Selective formation of formamidines, carbodiimides and formimidates from isocyanide complexes of Mn(i) mediated by Ag2O

Article abstract of DOI:10.1039/c8dt01200h

The isocyanide ligands in complexes fac-[Mn(CNR)(bipy)(CO)₃]⁺ are selectively transformed into formamidines, carbodiimides and formimidates upon nucleophilic addition of NH₂Me or alkoxides and subsequent treatment with Ag<

Full text of DOI:10.1039/c8dt01200h

View Article Online
View Journal
Dalton
Transactions
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: J. Ruiz, D. Sol, M.
A. Mateo and M. Vivanco, Dalton Trans., 2018, DOI: 10.1039/C8DT01200H.
This is an Accepted Manuscript, which has been through the
Volume 45 Number
1 7 January 2016 Pages 1–398
Royal Society of Chemistry peer review process and has been
accepted for publication.
Dalton
Transactions
Accepted Manuscripts are published online shortly after
An international journal of inorganic chemistry
www.rsc.org/dalton
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1477-9226
PAPER
Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
framework
a Zr-metal–organic
rsc.li/dalton

Please do not adjust margins
Dalton Transactions
Page 1 of 5
View Article Online
DOI: 10.1039/C8DT01200H
Journal Name
COMMUNICATION
Selective formation of formamidines, carbodiimides and
formimidates from isocyanide complexes of Mn(I) mediated by
Ag2O
Received 00th January 20xx,
Accepted 00th January 20xx
Javier Ruiz,*a Daniel Sol, a María A. Mateo a and Marilín Vivanco a
DOI: 10.1039/x0xx00000x
www.rsc.org/
The isocyanide ligands in complexes fac-[Mn(CNR)(bipy)(CO)3]+ are In relation with all the above and showing the amazing
selectively transformed into formamidines, carbodiimides and synthetic potential of the simple and easy accessible
formimidates upon nucleophilic addition of NH2Me or alkoxides [Mn(bipy)(CO)3]+ fragment, we describe herein several
and subsequent treatment with Ag2O, which promotes reactions of isocyanide ligands occurring at the coordination
tautomerization or oxidation processes of the former carbene sphere of manganese, mediated by silver(I) oxide, lately
ligands.
leading to the selective generation of a variety of organic
functionalities such as formamidines, carbodiimides or
formimidates.
Metal complexes derived from earth-abundant and
inexpensive manganese have gained increasing interest in
organometallic chemistry and catalysis in the recent years.1 In
particular, manganese(I) complexes containing the cationic
fragment [Mn(bipy)(CO)3]+ (bipy = 2,2’-bipyridine) have been
successfully applied in several catalytic processes. Notably,
complexes of formula fac-[MnBr(bipy)(CO)3] and fac-
[Mn(NCMe)(bipy)(CO)3]+ are efficient electrocatalysts for CO2
reduction to CO,2 with the additional possibility of utilizing
bulky3 or functionalized4 bipy ligands to improve this catalytic
process. Similar rhenium(I) complexes have been used in the
electrocatalytic reduction of CO2, with the disadvantage of
their high cost and the requirement of higher
overpotentials.2b,5 Selective reduction of CO2 to either formate
or CO is also accomplished by inmobilization of fac-
[MnBr(bipy)(CO)3] on a carbon nanotube electrode.6 Other
catalytic processes involving the [Mn(bipy)(CO)3]+ moiety
include hydrogenation of CO2 to formate and formamide7 and
dihydrogen production by reduction of trifluoroacetic acid as a
proton source.8 Some remarkable organometallic reactions
promoted by the fragment [Mn(bipy)(CO)3]+ have been
described by our group, and include the tautomerization of
imidazoles,9 oxazole10 and thiazole10 to N-heterocyclic
carbenes (NHCs), the formation of NHCs by coupling of
isocyanides and propargylamine11 and the generation of
unique metalla-NHCs.12
As we have previously described, the reaction of fac-
[Mn(CNR)(bipy)(CO)3]+ (1a, R = phenyl; 1b, R = 2-naphthyl; 1c
,
R = 4-methoxyphenyl; 1d, R = methyl; 1e, R = benzyl; 1f, R =
2,6-xylyl; 1g, R = 2-chloro-6-methylphenyl) with NH2Me leads
to the formation of the diaminocarbene complexes fac-
[Mn{CNHR(NHMe)}(bipy)(CO)3]+ (2a-g) after a few minutes of
stirring at room temperature.13 Now we have found that the
diaminocarbene ligands in these complexes can be selectively
converted to formamidines or carbodiimides, depending on
the reaction conditions (Scheme 1). Thus, the treatment of
dichloromethane solutions of complexes
2 with Ag2O, which
acts as a catalyst, leads to quantitative isomerization of the
carbene ligand to the corresponding formamidine, yielding
complexes 3 14
.
Tentatively, this process might involve some
interaction of the Ag(I) ion with the carbene carbon atom of
2,
which is reminiscent of the heterometallic Mn(I)/Au(I) carbene
intermediates we have found in homogeneous conditions for
the transfer of carbene ligands from Mn(I) to Au(I).15 This
reaction works pretty well with a variety of alkylic or arylic
substituents (R =Ph, 2-Naph 4-MeOPh, Me , Bn; complexes 2a-
e
); however, with more sterically demanding substituents such
as 2-6-xylyl or 2-Cl-6-MePh (complexes 2f and 2g), the above
isomerization reaction does not occur. In similar conditions,
addition of Cu2O instead of Ag2O leaves the diaminocarbene
complexes unchanged. Other metal oxides of variable nature,
such as V2O5, ZnO, MgO or CuO do not induce any reaction
either. Complexes 3a-e were characterized by spectroscopic
methods. The IR spectra reflect the reduced donor capability
of formamidines as ligands compared to their diaminocarbene
precursors, showing ν(CO) bands at higher frequencies.
Complexes 3a-d are isolated as a mixture of isomers, resulting
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 2 of 5
View Article Online
DOI: 10.1039/C8DT01200H
COMMUNICATION
Journal Name
Figure 1. A view of the structure of the cationic complex 3e with thermal ellipsoids set
at 30% probability. Hydrogen atoms of phenyl and bipy groups are omitted for clarity.
Selected bond lengths (Å) and angles (ο): Mn1-N3 2.0769(16), N3-C2 1.294(3), C2-N1
1.332(2); N1-C2-N3 127.6(2).
fac-[MnCl(bipy)(CO)3]. Interestingly, there are not steric
restrictions in the formation of the carbodiimide products, so
Scheme 1. Generation of diaminocarbene complexes 2a-g and their selective that isocyanide ligands with encumbered aryl substituents are
transformation into formamidine and carbodiimide functionalities induced by Ag2O.
also transformed into carbodiimides, in contrast to that
occurring with the above commented tautomerization of
from the formation of two formamidine tautomers, which
forces coordination of this molecule either through the NMe
group (showed in Scheme 1) or through the NR moiety (see
details in the Supplementary Information). In the case of 3e (R
diaminocarbenes to formamidines. However, the dialkyl
carbodiimides 6d,e could not be obtained, owing to the
extreme propensity of the corresponding dialkyl formamidinile
complexes to protonation, producing the diaminocarbene
1
= Bn), the H NMR spectrum of the reaction mixture showed
complexes 2d,e
(and subsequently the formamidine
the formation of a sole isomer, for which, after crystallization,
an X-ray diffraction study was undertaken. The structure of the
molecular cation (Figure 1) shows coordination of the
formamidine through the NMe group. The C2-N1 (1.332(2) Å)
and C2-N3 (1.294(3) Å) bond lengths are intermediate
derivatives 3d,e) before the oxidation process had taken place.
The selective formation of formamidines or carbodiimides
starting from the same manganese(I) diaminocarbene
complexes promoted by Ag2O is noteworthy. In this regard, it
must be emphasized the important contribution of Angelici on
gold metal-catalyzed reactions of isocyanides with primary
amines and oxygen to give carbodiimides,16 which is in sharp
contrast with the early results of Parks and Balch describing
the formation of formamidines by substitution reactions from
gold(I) diaminocarbene complexes.17
Under the activation of the rather stable [Mn(bipy)(CO)3]+
fragment, the isocyanide ligands can also be transformed into
formimidates upon reaction with sodium methoxide. The
whole reaction pathway starting from 1a,b is depicted in
Scheme 2 and involves firstly nucleophilic attack of the
alkoxide to the coordinated isocyanide ligand, affording the
neutral complexes 7a,b. These are further protonated at the
imine group by treatment with HBF4 to give the
between single and double bond, reflecting π-delocalization of
the lone pair of the N1 nitrogen atom along the NCN skeleton.
The coordinated formamidines can be liberated from the
metal center by heating under reflux acetonitrile solution of
the corresponding complexes, as exemplified with the
obtention of formamidines 4b and 4c (Scheme 1). The workup
includes separation of the formamidine from the crude
reaction mixture by extraction with diethyl ether. The
remaining manganese complex fac-[Mn(NCMe)(bipy)(CO)3]+
can be further transformed into the starting complexes 1b,c
by reaction with isocyanide, which allows recycling of these
metal complexes.
If the diaminocarbene complexes 2a-g are previously
transformed into the formamidinile derivatives 5a-g by
deprotonation (these were detected by IR spectroscopy but
not isolated), the treatment with Ag2O produces the oxidation
of the formamidinile ligand affording the unsymmetrically
alkoxyaminocarbene derivatives 8a,b
,
wich are finally
converted to their formimidate isomers 9a,b by treatment
with Ag2O, in a similar way as diaminocarbene complexes are
transformed into formamidine derivatives. Interestingly, the
[Mn(bipy)(CO)3]+ fragment is not only stable enough to allow
these transformations, but also behaves as an exceptional
witness to monitory all the reaction sequence by IR
substituted carbodiimides
6 within a few minutes of stirring at
room temperature in dichoromethane as solvent (Scheme 1).
The new carbodiimides were immediately detected by
recording the IR spectrum of the reaction mixture, which
showed a characteristic ν
(N=C=N) band at around 2140 cm-1,
spectroscopy in solution, with clear changes in the
bands in each reaction path (see ESI). In the 13C{1H} NMR
ν(CO)
and were conveniently isolated as colorless oils after workup.
A silver mirror was formed as a by-product together with a
carbonyl manganese complex which was identified as
spectra, significant changes are also observed in the chemical
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 3 of 5
View Article Online
DOI: 10.1039/C8DT01200H
Journal Name
COMMUNICATION
Figure 3. A view of the structure of the cationic complex 8a (left) and its tautomer
derivative 9a (right) with thermal ellipsoids set at 30% probability. Hydrogen atoms of
phenyl and bipy groups are omitted for clarity. Selected bond lengths (Å) and angles (ο):
8a Mn1-C2 2.057(2), O3-C2 1.326(2), C2-N1 1.310(2); N1-C2-O3 115.5(2). 9a Mn1-N1
2.1087(19), O3-C2 1.323(3), C2-N1 1.273(3); N1-C2-O3 120.4(2).
the naphthyl derivative 10b (Scheme 2). Reaction of 1a with
sodium ethoxide proceeds similarly, allowing for the obtention
of the corresponding alkoxyaminocarbene and formimidate
derivatives (see ESI).
The ability of Ag2O to transform diaminocarbene ligands to
formamidines in manganese(I) complexes was extended to
cyclic carbenes with similar results. As showed in Scheme 3,
the Mn(I)-NHC complex 11 is easily converted to the imidazole
complex 12 by treatment with Ag2O simply by stirring at room
temperature in CH2Cl2. As we had already described the
acid/base-promoted tautomerization of 1-phenylimidazole to
the corresponding NHC (Scheme 3),9 the present result
completes a totally reversible transformation between these
two tautomeric forms in the coordination sphere of
manganese. Note that metal-assisted tautomerization
reactions of imidazoles9,18 and other azaheterocycles10,19 to
NHCs have been intensely investigated in the last years and
that, in occasions, coordinated-NHCs can also be converted to
imidazoles.20 However, to our knowledge, this is the first time
that this transformation is found to be reversible.
To conclude, we have shown herein that [Mn(bipy)(CO)3]+
containing earth-abundant manganese is an excellent metallic
fragment to induce transformations of isocyanides into a
variety of organic functionalities such as diaminocarbenes,
formamidines, carbodiimides, alkoxyaminocarbenes and
formimidates, upon treatment with bases such as primary
amines and alkoxides, and with the singular contribution of
Ag2O as an isomerization or oxidation reagent.
Scheme 2. Reaction pathway for the formation of alkoxyaminocarbene complexes 8a,b
and their tautomerization to formimidate derivates mediated by Ag2O.
shift of the central carbon atom of the N-C-O skeleton, going
from about 203 ppm (7a,b) to 239 ppm (8a,b) and finally 170
ppm (9a,b). For complexes 7a, 8a and 9a an X-ray diffraction
study was undertaken (see Figures 2 and 3, together with
selected bond distances and angles), which definitively
confirmed the structure of these species. Note that the
relative disposition of the phenyl and methyl substituents at
the N1 and O3 atoms is maintained on going from 7a to 8a. In
1
the case of 8a, the H NMR spectrum shows the presence of
two conformers (approximate ratio 92:8) very likely arising
from the absence of free rotation around the carbon-nitrogen
bond of the carbene ligand, which is in accordance with the
rather short C2-N1 bond length (1.310(2) Å). Most probably
the structure in Figure 3 corresponds to the major isomer. Free
formimidates can be obtained in a similar way as described
above for formamidines, as exemplified with the isolation of
Figure 2. A view of the structure of complex 7a with thermal ellipsoids set at 30%
probability. Hydrogen atoms of phenyl and bipy groups are omitted for clarity. Selected
bond lengths (Å) and angles (ο): Mn1-C2 2.0809(12), O3-C2 1.3836(15), C2-N1
1.2767(16); N1-C2-O3 115.0(1).
Scheme 3. Reversible tautomerization of 1-phenylimidazole to the corresponding protic
NHC coordinated to the fragment [Mn(bipy)(CO)3]+.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 4 of 5
View Article Online
DOI: 10.1039/C8DT01200H
COMMUNICATION
Journal Name
Chem. Soc., 2002, 124
,
3202; (d) J. C. Lewis, S. H.
This work was supported by the Spanish Ministerio de
Economía y Competitividad (Project MINECO-FEDER CTQ2015-
66959-P) and by the Principado de Asturias (Project FC-15-
GRUPIN14-011). D. S. thanks the Principado de Asturias for a
scholarship. M. A. M. thanks the MINECO for a scholarship.
Wiedemann, R. G. Bergman and J. A. Ellman, Org. Lett., 2004,
, 35; (e) M. A. Huertos, J. Pérez, L. Riera and A. Menéndez-
6
Velázquez, J. Am. Chem. Soc., 2008, 130, 13530; (f) M. A.
Huertos, J. Pérez, L. Riera, J. Díaz and R. López, Angew.
Chem. Int. Ed., 2010, 49, 6409.
19 (a) F. Vattier, V. Salazar, M. Paneque, M. L. Poveda and E.
Álvarez, Organometallics, 2014, 33, 498; (b) M. Paneque, M.
L. Poveda, F. Vattier, E. Alvarez and E. Carmona, Chem.
Commun. 2009, 5561; (c) S. Conejero, P. Lara, M. Paneque,
A. Petronilho, M. L. Poveda, O. Serrano, F. Vattier, E. Álvarez,
C. Maya, V. Salazar and E. Carmona, Angew. Chem. Int. Ed.,
2008, 47, 4380; (d) M. A. Esteruelas, F. J. Fernández-Alvarez
and E. Oñate, J. Am. Chem. Soc., 2006, 128, 13044; (e) M. A.
Esteruelas, F. J. Fernández-Alvarez and E. Oñate,
Organometallics, 2008, 27, 6236; (f) M. A. Esteruelas, F. J.
Fernández-Alvarez, M. Oliván and E. Oñate, Organometallics,
2009, 28, 2276; (g) J. L. Gomez-Lopez, D. Chávez, M. Parra-
Hake, A. T. Royappa, A. L. Rheingold, D. B. Grotjahn and V.
Miranda-Soto, Organometallics, 2016, 35, 3148.
Conflicts of interest
There are no conflicts to declare.
Notes and references
1
Selected recent reviews: (a) H. Takeda, C. Cometto, O.
Ishitani and M. Robert, ACS Catal., 2017, , 70; (b) J. R.
Carney, B. R. Dillon and S. P. Thomas, Eur. J. Org. Chem.,
7
2016, 3912; (c) F. Kallmeier and R. Kempe, Angew. Chem. Int. 20 (a) Q. Liang, A. Salmon, P. J. Kim, L. Yan and D. Song, J. Am.
Ed., 2018, 57, 46; (d) M. Garbe, K. Junge and M. Beller, Eur. J.
Org. Chem., 2017, 4344; (e) D. A. Valyaev, G. Lavigne and N.
Lugan, Coord. Chem. Rev., 2016, 308, 191.
(a) M. Bourrez, F. Molton, S. Chardon-Noblat and A.
Deronzier, Angew. Chem. Int. Ed., 2011, 50, 9903; (b) C.
Riplinger, M. D. Sampson, A. M. Ritzmann, C. P. Kubiak and E.
A. Carter, J. Am. Chem. Soc., 2014, 136, 16285.
Chem. Soc., 2018, 140, 1263; (b) S. Burling, M. F. Mahon, R.
E. Powell, M. K. Whittlesey and J. M. J. Williams, J. Am.
Chem. Soc., 2006, 128, 13702; (c) X. Wang, H. Chen and X. Li,
Organometallics, 2007, 26, 4684.
2
3
4
(a) M. D. Sampson, A. D. Nguyen, K. A. Grice, C. E. Moore, A.
L. Rheingold and C. P. Kubiak, J. Am. Chem. Soc., 2014, 136,
5460; (b) M. D. Sampson and C. P. Kubiak, J. Am. Chem. Soc.,
2016, 138, 1386.
K. T. Ngo, M. McKinnon, B. Mahanti, R. Narayanan, D. C.
Grills, M. Z. Ertem and J. Rochford, J. Am. Chem. Soc., 2017,
139, 2604.
5
6
7
8
9
S. Sung, D. Kumar, M. Gil-Sepulcre and M. Nippe, J. Am.
Chem. Soc., 2017, 139, 13993.
B. Reuillard, K. H. Ly, T. E. Rosser, M. F. Kuehnel, I. Zebger
and E. Reisner, J. Am. Chem. Soc., 2017, 139, 14425.
A. Dubey, L. Nencini, R. R. Fayzullin, C. Nervi and J. R.
Khusnutdinova, ACS Catal., 2017, 7, 3864.
M. D. Sampson and C. P. Kubiak, Inorg. Chem., 2015, 54
,
6674.
J. Ruiz and B. F. Perandones, J. Am. Chem. Soc., 2007, 129
9298.
,
10 J. Ruiz and B. F. Perandones, Chem. Commun., 2009, 2741.
11 (a) J. Ruiz, G. García, M. E. G. Mosquera, B. F. Perandones, M.
P. Gonzalo and M. Vivanco, J. Am. Chem. Soc., 2005, 127
,
8584; (b) J. Ruiz, B. F. Perandones, G. García and M. E. G.
Mosquera, Organometallics, 2007, 26, 5687.
12 (a) J. Ruiz, L. García, B. F. Perandones and M. Vivanco,
Angew. Chem. Int. Ed., 2011, 50, 3010; (b) J. Ruiz, L. García,
M. Vivanco, A. Berros and J. F. Van der Maelen, Angew.
Chem. Int. Ed., 2015, 54, 4212.
13 J. Ruiz and B. F. Perandones, Organometallics, 2009, 28, 830.
14 We have already described the synthesis of 3a and 3d as
intermediates in the formation of metalla-N-heterocyclic
carbenes, see reference 12b.
15 J. Ruiz, D. Sol, J. F. Van der Maelen and M. Vivanco,
Organometallics, 2017, 36, 1035.
16 (a) M. Lazar and R. J. Angelici, J. Am. Chem. Soc., 2006, 128
,
10613; (b) R. J. Angelici, Catal. Sci. Technol., 2013, , 279.
3
17 J. E. Parks and A. L. Balch, J. Organomet. Chem., 1974, 71
,
453.
18 (a) F. He, P. Braunstein, M. Wesolek and A. A. Adanopoulos,
Chem. Commun., 2015, 51, 2814; (b) F. E. Hahn, A. R.
Naziruddin, A. Hepp and T. Pape, Organometallics, 2010, 29,
5283; (c) K. L. Tan, R. G. Bergman and J. A. Ellman, J. Am.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 5
Dalton Transactions
View Article Online
DOI: 10.1039/C8DT01200H
Selective formation of formamidines, carbodiimides and formimidates
from isocyanide complexes of Mn(I) mediated by Ag2O
Javier Ruiz, Daniel Sol, María A. Mateo and Marilín Vivanco
The easily accessible cation [Mn(bipy)(CO)3]+ induces transformations of isocyanides into a
variety of organic functionalities with the mediation of Ag2O.