Synthesis, characterization and catalytic activity of novel ruthenium complexes bearing NNN click based ligands

Article abstract of DOI:10.1039/c9dt01822k

Novel air stable ruthenium(ii) complexes bearing tridentate ligands bis((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)amine (L1), 1-(1-benzyl-1H-1,2,3-triazol-4-yl)-N-(pyridin-2-ylmethyl)methanamine (L2) or 2-(4-phenyl-1H-1,2,3-triazol-1-yl)-N-(pyridin-2-ylmethyl)ethan-1-amine (L3) were synthesised. The nitrogen based ligands were easily prepared by virtue of click chemistry using cheap and commercially available reagents. The ruthenium complexes were obtained by heating the Ru(PPh₃)₃Cl₂ precursor and the tridentate NNN ligand in toluene under reflux for 2 hours, achieving yields of 82-87%. These complexes were fully characterized by means of NMR, FT-IR and high resolution ESI spectroscopy. The crystal structure of one of the complexes was determined. These complexes showed excellent activity and selectivity in the hydrogenation of ketones and aldehydes. DFT calculations show that complex 3 may react through an outer-sphere catalytic cycle rather than via an inner-sphere mechanism.

Full text of DOI:10.1039/c9dt01822k

View Article Online
View Journal
Dalton
Transactions
An international journal of inorganic chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: R. Sole, M.
Bortoluzzi, A. Spannenberg, S. Tin, V. Beghetto and J. G. de Vries, Dalton Trans., 2019, DOI:
10.1039/C9DT01822K.
Volume 46
Number 10
14 March 2017
Pages 3073-3412
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Dalton
Transactions
An international journal of inorganic chemistry
rsc.li/dalton
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 0306-0012
COMMUNICATION
Douglas W. Stephen et al.
N-Heterocyclic carbene stabilized parent sulfenyl, selenenyl,
and tellurenyl cations (XH+, X = S, Se, Te)
rsc.li/dalton

Please do not adjust margins
Page 1 of 9
Dalton Transactions
View Article Online
DOI: 10.1039/C9DT01822K
ARTICLE
Synthesis, characterization and catalytic activity of novel
ruthenium complexes bearing NNN click based ligands
Received 00th January 20xx,
Accepted 00th January 20xx
Roberto Sole,a,b Marco Bortoluzzi,a Anke Spannenberg,b Sergey Tin,b Valentina Beghetto*a and
Johannes G. de Vries*b
DOI: 10.1039/x0xx00000x
Novel air stable ruthenium(II) complexes bearing tridentate ligands bis((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)amine (L1),
1-(1-benzyl-1H-1,2,3-triazol-4-yl)-N-(pyridin-2-ylmethyl)methanamine (L2) or 2-(4-phenyl-1H-1,2,3-triazol-1-yl)-N-(pyridin-
2-ylmethyl)ethan-1-amine (L3) were synthetised. The nitrogen based ligands were easily prepared by virtue of click
chemistry using cheap and commerciallly available reagents. The ruthenium complexes were obtained by heating the
Ru(PPh3)3Cl2 precursor and the tridentate NNN ligand in toluene under reflux for 2 hours, achieving yields of 82-87%. These
complexes were fully characterized by means of NMR, FT-IR and high resolution ESI spectroscopy. The crystal structure of
one of the complexes was determined. These complexes showed excellent activity and selectivity in the hydrogenation of
ketones and aldehydes. DFT calculations show that complex 3 may react through an outer-sphere catalytic cycle rather
than via an inner-sphere mechanism.
catalysis, in which the variation of substituents on ligands can
drastically affect the activity and the selectivity of the
complexes, triazole based ligands can be attractive candidates
Introduction
In 2001 K. B. Sharpless and co-workers coined the term Click
Chemistry,1 describing a novel concept of organic synthesis
based on the use of a few simple high-yielding reactions.2
Inspired by this vision, many researchers started to develop
new organic approaches which elegantly circumnavigate the
drawbacks of older organic procedures based on the use of
harsh reaction conditions, toxic reagents, long purification
processes and expensive waste treatments. The prime
example of click chemistry, the copper catalysed alkyne-azide
cycloaddition (CuAAC), has turned over the last decade into a
routine organic process for the synthesis of 1,4-disubstituted
1,2,3-triazoles.3 Due to their facile accessibility, click-based
triazole compounds have been extensively investigated for a
wide range of applications.4 In particular, the presence of an
N-donor atom in the five-membered ring structure has
recently led to an increasing number of publications aiming to
study the coordination chemistry of novel transition metal
complexes bearing triazole ligands.5 As a matter of fact,
several triazole based complexes act as effective
chemotherapeutics against various cancer cell lines6 or as
antimicrobials.7 They also show interesting electrochemical
and photophysical properties.8 In the field of homogeneous
as a new class of easily tunable, cheap and accessible ligands.
Late transition metal complexes bearing 1,4-disubtituted 1,2,3-
triazoles are active catalysts for the Suzuki-Miyaura cross
coupling,9 Heck olefin arylation10 and transfer hydrogenation
reactions.11 Notably, Leitner and co-workers recently reported
the transfer hydrogenation of ketones using a non-noble Mn(I)
aminotriazole bidentate complex.12 On the other hand, to the
best of our knowledge, the ruthenium catalysed
hydrogenation of carbonyl compounds under molecular
hydrogen pressure, bearing triazole based ligands was
reported in only one paper.13 The catalyst was not selective
towards C=O bond reduction in the presence of an alkene
group, hence the fully saturated compound was obtained.
The ruthenium-catalysed hydrogenation of C=O functional
groups usually requires electron-donating phosphorous ligands
which help to stabilise the metal centre.14 Extremely good
results have been obtained with a number of catalysts which
use the combination of diamine ligands and cheap and readily
accessible phosphorus ligands for the reduction of carbonyl
compounds.15 However, the use of more complex phosphine
ligands can lead to higher catalyst costs. The pioneering work
of Gusev and co-workers16 has demonstrated that several
phosphorus-free tridentate ligands can stabilise noble or non-
noble transition metal complexes for the reduction of a
number of different functional groups although even these
catalysts still require the stabilisation of an additional
phosphine or CO ligand.17 We believe that click based
a. DIpartimento di Scienze Molecolari e Nanosistemi,Università Ca´Foscari Venezia,
Via Torino 155, 30170, Venezia Mestre, Italy. Email: beghetto@unive.it
b. Leibniz Institut für Katalyse e.V. an der Universität Rostock, Albert-Einstein-Straße
29a, 18055, Rostock, Germany. Email: johannes.devries@catalysis.de
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
tridentate triazole ligands can represent
a sustainable
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 2 of 9
ARTICLE
Journal Name
alternative for the ruthenium-catalysed hydrogenation of
carbonyl compounds. Inspired by these considerations, we
herein report the synthesis of three novel ruthenium(II)
complexes Ru(NNN)(PPh3)Cl2 which are highly active in the
catalytic hydrogenation of ketones and aldehydes.
corresponding NNN ligand and Ru(PPh3)3Cl2 as tVhieew pArrtieclceuOrnslioner
(Scheme 3). After heating the solutions uDnOdIe: r10r.e10fl3u9x/Cin9DtTo0l1u8e2n2eK
for 2h followed by cooling them to room temperature, the
complexes precipitate as orange (1), yellow (2) or red (3)
solids. Washing these precipitates with diethyl ether afforded
the desired products in high purities. Analytical and
spectroscopic data (HRMS, IR, 1H, 31P NMR) support the
structures. The complexes were stored under aerobic
conditions. The spectroscopic data acquired after several
weeks confirmed that no significant changes had occurred,
leading to the conclusion that they are fairly stable under air.
Layering diethyl ether over a concentrated solution of 3 in
DCM afforded red crystals suitable for X-ray diffraction
analysis. The solid-state structure of 3 revealed that it is the
trans-(mer-NNNL2) dichloride complex (Figure 1).
Results and discussion
Synthesis and characterization
Ligands L1-L3 were prepared as shown in Scheme 1. Literature
procedures were used to prepare L118 and L2.19 L3, was
synthesized starting by reaction of 2-azidoethylamine and
phenylacetylene via CuAAC to yield 4-phenyl-1H-1,2,3-triazol-
1-amine. The condensation with 2-pyridinecarboxyaldehyde
and the subsequent reduction with NaBH4 led to the formation
of L3 in high yield.
H
R
i)
´
N
N
Bn
R
Bn
N
N3
N
N
N
N
L1 (yield = 95%)
i)
ii)
H
NH2
N
Bn
N
N
N
N
N
N
N
Ph
L2 (yield =66%)
3
N
O
iii, iv)
Fig. 1 Molecular structure of 3 with displacement ellipsoids drawn at the 50%
probability level. Hydrogen atoms except the N-bound are omitted for clarity.
´
R =
R =
N
H
N
H
N
N
N
H
N
NH2
Catalytic hydrogenation
N
N
Ph
With the complexes in hands, their catalytic activity towards
the hydrogenation of ketones and aldehydes was evaluated,
taking acetophenone as the model substrate. Hydrogenation
reactions were initially performed by using 1 mmol of the
substrate and 2 mL of the selected solvent, in the presence of
0.25 mol% of the metal complex and 2.5 mol% of KOtBu as
base, which is required to activate the pre-catalyst. Metal-
ligand-cooperation (MLC) is known to promote the formation
of the active dihydride species in Noyori-type pincer
complexes bearing NH moieties.20 Complexes 2 and 3, bearing
pyridine functionalities, can also be activated by the
aromatisation/dearomatisation process of the pyridine ring,
promoted by deprotonation of the benzylic protons.21
Hydrogenations were initially run for 18 hours, at 80°C and 40
bar of hydrogen pressure resulting in good activities by all
three catalysts, although 1 could not achieve full conversion
(Table 1, entry 1). Encouraged by these results, we reduced
the reaction time to 1 hour, maintaining the same loadings
both for the catalysts and the base (Table 1, entries 2-3) and
still achieving quantitative conversions of the substrate to the
corresponding alcohol. With the same reaction conditions,
different solvents were screened for the most active catalysts
2 and 3 (Table 1, entries 4-7). Toluene appeared to be the best
solvent. Looking for the activity limits of the catalysts, both
catalyst and base loading were decreased to 0.05 mol% and
1.25 mol% respectively and the hydrogen pressure was
L3 (yield = 85%)
Scheme 1 Synthesis of triazole based ligands L1-L3 i) MeOH, H2O, CuSO4·5H2O (5
mol%), sodium ascorbate (10 mol%), r.t., 18 h ii) MeOH, H2O, CuSO4·5H2O (5
mol%) r.t., 18 h iii) DCM, Na2SO4, r.t. 18 h iv) MeOH, NaBH4, 0°C-r.t., 18 h
H
L1
N
N
Bn
Bn
N
Cl
N
N
N
Ru
N
Cl
PPh3
1 (yield = 82%)
H
1 equiv.
L1 - L3
N
L2
Bn
N
[RuCl2(PPh3)3]
Cl
N
N
Ru
Toluene,
N
Cl
PPh3
reflux, 2 h
2 (yield = 85%)
H
N
Cl
N
N
Ru
L3
N
Cl
PPh3
3 (yield = 87%)
N
Ph
Scheme 2 Synthesis of [RuCl2(NNN)(PPh3)] complexes 1-3.
The preparation of the corresponding ruthenium complexes
was accomplished in a straightforward manner by reacting the
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 9
Dalton Transactions
Please do not adjust margins
Journal Name
ARTICLE
cyclohexene-1-carboxaldehyde (Entry 9). ItViewisArticlwe Oonrlitnhe
DOI: 10.1039/C9DT01822K
mentioning that high activity paired to excellent selectivity
reduced to 10 bar (Table 1, entries 8-9). Under these
conditions the ketone was fully converted to the alcohol.
towards α,β-unsaturated alcohols attained by complex 3 are
not achieved by most other ruthenium complexes used for the
reduction of ketones and aldehydes. Aromatic substrates with
electron-withdrawing groups were also fully hydrogenated to
the benzylic alcohols (entries 4 and 12) under the reaction
conditions, while the presence of an electron-donating moiety
seemed to slow down the reduction of the ketone (entry 5)
and even more of the aldehyde (entry 13). Biomass-derived
furfural (entry 10) was selectively hydrogenated to furfuryl
alcohol. 2,5-Bis(hydroxymethyl)furan,23, 24 an interesting bio-
based building block for polyesters (entry 11) was obtained in
only 52% isolated yield.
Table
1 Optimisation of the reaction conditions for the catalytic hydrogenation
O
OH
cat.1-3, KOtBu (2.5 mol%)
solvent, 40 bar H2, 80 °C
reactions
Entrya
Cat.
Solvent
Cat.
Time (h)
Yield (%)b
loading
(mol%)
1
2
3
4
5
1
2
3
2
2
3
3
2
3
2
3
3
3
/
Toluene
Toluene
Toluene
THF
i-PrOH
THF
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.05
0.05
0.05
0.05
0.05
0.05
/
18
1
1
1
1
1
1
1
1
1
1
1
1
1
95
> 99
> 99
84
53
89
Table 2 Hydrogenation of aldehydes and ketones with catalyst 3
cat. 3 (0.05 mol%)
6
OH
O
KOtBu (1.25 mol%)
7
i-PrOH
54
R
R´
8c
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
> 99
> 99
97
98
42
R
R´
10 bar H2 , 80 °C
Toluene
9c
R = Alkyl, Aryl
R´ = CH3,
10d
11d
12e
13f
14d
H
Entry a
1
Substrate
Product
Yield %b
0
0
O
OH
99
99
a Reaction conditions: acetophenone (1 mmol), solvent (2 mL), 40 bar of H2, 80 °C,
cat.1-3 (0.25 mol%), KOtBu (2.5 mol %), when catalyst loading was decreased to
0.05 mol%, KOtBu was also decreased to 1.25 mol%. b GC yields using dodecane as
internal standard. c H2 = 10 bar. d Temp. = 60 °C. e Temp. = 40 °C. f no base
O
O
OH
OH
2
At the same hydrogen pressure, almost full conversions were
reached even at 60 °C (Table 1, entries 10-11). The activity has
drastically decreased at 40 °C and 10 bar of hydrogen (Table 1,
entry 12). Finally, to confirm the crucial role of the base in the
activation of the complexes, a base-free reaction was run but no
conversion at all was observed (Table 1, entry 13). After
optimisation of the reaction conditions, catalyst 3 emerged as the
complex with slightly better performances. Similarly, Singh et al.
observed that N2 coordinating triazoles were more efficient
than ligands coordinating via their N3 site in the ruthenium
catalysed transfer hydrogenation of ketones.11d
The scope of catalyst 3 was evaluated and thus a range of
ketones and aldehydes was hydrogenated to the
corresponding alcohols (Table 2). The aliphatic ketone
cyclohexanone (entry 2) was efficiently hydrogenated and the
product alcohol isolated with 99% yield. The selective
hydrogenation of the carbonyl groups in α,β-unsaturated
aldehydes and ketones remains a daunting task.22 Notably,
α,β-unsaturated 2-cyclohexen-1-one (entry 3) and 1-
cyclohexene-1-carboxaldehyde (entry 8) were selectively
hydrogenated to the allylic alcohols in excellent yield, leaving
the C=C double bond untouched. Selective C=O bond
reduction was also achieved in the hydrogenation of 3-
3
4
99
98
OH
O
Cl
Cl
O
OH
OH
5
89
MeO
MeO
O
6
7
Traces
99
O
OH
H
O
OH
H
8
9
95
92
O
OH
H
O
OH
O
O
10
97
H
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 4 of 9
ARTICLE
Journal Name
HO
O
HO
OH
View Article Online
O
O
11c
12
52
97
DOI: 10.1039/C9DT01822K
H
H
N
H
H
N
KOtBu
H2
N
Cl
N
N
H
N
H
N
N
N
N
N
N
Ru
P
N
Ru
O
OH
OH
OH
Ru
KCl,
tBuOH
Ph
KCl,
tBuOH
Cl
N
Ph3
Cl
N
Cl
Ph
Ph
Ph3
Ph3
P
A
P
B
H
Cl
Cl
R1
R2
C
O
H
N
O
H
H
H
H
N
H
N
N
H
O
N
O
Ru
N
O
O
H
R2
R1
I
Ru
P
H
R2
PPh3
13
47
R2
N
N
N
R1
R2
R1
C
Ph
Ph3
N
MeO
MeO
R1
II'
II
I'
Ph
Bin
I
Bout
I
O
H
N
H
N
H
H
N
N
H
14
Traces
H
N
N
Outer-Sphere
N
N
Inner-Sphere
Ru
N
N
Ru
Ru
N
H
O
R2
N
PPh3
Ph
C
Ph3
P
B
Ph
N
N
N
Ph3
P
H
R1
BinII
BoutII
III'
Ph
Substrate (2 mmol), toluene (2 mL), cat. 3 (0.05 mol%), KOtBu (1.25 mol%), 80
°C, 10 bar of H2. b Isolated yields. c In THF (2 mL)
a
H
N
H
H
IV
IV'
III
H2
N
H2
H
H
N
Ru
N
N
N
Ru
OH
R2
N
N
PPh3
N
O
R2
R1
C
H
N
Ph
Ph3
P
H
H2
R1
Ph
BinIII
BoutIII
Some brown material, presumably humins, also formed in this
reaction. The formation of humins has often been observed in
reactions of 5-HMF.24 Moreover, due to the low solubility of 5-
HMF in toluene, the reaction was run in THF, which was
expected to decrease the catalyst activity based on the results
in Table 1. Finally, α,β-unsaturated cinnamaldehyde (entry 14)
and benzalacetone (entry 6) could not be converted to the
corresponding alcohols under these conditions. The reasons
for this are currently under investigation.
Scheme 3 Inner-sphere and Outer-sphere proposed mechanisms.
dihydride complexes.27
Preliminary DFT calculations carried out using the EDF2
functional allowed to ascertain the most stable isomer of
[RuH2(PPh3)L]. The isomers were chosen in order to place the
N-H and one M-H bond on the same side, as required in outer-
sphere hydrogenation. Five starting geometries were
considered, two of them with the N-donor moieties of L
mutually in the mer position (is1 and is2) and the other three
where the tridentate ligand occupies a face of the octahedron
(is3, is4 and is5). As observable in Figure 2, the fac isomers are
in general more stable than the mer ones, despite the fact that
the ligand occupies three coordination sites in the mer position
in the dichloro precursor. Among the fac isomers, is4 and is5
are the most stable, suggesting that triphenylphosphine
prefers to be in a trans position to the NH moiety or the
pyridine heterocycle rather than to the triazole ring, perhaps
because this last donor group is less electron rich, as
highlighted by population analyses. The interaction of the
dihydride with acetophenone was studied starting from the
most stable isomer, is4. Calculations were carried out at C-
PCM/B97X/def2-SVP level, considering toluene as continuous
Mechanistic studies
Catalytic homogenous hydrogenation of polar bonds such as
ketones and aldehydes are known to proceeds either via an
inner-sphere or an outer-sphere mechanism (Scheme
3).14,20a,21,22 The inner-sphere mechanism involves the
coordination of the substrate to a free site of the metal centre
made vacant by displacement of a ligand (BinI). Insertion of the
C=O bond into the metal hydride leads to the ruthenium
alkoxide complex (II) which forms the hydrogen complex (III)
from which the alcohol is released to reform the dihydride B.
On the other hand, Noyori and co-workers proposed a
different mechanism for the Ru-diphosphine-diamine type
catalysts. Several mechanistic studies confirmed that the NH
group in the ligands are directly involved in the catalytic cycle.
Coordination of the substrate in step I’ leads to the formation
of complex BoutI. Concerted migration of hydride and proton to
the substrate releases the product (II’) forming the
coordinative unsaturated amido complex BoutII. Coordination
of dihydrogen (III’) and successive heterosplitting regenerate
dihydride B. In both cases, activation of the dichloro-complex
by KOtBu under hydrogen atmosphere is expected to afford
medium. The ground-state stationary point is4acetophenone
,
out
depicted in Figure 3, shows very weak interactions between
the complex and the substrate. In particular, the NH---O
distance is 2.199 Å. The coordination of acetophenone to the
metal centre was therefore considered by assuming the
displacement of the longest Ru-N bond, that with pyridine. In
the stationary point thus obtained, indicated as is4acetophenone
,
in
the computed Ru---O distance is quite long, 2.274 Å,
suggesting weak coordination of acetophenone to the
complex. Moreover, is4acetophenone is less stable than
in
the corresponding dihydride
B
as active catalyst.26
is4acetophenone by about 6.3 kcal mol-1 (Gibbs free energy),
out
Experimental evidence (Table 1, entry 13) confirms that
catalyst 3 is not active in the absence of the base. It has been
demonstrated that these types of complexes may form
monohydride A which still requires base to be active thus
meaning these intermediates are just precursors for the
making an inner-sphere hydrogenation mechanism less likely.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 9
Dalton Transactions
Please do not adjust margins
Journal Name
ARTICLE
obtained from a solvent purification system (tolueneV,ieCwHA2rCtilc2l,e OEtn2liOne,
DOI: 10.1039/C9DT01822K
THF). GC analyses were carried out on an Agilent 7890B GC system
with a HP-5 normal-phase silica column, using He as a carrier gas
and dodecane as standard. NMR spectra were acquired on a Bruker
1
AV400, Bruker AV300 or Bruker Fourier300 NMR spectrometer. H
and 13C-NMR spectra were referenced w.r.t. the residual solvent
signal. All chemical shifts are in ppm, coupling constants in Hz. HR-
MS measurements were recorded on an Agilent 6210 time-of-flight
LC/MS (ESI) or Thermo Electron MAT 95-XP (EI, 70 eV). Peaks as
listed correspond to the highest abundant peak and are of the
expected isotope pattern. X-ray diffraction data were collected on a
Bruker Kappa APEX II Duo diffractometer. The structure was solved
by direct methods28 and refined by full-matrix least-squares
procedures on F2.29 XP (Bruker AXS) was used for graphical
representations. CCDC 1912232 contains the supplementary
crystallographic data for this paper. These data are provided free of
charge by The Cambridge Crystallographic Data Centre. The
computational geometry optimisations of the complexes were
carried out without symmetry constrains, using the hybrid-GGA
EDF2 functional30 in combination with the 6-31G(d,p) basis set and
the ECP-based LANL2DZ basis set for ruthenium.31 Further geometry
optimisations were performed using the range-separated hybrid
functional B97X 32 and the def2 split-valence polarized basis set of
Ahlrichs and Weigend, with 28 core electrons of ruthenium
enclosed in pseudopotential.33 The C-PCM implicit solvation model
was added to B97X calculations, considering toluene as
continuous medium.34 The ‘‘restricted” formalism was always
applied. The achievement of stationary points was confirmed by IR
simulations (harmonic approximation).35 Calculations were
performed with Spartan ’16 (Wavefunction Inc.), build 2.0.3.36
Gaussian '0937 was used for the C-PCM/B97X calculations.
Cartesian coordinates of the DFT-optimised structures can be found
Fig. 2. DFT EDF2-optimised geometries of the isomers of [RuH2(PPh3)L] and relative
energies (electronic energy plus nuclear repulsion) in kcal mol-1. Hydrogen atoms were
omitted for clarity, with the exceptions of N-H and M-H. Colour map: hydrogen, white;
carbon, grey; nitrogen, blue; phosphorus, orange; ruthenium, green. Cartesian
coordinates of the DFT-optimised structures can be found in the Electronic
Supplementary Information.
Fig. 3. DFT C-PCM/B97X-optimised geometries of ground-state adducts between
[RuH2(PPh3)L] (is4) and acetophenone and relative Gibbs free energies in kcal mol-1.
Hydrogen atoms were omitted for clarity, with the exceptions of N-H and M-H. Colour
map: hydrogen, white; carbon, grey; nitrogen, blue; oxygen, red; phosphorus, orange;
ruthenium, green. Cartesian coordinates of the DFT-optimised structures can be found
in the Electronic Supplementary Information.
in the Electronic Supplementary Information.
Conclusions
Synthesis of bis((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)amine
(L1): The ligand was prepared according to a literature
report:18 Dipropargylamine (0.306 g, 3.28 mmol) and benzyl
azide (0.875 g, 6.57 mmol) were dissolved in MeOH (25 mL)
and H2O (4 mL) was added. A solution of CuSO4·5H2O (0.04 g,
0.16 mmol) and sodium ascorbate (0.06 g, 0.32 mmol) in H2O
(1 mL), was added dropwise to the stirred reagent mixture
inducing a colour change to yellow-green. The reaction was
then stirred for 18 h at room temperature. After this time,
MeOH was removed under reduced pressure giving an orange
oil that was diluted with CH2Cl2 (20 mL) and extracted with a
saturated EDTA solution to remove copper salts traces. The
organic layer was dried over anhydrous MgSO4, filtered and
concentrated under vacuum to afford an orange solid (1.123 g,
95%). HRMS (ESI) calcd for C20H22N7 [M+H]+:360.1936; found:
360.1942. 1H NMR (400 MHz, DMSO-d6) δ (ppm) = 8.01 (s, 2H),
7.40- 7.28 (m, 10H), 5.57 (s, 4H), 3.87 (bs, 4H). 13C NMR (400
MHz, DMSO-d6) δ (ppm) = 136.2, 132.0, 128.7.1, 127.9, 122.9,
52.8.
In conclusion, we have developed new air-stable ruthenium
complexes bearing phosphine free, click based NNN-ligands,
synthetized from cheap and commercially available reagents,
in addition to cheap triphenylphosphine. The complexes have
been fully characterized and successfully applied in the
catalytic homogenous hydrogenation of ketones and
aldehydes. Most of the substrates were reduced to the
corresponding alcohols with high yields using 0.05 mol% of
catalyst. In the case of α,β-unsaturated 2-cyclohexenone and
cyclohex-1-ene-1-carbaldehyde a high selectivity towards the
unsaturated alcohol was observed. Based on DFT calculations,
an outer-sphere mechanism seems more favourable than an
inner-sphere mechanism.
Experimental section
General
Reagents and solvents were purchased from commercial sources
and used as received unless noted otherwise. Dry solvents were
Synthesis of 1-(1-benzyl-1H-1,2,3-triazol-4-yl)-N-(pyridin-2-
ylmethyl)methanamine (L2): Ligand L2 was prepared as
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 6 of 9
ARTICLE
Journal Name
View ArticfleoOunnlidne:
reported in the literature:18-19 Propargylamine (0.55 g, 10 HRMS (ESI) calcd for C16H18N5 [M+H]+:280.1562;
1
DOI: 10.1039/C9DT01822K
mmol) and 2-pyridinecarboxyaldehyde (1.07 g, 10 mmol) were 280.1569. H NMR (400 MHz, CDCl3) δ (ppm) = 8.52 (ddd, J=4.9
dissolved in 20 mL of DCM in the presence of 2 equivalents of Hz, 1,8 Hz, 0.9 Hz, 1H), 7.36-7.30 (m, 6H), 7.90 (s, 1H), 7.85-
Na2SO4 (3 g, 20 mmol). The reaction mixture was stirred at 7.77 (m, 2H), 7.62 (td, J=7.7, 1.8 Hz 1H), 7.44-7.38 (m, 2H),
room temperature overnight. After 18 hours, the reaction was 7.37-7.30 (m, 1H), 7.24 (ddt, J=7.3,1.4,0.8 Hz, 1H), 7.16 (m,
stopped, the solution was filtered and concentrated under 1H), 4.52 (t, J=6 Hz, 2H), 3.92 (s, 2H), 3.18 (t, J=6 Hz, 2H) 13C
reduced pressure. The resulting red oil was then dissolved in NMR (400 MHz, CDCl3) δ (ppm) = 159.1, 149.4, 147.8, 136.8,
MeOH (15 mL), the solution was cooled to 0°C and 2 130.7, 129.1, 128.9, 128.2, 125.8, 122.4, 122.3, 120.5, 54.7,
equivalents of NaBH4 were added in portions. The solution was 50.8, 50.7, 48.8.
then allowed to stir overnight (18 hours) at room temperature.
Afterwards, the reaction was quenched with a saturated
solution of NaHCO3 (15mL) and the product extracted with
DCM. The combined layers were dried over MgSO4, volatiles
were evaporated and the mixture was purified by flash column
chromatography using a mixture of DCM (95%) and MeOH
(5%) as an eluent (0.986 g, 6.8 mmol, 68% yield). The dark
orange oil obtained was treated with benzylazide (0.758 g, 5.7
mmol), CuSO4·5H2O (0.07 g, 0.28 mmol) and sodium ascorbate
(0.13 g, 0.57 mmol) in MeOH (25 mL) and H2O (5 mL). The
reaction was then stirred for 18 hours at room temperature.
Afterwards, the MeOH was removed under reduced pressure
giving an orange oil that was diluted with CH2Cl2 (20 mL) and
extracted with a saturated EDTA solution to remove copper
salts traces. The organic layer was dried over anhydrous
MgSO4, filtered and concentrated under vacuum to afford a
brown oil (66% yield). HRMS (ESI) calcd for C16H18N5
General
Ru(NNN)(PPh3)Cl2 complexes
procedure
for
the
synthesis
of
Under inert conditions Ru(PPh3)3Cl2 (0.48 g, 0.5 mmol) was
suspended in dry toluene (10 mL). After 30 min, the desired
ligand (0.5 mmol) was added and the solution was heated
under reflux for 2h. During the reaction the colour of the
solution turns from black to orange (1), yellow (2) or red (3).
After cooling down the solution to room temperature the
complex precipitated. The solid was collected by filtration,
washed with Et2O (2 x 15 mL) and dried under reduced
pressure.
Ru(NNNL1)(PPh3)Cl2 (1). The orange solid was obtained in 82%
yield (325 mg). El. Anal. Calcd for C38H36Cl2N7PRu: C, 57.48; H,
4.57; N, 12.36 P, 3.90; Cl, 8.94. Found: C, 57.51; H, 4.55; N,
12.34; P, 3.92; Cl, 8.96. 1H-NMR (400 MHz, DMSO-d6, 293 K): δ
(ppm) = 8.08 (s, 2H), 7.79-7.63 (m, 6H), 7.40-7.33 (m, 6H),
7.28-7.21 (m, 4H), 7.15 (ddd, J=7.3 Hz, 5.9 Hz, 1.9 Hz, 9H),
5.42-5.21 (q, J=15 Hz, 4H), 4.70-4.59 (m, 2H), 4.56-4.45 (m.
2H). 31P{1H}-NMR (400 MHz, DMSO-d6, 293 K), δ (ppm) = 58.5.
HRMS (ESI) calcd for C38H36N7PCl2Ru [M]+: 793.1190 found:
793.1189; C38H36N7PCl2RuNa [M+Na]+: 816.1088 found:
816.1054.
1
[M+H]+:280.1562; found: 280.1564. H NMR (300 MHz, CDCl3)
δ (ppm) = 8.54 (ddd, J=4.9 Hz, 1,7 Hz, 0.9 Hz, 1H), 7.62 (td,
J=7.7, 1.8 Hz 1H), 7.42 (s, 1H), 7.38-7.31 (m, 3H), 7.28 (dm,
J=7.8 Hz, 1H), 7.27-7.24 (m, 2H), 7.15 (ddd, J=7.6, 4.9, 1.2 Hz,
1H), 5.49 (s, 2H), 3.94 (s, 4H), 2.51 (bs, 1H). 13C NMR (300
MHz, CDCl3) δ (ppm) = 159.3, 149.4, 147.2, 136.5, 134.7, 129.2,
128.8, 128.2, 122.5, 122.1, 121.8, 54.6, 54.2, 44.5.
Synthesis of 2-(4-phenyl-1H-1,2,3-triazol-1-yl)-N-(pyridin-2-
ylmethyl)ethan-1-amine (L3): 2-azidoethylamine (0.50 g, 5.80
mmol) and phenylacetylene (0.59 g, 5.80 mmol) were
dissolved in MeOH (9 mL) and H2O (1 mL). CuSO4·5H2O (0.06 g,
0.25 mmol) was added in portions and the solution was
allowed to stir for 1 hour. Afterwards, the reaction mixture
was diluted with water (10 mL) and NH4OH (1 mL) and the
product was extracted with CH2Cl2 (3 x 10 mL). The combined
organic layers were dried over MgSO4, filtered and
concentrated in vacuo to give 4-phenyl-1H-1,2,3-triazol-1-
amine as a white powder (0.907 mg, 5.21 mmol, 90%). The
Ru(NNNL2)(PPh3)Cl2 (2). The yellow solid was obtained in 85%
yield (305 mg). El. Anal. Calcd for C34H32Cl2N5PRu: C, 57.23; H,
4.52; N, 9.81 P, 4.34; Cl, 9.94. Found: C, 57.18; H, 4.56; N, 9.88;
1
P, 4.36; Cl, 9.96. H-NMR (400 MHz, CD2Cl2, 293 K): δ (ppm) =
8.18-8.08 (m, 1H), 7.88-7.69 (m, 6H), 7.52-7.19 (m, 16H), 7.19-
7.05 (m, 2H), 6.78-6.61 (m, 2H), 6.30 (m, 1H), 5.74-5.59 (m,
1H), 4.97 (ddd, J=13.7, 10.9, 1.2 Hz, 1H), 4.62 (dt, J=14.1, 4.6
Hz, 1H), 4.47 (dt, J=13.7, 4.8 Hz, 1H). 31P{1H}-NMR (400 MHz,
CD2Cl2, 293 K), δ (ppm) = 56.5. HRMS (ESI) calcd for
C34H31Cl2N5PRu
C34H31Cl2N5PRuNa [M+Na]+: 736.0713 found: 736.0688.
[M]+:
713.0815
found:
713.0807;
aminotriazole
was
then
reacted
with
2-
pyridinecarboxyaldehyde (0.55 g, 5.21 mmol) in the presence
of 2 equivalents of Na2SO4 (1.42 g, 10 mmol) in DCM (10 mL).
After 18 hours, Na2SO4 was filtered off and the solution was
concentrated under reduced pressure. The resulting oil was
dissolved in MeOH (15 mL), the solution was cooled to 0 °C
and NaBH4 (0.3 g, 10 mmol) was added in portions. The
solution was allowed to stir overnight (18 hours) at room
temperature. Afterwards, the reaction was quenched with a
saturated solution of NaHCO3 (15 mL) and the product was
extracted with DCM. The combined layers were dried over
MgSO4, volatiles were evaporated under reduced pressure
yielding L3 as a fine white powder (1.39 g, 4.98 mmol, 85%).
Ru(NNNL3)(PPh3)Cl2 (3). The red solid was obtained in 87% yield
(314 mg). El. Anal. Calcd for C34H32Cl2N5PRu: C, 57.23; H, 4.52;
N, 9.81 P, 4.34; Cl, 9.94. Found: C, 57.21; H, 4.55; N, 9.83; P,
1
4.36; Cl, 9.98. H-NMR (400 MHz, DMSO-d6, 293 K): δ (ppm)
8.67 (s, 1H), 8.20 (d, J=5.7 Hz, 1H), 7.78 (ddt, J=8.0, 6.6, 1.8 Hz,
6H), 7.65-7.47 (m, 3H), 7.32-7.11 (m, 16H), 6.85-6.73 (m, 1H),
6.14 (d, J=11.8 Hz, 1H), 5.57 (dd, J=14.2, 8.0 Hz, 1H), 5.34 (t,
J=12.9 Hz, 1H), 4.63 (dd, J=14.1, 6.8 Hz, 1H), 4.47 (d, J=13.9 Hz,
1H), 3.75 (s, 1H). 31P{1H}-NMR (400 MHz, DMSO-d6, 293 K), δ
(ppm) = 53.6. HRMS (ESI) calcd for C34H31Cl2N5PRu [M]+:
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 9
Dalton Transactions
Please do not adjust margins
Journal Name
ARTICLE
713.0815 found: 713.0815; C34H31Cl2N5PRuNa [M+Na]+:
736.0713 found: 736.0649.
13C-NMR (300 MHz, CDCl3) δ(ppm) = 137.2, 122.5, 67.3, 30.4,
27.5, 26.1, 20.7.
View Article Online
DOI: 10.1039/C9DT01822K
3-cyclohexene-1-methanol (Table 2, Entry 9). Colourless
liquid. 1H-NMR (400 MHz, CDCl3) δ (ppm) = 5.67(s, 2H), 3.51(d,
J=5.9 Hz, 2H), 2.07 (m, 4H), 1.77 (m, 3H), 1.25 (m, 1H) .13C-
NMR (300 MHz, CDCl3) δ(ppm) = 127.1, 125.9, 67.7, 36.3, 28.1,
25.2, 24.6.
General procedure for hydrogenation reactions
Hydrogenation reactions were performed in 4 mL vials
equipped with magnetic stirring bars. Catalyst and solid
substrate were weighed in under air and the vials were then
closed with PTFE/rubber septa pierced with a needle, and
purged with argon. The solvent, a freshly prepared KOtBu
solution in THF (c= 1 [M]), dodecane, when used, and the
liquid reagent were then added in this order. The vials were
placed in a pre-purged 300 mL stainless steel autoclave which
was the sealed. The autoclave was purged with 3 cycles of N2
followed by 3 cycles of H2, pressurized with hydrogen to the
desired pressure and then heated to the desired temperature.
After the required time, the reactor was cooled to room
temperature, depressurized and, for the optimisation
reactions, a sample was taken, filtered over celite, diluted in
acetone and analyzed by GC. For the substrates scope, the
products were isolated by filtration through silica or by flash
column chromatography.
Furfuryl alcohol (Table 2, Entry 10). pale yellow liquid. 1H-
NMR (400 MHz, CDCl3) δ (ppm) = 7.36 (m, 1H), 6.31(m, 1H),
6.24 (d, J=3.6 Hz, 1H), 4.52 (s, 2H), 3.07 (bs, 1H) 13C-NMR (400
MHz, CDCl3) δ(ppm) = 154.1, 142.4, 110.3, 107.7, 57.1.
2,5-Di(hydroxymethyl)furan (Table 2, Entry 11). white solid.
1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 6.19 (s, 2H), 5.19(bs,
2H), 4.36 (s, 1H).13C-NMR (400 MHz, DMSO-d6) δ(ppm) =
154.7, 107.5, 55.8.
1
4-Chloro-benzyl alcohol (Table 2, Entry 12). white solid. H-
NMR (400 MHz, CDCl3) δ(ppm) = 7.35-7.17 (m, 4H), 4.61 (s,
2H), 1.92 (bs, 1H). 13C-NMR (400 MHz, CDCl3) δ(ppm) = 139.4,
133.5, 128.8, 128.4, 64.6.
1
4-Methoxy-benzyl alcohol (Table 2, Entry 13). white solid. H-
NMR (400 MHz, CDCl3) δ(ppm) = 7.36-7.17 (m, 2H), 7.00-6.79
(m, 2H), 4.58 (s, 2H), 3.82 (s, 3H), 2.66 (bs, 1H). 13C-NMR (400
MHz, CDCl3) δ(ppm) = 159.1, 133.2, 128.7, 128.6, 113.9, 64.8,
55.3.
1-Phenylethanol (Table 2, Entry 1). colourless liquid. 1H NMR
(400 MHz, CDCl3) δ (ppm) = 7.34-7.06 (m, 5H), 4.78 (q, J=6.4
Hz, 1H), 2.13 (s, 1H), 1.40 (d, J=6.5 Hz, 3H).13C NMR (400 MHz,
CDCl3) δ (ppm) = 145.9, 128.6, 127.5, 125.5, 70.4, 25.2
Conflicts of interest
1
Cyclohexanol (Table 2, Entry 2). colourless liquid. H NMR (400
The authors declare no conflicts of interest.
MHz, CDCl3) δ (ppm) = 3.63-3.48 (m, 1H), 2.11 (s, 1H), 1.94 –
1.79 (m, 2H), 1.75-1.60 (m, 2H), 1.50 (dd, J=13.5, 2.5 Hz, 1H),
1.33-1.00 (m, 5H). 13C NMR (400 MHz, CDCl3) δ (ppm) = 70.3,
35.6, 25.5, 24.2.
Acknowledgements
We thank Dr. C. Fischer, A. Koch, S. Buchholz, S. Schareina, A.
Lehmann and S. Rossmeisl at the LIKAT analytical department
for their indispensable support.
1
2-Cyclohexen-1-ol (Table 2, Entry 3). colourless liquid. H NMR
(300 MHz, CDCl3) δ (ppm) = 5.83-5.59 (m, 2H), 4.13 (s, 1H),
2.43 (d, J=5.2 Hz, 1H), 2.08-1.42 (m, 6H).13C NMR (300 MHz,
CDCl3) δ (ppm) = 130.2, 130.1, 65.4, 31.9, 31.9, 25.1, 19.1.
Notes and references
4-Chloro-α-methylbenzyl alcohol (Table 2, Entry 4). colourless
1
liquid. H NMR (400 MHz, CDCl3) δ (ppm) = 7.38- 7.12 (m, 4H),
1
(a) H. C. Kolb, M. G. Finn and K. B. Sharpless, Angew. Chem.
Int. Ed., 2001, 40, 2004; (b) V. V. Rostovtsev, L. G. Green, V.
V. Fokin and K. B. Sharpless, Angew. Chem. Int. Ed., 41, 2596.
P. T. Anastas and J. C.Warner, Green chemistry: theory and
practice. Oxford University Press, Oxford, 1998.
(a) M. Meldal and C. W. Tornøe, Chem. Rev., 2008, 108,
2952; (b) J. E. Hein and V. V. Fokin, Chem. Soc. Rev., 2010, 39,
1302; (c) P. L. Golas and K. Matyjaszewski, Chem. Soc. Rev.,
2010, 39, 1338.
4.80 (qd, J=6.4, 3.1 Hz, 1H), 2.81-2.60 (m, 1H), 1.42 (d, J=6.5 Hz,
3H). 13C NMR (400 MHz, CDCl3) (ppm) = 144.3, 130.02, 128.59,
126.9, 69.7, 25.3.
2
3
4-Methoxy-α-methylbenzyl alcohol (Table 2, Entry 5). colourless
1
liquid. H NMR (400 MHz, CDCl3) δ(ppm) = 7.37-7.17 (m, 2H),
6.97-6.75 (m, 2H), 4.80 (q, J=6.5 Hz, 1H), 3.79 (s, 3H), 2.91 (bs,
1H), 1.45 (d, J=6.5 Hz, 3H). 13C NMR (400 MHz, CDCl3) δ (ppm)
= 158.7, 138.1, 126.6, 130.7, 69.7, 55.2, 24.9.
4
5
(a) D. Fournier, R. Hoogenboom and U. S. Schubert, Chem.
Soc. Rev., 2007, 36, 1369; (b) L. Liang and D. Astruc, Coord.
Chem. Rev., 2011, 255, 2933. (c) M. Meldal, Macromol. Rapid
Commun.,2008, 29 , 1016.
(a) Q. V. C. van Hilst, N. R. Lagesse, D. Preston and J. D.
Crowley, Dalton Trans., 2018, 47, 997; (b) H. Struthers, T. L.
Mindt and R. Schibli, Dalton Trans., 2010, 39, 675; (c) D.
Huang, P. Zhao and D. Astruc, Coord. Chem. Rev, 2014, 272,
145. (d) D. Schweinfurth, L. Hettmanczyk, L. Suntrup and B.
Sarkar, Z. Anorg. Allg. Chem. 2017, 643, 554.
1
Benzyl alcohol (Table 2, Entry 7). colourless liquid. H-NMR
(400 MHz, CDCl3) δ(ppm) = 7.40-7.07 (m, 5H), 4.55 (s, 2H), 2.23
(s, 1H). 13C-NMR (400 MHz, CDCl3) δ(ppm) = 140.9, 128.6,
127.6, 127.1, 65.3.
1-cyclohexene-1-methanol (Table 2, Entry 8). Colourless
1
liquid. H-NMR (300 MHz, CDCl3) δ (ppm) = 5.70 (bs, 1H), 4.02
6
(a) S. C. Hockey, G. J. Barbante, P. S. Francis, J. M. Altimari, P.
Yoganantharajah, Y. Gibert and L. C. Henderson, Eur. J. Med.
Chem., 2016, 109, 305; (b) A. Maisonial, P. Serafin, M.
(s, 2H), 2.16 (m, 4H), 1.92 (m, 2H), 1.48 (m, 1H), 1.34 (s, 1H).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 8 of 9
ARTICLE
Journal Name
Traikia, E. Debiton, V. Thery, D. J. Aitken, P. Lemoine, B.
Viossat and A. Gautier, Eur. J. Inorg. Chem., 2008, 298.
Organic Synthesis 2, Science of Synthesis, Ed. J. G. de Vries,
Georg Thieme Verlag KG, Stuttgart, 2018, 7-45. View Article Online
DOI: 10.1039/C9DT01822K
7
8
(a) S. V. Kumar, S. O. Scottwell, E. Waugh, C. J. McAdam, L. R. 23 F. A. Kucherov, L. V. Romashov, K. I. Galkin and V. P.
Hanton, H. J. Brooks and J. D. Crowley, Inorg. Chem., 2016,
55, 9767; (b) J. C. Slootweg, S. van der Wal, H. C. Q. van 24 R. J. van Putten, J. C. van der Waal, E. de Jong,, C. B.
Ufford, E. Breukink, R. M. J. Liskamp and D. T. S. Rijkers,
Bioconjugate Chem., 2013, 24, 2058.
(a) B. Schulze, A. Winter, C. Friebe, E. Birckner and U. S. 25 (a) P. A. Dub, B. L. Scott and J. C. Gordon, J. Am. Chem. Soc.
Ananikov, ACS Sustainable Chem. Eng. 2018, 6, 8064−8092.
Rasrendra, H. J. Heeres and J. G. de Vries Chem. Rev. 2013,
113, 1499.
Schubert, ACS Macro Lett., 2017, 6, 181; (b) Y. Li, L. Chen, Y.
Ai, E. Y.-H. Hong, A. K.-W. Chan and V. W.-W. Yam, J. Am.
2017, 139, 1245. (b) S. E. Clapham, A. Hadzovic and R. H.
Morris, Coord. Chem. Rev. 2004, 248, 2201
Chem. Soc., 2017, 139, 13858; (c) B. Colasson, M. Save, P. 26 E. P. Cappellani, P. A. Maltby, R. H. Morris, C. T. Schweitzer
Milko, J. Roithová, D. Schröder, and O. Reinaud, Org. Lett.,
2007, 9, 4987.
(a) V. Ervithayasuporn, K. Kwanplod, J. Boonmak, S. Youngme
and M. R. Steele, Inorg. Chem. 1989, 28, 4437.
27 K. Abdur-Rashid, A.J. Lough and R. J. Morris, Organometallics
2000, 19, 2655.
9
and P. Sangtrirutnugul, J. Catal., 2015, 332, 62; (b) E. 28 G. M. Sheldrick, Acta Cryst. 2008, A64, 112.
Amadio, A. Scrivanti, V. Beghetto, M. Bertoldini, M. M. Alam 29 G. M. Sheldrick, Acta Cryst. 2015, C71, 3.
and U. Matteoli, RSC Adv., 2013, 3, 21636.
10 (a) B. Suijkerbuijk, B. N. H. Aerts, H. P. Dijkstra, M. Lutz, A. L.
Spek, G. van Koten and R. Klein Gebbink, Dalton Trans., 31 (a) W. J. Henre, R. Ditchfield and J. A. Pople, J. Chem. Phys.
30 C. Y. Lin, M. W. George and P. M. W. Gill, Aust. J. Chem.
2004, 57, 365.
2007, 1273; (b) E. M. Schuster, M. Botoshansky and M.
Gandelman, Angew. Chem. Int. Ed., 2008, 47, 4555.
11 (a) S. Hohloch, L. Suntrup and B. Sarkar, Organometallics,
2013, 32, 7376; (b) T. C. Johnson, W. G. Totty and M. Wills,
Org. Lett., 2012, 14, 5230; (c) X. C. Cambeiro, M. A. Pericas,
1972, 56, 2257; (b) P. J. Hay and W. R. Wadt, J. Chem. Phys.
1985, 82, 270; (c) M. Dolg, Effective core potentials, in: J.
Grotendorst (Ed.), Modern Methods and Algorithms of
Quantum Chemistry, Vol. 1, John Neumann Institute for
Computing, Jülich, 2000, pp. 479–508, NIC Series.
Adv. Synth. Catal. 2011, 353, 113; (d) F. Saleem, G. Kumar 32 (a) Yu. Minenkov, Å. Singstad, G. Occhipinti and V. R. Jensen,
Rao, A. Kumar, G. Mukherjee and A. K. Singh,
Organometallics, 2013, 32, 3595.
12 O. Martınez-Ferraté, C. Werlé, G.Franciò and W. Leitner,
ChemCatChem, 2018, 10, 4514.
13 S. Paganelli M. Alam, V. Beghetto A. Scrivanti, E. Amadio, M.
Bertoldini and U. Matteoli, Appl. Catal. A Gen., 2015, 503, 20.
Dalton Trans. 2012 41, 5526; (b) J.-D. Chai and M. Head-
Gordon, Phys. Chem. Chem. Phys. 2008, 10, 6615; (c) I. C.
Gerber and J. G. Ángyán, Chem. Phys. Lett. 2005, 415, 100.
33 (a) F. Weigend and R. Ahlrichs, Phys. Chem. Chem. Phys.
2005, 7, 3297; (b) D. Andrae, U. Haeussermann, M. Dolg, H.
Stoll and H. Preuss, Theor. Chim. Acta 1990, 77, 123.
14 (a) R. H. Morris in
Handbook of Homogeneous 34 (a) V. Barone and M. Cossi, J. Phys. Chem. 1998, A 102, 1995;
Hydrogenation, Vol I, J. G. de Vries, C. J. Elsevier, Eds., Wiley-
(b) M. Cossi, N. Rega, G. Scalmani and V. Barone, J. Comput.
Chem. 2003, 24, 669.
VCH, Weinheim, 2007, p45-70. (b) S. Gladiali, E. Alberico,
Chem. Soc. Rev., 2006, 35, 226; (c) J. S. M. Samec, J. E. 35 C. J. Cramer, Essentials of Computational Chemistry, second
Backvall, P. G. Andersson, P. Brandt, Chem. Soc. Rev., 2006,
ed., Wiley, Chichester, 2004.
35, 237; (d) R. Noyori, Angew. Chem. Int. Ed., 2002, 41, 2008. 36 (a) Spartan’16, Build 2.0.3, Wavefunction Inc., Irvine CA,
15 (a) T. Ohkuma, H. Ooka, S. Hashiguchi, T. Ikariya and R.
Noyori, J. Am. Chem. Soc. 1995, 117, 2675. (b) P. D. de
Koning, M. Jackson and I. C. Lennon, Org. Proc. Res. Dev.
2006, 10, 1054. (c) S. Baldino, S. Facchetti, A. Zanotti-Gerosa,
H. G. Nedden and W. Baratta, ChemCatChem 2016, 8, 2279
(d) S. Giboulot, S. Baldino, M. Ballico, R. Figliolia, A. Pöthig, S.
Zhang, D. Zuccaccia and W. Baratta, Organometallics, 2019,
38, 1127-1142.
USA, 2016.; (b) Y. Shao, Z. Gan, E. Epifanovsky, A. T. B.
Gilbert, M. Wormit, J. Kussmann, A. W. Lange, A. Behn, J.
Deng, X. Feng, D. Ghosh, M. Goldey, P. R. Horn, L. D.
Jacobson, I. Kaliman, R. Z. Khaliullin, T. Kus’, A. Landau, J. Liu,
E. I. Proynov, Y. M. Rhee, R. M. Richard, M. A. Rohrdanz, R. P.
Steele, E. J. Sundstrom, H. L. Woodcock III, P. M.
Zimmerman, D. Zuev, B. Albrecht, E. Alguire, B. Austin, G. J.
O. Beran, Y. A. Bernard, E. Berquist, K. Brandhorst, K. B.
Bravaya, S. T. Brown, D. Casanova, C.-M. Chang, Y. Chen, S.
H. Chien, K. D. Closser, D. L. Crittenden, M. Diedenhofen, R.
A. DiStasio Jr., H. Do, A. D. Dutoi, R. G. Edgar, S. Fatehi, L.
Fusti-Molnar, A. Ghysels, A. Golubeva-Zadorozhnaya, J.
Gomes, M. W. D. Hanson-Heine, P. H. P. Harbach, A. W.
Hauser, E. G. Hohenstein, Z. C. Holden, T.-C. Jagau, H. Ji, B.
Kaduk, K. Khistyaev, J. Kim, J. Kim, R. A. King, P. Klunzinger, D.
Kosenkov, T. Kowalczyk, C. M. Krauter, K. U. Lao, A. D.
Laurent, K. V. Lawler, S. V. Levchenko, C. Y. Lin, F. Liu, E.
Livshits, R. C. Lochan, A. Luenser, P. Manohar, S. F. Manzer,
S.-P. Mao, N. Mardirossian, A. V. Marenich, S. A. Maurer, N.
J. Mayhall, E. Neuscamman, C. Melania Oana, R. Olivares-
Amaya, D. P. O’Neill, J. A. Parkhill, T. M. Perrine, R. Peverati,
A. Prociuk, D. R. Rehn, E. Rosta, N. J. Russ, S. M. Sharada, S.
Sharma, D. W. Small, A. Sodt, T. Stein, D. Stück, Y.-C. Su, A. J.
W. Thom, T. Tsuchimochi, V. Vanovschi, L. Vogt, O. Vydrov, T.
Wang, M. A. Watson, J. Wenzel, A. White, C. F. Williams, J.
Yang, S. Yeganeh, S. R. Yost, Z.-Q. You, I. Y. Zhang, X. Zhang,
Y. Zhao, B. R. Brooks, G. K. L. Chan, D. M. Chipman, C. J.
Cramer, W. A. Goddard III, M. S. Gordon, W. J. Hehre, A.
Klamt, H. F. Schaefer III, M. W. Schmidt, C. David Sherrill, D.
G. Truhlar, A. Warshel, X. Xu, A. Aspuru-Guzik, R. Baer, A. T.
Bell, N. A. Besley, J.-D. Chai, A. Dreuw, B. D. Dunietz, T. R.
16 D. Spasyuk, S. Smith and D. G. Gusev, Angew. Chem. Int. Ed.,
2013, 52, 2538.
17 (a) P. A. Dub, B. L. Scott and J. C. Gordon, Organometallics
2015 34, 4464. (b) P. Puylaert, R. van Heck, Y. Fan, A.
Spannenberg, W. Baumann, M. Beller, J. Medlock, W.
Bonrath, L. Lefort, S. Hinze and J. G. de Vries, Chem. Eur. J.,
2017, 23, 8473 (c) B. M. Stadler, P. Puylaert, J. Diekamp, R.
van Heck, Y. Fan, A. Spannenberg, S. Hinze and J. G. de Vries,
Adv. Synth. Catal., 2018, 360, 1151.
18 S. I. Presolski, V. Hong, S.-H. Cho and M. G. Finn, J. Am.
Chem. Soc. 2010, 132, 14570.
19 H. Struthers, B. Spingler, T. L. Mindt and R. Schibli, Chem.
Eur. J. 2008, 14, 6173.
20 (a) S. Werkmeister, J. Neumann, K. Junge and M. Beller,
Chem. Eur. J., 2015, 21, 12226; (b) P. A. Dub and T. Ikariya,
ACS Catalysis, 2012, 2, 1728.
21 C. Gunanathan and D. Milstein, Acc. Chem. Res, 2011, 44,
588
22 (a) R. A. Farrar-Tobar, S. Tin, J. G. de Vries, in
Organometallics for Green Catalysis, P. H. Dixneuf, J.-H.
Soulé, eds., Topics in Organometallic Chemistry 2019, 63,
193-224. (b) N. Steinfeldt, K. Junge, in Catalytic Reduction in
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 9
Dalton Transactions
Please do not adjust margins
Journal Name
ARTICLE
Furlani, S. R. Gwaltney, C.-P. Hsu, Y. Jung, J. Kong, D. S.
Lambrecht, W. Liang, C. Ochsenfeld, V. A. Rassolov, L. V.
Slipchenko, J. E. Subotnik, T. Van Voorhis, J. M. Herbert, A. I.
Krylov, P. M. W. Gill and M. Head Gordon, Mol. Phys. 2015,
113, 184.
View Article Online
DOI: 10.1039/C9DT01822K
37 Gaussian 09, Revision C.01, M. J. Frisch, G. W. Trucks, H. B.
Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G.
Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H.
Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J.
Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery Jr., J.
E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K.
N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K.
Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi,
M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A.
Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D.
Daniels, Ö. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, D.
J. Fox, Gaussian Inc, Wallingford CT, 2010.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins