Alkynyl Fischer Carbenes as a Platform for the Production of Difluorodiazaborinine Complexes via β-Amino-azadienes

Article abstract of DOI:10.1002/ejoc.201901047

The results of a study of the reactivities of alkynyl Fischer carbenes in the syntheses of diazaborinine derivatives 7a-i are reported. The strategy employed included the use of β-amino-α,β-unsaturated carbenes (3a–j) with different amines in order to determine the scope of a previously unknown catalytic reaction in the presence of copper salts and anilines. The reaction was highly stereoselective, yielding (Z)-isomers of the β-amino-1-azadiene framework as the main products (4a–o). As an extension of this research, the compounds 4a–o proved to be suitable precursors for the syntheses of diazaborinine scaffolds in good yields (7a-i).

Full text of DOI:10.1002/ejoc.201901047

DOI: 10.1002/ejoc.201901047
Full Paper
Fischer Carbenes
Alkynyl Fischer Carbenes as a Platform for the Production of
Difluorodiazaborinine Complexes via ꢀ-Amino-azadienes
Luis J. Benítez-Puebla,[a] Julio López,[a] Marcos Flores-Álamo,[b] David Cruz Cruz,[a]
Eduardo Peña-Cabrera,[a] Francisco Delgado,[c] Joaquín Tamariz,[c] and Miguel A. Vázquez*[a]
Abstract: The results of a study of the reactivities of alkynyl reaction was highly stereoselective, yielding (Z)-isomers of the
Fischer carbenes in the syntheses of diazaborinine derivatives ꢀ-amino-1-azadiene framework as the main products (4a–o). As
7a-i are reported. The strategy employed included the use of an extension of this research, the compounds 4a–o proved to
ꢀ-amino-α,ꢀ-unsaturated carbenes (3a–j) with different amines be suitable precursors for the syntheses of diazaborinine scaf-
in order to determine the scope of a previously unknown cata- folds in good yields (7a-i).
lytic reaction in the presence of copper salts and anilines. The
Introduction
normal reaction conditions (Scheme 1 path C).[10] Several de-
tailed studies have been carried out with these systems, indicat-
ing that the nature of the substituent, solvent, additives and
degree of substitution have an influence on the selectivity for
the type of product obtained (Scheme 1, path D and E).[11–13]
An example in which steric effects of the substituent at the ꢀ-
position play a role has also been observed,[14] yielding cyclo-
penta[b]pyran derivatives through a double insertion of alkynes
(Scheme 1 path F). In a different approach, using Pd salts as
transmetalating agents, it was found that either a bis-Pd(II) carb-
α,ꢀ-Unsaturated Fischer carbenes have been widely applied in
a variety of cycloaddition reactions, generating compounds
with a wide range of structural diversity, in excellent selecti-
vity.[1–3] This capability may be attributed to the electrophilic
characteristics of the carbenes and their ability to follow differ-
ent reaction pathways depending on the reaction conditions
and functional groups present.[3–6] Historically, the majority of
the work on these compounds has focused on complexes bear-
ing electron-donating groups on their carbenoid carbon. How-
ever, these systems may display further versatility through sub-
stitution of electron-donating groups at their ꢀ-positions as
well. Their overall reactivity depends on the type of substituent,
degree of substitution, geometry of the double bond and the
reaction conditions. Given this versatility, it is not surprising
they are considered important building blocks in organometal-
lic chemistry.[7] Interesting results have been reported for the
reactions of ꢀ-amino alkenyl chromium(0) carbene complexes,
for instance, when these complexes were treated with isocyan-
ides, either the pyrrole derivatives were obtained in high yields
(Scheme 1 path A)[8] or 1,6-diazaspiro derivatives were obtained
(Scheme 1 path B).[9] De Meijere et al. described the reactivity
of these complexes with alkynes, leading to cyclopentadiene
derivatives, whereby the insertion of CO is not observed under
[a] Departamento de Química, Universidad de Guanajuato,
Noria Alta s/n, Col. Noria Alta, Guanajuato, Gto., México, C.P. 36050
E-mail: mvazquez@ugto.mx
[b] Unidad de Servicios de Apoyo a la Investigación, Universidad Nacional
Autónoma de México,
Ciudad Universitaria, CDMX, México, C.P. 04510
[c] Departamento de Química Orgánica, Escuela Nacional de Ciencias
Biológicas-Instituto Politécnico Nacional,
Scheme 1. Library of structures obtained from ꢀ-amino-α,ꢀ-unsaturated
Fischer carbenes. Substituents and reaction conditions: path A) R = Ph, iPr;
R1 = Ph; R2 = H; R2 = tBu, cC6H11; Y = Cr(CO)5, W(CO)5; R3NC, benzene, 80–
90 °C. B) R = Me; Y = Cr(CO)5; methyl isocyanide, C6H6, 20 °C, 4 d. C)R = Ph,
2-IPh; R1 = Ph; R2 = H; Y = Cr(CO)5; PdCl2(MeCN)2, MeCN, K2CO3, r.t. D) R =
Me; R1 = iPr, Me3; R2 = Me; R3 = tBu, Mes; Y = Cr(CO)5; alkyne, THF, 60 °C. E)
R = Me, iPr, Bn; R2 = H; R1 = nBu, Ph; R3 = nBu, Ph; Y = Cr(CO)5; alkyne, THF,
70 °C. F) R = Me; R2 = Me; R1 = Ph; R3 = nPr, Ph; Y = Cr(CO)5; alkyne, THF,
50–55 °C. G) R = Ph, 2-IPh; Y = Cr(CO)5; PdCl2(MeCN)2, MeCN, K2CO3, r.t. H)
R = Ph, 2-IPh; Y = Cr(CO)5; Pd(OAc)2, DMF, K2CO3, r.t.
Prol. Carpio y Plan de Ayala s/n, Col. Santo Tomás, CDMX, México, C.P.
11340
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejoc.201901047.
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ene complex or a set of quinolones/indoles might be obtained,
depending on the reaction conditions (Scheme 1, paths G and
H).[15]
Table 1. Michael additions for the synthesis of 3a–j.
In addition to the well-known transmetalation processes in-
volving palladium, carbene complexes show similar reactivities
with a range of metals including rhodium, nickel and copper.[16]
In particular, copper has been used in the syntheses of bimetal-
lic chromium(0) complexes[17] through cycloaddition reactions
with azides,[18] the dimerization of carbenes followed by cycliza-
tion to 2-cyclopentenones,[19] and cyclopropanation reac-
tions.[20] In other reports, this metal has been used with Fischer
carbenes in cross-coupling reactions with ethyl diazoacetate, as
well as transmetalation processes,[21] to form cyclopropanes or
γ-keto esters using electron-poor olefins,[20] or spirocyclic vinyl-
cyclopentadienes through π-cyclization processes.[22] Such ex-
amples have become very popular in chemical research as they
involve the use of inexpensive elements replicating the action
of traditional, expensive catalysts with the same or better re-
sults. To the best of our knowledge there are no reports on the
use of copper as catalyst with ꢀ-amino-α,ꢀ-unsaturated carb-
enes.
Entry
R1
R2
Product (M) [%]
1
2
3
4
5
6
7
8
Ph (1a)
Ph (1a)
4-CH3C6H4 (1b)
Ph (1a)
3-CH3C6H4 (1c)
4-OCH3C6H4 (1d)
4-OCH3C6H4 (1d)
thien-3-yl (1e)
thien-3-yl (1e)
Ph (1a)
2-IC6H4 (2a)
2-IC6H4 (2a)
4-BrC6H4 (2b)
4-IC6H4 (2c)
2-IC6H4 (2a)
4-IC6H4 (2c)
2-IC6H4 (2a)
4-ClC6H4 (2d)
2-IC6H4 (2a)
C6H5 (2e)
3a (Cr) [98]
3a′ (W) [99]
3b (Cr) [95]
3c (Cr) [96]
3d (Cr) [94]
3e (Cr) [90]
3f (Cr) [92]
3g (Cr) [88]
3h (Cr) [90]
3i (Cr) [98]
3j (Cr) [95]
9
10
11
thien-3-yl (1e)
4-IC6H4 (2c)
strongly favored due to the EtO···HN hydrogen bonding (3a′:
1.90 Å; 3d: 2.06 Å). Similar experiments were carried out with
alkynyl carbenes bearing R1 = -SiMe3, nPr and 1-cyclohexenyl,
but the yields were negligible. It was corroborated that a frac-
tion of the metallic complex 1 was recovered, as well as small
amount of its oxidized form (ester), while the rest of the mixture
was basically decomposed. As can be assumed, the unreacted
aniline was also recovered. This is in accordance with previous
reports that have indicated that the reactivity is different when
the substitution pattern changes from aryl to alkyl substitu-
Herein we present a study of the reactivity of ꢀ-amino-α,ꢀ-
unsaturated Fischer complexes using copper salts, leading to
stereoselective syntheses of ꢀ-amino-1-azadiene systems, and
the use of these frameworks as ligands to coordinate boron
difluoride units.
Results and Discussion
For the preparation of the ꢀ-aminoalkoxycarbenes 3a–j, quanti- ents.[24,25] When heteroaromatic amines were tested (e.g. 2-
tative Michael additions of aromatic amines 2a–e with alkynyl- aminopyridine), similarly unpromising results were obtained.
alkoxycarbenes 1a–e were carried out (Table 1). No traces of the
competing 1,2-adducts were detected due to the established
thermodynamics of the reaction.[7]
We envisaged that substrates 3a–j would undergo the trans-
metalation process through a copper-assisted mechanism to
produce complexes of type A (Scheme 2). However, after sev-
Figure 1 displays two X-ray structures associated with the eral attempts using conditions resembling those found in the
products 3a′[23] and 3d[23] that show that no substantial differ- literature,[15,21] 3a, CuI (0.05 equiv.), phenanthroline·H2O
ences in the organic moieties on the different metals. Each (0.18 equiv.) and K2CO3 (2 equiv.) were reacted in toluene at
maintains the Z configuration about the C=C bond, which is different temperatures (25 and 100 °C) and with different reac-
Figure 1. ORTEP diagrams (50 % probability) of 3a′ and 3d.
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Figure 2. ORTEP diagrams (50 % probability) of 5a and B.
tion times (12 to 24 h), however, compound A was not detected
by 13C NMR (Cu=C, 280 ppm).[21] Instead, the crude mixture was
comprised of an ester 5a (5 %) (Figure 2) and an aldehyde 6a
(15 %) (Scheme 2), which were isolated as intermediates in the
divergent catalysis with palladium,[15] along with complex B
(5 %) (Figure 2) and ꢀ-amino-1-azadiene (4a, 24 %) as the main
product (Scheme 2). This is presumably due to hydrolysis, which
generates the requisite aniline.
Table 2. Optimization for the synthesis of 4a.
Entry[a]
Solvent
T (° C)
Catalyst
Yield [%]
1
2
3
4
5
6
7
8
PhMe
PhMe
CH3CN
THF
THF
THF
THF
THF
Benzene
THF
THF
100
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
80
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
CuI
CuI
CuI
CuI
CuOAc
CuBr2
Cu(acac)2
Cu(acac)2
Cu(acac)2
CuCl2·H2O
AgOAc
None
Cu(acac)2
Cu(acac)2
Cu(acac)2
Cu(acac)2
30
61
50
76
66
68
88
74[b]
20[c]
66
9
10
11
12
13
14
15
16
Scheme 2. Formation of the ꢀ-amino-1-hazadiene 4a, as well as 5a, 6a and
B from 3a using a Cu catalyst.
34
THF
THF
THF
THF
0[d]
37[e]
38[f]
28[g]
45[h]
In order to optimize the conditions of this reaction, the ef-
fects of changing parameters such as solvent, temperature and
catalyst were studied. Another important factor to understand
the formation of 4a is the amount of aniline in the reaction.
In this regard, further experiments were carried out by adding
equimolar quantities of aniline with respect to 3a and deter-
mining that the yield of 4a increased accordingly (Table 2, en-
tries 1 and 2).
THF/H2O
[a] Reaction conditions: 2a (1 equiv.), 3a (1 equiv.), 1,10-phenanthroline·H2O
(0.2 equiv.), K2CO3 (2.0 equiv.), catalyst (0.05 equiv.), 15–24 h. [b] 1,10-phen-
anthroline·H2O was avoided, but anhydrous Na2SO4 (1 equiv.) was added
instead. [c] A Dean–Stark apparatus was adapted and anhydrous Na2SO4
(1 equiv.) was also added. [d] Only aldehyde 6a was isolated in 63 %. [e] 1,10-
Phenanthroline·H2O was not added. [f] 1.1 equiv. of 1,10-phenanthroline·H2O
was used. [g] K2CO3 was not added. [h] The relationship of THF/H2O was 7:3.
Table 2 shows that the metal (Cu or Ag) plays an important
role in the catalysis, as revealed by the lack of reactivity in its
absence (entry 12). Only metals of group 11 were tested as
catalysts, with the results indicating a clear advantage of copper overall performance of the reaction. Clearly, water is necessary
over silver salts. The oxidation state of the metal does not ap- for the reaction to proceed efficiently, however, water limited
pear to be of primary importance in the yield. Experiments were the yield when in excess, the observation of which is integral
performed to analyze the effect of amount of water (Table 2, when proposing a reaction mechanism for the transformation
entries 7, 8, 9, 16), with results indicating its importance in the (Scheme 3). The best result was obtained with the conditions
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Scheme 3. Probable mechanism involved in the formation of 4 and related species.
listed in entry 7, where the source of the water is hydrated
phenanthroline.
While the yields were remarkable compared with similar
structures reported previously,[26] these values were not partic-
ularly high overall due to the obtention of side products like
esters 5a–j (5–22 %), aldehydes 6a–j (5–15 %) as well as en-
aminone H (traces) (Scheme 3). The latter product was identi-
fied as coming from the hydrolysis of systems of type 4 (see
Supporting Information), releasing the corresponding aniline 2.
This hypothesis was confirmed through the reaction of com-
pound 4a with HCl 37 % (6 mmol) in MeOH/H20 (1:1) at reflux
for 48 h, which yielded H (23 %).
The stereoselectivity of the ꢀ-amino-1-azadienes 4a–o was
exclusively Z (Figure 3), which was established by 2D NMR and
X-ray crystallographic analyses of 4a,[23] 4c,[23] 4d[23] and 4g.[23]
Besides, the adopted s-cis conformation is integral to the suc-
cessful coordination (via formation of a hydrogen bonding) of
these compounds with appropriate Lewis acids through interac-
tions with the lone pairs on the nitrogen atoms.
Once optimized, this methodology was applied to obtain an
extensive selection of compounds with structures varied
through choice of anilines 2a–j and carbene complexes 3a–j
(Table 3). Not all of the attempts were successful, as several ꢀ-
aminoalkoxycarbenes 3 did not afford the desired product.
When carbene 3a was probed with allylamine, cyclopropyl-
amine, ammonium acetate and anilines with high steric hin-
drance (2,4–6-tri-tert-butylaniline or 2,4–6-trimethylaniline) the
transformation failed to proceed.
Table 3. Analysis of the scope of the methodology.
Compound 4g constitutes an unusual case, as its structure
differs from those observed in crystals of ꢀ-amino-1-azadienes
4a, c and d. As depicted in Figure 3, the constitutive imine and
enamine functionalities occupy the opposite nitrogen atoms
when compared to those of its homologues. This finding indi-
cated that structure 4 depicted in the equilibrium in Scheme 3
is disfavored in this compound, resulting in a final molecule
matching intermediate F.
The solid-state structure of 4a shows a number of interesting
features. Firstly, the angle between halogenated rings is 52.39°,
while the angles of these rings with respect to the conjugated
π system are 54.84° and 21.10°. The strong interaction between
N-1 and H-4, as indicated by the short distance between them
(1.961 Å), is likely the primary cause of the stabilization of the
Z isomer. Within the whole set of studied crystals, the dihedral
angles formed by the planes of the ꢀ-amino-1-azadiene frame-
works and the rings of the corresponding aniline are nearly
coplanar (21.22° (4a), 10.94° (4d), 6.67° (4g), 4.94° (4c)).
It is known that different carbenes (alkyl, alkenyl, aryl) are
Entry[a]
Carbene[b]
R3
Yield [%]
1
2
3
4
5
6
7
8
3a
3a′
3a
3a
3a
3a
3j
3a
3b
3c
3d
3e
3f
2-IC6H4 (2a)
2-IC6H4 (2a)
Ph (2e)
4-OCH3C6H4 (2f)
4-NO2C6H4(2g)
3,5-(CF3)2C6H3(2h)
4-IC6H4 (2c)
6-Nitrobenzothiazolyl (2i)
4-BrC6H4 (2b)
4-IC6H4 (2c)
2-IC6H4 (2a)
4-IC6H4 (2c)
2-IC6H4 (2a)
4-ClC6H4 (2d)
2-IC6H4 (2a)
4a (88)
4a (60)
4b (70)
4c (90)
4d (60)
4e (55)
4f (46)
4g (49)
4h (60)
4i (55)
4j (45)
4k (52)
4l (46)
4m (64)
4n (48)
4o (46)
9
10
11
12
13
14
15
16
3g
3h
3i
C6H5 (2e)
[a] Using the reaction conditions shown in Table 2, entry 7. [b] M = Cr, except
for 3a′ where M = W.
Electronic activation through the donating character of sub- involved in the generation of aldehydes with tertiary amines
stituents on R1 in 3a–j was an essential factor in the observed under basic conditions.[27] However, alkynyl carbenes have been
reactivity, as was the metal employed. While the reactions with shown to undergo 1,4-addition reactions under the same condi-
Cr proceeded efficiently (3a), the reaction of a W-containing tions.[28] In our work, no product was found in reactions per-
substrate showed decreased yield (3a′).
formed in the absence of Cu (Table 2, entry 12). A mechanistic
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Figure 3. ORTEP diagrams (50 % probability) of molecules 4a, 4c, 4d and 4g.
proposal that might account for the observed reactivity of the Due to the versatility in terms of the catalysis, a number of
metal is based on that reported by Barluenga et al.,[21] who different strategies have been used for their synthesis.[39–44]
In order to analyze the scope of this research in the forma-
tion of BODIPY analogs, the capacities of a number of ꢀ-amino-
1-azadienes 4 toward the coordination of boron were tested
using previously reported reaction conditions.[26] Scheme 4
gives a summary of the difluorodiazaborinines 7a-i synthesized.
To the edge of our knowledge, the substitution pattern of these
structures has not been reported, so they are interesting scaf-
folds to be studied.
Proof of successful coordination is provided by the emer-
gence of 19F NMR resonances at 150.7 and 150.8 ppm, and the
appearance of 11B NMR resonances at 1.01 and 1.03 ppm. Anal-
ysis of the solid-state structure of 7f (Figure 4) showed that the
molecule, belonging to the triclinic system, exhibited a slightly
deformed tetrahedral geometry at the boron atom with an
N–B–N angle measuring 108.46° and a F–B–F angle of 108.33°.
In accordance with a range of fluorophores derived from
BODIPY,[45] the observed distances N–B and B–F were found to
vary from 1.53 Å to 1.54 Å and 1.37 Å to 1.38 Å, respectively.[23]
Figure 5, A depicts the absorption and emission spectra of
proposed that the transmetalation process is a key step in the
formation of derivatives of 4 (Scheme 3, structure C). At this
point, other side products were isolated (5, 6 and B) as a result
of the basic conditions used, similarly to previous reports.[15]
The electrophilic copper carbene (C) could subsequently react
with anilines to render structure D, and the latter generates the
structures E and F through 1,3- or 1,5-hydrogen shifts.[28,29] The
final step involves the reductive elimination of the metal to
furnish structures 4 and G.[30]
Concerning the obtained products 4, ꢀ-amino-1-azadienes
are interesting scaffolds that have been used to form complexes
with metal centers such as La(III), Nd(III), Sm(III), Eu(III), Gd(III)
and Y(III) for use as polymerization catalysts,[31,32] with Cr(III) to
affect selective ortho-ortho, ortho-para and para-para homocou-
plings of phenols,[33] with Cu(II) in exceptionally reactive oxid-
ations of alcohols to aldehydes,[34] or as free units in the synthe-
ses of dyes,[35] diazepinium salts,[36] pyrimidine nucleoside ana-
logs,[37] antibacterial agents and antifungal drugs.[38] Addition-
ally, complexes of ꢀ-amino-1-azadienes have generated a great
deal of interest in the construction of tunable fluorescent 7f upon excitation at 385 nm, which is a representative photo-
probes analogous to the well-known fluorophore BODIPY.[26] physical profile of most of the diazaborinines 7. Figure 5, B
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weak fluorophores that could be tuned from blue to orange by
aggregation-induced emission effects.[26]
Scheme 4. Complexation reaction of ꢀ-amino-1-azadienes to produce diaza-
boninine systems.
Figure 5. A) Absorption spectrum (solid line) in THF (1 × 10–5 M) at 298 K and
emission spectrum (dashed line) in THF (1 × 10–5 M) at 298 K upon excitation
at 385 nm of 7f. B) Absorption spectrum (solid line) in THF (1 × 10–5 M) at
298 K and emission spectrum (dotted line) in THF (1 × 10–5 M) at 298 K upon
excitation at 385 nm of 7i.
Figure 4. ORTEP diagram at 50 % probability of diazaborinine 7f.
shows the spectra of 7i under similar conditions. From this com-
parison, it is clear that 7i displays unique and interesting lumi-
According to that study, it was suggested that the energies
nescent properties (Stokes shift = 50 nm) when compared with of the HOMO and LUMO are strongly dependent on the substi-
the rest of synthesized difluorodiazaborinines. In general, the tution pattern of the groups attached to the nitrogen atoms.
absorption bands are attributable to π→π* transitions with Meanwhile, the substituent bound to carbon atom of the imine
λabs = 370–386 nm and emissions at λemis = 386–432 nm. How- unit exerts a major influence on the LUMO, but not the HOMO.
ever, the most remarkable aspect of the set lies in the fact that For those systems, λabs = 355–391 nm, λecrmysist = 448–602 nm and
emis
all of the members except one (7i) exhibited an unexpected
λ
= 478–645 nm values were obtained, which are partially
amorph
lack of fluorescence, sometimes attributed to π–π stacking in- in agreement with our results. Indeed, the authors observed
teractions in the solid state. This situation arises despite the fact that the introduction of strong electron-donating substituents
that similar scaffolds bearing an substituent in the ꢀ-position can induce large red-shifted emissions. Finally, unlike other
of the imine functionality of the ligand were reported to be boron diiminates,[46] 7f did not show improvement in the lumi-
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Synthesis of ꢀ-amino-1-azadiene (4a–o): In a round-bottomed flask
0.55 mmol of 3a–j (1 equiv.) and 0.55 mmol of anilines 2a–i
(1 equiv.) were mixed with copper (II) acetylacetonate (0.05 equiv.),
1,10-phenanthroline monohydrate (0.2 equiv.) and 1.1 mmol of
potassium carbonate (2 equiv.). All of the reactants were suspended
in 15 mL of anhydrous THF. After 15–24 h of stirring at room tem-
perature, the products 4a–o were purified by chromatography us-
ing silica 230–400 mesh and gradient hexane/ethyl acetate.
nescence data due to crystallization-induced emission effects,
likely because of the high degree of molecular flexibility com-
monly associated with these structures. To better understand
the luminescent properties of the complexes reported here, fur-
ther experiments are being carried out, including theoretical
and electrochemical measurements.
Synthesis of difluorodiazaborinine complexes (7a-i): To a 0.3
M solu-
Conclusions
tion of 4a–o (1 equiv.) in toluene was added triethylamine
(1.5 equiv.), and the mixture was heated and stirred at room tem-
perature for 10 minutes. The mixture was then cooled, and BF3·Et2O
(2.5 equiv.) was added to the tube followed by heating for an addi-
tional 1–16 h. The solvent was removed by a rotary evaporator to
remove excess BF3·Et2O and the product was precipitated from
MeOH.
In summary, ꢀ-amino-α,ꢀ-unsaturated Fischer carbenes proved
to be efficient synthons for the construction of difluorodiaza-
borinine complexes 7a-i through a multistep 1,4-addition/trans-
metallation/1,2-addition/H-shift/de-coordination. Although in
some cases the yields are modest, there is a clear advantage in
the observed stereoselectivity compared to other methodolo-
gies used for similar molecules. In this work, ꢀ-amino-1-azadi-
ene 4a–o intermediates were exclusively obtained as their Z
isomers, in reactions that did not require expensive catalysts.
The reactivity reported here favors aromatic amines and carb-
enes, in contrast to reactions with aliphatic homologues. Differ-
ences in the substitution patterns of the probed ꢀ-amino-1-
azadienes 4a–o proved to be insignificant for the complexation
process, but highly important in the luminescent properties ex-
hibited in the final products 7a-i.
Fully characterization data of the products can be found in the
Supporting Information file.
Acknowledgments
This work was supported in part by the Consejo Nacional de
Ciencia y Tecnología (CONACyT) Scholarship N° 273685 (L. J. B.
P) as well as the CONACyT Research Grants N° 27694 (M. A. V.)
and 260373 (National Laboratory of Molecular Spectroscopy of
the Universidad de Guanajuato). F. D, gratefully acknowledges
CONACyT (grant 282033) and SIP-IPN (grants 20181332 and
20195287). J. T. is also thankful to the SIP-IPN (grants 20180198
and 20195228) and CONACYT (grants 178319, and A1-S-17131)
for financial support. F.D. and J.T. are fellows of the EDI-IPN and
COFAA-IPN programs.
Experimental Section
All reactions were carried out under nitrogen. Solvents were dried
before use. THF and Et2O were distilled from Na and dichloro-
methane was distilled from CaCl2. The products were purified by
column chromatography on silica gel (MN Kieselgel 60, 230–
400 mesh). Mixtures of ethyl acetate and hexane were used as elu-
ents. Analytical TLC was employed on aluminum sheets (silica gel
60 F/UV254) with visualization carried out with UV light and iodine.
Melting points were determined on a digital Electrothermal 90100
melting point apparatus and are uncorrected. 1H and 13C NMR spec-
tra (CDCl3) were recorded with a Varian Gemini 300 MHz, a Varian
VNMR System 500 MHz, a Bruker Ascend 400 MHz, or a Bruker
Ultrashield 500 MHz spectrometer. All chemical shifts are reported
in ppm relative to Me4Si and CHCl3 used as the internal standard.
IR spectra were recorded on potassium bromide plates with a Per-
kin-Elmer Spectrum 100 FT-IR spectrophotometer. High-resolution
mass spectra (HRMS) were determined with electrospray ionization
on a Bruker micrOTOF-Q II or electronebulization ionization on a
Bruker QTOF mass spectrometer. X-ray data were collected on an
Oxford Diffraction Gemini “A” diffractometer with a CCD area de-
tector.
Keywords: Alkynyl Fischer carbenes · ꢀ-Amino carbenes ·
ꢀ-Amino-1-azadiene · Diflourodiazaborinine
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Received: July 18, 2019
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