Ruthenium [NNN] and [NCN]-type pincer complexes with phosphine coligands: synthesis, structures and catalytic applications

Article abstract of DOI:10.1007/s11243-019-00362-y

A series of ruthenium [NNN]- or [NCN]-type complexes (3–7) bearing PPh₃ ancillary ligands have been synthesized from pyridine- or phenylene-bridged bis(triazoles) 1 and 2. In the case of [NNN]-pincer complex 3, an unusual and unexpected cis-orientation adopted by two sterically demanding PPh₃ ligands was observed, and such configuration proved to be unchanged in solution for a long time. By contrast and as expected, the two phosphines are found to be trans to each other in the case of [NCN]-type pincer complex 4, but an oxidation of Ru^II center to Ru^III occurred. Complex cis-3 underwent ligand exchanges leading to the formations of diphosphine derivatives 5 and 6. As a representative, cis-3 was treated with the base in isopropanol affording a mixture of Ru–hydrido complexes with various phosphine binding modes, one of which (trans-7) bearing two trans-standing phosphines has been successfully isolated and fully characterized. The catalytic performances of all newly synthesized Ru complexes have been examined and compared in transfer hydrogenations of ketones and enones, in which mono-phosphine complexes proved to be significantly superior to their diphosphine counterparts. The catalytic process proved to involve Ru–H key intermediates, but the trans-oriented Ru–H species is unlikely to be the main catalytic contributor. In particular, the best performer cis-3 exhibits high chemoselectivity in certain cases catalyzing α,β-unsaturated ketones, whose behavior is quite different compared to most precedents.

Full text of DOI:10.1007/s11243-019-00362-y

Transition Metal Chemistry
https://doi.org/10.1007/s11243-019-00362-y
Ruthenium [NNN] and [NCN]‑type pincer complexes with phosphine
coligands: synthesis, structures and catalytic applications
Bo Zhang · Haiying Wang · Xuechao Yan · Yu‑Ai Duan · Shuai Guo · Fei‑Xian Luo2
1
1
1
1
1
Received: 4 September 2019 / Accepted: 25 October 2019
©
Springer Nature Switzerland AG 2019
Abstract
A series of ruthenium [NNN]- or [NCN]-type complexes (3–7) bearing PPh ancillary ligands have been synthesized
3
from pyridine- or phenylene-bridged bis(triazoles) 1 and 2. In the case of [NNN]-pincer complex 3, an unusual and unex-
pected cis-orientation adopted by two sterically demanding PPh ligands was observed, and such conꢀguration proved to be
3
unchanged in solution for a long time. By contrast and as expected, the two phosphines are found to be trans to each other in
II
III
the case of [NCN]-type pincer complex 4, but an oxidation of Ru center to Ru occurred. Complex cis-3 underwent ligand
exchanges leading to the formations of diphosphine derivatives 5 and 6. As a representative, cis-3 was treated with the base
in isopropanol aꢁording a mixture of Ru–hydrido complexes with various phosphine binding modes, one of which (trans-7)
bearing two trans-standing phosphines has been successfully isolated and fully characterized. The catalytic performances of
all newly synthesized Ru complexes have been examined and compared in transfer hydrogenations of ketones and enones,
in which mono-phosphine complexes proved to be signiꢀcantly superior to their diphosphine counterparts. The catalytic
process proved to involve Ru–H key intermediates, but the trans-oriented Ru–H species is unlikely to be the main catalytic
contributor. In particular, the best performer cis-3 exhibits high chemoselectivity in certain cases catalyzing α,β-unsaturated
ketones, whose behavior is quite diꢁerent compared to most precedents.
Introduction
and this area has been comprehensively reviewed by Byrne
and Gunnlaugsson et al. [1].
Pyridine-bridged [NNN]-pincer frameworks, as exempli-
In respect of the coordination chemistry of btp ligands,
ruthenium is undoubtedly the most extensively studied
metal center. This is mainly owing to the promising optical
property of Ru–btp complexes, and such complexes can be
regarded as the homologues of the very successful Ru–Terpy
ꢀ
ed by Pybox and Terpy, have become “popular” ligands
in transition metal chemistry and homogenous catalysis. In
this regard, bis(1,2,3-triazol-4-yl)pyridines (btp, Fig. 1) have
1
received increasing interest in recent years. One appealing
3
synthetic advantage of such type of ligands is that they can
be very expediently constructed through simple Cu-cata-
complexes. However, surprisingly and to the best of our
knowledge, there is no catalytic investigation of Ru–btp
complexes thus far, although Ru complexes supported by
other types of [NNN]-pincer platforms have shown highly
2
lyzed azide–alkyne cycloadditions (CuAACs), making such
motifs easily accessible and stereoelectronically tunable.
Various btp-containing complexes have been documented,
4
remarkable performance in many catalytic transformations
5
,6
especially in THs (THs=transfer hydrogenations). Thus,
as a contribution to this less studied area, herein we report
a series of Ru–phosphine pincer complexes I (Fig. 1) and
their diphosphine derivatives, and systematically reveal their
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11243-019-00362-y) contains
supplementary material, which is available to authorized users.
1
For a related review, see [1].
For selected reviews, see [2–6].
For recent papers focusing on the Ru–btp complexes and their pho-
*
Shuai Guo
2
guoshuai@cnu.edu.cn
3
1
2
toluminescence applications, see [7–9].
Department of Chemistry, Capital Normal University,
Beijing, People’s Republic of China
4
For selected reviews on Ru pincer complexes, see [10–13].
For selected examples, see [14–20].
For selected examples, see [20–27].
5
College of Life and Environment Science, Minzu University
of China, Beijing, People’s Republic of China
6
Vol.:(0
1
123456789)
3

Transition Metal Chemistry
[
NNN]-pincer/bis(phosphine) complexes [14–27] predom-
inantly bear two mono-phosphines in trans positions. By
contrast, the cis-conꢀguration adopted by two phosphines
7
in cis-3 is much less common and unexpected, since such
coordination mode obviously increases the steric repulsion
of the two bulky binding phosphines as indicated by the
P–Ru–P angle amounting to 98.81(3)° (vide infra).
Complex cis-3 shows moderate solubility in DMSO,
isopropanol and CH Cl . Standing the solution of cis-3 in
Fig. 1 Ligand btp and the target system (I) in this work
2
2
6
d -DMSO at the ambient temperature for one week does
not lead to the formation of any isomerized or decomposed
versatile phosphine binding behaviors, reactivities/stabili-
ties, catalytic performances and mechanistic considerations
in THs of ketones as well as enones.
3
1
products like trans-3 (monitored by P NMR), which dem-
onstrates the high stability of such cis-oriented isomer.
Synthesis of [NCN]‑type pincer complexes bearing
monodentate phosphines
Results and discussion
Then, following the procedure accessing cis-3, phenylene-
Synthesis of (pro)ligands
II
based compound 2 was treated with [Ru Cl (PPh ) ].
2
3 3
NaOAc was added to assist the C-H activation and cyclo-
metalation (Scheme 3). However, in this case, an inseparable
mixture was always obtained despite several attempts. By
Pyridine- and phenylene-bridged bis(triazoles) 1 and 2,
which have been reported elsewhere [28–30], were synthe-
sized via copper-catalyzed “click” reactions of benzyl azide
Scheme 1 Synthesis of
bis(triazoles) 1 and 2
(
A) with commercially available alkynes B and C, respec-
evaporation of the solution of the crude product, we were
III
tively (Scheme 1). In an earlier study from our group [31],
copper(I) N-heterocyclic carbene complex i was found to be
eꢂcient precatalyst for accessing bis(triazole) compound 1,
thus which was also utilized herein to prepare its analogue 2.
able to obtain some single crystals which proved to be a Ru
complex trans-4. The formation of trans-4 clearly indicates
that an oxidation of the metal center has occurred, which is
II
likely due to the electron-rich feature of Ru center imparted
by the strongly donating aryl anion-based NCN ligand. Nota-
bly, such instability is also in sharp contrast to the other
Synthesis of [NNN]‑type pincer complexes bearing
monodentate phosphines
II
known Ru [NCN] pincer analogues, which are reported to
be fairly stable [25]. As expected, the two mono-phosphines
are both perpendicular to the [NCN] coordination plane
adopting a trans-orientation. The fact that all phosphines
are cis to the aryl donor can be rationalized by the known
First, pyridine-linked bis(triazole) 1 was treated with
II
[
Ru Cl (PPh ) ] in isopropanol successfully aꢁording pin-
2
3 3
cer complex cis-3 in a moderate yield of 62% (Scheme 2).
3
1
8
In the P NMR spectrum of cis-3, two doublets
transphobia eꢁect.
at 42.1 ppm and 37.7 ppm with a coupling constant of
3
0.4 Hz were observed, which is indicative of two cis-
7
To the best of our knowledge, there is only one report regarding Ru
standing phosphine ligands. Such coordination mode can
be further unambiguously conꢀrmed by X-ray diꢁraction
analysis (vide infra). Interestingly, previously reported Ru
NNN pincer complexes bearing two cis-standing mono-phosphines.
For this paper, see Ref. [15].
8
For the report in which the term “transphobia efect” was coined,
see [32].
1
3

Transition Metal Chemistry
Scheme 2 Synthesis of
bis(phosphine) complex cis-3
Scheme 3 Attempt to synthesize [NCN]-type pincer complex of ruthenium
Synthesis of pincer complexes bearing bidentate
phosphines
analogue 6. The formation of 5 was further veriꢀed by
X-ray single-crystal diꢁraction study (vide infra).
In previous reports, Ru complexes bearing bidentate phos-
phines show superior catalytic performance in TH reac-
tions compared to their counterparts with two monodentate
phosphines [15]. Thus, to further modify the structure, two
diphosphine ligands dppe and dppf were used, and via ligand
exchange reactions, complexes 5 and 6 can be obtained in
good yields (Scheme 4).
Hydrido complexes
Previously, Ru–hydrido species have been proposed or
9
proved to be key active intermediates in TH reactions. The
[NNN]-type pincer platform employed herein may make it
more feasible to access certain stable enough Ru–H com-
plexes. Thus, cis-3 serving as a representative was treated
1
i
In the H NMR spectra of 5, the benzylic protons give
with K CO , and PrOH was used as the solvent as well as
2
3
two doublets at 5.37 ppm and 5.27 ppm with a coupling
constant of ~ 15 Hz showing a “rooꢀng eꢁect”. Such char-
the hydrogen donor (Scheme 5).
1
H NMR spectroscopic analysis of the crude product
acteristics clearly indicate that the two NCH hydrogen
revealed the formations of several Ru–H complexes. The
selected region of the spectrum showing the hydrido signals
2
nuclei become diastereotopic thus resulting a geminal
coupling. This is likely owing to the rigidity of the bind-
is given in Fig. 2. The splitting pattern and coupling con-
2
ing diphosphines making the N-C
bond rotation more
stant ( J
) proved to be diagnostic, which are used to
P–Ru–H
benzyl
3
1
diꢂcult. P NMR spectroscopic analyses provided addi-
tional evidence for their formations. In the case of 5, two
doublets at 65.8 and 59.3 ppm with a coupling constant
of ~ 22 Hz were found, which can be assigned to the two
cis-standing phosphorus donors in dppe ligand. Similar
NMR features were also observed in the case of dppf
assign and distinguish the as-formed major Ru–H species.
It has been known that the coupling between P and H atoms
2
trans to each other ( J
) is markedly greater than
P(trans)–M–H
9
For a review, see [33].
1
3

Transition Metal Chemistry
Scheme 4 Synthesis of diphosphine complexes 5 and 6
Scheme 5 Synthesis of ruthenium–hydrido complexes
2
that ( J
) involving two cis-standing nuclei [34]. The
(trans-7 and cis-7) give an integration ratio of 1:1.2, clearly
indicating that the cis-orientation adopted by the mono-
phosphines of cis-3 has been partially changed during the
reaction.
P(cis)–M–H
coupling constant in the former case is generally >80 Hz,
while the latter one is only less than 40 Hz. Thus, the spe-
cies giving a triplet at −7.48 ppm with a coupling constant
1
of 24 Hz is assigned to trans-7. These H NMR features are
In addition, ESI mass spectrometry further veriꢀes the
formation of Ru–H species by the base peaks observed at
m/z 1020, 510 and 500 corresponding to the monocationic
also in line with the previously reported analogues [35–38].
In addition, a doublet of doublet at −8.64 ppm with two
coupling constants of 100 and 32 Hz was observed, which
is assigned to the hydrido ligand of cis-7. Such NMR char-
acteristics have been also observed in a previously reported
analogue [15]. Finally, the minor Ru–H species giving rise
to a doublet at −10.69 ppm cannot be unambiguously identi-
+
2+
fragments [7–Cl] as well as dicationic species [7–Cl–H]
2
+
and [7–Cl–H+CH CN] .
3
By using column chromatography, trans-7 can be iso-
lated although in a low yield. By contrast, several attempts
to isolate cis-7 were to no avail, which may implicate a
lower stability of such species versus trans-7. This is further
ꢀ
ed at the current stage. The two dominant hydrido species
1
3

Transition Metal Chemistry
1
Fig. 2 Selected region of H
NMR spectrum of the crude
product (including trans-7 and
cis-7, etc.) showing the hydrido
signals
Fig. 3 DFT-optimized struc-
tures and calculated relative
Gibbs free energies of trans-7
and cis-7. DFT settings: M11-
L/6-31G(d) (for C H N P);
ECP-SDD (for Ru)
supported by DFT calculations, which indicates that the
Gibbs free energy of cis-7 (Fig. 3) is 2.3 kcal/mol higher
compared to that for the trans isomer.
of cis-3, the P1-Ru–P2 bond angle is found to be remark-
ably larger than 90°, which is owing to the severe repulsion
of the two sterically demanding phosphines. Probably due
to the same reason, the Ru-P bond distances of cis-3 are
signiꢀcantly longer compared to those in the diphosphine
counterpart 5.
X‑ray diꢀractions
The solid-state structures of complexes cis-3, trans-4, 5 are
depicted in Fig. 4. Selected important crystallographic data
are listed in Table SI-1 (ESI). All ruthenium complexes
adopt distorted octahedral geometry. Notably, in the case
1
3

Transition Metal Chemistry
Fig. 4 Molecular structure of cis-3, trans-4 and 5 showing 50%
probability ellipsoids. Hydrogen atoms, solvent molecules and
counter anions have been omitted for clarity. Selected bond lengths
2.4531(7), Ru1-P1 2.3817(7), Ru1-P2 2.3128(8); for trans-4: P1-Ru1-
P2 175.97(8), P1-Ru1 2.3852(19), P2-Ru1 2.399(2). For 5: P1-Ru1-
P2 83.96(4), Ru1-Cl1 2.4856(12), Ru1-P1 2.2684(13), Ru1-P2
2.3134(12)
(
Å) and bond angles (deg): for cis-3: P2-Ru1-P1 98.81(3), Ru1-Cl1
Catalytic TH reactions
Despite these exciting precedents, easily accessible,
robust, eꢂcient and chemoselective Ru-based catalytic sys-
tems are still strongly appealing. First, the reported [NNN]-
pincer ligands used for THs typically require multiple and
sophisticated synthetic steps, and in certain cases undesired
harsh conditions are needed. In addition, the known Ru-
mediated catalytic systems predominantly focus on the trans-
formations of simple ketones, while THs of α,β-unsaturated
Ru-mediated transfer hydrogenation (TH) of ketones has
evolved to become a powerful approach to access alcohols
1
0
under mild conditions. With all ruthenium pincer com-
plexes in hand, their catalytic activities in TH reactions were
then examined and compared. In the model reaction, aceto-
phenone (8) was employed as the substrate, and 0.1 mol% of
Ru complex was used as the catalyst (Table 1). Isopropanol
was chosen to serve as the solvent as well as the hydrogen
donor, since it is cheap and environmentally benign. In addi-
tion, such hydrogen donor and its dehydrogenated product
1
1
ketones are much less investigated.
The reaction in the absence of base gives no formation
of the desired product (Entry 1). When K CO was utilized
2
3
as the base, a low yield was obtained at a reaction time of
(
i.e., acetone) can be very easily removed from the catalytic
2 h. A further extension of the reaction time to 24 h leads to
system via simple evaporation.
10
11
For selected reviews on TH reactions, see [39–43].
For a review on Ru-mediated THs of enones, see [44–48].
1
3

Transition Metal Chemistry
Table 1 Catalytic transfer hydrogenations between ketones and isopropanol
a
Entry
Cat.
Base
–
t (h)
Yield (%)
1
2
3
4
5
6
7
8
cis-3
cis-3
cis-3
cis-3
cis-3
5
2
2
24
0.5
2
2
2
2
0
9
82
62
98
6
K CO
2
3
K CO
2
3
i
PrOK
PrOK
PrOK
PrOK
PrOK
i
i
i
i
6
10
45
trans-7
Condition: 2 mmol of ketone, 2 mL of isopropanol, 2 mol% of base, 0.1 mol% of Ru catalyst, 82 °C
a
1
Yields were determined using H NMR spectroscopy
a largely improved yield (Entry 2 vs. Entry 3). A stronger
was reduced, and no alcohol-containing products 19b and
19c were observed. Such behavior is diꢁerent with most of
the reported Ru-based catalysts [44–48], and to the best of
our knowledge, only very few Ru complexes exhibit simi-
lar performance for this particular substrate [26, 46]. Such
chemoselectivity is found to be sensitive to the substrate
variation. When phenyl-substituted enone 20 was utilized,
completely hydrogenated species 21c was found to be the
predominant product. The attachment of a chlorine substitu-
ent to benzylideneacetone also brings a decreased selectivity
and activity (entry 7). The reason of such enone-dependent
chemoselectivity is not clear at the current stage and remains
to be further explored in the future.
i
base PrOK proved to be much superior. A moderate conver-
sion can be achieved at only 30 min, and the reaction can
proceed near quantitatively in 2 h (Entry 5). By contrast,
diphosphine complexes 5 and 6 exhibited much poorer per-
formance (Entries 6/7 vs. Entry 5). Such observation is in
sharp contrast to some previous reports, in which pincer-
type precatalysts coligated with diphosphines show com-
parable or even superior catalytic behaviors compared to
their mono-phosphine counterparts [15]. Interestingly, when
Ru–H complex trans-7 was utilized as the catalyst under the
same condition, a much lower yield was obtained (entry 7
vs. entry 5). This dramatic diꢁerence may imply that trans-7
is not the primary Ru–H intermediate during the catalysis
of cis-3, and less stable Ru–H species cis-7 is likely to be a
more signiꢀcant catalytic contributor.
Conclusion
The best performer complex cis-3 was chosen as the cata-
lyst to further expand the substrate scope (Table 2). For most
of the sterically and electronically varied simple ketones,
good yields can be obtained (entries 1–3). No activity was
observed for the case of stilbene indicating the catalytic
inertness toward simple carbon–carbon double bond (entry
In conclusion, we have reported a conveniently constructed
Ru pincer system supported by a triazole-based triden-
tate ligand platform and coligated with phosphines. In the
case employing phenylene-bridged [NCN]-pincer ligand,
II
III
an oxidation of Ru to Ru was observed. In contrast,
robust pincer complexes can be accessed when pyridine-
linked bis(triazoles) was used as the supporting ligand. For
Ru–chlorido complex 3, the two mono-phosphines are found
to bind in an unusual cis-standing fashion, which is diꢁerent
from most of the precedents. Such binding mode is (par-
tially) altered during the conversion of 3 to Ru–H complex
7. Experimental and computational studies implicate that
trans-oriented Ru–H species is more stable compared to the
4
). In addition, α,β-unsaturated ketones were also used as
the substrates to test the catalytic chemoselectivity. Enones
are known to be less active in TH reactions, and thus, the
catalyst loading was improved to 1 mol%. Benzylideneac-
etone (18) is one of the most studied enones for TH cataly-
sis. Interestingly, when this substrate was employed, the TH
reaction proceeded in a high chemoselective manner giv-
ing a moderate yield (entry 5). Only the C=C double bond
1
3

Transition Metal Chemistry
Table 2 Transfer
hydrogenations of ketones and
enones in isopropanol
a
Ent
Ketone/enone
t
Product and yield (%)
1
2
2
2
3
2
4
24
5
24
6
24
7
24
1
3

Transition Metal Chemistry
Table 2 (continued)
Condition: 2 mmol of the substrate, 2 mL of isopropanol, 2 mol% of base, 0.1 mol% (for entries 1–3) and
1
mol% (for entries 4–7) of Ru catalyst, 82 °C
a
1
Yields were determined using H NMR spectroscopy using 1,3,5-trimethoxybenzene as the internal stand-
ard
cis-isomer. In addition, diphosphine complexes 5/6 can be
prepared via ligand exchanges of cis-3. Catalytic studies on
TH reactions indicate: (1) mono-phosphine complex cis-3
shows much superior performance compared to diphosphine
counterparts 5/6; (2) the current catalytic system is likely
to be [Ru–H]-mediated, but trans-7 may not be the main
catalytic contributor; (3) the best performer cis-3 exhibits
good activity for most of simple ketones and shows high
chemoselectivity in the case of benzylideneacetone as the
enone substrate. Additionally, the selectivity is found to be
highly dependent on the enone skeletons.
pumped dry in vacuo aꢁording the product as an oꢁ-white
1
solid (87% for 1 and 82% for 2). The H NMR spectroscopic
data agree with the reported [28–30].
Synthesis of cis‑3
Compound 2 (78.7 mg, 0.2 mmol), [RuCl (PPh ) ]
2
3 3
(191.8 mg, 0.2 mmol) and isopropanol (5 mL) were mixed in
a Schlenk tube under N . The tube was sealed, and the reac-
2
tion mixture was stirred for 3 h at 85 °C. After cooling down
to the ambient temperature, the resulting precipitate was col-
lected and washed with ethyl acetate (3 × 5 mL) followed
by diethyl ether (3×5 mL). All the volatiles were removed
The “popular” btp pincer platform (btp=bis(1,2,3-tria-
zol-4-yl)-pyridine), although extensively studied, is applied
for Ru-based catalysis for the ꢀrst time. The structural elu-
cidations and catalytic investigations of Ru–btp system stud-
ied herein will facilitate the search for further applications
of such complexes. In addition, the uncommon phosphine
binding modes and high chemoselectivity in TH of enones
in vacuo aꢁording the product as a yellow solid (135 mg,
1
62%). H NMR (600 MHz, d -DMSO): δ (ppm) 8.99 (s, 2H,
6
5
3
Triazole-C –H), 8.04 (t, 1H, Ar–H, J =7.8 Hz), 7.86 (d,
H,H
3
2H, Ar–H, J =7.8 Hz), 7.43–7.14 (m, 30H, Ar–H), 6.73
H,H
(br s, 5H, Ar–H), 6.33 (br s, 5H, Ar–H), 5.60 (s, 4H, NCH ).
2
1
3
(
although limited to certain cases) have implications for the
C NMR (150 MHz, d -DMSO): δ (ppm) 149.9, 148.8,
6
design of corresponding systems. A more detailed mechanis-
tic study in catalysis as well as further structure variations of
Ru pincer complexes is underway in our laboratory.
138.2, 135.5, 135.2, 134.5 (d, J =9.6 Hz), 134.4, 132.6,
C,P
130.9, 130.6, 129.6, 129.1, 128.9, 128.8, 128.2, 127.5 (d,
J
=9 Hz), 127.1 (d, J =9.2 Hz), 125.3, 119.6 (Ar–C),
C,P
C,P
3
1
5
5.0 (NCH ). P NMR (162 MHz, d -DMSO): δ (ppm) 42.1
2
6
2
2
(
d, J =30.4 Hz), 37.7 (d, J =30.4 Hz). MS (ESI): m/z
P,P P,P
+
Experimental section
1054 [M–Cl] . Anal. Calcd. for C H Cl N P Ru: C, 65.01;
59 49 2 7 2
H, 4.53; N, 9.00; Found: C, 65.40; H, 4.35; N, 9.19%.
General considerations
Synthesis of 5
If not mentioned otherwise, all reagents and solvents were
1
13
used as received without further puriꢀcation. H, C and
C o m p l e x
3
( 8 7 . 2
m g ,
0 . 0 8
m m o l ) ,
3
1
P NMR spectra were recorded on a 600 MHz or 400 MHz
1,2-bis(diphenylphosphino)ethane (31.9 mg, 0.08 mmol) and
isopropanol (4 mL) were mixed in a Schlenk tube. The tube
was sealed, and the reaction mixture was stirred at 82 °C
overnight. After cooling down to the ambient temperature,
all the volatiles were removed in vacuo. The residue was
washed with diethyl ether (3×5 mL) and puriꢀed using ꢃash
column chromatography (SiO , CH Cl :CH OH (v:v)=8:1)
spectrometer. The chemical shifts (δ) were internally ref-
erenced to the residual solvent signals based on literature
[49]. ESI mass spectra were measured using an Agilent 6540
Q-TOF mass spectrometer. X-ray single-crystal diꢁractions
were done using a Rigaku XtaLAB P200 MM003 diꢁrac-
tometer. Elemental analyses were done on a vario EL cube
elemental analyzer.
2
2
2
3
1
aꢁording the product as a yellow solid (50 mg, 65%). H
NMR (600 MHz, d -DMSO): δ (ppm) 8.93 (s, 2H, Tria-
6
5
3
General procedure for the synthesis of 1 and 2
zole-C –H), 8.23 (t, 1H, Ar–H, J =7.8 Hz), 8.13–8.09
H,H
(
m, 6H, Ar–H), 7.45–7.42 (m, 7H, Ar–H), 7.35–7.33 (m,
A round-bottom ꢃask (50 mL) was charged with benzyl
azide (2.5 mmol), 2,6-diethynylbenzene (or 1,3-diethynylb-
enzene, 1 mmol) and the precatalyst [IPrCuCl] (9.8 mg,
4H, Ar–H), 7.18–7.16 (m, 6H, Ar–H), 6.87–6.84 (m, 4H,
Ar–H), 6.56–6.53 (m, 4H, Ar–H), 5.37 (d, 2H, NCH ,
2
3
3
J
= 14.6 Hz), 5.27 (d, 2H, NCH , J = 14.6 Hz),
H,H
2
H,H
13
0
.02 mmol). A mixture of ethanol (15 mL) and deionized
2.98–2.90 (m, 2H, CH ), 2.64–2.56 (m, 2H, CH ). C NMR
2
2
water (5 mL) was added. The reaction mixture was stirred
for 24 h at 60 °C. All the volatiles were removed in vacuo.
The residue was washed with ether (3×5 mL), and the solid
(150 MHz, d -DMSO): δ (ppm) 149.5, 148.5, 138.6, 136.4,
6
136.1, 134.2, 132.8 (d, J =9.9 Hz), 131.1, 130.9, 129.9 (d,
C,P
J
=9.0 Hz), 129.7, 129.5, 128.9, 128.8, 128.6, 128.1 (d,
H,P
1
3

Transition Metal Chemistry
2
13
JC,P =9.2 Hz), 127.7 (d, J =9.5 Hz), 125.2, 119.6 (Ar–C),
(t, 1H, J =24 Hz). C NMR (150 MHz, d -DMSO): δ
H,P 6
C,P
5
4.5 (NCH ), the resonances of CH (dppe) overlap with
(ppm) 149.1, 146.4, 134.7, 133.3, 133.2, 133.0, 132.8, 132.7,
2
2
3
1
the signal of DMSO. P NMR (162 MHz, d -DMSO): δ
132.6, 132.54, 132.50, 132.0 (d, J = 2.6 Hz), 131.5 (d,
6
C,P
2
2
(
ppm) 65.8 (d, J =22.2 Hz), 59.3 (d, J =22.2 Hz). MS
J
=9.6 Hz), 129.0, 128.9, 128.8, 128.75, 128.72, 128.4,
C,P
P,P
P,P
+
(
ESI): m/z 928 [M–Cl] . Anal. Calcd. for C H Cl N P Ru:
128.0, 127.62, 127.59, 127.56, 123.4, 117.9 (Ar–C), 54.2
49
43
2
7 2
3
1
C, 61.06; H, 4.50; N, 10.17; Found: C, 60.80; H, 4.75; N,
(NCH ). P NMR (162 MHz, d -DMSO): δ (ppm) 49.3 (s).
2 6
9
.86%.
Anal. Calcd. for C H ClN P Ru: C, 67.13; H, 4.77; N,
59 50 7 2
9
.29; Found: C, 67.42; H, 4.57; N, 9.46%.
Synthesis of 6
Catalytic transfer hydrogenations
Complex 3 (87.2 mg, 0.08 mmol), dppf (44.4 mg,
0
.08 mmol) and isopropanol (4 mL) were mixed in a Schlenk
In a typical run, to a 25-mL Schlenk tube, the substrate, Ru
catalyst and 2-propanol (2 mL) were added under a nitrogen
atmosphere. The tube was sealed, and the reaction mixture
was heated and stirred at 82 °C for 10 min. After addition of
the base, the reaction mixture was stirred and heated for in
a reaction time indicated in Table 1 or Table 2. After cool-
ing down to the ambient temperature, all the volatiles were
tube. The tube was sealed, and the reaction mixture was
stirred for 5 d at 82 °C. After cooling down to the ambi-
ent temperature, all the volatiles were removed in vacuo.
The crude product was washed with diethyl ether (3×5 mL)
and dried in vacuo aꢁording the product as a yellow solid
1
(
75.3 mg, 84%). H NMR (600 MHz, d -DMSO): δ (ppm)
6
5
1
9
7
7
6
.06 (s, 2H, Triazole-C –H), 8.01–7.97 (m, 5H, Ar–H),
.84–7.82 (m, 2H, Ar–H), 7.52–7.40 (m, 12H, Ar–H),
.33–7.30 (m, 4H, Ar–H), 7.18–7.15 (m, 2H, Ar–H),
.76–6.72 (m, 4H, Ar–H), 6.52–6.47 (m, 4H, Ar–H),
removed in vacuo. The crude product was analyzed by H
NMR spectroscopy.
X‑ray diꢀraction studies
2
5
.70 (d, 2H, NCH , J = 21.6 Hz), 5.52 (d, 2H, NCH ,
2
H,H
2
2
J
=21.6 Hz). 4.41–4.34 (m, 6H, Ar–H). 4.18 (br s, 2H,
Structural solution was carried out with the Olex2 program
[50]. The structure was solved using direct methods. All
non-hydrogen atoms were generally given anisotropic dis-
placement parameters in the ꢀnal model. All H atoms were
put at calculated positions.
H,H
1
3
Ar–H). C NMR (150 MHz, d -DMSO): δ (ppm) 150.0
6
(
d, J = 2.1 Hz), 148.5, 138.2, 137.9, 137.7, 134.8 (d,
C,P
J
= 10.1 Hz), 134.3, 132.2, 132.1, 131.9, 129.6, 129.1,
C,P
1
29.0 (d, J =3.9 Hz), 128.9, 127.2 (d, J =9.2 Hz), 126.9
C,P
C,P
(
d, J =9.2 Hz), 125.4, 119.5, 80.4 (dd, J =3.6, 43.4 Hz),
Reꢀnement model description for cis-3: (1) ꢀxed Uiso at
1.2 times of all C(H) groups and all C(H,H) groups; ꢀxed Uiso
at 1.5 times of all O(H,H) groups; (2) restrained distances.
O1–H1C=O1–H1D, 0.84 with sigma of 0.01; H1C-H1D,
1.39 with sigma of 0.02; H1A–H1C, − 2.1 with sigma of
C,P
C,P
7
7
5
7.6 (dd, J =2.8, 52.1 Hz), 74.6 (dd, J =9.3, 13.1 Hz),
C,P C,P
3.2 (d, J =4.7 Hz), 71.5 (d, J =4.7 Hz), 62.8 (Ar–C),
C,P
C,P
3
1
5.1 (NCH ). P NMR (133 MHz, d -DMSO): δ (ppm) 43.5
2
6
2
2
(
d, J =26.6 Hz), 35.1 (d, J =26.6 Hz). MS (ESI): m/z
P,P P,P
084 [M–Cl] . Anal. Calcd. for C H Cl FeN P Ru: C,
+
1
6
0.02; (3) secondary CH reꢀned with riding coordinates:
5
7
47
2
7
2
2
1.14; H, 4.23; N, 8.76; Found: C, 61.50; H, 4.11; N, 8.38%.
C1(H1A,H1B), C17(H17A,H17B), C24(H24A,H24B),
C25(H25A,H25B); aromatic/amide H reꢀned with riding
coordinates: C3–C8, C11–13, C16, C19(H19), C20(H20),
C21(H21), C22(H22), C23(H23), C27(H27), C28(H28),
C29(H29), C30(H30), C31(H31), C33(H33), C34(H34),
C35(H35), C36(H36), C37(H37), C39(H39), C40(H40),
C41(H41), C42(H42), C43(H43), C45(H45), C46(H46),
C47(H47), C48(H48), C49(H49), C50(H50), C51(H51),
C52(H52), C53(H53), C54(H54), C57(H57), C58(H58),
C59(H59), C60(H60), C61(H61).
Synthesis of trans‑7
Under a nitrogen atmosphere, complex 3 (109 mg,
0
.1 mmol), K CO (138.2 mg, 1 mmol) and isopropanol
2 3
(
5 mL) were mixed in a Schlenk tube. The tube was sealed,
and the reaction mixture was stirred for 8 h at 82 °C. After
cooling down to the ambient temperature, all the volatiles
were removed in vacuo. Dichloromethane was added, and
the insoluble was ꢀltered oꢁ. The organic phase was col-
lected and dried. The crude product was puriꢀed using col-
umn chromatography (SiO , CH Cl :CH OH (v:v) = 8:1)
Reꢀnement model description for trans-4: (1) twinned
data reꢀnement scales: 0.674(13), 0.326(13); (2) ꢀxed Uiso
at 1.2 times of all C(H) groups and all C(H,H) groups; (3)
Uiso/Uaniso restraints and constraints: Uanis(Ru1)≈ Ueq
with sigma of 0.01 and sigma for terminal atoms of 0.02;
(4) others: fixed Sof: Cl1(0.5) Cl1′(0.5) (5) secondary
2
2
2
3
1
aꢁording the product as a yellow solid (12 mg, 11%). H
NMR (600 MHz, d -DMSO): δ (ppm) 8.49 (s, 2H, Tria-
6
5
zole-C –H), 7.63–7.55 (m, 4H, Ar–H), 7.43–7.08 (m, 36H,
Ar–H), 6.90–6.89 (m, 3H, Ar–H), 5.29 (s, 4H, NCH ),-7.49
CH reꢀned with riding coordinates: C43(H43A,H43B),
2
2
1
3

Transition Metal Chemistry
C54(H54A,H54B), C61(H61A,H61B); aromatic/amide H
reꢀned with riding coordinates: C2(H2), C3(H3), C4(H4),
C5(H5), C6(H6), C8(H8), C9(H9), C10(H10), C11(H11),
C12(H12), C14(H14), C15(H15), C16(H16), C17(H17),
C18(H18), C20(H20), C21(H21), C22(H22), C23(H23),
C24(H24), C26(H26), C27(H27), C28(H28), C29(H29),
C30(H30), C32(H32), C33(H33), C34(H34), C35(H35),
C36(H36), C37(H37), C38(H38), C39(H39), C40(H40),
C41(H41), C44(H44), C47(H47), C48(H48), C49(H49),
C53(H53), C56(H56), C57(H57), C58(H58), C59(H59),
C60(H60).
Compliance with ethical standards
Conflict of interest The authors declare that they have no conꢃict of
interest.
References
1
2
.
.
Byrne JP, Kitchen JA, Gunnlaugsson T (2014) Chem Soc Rev
4
3:5302
Haldón E, Nicasio MC, Pérez PJ (2015) Org Biomol Chem
13:9528
3
4
5
6
.
.
.
.
Liang L, Astruc D (2011) Coord Chem Rev 255:2933
Hein JE, Fokin VV (2010) Chem Soc Rev 39:1302
Meldal M, Tornøe CW (2008) Chem Rev 108:2952
Kolb HC, Finn MG, Sharpless KB (2004) Angew Chem Int Ed
2001:40
Reꢀnement model description for 5: (1) ꢀxed Uiso at
1
1
.2 times of all C(H) groups and all C(H,H) groups; at
.5 times of all C(H,H,H) groups and all O(H) groups; (2)
Uiso/Uaniso restraints and constraints: Uanis(N2) ≈ Ueq,
Uanis(N7) ≈ Ueq with sigma of 0.005 and sigma for ter-
minal atoms of 0.01; Uanis(N3)≈ Ueq, Uanis(O3)≈ Ueq:
with sigma of 0.005 and sigma for terminal atoms of 0.01;
Uanis(C24)≈Ueq, Uanis(C7)≈Ueq: with sigma of 0.005
and sigma for terminal atoms of 0.01; (3) rigid body (RIGU)
restrains all non-hydrogen atoms with sigma for 1–2 dis-
tances of 0.004 and sigma for 1–3 distances of 0.004; (4)
ternary CH refined with riding coordinates: C41(H41),
7
.
Schulze B, Friebe C, Hager MD, Winter A, Hoogenboom R, Görls
H, Schubert US (2009) Dalton Trans 5:787
8
9
.
.
Yang W, Zhong Y (2013) Chin J Chem 31:329
Byrne JP, Kitchen JA, Kotova O, Leigh V, Bell AP, Boland JJ,
Albrecht M, Gunnlaugsson T (2014) Dalton Trans 43:196
1
1
0. Gunanathan C, Milstein D (2014) Chem Rev 114:12024
1. Younus HA, Su W, Ahmad N, Chen S, Verpoort F (2015) Adv
Synth Catal 357:283
1
2. Younus HA, Ahmad N, Su W, Verpoort F (2014) Coord Chem
Rev 276:112
1
1
1
1
3. Freeman GR, Williams JAG (2013) Top Organomet Chem 40:89
4. Deng H, Yu Z, Dong J, Wu S (2005) Organometallics 24:4110
5. Wang L, Liu T (2018) Chin J Catal 39:327
C53(H53), C57(H57); secondary CH refined with rid-
2
ing coordinates: C13(H13A,H13B), C14(H14A,H14B),
C27(H27A,H27B), C46(H46A,H46B); aromatic/amide
H refined with riding coordinates: C2(H2), C3(H3),
C4(H4), C5(H5), C6(H6), C8(H8), C9(H9), C10(H10),
C11(H11), C12(H12), C16(H16), C17(H17), C18(H18),
C19(H19), C20(H20), C22(H22), C23(H23), C24(H24),
C25(H25), C26(H26), C28(H28), C29(H29), C30(H30),
C31(H31), C32(H32), C34(H34), C37(H37), C38(H38),
C39(H39), C45(H45), C48(H48), C49(H49), C50(H50),
C51(H51), C52(H52); idealized Me refined as rotating
group: C60(H60A,H60B,H60C), C61(H61A,H61B,H61C),
C40(H40A,H40B,H40C), C42(H42A,H42B, H42C),
C54(H54A,H54B,H54C), C55(H55A,H55B,H55C),
C56(H56A,H56B,H56C), C58(H58A, H58B,H58C); ide-
alized tetrahedral OH reꢀned as rotating group: O1(H1),
O3(H3A), O4(H4A).
6. Wang Q, Chai H, Yu Z (2017) Organometallics 36:3638
17. Chai H, Liu T, Yu Z (2017) Organometallics 36:4136
1
1
2
2
8. Chai H, Wang Q, Liu T, Yu Z (2016) Dalton Trans 45:17843
9. Wang Q, Wu K, Yu Z (2016) Organometallics 35:1251
0. Chai H, Liu T, Wang Q, Yu Z (2015) Organometallics 34:5278
1. Menéndez-Pedregal E, Vaquero M, Lastra E, Gamasa P, Pizzano
A (2015) Chem Eur J 21:549
2
2. Li K, Niu J-L, Yang M-Z, Li Z, Wu L-Y, Hao X-Q, Song M-P
(
2015) Organometallics 34:1170
2
2
3. Paul B, Chakrabarti K, Kundu S (2016) Dalton Trans 45:11162
4. Shi J, Hu B, Chen X, Shang S, Deng D, Sun Y, Shi W, Yang X,
Chen D (2017) ACS Omega 2:3406
2
5. Toda T, Saitoh K, Yoshinari A, Ikariya T, Kuwata S (2017) Orga-
nometallics 36:1188
2
2
6. Melle P, Manoharan Y, Albrecht M (2018) Inorg Chem 57:11761
7. Shi J, Hu B, Gong D, Shang S, Hou G, Chen D (2016) Dalton
Trans 45:4828
2
2
8. Karthikeyan T, Sankararaman S (2009) Tetrahedron Lett 50:5834
9. Fabbrizzi P, Cicchi S, Brandi A, Sperotto E, van Koten G (2009)
Eur J Org Chem 31:5423
A summary of the most important crystallographic data
is given in Table SI-1. CCDC 1922403-1922405 contain the
supplementary crystallographic data for this paper. These
data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
3
0. Crowley JD, Bandeen PH, Hanton LR (2010) Polyhedron 29:70
31. Wang H, Zhang B, Yan X, Guo S (2018) Dalton Trans 47:528
3
3
3
2. Vicente J, Arcas A, Bautista D, Jones PG (1997) Organometallics
6:2127
3. Clapham SE, Hadzovic A, Morris RH (2004) Coord Chem Rev
1
2
48:2201
4. Bampos N, Field LD, Messerle BA (1993) Organometallics
12:2529
Acknowledgements The authors thank “General Project of Scientiꢀc
Research Program of Beijing Education Commission” (Grant No.
KM201810028007), National Natural Science Foundation of China
35. Wang Q, Chai H, Yu Z (2018) Organometallics 37:584
36. Du W, Wu P, Wang Q, Yu Z (2013) Organometallics 32:3083
37. Du W, Wang L, Wu P, Yu Z (2012) Chem Eur J 18:11550
38. Ye W, Zhao M, Du W, Jiang Q, Wu K, Wu P, Yu Z (2011) Chem
Eur J 17:4737
(
Grant No. 21502122) and Beijing Natural Science Foundation (Grant
No. 2192012) for ꢀnancial support. The author Dr. Shuai Guo also
highly appreciates the support from Yenching Young Scholar Cultiva-
tion Program of Capital Normal University.
39. Wang D, Astruc D (2015) Chem Rev 115:6621
1
3

Transition Metal Chemistry
4
4
0. Bartoszewicz A, Ahlsten N, Martín-Matute B (2013) Chem Eur J
9:7274
1. Li Y-Y, Yu S-L, Shen W-Y, Gao J-X (2015) Acc Chem Res
48. Liu T, Chai H, Wang L, Yu Z (2017) Organometallics 36:2914
49. Fulmer GR, Miller AJM, Sherden NH, Gottlieb HE, Nudelman
A, Stoltz BM, Bercaw JE, Goldberg KI (2010) Organometallics
29:2176
1
4
8:2587
4
4
4
2. Alonso F, Riente P, Yus M (2011) Acc Chem Res 44:379
3. Morris RH (2009) Chem Soc Rev 38:2282
50. Dolomanov OV, Bourhis LJ, Gildea RJ, Howard JAK, Puschmann
H (2009) J Appl Cryst 42:339
4. Farrar-Tobar RA, Tin S, de Vries JG (2018) Organometallics for
Green Catalysis. Topics Organomet Chem 63:193
5. Farrar-Tobar RA, Wei Z, Jiao H, Hinze S, de Vries JG (2018)
Chem Eur J 24:2725
Publisher’s Note Springer Nature remains neutral with regard to
4
jurisdictional claims in published maps and institutional aꢂliations.
4
4
6. Melle P, Albrecht M (2019) Chimia 73:299
7. Horn S, Gandolꢀ C, Albrecht M (2011) Eur J Inorg Chem 18:2863
1
3