Iron-catalysed hydroboration of non-activated imines and nitriles: Kinetic and mechanistic studies

Article abstract of DOI:10.1039/d1ra02001c

Iron-catalysed hydroboration of imines and nitriles has been developed under low catalyst loading (1 mol%) in the presence of HBpin. A wide scope of substrate was found to smoothly undergo hydroboration, including electron releasing/withdrawing and haloge

Full text of DOI:10.1039/d1ra02001c

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Iron-catalysed hydroboration of non-activated
imines and nitriles: kinetic and mechanistic studies†
Cite this: RSC Adv., 2021, 11, 15284
*
Adineh Rezaei Bazkiaei, Michael Wiseman and Michael Findlater
Iron-catalysed hydroboration of imines and nitriles has been developed under low catalyst loading (1 mol%)
in the presence of HBpin. A wide scope of substrate was found to smoothly undergo hydroboration,
including electron releasing/withdrawing and halogen substitution patterns and cyclic substrates which
all afforded the corresponding amines in good to excellent yields. Dihydroboration of nitriles was
achieved conveniently under solvent free and additive free conditions. Promisingly, this catalytic system
is also capable of the hydroboration of challenging ketimine substrates. Preliminary kinetic analysis of
imine hydroboration reveals a first-order dependence on catalyst concentration. Both HBpin and 4-
fluorophenyl-N-phenylmethanimine (1b) appear to exhibit saturation kinetics with first order dependence
up to 0.5 mmol HBpin and 0.75 mmol imine, respectively. Temperature-dependent rate experiments for
imine hydroboration have also been explored. Activation parameters for the hydroboration of FPhC]
NPh (1b) were determined from the Eyring and Arrhenius plots with DSs, DHs, and Ea values of ꢀ28.69
(ꢁ0.3) e.u., 12.95 (ꢁ0.04) kcal molꢀ1, and 15.22 (ꢁ0.09) kcal molꢀ1, respectively.
Received 13th March 2021
Accepted 16th April 2021
DOI: 10.1039/d1ra02001c
rsc.li/rsc-advances
catalysed hydroboration of allylamine in the presence of
HBcat.33 Select examples of complexes capable of effecting
Introduction
catalytic imine hydroboration are shown in Fig. 1.
Amines and their derivatives are found extensively in nature:
proteins, nucleic acids and alkaloids contain the amine func-
tionality. Amines are also key synthetic intermediates in the
synthesis of bactericides, herbicides, rubber accelerators and
many clinically applied drugs.1–5 A wide range of methods have
been reported for the preparation of amines; the reduction of
nitrogenous compounds using stoichiometric amounts of
alkaline metal hydrides, LiAlH4 or NaBH4,6,7 hydrogenation8,9
catalysed by precious metals in the presence of either pressur-
ized H2 or via hydrogen transfer10 and hydrosilylation.11
Hydroboration is an important transformation used to synthe-
size a wide variety of valuable products of industrial signicance
such as commodity and ne chemicals, agrochemicals and
materials.12–15 Thus it is unsurprising that catalytic hydro-
boration of nitriles,16–20 carbodiimides21–25 and imines26–28 are
common methods used to prepare amines. Many experimental
protocols have been studied;29 catalysts employed in imine
hydroboration range from main group elements,30–32 precious-
metals33–36 and, rare earth metals.21,37
In 2009, Clark and co-workers reported a boron-substituted
hydroxycyclopentadienyl ruthenium hydride catalyst with
a limited substrate scope, three examples of aldimines, in
hydroboration chemistry employing HBpin.34 Similarly, another
ruthenium-based system capable of aldimine hydroboration
was reported by Gunanathan in 2016 with a slightly broader
The rst report of imine hydroboration catalysed by a tran-
sition metal was by Baker and Westcott and used a bidentate
phosphine ligated gold(I) complex (5 mol%) and catecholborane
in 1995.38 In 2001, the Westcott group reported a rhodium
Department of Chemistry & Biochemistry, Texas Tech University, Lubbock, Texas
79409, USA. E-mail: michael.ndlater@ttu.edu
Fig. 1 Select (pre)catalysts reported in the literature for imine hydro-
† Electronic supplementary information (ESI) available: Full experimental details
and NMR spectra. See DOI: 10.1039/d1ra02001c
boration and this report.
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substrate scope.35 A fascinating dual-catalytic system was observed (Table S1†). A range of different iron salts, from
recently reported by the Zhu group. In this protocol, an inverse commercially available to synthesized complexes, was tested in
imine hydroboration (where boron adds to the carbon of the catalysis and showed little to moderate activity (Table 1). In the
C]N double bond) was achieved through cooperative organo- interests of disclosure, use of Fe(OTf)3 revealed similar catalytic
catalysis and photocatalysis.36 The Eisen group reported activity as dppBIANFe(Tol). However, our prior experience with
a thorium-catalysed hydroboration of aldimines with a broad dppBIANFe(Tol) and the synthetic modularity afforded by this
substrate scope, however, this catalyst proved unsuccessful in ligand persuaded us to choose this precatalyst for further study.
ketimine reduction.37 While, there are several reports of cata- The use of an activator (NaOtBu) in conjunction with dppBIAN-
lytic imine hydroboration employing transition metals, rst-row Fe(Tol) resulted in a modest improvement in yield. A number of
metal catalysis is still underdeveloped. In 2016, Gordon and co- reaction variables were screened in an effort to optimize
workers demonstrated the catalytic hydroboration of imines product yield: catalyst loading, temperature, solvent and, acti-
with pinacolborane employing Ni(bpy)(cod) (bpy ¼ 2,2-bipyr- vator. Ultimately, employing toluene and NaOtBu as the reac-
idine, cod ¼ 1,5-cyclooctadiene), as catalyst (in benzene) at tion solvent and activator, respectively, allowed us to maximize
room temperature with relatively low catalyst loadings. the yield of amine product (2a) to 97% (Tables S2–S4†). Finally,
However, the substrate scope was very limited.39
the reaction was found to be equally effective employing cat-
Another base metal catalysed imine hydroboration was re- echolborane (HBcat), the hydroboration product being isolated
ported by the Zhang group in 2018, a Co(II) coordination poly- in 90% yield. However, a diminished yield (45%) was obtained
mer was employed as precatalyst, though this system was also when a sterically encumbered borane ((9-borabicyclo[3.3.1]
effective with only a limited range of substrates.40 Very recently nonane)) was used. With optimized conditions in hand, we
an iron catalyst was employed in enantioselective hydro- screened a variety of aldimine and ketimine substrates, which
boration of N-alkyl imines with
a
chiral bis(ox- were easily accessed using well established literature proce-
azolinylmethylidene)isoindoline pincer ligand by the Gade dures.10 N-1-Diphenylethan-1-imine (1c) was cleanly converted
group. Asymmetric catalysis employing various acyclic N-alkyl to amine product (2c, 84%) at low catalyst loading (1 mol%)
imines afforded a-chiral amines in excellent yields.41 The within 1 h.
Schmidt group recently reported a cationic [(iminophosphine)
Encouraged by the successful conversion of a ketimine
nickel(allyl)]+ complex in the hydroboration of N-allylimines substrate employing dppBIANFe(Tol), we decided to examine
(5 mol%). However, no successful hydroboration of ketimine is more ketimine substrates. Substitution patterns ranging from
reported by this catalyst.42 Signicantly, across all reports there electron-releasing, withdrawing, heteroatom and sterically
have been limited examples of successful application of hindered groups were studied. Excellent product yields of more
hydroboration strategies employing ketimine substrates; than 90% (within ꢂ2 h) were obtained when employing
strongly indicating an ongoing need for more active/selective substrates which feature electron withdrawing groups (2e, 2f,
catalysts to be developed. The low abundance, high cost and 2k). Similarly, a more electron-rich substrate (2d) also afforded
toxicity of precious metal elements has prompted the catalytic product in very good yield (88%). A thiophene-based ketimine
community to focus heavily on an examination of the use of substrate (2g) was also found to perform well under optimized
base metals in catalysis.43 Our group has a long standing
interest in employing earth abundant metal catalysts in a variety
of transformations such as aldehyde and ketone hydro-
silylation,44 imine hydrosilylation,11 alkene and alkyne hydro-
boration,45 ester and amide reduction.46,47 Iron has emerged as
a leading candidate in 1st-row metal catalysis as it is the most
abundant transition metal and the fourth most abundant
element in the Earth's crust, it is environmentally benign, cost
effective and has long-term commercial availability.48 Given the
scarce number of literature reports in iron catalysed imine
hydroboration, coupled with a lack of success with ketimine
substrates specically, we decided to study the application of
iron systems in imine hydroboration.
Table 1 Optimization of hydroboration conditions employing various
iron saltsa
Entry
[Fe]
Yieldb (%)
1
2
3
4
5
6
7c
dppBIANFeCl2
Fe(CO)5
14
54
87
65
<10
84
97
dppBIANFe(Tol)
Fe(acac)3
Results and discussion
Catalytic hydroboration of imines
FeCl2-Bpy
Fe(OTf)3
dppBIANFe(Tol)
Initially, we examined the catalytic hydroboration of imines
a
using N-benzylideneaniline (1a) as our model substrate.
Reaction conditions: 1a (0.5 mmol), [Fe] (1 mol%), HBpin (1.5 equiv.),
dppBIANFe(Tol) is readily prepared following the reported liter- THF, 70 ꢃC, 20 h. b As determined by 1H NMR employing mesitylene as
c
ature procedure.44 Hydroboration of 1a proceeded smoothly, as
judged by 1H NMR. As a control, the hydroboration reaction was
repeated in the absence of dppBIANFe(Tol) and yield of 10% was
internal standard.
Optimized conditions: 1a (0.5 mmol),
dppBIANFe(Tol) (1 mol%), HBpin (1.5 equiv.), NaOtBu (2 mol%),
toluene, 70 ꢃC, 1 h.
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reaction conditions, achieving good conversion (88%) in only The reaction was carried out under solvent- and additive-free
1 h. Finally, substrates which feature an enlarged steric prole conditions under mild (RT) conditions. A small scope of
(2h, 2j) were also examined and revealed to be more recalcitrant substrate was explored, and the reaction was found to tolerate
substrates. Increased reaction times were required, and lower both electron-releasing and withdrawing substituents. Bromo-
overall yields were observed. Moreover, to demonstrate the and chloro-substitution were tolerated and aliphatic (cyclic)
convenience of our approach, we have isolated reaction prod- substrates all afforded diborylated amines in good to excellent
ucts as their ammonium salts following treatment with 1 M HCl yields. Substrates with electron-withdrawing functional groups
in diethyl ether. Three examples are presented, 2a, 2b and 2g, (–F, –Cl, –Br) on the backbone were well tolerated and yields
affording isolated yields of 85, 65 and, 75%, respectively ranging from good to excellent (81–95%) were obtained within 2
(Scheme 1). Moreover, a gram scale reaction of 1a was carried to 3 h at 70 ꢃC (4b–4d). A nitrile substrate with an electron
out to demonstrate the synthetic applicability of this protocol. releasing group (–OMe) afforded product in 99% yield within
An isolated yield of 90% was obtained as ammonium salt 6 h at 70 ꢃC (4e). Cyclohexanecarbonitrile also afforded the
(Scheme 1c).
corresponding diborylated product (4f) in 83% yield in 6 h
(Scheme 2). Following a similar procedure as employed in the
isolation of imine hydroboration products, the treatment of
nitrile hydroboration products with 1 M HCl (ether) facilitated
easy isolation of the corresponding ammonium salts. Two
substrates were chosen to demonstrate the utility of this
approach, 4b and 4d were isolated in 84 and 77% yields,
respectively.
Catalytic hydroboration of nitriles
We expanded our hydroboration studies to include nitriles,
employing benzonitrile (3a) as a model substrate.16–20,37,49 Thus,
exposure of 3a to dppBIANFe(Tol) (1 mol%) and 2.5 equiv. HBpin
afforded diborylated amine (4a) in 98% conversion within 3.5 h.
Preliminary mechanistic study of imine hydroboration
To gain insight into the mechanism of imine hydroboration
including possible modes of activation of the precatalyst
dppBIANFe(Tol), we conducted a series of experiments. Thus,
stoichiometric reactions to generate plausible reaction inter-
mediates, preliminary study of reactions kinetics including
temperature-dependent reaction rate experiments were per-
formed. Reactions between dppBIANFe(Tol) and model imine 1a
Scheme 1 Hydroboration of imines and their subsequent conversion
to secondary amines. Reaction conditions: imine (0.5 mmol), HBpin
(1.5 equiv.), dppBIANFe(Tol) (0.005 mmol), NaOtBu (0.01 mmol) at 70 ꢃC Scheme
2 Catalytic hydroboration of nitriles to diboryl amines.
in toluene; conversions were determined by 1H NMR employing aReaction conditions: nitriles (0.25 mmol), HBpin (2.5 equiv.),
mesitylene as internal standard. bIsolated yield as ammonium salt in dppBIANFe(Tol) (0.0025 mmol) at 70 ꢃC; yields were determined by 1H
parentheses. cScale-up reaction of catalytic hydroboration of N- NMR employing mesitylene as internal standard. bReaction was carried
benzylideneaniline; isolated yield as ammonium salt.
out at room temperature. cIsolated yield as ammonium salt in
parentheses.
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Fig. 2 Plot of initial reaction rates (dp/dt) vs. dppBIANFe(Tol).
(1 and 3 equiv. of the imine), were carried out at both room
temperature and 70 ꢃC; we concluded that dppBIANFe(Tol) by
itself, does not appear to react directly with imine substrate
even aer prolonged exposure at elevated temperature
(Fig. S8†). Moreover, stoichiometric reaction of dppBIANFe(Tol)
with HBpin at either room temperature or 70 ꢃC did not afford
any detectable new product(s), as evidenced by in situ moni-
toring employing 11B NMR spectroscopy. However, upon addi-
tion of stoichiometric amounts of NaOtBu to the same reaction
mixture we observed complete consumption of HBpin. The
signal attributed to HBpin at d 27 ppm in the 11B NMR spectrum
disappeared, followed by the formation of a new signal at
d 20 ppm (Fig. S9†). This result can be interpreted as the
requirement of precatalyst activation employing NaOtBu to
form an active catalyst either via direct interaction with
HBpin,50 then subsequent reaction with dppBIANFe(Tol) or
a synergistic effect of all three species. Alas, our attempts to
isolate organometallic species from stoichiometric reactions
were unsuccessful. Preliminary kinetic analysis of the catalytic
hydroboration reaction was performed by observing the disap-
pearance of 4-uorophenyl-N-phenylmethanimine (1b) which is
conveniently monitored using 19F NMR spectroscopy (Fig. S1†).
A plot of the initial rate of the disappearance of 1b exhibits
a rst-order dependence on the catalyst (Fig. 2). While varying
Scheme 3 Plausible mechanism for imine hydroboration.
the concentration of either HBpin or 1b appeared to reveal
saturation kinetics, whereby the reaction is rst order in both
HBpin and imine (1b) only up to 0.5 and 0.75 mmol respectively
(Fig. S2 and S4†).
The reaction prole of catalytic hydroboration of 4-uo-
rophenyl-N-phenylmethanimine at different temperatures is
depicted in Fig. 3. Activation parameters for the hydroboration
of FPhC]NPh were determined from the Eyring and Arrhenius
plots with DSs, DHs, and Ea values of ꢀ28.69 (ꢁ0.3) e.u., 12.95
(ꢁ0.04) kcal molꢀ1, and 15.22 (ꢁ0.09) kcal molꢀ1, respectively
(Fig. S6 and S7†). The negative activation entropy indicates that
the rate-determining step involves an associative process and
DHs and DSs data are consistent with concerted bond-cleavage
and bond-formation process with an organized four-centered
transition state, respectively. Data obtained at 70 ꢃC appears
to show anomalously high reaction rates. Multiple kinetics runs
at this same temperature showed the same data; we are still
investigating the cause.
On the basis of both our preliminary studies and previous
reported literature, a plausible hydroboration mechanism is
proposed for the reaction of dppBIANFe(Tol) and PhC]NPh (1a)
in the presence of HBpin (Scheme 3). The rst step in the
catalytic cycle is loss of toluene from dppBIANFe(Tol) concomi-
tant with generation of a new HBpin complex. Exposure of this
species to imine substrate produces an iron(boryl)(amine) aer
insertion of the C]N bond into an iron-hydride. Reductive
elimination of the aminoborane product followed by rebinding
of the toluene-cap would close the catalytic cycle.
Conclusions
In conclusion, the rapid hydroboration of imines to the corre-
sponding secondary amines have been developed using
dppBIANFe(Tol) as precatalyst in the presence of HBpin.
Hydroboration products can be conveniently isolated as the
corresponding ammonium salts via treatment with HCl as a 1 M
Fig. 3 Reaction profile of catalytic hydroboration of 4-fluorophenyl-
N-phenylmethanimine with HBpin using dppBIANFe(Tol) as catalyst at
different temperatures.
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solution in diethyl ether. To the best of our knowledge, this 16 T. Kitano, T. Komuro and H. Tobita, Organometallics, 2019,
catalyst has the highest TOF (198 hꢀ1) amongst previously re-
38, 1417–1420.
ported transition and rare earth metal complexes to carry out 17 H. Ben-Daat, C. L. Rock, M. Flores, T. L. Groy, A. C. Bowman
the efficient hydroboration of imines. Moreover, this catalytic and R. J. Trovitch, Chem. Commun., 2017, 53, 7333–7336.
system proved capable of the reduction of ketimine substrates 18 J. B. Geri and N. K. Szymczak, J. Am. Chem. Soc., 2015, 137,
in good to excellent yields, which are considered more chal- 12808–12814.
lenging substrates to reduce. In addition, dppBIANFe(Tol) was 19 M. Ito, M. Itazaki and H. Nakazawa, Inorg. Chem., 2017, 56,
found to be an effective precatalyst in the hydroboration of 13709–13714.
nitriles under solvent free and additive free condition to form 20 A. D. Ibrahim, S. W. Entsminger and A. R. Fout, ACS Catal.,
diboryl amines with excellent yields.
2017, 7, 3730–3734.
21 Y. Yuan, X. Wang, Y. Li, L. Fan, X. Xu, Y. Chen, G. Li and
W. Xia, Organometallics, 2011, 30, 4330–4341.
Author contributions
˜
´
22 A. Ramos, A. Antinolo, F. Carrillo-Hermosilla, R. Fernandez-
´
´
´
Galan and D. Garcıa-Vivo, Chem. Commun., 2019, 55, 3073–
ARB and MF designed and executed the project. ARB and MW
carried out the experimental work. ARB and MF wrote the
manuscript.
3076.
23 Y. Ding, X. Ma, Y. Liu, W. Liu, Z. Yang and H. W. Roesky,
Organometallics, 2019, 38, 3092–3097.
24 M. Rauch, S. Ruccolo and G. Parkin, J. Am. Chem. Soc., 2017,
139, 13264–13267.
Conflicts of interest
25 Q. Shen, X. Ma, W. Li, W. Liu, Y. Ding, Z. Yang and
H. W. Roesky, Chem.–Eur. J., 2019, 25, 11918–11923.
26 Q. Yin, Y. Soltani, R. L. Melen and M. Oestreich,
Organometallics, 2017, 36, 2381–2384.
There are no conicts to declare.
Acknowledgements
¨
27 M. Arrowsmith, M. S. Hill and G. Kociok-Kohn, Chem.–Eur.
The authors gratefully acknowledge the National Science
Foundation (CHE-1554906) for nancial support of this work.
J., 2013, 19, 2776–2783.
28 D. Bedi, A. Brar and M. Findlater, Green Chem., 2020, 22,
1125–1128.
29 D. Hayrapetyan and A. Y. Khalimon, Chem.–Asian J., 2020,
15, 2575–2587.
Notes and references
1 J. Verduyckt, R. Coeck and D. E. De Vos, ACS Sustainable 30 M. R. Adams, C. H. Tien, B. S. Huchenski, M. J. Ferguson and
Chem. Eng., 2017, 5, 3290–3295.
A. W. Speed, Angew. Chem., 2017, 56, 6268–6271.
31 M. K. Bisai, S. Pahar, T. Das, K. Vanka and S. S. Sen, Dalton
Trans., 2017, 46, 2420–2424.
32 C. H. Tien, M. R. Adams, M. J. Ferguson, E. R. Johnson and
A. W. Speed, Org. Lett., 2017, 19, 5565–5568.
33 C. M. Vogels, P. E. O'Connor, T. E. Phillips, K. J. Watson,
M. P. Shaver, P. G. Hayes and S. A. Westcott, Can. J. Chem.,
2001, 79, 1898–1905.
2 M. A. Blaskovich, J. Med. Chem., 2016, 59, 10807–10836.
3 R. Jastrz˛ab, L. Łomozik and B. Tylkowski, Phys. Sci. Rev.,
2016, 1, 69–106.
4 R. Mesnage, C. Benbrook and M. N. Antoniou, Food Chem.
Toxicol., 2019, 128, 137–145.
5 B. Movassagh, H. Rooh and H. Bijanzadeh, Chem. Heterocycl.
Compd., 2013, 48, 1719–1721.
6 J. T. Colyer, N. G. Andersen, J. S. Tedrow, T. S. Soukup and 34 L. Koren-Selfridge, H. N. Londino, J. K. Vellucci,
M. M. Faul, J. Org. Chem., 2006, 71, 6859–6862.
7 A. D. Dorsey, J. E. Barbarow and D. Trauner, Org. Lett., 2003,
5, 3237–3239.
8 S. F. Zhu, J. B. Xie, Y. Z. Zhang, S. Li and Q. L. Zhou, J. Am.
Chem. Soc., 2006, 128, 12886–12891.
B. J. Simmons, C. P. Casey and T. B. Clark,
Organometallics, 2009, 28, 2085–2090.
35 A. Kaithal, B. Chatterjee and C. Gunanathan, J. Org. Chem.,
2016, 81, 11153–11161.
36 N. Zhou, X. A. Yuan, Y. Zhao, J. Xie and C. Zhu, Angew. Chem.,
2018, 130, 4054–4058.
9 Y. Liu and H. Du, J. Am. Chem. Soc., 2013, 135, 6810–6813.
¨
10 J. S. Samec and J. E. Backvall, Chem.–Eur. J., 2002, 8, 2955– 37 S. Saha and M. S. Eisen, ACS Catal., 2019, 9, 5947–5956.
2961.
38 R. T. Baker, J. C. Calabrese and S. A. Westcott, J. Organomet.
Chem., 1995, 498, 109–117.
39 A. E. King, S. C. E. Stieber, N. J. Henson, S. A. Kozimor,
B. L. Scott, N. C. Smythe, A. D. Sutton and J. C. Gordon,
Eur. J. Inorg. Chem., 2016, 1635–1640.
11 A. Saini, C. R. Smith, F. S. Wekesa, A. K. Helms and
M. Findlater, Org. Biomol. Chem., 2018, 16, 9368–9372.
12 C. C. Chong, B. Rao and R. Kinjo, ACS Catal., 2017, 7, 5814–
5819.
13 J. Magano and J. R. Dunetz, Org. Process Res. Dev., 2012, 16, 40 J. Wu, H. Zeng, J. Cheng, S. Zheng, J. A. Golen, D. R. Manke
1156–1184.
and G. Zhang, J. Org. Chem., 2018, 83, 9442–9448.
14 S. R. Tamang, A. Singh, D. K. Unruh and M. Findlater, ACS 41 C. K. Blasius, N. F. Heinrich, V. Vasilenko and L. H. Gade,
Catal., 2018, 8, 6186–6191. Angew. Chem., 2020, 132, 16108–16111.
15 M. Haberberger and S. Enthaler, Chem.–Asian J., 2013, 8, 50– 42 I. Hossain and J. A. R. Schmidt, Eur. J. Inorg. Chem., 2020,
54.
1877–1884.
15288 | RSC Adv., 2021, 11, 15284–15289
© 2021 The Author(s). Published by the Royal Society of Chemistry

View Article Online
Paper
RSC Advances
43 S. R. Tamang and M. Findlater, Molecules, 2019, 24, 3194.
44 F. S. Wekesa, R. Arias-Ugarte, L. Kong, Z. Sumner,
G. P. McGovern and M. Findlater, Organometallics, 2015,
34, 5051–5056.
45 A. Singh, S. Shaei-Haghighi, C. R. Smith, D. K. Unruh and
M. Findlater, Asian J. Org. Chem., 2020, 9, 416–420.
46 S. R. Tamang, A. F. Cozzolino and M. Findlater, Org. Biomol.
Chem., 2019, 17, 1834–1838.
47 S. R. Tamang, A. Singh, D. Bedi, A. R. Bazkiaei, A. A. Warner,
K. Glogau, C. McDonald, D. K. Unruh and M. Findlater, Nat.
Catal., 2020, 3, 154–162.
48 M. D. Greenhalgh, A. S. Jones and S. P. Thomas,
ChemCatChem, 2015, 7, 190–222.
49 Z. Huang, S. Wang, X. Zhu, Q. Yuan, Y. Wei, S. Zhou and
X. Mu, Inorg. Chem., 2018, 57, 15069–15078.
50 J. H. Docherty, J. Peng, A. P. Dominey and S. P. Thomas, Nat.
Chem., 2017, 9, 595.
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