Protonolysis and Amide Exchange Reactions of a Three-Coordinate Cobalt Amide Complex Supported by an N-Heterocyclic Carbene Ligand

Article abstract of DOI:10.1021/ic502670x

A three-coordinate cobalt species, IPrCoCl{N-(SiMe₃)₂} [1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene], was synthesized by the reaction of {IPrCoCl₂}₂ with NaN(SiMe₃)₂. Compound 1 is a useful starting material for low-coordinate (IPr)Co species. 1 reacts with 2,6-di-tert-butyl-4-methylphenol (BHT-H) via aminolysis of the Co-N bond to generate a three-coordinate phenoxide complex, IPrCoCl(O-2,6-^tBu₂-4-MeC₆H₂) (2). The reaction of 1 with 2,6-diisopropylaniline (NH₂DIPP) generates IPrCoCl(NHDIPP) (4), which undergoes disproportionation to form a mixture of 4, {IPrCoCl₂}₂, and IPrCo(NHDIPP)₂ (3). The same product mixture is formed by the reaction of 1 with Li[NH(DIPP)], which unexpectedly proceeds by amide exchange. Compound 3 was synthesized independently by the reaction of {IPrCoCl₂}₂ with 4 equiv of Li[NH(DIPP)]. The reaction of 1 with the bulkier lithium 2,6-dimesitylanilide (LiNHDMP) also proceeds by amide exchange to generate IPrCoCl(NHDMP) (5), which is stable toward disproportionation. Compounds 1 and 2 exhibit trigonal-planar geometries at cobalt in the solid state. The solid-state structure of 3 also contains a trigonal-planar cobalt center and exhibits close Co---H contacts involving the methine hydrogen atoms of the NH(DIPP) groups in the axial positions. The solid-state structure of 5 features an interaction between cobalt and a flanking aryl group of the anilide ligand, resulting in pyramidalization of the cobalt center. (Chemical Equation Presented).

Full text of DOI:10.1021/ic502670x

Article
pubs.acs.org/IC
Protonolysis and Amide Exchange Reactions of a Three-Coordinate
Cobalt Amide Complex Supported by an N‑Heterocyclic Carbene
Ligand
Christopher B. Hansen,* Richard F. Jordan, and Gregory L. Hillhouse†
Department of Chemistry, The University of Chicago, 929 East 57th Street, Chicago, Illinois 60637, United States
S
* Supporting Information
ABSTRACT: A three-coordinate cobalt species, IPrCoCl{N-
(SiMe3)2} [1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-
ylidene], was synthesized by the reaction of {IPrCoCl2}2 with
NaN(SiMe3)2. Compound 1 is a useful starting material for low-
coordinate (IPr)Co species. 1 reacts with 2,6-di-tert-butyl-4-
methylphenol (BHT-H) via aminolysis of the Co−N bond to
generate a three-coordinate phenoxide complex, IPrCoCl(O-
2,6-tBu2-4-MeC6H2) (2). The reaction of 1 with 2,6-diisopropylani-
line (NH2DIPP) generates IPrCoCl(NHDIPP) (4), which under-
goes disproportionation to form a mixture of 4, {IPrCoCl2}2, and IPrCo(NHDIPP)2 (3). The same product mixture is formed by
the reaction of 1 with Li[NH(DIPP)], which unexpectedly proceeds by amide exchange. Compound 3 was synthesized
independently by the reaction of {IPrCoCl2}2 with 4 equiv of Li[NH(DIPP)]. The reaction of 1 with the bulkier lithium 2,6-
dimesitylanilide (LiNHDMP) also proceeds by amide exchange to generate IPrCoCl(NHDMP) (5), which is stable toward
disproportionation. Compounds 1 and 2 exhibit trigonal-planar geometries at cobalt in the solid state. The solid-state structure of
3 also contains a trigonal-planar cobalt center and exhibits close Co---H contacts involving the methine hydrogen atoms of the
NH(DIPP) groups in the axial positions. The solid-state structure of 5 features an interaction between cobalt and a flanking aryl
group of the anilide ligand, resulting in pyramidalization of the cobalt center.
reaction of {Co(μ-N(SiMe3)2)N(SiMe3)2}2 with [NHC-H]Br
imidazolium salts yields (NHC)2CoBr2 compounds.7 However,
it was recently discovered that by using bulky [NHC-H]Cl salts
such as [IMesH]Cl or [SIMesH]Cl [SIMes = 1,3-bis(2,4,6-
trimethylphenyl)-4,5-dihydroimidazolin-2-ylidene], the three-
coordinate mono-NHC species (NHC)CoCl{N(SiMe3)2}
could be isolated (eq 3).8 This route has the advantage that
compounds of NHC ligands that are not stable as free carbenes
may be efficiently synthesized. However, there are limitations to
this route. To obtain the mixed chloride amide (NHC)CoCl-
{N(SiMe3)2} species, the steric environment of the NHC must
be carefully selected to avoid oversubstitution or the formation of
ionic salts.8 The cobalt starting material for this preparation,
{Co(μ-N(SiMe3)2)N(SiMe3)2}2, is somewhat complicated to
prepare and does not store well.9−12 Here we describe the
synthesis of the mixed (NHC)Co amide chloride species
IPrCoCl{N(SiMe3)2} (1) and its utility as a synthetic entry
point to other low-coordinate cobalt species.
INTRODUCTION
■
Cobalt N-heterocyclic carbene (NHC) compounds have found
increasing utility as catalysts for cross coupling,1 alkyne
trimerization,2 alkene hydroarylation,3 and other reactions.4
Additionally, NHC-supported cobalt species have been shown to
activate aryl C−H bonds for further functionalization.5 While in
most of these cases the active cobalt species is generated in situ
and its structure is unknown, it is likely that low-coordinate
cobalt complexes are involved in critical steps of these reactions.
The preparation and characterization of such species is important
to better understand the mechanisms and optimize the
performance of these catalysts.
Several routes to low-coordinate NHC complexes of first-row
late transition metals have been reported. Salt metathesis
reaction of metal halides with alkali-metal alkyl, aryl, and
amido reagents is the most common route of accessing these
iron, cobalt, and nickel species. As a representative example,
{IPrCoCl2}2 [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-
ylidene] reacts with 4 equiv of Mg(CH2SiMe3)Br to afford
IPrCo(CH2SiMe3)2 (eq 1).1g Alternatively, displacement of
weaker ligands or coordination of unsaturated fragments allows
for access to two- and three-coordinate iron, cobalt, and nickel
species. This approach may be illustrated by the displacement of
PPh3 from CoCl(PPh3)3 by 1,3-bis(2,4,6-trimethylphenyl)-
imidazolin-2-ylidene (IMes) to yield (IMes)2CoCl (eq 2).6
Protonolysis of highly basic ligands offers another route of
accessing low-coordinate species. The double amine elimination
RESULTS AND DISCUSSION
■
Synthesis and Structure of 1. The amine elimination
reaction of {Co(μ-N(SiMe3)2)N(SiMe3)2}2 with 2 equiv of
[IPrH]Cl affords 1 (Scheme 1) as a bright-green air-sensitive
Received: November 7, 2014
© XXXX American Chemical Society
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Figure 1. Molecular structure of 1. Hydrogen atoms are omitted.
Selected metrical parameters (Å and deg): Co1−N1 1.9046(16), Co1−
C7 2.055(2), Co1−Cl1 2.2324(6); N1−Co1−C7 133.78(7), N1−
Co1−Cl1 112.94(5), C7−Co1−Cl1 113.27(5).
concomitant contraction of the C7−Co1−Cl1 and N1−Co−Cl1
bond angles. The plane of the NHC ring is almost perpendicular
to the cobalt trigonal plane [angle between planes = 86.60(6)°].
Layfield has noted that the torsion angle between the NHC plane
and the cobalt trigonal plane in related (NHC)Co{N(SiMe3)2}2
compounds can be correlated with the overall bulk of the
combined ligands, with bulkier ligands favoring smaller torsion
angles.13 The presence of a nearly perpendicular torsion angle in
1 is consistent with this observation because a chloride provides
less steric crowding than a second −N(SiMe3)2 ligand. The
amide group is nearly planar at nitrogen, with the slight deviation
from planarity again being attributable to steric crowding with
the NHC ligand. The Si1−N1−Si2 plane is nearly perpendicular
to the cobalt trigonal plane [angle between planes = 88.44(4)°].
Compound 1 exhibits a solution magnetic moment of 5.0(1)
μB as measured by the Evans method. This value is larger than the
predicted spin-only moment for high-spin cobalt(II) in a
trigonal-planar environment (S = 3/2; 3.87 μB) but is comparable
to values for similar compounds. For example, IMesCoCl{N-
(SiMe3)2},8 SIMesCoCl{N(SiMe3)2},8 IPrCo{N(SiMe3)2}2,13
Scheme 1
solid in 60% isolated yield. In our hands, however, this route
proved to be problematic. The {Co(μ-N(SiMe3)2)N(SiMe3)2}2
starting material is time-consuming to prepare, requiring
distillation and subsequent recrystallization,9−12 and the HN-
(SiMe3)2 coproduct from the reaction with [IPrH]Cl is difficult
to remove. The method is viable, but to avoid these issues, we
devised an alternative route to 1, as shown in Scheme 1. The
14
and (nacnac)CoN(SiMe3)2 exhibit solution magnetic mo-
ments of 4.8, 4.9, 4.7, and 4.9 μB, respectively. Other trigonal-
planar three-coordinate cobalt(II) complexes also exhibit μeff
values in this range.12,13 The higher-than-spin-only magnetic
moments in these compounds have been attributed to large zero-
field splitting and g-tensor anisotropy.12,14 In accordance with
the paramagnetic nature of 1, the 1H NMR spectrum is broad and
contains resonances in the range of δ +93 to −45, but this
spectrum is assignable based on peak integrations.
Reaction of 1 with 2,6-Di-tert-butyl-4-methylphenol
(BHT-H) To Yield IPrCoCl(BHT) (2). The reaction of 1 with
BHT-H in Et2O produces 2, which was isolated by crystallization
from Et2O/hexanes in 71% yield as an air-sensitive red powder
(Scheme 2). Compound 2 can also be prepared in 65% yield as a
red microcrystalline solid by the reaction of 2 equiv of Na[BHT]
with {IPrCoCl2}2 in tetrahydrofuran (THF) followed by
crystallization from toluene. However, the product from this
route was consistently contaminated with small amounts of
impurities, one of which was identified by X-ray diffraction as the
green salt [IPrH][Co(BHT)3] (see the Supporting Information,
SI).
1f,g
reaction of 1.98 equiv of NaN(SiMe3)2 with {IPrCoCl2}2 in
Et2O also affords 1 in 93% isolated yield. The use of slightly less
than 2 equiv of NaN(SiMe3)2 is important to avoid challenges
associated with removal of this starting material from the final
product. This route gave a better yield and cleaner product and
was more amenable to producing 1 on a large scale compared to
the amine elimination route. Furthermore, {IPrCoCl2}2 is easier
to prepare than {Co(μ-N(SiMe3)2)N(SiMe3)2}2.9−12 Com-
pound 1 is highly air-sensitive, changing from green to blue
upon exposure to the atmosphere.
Crystals of 1 suitable for X-ray diffraction were obtained by
crystallization from a 1:1 toluene/hexanes solution at −35 °C to
afford 1 as bright-green needles. The solid-state structure of 1 is
shown in Figure 1. The geometry around cobalt is trigonal-
planar, with the sum of the angles being 359.99(7)°. Steric
interactions between the NHC and −N(SiMe3)2 ligands result in
the C7−Co1−N1 angle being opened to 133.78(7)°, with a
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Generation of IPrCoCl(NHDIPP) (4) and Disproportio-
nation to IPrCo(NHDIPP)2 (3) and {IPrCoCl2}2. The reaction
of 1 with 1 equiv of 2,6-diisopropylaniline (NH2DIPP) in
toluene at room temperature over several days generates a
mixture of {IPrCoCl2}2, 3, and a species assigned as 4, along with
unreacted starting materials (Scheme 3). Heating the reaction to
70 °C in toluene-d8 for 36 h results in essentially quantitative
conversion of 1 to {IPrCoCl2}2, 3, and 4, along with
HN(SiMe3)2. Compound 3 was prepared independently as
described below. Interestingly, the reaction of 1 with 1 equiv of
Li[NH(DIPP)] also generates the same mixture of {IPrCoCl2}2,
3, and 4 although much more rapidly, implying that lithium
amide reacts with 1 via net amide exchange rather than the
expected salt metathesis with the Co−Cl group (Scheme 3).
Finally, the reaction of {IPrCoCl2}2 with 2 equiv of Li[NH-
(DIPP)] also generates a mixture of {IPrCoCl2}2, 3, and 4
(Scheme 3), as observed with the aminolysis and amide-
exchange reactions of 1. These results suggest that 4 is formed
initially in these reactions and undergoes disproportionation to
an equilibrium mixture of 4, 3, and {IPrCoCl2}2. The reaction of
{IPrCoCl2}2 with isolated 3 also generates a mixture of
{IPrCoCl2}2, 3, and of 4, confirming that these three species
are in equilibrium in solution. The equilibrium in benzene favors
{IPrCoCl2}2 and 3. The addition of an additional 1 equiv of
Li[NH(DIPP)] to the equilibrium mixture of {IPrCoCl2}2, 3,
and 4 results in complete conversion to 3.
Scheme 2
Slow diffusion of hexanes into a dilute Et2O solution of 2 at
−35 °C afforded X-ray-quality block-shaped red crystals. The
solid-state structure of 2 (Figure 2) is similar to that of 1. The
geometry at cobalt is trigonal-planar with a sum of angles at
cobalt equal to 357.28(9)°. The plane of the NHC ligand is
nearly perpendicular to the Cl−Co1−O1 plane; however, the
cobalt center is displaced 0.23 Å out of the NHC plane toward
the chloride as a result of steric crowding between tBu groups of
the phenoxide ligand and isopropyl groups of the NHC ligand, as
illustrated in Figure 2b,c.
Compound 2 exhibits a solution magnetic moment of 5.1(1)
μB (Evans method). This value is similar that of 1 [5.1(1) μB]. All
nine of the expected 1H NMR resonances for 2 are observed in
the range of δ +110 to −66 and can be assigned based on peak
integrations and a comparison to the spectrum of 1.
Generation of the same mixture of {IPrCoCl2}2, 3, and 4 via
several different routes (Scheme 3) and the ability to convert this
Figure 2. (a) Molecular structure of 2. Hydrogen atoms are omitted. Selected metrical parameters (Å and deg): Co1−C1 2.033(2), Co1−O1
1.8756(14), Co1−Cl1 2.2061(6); O1−Co1−C1 124.71(7), O1−Co1−Cl1 120.53(4), C1−Co1−Cl1 112.04(5). (b) Alternate view of 2 with hydrogen
atoms included. (c) Space-filling view of 2 in the same perspective as part b, illustrating the steric interactions between the iPr and tBu groups.
C
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Scheme 3
mixture entirely to 3 by adding Li[NH(DIPP)] support the
assignment of 4 as the mixed anilide chloride complex. An
analogous compound with a less sterically encumbering NHC
ligand, {SIMesCo(μ-Cl)(NHDIPP)}2, was recently reported
and shown to adopt a dimeric structure with bridging chlorides in
the solid state.15
The observed conversion of 1 to 4 and 3 via reaction with
Li[NH(DIPP)] and NH2DIPP has parallels in iron chemistry.
The iron analogue of 1, IPrFeCl{N(SiMe3)2}, also reacts with
either Li[NHDIPP}] or NH2DIPP to afford IPrFe(NHDIPP)2.8
Similarly, (Cp′)Fe{N(SiMe3)2} (Cp′ = 1,2,4-tBu3C5H2) reacts
with Li[NH(2,4,6-tBu3C6H2)] to yield an equilibrium mixture of
(Cp′)Fe{N(SiMe3)2} and (Cp′)Fe{NH(2,4,6-tBu3C6H2)}.
(Cp′)Fe{N(SiMe3)2} also reacts with p-toluidine to yield
[(Cp′)Fe{NH(4-Me-C6H4)}]2.16 The pKa of HN(SiMe3)2 is
26 in dimethyl sulfoxide (DMSO)17 and 25.8 in THF.18 A pKa
value for NH2DIPP could not be located, but it may reasonably
be approximated to be at least as large as that for NH2Ph, which is
30.6 in DMSO.19 The displacement of [N(SiMe3)2]− by
[NH(DIPP)]− in the cobalt and iron systems can be ascribed
to the greater basicity and nucleophilicity of [NH(DIPP)]−.
While simple acid−base considerations predict that NH2DIPP is
not sufficiently acidic for protonolysis of Co−N(SiMe3)2 or Fe−
N(SiMe3)2 bonds, these compounds do not behave as simple
salts because of the covalency in the M−N(SiMe3)2 bonds.
Synthesis and Characterization of 3. Compound 3 can be
prepared independently by the reaction of {IPrCoCl2}2 with 4
equiv of Li[NH(DIPP)] in THF. Removal of the solvent under
vacuum and extraction into dichloromethane affords 3 as an air-
sensitive dark-violet solid in 94% isolated yield (Scheme 4).
Alternatively, the reaction of 1 with 2 equiv of Li[NH(DIPP)]
generates 3 as the only product (Scheme 4).
Figure 3. Molecular structure of 3. Hydrogen atoms, except the N−H
(H2N) and short-contact CHMe2 (H9) hydrogen atoms, are omitted.
The structure contains half a unique molecule per asymmetric unit. The
NHC ligand diisopropylphenyl group is disordered over two positions,
only one of which is shown. Selected metrical parameters (Å and deg):
Co1−C1 2.061(2), Co1−N2 1.8934(13), Co1−H9 2.235(22), C9−H9
1.00(2); N2−Co1−N2 126.15(8), N2−Co1−C1 116.93(4).
contrast to 1 and 2, however, the Namide−Co−Namide plane is
nearly parallel to the NHC plane [angle between planes =
5.98(7)°]. The reduction of the torsion angle from 90° with
increasing steric demand is in agreement with Layfield’s
observations from (NHC)Co{N(SiMe3)2}2 compounds.13 This
geometry accommodates the bulky anilides by minimizing steric
interactions between the isopropylmethyl groups of the NHC
and anilide ligands. The solid-state structure of 3 also exhibits
short contacts between the cobalt center and two CHMe2
methine hydrogen atoms of the anilide ligand, rendering the
cobalt center pseudo-trigonal-bipyramidal [Co---H = 2.235(22)
Å]. The hydrogen atoms with close contacts were located in the
difference map and refined isotropically. However, the FTIR
spectrum of 3 did not display reduced-frequency C−H stretching
bands that could be conclusively assigned to the agostic Co---H−
C units. A related compound, (IMes′-NDIPP)Co(NHDIPP),
has been prepared and displays similar structural parameters,
including a close Co---H contact.20
Single crystals of 3 were obtained from a concentrated pentane
solution at −35 °C as dark-violet needles. The solid-state
structure of 3 is shown in Figure 3. Like compounds 1 and 2, 3
exhibits a trigonal-planar three-coordinate cobalt core. In
Scheme 4
Compound 3 exhibits a solution magnetic moment of 4.5(1)
μB, as measured by the Evans method in CD2Cl2. A similar value,
4.27 μB, was observed for 3 in the solid state by SQUID
magnetometry (see the SI). The related compound IPrCo-
(CH2SiMe3)2 has the same ligand orientation around the cobalt
center but has a solution magnetic moment of 5.1 μB.1g The low
magnetic moment for 3 may result from the short Co---H
contacts. Other high-spin cobalt(II) species in pseudo-trigonal-
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bipyramidal geometries have been shown to exhibit similar
magnetic moments.21 At 300 K, the solid-state magnetic moment
of 3 is somewhat lower than the solution value although still
higher than the S = 3/2 spin-only value. The small difference in
the solid-state and solution μeff values may reflect differences in
the strength of the Co---H interactions resulting from packing
forces or solvation. The μeff value determined by variable-
temperature SQUID magnetometry is relatively constant
between 100 and 300 K, indicating that there are no significant
structural changes over this temperature range.
a distorted tetrahedral geometry due to a cobalt−arene
interaction with a mesityl group of the anilide ligand, resulting
in pyramidalization of the cobalt center. The Co−Cipso distance
[2.577(3) Å] is well within the sum of the van der Waals radii
(4.17 Å)22 but is longer than those observed in cobalt η6-arene
complexes (ca. 2.15−2.20 Å).23 Power observed a similar Co−
arene interaction in the cobalt(II) arylamide species {2,6-
23
(2,6-iPr2Ph)2Ph}Co(NHDMP). The Co−Cispo distance in
that case (2.393 Å) is 0.184 Å shorter than that in 5, most likely
because of the lower coordination number, and both distances
are significantly longer than those in cobalt η6-arene complexes.
The pseudo-four-coordinate homoleptic cobalt(II) diamide
species Co(NHDMP)2 and Co{NH-2,6-(2,4,6-iPr2Ph)2Ph}2
also display short Co−arene contacts of 2.56 and 2.61 Å (avg),
respectively, which are comparable to that of pseudo-four-
coordinate 5.24
f
Compound 3 is thermally stable up to 85 °C in solution for
several days before eventually beginning to slowly plate out black
solid. Compound 3 reacts readily with an excess of dry oxygen to
form IPrO, NH2DIPP, and bis(2,6-diisopropyl)azobenzene,
1
as established by H NMR and electrospray ionization mass
spectrometry (ESI-MS).
Synthesis and Structure of IPrCoCl(NHDMP) (5). To
avoid the instability of 4 toward disproportionation, we utilized a
more sterically encumbering anilide ligand. The reaction of 2
equiv of lithium 2,6-dimesitylanilide (Li[NHDMP]) with
{IPrCoCl2}2 in diethyl ether at −35 °C and subsequent warming
afford 5, which was isolated in 78% yield as a dark-purple air-
sensitive solid (Scheme 5). The reaction of 1 with 1 equiv of
Compound 5 exhibits a solution magnetic moment of 3.7(1)
μB, as measured by the Evans method, which is close to the spin-
only value for high-spin cobalt(II) in a tetrahedral environment.
Thus, the low magnetic moment compared to those of 1−3 is
likely a result of pyramidalization of the cobalt center. Magnetic
moments close to the spin-only value were observed in other
pseudotetrahedral neutral NHC cobalt compounds such as
(IMes′-NDipp)Co(NHDipp) [3.9(1) μB],20 (IMes)2CoCl2
[3.9(1) μB],1g {PhB(tBuIm)3}CoCl [3.9(3) μB],25 and {PhB-
(tBuIm)3}CoNHtBu [4.0(3) μB].26
Scheme 5
CONCLUSIONS
■
The three-coordinate (NHC)Co complex 1 is a useful starting
material for the synthesis of other low-coordinate (NHC)Co
species by protonolysis and displacement of the −N(SiMe3)2
group. The protonolysis reaction of 1 with BHT-H results in the
clean formation of three-coordinate species 2. The reaction of 1
with NH2DIPP or 1 equiv of Li[NH(DIPP)] generates 4, which
is unstable toward disproportionation to an equilibrium mixture
of 4, 3, and {IPrCoCl2}2. The reaction of 1 with 2 equiv of
Li[NH(DIPP)] yields 3 as the only product. The reaction of 1
with Li[NHDMP] yields a stabile mixed anilide chloride
complex, 5, which displays a short contact between cobalt and
a flanking aryl ipso-carbon of the terphenylamide in the solid
state, rendering the compound pseudotetrahedral. In contrast to
the instability of 4, the sterics of the bulkier anilide and possible
additional stabilization afforded by arene coordination in 5
stabilize this species against disproportionation to {IPrCoCl2}2
and IPrCo(NHDMP)2. The rigorously three-coordinate com-
pounds 1 and 2 display solution magnetic moments of 5.0(1) and
5.1(1) μB, respectively. Conversely, 3 and 5 display solution
magnetic moments of 4.5(1) and 3.7(1) μB, respectively. The
reduced magnetic moments relative to 1 and 2 are consistent
with the cobalt−ligand interactions observed in the solid state
being maintained in solution.37
Li[NHDMP] gives the same product. Thus, as observed for the
reaction of 1 with Li[NH(DIPP)], net amide exchange instead of
salt metathesis is the favored pathway.
Single crystals of 5 were obtained from a concentrated toluene
solution at −35 °C as dark-purple blocks. The solid-state
structure of 5 is shown in Figure 4. The cobalt center of 5 exhibits
EXPERIMENTAL SECTION
■
General Considerations. Unless noted otherwise, all operations
were performed under a purified nitrogen atmosphere in a standard
MBraun Lab Master 130 drybox or under an argon atmosphere using
high-vacuum and Schlenk techniques. Hexanes, pentane, and toluene
were dried by passage through activated alumina and Q-5 columns
under nitrogen. Q-5 was activated by heating at 200 °C under 5% H2 in a
dinitrogen atmosphere. CH2Cl2 was dried by passage through two
activated alumina columns under nitrogen. THF was distilled from a
dark-purple THF solution of sodium benzophenone ketyl and stored
over 4 Å molecular sieves. Diethyl ether, benzene, and bis(trimethylsilyl)
ether were stirred for 24 h over metallic sodium and filtered under
Figure 4. Molecular structure of 5·2toluene. Solvent and hydrogen
atoms, except the amide N−H (H3N) hydrogen atom, are omitted.
Selected metrical parameters (Å and deg): Co1−C1 2.070(4), Co1−N3
1.901(3), Co1−Cl1 2.2391(12), Co1−C43 2.577(3); N3−Co1−C1
116.85(17), N3−Co1−Cl1 118.61(11), C1−Co1−Cl1 105.82(12).
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nitrogen through a plug of activated alumina. CD2Cl2 and C6D6 were
purchased from Cambridge Isotope Laboratory, degassed, dried over
CaH2, transferred under vacuum, and stored over 4 Å molecular sieves.
Molecular sieves, alumina, silica, and Celite were dried under dynamic
vacuum overnight at 180 °C. Unless noted, chemicals were purchased
from commercial sources and used without further purification. 2,6-
Diisopropylaniline (NH2DIPP) was distilled under vacuum and
lithiated with n-BuLi at −35 °C in pentane. [IPrH]Cl,27 {Co(μ-
N(SiMe3)2)N(SiMe3)2}2,9−12 {IPrCoCl2}2,1f,g Na[BHT],28 and Li-
[NHDMP]29 were prepared by literature methods.
All NMR spectra were recorded using a Bruker DRX-400 or DRX-
500 spectrometer. 1H NMR spectra were referenced to solvent residual
resonances at δ 7.16 for C6D6 and δ 5.32 for CD2Cl2. Solution magnetic
susceptibilities were calculated using the Evans method with bis-
(trimethylsilyl) ether as an internal standard.30 Elemental analyses were
performed by Robertson Microlit Laboratories (Ledgewood, NJ).
Fourier transform infrered (FTIR) spectra were recorded using a
Thermo Nicolet NEXUS 670 spectrometer. Mass spectra were recorded
using an Agilent 6130 Quadrupole LC/MS with electrospray ionization.
IPrCoCl(N(SiMe3)2) (1). Route A. A suspension of {IPrCoCl2}2
(0.500 g, 0.482 mmol, 1 equiv) in 5 mL of Et2O was cooled to −35 °C
and stirred. A solution of NaN(SiMe3)2 (173.0 mg, 0.955 mmol, 1.98
equiv) in 10 mL of Et2O was cooled to −35 °C and added dropwise to
the stirred suspension of {IPrCoCl2}2. The mixture was allowed to warm
to ambient temperature, resulting in dissolution of {IPrCoCl2}2 (<5
min) and a color change from blue to green. A white precipitate formed
within ca. 15 min. The mixture was stirred overnight, filtered through a
fine frit, and evaporated to dryness. The residue was extracted with
toluene and filtered through Celite. The solvent was evaporated under
vacuum to yield 0.5720 g (93% yield) of 1 as a bright-green solid.
Crystals suitable for X-ray diffraction were obtained by cooling a
saturated solution of 1 in 1:1 hexanes/toluene to −35 °C.
Route B. [IPrH]Cl (223.9 mg, 0.527 mmol, 2 equiv) was suspended
in 5 mL of toluene. {Co(μ-N(SiMe3)2)N(SiMe3)2}2 (200 mg, 0.263
mmol, 1 equiv) was dissolved in 3 mL of toluene and added to the stirred
suspension of [IPrH]Cl. [IPrH]Cl rapidly dissolved, and the mixture
darkened from green to green-brown (ca. 10 min). After stirring
overnight, the mixture was filtered through Celite, and the solvent was
removed under vacuum. Washing of the green-brown waxy solid with
hexanes afforded 203.4 mg of 1 (60% yield). 1H NMR (C6D6): δ 93.5
(br s, 2H, CHCH, NHC backbone), 72.4 (br s, 4H, CHMe2), 18.3 (br
s, 12H, CHMe2), −2.3 (br s, 18H, SiMe3), −29.0 (br s, 4H, m-Ar), −29.8
(br s, 2H, p-Ar), −43.4 (br s, 12H, CHMe2). μeff = 5.0(1) μB (C6D6,
Evans Method). Elemental analyses of multiple crystalline samples
returned results consistently low in carbon. Elem anal. Calcd for
C34H54N3Si2ClCo: C, 61.61; H, 8.46; N, 6.53. Found: C, 58.47; H, 8.60;
N, 6.25.
IPrCoCl(BHT) (2). Route A. Separate solutions of compound 1
(359.1 mg, 0.558 mmol, 1 equiv) and BHT-H (129.1 mg, 0.586 mmol,
1.05 equiv) in 5 mL of Et2O were prepared. The solution of 1 was stirred,
and the solution of BHT-H was added dropwise, resulting in a rapid
color change from green to dark red. Some product begins to precipitate
from the reaction mixture within ca. 30 min. The mixture was allowed to
stir for 3 h. The mixture was concentrated to 2 mL, to which 8 mL of
hexanes was added and stored at −35 °C overnight, resulting in the
formation of a red solid. Filtration of the reaction mixture on a fine frit
and washing of the red solid with 3 × 1 mL of cold hexanes yielded 307.6
mg of 2 (78.5% yield) as a red powder. Crystals suitable for X-ray
diffraction were obtained by diffusion of hexanes into a dilute ether
solution at −35 °C over the course of 1 week.
−35 °C overnight to yield a red solid, which was collected on a glass frit
and washed with cold hexanes. Further concentration of the mother
liquor yielded additional product. Total yield from three crops: 80.8 mg
(65% yield). Note: This product was contaminated by small amounts of
impurities, one of which was identified by single-crystal X-ray diffraction
1
as the green salt [IPrH][Co(BHT)3]. See the SI. H NMR (C6D6): δ
110.6 (br s, 4H, CHMe2), 93.4 (br s, 2H), 88.4 (br s, 2H, CHCH
NHC backbone and phenoxide m-Ar), 61.1 (br s, 3H, phenoxide p-Me),
14.8 (br s, 12H, CHMe2), −27.6, −27.7 (two overlapping broad
resonances, 6H total, NHC m-Ar and p-Ar), −37.7 (br s, 12H, CHMe2),
t
−66.1 (br s, 18H, Bu). μeff = 5.1(1) μB (C6D6; Evans method). Elem
anal. Calcd for C42H59N2OClCo: C, 71.83; H, 8.47; N, 3.99. Found: C,
71.74; H, 8.61; N, 3.99.
IPrCo(NHDIPP)2 (3). A solution of {IPrCoCl2}2 (220.0 mg, 0.212
mmol, 1 equiv) in 6 mL of THF was cooled to −35 °C and stirred. A
solution of Li[NH(DIPP)] (155.5 mg, 0.848 mmol, 4 equiv) in 6 mL of
THF was cooled to −35 °C. The solution of Li[NH(DIPP)] was added
dropwise to the stirred solution of {IPrCoCl2}2, and the mixture was
allowed to warm to ambient temperature, resulting in a rapid color
change from blue to dark violet. After stirring overnight, the solvent was
removed, and the residue was extracted with 10 mL of CH2Cl2. The
CH2Cl2 solution was filtered through Celite. Removal of the solvent
under vacuum yielded 319.7 mg (94% yield) of 3 as a dark-violet solid.
Crystals suitable for X-ray diffraction were obtained by cooling a
saturated solution of 3 in pentane.
From 1. Li[NHDIPP] (57.0 mg, 0.311 mmol, 2 equiv) was dissolved
in 3 mL of THF, and the solution was cooled to −35 °C. Compound 1
(100 mg, 0.155 mmol, 1 equiv) was dissolved in 5 mL of THF, and the
solution was cooled to −35 °C. The solution of Li[NH(DIPP)] was
added rapidly to the cold stirred solution of 1. The color changed quickly
from green to brown to dark violet. After stirring overnight, the reaction
mixture was filtered through Celite, and the solvent was removed under
vacuum. Extraction of the residue with dichloromethane and filtration
through Celite to remove a dark solid afforded a dark-violet solution.
The solution was concentrated, layered with bis(trimethylsilyl) ether,
and cooled to −35 °C to afford 57.0 mg (46% yield) of 3 as a dark-violet
solid. 1H NMR (CD2Cl2): δ 57.2 (br s, 4H), 54.2 (br s, 2H), 27.5 (br s,
4H, CHMe2), 6.5 (two overlapping broad resonances, 18H total, 12H,
CHMe2 + 6H), 1.2 (br s, 6H), −5.8, −6.2 (two overlapping broad
resonances, 6H total, m-Ar and p-Ar), −11.7 (br s, 12H, CHMe2), −90.1
(br s, 2H, CHCH NHC backbone). N−H resonances not observed.
1H NMR (C6D6): δ 58.1 (br s, 4H), 54.0 (br s, 2H), 28.0 (br s, 4H), 6.5
(two overlapping broad resonances, 18H total, 12H + 6H), 1.2 (br s,
6H), −5.5, −5.7 (two overlapping broad resonances, 6H total), −11.7
(br s, 12H), −94.9 (br s, 2H). μeff = 4.5(1) μB (CD2Cl2; Evans method).
FTIR (KBr pellet): 3368 cm−1 (N−H stretch). C−H stretches
associated with close Co---H contacts were not conclusively observed.
Elem anal. Calcd for C51H72N4Co: C, 76.56; H, 9.07; N, 7.00. Found: C,
76.32; H, 9.32; N, 6.81.
1
NMR Data for IPrCoCl(NHDIPP) (4). H NMR (C6D6): δ 86.0,
58.8, 9.2, 6.3 4.7, −13.8, −16.9, −112.1.
Reaction of 1 with NH2DIPP. At Ambient Conditions. NH2DIPP
(12.9 μL, 13.8 mg, 0.0777 mmol, 1 equiv) was added via micropipette to
a solution of 1 (50 mg, 0.0777 mmol, 1 equiv) in 5 mL of toluene. The
reaction was stirred for 3 days at ambient conditions, over which time
the color gradually turned from green to brown. A 1 mL aliquot was
filtered through Celite and the solvent removed under vacuum. An
NMR sample was prepared in C6D6, which showed that a mixture of
{IPrCoCl2}2, 3, 4, and unreacted starting materials was present.
At 70 °C. NH2DIPP (3.1 μL, 2.9 mg, 0.0163 mmol, 1.05 equiv) was
added via micropipette to a solution of 1 (10 mg, 0.0155 mmol, 1 equiv)
in ca. 700 μL of toluene-d8 in a J. Young NMR tube. The tube was sealed,
heated in an oil bath at 70 °C, and monitored by 1H NMR. After 36 h,
Route B. A solution of NaBHT (47.9 mg, 0.192 mmol, 2 equiv) in 3
mL of THF was cooled to −35 °C. A solution of {IPrCoCl2}2 (100.0 mg,
0.096 mmol, 1 equiv) in 5 mL of THF was cooled to −35 °C and stirred.
The solution of NaBHT was added dropwise to the stirred solution of
{IPrCoCl2}2, resulting in a color change from blue to brown and finally
dark red (ca. 1 h). The solution was allowed to warm to ambient
temperature and stirred overnight. The reaction mixture was filtered
through a fine frit to remove an off-white solid, and the solvent was
evaporated. The residue was extracted with 15 mL of toluene and filtered
through Celite. The filtrate was concentrated and stored in the freezer at
1
the reaction had essentially gone to completion and the H NMR
spectrum displayed resonances for {IPrCoCl2}2, 3, and 4, as well as
HN(SiMe3)2. The color rapidly changed from green to brown and then
gradually to deep violet during the course of the reaction. After
completion, the volatile materials were vacuum-transferred to a second J.
Young NMR tube and analyzed by 1H NMR, which showed that only
1
HN(SiMe3)2 and trace NH2DIPP were present. H NMR data of 3
F
DOI: 10.1021/ic502670x
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(toluene-d8): δ 58.3, 55.9, 28.0, 6.5 (overlaps with 4), 1.1, −4.7, −10.3,
−95.6. 1H NMR data of 4 (toluene-d8): δ 86.0, 60.1, 59.9 (two
overlapping peaks), 9.2, 6.5 (overlaps with 3), −14.2, −14.3 (two
of ϕ and ω scans to survey an entire sphere of reciprocal space and were
indexed using the APEX2 program suits.31 Data were corrected for
absorption effects using the empirical and multiscan methods, as
implemented in SADABS.32 Space groups were determined based on
systematic absences and intensity statistics. The structures were solved
using Patterson or direct methods and refined by full-matrix least-
squares refinement on F2 using the Bruker SHELXTL (version 6.14)
software package.33 All non-hydrogen atoms were refined anisotropi-
cally, and hydrogen atoms were placed in calculated positions, unless
specified otherwise. For further details on refinement, disorder
modeling, tables with atomic coordinates, and an extensive list of
geometric parameters, see the SI. All figures in the text are drawn at the
50% thermal ellipsoid probability level. Compound 3: Crystallized with
half a unique molecule per asymmetric unit. Short-contact CHMe2
(H9) hydrogen atoms were located in the difference map and refined
isotropically. The anilide N−H hydrogen atoms (H2N) were located in
the difference map, restrained to a typical N−H bond distance (0.88 Å),
and refined isotropically. The 2,6-diisopropylphenyl groups of the NHC
ligand were disordered over two positions, which converged to 55:45
occupancy. Compound 5: Crystallized with two molecules of toluene
per molecule of 5 in the asymmetric unit. The amide N−H hydrogen
atom (H3N) was located in the difference map, restrained to a typical
N−H bond distance (0.88 Å), and allowed to refine isotropically. The
data were restricted to 0.95 Å because of a lack of high-angle diffraction.
This may be a result of crystallization as thin plates or decomposition of
the crystal during data collection. The solution included in CIF was
solved in the Pbca space group (R1 = 4.99%, wR2 = 10.69%, and GOF =
1.140). A suitable solution in the monoclinic space group P21/c with β ≈
90° was able to be obtained but resulted in poorer refinement
parameters (R1 = 5.87%, wR2 = 12.93%, and GOF = 1.214).
[IPrH][Co(BHT)3]: Crystallized with three molecules of toluene and
half a molecule of hexane per asymmetric unit. The identities of the
solvent molecules could be determined; however, they exhibited heavy
disorder and very large thermal ellipsoids. This was treated by
application of the program SQUEEZE,34 as implemented in Platon35
using the “fab” file construct and ABIN command in XL. This construct
allows the use of a solvent density distribution to be added to calculation
of the structure factors rather than modifying the observed intensities
through subtraction of a solvent contribution. The SQUEEZE algorithm
located a void, centered at (0, 0.002, −0.056), with a volume of 2794 Å3
(ca. 32% of the unit cell volume) and an electron count of 581 e−. The
disordered solvent was expected to contain 700 e− of electron density.
This discrepancy may result from the partial occupancy of some of the
sites. Two isopropyl groups from the [IPrH] cation are disordered over
two positions each.
1
overlapping peaks), −17.3, −107.0. H NMR data of {IPrCoCl2}2
(toluene-d8): δ 36.6, 16.1, 4.4, −0.0, −0.6, −1.4. An assigned spectrum
of the reaction mixture is available in the SI.
Reaction of 1 with 1 equiv of Li[NH(DIPP)]. A solution of 1 (50
mg, 0.0777 mmol, 1 equiv) in 5 mL of THF was cooled to −35 °C and
stirred. A solution of Li[NH(DIPP)] (14.2 mg, 0.0777 mmol, 1 equiv)
in 3 mL of THF was cooled to −35 °C and added rapidly to the cold
stirring solution of 1. The color changed quickly from green to brown to
dark violet. After stirring for 3 h, the reaction mixture was filtered
through Celite, and the solvent was removed under vacuum. 1H NMR
analysis of a sample prepared in C6D6 showed that a mixture of
{IPrCoCl2}2, 3, and 4 was present.
Reaction of 3 with {IPrCoCl2}2. A solution of 1 (7.7 mg, 0.0096
mmol, 2 equiv) in 1 mL of C6D6 was added to solid {IPrCoCl2}2 (5.0
mg, 0.0048 mmol, 1 equiv), and the mixture was stirred overnight. The
violet solution was filtered into an NMR tube. A small amount of 4 was
generated and observed in the NMR spectrum, along with 3 and
{IPrCoCl2}2.
Reaction of 3 with Oxygen. Compound 3 (5.0 mg, 0.00625 mmol)
was added to an NMR tube with a J. Young tap and dissolved in 700 μL
of C6D6. The tube was attached to a high-vacuum line, the solution was
frozen, and the headspace was evacuated. The headspace was refilled
with an atmosphere of dry oxygen. The J. Young tap was closed, and the
solution was allowed to thaw. The color rapidly changed from dark violet
to brown, with concomitant disappearance of 3 from the NMR
spectrum. The sample was left at room temperature overnight, and a
dark solid deposited on the walls and bottom of the NMR tube. The
sample was filtered on the benchtop through a glass filter into a clean
NMR tube. The 1H HMR spectrum contained only diamagnetic
compounds, identified as IPrO, NH2DIPP, and bis(2,6-
diisopropylphenyl)azobenzene. The identities of these products were
1
confirmed by a comparison of the H NMR data to the NMR data of
authentic samples and by ESI-MS analysis.
IPrCoCl(NHDMP) (5). A suspension of {IPrCoCl2}2 (200 mg, 0.193
mmol, 1 equiv) in 4 mL of Et2O was cooled to −35 °C and stirred. A
solution of Li[NHDMP] (128.1 mg 0.386 mmol, 2 equiv) in 8 mL of
Et2O was cooled to −35 °C. The solution of Li[NHDMP] was added
dropwise to the stirring suspension of {IPrCoCl2}2 and allowed to warm
to ambient temperature, resulting in a color change from blue to dark
purple. The reaction was allowed to stir overnight. The reaction mixture
was filtered through a fine frit to remove a white solid, and the solvent
was removed under vacuum. The resulting dark-purple residue was
extracted with pentane (ca. 40 mL) and filtered through Celite. Removal
of the solvent under vacuum yielded 240 mg (77% yield) of 5 as a dark-
purple solid. Crystals suitable for X-ray diffraction were obtained by
cooling a concentrated toluene solution to −35 °C.
Magnetic Measurements. Magnetic data were collected using a
Quantum Design MPMS-XL SQUID magnetometer. Measurements for
3 were performed on a polycrystalline sample sealed in a polyethylene
bag under a dinitrogen atmosphere. Direct-current (dc) susceptibility
measurements were collected in the temperature range of 1.8−300 K
under an applied dc field of 1.0 T. dc susceptibility data were corrected
for diamagnetic contributions from the sample holder and for the core
diamagnetism of the sample. The core diamagnetism was estimated to
be −769 × 10−6 emu/mol using Pascal’s constants.36
From 1. 1 (10 mg, 0.015 mmol, 1 equiv) was dissolved in ca. 800 μL of
C6D6 and added to solid Li[NHDMP] (5.2 mg, 0.015 mmol, 1 equiv)
with stirring. The color changed quickly from green to brown to dark
purple. The reaction was stirred overnight. The solution was filtered
through a pipet filter containing Celite into an NMR tube. The NMR
spectrum showed the formation of 5 along with a −N(SiMe3)2
1
resonance at δ 0.12. The H NMR spectrum cannot be assigned with
confidence, but characteristic resonances are reported. 1H NMR
(C6D6): δ 50.6 (br s), 38.7 (br s), 6.8 (br s), 5.7 (br s), 3.5 (br s),
ASSOCIATED CONTENT
■
S
* Supporting Information
−1.8 (br s), −5.3 (br s), −10.3 (br s), −17.8 (br s), −82.4 (br s). μeff
=
1H NMR spectra for 1−3 and 5, the reaction of 1 with NH2DIPP,
dc susceptibility data and fitting for 3, FTIR spectrum of 3, and
CIF files giving crystallographic data for 1−3, 5, and [IPrH]-
[Co(BHT)3]. This material is available free of charge via the
Internet at http://pubs.acs.org.
3.7(1) μB (C6D6; Evans method). Elem anal. Calcd for C34H54N3ClCo:
C, 75.49; H, 7.70; N, 5.18. Found: C, 75.15; H, 7.36; N, 5.02.
Single-Crystal X-ray Diffraction. Crystals were loaded onto a glass
slide in the glovebox and covered with STP oil or fluorolube. Suitable
crystals were selected using stereo and polarizing microscopes under oil
blanketed with a stream of nitrogen, attached to the tip of a glass fiber,
mounted in a stream of cold dry nitrogen at 100(2) K, and centered in
the X-ray beam using a video camera. X-ray diffraction data were
collected on a Bruker D8 VENTURE with PHOTON 100 CMOS
detector system equipped with a microfocus molybdenum-target X-ray
tube (λ = 0.71073 Å). All data were collected at 100(2) K using a routine
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: chansen6@uchicago.edu.
G
DOI: 10.1021/ic502670x
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(16) Walter, M. D.; White, P. S. Inorg. Chem. 2012, 51, 11860.
Author Contributions
(17) Grimm, D. T.; Bartness, J. E. J. Am. Chem. Soc. 1992, 114, 1227.
(18) Fraser, R. R.; Mansour, T. S.; Savard, S. J. Org. Chem. 1985, 50,
3232.
The manuscript was written through contributions of all authors.
All authors have given approval to the final version of the
manuscript.
(19) Bordwell, F. G. Acc. Chem. Res. 1988, 21, 456.
Notes
(20) Zhang, L.; Liu, Y.; Deng, L. J. Am. Chem. Soc. 2014, 136, 15525.
(21) For representative examples, see: (a) Yeung, C.-T.; Sham, K.-C.;
Lee, W.-S.; Wong, W.-T.; Wong, W.-Y.; Kwong, H.-L. Inorg. Chim. Acta
The authors declare no competing financial interest.
†Deceased March 6, 2014.
́
2009, 362, 3267. (b) Champouret, Y. D. M.; Marechal, J.-D.; Chaggar,
R. K.; Fawcett, J.; Singh, K.; Maseras, F.; Solan, G. A. New J. Chem. 2007,
31, 75. (c) Judge, J. S.; Feiff, W. M.; Intille, G. M.; Ballway, P.; Baker, W.
A. J. Inorg. Nucl. Chem. 1967, 29, 1711. (d) Sacconi, L.; Bertini, I. J. Am.
Chem. Soc. 1968, 90, 5443. (e) Tenza, K.; Hanton, M. J.; Slawin, A. M. Z.
ACKNOWLEDGMENTS
■
This work was supported by the National Science Foundation
through Grants CHE-0957816 and CHE-1266281 (to G.L.H.).
The authors thank Prof. Michael D. Hopkins for helpful
discussions and assistance in manuscript preparation, Dr. Ian
Steele and Dr. Alexander Filatov for expert assistance with single-
crystal X-ray diffraction experiments and solutions, and Prof.
John Anderson for assistance in collecting magnetic susceptibility
data.
Organometallics 2009, 28, 4852. (f) Muller, G.; Klinga, M.; Leskela, M.;
̈
̈
Rieger, B. Z. Anorg. Allg. Chem. 2002, 628, 2839.
(22) Alvarez, S. Dalton Trans. 2013, 42, 8617.
(23) For select examples, see: (a) Radonovich, L. J.; Klabunde, K. J.;
Behrens, C. B.; McCollor, D. P.; Anderson, B. B. Inorg. Chem. 1980, 19,
1221. (b) Dai, X.; Kapoor, P.; Warren, T. J. J. Am. Chem. Soc. 2004, 126,
4798. (c) Duga, T. R.; Sun, X.; Rybak-Akimova, E. V.; Olatunji-Oho, O.;
Cundari, T. R.; Holland, P. L. J. Am. Chem. Soc. 2011, 133, 12418.
(d) Lei, H.; Ellis, B. D.; Ni, C.; Granjean, F.; Long, G. J.; Power, P. P.
Inorg. Chem. 2008, 47, 10205. (e) Nguyen, T.; Merrill, W. A.; Ni, C.; Lei,
H.; Fettinger, J. C.; Ellis, B. D.; Long, G. L.; Brynda, M.; Power, P. P.
Angew. Chem., Int. Ed. 2008, 47, 9115. (f) Ni, C.; Fettinger, J. C.; Long,
G. L.; Power, P. P. Inorg. Chem. 2009, 48, 2443. (g) Jones, C.; Schulten,
C.; Rose, R. P.; Stasch, A.; Aldridge, S.; Woodul, W. D.; Murray, K. S.;
Moubaraki, B.; Brynda, M.; La Macchia, G.; Gagliardi, L. Angew. Chem.,
Int. Ed. 2009, 48, 2406.
(24) Bryan, A. M.; Merrill, W. A.; Reiff, W. M.; Fettinger, J. C.; Power,
P. P. Inorg. Chem. 2012, 51, 3366.
(25) Cowley, R. E.; Bontchev, R. P.; Duesler, E. N.; Smith, J. M. Inorg.
Chem. 2006, 24, 9771.
(26) Cowley, R. E.; Bontchev, R. P.; Sorrell, J.; Sarracino, O.; Feng, Y.;
Wang, H.; Smith, J. M. J. Am. Chem. Soc. 2007, 129, 2424.
(27) Jafarpour, L.; Stevens, E. D.; Nolan, S. P. J. Organomet. Chem.
2000, 606, 49.
(28) Healy, M. D.; Barron, A. R. J. Organomet. Chem. 1990, 381, 165.
(29) Gavenonis, J.; Tilley, T. D. Organometallics 2002, 21, 5549.
(30) Evans, D. F. J. Chem. Soc. 1959, 2003.
REFERENCES
■
(1) (a) Hamaguchi, H.; Uemura, M.; Yasui, H.; Yorimitsu, H.; Oshima,
K. Chem. Lett. 2008, 37, 1178. (b) Xi, Z.; Liu, B.; Lu, C.; Chen, W. Dalton
Trans. 2009, 7008. (c) Hatakeyama, T.; Hashimoto, S.; Ishizuka, K.;
Nakamura, M. J. Am. Chem. Soc. 2009, 131, 11949. (d) Mo, Z.; Li, Y.;
Lee, H. K.; Deng, L. Organometallics 2011, 30, 4687. (e) Song, W.;
Ackermann, L. Angew. Chem., Int. Ed. 2012, 51, 8251. (f) Matsubara, K.;
Sueyasu, T.; Esaki, M.; Kumamoto, A.; Nagao, S.; Yamamoto, H.; Koga,
Y.; Kawata, S.; Matsumoto, T. Eur. J. Inorg. Chem. 2012, 3079.
(g) Przyojski, J. A.; Arman, H. D.; Tonzetich, Z. J. Organometallics 2013,
32, 723. (h) Gao, K.; Yoshikai, N. J. Am. Chem. Soc. 2013, 135, 9279.
(2) (a) Saino, N.; Kogure, D.; Okamoto, S. Org. Lett. 2005, 7, 3065.
(b) Geny, A.; Gaudrel, S.; Slowinski, F.; Amatore, M.; Chouraqui, G.;
Malacria, M.; Aubert, C.; Gandon, V. Adv. Synth. Catal. 2009, 351, 271.
(3) (a) Gao, K.; Yoshikai, N. J. Am. Chem. Soc. 2011, 133, 400.
(b) Ding, Z.; Yoshikai, N. Angew. Chem., Int. Ed. 2013, 52, 8574.
(c) Yamakawa, T.; Yoshikai, N. Chem.Asian J. 2014, 9, 1242.
(4) (a) Cesar, V.; Gade, L. H.; Bellemin-Laponnaz, S. NHC−Cobalt,
Rhodium and Iridium Complexes in Catalysis. In N-Heterocyclic
Carbenes: From Laboratory Curiosities to Efficient Synthetic Tools; Díez-
(31) APEX2, version 2014.9-0; Bruker AXS: Madison, WI, 2014.
(32) SADABS, version 2014/4; Bruker AXS: Madison, WI, 2014.
(33) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(34) van der Sluis, P.; Spek, A. L. Acta Crystallogr. 1990, A46, 194.
(35) Spek, A. L. Acta Crystallogr. 2009, D65, 148.
(36) Bain, G. A.; Berry, J. F. J. Chem. Educ. 2008, 84, 532.
(37) Massard, A.; Braunstein, P.; Danopoulos, A. A.; Choua, S.; Rabu,
P. Organometallics 2015, 10.1021/om501178p.
́
Gonzalez, S., Ed.; Royal Society of Chemistry: Cambridge, U.K., 2011;
Chapter 8, p 228. (b) Gibson, S. E.; Johnstone, C.; Loch, J. A.; Steed, J.
W.; Stevenazzi, A. Organometallics 2003, 22, 5374. (c) Someya, H.;
Ohmiya, H.; Yorimitsu, H.; Oshima, K. Org. Lett. 2007, 99, 1565.
(d) Someya, H.; Ohmiya, H.; Yorimitsu, H.; Oshima, K. Tetrahedron
2007, 63, 8609. (e) Kobayashi, T.; Ohmiya, H.; Yorimitsu, H.; Oshima,
K. J. Am. Chem. Soc. 2008, 130, 11276. (f) Park, S. R.; Findlay, N. J.;
Garnier, J.; Zhou, S.; Spicer, M. D.; Murphy, J. A. Tetrahedron 2009, 65,
10756. (g) Gu, S.; Xu, D.; Chen, W. Dalton Trans. 2011, 40, 1576.
(h) Yu, R. P.; Darmon, J. M.; Milsmann, C.; Margulieux, G. W.; Sieber, S.
C. E.; DeBeer, S.; Chirik, P. J. J. Am. Chem. Soc. 2013, 135, 13168.
(5) Gao, K.; Yoshikai, N. Acc. Chem. Res. 2014, 47, 1208.
(6) Mo, Z.; Chen, D.; Leng, X.; Deng, L. Organometallics 2012, 31,
7040.
NOTE ADDED IN PROOF
After submission of this manuscript, a publication reporting
similar work, including the synthesis of 3 was published.
■
(7) Danopoulos, A. A.; Wright, J. A.; Motherwell, W. B.; Ellwood, S.
Organometallics 2004, 23, 4807.
(8) Danopoulos, A. A.; Braunstein, P.; Stylianides, N.; Wesolek, M.
Organometallics 2011, 30, 6514.
(9) Burger, H.; Wannagat, U. Monatsh. Chem. 1963, 94, 1007.
̈
(10) Andersen, R. A.; Faegri, K.; Green, J. C.; Haaland, A.; Lappert, M.
F.; Leung, W. P.; Rypdal, K. Inorg. Chem. 1988, 27, 1782.
(11) Murray, D.; Power, P. P. Inorg. Chem. 1984, 23, 4584.
(12) Bryan, A. M.; Long, G. J.; Grandjean, F.; Power, P. P. Inorg. Chem.
2013, 52, 12152.
(13) Day, B. M.; Pal, K.; Pugh, T.; Tuck, J.; Layfield, R. A. Inorg. Chem.
2014, 53, 10578.
(14) Panda, A.; Stender, M.; Wright, R. J.; Olmstead, M. M.; Klavins,
P.; Power, P. P. Inorg. Chem. 2002, 41, 3909.
(15) Danopolous, A. A.; Braunstein, P. Dalton Trans. 2013, 42, 7276.
H
DOI: 10.1021/ic502670x
Inorg. Chem. XXXX, XXX, XXX−XXX