Manganese complexes with chelating and bridging di-triazolylidene ligands: synthesis and reactivity

Article abstract of DOI:10.1039/d1dt00444a

New manganese complexes bearing di-triazolylidene (di-trz) ligands are described. Depending on the wingtip substituents of the triazolylidene ligand and the synthetic procedure, two different ligand coordination modes were observed,i.e, bridging and chelating. A series of Mn(i) complexes of the general typefac-[Mn(di-trz^R)(CO)₃Br] (R = Me, Et, Mes) with a chelating di-trz ligand were preparedviaAg-transmetalation. In contrast, thein situdeprotonation of the triazolium salts with KOBu^tyielded the bimetallic Mn(0) complexes [Mn₂(CO)₈(μ-di-trz^R)] with a bridging di-trz ligand when short alkyl chains (Me, Et, i-Pr) are present as the N1 substituents of the triazolylidene ligand. The molecular structures of monometallic and bimetallic complexes were determined by X-ray diffraction studies. In addition, the cationicfac-[Mn(di-trz^Et)(CO)₂(PPh₃)₂]Br complex, a rare example of a dicarbonyl Mn(i) N-heterocyclic carbene, was obtained whenfac-[Mn(di-trz^Et)(CO)₃Br] was irradiated with visible light in the presence of PPh₃. The crystal structure revealed a slightly distorted octahedral geometry around the Mn(i) centre, with the chelating di-triazolylidene ligand situated intransposition to the two CO ligands in the equatorial plane, and the two phosphine ligands occupying the axial positions. Cyclic voltammetry studies show reversible redox processes for the monometallic Mn(i) complexes, and a quasi-reversible EC mechanism for the oxidation of the bimetallic complexes. Infrared spectroelectrochemical studies along with DFT calculations forfac-[Mn(di-trz^Et)(CO)₃Br] suggest that the observed two consecutive reductions both occur at the metal centre.

Full text of DOI:10.1039/d1dt00444a

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
Manganese complexes with chelating and bridging
di-triazolylidene ligands: synthesis and reactivity†
Cite this: Dalton Trans., 2021, 50,
5911
a
a
b
c
Sofia Friães, Sara Realista, Clara S. B. Gomes,
Paulo N. Martinho,
d
e
a
Luis F. Veiros, Martin Albrecht
and Beatriz Royo
*
New manganese complexes bearing di-triazolylidene (di-trz) ligands are described. Depending on the
wingtip substituents of the triazolylidene ligand and the synthetic procedure, two different ligand coordi-
nation modes were observed, i.e, bridging and chelating. A series of Mn(I) complexes of the general type
R
fac-[Mn(di-trz )(CO)
3
Br] (R = Me, Et, Mes) with a chelating di-trz ligand were prepared via Ag-transmetala-
t
tion. In contrast, the in situ deprotonation of the triazolium salts with KOBu yielded the bimetallic Mn(0)
R
complexes [Mn
2
(CO)
8
(μ-di-trz )] with a bridging di-trz ligand when short alkyl chains (Me, Et, i-Pr) are
present as the N1 substituents of the triazolylidene ligand. The molecular structures of monometallic and bi-
Et
metallic complexes were determined by X-ray diffraction studies. In addition, the cationic fac-[Mn(di-trz )
(
CO)
2
(PPh
3
)
2
]Br complex, a rare example of a dicarbonyl Mn(I) N-heterocyclic carbene, was obtained when
Et
fac-[Mn(di-trz )(CO)
3 3
Br] was irradiated with visible light in the presence of PPh . The crystal structure
revealed a slightly distorted octahedral geometry around the Mn(I) centre, with the chelating di-triazolyl-
idene ligand situated in trans position to the two CO ligands in the equatorial plane, and the two phosphine
ligands occupying the axial positions. Cyclic voltammetry studies show reversible redox processes for the
monometallic Mn(I) complexes, and a quasi-reversible EC mechanism for the oxidation of the bimetallic
Received 9th February 2021,
Accepted 6th April 2021
DOI: 10.1039/d1dt00444a
Et
complexes. Infrared spectroelectrochemical studies along with DFT calculations for fac-[Mn(di-trz )
rsc.li/dalton
3
(CO) Br] suggest that the observed two consecutive reductions both occur at the metal centre.
6
–9
their potential in other fields such as photochemistry,
supramolecular chemistry,
Introduction
1
0,11
12
and electrocatalysis has been
Triazolylidenes (trz) have developed in recent years as a bur- recently demonstrated. Most examples of triazolylidene com-
1
–5
geoning subclass of NHC ligands.
Their modular synthesis plexes reported in the literature contain second- and third-row
through Cu(I) catalysed click reactions, which allows for tailor- transition metals, while the trz chemistry of first-row transition
1
3–19
ing them to specific functions, and their strong sigma-donor metals remains poorly developed.
properties have made them excellent candidates as carbene plexes bearing triazolylidene ligands are very scarce.
ligands for transition metals. To date, triazolylidene metal In line with our interest in N-heterocyclic carbene chemistry
In particular, Mn com-
20,21
3
14,15,22–34
complexes have been mainly applied in catalysis. However, of 3d metals,
performances
and motivated by the excellent catalytic
Mn complexes bearing bis-NHC
we recently described two
rare examples of Mn complexes incorporating di(1,2,3-triazolyl-
of
2
1–25
(
N-heterocylic carbene) ligands,
a
ITQB NOVA, Instituto de Tecnologia Química e Biológica António Xavier,
Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal.
2
1
idene) (di-trz) ligands (Chart 1). Notably, the only other
E-mail: broyo@itqb.unl.pt
b
LAQV- and UCIBIO-REQUIMTE, Departamento de Química, Faculdade de Ciências e example of a Mn-triazolylidene complex reported so far is a
Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal
c
Biosystems and Integrative Sciences Institute (BioISI), Faculdade de Ciências,
Universidade de Lisboa, Campo Grande, Lisboa, 1749-016, Portugal
d
Centro de Química Estrutural and Departamento de Engenharia Química, Instituto
Superior Técnico, Universidade de Lisboa, Av Rovisco Pais, 1049-001 Lisboa,
Portugal
e
Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012
Bern, Switzerland
†
Electronic supplementary information (ESI) available: Spectroscopic and
electrochemical data, crystallographic and DFT details. CCDC 2060440–2060444.
For ESI and crystallographic data in CIF or other electronic format see DOI:
1
0.1039/d1dt00444a
Chart 1 Manganese triazolylidene complexes reported in the literature.
Dalton Trans., 2021, 50, 5911–5920 | 5911
This journal is © The Royal Society of Chemistry 2021

View Article Online
Paper
Dalton Transactions
Mn(0) tricarbonyl complex bearing a 1,2,3-triazolylidene-based
tripodal ligand, described by Smith and co-workers in 2013
2
0
(
Chart 1). In our recent studies, directly linked di-trz ligands
were coordinated to Mn by reaction of their di-triazolium salts
t
with Mn(CO) Br in the presence of KOBu . When the di-trz
5
ligand contains an ethyl substituent in the N1 positions, the
reaction led to a bimetallic Mn(0) complex, in which the
ligand adopted a bridging rather than chelating binding mode
(Chart 1). In contrast, coordination of di-trz with the bulky
Scheme 2 Synthesis of Mn(0) complexes 1–3.
mesityl substituents in N1, yielded a manganese complex with
chelating di-trz ligand (Chart 1). While the selectivity was
remarkable, the origin of the different product formation was
unclear. In this work here, we have extended our studies to
Complexes 1 and 3 have been fully characterized by NMR
investigate the influence of the wingtip substituents (Me, i-Pr, and IR spectroscopy, and in the case of 3 by X-ray diffraction
n-Bu, p-tolyl) of the di-trz ligand on the product obtained by studies, Fig. 1. Coordination of L2a and L2c was corroborated
metalation of the triazolium salts. In addition, we demonstrate by the disappearance of the signals of the triazolium protons
1
that the metalation procedure determines the type of product at 9.5–9.7 ppm in the H NMR spectra, and the appearance of
1
3
obtained. Specifically, coordination of di(1,2,3-triazolylidenes) the characteristic resonance of the metalated carbon in the
C
to Mn(CO)
5
Br via Ag-transmetalation route selectively affords NMR spectra at 181.5 ppm (for 1) and 180.3 ppm (for 3). The
monometallic fac-[Mn(di-trz)(CO) Br] complexes. In contrast, carbonyl ligands in 1 and 3 showed the expected pattern in the
3
the in situ deprotonation of the corresponding triazolium salts IR spectra, displaying three strong IR bands (in the region
t
−1
−1
with KOBu yields bimetallic or monometallic Mn complexes 1971–1874 cm ) and a relatively week band at 2040 cm (for
or mixtures of the two, depending on the N1 substituents of 1) and 2037 cm− (for 3), and four resonances at 231, 229, 225,
1
1
3
the di-trz ligand.
and 223 ppm in their C NMR spectra.
In contrast to the results obtained with proligands L2a–L2c,
application of the same synthetic approach for L2d and L2e
afforded a mixture of the corresponding bimetallic and mono-
metallic complexes (Scheme 3). The ratio of bimetallic vs.
Results and discussion
Synthesis and characterisation
monometallic complexes in these mixtures was 57 : 43 (for
1
The new C4-linked ditriazoles L1a, L1c, and L1d were obtained 4 : 6) and 61 : 39 (for 5 : 7) according to H NMR spectroscopy
employing the well-established copper-catalysed click [3 + 2] (Fig. S25 and S26†). These mixtures were difficult to separate,
cycloaddition reaction that has been previously described for and complexes 4–7 could not be isolated in pure form.
3
5,36
the preparation of L1b, L1e, and L1f.
Subsequent methyl- However, single crystals of 4 and 5 were obtained after several
ation of the isolated di-triazoles with methyl triflate, followed crystallizations and their structures were determined by X-ray
by anion exchange with tetra-n-butylammonium bromide diffraction studies (Fig. 1(b) and (c), respectively).
afforded the di-triazolium bromide salts L2a–f in good yields
The Mn(0) centres in complexes 3–5 display a slightly dis-
1
(
Scheme 1). Compounds L2a–f were characterised by H and torted octahedral geometry, with bond angles close to the
1
3
C NMR spectroscopy and HR-MS analysis.
expected 90° (Fig. 1). In complex 3, the bond length between
Coordination of proligands L2a and L2c–e to manganese the two Mn(0) metal centres (Mn1–Mn2) is 2.9468(10) Å,
was investigated following the same synthetic approach that whereas the Mn1–C1 and Mn2–C7 bond distances are 2.050(4)
was previously reported by us for the coordination of L2b (R = and 2.051(4) Å, respectively. These values and the remaining
2
1
Et) and L2f (R = Mes). When L2a and L2c, bearing the Me bond distances in the molecule are similar to those observed
and i-Pr groups on the wingtips, respectively, were treated with for complexes 4 and 5 (e.g. Mn–Mn distances 2.9797(13) Å for
t
Mn(CO) Br in the presence of two equivalents of KOBu , the bi- 4 and 2.9324(7) Å for 5). In complex 4, the dihedral angles
5
R
metallic manganese(0) complexes [Mn
2
(CO)
8
(μ-di-trz )] [R = between the two triazolylidene rings are 50.96(10)° and 49.5
Me (1) and R = i-Pr (3)], in which the ligand adopts a bridging (4)°, for PART 1 and PART 2, respectively, which are very
binding mode, were isolated as the only products (Scheme 2).
similar to the observed for complex 3 (50.18(17)°). However, in
the case of complex 5, a dihedral angle of 47.36(14)°, closer to
that determined for the previously reported complex 2 (46.92
2
1
(
9)°), was observed.
These results show that the chelating bonding mode is
more preferred when bulkier trz ligands are present (2 : 3 for R
p-tolyl vs. 1 : 0 for R = mesityl). However, when the Ag-trans-
=
metalation route was applied for the coordination of L2a, L2b,
and L2f, the air stable yellow monometallic Mn(I) tricarbonyl
complexes containing chelating di-triazolylidene ligands fac-
Scheme 1 Synthesis of di-triazolium bromide salts L2.
5912 | Dalton Trans., 2021, 50, 5911–5920
This journal is © The Royal Society of Chemistry 2021

View Article Online
Dalton Transactions
Paper
Fig. 1 ORTEP-3 diagrams of complexes (a) 3, (b) 4 and (c) 5 using 50% probability level ellipsoids. All hydrogen atoms were omitted for clarity. In 4,
atoms Mn2, C8, N4, N5, N6, C11, C12 and C13 were found to be disordered over two positions with 80% (PART 1) and 20% (PART 2) probability,
depicted in solid and dashed bonds, respectively. In 5, half molecule was generated by symmetry operations. Selected bond lengths for 3: Mn1–Mn2
2.9468(10) Å, Mn1–C1 2.050(4) Å, Mn2–C7 2.051(4) Å, Mn1–CO between 1.801(4) and 1.831(4) Å, Mn2–CO between 1.798(5) and 1.854(5) Å.
Selected bond lengths for 4: PART 1 – Mn1–Mn2 2.9797(13) Å, Mn1–C1 2.0443(13) Å, Mn2–C8 2.051(4) Å, Mn1–CO between 1.8000(16) and 1.8518(16)
Å, Mn2–CO between 1.752(2) and 1.858(2) Å. Selected bond lengths for 5: Mn1–Mn1# 2.9324(7) Å, Mn1–C1 2.047(3) Å, Mn1–CO between 1.788(3)
and 1.843(3) Å.
were obtained for complex 10 (Fig. 2). Complex 10 features a
slightly distorted octahedral Mn(I) centre with bond angles in
the coordination sphere very close to 90°. The chelating di-
triazolylidene ligand displays a C1–Mn–C13A bite angle of
7
7.4(2)°. The Mn–Br bond length is 2.5568(11) Å and the Mn–
CCO distances vary between 1.774(7) and 1.833(6) Å, similar to
the Mn(0)–CO bond lengths. Likewise, the Mn–Ctrz bond
lengths (2.038(6) and 2.048(6) Å are essentially identical to
Scheme 3 Synthesis of complexes 4–7 from di-triazolium bromide
salts L2d–L2e.
R
[
Mn(di-trz )(CO)
3
Br] [R = Me (8), Et (9), and Mes (10)] were, in
all cases, isolated as the only product (Scheme 4).
The identity of complexes 8–10 was determined by spectro-
scopic techniques and elemental analysis. Complex 10 has
2
1
been previously reported by us. Consistent with the proposed
structures, the IR spectra of these complexes displayed the
2
2,23
typical patterns for fac-carbonyl ligands.
The values of the
symmetrical CO stretching vibrations of 8–10 appear at lower
wavenumbers than those reported for the imidazole-2-ylidene
R
−1
analogue fac-[Mn(bis-NHC )(CO)
3
Br] (2004 cm for R = Me,
and 2007 cm− for R = Mes), reflecting the stronger donor
1
capacity of triazolylidenes compared to imidazolylidene
2
2,23
ligands.
Single crystals suitable for X-ray structure analysis
Fig. 2 ORTEP-3 diagram of complex 10, using 50% probability level
ellipsoids. All hydrogen atoms, two dichloromethane molecules and a
Mes
3
second [Mn(CO) (di-trz )Br] complex were omitted for clarity.
Selected bond lengths: Mn1–Br1 2.5568(11) Å, Mn1–C1 2.038(6) Å,
Mn1–C13 2.048(6) Å, Mn1–CO between 1.774(7) and 1.833(6) Å.
Scheme 4 Synthesis of Mn(I) complexes 8–10.
This journal is © The Royal Society of Chemistry 2021
Dalton Trans., 2021, 50, 5911–5920 | 5913

View Article Online
Paper
Dalton Transactions
those observed in the bridging coordination mode to Mn(0). weight loss in the 146–210 °C temperature ranges, and a more
The dihedral angle between the two triazolylidene rings is 7.4 gradual further 25% loss up to about 400 °C, commensurate
(
2)°, which reflects an essentially planar backbone of the with an initial dissociation of bromide and one CO, followed
ligand as expected for a chelating bonding mode of this by loss of a Mn(CO) fragment. For both complexes, the minor
2
ligand.
weight loss up to ca. 150 °C may be due to the loss of residual
The formation of the bimetallic Mn(0) complexes 1–5 is solvent molecules.
mechanistically intriguing as it involves a reduction of the
In addition, we were interested in investigating the photo-
metal center. Initially, the base was assumed to be critical for chemical stability of 2 and 9. We observed the loss of carbonyl
reducing the Mn(I) precursor. Monitoring the interaction of ligands when acetonitrile solutions of 2 and 9 were exposed to
t
Mn(CO)
5
Br with KOBu by FT-IR revealed a depletion of the visible light irradiation for several hours (LED, ca. 415 nm,
carbonyl stretching bands of the precursor at 2046 and 6 h). However, the identification of the products obtained in
1
2
1
007 cm− , and the gradual appearance of three new bands at these decarbonylating reactions was not possible.
−
1
974, 1936, and 1900 cm , attributed to the in situ formation Interestingly, when the irradiation of acetonitrile solutions of
of the alkoxide complex [Mn(CO) (OBu )] , yet no reduction 9 was performed in the presence of two equivalents of PPh ,
to Mn(0) was observed (Fig. S53†). Moreover, when the metala- the cationic dicarbonyl [Mn(di-trz )(CO)
t
37
n
x
3
Et
2
(PPh
3
)
2
]Br (11)
t
tion was performed with 4 moleq. KOBu in order to account complex was isolated as a pure compound (Scheme 6).
for the two deprotonation steps of the di-trz ligand precursor Complex 11 has been fully characterised by spectroscopic
and the two reduction processes at the metal center, the reac- methods, and its molecular structure was determined by X-ray
tion proceeded very sluggishly and the yields of complex 2 diffraction studies. Although the quality of the crystallographic
markedly dropped from 35% to traces only, strongly suggesting data was poor, it confirmed the proposed structure (Fig. S52†).
that the base is actually not involved in the reduction of the Complex 11 features a trans arrangement of the NHC and the
Mn(I) precursor. In support of this conclusion, replacement of carbonyl ligands in an octahedral geometry where the PPh
KOBu with LiOPr as an actual reducing agent did not lead to ligands are located mutually trans and occupying the axial
3
t
i
any detectable formation of Mn(0) or the formation of acetone positions. As expected for this type of geometry, the IR spec-
(
Fig. S54†). We therefore speculate that Mn(I) reduction may be trum of 11 showed two strong resonances at 1916 and
promoted either by the proximity of two Mn–Br units, 1834 cm− for the symmetric and asymmetric CO vibrations,
1
3
1
imparted by the ditopic di-trz ligand and ensuing Br
2
elimin- respectively, while the P NMR spectrum features one single
ation, or by a disproportionation involving a Mn(I)–trz unit resonance at δ 69.2 ppm for the two identical phosphorus
1
3
and a non-coordinated Mn(I) precursor salt.
In this context, it is interesting to note that the reaction of the Ctrz atom at δ 196.3 ppm, and one resonance at δ
the dimetallic Mn(0) complex 2 with Br led to the monometal- 230.9 ppm for the two symmetry-related carbonyl ligands.
atoms. The C NMR spectrum of 11 displays a resonance of
2
lic complex 9 with the concomitant formation of Mn(CO) Br, Complex 11 represents a rare example of a Mn(I) dicarbonyl
5
suggesting facile Mn–Ctrz and Mn–CO bond making and break- NHC complex. To the best of our knowledge, the only other
ing (Scheme 5). This process may tentatively involve CO dis- example reported in the literature corresponds to a Mn
sociation and subsequent addition of Br across both Mn(0) complex containing a NH,NH-substituted saturated cyclic dia-
2
2
sites. Similar reaction with H did not allow the isolation of minocarbene with a bidentate diphosphine ligand occupying
3
8
the corresponding hydride species.
All complexes 1–10 are air and moisture stable. They can be
stored in the dark under air atmosphere during weeks without of PPh
one cis and one trans position to the NHC donor.
When 9 is irradiated in the presence of only one equivalent
, we observed the formation of complex 11 that precipi-
any notable decomposition. The thermal stability of complexes tated from the acetonitrile solution, along with the formation
3
2
2
and 9 was analysed by thermogravimetric analysis. Complex of two new Mn complexes that remained in the solution. The
3
1
starts to decompose around 164 °C with 58% weight loss up
(CO) frag- δ 73.25 ppm, a peak at δ 69 ppm, which corresponds to 11,
ment (58.9%; Fig. S33†). Complex 9 is slightly less stable than and a peak at δ 55 ppm, in a ratio 1 : 0.3 : 0.2, respectively
, starting to decompose at 146 °C (Fig. S34†). In contrast to (Fig. S40a†). The peak at δ 55 ppm was assigned to the Mn(0)
P NMR of the acetonitrile solution showed one major peak at
to 300 °C, which may suggest the loss of the Mn
2
8
2
complex 2, complex 9 shows two distinct steps, a sharper 25%
Scheme 6 Reaction of 9 with two equivalents of PPh
light (LED, ca. 415 nm) irradiation.
3
under visible
Scheme 5 Reaction of 2 with bromine.
5914 | Dalton Trans., 2021, 50, 5911–5920
This journal is © The Royal Society of Chemistry 2021

View Article Online
Dalton Transactions
Paper
3
Scheme 7 Reaction of 9 with one equivalent of PPh under visible light
(
LED, ca. 415 nm) irradiation.
3
9
2 8 3 2
dimer species [Mn (CO) (PPh ) ]. We propose that the peak
3
1
at δ 73.25 ppm observed in the P NMR corresponds to the
Et
cationic tricarbonyl mono phosphine fac-[Mn(di-trz )
(
3 3
CO) (PPh )]Br (12) complex (Scheme 7). This proposal is
1
3
based on the information obtained from the C NMR spec-
trum of the mixture, which showed the expected resonances
for a tricarbonyl Mn complex, two resonances at δ 223 and Fig. 3 Cyclic voltammograms of complexes 9 and 10 (1 mM) in CH CN,
3
2
19 ppm for the carbonyl groups, and one resonance for the
N
0
2
saturated solutions using TBAPF
6
as supporting electrolyte (0.1 M) at
.1 V s− . Glassy carbon (3 mm diameter) was used as working, platinum
1
carbene at δ 187 ppm (Fig. S40b†). Unfortunately, 12 could not
be isolated in pure form from the reaction mixture.
wire as counter and 3 M Ag/AgCl as reference electrodes.
Irradiation of the dimetallic complex 2 with visible light
(
LED, ca. 415 nm) in the presence of two equivalents of PPh
afforded a mixture of Mn complexes 11, 12, [Mn (CO) (PPh ],
along with a new Mn species of unknown identity that dis-
played a resonance at δ 92.76 ppm (Fig. S41†).
3
2
8
3 2
)
P
Cyclic voltammetry, infrared spectroelectrochemistry and DFT
calculations
2
1
As previously found for the bimetallic Mn(0) complex 2, both
and 3 also exhibited one quasi-reversible oxidation process
1
+
at E1/2 = −0.05 and −0.06 V (potential vs. Fc/Fc ), respectively,
and their responses are indicative of electron-transfer followed
by a chemical reaction (EC) mechanism (Tables S1 and S2 and
Fig. S42†). Complexes 9 and 10 showed a reversible oxidation
process at E1/2 ≈ 0.3 V (Fig. 3), shifted to a higher potential in
2
1
comparison with the bimetallic Mn(0) counterparts. The
mixtures of 4 and 6, and those of 5 and 7 showed two oxi-
dation events around −0.05 and +0.3 V, supporting the pres-
ence of a mixture of di-Mn(0) and monometallic Mn(I) com-
plexes as deduced by NMR spectroscopy (Fig. S44†). In
addition to the oxidation processes, the CV of 9 and 10 showed
two irreversible one-electron reduction events at E1/2 = −2.18
and −2.45 V (for 9) and E1/2 = −2.11 and −2.74 V (for 10)
Fig. 4 FTIR-SEC experiments during the first reduction (at ca. −2.1 V)
using 5 mM of 9 and 0.1 M TBAPF in a N saturated CH CN solution, Pt
6 2 3
grids as working and counter electrodes and Ag wire as pseudo-refer-
ence electrodes. Blue spectrum corresponds to 0 min and red corres-
ponds to the spectrum recorded after 10 min of experiment.
(Fig. 3). As expected, the cathodic wave of 9 (E1/2 = −2.18 V) is
negatively shifted when compared to that of 10 (E1/2 = −2.11 equilibrium between the neutral starting complex 9 and the
Me
+
+
V), reflecting the stronger donor capacity of the triazolylidene acetonitrile adduct [Mn(CO)
3
(di-trz )(CH
3 3
CN)] (9CH CN )
ligand bearing an ethyl group in the N1 position vs. a mesityl.
(Scheme 8). This phenomenon has been previously observed
To gain insight into the species formed in the reduction for the [Mn(CO) (bis-NHC )Br] complex, and it demon-
3
Me
22
process, the reduction behaviour of 9 was further investigated strates the ability of these complexes to easily replace the
by infrared spectroelectrochemistry (FTIR-SEC). Experiments bromide ligand by acetonitrile. Upon the first reduction event
were performed in acetonitrile. Before applying any potential, (at ca.−2.1 V vs. Ag pseudo reference), the FTIR-SEC spectra
we observed that the CO stretching bands at 1999, 1904, showed the depletion of the v(CO) bands of the parent com-
1
−1
1
887 cm− of complex 9 slowly disappeared, and new bands at plexes with new bands growing at 1943, 1886 cm (Fig. 4, red
−1
2
019 and 1923 (broad resonance) cm started to appear in the spectrum). In agreement with DFT calculations and previous
2
2
22
−1
spectrum (Fig. 4, blue spectrum). Based on literature data,
studies, the new bands at 1943 and 1886 cm correspond to
we propose that this process corresponds to a slow solvolysis five-coordinate species 9′ (Scheme 8). This assignment is
This journal is © The Royal Society of Chemistry 2021
Dalton Trans., 2021, 50, 5911–5920 | 5915

View Article Online
Paper
Dalton Transactions
substrate binding. Evaluation of the (electro)catalytic activity of
these complexes is currently under investigation in our
laboratories.
Experimental details
General methods
All reactions and manipulations were carried out under nitro-
gen atmosphere using standard Schlenk techniques, and sol-
vents were purified from appropriate drying agents.
Deuterated solvents were degassed and stored over molecular
sieves. All other reagents were purchased from commercial
suppliers and used without further purification. Preparation of
compounds L1b, L1f, L2b, L2f were performed following the
Scheme 8 Proposed species formed in the 2e− reduction of 9 in
acetonitrile.
3
5,36
procedure reported in the literature.
pared according to a literature procedure.
Complex 2 was pre-
2
1 1
13
H and C NMR
Table 1 Experimental and DFT calculated harmonic vibrational fre-
spectra were recorded on a Bruker Avance III 400 MHz and
Bruker Avance II 500 MHz. Electrospray mass spectra (ESI-MS)
were recorded on a Micromass Quatro LC instrument; nitrogen
was employed as drying and nebulising gas. Elemental ana-
lyses were performed in our ITQB laboratory services. TGA ana-
lyses were performed in TGA Q50 V6.7 Build 203 instrument,
with 9–12 mg sample in an aluminium pan, over a temperature
a
quencies for the highest CO stretching frequency
Experimental ѵCO (cm−1
Calculated ѵCO (cm−1
)
Species
)
9
1999
2019
1943
1844
2000
2022
1940
1855
+
9
9
3
CH CN
′
−
[
9′]
a
range of 25–500 °C, under nitrogen atmosphere at a heating
Details can be found in the ESI.†
rate of 5 °C min−
1
.
General procedure for the synthesis of L1a, c, and d
the DFT-calculated IR spectrum of 9′ (Table 1). The second A mixture of RI (R = Me, i-Pr, n-Bu) (4.49 mmol) and NaN
based on the good correlation between the experimental and
3
reduction shows the appearance of new bands that reasonably (875 mg, 13.50 mmol) in THF/H
2
O (30 mL, 1 : 1 v/v) was stirred
−
agree with the calculated CO stretching frequencies for [9′]
at room temperature for 16 h. Then, 1,4-bis(trimethyl)silylbu-
(
Fig. S49,† Table 1). DFT calculations suggest that both tadiyne (411 mg, 2.10 mmol), pyridine (0.298 ml, 3.70 mmol),
reduction events occur mainly in the metal centre, as shown
CO (582 mg, 4.20 mmol), CuSO (73 mg, 0.46 mmol), and
K
2
3
4
by a spin density located at the Mn-atom in the resulting spin Na-ascorbate (589 mg, 3.00 mmol), were added, and the reac-
doublet intermediate with a square pyramidal geometry, 9′, tion mixture was refluxed for 48 h. After cooling to room temp-
−
and the spin singlet intermediate, [9′] , with a trigonal bipyra- erature, the solvent was removed under vacuum, and the
midal geometry (Fig. S50 and S51,† respectively).
2 2
residue was extracted with CH Cl (3 × 50 mL). The combined
organic layers were washed with 10% ammonium hydroxide
solution (2 × 50 mL), water (2 × 50 mL) and brine (2 × 50 mL),
dried over Na
2 4
SO , and filtered. All volatiles were removed
Conclusions
from the filtrate under reduced pressure to yield the corres-
Here we demonstrate the versatility of di-triazolylidene ponding ditriazoles L1a, L1c, and L1d as white solids.
1
ligands to stabilize both bimetallic Mn(0) as well as monome-
Characterisation of L1a. (39%, 134 mg). H NMR (400 MHz,
1
3
tallic Mn(I) complexes. Depending on the applied synthetic DMSO-d , 298 K) δ = 8.41 (s, 2H, Htrz), 4.09 (s, 6H, NCH
̲
3).
C
6
1
procedure and the steric demand of the triazole wingtip { H} NMR (100 MHz, DMSO-d
6
, 298 K): δ = 139.17 (C
̲
trz–NCH ),
3
groups, this ditopic ligand assumes either a bridging coordi- 122.38 (C
nation mode to two Mn(0) centres, or a chelating bonding
mode to a single Mn(I) centre. A facile oxidation strategy using DMSO-d
bromine allows to convert the bridging into the chelating NCH(CH
t 3
̲ rz–H), 36.38 (NC ̲H ).
1
Characterisation of L1c. (59%, 273 mg). H NMR (400 MHz,
6
, 298 K): δ 8.53 (s, 2H, Htrz), 4.90–4.84 (m, 2H,
), 1.54 (s, 6H, NCH(CH ), 1.52 (s, 6H, NCH(CH ).
C{ H} NMR (100 MHz, DMSO-d , 298 K): δ 139.18 (C –NCH
̲
1
3
)
2
̲
3
)
2
3 2
̲ )
1
3
bonding mode. Further functionalization provided access to
̲
6
trz
Et
[
Mn(di-trz )(CO)
2
(PPh
3
)
2
]Br, a rare example of a Mn dicarbo- (CH
3
3
)
)
2
), 119.45 (C
3 2
̲trz–H), 52.52 (NC ̲H (CH ) ), 22.59 (NCH
nyl NHC complex and demonstrates the potential for ligand (C
substitution and tailoring of the properties of the Mn(di-trz)
unit. Moreover, electrochemical reduction suggests the for- CDCl
mation of a coordinatively unsaturated Mn(0) complex with a NCH
̲H
2
).
1
Characterisation of L1d. (79%, 412 mg). H NMR (400 MHz,
, 298 K): δ 8.03 (s, 2H, Htrz), 4.41 (t, J = 7.16 Hz, 4H,
CH CH CH ), 1.96–1.88 (m, 4H, NCH CH CH CH ),
free coordination site, which provides ample opportunities for 1.42–1.33 (m, 4H, NCH CH CH CH ), 0.93 (t, J = 7.42 Hz, 6H,
3
̲
2
2
2
3
2
̲
2
2
3
̲
2
2
2
3
5916 | Dalton Trans., 2021, 50, 5911–5920
This journal is © The Royal Society of Chemistry 2021

View Article Online
Dalton Transactions
Paper
1
3
1
1
NCH
2
CH
2
CH
2
CH
̲
3
). C{ H} NMR (100 MHz, CDCl
3
, 298 K): δ
Characterisation of L2f. (83%, 922 mg). H NMR (400 MHz,
1
40.31 (C
̲
trz–H), 120.46 (C
̲
–NCH CH CH CH ), 50.32 DMSO-d , 298 K): δ 10.12 (s, 2H, Htrz), 7.29 (s, 4H, CH
̲
-Mes),
-Mes), 2.16 (s, 12H, CH
, 298 K): δ 142.41, 134.53
-Mes), 128.37, 40.59
-Mes). ESI-HRMS m/z [M
trz
2
2
2
3
6
(
(
NC
NCH
̲
H
2
CH
CH
2
CH
2
CH
CH
3
),
32.32
(NCH
2
C
̲
2
CH
2
CH
3
),
19.77 4.63 (s, 6H, NCH
̲
3
), 2.40 (s, 6H, CH
̲
3
̲ -
1
3
2
2
C
̲
H
2
3
), 13.55 (NCH
2
CH CH
2
2
H
3
).
Mes). C NMR (100 MHz, DMSO-d
6
(
(
C̲ –H), 134.31, 130.86, 129.64 (CH̲
trz
General procedure for the preparation of L2a–f
NC
̲
3
), 20.75 (C
̲
3
-Mes), 16.93 (C
̲
3
2
+
The appropriate ditriazole L1 (1.98 mmol) was dissolved in the − 2Br] 201.1252, calcd 201.1266.
minimum quantity of dichloromethane, and MeOTf (0.87 mL,
7
.92 mmol) was added at 0 °C. The mixture was stirred at
General procedure for the synthesis of complexes 1 and 3
room temperature for 48 h. Then, diethyl ether was added to
the mixture to yield a white precipitate that was collected by fil- Solid Mn(CO) Br (175 mg, 0.64 mmol) was suspended in THF
5
tration, dried in vacuum, redissolved in a minimum amount (20 mL) and potassium tert-butoxide (124 mg, 1.11 mmol) was
of acetone, and treated with tetra-n-butyl ammonium bromide added first, followed by addition of the ditriazolium bromide
(
996 mg, 3.09 mmol). After stirring for 10 min, a white solid salt (0.5 mmol) at 60 °C. The resulting suspension was heated
precipitated from the solution. The solid was isolated by fil- to 60 °C for 16 h under stirring. All volatiles were removed
tration, washed with acetone and ether, and dried under under vacuum, the residue was washed with Et O (3 × 15 mL)
vacuum to yield the corresponding di-triazolium bromide salts and re-dissolved in CH Cl (80 mL). The CH Cl solution was
2
2
2
2
2
L2a–L2f, as white solids.
Characterisation of L2a. (88%, 616 mg). H NMR (400 MHz, with Na
then washed with water (80 mL) and the organic extract dried
SO . The solution was filtered and concentrated to
1
2
4
DMSO-d , 298 K): δ 9.45 (s, 2H, H ), 4.47 (s, 6H, NCH ), 4.34 dryness under vacuum to yield complexes 1 and 3, which were
6
trz
3
1
3
1
(
1
s, 6H, NCH
33.89 (Ctrz–NCH
3
). C{ H} NMR (100 MHz, DMSO-d
), 126.42 (Ctrz–H), 40.60 (NCH
6
, 298 K): δ isolated as orange solids.
). ESI-HRMS
1
3
̲
3
Characterisation of 1. (35%, 59 mg). H NMR (400 MHz,
2
+
13
m/z [M − 2Br] 97.0633, calcd 97.0640.
Characterisation of L2b. (65%, 493 mg). H NMR (400 MHz, NMR (125 MHz, DMSO-d
DMSO-d , 298 K): δ = 9.68 (s, 2H, Htrz), 4.83 (q, J = 7.28 Hz, 4H, 225.29 (CO), 223.60 (CO), 181.52 (Ctrz), 138.52 (Ctrz–NCH
DMSO-d , 298 K): δ 4.35 (s, 6H, NCH ), 4.14 (s, 6H, NCH ).
C
6
3
3
1
6
, 298 K): δ 231.34 (CO), 229.37 (CO),
),
6
3
−1
NCH CH ), 4.41 (s, 6H, NCH ), 1.62 (t, J = 7.29 Hz, 6H, 40.77 (NCH ), 38.33 (NCH ). IR (KBr, cm ): 2040 (vs), 1971
2
3
3
3
3
1
3
1
NCH
(
(
2
CH
3
). C{ H} NMR (100 MHz, DMSO-d
6
, 298 K) δ 132.67 (vs), 1943 (vs), 1924 (vs), 1885 (vs).
CH ), 14.16 Characterisation of 3. (32%, 50 mg). H NMR (400 MHz,
1
C
trz–H), 126.58 (Ctrz–NCH
3
), 49.59 (NCH
2
3
+
NCH CH ). ESI-HRMS m/z [M − 2Br + MeO] 253.1762, calcd DMSO-d , 298 K): δ 5.56–5.49 (m, 2H, NCH(CH ) ), 4.17 (s, 6H,
2
3
6
3 2
2
53.1777.
NCH
3
), 1.71 (d, J = 6.65 Hz, 6H, NCH(CH
3
)
2
), 1.57 (d, J = 6.58
1
13
3 2 6
Characterisation of L2c. (78%, 631 mg). H NMR (400 MHz, Hz, 6H, NCH(CH ) ). C NMR (125 MHz, DMSO-d , 298 K): δ
DMSO-d , 298 K): δ 9.70 (s, 2H, Htrz), 5.30–5.23 (m, 2H, 231.17 (CO), 229.27 (CO), 225.31 (CO), 222.99 (CO), 180.28
6
NCH(CH
3
)
2
), 4.42 (s, 6H, NCH
3
), 1.68 (d, J = 6.67 Hz, 12H, NCH (Ctrz), 137.47 (Ctrz–NCH(CH
3
)
2
), 56.65 (NCH(CH
3 2
) ), 38.77
1
3
1
(
(
(
CH
3
)
2
). C{ H} NMR (100 MHz, DMSO-d , 298 K): δ 131.46 (NCH ), 23.44 (NCH(CH ), 22.34 (NCH(CH )
6
3
3
)
2
3 2
). IR (KBr,
−
1
Ctrz–NCH(CH ) ), 126.74 (Ctrz–H), 58.44 (NCH(CH ) ), 39.66 cm ): 2037 (m), 1970 (s), 1931 (vs), 1912 (vs), 1881 (s). Elem.
NCH
3 2
3 2
+
3
), 21.73 (NCH(CH
3
)
2
). ESI-HRMS m/z [M
−
Br]
2 6 8
anal. calcd for C20H20Mn N O : C 41.25; H 3.46; N 14.43%.
2
+
3
29.10768, calcd 329.10893; [M − 2Br] 125.09459, calcd Found: C 41.03; H 3.65; N 14.12%.
25.09529. General procedure for the synthesis of complexes [(di-trz)Mn
Characterisation of L2d. (73%, 635 mg). H NMR (400 MHz, (CO) Br] 8 and 9. The appropriate di-triazolium bromide
DMSO-d , 298 K): δ 9.54 (s, 2H, Htrz), 4.79 (t, J = 7.04 Hz, 4H, (1 mmol) salt was dissolved in dry dichloromethane, Ag
1
1
3
6
2
O
NCH CH CH CH ), 4.36 (s, 6H, NCH ), 2.02–1.93 (m, 4H, (1.2 mmol) was added at room temperature, and the mixture
2
2
2
3
3
NCH
2
CH
=
2
CH
2
CH
3
), 1.43–1.34 (m, 4H, NCH
2
CH
2
CH
2
CH
3
), 0.95 was stirred for 24 h. Then, Mn(CO)
C{ H} NMR and the mixture was heated at 50 °C for 72 h. After cooling to
room temperature, the solution was filtered through a pad of
30.67 Celite, and concentrated to dryness. The residue was washed
13.23 with Et O (3 × 15 mL), redissolved in CH Cl (80 mL), and the
solution was washed with water (80 mL). The organic phase
SO , filtered, and the solvent removed
under vacuum to yield the desired complex isolated as a yellow
Characterisation of L2e. (84%, 840 mg). H NMR (400 MHz, solid.
DMSO-d , 298 K): δ 10.37 (s, 2H, Htrz), 8.05 (d, J = 8.39 Hz, 4H, Characterisation of 8. (75%, 105 mg). H NMR (400 MHz,
CH-p-tolyl), 7.65 (d, J = 8.32 Hz, 4H, CH-p-tolyl), 4.65 (s, 6H, DMSO-d
NCH -p-tolyl). C NMR (100 MHz, DMSO-d6, NMR (125 MHz, DMSO-d , 298 K): δ 218.83 (CO), 218.46 (CO),
5
Br (1 mmol) was added,
1
3
1
(
(
t,
J
2 2 2 3
7.37 Hz, 6H, NCH CH CH CH ).
100 MHz, DMSO-d , 298 K): δ 132.80 (Ctrz–H), 126.78 (Ctrz
–
6
NCH
2
CH
CH
NCH CH CH CH ).
2
CH
2
CH
3
),
53.63
18.66
(NCH
(NCH
2
CH
CH
2
CH
CH
2
CH
CH
3
),
),
(
(
NCH
2
2
CH
2
CH
3
),
2
2
2
3
2
2
2
2
2
2
3
+
ESI-HRMS m/z [M − Br] 359.13692, calcd 359.13818; [M − was dried with Na
2
4
2
+
2
Br] 139.11026, calcd 139.11094.
1
1
6
1
3
̲
̲
6
, 298 K): δ 4.54 (s, 6H, NCH
3
), 4.33 (s, 6H, NCH
3
).
C
1
3
̲
3), 2.48 (s, 6H, CH̲
3
6
). IR (KBr, cm− ): 1999 (vs), 1885
1
2
98 K): δ 142.66, 132.29, 131.03 (C
̲
trz–H), 130.90 (C
-p-tolyl). ESI-HRMS m/z (vs). Elem. anal. calcd for C11
20.44%. Found: C 31.91; H 2.64; N 20.83%.
̲H -p-tolyl), 182.19 (Ctrz), 141.66 (NCH
3
1
27.39, 121.66 (CH-p-tolyl), 20.84 (CH
̲
̲
3
H
12BrMnN : C 32.14; H 2.94; N
6 3
O
2
+
[M − 2Br] 173.0942, calcd 173.0953.
This journal is © The Royal Society of Chemistry 2021
Dalton Trans., 2021, 50, 5911–5920 | 5917

View Article Online
Paper
Dalton Transactions
1
Characterisation of 9. (46%, 102 mg). H NMR (400 MHz, lised from hot ethanol). All potentials are referenced to ferro-
DMSO-d , 298 K): δ 4.66 (q, 4H, NCH CH ), 4.51 (s, 6H, NCH ), cene/ferrocenium couple. The working electrode was polished
6
2
3
3
1
3
1
2 3
.58 (t, J = 7.2 Hz, 6H, NCH CH ). C NMR (125 MHz, DMSO- with alumina pastes of 1 and 0.05 μm diameter sizes and
6
d , 298 K): δ 219.00 (CO), 218.72 (CO), 180.91 (Ctrz), 141.61 washed thoroughly with Milli-Q water and dried under a nitro-
(
Ctrz–NCH CH ), 48.32 (NCH CH ), 15.41 (NCH CH ). IR (KBr gen flux. All complexes 1–10 were studied in CH CN solutions
2
3
2
3
2
3
3
−
1
cm ): 1996 (vs), 1899 (vs), 1883 (vs). Elem. anal. calcd for whereas complex 11 was studied in CH
2
Cl
2
solution. The cyclic
C
13
H
16BrMnN
6
O
3
: C 35.56; H 3.67; N 19.14%. Found: C 35.22; voltammograms were recorded using a Bioanalytical Systems
CV-50 W Voltammetric Analyzer (BASi) controlled by software.
H 3.33; N 18.91%.
Synthesis of 9 from complex 2. Complex 2 (96 mg, FTIR-SEC experiments were performed using a cell acquired
0
.17 mmol) was dissolved in the minimum quantity of di- from LabOmak. This cell has two platinum grids as working
chloromethane and bromine (2 eq.) was added to the sample. and counter electrodes and an Ag wire as the pseudo-reference
The mixture was stirred for 2 h, and then, all volatiles were electrode. A N saturated CH CN solution with 5 mM of 9 and
removed under vacuum. The residue was extracted in a 0.1 M of TBAPF was injected in the FTIR-SEC cell. A linear vol-
mixture of dichloromethane and water. The organic phase was tammogram was performed using a scan rate of 10 mV s to
dried with Na SO , filtered, and the solvent was removed reach the desired reduction process. The IR spectra were
under vacuum to yield 9 as a yellow solid (99%, 74 mg). obtained using a Nicolet Nexus 6700 FTIR spectrophotometer
Synthesis of complex 10. The ditriazolium bromide salt L2f with a resolution of 4 cm , mirror velocity of 0.3165, aperture
2
3
6
−
1
2
4
−1
O (162 mg, 0.7 mmol) and KBr 32, gain 4 with 16 scans between 2200–1780 cm− . The back-
1
(
(
112 mg, 0.2 mmol), Ag
238 mg, 2 mmol) were suspended in dry acetonitrile (10 mL), ground spectrum was performed with the sample at the open
2
and the mixture was stirred under exclusion from light for 2 circuit potential.
days at 50 °C. Then, the solution was filtered through a pad of
X-Ray data collection. Crystals for single-crystal X-ray ana-
Celite and the filtrate evaporated to dryness. The crude lysis of complexes 3, 4, 5, 10, and 11 were selected and covered
obtained was redissolved in dry tetrahydrofuran (15 mL), Mn with Fomblin (polyfluoro ether oil) and mounted on a nylon
5
(CO) Br (27 mg, 0.1 mmol) was added, and the mixture was loop. The data were collected at 110 K on a Bruker D8 Venture
stirred at 60 °C for 2 days. The solution was then filtered diffractometer equipped with a Photon 100 CMOS detector
through a pad of Celite and evaporated to dryness. The residue and an Oxford Cryosystem Cooler, using graphite monochro-
was washed with Et
80 mL). The CH Cl
and the organic phase dried with Na SO (40%, 25 mg).
2
O (3 × 15 mL), and redissolved in CH
2
Cl
2
mated Mo-Kα radiation (λ = 0.71073 Å). The data was processed
(
2
2
solution was washed with water (80 mL) using the APEX3 suite software package, which includes inte-
1
H
gration and scaling (SAINT), absorption corrections
2
4
4
0
NMR, IR spectroscopy and elemental analysis data were in (SADABS ) and space group determination (XPREP). Structure
2
1
accord with previously data reported for complex 10. Single solution and refinement were done using direct methods with
4
1
crystals of 10 were obtained by crystallization with CH Cl / the programs SHELXT 2014/5 and SHELXL (version 2018/3)
2
2
4
2
43
Et
2
O.
Synthesis of [Mn(di-trz )(CO)
Schlenk tube was charged with complex
.05 mmol), two equivalents of PPh (32 mg, 0.13 mmol), and crystal size, poor quality, and diffracting power of 11 gave rise
inbuilt in APEX, SIR2019 and WinGX-Version 2020.1 soft-
]Br (11). A 5 mL ware packages. In the crystal structure of 4, a certain extent of
(22.4 mg, disorder is observed, with 80% and 20% occupancy. The
Et
2
3 2
(PPh )
9
0
3
acetonitrile (2 mL). The mixture was stirred at room tempera- to low quality data. Multiple attempts were made to grow
ture and irradiated with violet LEDs (ca. 415 nm, 9.5 W) for better diffracting crystals, all of them unsuccessful.
8
h. Then, a precipitate was formed, which was isolated by fil- Nevertheless, the structure refined to convergence and all
tration, washed with diethyl ether and dried under vacuum to results were consistent with the model reported herein
1
yield 11 as a yellow solid (25%, 12 mg). H NMR (400 MHz, (Fig. S52†). All non-hydrogen atoms were refined anisotropi-
CD
.18 (q, 4H, NCH
NMR (125 MHz, CD Cl , 298 K): δ 230.87 (CO), 196.31 (C ), with C–H distances of 0.95 Å, 0.98 Å, 0.99 Å, and 1.00 Å for aro-
2
Cl
2
, 298 K): δ 7.27 (s, 30H, CH-PPh
3 3
), 4.71 (s, 6H, NCH ), cally. Hydrogen atoms were inserted in idealized positions and
1
3
3
2
CH ), 0.90 (t, J = 6.90 Hz, 6H, NCH
3
2
CH
3
).
C
allowed to refine riding on the parent carbon or oxygen atom
2
2
trz
1
1
39.77, 138.08, 137.94, 137.81, 134.20, 134.06, 133.32, 129.61, matic, methyl, methylene and methine H atoms, respectively.
28.94, 128.39, 47.90 (NCH CH ), 41.31 (NCH ), 12.64 The molecular diagrams were drawn with ORTEP-3 (version
2
3
3
3
1
44,45
(
NCH CH ). P NMR (400 MHz, CD Cl , 298 K): δ 69.23. IR 2020.1),
included in the software package. Crystal and
KBr, cm− ): 1916 (s), 1834 (vs). HRMS m/z [M − Br] 855.2526, structure refinement data are given in Table S9.† The data
were deposited in the CCDC under deposit numbers 2060440
2
3
1
2
2
+
(
calcd 855.2524.
Electrochemical studies. Cyclic voltammetry experiments for 3, 2060441 for 4, 2060442 for 5 and 2060443 for 10, and
were performed in a three-electrode one compartment electro- 2060444 for 11.†
chemical cell using glassy carbon (CHI Instruments, 3 mm dia-
Computational details. All calculations were performed
4
6
meter) and platinum wire as working and counter electrodes, using the GAUSSIAN 09 software package and the PBE0 func-
respectively. Ag/AgCl 3 M KCl electrode (CHI Instruments) was tional without symmetry constraints. That functional uses a
used as reference electrode and tetrabutylammonium hexa- hybrid generalized gradient approximation (GGA), including
4
7
48
fluorophosphate (TBAPF ) as supporting electrolyte (recrystal- 25% mixture of Hartree-Fock
exchange with DFT
6
5918 | Dalton Trans., 2021, 50, 5911–5920
This journal is © The Royal Society of Chemistry 2021

View Article Online
Dalton Transactions
Paper
exchange–correlation, given by Perdew, Burke and Ernzerhof
7 P. Chábera, Y. Liu, O. Prakash, E. Thyrhaug, A. E. Nahhas,
A. Honarfar, S. Essén, L. A. Fredin, T. C. B. Harlang,
K. S. Kjær, K. Handrup, F. Ericson, H. Tatsuno, K. Morgan,
J. Schnadt, L. Häggström, T. Ericsson, A. Sobkowiak,
S. Lidin, P. Huang, S. Styring, J. Uhlig, J. Bendix, R. Lomoth,
V. Sundström and K. Wärnmark, Nature, 2017, 543, 695–699.
8 D. Schweinfurth, L. Hettmanczyk, L. Suntrup and
B. Sarkar, Z. Anorg. Allg. Chemie., 2017, 643, 554–584.
9 J. F. Schlagintweit, C. H. G. Jakob, K. Meigen-Berger,
T. F. Gronauer, A. Weigert Muñoz, V. Weiß, M. Feige,
S. A. Sieber, J. D. G. Correia and F. E. Kühn, Dalton Trans.,
2021, 50, 2158–2166.
4
9–51
functional (PBE).
The basis set used consisted of the
5
2–54
Stuttgart/Dresden ECP (SDD) basis set
with a f-polarization
function added to describe the electrons of manganese and
5
5
5
6
the same basis set with a d-polarization function added for
bromine; the remaining elements were described by a stan-
5
7–61
dard 6-31G(d,p) basis set.
Frequency calculations were per-
formed on the optimized geometries showing no imaginary
modes and confirming the stationary points as minima.
Solvent effects (acetonitrile) were considered in all calculations
(
geometry optimizations included) using the Polarizable
Continuum Model (PCM) initially devised by Tomasi and
6
2–65
coworkers
with radii and non-electrostatic terms of the 10 F. Al-Shnani, G. Guisado-Barrios, D. Sainz and E. Peris,
6
6
SMD solvation model, developed by Truhlar et al.
The values presented for the CO stretching frequencies are 11 C. Mejuto, B. Royo, G. Guisado-Barrios and E. Peris,
affected by a 0.955 scale factor. That factor results from the Beilstein J. Org. Chem., 2015, 11, 2584–2590.
ratio between the experimental value for the highest v(CO) of 12 M. Van Der Meer, E. Glais, I. Siewert and B. Sarkar, Angew.
(bis-NHC )Br] (9), 1999 cm , and the calculated
one: 2094 cm
Organometallics, 2019, 38, 697–701.
Et
−1
[
Mn(CO)
3
Chem., Int. Ed., 2015, 54, 13792–13795.
13 H. Iwasaki, Y. Yamada, R. Ishikawa, Y. Koga and
K. Matsubara, Eur. J. Org. Chem., 2016, 2016, 1651–1654.
−
1
.
1
1
1
1
1
1
2
2
4 C. Johnson and M. Albrecht, Organometallics, 2017, 36,
2902–2913.
5 Y. Wei, S. X. Liu, H. Mueller-Bunz and M. Albrecht, ACS
Catal., 2016, 6, 8192–8200.
Conflicts of interest
There are no conflicts to declare.
6 S. G. Mncube and M. D. Bala, Mol. Catal., 2020, 482,
100107–100115.
Acknowledgements
7 A. Petronilho, H. Müller-Bunz and M. Albrecht, Chem.
Commun., 2012, 48, 6499–6501.
8 H. Iwasaki, Y. Teshima, Y. Yamada, R. Ishikawa, Y. Koga
and K. Matsubara, Dalton Trans., 2016, 45, 5713–5719.
9 C. Romain, S. Bellemin-Laponnza and S. Dagorne, Coord.
Chem. Rev., 2020, 422, 213411–213442.
0 W.-T. Lee, D. A. Dickie, A. J. Metta-Magaña and J. M. Smith,
Inorg. Chem., 2013, 52, 12842–12846.
1 M. F. Pinto, M. Olivares, Á. Vivancos, G. Guisado-Barrios,
M. Albrecht and B. Royo, Catal. Sci. Technol., 2019, 9, 2421–
We are grateful to Fundação da Ciência e a Tecnologia, FCT,
for
Projects
PTDC/QUI-QIN/28151/2017,
Project
MOSTMICRO-ITQB UIDB/04612/2020, and UIPD/04612/2020
and the Swiss National Science Foundation (200021_182663)
for financial support of this work. The NMR spectrometers at
CERMAX through project 022162, and C. Almeida for HR-MS
and elemental analysis at ITQB laboratories. S.R. and S.F.
thank FCT for contract PTDC/QUI-QIN/28151/2017 and grant
SFRH/BD/131955/2017, respectively. C.S.B. Gomes acknowl-
edges LAQV and UCIBIO (UIDB/50006/2020, UIDP/50006/2020,
UIDB/04378/2020, UIDP/04378/2020). Centro de Química
Estrutural acknowledges the financial support of FCT (UIDB/
2425.
2
2
2
2
2 F. Franco, M. F. Pinto, B. Royo and J. Lloret-Fillol, Angew.
Chem., Int. Ed., 2018, 57, 4603–4606.
3 M. Pinto, S. Friães, F. Franco, J. Lloret-Fillol and B. Royo,
ChemCatChem, 2018, 10, 2734–2740.
4 S. C. A. Sousa, C. J. Carrasco, M. F. Pinto and B. Royo,
ChemCatChem, 2019, 11, 3839–3843.
0
0100/2020). P.N.M. acknowledges BioISI (UIDB/04565/2020)
and FTC for financial support (CEECIND/00509/2017).
5 S. C. A. Sousa, S. Realista and B. Royo, Adv. Synth. Catal.,
Notes and references
2020, 1–8.
1
2
3
4
P. Mathew, A. Neels and M. Albrecht, J. Am. Chem. Soc., 26 J. M. S. Cardoso, A. Fernandes, B. D. P. Cardoso,
2
008, 130, 13534–13535.
M. D. Carvalho, L. P. Ferreira, M. J. Calhorda and B. Royo,
Organometallics, 2014, 33, 5670–5677.
27 J. M. S. Cardoso and B. Royo, Chem. Commun., 2012, 48,
4944–4946.
G. Guisado-Barrios, J. Bouffard, B. Donnadieu and
G. Bertrand, Angew. Chem., Int. Ed., 2010, 49, 4759–4762.
Á. Vivancos, C. Segarra and M. Albrecht, Chem. Rev., 2018,
1
18, 9493–9586.
28 J. M. S. Cardoso, R. Lopes and B. Royo, J. Organomet.
Chem., 2015, 775, 173–177.
29 S. Warratz, L. Postigo and B. Royo, Organometallics, 2013,
32, 893–897.
K. F. Donnelly, A. Petronilho and M. Albrecht, Chem.
Commun., 2013, 49, 1145–1159.
R. H. Crabtree, Coord. Chem. Rev., 2013, 257, 755–766.
5
6
B. Sarkar and L. Suntrup, Angew. Chem., Int. Ed., 2017, 56, 30 S. Pottabathula and B. Royo, Tetrahedron Lett., 2012, 53,
938–8940. 5156–5158.
8
This journal is © The Royal Society of Chemistry 2021
Dalton Trans., 2021, 50, 5911–5920 | 5919

View Article Online
Paper
Dalton Transactions
3
3
3
3
3
3
3
3
3
1 R. Lopes, J. M. S. Cardoso, L. Postigo and B. Royo, Catal.
Lett., 2013, 143, 1061–1066.
2 V. V. K. M. Kandepi, J. M. S. Cardoso, E. Peris and B. Royo,
Organometallics, 2010, 29, 2777–2782.
3 M. F. Pinto, B. D. P. Cardoso, S. Barroso, A. M. Martins and
B. Royo, Dalton Trans., 2016, 45, 13541–13546.
J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas,
J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox,
Gaussian, Inc, Wallingford CT, 2009.
47 W. J. Hehre, L. Radom, P. v. R. Schleyer and J. A. Pople, Ab
Initio Molecular Orbital Theory, John Wiley & Sons, NY,
1986.
4 S. Bertini and M. Albrecht, Organometallics, 2020, 39, 3413– 48 R. G. Parr and W. Yang, Density Functional Theory of Atoms
3
424.
5 Á. Vivancos and M. Albrecht, Organometallics, 2017, 36,
580–1590.
and Molecules, Oxford University Press, New York, 1989.
Values obtained at the PBE0-D3/6-311++G**//PBE0/b1 level.
49 J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett.,
1996, 77, 3865–3868.
50 J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett.,
1997, 78, 1396–1396.
51 J. P. Perdew, Phys. Rev. B: Condens. Matter Mater. Phys.,
1986, 33, 8822–8824.
52 U. Haeusermann, M. Dolg, H. Stoll, H. Preuss,
P. Schwerdtfeger and R. M. Pitzer, Mol. Phys., 1993, 78,
1211–1224.
1
6 G. Guisado-Barrios, J. Bouffard, B. Donnadieu and
G. Bertrand, Organometallics, 2011, 30, 6017–6021.
7 E. W. Abel, G. Farrow and I. D. H. Towle, J. Chem. Soc.,
Dalton Trans., 1979, 71–73.
8 V. Blase, T. Pape and F. E. Hahn, J. Organomet. Chem.,
2
011, 696, 3337–3342.
9 Single crystals of [Mn (CO) (PPh ) ] were isolated from the
2
8
3 2
mixture and studied by X-ray diffraction. Y. Zhao,
H. W. Schmalle and H. Berke, CSD Commun., 2016.
0 SADABS 2016/2: L. Krause, R. Herbst-Irmer, G. M. Sheldrick
and D. Stalke, J. Appl. Crystallogr., 2015, 48, 3–10.
1 SHELXL: G. M. Sheldrick, Acta Crystallogr., Sect. C: Struct.
Chem., 2015, 71, 3–8.
53 W. Kuechle, M. Dolg, H. Stoll and H. Preuss, J. Chem. Phys.,
1994, 100, 7535–7542.
4
4
4
4
54 T. Leininger, A. Nicklass, H. Stoll, M. Dolg and
P. Schwerdtfeger, J. Chem. Phys., 1996, 105, 1052–1059.
55 E. A. Whlers, M. Böhme, S. Dapprich, A. Gobbi,
A. Höllwarth, V. Jonas, K. F. Köhler, R. Stegmann,
A. Veldkamp and G. A. Frenking, Phys. Lett., 1993, 208,
111–114.
2 C. B. Hübschle, G. M. Sheldrick and B. Dittrich, J. Appl.
Crystallogr., 2011, 44, 1281–1284.
3 M. C. Burla, R. Caliandro, B. Carrozzini, G. L. Cascarano,
C. Cuocci, C. Giacovazzo, M. Mallamo, A. Mazzone and 56 A. Höllwarth, M. Böhme, S. Dapprich, A. W. Ehlers,
G. Polidori, J. Appl. Crystallogr., 2015, 48, 306–309.
4 L. J. Farrugia, J. Appl. Crystallogr., 2012, 45, 849–854.
5 C. R. Groom, I. J. Bruno, M. P. Lightfoot and S. C. Ward, 57 R. Ditchfield, W. J. Hehre and J. A. Pople, J. Chem. Phys.,
A. Gobbi, V. Jonas, K. F. Köhler, R. Stegmann, A. Veldkamp
and G. Frenking, Chem. Phys. Lett., 1993, 208, 237–240.
4
4
Acta Crystallogr., Sect. B: Struct. Sci., Cryst. Eng. Mater.,
016, 72, 171–179.
6 Gaussian 09, Revision A.01, M. J. Frisch, G. W. Trucks,
1971, 54, 724–728.
58 W. J. Hehre, R. Ditchfield and J. A. Pople, J. Chem. Phys.,
1972, 56, 2257–2261.
2
4
H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, 59 P. C. Hariharan and J. A. Pople, Mol. Phys., 1974, 27, 209–
G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, 214.
H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, 60 M. S. Gordon, Chem. Phys. Lett., 1980, 76, 163–168.
A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, 61 P. C. Hariharan and J. A. Pople, Chim. Acta, 1973, 28, 213–
M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, 62 M. T. Cancès, B. Mennucci and J. J. Tomasi, Chem. Phys.,
T. Vreven Jr. J. A. Montgomery, J. E. Peralta, F. Ogliaro, 1997, 107, 3032–3041.
M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, 63 M. Cossi, V. Barone, B. Mennucci and J. Tomasi, Chem.
V. N. Staroverov, R. Kobayashi, J. Normand, Phys. Lett., 1998, 286, 253–260.
K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, 64 B. Mennucci and J. Tomasi, J. Chem. Phys., 1997, 106,
J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, 5151–5158.
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, 65 J. Tomasi, B. Mennucci and R. Cammi, Chem. Rev., 2005,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, 105, 2999–3094.
R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, 66 A. V. Marenich, C. J. Cramer and D. G. Truhlar, J. Phys.
222.
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,
Chem. B, 2009, 113, 6378–6396.
5920 | Dalton Trans., 2021, 50, 5911–5920
This journal is © The Royal Society of Chemistry 2021