Reactions of CO2 with heteroleptic zinc and zinc-NHC complexes

Article abstract of DOI:10.1021/om401000s

The heteroleptic compound CpZnC₆F₅ (1) reacts with carbenes to give CpZnC₆F₅(L) (L = ItBu, 2; IDipp, 3; IMes, 4), in which the presence of the carbene ligand induces slippage of the C ₅Me₅

Full text of DOI:10.1021/om401000s

Article
pubs.acs.org/Organometallics
Reactions of CO2 with Heteroleptic Zinc and Zinc−NHC Complexes
Phillip Jochmann and Douglas W. Stephan*
Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, Canada
S
* Supporting Information
ABSTRACT: The heteroleptic compound Cp*ZnC6F5 (1) reacts with
carbenes to give Cp*ZnC6F5(L) (L = ItBu, 2; IDipp, 3; IMes, 4), in which
the presence of the carbene ligand induces slippage of the C5Me5 ligands.
The species 1 and 2 react with CO2 to give the hexameric species
[(C5Me5CO2)ZnC6F5]6 (5) and the monomeric (C5Me5CO2)ZnC6F5(ItBu)
(6), respectively.
reactivity of these products with CO2 is also reported, and the
nature of the resulting Zn-organocarboxylates is described.
INTRODUCTION
■
The great potential of N-heterocyclic carbene (NHC) ligands
in late transition metal chemistry has been illustrated, as
systems employing NHCs have demonstrated superior proper-
ties1 in a diversity of transformations, including C−C
coupling,2−12 metathesis,13−20 and polymerization21−28 reac-
tions. As strong σ-donors, NHCs can prevent thermal or
hydrolytic decomposition, but also offer the ability for facile
variation of steric bulk and electronic properties. The latter
features can be utilized to prevent di/oligomerization of metal
organyls and to block specific coordination sites. Despite the
broad use of NHCs in transition metal chemistry, the chemistry
of NHC complexes of zinc is underdeveloped.29 This seems
surprising, as recent efforts led to zinc catalysts that are active in
important transformations, such as hydrogenations,30−32
polymerizations,33−38 hydrosilylations,39−44 dehydrocou-
pling,40,45 and hydroaminations.46−52 Enantioselective reactions
have been reported.31,42−44,53 Since Arduengo et al. reported
the first isolated zinc NHC complex,54,55 a small number of zinc
NHC compounds have been prepared and tested in catalytic
reactions. Tolman and Hillmyer et al. described NHC-
supported zinc alkoxides for the (stereoelective) polymerization
of D,L-lactide,33,34 whereas Arnold et al. have used tethered
alkoxy-carbene ligands to achieve zinc-catalyzed polymerization
of rac-lactide. The copolymerization of CO2 with cyclohexene
oxide was achieved with IMes (IMes = 1,3-bis(2,4,6-
trimethylphenyl)imidazol-2-ylidene)-supported zinc chlorides
and acetates.36 In a similar approach, the cycloaddition of CO2
to epoxides was reported to be catalyzed by a ZnBr2(NHC)
system.56 Ring-opening polymerization of epoxides is another
example demonstrating the potential of NHC-supported zinc
complexes.36,57
RESULTS AND DISCUSSION
■
The heteroleptic complex ZnCp*(C6F5) (1) can be isolated in
90% yield by dismutation of equimolar amounts of ZnCp*2 and
Zn(C6F5)2 in toluene at room temperature (Scheme 1).
Scheme 1. Generation of ZnCp*(C6F5) (1) and Conversion
with NHCs To Yield Adducts 2−4
Solutions of 1 in C6D6 display a singlet at 1.94 ppm in the
1H NMR spectrum, indicating a pentahapto coordination mode
of the Cp* ligand. Crystallization of 1 from a cooled toluene
solution afforded colorless single crystals, suitable for X-ray
structure determination.
The molecular unit of 1 in the solid state shows an η5-Cp*
ligand (Zn−C = 2.167(2) to 2.258(2) Å) and a C6F5 ligand
(Zn−Cipso = 1.925(2) Å) coordinated to Zn(II) (Figure 1). The
slightly bent molecule (Cp*centroid −Zn−Cipso = 170.62°)
displays a remarkable packing in the crystalline state.
The Cp* and C6F5 rings of four molecular units are oriented
in such a way that π-stacking between four aromatic rings in the
order Cp*−C6F5−C6F5−Cp* is realized. This results in a two-
dimensional layer of molecules of 1 along the crystallographic
bc plane. Within this layer π-interactions between the electron-
rich ligands (Cp*) and electron-poor substituents (C6F5) are
Recently, we have shown that whereas decamethylzincocene
(ZnCp*2) reacts with H2 to give the reduced Zn(I) compound
Zn2Cp*2, the presence of NHCs intervenes and species of the
form Zn(Cp*)(H)(SIMes) can be intercepted.32 Moreover this
Zn-hydride is an effective catalyst for the hydrogenation of
imines. Herein we further explore the reactions of the
heteroleptic species ZnCp*(C6F5) with NHCs. The subsequent
Received: October 11, 2013
Published: December 5, 2013
© 2013 American Chemical Society
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CC6F5 = 2.058(3) Å), the η1-Cp* ligand shows a somewhat
longer distance (Zn−C = 2.097(3) Å). Ring slippage of the
Cp* ligand results in a pyramidalization of the zinc-bound
carbon atom. One tBu group on the NHC ligand showed
disorder and has been refined with split positions.
In analogy with the formation of 2, the formation and
isolation of ZnCp*(C6F5)(IDipp) (3) as a yellow solid was
achieved by mixing equimolar amounts of 1 and IDipp in
toluene (Scheme 1). This product was isolated in quantitative
yield and showed resonances at 1.82 and 180.11 ppm in the 1H
and 13C NMR spectrum, respectively. This is indicative of an
η5-Cp* and coordinated IDipp ligand in the coordination
sphere of Zn(II). 1H NMR spectra of a D8-toluene solution of 3
showed no η1-Cp* coupling pattern at low temperature, and
only the η5-Cp* complex was observed at −73 °C.
Crystallization of 3 from a cooled toluene solution afforded
yellow single crystals, suitable for X-ray structure determi-
nation. The solid-state structure of 3 is similar to the one
observed for 2, and the zinc center is surrounded by the Cp*,
C6F5, and IDipp ligands in a trigonal planar geometry (Figure
3). Again, the longest Zn−C bond length is observed for the η1-
Figure 1. POV-Ray depiction of 1. (a) Molecular structure. (b)
Packing in unit cell. Hydrogen atoms are omitted for clarity. C, gray; F,
pink; Zn, green.
evident. The intermolecular Cp*−C6F5 and C6F5−C6F5
centroid distances are 3.604 and 3.315 Å, respectively. The
tendency of perfluorophenyl moieties to undergo interactions
with arenes is well known,58,59 and its importance for self-
assembled aggregates, preorganized syntheses, and liquid crystal
phases has been early recognized.60,61 Recent publications
highlighted the importance of anion−π-interactions,62,63 and
examples of C6F5−Cp interactions have been reported.64 When
solutions of equimolar amounts of 1 and ItBu in aromatic
solvents were combined, the immediate and quantitative
formation of ZnCp*(C6F5)(ItBu) (2) was observed by NMR
spectroscopy (Scheme 1). In C6D6 solution, 2 displays a singlet
at 2.06 ppm in the 1H NMR spectrum, which is attributed to an
η5-Cp* ligand. The coordinated ItBu ligand displays a
resonance at 173.8 ppm in the 13C NMR spectrum, due to
Figure 3. POV-Ray depiction of 3. Hydrogen atoms are omitted for
clarity. C, gray; N, blue; F, pink; Zn, green.
1
the Zn-bound carbon atom. H NMR spectra of a D8-toluene
solution of 2 showed no η1-Cp* coupling pattern at low
temperature, and only the η5-Cp* complex was observed at
−78 °C. Colorless single crystals of 2 were obtained from
cooled toluene solutions and subjected to X-ray structure
determination. The molecular structure of 2 in the solid state
shows a trigonal planar coordination around the zinc center
(Figure 2). Whereas the C6F5 and ItBu ligands show very
similar carbon−metal contacts (Zn−CItBu = 2.054(3) Å, Zn−
Cp* ligand (2.1428(18) Å), whereas the C6F5 and IDipp
ligands display bond lengths of Zn−CC6F5 = 2.0228(19) Å and
Zn−CIDipp = 2.0903(17) Å. The monohapto Cp* ligand is
oriented away from the carbene ligand, which is likely the
consequence of steric crowding close to the metal center.
The adduct ZnCp*(C6F5)(IMes) (4) was obtained in the
same vein by combining equimolar amounts of 1 and IMes
(Scheme 1). 4 crystallizes in high yield as a solvate from
benzene or toluene solutions but can be obtained solvent free
by repeated washing with pentane and extended drying in
1
vacuo. Compound 4 shows H and 13C NMR resonances at
1.86 and 178.75 ppm, respectively, attributed to an η5-Cp* and
1
a coordinated IMes ligand. Although the H NMR spectra of a
D8-toluene solution of 4 were of low quality due to
crystallization and showed broad signals at low temperature,
the presence of an η1-Cp* coupling pattern at −78 °C can be
excluded.
The solid-state structure of 4 is similar to the one observed
for 3; however the Cp* ligand adopts a coordination mode
between η2 and η1 (Figure 4). The two closest Zn−Cp*
contacts (2.144(4) and 2.307(4) Å) are somewhat longer than
the Zn−IMes distance (2.053(4) Å), and the shortest distance
is observed for Zn−CC6F5 (2.008(4) Å). The notion of a slip
Figure 2. POV-Ray depiction of 2. Hydrogen atoms are omitted for
clarity. C, gray; N, blue; F, pink; Zn, green.
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Figure 4. POV-Ray depiction of 4. Hydrogen atoms and non-
coordinating benzene molecule are omitted for clarity. C, gray; N,
blue; F, pink; Zn, green.
from an η1- to an η2-Cp* ligand is consistent with a deviation
from the trigonal planar geometry around Zn and almost no
pyramidalization around the zinc-bound carbon atoms of the
pentamethylcyclopentadienyl ligand. Although 30 min may be
required to acquire NMR data or complete the workup of 2−4,
we believe these adduct formations are instantaneous.
The reactivity of the new zinc compounds toward CO2 was
explored by exposing benzene solutions of 1−4 to 1 bar of
CO2. The reaction of 1 with 1 bar of CO2 resulted in the
insertion of CO2 into the Zn−CCp* bond, quantitatively
producing a product with the empirical formula Zn-
(O2CC5Me5)(C6F5) (5, Scheme 2). This reaction was slow at
ambient temperature (6 d), but complete after 24 h at 50 °C.
Figure 5. POV-Ray depiction of 5. (a) Asymmetric unit. (b) Hexamer
with C6F5 ligands omitted for clarity. Hydrogen atoms and solvent
molecules are omitted for clarity. C, gray; N, blue; O, red; F, pink; Zn,
green.
The observation of an oligonuclear structure for 5 in the
absence of NHC ligands is unsurprising due to the introduction
of carboxylic functional groups. The hexamer bears bridging
Cp*CO2 moieties that lead to three different coordination
geometries around Zn. Zn1 is surrounded by three oxygen and
one CC6F5 atom, resulting in a coordination number of four and
a trigonal pyramidal geometry around the metal center, which is
located in the base plane. The Cp*CO2 ligands capping the
hexamer realize a μ2-κ2-coordination mode, so that Zn2 is
surrounded not only by two oxygen and one CC6F5 atom but
also by a double bond of the σ-bound Cp* fragment. This leads
to a pseudotetrahedral geometry around Zn2. A square
pyramidal coordination geometry is found for Zn3, consisting
of four oxygen and one CC6F5 atom. The zinc−oxygen bond
lengths vary between 1.943(3) and 2.299(3) Å with an average
of ca. 2.05 Å. This is longer than found for the related
compound [Zn4(μ4-O)(O2CCp*)6] (1.927(1) to 1.962(1)
Å).65 Expectedly, the C−O bond lengths range from
1.241(5) to 1.295(5) Å, indicative of charge distribution of
the carboxylic functionalities.
The reactions of carbene adducts 2−4 with CO2 showed
complete conversion of the starting material before the first
NMR data were acquired (Scheme 3). Although 30 min may be
required to acquire NMR data or complete the workup, we
believe these reactions are almost instantaneous. Only for 2 was
a single product observed, which was unambiguously identified
as Zn(O2CC5Me5)(C6F5)(ItBu) (6) by NMR spectroscopy and
single-crystal structure determination. Product 6 was isolated
and shows resonances at 185.2 and 171.34 ppm in the 13C
Scheme 2. Reaction of 1 with CO2 and Formation of 5
It is noteworthy that the presence of NHCs dramatically
accelerates the insertion of CO2 into the metal Cp* bond (vide
infra). Compound 5 shows an η1-Cp* and a C6F5-coupling
1
pattern in the H and 19F NMR spectra, respectively. The
newly formed C−C bond gives rise to 13C nuclear resonances
at 184.72 and 65.54 ppm, for the carboxylic and adjacent Cp*
carbon atoms, respectively. A second insertion of CO2 into the
Zn−CC6F5 bond to afford Zn(O2CC5Me5)(O2CC6F5) was not
observed, even after heating to 70 °C. Crystallization of 5 from
a cooled toluene solution afforded colorless single crystals,
suitable for X-ray structure determination (Figure 5). Zinc
carboxylate 5 crystallizes as the centrosymmetric hexamer
[Zn(O2CC5Me5)(C6F5)]6 with one noncoordinating toluene
molecule.
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adducts. Whereas all isolated zinc compounds react with CO2,
the presence of NHCs was observed to increase the reaction
rate. The obtained zinc carboxylates are mononuclear in the
solid state when NHCs were employed but oligonuclear in their
absence. Noteworthy, thermodynamically very stable NHC−
CO2 adducts were observed at no time. The present results
demonstrate the facile and transition metal free formation of
soluble and mononuclear organozinc carboxylates. The NHC-
accelerated insertion of CO2 into the Zn−C bond under mild
conditions appears to be a general motif, thus allowing for the
isolation of other NHC-supported zinc carboxylates. The latter
might be of interest as active reagents, e.g., in the lactide
polymerization or epoxide/CO2 copolymerization.
Scheme 3. Reaction of Adducts 2−4 with CO2 and
a
Formation of Carboxylates 6−8
a
EXPERIMENTAL SECTION
Note: 7 and 8 were not isolated.
■
General Considerations. All manipulations were performed
under an atmosphere of dry, oxygen-free N2 by means of standard
Schlenk or glovebox techniques (MBraun glovebox equipped with a
−38 °C freezer) unless otherwise noted. C6D6 and D8-toluene were
dried over Na/benzophenone ketyl and vacuum transferred before use.
Other solvents were purified using an Innovative Technologies solvent
ItBu
NMR spectrum, which are assigned to the Cp*CO2 and C2
carbon atoms, respectively. Comparison to 5 shows that the
presence of ItBu has only a minor effect on the 1H, 13C, and 19
F
chemical shifts of the Zn(O2CC5Me5)(C6F5) unit. Compound
6 was obtained as a monosolvate by recrystallization from
toluene. Compound 6 crystallizes with two very similar yet
independent molecules in the asymmetric unit (Figure 6). The
66
67
purification system. ZnCp*2 and Zn(C6F5)2 were prepared
according to published protocols. ItBu (TCI), IDipp (Aldrich), and
IMes (Aldrich) were used as received. CO2 (Linde, grade 4.0) was
purified through a Dririte column. NMR spectra were recorded on a
Bruker Avance 400 MHz, an Agilent DD2 500, or an Agilent DD2 600
NHC
Hz spectrometer. C2
shifts were determined by HMBC experi-
ments if not observed by 1D 13C NMR spectroscopy. Chemical shifts
were referenced internally using the residual solvent resonances and
reported relative to tetramethylsilane. X-ray crystallography (Bruker
Kappa Apex II) and elemental analysis (Perkin-Elmer CHN analyzer)
were performed in house.
ZnCp*(C6F5) (1). A solution of ZnCp*2 (49 mg, 0.15 mmol) in 1.5
mL of toluene was added to a solution of Zn(C6F5)2 (58 mg, 0.15
mmol) in 1.5 mL of toluene. The mixture was stirred for 1 h, and the
volume of the solution was reduced before the mixture was cooled to
−38 °C. Repeated crystallization at this temperature and drying
afforded 1 as a colorless product (99 mg, 0.27 mmol, 90%). 1H NMR
(400 MHz, C6D6): δ 1.94 (s, 15H). 13C{1H} NMR (100 MHz, C6D6):
1
2
1
δ 149.6 (ddm, JCF = 230 Hz, JCF = 24 Hz, o-CF), 141.5 (dm, JCF
=
1
2
250 Hz, p-CF), 137.4 (ddd, JCF = 254 Hz, JCF = 13, 30 Hz, m-CF),
122.8 (tm, 2JCF = 83 Hz, i-C), 109.1 (CCp*), 10.1 (MeCp*). 19F NMR
Figure 6. POV-Ray depiction of 6. Only one of two independent
molecules is shown. Hydrogen atoms are omitted for clarity. C, gray;
N, blue; O, red; F, pink; Zn, green.
3
(282 MHz, C6D6): δ −113.85 (m, 2F, o-CF), −153.57 (t, 1F, JFF
=
19.6 Hz, p-CF), −160.76 (m, 2F, m-CF). Anal. Calcd for C16H15F5Zn:
C, 52.27; H, 4.11. Found: C, 51.89; H, 4.48.
ZnCp*(C6F5)(ItBu) (2). A solution of ItBu (10 mg, 0.055 mmol) in
1 mL of toluene was added to a solution of 1 (20 mg, 0.054 mmol) in
1 mL of toluene. The mixture was stirred for 30 min, and the volume
of the solution was reduced before the mixture was cooled to −38 °C.
Repeated crystallization at this temperature and drying afforded 2 as a
shortest distance is observed for Zn−CC6F5 (1.991(2) and
1.994(2) Å). While the ItBu ligands strongly coordinate the
zinc centers (2.018(2) and 2.027(2) Å), the longest bonds are
observed to the η2-carboxylate moieties (Zn−O of 2.086(2) to
2.200(2) Å). The latter distances are again longer than
observed for the related compound [Zn4(μ4-O)(O2CCp*)6].65
When 3 and 4 were reacted with CO2, mixtures of
carboxylated products were obtained. After one and two days
of equilibration, the reaction mixture resulting from 3 gave rise
1
colorless product (22 mg, 0.040 mmol, 73%). H NMR (400 MHz,
C6D6): δ 6.31 (s, 2H, CHIm), 2.06 (s, 15H, MeCp*), 1.10 (s, 18H,
tBu). 13C{1H} NMR (100 MHz, C6D6): δ 173.8 (CIm), 149.2 (dd, 1JCF
2
1
= 221 Hz, JCF = 32 Hz, o-CF), 140.2 (dm, JCF = 240 Hz, p-CF),
1
2
137.4 (ddd, JCF = 254 Hz, 2JCF = 12, 33 Hz, m-CF), 125.2 (tt, JCF
=
71 Hz, JCF = 6 Hz, i-C), 119.0 (CHIm), 118.1 (CCp*), 57.9 (CtBu),
3
1
to H, 13C, and 19F NMR data that implied the presence of
30.1 (MetBu), 13.3 (MeCp*). 19F NMR (375 MHz, C6D6): δ −112.88
(m, 2F, o-CF), −157.64 (t, 1H, 3JFF = 20.0 Hz, p-CF), (br t, 2F, 3JFF
=
Zn(O2CC5Me5)(C6F5)(IDipp) (7, see SI for in situ NMR
37
spectrum), Zn(O2CC5Me5)2,65 and Zn(C6F5)2(IDipp)2 in an
20.9 Hz, m-CF). Anal. Calcd for C27H35F5N2Zn: C, 59.18; H, 6.44; N,
5.11. Found: C, 57.28; H, 6.38; H 4.93. Repeated elemental analysis
gave unsatisfactory values for carbon in 2. Low carbon contents were
previously reported for zinc complexes.68
ZnCp*(C6F5)(IDipp) (3). A solution of IDipp (10 mg, 0.026 mmol)
in 1 mL of toluene was added to a solution of 1 (9 mg, 0.024 mmol) in
1 mL of toluene, which resulted in a color change to yellow. The
mixture was stirred for 30 min, and the volume of the solution was
reduced before the mixture was cooled to −38 °C. Repeated
crystallization at this temperature and drying afforded 3 as a yellow
approximate ratio of 1:1:1. Similarly, the reaction mixture
resulting from 4 showed Zn(O2CC5Me5)(C6F5)(IMes) (8, see
SI for in situ NMR spectrum), Zn(O2CC5Me5)2, and
37
Zn(C6F5)2(IMes)2 in an approximate ratio of 2:1:1
CONCLUSION
■
The heteroleptic compound Zn(η5-Cp*)(C6F5) was prepared
by facile ligand exchange and used to prepare a series of NHC
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1
product (18 mg, 0.024 mmol, 100%). H NMR (400 MHz, C6D6): δ
AUTHOR INFORMATION
Corresponding Author
*E-mail: dstephan@chem.utoronto.ca. Homepage: http://
www.chem.utoronto.ca/staff/dstephan.
■
7.22 (t, 2H, JHH = 7.8 Hz, p-CHDipp), 7.01 (d, 4H, 3JHH = 7.8 Hz, m-
3
CHDipp), 6.33 (s, 2H, CHIm), 2.66 (sept, 4H, JHH = 6.8 Hz, CHDipp),
3
1.82 (s, 15H, MeCp*), 1.22 (d, 12H, JHH = 7.0 Hz, MeDipp), 0.86 (d,
3
12H, JHH = 6.6 Hz, MeDipp). 13C{1H} NMR (100 MHz, C6D6): δ
3
180.1 (CIm), 148.9 (dd, 1JCF = 223 Hz, 2JCF = 27 Hz, o-CF), 145.6 (o-
Notes
1
1
C
Dipp), 139.0 (d, JCF = 228 Hz, p-CF), 136.7 (d, JCF = 286 Hz, m-
The authors declare no competing financial interest.
CF), 135.7 (i-CDipp), 131.4 (p-CHDipp), 125.29 (CHIm), 125.0 (m-
CHDipp), 123.2 (tt, 2JCF = 72 Hz, 3JCF = 6 Hz, i-C), 114.8 (CCp*), 29.4
(CHDipp), 26.3 and 22.6 (MeDipp), 12.0 (MeCp*). 19F NMR (375 MHz,
ACKNOWLEDGMENTS
■
3
P.J. thanks the Alexander von Humboldt Foundation for a
Feodor Lynen Research Fellowship. D.W.S. gratefully acknowl-
edges the financial support of the NSERC of Canada and the
award of a Canada Research Chair.
C6D6): δ −111.19 (m, 2F, o-CF), −161.05 (t, 1F, JFF = 19.8 Hz, p-
3
CF), −164.66 (br t, 2F, JFF = 19.8 Hz, m-CF). Anal. Calcd for
C43H51F5N2Zn: C, 68.29; H, 6.80; N, 3.70. Found: C, 68.22; H, 6.88;
N, 3.80.
ZnCp*(C6F5)(IMes) (4). A solution of IMes (10 mg, 0.033 mmol)
in 1 mL of toluene was added to a solution of 1 (12 mg, 0.033 mmol)
in 1 mL of toluene, which resulted in a color change to light yellow.
The mixture was stirred for 30 min, and the volume of the solution
was reduced before the mixture was cooled to −38 °C. Repeated
crystallization at this temperature and drying afforded 4 as an off-white
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1
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C6D6): δ 1.71 (s, 6H, MeCp*), 1.52 (s, 6H, MeCp*), 1.26 (s, 3H,
MeCp*). 13C{1H} NMR (125 MHz, C6D6): δ 184.7 (O2CCp*), 149.9
(dd, 1JCF = 229 Hz, 2JCF = 26 Hz, o-CF), 142.2 (CCp*), 140.8 (CCp*),
Int. Ed. 2007, 46, 2768−2813.
1
1
139.3 (dm, JCF = 225 Hz, p-CF), 137.2 (dm, JCF = 251 Hz, m-CF),
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114.4 (br t, JCF = 67 Hz, i-C), 65.5 (O2CCp*), 17.7 (MeCp*), 11.5
2
(MeCp*), 11.1 (MeCp*). 19F NMR (282 MHz, C6D6): δ −117.43 (br
m, 2F, o-CF), −154.52 (t, 1F, 3JFF = 19 Hz, p-CF), −161.39 (br t, 2F,
3JFF = 18 Hz, m-CF). Anal. Calcd for C17H15F5O2Zn: C, 49.60; H,
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recrystallization from toluene at −38 °C.
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1
give a colorless solid (4 mg, 0.007 mmol, 44%). H NMR (400 MHz,
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C6D6): δ 6.43 (s, 2H, CHIm), 2.04 (s, 6H, MeCp*), 1.72 (s, 6H,
MeCp*), 1.63 (s, 3H, MeCp*), 1.32 (s, 18H, tBu). 13C{1H} NMR (125
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Hz, JCF = 27 Hz, o-CF), 140.3 (dm, JCF = 247 Hz, p-CF), 139.8
(CCp*), 137.5 (ddd, JCF = 253 Hz, JCF = 13, 32 Hz, m-CF), 135.8
(CCp*), 121.3 (tt, 2JCF = 65 Hz, 3JCF = 5 Hz, i-C), 118.8 (CHIm), 64.8
(O2CCp*), 59.2 (CtBu), 30.9 (MetBu), 19.9 (MeCp*), 11.7 (MeCp*),
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1
2
3
−157.42 (t, 1F, JFF = 19 Hz, p-CF), −162.22 (m, 2F, m-CF). Anal.
Calcd for C28H35F5N2O2Zn: C, 56.81; H, 5.96; N, 4.73. Found: C,
56.89; H 6.02; N, 4.80. Single crystals were obtained by
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ASSOCIATED CONTENT
* Supporting Information
■
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F.; Trzeciak, A. M.; Ziołkowski, J. J. J.
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