Synthesis, solution dynamics, and x-ray crystal structure of bis(2,4,6-tris(trifluoromethyl)-phenyl)(1,2-dimethoxyethane)nickel

Article abstract of DOI:10.1021/om0100784

Reaction of dichloro(1,2-dimethoxyethane)nickel with 2 equiv of (tris(2,4,6-trifluoromethyl)-phenyl)lithium, generated in situ, produced bis(2,4,6-tris(trifluoromethyl)phenyl)(1,2-dimethoxyethane)nickel. Significant nickel-fluorine interactions are reveal

Full text of DOI:10.1021/om0100784

Organometallics 2001, 20, 2565-2569
2565
Syn th esis, Solu tion Dyn a m ics, a n d X-r a y Cr ysta l
Str u ctu r e of Bis(2,4,6-tr is(tr iflu or om eth yl)-
p h en yl)(1,2-d im eth oxyeth a n e)n ick el
George M. Benedikt, Brian L. Goodall,*,1 Suri Iyer,2 Lester H. McIntosh III,3
Richard Mimna, and Larry F. Rhodes*
The BFGoodrich Company, 9921 Brecksville Road, Brecksville, Ohio 44141
Cynthia S. Day and Victor W. Day
Crystalytics Company, P.O. Box 82286, Lincoln, Nebraska 68501
Received J anuary 31, 2001
Reaction of dichloro(1,2-dimethoxyethane)nickel with 2 equiv of (tris(2,4,6-trifluoromethyl)-
phenyl)lithium, generated in situ, produced bis(2,4,6-tris(trifluoromethyl)phenyl)(1,2-
dimethoxyethane)nickel. Significant nickel-fluorine interactions are revealed both in the
solid state (X-ray crystal structure data) and in solution (variable-temperature 19F NMR
spectral data).
In tr od u ction
only in the presence of donor ligands. Given the appar-
ent coordinative unsaturation of this complex (a formal
12-electron complex), one might expect electron donation
from the fluorines of the o-trifluoromethyl substituents
on the aryl ring. We report herein the synthesis, solution
dynamics, and X-ray crystal structure of the bis(2,4,6-
tris(trifluoromethyl)phenyl)nickel fragment containing
the donor ligand 1,2-dimethoxyethane. This compound
does exhibit significant interactions between the fluo-
rines of the o-trifluoromethyl substituents and the
nickel center despite being formally a 16-electron com-
plex.
The activation of halocarbons, in particular fluoro-
carbons, by metals has become increasingly of interest
over the past decade.4 A prelude to activation is thought
to be, in many cases, coordination of the halocarbon to
the metal center. A review of the coordination chemistry
of fluorocarbons has been published recently.5
Complexes containing electron-withdrawing aryl
ligands (i.e., those that are highly substituted with
halogens) are known for many of the late transition
metals, especially group 10. One subset of these types
of ligands, 2,4,6-tris(trifluoromethyl)phenyl, is thought
to exhibit an ideal combination of electronic and steric
characteristics, since it can withdraw electrons from the
metal inductively but can donate electron density to the
metal from the fluorine atoms of the o-CF3 substituents
on the aryl ligand.6
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were carried
out under an atmosphere of prepurified nitrogen using stan-
dard Schlenk or drybox techniques. Solvents were dried and
degassed with prepurified nitrogen. The 1H and 19F NMR
spectra were recorded on a Bruker AMX-500 NMR spectrom-
eter operating at 500.14 and 470.53 MHz, respectively. Chemi-
cal shifts for 1H NMR spectra were referenced using internal
solvent resonances and are reported relative to tetramethyl-
silane. The 19F NMR spectra were referenced to external
CFCl3. The mass spectra were recorded on a Finnigan MAT
95Q mass spectrometer. Elemental analysis was carried out
by Robertson Microlit Laboratories, Madison, NJ .
A nickel complex has been synthesized and character-
ized as the homoleptic bis(2,4,6-tris(trifluoromethyl)-
phenyl)nickel.7 This complex is noteworthy, since ho-
moleptic diaryl derivatives of nickel are normally stable
Tris(trifluoromethyl)benzene was purchased from Aldrich
and used as received. Dichloro(1,2-dimethoxyethane)nickel was
obtained from Strem Chemicals and used without further
purification.
Syn th esis of Bis(2,4,6-tr is(tr iflu or om eth yl)p h en yl)(1,2-
d im eth oxyeth a n e)n ick el (1). 1,3,5-Tris(trifluoromethyl)-
benzene (1.65 mL, 8.86 mmol) was dissolved in 20 mL of
hexane and 20 mL of ether. The solution was cooled to -78
°C, and n-BuLi (5.80 mL of a 1.60 M solution in hexane, 9.28
mmol) was added. A yellow color developed. The solution was
removed from the cooling bath and warmed to room temper-
ature over 1 h. This solution was then transferred by cannula
* To whom correspondence should be addressed. B.L.G.: e-mail,
brian_goodall@albemarle.com; fax, 225-768-5689. L.F.R.: e-mail,
rhodes@brk.bfg.com; fax, 216-447-5464.
(1) Present address: Albemarle Corporation, P.O. Box 14799, Baton
Rouge, LA 70898.
(2) Present address: Emory University, 5329 WMRB, Dept. of
Surgery Research Labs, 1639 Pierce Dr., Atlanta, GA 30322.
(3) Present address: 3M Company, 3M Center, Bldg. 201-2N-20,
St. Paul, MN 55144.
(4) Kiplinger, J . L.; Richmond, T. G.; Osterberg, C. E. Chem. Rev.
1994, 94, 373.
(5) Plenio, H. Chem. Rev. 1997, 97, 3363.
(6) Edelman, F. T. Comments Inorg. Chem. 1992, 12(5), 259.
(7) Belay, M.; Edelmann, F. T. J . Organomet. Chem. 1994, 479(1-
2), C21.
10.1021/om0100784 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 05/09/2001

2566 Organometallics, Vol. 20, No. 12, 2001
Benedikt et al.
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta for 1
to a suspension of dichloro(1,2-dimethoxyethane)nickel (0.973
g, 4.43 mmol) in 20 mL of hexane and 20 mL of ether which
had been cooled to -78 °C. No immediate change was noted.
The mixture was warmed to room temperature. A brown color
developed over time. Volatiles were removed under vacuum
after 3 h. The resulting solid was extracted with 40 mL of
toluene. The extract was filtered through Celite filtering aid
to give a red solution. Hexane was added to the solution,
resulting in the precipitation of purple microcrystals. The
crystals were filtered and washed with hexane three times:
yield 0.26 g (8%); mp 180-185 °C dec. Attempts to improve
the yield by carrying out the reaction in the presence of 1,2-
chem formula
fw
NiC22H14F18O2
711.04
temp
293(2) K
wavelength
1.541 84 Å
crystal syst
monoclinic
space group
P21/n
a
12.167(3) Å
b
16.373(4) Å
c
12.991(3) Å
R
90.00°
91.18(2)°
â
γ
90.00°
1
V, Å3
2587.4(11) Å3
4
dimethoxyethane or THF were unsuccessful. H NMR (C6D6):
δ 7.75 (s, 2H), 2.17 (br s, 4H), 2.07 (s, 6H). 19F NMR (C6D6):
δ -58.2 (v br s, 6F), -63.2 (s, 3F). IR (Nujol): 1618 m, 1567
m, 1277 s, 1188 s, 1124 s, 1048 m, 1017 m, 912 s, 870 s, 831
s cm-1. FI-MS: m/z 710 [M+]. Anal. Found for C22H14F18O2Ni:
C, 37.10; H, 1.90. Calcd: C, 37.16; H, 1.97.
Z
Dcalcd
abs coeff
F(000)
1.825 g cm-3
2.523 mm-1
1408
cryst size
θ range for collection
limiting indices
0.40 × 0.25 × 0.20 mm
4.35-60.14°
-13 e h e 13, 0 e k e 18,
0 e l e 14
X-r a y Cr ysta llogr a p h ic stu d y of 1. Crystal data for single
crystals of bis(2,4,6-(tris(trifluoromethyl)phenyl)(1,2-dimeth-
oxyethane)nickel (1), at 20.1 °C: monoclinic, space group P21/n
(an alternate setting of P21/c-C2h5 (No. 14)) with a ) 12.167(3)
Å, b ) 16.373(4) Å, c ) 12.991(3) Å, â ) 91.18(2)°, V )
2587.4(11) Å3, and Z ) 4 (dcalcd ) 1.825 g cm-3; µa(Cu KR) )
2.523 mm-1). A total of 4035 reflections having 2θ(Cu KR) <
120.3° (the equivalent of a 0.65 limiting Cu KR sphere) were
collected on a computer-controlled Nicolet autodiffractometer
using 2.00° wide θ-2θ scans and Ni-filtered Cu KR radiation;
3849 of these reflections were unique. The Bruker SHELXTL-
PC (version 5.0) software package was used to solve and refine
the structure. “Direct methods” techniques were used to solve
the structure, and the resulting structural parameters have
been refined with F2 data to convergence using counter-
weighted full-matrix least-squares techniques and a structural
model which incorporated anisotropic thermal parameters for
all non-hydrogen atoms and isotropic thermal parameters for
all hydrogen atoms. Final agreement factors are as follows:
R1(unweighted, based on F) ) 0.078 for 2032 independent
absorption-corrected reflections having 2θ (Cu KR) < 120.3°
and I > 2σ(I); R1(unweighted, based on F) ) 0.131 and wR2-
(weighted, based on F2) ) 0.215 for all 3849 independent
absorption-corrected reflections having 2θ(Cu KR) < 120.3°.
A summary of crystallographic data can be found in Table 1.
no. of rflns collected
no. of indep rflns
abs cor
refinement method
max and min transmissn
no. of data/restraints/params
goodness of fit on F2
final R indices (I > 2σ(I))
R indices (all data)
extinction coeff
4035
3849 (Rint ) 0.0569)
integration
full-matrix least squares on F2
0.6641 and 0.4254
3849/0/453
0.957
R1 ) 0.0778, wR2 ) 0.1870
R1 ) 0.1307, wR2 ) 0.2153
0.0017(3)
largest diff peak and hole
0.518 and -0.693 e Å-3
Ta ble 2. Selected Bon d Dista n ces a n d An gles in 1
distance (Å) or
angle (deg)
distance (Å) or
angle (deg)
type
type
Ni-O1
2.013(6)
2.017(6)
1.873(8)
1.886(6)
2.592(5)
2.595(5)
80.7(3)
O1-Ni-C11
C11-Ni-C21
O2-Ni-C21
O2-Ni-C11
O1-Ni-C21
F191‚‚‚Ni‚‚‚F291
92.8(3)
97.2(3)
92.8(3)
163.0(3)
163.7(3)
152.3(2)
Ni-O2
Ni-C11
Ni-C21
Ni‚‚‚F191
Ni‚‚‚F291
O1-Ni-O2
Resu lts a n d Discu ssion
Syn th esis an d Ch ar acter ization . We chose dichloro-
(1,2-dimethoxyethane)nickel as the starting material
(Edelmann used NiCl2) for the reaction with (tris(2,4,6-
trifluoromethyl)phenyl)lithium generated in situ (see eq
1). After appropriate workup, a low yield of a purple,
Non-methyl hydrogen atoms were included in the structure
factor calculations as idealized atoms (assuming sp2 or sp3
hybridization of the carbon atoms and C-H bond lengths of
0.93-0.97 Å) “riding” on their respective carbon atoms. The
two methyl groups (C1, C4, and their hydrogens) were refined
as rigid rotors (using idealized sp3-hybridized geometry and a
C-H bond length of 0.96 Å) which were allowed to rotate about
their C-C bonds in least-squares cycles. The isotropic thermal
parameters of all hydrogen atoms were fixed at values 1.2
(non-methyl) or 1.5 times (methyl) the equivalent isotropic
thermal parameters of the carbon atoms to which they are
covalently bonded.
Two of the CF3 groups (C18 and C28) are disordered, with
two alternate orientations about the C-C bond. Both have
major orientations which are occupied 53% and 77% of the
time, respectively, and minor orientations which are occupied
47% and 23% of the time, respectively. The major (53%)
orientation for C18 is specified by fluorine atoms F181, F182, and
F
183, and the major (77%) orientation for C28 is specified by
fluorine atoms F281, F282, and F283. The minor (47%) orientation
for C18 is specified by fluorine atoms F184, F185, and F186, and
the minor (23%) orientation for C28 is specified by fluorine
atoms F284, F285, and F286
.
microcrystalline compound was obtained. The complex
exhibited a rather simple H NMR spectral signature
at room temperature. One peak is observed at 7.75 ppm
due to equivalent protons at the 3- and 5-positions on
Selected bond lengths and angles can be found in Table 2.
Listings of anisotropic thermal parameters, atomic coordinates,
and all bond lengths and angles can be found in the Supporting
Information.
1

(2,4,6-(CF3)3C6H3)2(1,2-(MeO)2C2H4)Ni
Organometallics, Vol. 20, No. 12, 2001 2567
F igu r e 2. Perspective drawing of
F191‚‚‚Ni‚‚‚F291 axis.
1
along the
F igu r e 1. Perspective drawing of 1.
the aryl ring. Edelmann reports a similar peak at 7.65
ppm for the brown nickel bis(tris(2,4,6-trifluoromethyl)-
phenyl)nickel complex in the same solvent. However,
the purple complex isolated herein exhibits additional
peaks, one sharp at 2.07 ppm and one broad at 2.17
ppm, in the 1H NMR spectrum. The position and
intensity of these peaks are in agreement with the
methyl and methylene protons, respectively, for a 1,2-
dimethoxyethane adduct of bis(tris(2,4,6-trifluorometh-
yl)phenyl)nickel. Indeed, analytical data (both elemental
and MS) support the formulation of the purple complex
as bis(2,4,6-tris(trifluoromethyl)phenyl)(1,2-dimethoxy-
ethane)nickel (1).
Two peaks are observed in the 19F NMR spectrum of
1 at room temperature. The intensities observed are in
agreement with two equivalent o-CF3 (-58.2 ppm) and
one p-CF3 (-63.2 ppm) substituent on the aryl ring.
However, the o-CF3 resonance is extremely broad (ca.
800 Hz at half-height) and the p-CF3 resonance is very
sharp, indicating some sort of dynamic behavior (see
below).
X-r a y Cr ysta l Str u ctu r e. Crystals of 1 were grown
from cold toluene solution. The results of the crystal-
lographic study are given in Figure 1, which shows a
perspective drawing of 1. A listing of selected bond
distances and angles for 1 can be found in Table 2.
The oxygens of the complexed 1,2-dimethoxyethane
and the ipso carbons of the tris(2,4,6-trifluoromethyl)-
phenyl ligands form the inner coordination sphere of 1.
The geometry around nickel in 1 can be described as
distorted square planar. The sum of the four “square”
bond angles around Ni is 3.5° larger than the idealized
value of 360°. The “square” is S4-ruffled with displace-
ments of 0.23-0.25 Å from the five-atom mean plane
for the Ni and coordinated oxygen and carbon atoms.
As can be seen from Figure 1, however, the ipso carbons
of the aryl ligands, C11 and C21, reside above and below
(0.51 and 0.49 Å, respectively) the plane defined by the
Ni and two oxygens of the 1,2-dimethoxyethane ligand.
A similar distorted-square-planar geometry has been
reported for the homologous complex bis(2,4,6-tris-
(trifluoromethyl)phenyl)(2,2′-bipyridine)palladium.8
The Ni-O distances of 2.013(6) and 2.017(6) Å in 1
are identical within experimental error, as are the Ni-C
distances of 1.873(6) and 1.886(6) Å. Cis coordination
of two σ-bonded aryl ligands which each contain a pair
of o-CF3 substituents introduces steric congestion above
and below the “square” NiO2C2 coordination plane.
Nonbonded repulsions between a given pair of these
o-CF3 groups on the same side of the “square” are mini-
mized by tilting the Ni-C bonds for the two phenyl rings
in opposite directions perpendicular to the “square”.
This motion allows one o-CF3 group from each aryl lig-
and to move to an “axial” octahedral coordination site
of the Ni and leaves two fluorines of the remaining o-CF3
group on that side of the “square” in close contact with
the cis aryl ligand. Even with this movement, several
interligand nonbonded F‚‚‚C and F‚‚‚F contacts have
values less than or equal to the sum of the appropriate
van der Waals radii (2.94 Å for F‚‚‚F and 3.17 Å for
C‚‚‚F9): F172‚‚‚F291, 2.68 Å; F172‚‚‚C29, 3.16 Å; F173‚‚‚C21,
2.92 Å; F173‚‚‚C26, 3.01 Å; F271‚‚‚C11, 2.93 Å; F271‚‚‚C16,
3.08 Å; F273‚‚‚F191, 2.60 Å; F273‚‚‚C19, 3.09 Å. The
observed arrangement for the two cis-bonded tris(2,4,6-
trifluoromethyl)phenyl ligands therefore represents one
of two preferred conformations for this portion of the
molecule; the other is related to the observed one by a
C2 axis passing through the Ni atom and the midpoint
of the C11fC21 vector. In some ways, the cis-bonded bis-
(aryl) unit in 1 can therefore be viewed as a tetradentate
ligand with rigid planar halves whose relative orienta-
tions are determined by nonbonded contacts between
these halves. More specifically, these nonbonded con-
tacts determine the relative orientations of the four
atoms interacting directly with the metal. This, in turn,
determines the extent to which the geometrical require-
ments of square-planar and/or octahedral coordination
can be satisfied. These interligand nonbonded contacts
therefore determine the extent to which C11 and C12 can
be coplanar with the Ni, O1, and O2 atoms. The “bite”
of the “chelating” ligands defined by C11fF191 and
C21fF291 then determine how close the interacting
fluorines can approach idealized “axial” octahedral sites
once the carbons are bonded to Ni. The steric constraints
of this cis-aryl grouping in 1 causes the interacting
o-CF3 group for each aryl ligand to move slightly
(approximately 0.6 Å) off its idealized trans octahedral
site to a position above or below the coordinated 1,2-
dimethoxyethane ligand; this reduces the F191‚‚‚Ni‚‚‚F291
(8) Bartolome´, C.; Espinet, P.; Villafan˜e, F.; Giesa, S.; Mart´ın, A.;
Orpen, A. G. Organometallics 1996, 15, 2019.
(9) Bondi, A. J . Phys. Chem. 1964, 68, 441.

2568 Organometallics, Vol. 20, No. 12, 2001
Benedikt et al.
F igu r e 3. Stacked plot of variable-temperature 19F NMR spectra of 1 in toluene-d8.
angle from 180° to 152.3(2)°. The aryl ligands are also
rotated by approximately 25° about their Ni-C bonds
from an orientation perpendicular to the “square”.
Figure 2 shows these effects clearly. In contrast to the
o-CF3 groups, the p-CF3 groups of both aryl ligands are
not sterically locked into a specific conformation and are
rotationally disordered about their C-C bonds.
While the two “axial” Ni-F interactions, with nearly
identical lengths of 2.592(5) and 2.595(5) Å, are non-
bonding (the sum of the covalent radii for Ni and F is
1.87 Å10), they are considerably shorter than the 3.10
Å11 sum of the respective van der Waals radii for Ni
and F. These separations are therefore consistent with
a significant interaction between Ni and F. Similar close
contacts between metal and fluorine have been docu-
mented for the palladium bipyridine complex cited
above and in (2,4,6-tris(trifluoromethyl)phenyl)lithium,
-tin, -lead, -vanadium, and -zinc complexes.12
nickel serves to reduce the symmetry of 1 from an
approximate C2v to C2. The consequence of this reduc-
tion in symmetry is observed in the solution structure
of 1 at low temperatures, as monitored by 19F NMR (see
below).
Solu tion Dyn a m ics. Variable-temperature 19F NMR
spectra were recorded for 1 from 168 to 373 K (see
Figure 3). At the high temperature limit, two relatively
sharp peaks in a 2:1 ratio are observed due to two
equivalent o-CF3 (ca. -57.1 ppm) and one p-CF3 group
(ca. -61.5 ppm), respectively. As the sample is cooled,
the o-CF3 resonance broadens considerably. Coalescence
occurs at about 280 K. Below this temperature, this
peak splits into two resonances at about -55.2 and
-59.0 ppm. As the sample is cooled further, the most
downfield resonance begins to broaden further while the
peak at -59.0 ppm remains sharp. The p-CF3 peak
remains relatively sharp throughout the explored tem-
perature regime.
The low-temperature solution NMR spectra are con-
sistent with the X-ray crystal structure results. In this
region of slow exchange, three distinct CF3 groups per
aryl ligand are observed. They are the o-CF3 group that
interacts with the Ni center, the noninteracting o-CF3
group, and the p-CF3 group. As the temperature is
raised, the two o-CF3 groups participate in a two-site
exchange process that makes all four o-CF3 groups
equivalent. A simple fluxional process that is consistent
with this behavior is a “windshield wiper” motion in
which the two o-CF3 substituents that are in close
contact with nickel are replaced by the remaining two
The inclusion of fluorine from two o-CF3 substituents
on different aryl ligands in the coordination sphere of
(10) Hugheey, J . E. Inorganic Chemistry: Principles of Structure
and Reactivity; Harper and Row: New York, 1978; p 232.
(11) See ref 9.
(12) (a) Stalke, D.; Whitmire, K. H. J . Chem. Soc., Chem. Commun.
1990, 833. (b) Klinkhammer, K. W.; Fa˜ssler, T. F.; Gru¨tzmacher, H.-
J . Angew. Chem., Int. Ed. 1998, 37, 124. (c) Gru¨tzmacher, H.-J .;
Pritzkow, H.; Edelmann, F. T. Organometallics 1991, 10, 23. (d)
Brooker, S.; Buijink, J .-K.; Edelmann, F. T. Organometallics 1991, 10,
25. (e) Gibson, V. C.; Redshaw, C.; Sequeira, L. J .; Dillon, K. B.; Clegg,
W.; Elsegood, M. R. J . J . Chem. Soc., Chem. Commun. 1996, 2151. (f)
Dillon, K. B.; Gibson, V. C.; Howard, J . A. K.; Redshaw, C.; Sequeira,
L.; Yao, J . W. J . Organomet. Chem. 1997, 528, 179. (g) Brooker, S.;
Bertel, N.; Stalke, D.; Noltemeyer, M.; Roesky, H. W.; Sheldrick, G.
M.; Edelmann, F. T. Organometallics 1992, 11, 192.

(2,4,6-(CF3)3C6H3)2(1,2-(MeO)2C2H4)Ni
Organometallics, Vol. 20, No. 12, 2001 2569
o-CF3 groups. The energy of activation (∆Gq) for this
process was determined to be 12.5 kcal/mol by line-
shape analysis.13 Related processes involving intramo-
lecular exchange of fluorinated aryl ligands in early
transition metals exhibit similar activation energies.14
Interestingly, the analagous fluxional process could not
be frozen out in the related palladium complex bis(2,4,6-
tris(trifluoromethyl)phenyl)(2,2′-bipyridine)palladium,
even at 183 K.15
significant broadening independent of the other two
resonances. Unfortunately, this exchange process could
not be explored further, due to temperature limitations
of the solvent used (d8-toluene). However, it is likely that
this broadening is due to slowing of the C(phenyl)-
C(trifluoromethyl) bond rotation of the o-CF3 groups
interacting with the metal. This interpretation of the
observed broadening allows us to make the following
assignments of the downfield resonances: the peak at
-55.2 ppm is due to the o-CF3 group interacting with
the metal, and the peak at -59.0 ppm is due to the “free”
o-CF3 substituent. A downfield chemical shift in the 19F
NMR spectrum due to interaction of a fluorocarbon
residue with a metal is common and has become a
diagnostic test for such complexes.16
Ack n ow led gm en t. This research was supported by
the Advanced Technology Program of the NIST (ATP
Project 95-05-0038) and the BFGoodrich Pacing Re-
search Fund. We thank Dr. R. Lattimer for recording
the FD-MS of 1 and Prof. J uan Fornie´s for insightful
comments.
Su p p or tin g In for m a tion Ava ila ble: Listings of atomic
coordinates, anisotropic thermal parameters, and all bond
lengths and angles for 1. This material is available free of
charge via the Internet at http://pubs.acs.org.
Below 195 K, the -55.2 ppm resonance, due to the
o-CF3 substituent interacting with Ni in 1, experiences
(13) Breitmaier, E.; Wolfgang, W. Carbon-13 NMR Spectroscopy, 3rd
ed.; VCH: Weinheim, Germany, 1987.
(14) (a) Karl, J .; Erker, G.; Frohlich, R. J . Am. Chem. Soc. 1997,
119, 11165. (b) Siedle, A. R.; Newmark, R. A.; Lamanna, W. M.;
Huffman, J . C. Organometallics 1993, 12, 1491.
(15) See ref 8.
OM0100784
(16) A more complete listing of examples in which 19F NMR has been
used for determining or confirming the presence of significant fluoro-
carbon-metal interaction can be found in the reviews in refs 4 and 5.