Highly Efficient Rh(I) Homo- and Heterogeneous Catalysts for C-N Couplings via Hydrogen Borrowing

Article abstract of DOI:10.1021/acs.inorgchem.7b02586

Rhodium(I) complexes were explored as catalysts for the hydrogen borrowing reactions of amines and alcohols. Bidentate carbene-triazole ligands were readily synthesized via "click" reactions which allowed a diversity of ligand backbones to be accessed. The catalytic transformations are highly efficient, able to reach completion in under 6 h, and promote C-N bond formation across a range of primary alcohol and amine substrates. Moreover, site-selective catalysis can be achieved using substrates with more than one reactive site. A rhodium(I) complex covalently attached to a carbon black surface was also deployed in the hydrogen borrowing coupling reaction of aniline with benzyl alcohol. This represents the first report of a heterogeneous rhodium catalyst used for hydrogen borrowing.

Full text of DOI:10.1021/acs.inorgchem.7b02586

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX-XXX
Highly Efficient Rh(I) Homo- and Heterogeneous Catalysts for C−N
Couplings via Hydrogen Borrowing
Chin M. Wong,†,‡ Matthew B. Peterson,†,‡ Indrek Pernik,† Roy T. McBurney,†
and Barbara A. Messerle*,†
†Chemistry and Biomolecular Sciences, Macquarie University, Sydney, NSW, 2109, Australia
‡School of Chemistry, University of New South Wales, Australia, Sydney, NSW, 2052, Australia
S
* Supporting Information
ABSTRACT: Rhodium(I) complexes were explored as
catalysts for the hydrogen borrowing reactions of amines and
alcohols. Bidentate carbene-triazole ligands were readily
synthesized via “click” reactions which allowed a diversity of
ligand backbones to be accessed. The catalytic transformations
are highly efficient, able to reach completion in under 6 h, and
promote C−N bond formation across a range of primary
alcohol and amine substrates. Moreover, site-selective catalysis
can be achieved using substrates with more than one reactive
site. A rhodium(I) complex covalently attached to a carbon
black surface was also deployed in the hydrogen borrowing
coupling reaction of aniline with benzyl alcohol. This
represents the first report of a heterogeneous rhodium catalyst
used for hydrogen borrowing.
catalysis”,13 has the potential to increase their industrial
INTRODUCTION
■
applicability.
Alkylated amines are an important structural motif found in
Encouraged by the results using iridium complexes as
many bulk and fine chemicals.1 Traditional synthetic routes to
hydrogen borrowing catalysts and the relatively scarce use of
alkylated amines typically involve the use of potentially
rhodium, we were curious to probe the catalytic ability of Rh(I)
expensive and/or toxic reagents, the formation of stoichio-
complexes as catalysts for the hydrogen borrowing reaction. To
metric amounts of waste, unwanted side reactions, and tedious
obtain a direct comparison, the rhodium complexes chosen are
workup procedures.2 “Hydrogen borrowing” provides an
analogous to the iridium complexes recently investigated in our
group.14 Herein, we report a series of readily synthesized Rh(I)-
alternate, sustainable synthetic pathway for directly reacting
alcohols with amines to form new C−N bonds.1,3 Homoge-
carbene-triazole complexes (Scheme 1) that act as homoge-
neously catalyzed bond formations via hydrogen borrowing
neous catalysts with excellent activity and efficiency for C−N
have largely been achieved using ruthenium,4 iridium,5 and
bond formation reactions.
more recently manganese,6 cobalt,7 iron,7b and nickel8
These rhodium catalysts outperform the current best Rh(I)
complexes. Despite RhH(PPh3)4 being first used over 35
years ago to catalyze a hydrogen borrowing C−N bond
formation reaction,9 rhodium has since received very little
attention. The only other reports featuring rhodium salts as
catalysts for hydrogen borrowing relied on either high
temperature (200 °C)10 or high catalyst loadings (5 mol %)
in order to achieve short reaction times (8 h).11
catalyst reported to date in the literature and are within the
same ballpark as the analogous iridium catalyst14 for coupling of
benzyl alcohol with aniline via hydrogen borrowing.10 A hybrid
heterogeneous catalyst was generated by covalently attaching
one of these Rh(I) complexes to a carbon black surface,13,14
and its efficiency was demonstrated in the coupling of benzyl
alcohol with aniline.
Current progress in this field has delivered some iridium
based catalyst systems that show high reactivity at low catalyst
loadings (<0.5 mol %) or comparatively mild temperatures
(≤70 °C), though these examples do require longer reaction
times.12 Hence, catalysts possessing greater catalytic activity,
which work at lower temperatures and have shorter reaction
times, are highly desirable. Furthermore, coupling excellent
homogeneous catalytic activity with the ease of separation and
recyclability offered by heterogeneous catalysis, “hybrid
RESULTS AND DISCUSSION
■
Complex Synthesis. The ligand synthesis took full
advantage of the modular nature of triazole formation via a
Cu-catalyzed “click” reaction (Scheme 1).15 Various aryl units
were introduced, allowing rapid access to ligands, 1a−f,
Received: October 9, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b02586
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
conversion observed using isolated complex 2a. With this
simpler in situ protocol established, ligands 1a−e were used to
generate Rh(I) complexes 7a−e (Figure 1b), and the efficiency
Scheme 1. Synthesis of Homogeneous Rh(I) Catalysts
possessing different electronic characteristics (H, NO2, CH3,
para/meta-CF3) with the triazole moiety used as a ligating site.
A carbene unit was chosen as it provides a strong σ-donor,
ensuring a strong rhodium−ligand bond which in turn results in
a more stable catalyst.16 The triazole moiety provides a second,
weaker ligation site to accommodate the coordination require-
ments of the metal ion during the catalysis. A silver
transmetalation route was used to prepare rhodium(I) catalyst
2a with COD co-ligands from which 3 with CO co-ligands was
prepared.
Figure 1. Catalyst screening results. (a) Hydrogen borrowing reaction
of benzyl alcohol 4a and aniline 5a. (b) In situ formed catalysts 7a−e.
(c) Catalyst screening for hydrogen borrowing C−N bond formation.
Reagents and conditions: benzyl alcohol 4a (1.1 equiv), aniline 5a (1.0
equiv), ligand 1a−e (1 mol %), [Rh(COD)Cl]2 (0.5 mol %), KOtBu
(1.1 equiv), Na[BArF ] (1 mol %), toluene-d8, 100 °C, 6 h.
4
Initial Catalytic Studies. The catalyzed hydrogen borrow-
ing reaction of benzyl alcohol (4a) with aniline (5a) to produce
N-benzylaniline (6a) was chosen as a test reaction to allow
direct comparison with reported catalysts.14 Reaction progress
using catalysts 2a and 3 was assessed at 6 h, as was the effect of
varying the catalyst loadings (Table 1). Catalysts 2a and 3
of these catalysts was investigated for the same C−N bond
formation reaction (Figure 1c). All in situ generated Rh(I)
complexes gave good to excellent conversions of 4a and 5a to
6a, with the para-CF3 containing catalyst 7d giving the highest
conversion at 94% (93% isolated yield). The complex with the
ligand which contains the electron-donating para-CH3
substituent (7c) gave the lowest conversion at 80%, implying
that an electron-rich environment around the metal center
decreases catalytic efficiency.
a
Table 1. Effect of Catalyst Loadings
Rh(I)-Catalyzed Hydrogen Borrowing Reaction Scope.
In situ generated Rh(I) catalyst 7d was tested in a series of
reactions where either the alcohol (4) or the amine substrate
(5) was varied (Scheme 2). All in situ catalyzed reactions of
aniline (5a) with alcohol functionalized substrates containing
electron-donating substituents or an aliphatic chain yielded
>98% conversions (products 6b−d, 6f, and 6i) after 6 h at 100
°C. Slightly lower yields were obtained upon using cyclic
aliphatic alcohols as substrates (6g, 6h). The catalytic
conversion of 4-bromobenzyl alcohol (4e) and aniline (5a)
to form 6e, led to substantially lower conversion (40%), due to
side reactions occurring, including dehalogenation. Signifi-
cantly, some reactions also proceeded at a lower temperature of
60 °C for 24 h. The reaction of piperonyl alcohol with aniline
(5a) at 60 °C achieved an identical conversion (>98%) to 6f as
achieved at 100 °C, whereas the reaction of 2-methylbenzyl
alcohol and aniline at 60 °C resulted in 73% conversion to
product 6c. Secondary alcohols (such as 1-phenylethane-1-ol)
did not react under any of the reaction conditions used in this
study.
Various amine substrates were then tested. The reaction
proved tolerant of most tested substituents on aniline (p-
halogen, p-OCH3, p-CH3, 1-naphthyl, 4-morpholino), 5-amino-
N-methylindole, and furfurylamine with high conversions
(>90%) in most cases (Scheme 2). Upon using the highly
electron-withdrawing p-CF3 (6n), only 17% conversion was
seen. Interestingly, when comparing the three para-halogenated
aniline containing reactions (6k−m), the more electron-
withdrawing para-substituent led to better conversion (F >
b
catalyst
catalyst loading, mol % % conv.
TON
1
2
3
4
5
6
7
8
9
2a
2a
2a
3
1.0
0.5
0.1
1.0
0.5
0.1
0.5
0.5
0.5
99
95
55
99
86
53
44
50
47
99
190
550
99
3
172
530
88
3
[Rh(COD)Cl]2
[Rh(CO)2Cl]2
[Rh(COD)Cl]2
100
94
c
a
Reagents and conditions: benzyl alcohol 4a (1.1 equiv), aniline 5a
b
(1.0 equiv), KOtBu (1.1 equiv), toluene-d8, 100 °C, 6 h.
%
1
conversions to 6a were calculated using H NMR spectral analysis
c
of crude product mixture. 1 mol % Na[BArF ] added.
4
performed well at loadings of 1.0 and 0.5 mol %; however,
performance deteriorated at 0.1 mol % loading with just over
50% conversion obtained (TON > 500). Control experiments
confirmed the superior performance of our organometallic
catalysts to that of the Rh(I) precursors (Table 1, entries 7−9).
During the initial catalysis investigation, we found that the
[BArF ]− anion analogue of 2a could be generated in situ using
4
[Rh(COD)Cl]2 (0.5 mol %), ligand 1a (1.0 mol %), and
Na[BArF ] (1.0 mol %). Under the same hydrogen borrowing
4
reaction conditions, in situ generated catalyst 7a promoted 91%
conversion of the substrates to 6a, comparable to the
B
DOI: 10.1021/acs.inorgchem.7b02586
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
We also determined the efficiency of the catalysts for the
synthesis of some selected biologically significant molecules
containing a 2-phenethylamine core. These motifs (Scheme 2,
6v−z) are often found in pharmaceuticals such as anti-obesity
medication.18 Rh(I) complex 7d catalyzed the formation of
products containing these biologically relevant motifs (6v−z)
in moderate to good conversions (54−71%) after 24 h at 100
°C. The efficiency of the analogous iridium complexes14 for the
synthesis of these same biologically active species was also
tested here in order to broaden our understanding of the
differences between the rhodium and iridium systems.
Interestingly, in all cases, under the same reaction conditions,
no conversion was obtained when using the iridium(III)
complex as the catalyst (Supporting Information S1.4). Thus,
rhodium provides an enhanced catalyst relative to the iridium
analogue for hydrogen borrowing using these particular
substrates (6v−z).
Scheme 2. Scope of the Reaction Using the in Situ Generated
Catalyst 7d
a
Site-Selective Hydrogen Borrowing Catalysis. The
significantly different reactivity of the catalyst 7d toward
some substrates (i.e., primary vs secondary alcohols, and the
ethyl-linker containing amines/alcohols) allowed us to probe
this rhodium catalyst as a site-selective hydrogen borrowing
catalyst. This is a useful ability, as it allows for one reactive site
to be functionalized while leaving the other one untouched.
The substrates chosen were 1-(4-aminophenyl)ethan-1-ol
(5aa) and 4-(2-aminoethyl)aniline (5ab), which were both
reacted with benzyl alcohol (4) (Scheme 3).
Scheme 3. Selectivity Studies Using Reagents with Different
a
Amine/Alcohol Groups
a
Conditions: [Rh(COD)Cl]2 (0.5 mol %), 1d (1.0 mol %), Na[BArF ]
4
(1.0 mol %), KOtBu (1.1 equiv), toluene-d8, 100 °C, 6 h. (a) 4a:5aa
ratio = 1:1. (b) 4a:5ab ratio = 1:1. % conversions were calculated using
1H NMR spectral analysis of crude product mixture. Isolated yields are
a
1
Substrate ratio 4:5 1.1:1. % conversions were calculated using H
NMR spectral analysis of crude product mixture. Isolated yields are
b
given in parentheses. 2.1 equiv of KOtBu was used.
b
c
given in parentheses. Product isolation was not attempted. 24 h.
To gain from the inactivity toward the secondary alcohols,
the hydrogen borrowing reaction was conducted using
substrates 4a and 5aa. As postulated, this allowed for the
selective reaction of the amine with benzyl alcohol (83%
conversion), while no reactivity toward the secondary alcohol
was observed (Scheme 3a). In order to obtain high conversion
to 6aa, an extra equivalent of potassium tert-butoxide was used.
The standard conditions (1.1 equiv of KOtBu) resulted in only
34% conversion, indicating that, although no hydrogen
borrowing transformation is observed with secondary alcohols,
a reaction with the base is still occurring. Another selectivity
reaction was designed to allow for discrimination between the
aryl and alkyl primary amines. Upon comparing the formation
of 6a and 6y, it is clear that a longer aliphatic chain between the
amine group and the aromatic ring leads to lower yields (96%
conversion after 6 h vs 64% conversion after 24 h, respectively).
To compare the reactivity with both amine groups simulta-
Cl > Br). This is likely due to the weaker C−Cl and C−Br
bonds allowing for unwanted side reactions to occur, rather
than the electron-withdrawing properties of the para-group.17
1
Indeed, the H NMR spectra of these reactions reveal the
formation of dehalogenated species (cf. 6e). Interestingly, this
trend was not observed upon using the analogous iridium(III)
catalyst reported by us recently.14
In situ prepared Rh(I) complex 7d was shown to be efficient
for promoting the reaction of benzyl alcohol with 2-
aminopyridine, with complete conversion (>98%) to product
6p (Scheme 2). This is a challenging reaction as both the
substrate and the formed product could feasibly coordinate to
the metal center and inhibit the catalyst. The formation of 6p
has been reported previously using rhodium-based catalysts, but
at lower yields (67−85%) and at longer reaction times (12−20
h) with higher temperatures required (120−150 °C).11
C
DOI: 10.1021/acs.inorgchem.7b02586
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
neously, a hydrogen borrowing reaction was carried out using
substrates 4a and 5ab (Scheme 3b). After 6 h at 100 °C, the
reaction led to the selective formation of 6ab as the main
product.
Heterogeneous Catalysis. In recent years, we have seen
substantial enhancement in catalyst turnover numbers upon
grafting the organometallic complexes to carbon surfaces.13,14,19
In addition, the use of a solid support allows for the recovery of
the catalyst, and in particular, the use of a covalent C−C bond
as a connection to the surface results in a stable system that can
handle basic conditions and relatively high temperatures.
Through an established diazonium route,13,14 the rhodium
complex was covalently attached to carbon black, forming
catalyst 2-CB (Scheme 4, inset). The Rh(I) hybrid complex 2-
to Rh(I), generates catalysts that surpass the best rhodium(I)
catalyst reported to-date for the direct coupling of benzyl
alcohol with aniline via a hydrogen borrowing reaction. In the
case of some of the more demanding substrates, the rhodium
catalyst 7d outperformed its iridium(III) analogue. In addition,
high selectivity toward one product was obtained upon using
reagents with two reactive sites. Significantly, we demonstrated
that the catalysts could be formed in situ, greatly simplifying the
catalysis reaction. A heterogeneous catalyst composed of a
Rh(I) complex covalently attached to carbon black was
deployed as a catalyst for the reaction of benzyl alcohol with
aniline, achieving a TON of 977.
EXPERIMENTAL SECTION
■
Catalysis Procedure Using Isolated Rh(I) Complexes 2a and
3a. All preparations of catalysis mixtures were performed in air. The
Rh(I) complexes 2a−3a (0.0005 mmol, 0.1 mol %, 0.0025 mmol, 0.5
mol %, or 0.005 mmol, 1.0 mol %), aniline (5a) (0.5 mmol), benzyl
alcohol (4a) (0.55 mmol), and KOtBu (0.55 mmol) were weighed into
a 4 mL glass vial fitted with a close-top melamine cap with PTFE liner.
Toluene-d8 (400 mg) was then added to the mixture. The headspace
was then purged with nitrogen, and the vial sealed. The reaction
mixture was stirred at room temperature for 5 min until a
homogeneous mixture is observed. The reaction mixture was then
placed in an oil bath at either 100 or 60 °C. After 6 or 24 h,
respectively, the reaction mixture was taken out of the oil bath and
immediately cooled in the fridge. Subsequently, an NMR sample was
prepared by taking an aliquot of the mixture and dissolving it in either
toluene-d8 or chloroform-d1.
Scheme 4. Hydrogen Borrowing Catalysis Using the Carbon
a
Surface-Bound Rhodium Catalyst 2-CB
a
Conditions: 2-CB (0.05 mol %), KOtBu (1.1 equiv), toluene-d8, 100
°C, 24 h. Substrate ratio: 4a:5a 1.1:1.
CB was tested as a catalyst for the hydrogen borrowing reaction
of benzyl alcohol (4a) with aniline (5a) (Scheme 4). The Rh(I)
hybrid catalyst 2-CB at a loading of 0.05 mol % gave a
moderate 53% conversion to N-benzylaniline (6a) after 24 h at
100 °C, which corresponded to a TON of 977. While
homogeneous Rh(I) complex 2a reached a higher 86%
conversion in a shorter reaction time (6 h), the heterogeneous
reactions achieved a 5 times larger turnover number due to the
lower catalyst loading. Hybrid catalyst 2-CB was significantly
more efficient than the hybrid Ir(III) complex on silica reported
by Wang et al. for the reaction of benzyl alcohol (4a) and
aniline (5a), with a turnover number 16 times larger achieved
in a shorter reaction time.20 Our turnover number was lower
compared to the 46 000 obtained by Seayad using a hybrid Pd
on silica after 72 h.21 The direct comparison to the analogous
iridium complex14 revealed that, although under homogeneous
conditions similar catalytic conversions were obtained for both
iridium and rhodium, the use of iridium leads to a more active
hybrid catalyst reaching to a TON of >4000. Both of the hybrid
catalysis results were obtained using significantly lower catalyst
loadings than in the case of 2-CB.
Catalysis Procedure Using in Situ Generated Rh(I) Catalysts
to Form Products 6a−6u. The in situ Rh(I) complexes 7a−e were
generated using the ligands (1a−e) (0.005 mmol, 1.0 mol %),
[Rh(COD)Cl]2 (0.0025 mmol, 0.5 mol %), and Na[BArF ] (0.005
4
mmol, 1.0 mol %). The catalytic reactions using these catalysts were
prepared and analyzed following the same procedure as in the case of
isolated Rh(I) catalysis (6 h) with amine substrates (5a−u) (0.5
mmol), alcohol substrate (4a−i) (0.55 mmol), and KOtBu (0.55
mmol) in toluene-d8 (400 mg). The reaction mixture was filtered to
remove base, and the conversion calculated by 1H NMR using
comparison of substrate and product peaks. Products were isolated by
column chromatography using ethyl acetate/n-hexane as eluent.
Catalysis Procedure Using in Situ Formed Rh(I) Catalysts to
Form Products 6v−6z and 6aa−6ab. The in situ Rh(I) complexes
7a−e were generated using the ligands (1a−e) (0.0025 mmol, 5.0 mol
%), [Rh(COD)Cl]2 (0.0125 mmol, 2.5 mol %), and Na[BArF ]
4
(0.0025 mmol, 5.0 mol %). The catalytic reactions using these catalysts
were prepared and analyzed following the same procedure as in the
case of isolated Rh(I) catalysis (24 h) with relevant substrates (amine
0.55 mmol, alcohol 0.55 mmol), and KOtBu (0.55 mmol) in toluene-
d8 (400 mg). The reaction mixture was filtered to remove base, and the
1
conversion calculated by H NMR using comparison of substrate and
product peaks. Products were isolated by column chromatography
2-CB has previously been shown to be a highly stable
heterogeneous catalyst, with only limited leaching of Rh,
attributed to loss of Rh physisorbed on the surface and not
from the covalently attached catalyst.13,14 Upon using 2-CB as a
catalyst for a hydrosilylation reaction, no appreciable loss of
reactivity of the catalyst was observed over several reaction
cycles.13 In addition, the iridium analogue of 2-CB was recently
reported as a recyclable hydrogen borrowing catalyst under the
same reaction conditions as reported here.14 On the basis of
these data, any leaching of the rhodium complex from 2-CB is
highly unlikely.
using ethyl acetate/n-hexane as eluent.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b02586.
Experimental methods and data, and catalysis procedures
(PDF)
AUTHOR INFORMATION
CONCLUSION
In summary, we have developed a bidentate ligand containing a
triazole and carbene coordination motif that, when coordinated
■
■
Corresponding Author
*E-mail: barbara.messerle@mq.edu.au.
D
DOI: 10.1021/acs.inorgchem.7b02586
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Catal. 2016, 6, 2205−2210. (g) Watanabe, Y.; Tsuji, Y.; Ohsugi, Y.
The ruthenium catalyzed N-alkylation and N-heterocyclization of
aniline using alcohols and aldehydes. Tetrahedron Lett. 1981, 22,
2667−2670.
ORCID
Roy T. McBurney: 0000-0002-2383-8450
Barbara A. Messerle: 0000-0002-1928-5961
Notes
(5) (a) Frost, J. R.; Cheong, C. B.; Akhtar, W. M.; Caputo, D. F. J.;
Stevenson, N. G.; Donohoe, T. J. Strategic Application and
Transformation of ortho-Disubstituted Phenyl and Cyclopropyl
Ketones To Expand the Scope of Hydrogen Borrowing Catalysis. J.
Am. Chem. Soc. 2015, 137, 15664−15667. (b) Ruiz-Botella, S.; Peris, E.
Unveiling the Importance of π-Stacking in Borrowing-Hydrogen
Processes Catalysed by Iridium Complexes with Pyrene Tags. Chem. -
Eur. J. 2015, 21, 15263−15271. (c) Shen, D.; Poole, D. L.; Shotton, C.
C.; Kornahrens, A. F.; Healy, M. P.; Donohoe, T. J. Hydrogen-
Borrowing and Interrupted-Hydrogen-Borrowing Reactions of Ke-
tones and Methanol Catalyzed by Iridium. Angew. Chem., Int. Ed. 2015,
54, 1642−1645. (d) Zhang, Y.; Lim, C.-S.; Sim, D. S. B.; Pan, H.-J.;
Zhao, Y. Catalytic Enantioselective Amination of Alcohols by the Use
of Borrowing Hydrogen Methodology: Cooperative Catalysis by
Iridium and a Chiral Phosphoric Acid. Angew. Chem., Int. Ed. 2014, 53,
1399−1403. (e) Wang, D.; Zhao, K.; Yu, X.; Miao, H.; Ding, Y.
Iridium-CNP complex catalyzed cross-coupling of primary alcohols
and secondary alcohols by a borrowing hydrogen strategy. RSC Adv.
2014, 4, 42924−42929. (f) Saidi, O.; Blacker, A. J.; Farah, M. M.;
Marsden, S. P.; Williams, J. M. J. Selective Amine Cross-Coupling
Using Iridium-Catalyzed “Borrowing Hydrogen” Methodology. Angew.
Chem., Int. Ed. 2009, 48, 7375−7378. (g) Saidi, O.; Williams, J. M. J.
Iridium-Catalyzed Hydrogen Transfer Reactions; Springer: Berlin, 2011;
pp 77−106. (h) Zou, Q.; Wang, C.; Smith, J.; Xue, D.; Xiao, J.
Alkylation of Amines with Alcohols and Amines by a Single Catalyst
under Mild Conditions. Chem. - Eur. J. 2015, 21, 9656−9661.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support from Macquarie University, University of
New South Wales, and the Australian Research Council is
gratefully acknowledged. This research was supported under
the Australian Research Council’s Discovery Projects funding
scheme (project number DP130101838). We are grateful to the
NMR facilities at the Mark Wainwright Analytical Centre,
UNSW, and Macquarie University. We are grateful to the
Cabot Corporation for the donation of the carbon black
(Vulcan XC-72R). C.M.W. thanks the Australian Government
for the award of an International Postgraduate Research
Scholarship (IPRS). M.B.P. thanks the Australian Government
for the Australian Government Research Training Program
Scholarship (AGRTPS).
REFERENCES
■
(1) Leonard, J.; Blacker, A. J.; Marsden, S. P.; Jones, M. F.;
Mulholland, K. R.; Newton, R. A Survey of the Borrowing Hydrogen
Approach to the Synthesis of some Pharmaceutically Relevant
Intermediates. Org. Process Res. Dev. 2015, 19, 1400−1410.
(2) (a) Fernandez, E.; Brown, J. M. Electrophilic Amination Routes
from Alkenes; Wiley-VCH Verlag GmbH: Weinheim, 2007. (b) Genet,
J.-P.; Greck, C.; Lavergne, D. Stereoselective Electrophilic Amination with
Sulfonyloxycarbamates and Azodicarboxylates; Wiley-VCH Verlag
GmbH: Weinheim, 2007. (c) Gribble, G. W. Sodium borohydride in
carboxylic acid media: a phenomenal reduction system. Chem. Soc. Rev.
1998, 27, 395−404. (d) Hartwig, J. F. Palladium-Catalyzed Amination
of Aryl Halides and Sulfonates; Wiley-VCH Verlag GmbH: Weinheim,
2007.
́
(6) Pena-Lopez, M.; Piehl, P.; Elangovan, S.; Neumann, H.; Beller,
̃
M. Manganese-Catalyzed Hydrogen-Autotransfer C−C Bond For-
mation: α-Alkylation of Ketones with Primary Alcohols. Angew. Chem.,
Int. Ed. 2016, 55, 14967−14971.
(7) (a) Zhang, G.; Yin, Z.; Zheng, S. Cobalt-Catalyzed N-Alkylation
of Amines with Alcohols. Org. Lett. 2016, 18, 300−303. (b) Quintard,
A.; Rodriguez, J. A Step into an eco-Compatible Future: Iron- and
Cobalt-catalyzed Borrowing Hydrogen Transformation. ChemSusChem
(3) (a) Crabtree, R. H. An Organometallic Future in Green and
Energy Chemistry? Organometallics 2011, 30, 17−19. (b) Bahn, S.;
2016, 9, 28−30. (c) Rosler, S.; Ertl, M.; Irrgang, T.; Kempe, R. Cobalt-
̈
̈
Catalyzed Alkylation of Aromatic Amines by Alcohols. Angew. Chem.,
Int. Ed. 2015, 54, 15046−15050.
Imm, S.; Neubert, L.; Zhang, M.; Neumann, H.; Beller, M. The
Catalytic Amination of Alcohols. ChemCatChem 2011, 3, 1853−1864.
(c) Yang, Q.; Wang, Q.; Yu, Z. Substitution of alcohols by N-
nucleophiles via transition metal-catalyzed dehydrogenation. Chem.
Soc. Rev. 2015, 44, 2305−2329. (d) Nixon, T. D.; Whittlesey, M. K.;
Williams, J. M. J. Transition metal catalysed reactions of alcohols using
borrowing hydrogen methodology. Dalton Trans. 2009, 2009, 753−
762. (e) Watson, A. J. A.; Williams, J. M. J. The Give and Take of
Alcohol Activation. Science 2010, 329, 635−636. (f) Marr, A. C.
Organometallic hydrogen transfer and dehydrogenation catalysts for
the conversion of bio-renewable alcohols. Catal. Sci. Technol. 2012, 2,
279−287.
(8) Shimizu, K.-i.; Imaiida, N.; Kon, K.; Hakim Siddiki, S. M. A.;
Satsuma, A. Heterogeneous Ni Catalysts for N-Alkylation of Amines
with Alcohols. ACS Catal. 2013, 3, 998−1005.
(9) Grigg, R.; Mitchell, T. R. B.; Sutthivaiyakit, S.; Tongpenyai, N.
Transition metal-catalyzed N-alkylation of amines by alcohols. J. Chem.
Soc., Chem. Commun. 1981, 1981, 611−612.
(10) Tanaka, N.; Hatanaka, M.; Watanabe, Y. Transition metal-
catalyzed N-alkylation of NH groups of azoles with alcohols. Chem.
Lett. 1992, 21, 575−578.
(11) Liu, C.; Liao, S.; Li, Q.; Feng, S.; Sun, Q.; Yu, X.; Xu, Q.
Discovery and Mechanistic Studies of a General Air-Promoted Metal-
Catalyzed Aerobic N-Alkylation Reaction of Amides and Amines with
Alcohols. J. Org. Chem. 2011, 76, 5759−5773.
(12) (a) Blank, B.; Michlik, S.; Kempe, R. Selective iridium-catalyzed
alkylation of (hetero)aromatic amines and diamines with alcohols
under mild reaction conditions. Chem. - Eur. J. 2009, 15, 3790−3799.
(b) Michlik, S.; Hille, T.; Kempe, R. The Iridium-Catalyzed Synthesis
of Symmetrically and Unsymmetrically Alkylated Diamines under Mild
Reaction Conditions. Adv. Synth. Catal. 2012, 354, 847−862.
(c) Michlik, S.; Kempe, R. New Iridium Catalysts for the Efficient
Alkylation of Anilines by Alcohols under Mild Conditions. Chem. - Eur.
J. 2010, 16, 13193−13198. (d) Ruch, S.; Irrgang, T.; Kempe, R. New
Iridium Catalysts for the Selective Alkylation of Amines by Alcohols
under Mild Conditions and for the Synthesis of Quinolines by
Acceptor-less Dehydrogenative Condensation. Chem. - Eur. J. 2014,
20, 13279−13285. (e) Jumde, V. R.; Gonsalvi, L.; Guerriero, A.;
Peruzzini, M.; Taddei, M. A Ruthenium-Based Catalytic System for a
(4) (a) Dang, T. T.; Ramalingam, B.; Seayad, A. M. Efficient
Ruthenium-Catalyzed N-Methylation of Amines Using Methanol. ACS
Catal. 2015, 5, 4082−4088. (b) Eka Putra, A.; Oe, Y.; Ohta, T.
Ruthenium-Catalyzed Enantioselective Synthesis of β-Amino Alcohols
from 1,2-Diols by “Borrowing Hydrogen. Eur. J. Org. Chem. 2013,
2013, 6146−6151. (c) Enyong, A. B.; Moasser, B. Ruthenium-
Catalyzed N-Alkylation of Amines with Alcohols under Mild
Conditions Using the Borrowing Hydrogen Methodology. J. Org.
Chem. 2014, 79, 7553−7563. (d) Hamid, M. H. S. A.; Allen, C. L.;
Lamb, G. W.; Maxwell, A. C.; Maytum, H. C.; Watson, A. J. A.;
Williams, J. M. J. Ruthenium-Catalyzed N-Alkylation of Amines and
Sulfonamides Using Borrowing Hydrogen Methodology. J. Am. Chem.
Soc. 2009, 131, 1766−1774. (e) Hollmann, D.; Bahn, S.; Tillack, A.;
̈
Parton, R.; Altink, R.; Beller, M. A novel salt-free ruthenium-catalyzed
alkylation of aryl amines. Tetrahedron Lett. 2008, 49, 5742−5745.
(f) Marichev, K. O.; Takacs, J. M. Ruthenium-Catalyzed Amination of
Secondary Alcohols Using Borrowing Hydrogen Methodology. ACS
E
DOI: 10.1021/acs.inorgchem.7b02586
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Mild Borrowing-Hydrogen Process. Eur. J. Org. Chem. 2015, 2015,
1829−1833.
(13) Wong, C. M.; Walker, D. B.; Soeriyadi, A. H.; Gooding, J. J.;
Messerle, B. A. A versatile method for the preparation of carbon-
rhodium hybrid catalysts on graphene and carbon black. Chem. Sci.
2016, 7, 1996−2004.
(14) Wong, C. M.; McBurney, R. T.; Binding, S. C.; Peterson, M. B.;
Goncales, V. R.; Gooding, J. J.; Messerle, B. A. Iridium(III) homo- and
heterogeneous catalysed hydrogen borrowing C-N bond formation.
Green Chem. 2017, 19, 3142−3151.
(15) (a) Vuong, K. Q.; Timerbulatova, M. G.; Peterson, M. B.;
Bhadbhade, M.; Messerle, B. A. Cationic Rh and Ir complexes
containing bidentate imidazolylidene-1,2,3-triazole donor ligands:
synthesis and preliminary catalytic studies. Dalton Trans. 2013, 42,
14298−14308. (b) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Click
Chemistry: Diverse Chemical Function from a Few Good Reactions.
Angew. Chem., Int. Ed. 2001, 40, 2004−2021.
(16) (a) Busetto, L.; Cassani, M. C.; Femoni, C.; Mancinelli, M.;
Mazzanti, A.; Mazzoni, R.; Solinas, G. N-Heterocyclic Carbene-Amide
Rhodium(I) Complexes: Structures, Dynamics, and Catalysis. Organo-
metallics 2011, 30, 5258−5272. (b) Rivera, G.; Elizalde, O.; Roa, G.;
̀
Montiel, I.; Bernes, S. Fluorinated N-heterocyclic carbenes rhodium
(I) complexes and their activity in hydrosilylation of propargylic
alcohols. J. Organomet. Chem. 2012, 699, 82−86.
(17) Weaver, J.; Senaweera, S. C−F activation and functionalization
of perfluoro- and polyfluoroarenes. Tetrahedron 2014, 70, 7413−7428.
(18) (a) Akizawa, T.; Kurita, N.; Mizobuchi, M.; Fukagawa, M.;
Onishi, Y.; Yamaguchi, T.; Ellis, A. R.; Fukuma, S.; Alan Brookhart, M.;
Hasegawa, T.; Kurokawa, K.; Fukuhara, S. PTH-dependence of the
effectiveness of cinacalcet in hemodialysis patients with secondary
hyperparathyroidism. Sci. Rep. 2016, 6, 19612. (b) Daubresse, M.;
Alexander, G. C. The uphill battle facing antiobesity drugs. Int. J. Obes.
2015, 39, 377−378.
(19) Tregubov, A. A.; Vuong, K. Q.; Luais, E.; Gooding, J. J.;
Messerle, B. A. Rh(I) Complexes Bearing N,N and N,P Ligands
Anchored on Glassy Carbon Electrodes: Toward Recyclable Hydro-
amination Catalysts. J. Am. Chem. Soc. 2013, 135, 16429−16437.
(20) Wang, D.; Guo, X.-Q.; Wang, C.-X.; Wang, Y.-N.; Zhong, R.;
Zhu, X.-H.; Cai, L.-H.; Gao, Z.-W.; Hou, X.-F. An Efficient and
Recyclable Catalyst for N-Alkylation of Amines and β-Alkylation of
Secondary Alcohols with Primary Alcohols: SBA-15 Supported N-
Heterocyclic Carbene Iridium Complex. Adv. Synth. Catal. 2013, 355,
1117−1125.
(21) Dang, T. T.; Shan, S. P.; Ramalingam, B.; Seayad, A. M. An
efficient heterogenized palladium catalyst for N-alkylation of amines
and α-alkylation of ketones using alcohols. RSC Adv. 2015, 5, 42399−
42406.
F
DOI: 10.1021/acs.inorgchem.7b02586
Inorg. Chem. XXXX, XXX, XXX−XXX