α-Diphenylphosphino-N-(pyrazin-2-yl)glycine as a ligand in Ni-catalyzed ethylene oligomerization

Article abstract of DOI:10.1016/j.mencom.2019.09.033

α-Diphenylphosphino-N-(pyrazin-2-yl)glycine was synthesized by the three-component condensation of diphenylphosphine, glyoxylic acid hydrate, and 2-aminopyrazine and its structure was confirmed by X-ray diffraction. It reacted with [Ni(COD)₂] (COD is cycloocta-1,5-diene) to give complexes that were tested as catalysts for selective dimerization/oligomerization of ethylene to but-1-ene (main product) and C₆–C₁₄ α-olefins, respectively.

Full text of DOI:10.1016/j.mencom.2019.09.033

Mendeleev
Communications
Mendeleev Commun., 2019, 29, 575–577
a-Diphenylphosphino-N-(pyrazin-2-yl)glycine as a ligand
in Ni-catalyzed ethylene oligomerization
Olga S. Soficheva, Giyjaz E. Bekmukhamedov, Alexey B. Dobrynin,a
a
a,b
c
a
a,b
Joachim W. Heinicke, Oleg G. Sinyashin and Dmitry G. Yakhvarov*
a
A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center of the Russian Academy
of Sciences, 420088 Kazan, Russian Federation. Fax: +7 843 273 2253; e-mail: yakhvar@iopc.ru
Kazan Federal University, 420008 Kazan, Russian Federation
b
c
Institute of Biochemistry, Ernst-Moritz-Arndt University of Greifswald, 17487 Greifswald, Germany
DOI: 10.1016/j.mencom.2019.09.033
a-Diphenylphosphino-N-(pyrazin-2-yl)glycine was synthesized
by the three-component condensation of diphenylphosphine,
glyoxylic acid hydrate, and 2-aminopyrazine and its structure
wasconfirmedbyX-raydiffraction. Itreactedwith[Ni(COD)2]
NH2
Cꢀ9ꢁ
Pꢀ1ꢁ
N
Cꢀ2ꢁ
Ph2PH + (HO)2CHCOOH +
N
(COD is cycloocta-1,5-diene) to give complexes that were
Cꢀꢂꢁ
Nꢀ1ꢁ
tested as catalysts for selective dimerization/oligomerization
of ethylene to but-1-ene (main product) and C –C a-olefins,
6
14
respectively.
Linear alpha olefins (LAO) are produced in large scale by various
industrial processes as base materials for oxo alcohols used in
via 2 corresponds to the usual behaviour of sterically unhindered
1
primary alkylamines or anilines in the three-component
9
,10
biodegradable detergents and plasticizers (C –C ), as co-
reactions.
10
18
monomers for producing different types of alkyl-branched
polyethylenes or lubricants (C –C ), and as starting materials for
The structure of compound 1 was unambiguously proved by
1H, 13C and P NMR spectroscopy and by X-ray crystal structure
31
4
8
†
other products. The industrial need for short LAOs with four–
eight carbon atoms is ever growing and requires new catalysts
analysis (Figure 1).
Compound 1 crystallizes in the centrosymmetric monoclinic
2
for oligomerization of ethylene to short LAOs or selective di-,
space group P2 /n with each one molecule with R- and
1
3
tri- and tetramerization. One of the most important processes
S-configuration of the α-C atom in the unit cell. The phosphorus
for the production of LAOs is the Shell Higher Olefin Process
atom displays the typical pyramidal configuration, the Newman
-
(
SHOP) that involves the step of P–C–C–O –Ni chelate-
1(b),4
catalyzed oligomerization of ethylene.
nature of the P–C–C–O ligands, oligomers or polymers are
produced; very short linear α-olefins are also obtained in the
presence of Ph P, whereas the exclusive formation of butenes in
Depending on the
-
Ph PH
+
2
+
NH3
5
COO–
HO
6
(HO)2CHCOOH
+
3
–H2O
N
the absence of this additive is rare for neutral phosphine-based
PPh2
2
(a)
+
+
NH2
N
catalysts. Highly active acidic P,OR or P,OH –Ni catalysts,
producing mainly butenes, are usually less selective and provide
2
N
7
mixtures of isomers. Having performed studies on phosphino-
N
H
phenols and their use for generation of Ni catalysts for oligo- or
N
N
COOH
PPh2
5
(a),8
polymerization of ethylene,
we focussed on α-phosphino
9
10
amino acids, in particular, phosphinoglycines readily accessible
by three-component one-pot reactions, and their potential to
form Ni catalysts for ethylene oligomerization.
–H2O
N
1
Here we describe the synthesis of new N-(pyrazin-2-yl)-
substituted diphenylphosphinoglycine 1, its structure and data
on ligand screening in the nickel-catalyzed oligomerization of
ethylene. Compound 1 was obtained by addition of a solution
containing diphenylphosphine and 2-aminopyrazine to a solution
of glyoxylic acid hydrate in diethyl ether or methanol or in a
mixture of these solvents. The reaction proceeds at room
Scheme 1 Reagents and conditions: Et O or MeOH, room temperature.
2
†
For synthesis and NMR data of 1, see Online Supplementary Materials.
Crystallographic data for 1: crystals of C H N OP (M = 337.31) are
18
16
3
monoclinic, space group P2 /n, at 100 K: a = 6.2160(5), b = 21.3663(17)
1
3
and c = 12.0547(10) Å, b = 102.399(4)°, V = 1563.7(2) Å , Z = 4, d
1.433 g cm , μ(MoKa) = 0.192 mm , F(000) = 704. 28744 reflections
=
calc
–3
–1
=
temperature via the corresponding pyrazine-ammonium diphenyl-
phosphinoglycolate 2 (d31P = 6.0 ppm), which immediately
were measured and 3749 independent reflections (Rint = 0.111) were used
in a further refinement. The refinement converged to wR2 = 0.1693 and
precipitates in diethyl ether after mixing, and in MeOH it
GOF = 1.11 for all independent reflections [R = 0.0550 was calculated
1
converts slowly to compound 1 (Scheme 1). This formation of 1
against F for 2360 observed reflections with I > 2s(I)].
©
2019 Mendeleev Communications. Published by ELSEVIER B.V.
–
575 –
on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.

Mendeleev Commun., 2019, 29, 575–577
Table 1 Catalytic homogeneous oligomerization of ethylene catalyzed by [Ni(COD) ]/1 (~1:1 molar ratio) system in THF (125–200 ml per mmol of the
2
catalyst).
=
a
Product composition (%)
S(αC ) (%)
[
Ni]/mol% to
Conversion of C H (%)/
2 4
TON
Entry
T/°C
C H applied
2
4
C4
C6
1
1c
C8
C10
1
C12
3
SC –C
polymer
14
30
1
2
3
4
5
6
25
25
0.052
0.035
0.040
0.040d
0.032
0.045
10/192
5/158
1
1
n.d.b
9
85
98
6
–
–
80
69/1763
41/1464
58/2493
49/1202
44
37
24
46
19
14
14
26
13
7
8
8
5
7
9
3
5
24
30
2
96.2
96.4
97.3
99.7
100
100
120
3
9
10
7
3
14
2
a
=
b
c
d
S(αC ) is selectivity to α-olefins vs. internal ones determined by GC-MS as the average for C –C
Not detected. Total for C –C olefins. [Ni(COD) ]/1
10
14.
6
30
2
ratio was 1.4:1.
ꢀ
ꢁ
2
0
0
ꢀ
2
1
Cꢀ9ꢁ
0
0
Pꢀ1ꢁ Cꢀ2ꢁ
Cꢀꢂꢁ
Nꢀ1ꢁ
0
ꢂ
10
1ꢂ
tꢃh
Figure 2 Pressure–time plots for batch oligomerization of ethylene with
/[Ni(COD) ] in THF at different bath temperatures: (1) 25 °C, (2) 80 °C
1
2
and (3) 100 °C.
Figure 1 The structure of α-diphenylphosphino-N-(pyrazin-2-yl)glycine 1
‡
in the crystal.
ene as the major product, were formed. Figure 2 depicts the
experimentally observed kinetic curve of the ethylene
consumption, superimposed by the growing vapor pressure of
low-boiling ethylene dimers and trimers, at different
temperatures. A slight increase in the pressure at 25 °C and
formation of small amounts of polymers and traces of oligomers
(Table 1, entries 1 and 2) indicate slow exothermic conversion
of ethylene already at room temperature. More rapid reaction,
as shown by the curve recorded at 80 °C, and higher conversion
(entry 3) require moderate heating. Polymers are formed only
in traces, while the predominant product is but-1-ene,
accompanied by small amounts of linear α-olefins from hex-1-
ene to dodec-1-ene. The processing at 100 °C, usual for N-aryl-
projection along the C(2)–P(1) bond shows that one P-phenyl
group locates in trans-position to the C(2)–N(1) bond, the other
in gauche-position [torsion angles C(9)P(1)C(2)N(1) 177.11°,
C(3)P(1)C(2)N(1) –76.91°].
The interesting point with respect to potential use of
diphenylphosphinoglycine 1 as a ligand for nickel-catalyzed
ethylene oligomerization is that the latter possesses the same
-
P–C–C–O structure motive as diphenylphosphinoacetic acid
used to obtain high active nickel catalysts for the industrial
process of ethylene oligomerization.1 It should be also noted
that some phosphinoglycines with various N-aryl or N-alkyl
,4
1
0
substituents in combination with [Ni(COD) ] have already
or N-alkylphosphinoglycinate Ni catalysts, or even at 120 °C,
would slightly diminish the catalyst activity, life cycles and
ethylene conversion (entries 4–6).
In summary, catalytic system [Ni]–ligand 1 provides high
selectivity towards short linear α-olefins in ethylene oligomeri-
zation. This is one of the rare examples of neutral Ni catalysts for
generation of mainly but-1-ene among smaller amounts of other
linear α-olefins. The known cationic Ni catalysts are usually less
selective and produce mixtures of various isomers including
2
been tested in ethylene oligomerization process. However, in
case of N-heterocyclic substituents, these attempts have failed
due to possible blocking of the catalytically active Ni-center by
additional N-coordination of the N-heterocyclic group. A
related behaviour is also characteristic of some new water-
soluble ligands based on P-pyridyl-containing phospholane
oxides that are capable to form bis-N,O-chelate nickel(ii)
1
1
complexes.
7
The investigation of the activity of the catalysts generated
branched derivatives. The isolation and characterization of main
from ligand 1 and [Ni(COD) ] in the ethylene oligomerization
process was performed in THF as the most suitable solvent.
intermediates of the process and elucidating of the nature of
catalytically active species formed in the catalytic process are
currently under investigation.
2
9
,10
At 80–120 °C, short linear α-olefins C –C , containing but-1-
4
14
The measurements were performed on a Bruker Smart Apex II CCD
diffractometer with graphite-monochromated Mo–Kα radiation (l =
0.71073 Å). The structure was solved by direct methods, and the non-
This work was supported by the RussianAcademy of Sciences
Basic research program no. 14) and the Government of the
Russian Federation (Program for Competitive Growth of the
Kazan Federal University). The authors gratefully acknowledge
the CSF-SAC FRC KSC RAS for providing necessary facilities
to carry out this work.
(
=
hydrogen atoms were located from the trial structure and then refined
anisotropically with SHELXTL using a full-matrix least-squares procedure
2
based on F . The hydrogen atom positions were fixed geometrically at
calculated distances and allowed to ride on the parent atoms.
CCDC 1939537 contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via http://www.ccdc.cam.ac.uk.
‡
For the details of the catalytic experiments, see Online Supplementary
Materials.
–
576 –

Mendeleev Commun., 2019, 29, 575–577
This article is dedicated to the memory of Professor Dr. Dr.
h.c. Wilhelm Keim.
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Online Supplementary Materials
Supplementary data associated with this article can be found
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Received: 18th January 2019; Com. 19/5807
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