Iridium and Rhodium Complexes Containing Enantiopure Primary Amine-Tethered N-Heterocyclic Carbenes: Synthesis, Characterization, Reactivity, and Catalytic Asymmetric Hydrogenation of Ketones

Article abstract of DOI:10.1021/acs.organomet.7b00915

The imidazolium salt [(S,S)-tBuNC₃H₃NCHPhCHPhNH₂]PF₆, (S,S)-11·HPF₆ is a precursor to the enantiopure "Kaibene" ligand, tBu-Kaibene, (S,S)-11 featuring a tert-butyl group on the N-heterocyclic carbene (NHC) ring-nitrogen atoms. It has been prepared in high yield and purity by refluxing a chiral cyclic sulfamidate with 1-tert-butylimidazole. Similarly (S,S)-12·HPF₆ with a mesityl group at the imidazolium ring-nitrogen atom has been prepared in the same fashion and serves as a source of Mes-Kaibene, (S,S)-12. These bidentate Kaibene ligands feature an NHC and a primary amine separated by a chiral linker. Salts (S,S)-11·HPF₆ or (S,S)-12·HPF₆ react with base and AgI or CuI to give a total of four M(Kaibene)₂I compounds (M = Ag or Cu). At 22 °C, the amine-functionalized imidazolium cations undergo oxidative addition to iridium(I) in [IrCl(cod)]₂ (cod = 1,5-cyclooctadiene) to generate iridium(III) hydride R-Kaibene compounds [IrHCl(cod)((S,S)-11)](PF₆) (17) and [IrHCl(cod)((S,S)-12)](PF₆) (18), respectively, each as a mixture of six configurational isomers. In contrast, the salt (S,S)-11·HPF₆ reacts with [Ir(OtBu)(cod)]₂ to produce a bimetallic iridium compound with (S,S)-11 as the bridging ligand. This compound contains interesting NH···Cl and NH···Ir noncovalent intramolecular interactions. Salt (S,S)-12·HPF₆ reacts with silver oxide to yield [Ag₂((S,S)-12)₂](PF₆)₂ (20). Reagent 20 serves as an efficient transmetalation reagent to deliver to each rhodium in [RhCl(cod)]₂ 1 equiv of (S,S)-12 as a bidentate ligand to give [Rh(cod)((S,S)-12)](PF₆). In the reaction between [IrCl(cod)]₂ and 20, (S,S)-12 ends up coordinated in an iridium(III) hydride complex (22) as a tridentate ligand via the NHC, NH₂, and a cyclometalated phenyl group. The two iridium hydride compounds, 18 and 22, are catalysts for the hydrogenation of a range of ketones (turnover number up to 499, turnover frequency up to 249 h^-1, with er (enantiomeric ratio) up to 35:65 R:S).

Full text of DOI:10.1021/acs.organomet.7b00915

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
Iridium and Rhodium Complexes Containing Enantiopure Primary
Amine-Tethered N‑Heterocyclic Carbenes: Synthesis,
Characterization, Reactivity, and Catalytic Asymmetric
Hydrogenation of Ketones
Kai Y. Wan,† Florian Roelfes,‡ Alan J. Lough,† F. Ekkehardt Hahn,*,‡ and Robert H. Morris*,†
†Department of Chemistry, University of Toronto, 80 Saint George Street, Toronto, Ontario M5S 3H6, Canada
‡Institut fur Anorganische und Analytische Chemie, Westfalische Wilhelms-Universitat Munster, Corrensstraße 30, D-48149 Munster,
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Germany
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* Supporting Information
A B S T R A C T : T h e i m i d a z o l i u m s a l t [ ( S , S ) -
tBuNC3H3NCHPhCHPhNH2]PF6, (S,S)-11·HPF6 is a pre-
cursor to the enantiopure “Kaibene” ligand, tBu-Kaibene,
(S,S)-11 featuring a tert-butyl group on the N-heterocyclic
carbene (NHC) ring-nitrogen atoms. It has been prepared in
high yield and purity by refluxing a chiral cyclic sulfamidate
with 1-tert-butylimidazole. Similarly (S,S)-12·HPF6 with a
mesityl group at the imidazolium ring-nitrogen atom has been prepared in the same fashion and serves as a source of Mes-
Kaibene, (S,S)-12. These bidentate Kaibene ligands feature an NHC and a primary amine separated by a chiral linker. Salts (S,S)-
11·HPF6 or (S,S)-12·HPF6 react with base and AgI or CuI to give a total of four M(Kaibene)2I compounds (M = Ag or Cu). At
22 °C, the amine-functionalized imidazolium cations undergo oxidative addition to iridium(I) in [IrCl(cod)]2 (cod = 1,5-
cyclooctadiene) to generate iridium(III) hydride R-Kaibene compounds [IrHCl(cod)((S,S)-11)](PF6) (17) and [IrHCl(cod)-
((S,S)-12)](PF6) (18), respectively, each as a mixture of six configurational isomers. In contrast, the salt (S,S)-11·HPF6 reacts
with [Ir(OtBu)(cod)]2 to produce a bimetallic iridium compound with (S,S)-11 as the bridging ligand. This compound contains
interesting NH···Cl and NH···Ir noncovalent intramolecular interactions. Salt (S,S)-12·HPF6 reacts with silver oxide to yield
[Ag2((S,S)-12)2](PF6)2 (20). Reagent 20 serves as an efficient transmetalation reagent to deliver to each rhodium in
[RhCl(cod)]2 1 equiv of (S,S)-12 as a bidentate ligand to give [Rh(cod)((S,S)-12)](PF6). In the reaction between [IrCl(cod)]2
and 20, (S,S)-12 ends up coordinated in an iridium(III) hydride complex (22) as a tridentate ligand via the NHC, NH2, and a
cyclometalated phenyl group. The two iridium hydride compounds, 18 and 22, are catalysts for the hydrogenation of a range of
ketones (turnover number up to 499, turnover frequency up to 249 h−1, with er (enantiomeric ratio) up to 35:65 R:S).
INTRODUCTION
■
The synthesis of chiral molecules receives broad industrial
interest due to its applications in the pharmaceutical,
agricultural, and fragrance sectors.1−4 As a result, many enantio-
and diastereoselective catalytic processes have been developed
on the basis of transition metals with chiral ligands that convert
the corresponding prochiral substrate to the desired homochiral
product.5−16 Most of the chiral ligands used in asymmetric
catalysis, however, are based on phosphines, some of which are
air-sensitive and are produced using environmentally harmful
reagents.13,17−21 In recent years, the substitution of phosphine
by N-heterocyclic carbene (NHC) in asymmetric transition
metal catalysis has received much interest.22,23 The NHC
ligands have tunable electronic and steric properties and their
precursor imidazolium salts are usually air-stable.22−27
Figure 1. Outer-sphere low energy barrier six-membered ring
transition state during ketone and imine hydrogenation utilizing the
“N−H” effect.
activate the polar bond of the substrate in the outer
coordination sphere to hydride attack and to position the
groups on the substrate for enantioselective reaction.
The investigation of homogeneous catalysts containing an
NHC bearing a pendant N−H functionality dates back to
2009.29 Initially, an achiral ligand (1) was synthesized through
In the past few years, some of us have focused on the
discovery of primary amine-functionalized NHC ligands due to
their ability to access a six-membered ring transition state with a
low energy barrier for ketone and imine reduction (Figure 1).28
The N−H group in the transition state structure serves to
Received: December 29, 2017
© XXXX American Chemical Society
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Figure 2. Achiral N−H-functionalized compound 1 and its group 8 and 9 compounds.
the in situ reduction of a nitrile-functionalized NHC
coordinated to nickel, to generate excellent transmetalation
reagent 2 (Figure 2).29 The NHC∧amine ligand in complex 2
can then be transferred to ruthenium or iridium in order to
synthesize compounds 3−6, all of which catalyze ketone
reduction using either 2-propanol or hydrogen gas as the
reductant.29−34 Of the two iridium complexes, compound 6
exhibits a higher reactivity than that of 5. Computational
studies supported the proposal that within the catalytic cycle
the Cp* (1,2,3,4,5-pentamethylcyclopentadienyl) ligand in
compound 5 was converted into 1,2,3,4,5-pentamethylcyclo-
pentadiene that acted as a spectator diene ligand. One
consistent observation in these catalytic systems was that
complexes bearing the NHC∧NH2 chelate ligand outperformed
using either silver or copper transmetalation techniques, we
produced two ruthenium-based ketone hydrogenation catalysts,
8 and 9.35,36 Complex 9 exhibited an exceptionally high
turnover number (TON up to 10 000) and turnover frequency
(TOF up to 48 s−1) for ketone reduction at very low catalyst
concentration (0.057 mM, catalyst/base/ketone = 1:8:5000 in
2-propanol) and under relatively mild conditions (25 bar H2, 50
°C). However, in spite of its high reactivity in ketone reduction,
complexes of ligand (S,S)-7 only provide low enantioselectivity
(up to 60% ee at the beginning of catalysis with 9).
In this study, two analogues of “Me-Kaibene” ((S,S)-7) have
been synthesized in an attempt to improve the effectiveness for
asymmetric ketone hydrogenation. One analogue (S,S)-11 has
a tert-butyl group in place of a methyl at the N3 ring atom of
the NHC while the other, (S,S)-12, features a mesityl group on
the NHC. These new R-Kaibene ligands have been used to
prepare several copper, silver, rhodium, and iridium com-
pounds. Two of the prepared iridium compounds have been
tested as catalysts for the asymmetric hydrogenation of a range
of ketones.
∧
the corresponding complexes bearing PPh2 NH2 chelates
where the NHC donor was replaced by a diphenylalkylphos-
phine donor.32,33
After the success in improving catalytic performance by using
NHCs instead of PPh2 in these systems, we were interested in
learning whether these systems could be rendered enantiose-
lective to create highly active, enantioselective catalysts based
on NHCs. In 2016, some of us reported the synthesis of the
first isolable imidazolium salt of this type that contains a
primary amine functional group, (S,S)-7·HPF6 (Figure 3).35 By
RESULTS AND DISCUSSION
■
Synthesis of Bulky Imidazolium Salts Based on
Kaibene. Two new ligands were synthesized with different
inductive effects compared to (S,S)-7: the basic derivative tBu-
Kaibene, (S,S)-11, with a tert-butyl group, and the less basic
Mes-Kaibene, (S,S)-12, with a Mes group bound to ring-
nitrogen atom N3 (Scheme 1). Imidazolium salt (S,S)-11·HPF6
was prepared in analogy to (S,S)-7·HPF6.35 A sample of 1-tert-
butylimidazole and chiral, Boc-protected (R,S)-sulfamidate 1037
was refluxed in toluene for 1 h to allow a concerted nucleophilic
substitution (SN2) reaction, which results in the full inversion
of one stereocenter. Then, 2 equiv of 1-tert-butylimidazole per
1 equiv of 10 was used as the optimal nucleophile/electrophile
ratio. Subsequent Boc deprotection was performed using
concentrated hydrochloric acid. Finally, neutralization with
sodium carbonate and salt metathesis with potassium
Figure 3. Enantiopure N−H functionalized compound (S,S)-7·HPF6
and ruthenium complexes of Me-Kaibene, (S,S)-7.
Scheme 1. Synthesis of (S,S)-11·HPF6 and (S,S)-12·HPF6
B
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hexafluorophosphate provided (S,S)-11·HPF6 in high purity as
a white powder in 79% yield. The mesityl derivative, (S,S)-12·
HPF6, however, was synthesized using a lower reaction
temperature and acetonitrile as the solvent. The starting
nucleophile and electrophile in a 1:1 stoichiometric ratio were
refluxed overnight to facilitate the substitution reaction. By
using similar workup procedures to those of (S,S)-11·HPF6, the
reaction afforded imidazolium salt (S,S)-12·HPF6 in 71% yield
as a white powder. This synthesis method for the generation of
Kaibene derivatives with different diamine backbones and
imidazole substituents is highly versatile.
primary amine group was detected as a doublet (3JHH = 4.5 Hz)
at δ = 1.58 ppm due to the coupling to a methine hydrogen
atom in the backbone. The observed doublet with a relative
intensity of two indicates a dangling amine group that is not
coordinated to the silver atom and can rotate freely. The
13C{1H} NMR spectrum of complex 13 revealed a resonance at
δ = 181.8 ppm for the carbene carbon atom in the typical
region for silver NHC complexes. Remarkably, the resonance of
the carbene carbon atom shows no sign of coupling to the
NMR active silver isotopes. This indicates a fluxional exchange
process of the silver carbene and partially explains the instability
of complex 13.38
Both (S,S)-11·HPF6 and (S,S)-12·HPF6 were fully charac-
terized by NMR spectroscopy, high-resolution mass spectros-
copy, and elemental analysis. The HR-ESI mass spectrum of
(S,S)-11·HPF6 showed the signal with the highest intensity at
m/z = 320.2128 (calcd for [M − PF6]+: 320.2127) with the
Since silver complex 13 is extremely light-sensitive, the
analogous copper complex 14 was also synthesized. This
complex was obtained in high yield (95%) by reaction of
imidazolium salt (S,S)-11·HPF6 with 0.5 equiv of CuI and a
slight excess of KHMDS in THF at ambient temperature. The
formation of the NHC copper iodide complex was signaled by
the disappearance of the resonance for the imidazolium C2
hydrogen atom and the appearance of a doublet at δ = 1.55
ppm assigned to the primary amine in 1H NMR spectrum. The
carbene carbon resonance was found at δ = 177.9 ppm in the
13C{1H} NMR spectrum. The carbene resonance of 14 falls in
the expected range of copper carbene complexes.38−40 With
improved stability in light, compound 14 can be characterized
by MALDI-TOF spectrometry where a signal for the cationic
fragment [14 − I]+ was observed at m/z = 701. The elemental
analysis is also consistent with the proposed composition.
Through similar procedures and characterization techniques,
bisNHC silver and copper iodide complexes of (S,S)-12 were
also prepared in good yields (quantitative for 15, Ag; and 92%
for 16, Cu). Complexes 15 and 16 feature carbene signal at δ =
184.3 and 181.8 ppm, respectively, in their 13C{1H} NMR
spectra. Compared to complex 13, complex 15 is less sensitive
but still decomposes after prolonged exposure to light.
Complexes 13−16 are assumed to have similar structures to
those of previously reported MI(Me-Kaibene)2 compounds (M
= Cu and Ag) where the two NHC donors in the complex are
coordinated trans to each other while the iodide ion is within
ion-pairing distance which produces an overall T-shaped
structure.35,36 Complexes 13−16 are highly water sensitive.
Although carbene compounds were observed by NMR
spectroscopy, only imidazolium salts were observed by ESI
mass spectrometry. So far complexes 13−16 have not been
successfully used as transmetalation reagents.
1
correct isotope distribution. The H NMR (CD2Cl2) spectrum
of (S,S)-11·HPF6 revealed a signal for the imidazolium
hydrogen at δ = 8.82 ppm as a pseudotriplet (4JHH = 1.7 Hz)
due to the coupling to the other two hydrogens in the
imidazolium ring. Similarly, the mass spectrum of (S,S)-12·
HPF6 revealed the most intense peak at m/z = 382.2283 (calcd
for [M − PF6]+: 382.2278, HR-ESI) and the imidazolium
4
hydrogen was detected at δ = 9.76 ppm (pseudotriplet, JHH
=
1
1.4 Hz) in the H NMR (DMSO-d6) spectrum. The elemental
analysis together with the signals in the 31P{1H} and the 19F
NMR spectra confirmed that the anions initially present were
completely replaced by the PF6 anion for both (S,S)-11·HPF6
and (S,S)-12·HPF6.
Synthesis of Bis(Kaibene) Group 11 Complexes
Containing (S,S)-11 or (S,S)-12. Free carbene (S,S)-11
with the donating tert-butyl group on the NHC is strongly basic
like (S,S)-7, and silver oxide was found to be insufficiently basic
to deprotonate the imidazolium salt. Therefore, silver iodide
and potassium bis(trimethylsilyl)amide were used to generate
silver complex 13 in good yield (69%) from (S,S)-11·HPF6.
Potential silver intermediates were stabilized by addition of 2.5
equiv of KI (Scheme 2). Complex 13 was characterized by
Scheme 2. Group 11 Compounds Synthesized Using (S,S)-
11·HPF6 and (S,S)-12·HPF6
Oxidative Addition of the Imidazolium Groups of tBu-
and Mes-Kaibene to Iridium(I). A different approach based
on the C2−H activation of the imidazolium moiety was used to
generate an organometallic compound containing tBu-Kaibene,
(S,S)-11. Iridium(I) is renowned for its ability to oxidatively
add polarized C−H bonds and some literature precedents exist
where an imidazolium salt and an iridium(I) precursor reacted
at ambient temperature to afford iridium(III) carbene hydride
species.41−44 The C2−H oxidative addition of azolium salts is
aided by the presence of a donor function tethered to one of
the azolium ring-nitrogen atoms.45 For the synthesis of
carbene-hydride complexes by oxidative addition, a Schlenk
flask was charged with (S,S)-11·HPF6 and 0.5 equiv of
[IrCl(cod)]2 in chloroform-d. After approximately 30 min,
the resulting mixture contained six hydride species of the type
17 (Scheme 3) that were observable by 1H NMR spectroscopy
with approximately 29% conversion from the imidazolium salt
(major ones at δ = −13.29 ppm with 62% of the total hydride
NMR spectroscopy. It is exceptionally light-sensitive so that
additional analytical data could not be obtained. Reactions of
(S,S)-11·HPF6 with silver bromide, silver hexafluorophosphate,
or silver tetrafluoroborate were also attempted, but the
products were substantially more unstable compared to the
complex obtained from silver iodide. The 1H NMR spectrum of
13 no longer showed any signal for the imidazolium hydrogen
atom in (S,S)-11·HPF6, which indicated the formation and
coordination of an NHC to the silver ion. The signal for the
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converted to the amine adduct shown in Figure 4. Its identity
Scheme 3. C−H Activation of (S,S)-11·HPF6 and (S,S)-12·
HPF6 by Iridium in CDCl3
was determined by 1H and 1H−1H gCOSY NMR experiments.
Figure 4. Proposed structure of an (S,S)-11·HPF6−IrCl(cod) adduct.
The two hydrogen atoms of the amino group are diastereotopic
because the coordination to the iridium prevents amine
inversion. As illustrated in Figure 4, the splitting pattern of
the methine hydrogen H15 switches from a doublet to a triplet
on going from the free amine to the complex, which is an
indication of additional coupling (3JHH = 11.5 Hz) to a
1
hydrogen atom at the noninverting nitrogen. The H NMR
signal corresponding to the amine protons should change from
a broad signal at 1.73 ppm to a pair of triplets upon
coordination. Only one of these N−H protons can be observed
at 3.61 ppm (3JHH = 11.5 Hz), while the other N−H proton is
buried within the CH2 signals of the cod. Also, there is a global
downfield shift of hydrogen resonances of (S,S)-11 compared
to (S,S)-11·HPF6 and a desymmetrization of the cod signals of
the IrCl(cod) moiety was observed. The former observation
can be explained by the formation of a hydrogen bond between
H4 and the chloride ligand. The latter is further evidence for
the coordination of the amine of (S,S)-11·HPF6, resulting from
the splitting of the chloride bridges of the dimeric iridium
precursor. The reaction mixture was then added to a solution of
KHMDS in THF to deprotonate the imidazolium group and
generate tBu-Kaibene. No imidazolium group signals remained
after the addition of the base, and mass spectrometry revealed a
peak at m/z = 620.2612 for [Ir(tBu-Kaibene)(cod)]+ with the
correct isotope pattern. However, multiple peaks were observed
in the 1H NMR spectrum. A pure sample of [Ir(tBu-
Kaibene)(cod)](PF6) was not obtained.
Compared to (S,S)-11·HPF6, the imidazolium (S,S)-12·
HPF6 is expected to be more acidic and more prone to
oxidative addition since the mesityl group of (S,S)-12·HPF6 is
less donating than the t-butyl group of (S,S)-11·HPF6.
Therefore, a reaction between (S,S)-12·HPF6 and [IrCl(cod)]2
could potentially yield an oxidative addition product in higher
yield. The first attempt of a reaction between (S,S)-12·HPF6
and [IrCl(cod)]2 in CD2Cl2 proved unsuccessful as less than
10% of the (S,S)-12·HPF6 was converted to a mixture of
hydride isomers 18. When CDCl3 was used, a similar set of
isomers 18 was observed but with a significantly higher
conversion (>99% consumption of (S,S)-12·HPF6, Scheme 3).
Six hydride species produced singlets between δ = −12.90 and
−15.70 ppm with two dominant peaks at δ = −14.56 and
−14.19 ppm (Scheme 3). Despite the presence of isomers, the
purity of 18 was confirmed by both HR-ESI (calcd for
[Ir(H)(Cl)(Mes-Kaibene)(cod)]+ m/z = 718.2528, found
718.2526) and elemental analysis. Thus, both 17 and 18
consist of a mixture of six isomers of hydride complexes. The
structures of the two most abundant isomers are assigned to
those illustrated in Scheme 3, with reference to DFT
integration and δ = −13.01 ppm with 22%). The other four
isomers are shown in Figure S1. The ratio between the iridium
carbene hydrides and the imidazolium salt remained constant
regardless of the reaction temperature. This constitutes
evidence for an equilibrium between the imidazolium salt and
an iridium carbene hydride species (Scheme 3) as previously
suggested by others.41,43,46,47 The mechanism of the formation
of the hydride complex is also illustrated in Scheme 3 where an
amine adduct is assumed to form first between iridium and the
amine-tethered imidazolium salt. Subsequently, an intra-
molecular C−H bond oxidative addition to the iridium atoms
affords complexes of the type 17. The corresponding
mechanism of this type of C−H bond oxidative addition to
Pd(0) had been investigated by computational chemistry,46,47
showing that the oxidative addition is in equilibrium with the
reductive elimination step. Therefore, a clean hydride sample
from complete conversion was not obtained in the reaction of
(S,S)-11·HPF6. The cationic hydride is estimated to have a pKa
of ∼2 in CDCl3;48 thus, a weak base like triethylamine is
sufficient to deprotonate the M−H bond. Similar reactions have
been performed by Peris et al.41 After adding triethylamine to a
mixture of the imidazolium salt and the iridium precursor in
THF, we observed after 3 h a small peak in the mass spectrum
at m/z = 620.2614 au with an isotopic pattern that corresponds
to the formula of [Ir(tBu-Kaibene)(cod)]+ (calculated
C29H37IrN3 620.2612). However, complete conversion to this
compound could not be achieved.
The same experiment was subsequently performed in
dichloromethane-d2 but an even smaller extent of C−H
1
oxidative addition was observed by H NMR spectroscopy
(approximately 8% with two major iridium(III) hydrides at δ =
−14.46 and −15.01 ppm). The remaining iridium was
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calculations performed previously on a similar achiral system.33
The most stable structures feature the high trans-influence
hydride in trans positions to donors of low trans-influence (Cl,
NH2).
Although the C−H oxidative addition of imidazolium salts to
transition metals has been known for decades, most of these
reactions were based on zero-valent group 10 metals with
strongly donating, tethered donor ligands such as phosphines
or NHCs.46,47,49−53 While some literature examples of Ir(I) and
Rh(I) are known for this type of reaction, in most cases, heating
or the use of a donor-functionalized NHC imidazolium salt is
required.41−43,54 The formation of mixtures 17 and 18 is the
first example of the use of a primary-amine tether in facilitating
the oxidative addition at ambient temperature.
Synthesis of Silver, Rhodium, and Iridium Com-
pounds of Kaibene with Amine Coordination. Song et
al.43,55 generated [Ir(OtBu)(cod)]2 in situ from [IrCl(cod)]2
and KOtBu and used this alkoxide-bridged intermediate to
generate carbene compounds from imidazolium salts. With the
goal of isolating a mononuclear iridium complex bearing a
chelating Kaibene ligand, (S,S)-11·HPF6 was stirred with in situ
generated [Ir(OtBu)(cod)]2 in THF at ambient temperature
with a 1:1 ligand/metal ratio. Instead of a mononuclear chelate
complex, complex 19 with two [IrCl(cod)] fragments bridged
by the amine-tethered NHC ligand was isolated (Scheme 4).
Figure 5. Molecular structure of 19: displacement ellipsoids are shown
with 50% probability. Nonrelevant hydrogen atoms have been omitted
for clarity. Selected bond lengths (Å) and angles (deg): Ir1−N1
2.136(3), Ir2−C15 2.045(3), Ir2···H2A 2.653, Cl2···H2N 2.57(4),
C15−Ir2−Cl2 88.03(9), H1−Ir1−Cl1 87.62(8), C2−H2A···Ir2 123.1,
N1−H2N···Cl2 153(3).
interaction between Ir2 and the methine hydrogen H2A. The
distance between Ir2 and H2A measures 2.653 Å. This
interaction represents a rare example of a preagostic interaction
as described by Crabtree and Bergman.58,59 We believe these
two noncovalent interactions are maintained in solution and are
responsible for the abnormal downfield shifts of the H2N and
H2A hydrogen atoms observed in the 1H NMR spectrum of the
complex in CD2Cl2 solution as described below. The ligand
conformation in 19 is very similar to that of (S,S)-7 in a silver
polymer [Ag(Me-Kaibene)]n(PF6)n35 where (S,S)-7 is bridging
between silver ions to generate a Λ-helical polymeric structure.
In both structures, the two methine hydrogen atoms are anti to
each other with the phenyl groups mutually gauche. This
arrangement minimizes steric repulsions and explains the high
stability of (S,S)-7 silver polymer, as well as the formation of 19
Scheme 4. Formation of Bridging tBu-Kaibene Di(iridium)
Compound
1
as the major product. The H NMR spectrum of complex 19
revealed two signals for the hydrogen atoms of the coordinating
primary amine at δ = 4.76 and 2.57 ppm, respectively. The
coupling pattern showed geminal coupling between the two
hydrogens (2JHH = 11.5 Hz) as well as a coupling between the
methine hydrogen H1A (3JHH = 11.8 Hz) and the NH proton
at δ = 4.76 ppm. The signal for the methine hydrogen H1A was
detected at δ = 5.24 ppm with an appropriate pattern for
Adjustment of the stoichiometry to 1:2 imidazolium salt/
iridium resulted in the isolation of complex 19 in low yield
1
(38%). Although multiple species were observed in the H
NMR spectrum of a sample from the reaction mixture, only this
bimetallic compound could be isolated cleanly.
Complex 19 was characterized by MALDI-TOF mass
spectrometry, NMR spectroscopy, elemental analysis, and X-
ray crystallography (Figure 5). The MALDI-TOF mass
spectrum showed a signal for cationic complex [19]+ at m/z
= 991 with the correct isotope distribution. The molecular
structure of 19 shows the iridium atoms coordinated in a
distorted square-planar coordination environment with one cod
ligand, one chloride ligand, and one NHC or amine donor,
respectively. The bond distance between iridium and the NHC
carbon measures 2.045(3) Å, which agrees well with the median
value (2.044 Å) of iridium−carbon NHC bond distances found
in the 2017 Cambridge Crystallographic Database (CCD).
Interestingly, several noncovalent interactions are observed in
the molecular structure. The distance between an amine
hydrogen H2N and chloride Cl2 measures 2.57(4) Å and the
N1−H2N···Cl2 angle of 153(3)° fit the criteria for hydrogen
bonding.56,57 Remarkably, there is also a noncovalent
coupling to the amine and the methine hydrogen H2A (3JHH
=
11.8 Hz). Interestingly, the resonance for H2A was detected at
δ = 8.17 ppm with a downfield shift of Δδ = 2.44 ppm
compared to the resonance of imidazolium salt (δ = 5.73 ppm).
This downfield shift and the downfield-shifted signal for one of
the amine hydrogens indicate strong noncovalent interactions
such as hydrogen bonding in complex 19. The characteristic
downfield shift in the 1H NMR spectrum of the C−H group in
a preagostic bond with d8 square planar metal complexes has
been reported by Zhang et al.60 The 13C{1H} NMR spectrum
of complex 19 has a signal for the carbene carbon atom C15 at
δ = 181.3 ppm.
In the chemistry of tBu-Kaibene described above, two
challenges were encountered. These are the sensitivity of its
coordination compounds and its weakly chelating primary
amine group when in competition with chloride. Therefore, the
preparation of organometallic compounds based on the less
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Scheme 5. Organometallic Compounds of Mes-Kaibene (S,S)-12
Figure 6. ESI-MS spectrum of 20.
basic Mes-Kaibene (S,S)-12 seemed more promising. Indeed,
gently heating (S,S)-12·HPF6 with silver oxide in the presence
of activated 4 Å molecular sieves afforded silver compound 20
cleanly in good yield (Scheme 5).
20, a broad peak representing the NH2 groups was observed at
δ = 4.67 ppm, a chemical shift close to that of the NH2 group of
the crystallographically characterized [Ag(Me-Kaibe-
ne)]n(PF6)n polymer.35 However, complex 20 has a higher
solubility in nonpolar organic solvents like dichloromethane
compared to the Me-Kaibene polymer, which is only soluble in
highly polar organic solvents such as DMSO or acetonitrile.
Thus, if 20 is a polymer, then it likely has a lower degree of
polymerization than the Me-Kaibene polymer. The broad NH2
peak and methine peaks of the backbone of (S,S)-12 in the 1H
NMR spectrum of 20 also provide evidence for a polymeric
structure where these hydrogens experience different chemical
Note that in order to ensure complete conversion of (S,S)-
12·HPF6 to 20, it is necessary to use molecular sieves that have
been activated under high vacuum and by heating. Once the
silver complex is formed, it can be stored in air and is stable in
wet DMSO-d6. One of the possible structures of compound 20
is the head-to-tail dimer illustrated in Scheme 5. However, a
higher molecular weight structure, such as a trimer or other
1
oligomers may also be possible. In the H NMR spectrum of
F
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environments depending on the ligands’ positions in the
macromolecule. Fortunately, several fragments were observed
in the mass spectra that provide insight into the structure. In
the ESI-MS spectrum (Figure 6), peaks due to fragments
possibly representing the dimeric structure were observed,
along with that of a [bis(Mes-Kaibene)Ag]+ fragment. The
imidazolium salt was also observed in the spectrum due to the
acidic conditions of the solution used in the ESI analysis.
Similar fragments were also observed by MALDI-MS where the
imidazolium salt signal was significantly smaller, and the
[bis(Mes-Kaibene)Ag]+ fragment is the dominant species
observed. The 13C{1H} NMR spectrum of 20 displayed the
carbene carbon resonance at δ = 181.5 ppm, which falls within
the expected range of Ag-NHC complexes.38
In the reaction with [RhCl(cod)]2 or [IrCl(cod)]2,
compound 20 proved to be a better transmetalation reagent
for (S,S)-12 than 15 or 16. This could be due to the release
AgPF6 as a secondary reactant which in turn caused the
precipitation of silver chloride which was observed after 18 h of
reaction and allowed not only the NHC but also the amine of
Mes-Kaibene to coordinate. Removal of silver chloride and
subsequent purification by washing with diethyl ether yielded
rhodium and iridium complexes 21 and 22, respectively, in high
purity and good yields (Scheme 5). Although the starting
materials have similar dimeric structures [MCl(cod)]2 (M =
Rh, Ir), the products generated from their reactions with 20 are
significantly different regarding the oxidation state and
geometry of rhodium versus iridium. The expected [Rh(cod)-
(Mes-Kaibene)](PF6) (21) compound was obtained as a result
of halide abstraction and ligand coordination. In contrast, an
Ir(III) hydride compound [Ir(H)(cod)(o-metalated Mes-
Kaibene)](PF6) (22) was obtained with one phenyl group
orthometalated. An [Ir(cod)(Mes-Kaibene)](PF6) complex
with a structure similar to that of 21 might be an intermediate
in the formation of 22. In compound 22, Mes-Kaibene is
coordinated to iridium as a tridentate ligand, forming three
stable and rigid six-membered metalacycles.
−
Figure 7. Molecular structure of 21. The PF6 anion and irrelevant
hydrogen atoms were omitted for clarity. Selected bond lengths (Å)
and angles (deg): Rh1−C2 2.056(4), Rh1−N4 2.165(4), Rh−C29
2.190(4), Rh1−C30 2.210(5), Rh1−C33 2.134(4), Rh1−C34
2.146(4), C2−Rh1−N4 88.0(2)
a hydride signal is observed at δ = −15.49 ppm and the two N−
H hydrogens for the coordinated amine are found at δ = 6.02
and 5.15 ppm. The carbene carbon of 22 causes a resonance at
δ = 153.61 ppm in the 13C{1H} NMR spectrum. An X-ray
crystallographic study shows that 22 has a distorted octahedral
structure (Figure 8), consistent with iridium(III) with a d6
Both compounds 21 and 22 were fully characterized by
NMR spectroscopy, HR-ESI, elemental analysis, and X-ray
crystallography. The HR-ESI spectrum of 21 features a peak at
m/z = 592.2195 which corresponds to the mass of the fragment
1
of [Rh(Mes-Kaibene)(cod)]+ (calcd 592.2194). The H NMR
spectrum of 21 reveals two N−H hydrogen atoms of the
coordinated amine at δ = 4.90 and 4.33 ppm. The 13C{1H}
NMR spectrum of 21 shows the carbene carbon resonance at δ
= 173.4 ppm with a single bond coupling to rhodium (1JRh−C
=
53.2 Hz). The molecular structure of 21 (Figure 7) exhibits a
distorted square planar geometry, consistent with the d8 Rh(I)
configuration. The Rh−C(NHC) distance of 2.056(4) Å falls
within the expected range of Rh−NHC bonds and is slightly
longer than the mean Rh−C(NHC) distance (2.033 Å)
determined by searching the 2017 CCD. The Rh-NH2 distance
of 2.165(4) falls within the longest 10% of Rh−amine bonds
according to the 2017 CCD. The bond distances between the
metal center and the olefin carbons are longer where the olefin
is trans to the NHC, consistent with the stronger trans influence
and the σ-donor ability of the NHC. The two phenyl groups on
the backbone are oriented anti to each other and axial in the
five-member Rh−C−N−C−C−N ring.
Figure 8. Molecular structure of 22. Nonrelevant hydrogen atoms, one
PF6− anion, half of a dichloromethane, and half of a pentane molecules
have been omitted for clarity. Selected bond lengths (Å) and angles
(deg): Ir1−hydride 1.51(4), Ir1−C2 2.027(4), Ir1−N4 2.256(4), Ir1−
C17 2.070(5), Ir1−C29 2.296(6), Ir1−C30 2.308(5), Ir1−C33
2.266(5), Ir1−C34 2.253(5), hydride−Ir1−C2 87(2), hydride−Ir1−
N4 170(2), hydride−Ir1−C17 88(2), C2−Ir1−N4 87.4(2), C2−Ir1−
C17 82.9(2), N4−Ir1−C17 83.4(2).
electron configuration. The Ir−hydride distance measures
1.51(4) Å and falls within the expected range of iridium
hydride distances determined by X-ray crystallography
according to the 2017 CCD. Similarly, the 2.027(4) Å Ir−
C(NHC) distance and 2.070(5) Å Ir−C(Ph) distance fall
within the expected range according to previously reported
data. Interestingly, the 2.256(4) Å Ir−NH2 distance is much
longer than most of the Ir−NH2R bond reported in literature
The HR-ESI mass spectrum of 22 reveals the presence of the
major component with a peak at m/z = 680.2750 with an
isotopic pattern matching for [Ir(H)(cod)(o-metalated Mes-
1
Kaibene)]+ (calcd 680.2744). In the H NMR spectrum of 22,
G
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Table 1. Hydrogenation of Ketone Substrates by Compound 18 and 22: Select Substrates
and falls within the longest 0.5% percentile due to the strong
trans influence of the hydride ligand. The other three examples
with comparable Ir−NH2R distance all have the primary amine
trans to either hydride or aryl ligands.61−63 In 22, the phenyl,
the NHC, and the amine donor groups from Mes-Kaibene are
coordinated to the metal center in a mer configuration, forming
three six-membered metalacycles. The other ligands in 22 take
up positions with strong trans influence donors trans to weak
donors. Thus, the stronger σ-donors from Mes-Kaibene phenyl
and NHC, are arranged trans to the weaker olefin groups of the
cod ligand. The weak σ-donor amine is found in trans position
to the strong σ-donor hydride.
Catalytic Direct Ketone Hydrogenation by 18 and 22.
Iridium complexes 18 and 22 were then tested in the direct
hydrogenation of 25 different ketones with varied steric and
electronic properties. The catalysts:base:substrate ratio was
controlled at 1:8:500 at 0.37 mM of the catalyst. The catalytic
mixture was heated at 50 °C under 25 bar of H2 for 2 h, and the
product mixture was analyzed by gas chromatography. Selected
catalytic results are listed in Table 1 and the comprehensive list
of catalytic outcomes of all substrates are included in the
Supporting Information.
In general, compound 18 and 22 are effective in reducing
aryl-alkyl ketones (entries 1−3, Table 1) but with low
enantioselectivity. These two complexes are also efficient in
H
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Scheme 6. Hydrogenation of Benzylideneacetone by 18 and 22
using standard Schlenk-line or glovebox techniques unless stated
otherwise. Synthesis of sulfamidate 10 was reported previously.37 All
other reagents used were purchased from commercial sources and
used without further purifications. All solvents were degassed and
dried using standard procedures prior to all manipulations and
reactions unless stated otherwise. Deuterated solvents were purchased
from Cambridge Isotope Laboratories or Sigma-Aldrich, degassed, and
dried over activated molecular sieves prior to use. NMR spectra were
recorded at ambient temperature and pressure using a Bruker
reducing benzyl 4-chlorophenyl ketone (entry 4, Table 1) with
some degree of enantioselectivity. In comparison, compound
22 provides a higher stereoselectivity to the reduction most
likely due to its more rigid structure compared to compound
18. Compounds 18 and 22 can also reduce a range of
derivatized acetophenone compounds including chloro-,
methoxy-, o-phenylene-, methyl-, and trifluoromethyl- sub-
stituents (entries 5−11, Tables 1 and S1). Overall compounds
18 and 22 are effective ketone hydrogenation catalysts with
TON up to 499 and TOF up to 249 h−1.
We also tested compound 18 and 22 for the hydrogenation
of benzylideneacetone to observe their selectivity between
olefin and ketone (Scheme 6). As expected, the iridium
hydrides are effective alkene hydrogenation catalysts. The
alkene functional group in benzylideneacetone was almost
completely hydrogenated along with the ketone to a small
extent to give both the allyl alcohol and the saturated alcohol.
1
AVANCE I 400 (400 MHz for H, 101 MHz for 13C, 376 MHz for
1
19F), Bruker AVANCE III 400 (400 MHz for H, 101 MHz for 13C,
376 MHz for 19F), Varian Gemini 400 MHz spectrometer (400 MHz
1
for H, 100 MHz for 13C, 376 MHz for 19F), Agilent DD2−500 MHz
spectrometer (500 MHz for 1H, 126 MHz for 13C), an Agilent DD2−
600 MHz spectrometer (600 MHz for 1H, 151 MHz for 13C, 564 MHz
for 19F), or an Agilent DD2−700 MHz. All assignments of signals were
1
completed by 2D experiments. The H and 13C NMR spectra were
measured relative to partially deuterated solvent peaks but are reported
relative to tetramethylsilane (TMS). GC-FID equipped with a chiral
column was used to analyze the conversion and enantioselectivity. The
details of GC temperature and chromatographs were identical to those
found in Demmans et al.65 Abbreviations: Phi = ipso carbon of ring;
Pho = ortho carbon; etc.
CONCLUSIONS
■
Two bulky new members of the class of Kaibene ligands, tBu-
Kaibene (S,S)-11 and Mes-Kaibene (S,S)-12, composed of an
NHC and a primary amine which are connected by a chiral
backbone have been prepared in high yield and purity. In the
presence of base and group 11 metal halides, four compounds
containing a ligand/metal ratio of 2 have been prepared. The
oxidative addition of the imidazolium salts to iridium(I) to
generate iridium(III) hydride Kaibene compounds was also
observed with 29% conversion for (S,S)-11 and 99%
conversion for (S,S)-12. Using an internal alkoxide base as in
[Ir(OtBu)(cod)]2 allows the preparation of a bimetallic iridium
compound with (S,S)-11 as the bridging ligand. This ligand
exhibits interesting noncovalent interactions within the
bimetallic molecule, which can be observed through spectros-
copy and by X-ray diffraction studies. Using silver oxide as the
base, efficient silver-based transmetalation reagent 20 has been
generated for the transfer of ligand (S,S)-12. This trans-
metalation reagent can deliver 1 equiv of (S,S)-12 to rhodium
and iridium as a bidentate NHC∧amine chelate ligand. The
iridium compound prepared using [IrCl(cod)]2 and 20 also
facilitates an oxidative addition of an ortho C−H bond of the
phenyl substituent on the ligand backbone to produce an
iridium(III) hydride complex. The two iridium hydride
compounds, 18 and 22 were tested for ketone hydrogenation
and were shown to be effective ketone hydrogenation catalysts
(TON 499, TOF 249 s−1) but ineffective for their asymmetric
hydrogenation. The bifunctional activity of these ligand places
them among the family of Smart NHC ligands, which were
recently reviewed by Peris.64
3-((1S,2S)-1,2-Diphenyl-2-aminoethyl)-1-tert-butylimidazo-
lium hexafluorophosphate, tBu-KaibeneHPF6, (S,S)-11·HPF6. A
round-bottomed flask was charged with 1-tert-butylimidazole (621 mg,
5.0 mmol, 2 equiv), the sulfamidate (4S,5R)-1,2,3-oxathiazolidine-3-
carboxylic acid,4,5-diphenyl-1,1-dimethylethylester-2,2-dioxide (10,
938 mg, 2.5 mmol, 1 equiv), and toluene (4 mL). The mixture was
heated to reflux for 1 h after which time a precipitate formed. After
cooling to room temperature, diethyl ether (40 mL) was added, and
the resulting precipitate was collected by filtration. The solid was
treated with HCl (37% in H2O, 5 mL) and stirred for 1 h. Na2CO3 was
added to neutralize the mixture and make the solution basic. KPF6
(460 mg, 2.5 mmol, 1 equiv) was added, and the suspension was
stirred for 18 h. The solid was collected by filtration and purified by
recrystallization in CH2Cl2/diethyl ether to yield (S,S)-11·HPF6 as an
off-white solid. Yield: 918 mg (1.97 mmol, 79%). 1H NMR (500 MHz,
CD2Cl2, 298 K) δ 8.82 (t, 3JHH = 1.7 Hz, 1H, NCHN), 7.52 (t, 3JHH
=
1.9 Hz, 1H, NCHCHN), 7.44−7.15 (m, 11H, Ph−CH and
3
NCHCHN), 5.73 (d, JHH = 8.4 Hz, 1H, ImidCHPhCHPhNH2),
3
4.78 (d, JHH = 8.4 Hz, 1H, ImidCHPhCHPhNH2), 1.73 (br, 2H,
NH2), 1.63 (s, 9H, tBu). 13C{1H} NMR (126 MHz, CD2Cl2, 298 K) δ
141.1 (NCN), 134.5 (NCHCHN), 134.1 (NCHCHN), 129.3 (Pho or
Phm), 129.2 (Phi), 128.9 (Pho or Phm), 127.9(Phi), 127.8 (Pho or
Phm), 126.5 (Pho or Phm), 121.9 (Php), 119.1 (Php), 70.0
( I m i d C H P h C H P h N H 2 ) , 6 0 . 4 ( C ( C H 3 ) 3 ) , 5 8 . 3
(ImidCHPhCHPhNH2), 29.4 (C(CH3)3). 19F NMR (376 MHz,
1
CDCl3, 298 K): δ −71.4 (d, JFP = 713.3 Hz). 31P NMR (121 MHz,
CD2Cl2, 298 K): δ −144.2 (heptet, 1JPF = 713.3 Hz). HRMS (ESI, m/
+
z): calc. for C21H36N3 [M]+ 320.2127, found 320.2128. Anal. Calcd
for C21H36N3PF6: C, 54.19; H, 5.63; N, 9.03%. Found: C, 54.07; H,
5.88; N, 8.94%.
3-((1S,2S)-1,2-Diphenyl-2-aminoethyl)-1-mesityl-imidazo-
lium Hexafluorophosphate, Mes-KaibeneHPF6, (S,S)-12 HPF6.
The sulfamidate 10 (624 mg, 1.66 mmol, 1 equiv) and 1-(Mes)-
imidazole (309 mg, 1.66 mmol, 1 equiv) were suspended in about 5
mL of MeCN. The mixture was refluxed overnight. After cooling to
EXPERIMENTAL SECTION
General Considerations. All of the syntheses of transition metal
complexes were performed under an argon or nitrogen atmosphere
■
I
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room temperature, 5 mL concentrated HCl was added, and the
reaction mixture was stirred for few hours. Then, sufficient sodium
carbonate solution was added to neutralize the solution, and KPF6
(320 mg, 1.74 mmol, 1.05 equiv) was added. The solution was stirred
overnight, and the product was extracted with dichloromethane
(product forms a yellow solution in DCM). The extracts were quickly
dried over magnesium sulfate, and all DCM were removed under
vacuum. The yellow oil obtained was reprecipitated from DCM/
hexane. Yield: 619 mg (1.17 mmol, 71%). 1H NMR (400 MHz,
DMSO-d6, 298 K) δ 9.76 (t, 4JHH = 1.4 Hz, 1H, NCHN), 8.23 (t, 3JHH
(Php), 128.4 (Php), 127.8 (Pho or Phm), 127.6 (Pho or Phm), 120.4
(NCHCHN), 119.3 (NCHCHN), 72.4 (ImidCHPhCHPhNH2), 59.1
(ImidCHPhCHPhNH2), 58.2 (C(CH3)3), 32.0 (C(CH3)3). MS
(MALDI-TOF, DCTB, m/z): 701 [M − I]+. Anal. Calcd for
C42H50CuIN6·0.5 CH2Cl2: C, 58.55; H, 5.90; N, 9.64%. Found: C,
58.39; H, 6.26; N, 9.29%.
Bis[3-((1S,2S)-1,2-diphenyl-2-aminoethyl)-1-mesityl-butyli-
midazol-2-ylidene]iodosilver, AgI(Mes-Kaibene)2, 15. Com-
pound 15 is synthesized as an off-white powder using a similar
procedure as that for making 13 with 300 mg of 12·HPF6. Yield: 283
1
3
mg (quantitative). H NMR (500 MHz, DMSO-d6, 298 K) δ 7.63−
= 1.7 Hz, 1H, NCHCHN), 7.96 (t, JHH = 1.5 H, 1H, NCHCHN),
6.73 (m, 28H, Ph−CH, NCHCHN, Mes−CH), 5.68 (br, 2H,
ImidCHPhCHPhNH2), 5.04 (m, 2H, ImidCHPhCHPhNH2), 2.31
(s, 6H, p-CH3 in Mes), 1.90 (d, 3JHH = 3.2 Hz, 4H, NH2), 1.71 (s, 6H,
o-CH3 in Mes), 1.32 (s, 6H, o-CH3 in Mes). 13C{1H} NMR (126
MHz, CD2Cl2, 298 K): δ 184.3 (NCN), 141.3 (Phi, Mesi, Meso, or
Mesp), 139.9 (Phi, Mesi, Meso, or Mesp), 137.9 (Phi, Mesi, Meso, or
Mesp), 136.1 (Phi, Mesi, Meso, or Mesp), 135.5 (Phi, Mesi, Meso, or
Mesp), 135.3 (Phi, Mesi, Meso, or Mesp), 129.7 (Ph−CH or Mes−
CH), 129.6 (Ph−CH or Mes−CH), 129.6 (Ph−CH or Mes−CH),
129.0 (Ph−CH or Mes−CH), 128.8 (Ph−CH or Mes−CH), 128.1
(Ph−CH or Mes−CH), 127.2 (Ph−CH or Mes−CH), 127.1 (Ph−
CH or Mes−CH), 122.9 (NCHCHN), 122.8 (NCHCHN), 71.5
(ImidCHPhCHPhNH2), 58.3 (ImidCHPhCHPhNH2), 21.4 (p-CH3 in
Mes), 18.1 (o-CH3 in Mes), 17.9 (o-CH3 in Mes). Anal. Calcd for
C52H54AgIN6: C, 62.59; H, 5.46; N, 8.42%. Found: C, 57.33; H, 5.81;
N, 6.71%. Satisfactory elementary analysis cannot be obtained due to
the relatively high instability of 15 in light and in air.
7.46 (m, 2H, o-Ph−CH adjacent to Imid.), 7.34 (d, 2H, o-Ph−CH
adjacent to NH2), 7.31 (t, 2H, m-Ph−CH adjacent to Imid.), 7.27 (t,
1H, p-Ph−CH adjacent to Imid.), 7.24 (t, 2H, m-Ph−CH adjacent to
NH2), 7.17 (s, 2H, Mes−CH), 7.15 (t, 1H, p-Ph−CH adjacent to
3
NH2), 5.89 (d, JHH = 9.7 Hz, 1H, ImidCHPhCHPhNH2), 4.90 (d,
3JHH = 9.7 Hz, 1H, ImidCHPhCHPhNH2), 2.35 (s, 3H, p-Me in Mes),
2.34 (br, 2H, NH2), 2.02 (s, 3H, o-Me in Mes), 2.00 (s, 3H, o-Me in
Mes). 13C{1H} NMR (101 MHz, DMSO-d6, 298 K) δ 142.5 (Phi in
Ph adjacent to NH2), 140.3 (Mesp), 137.3 (NCHN), 136.1 (Phi in Ph
adjacent to Imid.), 134.1 (Meso), 131.1 (Mesi), 129.2 (m-Mes−CH),
128.7 (m-Ph−CH adjacent to Imid.), 128.6 (p-Ph−CH adjacent to
Imid.), 128.2 (m-Ph−CH adjacent to NH2), 127.7 (o-Ph−CH
adjacent to Imid.), 127.1 (p-Ph−CH adjacent to NH2), 126.9 (o-
Ph−CH adjacent to NH2), 123.7 (NCHCHN), 122.8 (NCHCHN),
69.6 (ImidCHPhCHPhNH2), 57.6 (ImidCHPhCHPhNH2), 20.5 (p-
1
CH3 in Mes), 16.8 (o-CH3 in Mes), 16.7 (o-CH3 in Mes). H−15N
HMBC NMR (400 MHz, DMSO-d6, 298 K) δ 192.7 (NCHCHN,
chiral backbone substituted), 181.7 (NCHCHN, Mes substituted),
35.3 (NH2). 19F NMR (376 MHz, DMSO-d6, 298 K) δ −70.1 (d, PF6,
1JFP = 711 Hz). 31P NMR (162 MHz, DMSO-d6, 298 K) δ −144.1
Bis[3-((1S,2S)-1,2-diphenyl-2-aminoethyl)-1-mesityl-butyli-
midazol-2-ylidene]iodocopper, CuI(Mes-Kaibene)2, 16. Com-
pound 16 is synthesized as an off-white powder with a procedure
similar to that for making 14 with 300 mg of 12·HPF6. Yield: 250 mg
+
(heptet, PF6, 1JFP = 711 Hz). HRMS (ESI, m/z): calcd for C26H28N3
1
3
[M]+ 382.2278, found 382.2283. Anal. Calcd for C26H28N3PF6: C,
59.20; H, 5.35; N, 7.97%. Found: C, 60.01; H, 5.41; N, 7.86%.
Bis[3-((1S,2S)-1,2-diphenyl-2-aminoethyl)-1-tert-butylimida-
zol-2-ylidene]iodosilver, AgI(tBu-Kaibene)2, 13. In a nitrogen
glovebox and protected from light, 11·HPF6 (100 mg, 0.215 mmol, 1
equiv), AgI (26 mg, 0.107 mmol, 0.5 equiv), KI (89 mg, 0.538 mmol,
2.5 equiv), and KHMDS (47 mg, 0.237 mmol, 1.1 equiv) were
dissolved in THF (10 mL). The initially clear solution was stirred at
room temperature for 18 h. The resulting suspension was filtered
through a pad of Celite, and the volatiles were removed in vacuo. The
residue was redissolved in CH2Cl2 (2 mL) and filtered through a pad
of Celite. Addition of pentane (20 mL) gave 13 as an off-white, very
light sensitive solid. Yield: 65 mg, (0.074 mmol, 69%). 1H NMR (400
MHz, CD2Cl2, 298 K): δ 7.66 (d, 3JHH = 2.0 Hz, 2H, NCHCHN), 7.33
(92%). H NMR (500 MHz, DMSO-d6, 298 K) δ 7.95 (d, JHH = 1.8
Hz, 2H, NCHCHN), 7.42 (d, 3JHH = 1.8 Hz, 2H, NCHCHN), 7.35−
7.23 (m, 6H, Ph−CH), 7.23−7.03 (m, 14H, Ph−CH), 6.97 (s, 2H,
Mes−CH), 6.93 (s, 2H, Mes−CH) 5.42 (br, 2H,
ImidCHPhCHPhNH2), 5.01 (m, 2H, ImidCHPhCHPhNH2), 2.23
(s, 6H, p-CH3 in Mes), 1.87 (d, 3JHH = 3.2 Hz, 4H, NH2), 1.75 (s, 6H,
o-CH3 in Mes), 1.64 (s, 6H, o-CH3 in Mes). 13C{1H} NMR (126
MHz, DMSO-d6, 298 K): δ 181.8 (NCN), 140.6 (Phi, Mesi, Meso, or
Mesp), 138.3 (Phi, Mesi, Meso, or Mesp), 137.9 (Phi, Mesi, Meso, or
Mesp), 135.9 (Phi, Mesi, Meso, or Mesp), 134.9 (Phi, Mesi, Meso, or
Mesp), 134.1 (Phi, Mesi, Meso, or Mesp), 128.9 (Pho, Phm, Php,
NCHCHN or Mes−CH), 128.4 (Pho, Phm, Php, NCHCHN or Mes−
CH), 127.7 (Pho, Phm, Php, NCHCHN or Mes−CH), 126.8 (Pho,
Phm, Php, NCHCHN or Mes−CH), 126.6 (Pho, Phm, Php, NCHCHN
or Mes−CH), 121.8 (Pho, Phm, Php, NCHCHN or Mes−CH), 68.7
(ImidCHPhCHPhNH2), 57.0 (ImidCHPhCHPhNH2), 20.7 (p-CH3
in Mes), 17.1 (o-CH3 in Mes), 16.8 (o-CH3 in Mes). Anal. Calcd for
C52H54CuIN6·2H2O: C, 63.12; H, 5.91; N, 8.49%. Found: C, 62.84; H,
6.00; N, 8.36%.
3
(d, JHH = 2.0 Hz, 2H, NCHCHN), 7.30−7.06 (m, 20H, Ph−CH),
3
3
5.93 (d, JHH = 7.7 Hz, 2H, ImidCHPhCHPhNH2), 4.99 (dt, JHH
=
7.7 Hz, 3JHH = 4.5 Hz, 2H, ImidCHPhCHPhNH2), 1.64 (s, 18H, tBu),
1.58 (d, 3JHH = 4.5 Hz, 4H, NH2). 13C{1H} NMR (126 MHz, CD2Cl2,
298 K): δ 181.8 (NCN), 141.7 (Phi), 138.0 (Phi), 129.2 (Pho or Phm),
128.9 (Pho or Phm), 128.6 (Php), 127.9 (Php), 127.9 (Pho or Phm),
127.7 (Pho or Phm), 120.0 (NCHCHN), 119.3 (NCHCHN), 73.7
(ImidCHPhCHPhNH2), 58.9 (ImidCHPhCHPhNH2), 58.1
(C(CH3)3), 32.0 (C(CH3)3).
Chloridohydrido(η2,η2-cycloocta-1,5-diene)[3-((1S,2S)-1,2-di-
phenyl-2-aminoethyl)-1-mesityl-imidazol-2-ylidene]iridium-
(III), [Ir(cod)(Cl)(H)(Mes-Kaibene)](PF6), 18. [IrCl(cod)]2 (128 mg,
0.191 mmol, 0.5 equiv) and 12·HPF6 (200 mg, 0.379 mmol, 1 equiv)
were dissolved in 5 mL of anhydrous chloroform and stirred at room
temperature for 18 h. The solution was then filtered through a pad of
Celite to remove any insolubles. The residue yellow solid was then
washed with diethyl ether for 3 h, collected by filtration, and dried in
Bis[3-((1S,2S)-1,2-diphenyl-2-aminoethyl)-1-tert-butylimida-
zol-2-ylidene]iodocopper, CuI(tBu-Kaibene)2, 14. In a nitrogen
Schlenk flask, 11·HPF6 (100 mg, 0.214 mmol, 1 equiv), CuI (21 mg,
0.107 mmol, 0.5 equiv), and KHMDS (50 mg, 0.251 mmol, 1.17
equiv) were dissolved in THF (10 mL). The initially clear, orange
solution was stirred at room temperature overnight. The resulting
suspension was filtered over a pad of Celite, and the volatiles were
removed in vacuo. The residue was redissolved in CH2Cl2 (2 mL) and
filtered. Removal of all volatiles in vacuo and washing with Et2O (3 × 5
1
vacuum for 18 h. Yield: 310 mg (0.359 mmol, 95%). H NMR (400
MHz, CDCl3, 298 K) δ Major (69%): 7.51−6.76 (m, 14H, Ph−CH,
Mes−CH, and NCHCHN), 7.09 (s, 1H, NCHCHN), 6.25 (s, 1H,
NCHCHN), 6.13 (d, 1H, ImidCHPhCHPhNH2), 5.39 (m, 1H, NH2),
3
5.11 (m, JHH = 9.7 Hz, 1H, ImidCHPhCHPhNH2), 5.17 (m, 1H,
1
cod−CH), 4.44 (m, 1H, cod−CH), 4.41 (m, 1H, cod−CH), 4.28 (m,
1H, cod−CH), 3.66 (d, 3JHH = 10.9 Hz, 1H, NH2), 2.92 (m, 1H, cod−
CH2), 2.91 (m, 1H, cod−CH2), 2.81 (m, 1H, cod−CH2), 2.67 (m,
1H, cod−CH2), 2.44 (m, 1H, cod−CH2), 2.30 (m, 1H, cod−CH2),
2.19 (m, 1H, cod−CH2), 2.18 (m, 1H, cod−CH2), 2.29 (s, p-CH3 in
Mes), 2.02 (s, o-CH3 in Mes), 1.96 (s, o-CH3 in Mes); hydride region:
mL) gave 14 as a white solid. Yield: 83 mg, (0.102 mmol, 95%). H
NMR (399 MHz, CD2Cl2): δ 7.66−6.91 (m, 24H, Ph−CH and
NCHCHN), 5.77 (d, 3JHH = 6.6 Hz, 2H, ImidCHPhCHPhNH2), 4.93
(m, 2H, ImidCHPhCHPhNH2), 1.62 (s, 18H, tBu), 1.55 (m, 4H,
NH2). 13C{1H} NMR (101 MHz, CD2Cl2): δ 177.9 (NCN), 141.2
(Phi), 138.1 (Phi), 129.5 (Pho or Phm), 128.9 (Pho or Phm), 128.8
J
DOI: 10.1021/acs.organomet.7b00915
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Major (cis-H/Cl, 69%): −14.25 (s, 1H, IrH); Minor (trans-H/Cl,
22%): −14.63 (s, 1H, IrH); other isomers: −12.94, −13.25, −14.73,
−15.65 (s, 1H, IrH). 13C{1H} NMR (101 MHz, CDCl3, 298 K) δ
Major (69%): 154.7 (NCN), 141.0 (Phi), 129.8 (Phi), 129.3
(NCHCHN), 123.3 (NCHCHN), 130.5−123.5 (Pho, Phm, Php,
Mesi, Meso, Mesm, and Mesp), 96.9 (cod−CH), 94.7 (cod−CH),
76.3 (cod−CH), 74.6 (cod−CH), 67.8 (ImidCHPhCHPhNH2), 61.3
(ImidCHPhCHPhNH2), 34.1 (cod−CH2), 31.7 (cod−CH2), 30.9
(cod−CH2), 27.3 (cod−CH2), 21.1 (p-CH3 in Mes), 17.5 (o-CH3 in
Mes), 17.5 (o-CH3 in Mes). 1H−15N HSQC/HMBC NMR (700
(HSQC) and 400 (HMBC) MHz, CDCl3, 298 K) δ Major (69%):
204.2 (NCHCHN, Mes-substituted), 182.4 (NCHCHN, chiral
backbone substituted), 0.75 (NH2). 19F NMR (376 MHz, CDCl3,
298 K) δ −71.6 (d, PF6). 31P NMR (162 MHz, CDCl3, 298 K) δ
−144.1 (heptet, PF6). HRMS (ESI, m/z): Calcd for [C34H40N3ClIr]+
718.2528, found 718.2526; calcd for [C34H39N3Ir]+ 682.2769, found
682.2766; calcd for [C34H39N3Cl2Ir]+ 752.2132, found 752.2136. Anal.
Calcd for C34H40ClN3PF6Ir: C, 47.30; H, 4.67; N, 4.87%. Found: C,
47.21; H, 4.70; N, 4.93%.
was washed by more anhydrous dichloromethane (5 mL × 2). The
organic washings and filtrate were then combined, and volatiles were
removed under reduced pressure. The residue obtained was then
suspended in a pentane/diethyl ether mixture (10 mL, 1:1 ratio) and
stirred vigorously for 3.5 h. The white power formed was collected by
filtration and dried under vacuum for 18 h. Yield: 395 mg (0.31 mmol,
82%). 1H NMR (400 MHz, DMSO-d6, 298 K) δ 8.06 (s, 1H,
NCHCHN), 7.80−6.80 (m, 13H, Ph−CH, Mes−CH group, and
NCHCHN), 5.94 (br, 1H, ImidCHPhCHPhNH2), 5.61 (br, 1H,
ImidCHPhCHPhNH2), 4.67 (br, 2H, NH2), 2.30 (s, 3H, p-CH3 in
Mes), 1.96 (s, 3H, o-CH3 in Mes), 1.71 (s, 3H, o-CH3 in Mes).
13C{1H} NMR (101 MHz, DMSO-d6, 298 K) δ 181.5 (NCN), 138.7
(Phi), 134.1 (Phi), 126.7 (NCHCHN), 119.8 (NCHCHN), 129−127
(Pho, Phm, Php, Meso, Mesm, and Mesp), 73.0 (br, 1H,
ImidCHPhCHPhNH2), 55.6 (br, 1H, ImidCHPhCHPhNH2), 20.5
(p-CH3 in Mes), 18.0 (o-CH3 in Mes), 17.0 (o-CH3 in Mes). (These
peaks were determined through a combination of 13C{1H} NMR,
gHSQC (1H−13C) NMR, and gHMBC (1H−13C) NMR). 19F NMR
(376 MHz, DMSO-d6, 298 K) δ −70.1 (d, PF6). 31P NMR (162 MHz,
Chlorido(η2,η2-cycloocta-1,5-diene)iridium(I)-μ-[3-((1S,2S)-
1,2-diphenyl-2-amino-κN-ethyl)-1-tert-butylimidazol-2-yli-
dene-κC]chlorido(η2,η2-cycloocta-1,5-diene)iridium(I), (cod)-
IrCl(κ-tBu-Kaibene)IrCl(cod), 19. In a nitrogen glovebox a 3 mL
scintillation vial was charged with 11·HPF6 (50 mg, 0.107 mmol, 1
equiv), [IrCl(cod)]2 (72 mg, 0.107 mmol, 1 equiv), and KOtBu (14
mg, 0.128 mmol, 1.2 equiv). The mixture was dissolved in THF (1
mL) and stirred at room temperature for 3 h. The volatiles were
removed in vacuo; the residue was redissolved in CH2Cl2 (1 mL) and
filtered over a pad of Celite. The Celite was washed with 1 mL of
CH2Cl2. n-Pentane (10 mL) was added to the filtrate, and the resulting
suspension was filtered. The second filtrate was reduced to 2 mL, and
n-pentane was added (10 mL). Compound 19 precipitated as a bright
yellow powder and was collected via filtration and dried in vacuo.
Single crystals suitable for an X-ray diffraction study were obtained by
slow diffusion of pentane into a saturated solution of 19 in THF under
DMSO-d6, 298 K) δ −144.2 (heptet, PF6). HRMS (ESI, m/z): calcd
2+
for [C26H27N3Ag]2
488.1250, found 488.1251. Calcd for
[C52H54N6Ag]+ 869.3455, found 869.3464. MS (MALDI-TOF,
2+
DCTB, m/z): Calcd for [C26H27N3Ag]2 488.1250, found 488.125.
Calcd for [C52H54N6Ag]+ 869.3455, found 869.364. Anal. Calcd for
C26H27AgF6N3P: C, 49.23; H, 4.29; N, 6.62%. Found: C, 52.86; H,
4.44; N, 6.77%. Unsatisfactory carbon analyses but acceptable
hydrogen and nitrogen content were measured, even in the presence
of V2O5, because of a combustion problem due to the presence of the
hexafluorophosphate anion.66
(η2,η2-Cycloocta-1,5-diene)[3-((1S,2S)-1,2-diphenyl-2-amino-
ethyl)-1-mesityl-butylimidazol-2-ylidene]rhodium Hexafluoro-
phosphate, [Rh(cod)(Mes-Kaibene)](PF6), 21. [RhCl(cod)]2 (20
mg, 0.041 mmol, 1.03 equiv) and 20 (50 mg, 0.039 mmol, 1 equiv)
were dissolved in 2 mL of anhydrous dichloromethane and stirred at
room temperature for 18 h, protected from light. White precipitate
slowly formed over time was filtered off, and the residue was washed
with more anhydrous dichloromethane. Dichloromethane was then
evaporated under reduced pressure, and the residue was redissolved in
dichloromethane. More precipitate that might form was removed by
filtration. This process was repeated until no suspension was observed
when the solid was dissolved in DCM. Then, the yellow solid was
washed with diethyl ether for 3 h, collected by filtration, and dried
under vacuum for 18 h. Crystals suitable for an X-ray diffraction study
were obtained by slow diffusion of pentane into a saturated solution of
1
a nitrogen atmosphere. Yield: 40 mg (0.04 mmol, 38%). H NMR
3
(500 MHz, CD2Cl2, 298 K): δ 8.17 (d, JHH = 11.3 Hz, 1H,
3
ImidCHPhCHPhNH2), 7.76−7.71 (m, 2H, Ph−CH), 7.66 (d, JHH
=
2.2 Hz, 1H, NCHCHN), 7.46−7.41 (m, 2H, Ph−CH), 7.41−7.35 (m,
2H, Ph−CH and NCHCHN), 7.29−7.20 (m, 5H, Ph−CH), 5.24 (m,
3JHH = 11.8 Hz, JHH = 11.3 Hz, JHH = 2.6 Hz, 1H,
3
3
3
3
ImidCHPhCHPhNH2), 4.93 (td, JHH = 7.6 Hz, JHH = 2.7 Hz, 1H,
cod−CH), 4.76 (dd, 3JHH = 11.8 Hz, 2J = 11.5 Hz, 1H, NH2), 4.41 (m,
1H, cod−CH), 3.93 (td, 3JHH = 7.4 Hz, 3JHH = 2.7 Hz, 1H, cod−CH),
1
3.79 (td, 3JHH = 7.6 Hz, 3JHH = 3.9 Hz, 1H, cod−CH), 3.44 (td, 3JHH
=
=
=
21 in dichloromethane. Yield: 42 mg (0.057 mmol, 72%). H NMR
7.4 Hz, 3JHH = 2.9 Hz, 1H, cod−CH), 3.12 (m, JHH = 8.5 Hz, 3JHH
3
(400 MHz, DMSO-d6, 298 K) δ 7.54 (t, 2H, m-Ph−CH adjacent to
Imid.), 7.47 (m, 2H, o-Ph−CH adjacent to Imid.), 7.44 (t, 1H, p-Ph−
CH adjacent to Imid.), 7.32 (t, 2H, m-Ph−CH adjacent to NH2), 7.30
(t, 1H, p-Ph−CH adjacent to NH2), 7.29 (d, 1H, NCHCHN), 7.26 (d,
2H, o-Ph−CH adjacent to NH2), 7.17 (d, 1H, NCHCHN), 7.17 (s,
6.8 Hz, 3JHH = 2.0 Hz, 1H, cod−CH), 2.74 (td, 3JHH = 7.7 Hz, 3JHH
2
4.0 Hz, 1H, cod−CH), 2.57 (d, J = 11.5 Hz, 1H, NH2), 2.52−2.41
(m, 1H, cod−CH2), 2.37−2.22 (m, 2H, cod−CH and cod−CH2),
2.18−1.84 (m, 4H, cod−CH2), 1.92 (s, 9H, tBu), 1.74−1.66 (m, 2H,
cod−CH2), 1.53−1.42 (m, 1H, cod−CH2), 1.34−1.11 (m, 6H, cod−
CH2), 0.98−0.90 (m, 1H, cod−CH2). 13C{1H} NMR (126 MHz,
CD2Cl2, 298 K): δ 181.3 (NCN), 139.4 (Phi), 138.0 (Phi), 130.1 (Pho
or Phm), 129.3 (Pho or Phm), 129.1 (Php), 129.1 (Pho or Phm), 128.8
(Php), 128.3 (Pho or Phm), 123.1 (NCHCHN), 118.8 (NCHCHN),
84.5 (cod−CH), 79.3 (cod−CH), 71.4 (ImidCHPhCHPhNH2), 67.1
(cod−CH), 64.6 (cod−CH), 63.3 (ImidCHPhCHPhNH2), 60.2
(C(CH3)3), 58.1 (cod−CH), 57.4 (cod−CH), 54.4 (cod−CH), 54.0
(cod−CH), 34.9 (cod−CH2), 33.0 (C(CH3)3), 32.2 (cod−CH2), 31.9
(cod−CH2), 31.5 (cod−CH2), 31.5 (cod−CH2), 31.2 (cod−CH2),
30.7 (cod−CH2), 28.0 (cod−CH2). MS (MALDI-TOF, DCTB, m/z):
991 [M]+. Anal. Calcd for C37H49Cl2Ir2N3: C, 44.84; H, 4.98; N,
4.24%. Found: C, 44.63; H, 5.39; N, 3.73%.
[3-((1S,2S)-1,2-Diphenyl-2-aminoethyl)-1-mesityl-butylimi-
dazol-2-ylidene]silver Hexafluorophosphate Dimer, [Ag(Mes-
Kaibene)]2(PF6)2, 20. 12·HPF6 (400 mg, 0.76 mmol, 1 equiv), Ag2O
(300 mg, 1.29 mmol, 1.71 equiv), and 1 g of activated 4 Å molecular
sieves were suspended in 10 mL of anhydrous dichloromethane, and
the reaction mixture was stirred at 35 °C for 18 h, protected from light.
Then, all the insolubles were removed by filtration, and the residue
3
1H, Mes−CH), 7.01 (s, 1H, Mes−CH), 5.83 (d, JHH = 1.0 Hz, 1H,
3
ImCHPhCHPhNH2 ), 5.10 (d, JH H
= 7.5 Hz, 1H,
3
ImCHPhCHPhNH2), 4.90 (dd, JHH = 12.9, 8.1 Hz, 1H, NH2), 4.55
(m, 1H, cod−CH), 4.33 (d, JHH = 12.9 Hz, 1H, NH2), 4.07 (m, 1H,
3
cod−CH), 3.37 (m, 1H, cod−CH), 2.62 (m, 1H, cod−CH), 2.50 (s,
3H, p-CH3 in Mes), 2.31 (s, 3H, o-CH3 in Mes), 2.26 (m, 1H, cod−
CH2), 1.94 (m, 1H, cod−CH2), 1.92 (s, 3H, o-CH3 in Mes), 1.65 (m,
1H, cod−CH2), 1.45 (m, 3H, cod−CH2), 1.29 (m, 2H, cod−CH2).
13C{1H} NMR (101 MHz, DMSO-d6, 298 K) δ 173.4 (d, 1JRh−C = 53.2
Hz, NCN), 139.0 (Phi in Ph adjacent to Imid.), 138.7 (Mesp), 138.7
(Phi in Ph adjacent to NH2), 135.5 (Mesi), 134.8 (Meso), 134.4
(Meso), 128.9 (Mesm), 128.8 (Mesm), 128.3 (Phm in Ph adjacent to
Imid.), 128.0 (Phm in Ph adjacent to NH2), 127.6 (Php), 127.1 (Pho in
Ph adjacent to Imid.), 126.7 (Pho in Ph adjacent to NH2), 124.4
1
(NCHCHN), 123.2 (NCHCHN), 92.9 (d, JRh−C = 7.6 Hz, cod−
1
1
CH), 92.3 (d, JRh−C = 7.8 Hz, cod−CH), 73.1 (d, JRh−C = 12.3 Hz,
1
cod−CH), 71.4 (d, JRh−C
= 12.9 Hz, cod−CH), 68.6
(ImidCHPhCHPhNH2), 51.9 (ImidCHPhCHPhNH2), 32.4 (cod−
CH2), 30.0 (cod−CH2), 29.6 (cod−CH2), 25.8 (cod−CH2), 20.5 (p-
CH3 in Mes), 18.9 (o-CH3 in Mes), 17.3 (o-CH3 in Mes). H−15N
1
K
DOI: 10.1021/acs.organomet.7b00915
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
HMBC NMR (400 MHz, DMSO-d6, 298 K) δ 194.5 (NCHCHN,
Mes substituted), 190.9 (NCHCHN, chiral backbone substituted), 4.8
(NH2). 19F NMR (376 MHz, DMSO-d6, 298 K) δ −70.2 (d, PF6, 1JFP
= 711 Hz). 31P NMR (162 MHz, DMSO-d6, 298 K) δ −144.2 (heptet,
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00915.
■
S
1
PF6, JFP = 711 Hz). HRMS (ESI, m/z): Calcd for [C34H39N3Rh]+
592.2194, found 592.2195. Anal. Calcd for C34H39N3PF6Rh: C, 55.37;
H, 5.33; N, 5.70%. Found: C, 55.13; H, 5.38; N, 5.55%.
The proposed structures of all of the isomers of 17 and
Hydrido(η2,η2-cycloocta-1,5-diene)[o-metalated-3-((1S,2S)-
1,2-diphenyl-2-aminoethyl)-1-mesityl-butylimidazol-2-
ylidene]iridium Hexafluorophosphate, [Ir(cod)(H)(o-metalated
Mes-Kaibene)](PF6), 22. [IrCl(cod)]2 (106 mg, 0.158 mmol, 1
equiv) and 20 (200 mg, 0.158 mmol, 1 equiv) were dissolved in 5 mL
of anhydrous dichloromethane and stirred at room temperature for 18
h, protected from light. White precipitate slowly formed overtime was
filtered off, and the residue was washed with more anhydrous
dichloromethane. Dichloromethane was then evaporated under
reduced pressure, and the residue was redissolved in dichloromethane.
More precipitate that might form was removed by filtration. This
process was repeated until no suspension was observed when the solid
was dissolved in DCM. Then, the yellow solid was washed with diethyl
ether for 3 h and collected by filtration, dried in vacuum for 18 h.
Single crystals suitable for an X-ray diffraction study were obtained by
slow diffusion of pentane into a saturated solution of 22 in
1
18, H, 13C, 19F, and 31P NMR spectra and table of
hydrogenation results (PDF)
Accession Codes
CCDC 1813983−1813985 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing 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 Authors
*E-mail: fehahn@uni-muenster.de.
*E-mail: rmorris@chem.utoronto.ca.
■
1
dichloromethane. Yield: 219 mg (0.265 mmol, 84%). H NMR (400
MHz, DMSO-d6, 298 K) δ 7.47 (d, 1H, o-Ph−CH in Ph adjacent to
Imid.), 7.33 (t, 1H, p-Ph−CH in Ph adjacent to NH2), 7.32 (m, 3H,
m-Ph−CH in Ph adjacent to NH2, CH adjacent to phenyl ligand), 7.14
(m, 4H, Mes−CH, NCHCHN), 7.10 (d, 2H, o-Ph−CH in Ph adjacent
to NH2), 6.98 (t, 1H, m-Ph−CH in Ph adjacent to Imid.), 6.88 (t, 1H,
ORCID
Kai Y. Wan: 0000-0001-7590-1848
F. Ekkehardt Hahn: 0000-0002-2807-7232
Robert H. Morris: 0000-0002-7574-9388
2
3
p-Ph−CH in Ph adjacent to Imid.), 6.02 (dd, JHH = 12.5 Hz, JHH
=
Notes
3
9.0 Hz, 1H, NH2), 5.70 (d, JHH = 2.5 Hz, 1H, ImCHPhCHPhNH2),
The authors declare no competing financial interest.
2
5.32 (m, 1H, cod−CH), 5.15 (d, JHH = 12.5 Hz, 1H, NH2), 4.41 (d,
3JHH = 9.0 Hz, 1H, ImCHPhCHPhNH2), 4.37 (m, 1H, cod−CH), 4.34
(m, 1H, cod−CH), 4.06 (m, 1H, cod−CH), 2.90 (m, 1H, cod−CH2),
2.65 (m, 1H, cod−CH2), 2.40 (m, 1H, cod−CH2), 2.36 (s, 3H, p-CH3
in Mes), 2.35 (m, 2H, cod−CH2), 2.06 (s, 3H, o−CH3 in Mes), 1.77
(s, 3H, o−CH3 in Mes), 1.72 (m, 2H, cod−CH2), 1.63 (m, 1H, cod−
CH2) −15.49 (s, 1H, IrH). 13C{1H} NMR (101 MHz, DMSO-d6, 298
K) δ 153.6 (NCN), 139.2 (Mesp), 138.3 (Phi in Ph adjacent to NH2),
138.1 (Phi in Ph adjacent to Imid.), 137.2 (Pho in phenyl ligand),
135.5 (Mesi), 135.5 (Pho and Phm in phenyl ligand), 135.2 (Meso),
134.6 (Meso), 129.3 (Mesm), 128.7 (Mesm), 128.1 (Phm in Ph adjacent
to NH2), 127.7 (Php in Ph adjacent to NH2), 126.7 (Php in Ph
adjacent to Imid., and Pho in Ph adjacent to NH2), 125.9 (Pho in Ph
adjacent to Imid.), 123.2 (Phm in Ph adjacent to Imid.), 122.9
(NCHCHN), 122.6 (NCHCHN), 90.8 (cod−CH), 89.2 (cod−CH),
87.7 (cod−CH), 85.3 (cod−CH), 73.8 (ImidCHPhCHPhNH2), 50.8
(ImidCHPhCHPhNH2), 37.0 (cod−CH2), 30.3 (cod−CH2), 27.0
(cod−CH2), 25.6 (cod−CH2), 20.5 (p-CH3 in Mes), 17.6 (o-CH3 in
Mes), 17.0 (o-CH3 in Mes). 1H−15N HSQC/HMBC NMR (400
MHz, DMSO-d6, 298 K) δ 189.8 (NCHCHN, Mes-substituted), 185.1
(NCHCHN, chiral backbone substituted), −24.7 (NH2). 19F NMR
ACKNOWLEDGMENTS
■
NSERC Canada is thanked for a Discovery Grant to R.H.M.
and two graduate scholarships to K.Y.W. We acknowledge the
Canadian Foundation for Innovation, project number 19119,
and the Ontario Research Fund for funding of the Centre for
Spectroscopic Investigation of Complex Organic Molecules and
Polymers. We acknowledge the Centre for Catalysis Research
and Innovation at University of Ottawa. R.H.M. thanks the
Canada Council for the Arts for a Killam Research Fellowship.
The Deutsche Forschungsgemeinschaft (IRTG 2027) is
thanked for financial support for F.R. and F.E.H.
REFERENCES
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1
(376 MHz, DMSO-d6, 298 K) δ −70.2 (d, PF6, JFP = 711 Hz). 31P
NMR (162 MHz, DMSO-d6, 298 K) δ −144.2 (heptet, PF6, 1JFP = 711
Hz). HRMS (ESI, m/z): calcd for [C34H39N3Ir]+ 680.2744, found
680.2750. Anal. Calcd for C34H39N3PF6Ir: C, 49.39; H, 4.75; N, 5.08%.
Found: C, 49.14; H, 4.67; N, 5.12%.
General Procedure for Ketone Hydrogenation Testing. The
experiments were conducted at the Centre for Catalysis Research and
Innovation at the University of Ottawa. Into a 1 mL glass liner was
added 0.1 mL of THF solution of 1.48 mM catalyst, 0.1 mL of THF
solution of 12 mM KOtBu, 0.2 mL of THF solution of 370 mM
substrate, and two glass beads. This glass liner was placed within a 96-
well stainless plate with other testing solutions. Then, the plate was
sealed with one layer of paraffin and one layer of PTFE with one small
hole above each well for the introduction of hydrogen. The plate was
then placed in a large hydrogenation block and sealed to withstand
elevated pressures. The block was then pressurized with H2(g), heated,
and shaken. The conversion of the reaction mixture at the end of the
catalytic run was analyzed by chiral GC.
L
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