Cationic PCP and PCN NHC Core Pincer-Type Mn(I) Complexes: From Synthesis to Catalysis

Article abstract of DOI:10.1021/acs.organomet.0c00717

The coordination chemistry of NHC core pincer-type PCP and PCN ligands with a Mn(I) center was systematically investigated. The reaction of [Mn(CO)5Br] with free carbenes, conveniently prepared from the corresponding imidazolium salts and a strong base, leads to the initial formation of bidentate fac-[MnBr(CO)3(κ2P,C,L)] complexes bearing a pending phosphine or pyridine donor extremity (L), which upon bromide abstraction, afford cationic [Mn(CO)3(κ3P,C,L)](OTf) derivatives exhibiting a meridional or a facial coordinating geometry of tridentate NHC core ligand depending on its relative flexibility. All bi- A nd tridentate Mn(I) complexes were characterized by X-ray diffraction analysis. The impact of the tridentate ligand structure on catalytic performance was illustrated in the Mn-catalyzed hydrogenation of acetophenone revealing fac-[Mn(CO)3(κ3P,C,N)](OTf) based on a 5,6-membered metallacyclic architecture to be the most active, thus evidencing the role of the pyridine arm lability in the catalytic cycle.

Full text of DOI:10.1021/acs.organomet.0c00717

pubs.acs.org/Organometallics
Article
Cationic PCP and PCN NHC Core Pincer-Type Mn(I) Complexes: From
Synthesis to Catalysis
Ruqaya Buhaibeh, Carine Duhayon, Dmitry A. Valyaev,* Jean-Baptiste Sortais,* and Yves Canac*
Cite This: Organometallics 2021, 40, 231−241
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: The coordination chemistry of NHC core pincer-
type PCP and PCN ligands with a Mn(I) center was systematically
investigated. The reaction of [Mn(CO)5Br] with free carbenes,
conveniently prepared from the corresponding imidazolium salts
and a strong base, leads to the initial formation of bidentate fac-
[MnBr(CO)3(κ2P,C,L)] complexes bearing a pending phosphine
or pyridine donor extremity (L), which upon bromide abstraction,
afford cationic [Mn(CO)3(κ3P,C,L)](OTf) derivatives exhibiting a
meridional or a facial coordinating geometry of tridentate NHC
core ligand depending on its relative flexibility. All bi- and
tridentate Mn(I) complexes were characterized by X-ray diffraction
analysis. The impact of the tridentate ligand structure on catalytic
performance was illustrated in the Mn-catalyzed hydrogenation of
acetophenone revealing fac-[Mn(CO)3(κ3P,C,N)](OTf) based on a 5,6-membered metallacyclic architecture to be the most active,
thus evidencing the role of the pyridine arm lability in the catalytic cycle.
series for the cationic [(CNP)Mn(CO)3]+ complex exhibiting
a NHC−amine−phosphine ligand13 and in the bidentate series
INTRODUCTION
Following the early generation of phosphines, N-heterocyclic
■
carbenes (NHCs) have attracted much attention, leading to
remarkable advances in different areas, such as organometallic
chemistry, functional materials, and homogeneous catalysis.1
For catalytic purposes, it is today generally accepted that
NHCs not only are phosphine mimics but also surpass their
phosphine congeners in terms of activity and application
scope.2 On the basis of this knowledge, considerable effort has
been provided to introduce structural diversity, and a large
variety of polydentate NHC ligands3 bearing coordinating
atoms of different nature (N, P, O, and C) have been prepared
improving the efficiency and selectivity of metal complexation.
In particular, NHC-based ligands exhibiting L-type coordinat-
ing extremities such as pyridine4 and phosphine5 donors or X-
type such as phenolate6 and phosphonium ylide7 donors were
notably devised in the bi- and tridentate series naturally
extending the scope of accessible metal fragments.
for the neutral [(CN)Mn(CO)3Br] and [(CP)Mn(CO)3Br]
complexes based on NHC−amine17 and NHC−phosphine18
ligands, respectively.
On the basis of the general structure of bidentate NHC−
phosphine ligand A recently described by our group, we
wondered about the possible impact on catalytic activity of
changing the “spectator” N-mesityl substituent by a donor
group capable of interacting with the metal center. In this
contribution, we turned our attention to the preparation, the
coordinating properties, and the catalytic activity of the novel
NHC core tridentate ligands of type B bearing phosphine and
pyridine donor arms (Scheme 1). In a larger context, this
comparative study also aimed to assess whether the improve-
ment in catalytic performance necessarily involved the design
of more complex architectures, as are pincer systems with
respect to their bidentate versions.
For catalytic applications,8 especially in the field of
hydrogenation,9 Mn-based complexes have recently been the
subject of intensive research, and many platforms have been
developed over last five years. Pincer-type Mn(I) complexes
based on a PNP,10 PNN,11 NNN,12 or CNP13 skeleton were
reported as valuable catalysts for hydrogenation-type reactions.
However, less sophisticated complexes featuring bidentate
PN,14 PP,15 NN,16 CN,17 or CP18 scaffolds were also found to
efficiently catalyze such transformations. In this competitive
area of catalysis, NHC-based ligands have also demonstrated
their high potential as illustrated very recently in the tridentate
Received: November 9, 2020
Published: January 6, 2021
https://dx.doi.org/10.1021/acs.organomet.0c00717
© 2021 American Chemical Society
Organometallics 2021, 40, 231−241
231

Organometallics
pubs.acs.org/Organometallics
Article
moieties into phosphines using the strongly reducing agent
HSiCl3 was found to be nonselective, resulting in partial
reduction of the pyridine nucleus. Gratifyingly, the application
of the alternative organocatalytic protocol19 enabled the
formation of target preligands [7](OTs) and [10](OTs)
isolated in 89 and 86% yield, respectively.
Scheme 1. Representation of Recently Reported Bidentate
NHC-Phosphine Ligand A18 and Related Tridentate NHC
Core Systems B Targeted in This Study
The identity of all preligands was mainly established on the
1
basis of their characteristic 31P, H, and 13C NMR resonances
(Table 1). For imidazolium salts [3](OTs), [6](OTs), and
RESULTS AND DISCUSSION
■
1
Table 1. Selected 31P, H, and 13C NMR Chemical Shifts in
Synthesis and NMR Characterization of NHC-Based
Preligands. The first representative ligand of the family, B-1,
was prepared from N-phosphine oxide substituted imidazole 2
isolated in 70% yield by treating 1H-imidazole 1 with 1.0 equiv
of Ph2P(O)CH2OTs in the presence of K2CO3 in DMSO at 90
°C (Scheme 2, left). The second phosphine oxide arm was
CDCl3 (ppm) for Imidazolium Salts [3](OTs), [4](OTs),
[6](OTs), [7](OTs), [9](OTs), and [10](OTs)
[3]+
[4]+
[6]+
[7]+
[9]+
[10]+
δP
26.5
9.85
138.6
−12.4
9.62
138.1
27.1
10.44
135.6
−11.1
10.59
136.0
27.2
9.95
138.5
−12.2
9.56
137.5
δCH
δCH
Scheme 2. Preparation of Tridentate PCP and PCN
Preligands [4](OTs), [7](OTs), and [10](OTs)
[9](OTs) exhibiting a phosphine oxide moiety, the 31P NMR
spectrum displayed a single signal at δP 26.5−27.2 ppm in the
typical range for such P(V)-based derivatives. As expected, the
31P NMR singlet of N-(phosphino)imidazolium salts [4]-
(OTs), [7](OTs), and [10](OTs) appeared at further upfield
at δP −11.1 to −12.4 ppm, in agreement with the presence of
P(III) donor extremities of alkyl(diphenyl)phosphine nature.
The cationic character of these salts was confirmed by 1H and
13C NMR spectroscopy by the characteristic low field signals of
the CH imidazolium fragment at δH 9.56−10.59 ppm and δCH
136.0−138.6 ppm.
Synthesis and Spectroscopic Characterization of
NHC-Based Mn(I) Complexes. The complexation of
preligands [4](OTs), [7](OTs), and [10](OTs) was envi-
sioned following a strategy developed recently in the case of N-
mesityl substituted NHC−phosphine A (Scheme 1).18 Indeed,
complexes 11, 13/14, and 16 were thus readily obtained from
the corresponding precursors through the sequential addition
of equimolar quantities of KHMDS and [Mn(CO)5Br] in 71,
80, and 60% isolated yield, respectively (Scheme 3).
While only bidentate coordination was observed in all
formed neutral Mn(I) complexes, a notable difference in the
coordination mode was observed between the two ligands B-2
and B-3 bearing a pyridine extremity. From [7](OTs), in
which the pyridine is directly connected to the imidazole core,
two isomeric complexes 13 and 14 in a ca. 1:3 ratio were
evidenced due to the possible formation of two thermodynami-
cally favored five-membered metallacycles upon coordination
of the phosphine or the pyridine arms. By contrast, in the case
of [10](OTs), only bidentate complex 16 resulting from the
concomitant coordination of NHC and PPh2 donor units was
observed, the coordination of pyridine would indeed have led
to a less stable six-membered metallacycle. With the aim of
synthetizing new NHC core tridentate Mn(I) systems, the
access to both neutral [(L3)Mn(CO)2Br] and cationic
[(L3)Mn(CO)3]+Br− complexes was then considered.
Facing the nonselective formation of [(L3)Mn(CO)2Br]
complexes upon CO dissociation under photochemical and
thermal activation of stable bidentate [(κ2P,C,L)Mn(CO)3Br]
species, the latter were treated by a stoichiometric amount of
AgOTf in CH2Cl2 to induce the bromide abstraction and thus
force the coordination of a pendant donor arm. Under these
conditions, air-stable cationic tridentate complexes [12](OTf),
[15](OTf), and [17](OTf) were easily obtained as single
then introduced by the alkylation of imidazole 2 with the same
tosylate precursor in toluene at 130 °C, allowing bis(N-
phosphine oxide)imidazolium salt [3](OTs) to be isolated in
87% yield. The reduction of the latter under classic conditions
(excess of HSiCl3 in chlorobenzene at 80 °C)5b,18 led to target
bis(N-phosphino)imidazolium salt [4](OTs) in ca. 80% yield.
The formation yield of this product can be improved to 89%
by organocatalytic reduction approach19 by heating [3](OTs)
in toluene at 110 °C with an excess of PhSiH3 in the presence
of bis(4-nitrophenyl)phosphate.
PCN ligands B-2 (Scheme 2, middle) and B-3 (Scheme 2,
right) were prepared from readily available N-pyridyl 520 and
N-pyridylmethyl 821 substituted imidazoles following the same
two-step strategy. In the first step, imidazolium salts [6](OTs)
and [9](OTs) featuring phosphine oxide arms were prepared
in 90 and 87% yield, respectively, upon solvent-free
quaternization of the corresponding imidazoles with Ph2P(O)-
CH2OTs. In both cases, the transformation of phosphine oxide
232
https://dx.doi.org/10.1021/acs.organomet.0c00717
Organometallics 2021, 40, 231−241

Organometallics
pubs.acs.org/Organometallics
Article
exhibited three strong νCO bands consistent with the presence
of three CO ligands in a facial arrangement. The small
differences observed between these frequency values seem to
indicate that the three ligands of interest have similar electronic
properties. In the tridentate series, complexes [12](OTf),
[15](OTf), and [17](OTf) featured three νCO bands with
different relative intensities (Table 2) suggesting two distinct
CO ligand arrangements.
Scheme 3. Syntheses of Cationic NHC Core Tridentate
Mn(I) Complexes [12](OTf), [15](OTf), and [17](OTf)
from Corresponding PCP [4](OTs) and PCN Ligand
Precursors [7](OTs) and [10](OTs)
Complementary to these IR frequency values, 13C NMR
data revealed for complexes [12](OTf) and [15](OTf) the
presence of two CO resonances ([12](OTf): δC 220.7 (brt, JPC
= 10.5 Hz), 213.6 (brt, JPC = 19.0 Hz); [15](OTf): δC 218.4
(d, JPC = 9.7 Hz), 212.7 (d, JPC = 17.7 Hz)) and three
resonances for [17](OTf) (δC 219.6 (brd, JPC = 25.5 Hz),
218.7 (d, JPC = 18.5 Hz)), 216.9 (d, JPC = 23.5 Hz)), indicating
for the latter a lower molecular symmetry than for the two
former complexes and suggesting that the NHC core backbone
is a priori coordinated to the metal center in a meridional
fashion within complexes [12](OTf) and [15](OTf) and
rather adopts a tripodal coordination mode in [17](OTf).
X-ray Diffraction Structural Studies of Bidentate and
Tridentate NHC-Based Mn(I) Complexes. Single-crystal X-
ray diffraction studies allowed us to establish the solid-state
structures of imidazolium salt [4](OTs) (Figure S1), neutral
bidentate Mn(I) complexes 13, 14, and 16 (Figure 1, upper
line), and their cationic tridentate congeners ([12](OTf),
[15](OTf) and [17](OTf), Figure 1, lower line). The most
important metrical data are presented in Table 3. In all
complexes, the hexacoordinate Mn(I) atom resides in a
distorted octahedral environment. As anticipated by NMR
and IR spectroscopy, three carbonyl coligands adopt a facial
arrangement in all bidentate representatives. In the tridentate
series, complexes [12](OTf) and [15](OTf) can be regarded
as real pincers exhibiting the meridional coordination of the
NHC core ligand with two CO coligands positioned in trans
with respect to each other, while in [17](OTf) the PCN
backbone acts as a tripodal ligand with the three CO coligands
located cis to each other. Though such a fac-arrangement is
less common for [Mn(CO)3(L3)]+ complexes, several
examples based on pincer-type PNP,24 CNP,13 NNN,12,25
NNS,26 and NSN27 ligands have been recently reported.
In the pincer systems, the two coordinating heteroatoms are
positioned in a pseudo-trans position with respect to the metal
center ([12](OTf): P1−Mn1−P2 = 160.148(14); [15](OTf):
P1−Mn1−N3 = 153.76(4)°) as opposed to that in tripodal
isomers in 88, 76, and 96% yield, respectively. These
compounds are rare examples of NHC-containing manganese
pincer-type complexes13,22,23 and constitute the first proto-
types based on NHC core L3-type ligand scaffolds.
The most pertinent spectroscopic data for the Mn(I) NHC
complexes are presented in Table 2. The formation of Mn(I)
1
NHC complexes was clearly indicated by H and 13C NMR
spectroscopy showing the disappearance of the C−H
imidazolium signals of preligands [4](OTs), [7](OTs), and
[10](OTs). Regardless of their coordination mode, in the 13C
NMR spectra, the N2C−Mn carbon atoms of NHC core
complexes (δN2C 195.6−206.5 ppm) were typically found to be
strongly deshielded with proper multiplicity with respect to the
N2CH carbon atoms of corresponding precursors (δCH 136.0−
138.6 ppm). The coordination of the N-substituted NHC−
phosphine moiety was also apparent from the downfield shift
of the 31P NMR resonances, ranging from δP −(11.1−12.4)
ppm in the preligands to δP 71.0−71.8 ppm in the bidentate
complexes and δP 89.6−97.4 ppm in their tridentate analogues.
Solution IR spectra of all bidentate NHC Mn(I) complexes
Table 2. Selected 31P and 13C NMR Chemical Shifts in CD2Cl2 (ppm), and IR νCO Frequencies in THF Solution (cm−1) for
NHC-Based Mn(I) Complexes of Bidentate (11, 13, 14, and 16) and Tridentate ([12](OTf), [15](OTf), and [17](OTf))
a
Nature
b
c
11
[12](OTf)
89.6 (s)
13
71.8 (s)
14
[15](OTf)
16
71.2 (s)
[17](OTf)
93.3 (s)
71.0 (s)
δP
−15.9 (s)
97.4 (s)
−17.0 (s)
δN2C
197.1 (d, 16.5)
222.9 (d, 17.8)
221.4 (d, 31.0)
220.1 (d, 21.5)
2015 (s)
195.6 (t, 13.1)
220.7 (brt, 10.5)
213.6 (brt, 19.0)
198.1 (d, 15.1)
223.9 (d, 18.2)
220.2 (d, 18.2)
218.5 (d, 32.3)
2016 (s)
206.0 (s)
226.4 (s)
221.3 (s)
218.0 (s)
2016 (s)
1930 (s)
1907 (s)
206.5 (d, 18.9)
218.4 (d, 9.7)
212.7 (d, 17.7)
197.7 (d, 17.5)
222.8 (brd, 16.8)
220.8 (brd, 30.1)
220.2 (brd, 20.8)
2018 (s)
202.9 (d, 22.3)
219.6 (brd, 25.5)
218.7 (brd, 18.5)
216.9 (brd, 23.5)
2024 (s)
δCO
2045 (w)
1966 (vs)
1942 (s)
2052 (w)
1969 (vs)
1941 (s)
νCO
1940 (s)
1910 (s)
1939 (s)
1904 (s)
1941 (s)
1913 (s)
1947 (s)
1929 (s)
a
For 31P and 13C NMR chemical shifts, signal multiplicity and JCP coupling constants (Hz) are given in parentheses, and for IR νCO frequencies,
b
c
relative intensity is given in parentheses. IR νCO frequencies were measured in a toluene solution. NMR data was recorded in CDCl3.
233
https://dx.doi.org/10.1021/acs.organomet.0c00717
Organometallics 2021, 40, 231−241

Organometallics
pubs.acs.org/Organometallics
Article
Figure 1. Perspective views of bidentate (13, 14, and 16, upper line) and tridentate ([12](OTf), [15](OTf), and [17](OTf), lower line) Mn(I)
NHC complexes with thermal ellipsoids drawn at the 30% probability level. The hydrogen atoms are omitted for clarity.
Table 3. Selected Bond Lengths (Å) and Bond Angles (deg) for Bidentate and Tridentate Mn(I) NHC Complexes
Complex
13
14
16
[12](OTf)
[15](OTf)
[17](OTf)
C1−Mn1
P1−Mn1
P2−Mn1
2.054(2)
2.3175(7)
1.993(2)
2.049(3)
2.2861(9)
1.9726(12)
2.2627(3)
2.2661(3)
1.9360(16)
2.2712(5)
1.9881(11)
2.3348(3)
N3−Mn1
Mn1−Br
2.0753(17)
2.5354(4)
2.0894(14)
78.15(5)
2.1095(9)
75.16(6)
82.90(4)
91.92(3)
2.5510(5)
79.02(7)
2.5527(5)
79.95(9)
C1−Mn1−P1
C1−Mn1−P2
C1−Mn1−N3
P1−Mn1−P2
P1−Mn1−N3
79.88(4)
80.30(4)
78.17(8)
75.67(6)
160.148(14)
153.76(4)
complex [17](OTf), where the related coordination angle is
much more acute (P1−Mn1−N3 = 91.92(3)°). As generally
observed in mer-Mn(I) complexes, the C−O distances in the
mutually trans CO ligands are shorter ([12](OTf):
1.1407(17), 1.1383(17) Å; [15](OTf): 1.139(2), 1.138(2)
Å) than in the CO trans to the ligand, in this case, the NHC
core ([12](OTf): 1.1423(16) Å; [15](OTf): 1.151(2) Å).28
PCP and PCN pincer structures [12](OTf) and [15](OTf)
are defined by the presence of two fused 5-membered
metallacycles with the PCP backbone in the former symmetri-
cally linked to Mn through two quasi-equal P−Mn bonds
(2.2627(3) and 2.2661(3) Å). The facial geometry observed in
[17](OTf) can be rationalized by the presence of a longer
lateral chain which offers more flexibility accommodating the
formation of a six-membered metallacycle upon pyridine
coordination.29 As general trend, the Mn−NHC bond
distances are significantly shortened in the tridentate systems
compared to their bidentate precursors, a difference that may
be attributed to the more constrained geometries and the
cationic nature of the pincer-type complexes. It is noteworthy,
that the Mn-carbene bond in pincer complex [15](OTf)
(1.9360(16) Å) is significantly shorter than that observed in
binuclear [Mn2(CO)7(PCN)] complex bearing structurally
close tridentate PCN ligand in the bridging μ-κ2C,N-M;κ1P-M-
coordination mode (1.9700(17) Å)30 and indeed represents
one of the shortest distance known to date for manganese
imidazol-2-ylidene complexes.31 Since a similar trend was
previously observed for related Ni(II) complex,4d it may be
assumed that the rigid character of such PCN ligands forming
two five-membered metallacycles is particularly favorable to
strengthen metal−NHC bonding.
Catalytic Investigations. On the basis of the recent
observation that a Mn(I) complex of bidentate NHC−
phosphine ligand A behaves as one of the most efficient Mn-
based catalytic systems for the hydrogenation of ketones,18 this
transformation was naturally selected to evaluate the influence
of an additional coordinating arm. For such comparative study,
three pincer-type complexes were considered: [12](OTf),
[15](OTf), and [17](OTf), differing only by the nature of one
donor end. The catalytic tests were performed under H2
pressure (50 bar) in t-AmOH at 60 or 100 °C and in the
presence of 10 mol % t-BuOK (Table 4). Gratifyingly at 100
°C, in the presence of 1.0 mol % [17](OTf), acetophenone
was fully reduced to 1-phenylethanol (entry 9). The catalytic
charge could be decreased to 0.5 mol % at the same
temperature keeping a good conversion of 80% (entry 10).
234
https://dx.doi.org/10.1021/acs.organomet.0c00717
Organometallics 2021, 40, 231−241

Organometallics
pubs.acs.org/Organometallics
Article
Table 4. Catalytic Hydrogenation of Acetophenone with
NHC Core Mn(I) Complexes [12](OTf), [15](OTf), and
[17](OTf)
CONCLUSION
■
A family of cationic NHC−phosphine Mn(I) pincer-type
complexes [Mn(CO)3(κ3P,C,L])(OTf) with a variable third
donor extremity were efficiently prepared from the readily
available imidazolium salts by a sequence of free NHCs
coordination to [Mn(CO)5Br] and bromide abstraction in the
resulting bidentate complexes fac-[MnBr(CO)3(κ2P,C,L)].
The complete series of bi- and tridentate Mn(I) species have
been fully characterized and systematically studied by X-ray
diffraction analysis revealing in particular two different
coordination modes for the nonsymmetrical PCN ligands in
complexes mer-[Mn(CO)3(κ3P,C,N)](OTf) ([15](OTf)) and
fac-[Mn(CO)3(κ3P,C,N)](OTf) ([17](OTf)) rationalized by
the higher flexibility of ligand with CH2Py extremity in the
latter case. The evaluation of these compounds in catalytic
hydrogenation of acetophenone revealed the fac-[Mn-
(CO)3(κ3P,C,N)(OTf) precatalyst to be the most active
system, the efficiency of which was attributed to the presence
of a 5,6-fused membered architecture promoting the
dissociation of the pyridine arm and thereby releasing a vacant
site beneficial to the catalytic process. Future studies will aim
to engage these Mn(I) complexes in other catalytic processes,
but also to implant this new class of NHC core pincer-type
ligands on different transition metal centers.
a
b
entry
complex
cat. (mol %)
temp. (°C)
conv. %
1
2
3
4
5
6
7
8
[12](OTf)
[12](OTf)
[12](OTf)
[12](OTf)
[15](OTf)
[15](OTf)
[15](OTf)
[15](OTf)
[17](OTf)
[17](OTf)
[17](OTf)
[17](OTf)
11
1.0
0.5
1.0
0.5
1.0
0.5
1.0
0.5
1.0
0.5
1.0
0.5
1.0
1.0
1.0
100
100
60
27
19
6
3
39
21
22
11
100 (95)
80
30
20
42
60
100
100
60
60
9
100
100
60
10
11
12
13
14
15
EXPERIMENTAL SECTION
■
60
General Remarks. All manipulations were performed under an
inert atmosphere of dry nitrogen by using standard vacuum line and
Schlenk tube techniques. Glassware was dried at 120 °C in an oven
for at least 3 h. Dry and oxygen-free organic solvents (THF, Et2O,
CH2Cl2, toluene, and pentane) were obtained using a LabSolv
(Innovative Technology) solvent purification system. Acetonitrile was
dried and distilled over P2O5 under argon. Chromatographic
purification was carried out on silica gel (SiO2, 63−200 μm) and
activated basic alumina (Brockmann I). 1H, 31P, and 13C NMR
spectra were obtained on Bruker AV300, AV400, or NEO600
spectrometers. NMR chemical shifts δ are in ppm, with positive values
100
100
100
14
16
33
98
a
Procedure: An autoclave was charged with a precatalyst,
acetophenone (1.0 mmol), t-BuOK (10 mol %) in t-AmOH (2
b
mL) under H2 (50 bar) at 60 or 100 °C. Conversions determined by
1
GC and H NMR; isolated yield is given in parentheses.
1
to high frequency relative to the tetramethylsilane reference for H
At 60 °C, the alcohol was produced in lower yields with
conversions of 30 and 20% by using 1.0 and 0.5 mol %
[17](OTf), respectively (entries 11 and 12). Notably, no
reaction took place in the absence of base. The two other
selected complexes were found to be significantly less active in
this process. For instance, at 100 °C, with a catalytic charge of
1.0 mol % precatalysts [12](OTf) and [15](OTf), the
acetophenone was only converted into the corresponding
alcohol in 27 and 39% yields, respectively (entries 1 and 5).
The superiority of fac-complex [17](OTf) was tentatively
attributed to the presence of a six-membered metallacycle
resulting in greater lability of the pyridine arm and thus
allowing the release of a vacant site during the catalytic cycle.13
The lability of a donor extremity was also supported in other
systems by the catalytic activities of bidentate complexes 11,
14, and 16 which were found to be very close to those
obtained with their corresponding tridentate forms, [12]-
(OTf), [15](OTf), and [17](OTf) (entries 13−15). These
results suggest that the same type of catalytic active species is
certainly involved in both series. Notably, the performance of
complex [17](OTf) remains lower than that of the parent
complex based on bidentate NHC−phosphine ligand A,18
showing that the development of more elaborate structures is
not always a prerequisite to reach higher activities in the field
of catalysis.
and 13C and to 85% H3PO4 for 31P. If necessary, then additional
information on the carbon signal attribution was obtained using
13C{1H, 31P}, J-modulated spin−echo (JMOD) 13C{1H}, 1H−13C
HMQC, and/or HMBC experiments. Solution IR spectra were
recorded in 0.1 mm CaF2 cells using a PerkinElmer Frontier FT-IR
spectrometer and given in cm−1 with relative intensity in parentheses.
GC analyses were performed with GC-2014 (Shimadzu) 2010
equipped with a capillary column (Supelco, SPBTM-20, fused silica
capillary column, 30 m × 0.25 mm × 0.25 mm film thickness). High-
resolution mass spectra (ESI positive mode) were obtained using a
Xevo G2 QTof (Waters) spectrometer. Elemental analyses were
carried out at the LCC−CNRS (Toulouse) using a PerkinElmer 2400
series II analyzer. Nonstirred “Autoclave Maxitech” autoclaves (50
mL) were used for the hydrogenation. Ph2P(O)CH2OTs,18 2-(1H-
imidazol-1-yl)pyridine 5,20 and 2-(1H-imidazol-1-yl-methyl)pyridine
821 were prepared according to known methods. All other reagent-
grade chemicals purchased from commercial sources were used as
received.
Synthesis of Ph2P(O)CH2Im (2). A Schlenk tube was charged
with Ph2P(O)CH2OTs (4.0 g, 10.4 mmol), 1H-imidazole (0.71 g,
10.4 mmol), and K2CO3 (9.67 g, 70.0 mmol) under an air
atmosphere. After addition of DMSO (40 mL), the suspension was
vigorously stirred at 90 °C for 24 h. The reaction mixture was cooled
to 50 °C, and DMSO was removed under reduced pressure. The solid
residue was dissolved in CHCl3 (20 mL), the solution was washed
several times with H2O, dried over MgSO4 and evaporated under
reduced pressure. The resulting solid was washed with Et2O (20 mL)
and dried under vacuum to afford 2 as a white powder (1.98 g, 70%).
235
https://dx.doi.org/10.1021/acs.organomet.0c00717
Organometallics 2021, 40, 231−241

Organometallics
pubs.acs.org/Organometallics
Article
1H NMR (400 MHz, CDCl3, 25 °C): δ 7.70−7.65 (m, 4H, CHPh),
7.61−7.57 (m, 2H, CHPh), 7.52−7.47 (m, 4H, CHPh), 7.30 (brs, 1H,
CHIm‑2), 6.96 (brs, 1H, CHIm‑4,5), 6.91 (brs, 1H, CHIm‑4,5), 4.77 (d,
7.47−7.39 (m, 6H, CHAr), 7.32−7.28 (m, 1H, CHAr), 7.08 (d, JHH =
7.8 Hz, 2H, CHTs), 5.75 (d, JPH = 6.3 Hz, 2H, P(O)CH2), 2.27 (s,
3H, CH3Ts). 31P{1H} NMR (162 MHz, CDCl3, 25 °C): δ 27.1 (s).
13C{1H} NMR (101 MHz, CDCl3, 25 °C): δ 148.8 (s, CHPy), 145.7
J
PH = 4.5 Hz, 2H, CH2). 31P{1H} NMR (162 MHz, CDCl3, 25 °C): δ
25.7 (s). 13C{1H} NMR (101 MHz, CDCl3, 25 °C): δ 137.9 (brs,
CHIm‑2), 132.9 (d, JPC = 2.5 Hz, CHPh), 131.2 (d, JPC = 9.5 Hz, CHPh),
(s, CPy), 143.3 (s, CTs), 140.5 (s, CHPy), 139.5 (s, CTs), 135.6 (d, JPC =
2.6 Hz, CHIm‑2), 133.0 (d, JPC = 2.6 Hz, CHPh), 131.3 (d, JPC = 9.9
Hz, CHPh), 129.2 (d, JPC = 12.5 Hz, CHPh), 128.7 (s, CHTs), 127.9 (d,
JPC = 103.6 Hz, CipsoPh), 125.9 (s, CHTs), 125.0 (s, CHPy), 124.3 (s,
CHPy), 118.6 (s, CHIm‑4,5), 114.4 (s, CHIm‑4,5), 49.2 (d, JPC = 66.5 Hz,
P(O)CH2), 21.3 (s, CH3Ts). Anal. Found: C, 61.26; H, 4.87; N, 7.76.
Calcd (%) for C28H26N3O4PS. 0.25 (CH2Cl2): C, 61.38; H, 4.83; N,
7.60. MS (ES+): m/z: 360.1 [M]+. HRMS (ES+): calcd for
C21H19N3OP+ 360.1266. Found: 360.1266 (εr = 0.0 ppm).
129.7 (s, CHIm‑4,5), 129.1 (d, JPC = 103.7 Hz, CipsoPh), 129.0 (d, JPC
=
18.0 Hz, CHPh), 120.3 (s, CHIm‑4,5), 47.8 (d, JPC = 73.9 Hz, CH2).
Anal. Found: C, 65.58; H, 5.63; N, 9.48. Calcd (%) for C16H15N2OP.
0.25 (DMSO): C, 65.66; H, 5.51; N, 9.28. MS (ES+): m/z: 283.1 [M
+ H]+. HRMS (ES+): calcd for C16H16N2OP+ 283.1000. Found:
283.1006 (εr = 2.1 ppm).
Synthesis of [(Ph2P(O)CH2)2Im](OTs), [3](OTs). A mixture of 2
(1.26 g, 4.5 mmol) and Ph2P(O)CH2OTs (1.70 g, 4.5 mmol) was
heated under stirring in toluene (5 mL) at 130 °C for 16 h. After
cooling to room temperature, the light-brown solid formed was
dissolved in CH2Cl2 (5 mL), and then Et2O (50 mL) was added. The
resulting precipitate was triturated with Et2O (20 mL) until the
formation of a white powder (ca. 30 min). The supernatant was then
removed by decantation and the precipitate was washed with Et2O
(10 mL) and dried under vacuum to afford [3](OTs) as a white
powder (2.6 g, 87%). 1H NMR (400 MHz, CDCl3, 25 °C): δ 9.85 (s,
1H, CHIm‑2), 7.82−7.77 (m, 10H, CHAr), 7.48−7.42 (m, 6H, CHAr),
7.34−7.30 (m, 8H, CHAr), 7.08 (d, JHH = 7.8 Hz, 2H, CHTs), 5.28 (d,
JPH = 6.3 Hz, 4H, CH2), 2.30 (s, 3H, CH3Ts). 31P{1H} NMR (162
MHz, CDCl3, 25 °C): δ 26.5 (s). 13C{1H} NMR (101 MHz, CDCl3,
25 °C): δ 143.6 (s, CTs), 139.6 (s, CTs), 138.6 (s, CHIm‑2), 133.0 (d,
Synthesis of [Ph2PCH2ImPy](OTs), [7](OTs). A dried Schlenk
tube containing a stirring bar was charged with bis(4-nitrophenyl)
phosphate (128 mg, 0.38 mmol) and [6](OTs) (2.0 g, 3.8 mmol)
under N2 flow. Dry toluene (40 mL) and PhSiH3 (1.9 mL, 15 mmol)
were added. The mixture was stirred at 140 °C for 16 h and cooled to
room temperature, and the volatiles were removed under vacuum.
The resulting solid was dissolved in degassed CH2Cl2 (5 mL) and
then degassed Et2O (50 mL) was added. The resulting precipitate was
washed with degassed Et2O (20 mL) and dried under vacuum to
afford [7](OTs) as a beige powder (1.7 g, 89%). 1H NMR (600 MHz,
CDCl3, 25 °C): δ 10.59 (s, 1H, CHIm‑2), 8.40 (d, J = 4.5 Hz, 1H,
CHAr), 8.26 (d, J = 8.2 Hz, 1H, CHAr), 8.08 (s, 1H, CHAr), 7.90−7.88
(m, 1H, CHAr), 7.79 (d, JHH = 7.8 Hz, 2H, CHTs), 7.54−7.51 (m, 4H,
CHAr), 7.37−7.32 (m, 7H, CHAr), 7.22 (s, 1H, CHAr), 7.09 (d, JHH
=
7.8 Hz, 2H, CHTs), 5.34 (d, JPH = 5.3 Hz, 2H, P(O)CH2), 2.30 (s,
3H, CH3Ts). 31P{1H} NMR (162 MHz CDCl3, 25 °C): δ −11.1 (s).
13C{1H} NMR (151 MHz, CDCl3, 25 °C): δ 148.9 (s, CHPy), 146.0
(s, CPy), 143.6 (s, CTs), 140.8 (s, CHPy), 139.5 (s, CTs), 136.0 (s,
CHIm‑2), 133.4 (d, JPC = 19.8 Hz, CHPh), 132.9 (d, JPC = 12.0 Hz,
CipsoPh), 130.3 (s, CHPh), 129.3 (d, JPC = 7.3 Hz, CHPh), 128.8 (s,
CHTs), 126.1 (s, CHTs), 125.0 (s, CHPy), 122.7 (s, CHPy), 118.7 (s,
CHIm‑4,5), 115.0 (s, CHIm‑4,5), 49.7 (d, JPC = 21.9 Hz, PCH2), 21.4 (s,
CH3Ts). Anal. Found: C, 61.43; H, 4.91; N, 7.31. Calcd (%) for
C28H26N3O3PS. 0.50 (CH2Cl2): C, 61.34; H, 4.88; N, 7.53. MS
(ES+): m/z: 344.1 [M]+. HRMS (ES+): calcd for C21H19N3P+
344.1317. Found: 344.1317 (εr = 0.0 ppm).
JPC = 2.0 Hz, CHPh), 131.3 (d, JPC = 9.9 Hz, CHPh), 129.2 (d, JPC
=
12.5 Hz, CHPh), 128.8 (s, CHTs), 127.9 (d, JPC = 103.8 Hz, CipsoPh),
126.0 (s, CHTs), 123.2 (s, CHIm‑4,5), 48.6 (d, JPC = 66.0 Hz, CH2),
21.4 (s, CH3Ts). Anal. Found: C, 59.71; H, 4.97; N, 3.84. Calcd (%)
for C36H34N2O5P2S. 0.85 (CH2Cl2): C, 59.74; H, 4.86; N, 3.78. MS
+
(ES+): m/z: 497.1 [M]+. HRMS (ES+): calcd for C29H27N2O2P2
497.1548. Found: 497.1534 (εr = 2.8 ppm).
Synthesis of [(Ph2PCH2)2Im](OTs), [4](OTs). A Schlenk tube
was charged with bis(4-nitrophenyl)phosphate (408 mg, 1.2 mmol)
and [3](OTs) (4.0 g, 6.0 mmol) under N2 flow. Dry toluene (40 mL)
and PhSiH3 (6 mL, 48 mmol) were added, and the mixture was
stirred at 110 °C for 16 h. After cooling to room temperature, the
volatiles were removed under vacuum. The resulting solid was
dissolved in degassed CH2Cl2 (10 mL), and then degassed Et2O was
added (100 mL). The resulting precipitate was washed with degassed
Et2O (30 mL) and dried under vacuum to afford [4](OTs) as a beige
powder (3.4 g, 89%). Single crystals suitable for XRD were obtained
by slow evaporation of a concentrated CH2Cl2 solution at room
Synthesis of [Ph2P(O)CH2ImCH2Py](OTs), [9](OTs). A mixture
of 8 (1.98 g, 12.4 mmol) and Ph2P(O)CH2OTs (4.00 g, 10.4 mmol)
was heated under stirring at 140 °C for 16 h. After cooling to room
temperature, the brown solid formed was dissolved in CH2Cl2 (5
mL), and then Et2O (100 mL) was added. The resulting precipitate
was triturated with Et2O (30 mL) until the formation of a white/
brown powder (ca. 30 min). The supernatant was removed by
decantation and the precipitate was washed with Et2O (10 mL) and
dried under vacuum to afford [9](OTs) (4.8 g, 87%) as very
1
temperature. H NMR (400 MHz, CDCl3, 25 °C): δ 9.62 (s, 1H,
CHIm‑2), 7.79 (d, JHH = 8.1 Hz, 2H, CHTs), 7.43−7.30 (m, 20H,
CHPh), 7.10 (d, JHH = 7.9 Hz, 2H, CHTs), 6.88 (brs, 2H, CHIm‑4,5),
4.92 (d, JPH = 5.5 Hz, 4H, CH2), 2.31 (s, 3H, CH3Ts). 31P{1H} NMR
(162 MHz, CDCl3, 25 °C): δ −12.4 (s). 13C{1H} NMR (101 MHz,
CDCl3, 25 °C): δ 143.9 (s, CTs), 139.3 (s, CTs), 138.1 (s, CHIm‑2),
133.1 (d, JPC = 19.8 Hz, CHPh), 133.0 (d, JPC = 13.1 Hz, CipsoPh), 130.2
(s, CHPh), 129.3 (d, JPC = 7.0 Hz, CHPh), 128.7 (s, CHTs), 126.2 (s,
CHTs), 121.9 (d, JPC = 4.2 Hz, CH Im‑4,5), 48.9 (d, JPC = 21.1 Hz,
CH2), 21.4 (s, CH3Ts). Anal. Found: C, 65.83; H, 5.19; N, 4.25. Calcd
(%) for C36H34N2O3P2S. 0.30 (CH2Cl2): C, 65.84; H, 5.27; N, 4.23.
1
hygroscopic brown crystals. H NMR (400 MHz, CDCl3, 25 °C): δ
9.95 (s, 1H, CHIm‑2), 8.43 (d, J = 4.8 Hz, 1H, CHAr), 7.97−7.88 (m,
4H, CHAr), 7.79 (d, JHH = 7.7 Hz, 2H, CHTs), 7.65 (s, 1H, CHAr),
7.63−7.58 (m, 1H, CHAr), 7.51−7.45 (m, 2H, CHAr), 7.43−7.35 (m,
4H, CHAr), 7.36−7.29 (m, 2H, CHAr), 7.24−7.19 (m, 1H, CHAr),
7.12 (d, JHH = 7.8 Hz, 2H, CHTs), 5.46 (d, JPH = 6.2 Hz, 2H,
P(O)CH2), 5.33 (s, 2H, PyCH2), 2.32 (s, 3H, CH3Ts). 31P{1H} NMR
(162 MHz, CDCl3, 25 °C): δ 27.2 (s). 13C{1H} NMR (101 MHz,
CDCl3, 25 °C): δ 152.3 (s, CPy), 149.9 (s, CHPy), 143.5 (s, CTs),
139.6 (s, CTs), 138.5 (d, JPC = 2.3 Hz, CHIm‑2), 137.7 (s, CHPy), 133.1
(d, JPC = 2.3 Hz, CHPh), 131.4 (d, JPC = 10.0 Hz, CHPh), 129.3 (d, JPC
= 12.5 Hz, CHPh), 128.8 (s, CHTs), 127.9 (d, JPC = 103.3 Hz, CipsoPh),
126.0 (s, CHTs), 124.0 (s, CHPy), 123.5 (s, CHPy), 123.4 (s, CHIm‑4,5),
122.3 (s, CHIm‑4,5), 54.3 (s, PyCH2), 48.9 (d, JPC = 66.0 Hz, P(O)
CH2), 21.4 (s, CH3Ts). Anal. Found: C, 61.20; H, 5.02; N, 7.64. Calcd
(%) for C29H28N3O4PS. 0.35 (CH2Cl2): C, 61.27; H, 5.03; N, 7.30.
MS (ES+): m/z: 374.1 [M]+. HRMS (ES+): calcd for C22H21N3OP+
374.1422. Found: 374.1431 (εr = 2.4 ppm).
+
MS (ES+): m/z: 465.1 [M]+. HRMS (ES+): calcd for C29H27N2P2
465.1649. Found: 465.1648 (εr = 0.2 ppm).
Synthesis of [Ph2P(O)CH2ImPy](OTs), [6](OTs). A mixture of 5
(0.68 g, 4.7 mmol) and Ph2P(O)CH2OTs (1.5 g, 3.9 mmol) was
heated under stirring at 150 °C for 16 h. After cooling to room
temperature, the resulting brown solid was dissolved in CH2Cl2 (5
mL), and then Et2O (100 mL) was added. The resulting precipitate
was triturated with Et2O (30 mL) until the formation of a white
powder (ca. 30 min). The supernatant was removed by decantation,
and the precipitate was washed with Et2O (10 mL) and dried under
vacuum to afford [6](OTs) as a very hygroscopic white powder (1.8
g, 90%). 1H NMR (400 MHz, CDCl3, 25 °C): δ 10.44 (s, 1H,
CHIm‑2), 8.34 (d, JHH = 4.6 Hz, 1H, CHAr), 8.08 (s, 1H, CHAr), 7.99−
7.94 (m, 5H, CHAr), 7.86 (s, 1H, CHAr), 7.79−7.82 (m, 3H, CHAr),
Synthesis of [Ph2PCH2ImCH2Py](OTs), [10](OTs). A Schlenk
tube was charged with bis(4-nitrophenyl) phosphate (180 mg, 0.53
mmol) and [9](OTs) (2.8 g, 5.3 mmol) under N2 flow. Dry toluene
(30 mL) and PhSiH3 (2.6 mL, 21 mmol) were added, and the mixture
236
https://dx.doi.org/10.1021/acs.organomet.0c00717
Organometallics 2021, 40, 231−241

Organometallics
pubs.acs.org/Organometallics
Article
+
was stirred at 110 °C for 16 h. After cooling to room temperature, the
volatiles were removed under vacuum. The solid residue was dissolved
in degassed CH2Cl2 (5 mL), and then degassed Et2O was added (50
mL). The precipitate formed was washed with degassed Et2O (20
mL) and dried under vacuum to afford [10](OTs) (2.4 g, 86%) as
603.1 [M]+. HRMS (ES+): calcd for C32H26MnN2O3P2 603.0799.
Found: 603.0816 (εr = 2.8 ppm).
Synthesis of PCN Bidentate Complexes 13 and 14. To a
stirred suspension of [7](OTs) (0.20 g, 0.39 mmol) in THF (30 mL)
was added a solution of KHMDS (0.5 M in toluene, 0.9 mL, 0.43
mmol) at room temperature, and then the resulting brown suspension
was sonicated during 5 min and stirred for additional 5 min. Solid
[Mn(CO)5Br] (0.11 g, 0.39 mmol) was added in one portion
inducing a vigorous CO evolution. The resulting orange solution was
then stirred for 15 min at room temperature. After filtration through
Celite and evaporation of the solvent under vacuum, a mixture of two
complexes 13 and 14 in a 1:3 ratio was obtained as yellow-orange
powder (0.16 g, 80%). The crude residue was recrystallized in THF/
Et2O mixture affording complex 14 as a yellow-orange powder (0.11
g, 51%). Single crystals for both complexes suitable for XRD were
obtained by slow evaporation of CH2Cl2 solutions at room
temperature. MS (ES+): m/z: 562.0 [M + H]+. HRMS (ES+): calcd
for C24H19MnBrN3O3P+ 561.9728. Found: 561.9730 (εr = 0.4 ppm).
The NMR and IR data of complex 13 were deduced from the 13/14
mixture.
1
very hygroscopic brown crystals. H NMR (400 MHz, CDCl3, 25
°C): δ 9.56 (s, 1H, CHIm‑2), 8.37 (d, J = 4.8 Hz, 1H, CHAr), 7.74 (d,
JHH = 7.7 Hz, 2H, CHTs), 7.55−7.52 (m, 1H, CHAr), 7.44 (s, 1H,
CHAr), 7.39−7.36 (m, 5H, CHAr), 7.30−7.20 (m, 6H, CHAr), 7.18−
7.10 (m, 2H, CHAr), 7.04 (d, JHH = 7.7 Hz, 2H, CHTs), 5.36 (s, 2H,
PyCH2), 4.95 (d, JPH = 5.4 Hz, 2H, PCH2), 2.26 (s, 3H, CH3Ts).
31P{1H} NMR (162 MHz, CDCl3, 25 °C): δ −12.2 (s). 13C{1H}
NMR (101 MHz, CDCl3, 25 °C): δ 152.6 (s, CPy), 149.5 (s, CHPy),
143.9 (s, CTs), 139.0 (s, CTs), 137.5 (s, CHIm‑2), 137.3 (s, CHPy),
133.0 (d, JPC = 19.4 Hz, CHPh), 132.9 (d, JPC = 11.4 Hz, CipsoPh), 129.9
(s, CHPh), 128.9 (d, JPC = 7.4 Hz, CHPh), 128.5 (s, CHTs), 125.9 (s,
CHTs), 123.5 (s, CHPy), 123.4 (s, CHPy), 122.7 (s, CHIm‑4,5), 121.9 (s,
CHIm‑4,5), 53.7 (s, PyCH2), 48.7 (d, JPC = 22.1 Hz, PCH2), 21.2 (s,
CH3Ts). Anal. Found: C, 63.25; H, 5.06; N, 8.15. Calcd (%) for
C29H28N3O3PS. 0.3CH2Cl2: C, 63.40; H, 5.19; N, 7.57. MS (ES+): m/
z: 358.1 [M]+. HRMS (ES+): calcd for C22H21N3P+ 358.1473. Found:
358.1482 (εr = 2.5 ppm).
1
13. H NMR (400 MHz, CD2Cl2): δ 8.67 (d, J = 4.0 Hz, 1H,
CHAr), 7.98−7.94 (m, 3H, CHAr), 7.61−7.24 (m, 12H, CHAr), 5.11
(t, J = 12.0 Hz, 1H, PCH2), 4.97 (d, J = 12.0 Hz, 1H, PCH2). 31P{1H}
NMR (162 MHz, CD2Cl2, 25 °C): δ 71.8 (s). 13C{1H} NMR (101
MHz, CD2Cl2): δ 223.9 (d, JPC = 18.2 Hz, CO), 220.2 (d, JPC = 18.2
Hz, CO), 218.5 (d, JPC = 32.3 Hz, CO), 198.1 (d, JPC = 15.1 Hz,
CN2), 153.1 (s, CPy), 150.0 (s, CHPy), 139.3 (s, CHPy), 136.1 (d, JPC
37.4 Hz, CipsoPh), 135.0 (d, JPC = 10.1 Hz, CHPh), 131.9 (d, JPC = 2.0
Hz, CHPh), 130.5 (s, CHPh), 130.4 (d, JPC = 10.1 Hz, CHPh), 129.3 (d,
Synthesis of PCP Bidentate Complex 11. To a stirred
suspension of [4](OTs) (0.40 g, 0.63 mmol) in toluene (30 mL)
was added a solution of KHMDS (0.5 M in toluene, 1.3 mL, 0.66
mmol) at room temperature, and then the resulting yellow suspension
was sonicated during 5 min and stirred for additional 15 min. Solid
[Mn(CO)5Br] (0.17 g, 0.63 mmol) was added in one portion
inducing a vigorous CO evolution. The resulting orange solution was
then stirred for 2 h at 60 °C. After cooling the reaction mixture to
room temperature, filtration through Celite and evaporation of the
solvent under vacuum, the crude product was crystallized in a THF/
=
J
PC = 9.1 Hz, CHPh), 129.2 (d, JPC = 9.1 Hz, CHPh), 125.2 (s, CHPy),
125.1 (s, CHPy), 122.2 (s, CHIm‑4,5), 120.9 (d, JPC = 4.0 Hz CHIm‑4,5),
52.2 (d, JPC = 30.3 Hz, PCH2). IR (THF): νCO 2016 (s), 1939 (s),
1904 (s) cm−1.
1
pentane mixture to afford 11 as a yellow powder (0.32 g, 71%). H
1
14. H NMR (400 MHz, CD2Cl2, 25 °C): δ 8.97 (d, J = 5.5 Hz,
NMR (400 MHz, CD2Cl2, 25 °C): δ 7.93 (t, J = 8.7 Hz, 2H, CHPh),
7.56−7.35 (m, 16H, CHPh), 7.21−7.13 (m, 3H, CHPh), 6.99 (brs, 1H,
CHIm‑4,5), 5.22 (dd, JHH = 14.2 Hz, JPH = 4.4 Hz, 1H, PCH2), 5.07
(dd, JHH = 14.2 Hz, JPH = 3.5 Hz, 1H, PCH2), 4.88−4.98 (m, 2H,
PCH2). 31P{1H} NMR (162 MHz, CD2Cl2, 25 °C): δ 71.0 (s), −17.0
1H, CHAr), 7.94 (t, J = 8.0 Hz, 1H, CHAr), 7.60−7.48 (m, 6H, CHAr),
7.45−7.37 (m, 6H, CHAr), 7.30 (t, J = 4.0 Hz, 1H, CHAr), 6.83 (s, 1H,
CHAr), 5.37 (dd, J = 14.1, 8.2 Hz, 1H, PCH2), 4.99 (dd, J = 14.1, 1.8
Hz, 1H, PCH2). 31P{1H} NMR (162 MHz, CD2Cl2, 25 °C): δ −15.9
(s). 13C{1H} NMR (101 MHz, CD2Cl2, 25 °C): δ 226.4 (s, CO),
221.3 (s, CO), 218.0 (s, CO), 206.0 (s, CN2), 153.9 (s, CHPy), 153.0
(s, CPy), 140.6 (s, CHPy), 135.4 (d, JPC = 13.2 Hz, CipsoPh), 135.0 (d,
(s). 13C{1H} NMR (101 MHz, CD2Cl2, 25 °C): δ 222.9 (d, JPC
=
17.8 Hz, CO), 221.4 (d, JPC = 31.0 Hz, CO), 220.1 (d, JPC = 21.5 Hz,
CO), 197.1 (d, JPC = 16.5 Hz, CN2), 135.6 (d, JPC = 3.0 Hz, CipsoPh),
135.4 (d, JPC = 21.2 Hz, CipsoPh), 135.2 (d, JPC = 8.1 Hz, CipsoPh), 134.7
(d, JPC = 9.9 Hz, CHPh), 133.6 (d, JPC = 19.8 Hz, CHPh), 133.2 (d, JPC
= 19.1 Hz, CHPh), 131.8 (s, CHPh), 130.6 (d, JPC = 10.1 Hz, CHPh),
130.5 (s, CHPh), 130.1 (s, CHPh), 129.9 (s, CHPh), 129.4 (s, CHPh),
129.2 (d, JPC = 6.1 Hz, CHPh), 129.1 (s, CHPh), 124.2 (d, JPC = 9.9
Hz, CHIm‑4,5), 120.5 (d, JPC = 6.8 Hz, CHIm‑4,5), 52.3 (d, JPC = 30.3
Hz, PCH2), 52.2 (d, JPC = 17.2 Hz, PCH2). IR (toluene): νCO 2015
(s), 1940 (s), 1910 (s) cm−1. Anal. Found: C, 54.50; H, 3.33; N, 4.13.
Calcd (%) for C32H26BrMnN2O3P2 0.35 (CH2Cl2): C, 54.49; H, 3.77;
N, 3.93. MS (ES+): m/z: 603.1 [M − Br]+. HRMS (ES+): calcd for
J
PC = 14.0 Hz, CipsoPh), 134.1 (d, JPC = 19.9 Hz, CHPh), 132.9 (d, JPC =
18.8 Hz, CHPh), 130.5 (s, CHPh), 129.9 (s, CHPh), 129.5 (d, JPC = 7.3
Hz, CHPh), 129.3 (d, JPC = 6.5 Hz, CHPh), 125.1 (d, JPC = 5.8 Hz,
CHIm‑4,5), 122.8 (s, CHIm‑4,5), 115.9 (s, CHPy), 111.7 (s, CHPy), 51.9
(d, JPC = 17.5 Hz, PCH2). IR (THF): νCO 2016 (s), 1930 (s), 1907
(s) cm−1. Anal. Found: C, 51.28; H, 2.71; N, 7.46. Calcd (%) for
C24H18BrMnN3O3P: C, 51.27; H, 3.23; N, 7.47.
Synthesis of PCN Tridentate Complex [15](OTf). To a
solution of the mixture of complexes 13 and 14 (0.20 g, 0.36
mmol) in CH2Cl2 (20 mL) was added AgOTf (0.10 g, 0.39 mmol) as
a solid. The reaction mixture was stirred at room temperature for 2 h.
After filtration through Celite and evaporation of the solvent under
vacuum, the crude residue was crystallized in THF/Et2O mixture
affording complex [15](OTf) as a green-yellow powder (0.17 g,
76%). Single crystals suitable for XRD were obtained by slow
evaporation of the complex solution in CH2Cl2 at room temperature.
1H NMR (400 MHz, CDCl3, 25 °C): δ 8.58 (brs, 2H, CHAr), 8.25
(brs, 1H, CHAr), 8.10 (brs, 2H CHAr), 7.46−7.44 (m, 11H, CHAr),
5.51 (brs, 2H, PCH2). 31P{1H} NMR (162 MHz, CD2Cl2, 25 °C): δ
+
C32H26MnN2O3P2 603.0799. Found: 603.0799 (εr = 0.0 ppm).
Synthesis of PCP Tridentate Complex [12](OTf). To a solution
of 11 (0.4 g, 0.58 mmol) in CH2Cl2 (30 mL) was added AgOTf (0.17
g, 0.66 mmol) as a solid. The reaction mixture was then stirred at
room temperature for 2 h. After filtration through Celite and
evaporation of the solvent under vacuum, [12](OTf) was obtained as
a pale-yellow powder (0.39 g, 88%). Single crystals suitable for XRD
were obtained by slow evaporation of a CH2Cl2/toluene solution at
room temperature. 1H NMR (400 MHz, CD2Cl2, 25 °C): δ 7.82 (brs,
2H, CHAr), 7.58−7.50 (m, 20H, CHAr), 5.26−5.24 (m, 4H, PCH2).
31P{1H} NMR (162 MHz, CD2Cl2, 25 °C): δ 89.6 (s). 13C{1H} NMR
(101 MHz, CD2Cl2, 25 °C): δ 220.7 (brt, JPC = 10.5 Hz, CO), 213.6
(brt, JPC = 19.0 Hz, CO), 195.6 (t, JPC = 13.1 Hz, CN2), 133.8 (m,
CipsoPh) 132.2 (s, CHPh), 131.7−132.0 (m, CHPh), 129.8−130.2 (m,
CHPh), 124.9 (s, CHIm‑4,5), 121.6 (q, JCF = 321.4 Hz, CF3), 56.2 (m,
PCH2). IR (THF): νCO 2045 (w), 1966 (vs), 1942 (s) cm−1. Anal.
Found: C, 52.34; H, 3.82; N, 3.60. Calcd (%) for
C33H26F3MnN2O6P2S: C, 52.67; H, 3.48; N, 3.72. MS (ES+): m/z:
97.4 (s). 13C{1H} NMR (101 MHz, CDCl3, 25 °C): δ 218.4 (d, JPC
9.7 Hz, CO), 212.7 (d, JPC = 17.7 Hz, CO), 206.5 (d, JPC = 18.9 Hz,
CN2), 156.0 (s, CHPy), 154.6 (s, CPy), 141.8 (s, CHAr), 133.8 (d, JPC
42.8 Hz, CipsoPh), 131.6 (d, JPC = 2.4 Hz, CHPh), 131.4 (d, JPC = 11.0
Hz, CHPh), 129.5 (d, JPC = 10.4 Hz, CHPh), 125.4 (d, JPC = 6.0 Hz,
CHIm‑4,5), 123.4 (s, CHIm‑4,5), 120.8 (s, CHPy), 114.2 (s, CHPy), 58.1
(d, JPC = 37.4 Hz, PCH2). IR (THF): νCO 2052 (w), 1969 (vs), 1941
(s) cm−1. Anal. Found: C, 47.60; H, 2.45; N, 6.45. Calcd (%) for
C25H18F3MnN3O6PS: C, 47.56; H, 2.87; N, 6.66. MS (ES+): m/z:
=
=
237
https://dx.doi.org/10.1021/acs.organomet.0c00717
Organometallics 2021, 40, 231−241

Organometallics
pubs.acs.org/Organometallics
Article
482.0 [M]+. HRMS (ES+): calcd for C24H18MnN3O3P+ 482.0466.
Found: 482.0466 (εr = 0 ppm).
ethyl acetate (2.0 mL) and filtered through a small pad of Celite (2
cm in a Pasteur pipet) and the solution was analyzed by GC and H
NMR spectroscopy. To isolate the product, the crude residue was
purified by column chromatography on silica using petroleum ether/
ethyl acetate mixtures as eluent.
1
Synthesis of PCN Bidentate Complex 16. To a stirred
suspension of [10](OTs) (0.32 g, 0.60 mmol) in THF (20 mL)
was added a solution of KHMDS (0.5 M in toluene, 1.3 mL, 0.66
mmol) at room temperature, and then the resulting brown suspension
was sonicated during 5 min and stirred for additional 15 min. Solid
[Mn(CO)5Br] (0.17 g, 0.60 mmol) was added in one portion
inducing a vigorous CO evolution. The resulting dark orange solution
was then stirred for 2 h at 50 °C. After cooling the reaction mixture to
room temperature, filtration through Celite and evaporation of the
solvent under vacuum, the crude product was purified by column
chromatography on basic activated aluminum oxide using THF/
toluene mixture as eluent affording complex 16 as a yellow-orange
powder (0.21 g, 60%). Single crystals suitable for XRD were obtained
by slow evaporation of complex solution in CH2Cl2/toluene mixture
Single-Crystal X-ray Diffraction Analyses. Single crystals
suitable for X-ray diffraction were coated with paratone oil and
mounted onto the goniometer. The X-ray crystallographic data were
obtained at low temperature from a Bruker Apex2 diffractometer (Mo
Kα radiation source) equipped with an Oxford Cryosystem. The
structures have been solved with Superflip32 and refined by means of
least-squares procedures on F or F2 using the PC version of the
program CRYSTALS.33 The scattering factors for all the atoms were
used as listed in the International Tables for X-ray Crystallography.
Absorption correction was performed using a multiscan procedure. All
non-hydrogen atoms were refined anisotropically. The H atoms were
located in a difference map, but those attached to carbon atoms were
repositioned geometrically. The H atoms were initially refined with
soft restraints on the bond lengths and angles to regularize their
geometry and U[iso](H) (in the range 1.2−1.5 times U[eq] of the
parent atom), after which the positions were refined with riding
constraints. Detailed crystallographic data and structural refinement
parameters are given in Table S1.
1
at room temperature. H NMR (400 MHz, CD2Cl2, 25 °C): δ 8.57
(d, J = 4.7 Hz, 1H, CHAr), 8.00−7.91 (m, 2H, CHAr), 7.68−7.65 (m,
1H, CHAr), 7.57−7.50 (m, 3H, CHAr), 7.43−7.32 (m, 4H, CHAr),
7.27−7.13 (m, 5H, CHAr), 5.74 (d, JHH = 16.0 Hz, 1H, PyCH2), 5.64
(d, JHH = 16.0 Hz, 1H, PyCH2), 4.96−5.05 (m, 2H, PCH2). 31P{1H}
NMR (162 MHz, CDCl3, 25 °C): δ 71.2 (s). 13C{1H} NMR (101
MHz, CD2Cl2, 25 °C): δ 222.8 (brd, JPC = 16.8 Hz, CO), 220.8 (brd,
JPC = 30.1 Hz, CO), 220.2 (brd, JPC = 20.8 Hz, CO), 197.7 (d, JPC
=
17.5 Hz, CN2), 156.5 (s, CPy), 150.0 (s, CHAr), 137.6 (s, CHAr), 135.7
(d, JPC = 36.6 Hz, CipsoPh), 134.9 (d, JPC = 9.8 Hz, CHAr), 132.0 (s,
CHAr), 130.7 (m, 2 CHAr), 129.4 (d, JPC = 9.0 Hz, CHAr), 129.3 (d,
JPC = 9.0 Hz, CHAr), 125.2 (s, CHAr), 123.4 (s, CHAr), 122.3 (s,
CHIm‑4,5), 121.3 (d, JPC = 7.2 Hz, CHIm‑4,5), 57.1 (s, PyCH2), 52.3 (d,
JPC = 31.5 Hz, PCH2). IR (THF): νCO 2018 (s), 1941 (s), 1913 (s)
cm−1. Anal. Found: C, 51.61; H, 3.38; N, 7.03. Calcd (%) for
C25H20BrMnN3O3P: C, 52.11; H, 3.50; N, 7.29. MS (ES+): m/z:
576.0 [M + H]+. HRMS (ES+): calcd for C25H21BrMnN3O3P
575.9884. Found: 575.9893 (εr = 1.6 ppm).
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.0c00717.
Copies of 1H, 31P, 13C NMR, and IR spectra,
representation of X-ray structure of [4](OTs), crystallo-
graphic data and structural refinement parameters for all
studied compounds (PDF)
Synthesis of PCN Tridentate Complex [17](OTf). To a
solution of 16 (0.20 g, 0.34 mmol) in CH2Cl2 (20 mL) was added
AgOTf (0.10 g, 0.37 mmol) as a solid. The reaction mixture was
stirred at room temperature for 2 h. After filtration through Celite and
evaporation of the solvent under vacuum, [17](OTf) was obtained as
a yellow-brown powder (0.21 g, 96%). Single crystals suitable for
XRD were obtained by slow evaporation of the concentrated CH2Cl2
solution at room temperature. 1H NMR (400 MHz, CD2Cl2, 25 °C):
δ 8.02 (dd, J = 7.4 and 10.9 Hz, 2H, CHAr), 7.88 (s, 1H, CHAr), 7.82−
7.70 (m, 5H, CHAr), 7.66−7.61 (m, 2H, CHAr), 7.16 (t, J = 7.5 Hz,
1H, CHAr), 6.96 (t, J = 7.8 Hz, 2H, CHAr), 6.60 (t, J = 6.6 Hz, 1H,
CHAr), 5.95 (t, J = 8.0 Hz, 2H, CHAr), 5.89 (d, J = 16.0 Hz, 1H,
PyCH2), 5.54 (d, J = 16.0 Hz, 1H, PyCH2), 5.36 (t, J = 12.0 Hz, 1H,
PCH2), 4.91 (dd, J = 8.9 and 12.0 Hz, 1H, PCH2). 31P{1H} NMR
(162 MHz, CD2Cl2, 25 °C): δ 93.3 (s). 13C{1H} NMR (101 MHz,
Accession Codes
CCDC 2042375−2042380 and 2042403 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/
cif, or by emailing data_request@ccdc.cam.ac.uk, or by
contacting The Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
■
Corresponding Authors
Dmitry A. Valyaev − LCC−CNRS, Université de Toulouse,
CNRS, UPS, Toulouse CEDEX 4 31077, France;
orcid.org/0000-0002-1772-844X;
CD2Cl2, 25 °C): δ 219.6 (brd, JPC = 25.5 Hz, CO), 218.7 (brd, JPC
=
Email: dmitry.valyaev@lcc-toulouse.fr
18.5 Hz, CO), 216.9 (brd, JPC = 23.5 Hz, CO), 202.9 (d, JPC = 22.3
Hz, CN2), 157.7 (d, JPC = 3.4 Hz, CHAr), 156.9 (s, CPy), 139.5 (s,
CHAr), 134.4 (d, JPC = 10.7 Hz, CHAr), 133.6 (d, JPC = 2.0 Hz, CHAr),
131.2 (d, JPC = 2.4 Hz, CHAr), 130.4 (d, JPC = 9.9 Hz, CHAr), 129.7
Jean-Baptiste Sortais − LCC−CNRS, Université de Toulouse,
CNRS, UPS, Toulouse CEDEX 4 31077, France; Institut
Universitaire de France, Paris CEDEX 5 75231, France;
orcid.org/0000-0003-1178-8588; Email: jean-
baptiste.sortais@lcc-toulouse.fr
Yves Canac − LCC−CNRS, Université de Toulouse, CNRS,
UPS, Toulouse CEDEX 4 31077, France; orcid.org/
0000-0002-3747-554X; Email: yves.canac@lcc-toulouse.fr
(d, JPC = 9.7 Hz, CHAr), 129.6 (d, JPC = 9.4 Hz, CHAr), 127.5 (d, JPC
=
36.6 Hz, CipsoPh), 127.4 (s, CHAr), 126.3 (s, CHAr), 124.7 (s, CHAr),
123.1 (d, JPC = 1.7 Hz, CHAr), 55.8 (d, JPC = 37.9 Hz, PCH2), 55.6 (s,
PyCH2). IR (THF): νCO 2024 (s), 1947 (s), 1929 (s) cm−1. Anal.
Found: C, 47.17; H, 2.84; N, 6.34. Calcd (%) for
C26H20F3MnN3O6PS. 0.25 (CH2Cl2): C, 47.29; H, 3.10; N, 6.30.
MS (ES+): m/z: 496.1 [M]+. HRMS (ES+): calcd for
C25H20MnN3O3P 496.0623. Found: 496.0626 (εr = 0.6 ppm).
General Procedure for the Hydrogenation of Acetophe-
none. Under a N2 atmosphere, a Schlenk tube was charged with
selected complex and acetophenone (1 mmol, 117 μL) in 2 mL of t-
AmOH, the solution was placed in a steel autoclave. Then t-BuOK
(10 mol %) was added, and the autoclave was immediately
pressurized with H2 (50 bar) and kept under stirring in an oil bath
at 60 or 100 °C for 24 h. After cooling the reactor to room
temperature and release of H2, the reaction mixture was diluted with
Authors
Ruqaya Buhaibeh − LCC−CNRS, Université de Toulouse,
CNRS, UPS, Toulouse CEDEX 4 31077, France
Carine Duhayon − LCC−CNRS, Université de Toulouse,
CNRS, UPS, Toulouse CEDEX 4 31077, France;
orcid.org/0000-0001-7345-8782
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.0c00717
238
https://dx.doi.org/10.1021/acs.organomet.0c00717
Organometallics 2021, 40, 231−241

Organometallics
pubs.acs.org/Organometallics
Article
lin-2-ylidene ligands. Organometallics 2006, 25, 5927−5936. (b) Da-
nopoulos, A. A.; Tsoureas, N.; Macgregor, S. A.; Smith, C. Phosphine-
and pyridine-functionalized N-heterocyclic carbene methyl and allyl
complexes of palladium. Unexpected regiospecificity of the proto-
nation reaction of the dimethyl complexes. Organometallics 2007, 26,
253−263. (c) Hill, A. F.; McQueen, C. M. A. Dihydroperimidine-
derived N-heterocyclic pincer carbene complexes via double C−H
activation. Organometallics 2012, 31, 8051−8054. (d) Salem, H.;
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
The authors thank the Centre National de la Recherche
Scientifique (CNRS), the Universite Toulouse III, Paul
■
́
Sabatier, and the Institut Universitaire de France (IUF) for
general support of this project. R.B. is grateful to the Embassy
of Yemen in Paris and the program Pause for financial support.
Schmitt, M.; Herrlich, U.; Kuhnel, E.; Brill, M.; Nagele, P.; Bogado, A.
̈
̈
L.; Rominger, F.; Hofmann, P. Bulky N-phosphinomethyl-function-
alized N-heterocyclic carbene chelate ligands: synthesis, molecular
geometry, electronic structure, and their ruthenium alkylidene
complexes. Organometallics 2013, 32, 29−46. (e) Fuku-en, S.;
Yamamoto, J.; Kojima, S.; Yamamoto, Y. Synthesis and application
of new dipyrido-annulated N-heterocyclic carbene with phosphorus
substituents. Chem. Lett. 2014, 43, 468−470. (f) Valyaev, D. A.;
Filippov, O. A.; Lugan, N.; Lavigne, G.; Ustynyuk, N. A. Umpolung of
methylenephosphonium ions in their manganese half-sandwich
complexes and application to the synthesis of chiral phosphorus-
containing ligand scaffolds. Angew. Chem., Int. Ed. 2015, 54, 6315−
REFERENCES
■
(1) (a) Bourissou, D.; Guerret, O.; Gabbaï, F. P.; Bertrand, G. Stable
carbenes. Chem. Rev. 2000, 100, 39−91. (b) Canac, Y.; Soleilhavoup,
M.; Conejero, S.; Bertrand, G. Stable non-N-heterocyclic carbenes
(non-NHC): recent progress. J. Organomet. Chem. 2004, 689, 3857−
3865. (c) Melaimi, M.; Soleilhavoup, M.; Bertrand, G. Stable carbenes
and related species beyond diaminocarbenes. Angew. Chem., Int. Ed.
2010, 49, 8810−8849. (d) Hopkinson, M. N.; Richter, C.; Schedler,
M.; Glorius, F. An overview of N-Heterocyclic carbenes. Nature 2014,
510, 485−496. (e) Vivancos, A.; Segarra, C.; Albrecht, M. Mesoionic
and related less heteroatom-stabilized N-heterocyclic carbene
complexes: synthesis, catalysis, and other applications. Chem. Rev.
2018, 118, 9493−9586. (f) Sau, S. C.; Hota, P. K.; Mandal, S. K.;
Soleilhavoup, M.; Bertrand, G. Stable abnormal N-heterocyclic
carbenes and their applications. Chem. Soc. Rev. 2020, 49, 1233−1252.
(2) (a) Froese, R. D. J.; Lombardi, C.; Pompeo, M.; Rucker, R. P.;
Organ, M. G. Designing Pd−N-heterocyclic carbene complexes for
high reactivity and selectivity for cross-coupling applications. Acc.
Chem. Res. 2017, 50, 2244−2253. (b) Janssen-Muller, D.;
Schlepphorst, C.; Glorius, F. Privileged chiral N-heterocyclic carbene
ligands for asymmetric transition-metal catalysis. Chem. Soc. Rev.
2017, 46, 4845−4854. (c) Melaimi, M.; Jazzar, R.; Soleilhavoup, M.;
Bertrand, G. Cyclic (alkyl)(amino)carbenes (CAACs): recent
developments. Angew. Chem., Int. Ed. 2017, 56, 10046−10068.
(d) Ogba, O. M.; Warner, N. C.; O’Leary, D. J.; Grubbs, R. H. Recent
advances in ruthenium-based olefin metathesis. Chem. Soc. Rev. 2018,
47, 4510−4544.
̈
6319. (g) Plikhta, A.; Pothig, A.; Herdtweck, E.; Rieger, B. Toward
new organometallic architectures: synthesis of carbene-centered
rhodium and palladium bisphosphine complexes. Stability and
reactivity of [PCBImPRh(L)][PF6] pincers. Inorg. Chem. 2015, 54,
9517−9528. (h) Matoba, K.; Eizawa, A.; Nishimura, S.; Arashiba, K.;
Nakajima, K.; Nishibayashi, Y. Practical synthesis of a PCP-type
pincer ligand and its metal complexes. Synthesis 2018, 50, 1015−1019.
(6) (a) Aihara, H.; Matsuo, T.; Kawaguchi, H. Titanium N-
heterocyclic carbene complexes incorporating an imidazolium-linked
bis(phenol). Chem. Commun. 2003, 2204−2205. (b) Waltman, A. W.;
Grubbs, R. H. A new class of chelating N-Heterocyclic carbene
ligands and their complexes with palladium. Organometallics 2004, 23,
3105−3107. (c) Romain, C.; Brelot, L.; Bellemin-Laponnaz, S.;
Dagorne, S. Synthesis and structural characterization of a novel family
of titanium complexes bearing a tridentate bis-phenolate-N-hetero-
cyclic carbene dianionic ligand and their use in the controlled ROP of
rac-lactide. Organometallics 2010, 29, 1191−1198. (d) Taakili, R.;
Canac, Y. NHC core pincer ligands exhibiting two anionic
coordinating extremities. Molecules 2020, 25, 2231.
(3) (a) Mata, J. A.; Poyatos, M.; Peris, E. Structural and catalytic
properties of chelating bis- and tris-N-heterocyclic carbenes. Coord.
Chem. Rev. 2007, 251, 841−859. (b) Poyatos, M.; Mata, J. A.; Peris, E.
Complexes with poly(N-heterocyclic carbene) ligands: structural
features and catalytic applications. Chem. Rev. 2009, 109, 3677−3707.
(c) Schick, S.; Pape, T.; Hahn, F. E. Coordination chemistry of
bidentate bis(NHC) ligands with two different NHC donors.
(7) (a) Benaissa, I.; Taakili, R.; Lugan, N.; Canac, Y. A convenient
access to N-phosphonio-substituted NHC metal complexes [M =
Ag(I), Rh(I), Pd(II)]. Dalton Trans. 2017, 46, 12293−12305.
(b) Barthes, C.; Bijani, C.; Lugan, N.; Canac, Y. A palladium(II)
complex of a C4 chelating bis(NHC) diphosphonium bis(ylide)
ligand. Organometallics 2018, 37, 673−678. (c) Taakili, R.; Lepetit,
C.; Duhayon, C.; Valyaev, D. A.; Lugan, N.; Canac, Y. Palladium(II)
pincer complexes of a C,C,C-NHC, diphosphonium bis(ylide) ligand.
Dalton Trans. 2019, 48, 1709−1721. (d) Taakili, R.; Barthes, C.;
́
Organometallics 2014, 33, 4035−4041. (d) Charra, V.; de Fremont,
P.; Braunstein, P. Multidentate N-heterocyclic carbene complexes of
the 3d metals: synthesis, structure, reactivity and catalysis. Coord.
Chem. Rev. 2017, 341, 53−176.
̈
Goeffon, A.; Lepetit, C.; Duhayon, C.; Valyaev, D. A.; Canac, Y. NHC
core phosphonium ylide-based palladium(II) pincer complexes: the
second ylide extremity makes the difference. Inorg. Chem. 2020, 59,
7082−7096.
(4) (a) Chen, J. C. C.; Lin, I. J. B. Palladium complexes containing a
hemilabile pyridylcarbene ligand. Organometallics 2000, 19, 5113−
5121. (b) Tulloch, A. A. D.; Danopoulos, A. A.; Kleinhenz, S.; Light,
M. E.; Hursthouse, M. B.; Eastham, G. Structural diversity in pyridine-
N-functionalized carbene copper(I) complexes. Organometallics 2001,
20, 2027−2031. (c) Magill, A. M.; McGuinness, D. S.; Cavell, K. J.;
Britovsek, G. J. P.; Gibson, V. C.; White, A. J. P.; Williams, D. J.;
White, A. H.; Skelton, B. W. Palladium(II) complexes containing
mono-, bi- and tridentate carbene ligands. Synthesis, characterization
and application as catalysts in C−C coupling reactions. J. Organomet.
Chem. 2001, 617−618, 546−560. (d) Valyaev, D. A.; Willot, J.;
Mangin, L. P.; Zargarian, D.; Lugan, N. Manganese-mediated
synthesis of an NHC core non-symmetric pincer ligand and
evaluation of its coordinating propeties. Dalton Trans. 2017, 46,
10193−10196. (e) Jiang, Y.; Gendy, C.; Roesler, R. Nickel,
ruthenium, and rhodium NCN-pincer complexes featuring a six-
membered N-heterocyclic carbene central moiety and pyridyl pendant
arms. Organometallics 2018, 37, 1123−1132.
(8) (a) Valyaev, D. A.; Lavigne, G.; Lugan, N. Manganese
organometallic compounds in homogeneous catalysis: past, present
and prospects. Coord. Chem. Rev. 2016, 308, 191−235. (b) Trovitch,
R. J. The emergence of manganese-based carbonyl hydrosilylation
catalysts. Acc. Chem. Res. 2017, 50, 2842−2852. (c) Hu, Y.; Zhou, B.;
Wang, C. Inert C−H bond transformations enabled by organometallic
manganese catalysis. Acc. Chem. Res. 2018, 51, 816−827. (d) Stanbury,
M.; Compain, J.-D.; Chardon-Noblat, S. Electro and photoreduction
of CO2 driven by manganese-carbonyl molecular catalysts. Coord.
Chem. Rev. 2018, 361, 120−137. (e) Kaim, V.; Kaur-Ghumaan, S.
Manganese complexes: hydrogen generation and oxidation. Eur. J.
Inorg. Chem. 2019, 2019, 5041−5051.
(9) (a) Garbe, M.; Junge, K.; Beller, M. Homogeneous catalysis by
manganese-based pincer complexes. Eur. J. Org. Chem. 2017, 2017,
4344−4362. (b) Maji, B.; Barman, M. K. Recent developments of
manganese complexes for catalytic hydrogenation and dehydrogen-
ation reactions. Synthesis 2017, 49, 3377−3393. (c) Kallmeier, F.;
(5) (a) Hahn, F. E.; Jahnke, M. C.; Pape, T. Synthesis of palladium
and platinum complexes with phosphine-functionalized benzimidazo-
239
https://dx.doi.org/10.1021/acs.organomet.0c00717
Organometallics 2021, 40, 231−241

Organometallics
pubs.acs.org/Organometallics
Article
Kempe, R. Manganese complexes for (de)hydrogenation catalysis: a
comparison to cobalt and iron catalysts. Angew. Chem., Int. Ed. 2018,
57, 46−60. Manganese-catalyzed hydrogenation and hydrogen
transfer reactions: (d) Sortais, J.-B.; Buhaibeh, R.; Canac, Y. In
Manganese Catalysis in Organic Synthesis; Sortais, J.-B., Ed.; Wiley-
VCH, in press.
(10) (a) Elangovan, S.; Topf, C.; Fischer, S.; Jiao, H.; Spannenberg,
A.; Baumann, W.; Ludwig, R.; Junge, K.; Beller, M. Selective catalytic
hydrogenations of nitriles, ketones, and aldehydes by well-defined
manganese pincer complexes. J. Am. Chem. Soc. 2016, 138, 8809−
8814. (b) Kallmeier, F.; Irrgang, T.; Dietel, T.; Kempe, R. Highly
active and selective manganese C = O bond hydrogenation catalysts:
the importance of the multidentate ligand, the ancillary ligands, and
the oxidation state. Angew. Chem., Int. Ed. 2016, 55, 11806−11809.
(c) Bruneau-Voisine, A.; Wang, D.; Roisnel, T.; Darcel, C.; Sortais, J.-
B. Hydrogenation of ketones with a manganese PN3P pincer pre-
catalyst. Catal. Commun. 2017, 92, 1−4.
(11) (a) Espinosa-Jalapa, N. A.; Nerush, A.; Shimon, L. J. W.; Leitus,
G.; Avram, L.; Ben-David, Y.; Milstein, D. Manganese-catalyzed
hydrogenation of esters to alcohols. Chem. - Eur. J. 2017, 23, 5934−
5938. (b) Zhang, L.; Tang, Y.; Han, Z.; Ding, K. Lutidine-based chiral
pincer manganese catalysts for enantioselective hydrogenation of
ketones. Angew. Chem., Int. Ed. 2019, 58, 4973−4977.
(12) Perez, M.; Elangovan, S.; Spannenberg, A.; Junge, K.; Beller, M.
Molecularly defined manganese pincer complexes for selective transfer
hydrogenation of ketones. ChemSusChem 2017, 10, 83−86.
(13) Yang, W.; Chernyshov, I. Y.; van Schendel, R. K. A.; Weber, M.;
(20) Raba, A.; Anneser, M. R.; Jantke, D.; Cokoja, M.; Herrmann,
̈
W. A.; Kuhn, F. E. Facile and scalable preparation of 2-
imidazolylpyridines. Tetrahedron Lett. 2013, 54, 3384−3387.
(21) Chiu, P. L.; Lai, C.-L.; Chang, C.-F.; Hu, C.-H.; Lee, H. M.
Synthesis, structural characterization, computational study, and
catalytic activity of metal complexes based on tetradentate pyridine/
N-Heterocyclic carbene ligand. Organometallics 2005, 24, 6169−6178.
(22) For manganese NHC−pyridine−NHC complexes, see
(a) Pugh, D.; Wright, J. A.; Freeman, S.; Danopoulos, A. A. ‘Pincer’
dicarbene complexes of some early transition metals and uranium.
Dalton Trans. 2006, 775−782. (b) Myren, T. H. T.; Lilio, A. M.;
Huntzinger, C. G.; Horstman, J. W.; Stinson, T. A.; Donadt, T. B.;
Moore, C.; Lama, B.; Funke, H. H.; Luca, O. R. Manganese N-
heterocyclic carbene pincers for the electrocatalytic reduction of
carbon dioxide. Organometallics 2019, 38, 1248−1253.
(23) For the sole example of Mn(III) complex bearing NHC core
LX2-type ligand, see Bellemin-Laponnaz, S.; Welter, R.; Brelot, L.;
Dagorne, S. Synthesis and structure of V(V) and Mn(III) NHC
complexes supported by a tridentate bis-aryloxide-N-heterocyclic
carbene ligand. J. Organomet. Chem. 2009, 694, 604−606.
(24) Elangovan, S.; Garbe, M.; Jiao, H.; Spannenberg, A.; Junge, K.;
Beller, M. Hydrogenation of esters to alcohols catalyzed by defined
manganese pincer complexes. Angew. Chem., Int. Ed. 2016, 55,
15364−15368.
(25) (a) Gonzalez, M. A.; Yim, M. A.; Cheng, S.; Moyes, A.; Hobbs,
A. J.; Mascharak, P. K. Manganese carbonyls bearing tripodal
polypyridine ligands as photoactive carbon monoxide-releasing
molecules. Inorg. Chem. 2012, 51, 601−608. (b) G, U. R.; Axthelm,
Muller, C.; Filonenko, G. A.; Pidko, E. A. Phosphine ligand
̈
̈
̈
J.; Hoffmann, P.; Taye, N.; Glaser, S.; Gorls, H.; Hopkins, S. L.; Plass,
W.; Neugebauer, U.; Bonnet, S.; Schiller, A. Co-registered molecular
logic gate with a CO-releasing molecule triggered by light and
peroxide. J. Am. Chem. Soc. 2017, 139, 4991−4994. (c) Ganguli, K.;
Shee, S.; Panja, D.; Kundu, S. Cooperative Mn(I)-complex catalyzed
transfer hydrogenation of ketones and imines. Dalton Trans. 2019, 48,
7358−7366.
hemilability as a route towards robust and efficient hydrogenation
with Mn(I) complexes. ChemRxiv, April 22, 2020. DOI: 10.26434/
chemrxiv.12164262.v1.
(14) (a) van Putten, R.; Uslamin, E. A.; Garbe, M.; Liu, C.;
Gonzalez-de-Castro, A.; Lutz, M.; Junge, K.; Hensen, E. J. M.; Beller,
M.; Lefort, L.; Pidko, E. A. Non-pincer-type manganese complexes as
efficient catalysts for the hydrogenation of esters. Angew. Chem., Int.
Ed. 2017, 56, 7531−7534. (b) Wei, D.; Bruneau-Voisine, A.; Chauvin,
T.; Dorcet, V.; Roisnel, T.; Valyaev, D. A.; Lugan, N.; Sortais, J.-B.
Hydrogenation of carbonyl derivatives catalyzed by manganese
complexes bearing bidentate pyridinyl-phosphine ligands. Adv.
Synth. Catal. 2018, 360, 676−681.
(26) (a) Das, K.; Mondal, A.; Srimani, D. Phosphine free Mn-
complex catalysed dehydrogenative C−C and C−heteroatom bond
formation: a sustainable approach to synthesize quinoxaline, pyrazine,
benzothiazole and quinoline derivatives. Chem. Commun. 2018, 54,
10582−10585. (b) Das, K.; Mondal, A.; Srimani, D. Selective
synthesis of 2-substituted and 1,2-disubstituted benzimidazoles
directly from aromatic diamines and alcohols catalyzed by molecularly
defined nonphosphine manganese(I) complex. J. Org. Chem. 2018, 83,
9553−9560. (c) Das, K.; Mondal, A.; Pal, D.; Srivastava, H. K.;
Srimani, D. Phosphine-free well-defined Mn(I) complex-catalyzed
synthesis of amine, imine, and 2,3-dihydro-1H-perimidine via
hydrogen autotransfer or acceptorless dehydrogenative coupling of
amine and alcohol. Organometallics 2019, 38, 1815−1825.
̈
(15) (a) Weber, S.; Stoger, B.; Kirchner, K. Hydrogenation of
nitriles and ketones catalyzed by an air-stable bisphosphine Mn(I)
complex. Org. Lett. 2018, 20, 7212−7215. (b) Garduno, J. A.; García,
̃
J. J. Non-pincer Mn(I) organometallics for the selective catalytic
hydrogenation of nitriles to primary amines. ACS Catal. 2019, 9,
392−401.
(16) (a) Bruneau-Voisine, A.; Wang, D.; Dorcet, V.; Roisnel, T.;
Darcel, C.; Sortais, J.-B. Transfer hydrogenation of carbonyl
derivatives catalyzed by an inexpensive phosphine-free manganese
̈
(27) Mede, R.; Hoffmann, P.; Klein, M.; Gorls, H.; Schmitt, M.;
́
precatalyst. Org. Lett. 2017, 19, 3656−3659. (b) Martinez-Ferrate, O.;
Neugebauer, U.; Gessner, G.; Heinemann, S. H.; Popp, J.;
Westerhausen, M. A water-soluble Mn(CO)3-based and non-toxic
photoCORM for administration of carbon monoxide inside of cells. Z.
Anorg. Allg. Chem. 2017, 643, 2057−2062.
́
Werle, C.; Francio, G.; Leitner, W. Aminotriazole Mn(I) complexes as
effective catalysts for transfer hydrogenation of ketones. ChemCatCh-
em 2018, 10, 4514−4518. (c) Wang, D.; Bruneau-Voisine, A.; Sortais,
J.- B. Practical (asymmetric) transfer hydrogenation of ketones
catalyzed by manganese with (chiral) diamine ligands. Catal.
Commun. 2018, 105, 31−36.
(17) van Putten, R.; Benschop, J.; de Munck, V. J.; Weber, M.;
Muller, C.; Filonenko, G. A.; Pidko, E. A. Efficient and pratical
̈
transfer hydrogenation of ketones catalyzed by a simple bidentate
Mn−NHC complex. ChemCatChem 2019, 11, 5232−5235.
(18) Buhaibeh, R.; Filippov, O. A.; Bruneau-Voisine, A.; Willot, J.;
Duhayon, C.; Valyaev, D. A.; Lugan, N.; Canac, Y.; Sortais, J.-B.
Phosphine-NHC manganese hydrogenation catalyst exhibiting a non-
classical metal-ligand cooperative H2 activation mode. Angew. Chem.,
Int. Ed. 2019, 58, 6727−6731.
(19) Li, Y.; Lu, L.-Q.; Das, S.; Pisiewicz, S.; Junge, K.; Beller, M.
Highly chemoselective metal-free reduction of phosphine oxides to
phosphines. J. Am. Chem. Soc. 2012, 134, 18325−18329.
(28) Passera, A.; Mezzetti, A. Mn(I) and Fe(II)/PN(H)P catalysts
for the hydrogenation of ketones: a comparison by experiment and
calculation. Adv. Synth. Catal. 2019, 361, 4691−4706.
(29) Although it has already been shown in related Re(I) pincer
systems that fac-isomers correspond generally to the kinetic products,
complex [17](OTf) was found to be stable in solution up to 100 °C
before slowly starting to decompose; see Wei, D.; Sadek, O.; Dorcet,
V.; Roisnel, T.; Darcel, C.; Gras, E.; Clot, E.; Sortais, J.-B. Selective
mono N-methylation of anilines with methanol catalyzed by rhenium
complexes: an experimental and theoretical study. J. Catal. 2018, 366,
300−309.
(30) Willot, J.; Lugan, N.; Valyaev, D. A. Binuclear Cu(I) and
Mn(0) complexes with a tridentate pyridine-NHC-phosphane ligand
in a μ-κ2C,N-M;κ1P-M coordination mode. Eur. J. Inorg. Chem. 2019,
2019, 4358−4364.
240
https://dx.doi.org/10.1021/acs.organomet.0c00717
Organometallics 2021, 40, 231−241

Organometallics
pubs.acs.org/Organometallics
Article
(31) The only comparable value of 1.938(2) Å was observed in
Mn(IV) nitride complex beating tripodal anionic PhB(NHC)3 ligand;
̀
see Ding, M.; Cutsail, G. E., III; Aravena, D.; Amoza, M.; Rouzieres,
́
M.; Dechambenoit, P.; Losovyj, Ya.; Pink, M.; Ruiz, E.; Clerac, R.;
Smith, J. M. A low spin manganese(iv) nitride single molecule
magnet. Chem. Sci. 2016, 7, 6132−6140.
(32) Palatinus, L.; Chapuis, G. Superflip − a computer program for
the solution of crystal structures by charge flipping in arbitrary
dimensions. J. Appl. Crystallogr. 2007, 40, 786−790.
(33) Betteridge, P. W.; Carruthers, J. R.; Cooper, R. I.; Prout, K.;
Watkin, D. J. Crystals version 12: software for guided crystal structure
analysis. J. Appl. Crystallogr. 2003, 36, 1487.
241
https://dx.doi.org/10.1021/acs.organomet.0c00717
Organometallics 2021, 40, 231−241