Easy Access to Versatile Catalytic Systems for C?H Activation and Reductive Amination Based on Tetrahydrofluorenyl Rhodium(III) Complexes

Article abstract of DOI:10.1002/chem.202100572

On the basis of the 1,2,3,4-tetrahydrofluorenyl ligand, a simple approach was developed to new effective rhodium catalysts for the construction of C?C and C?N bonds. The halide compounds [(η⁵-tetrahydrofluorenyl)RhX₂]₂ (2

Full text of DOI:10.1002/chem.202100572

Accepted Article
Accepted Article
Title: Easy Access to Versatile Catalytic Systems for C-H Activation
and Reductive Amination Based on Tetrahydrofluorenyl
Rhodium(III) Complexes
Authors: Vladimir B. Kharitonov, Sofiya A. Runikhina, Yulia V.
Nelyubina, Dmitry V. Muratov, Denis Chusov, and Dmitry
Loginov
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To be cited as: Chem. Eur. J. 10.1002/chem.202100572
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01/2020

10.1002/chem.202100572
Chemistry - A European Journal
Easy Access to Versatile Catalytic Systems for C-H Activation and Reductive Amination
Based on Tetrahydrofluorenyl Rhodium(III) Complexes
Vladimir B. Kharitonov,[a,b] Sofiya A. Runikhina,[a] Yulia V. Nelyubina,[a] Dmitry V. Muratov,[a]
Denis Chusov,[a,c] Dmitry A. Loginov*[a,c]
Abstract
On the basis of 1,2,3,4-tetrahydrofluorenyl ligand, a simple approach was developed to new
effective rhodium catalysts for the construction of C−C and C−N bonds. The halide compounds
[(η5-tetrahydrofluorenyl)RhX2]2 (2a: X = Br; 2b: X = I) were synthesized by treatment of the
bis(ethylene) derivative (η5-tetrahydrofluorenyl)Rh(C2H4)2 (1a) with halogens. An analogous
reaction of the cyclooctadiene complex (η5-tetrahydrofluorenyl)Rh(cod) (1b) with I2 is
complicated by the side formation of [(cod)RhI]2. The reaction of 2b with 2,2ʹ-bipyridyl leads to
cation [(η5-tetrahydrofluorenyl)Rh(2,2ʹ-bipyridyl)I]+ (3). The halide abstraction from 2a,b with
thallium or silver salts allowed us to prepare sandwich compounds with incoming
cyclopentadienyl, dicarbollide and mesitylene ligands [(η5-tetrahydrofluorenyl)RhCp]+ (4), (η5-
tetrahydrofluorenyl)Rh(η-7,8-C2B9H11) (5), and [(η5-tetrahydrofluorenyl)Rh(η-mesitylene)]2+
(6). The structures of 1b, 2b∙2I2, 3PF6, 4TlI4, 5, and [(cod)RhI]2 were determined by X-ray
diffraction. Compounds 2a,b efficiently catalyze the oxidative coupling of benzoic acids with
alkynes to selectively give isocoumarins or naphthalenes, depending on the reaction temperature.
Moreover, they showed moderate catalytic activity in other annulations of alkynes with aromatic
compounds (such as benzamide, acetanilide, etc.) which proceed through CH activation.
Compound 2b also effectively catalyzes the reductive amination of aldehydes and ketones in the
presence of carbon monoxide and water via water-gas shift reaction, giving amines in high yields
(67−99%).
[a] V. B. Kharitonov, Dr. S. A. Runikhina, Dr. D. V. Muratov, Prof. Dr. Y. V. Nelyubina, Prof.
Dr. D. Chusov, Prof. Dr. D. A. Loginov
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
ul. Vavilova 28, 119991 Moscow, Russian Federation
E-mail: dloginov@ineos.ac.ru
http://www.ineos.ac.ru/en
[b] V. B. Kharitonov
Dmitry Mendeleev University of Chemical Technology of Russia, Miusskaya sq. 9, Moscow
125047, Russian Federation
[c] Prof. Dr. D. Chusov, Prof. Dr. D. A. Loginov
G.V. Plekhanov Russian University of Economics, 36 Stremyanny Per., Moscow 117997,
Russian Federation
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Introduction
The pentamethylcyclopentadienyl rhodium complex [Cp*RhCl2]2 and its derivatives of
type [Cp*RhL3]2+ (L are auxiliary ligands, such as MeCN, Me2CO, arene, etc.) are of great
importance for homogeneous catalysis, especially as catalysts for CH activation reactions.1 Their
widespread catalytic use is explained by the strong bonding of rhodium with Cp* (which acts as
a supporting ligand) as well as easy substitutional lability of auxiliary ligands, thus providing
free coordination sites on rhodium for catalytic processes. Moreover, the design of substituents
in the Cp ring allows one to control the catalytic activity and selectivity. For example, Shibata
and Tanaka with co-workers have shown that electron-withdrawing ethoxycarbonyl groups
(COOEt) lead to a considerable increase in catalytic activity in oxidative coupling reactions
through the cleavage of sp2 C−H bonds due to an increase in the electrophilicity of rhodium.2
Rovis and Perekalin have found that steric hindrance of branched alkyl substituents improves the
regioselectivity of alkene insertion in CH activation reactions.3 Rhodium complexes with chiral
cyclopentadienyl ligands for enantioselective CH activation have been developed.4 We have
demonstrated that carboranes and boron heterocycles can be successfully used as supporting
ligands for catalyst design instead of cyclopentadienyl.5
By analogy with cyclopentadienyl, indenyl ligand is another readily available supporting
ligand for catalyst design.6 In particular, indenyl is capable to provide an additional free
coordination site at a metal atom as a result of an easy slippage of indenyl ligand from η5 to η3
coordination mode (the so called “indenyl effect”).7 However, this flexibility leads to a
weakening of the metal−indenyl bond, which limits the catalytic applications of indenyl
complexes.6a For example, while rhodium complexes with the parent unsubstituted indenyl
ligand C9H7 efficiently catalyze the reductive amination of carbonyl compounds,8 they are
almost inactive in the oxidative coupling of benzoic acids with alkynes due to the loss of the
indenyl ligand.8a At the same time, the introduction of alkyl or aryl substituents into the indenyl
moiety leads to the stabilization of the rhodium complexes and thereby to an increase in their
catalytic activity.9 Thus, the penta- and heptamethylindenyl rhodium complexes [(5-
C9H2Me5)Rh(C6H6)]2+ and [(5-C9Me7)RhCl2]2 showed good catalytic activity in the annulations
of benzoic acids with alkynes5e and benzamides with 3,3-disubstituted cyclopropenes,3c
respectively. However, methylated indenes are not easily available, since their synthesis requires
multi-stage procedures.10
Herein we report a simple approach to stabilized indenyl rhodium complexes based on
the use of 1,2,3,4-tetrahydrofluorene. Structural features, reactivity, and catalytic applications of
the complexes prepared are also described.
2
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Results and Discussion
Synthesis of the halide complexes [(η5-1,2,3,4-tetrahydrofluorenyl)RhX2]2 (X = Br, I;
2a,b). The halide complexes 2a,b were synthesized via the bis(ethylene) derivative (η5-1,2,3,4-
tetrahydrofluorenyl)Rh(C2H4)2 (1a) in accordance with two-step general approach, which is
given in Scheme 1. Previously, we have successfully used this method for the synthesis of the
rhodium halides with the unsubstituted indenyl ligand.8b On the first stage, compound 1a was
prepared by reaction of the Cramer complex [(C2H4)2RhCl]2 with Li[1,2,3,4-tetrahydrofluorenyl]
(generated from 1,2,3,4-tetrahydrofluorene and BuLi). Further oxidation of 1a with halogens led
to the target halides 2a,b in 70−80% yields. The easy availability of 2a,b is also supported by the
fact that the starting 1,2,3,4-tetrahydrofluorene can be readily synthesized from fluorene by
Benkeser’s hydrogenation.11 To the best of our knowledge, the complexes with the 1,2,3,4-
tetrahydrofluorenyl ligand were known before our work only for Group 4 metals (titanium and
zirconium).12
Li+
+
Rh
Cl
2
X2
Rh
Rh
X
X
2
1a
X = Br (2a); I (2b)
Scheme 1. Synthesis of the halide complexes 2a,b.
It is noteworthy that during the synthesis of the iodine derivative 2b, an excess of iodine
(which may arise due to the low stability of the bis(ethylene) complex 1a) should be avoided.
Otherwise, the formation of polyiodides was observed. In particular, we were able to grow single
crystals of compound 2b∙2I2 (for the X-ray diffraction structure, see Figure 1). This compound
has the expected dimeric structure with two bridging and two terminal iodide ligands. The
concomitant iodine molecules form I···I contacts with terminal iodides with 3.148 Å distance.
The tetrahydrofluorenyl ligand is disordered by two positions with an overlay of benzene and
cyclohexene moieties in a 65:35 ratio. The metal-ring plane Rh···C5 distance in 2b (1.825 Å) is
the longest among the related cyclopentadienyl analogs, such as [(-C5H4Me)RhI2]2 (1.786 Å),13
3
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[Cp*RhI2]2 (1.798 Å),14 and [(-C5Me4Et)RhI2]2 (1.793 Å),15 suggesting a weaker bonding of
rhodium with tetrahydrofluorenyl ligand than with cyclopentadienides.
Figure 1. Crystal structure of the compound 2b∙2I2 in 50% thermal ellipsoids. All hydrogen
atoms are omitted for clarity. Selected bond lengths (Å): Rh1I1 2.7328(7), Rh1I2 2.6768(7),
Rh1C4a 2.222(7), Rh1C5a 2.206(7), Rh1C8a 2.212(7, Rh1C9a 2.232(6), Rh1C9 2.128(7),
С4aC5a 1.466(10), С4aC9a 1.437(10), С5aC8a 1.435(10), С9C9a 1.438(10), С9C8a
1.452(10), I2I3 3.1484(7), I3I4 2.7818(7).
In contrast to bis(ethylene) derivatives, the corresponding cyclooctadiene complexes are
known to be more stable and can also be used as starting materials for the synthesis of related
halides.13,16 We tried to use this approach to synthesize 2b (Scheme 2). However, the reaction of
the cyclooctadiene complex (η5-1,2,3,4-tetrahydrofluorenyl)Rh(cod) (1b; cod = 1,5-
cyclooctadiene) with iodine is complicated by the side formation of complex [(cod)RhI]2 in ca.
1
25% yield (according to H NMR). Although the latter has a significantly higher solubility in
organic solvents than 2b, we were unable to purify 2b by washing with dichloromethane or
acetone. It suggests that initially the formation of the mixed dimer [(η5-1,2,3,4-
tetrahydrofluorenyl)RhI2][(cod)RhI] can occur. Only long-term exposure of the reaction residue
with acetone leads to the appearance of pure [(cod)RhI]2. DFT calculations showed that the
conversion of the mixed dimer into 2b and [(cod)RhI]2 is exothermic, the reaction energy being
2.43 kcal mol−1 at the BP86-D3/TZP level.
4
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Scheme 2. Reaction of the cyclooctadiene complex 1b with I2.
The complex [(cod)RhI]2 has a bent dimeric structure (Figure 2), the bending angle (the
angle between the two squares along the I…I line) being equal to 96.7. Noteworthy, the
17
18
corresponding chloro and bromo analogs [(cod)RhCl]2 and [(cod)RhBr]2 are only slightly
folded with bending angles 169.3 and 148.7, respectively. The increase in bending from Cl to I
is consistent with the results of ab initio calculations previously performed by Lledos and
Alvarez.19 They have found that the attractive interaction between the filled 4dz2 and the empty
5pz orbitals of different rhodium atoms is responsible for the stabilization of the bent structure.
We calculated the energy difference between the bent and the planar forms (E), which
correlates well with experimental structural data (Table 1). For example, this value increases
from Cl to I in accordance with a decrease of the bending angle. At the same time, the maximum
difference, which is reached for iodide [(cod)RhI]2, is quite small and equal to only 3.35 kcal
mol−1. At the same time, analysis of the dissociation energies (De) for monomeric species
showed that the chloride and the bromide (both in the bent and the planar forms) are more stable
to monomerization than the iodide. To further clarify the nature of the Rh···Rh interaction, we
performed the AIM analysis20 (see Supporting Information) for the bent forms with different
bridging halogen atoms. It was found that the values of the electron density at the bond critical
point (r) decrease from Cl to I (0.0231, 0.0225, and 0.021 e bohr−3 for Cl, Br, and I,
respectively). The values of the Laplacian of the electron density 2(r) are positive for all
halogens, whereas the values of the Cremer and Kraka energy density H(r) are negative, which
give evidence of the partial covalent nature of the Rh···Rh interaction.21 Nevertheless, small
values of (r) suggest that this interaction is very weak.
5
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Figure 2. Crystal structure of [(cod)RhI]2 in 50% thermal ellipsoids. All hydrogen atoms are
omitted for clarity. Selected bond lengths (Å): Rh1Rh1 2.9811(12), Rh1I1 2.7115(8), Rh1C1
2.112(9), Rh1C2 2.109(9), Rh1C5 2.107(8), Rh1C6 2.110(9), C1C2 1.404(15), C5C6
1.407(15).
Table 1. Calculated energy parameters (E and De, in kcal mol−1) for complexes [(cod)RhX]2 (X
= Cl, Br, I) in the bent and the planar forms at the BP86-D3/TZP level.
X = Cl
planar
1.64
48.57
X = Br
planar
2.51
49.25
X = I
planar
3.35
47.51
bent
bent
bent
Ea
b
De
51.33
52.06
51.07
a E is the relative energy difference between the bent and the planar forms. De is the energy of
dissociation of the dimers [(cod)RhX]2 to monomeric species (cod)RhX.
Reactivity of the halide complexes 2a,b. Complexes 2a,b are indefinitely stable in air
and poorly soluble in non-coordinating solvents (e.g., dichloromethane and acetone). At the
same time, they are readily soluble in dimethyl sulfoxide with the cleavage of the dimeric
structure and the formation of adducts (η5-1,2,3,4-tetrahydrofluorenyl)RhX2(dmso). We also
found that the iodide 2b reacts with 2,2ʹ-bipyridyl to form the cation [(η5-1,2,3,4-
tetrahydrofluorenyl)Rh(2,2ʹ-bipyridyl)I]+ (3, Scheme 3).
Scheme 3. Synthesis of the bipyridyl complex 3.
To examine the applicability of 2a,b as synthons of the cationic fragment [(η5-1,2,3,4-
tetrahydrofluorenyl)Rh]2+ for the synthesis of sandwich compounds, we studied their reactions
with thallium salts of cyclopentadienide and dicarbollide anions (Scheme 4). In the case of TlCp,
both bromide 2a and iodide 2b afford the desired cation [(η5-1,2,3,4-tetrahydrofluorenyl)RhCp]+
(4) in moderate yields (40−50%). Noteworthy, the use of crude 2b (containing polyiodide
admixtures) results in the side formation of the [TlI4] counterion (see below). Some examples of
the accidental formation of [TlI4]from Tl(I) salts in the presence of excess iodine have been
observed earlier.22 The reaction of 2b with Tl[Tl(η-7,8-C2B9H11)] proceeds more smoothly and
6
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gives rhodacarborane (η5-1,2,3,4-tetrahydrofluorenyl)Rh(η-7,8-C2B9H11) (5) in 65% yield. The
use of thallium salts rather than sodium or potassium ones is necessary to facilitate the halide
abstraction from 2a,b.
Scheme 4. Synthesis of the sandwich compounds 4 and 5.
We found that complexes 2a,b can also be applied for the synthesis of arene complexes.
In this case, the affinity of thallium salts for the halide is insufficient, and therefore silver
derivatives should be used. For example, the reaction of iodide 2b with mesitylene in the
presence of AgSbF6 leads to the arene complex [(η5-1,2,3,4-tetrahydrofluorenyl)Rh(η-
mesitylene)]2+ (6) in 54% yield (Scheme 5).
Scheme 5. Synthesis of the arene complex 6.
In the 13C NMR spectra of the complexes prepared, the signals of the carbon atoms
1
bonded to rhodium were observed as doublets with JRh−C ≈ 59 Hz in accordance with 100%
naturally abundant spin 1/2 nucleus 103Rh, while the signals of non-coordinated carbon atoms
were revealed as singlets (see Supporting Information). However, we were unable to observe
1
2JRh−H spin-spin coupling in the H NMR spectra, which is characteristic of rhodium sandwich
compounds and is usually close to 1 Hz.13,23 It can be explained by the insufficient resolution of
the used NMR equipment. The 11B{1H} NMR spectrum of 5 shows a 1:2:1:1:1:2:1 pattern of
broad singlets and suggests a decrease in symmetry in the closo-3,1,2-RhC2B9 cluster (from Cs to
C1) due to the presence of the tetrahydrofluorenyl ligand.24
The structures of compounds 1b, 3PF6, 4TlI4, and 5 were determined by X-ray diffraction
(Figures 36). In 1b, 4TlI4, and 5, the tetrahydrofluorenyl ligand is disordered by two positions
with an overlay of benzene and cyclohexene moieties in ratios of 58:42, 50:50 and 76:24,
7
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respectively. The indenyl moiety in cation 3 is less slipped than that in rhodium complexes with
an unsubstituted indenyl ligand;8 the slip parameter (defined as the difference in average
distances from metal to the bridgehead carbons and from metal to the adjacent carbon atoms)25 is
equal to 0.065 Å. The metal-ring plane Rh···C5 distance in 1b (1.926 Å) is considerably longer
than in 3PF6 (1.830 Å), 4TlI4 (1.822 Å), and 5 (1.842 Å), which can be explained by higher
formal oxidation state of rhodium (+3) in the latter complexes as compared with +1 in 1b. In
general, there is a similarity between the structures of tetrahydrofluorenyl complexes and their
cyclopentadienyl analogs. In particular, the distances Rh···Cp in cation 3 (1.811 Å) and
Rh···C2B3 in compound 5 (1.587 Å) are very close to those in [RhCp2]+ (1.808 Å)26 and CpRh(η-
7,8-C2B9H11) (1.578 Å),27 respectively.
Figure 3. Crystal structure of the compound 1b in 50% thermal ellipsoids. All hydrogen atoms
are omitted for clarity. Selected bond lengths (Å): Rh1C4a 2.320(3), Rh1C5a 2.316(3),
Rh1C8a 2.303(3), Rh1C9a 2.295(3), Rh1C9 2.177(3), Rh1C10 2.143(4), Rh1C13
2.113(3), Rh1C14 2.125(3), Rh1C17 2.128(3), С4aC5a 1.442(5), С4aC9a 1.426(5),
С5aC8a 1.422(5), С9C9a 1.442(5), С9C8a 1.443(5), С10C17 1.398(5), С13C14 1.420(5).
8
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Figure 4. Crystal structure of the cation 3 in 50% thermal ellipsoids. All hydrogen atoms are
omitted for clarity. Selected bond lengths (Å): Rh1I1 2.6985(3), Rh1N1b 2.095(2), Rh1N1bʹ
2.045(3), Rh1C4a 2.179(3), Rh1C5a 2.247(3), Rh1C8a 2.238(3), Rh1C9a 2.203(3),
Rh1C9 2.150(3), С4aC5a 1.452(4), С4aC9a 1.435(4), С5aC8a 1.433(4), С9C9a 1.436(4),
С9C8a 1.458(4).
Figure 5. Crystal structure of the cation 4 in 50% thermal ellipsoids. All hydrogen atoms are
omitted for clarity. Selected bond lengths (Å): Rh1C4a 2.203(12), Rh1C5a 2.191(12),
Rh1C8a 2.202(12), Rh1C9a 2.209(12), Rh1C9 2.165(12), Rh1C10 2.169(12), Rh1C11
2.176(12), Rh1C12 2.175(12), Rh1C13 2.186(14), Rh1C14 2.171(12), С4aC5a 1.443(19),
С4aC9a 1.455(17), С5aC8a 1.44(2), С9C9a 1.416(17), С9C8a 1.433(18), С10C11
1.410(18), С11C12 1.406(19), С12C13 1.44(2), С13C14 1.40(2), С10C14 1.430(18).
9
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Figure 6. Crystal structure of the compound 5 in 50% thermal ellipsoids. All hydrogen atoms are
omitted for clarity. Selected bond lengths (Å): Rh1C4a 2.235(5), Rh1C5a 2.234(4), Rh1C8a
2.221(4), Rh1C9a 2.217(4), Rh1C9 2.153(4), Rh1C1b 2.173(4), Rh1C2b 2.153(4), Rh1B4
2.175(5), Rh1B7 2.172(5), Rh1B8 2.211(5), С4aC5a 1.448(6), С4aC9a 1.426(6), С5aC8a
1.439(6), С9C9a 1.430(6), С9C8a 1.444(7), С1bC2b 1.631(7), С1bB4 1.735(7), С2bB7
1.751(7), B4B8 1.812(7), B7B8 1.834(7).
Catalytic activity of the halide complexes 2a,b. First of all we tested the halides 2a,b as
catalysts in CH activation of aromatic compounds. In particular, the iodide 2b (in 2.5 mol %
loading) showed good catalytic activity in the oxidative coupling of benzoic acid with internal
alkynes to give the corresponding isocoumarins or naphthalenes depending on the reaction
conditions (Table 2). Refluxing in methanol at 80 C in the presence of AgOAc as an oxidant is
standard conditions for the formation of isocoumarins (entries 13), while the increase of
temperature to 150 C in o-xylene with the addition of Cu(OAc)2 facilitates the decarboxylation
of benzoic acid and the formation of naphthalenes (entries 57). An analogous crucial impact of
the reaction temperature on the selectivity has been observed earlier for cyclopentadienyl iridium
complexes.28 All reactions demonstrate high selectivity, except for the reaction with
diethylacetylene at 150 C in o-xylene, where the formation of a mixture of the corresponding
isocoumarin and naphthalene in a 1:2 ratio is observed (entry 7). At the same time, the decrease
of temperature to 100 C for the reaction with diphenylacetylene in o-xylene leads only to a
decrease in the yield of naphthalene, but does not change the reaction selectivity (entry 9). In
general, the catalytic activity of the tetrahydrofluorenyl complex 2b is comparable with the
10
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cyclopentadienyl complexes [CpRhI2]n and [Cp*RhCl2]2 (entries 13, 5, and 6 vs 10 and 11),29
and exceeds that of the indenyl derivatives [(η5-indenyl)RhI2]n and [(η5-1,2,3,4,7-
pentamethylindenyl)Rh(η-benzene)]2+ (entries 5 and 6 vs 12 and 13).5b,e The bromide 2a proved
to be less catalytically active than 2b (entry 14 vs 6), but it can still be used as a catalyst for the
preparative synthesis of the corresponding naphthalene at 5 mol % loading (entry 15).
We found that diphenyl- and diethylacetylenes as well as 1-phenyl-1-propyne are suitable
for the oxidative coupling with benzoic acid catalyzed by 2b. Interestingly, the reactions with 1-
phenyl-1-propyne and diethylacetylene gave higher yields of the target products than with
diphenylacetylene (Table 2, entries 2, 3, and 6 vs 1 and 5), which can be explained by a decrease
of the oxidation potentials of the reaction intermediates in the case of the former alkynes due to
the donor ability of alkyl substituents. Moreover, the method is highly regioselective and gives
only one regioisomer in both the isocoumarin and naphthalene formation when using 1-phenyl-
1-propyne (entries 2 and 6). The same regioselectivity has been observed earlier for other
rhodium-catalyzed annulations with unsymmetric alkylphenylacetylenes29,30 and has no clear
explanation. However, Stuart and Fagnou have shown experimentally that both steric and
electronic effects can influence the regioselectivity of unsymmetrical alkyne insertion, and the
more electron-deficient substituent tends to occupy the position near heteroatom.31 Thus, we can
propose that the high selectivity for reactions with 1-phenyl-1-propyne is determined by the
lower donor ability of the phenyl group as compared with the methyl one.
Table 2. Oxidative coupling of benzoic acids with alkynes catalyzed by rhodium complexes.a
Entr Catalyst
y
Oxidant
Solvent, Temperature, R1, R2
Time
Yield
the
of Yield
the
of
isocoumari naphthalen
n, %b
e, %b
traces
2
1c
AgOAc
AgOAc
AgOAc
MeOH, 80ºC, 24h
MeOH, 80ºC, 24h
MeOH, 80ºC, 24h
Ph, Ph
Ph, Me
Et, Et
2b
60
2
3
4
5
2b
2b
2b
2b
82
traces
20
91
Cu(OAc)2 MeOH, 80ºC, 24h
Ph, Ph
Ph, Ph
3
Cu(OAc)2 o-xylene, 150ºC, 10h
traces
57
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6
7
8
9
Cu(OAc)2 o-xylene, 150ºC, 10h
Cu(OAc)2 o-xylene, 150ºC, 10h
Ph, Me
Et, Et
traces
31
2b
2b
2b
2b
99
65
19
37
91
-
AgOAc
o-xylene, 150ºC, 10h
Ph, Ph
Ph, Ph
Ph, Ph
Ph, Me
11
Cu(OAc)2 o-xylene, 100ºC, 17h
Cu(OAc)2 o-xylene, 150ºC, 6h
traces
-
10d [CpRhI2]n
11e
[Cp*RhCl2] Cu(OAc)2 o-xylene, 120ºC, 6h
86
2
12f
[(η5-
Cu(OAc)2 o-xylene, 150ºC, 6h
Cu(OAc)2 o-xylene, 150ºC, 6h
Ph, Ph
Ph, Ph
-
17
57
indenyl)RhI
]
2 n
13g [(η5-
1,2,3,4,7-
18
pentamethyl
indenyl)Rh(
η-
benzene)]2+
14
15h
Cu(OAc)2 o-xylene, 150ºC, 10h
Cu(OAc)2 o-xylene, 150ºC, 10h
Ph, Me
Ph, Me
traces
traces
45
72
2a
2a
a
25 mmol (31 mg) of benzoic acid, 0.5 mmol of alkyne, 0.5 mmol of silver or copper acetate,
b
c
2.5 mol % of the catalyst, 2 ml of the solvent. Yields are given after purification. 1,2,3-
Triphenylnaphthalene and hexaphenylbenzene were also isolated in 12 and 16% yields,
respectively. d Ref.29a e Ref.29b f Ref.5b g Ref.5e h 5 mol % of the catalyst.
We found out that 2b also catalyzes some other annulations of aromatic compounds and
alkynes, which proceed via CH activation (Scheme 6). For example, the reaction of p-
anisaldehyde and p-toluidine with diphenylacetylene at 2.5 mol % loading of 2b and 90 C in
methanol gave the corresponding isoquinolinium salt in 67% yield, which is comparable with
that for the ruthenium catalyst [(p-cymene)RuCl2]2,32 the latter working at higher temperature
(110 C in ethanol). In our case, the increase of the reaction temperature to 120 C in DCE only
slightly increases the yield of the target product (to 70%).33 Complex 2b also exhibited moderate
catalytic activity in the reaction of benzamide with two equivalents of diphenylacetylene to form
8H-isoquinolino[3,2-a]isoquinolin-8-one in 49% yield via double CH activation.34 At the same
time, the reaction of acetanilide with 1-phenyl-1-propyne catalyzed by 2b gave the
corresponding indole derivative in 25% yield, which is comparable with that for the classical
12
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10.1002/chem.202100572
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catalyst [Cp*RhCl2]2,35 but lower than for the functionalized indenyl derivative [(η5-5-1-
(COOEt)-2-Me-3-benzyl-indenyl)RhI2]2.9b
Scheme 6. Other CH activation reactions catalyzed by 2b.
To summarize the CH activation reactions discussed above, we can conclude that the
tetrahydrofluorenyl rhodium complexes 2a,b have good or moderate catalytic activity in these
processes. Probably, this success is mainly caused by the strengthening of the rhodium−indenyl
bond due to the donor effects of the –(CH2)4− linker in the tetrahydrofluorenyl ligand, which acts
as a supporting ligand.
Next, we tried to use halides 2a,b as catalysts for the reductive amination of carbonyl
compounds in the presence of carbon monoxide,36 which is an efficient approach for the creation
of a C−N bond in the synthesis of amines.37 We found that the reaction catalyzed by 2b does not
work well in organic solvents via the reduction without an external hydrogen source (Table 3,
entries 1−6). However, this complex proved to be an effective catalyst in water via the water-gas
shift reaction (entry 7).
Table 3. The solvent influence on the reductive amination reaction catalyzed by 2b.a
13
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Entry
Solvent
toluene
Yield,b %
1
2
3
4
5
6
0
MeCN
THF
5
8
neat
9
EtOH
DCM
H2O
12
13
95
7
a
39.2 mg (0.32 mmol) anisidine, 25 μL (0.21 mmol) tolylaldehyde, 200 µL of solvent, 30 bar
CO, 120 ºC, 4 h, 0.65 mol % of 2b. b Yields were determined by NMR.
Since, the activity of 2a,b at 0.65 mol % loading and 120C in water was very high
(Table 4, entries 1−2), we decided to decrease the catalyst loading to 0.2 mol % and the reaction
temperature to 100C. Under these conditions, compound 2b showed a lower catalytic activity
than the parent unsubstituted complex [(5-indenyl)RhI2]n (entries 5 vs. 4), which can be
explained by an easier 5-3 isomerization/elimination of indenyl moiety in the latter. At the
same time, the iodide 2b showed a higher activity as compared with the bromide 2a (entries 4 vs.
3), which can be explained by better stabilization of rhodium catalytic species by iodide anions
than bromides after elimination of the tetrahydrofluorenyl ligand. Noteworthy, the bipyridyl
complex 3PF6 has a similar activity with 2b (entry 6), which additionally suggests that the
tetrahydrofluorenyl moiety can act as a leaving ligand,38 and 2,2ʹ-bipyridyl is the supporting
ligand in this case. The HRMS-ESI spectra of the reaction mixtures also gave evidence for the
elimination of the tetrahydrofluorenyl ligand (see Supporting Information). Thus, we can
conclude that the best catalyst for the reductive amination requires some strongly bonded
ligands, which are capable to block 2-3 coordination sites at the metal atom. When the complex
has more strongly bound ligands, the catalyst becomes almost inactive. For example, when 2b
was premixed with an excess of 2,2ʹ-bipyridyl, the catalytic system became inactive (entry 7). It
is interesting to note that the rhodium(I) complexes proved to be inactive in the reductive
amination via water-gas shift reaction (entries 8−9). An exception is the unstable complex
[(CO)2RhI]2 (entry 10). Thus, the rhodium(III) complexes are much more suitable for this
reaction. However, we found out that simple rhodium(III) chloride is totally inactive as
compared with indenyl derivatives (entry 11), which can be explained by the absence of good
leaving ligands in RhCl3.
Table 4. Catalyst screening in the reductive amination reaction.a
14
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Entry
Catalyst
Loading catalyst,
Yield,b %
Temperature, C
mol %
0.65
0.65
0.2
1
120
120
100
100
100
100
100
100
100
100
100
93
95
2
2a
2
2b
3
2a
4
0.2
37
80
30
5
2b
[(5-indenyl)RhI2]n
5
0.4
6
3PF6
0.4
0.2
0.4
0.2
0.2
0.4
7
2b + 2,2ʹ-bipyridylc
(5-indenyl)Rh(C2H4)2
[(CO)2RhCl]2
[(CO)2RhI]2
8
3
9
0
10
8–51
0
11
RhCl3
a
39.2–78.4 mg (0.32–0.64 mmol) anisidine, 25–50 μL (0.21–0.22 mmol) tolylaldehyde, 0.4–1.3
c
mol % of catalyst, 200–400 μL of water. b Yields were determined by NMR. An excess of 2,2ʹ-
bipyridyl was added.
We found that all combination of amines and carbonyl compounds are suitable for the
catalysis of the reductive amination by 2b (Scheme 7). The ketones proved to be less active than
aldehydes. For example, N-isopropyl-p-anisidine was prepared from acetone and anisidine in
lower yield (67% after isolation). At the same time, both aliphatic aldehydes and amines worked
well giving the corresponding amines in almost quantitative yields.
15
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10.1002/chem.202100572
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Scheme 7. Substrate scope for the reductive amination catalyzed by 2b. The isolated yields are
given in parentheses.
Conclusions
We developed a family of versatile rhodium catalysts based on 1,2,3,4-
tetrahydrofluorene, which proved to be efficient for C−C and C−N bonds formation via CH
activation and reductive amination reactions. The widespread use of novel catalytic systems is
provided by the dual role of the tetrahydrofluorenyl moiety, which can act as a good supporting
or leaving ligand in catalytic processes. An additional advantage of the proposed approach is the
easy availability of this ligand. We hope that the presented catalysts will be in demand organic
synthesis and homogeneous catalysis.
Acknowledgements
This work was supported by the Russian Science Foundation (Grant No. 19-73-20212).
V.B.K., D.A.L., and D.C. are also thankful to the Dmitry Mendeleev University of Chemical
Technology and the Plekhanov Russian University of Economics for providing access to
computation resources for DFT calculations. The NMR studies were performed with the
financial support from Ministry of Science and Higher Education of the Russian Federation
using the equipment of Center for molecular composition studies of INEOS RAS.
Conflict of interest
The authors declare no conflict of interest.
16
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Table of Contents entry
A short text
A versatile rhodium catalyst for the formation C−N and C−C bonds was synthesized based on
easily available 1,2,3,4-tetrahydrofluorene. The catalyst efficiently works for the reductive
amination of carbonyl compounds via elimination of tetrahydrofluorenyl ligand as well as for
CH activation of aromatic compounds with the retention of this ligand.
Graphical Element
Keywords: CH activation; Homogeneous catalysis; Reductive amination; Rhodium; Sandwich
complexes
17
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References
1 For reviews, see: a) T. Satoh, M. Miura, in Rhodium Catalysis in Organic Synthesis: Methods
and Reactions (Ed.: K. Tanaka), Wiley-VCH, Weinheim, 2019, p. 487; b) Y. Yang, K. Li, Y.
Cheng, D. Wan, M. Li, J. You, Chem. Commun. 2016, 52, 2872−2884; c) G. Song, X. Li, Acc.
Chem. Res. 2015, 48, 1007−1020; d) G. Song, F. Wang, X. Li, Chem. Soc. Rev. 2012, 41, 3651–
3678; e) F. W. Patureau, J. Wencel-Delord, F. Glorius, Aldrichimica Acta 2012, 45, 31–41; f) T.
Satoh, M. Miura, Chem. Eur. J. 2010, 16, 11212–11222.
2 For selected works, see: a) Y. Honjo, Y. Shibata, K. Tanaka, Chem. Eur. J. 2019, 25, 9427–
9432; b) J. Terasawa, Y. Shibata, M. Fukui, K. Tanaka, Molecules 2018, 23, 3325; c) Y. Honjo,
Y. Shibata, E. Kudo, T. Namba, K. Masutomi, K. Tanaka, Chem. Eur. J. 2018, 24, 317–321; d)
E. Kudo, Y. Shibata, M. Yamazaki, K. Masutomi, Y. Miyauchi, M. Fukui, H. Sugiyama, H.
Uekusa, T. Satoh, M. Miura, K. Tanaka, Chem. Eur. J. 2016, 22, 14190–14194; e) Y. Shibata, K.
Tanaka, Angew. Chem. Int. Ed. 2011, 50, 10917–10921.
3 a) T. Piou, T. Rovis, Acc. Chem. Res. 2018, 51, 170−180; b) E. A. Trifonova, N. M.
Ankudinov, M. V. Kozlov, M. Y. Sharipov, Y. V. Nelyubina, D. S. Perekalin, Chem. Eur. J.
2018, 24, 16570–16575; c) N. Semakul, K. E. Jackson, R. S. Paton, T. Rovis, Chem. Sci. 2017,
8, 1015–1020; d) T. K. Hyster, D. M. Dalton, T. Rovis, Chem. Sci. 2015, 6, 254–258; e) T. Piou,
T. Rovis, Nature 2015, 527, 86–90; f) T. Piou, T. Rovis, J. Am. Chem. Soc. 2014, 136, 11292–
11295.
4 For selected works, see: a) J. Mas‐Roselló, A. G. Herraiz, B. Audic, A. Laverny, N. Cramer,
Angew. Chem., Int. Ed., doi: 10.1002/anie.202008166; b) S. Shaaban, C. Davies, H. Waldmann,
Eur. J. Org. Chem. 2020, 2020, 6512–6524; c) W.-J. Cui, Z.-J. Wu, Q. Gu, S.-L. You, J. Am.
Chem. Soc. 2020, 142, 7379−7385; d) R. A. Pototskiy, A. V. Kolos, Y. V. Nelyubina, D. S.
Perekalin, Eur. J. Org. Chem. 2020, 2020, 6019–6025; e) T. Yoshino, S. Satake, S. Matsunaga,
Chem. Eur. J. 2020, 26, 7346–7357; f) E. A. Trifonova, N. M. Ankudinov, A. A. Mikhaylov, D.
A. Chusov, Y. V. Nelyubina, D. S. Perekalin, Angew. Chem., Int. Ed. 2018, 57, 7714–7718; g)
C. G. Newton, S.-G. Wang, C. C. Oliveira, N. Cramer, Chem. Rev. 2017, 117, 8908–8976; h) B.
Ye, N. Cramer, J. Am. Chem. Soc. 2013, 135, 636–639; i) B. Ye, N. Cramer, Science 2012, 338,
504–506; j) T. K. Hyster, L. Knörr, T. R. Ward, T. Rovis, Science 2012, 338, 500–503.
5 a) M. M. Vinogradov, D. A. Loginov, J. Organomet. Chem. 2020, 910, 121135; b) D. A.
Loginov, V. E. Konoplev, J. Organomet. Chem. 2018, 867, 14–24; c) D. A. Loginov, D. V.
Muratov, Y. V. Nelyubina, J. Laskova, A. R. Kudinov, J. Mol. Catal. A: Chemical 2017, 426,
393–397; d) D. A. Loginov, A. O. Belova, A. V. Vologzhanina, A. R. Kudinov, J. Organomet.
18
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10.1002/chem.202100572
Chemistry - A European Journal
Chem. 2015, 793, 232–240; e) D. A. Loginov, A. O. Belova, A. R. Kudinov, Russ. Chem. Bull.
2014, 63, 983−986.
6 a) V. B. Kharitonov, D. V. Muratov, D. A. Loginov, Coord. Chem. Rev. 2019, 399, 213027; b)
B. M. Trost, M. C. Ryan, Angew. Chem. Int. Ed. 2017, 56, 2862–2879; c) M. Hapke, K. Kral, C.
Fischer, A. Spannenberg, A. Gutnov, D. Redkin, B. Heller, J. Org. Chem. 2010, 75, 3993–4003;
d) L. Mantovani, A. Ceccon, A. Gambaro, S. Santi, P. Ganis, A. Venzo, Organometallics 1997,
16, 2682–2690; e) A. Ceccon, A. Gambaro, S. Santi, A. Venzo, J. Mol. Catal. 1991, 69, L1−L6.
7 a) F. Pammer, W.R. Thiel, Coord. Chem. Rev. 2014, 270–271, 14–30; b) M. J. Calhorda, C. C.
Romaо, L. F. Veiros, Chem. Eur. J. 2002, 8, 868–875; c) J. M. O'Connor, C. P. Casey, Chem.
Rev. 1987, 87, 307–318.
8 a) V. B. Kharitonov, M. Makarova, M. A. Arsenov, Yu. V. Nelyubina, O. Chusova, A. S.
Peregudov, S. S. Zlotskii, D. Chusov, D. A. Loginov, Organometallics 2018, 37, 2553−2562; b)
S. A. Runikhina, M. A. Arsenov, V. B. Kharitonov, E. R. Sovdagarova, O. Chusova, Y. V.
Nelyubina, G. L. Denisov, D. L. Usanov, D. Chusov, D. A. Loginov, J. Organomet. Chem. 2018,
867, 106–112.
9 a) C. M. B. Farr, A. M. Kazerouni, B. Park, C. D. Poff, J. Won, K. R. Sharp, M.-H. Baik, S. B.
Blakey, J. Am. Chem. Soc. 2020, 142, 13996–14004; b) J. Terasawa, Y. Shibata, Y. Kimura, K.
Tanaka, Chem. – Asian J. 2018, 13, 505–509.
10 a) T. A. Q. Arnold, J.-C. Buffet, Z. R. Turner, D. O'Hare, J. Organomet. Chem. 2015, 792, 55–
65; b) D. A. Loginov, M. M. Vinogradov, Z. A. Starikova, E. A. Petrovskaya, P. Zanello, F.
Laschi, F. Rossi, A. Cinquantini, A. R. Kudinov, J. Organomet. Chem. 2007, 692, 5777–5787; c)
T. E. Ready, J. C. W. Chien, M. D. Rausch, J. Organomet. Chem. 1999, 583, 11–27; d) D.
O’Hare, J. C. Green, T. Marder, S. Collins, G. Stringer, A. K. Kakkar, N. Kaltsoyannis, A. Kuhn,
R. Lewis, C. Mehnert, P. Scott, M. Kurmoo, S. Pugh, Organometallics 1992, 11, 48–55.
11 a) R. J. Adamski, J. G. Cannon, J. Org. Chem. 1964, 29, 3693–3695; b) R. A. Benkeser,
Advances in Chemistry Series, Vol. 23, American Chemical Society. Washington, D. C., 1959,
p. 58.
12 a) E. J. Thomas, M. D. Rausch, J. C. W. Chien, J. Organomet. Chem. 2001, 631, 29–35; b) E.
J. Thomas, M. D. Rausch, J. C. W. Chien, Organometallics 2000, 19, 5744–5749.
13 M. Jochriem, L. A. Casper, S. Vanicek, D. Petersen, H. Kopacka, K. Wurst, T. Müller, R. F.
Winter, B. Bildstein, Eur. J. Inorg. Chem. 2020, 1300–1310
14 M. R. Churchill, S. A. Julis, Inorg. Chem. 1979, 18, 2918–2920.
15 I. W. Nowell, G. Fairhurst, C. White, Inorg. Chim. Acta 1980, 41, 61–66.
19
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10.1002/chem.202100572
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16 a) A. V. Kolos, D. S. Perekalin, Mendeleev Commun. 2021, 31, 1–7; b) M. M. Vinogradov, Z.
A. Starikova, D. A. Loginov, A. R. Kudinov, J. Organomet. Chem. 2013, 738, 59–65; c) D. A.
Loginov, Z. A. Starikova, P. V. Petrovskii, J. Holub, A. R. Kudinov, Inorg. Chem. Commun.
2011, 14, 313–315; d) D. A. Loginov, M. M. Vinogradov, Z. A. Starikova, P. V. Petrovskii, A.
R. Kudinov, Russ. Chem. Bull. 2004, 53, 1949–1953.
17 D. J. A. De Ridder, P. Imhoff, Acta Cryst. 1994, C50, 1569–1572.
18 C. Pettinari, F. Marchetti, A. Cingolani, G. Bianchini, A. Drozdov, V. Vertlib, S. Troyanov, J.
Organomet. Chem. 2002, 651, 5–14.
19 G. Aullon, G. Ujaque, A. Lledos, S. Alvarez, P. Alemany, Inorg. Chem. 1998, 37, 804–813
20 R. F. W. Bader, Acc. Chem. Res. 1985, 18, 9–15.
21 a) D. Cremer, E. Kraka, Croat. Chem. Acta 1984, 56, 1259–1281; b) O. A. Filippov, A. A.
Titov, E. A. Guseva, D. A. Loginov, A. F. Smol’yakov, F. M. Dolgushin, N. V. Belkova, L. M.
Epstein, E. S. Shubina, Chem. Eur. J. 2015, 21, 13176–13180.
22 a) F. Rieger, A.-V. Mudring, Inorg. Chem. 2005, 44, 9340−9346; b) P. A. Slavin, J. Reglinski,
M. D. Spicer, A. R. Kennedy, J. Chem. Soc. Dalton Trans. 2000, 239–240; c) V. Riera, M. A.
Ruiz, F. Villafane, C. Bois, Y. Jeannin, J. Organomet. Chem. 1989, 375, C23–C26; d) K.-F.
Tebbe, M. El Essawi, S. A. El Khalik, Z. Naturforsch. Teil B 1995, 50, 1429–1439.
23 a) K. Moseley, J. W. Rangand, P. M. Maitlis, J. Chem. Soc. (A) 1970, 2875–2883; b) E. O.
Fischer, H. Wawersik, J. Organomet. Chem. 1966, 5, 559–567.
24 The dicarbollide rhodium complexes with the Cs symmetry display 1:1:2:2:2:1 pattern in the
11B NMR spectra: a) X. L. R. Fontaine, N. N. Greenwood, J. D. Kennedy, K. Nestor, M.
Thornton-Pett, S. Hermanek, T. Jelinek, B. Stibr, J. Chem. Soc., Dalton Trans. 1990, 681–689;
b) M. A. Arsenov, V. B. Kharitonov, E. R. Sovdagarova, A. F. Smol'yakov, D. A. Loginov, J.
Organomet. Chem. 2018, 865, 45–50.
25 S. A. Westcott, A. K. Kakkar, G. Stringer, N. J. Taylor, T. B. Marder, J. Organomet. Chem.
1990, 394, 777–794.
26 B. Klingert, G. Rihs, J. Incl. Phenom. Mol. Recognit. Chem. 1991, 10, 255–265.
27 D. A. Loginov, Z. A. Starikova, M. Corsini, P. Zanello, A. R. Kudinov, J. Organomet. Chem.
2013, 747, 69–75.
28 a) V. P. Datsenko, Y. V. Nelyubina, A. F. Smol'yakov, D. A. Loginov, J. Organomet. Chem.
2018, 874, 7–12; b) D. A. Frasco, C. P. Lilly, P. D. Boyle, E. A. Ison, ACS Catal. 2013, 3, 2421–
2429.
29 a) A. P. Molotkov, M. A. Arsenov, D. A. Kapustin, D. V. Muratov, N. E. Shepel’, Y. V.
Fedorov, A. F. Smol’yakov, E. I. Knyazeva, D. A. Lypenko, A. V. Dmitriev, A. E. Aleksandrov,
20
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E. I. Maltsev, D. A. Loginov, ChemPlusChem 2020, 85, 334–345; b) K. Ueura, T. Satoh, M.
Miura, J. Org. Chem. 2007, 72, 5362–5367.
30 For example, see: a) D. R. Stuart, M. Bertrand-Laperle, K. M. N. Burgess, K. Fagnou, J. Am.
Chem. Soc. 2008, 130, 16474–16475; b) T. Fukutani, K. Hirano, T. Satoh, M. Miura, Org. Lett.
2009, 11, 5198–5201; c) F. W. Patureau, T. Besset, N. Kuhl, F. Glorius, J. Am. Chem. Soc. 2011,
133, 2154–2156.
31 D. R. Stuart, P. Alsabeh, M. Kuhn, K. Fagnou, J. Am. Chem. Soc. 2010, 132, 18326–18339.
32 K. Parthasarathy, N. Senthilkumar, J. Jayakumar, C.-H. Cheng, Org. Lett. 2012, 14, 3478–
3481.
33 For other rhodium catalyzed annulations of benzaldehydes, anilines, and alkynes, see: V. D.
Kadam, B. Feng, X. Chen, W. Liang, F. Zhou, Y. Liu, G. Gao, J. You, Org. Lett. 2018, 20,
7071–7075.
34 For the Rh-catalyzed oxidative coupling of benzamides and alkynes, see: G. Song, D. Chen,
C.-L. Pan, R. H. Crabtree, X. Li, J. Org. Chem. 2010, 75, 7487–7490.
35 Y. Hoshino, Y. Shibata, K. Tanaka, Adv. Synth. Catal. 2014, 356, 1577–1585.
36 For recent works on the reductive amination using carbon monoxide as the reductant, see: a)
O. I. Afanasyev, E. A. Kuchuk, K. M. Muratov, G. L. Denisov, D. Chusov, Eur. J. Org. Chem.
2021, 2021, 543–586; b) M. M. Vinogradov, O. I. Afanasyev, Y. V. Nelyubina, G. L. Denisov,
D. A. Loginov, D. Chusov, Mol. Cat. 2020, 498, 111260; c) O. I. Afanasyev, I. Cherkashchenko,
A. Kuznetsov, F. Kliuev, S. Semenov, O. Chusova, G. Denisov, D. Chusov, Mendeleev
Commun. 2020, 30, 112–113, d) Podyacheva, O. I. Afanasyev, A. A. Tsygankov, M. Makarova,
D. Chusov, Synthesis, 2019, 51, 2667–2677, e) A. A. Tsygankov, M. Makarova, D. Chusov,
Mendeleev Commun. 2018, 28, 113–122.
37 For some other recent important methods for the synthesis of amines, see: a) R. Kumar, N.J.
Flodén, W.G. Whitehurst, M.J. Gaunt, Nature 2020, 581, 415–420; b) J. Bianga, N. Kopplin, J.
Hülsmann, D. Vogt, T. Seidensticker, Adv. Synth. Catal. 2020, 362, 4415–4424; c) C. Nogues,
G. Argouarch, ChemistrySelect 2020, 5, 8319–8327; d) T. Irrgang, R. Kempe, Chem. Rev. 2019,
119, 2524–2549; d) A. Gevorgyan, S. Mkrtchyan, T. Grigoryan, V.O. Iaroshenko,
ChemPlusChem 2018, 83, 375–382; e) A. Gevorgyan, S. Mkrtchyan, T. Grigoryan, V.O.
Iaroshenko, Org. Chem. Front. 2017, 4, 2437–2444.
38 For an example of application of fluorene as a leaving group in the reductive amination, see:
V. B. Kharitonov, E. Podyacheva, Y. V. Nelyubina, D. V. Muratov, A. S. Peregudov, G.
Denisov, D. Chusov, D. A. Loginov, Organometallics 2019, 38, 3151−3158
21
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