Synthesis and structural characterization of half-sandwich nickel complexes bearing two different n-heterocyclic carbene ligands

Article abstract of DOI:10.1021/om200864z

Cationic cyclopentadienyl mixed bis-N-heterocyclic carbene (NHC) nickel complexes of the general formula [Ni(NHC)(NHC′)Cp](PF₆) (NHC/NHC′ = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (Mes ₂NHC) a, 1,3-dimethylimidazol-2-ylidene (Me₂NHC) b, 1-isopropyl-3-methyl-imidazol-2-ylidene (iPr-NHC-Me) c; Cp = η⁵-C₅H₅) were prepared by the reaction of the cationic monocarbene complex [Ni(Mes₂NHC)(NCMe)Cp](PF ₆) 1a or [Ni(Me₂NHC)(NCMe)Cp](BF₄) 1b with the appropriate free carbene. The new mixed bis(carbene) complexes [Ni(Mes ₂NHC)(Me₂NHC)Cp](PF₆) 2ab, [Ni(Mes ₂NHC)(iPr-NHC-Me)Cp](PF₆) 2ac, and [Ni(Me ₂NHC)(iPr-NHC-Me)Cp](BF₄) 2bc were obtained in moderate-to-high yields and were fully characterized by ¹H and ¹³C NMR spectroscopies, elemental analyses, and, in the case of 2ab, by a single-crystal X-ray diffraction study. The monocarbene precursor 1b was also structurally characterized. The mixed bis-NHC complexes 2ab and 2ac were tested as catalysts for the Suzuki-Miyaura cross-coupling of phenylboronic acid with 4′-bromoacetophenone, and their activities were compared to that of related monocarbene CpNi complexes.

Full text of DOI:10.1021/om200864z

Article
pubs.acs.org/Organometallics
Synthesis and Structural Characterization of Half-Sandwich Nickel
Complexes Bearing Two Different N-Heterocyclic Carbene Ligands
Anna Magdalena Oertel, Vincent Ritleng,* Loïc Burr, and Michael J. Chetcuti*
Laboratoire de Chimie Organomet
́
allique Appliquee
́ ́ ̀ ́
, UMR CNRS 7509, Ecole Europeenne de Chimie, Polymeres et Materiaux,
Universite
́
de Strasbourg, 25 rue Becquerel, 67087 Strasbourg, France
S
* Supporting Information
ABSTRACT: Cationic cyclopentadienyl mixed bis-N-heterocy-
clic carbene (NHC) nickel complexes of the general formula
[Ni(NHC)(NHC′)Cp](PF6) (NHC/NHC′ = 1,3-bis(2,4,6-
trimethylphenyl)imidazol-2-ylidene (Mes2NHC) a, 1,3-dimethyl-
imidazol-2-ylidene (Me2NHC) b, 1-isopropyl-3-methyl-imidazol-
2-ylidene (iPr-NHC-Me) c; Cp = η5-C5H5) were prepared by the
reaction of the cationic monocarbene complex [Ni(Mes2NHC)-
(NCMe)Cp](PF6) 1a or [Ni(Me2NHC)(NCMe)Cp](BF4) 1b with the appropriate free carbene. The new mixed bis(carbene)
complexes [Ni(Mes2NHC)(Me2NHC)Cp](PF6) 2ab, [Ni(Mes2NHC)(iPr-NHC-Me)Cp](PF6) 2ac, and [Ni(Me2NHC)(iPr-
NHC-Me)Cp](BF4) 2bc were obtained in moderate-to-high yields and were fully characterized by 1H and 13C NMR
spectroscopies, elemental analyses, and, in the case of 2ab, by a single-crystal X-ray diffraction study. The monocarbene precursor
1b was also structurally characterized. The mixed bis-NHC complexes 2ab and 2ac were tested as catalysts for the Suzuki−
Miyaura cross-coupling of phenylboronic acid with 4′-bromoacetophenone, and their activities were compared to that of related
monocarbene CpNi complexes.
cocatalyst, and TOFs of up to 190 h−1, a high rate for Ni(II)
INTRODUCTION
■
complexes under similar conditions,7,25 have been observed.
However, fast deactivation of the active (presumably a Ni(0))
species remained an issue. As the presence of a second NHC
unit on the nickel center may stabilize a coordinatively
unsaturated intermediate that could appear during the catalytic
cycle (metal−NHC bonds are regarded as especially stable4),
and as bis-NHC−nickel(0)7i,8a,d,11c,15,16a,18a,26 or bis-NHC−
nickel(I)27 species are proposed to be either the active catalysts
or intermediates in some of the above-cited organic reactions,
we decided to investigate the stability and catalytic activity of
half-sandwich nickel complexes that bear two NHC ligands.
Despite the relative diversity of NHC−Ni complexes bear-
ing two NHC ligands,7e,f,i,8a,e−g,10,16a,18a,26−28 only one
example of a cyclopentadienyl-bis-NHC−nickel complex, [Ni-
(Me4NHC)2Cp]+Cp−, has hitherto been reported; this species
was obtained by the direct reaction of 1,3,4,5-tetramethylimi-
dazol-2-ylidene (Me4NHC) with nickelocene.29 Moreover, the
first nickel complexes bearing two different NHCs have only
just appeared.30 It was, therefore, of interest to develop a
general procedure that allows the successive attachment of two
different NHC ligands onto one metal center, and we have
developed a synthetic route that allows the facile generation of
cationic mixed bis-NHC complexes of the general formula
[Ni(NHC)(NHC′)Cp]+. Herein, we report the synthesis of
three such complexes by the reaction of a cationic acetonitrile
complex [Ni(NHC)(NCCH3)Cp]+ with the appropriate free
Since the first isolation of a stable imidazol-2-ylidene,1 N-
heterocyclic carbenes (NHCs) have become an important class
of ligands in organometallic chemistry.2 The easy preparation
and handling of their precursors, their high modularity, and
their strong σ-donor properties,3 which allow them to form
strong NHC−metal bonds that prevent ligand dissociation,4
have rendered them extremely popular as supporting ligands in
transition-metal catalysis: NHC complexes have shown
unprecedented catalytic activity in many important organic
reactions.2,5
Nickel−NHC systems are somewhat less developed than
palladium−, ruthenium−, or even rhodium−NHC systems.2b
Nevertheless, the past decade has seen the emergence of a
number of NHC−nickel catalytic systems that have now found
applications in a vast number of organic transformations,
including, notably, traditional C−C cross-coupling reac-
tions;6−10 the amination11 and dehalogenation11b,12 of aryl
halides; the oxidation of secondary alcohols;13,14 C−S
couplings;15 the activation of C−F bonds;16,17 the hydro-
silylation of internal alkynes;18 three-component couplings of
unsaturated hydrocarbons, aldehydes, and silyl derivatives;19
and [2 + 2 + 2] cycloadditions.20−22
Following our ongoing interest in NHC−Ni compounds,23
we have recently reported that the neutral [Ni(Ar2NHC)-
ClCp†] and cationic [Ni(Ar2NHC)(NCCH3)Cp†](PF6)
[Ar2NHC = 1,3-diarylimidazol-2-ylidene; Cp† = Cp(η5-C5H5),
Cp*(η5-C5Me5)] half-sandwich complexes are efficient pre-
catalysts for the fast Suzuki coupling of aryl halides.24 These
catalysts function without the addition of a reductant or a
Received: September 15, 2011
Published: November 28, 2011
© 2011 American Chemical Society
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Scheme 1. Formation of the Mixed Bis(carbene) Nickel Complexes 2
NHC′. The molecular structure of one of these mixed bis-NHC
complexes was established by a single-crystal X-ray diffraction
study and is compared to those of its monocarbene precursors,
[Ni(NHC)(NCCH3)Cp]+ and [Ni(NHC′)(NCCH3)Cp]+.
Finally, limited studies into the catalytic activity of two of
these species in Suzuki−Miyaura cross-coupling are presented
and show that the coordination of a second NHC unit to an
already crowded CpNi−NHC moiety dramatically stabilizes the
resulting complex.
monocarbene nickel complex precursor 1b with the asym-
metrically substituted free carbene c. All compounds were
isolated as air-stable green solids. They were characterized by
1H and 13C{1H} NMR spectroscopy and by elemental analysis.
The molecular structure of 2ab was established by a single-
crystal X-ray diffraction study (vide infra).
The 1H and 13C{1H} NMR spectra of the mixed
bis(carbene) complexes 2 at ambient temperature present no
anomalies: all show the presence of one η5-Cp group and of
two NHC ligands. The carbene carbons are observed in the
158−168 ppm range in the 13C NMR spectra, whereas the Cp
carbon atoms appear at ca. 92 ppm, as is the case for closely
related monoimidazol-2-ylidene nickel Cp species, such as 1a
and 1b,23a−d,24,31 and for the only other known half-sandwich
bis-NHC−nickel complex, [Ni(Me4NHC)2Cp]+Cp−.29 Inter-
RESULTS AND DISCUSSION
■
Synthesis of the Mixed Bis-NHC−Nickel Complexes. We
have recently described the synthesis and structure of several
cationic acetonitrile complexes, [Ni(Ar2NHC)(NCCH3)-
Cp†]+PF6 , including [Ni(Mes2NHC)(NCCH3)Cp]+PF6
−
−
1
estingly, in the H NMR spectra, the Cp protons of the mixed
1a,23b,24 which is depicted in Scheme 1 (Mes2NHC = 1,3-bis-
2,4,6,trimethylphenylimidazol-2-ylidene, a). These com-
plexes are readily accessible via reaction of their correspond-
ing neutral chloro complexes [Ni(Ar2NHC)ClCp†] with
KPF6 in acetonitrile at room temperature.24 The acetonitrile
ligands in these complexes are labile, and free exchange is
observed between free and coordinated CH3CN, as shown
alkyl- and aryl-substituted-NHC compounds 2ab and 2ac
resonate as a singlet in the same range as observed for the Cp
protons of aryl-substituted complexes, such as 1a, at 4.6−4.8
ppm,24,31 rather than in the range observed for alkyl-substituted
complexes, such as 1b, 2bc, or [Ni(Me4NHC)2Cp]+Cp−, at
5.3−5.5 ppm.23a,c,29
As for the cationic monocarbene compounds 1a24 and 1b,
the spectra of 2ab reveal that an effective plane of symmetry
that bisects the molecule exists in solution on the NMR time
scale. This effective mirror plane contains the nickel atom, both
NHC carbene carbons, and the Cp ring centroid. The protons
of the Me2NHC ring and the NMe groups thus resonate as two
by H and 13C{1H} NMR studies in CD3CN. The hitherto
1
unreported complex, [Ni(Me2NHC)(NCCH3)Cp]+BF4 1b,
−
which contains the much less sterically demanding 1,3-
dimethylimidazol-2-ylidene (Me2NHC) b, was prepared
according to a similar procedure by reacting the neutral
iodo complex [Ni(Me2NHC)ICp]23c with AgBF4, and its
structure was established by a single-crystal X-ray diffraction
study (vide infra).
1
singlets in a 1:3 integrated ratio, in the molecule’s H NMR
spectrum. The protons of the Mes2NHC ring, the ortho-methyl
groups, the meta-hydrogens, and the para-methyl groups of the
mesityl groups all appear as four singlets in a 1:6:2:3 integrated
When a solution of complex 1a in tetrahydrofuran was
treated at room temperature with a freshly prepared solution of
the free carbene Me2NHC b (see the Experimental Section),
the labile acetonitrile ligand was rapidly displaced and the half-
sandwich mixed bis(carbene) complex [Ni(Mes2NHC)-
1
ratio in the H NMR signals of this molecule. This indicates
that no apparent rotational barrier is present on the NMR time
scale at ambient temperature in 2ab.
(Me2NHC)Cp]+PF6 2ab could be isolated in 74% yield
−
Despite the absence of an effective molecular mirror plane, a
similar situation in the asymmetric complex 2bc leads to a
single resonance for the two protons of the NHC ring and for
the two NMe groups of the Me2NHC ligand, respectively.
(Scheme 1a). Similarly, the reaction between a solution of 1a
and a freshly prepared solution of 1-isopropyl-3-methyl-
imidazol-2-ylidene (iPr-NHC-Me), c, afforded the mixed
bis(carbene) complex [Ni(Mes2NHC)(iPr-NHC-Me)-
1
However, in the H NMR spectrum of the sterically more
Cp]+PF6 2ac in good yield as well (Scheme 1a). Finally a
−
congested complex 2ac, the four meta-hydrogen atoms of the
two mesityl groups are displayed as two singlets in a 1:1
integrated ratio and the four ortho- and the two para-methyl
groups as three singlets in a 3:3:3 relative integrated ratio; the
third member of this series, [Ni(Me2NHC)(iPr-NHC-Me)-
Cp]+BF4− 2bc, could be obtained in moderate yield by reaction
in acetonitrile of the less-bulky (and THF insoluble)
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Scheme 2. Deprotonation of Coordinated CH3CN by the Bulky Free Carbene a
corresponding protons of the Mes2NHC ring remain
isochronous. These results likely indicate that rotation is
restricted about the N−mesityl bonds in 2ac, as we observed
previously in sterically congested neutral monocarbene Cp*
complexes [Ni(Ar2NHC)ClCp*].23c
It is not coincidental that all the bis(carbene) complexes
synthesized contain at least one NHC ligand with small- to
medium-sized substituents on the two nitrogen atoms. Despite
repeated attempts, we were unable to synthesize the bis-
Mes2NHC complex [Ni(Mes2NHC)2Cp]+ by reacting free
Mes2NHC a32 with 1a. Massive decomposition occurred
instead, and small amounts of the imidazolium salt
(Mes2NHC-H)+PF6 were isolated, together with less than
−
5% of the neutral cyanomethyl complex [Ni(Mes2NHC)-
Figure 1. Molecular structure of the cation of [Ni(Me2NHC)-
(NCMe)Cp]+(BF4)−, 1b, showing all non-H atoms. Ellipsoids are
shown at the 50% probability level, and key atoms are labeled.
(CH2CN)Cp] (Scheme 2), which we recently reported to be
readily obtained by reaction of 1a with KOtBu.23a,b The bulky
free carbene a thus behaves here not as a two-electron donor
ligand, but as a strong base, and in this role, it promotes the
base-assisted C−H activation of the acetonitrile ligand. This
result indicates that two Mes2NHC groups are too voluminous
to simultaneously bind to the nickel atom. A similar observation
was made by Cowley and co-workers, who reported the
formation of the half-sandwich bis(carbene) complex [Ni-
(Me4NHC)2Cp]+Cp− when nickelocene was treated with the
medium-sized carbene Me4NHC, but observed the formation
of the monocarbene complex [Ni(Mes2NHC)(η1-C5H5)Cp]
when nickelocene was treated with the more bulky Mes2NHC
a.29 Presumably, steric congestion approaches critical propor-
tions in bis-Mes2NHC nickel cyclopentadienyl systems, and
such species cannot be made.
Structural Studies of [Ni(Me2NHC)(NCMe)Cp](BF4) (1b)
and [Ni(Mes2NHC)(Me2NHC)Cp](PF6) (2ab). The structures
of the monocarbene complex 1b33 and of the mixed bis-NHC
complex 2ab34 were established by X-ray diffraction studies.
Crystals suitable for X-ray structure determination were grown
from solutions of acetonitrile/diethylether (1b) and CH2Cl2/
diethylether (2ab). The molecular structures of the cationic
parts of 1b and of 2ab are shown in similar orientations in
Figures 1 and 2, respectively. A list of selected bond lengths and
angles for 1b and 2ab, as well as for 1a23b (for comparison
purposes), appear in Table 1.
The structure of the cationic part of 1b is similar to that of its
related neutral analogues [Ni(Me2NHC)ICp†] (Cp† = Cp,
Cp*), which have been fully discussed earlier.23c It can also be
compared to the cationic part of the monocarbene complex 1a,
namely, [Ni(Mes2NHC)(NCMe)Cp]+.23b The acetonitrile
ligand in both structures is essentially linear [C4−C3−N =
178.6(2)° in 1b and 177.9(2)° for 1a]23b and is also linearly
coordinated to the nickel atom [the Ni−N−C3 angles are
175.6(2)° in 1b and 174.5(2)° for 1a]. Cp carbon distances, to
each other and to the nickel atom, exhibit significant variations,
but most of this is doubtless a result of the significant thermal
motion and relatively poor localization of the Cp carbon atoms.
A number of weak H-interactions may be present between
Figure 2. Molecular structure of the cation of [Ni(Mes2NHC)-
(Me2NHC)Cp]+(PF6)−, 2ab, showing all non-H atoms. Ellipsoids are
shown at the 50% probability level, and key atoms are labeled.
various hydrogen atoms from acetonitrile, NHC, and Cp
−
groups all with fluorine atoms in the BF4 anions (the H···F
distances range from 2.380 to 2.666 Å).
The molecular structure of the cation of 2ab features a nickel
atom bonded to a η5-Cp group, a Mes2NHC, and a Me2NHC
moiety in a two-legged piano stool geometry. The coordination
is globally similar to that of other half-sandwich complexes of
the general formula [Ni(NHC)LCp†],23a−c,24,31,35 such as 1a23b
and 1b, and is directly comparable to that of [Ni-
(Me4NHC)2Cp]+.29 If one considers the Cp group as a single
ligand, the nickel atom lies at the center of a pseudotrigonal
plane formed by the ring centroid, the carbene carbon atom
C(1) of the Me2NHC ligand b, and the carbene carbon atom
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a
Table 1. Selected Bond Lengths (Å) and Angles (°) for Complexes 1a, 1b, and 2ab with esd’s in Parentheses
1a23b
1b
2ab
Ni−C(1) and/or Ni−C(2)
Ni−N (1a, 1b)
Ni−Cpcent
1.902(2)
1.869(2)
1.760
1.888(2)
1.857(2)
1.751
1.906(3), 1.899(3)
1.772
2.136
Ni−CCp av
2.131
2.094
Ni−N−CCN
174.5(2)
175.6(2)
N−CCN−CMe
177.9(2)
96.93(8)
131.8
178.6(2)
98.86(7)
129.8
CNHC−Ni−N (1a, 1b) or C(1)−Ni−C(2) (2ab)
C(1)−Ni−Cpcent and/or C(2)−Ni−Cpcent
N−Ni−Cpcent (1a, 1b)
96.91(11)
136.0, 126.9
131.2
131.3
a
C(1) = carbene carbon of the Me2NHC ligand. C(2) = carbene carbon of the Mes2NHC ligand. N = acetonitrile nitrogen. Cpcent = centroid of the
Cp group.
C(2) of the Mes2NHC ligand a; the sum of the angles
subtended by these atoms is indeed almost exactly 360°.
However, there are significant departures from the idealized
120° angles of a trigonal structure (Table 1). Thus, the
carbenoid carbons C(1) and C(2) of 2ab subtend an angle of
96.91(11)° at the nickel atom, a value that is typical of CpNiL2
(or CpNiLL′) complexes: the L−Ni−L′ angles observed for
PhB(OH)2 and 2.6 equiv of K3PO4 as the sole additive in
toluene at 90−110 °C.24 Under these conditions, 2ab and 2ac
(1 mol %) give the desired product, 4-acetylbiphenyl, in,
respectively, 20% and 32% yield after 1 h of reaction (Scheme 3).
Scheme 3. Suzuki−Miyaura Cross-Coupling of 4′-
Bromoacetophenone with Phenylboronic Acid Catalyzed by
2ab and 2ac
29
1a,23b 1b, and [Ni(Me4NHC)2Cp]+ are 96.93(8), 98.86(7)
and 97.07(2)°, respectively.
Despite the different steric footprints of the two NHC
ligands, the two nickel−carbene carbon bond lengths of 2ab are
not significantly different from each other [Ni−C(1) =
1.899(3) Å; Ni−C(2) = 1.906(3) Å]. Moreover, these values
are remarkably close to those observed for the Mes2NHC- and
Me2NHC-containing monocarbene analogues 1a [Ni−C(2) =
1.902(2) Å]23b and 1b [Ni−C(1) = 1.888(2) Å] and are in the
range of those reported for [Ni(Me4NHC)2Cp]+,29 in which
values of 1.883(2) Å were observed for both nickel−carbene
carbon distances. However, the bigger carbene subtends a
larger angle at the nickel with the Cp centroid (126.9° and
136.0° for Me2NHC and Mes2NHC, respectively).
The planes defined by the two five-membered imidazol-2-
ylidene rings of 2ab are almost orthogonal to each other
(74.6°), and the two mesityl rings are close to perpendicular to
the Mes2NHC ring plane (the plane of each aryl ring makes
angles of 74.5° and 84° with the imidazol-2-ylidene plane),
presumably to minimize steric interactions. The plane that
contains the Me2NHC ring in 2ab makes an angle of 73° to the
C(1)−Ni−Cpcent plane (compared with 88.2°, 1b), but the
plane that contains the Mes2NHC ring makes a much smaller
angle of 34° with the C(2)−Ni−Cpcent plane.
The Cp ring of the mixed bis(carbene) complex 2ab exhibits
structural distortions, as there are significant variations in the Ni−
CCp distances, as well as fluctuations in the CCp−CCp distances.
Similar distortions have been previously observed and studied in
other Cp or Cp*Ni systems.36 Some of the imidazolylidene
hydrogen atoms are relatively close and interact weakly with some
F atoms of the PF6− anion (H···F distances lie in the 2.35−2.55 Å
range). The Me2NHC ring and one of the mesityl rings are close
to coplanar (interplanar angle = 9.5°), suggesting that there might
be some π-stacking interactions between the rings.
No homocoupling product, 4,4′-diacetybiphenyl, is detected.
Compared to the very high rate seen for a Ni(II)-based catalyst
in the absence of a cocatalyst or reductant with the
monocarbene half-sandwich catalyst [Ni{(iPr2Ph)2NHC}-
(NCMe)Cp*]+PF6 [(iPr2Ph)2NHC = 1,3-bis-2,6-diisopropyl-
−
phenylimidazol-2-ylidene] (95% conversion after 10 min at 90 °C
with 3 mol % loading, or 60% conversion after 1 h at 110 °C
with 1 mol % loading),24 these results were clearly
disappointing.
To establish whether these low reactivities were due to an
intrinsic stability of 2ab and 2ac, several reactivity tests were
conducted on both species. They all demonstrated the high
intrinsic stability of these cationic bis(carbene) complexes: for
example, both complexes 2ab and 2ac species are unaffected by
added acid; neither reaction nor decomposition was observed.37
Thus, it appears that the coordination of a second NHC ligand
onto a Cp-Ni(Mes2NHC) moiety stabilizes the catalyst
precursor to such an extent that the complex is almost
catalytically inert. One reasonable explanation may be that the
demanding steric footprints of the bulky Mes2NHC, the smaller
Me2NHC or iPr-NHC-Me, and the Cp ligand all together
probably render the nickel center almost inaccessible.
Preliminary studies into the reactivity of the much less sterically
congested species 2bc tend to confirm this diagnostic.
CONCLUSION
■
In summary, a general methodology for the synthesis of half-
sandwich Ni(II) complexes bearing two different NHC ligands
has been developed. Thus, the mixed bis(carbene) complexes
Short Study of the Catalytic Activities of (2ab) and
(2ac) in Suzuki−Miyaura Cross-Coupling. The catalytic
activity of the mixed bis(carbene) complexes 2ab and 2ac in
the cross-coupling of phenylboronic acid with 4′-bromoaceto-
phenone was examined under the standard conditions we have
established with related monocarbene complexes [Ni(NHC)-
[Ni(Mes2NHC)(Me2NHC)Cp]+PF6 2ab, [Ni(Mes2NHC)-
−
(iPr-NHC-Me)Cp]+PF6 2ac, and [Ni(Me2NHC)(iPr-NHC-
−
Me)Cp]+BF4 2bc were isolated in moderate-to-high yields
−
from the reaction of the cationic acetonitrile complex
[Ni(Mes2NHC)(CH3CN)Cp]+PF6 1a or [Ni(Me2NHC)-
−
LCp†] (L = Cl−, or NCMe, PF6 ), that is, with 1.3 equiv of
(CH3CN)Cp]+BF4 1b with the appropriate free NHC.
−
−
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Synthesis of [Ni(Me2NHC)(NCMe)Cp]+BF4 (1b). AgBF4 (509
mg, 2.61 mmol) was added to a solution of [Ni(Me2NHC)ICp] (905
mg, 2.61 mmol) in acetonitrile (30 mL). The color immediately
changed from red to green. After 10 min, the reaction medium was
filtered through Celite, which, in turn, was rinsed with acetonitrile (4 ×
5 mL), and the solvent was then concentrated to ca. 1 mL. Treatment
with diethylether gave green crystals after standing at −32 °C
overnight. The mother liquor was removed by syringe and the solid
washed with diethylether (3 × 5 mL) and dried under vacuum to give
1b (730 mg, 2.10 mmol, 80%). 1H NMR (CD3CN, 300.13 MHz): δ =
7.20 (s, 2H, NCH), 5.44 (s, 5H, η5-C5H5), 4.07 (s, 6H, Me). Free
CH3CN that results from exchange with CD3CN is seen as a singlet
(at 1.96 ppm) on the downfield side of the multiplet due to residual
CHD2CN observed at 1.94 ppm. 13C{1H} NMR (CD3CN, 75.47
MHz): δ = 156.2 (NCN), 125.8 (NCH), 93.8 (η5-C5H5), 39.2 (Me).
Free CH3CN that results from exchange with CD3CN is seen as two
singlets (at 1.77 and 118.3 ppm) overlapping with the multiplet due to
residual CHD2CN at 1.32 ppm and with the singlet due to CD3CN at
118.3 ppm.
−
A single-crystal X-ray diffraction study established the mole-
cular structure of the sterically congested 2ab, which was
compared to those of its monocarbene analogues, 1a and 1b,
and to that of its less sterically encumbered homologue
[Ni(Me4NHC)2Cp]+Cp−. It is not coincidental that all the
bis(carbene) complexes synthesized contain at least one NHC
ligand with small- to medium-sized substituents on the two
nitrogen atoms. The repeated failures in synthesizing the bis-
Mes2NHC complex [Ni(Mes2NHC)2Cp]+ by reacting free
Mes2NHC with 1a, and the deprotonaton of the acetonitrile
ligand of 1a instead, indeed, strongly suggest that two
Mes2NHC groups together with a Cp ligand are too
voluminous to bind simultaneously to the nickel atom. The
important steric congestion of the half-sandwich mixed
bis(carbene) complexes 2ab and 2ac, which contain the bulky
Mes2NHC and a smaller Me2NHC or iPr-NHC-Me ligand, is
most probably responsible for their great stability and hence the
low reactivity of 2ab and 2ac in the Suzuki−Miyaura cross-
coupling of 4′-bromoacetophenone with phenylboronic acid.
The reactivity of 2bc, which bears two small NHCs, is more
promising and is currently under investigation.
Synthesis of [Ni(Mes2NHC)(Me2NHC)Cp]+PF6 (2ab). n-Butyl-
−
lithium (0.20 mL, 0.32 mmol, 1.6 M in hexanes) was added dropwise
to a suspension of 1,3-dimethylimidazolium iodide (222 mg, 0.32
mmol) in THF (3 mL) and stirred for 10 min at room temperature.
The reaction mixture was filtered through Celite, and the resulting
solution of b was added to a solution of 1a (211 mg, 0.32 mmol) in
THF (5 mL) under vigorous stirring. The mixture was stirred at this
temperature for 15 min, and then the volatiles were evaporated under
vacuum. The residue was extracted with CH2Cl2 (3 × 5 mL) and
filtered through Celite, which was rinsed with CH2Cl2 (3 × 5 mL).
The solvent was evaporated under vacuum, and 2ab crystallized from a
cold solution of CH2Cl2 and diethyl ether. 2ab was isolated as green
crystals (170 mg, 0.25 mmol, 74%). Anal. Calcd for C31H37F6N4NiP:
EXPERIMENTAL SECTION
■
General Comments. All reactions were carried out using standard
Schlenk techniques under an atmosphere of dry argon. Solvents were
distilled from appropriate drying agents under argon prior to use.
Solution NMR spectra were recorded at 298 K on FT-Bruker Ultra
Shield 300 and FT-Bruker Spectrospin 400 spectrometers operating at
300.13 or 400.14 MHz for 1H and at 75.47 or 100.61 MHz for
13C{1H}. The assignments of the 13C{1H} NMR spectra were made
1
C, 55.63; H, 5.57; N, 8.37. Found: C, 55.48; H, 5.62; N, 8.38. H
NMR (CDCl3, 400.13 MHz): δ = 7.03 (s, 4H, m-H), 6.98 and 6.93
(2s, 2 × 2H, NCH), 4.76 (s, 5H, C5H5), 3.42 (s, 6H, NMe), 2.39 (s,
6H, p-Me), 1.98 (s, 12H, o-Me). 13C{1H} NMR (CDCl3, 100.61
MHz): δ = 168.2 and 160.3 (NCN), 140.0 and 136.3 (ispo-/p-CAr),
135.1 (o-CAr), 129.8 (m-CAr), 125.8 and 124.8 (NCH), 91.9 (C5H5),
38.9 (NMe), 21.2 (p-Me), 18.1 (o-Me).
with the aid of DEPT 13C spectra for all complexes and of H/13C
1
HSQC correlation for complex 2ac. The chemical shifts are referenced
to residual deuterated solvent peaks. Chemical shifts (δ) and coupling
constants (J) are expressed in parts per million and hertz, respectively.
Elemental analysis for complexes 2 were performed by the Service
d′Analyses, de Mesures Physiques et de Spectroscopie Optique, UMR
Synthesis of [Ni(Mes2NHC)(i-Pr-NHC-Me)Cp]+PF6 (2ac). n-
−
́
CNRS 7177, at the Institut de Chimie, Universite de Strasbourg.
Butyllithium (0.3 mL, 0.48 mmol, 1.6 M in hexanes) was added
dropwise to a suspension of 1-isopropyl-(3-methyl)imidazolium iodide
(109 mg, 0.43 mmol) in THF (5 mL) and stirred for 10 min at room
temperature. The reaction mixture was filtered through Celite, and the
resulting solution of c was added to a solution of 1a (267 mg, 0.43
mmol) in THF (5 mL) under vigorous stirring. The mixture was
stirred at this temperature for 15 min, and then the volatiles were
evaporated under vacuum. The residue was dissolved in CH3CN (5
mL) and filtered through alumina, which was rinsed with CH3CN (3 ×
10 mL). The solvent was evaporated under reduced pressure, and 2ac
was crystallized from a cold solution of THF and pentane. 2ac was
isolated as green crystals (228 mg, 0.33 mmol, 76%). Anal. Calcd for
C33H41F61N4NiP: C, 56.84; H, 5.93; N, 8.03. Found: C, 56.74; H, 6.17;
N, 7.94. H NMR (CDCl3, 300.13 MHz): δ = 7.15 (bs, 2H, m-H),
Commercial compounds were used as received. 1-Isopropyl-1H-
imidazole,38 Mes2NHC a,39 [Ni(Me2NHC)ICp],23c and [Ni-
(Mes2NHC)(NCMe)Cp](PF6) 1a24 were prepared according to
published methods. The preparations of 1,3-dimethylimidazolium
iodide40 and 1-isopropyl-(3-methyl)imidazolium iodide41 were
adapted from published syntheses, and the improved procedures are
given below.
Synthesis of 1,3-Dimethylimidazolium Iodide. Iodomethane
(1.64 mL, 20.0 mmol) was added to a solution of 1-methyl-1H-
imidazole (1.6 mL, 20.0 mmol) in toluene (80 mL). The mixture was
stirred at 50 °C overnight. The overlaying solution was removed by
syringe, and the resulting white solid was washed with diethyl ether (3
× 7 mL) and dried in vacuo for 2 h. 1,3-Dimethylimidazolium iodide
1
3
was obtained as a white solid in 97% yield (4.37 g, 19.5 mmol). H
7.05 and 6.96 (2d, 2 × 1H, NCH-c, J = 2.1), 7.00 (s, 2H, NCH-a),
6.94 (bs, 2H, m-H), 5.43 (sept, 1H, CHMe2, J = 6.8), 4.72 (s, 5H,
3
NMR (CDCl3, 300.13 MHz): δ = 10.01 (s, 1H, NCHN), 7.41 (s, 2H,
NCH), 4.09 (s, 6H, Me).
C5H5), 2.87 (s, 3H, NMe), 2.40 (s, 6H, p-Me), 2.28 and 1.58 (2s, 2 ×
6H, o-Me), 1.30 and 1.29 (2d, 3H, CH(CH3)2, J = 6.8). 13C{1H}
3
Synthesis of 1-Isopropyl-3-methylimidazolium Iodide. Iodo-
methane (1.42 g, 0.62 mL, 10.0 mmol) was added dropwise over a 5
min period to a solution of 1-isopropyl-1H-imidazole (1.102 g, 10.0
mmol) in toluene (20 mL). The solution was heated at 50 °C and
stirred at this temperature for 8 h. The overlaying solution was
removed by syringe, and the resulting white solid was washed with
diethyl ether (3 × 7 mL) and dried in vacuo for 2 h. 1-Isopropyl-(3-
methyl)imidazolium iodide was obtained as a white solid in 95% yield
(2.40 g, 9.5 mmol). 1H NMR (CDCl3, 300.13 MHz): δ = 10.20 (s, 1H,
NCHN), 7.43 and 7.40 (s, 1H, NCH), 4.83 (septet, 3J = 6.6, 1H, CH),
NMR (CDCl3, 75.47 MHz): δ = 168.1 and 158.1 (NCN), 140.3 and
136.2 (ipso-/p-CAr), 135.4 and 135.3 (o-CAr), 129.9 and 129.6 (m-CAr),
126.1 (NCH-a), 125.7 and 119.5 (NCH-b), 91.8 (C5H5), 53.2
(CH(CH3)2), 37.3 (NMe), 24.5 and 22.8 (CH(CH3)2), 21.1 (p-Me),
18.5 and 17.4 (o-Me).
Synthesis of [Ni(Me2NHC)(i-Pr-NHC-Me)Cp]+BF4 (2bc). n-
−
Butyllithium (1 mL, 1.60 mmol, 1.6 M in hexanes) was added
dropwise to a suspension of 1-isopropyl-(3-methyl)imidazolium iodide
(403 mg, 1.60 mmol) in THF (16 mL) and stirred for 10 min at room
temperature. The reaction mixture was filtered through Celite, and the
resulting solution of c was added to a solution of 1b (540 mg, 1.55
mmol) in acetonitrile (20 mL) under vigorous stirring. The mixture
3
4.13 (s, 3H, Me), 1.66 (d, J = 6.6, CHMe2). 13C{1H} NMR (CDCl3,
75.47 MHz): δ = 136.0 (NCHN), 123.9 and 120.2 (NCH), 53.6
(CH), 37.2 (Me), 23.3 (CHMe2).
6689
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Organometallics
Article
Mr. Michel Schmitt in obtaining the 1H/13C HSQC correlation
for complex 2ac.
was stirred at this temperature for 15 min, and then the volatiles were
evaporated under vacuum. The residue was then dissolved in
acetonitrile (5 mL) and filtered on alumina, which was rinsed with
acetonitrile (3 × 5 mL). The solvent was concentrated under reduced
pressure, and 2bc was precipitated by addition of diethylether. 2bc was
isolated as a green powder (290 mg, 0.67 mmol, 43%). Anal. Calcd for
C17H25BF4N4Ni: C, 47.38; H, 5.85, N; 13.00. Found: C, 47.52; H,
REFERENCES
■
(1) Arduengo, A. J.; Harlow, R. L.; Kline, M. J. Am. Chem. Soc. 1991,
113, 361.
1
(2) (a) Poyatos, M.; Mata, J. A.; Peris, E. Chem. Rev. 2009, 109, 3677.
(b) Díez-Gonzalez, S.; Marion, N.; Nolan, S. P. Chem. Rev. 2009, 109,
́
3612. (c) Arnold, P. L.; Casely, I. J. Chem. Rev. 2009, 109, 3599.
(d) Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47, 3122.
(e) Gade, L. H.; Bellemin-Laponnaz, S. Coord. Chem. Rev. 2007, 251,
718. (f) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290.
6.30; N, 12.49. H NMR (CD3CN, 300.13 MHz): δ = 7.17 and 7.15
3
(2d, 2 × 1H, NCH-c, J = 2.0), 7.08 (s, 2H, NCH-b), 5.45 (s, 5H,
C5H5), 5.41 (sept, 1H, CHMe2, 3J = 6.8), 3.98 (s, 3H, NMe-c), 3.85 (s,
3
6H, NMe-b), 1.20 (d, 6H, CH(CH3)2, J = 6.77). 13C{1H} NMR
(CD3CN, 75.47 MHz): δ = 164.2 and 162.5 (NCN), 126.4 and 120.0
(NCH-c), 125.4 (NCH-b), 92.3 (C5H5), 54.2 (CH(CH3)2), 39.7
(NMe-c), 39.3 (NMe-b), 23.1 (CH(CH3)2).
́
(3) (a) Díez-Gonzalez, S.; Nolan, S. P. Coord. Chem. Rev. 2007, 251,
874. (b) Cavallo, L.; Correa, A.; Costabile, C.; Jacobsen, H. J.
Organomet. Chem. 2005, 690, 5407. (c) Strassner, T. Top. Organomet.
Chem. 2004, 13, 1.
Procedure for the Suzuki−Miyaura Cross-Coupling Reac-
tions. A Schlenk tube, placed under an argon atmosphere, was
charged with 4′-bromoacetophenone (1.0 mmol), phenylboronic acid
(1.3 mmol), K3PO4 (2.6 mmol), 2ab or 2ac (0.01 mmol, 1 mol %),
and toluene (3 mL) and was immediately heated with vigorous stirring
by placing it into an oil bath at 110 °C. After 60 min, the reaction was
stopped by cooling the reaction to room temperature and allowing air
to enter the Schlenk tube. NMR yields were determined by removing a
sample with a syringe, drying it under vacuum, extracting the residue
with CDCl3, and filtering the solution in an NMR tube. The obtained
yields are the average values of three runs.
X-ray Diffraction Studies. Structure Determination and
Refinement. Single crystals of 1b and 2ab suitable for X-ray
diffraction studies were selected from batches of crystals obtained at
−32 °C from acetonitrile/diethylether and CH2Cl2/diethylether
solutions, respectively. Diffraction data for all crystals were collected
on a Nonius Kappa-CCD area detector diffractometer using graphite-
monochromated Mo−Kα radiation (λ = 0.71073 Å). A summary of
crystal data, data collection parameters, and structure refinements is
given in Table 1. Cell parameters were determined from reflections
taken from one set of 10 frames (1.0° steps in ϕ angle), each at 20 s
exposure. The structures were solved using direct methods with
SHELXS-97 and refined against F2 for all reflections using the
SHELXL-97 software.42 Multiscan absorption corrections (MULsca-
nABS in PLATON) were applied.43 All non-hydrogen atoms were
refined with anisotropic displacement parameters. Hydrogen atoms
were generated according to stereochemistry and refined as fixed
contributors using a riding model in SHELXL-97.
(4) (a) Jacobsen, H.; Correa, A.; Poater, A.; Costabile, C.; Cavallo, L.
Coord. Chem. Rev. 2009, 253, 687. (b) Radius, U.; Bickelhaupt, F. M.
Coord. Chem. Rev. 2009, 253, 678. (c) Frenkin, G.; Sola,
̀
M.;
Vyboishchikov, S. F. J. Organomet. Chem. 2005, 690, 6178.
(5) Herrmann, W. A.; Elison, M.; Fischer, J.; Kocher, C.; Artus, G. R.
J. Angew. Chem., Int. Ed. Engl. 1995, 34, 2371.
(6) For Heck couplings, see: (a) Inamoto, K.; Kuroda, J.-i.; Hiroya,
K.; Noda, Y.; Watanabe, M.; Sakamoto, T. Organometallics 2006, 25,
3095. (b) Inamoto, K.; Kuroda, J.-i.; Danjo, T.; Sakamoto, T. Synlett
2005, 1624.
(7) For Suzuki couplings, see ref 6a and: (a) Inamoto, K.; Kuroda, J.-
i.; Kwon, E.; Hiroya, K.; Doi, T. J. Organomet. Chem. 2009, 694, 389.
(b) Kuroda, J.-i.; Inamoto, K.; Hiroya, K.; Doi, T. Eur. J. Org. Chem.
2009, 2251. (c) Zhou, Y.; Xi, Z.; Chen, W.; Wang, D. Organometallics
2008, 27, 5911. (d) Xi, Z.; Zhang, X.; Chen, W.; Fu, S.; Wang, D.
Organometallics 2007, 26, 6636. (e) Liao, C.-Y.; Chan, K.-T.; Chang,
Y.-C.; Chen, C.-Y.; Tu, C.-Y.; Hu, C.-H.; Lee, H. M. Organometallics
2007, 26, 5826. (f) Lee, C.-C.; Ke, W.-C.; Chan, K.-T.; Lai, C.-L.; Hu,
C.-H.; Lee, H. M. Chem.Eur. J. 2007, 13, 582. (g) Inamoto, K.;
Kuroda, J.-i.; Sakamoto, T.; Hiroya, K. Synthesis 2007, 2853. (h) Chiu,
P. L.; Lai, C.-L.; Chang, C.-F.; Hu, C.-H.; Lee, H. M. Organometallics
2005, 24, 6169. (i) McGuinness, D. S.; Cavell, K. J.; Skelton, B. W.;
White, A. H. Organometallics 1999, 18, 1596.
(8) For Kumada couplings, see refs 7c and 7g and: (a) Berding, J.;
van Dijkman, T. F.; Lutz, M.; Spek, A. L.; Bouwman, E. Dalton Trans.
2009, 6948. (b) Zhang, C.; Wang, Z.-X. Organometallics 2009, 28,
6507. (c) Liu, A.; Zhang, X.; Chen, W. Organometallics 2009, 28, 4868.
(d) Berding, J.; Lutz, M.; Spek, A. L.; Bouwman, E. Organometallics
2009, 28, 1845. (e) Gu, S.; Chen, W. Organometallics 2009, 28, 909.
(f) Xi, Z.; Liu, B.; Chen, W. J. Org. Chem. 2008, 73, 3954.
(g) Matsubara, K.; Ueno, K.; Shibata, Y. Organometallics 2006, 25,
ASSOCIATED CONTENT
* Supporting Information
■
S
CIF files giving X-ray structural data, including data collection
parameters, positional and thermal parameters, and bond
distances and angles for complexes 1b and 2ab. This material
is available free of charge via the Internet at http://pubs.acs.org.
Crystallographic data (excluding structure factors) have also
been deposited in the Cambridge Crystallographic Data Centre
as Supplementary publications nos. CCDC 824508 (1b) and
824507 (2ab), respectively. Copies of the data can be obtained
free of charge from the CCDC via www.ccdc.cam.ac.uk/data_
request/cif.
3422. (h) Bohm, V. P. W.; Weskamp, T.; Gstottmayr, C. W. K.;
̈
̈
Herrmann, W. A. Angew. Chem., Int. Ed. 2000, 39, 1602.
(9) For Negishi couplings, see ref 8b and: Xi, Z.; Zhou, Y.; Chen, W.
J. Org. Chem. 2008, 73, 8497.
(10) For Ullmann couplings, see: Huynh, H. V.; Wong, L. R.; Ng, P.
S. Organometallics 2008, 27, 2231.
(11) (a) Matsubara, K.; Ueno, K.; Koga, Y.; Hara, K. J. Org. Chem.
́
2007, 72, 5069. (b) Kelly, R. A. III; Scott, N. M.; Díez-Gonzalez, S.;
Stevens, E. D.; Nolan, S. P. Organometallics 2005, 24, 3442. (c) Kuhl,
S.; Fort, Y.; Schneider, R. J. Organomet. Chem. 2005, 690, 6169.
(d) Omar-Amrani, R.; Thomas, A.; Brenner, E.; Schneider, R.; Fort, Y.
Org. Lett. 2003, 5, 2311. (e) Desmarets, C.; Schneider, R.; Fort, Y. J.
Org. Chem. 2002, 67, 3029. (f) Gradel, B.; Brenner, E.; Schneider, R.;
Fort, Y. Tetrahedron Lett. 2001, 42, 5689.
AUTHOR INFORMATION
Corresponding Author
*E-mail: vritleng@unistra.fr (V.R.), michael.chetcuti@unistra.fr
(M.J.C.). Tel: + 33 3 68 85 26 31.
■
(12) Desmarets, C.; Kuhl, S.; Schneider, R.; Fort, Y. Organometallics
2002, 21, 1554.
(13) (a) Berini, C.; Winkelmann, O. H.; Otten, J.; Vicic, D. A.;
Navarro, O. Chem.Eur. J. 2010, 16, 6857. (b) Berini, C.; Brayton, D.
F.; Mocka, C.; Navarro, O. Org. Lett. 2009, 11, 4244.
(14) For very interesting combined oxidation−addition protocols to
give tertiary alcohols from primary or secondary alcohols, see:
(a) Berini, C.; Navarro, O. Chem. Commun. DOI: 10.1039/
ACKNOWLEDGMENTS
■
A.M.O. thanks the Minister
̀
e de l′Enseignement Super
́
ieur et de
la Recherche for a doctoral fellowship. We are grateful to the
CNRS and the University of Strasbourg for their financial help.
Dr. Lydia Brelot is gratefully acknowledged for her work with
the X-ray structure resolutions. We appreciate the assistance of
6690
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Organometallics
Article
c1cc10826c. (b) Maekawa, T.; Sekizawa, H.; Itami, K. Angew. Chem.,
Int. Ed. 2011, 50, 7022.
(31) Abernethy, C. D.; Cowley, A. H.; Jones, R. A. J. Organomet.
Chem. 2000, 596, 3.
(32) Isolated free carbene Mes2NHC a was used. The formation of
the cyanomethyl complex [Ni(Mes2NHC)(CH2CN)Cp] can, there-
fore, not result from the reaction with unreacted base.
(15) Zhang, Y.; Ngeow, K. C.; Ying, J. Y. Org. Lett. 2007, 9, 3495.
(16) For cross-coupling reactions of fluorinated arenes, see ref 7g
and: (a) Schaub, T.; Backes, M.; Radius, U. J. Am. Chem. Soc. 2006,
(33) Crystal data for 1b: C H N Ni·BF , FW = 347.80; triclinic, P1;
̅
128, 15964. (b) Bohm, V. P. W; Gstottmayr, C. W. K.; Weskamp, T.;
̈
̈
12 16
3
4
a = 6.8787(6) Å, b = 10.1410(8) Å, c = 10.8037(9); α = 97.351(2)°,
Herrmann, W. A. Angew. Chem., Int. Ed. 2001, 40, 3387.
(17) For an example of catalytic defluorination of fluoroarenes, see:
Kuhl, S.; Schneider, R.; Fort, Y. Adv. Synth. Catal. 2003, 345, 341.
(18) (a) Berding, J.; van Paridon, J. A.; van Rixel, V. H. S.; Bouwman,
E. Eur. J. Inorg. Chem. 2011, 2450. (b) Chaulagain, M. R.; Mahandru,
G. M.; Montgomery, J. Tetrahedron 2006, 62, 7560.
β = 93.501(2)°, γ = 93.098(2)°; V = 744.59(11) Å3; Z = 2; Dcalcd
=
1.551 mg·m−3; μ = 1.340 mm−1; T = 173(2) K; crystal form, color =
block, green; crystal size = 0.48 × 0.40 × 0.30, hmax = 9, kmax = 14,
lmax = 12; Tmin = 0.5655, Tmax = 0.6893; 10 183 collected reflns, 4643
independent, 4182 with I > 2σ(I), R = 0.0392, wR2 = 0.0986; GOF =
1.060.
(19) (a) Sato, Y.; Hinata, Y.; Seki, R.; Oonishi, Y.; Saito, N. Org. Lett.
2007, 9, 5597. (b) Ho, C.-Y.; Jamison, T. F. Angew. Chem., Int. Ed.
2007, 46, 782. (c) Ng, S.-S.; Jamison, T. F. J. Am. Chem. Soc. 2005,
127, 7320. (d) Mahandru, G. M.; Liu, G.; Montgomery, J. J. Am. Chem.
Soc. 2004, 126, 3698. (e) Sawaki, R.; Sato, Y.; Mori, M. Org. Lett. 2004,
6, 1131. (f) Sato, Y.; Sawaki, R.; Mori, M. Organometallics 2001, 20,
5510.
(20) (a) McCormick, M. M.; Duong, H. A.; Zuo, G.; Louie, J. J. Am.
Chem. Soc. 2005, 127, 5030. (b) Duong, H. A.; Cross, M. J.; Louie, J. J.
Am. Chem. Soc. 2004, 126, 11438. (c) Louie, J.; Gibby, J. E.;
Farnworth, M. V.; Tekavec, T. N. J. Am. Chem. Soc. 2002, 124, 15188.
(d) Tekavec, T. N.; Zuo, G.; Simon, K.; Louie, J. J. Org. Chem. 2006,
71, 5834.
(34) Crystal data for 2ab: C31H37N4Ni.F6P, FW = 669.33;
monoclinic, P21/c; a = 9.1782(2) Å, b = 18.5195(6) Å, c =
18.6420(6), β = 97.070(2)°; V = 3144.59(16) Å3; Z = 4; Dcalcd
=
1.414 mg·m−3; μ = 0.731 mm−1; T = 173(2) K; crystal form, color =
prism, green; crystal size = 0.46 × 0.22 × 0.15, hmax = 11, kmax = 24, lmax
= 24; 23 130 collected reflns, 7155 independent, 5568 with I > 2σ(I),
R = 0.0510, wR2 = 0.1450; GOF = 1.042.
(35) (a) Malyshev, D. A.; Scott, N. M.; Marion, N.; Stevens, E. D.;
Ananikov, V. P.; Beletskaya, I. P.; Nolan, S. P. Organometallics 2006,
25, 4462. (b) Buchowicz, W.; Koziol, A.; Jerzykiewicz, L. B.; Lis, T.;
Pasynkiewicz, S.; Pecherzewska, A.; Pietrzykowski, A. J. Mol. Catal. A
2006, 257, 118. (c) Kelly, R. A. III; Scott, N. M.; Díez-Gonzal
́
ez, S.;
Stevens, E. D.; Nolan, S. P. Organometallics 2005, 24, 3442.
(21) For an example of cycloaddition of unsaturated hydrocarbons,
aldehydes, and ketones, see: Tekavec, T. N.; Louie, J. J. Org. Chem.
2008, 73, 2641.
(36) (a) Smith, M. E.; Andersen, R. A. J. Am. Chem. Soc. 1996, 118,
11119. (b) Holland, P. L.; Smith, M. E.; Andersen, R. A.; Bergman, R.
G. J. Am. Chem. Soc. 1997, 119, 12815. (c) Carmona, C. C.; Clapham,
S.; Gonidec, M.; Ritleng, V.; Braunstein, P.; Welter, R.; Chetcuti, M. J.
Eur. J. Inorg. Chem. 2010, 403.
(37) Attempts to labilize the Cp group of 2ab or 2ac by treating
them with 0.01 M solutions of acetic acid, HCl, HBF4, or HNO3 in a
coordinating solvent in the presence of KPF6 resulted in no reaction in
all cases.
(38) Starikova, O. V.; Doglushin, G. V.; Larina, L. I.; Komarova, T.
N.; Lopyrev, V. A. ARKIVOK 2003, 13, 119.
(39) Arduengo, A. J.; Dias, H. V. R.; Harlow, R. L.; Kline, M. J. Am.
Chem. Soc. 1992, 114, 5530.
(22) For a recent review about [2 + 2 + 2] cycloaddition reactions,
see: Chopade, P. R.; Louie, J. Adv. Synth. Catal. 2006, 348, 2307.
(23) (a) Oertel, A. M.; Freudenreich, J.; Gein, J.; Ritleng, V.; Veiros,
L. F.; Chetcuti, M. J. Organometallics 2011, 30, 3400. (b) Oertel, A.
M.; Ritleng, V.; Chetcuti, M. J.; Veiros, L. F. J. Am. Chem. Soc. 2010,
132, 13588. (c) Ritleng, V.; Barth, C.; Brenner, E.; Milosevic, S.;
Chetcuti, M. J. Organometallics 2008, 27, 4223. (d) Ritleng, V.;
Brenner, E.; Chetcuti, M. J. J. Chem. Educ. 2008, 85, 1646.
(e) Milosevic, S.; Brenner, E.; Ritleng, V.; Chetcuti, M. J. Dalton
Trans. 2008, 1973.
(24) Ritleng, V.; Oertel, A. M.; Chetcuti, M. J. Dalton Trans. 2010,
39, 8153.
(40) See, for example: (a) Vlahakis, J. Z.; Lazar, C.; Crandall, I. E.;
Szarek, W. A. Bioorg. Med. Chem. 2010, 18, 6184. (b) Zhao, H.; Foss,
F. W. Jr.; Breslow, R. J. Am. Chem. Soc. 2008, 130, 12590.
(41) Sashuk, V.; Peeck, L. H.; Plenio, H. Chem.Eur. J. 2010, 16,
3983.
(25) (a) Chen, C.; Yang, L.-M. Tetrahedron Lett. 2007, 48, 2427.
(b) Percec, V.; Golding, G. M.; Smidrkal, J.; Weichold, O. J. Org.
Chem. 2004, 69, 3447. (c) Zim, D.; Lando, V. R.; Dupont, J.;
Monteiro, A. L. Org. Lett. 2001, 3, 3049. (d) Inada, K.; Miyaura, N.
Tetrahedron 2000, 56, 8657. (e) Indolese, A. F. Tetrahedron Lett. 1997,
38, 3513.
(42) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(43) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7.
(26) (a) Matsubara, K.; Miyazaki, S.; Koga, Y.; Nibu, Y.; Hashimura,
T.; Matsumoto, T. Organometallics 2008, 27, 6020. (b) Schaub, T.;
Radius, U. Chem.Eur. J. 2005, 11, 5024.
(27) (a) Zhang, K.; Conda-Sheridan, M.; Cooke, S. R.; Louie, J.
Organometallics 2011, 30, 2546. (b) Miyazaki, S.; Koga, Y.;
Matsumoto, T.; Matsubara, K. Chem. Commun. 2010, 46, 1932.
(28) (a) Kong, Y.; Cheng, M.; Ren, H.; Xu, S.; Song, H.; Yang, M.;
Liu, B.; Wang, B. Organometallics 2011, 30, 1677. (b) O, W. W. N.;
Lough, A. J.; Morris, R. H. Organometallics 2009, 28, 6755. (c) Zhang,
X.; Liu, B.; Liu, A.; Xie, W.; Chen, W. Organometallics 2009, 28, 1336.
(d) Yang, W.-H.; Lee, C.-S.; Pal, S.; Chen, Y.-N.; Hwang, W.-S.; Lin, I.
J. B.; Wang, J.-C. J. Organomet. Chem. 2008, 693, 3729. (e) Wang, X.;
Jin, G.-X. Organometallics 2004, 23, 6002. (f) McGuinness, D. S.;
Mueller, W.; Wasserscheid, P.; Cavell, K. J.; Skelton, B. W.; White, A.
H.; Englert, U. Organometallics 2002, 21, 175. (g) Herrmann, W. A.;
Gerstberger, G.; Spiegler, M. Organometallics 1997, 16, 2209.
(h) Arduengo, A. J.; Gamper, S. F.; Calabrese, J. C.; Davidson, F. J.
Am. Chem. Soc. 1994, 116, 4391.
(29) Abernethy, C. D.; Clyburne, J. A. C.; Cowley, A. H.; Jones, R. A.
J. Am. Chem. Soc. 1999, 121, 2329.
(30) Liu, Z.-h.; Xu, Y.-C.; Xie, L.-Z.; Sun, H.-M.; Shen, Q.; Zhang, Y.
Dalton Trans. 2011, 40, 4697.
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