K, 300.13
MHz): δ 0.74 and 0.86 (t, 6H, Et-CH3, 3JHH = 7.7 Hz); 1.92 (dq,
3
3
Supporting Information Available: Full details of crystal-
lographic information in CIF format for compounds 1, 3, 4, 6,
and 9 in addition to select experimental NMR spectra. This
material is available free of charge via the Internet at http://
pubs.acs.org.
2H, Et-CH2, JHH = 7.7 Hz, JHH = 7.0 Hz); 2.17 (q, 2H,
Et-CH2, 3JHH = 7.7 Hz); 5.23 (t, H, CH, 3JHH = 7.0 Hz); 6.37
(dddd, 1H, 6-Ar-H, 3JHF = 13.6, 5JHF = 8.6 Hz, 4JHF = 2.6 Hz,
4JHF = 2.6 Hz). 19F{1H} NMR (C6D6, 298 K, 282.4 MHz): δ
-141.1 (ddd, 1F, 2-Ar-F, 3JFF = 21.3 Hz, 5JFF = 12.5 Hz, 4JFF
=
1.9 Hz); -142.4 (ddd, 1F, 5-Ar-F, 3JFF = 21.0 Hz, 5JFF = 12.3
Hz, 4JFF = 2.4 Hz); -156.7 (ddd, 1F, 3-Ar-F, 3JFF = 21.3 Hz,
=
(49) SMART, Molecular Analysis Research Tool; Bruker AXS Inc.:
Madison, WI,: 2001.
(50) SAINTPlus, Data Reduction and Correction Program; Bruker
AXS Inc.: Madison, WI, 2001.
(51) SADABS, An Empirical Absorption Correction Program; Bruker
AXS Inc.: Madison, WI, 2001.
(52) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.;
Spagna, R. J. Appl. Crystallogr. 1999, 32, 115.
(53) Sheldrick, G. M. SHELXL-97; Universitat Gottingen: Gottingen,
1997.
(54) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32 (4), 837.
(55) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30 (5, Pt. 1), 565.
3JFF = 19.7 Hz, 4JFF = 1.9 Hz); -159.2 (ddd, 1F, 4-Ar-F, 3JFF
21.3 Hz, 3JFF = 19.7 Hz, 4JFF = 1.9 Hz).
Synthesis of the 3-Hexyne Adduct (PEt3)2Ni(η2-EtCtCEt),
16. The anthracene adduct (PEt3)2Ni(η2-C14H10) (28.6 mg,
0.061 mmol) and 3-hexyne (5 mg, 0.061 mmol) were dissolved
in pentane, whereupon the solution turned orange. The precipitated
anthracene was filtered, and the resultant solution was used in
1
subsequent reactions (quantitative by NMR). H NMR (C6D6,
298 K, 300.13 MHz): δ0.99 (t, 18H, Et-CH3, 3JHH = 7.2 Hz); 1.44
(q, 12H, Et-CH2, 3JHH = 7.2 Hz); 1.47 (m, 6H, hexyne-CH3);