Chiral NHC-Iridium Complexes and Their Performance in Enantioselective Intramolecular Hydroamination and Ring-Opening Amination Reactions

Article abstract of DOI:10.1021/acs.organomet.9b00770

A series of chiral N-heterocyclic carbene (NHC)-iridium complexes of general formula [(NHC*)Ir(diene)Cl] bearing TFB (tetrafluorobenzobarrelene), TCB (tetrachlorobenzobarrelene), BB (benzobarrelene), and COD (cyclooctadiene) as diene ligands were synthesized and fully characterized. Chiral NHC ligands used were of the type previously reported from our group, with backbone stereocenters as well as axial chirality present. The cationic NHC-iridium complexes [(NHC*)Ir(diene)][PF₆] were obtained via chloride abstraction from [(NHC*)Ir(diene)Cl] with AgPF₆. X-ray crystallographic data for some of the neutral and cationic complexes were obtained and analyzed. The topographic steric bulk of the chiral NHC ligands was calculated using the SambVca 2.0 program. While attempting to get a single crystal of the unstable (R_a,R_a,S,S)-[(DiPh-2-SICyoctNap)Ir(BB)][PF₆] complex, a decomposition product with an unexpected pincer-type NHC*-diene ligand was obtained. The series of chiral cationic NHC-iridium complexes were either isolated or freshly made and used in the representative enantioselective intramolecular hydroamination of N-benzyl-2,2-diphenylpent-4-en-1 amine to produce methylated pyrrolidine product with varying yields and enantioselectivities. More importantly, the catalyst performance of these chiral cationic NHC-iridium complexes was expanded to the enantioselective ring-opening aminations of oxabicycles, where a highly enantioselective catalyst system was identified. Furthermore, we discovered that using the opposite axial stereochemistry on the NHC ligand completely switched the absolute configuration of the product, again showing high optical purity for the enantiomer of the product.

Full text of DOI:10.1021/acs.organomet.9b00770

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Chiral NHC-Iridium Complexes and Their Performance in
Enantioselective Intramolecular Hydroamination and Ring-Opening
Amination Reactions
́
Pengchao Gao, Daven Foster, Gellert Sipos, Brian W. Skelton, Alexandre N. Sobolev, and Reto Dorta*
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ABSTRACT: A series of chiral N-heterocyclic carbene (NHC)-
iridium complexes of general formula [(NHC*)Ir(diene)Cl] bearing
TFB (tetrafluorobenzobarrelene), TCB (tetrachlorobenzobarre-
lene), BB (benzobarrelene), and COD (cyclooctadiene) as diene
ligands were synthesized and fully characterized. Chiral NHC ligands
used were of the type previously reported from our group, with
backbone stereocenters as well as axial chirality present. The cationic
NHC-iridium complexes [(NHC*)Ir(diene)][PF6] were obtained
via chloride abstraction from [(NHC*)Ir(diene)Cl] with AgPF6. X-
ray crystallographic data for some of the neutral and cationic
complexes were obtained and analyzed. The topographic steric bulk
of the chiral NHC ligands was calculated using the SambVca 2.0
program. While attempting to get a single crystal of the unstable
(Ra,Ra,S,S)-[(DiPh-2-SICyoctNap)Ir(BB)][PF6] complex, a decomposition product with an unexpected pincer-type NHC*-diene
ligand was obtained. The series of chiral cationic NHC-iridium complexes were either isolated or freshly made and used in the
representative enantioselective intramolecular hydroamination of N-benzyl-2,2-diphenylpent-4-en-1 amine to produce methylated
pyrrolidine product with varying yields and enantioselectivities. More importantly, the catalyst performance of these chiral cationic
NHC-iridium complexes was expanded to the enantioselective ring-opening aminations of oxabicycles, where a highly
enantioselective catalyst system was identified. Furthermore, we discovered that using the opposite axial stereochemistry on the
NHC ligand completely switched the absolute configuration of the product, again showing high optical purity for the enantiomer of
the product.
transferred, creating a C2-symmetric environment at the
metal center that confers enantioselectivity in asymmetric
transformations.
1. INTRODUCTION
Metal catalysts featuring chiral, monodentate N-heterocyclic
carbene (NHC) ligands have been extensively investigated
over the past two decades.1 Figure 1 shows the most promising
Our group has contributed to this design by introducing 1-
naphthyl wingtips with appropriately placed alkyl groups (2 or
2,7-substitution) and we have been able to show that such a
ligand structure can achieve excellent enantioselectivities in
palladium-catalyzed applications.4 More recently, we have
applied the same ligand design and described the synthesis of
an unusual, highly unsaturated chiral cationic NHC-iridium
complex of formula [(DiPh-2,7-SICyNap)Ir(COD)]+
(Scheme 1). This complex, when applied as a catalyst in the
enantioselective intramolecular hydroamination of unactivated
aminoalkenes, gave the methylated pyrrolidine product with
excellent reactivity and near perfect enantioselectivity (Scheme
Figure 1. Privileged ligand designs for monodentate chiral NHCs.
approaches to providing NHC ligands (structures A−C) that
can be widely applied and that may become privileged
structures.1−3 One of these structures goes back to an idea
first introduced by Grubbs et al.,3c,d who have placed
stereocenters onto the N-heterocyclic backbone of saturated
NHC structures [Figure 1, middle, normally with R = phenyl
groups on the backbone]. Through steric interactions with
appropriately substituted NHC side chains, chirality is
Received: November 11, 2019
https://dx.doi.org/10.1021/acs.organomet.9b00770
© XXXX American Chemical Society
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Scheme 1. Chiral Cationic NHC-Iridium Complex Showing Excellent Reactivity and Enantioselectivity in the Hydroamination
of Unactivated Aminoolefins
Scheme 2. Preparation of NHC Iridium Complexes
1).5 During our preliminary mechanistic studies, we noticed
that the diene ligand [COD; 1,5-cyclooctadiene] stayed bound
to the metal throughout catalysis.6 In this first report, we also
presented a single example for an asymmetric ring-opening
B
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amination reaction using the same catalyst that gave the
product with rather modest enantioselectivities (ee = 74%),
but underlined the mechanistic similarities between the two
reactions.
2. RESULTS AND DISCUSSION
2.1. Synthesis of [(NHC*)Ir(diene)Cl] (diene = COD,
BB, TCB, and TFB). The precursor NHC salts 1−3·HBF4
were obtained as previously described4c,5,15 and are usually
present as three diastereomers with different axial chirality:
(Ra,Sa,S,S)-isomer, (Sa,Sa,S,S)-isomer, and (Ra,Ra,S,S)-isomer.
As can be seen in Scheme 2, formation of the (Ra,Ra,S,S)-
isomer is heavily favored, with (Ra,Ra,S,S)-3·HBF4 only
showing trace amounts of the other two.
These transition metal catalyzed enantioselective ring-
opening reactions of oxa- and azabicyclic alkenes have
established themselves as powerful methods to access
substituted dihydronaphthalene scaffolds, which are present
in many pharmaceutically relevant molecules and can be
further modified. Pioneering work in this field has been
reported by Lautens and his group over the past two
decades.7,8 They were able to develop a series of rhodium-
catalyzed asymmetric ring-opening reactions between oxabi-
cycles and C/O/N/S-nucleophiles (dialkylzinc reagents,
phenols, amines, thiols, etc.). More recent efforts have shown
that iridium catalysts may also be used in this asymmetric ring-
opening amination of oxabicycles.9−11 What almost all of these
systems have in common is the use of chiral phosphine-based
ligands, with only two reports by Lautens et al. and Shi et al.
pointing toward the relative usefulness of chiral NHC ligands
in this research area (for asymmetric ring-opening arylation
reactions).12
Following our reported procedure,5,15 the [(NHC*)Ir-
(diene)Cl] complexes were synthesized via in situ generation
of the NHC* carbene through reaction with an equimolar
t
amount of BuOK in the presence of the corresponding
[Ir(diene)2Cl] (diene = BB, TCB, and TFB) or [Ir(COD)Cl]2
in a THF solution. The reaction mixture was routinely
analyzed after 8 h via 1H NMR spectroscopy, showing
complete consumption of starting materials. What came as a
big surprise was the fact that the isomer ratio found in the
NHC* salt had changed during complexation to the iridium
precursors with Table 1 giving an overview for all complexes.
Table 1. Diastereomer Ratio of NHC Salts and
a
[(NHC*)Ir(diene)Cl]
The aim of the present work was to study the reactivity and
enantioselectivity profile of our catalyst platform with respect
to the intramolecular hydroamination reaction in order to be
able to hopefully identify useful individual catalysts for the
asymmetric ring-opening amination of oxabicycles. To do that
and to understand our catalyst system in more detail, we
wanted to introduce both electronic and steric variations to the
structure of our previously reported NHC-iridium complex
[(DiPh-2,7-SICyNap)Ir(COD)]+. This was done following
two strategies. First, we slightly modified our chiral NHC
ligand by introducing steric changes on the naphthyl wingtips.
This was achieved by using DiPh-2-SICyoctNap·HBF4 (3·
HBF4), which was previously identified as our best ligand in a
palladium-catalyzed α-arylation reaction,4c and by introducing
DiPh-2-SICyNap·HBF4 (2·HBF4) as a slightly less bulky
member of the same ligand family. Second, we wanted to
electronically (and sterically) modify our catalyst platform via
introduction of suitable COD alternatives. These included the
smaller bite angle BB diene (BB = benzobarrelene) and the
electronically modified TCB (TCB = tetrachlorobarrelene)
and TFB (tetrafluorobarrelene) analogues. It should be noted
here that this last diene framework (TFB) has seen growing
interest in asymmetric iridium catalysis through Hayashi’s and
Nishimura’s recent contributions to the development of chiral
TFB variants.13,14
a
Determined by 1H NMR; percentages for iridium complex are based
on analysis of the crude mixture before purification.
Herein, we disclose the synthesis and full characterization
(including via X-ray crystallography) of a series of chiral NHC
iridium complexes of general formula [(NHC*)Ir(diene)Cl]
(diene = COD, BB, TCB, and TFB) and, where possible, of
their highly unsaturated, cationic congeners [(NHC*)Ir-
(diene)][PF6]. These latter species were then benchmarked
in the enantioselective intramolecular hydroamination of N-
benzyl-2,2-diphenylpent-4-en-1 amine to give the correspond-
ing optically active methylated pyrrolidine. More importantly,
their catalytic utility was tested in the asymmetric ring-opening
amination of oxabicycles, where we were able to access both
enantiomers of the ring-opened products in high yield and high
optical purity when selecting the optimal catalyst and
conditions.
The diastereomer ratio of these complexes can be easily
identified by analyzing the H NMR signals characteristic to
1
the NHC backbone protons of the reaction crude before
purification. In general, the (Ra,Ra,S,S)-isomer remained the
major isomer, especially when the (DiPh-2,7-SICyNap·HBF4)
(1·HBF4) ligand was used. Isomer fidelity was worst for the 2-
substituted ligands 2·HBF4 and 3·HBF4, particularly when
complexed to [Ir(TCB)2Cl] and [Ir(TFB)2Cl], with the
extreme case of [(DiPh-2-SICyNap)Ir(TCB)Cl] (2c) showing
complete reversal of axial chirality to give (Sa,Sa,S,S)-2c as the
major diastereomer. These unexpected problems were
especially unfortunate for ligand 3·HBF4, where its high
diastereomeric purity as a salt {97% (Ra,Ra,S,S)-3·HBF4} was
eroded during deprotonation and subsequent complexation.16
C
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19
1
Figure 2. (a) Simplified top view of 2a. (b) Excerpts from the H NMR spectra of 2a.
1
Table 2. Summary of H NMR Spectroscopy Data of Free Dienes and Dienes of NHC-Iridium Complexes
a
a
“bridge” H’s
2.37(8H)
4.92(2H)
5.46(2H)
5.32(2H)
olefinic H’s
COD
BB
TCB
TFB
5.58(4H)
6.86(4H)
6.93(4H)
6.91(4H)
trans to NHC
trans to Cl
(Ra,Ra,S,S)-1a
(Ra,Ra,S,S)-1b
(Ra,Ra,S,S)-1c
(Ra,Ra,S,S)-1d
(Ra,Ra,S,S)-2a
(Ra,Ra,S,S)-2b
(Sa,Sa,S,S)-2c
(Ra,Ra,S,S)-2d
(Sa,Sa,S,S)-3a
(Ra,Ra,S,S)-3a
(Ra,Ra,S,S)-3b
(Ra,Ra,S,S)-3c
(Ra,Ra,S,S)-3d
1.86−0.84(8H)
4.61
5.23
5.03
1.67−0.85(8H)
4.63
4.61
5.05
1.15−0.43(8H)
1.89−0.87(8H)
4.64
5.23
5.05
3.98
3.38
3.30
3.31
3.99
3.43
2.96
3.34
3.69
4.00
3.45
3.35
3.36
3.96
3.30
3.23
3.25
3.94
3.34
2.79
3.27
3.65
3.94
3.37
3.28
3.29
3.10
2.10
1.99
2.02
3.12
2.15
2.05
2.07
3.21
3.16
2.11
1.98
2.02
2.77
4.08
4.58
4.45
0.48
0.34
0.41
2.36
0.46
0.72
0.36
2.48
2.35
0.37
0.18
0.26
4.08
3.76
4.46
4.12
4.63
4.49
trans to NHC
trans to open site
3.27
(Ra,Ra,S,S)-1a[PF6]
(Ra,Ra,S,S)-2a[PF6]
(Ra,Ra,S,S)-2b[PF6]
(Ra,Ra,S,S)-2d[PF6]
(Sa,Sa,S,S)-3a[PF6]
(Ra,Ra,S,S)-3a[PF6]
1.88−1.17(8H)
1.34−0.78(8H)
4.27
4.64
1.56−0.80(8H)
1.49−0.85(8H)
1.82
1.96
2.34
2.28
2.46
2.06
1.67
1.49
1.49
1.40
1.54
1.55
2.89
2.30
0.64
0.08
2.56
2.39
3.16
2.12
1.98
3.50
3.25
4.13
4.50
a
NMR spectra recorded in CD2Cl2, integration for 1H unless otherwise specified.
Separation of the different diastereomers of our [(NHC*)-
with ligands 2 and 3, showed signs of decomposition during
chromatographic workup, which in these cases had to be
performed in a glovebox. The (Ra,Sa,S,S)-isomer was eluted
first from column chromatography, followed by the (Sa,Sa,S,S)-
isomer and then the (Ra,Ra,S,S)-isomer, making isolation (in
pure form) of the last eluted isomer somewhat easier.
Ir(diene)Cl] complexes was generally accomplished by column
chromatography, with Scheme 2 giving an overview of the
complexes that could be isolated as pure major isomers. It
should be noted that some of these chloro-complexes,
especially the ones with the BB, TCB, and TFB in combination
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2.2. Synthesis of [(NHC*)Ir(diene)][PF6] (diene = COD,
BB, TCB, and TFB). As shown at the bottom of Scheme 2, the
cationic iridium complexes could be obtained in high yields via
chloride abstraction of [(NHC*)Ir(COD)Cl] with AgPF6.17
For all complexes bearing COD as the diene ligands
{(Ra,Ra,S,S)-1a[PF6], (Ra,Ra,S,S)-2a[PF6], (Sa,Sa,S,S)-3a[PF6],
and (Ra,Ra,S,S)-3a[PF6]}, these highly unsaturated compounds
were obtained in high yield and were fully characterized by
NMR spectroscopy and elemental analysis. However, when
performing the chloride abstraction on [(NHC*)Ir(diene)Cl]
compounds that contained dienes with smaller bite angle (BB,
TCB, and TFB), these cationic iridium complexes displayed
limited stability in solution, meaning that appropriately
complete NMR data (13C NMR) could not be obtained.
NHC’s naphthyl wingtips, giving rise to the corresponding
crosspeaks. Together with the fact that the NHC rotation
around the Ir−C bond is impeded, we therefore have a
situation where all four olefinic protons are distinct and where
the proton signals that are experiencing shielding from the π-
electron cloud of the naphthyl move upfield. An analysis of the
clearly bigger upfield shifts seen for BB, TFB, and TCB
compared to COD upon coordination to the metal though
seems less straightforward.
The most diagnostic signal in the 13C NMR spectrum arises
from the carbene carbon, located between δ 204 and 207 ppm,
with complexes incorporating COD showing slightly lower
field signals (δ 211 to 213 ppm). These noticeable differences
seem to be directly related to the smaller bite angles for BB,
TCB, and TFB and not to their electronic characteristics (BB
being similar to COD), probably originating from less optimal
overlap with the metal d orbital involved in binding NHC and
olefin trans to it.
1
Although the H NMR spectra of freshly made (Ra,Ra,S,S)-
1b[PF6], (Ra,Ra,S,S)-1c[PF6], (Ra,Ra,S,S)-1d[PF6], (Ra,Ra,S,S)-
2b[PF6], (Sa,Sa,S,S)-2c[PF6], (Ra,Ra,S,S)-2d[PF6], (Ra,Ra,S,S)-
3b[PF6], (Ra,Ra,S,S)-3c[PF6], and (Ra,Ra,S,S)-3d[PF6] clearly
showed clean formation of the cationic species for all of these,
decomposition signals were generated slowly during further
NMR data acquisition, preventing full characterization for
(Ra,Ra,S,S)-1b[PF6], (Ra,Ra,S,S)-1c[PF6], (Ra,Ra,S,S)-1d[PF6],
(Sa,Sa,S,S)-2c[PF6], (Ra,Ra,S,S)-3b[PF6], (Ra,Ra,S,S)-3c[PF6],
and (Ra,Ra,S,S)-3d[PF6]. In contrast, the cationic, formally 14-
electron complexes (Ra,Ra,S,S)-2b[PF6] and (Ra,Ra,S,S)-
2d[PF6] were stable enough to be fully characterized by
NMR and elemental analysis. In terms of catalytic evaluations
of the complexes (see the “Catalytic Results and Discussion”
section below), the cationic species with BB, TCB, and TFB
diene ligands were freshly generated and used immediately.
2.3. NMR Spectroscopic Analysis of Chiral [(NHC*)Ir-
(diene)Cl] Complexes. In-depth NMR spectroscopic analysis
of our chloride complexes [(NHC)Ir(diene)Cl] was per-
formed next using various 2D NMR data. In all of these neutral
complexes, two distinct sets of aromatic signals belonging to
2.4. NMR Spectroscopic Analysis of Cationic [(NHC*)-
Ir(diene)][PF6] Complexes. When moving from the chloro-
complexes to the cationic, formally 14-electron compounds,
(Ra,Ra,S,S)-1a[PF6], (Ra,Ra,S,S)-2a[PF6], (Ra,Ra,S,S)-2b[PF6],
(Ra,Ra,S,S)-2d[PF6], (Sa,Sa,S,S)-3a[PF6] and (Ra,Ra,S,S)-
1
3a[PF6], the signal patterns in the H NMR spectra become
much simpler. For instance, the two naphthyl side chains
appear as a single set of signals. This suggest that fast rotation
around the NHC−iridium bond is now possible resulting in
equivalent signals for these. For cationic complexes (Ra,Ra,S,S)-
1b[PF6], (Ra,Ra,S,S)-1c[PF6], (Ra,Ra,S,S)-1d[PF6], (Sa,Sa,S,S)-
2c[PF6], (Ra,Ra,S,S)-3b[PF6], (Ra,Ra,S,S)-3c[PF6], and
(Ra,Ra,S,S)-3d[PF6] that showed limited stability and could
not be fully characterized, we observed the same simplification
of the NMR spectrum upon following the salt metathesis
reaction in situ in deuterated DCM. The most significant
change in the 13C NMR spectra was observed for the NHC-
carbene signal, which showed a large upfield shift (Table 3). As
1
one naphthyl wingtip each can be observed in both their H
and 13C NMR spectra, meaning that rotation around the
NHC(C)−Ir bond is inhibited.15,17 Even more convincing
evidence for this comes when looking at the backbone proton
signals of the central N-heterocycle, where two distinct doublet
signals integrating for one proton each are found (J3 = 11.3
Hz).18 As mentioned above, these characteristic signals were
also used to determine the ratio of the three diastereomers (see
Table 1).
Table 3. Summary of NHC-Carbene Chemical Shift in 13C
NMR for [(NHC*)Ir(diene)Cl] and
[(NHC*)Ir(diene)][PF6] Complexes
complexes
δ carbene
Δδ
diene
COD
(Ra,Ra,S,S)-1a
(Ra,Ra,S,S)-1a[PF6]
(Ra,Ra,S,S)-2a
209.0
186.8
212.5
190.3
206.6
195.2
205.4
194.3
211.7
187.6
213.5
191.1
22.2
The stereochemistry of the different diastereomers can
22.2
11.4
11.1
24.1
22.4
COD
BB
(Ra,Ra,S,S)-2a[PF6]
(Ra,Ra,S,S)-2b
(Ra,Ra,S,S)-2b[PF6]
(Ra,Ra,S,S)-2d
(Ra,Ra,S,S)-2d[PF6]
(Sa,Sa,S,S)-3a
(Sa,Sa,S,S)-3a[PF6]
(Ra,Ra,S,S)-3a
1
equally be deduced from the H NMR spectra in DCM-d2 as
shown for [(DiPh-2-SICyNap)Ir(COD)Cl] (2a), where all
three isomers were separated. Characteristic signals corre-
sponding to methylene H atoms of the cyclohexyl groups were
found at low ppm values in isomers where the cyclohexyl and
the corresponding phenyl group of the backbone is in the same
octave of the sphere and where the phenyl group is able to
shield these particular methylene protons (Figure 2).
TFB
COD
COD
(Ra,Ra,S,S)-3a[PF6]
Next, we moved to the assignment of bridge (for BB, TFB,
TCB) and olefinic protons of the diene ligands. The signals of
the olefinic protons for all of these diene ligands significantly
shift upfield when coordinated to iridium (Table 2). One set of
these protons (trans to NHC) is assigned slightly downfield
compared to the other set (trans to Cl). On the grounds of the
electron donor/acceptor properties of NHC versus Cl−
ligands, these values might appear at odds. H NOESY NMR
of (Ra,Ra,S,S)-2a however shows how the olefinic protons trans
to the chloride ligand are placed directly under one of the
a
13C NMR measured in CD2Cl2 at 298 K.
discussed in a previous contribution,15 these unusually large
chemical shift differences are due not only to the fact that we
are moving from a neutral to a cationic complex but also from
a misalignment of the atomic orbitals of the NHC(C) and
metal that is due to the NHC tilt seen in the solid state (see
the “Catalytic Results and Discussion” section below). Further
evidence that this NHC tilt is maintained in solution comes
1
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Figure 3. Solid-state molecular structures of (Ra,Ra,S,S)-1a, (Ra,Ra,S,S)-1b, (Ra,Ra,S,S)-1d, (Ra,Ra,S,S)-2a, and (Ra,Ra,S,S)-2b and corresponding
topographic steric maps (below). Ellipsoids are drawn at the 50% probability level. For clarity, all hydrogen atoms are omitted, and some motifs are
represented as wireframes.
Table 4. Selected Bond Lengths [Å] and Angles [°]
a
b
Ir−Ccarbene
Ir−C101
Ir−C102
Ir−C103
Ir−C104
Ir−Cl
bite angle
tilt angle
(Ra,Ra,S,S)-1a
(Ra,Ra,S,S)-1b
(Ra,Ra,S,S)-1d
(Ra,Ra,S,S)-2a
(Ra,Ra,S,S)-2b
2.053(5)
2.020(7)
2.016(9)
2.039(2)
2.028(7)
2.198(6)
2.212(7)
2.196(9)
2.202(3)
2.196(6)
2.212(6)
2.203 7)
2.215(7)
2.172(3)
2.180(6)
2.121(6)
2.116(8)
2.106(8)
2.129(3)
2.130(6)
2.117(5)
2.142(9)
2.123(8)
2.122(3)
2.3475(15)
2.326(2)
2.3326(18)
2.3576(7)
2.3375(16)
86.83
68.84
69.51
86.44
69.52
175.98
172.70
170.68
174.75
171.10
2.124(6)
a
b
Bite angle is calculated by Ctd1-Ir-Ctd2 (Ctd1 and Ctd2 = centroid of double bond). Tilt angle is calculated by NHC(C)-Ir-Ctd (olefin trans to
NHC).
from looking at the olefinic protons of the dienes in
(Ra,Ra,S,S)-2b[PF6] and (Sa,Sa,S,S)-3a[PF6] {as well as
(Ra,Ra,S,S)-1a[PF6], (Ra,Ra,S,S)-2a[PF6], (Ra,Ra,S,S)-2d[PF6],
and (Ra,Ra,S,S)-3a[PF6]}. The NHC tilt results in a situation
where the corresponding naphthyl group closely approaches
the metal center and the olefin located trans to the NHC. As a
consequence, we note a significant upfield shift of the alkene
proton signals that experience the effect of the aromatic π
system of the tilted naphthyl unit, much the same way as was
seen for the olefinic protons trans to the chloride ligand in our
neutral complexes.
2.5. X-ray Crystallographic Data of Neutral [(NHC)Ir-
(diene)Cl] Complexes. Single crystals suitable for X-ray
diffraction analyses were obtained by slow diffusion of pentane
into a concentrated DCM solution of the complexes at room
temperature. These neutral complexes show square-planar
geometry around the IrI center with a monodentate NHC and
a chloride ligand trans to the diene ligand (Figure 3). As
mentioned above, the new dienes (BB, TFB, and TCB) show
significantly smaller bite angles (68−69°) than COD (86−
87°) (Table 4).
not seem to matter (one cyclohexyl vs two cyclohexyl groups),
whereas the relative orientiation of the naphthyl wingtips does,
where the 2-cycloalkyl substitutions of these naphthyls orient
either toward or away from the metal center. Overall, the
relative flexibility of these NHC structures influence the
outcome of the %VBur measurements and direct conclusions on
the steric profiles of our ligands [DiPh-2,7-SICyNap (1) vs
DiPh-2-SICyNap (2)] are not straightforward.
2.6. X-ray Crystallographic Data of Cationic [(NHC)-
Ir(diene)][PF6] Complexes. Crystals suitable for X-ray
crystallographic analysis of the stable members of these
cationic iridium complexes were obtained by slow diffusion
of diethyl ether into a concentrated DCM solution at room
temperature. The structures of (Ra,Ra,S,S)-[(DiPh-2-
SICyNap)Ir(COD)][PF6] {(Ra,Ra,S,S)-2a[PF6]}, (Ra,Ra,S,S)-
[(DiPh-2-SICyNap)Ir(BB)][PF6] {(Ra,Ra,S,S)-2b[PF6]}, and
(Sa ,Sa ,S,S)-[(DiPh-2-SICyoctNap)Ir(COD)][PF6 ]
{(Sa,Sa,S,S)-3a[PF6]} clearly show that cyclometalation of the
pendant side chains has not occurred, leading to a
pseudosquare planar coordination geometry.21 Instead, an
arene−metal interaction between the iridium center and the
C8/C8a carbon atoms of the naphthyl moiety occurs, which by
doing so brings one of the naphthyl wingtips into close
proximity to the empty coordination site, where the metal then
engages in a bonding interaction with this moiety. The tilt
angles of (Ra,Ra,S,S)-2a[PF6] and (Sa,Sa,S,S)-3a[PF6] which
Topographic steric maps of NHC ligands were calculated by
using the SambVca 2.0 program developed by Cavallo et al.20
For the 5 structures investigated, the calculations result in a %
VBur value of between 35 and 39.3. Interestingly, the
substitution pattern on the naphthyl rings of the NHC does
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Figure 4. Solid-state structures of (Ra,Ra,S,S)-2a[PF6], (Ra,Ra,S,S)-2b[PF6], (Sa,Sa,S,S)-3a[PF6], and (Ra,Ra,S,S)-3b″[PF6]. All hydrogen atoms are
omitted, and cycloalkyl and phenyl groups are represented as wireframes for clarity. Ellipsoids are drawn as 50% probability level. Selected lengths
(Å) and angles (deg) are as follows: For (Ra,Ra,S,S)-2a[PF6], Ir−C1 2.017(6), Ir−C102 2.109(17), Ir−C101 2.066(13), Ir−C104 2.26(2), Ir−
C103 2.267(13), Ir−C58 2.504(8), Ir−C58A 2.456(6); Ir−C1−N2 139.5(5), Ir−C1−N5 111.1(4) bite angle of diene, 85.96, NHC(C)−Ir−
centroid of C103 and C104, 163.34. For (Ra,Ra,S,S)-2b[PF6], Ir−C11 2.007(16), Ir−C101 2.223(13), Ir−C102 2.228 (12), Ir−C103 2.121(14),
Ir−C104 2.087(14), Ir−C120 2.365 (12), Ir−C129 2.421 (14); Ir−C11−N12 112.4(11), Ir−C11−N15 137.4(11), bite angle of diene, 69.14,
NHC(C)−Ir−centroid of C101 and C102, 171.23. For (Sa,Sa,S,S)-3a[PF6], Ir−C11 2.030(15), Ir−C101 2.201(15), Ir−C102 2.216(19), Ir−C103
2.111(13), Ir−C104 2.121(16), Ir−C150 2.457(15), Ir−C159 2.516(14); Ir−C11−N12 145.8(10), Ir−C11−N15 104.0(10), bite angle of diene,
87.64, NHC(C)-Ir-centroid of C101 and C102, 170.67. For (Ra,Ra,S,S)-3b″[PF6], Ir−C1 1.943(6), Ir−O103 2.213(5), Ir−C522 2.236(6), Ir−
C523 2.182(6), Ir−C222 2.14(2), Ir−C223 2.22(1); Ir−C1−N2 120.7(4), Ir−C1−N5 130.9(4), Ir−centroid of C522 and C523, 2.095, Ir−
centroid of C222 and C223, 2.064, C222−C223, 1.42(2), C522−C523, 1.396(9).
Scheme 3. Proposed Reaction Pathway for the Formation of Unusual Crystalline Complex (Ra,Ra,S,S)-3b″[PF6]
contain COD as the diene ligand are 163.34 and 170.85°,
respectively, while (Ra,Ra,S,S)-2b[PF6] which features the BB
diene ligand shows a tilt of 16.3° {C58, C58A in the
crystallographic numbering of (Ra,Ra,S,S)-2a[PF6]; C120,
C129 in the crystallographic numbering of (Ra,Ra,S,S)-
2b[PF6]; C150, C159 in the crystallographic numbering of
(Ra,Ra,S,S)-3a[PF6]}. Obviously, due to the large tilting of the
NHC that essentially renders it a chelating ligand, the %VBur
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values for the NHC of these cationic iridium species are
significantly larger compared to the neutral iridium chloride
complexes, with a space occupation increased on the side of
the arene−iridium interaction.
3. CATALYTIC RESULTS AND DISCUSSION
3.1. Chiral Cationic NHC-Iridium Complexes in
Enantioselective Intramolecular Hydroamination Reac-
tion. Our primary goal in catalysis with the complexes
synthesized above was to expand the utility of the [NHC*Ir-
(diene)][X] catalyst platform to the ring-opening amination of
oxabicycles, where the use of chiral NHC ligands has not been
reported so far. As a first aim though and in order to
understand how these new systems behave in asymmetric
catalysis, we utilized them in the enantioselective intra-
molecular hydroamination. Here, our previous work had
identified (Ra,Ra,S,S)-1a[X] as extremely selective and highly
active catalyst that indeed is difficult to better.5 We chose N-
benzyl-2,2-diphenylpent-4-en-1 amine (4) as a substrate to
access the corresponding methylated pyrrolidine product (5,
Table 5) using either isolated cationic (Ra,Ra,S,S)-1a[PF6],
2.7. The First Iridium Crystal with a Diethyl Ether
Ligand. Chloride abstraction from (Ra,Ra,S,S)-3b with AgPF6
gave rise to the corresponding (Ra,Ra,S,S)-3b[PF6] cation as
1
evidenced by following the reaction with H NMR spectros-
copy in DCM-d2. However, leaving (Ra,Ra,S,S)-3b[PF6] in
solution resulted in slow decomposition of the complex,
preventing characterization by 13C NMR as discussed above.
We nevertheless attempted to obtain single crystals of the
compound by layering diethyl ether onto a concentrated DCM
solution at room temperature. This repeatedly (2 attempts
made) resulted in the formation of red needle-like crystals over
a period of 2 days. X-ray diffraction analysis showed that
indeed (Ra,Ra,S,S)-3b[PF6] had decomposed to give the highly
unusual IrI species 3b″[PF6] (Figure 4, right). Unfortunately,
attempts at obtaining solution spectra (1H NMR) of the
crystalline material in THF-d8 showed complicated signal
patterns that could not be interpreted properly. Nevertheless,
the spectrum confirmed the absence of any hydride signals (see
the Supporting Information).
The crystal structure of 3b″[PF6] shows that the initial
monodentate NHC ligand has been converted to serve as a
pincer-type ligand via what appears to be a double cyclo-
metalation of the pendant cyclooctyl groups of original ligand
3. The square-planar geometry of complex 3b″[PF6] is
completed by coordination of a diethyl ether molecule trans
to the NHC(carbene). Analyzing the structure further reveals a
shortened NHC(C)−Ir distance compared to the other neutral
and cationic complexes described in this paper {for 3b″[PF6],
1.944(6) Å; for 2a[PF6], 2.017(6) Å; for 2b[PF6], 2.007(16)
Å; for 3a[PF6], 2.032(14) Å}. Furthermore, tilting of the NHC
as seen for the other cationic complexes is not present in
3b″[PF6]. The distances from iridium to the olefin of the
cyclooctenyl groups are 2.095(6) and 2.064(15) Å, respec-
tively. The distance of the diethyl ether to the iridium is
2.213(5) Å. Comparison to any other diethyl ether-Ir
complexes is not possible, as the present structure represents
the first example of a crystallographically characterized diethyl
ether complex of iridium. Indeed, rhodium complexes of this
type are also unknown.22 Given the pincer type nature of the
ligand, its overall bulk is significantly increased, resulting in a %
VBur of 76.0 when using SambVca 2.0.
Table 5. Chiral NHC-Iridium Complexes in
Enantioselective Intramolecular Hydroamination
yield
ee
d
entry
1
cat (mol %)
(%) (%)
(Ra,Ra,S,S)-[(DiPh-2,7-SICyNap)Ir(COD)][PF6]
(Ra,Ra,S,S)-1a[PF6]
c
95
>99
(Ra,Ra,S,S)-[(DiPh-2,7-SICyNap)Ir(BB)][PF6]
(Ra,Ra,S,S)-1b[PF6]
a
c
2
88
93
(Ra,Ra,S,S)-[(DiPh-2,7-SICyNap)Ir(TCB)][PF6]
(Ra,Ra,S,S)-1c[PF6]
a
b
3
8
(Ra,Ra,S,S)-[(DiPh-2,7-SICyNap)Ir(TFB)][PF6]
(Ra,Ra,S,S)-1d[PF6]
a
b
4
6
(Ra,Ra,S,S)-[(DiPh-2-SICyNap)Ir(COD)][PF6]
(Ra,Ra,S,S)-2a[PF6]
c
c
5
90
91
82
(Ra,Ra,S,S)-[(DiPh-2-SICyNap)Ir(BB)][PF6]
(Ra,Ra,S,S)-2b[PF6]
a
6
89
(Sa,Sa,S,S)-[(DiPh-2-SICyNap)Ir(TCB)][PF6]
(Sa,Sa,S,S)-2c[PF6]
a
b
7
3
(Ra,Ra,S,S)-[(DiPh-2-SICyNap)Ir(TFB)][PF6]
(Ra,Ra,S,S)-2d[PF6]
a
b
b
b
8
10
26
11
(Ra,Ra,S,S)-[(DiPh-2-SICyoctNap)Ir(COD)][PF6]
(Ra,Ra,S,S)-3a[PF6]
9
(Ra,Ra,S,S)-[(DiPh-2-SICyoctNap)Ir(BB)][PF6]
(Ra,Ra,S,S)-3b[PF6]
a
10
(Ra,Ra,S,S)-[(DiPh-2-SICyoctNap)Ir(TCB)][PF6]
(Ra,Ra,S,S)-3c[PF6]
a
b
11
4
A reaction pathway to this unusual cationic iridium species is
shown in Scheme 3. Chloride abstraction with AgPF6 initially
gives iridium(I) species (Ra,Ra,S,S)-3b[PF6] as evidenced by
1H NMR. Because of the steric bulk of the pendant cyclooctyl
and the pressure exerted by the backbone phenyl groups onto
this moiety in the (Ra,Ra,S,S)-isomer and the fact that a diene
with a small bite angle is present, the first cyclooctyl group
approaches the metal and undergoes the initial cyclometalation
(A to B). A series of events then leads to complete
dehydrogenation/hydrogenation and species 3b′[PF6], which
after a second cyclometalation event would eventually generate
3b″[PF6] in a similar pathway. An indirect proof of such a
mechanism was found when analyzing the reaction solution via
HRMS, where we identified 1,2,3,4-tetrahydro-1,4-ethano-
naphthalene (together with BB and 1,4-dihydro-1,4-ethano-
naphthalene, see the Supporting Information for details).
(Ra,Ra,S,S)-[(DiPh-2-SICyoctNap)Ir(TFB)][PF6]
a
b
12
6
(Ra,Ra,S,S)-3d[PF6]
Using 0.6 M, freshly prepared catalyst. Conversion obtained by 1H
NMR of the reaction crude. Isolated yield. Determined by HPLC.
a
b
c
d
(Ra,Ra,S,S)-2a[PF6] and (Ra,Ra,S,S)-3a[PF6], or freshly pre-
pared cationic iridium complexes (see the Experimental
Section for details).23
For all three NHC* ligands used, we can see a clear
difference in reactivity between iridium catalysts that
incorporate COD and BB as dienes and the ones that feature
electron-poor TFB and TCB. The latter are unable to provide
more than trace amounts of product 5 under our standard
t
reaction conditions (2 mol % catalyst, BuOH, 0.6M, 60 °C).
Between the electronically neutral diene ligands BB and COD,
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we can observe a far smaller difference in both reactivity and
enantioselectivity (entry 1 vs 2; entry 5 vs 6).
Table 6. Optimization of Ring-Opening Reaction
Conditions
When looking at the three different NHC* ligands, we note
a clear tendency that shows that the 2,7-substituted DiPh-2,7-
SICyNap (1) ligand is superior to the 2-substituted derivatives
DiPh-2-SICyNap (2) and DiPh-2-SICyoctNap (3). What is
somewhat surprising is the fact that ligand 3 which in terms of
its structure looks very similar to 2 and is underperforming and
that all (Ra,Ra,S,S)-3a−3d[PF6] are not able to effect the
hydroamination to any significant degree.
Overall, Table 5 shows that the modifications made to
1a[PF6] are not beneficial to the catalyst performance in the
asymmetric hydroamination. This is especially true when we
substitute the original COD ligand with more electron-poor
diene ligands TCB and TFB.
3.2. Chiral NHC-Iridium Cationic Complexes in
Enantioselective Ring-Opening Amination of Oxabi-
cycles. With these first results in hand, we moved to our main
catalytic target reaction and started studying our catalysts in
the asymmetric ring-opening amination of oxabicycles, in
particular 1,4-dihydro-1,4-epoxynaphthalene in combination
with N-methylaniline (and its derivatives). Literature data from
Lautens8 and others10 for known rhodium or iridium systems
indicated that ether solvents are particularly suited as reaction
media. We therefore started our catalyst screen with dioxane as
the solvent. Catalyst loading was set at 2 mol % to evaluate the
catalysts under identical conditions, and our cationic
complexes 1a[PF6]−1d[PF6], 2a[PF6]−2d[PF6], and
3a[PF6]−3d[PF6] were freshly prepared and used immediately
in the reaction. The results (Table 6, entries 1−12) indicated
that all of our catalysts were able to produce product 8a in
reasonably high yield, a result that is in stark contrast to the
hydroamination runs, where TFB- and TCB-containing
catalysts showed negligible reactivity. The highest isolated
yields were recorded with catalysts 1a[PF6] and 3a[PF6]
(87%). The enantioselectivities varied between 54% ee (for
1d[PF6]) and 75% ee (for 2d[PF6], 3a[PF6], and 3d[PF6]).
Overall, we selected (Ra,Ra,S,S)-[(DiPh-2-SICyoctNap)Ir-
(COD)][PF6] {(Ra,Ra,S,S)-3a[PF6]} for further studies as it
combined high reactivity with good enantioselectivity.
a
c
entry
cat.
solvent
T (°C) yield (%)
ee (%)
1
2
3
4
5
6
7
8
(Ra,Ra,S,S)-1a[PF6]
(Ra,Ra,S,S)-1b[PF6]
(Ra,Ra,S,S)-1c[PF6]
(Ra,Ra,S,S)-1d[PF6]
(Ra,Ra,S,S)-2a[PF6]
(Ra,Ra,S,S)-2b[PF6]
(Sa,Sa,S,S)-2c[PF6]
(Ra,Ra,S,S)-2d[PF6]
(Ra,Ra,S,S)-3a[PF6]
(Ra,Ra,S,S)-3b[PF6]
(Ra,Ra,S,S)-3c[PF6]
(Ra,Ra,S,S)-3d[PF6]
(Ra,Ra,S,S)-3a[PF6]
(Ra,Ra,S,S)-3a[PF6]
(Ra,Ra,S,S)-3a[PF6]
(Ra,Ra,S,S)-3a[PF6]
(Ra,Ra,S,S)-3a[PF6]
(Ra,Ra,S,S)-3a[PF6]
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
THF
70
70
70
70
70
70
70
70
70
70
70
70
70
70
70
70
70
70
87
82
79
83
81
64
66
73
87
77
72
68
83
75
78
52
74
87
57
71
60
54
73
73
−32
75
75
65
69
75
71
58
66
72
69
54
9
10
11
12
13
14
15
16
17
18
tol
tBuOH
b
TFT
DME
DMF
19
20
21
22
(Ra,Ra,S,S)-3a[PF6]
(Ra,Ra,S,S)-3a[PF6]
(Ra,Ra,S,S)-3a[PF6]
CH3CN
CH3CN
CH3CN
CH3CN
70
50
rt
93
91
67
89
87
88
91
84
(Ra,Ra,S,S)-3a[PF6]
90
a
b
c
Isolated yield. α,α,α-Trifluorotoluene. Determined by HPLC;
absolute configuration was deduced by comparison with literature
data.8a
was applied in the ring-opening amination reaction, it
outperformed its (Ra,Ra,S,S)-3a[PF6] sibling both in terms of
activity and enantioselectivity (cf. Tables 7 and 8). With
(Sa,Sa,S,S)-3a[PF6], a reaction run at room temperature
resulted in complete conversion and high isolated yield
(94%) with an optical purity of 96% ee. As could be
anticipated given that we have completely switched axial
chirality in this complex, we also produced ent-8 instead of 8.
To get a first idea about the mechanism at play in this
reaction, the ring-opening reaction was carried out in CD3CN
at room temperature with an increased catalyst loading of 4
We then moved to screen a series of commonly used polar
protic and aprotic solvents (entries 13−19) with (Ra,Ra,S,S)-
3a[PF6]. As can be seen from these data, reactions performed
in CH3CN resulted in the best activity and the best
1
enantioselectivity (entry 19). Incidentally, H NMR analysis
of the reaction crude when using CH3CN as a solvent also
showed much cleaner spectra before workup and purification.
We finally proceeded to survey the effect of changing the
temperature on activity and selectivity of the catalytic system
(entries 20−22). These last optimizations indicated that the
best compromise between high activity and high selectivity was
reached at 50−70 °C, whereas higher temperature decreased
the enantioselectivity (entry 22). Rather surprising was the fact
that catalyst (Ra,Ra,S,S)-3a[PF6] was able to generate product
8a even at room temperature in good yield (67%) and
excellent enantioselectivity (91% ee), as literature data suggest
that elevated temperatures are inevitable and need to be used
for these ring-opening transformations to occur.8,10
1
mol % (Ra,Ra,S,S)-3a[PF6] and was monitored via H NMR
spectroscopy. This study revealed that formation of iridium
hydrides as well as liberation of the COD ligand (or its
hydrogenated derivatives) was not observed throughout the
reaction process. Nevertheless and given our faster and cleaner
reaction outcome in acetonitrile, we believe that coordination
of the solvent is occurring, and the proposed reaction pathway
catalyzed by (Ra,Ra,S,S)-3a[PF6] is depicted in Scheme 4. First,
the cationic iridium acetonitrile complex (B) is generated in
situ (as also observed from the immediate color change from
dark red to yellow), followed by its liberation and concomitant
coordination of the oxabicycle to iridium as a chelating moiety
to give five-coordinate intermediate C. This is then followed by
oxidative addition of the C−O bond to give octahedral, six-
coordinated iridium(III) acetonitrile complex D. The oxidative
addition step is also the enantiodetermining step with steric
pressure exerted by the cyclooctyl group of the corresponding
We also proceeded in testing (Sa,Sa,S,S)-3a[PF6] in this
reaction. From previous experiences in our lab, we knew that
this diastereomer of the ligand (opposite axial chirality) is
normally much less selective when used in the same catalytic
transformation.24 To our surprise, when (Sa,Sa,S,S)-3a[PF6]
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Table 7. Substrate Scope with (Ra,Ra,S,S)-3a[PF6]
Scheme 4. Proposed Catalytic Cycle for the Ring-Opening
Amination of Oxabicycle with (Ra,Ra,S,S)-3a[PF6]
a
b
Isolated yield, average of two runs. Determined by HPLC; absolute
configuration was deduced by comparison with the literature (13,25
14,25 15).26
Table 8. Substrate Scope with (Sa,Sa,S,S)-3a[PF6]
iridium-alkoxy species E. Finally, proton transfer and liberation
of the product (R,R-configuration) reforms cationic catalyst B.
A similar reaction pathway catalyzed by (Sa,Sa,S,S)-3a[PF6] is
proposed in Scheme 5. The main difference here is that the
Scheme 5. Proposed Catalytic Cycle for the Ring-Opening
Amination of Oxabicycle with (Sa,Sa,S,S)-3a[PF6]
a
b
Isolated yield, average of two runs. Determined by HPLC; absolute
c
configuration was deduced by comparison with literature data. Using
4 mol % cat.
naphthyl side chain forcing the C−O bond close to it to be
broken (Scheme 4). Subsequent external nucleophilic attack of
the primary or secondary amine from the sterically accessible
side of the double bond (the anti product is the only
diastereomer formed) generates the new carbon−nitrogen
bond and, after reductive elimination, low-valent neutral
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oxidative addition of the C−O bond occurs on the other side
of the oxygen bridge of the substrate, which subsequently gives
the (S,S)-configured product.
5. EXPERIMENTAL SECTION
5.1. General Considerations. All reactions were performed with
standard Schlenk (nitrogen) or glovebox (Innovative Technology,
argon) techniques unless otherwise specified. THF, diethyl ether,
pentane, toluene, DCM, and hexane were purged with argon and
passed through active alumina columns (Innovative Technology,
inert) and stored with activated molecular sieves in argon-filled glove
boxes. CH3CN was distilled from CaH2 under a nitrogen atmosphere
and stored over molecular sieves inside the glovebox. All other
reagents were used as received unless otherwise noted. Deuterated
solvents for NMR analysis were degassed and stored in glove boxes
over activated molecular sieves.
4. CONCLUSION
The main goal of this study was to develop the first chiral
NHC*-metal catalysts that may be used for the asymmetric
ring-opening amination reaction. This intermolecular amina-
tion reaction seems to be mechanistically closely related to our
previously reported results on the intramolecular hydro-
amination reaction catalyzed by {(Ra,Ra,S,S)-1a[PF6]}. In
order to understand possible catalyst design subtleties, we
herein described the utilization of BB, TCB, and TFB as
alternative diene ligands to COD in the generation of iridium
complexes of general formula [(NHC*)Ir(diene)Cl] and
[(NHC*)Ir(diene)][PF6]. Three sterically slightly different
chiral NHC* ligands were also employed for this purpose.
A total of 10 new [(NHC*)Ir(diene)Cl] compounds were
synthesized, and full characterization of most of them included
X-ray crystallographic studies. When attempting to generate
the corresponding cationic [(NHC*)Ir(diene)][PF6] com-
plexes, we discovered that several diene/NHC* combinations
led to relatively unstable cationic structures, while 2b[PF6],
2d[PF6], and 3a[PF6] could be fully characterized, including
X-ray crystallography. The relative instability of these
complexes also led to the isolation of a highly unusual,
pincer-type NHC-diolefin Ir(I) complex 3b″[PF6], with a
coordinated diethyl ether ligand, obtained during attempted
crystallizations of 3b[PF6].
BB,27 TCB,27 TFB,28 [Ir(BB)2Cl],23 [Ir(TCB)2Cl],23 [Ir-
(TFB)2Cl],23 [Ir(COD)Cl]2,29 and [Ir(COE)2Cl]2,30 were prepared
according to literature procedures. NHC salts DiPh-2,7-SICyNap·
HBF4 (1·HBF4),5 DiPh-2-SICyNap·HBF4 (2·HBF4),15 DiPh-2-
SICyoctNap·HBF4 (3·HBF4),4c (Ra,Ra,S,S)-[(DiPh-2,7-SICyNap)Ir-
(COD)Cl] {(Ra,Ra,S,S)-1a},5 (Ra,Ra,S,S)-[(DiPh-2-SICyNap)Ir-
(COD)Cl] {(Ra,Ra,S,S)-2a},15 (Ra,Ra,S,S)-1a[PF6],5 and (Ra,Ra,S,S)-
2a[PF6],15 were synthesized according to the group’s previous
procedures.15 N-Benzyl-2,2-diphenylpent-4-en-1-amine was synthe-
sized according to a literature procedure.31
NMR spectra were recorded with Bruker Avance IIIHD600 or
Bruker Avance IIIHD 500 instruments. Samples were dried for ca. 30
min before recording spectra and can show signals from residual
pentane. Chemical shifts are displayed in ppm. Multiplicities are
abbreviated as the following: singlet (s), doublet (d), triplet (t),
quartet (q), multiplet (m), and broad (b).
Topographic steric maps for NHC ligands for the complexes were
calculated using SambVca 2.0.20 The default parameters in SambVca
2.0 were used: sphere radius 3.5 Å, atom radii 1.17 Å, distance of the
coordination point from the center of the sphere 0, mesh spacing for
numerical integration 0.1 Å, H atoms omitted.
A first assessment of their catalytic performance included
benchmarking these catalysts against 1a[PF6] in the asym-
metric intramolecular hydroamination to give a methylated
pyrrolidine. Results indicated that electron-poor diolefin
ligands (TFB and TCB) completely shut down reactivity of
the catalyst, while BB analogues suffered from an erosion of
enantioselectivity when compared to COD complexes 1a[PF6]
and 2a[PF6]. Somewhat surprisingly, catalysts incorporating
ligand 3 did not show any appreciable activity.
Differences in catalyst activity were much more subtle in the
ring-opening amination of oxabicycles. Here, we identified
3a[PF6] as the best catalyst system. We also discovered that a
simple switch of the axial chirality of the NHC ligand generates
a catalyst that provides the enantiomer of the product.
Catalysts 3a[PF6] show high reactivity as they provide product
8 even at room temperature, a first in this type of chemistry,
and generate the products with high optical purities of up to
96% ee.
On the basis of the catalytic results gathered here for the
intramolecular hydroamination and the ring-opening amina-
tion of oxabicycles, we conclude that a catalyst such as 3a[PF6]
with overall less sterically demanding and more flexible
wingtips on the NHC* ligand (2-cyclooctyl substitution on
the naphthyl) is favored in the asymmetric ring-opening
amination of oxabicycles, while the more rigid, 2,7-dicyclohexyl
substituted naphthyl side chains create an NHC* ligand and a
catalyst ([1a[PF6]) that achieves excellent enantioselectivity
and reactivity in the intramolecular hydroamination reaction.
These differences in catalyst structure and the effects seen here
underline the validity of the overall design of these [(NHC*)-
Ir(diene)][X] species and are stimulating us to expand their
use further. Pertinent results will be reported in due course.
Elemental analyses of samples dried for at least 12 h under high
vacuum were performed at London Metropolitan University (UK) by
Dr. Stephen Boyer.
5.2. General Procedure for the Synthesis of [(NHC*)Ir-
(diene)Cl] Complexes. To a Schlenk tube (20 mL content size) was
added the appropriate NHC salt, [Ir(diene)2Cl] or [Ir(COD)Cl], and
t
THF. After stirring for 5 min, BuOK was added as a solid. The
resulting mixture was stirred at room temperature overnight. The
appropriate amount of silica gel was added to the reaction crude and
reduced to a free-flowing consistency, put on a silica gel column, and
eluted with hexane/diethyl ether to get the [(NHC*)Ir(diene)Cl]
complexes.
5.2.1. Synthesis of (Ra,Ra,S,S)-[(DiPh-2,7-SICyNap)Ir(BB)Cl]
{(Ra,Ra,S,S)-1b}. Following the general procedure, the following
amounts of materials were used: DiPh-2,7-SICyNap·HBF4 (731 mg,
0.821 mmol), [Ir(BB)2Cl] (440 mg, 0.821 mmol), THF (10 mL), and
tBuOK (100 mg, 0.821 mmol). The title compound (Ra,Ra,S,S)-1b
was purified by column chromatography (column size, diameter = 6
cm, height = 40 cm, eluent = hexane/diethyl ether 10/1), and the
relevant fractions were collected. Drying under vacuum gave
(Ra,Ra,S,S)-1b as a yellow solid, which was triturated with additional
pentane before being dried again under high vacuum (428 mg, 0.361
mmol, yield 44%). 1H NMR (500 MHz, CD2Cl2) δ 8.51 (s, 1H), 7.88
(dd, J = 8.5, 6.2 Hz, 2H), 7.82 (dd, J = 8.5, 5.1 Hz, 2H), 7.69 (s, 1H),
7.51−7.47 (m, 2H), 7.43 (dd, J = 8.4, 1.5 Hz, 1H), 7.35 (d, J = 8.6
Hz, 1H), 7.26−7.15 (m, 8H), 7.09 (d, J = 7.0 Hz, 2H), 6.88−6.81 (m,
3H), 6.75−6.71 (m, 1H), 6.02 (backbone of NHC, d, J = 11.2 Hz,
1H), 5.82 (backbone of NHC, J = 11.2 Hz, 1H), 4.61 (bridge of BB, t,
J = 5.6 Hz, 1H), 4.08 (bridge of BB, t, J = 5.9 Hz, 1H), 3.38 (olefinic
proton trans to NHC, BB, t, J = 5.7 Hz, 1H), 3.35−3.24 (olefinic
proton trans to NHC overlapping with another 2 protons of Cy, BB,
m, 3H), 3.15 (m, 2H), 3.05 (m, 1H), 2.96 (m, 1H), 2.30−1.07 [m,
47H (37H expected), olefinic proton trans to Cl buried (ca. 2.1 ppm),
corresponding carbon located at 26.3 ppm in 13C NMR, residual
pentane buried (1.27 ppm)], 0.89 (t, J = 6.8 Hz, 2.5H, pentane), 0.48
(olefinic proton trans to Cl, BB, t, J = 5.3 Hz, 1H), 0.00 (d, J = 12.5
K
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Hz, 1H), −0.25 (d, J = 12.9 Hz, 1H) ppm. 13C NMR (126 MHz,
CD2Cl2) δ 205.17 (NCN), 147.54 and 147.43 (C BB), 147.23,
146.87, 145.28, 144.98, 137.26, 137.07, 132.56, 132.53, 132.01,
131.96, 131.72, 131.06 (from 147.23 to 131.06, C Nap), 129.77,
129.44, 129.39, 129.35, 129.10, 129.06, 128.86, 128.82, 128.17,
126.53, 125.59 (CH, BB), 125.38, 125.29, 125.24, 124.41, 122.04
(CH, BB), 121.94 (CH, BB), 120.13, 75.12, and 74.87 (backbone of
NHC), 66.86 and 65.77 (olefinic carbon trans to NHC, BB), 48.50
and 47.32 (bridge of BB), 47.00, 46.86, 40.54, 39.91, 35.51, 35.45,
35.28, 35.25, 35.10, 34.82 (pentane), 33.63, 33.57, 33.51 (olefinic
carbon trans to Cl, BB), 32.00, 27.81, 27.79, 27.72, 27.60, 27.50,
27.37, 27.08, 26.86, 26.81, 26.71, 26.55, 26.32 (olefinic carbon trans
to Cl, BB), 23.07 (pentane), 14.28 (pentane) ppm. Elemental
Analysis (%) for C71H76ClIrN2: C, 71.96; H, 6.46; N, 2.36. Found: C,
71.82, 71.87; H, 6.47, 6.59; N, 2.46, 2.42.
1H), 3.32 (olefinic proton trans to NHC, TFB, m, 1H), 3.22 (olefinic
proton trans to NHC overlapping with another H of Cy, TFB, m,
2H), 3.14 (m, 2H), 3.00 (m, 3H), 2.28−1.08 [m, 54H (37H
expected), olefinic proton trans to Cl buried (ca. 2.0 ppm),
corresponding carbon located at 23.8 ppm in 13C NMR, residual
pentane (ca. 1.28 ppm), 0.89 (t, J = 6.9 Hz, 2.5H, pentane), 0.41
(olefinic proton trans to Cl, TFB, t, J = 5.3 Hz, 1H), −0.03 (H Cy, d,
J = 12.5 Hz, 1H), −0.27 (H Cy, d, J = 12.7 Hz, 1H) ppm. 13C NMR
(151 MHz, CD2Cl2) δ 204.45 (NCN), 163.75, 147.64 (C Nap),
147.56 (C Nap), 145.25 (C Nap), 145.16 (C Nap), 140.50, 139.34,
138.90, 137.68 (from 140.50 to 137.68, m, CF TFB), 136.98, 136.82,
132.97, 132.22, 132.16, 132.05, 131.93, 131.82, 131.76, 131.30,
130.94, 130.14, 130.02, 129.76, 129.26, 128.94, 128.78, 128.33,
124.55, 120.50, 75.16, and 74.90 (backbone of NHC), 63.82 and
62.36 (olefinic carbon trans to NHC, TFB), 47.03, 46.96, 40.63,
39.91, 39.82, and 38.85 (bridge of TFB), 35.64, 35.56, 35.36, 35.19,
35.10, 34.81 (pentane), 33.56, 33.49, 32.00, 30.81 (olefinic carbon
trans to Cl, TFB), 27.77, 27.73, 27.70, 27.57, 27.49, 27.35, 27.06,
26.78, 26.64, 26.52, 23.75 (olefinic carbon trans to Cl, TFB) ppm,
23.06 (pentane), 14.28 (pentane) ppm. Elemental Analysis (%) for
C71H72ClF4IrN2: C, 67.84; H, 5.77; N, 2.23. Found: C, 67.83, 67.83;
H, 5.85, 5.89; N, 2.26, 2.16.
5.2.2. Synthesis of (Ra,Ra,S,S)-[(DiPh-2,7-SICyNap)Ir(TCB)Cl]
{(Ra,Ra,S,S)-1c}. Following the general procedure, the following
amounts of materials were used: DiPh-2,7-SICyNap·HBF4 (575 mg,
0.646 mmol), [Ir(TCB)2Cl] (524 mg, 0.646 mmol), THF (20 mL),
and tBuOK (79 mg, 0.646 mmol). The title compound (Ra,Ra,S,S)-1c
was purified by column chromatography (column size, diameter = 6
cm, height = 40 cm, eluent = hexane/diethyl ether 10/1), and the
relevant fractions were collected. Drying under vacuum gave
(Ra,Ra,S,S)-1c as a yellow solid, which was triturated with additional
pentane before being dried again under high vacuum (567 mg, 0.297
mmol, yield 46%). 1H NMR (600 MHz, CD2Cl2) δ 8.50 (s, 1H), 7.89
(dd, J = 11.8, 8.5 Hz, 2H), 7.84 (dd, J = 8.5, 5.3 Hz, 2H), 7.67 (s,
1H), 7.51 (dd, J = 8.5, 1.9 Hz, 2H), 7.44 (dd, J = 8.4, 1.6 Hz, 1H),
7.35 (d, J = 8.6 Hz, 1H), 7.28−7.15 (m, 8H), 7.09 (d, J = 7.5 Hz,
2H), 6.04 (backbone of NHC, d, J = 11.3 Hz, 1H), 5.84 (backbone of
NHC, d, J = 11.3 Hz, 1H), 5.23 (bridge of TCB, t, J = 5.7 Hz, 1H),
4.58 (bridge of TCB, t, J = 5.9 Hz, 1H), 3.30 (olefinic proton trans to
NHC, TCB, m, 1H), 3.23 (olefinic proton trans to NHC overlapping
with another H of Cy, TCB, m, 2H), 3.16 (m, 2H), 3.09 (d, J = 13.6
Hz, 1H), 3.06−3.00 (m, 1H), 3.00−2.92 (m, 1H), 2.28−1.08 [m,
58H (37H expected), olefinic proton trans to Cl buried (ca. 2.0 ppm),
corresponding carbon located at 23.3 ppm in 13C NMR, residual
pentane (ca. 1.28 ppm), 0.88 (4H, residual pentane), 0.34 (olefinic
proton trans to Cl, TCB, t, J = 5.3 Hz, 1H), −0.04 (d, J = 12.6 Hz,
1H), −0.27 (d, J = 12.8 Hz, 1H) ppm. 13C NMR (151 MHz, CD2Cl2)
δ 204.14 (NCN), 147.64 (C Nap), 147.57 (C Nap), 145.30 (m, CCl
TCB), 137.01, 136.82, 132.23, 132.18, 132.05, 131.84, 131.77, 130.96,
129.86 (from 137.01 to 129.86, C Nap), 129.57, 129.53, 129.39,
129.36, 129.17, 129.13, 129.00, 128.95, 128.25, 126.34 (from 129.57
to 126.34, CH Nap), 125.64 (C TCB), 125.54 (C TCB), 125.34 (C
TCB), 124.40, 119.94, 75.17, and 74.84 (backbone of NHC), 63.99
and 62.30 (olefinic carbon trans to NHC, TCB), 47.03, 46.94, 45.60,
and 44.39 (bridge of TCB), 40.62, 39.93, 35.74, 35.56, 35.35, 35.21,
35.11, 34.81 (pentane), 33.62, 33.54, 32.00, 30.25 (olefinic carbon
trans to Cl, TCB), 27.83, 27.78, 27.73, 27.58, 27.50, 27.36, 27.05,
26.83, 26.80, 26.65, 26.53, 23.34 (olefinic carbon trans to Cl, TCB),
23.06 (pentane), 14.28 (pentane) ppm. Elemental Analysis (%) for
C71H72Cl5IrN2: C, 64.46; H, 5.49; N, 2.12. Found: C, 64.60, 64.52; H,
5.36, 5.35; N, 2.14, 2.20.
5.2.4. Synthesis of (Ra,Ra,S,S)-[(DiPh-2-SICyNap)Ir(BB)Cl]
{(Ra,Ra,S,S)-2b}. Following the general procedure, the following
amounts of materials were used: DiPh-2-SICyNap·HBF4 (698 mg,
0.961 mmol), [Ir(BB)2Cl] (515 mg, 0.961 mmol), THF (20 mL), and
tBuOK (117 mg, 0.961 mmol). The title compound (Ra,Ra,S,S)-2b
was purified by column chromatography (column size, diameter = 5
cm, height = 40 cm, eluent = hexane/diethyl ether 10/1), and the
relevant fractions were collected. Drying under vacuum gave
(Ra,Ra,S,S)-2b as a yellow solid, which was triturated with additional
pentane before being dried again under high vacuum (647 mg, 0.634
1
mmol, yield 66%). H NMR (500 MHz, CD2Cl2) δ 8.74 (d, J = 8.5
Hz, 1H), 7.96−7.83 (m, 6H), 7.70 (t, J = 7.6 Hz, 1H), 7.60 (t, J = 7.4
Hz, 1H), 7.55 (d, J = 8.7 Hz, 1H), 7.51 (t, J = 7.5 Hz, 1H), 7.43 (d, J
= 8.7 Hz, 1H), 7.25−7.14 (m, 8H), 7.00 (d, J = 7.2 Hz, 2H), 6.85 (d,
J = 10.6 Hz, 3H), 6.72 (d, J = 6.9 Hz, 1H), 5.97 (backbone of NHC,
d, J = 11.1 Hz, 1H), 5.76 (backbone of NHC, d, J = 11.1 Hz, 1H),
4.63 (bridge of BB, t, J = 5.8 Hz, 1H), 4.08 (bridge of BB, t, J = 5.9
Hz, 1H), 3.42 (olefinic proton trans to NHC, BB, m, 1H), 3.35
(olefinic proton trans to NHC, overlapping with another proton of
Cy, BB, m, 2H), 3.19−3.04 (m, 2H), 3.01 (m, 1H), 2.18−2.07
(olefinic proton trans to Cl, BB, m, 2H, overlay with another proton
of Cy), 1.89−0.95 [m, 30H (15H expected), residual pentane buried
(1.27 ppm)], 0.88 (8H, pentane), 0.46 (olefinic proton trans to Cl,
BB, t, J = 5.4 Hz, 1H), 0.04 (d, J = 12.6 Hz, 1H), −0.30 (d, J = 12.7
Hz, 1H) ppm. 13C NMR (126 MHz, CD2Cl2) δ 206.56 (NCN),
147.62 (C Nap), 147.03 and 146.78 (C BB), 145.51, 137.19, 136.81,
133.33, 133.09, 133.05, 132.98, 131.96, 131.10, 129.73, 129.45,
129.37, 129.26, 129.21, 129.19, 128.37, 128.31, 127.45, 126.50,
125.86, 125.80, 125.73 (from 145.51 to 125.73, CH Nap), 125.48
(CH BB), 125.41 (CH Nap), 122.68 (CH Nap), 122.04 and 122.00
(CH BB), 75.45 and 75.17 (backbone of NHC), 67.64 and 66.28
(olefinic carbon trans to NHC, BB), 48.47 and 47.25 (bridge of BB),
40.51, 39.85, 35.18, 35.00 (pentane), 33.80, 33.51, 33.22 (olefinic
carbon trans to Cl, BB), 32.00, 27.82, 27.47, 26.86 (olefinic carbon
trans to Cl, BB), 26.79, 26.64, 23.06 (pentane), 14.28 (pentane) ppm.
HRMS (ES+ mode; m/z) calcd for [C59H56N2Ir]+ [M − Cl]+
985.4073. Found 985.4070. [C61H59N3Ir]+ [M − Cl + ACN]+
1026.4338. Found 1026.4408.
5.2.3. Synthesis of (Ra,Ra,S,S)-[(DiPh-2,7-SICyNap)Ir(TFB)Cl]
{(Ra,Ra,S,S)-1d}. Following the general procedure, the following
amounts of materials were used: DiPh-2,7-SICyNap·HBF4 (1 g,
1.122 mmol), [Ir(TFB)2Cl] (763.2 mg, 1.122 mmol), THF (20 mL),
t
and BuOK (137 mg, 1.122 mmol). The title compound (Ra,Ra,S,S)-
1d was purified by column chromatography (column size, diameter =
6 cm, height = 40 cm, eluent = hexane/diethyl ether 10/1), and the
relevant fractions were collected. Drying under vacuum gave
(Ra,Ra,S,S)-1d as a yellow solid, which was triturated with additional
pentane before being dried again under high vacuum (588 mg, 0.471
mmol, yield 42%). 1H NMR (600 MHz, CD2Cl2) δ 8.50 (s, 1H), 7.90
(dd, J = 8.5, 5.7 Hz, 2H), 7.84 (dd, J = 8.5, 5.6 Hz, 2H), 7.67 (s, 1H),
7.52−7.48 (m, 2H), 7.45 (m, 1H), 7.35 (d, J = 8.5 Hz, 1H), 7.27−
7.15 (m, 8H), 7.09 (d, J = 7.6 Hz, 2H), 6.03 (backbone of NHC, d, J
= 11.3 Hz, 1H), 5.83 (backbone of NHC, d, J = 11.2 Hz, 1H), 5.03
(bridge of TFB, t, J = 5.9 Hz, 1H), 4.45 (bridge of TFB, t, J = 6.0 Hz,
5.2.5. Synthesis of (Sa,Sa,S,S)-[(DiPh-2-SICyNap)Ir(TCB)Cl]
{(Sa,Sa,S,S)-2c}. Following the general procedure, the following
amounts of materials were used: DiPh-2-SICyNap·HBF4 (197 mg,
0.271 mmol), [Ir(TCB)2Cl] (200 mg, 0.246 mmol), THF (20 mL),
and tBuOK (33 mg, 0.271 mmol). The title compound (Sa,Sa,S,S)-2c
was purified by column chromatography (column size, diameter = 5
cm, height = 40 cm, eluent = hexane/diethyl ether 10/1), and the
relevant fractions were collected. Drying under vacuum gave
(Sa,Sa,S,S)-2c as a yellow solid, which was triturated with additional
pentane before being dried again under high vacuum (114 mg, 0.098
L
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1
mmol, yield 40%). H NMR (600 MHz, CD2Cl2) δ 8.92 (d, J = 8.4
Hz, 1H), 8.21 (d, J = 7.5 Hz, 1H), 7.96 (d, J = 8.6 Hz, 1H), 7.87 (d, J
= 9.5 Hz, 3H), 7.62 (d, J = 7.5 Hz, 2H), 7.58−7.43 (m, 6H), 7.38−
7.23 (m, 5H), 7.10 (d, J = 8.3 Hz, 3H), 5.98 (backbone of NHC, d, J
= 8.6 Hz, 1H), 5.27 (backbone of NHC, d, J = 8.6 Hz, 1H), 4.61
(bridge of TCB, t, J = 5.8 Hz, 1H), 3.78−3.66 (bridge of TCB,
overlapping with a proton of Cy, m, 2H), 3.28 (s, 1H), 2.96 (olefinic
proton trans to NHC, TCB, t, J = 5.8 Hz, 1H), 2.79 (olefinic proton
trans to NHC, TCB, t, J = 5.6 Hz, 1H), 2.59 (m, 1H), 2.14−1.19 [m,
24H (20H excpected), olefinic proton trans to Cl buried (ca. 2.0
ppm), corresponding carbon located at 29.1 ppm in 13C NMR], 0.88
(t, J = 6.9 Hz, 2H, pentane), 0.73 (olefinic proton trans to Cl, TCB, t,
J = 5.3 Hz, 1H) ppm. 13C NMR (151 MHz, CD2Cl2) δ 211.01
(NCN), 145.62 and 145.16 (C TCB), 143.27, 141.27, 138.99, 138.53,
134.50 (from 143.27 to 134.50, C Nap), 133.2 (m, CCl TCB),
129.76, 129.54, 129.39, 129.29, 129.14, 129.02, 128.64, 127.91,
126.78, 126.46, 126.19, 125.64, 125.43, 124.99 (from 129.76 to
124.99, CH Nap), 79.36 and 78.96 (backbone of NHC), 62.60 and
59.65 (olefinic carbon trans to NHC, TCB), 44.55 and 44.45 (bridge
of TCB), 41.61, 39.65, 35.30, 34.72 (pentane), 34.54, 34.11, 32.00,
29.08 and 29.01 (olefinic carbon trans to Cl, TCB), 27.88, 27.59,
27.33, 26.92, 26.78, 26.35, 23.06 (pentane), 22.75, 14.28 (pentane),
14.22 ppm. Elemental Analysis (%) for C59H52Cl5IrN2: C, 61.17; H,
4.52; N, 2.42. Found: C, 61.23, 61.29; H, 4.68, 4.64; N, 2.48, 2.43.
5.2.6. Synthesis of (Ra,Ra,S,S)-[(DiPh-2-SICyNap)Ir(TFB)Cl]
{(Ra,Ra,S,S)-2d}. Following the general procedure, the following
amounts of materials were used: DiPh-2-SICyNap·HBF4 (298 mg,
0.410 mmol), [Ir(TFB)2Cl] (279 mg, 0.410 mmol), THF (20 mL),
and tBuOK (50 mg, 0.410 mmol). The title compound (Ra,Ra,S,S)-2d
was purified by column chromatography (column size, diameter = 5
cm, height = 40 cm, eluent = hexane/diethyl ether 10/1), and the
relevant fractions were collected. Drying under vacuum gave
(Ra,Ra,S,S)-2d as a yellow solid, which was triturated with additional
pentane before being dried again under high vacuum (117 mg, 0.107
additional pentane before being dried again under high vacuum (253
mg, 0.248 mmol, yield 33%). 1H NMR (500 MHz, CD2Cl2) δ 9.13 (d,
J = 8.5 Hz, 1H), 8.50 (d, J = 8.4 Hz, 1H), 7.78 (m, 3H), 7.66 (m,
1H), 7.54−7.48 (m, 3H), 7.48−7.36 (m, 7H), 7.21−7.12 (m, 6H),
5.92 (backbone of NHC, d, J = 9.3 Hz, 1H), 5.47 (backbone of NHC,
d, J = 9.4 Hz, 1H), 3.82 (t, J = 9.5 Hz, 1H), 3.69 (CHCH, trans to
NHC, COD, m, 1H), 3.66 (CHCH, trans to NHC, COD, m, 1H),
3.42 (m, 1H), 3.21 (CHCH, trans to Cl, COD, m, 1H), 2.64 (m,
1H), 2.48 (CHCH, trans to Cl, COD, m, 1H), 2.29 (m, 1H),
2.18−1.47 (m, 30H), 1.27 (m, 4H, with residual pentane), 1.18−1.04
(m, 1H), 0.98 (m, 1H), 0.91−0.67 (m, 7H, with residual pentane),
0.50−0.37 (m, 1H) ppm. 13C NMR (126 MHz, CD2Cl2) δ 211.73
(NCN), 147.22, 144.49, 138.94, 138.75, 133.00, 132.90, 132.74,
132.57, 132.13, 132.07 (from 147.22 to 132.07, C Aryl), 130.25,
129.55, 129.23, 129.18, 128.97, 128.91, 128.88, 128.81, 128.10,
127.93, 127.19, 126.67, 126.51, 126.31, 125.56, 125.31, 125.14,
124.92 (from 130.25 to 124.93, CH Aryl), 84.24 and 82.23 (CH
CH, trans to NHC, COD), 79.46 and 78.39 (backbone of NHC),
55.41 and 52.46 (CHCH, trans to Cl, COD), 41.43, 40.57, 37.92,
37.24, 35.27, 34.97 (pentane), 34.47, 32.00, 31.78, 29.51, 28.19,
28.12, 27.52, 27.48, 27.33, 26.74, 26.67, 26.59, 26.13 (pentane), 14.28
(pentane) ppm. Elemental Analysis (%) for C59H66ClIrN2: C, 68.74;
H, 6.45; N, 2.72. Found: C, 68.51, H, 6.39; N, 2.59.
5.2.8. Synthesis of (Ra,Ra,S,S)-[(DiPh-2-SICyoctNap)Ir(COD)Cl]
{(Ra,Ra,S,S)-3a}. Following the general procedure, the following
amounts of materials were used: DiPh-2-SIoctCyNap·HBF4 (600
mg, 0.767 mmol), [Ir(COD)Cl]2 (252 mg, 0.376 mmol), THF (10
mL), and tBuOK (94 mg, 0.767 mmol). The title compound
(Ra,Ra,S,S)-3a was purified by column chromatography (column size,
diameter = 6 cm, height = 40 cm, eluent = hexane/diethyl ether 10/
1), and the relevant fractions were collected. Drying under vacuum
gave (Ra,Ra,S,S)-3a as a yellow solid, which was triturated with
additional pentane before being dried again under high vacuum (320
mg, 0.308 mmol, yield 41%). 1H NMR (500 MHz, CD2Cl2) δ 9.04 (d,
J = 8.5 Hz, 1H), 8.20 (d, J = 8.5 Hz, 1H), 8.00 (dd, J = 8.2, 1.2 Hz,
1H), 7.93−7.84 (m, 3H), 7.81 (m, 2H), 7.65−7.57 (m, 2H), 7.52 (d,
J = 8.6 Hz, 1H), 7.36 (d, J = 8.7 Hz, 1H), 7.32 (d, J = 6.9 Hz, 2H),
7.29−7.20 (m, 3H), 7.14 (m, 1H), 7.07 (t, J = 7.6 Hz, 2H), 6.85 (d, J
= 7.6 Hz, 2H), 6.06 (backbone of NHC, d, J = 12.1 Hz, 1H), 5.85
(backbone of NHC, d, J = 12.1 Hz, 1H), 4.01 (CHCH, trans to
NHC, COD, m, 1H), 3.98 (CHCH, COD, trans to NHC, m, 1H),
3.63 (m, 1H), 3.20−3.08 (CHCH, trans to Cl overlapping with
another proton of Cy, COD, m, 2H), 2.75−2.66 (m, 1H), 2.34
(CHCH, trans to Cl, COD, m, 1H), 2.22−2.13 (m, 1H), 1.99 (m,
1H), 1.91−0.88 [m, 50H (31H expected), residual pentane], −0.00
(m, 1H), −0.40 (m, 1H) ppm. 13C NMR (126 MHz, CD2Cl2) δ
213.51 (NCN), 149.06, 147.79, 138.11, 134.77, 133.45, 133.35,
133.07, 132.66, 131.50, 130.71 (from 149.06 to 130.71, C Aryl),
129.74, 129.69, 129.65, 129.51, 129.48, 129.43, 129.35, 129.33,
129.11, 128.94, 127.97, 127.43, 127.28, 126.04, 125.85, 125.63,
125.55, 123.83 (from 129.74, to 123.83, CH Aryl), 85.15 and 83.09
(CHCH, trans to NHC, COD), 75.38 and 74.69 (backbone of
NHC), 55.14 and 48.75 (CHCH, trans to Cl, COD), 42.32, 41.46,
34.62 (pentane), 34.51, 34.13, 33.79, 32.22, 32.06, 32.00, 30.27,
28.96, 28.72, 28.32, 28.01, 27.56, 26.96, 26.86, 26.81, 26.44, 25.93,
23.86, 23.06 (pentane), 14.28 (pentane) ppm. Elemental Analysis (%)
for C59H66ClIrN2: C, 68.74; H, 6.45; N, 2.72. Found: C, 68.65, 68.74;
H, 6.39, 6.32; N, 2.73, 2.73.
1
mmol, yield 26%). H NMR (600 MHz, CD2Cl2) δ 8.72 (d, J = 8.4
Hz, 1H), 7.96 (dd, J = 8.3, 5.9 Hz, 2H), 7.92 (d, J = 8.2 Hz, 2H),
7.90−7.84 (m, 2H), 7.73 (t, J = 7.6 Hz, 1H), 7.61 (t, J = 7.4 Hz, 1H),
7.58−7.51 (m, 2H), 7.42 (d, J = 8.6 Hz, 1H), 7.26−7.15 (m, 8H),
7.00 (d, J = 7.4 Hz, 2H), 6.00 (backbone of NHC, d, J = 11.2 Hz,
1H), 5.79 (backbone of NHC, d, J = 11.1 Hz, 1H), 5.05 (bridge of
TFB, t, J = 6.0 Hz, 1H), 4.46 (bridge of TFB, t, J = 6.1 Hz, 1H), 3.34
(olefinic proton trans to NHC, TFB, m, 1H), 3.27 (olefinic proton
trans to NHC overlapping with another proton of Cy, TFB, m, 2H),
3.06 (m, 2H), 2.94 (d, J = 13.5 Hz, 1H), 2.17−2.09 (m, 1H), 2.07
(olefinic proton trans to Cl, TFB, t, J = 5.1 Hz, 1H), 1.90−1.78 (m,
3H), 1.73−1.51 (m, 6H), 1.44−1.01 [m, 11H (5H expected), residual
pentane), 0.89 (t, J = 7.0 Hz, 3H, pentane), 0.36 (olefinic proton trans
to Cl, TFB, t, J = 5.4 Hz, 1H), 0.02 (d, J = 12.5 Hz, 1H), −0.30 (d, J =
12.9 Hz, 1H) ppm. 13C NMR (151 MHz, CD2Cl2) δ 205.44 (NCN),
147.65 and 145.44 (C Nap), 139.48 (m, CF TFB), 136.86, 136.56,
133.32, 133.07, 132.69, 132.65, 131.90, 130.96 (from 136.86 to
130.96, C Nap), 129.93 (m, C TFB), 129.57, 129.50, 129.42, 129.39,
129.32, 129.29, 129.18, 128.38, 128.18, 127.56, 126.56, 125.88,
125.85, 125.38, 122.44, 75.44 and 75.12 (backbone of NHC), 64.42
and 62.67 (olefinic carbon trans to NHC, TFB), 40.59, 39.88 (bridge
of TFB), 39.80, 38.82 (bridge of TFB), 35.27, 35.18 (pentane), 33.73,
33.46, 32.00, 30.59 (olefinic carbon trans to Cl, TFB), 27.80, 27.77,
27.45, 26.75, 26.56, 24.23 (olefinic carbon trans to Cl, TFB), 23.06
(pentane), 14.28 (pentane) ppm. Elemental Analysis (%) for
C59H52ClF4IrN2: C, 64.85; H, 4.80; N, 2.56. Found: C, 65.02,
64.87; H, 4.74, 4.81; N, 2.53, 2.60.
5.2.9. Synthesis of (Ra,Ra,S,S)-[(DiPh-2-SICyoctNap)Ir(BB)Cl]
{(Ra,Ra,S,S)-3b}. Following the general procedure, the following
amounts of materials were used: DiPh-2-SICyoctNap·HBF4 (1486
mg, 1.792 mmol), [Ir(BB)2Cl] (961 mg, 1.792 mmol), THF (20 mL),
5.2.7. Synthesis of (Sa,Sa,S,S)-[(DiPh-2-SICyoctNap)Ir(COD)Cl]
{(Sa,Sa,S,S)-3a}. Following the general procedure, the following
amounts of materials were used: DiPh-2-SIoctCyNap·HBF4 (600
mg, 0.767 mmol), [Ir(COD)Cl]2 (252 mg, 0.376 mmol), THF (10
mL), and tBuOK (94 mg, 0.767 mmol). The title compound
(Sa,Sa,S,S)-3a was purified by column chromatography (column size,
diameter = 6 cm, height = 40 cm, eluent = hexane/diethyl ether 10/
1), and the relevant fractions were collected. Drying under vacuum
gave (Sa,Sa,S,S)-3a as a yellow solid, which was triturated with
t
and BuOK (219 mg, 1.792 mmol). The title compound (Ra,Ra,S,S)-
3b was purified by column chromatography (column size, diameter =
5 cm, height = 40 cm, eluent = hexane/diethyl ether 10/1), and the
relevant fractions were collected. Drying under vacuum gave
(Ra,Ra,S,S)-3b as a yellow solid, which was triturated with additional
pentane before being dried again under high vacuum (493 mg, 0.466
1
mmol, yield 26%). H NMR (600 MHz, CD2Cl2) δ 8.75 (d, J = 8.5
Hz, 1H), 7.94−7.86 (m, 5H), 7.83 (ddd, J = 8.2, 6.7, 1.4 Hz, 1H),
M
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7.67 (ddd, J = 8.3, 6.7, 1.3 Hz, 1H), 7.59 (t, J = 7.9 Hz, 2H), 7.50 (t, J
= 7.4 Hz, 1H), 7.46 (d, J = 8.6 Hz, 1H), 7.25−7.21 (m, 3H), 7.16 (t, J
= 5.0 Hz, 3H), 7.10 (t, J = 7.5 Hz, 2H), 6.89−6.82 (m, 5H), 6.74 (d, J
= 7.0 Hz, 1H), 6.09 (backbone of NHC, d, J = 12.0 Hz, 1H), 5.77
(backbone of NHC, d, J = 12.0 Hz, 1H), 4.64 (bridge of BB, t, J = 5.7
Hz, 1H), 4.12 (bridge of BB, t, J = 5.8 Hz, 1H), 3.55 (m, 1H), 3.45
(olefinic proton trans to NHC, BB, t, J = 5.8 Hz, 1H), 3.36 (olefinic
proton trans to NHC, BB, t, J = 5.8 Hz, 1H), 3.31−3.20 (m, 2H),
2.95 (m, 1H), 2.11 (m, 3H, olefinic proton trans to Cl overlapping
with Cyoct, corresponding carbon located at 27.6 ppm in 13C NMR),
2.04−1.42 [m, 26H (20H expected)], 1.34−1.23 (m, 4H [2H
expected, residual pentane overlap)], 0.89 (t, J = 7.1 Hz, 1H,
pentane), 0.37 (olefinic proton trans to Cl, BB, t, J = 5.3 Hz, 1H),
0.25 (m, 1H), −0.02 to −0.11 (m, 1H) ppm. 13C NMR (151 MHz,
CD2Cl2) δ 207.52 (NCN), 149.51 and 147.57 (C Nap), 147.00 and
146.82 (C BB), 136.99, 135.53, 133.24, 133.03, 132.57, 131.87,
131.76, 131.23 (from 136.99 to 131.23, C Nap), 129.69, 129.42,
129.37 (CH BB), 129.27, 129.22, 129.20, 129.16, 128.97, 128.81,
128.19, 127.41, 126.95, 125.91, 125.81, 125.76, 125.65, 125.49 (CH
BB), 122.73, 122.04 and 122.01 (CH BB), 74.71 and 74.64 (backbone
of NHC), 67.96 and 66.28 (olefinic carbon trans to NHC, BB), 48.59
and 47.31 (bridge of BB), 42.68, 41.78, 35.54, 34.65, 33.30 (olefinic
carbon trans to Cl, BB), 32.37, 32.08, 30.10, 28.97, 28.32, 28.23,
28.07, 27.63, 27.55 (olefinic carbon trans to Cl, BB), 27.06, 26.66,
26.37, 24.79, 24.59 ppm. Elemental Analysis (%) for C63H64ClIrN2:
C, 70.27; H, 5.99; N, 2.60. Found: C, 70.16, 70.19; H, 6.06, 6.13; N,
2.62, 2.65. HRMS (ES+ mode; m/z) calcd for [C63H64N2Ir]+ [M −
Cl]+ 1041.4699. Found 1041.4708. [C65H67N3Ir]+ [M − Cl + ACN]+
1082.4964. Found 1082.5087.
(Ra,Ra,S,S)-3d was purified by column chromatography (column size,
diameter = 5 cm, height = 40 cm, eluent = hexane/diethyl ether 10/1)
and obtained as a yellow solid, which was triturated with additional
pentane before being dried again under high vacuum (37.5 mg,
0.0326 mmol, yield 21%). ((Ra,Sa,S,S)-3d and (Sa,Sa,S,S)-3d were
1
collected as an inseparable mixture with this procedure.) H NMR
(600 MHz, CD2Cl2) δ 8.71 (d, J = 8.5 Hz, 1H), 7.98−7.86 (m, 5H),
7.83 (ddd, J = 8.3, 6.7, 1.3 Hz, 1H), 7.72−7.65 (m, 1H), 7.59 (dd, J =
10.0, 8.0 Hz, 2H), 7.52 (t, J = 7.4 Hz, 1H), 7.45 (d, J = 8.6 Hz, 1H),
7.25−7.21 (m, 3H), 7.19−7.13 (m, 3H), 7.11 (t, J = 7.6 Hz, 2H),
6.85 (d, J = 7.6 Hz, 2H), 6.12 (backbone of NHC, d, J = 12.1 Hz,
1H), 5.79 (backbone of NHC, d, J = 12.1 Hz, 1H), 5.05 (bridge of
TFB, t, J = 5.8 Hz, 1H), 4.49 (bridge of TFB, t, J = 6.1 Hz, 1H),
3.51−3.44 (m, 1H), 3.36 (olefinic proton trans to NHC, TFB, t, J =
5.7 Hz, 1H), 3.29 (olefinic proton trans to NHC, TFB, t, J = 5.7 Hz,
1H), 3.20 (d, J = 11.6 Hz, 2H), 2.91−2.82 (m, 1H), 2.36−0.80 [48H
(25H expected), 2.02, olefinic proton trans to Cl overlaps with Cyoct,
corresponding carbon located at 24.96 ppm in 13C{H} NMR, residual
pentane], 0.29−0.17 (δ 0.26, olefinic proton trans to Cl overlaps with
Cyoct, corresponding carbon located at 30.68 ppm in 13C{H} NMR
m, 2H), −0.07 (t, J = 12.0 Hz, 1H) ppm. 13C{H} NMR (151 MHz,
CD2Cl2) δ 206.54 (NCN), 149.52 and 147.51 (C Nap), 136.67,
135.23, 133.24, 133.05, 132.17, 131.67, 131.52, 131.09 (from 136.67
to 131.09, C Nap), 129.89, 129.54, 129.43, 129.39, 129.28, 129.18,
128.63, 128.25, 127.50, 127.00, 125.88, 125.85, 125.80, 125.77,
122.49, 74.70 and 74.57 (backbone of NHC), 64.72 and 62.67
(olefinic carbon trans to NHC, TFB), 54.20, 54.02, 53.83, 53.66,
53.47, 42.72, 41.86, 39.98 and 38.90 (bridge of TFB), 35.63, 34.82
(pentane), 32.33, 32.12, 32.00, 30.68 (olefinic carbon trans to Cl,
TFB), 30.10, 28.86, 28.26, 28.20, 28.04, 27.62, 27.03, 26.62, 26.29,
24.96 (olefinic carbon trans to Cl, TFB), 24.69, 24.61, 23.06
(pentane), 14.28 (pentane) ppm. HRMS (APCI+ mode; m/z) calcd
for [C63H60N2F4Ir]+ [M − Cl]+ 1113.4322. Found 1113.4381.
[C63H61N2ClF4Ir]+ [M + H]+ 1149.4098. Found 1149.4154.
5.2.10. Synthesis of (Ra,Ra,S,S)-[(DiPh-2-SICyoctNap)Ir(TCB)Cl]
{(Ra,Ra,S,S)-3c}. Following the general procedure, the following
amounts of materials were used: DiPh-2- SICyoctNap·HBF4 (120
mg, 0.153 mmol), [Ir(TCB)2Cl] (124 mg, 0.153 mmol), THF (5
t
mL), and BuOK (18.7 mg, 0.153 mmol). The title compound
(Ra,Ra,S,S)-3c was purified by column chromatography (column size,
diameter = 5 cm, height = 40 cm, eluent = hexane/diethyl ether 10/1)
and obtained as a yellow solid, which was triturated with additional
pentane before being dried again under high vacuum (99 mg, 0.0813
mmol, yield 53%). ((Ra,Sa,S,S)-3c and (Sa,Sa,S,S)-3c were collected as
5.3. Synthesis of (Ra,Ra,S,S)-[(DiPh-2-SICyNap)Ir(BB)][PF6]
{(Ra,Ra,S,S)-2b[PF6]}. To a 20 mL vial equipped with a stir bar was
added (Ra,Ra,S,S)-[(DiPh-2-SICyNap)Ir(BB)Cl] (25 mg, 0.0225
mmol) in DCM (2 mL). Under stirring, a solution of AgPF6 (6.8
mg, 0.0269 mmol) in DCM (2 mL) was added, leading to a color
change from yellow (solution) to deep red (suspension). The mixture
was stirred at room temperature for 1 h in the dark. The precipitated
AgCl was removed by filtration through a Celite/cotton pipet and
washed with additional DCM (1 mL). The filtered solution was
concentrated to about 1 mL before pentane (5 mL) was added to
form a red precipitate, then the vial was dried under high vacuum to
give (Ra,Ra,S,S)-2b[PF6] as a red powder (27 mg, 0.0216 mmol, yield
1
an inseparable mixture with this procedure.) H NMR (500 MHz,
CD2Cl2) δ 8.72 (d, J = 8.5 Hz, 1H), 7.95−7.83 (m, 6H), 7.68 (m,
1H), 7.61−7.59 (m, 2H), 7.51 (t, J = 7.4 Hz, 1H), 7.46 (d, J = 8.7 Hz,
1H), 7.23 (m, 3H), 7.16 (m, 3H), 7.11 (t, J = 7.5 Hz, 2H), 6.86 (d, J
= 7.3 Hz, 2H), 6.13 (backbone of NHC, d, J = 12.1 Hz, 1H), 5.81
(backbone of NHC, d, J = 12.1 Hz, 1H), 5.23 (bridge of TCB, t, J =
5.7 Hz, 1H), 4.63 (bridge of TCB, t, J = 5.9 Hz, 1H), 3.47 (m, 1H),
3.35 (olefinic proton trans to NHC, t, J = 5.6 Hz, 1H), 3.28 (olefinic
proton trans to NHC, t, J = 5.7 Hz, 1H), 3.21−3.19 (m, 2H), 2.94
(m, 1H), 2.22−1.06 [34H (25H expected), 1.98, olefinic proton trans
to Cl, corresponding carbon located at 24.69 ppm in 13C{H} NMR,
m, 34H], 0.89−0.86 (m, 4H, pentane), 0.27−0.20 (m, 1H), 0.18
(olefinic proton trans to Cl, t, J = 5.3 Hz, 1H), −0.06 (m, 1H) ppm.
13C{H} NMR (126 MHz, CD Cl ) δ 206.09, 149.48, 147.59, 145.27,
1
96%). H NMR (600 MHz, CD2Cl2) δ 7.97 (m, 4H), 7.79 (s, 2H),
7.63 (s, 2H), 7.53 (t, J = 7.5 Hz, 2H), 7.37 (m, 8H), 6.85 (m, 2H),
6.76 (m, 2H), 6.21 (s, 2H), 4.27 (bridge proton, BB, t, J = 5.8 Hz,
1H), 4.13 (bridge proton, BB, t, J = 5.7 Hz, 1H), 2.90 (s, 2H), 2.34
(olefinic proton, t, J = 5.7 Hz, 1H), 2.19 (s, 2H), 2.12 (olefinic
proton, t, J = 5.1 Hz, 1H), 1.89 (m, 2H), 1.77−1.05 [m, 24H (15H
expected), one olefinic proton buried here, corresponding carbon
located at 77.2 ppm in 13C NMR, residual pentane], 0.88 (m, 6H,
pentane), 0.64 (olefinic proton, t, J = 5.2 Hz, 1H), 0.47 (s, 2H) ppm.
13C NMR (151 MHz, CD2Cl2) δ 195.22 (NCN), 146.27 (C Nap),
145.72 and 144.12 (C BB), 130.86, 129.98, 129.61, 126.75 (from
130.86 to 126.75, CH Aryl), 126.42 and 126.32 (CH BB), 122.92 and
122.88 (CH BB), 77.18 and 70.91 (olefinic carbon, BB), 47.53 and
47.35 (bridge carbon), 40.92, 38.68 and 37.09 (olefinic carbon, BB),
36.75, 34.53 (pentane), 30.10, 28.21, 26.67, 26.48, 22.74 (pentane),
14.22 (pentane) ppm. Elemental Analysis (%) for C59H56F6IrN2P: C,
62.70, H, 4.99; N, 2.48. Found: C, 62.62, 62.56; H, 5.03, 5.08; N,
2.31, 2.37.
2
2
145.25, 136.68, 135.23, 133.23, 133.06, 132.26, 131.72, 131.51,
131.12, 129.87, 129.53, 129.51, 129.44, 129.40, 129.29, 129.20,
129.18, 128.63, 128.26, 127.51, 126.98, 125.87, 125.84, 125.77,
125.62, 125.56, 122.48, 74.72 and 74.55 (backbone of NHC), 64.83
and 62.63 (olefinic carbon trans to NHC), 54.27, 54.06, 53.84, 53.62,
53.41, 45.69 and 44.43 (bridge of TCB), 42.66, 41.92, 35.46, 35.01
(pentane), 32.39, 32.15, 32.00, 30.20 (olefinic carbon trans to Cl,
28.82, 28.31, 28.26, 28.01, 27.72, 27.01, 26.67, 26.28, 24.69 (olefinic
carbon trans to Cl), 24.64, 23.07 (pentane), 14.29 (pentane) ppm.
HRMS (APCI+ mode; m/z) calcd for [C63H60N2Cl4Ir]+ [M − Cl]+
1177.3140. Found 1177.3164. [C63H61N2Cl5Ir]+ [M + H]+
1215.2877. Found 1215.2841.
5.4. Synthesis of (Ra,Ra,S,S)-[(DiPh-2-SICyNap)Ir (TFB)][PF6]
{(Ra,Ra,S,S)-2d[PF6]}. To a 20 mL vial equipped with a stir bar was
added (Ra,Ra,S,S)-[(DiPh-2-SICyNap)Ir (TFB)Cl] (60 mg, 0.055
mmol) in DCM (2 mL). Under stirring, a solution of AgPF6 (14.5
mg, 0.0575 mmol) in DCM (2 mL) was added, leading to a color
change from yellow (solution) to deep red (suspension). The mixture
5.2.11. Synthesis of (Ra,Ra,S,S)-[(DiPh-2-SICyoctNap)Ir(TFB)Cl]
{(Ra,Ra,S,S)-3d}. Following the general procedure, the following
amounts of materials were used: DiPh-2- SICyoctNap·HBF4 (120
mg, 0.153 mmol), [Ir(TFB)2Cl] (104 mg, 0.153 mmol), THF (5
t
mL), and BuOK (18.7 mg, 0.153 mmol). The title compound
N
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was stirred at room temperature for 1 h in the dark. The precipitated
AgCl was removed by filtration through a Celite/cotton pipet and
washed with additional DCM (1 mL). The filtered solution was
concentrated to about 1 mL before pentane (5 mL) was slowly added
to form a red precipitate, then the vial was dried under high vacuum
to give (Ra,Ra,S,S)-2d[PF6] as a red powder (65 mg, 0.054 mmol,
COD (ca. 1.6 ppm), corresponding carbon located at 95.6 ppm in 13C
NMR, residual pentane], 0.38 (m, 2H) ppm. 13C NMR (151 MHz,
CD2Cl2) δ 191.06 (NCN), 149.73, 134.92, 132.16, 131.87, 131.24,
130.80, 130.62, 130.14, 129.49, 128.21, 127.35, 95.60, and 90.46
(CHCH, COD), 75.12 (backbone of NHC), 59.11 and 58.16
(CHCH, COD), 41.75, 36.26, 34.54 (pentane), 34.18, 33.49,
32.14, 28.63, 28.25, 27.67, 27.59, 26.98, 25.80, 25.48, 22.75
(pentane), 14.22 (pentane) ppm. Elemental Analysis (%) for
C61H72F6IrN2P: C, 62.60; H, 6.20; N, 2.39. Found: C, 62.72, 62.63;
H, 6.23, 6.31; N, 2.40, 2.32.
1
yield 99%). H NMR (500 MHz, CD2Cl2) δ 8.15−7.18 (m, 22H),
6.25 (backbone of NHC, s, 2H), 4.64 (bridge of TFB, t, J = 6.1 Hz,
1H), 4.51 (bridge of TFB, d, J = 6.0 Hz, 1H), 2.88 (s, 2H), 2.28
(olefinic proton, TFB, m, 1H), 2.20 (m, 2H), 1.98 (olefinic proton,
TFB, m, 1H), 1.91−1.03 [m, 20H, 17H expected, 1 olefinic proton
buried (ca. 1.4 ppm), corresponding carbon located at 74.6 ppm in
13C NMR, residual pentane], 0.88 (t, 1H, pentane), 0.47 (m, 2H),
5.7. General Procedure for the Intramolecular Hydro-
amination Reaction. Inside a glovebox, to a vial was added
AgPF6 (4 mg) and DCM (5 mL) to make a 0.8 mg/mL stock
solution. To another 20 mL vial was added the corresponding
[(NHC*)Ir(diene)Cl] complex (0.003 mmol) and DCM (1 mL).
Under stirring, the stock solution of the AgPF6 solution (1 mL) was
slowly added via syringe. The resulting mixture was stirred for 5 min
in the dark at room temperature and filtered through a Celite/cotton
pipet that was washed with additional DCM (1 mL). The filtered
solution was transferred into a pencil-shaped Schlenk tube (20 mL
content size) fitted with a Young valve and a stir bar, and the solution
was taken to dryness under high vacuum. (For catalysts (Ra,Ra,S,S)-
1a[PF6], (Ra,Ra,S,S)-2a[PF6], and (Ra,Ra,S,S)-3a[PF6], 0.003 mmol of
isolated catalyst was added as a solid.) N-Benzyl-2,2-diphenylpent-4-
en-1-amine (5, 0.15 mmol) was added as a solid, followed by addition
0.08 (olefinic proton, BB, s, 1H) ppm. 13C NMR (126 MHz, CD2Cl2)
δ 194.28 (NCN), 146.66 (C Nap), 141.33 (m, CF TFB), 140.03 (m,
CF TFB), 139.38 (m, C TFB), 130.92, 130.56, 130.01, 129.64, 126.91
(from 130.92 to 126.91, CH Aryl), 74.57 and 73.60 (olefinic carbon,
TFB), 40.91 and 40.41 (bridge of TFB), 39.24, 38.93, 36.91, 35.34,
34.53 (pentane), 33.19 (olefinic carbon, TFB), 30.78, 30.09, 28.11,
27.69, 27.28, 26.59, 26.44 (olefinic carbon, TFB), 25.31, 22.75
(pentane), 15.48, 14.22 (pentane) ppm. Elemental Analysis (%) for
C59H52F10IrN2P: C, 58.94; H, 4.36; N, 2.33. Found: C, 58.80, 58.88;
H, 4.42, 4.36; N, 2.23, 2.19.
5.5. Synthesis of (Sa,Sa,S,S)-[(DiPh-2-SICyoctNap)Ir (COD)]-
[PF6] {(Sa,Sa,S,S)-3a[PF6]}. To a 20 mL vial equipped with a stir bar
was added (Sa,Sa,S,S)-[(DiPh-2-SICyoctNap)Ir(COD)Cl] (50 mg,
0.0485 mmol) in DCM (2 mL). Under stirring a solution of AgPF6
(13 mg, 0.051 mmol) in DCM (2 mL) was added, leading to a color
change from yellow (solution) to deep red (suspension). The mixture
was stirred at room temperature for 1 h in the dark. The precipitated
AgCl was removed by filtration through a Celite/cotton pipet and
washed with additional DCM (1 mL). The filtered solution was
concentrated to about 1 mL before pentane (5 mL) was added to
form a red precipitate, then the vial was dried under high vacuum to
give (Sa,Sa,S,S)-3a[PF6] as a red powder (54 mg, 0.0475 mmol, yield
98%). 1H NMR (500 MHz, CD2Cl2) δ 8.03 (d, J = 8.5, 4H), 7.90 (C8
Nap, d, J = 8.1 Hz, 2H), 7.82 (t, J = 8.2, 2H), 7.72 (d, J = 8.7 Hz, 2H),
7.60 (t, J = 8.2 Hz, 2H), 7.42−7.35 (m, 4H), 7.23 (m, 6H), 6.09 (s,
2H), 3.78−3.63 (m, 2H), 3.54−3.46 (CHCH, COD, m, 1H), 2.57
(CHCH, COD, m, 1H), 2.45 (CHCH, COD, m, 1H), 2.40 (m,
2H), 2.35−1.90 [m, 28H (22H expected)], 1.54 (CHCH
overlapping with Cy, COD, m, 3H), 1.39−1.09 (m, 11H, with
residual pentane), 0.92 (t, J = 7.1 Hz, 2H, pentane), 0.83 (m, 1H)
ppm. 13C NMR (126 MHz, CD2Cl2) δ 187.61 (NCN), 146.68 (C
Nap), 134.28, 133.34, 132.05, 131.27, 130.87, 130.51, 129.53, 128.73,
127.96, 127.43, 125.34 (C Aryl), 124.74 (C Aryl), 110.00 (C8 Nap),
93.90 and 89.27 (CHCH, COD), 78.01, 59.64 and 57.41 (CH
CH, COD), 41.55, 37.25, 34.91, 34.54 (pentane), 34.36, 32.82, 30.10,
28.34, 28.24, 27.41, 27.19, 27.18, 27.12, 26.71, 22.75 (pentane), 14.22
(pentane) ppm. Elemental Analysis (%) for C61H72F6IrN2P: C, 62.60;
H, 6.20; N, 2.39. Found: C, 62.41, 62.55; H, 5.85, 5.93; N, 2.35, 2.35.
5.6. Synthesis of (Ra,Ra,S,S)-[(DiPh-2-SICyoctNap)Ir(COD)]-
[PF6] {(Ra,Ra,S,S)-3a[PF6]}. To a 20 mL vial equipped with a stir bar
was added (Ra,Ra,S,S)-[(DiPh-2-SICyoctNap)Ir(BB)Cl] (50 mg,
0.0485 mmol) in DCM (2 mL). Under stirring, a solution of
AgPF6 (13 mg, 0.051 mmol) in DCM (2 mL) was added, leading to a
color change from yellow (solution) to deep red (suspension). The
mixture was stirred at room temperature for 1 h in the dark. The
precipitated AgCl was removed by filtration through a Celite/cotton
pipet and washed with additional DCM (1 mL). The filtered solution
was concentrated to about 1 mL before pentane (5 mL) was added to
form a red precipitate, then the vial was dried under high vacuum to
give (Ra,Ra,S,S)-3a[PF6] as a red powder (54 mg, 0.047 mmol, yield
97%). 1H NMR (600 MHz, CD2Cl2) δ 8.18 (d, J = 8.1 Hz, 2H), 8.08
(d, J = 8.7 Hz, 2H), 8.02 (t, J = 7.5 Hz, 2H), 7.95 (C8 Nap, d, J = 8.1
Hz, 2H), 7.80 (t, J = 7.5 Hz, 2H), 7.61 (d, J = 8.7 Hz, 2H), 7.40−7.36
(m, 2H), 7.33 (t, J = 7.5 Hz, 4H), 7.20 (d, J = 7.5 Hz, 4H), 6.06
(backbone of NHC, s, 2H), 3.25 (CHCH, COD, m, 1H), 3.16 (m,
2H), 2.39 (CHCH, COD, m, 1H), 2.22 (m, 2H), 2.06 (CHCH,
COD, m, 1H), 2.00−0.85 [m, 46H (33H expected), one CHCH
t
of BuOH (0.25 mL) via syringe. The tube was sealed, taken out of
glovebox, and put into a preheated oil bath (60 °C). After 12 h, a
small amount of reaction crude (ca. 0.01 mL) was transferred into an
1
NMR tube containing CDCl3 (0.5 mL) and analyzed by H NMR.
The conversion was calculated by comparing the benzylic proton of
product (doublet, 4.01 ppm) and olefinic proton of starting material
(multiplet, 5.0 ppm). To the reaction crude was added 0.5 g of silica
gel, and the mixture was reduced to a free-flowing consistency, put on
a silica gel column (column size: 1 cm diameter, 20 cm height), and
eluted with hexane/diethyl ether = 20/1. The collection tubes with
product were combined, the solvent evaporated on a rotary
evaporator, and the solid dried under high vacuum. HPLC analysis
was performed with a JASCO Chrompass system with a Daicel
Chiralcel OJ-H column (0.46 cm × 25 cm), with hexane/iPrOH =
90/10 as eluents with a flow rate of 1.0 mL/min. Retention times:
Tmajor = 7.3 min, Tminor = 11.3 min. See the Supporting Information
for details.
5.8. General Procedure for the Asymmetric Ring-Opening
Amination of Oxabicycles. Inside a glovebox, to a vial was added
AgPF6 (4 mg) and DCM (5 mL) to make a 0.8 mg/mL stock
solution. To another 20 mL vial was added the corresponding
[(NHC*)Ir(diene)Cl] complex (0.003 mmol) and DCM (1 mL).
Under stirring, the stock solution of the AgPF6 solution (1 mL) was
slowly added via syringe. The resulting mixture was stirred for 5 min
in the dark at room temperature and filtered through a Celite/cotton
pipet that was washed with additional DCM (1 mL). The filtered
solution was transferred into a pencil-shaped Schlenk tube (20 mL
content size) fitted with a Young valve and a stir bar, and the solution
was taken to dryness under high vacuum. (For catalysts (Sa,Sa,S,S)-
3a[PF6] and (Ra,Ra,S,S)-3a[PF6], 3.4 mg (0.003 mmol) of isolated
catalyst was added as a solid.) Oxabicyclic substrate (6, 0.15 mmol)
was added as a solid, followed by addition of the amine (7, 0.225
mmol) and solvent (0.25 mL) via syringe. The tube was sealed, taken
out of the glovebox, and put into a preheated oil bath. After 12 h, a
small amount of reaction crude (ca. 0.01 mL) was transferred into an
1
NMR tube containing CDCl3 (0.5 mL) and analyzed by H NMR.
The conversion was calculated by comparing the characteristic signal
of product and signal of oxabicyclic starting material. To the reaction
crude was added 0.5 gof silica gel, and the suspension was reduced to
a free-flowing consistency, put on a silica gel column (column size: 1
cm diameter, 20 cm height), and eluted with hexane/diethyl ether.
The collection tubes with product were combined, the solvent
evaporated on a rotary evaporator, and the solid dried under high
vacuum. HPLC analysis was performed on a JASCO Chrompass
system with a Daicel Chiralcel OD-H or AD-H (0.46 cm × 25 cm)
O
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pubs.acs.org/Organometallics
Article
column using hexane/iPrOH as eluents with a flow rate of 1.0 mL/
min. See the Supporting Information for details.
Notes
The authors declare no competing financial interest.
5.9. X-ray Crystallographic Data. Crystallographic data for the
structures were collected at 100(2) K on an Oxford Diffraction
Gemini diffractometer or an Oxford Diffraction Xcalibur diffrac-
tometer using Mo Kα radiation (λ = 0.71073 Å) or Cu Kα radiation
(λ = 1.54178 Å). Lp and absorption corrections were applied. The
structures were solved by direct methods and refined against F2 with
full-matrix least-squares using the program suit SHELXL.32
Anisotropic displacement parameters were employed for the non-
hydrogen atoms. All hydrogen atoms were added at calculated
positions and refined by use of a riding model with isotropic
displacement parameters based on those of the parent atom.
Crystallographic data for the structures reported in this paper can
be found in the Supporting Information of this paper and have been
deposited at the Cambridge Crystallographic Data Centre. Copies of
the data for (Ra,Ra,S,S)-1a, (Ra,Ra,S,S)-1b, (Ra,Ra,S,S)-1d, (Ra,Ra,S,S)-
2a, (Ra,Ra,S,S)-2b, (Ra,Ra,S,S)-2a[PF6], (Ra,Ra,S,S)-2b[PF6],
(Sa,Sa,S,S)-3a[PF6], and (Ra,Ra,S,S)-3b″[PF6] with CCDC numbers
1961910−1961918 can be obtained free of charge on application to
CCDC, 12 Union Rd, Cambridge CB21EZ, UK (fax +441223336033;
email deposit@ccdc.cam.ac.uk). Key details of the crystal and
structure refinement data are summarized in the Supporting
Information.
ACKNOWLEDGMENTS
■
P.G. and D.F. thank UWA for a Research Training
Postgraduate (RTP) Scholarship. G.S. thanks UWA for an
International Postgraduate Research Scholarship (IPRS). R.D.
thanks the Australian Research Council for generous funding
(FT130101713). The Centre for Microscopy, Characterisation
& Analysis at UWA is thanked for providing facilities and
assistance.
REFERENCES
■
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.9b00770.
■
sı
Additional experimental and crystallographic data,
including copies of NMR spectra (PDF)
Accession Codes
CCDC 1961910−1961918 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
■
Reto Dorta − Department of Chemistry, School of Molecular
Sciences, University of Western Australia, 6009 Perth, Western
Australia, Australia; orcid.org/0000-0003-1240-2755;
Email: reto.dorta@uwa.edu.au
Authors
Pengchao Gao − Department of Chemistry, School of Molecular
Sciences, University of Western Australia, 6009 Perth, Western
Australia, Australia
Daven Foster − Department of Chemistry, School of Molecular
Sciences, University of Western Australia, 6009 Perth, Western
Australia, Australia
́
Gellert Sipos − Department of Chemistry, School of Molecular
Sciences, University of Western Australia, 6009 Perth, Western
Australia, Australia
Brian W. Skelton − Department of Chemistry, School of
Molecular Sciences, University of Western Australia, 6009 Perth,
Western Australia, Australia
Alexandre N. Sobolev − Centre for Microscopy,
Characterisation and Analysis, University of Western Australia,
6009 Perth, Western Australia, Australia
(4) (a) Luan, X.; Mariz, R.; Robert, C.; Gatti, M.; Blumentritt, S.;
Linden, A.; Dorta, R. Matching the Chirality of Monodentate N-
Heterocyclic Carbene Ligands: A Case Study on Well-Defined
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.9b00770
P
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https://dx.doi.org/10.1021/acs.organomet.9b00770
Organometallics XXXX, XXX, XXX−XXX