Carbon—carbon and carbon—nitrogen bond formation reactions catalyzed by the magnesium and calcium acenaphthene-1,2-diimine complexes

Article abstract of DOI:10.1007/s11172-018-2095-6

A mixture of allylbromide and diphenylacetonitrile is reduced to afford 2,2-diphenylpentene-4-nitrile as a major product in the presence of catalytic amounts of the magnesium complex (dpp-bian)Mg(thf)3 (dpp-bian is 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene dianion). The overall conversion of nitrile is 71% within 3 h at 85 °С. 4,4-Diphenylbutene-1 and diphenylmethane are by-products in this process. Complexes (dpp-bian)Mg(thf)₃ and (dpp-bian)Ca(thf)₄ (in an amount of 0.5—5 mol.%) catalyze the intramolecular hydroamination of some aminopentenes and aminohexenes with the conversion from 67 to 99%.

Full text of DOI:10.1007/s11172-018-2095-6

Russian Chemical Bulletin, International Edition, Vol. 67, No. 3, pp. 473—478, March, 2018
473
Carbon—carbon and carbon—nitrogen bond formation reactions catalyzed
by the magnesium and calcium acenaphthene-1,2-diimine complexes*
A. M. Yakub, M. V. Moskalev, N. L. Bazyakina, and I. L. Fedushkin
G. A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences,
49 ul. Tropinina, 603950 Nizhni Novgorod, Russian Federation.
Fax: +7 (831) 462 7497. E-mail: igorfed@iomc.ras.ru
A mixture of allyl bromide and diphenylacetonitrile is reduced to afford 2,2-diphenylpentene-
4-nitrile as a major product in the presence of catalytic amounts of the magnesium complex
(dpp-bian)Mg(thf)3 (dpp-bian is 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene dianion).
The overall conversion of nitrile is 71% within 3 h at 85 С. 4,4-Diphenylbutene-1 and diphenyl
methane are by-products in this process. Complexes (dpp-bian)Mg(thf)3 and (dpp-bian)Ca(thf)4
(in an amount of 0.5—5 mol.%) catalyze the intramolecular hydroamination of some amino-
pentenes and aminohexenes with the conversion from 67 to 99%.
Key words: alkaline-earth metals, N,N-ligands, hydroamination, catalysis.
The chemistry of metal complexes containing -di-
imine ligands is being intensely developed for the recent
two decades. Among them conformationally rigid N-donor
1,2-bis[(aryl)imino]acenaphthenes (aryl-bian) capable of
stepwise one-electron oxidizing/reducing in the coordina-
tion sphere of the metal are of special interest. The com-
pounds of transition metals (Pd, Ni, Fe, and Co) based
on the aryl-bian ligands are catalysts of C—C bond forma-
tion,1—4 hydrogenation,5,6 hydrosilylation,7,8 polymeriza-
tion,9—18 and copolymerization19—23 of olefins. In these
catalysts, aryliminoacenaphthenes act as neutral ligand-
"spectators" and the chemical properties of the metal
complexes, including the catalytic properties, are mainly
determined by the type of the transition metal.
The complexes of main group metals with the aryl-bian
ligands, in particular, with 1,2-bis[(2,6-diisopropylphenyl)
imino]acenaphthene (dpp-bian), have other properties.
The ability of the ligand to accept and donate electrons
with the retention of coordination with the central atom
makes it possible to carry out a series of transformations
that are not characteristic of non-transition metal ions.
The redox-active ligand, as the metal, is directly involved
in chemical transformations. The reaction of complex
(dpp-bian)Mg(thf)3 (1) with phenylacetylene24,25 is acid-
base in character, whereas its reaction with 9(10H)-
anthracenone proceeds via the redox route (Scheme 1).26
At the same time, the regioselective cycloaddition of
phenylacetylene at the metal fragment is observed in the
gallium27 and aluminum28 complexes with the dpp-bian
dianion (Scheme 2).
Digallane (dpp-bian)Ga—Ga(dpp-bian) binds revers-
ibly phenylacetylene and some other alkynes similarly to
the coordination of unsaturated organic molecules by
transition metal complexes. This made it possible to con-
duct the hydroamination29 and hydroarylation30 of alkynes
by aromatic amines using digallane (dpp-bian)Ga—
Ga(dpp-bian) as a catalyst. Its activity turned out to be
comparable with that of the catalytic systems based on
transition metals.
Thus, a combination "non-transition metal—redox-
active ligand" resembles the systems based on transition
metals applied in catalysis of functionalization of unsatu-
rated organic compounds. Therefore, investigations of the
catalytic activity of complexes of main group metals con-
taining the redox-active dpp-bian ligand seem to be
promising from the viewpoint of the preparation of a new
type of catalysts of chemical processes.
The purpose of this work is to study the catalytic activ-
ity of the magnesium (dpp-bian)Mg(thf)3 (1) and calcium
(dpp-bian)Ca(thf)4 (2)24 complexes in the intramolecular
hydroamination of some aminoalkenes and in the cross-
coupling of diphenylacetonitrile and allyl bromide in the
presence of magnesium promoted by compound 1. The
first type of reactions is atom-economy and makes it pos-
sible to synthesize five- and six-membered heterocyclic
derivatives with biological activity. A fairly wide range of
catalysts is presently used for these purposes.31—42 The
second reaction is a particular example of the method for
preparation of alkenenitriles, which are precursors in the
synthesis of aminoalkenes and related heterocycles. This
method implies the formal cross-coupling of halogenalk-
ene and nitrile containing one or more hydrogen atoms in
the -position to the CN group by dehydrohalogenation.
* Dedicated to Academician of the Russian Academy of Sciences
I. P. Beletskaya.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 0473—0478, March, 2018.
1066-5285/18/6703-0473 © 2018 Springer Science+Business Media, Inc.

474
Russ. Chem. Bull., Int. Ed., Vol. 67, No. 3, March, 2018
Yakub et al.
Scheme 1
Scheme 2
M = Ga, Al
Lithium amides are traditionally used as binding agents.
Unlike the organomagnesium derivatives, lithium amides
selectively deprotonate a disubstituted nitrile molecule,
and the subsequent exchange reaction of the lithium-
containing intermediate and halogenalkene occurs rapidly
to form the target product (Scheme 3).
tions will allow one to develop alternative routes for the
synthesis of both alkenenitriles and other polyfunctional
organic compounds.
Results and Discussion
We believe that the use of the magnesium catalysts
containing the dpp-bian ligand in the cross-coupling reac-
Cross-coupling of diphenylacetonitrile with allyl bromide
in the presence of complex (dpp-bian)Mg(thf)3 (1). We have
previously found that the bis(amide) magnesium derivative
(dpp-bian)Mg(thf)3 (1) easily reacts with nitriles. Mag-
nesium enimide 3 is formed when diphenylacetonitrile is
used (Scheme 4).43 Compound 3 is an analog of lithium
intermediates formed in the reactions of disubstituted
nitriles with lithium amides (see Scheme 3). A substantial
distinction in these two reactions is that the mobile hy-
drogen atom of nitrile in the reaction with complex 1 is
Scheme 3
Scheme 4

Acenaphthene-1,2-diimine complexes as catalysts
Russ. Chem. Bull., Int. Ed., Vol. 67, No. 3, March, 2018
475
Scheme 5
not eliminated to form amine HNR2 (see Scheme 3) but
is bound by complex 1. The dpp-bian ligand transits from
the bis(amide) to amino—amide form (see Scheme 4).
Therefore, we decided to use compound 1 for binding HBr
in order to obtain the cross-coupling product of allyl
bromide and diphenylacetonitrile.
The consecutive interaction of stoichiometric amounts
of complex 1 with diphenylacetonitrile and then with allyl
bromide afforded the product of cross-coupling of two
latter reactants: 2,2-diphenylpentene-4-nitrile. Alkyl
halogen was used in deficient to avoid the formation the
(dpp-bian-allyl)MgBr(thf)2 derivative, the analog of which
is compound (dpp-bian-Et)MgBr(thf)2 formed in the
reactions of complex 1 with ethyl halides.44 The 1H NMR
spectrum of the reaction mixture (1 + Ph2CHCN +
+ allylBr) exhibits signals of the protons of the allyl frag-
ment of 2,2-diphenylpentene-4-nitrile (Fig. 1): a multiplet
in the range  5.59—5.85 (—CH2—CH=CH2), a doublet
of doublets at  5.17—5.30 (—CH2—CH=CH2) overlapped
with the singlet of the proton of the tertiary carbon atom
of unreacted diphenylacetonitrile ( 5.15, Ph2CHCN), and
a doublet at  3.16 (—CH2—CH=CH2). The signals at
 7.89 (d, 2 H), 6.65 (d, 2 H), 3.04 (sept, 4 H), 1.25
(d, 12 H), and 0.99 (d, 12 H) are assigned to free dpp-bian.
2,2-Diphenylpentene-4-nitrile is formed along with the
(dpp-bianH)MgBr(thf)n complex (4) due to the reaction
of imide 3 with allyl bromide. The treatment of complex
4 with magnesium excess results in hydrogen evolution,
magnesium bromide formation, and reduction of the (dpp-
bian)Mg(thf)3 complex (1) reactive toward nitrile.
To confirm this hypothesis, we carried out the reaction
of allyl bromide with diphenylacetonitrile in tetrahydro-
furan using metallic magnesium excess and a catalytic
amount of compound 1 (20 mol.% relative to the substrates
taken in a concentration of 0.04 mol L–1). After the reac-
tion occurred for 3 h at 85 С, the obtained mixture was
analyzed by 1H NMR spectroscopy and separated by
column chromatography. It is established that the reaction
affords 4,4-diphenylbutene-1 and diphenylmethane along
with the target 2,2-diphenylpentene-4-nitrile (Scheme 5).
The presence of these products in the reaction mixture
was confirmed by a comparison of the 1H, 13С, and
13C-DEPT NMR spectra with the literature data.45,46 The
Reagents and conditions: i. [Mg] : [1], thf, 3 h, 85 С.
mixture of the products contained unreacted diphenylace-
tonitrile, while no allyl bromide was observed. Based on
1
an analysis of the H NMR spectrum of the reaction
products and assignment of the integral intensities of
signals of protons characteristic of each component, we
determined the conversion of diphenylacetonitrile to the
products being 71% and the ratio of 2,2-diphenylpentene-
4-nitrile, 4,4-diphenylbutene-1, and diphenylmethane
equal to 5.5 : 1 : 1.4 , respectively.
It should be mentioned that this reaction in the absence
of complex 1 is accompanied by a decrease in the conversion
of diphenylacetonitrile to 63%. The ratio of the products
2,2-diphenylpentene-4-nitrile, 4,4-diphenylbutene-1, and
diphenylmethane also changes to 2.3 : 1 : 2.5, respectively,
which corresponds to a decrease in the selectivity of the
process for target alkenenitrile by 1.7 times. Thus, the
system consisting of complex 1 and metallic magnesium
is a catalyst of cross-coupling of allyl bromide with diphe-
nylacetonitrile. The assumed catalytic cycle of the forma-
tion of the major reaction product is presented in Scheme 6.
Scheme 6
8.0 7.5 7.0 6.5 6.0 5.5 5.0 3.5 3.0 1.5 1.0 0.5

Fig. 1. 1H NMR spectrum (200 MHz, CDCl3, 25 С) of a mix-
ture of products of the reaction of complex 1, diphenylacetonitrile,
and allyl bromide.
Catalytic activity of complexes (dpp-bian)Mg(thf)3 (1)
and (dpp-bian)Ca(thf)4 (2) in intramolecular hydroamination
of aminoalkenes. The catalytic activity of bis(amides) 1

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Russ. Chem. Bull., Int. Ed., Vol. 67, No. 3, March, 2018
Yakub et al.
and 2 was checked in the intramolecular hydroamination/
cyclization of some aminoalkenes (Scheme 7). The results
of experiments and their conditions are given in Table 1.
The data obtained show that the activity of complex 1
decreases with a decrease in the volume of substituents at
the -carbon atom of 1-aminopent-4-enes in the series
Ia > IIa, IIIa > IVa > Va > VIa (see Table 1, entries
No. 1, 2, 6, 7, and 9—14), which is well consistent with
the Thorpe—Ingold effect.47 A lower reactivity of com-
pound IIa compared to that of Ia is due, most likely, to
the low polarizability of the cyclohexyl radical, in spite of
the comparable volumes of the Ph and Cy groups (see
Table 1, entries No. 1 and 6).
methylpyrrolidine Vb from catalyst 1 and also prevents
the coordination of product Vb by the magnesium atom.
Note that aminopentene IIa was obtained by us for
the first time (see Experimental). 2-Methyl-4-phenyl-4-
cyclohexylpyrrolidine (IIb) obtained by the intramolecu-
lar cyclization of IIa was not characterized earlier. It is
1
difficult to identify it by H NMR spectroscopy because
of the formation of isomeric products. Nevertheless, we
succeeded to establish ratios between two isomers from
signals of the hydrogen atom bound to the asymmetric
carbon atom in the pyrrolidine ring (Fig. 2, range of
2.37—2.10 ppm).
The proposed catalytic cycle of intramolecular hy-
droamination is presented in Scheme 8.
Scheme 7
Scheme 8
Comparable results of the catalytic activity of the
complexes of 2 group metals with the ligands similar
in structure to dpp-bian were recently published.48
Reagents and conditions: i. catalyst 1 or 2, C6D6.
Compounds
I
II
III
IV
V
R1
Ph
Ph
R2
Ph
Cy
R3
H
H
H
H
—(CH2)5—
Me
H
H
Me
H
H
Me
H
VI
It should be mentioned that the presence of the methyl
group at the -carbon atom in aminopentene Va does not
decrease the activity of complex 1 but, on the contrary,
makes it possible to achieve a higher conversion within
the shorter time over the experiment with substrate VIa
(see Table 1, entries No. 13 and 14). We assume that for
compound Va an increase in steric hindrance in the im-
mediate vicinity from one of the reaction centers of the
molecule accelerates the elimination of formed 2,5-di-
7.5 7.0 6.5
3.5 3.0 2.5 2.0 1.5 1.0 0.5

Fig. 2. 1H NMR spectrum of a mixture of products of the intra-
molecular hydroamination of compound IIa in the presence of
complex 1 (1 mol.%) (200 MHz, C6D6, 25 С).

Acenaphthene-1,2-diimine complexes as catalysts
Russ. Chem. Bull., Int. Ed., Vol. 67, No. 3, March, 2018
477
Table 1. Intramolecular hydroamination/cyclization of aminoalkenes Ia—IXa catalyzed by complexes 1
and 2a
Entry
Substrate
Catalyst (mol.%)
T/С
/h
Conversion (%)
1
2
3
4
5
6
7
8
Ia
Ia
Ia
Ia
Ia
IIa
IIa
IIa
IIIa
IIIa
IVa
IVa
Va
VIa
VIIa
VIIIa
VIIIa
IXa
IXa
1 (2.0)
1 (1.0)
1 (0.5)
2 (5.0)
2 (0.5)
1 (5.0)
1 (5.0)
2 (5.0)
1 (2.0)
1 (2.0)
1 (2.0)
2 (2.0)
1 (2.0)
1 (2.0)
1 (2.0)
1 (5.0)
1 (5.0)
1 (5.0)
1 (5.0)
25
25
5
10
5
99
99
98
98
95
2
60
25
3.33
25
15
2
0.1
0.083
120
5
12
10
20
100
12
7
15
10
15
25
90
90
25
98b
99b
92
99
99
90
99c
67
99
0
9
10
11
12
13
14
15
16
17
18
19
60
60
60
100
100
100
25
60
0
25
0
90
0
a The conversion values were determined by 1H NMR spectroscopy, solvent C6D6 (0.65 mL).
b Ratio of isomers cis : trans = 2 : 1.
c Ratio of isomers cis : trans = 5 : 1.
benzophenone and distilled off/condensed in vacuo to a reaction
ampule or an NMR tube prior to use. Deuterated chloroform
(DalKhim) was used as received. Allyl bromide (Aldrich) was
dehydrated with a minor amount of calcium hydride and distilled
off in vacuo prior to use. Diphenylacetonitrile (Aldrich) was used
without preliminary purification.
Experiments on cross-coupling of allyl bromide with di-
phenylacetonitrile were carried out as follows. Metallic magne-
sium (6 g, 25 mmol) and diphenylacetonitrile (193 mg, 1 mmol)
were placed in a glass ampule, and the ampule was degassed. Allyl
bromide (121 mg, 1 mmol) and thf (15 mL) were samples by
condensation in vacuo, and the ampule was sealed off. The am-
pule with the reaction mixture was heated for 3 h at 85 С and
opened. Volatile fractions were removed under reduced pressure,
and the residue was separated by column chromatography (petrol-
eum ether as eluent). The reaction products, viz., 2,2-diphenyl-
pentene-4-nitrile, 4,4-diphenylbutene-1, and diphenylmethane,
were identified by a comparison of the 1H, 13С, and 13C-DEPT
NMR spectra with the published data.45,46
The catalytic activity of the yttrium and zirconium de-
rivatives obtained from diamine (dpp-bian)H2 is also
known.49
To conclude, we demonstrated the principal possibil-
ity of using the system consisting of metallic magnesium
and complex 1 as a catalyst of cross-coupling of allyl
bromide and diphenylacetonitrile and also studied the
catalytic activity of complexes 1 and 2 as catalysts in the
intramolecular hydroamination of some alkeneamines.
The activity of the complexes in these reactions turned out
to be comparable with that of the alkaline-earth metal
complexes based on dearomatized dpp-bian48 and the
yttrium and zirconium complexes with the deprotonated
form of dpp-bian, (dpp-bian)H2.49 These complexes were
specially chosen for comparison, because the structure of
their ligand is maximum close to that of dpp-bian.
However, an advantage of our complexes is that they can
be obtained by direct synthesis from metallic magnesium
or calcium and free dpp-bian24 and do not require addi-
tional functionalization of the ligand.
Alkeneamines Ia,51 IIIa,51 IVa,51 VIIa,51 Va,52 VIa,52 and
IXa53 were synthesized according to the previously described
procedures. Compound VIIIa (Aldrich) was used without pre-
liminary purification. Compound IIa was synthesized similarly
to compound Ia using cyclohexylphenylacetonitrile instead of
diphenylacetonitrile. 1H NMR spectra were recorded using
Bruker DPX-200 and Bruker AV-400 spectrometers.
Experimental
Compounds 1 and 2 are sensitive to air oxygen and moisture
and, hence, all procedures including their preparation were car-
ried out in vacuo or in an atmosphere of nitrogen (special pure
grade) using glass ampules, Schlenk flasks, and NMR tubes.
Diimine dpp-bian50 and complexes 124 and 224 were synthesized
according to earlier described procedures. Benzene (Vekos), thf
(DalKhim), and benzene-d6 (Aldrich) were dried over sodium
1-Amine-2-cyclohexyl-2-phenylpentene-4 (IIa). Found (%):
С, 83.84; H, 10.34; N, 5.69. C17H25N (243.39). Calculated (%):
С, 83.89; H, 10.35; N, 5.75. 1H NMR (200 MHz, CCl3D, 298 К),
: 7.43—7.05 (m, 5 H); 5.84 (ddt, 1 H, J = 17.0 Hz, J = 10.0 Hz,
J = 7.1 Hz); 5.09 (dd, 2 H, J = 17.0 Hz, J = 10.0 Hz); 3.09 (dd,
2 H, J = 18.4 Hz, J = 13.8 Hz); 2.68 (d, 2 H, J = 7.1 Hz);
1.85—0.65 (m, 13 H).

478
Russ. Chem. Bull., Int. Ed., Vol. 67, No. 3, March, 2018
Yakub et al.
Catalytic experiments. All procedures were carried out in the
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grade, content of water and oxygen lower than 0.1 ppm). In
a standard catalytic test, the catalyst was placed in an NMR tube
and a solution of one of alkeneamines Ia—IXa in C6D6 was
added. Then the tube was shaken several times to achieve homo-
geneity of the mixture. The 1H NMR spectra of the intramo-
lecular amination products Ib,51 IIIb,51 IVb,51 VIIb,51 Vb,52 and
VIb52 corresponded to literature data.
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This work was financially supported by the Russian
Science Foundation (Project No. 14-13-01063).
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Received December 28, 2017;
in revised form January 29, 2018;
accepted February 1, 2018