Nickel(I) complex as the final product of the sequence of spontaneous transformations in the system Ni(Allyl)2-(2,6-diisopropylphenyl) diazabutadiene

Article abstract of DOI:10.1134/S1070328412050053

A reaction of Ni(Allyl)₂ with bis(2,6-diisopropylphenyl) diazabutadiene gave an imino amide allyl nickel(II) complex (I). Complicated rearrangements of the imino amide ligand in the coordination sphere of complex I spontaneously yielded a paramagnetic Ni(I) π-allyl complex as a final reaction product. The nickel complexes produced in this system were studied by EPR, IR, and 2D NMR spectroscopy and mass spectrometry. Structure I was examined by X-ray diffraction. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S1070328412050053

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2012, Vol. 38, No. 6, pp. 416–425. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © P.B. Kraikivskii, V.V. Saraev, V.V. Bocharova, G.V. Romanenko, D.A. Matveev, S.K. Petrovskii, A.S. Kuzakov, 2012, published in Koordinatsionnaya
Khimiya, 2012, Vol. 38, No. 6, pp. 436–445.
Nickel(I) Complex as the Final Product of the Sequence
of Spontaneous Transformations
in the System Ni(Allyl)2–(2,6ꢀDiisopropylphenyl)diazabutadiene
P. B. Kraikivskiia, *, V. V. Saraeva, V. V. Bocharovaa, G. V. Romanenkob, D. A. Matveeva,
S. K. Petrovskiia, and A. S. Kuzakova
a Irkutsk State University, Irkutsk, Russia
b Institute “International Tomography Center”, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
*eꢀmail: peter10@list.ru
Received April 13, 2011
Abstract—A reaction of Ni(Allyl)2 with bis(2,6ꢀdiisopropylphenyl)diazabutadiene gave an imino amide allyl
nickel(II) complex (
complex spontaneously yielded a paramagnetic Ni(I)
complexes produced in this system were studied by EPR, IR, and 2D NMR spectroscopy and mass spectromꢀ
etry. Structure was examined by Xꢀray diffraction.
I). Complicated rearrangements of the imino amide ligand in the coordination sphere of
I
π
ꢀallyl complex as a final reaction product. The nickel
I
DOI: 10.1134/S1070328412050053
A survey of the literature data on transition metal overwhelming majority of relevant studies are based on
nickel(0) and nickel(2) complexes. The Ni+2 form is
complexes with allyl ligands since the synthesis of their
regarded as the second most stable species inferior
only to colloidal nickel [9, 13–15]. However, some
authors do note the formation of nickel(I) complexes
from both nickel(II) complexes with allyl [6] and
diimine ligands [10, 11].
first representatives [1, 2] till now [3–6] has revealed
that the ꢀallyl structure of transition metal complexes
takes an important part in catalytic reactions. This
relates to ꢀallyl fragments both originally present in a
transition metal complex or formed immediately in its
coordination sphere during reactions of complexes
π
π
Furthermore, despite much research dealing with
with olefins at a metal complex catalyst. As a rule, a allyl complexes of transition metals, the literature data
on nickel allyl systems are very scarce because the
attention of researchers is mainly focused on allyl
complexes of palladium [16]. Obviously, this is due to
both the relatively low stability of allyl complexes of
nickel and the limited scope of their study by the most
commonly used method (NMR spectroscopy) [17].
π
ꢀallyl complex in catalytic systems is stabilized by
various organometallic ligands. A catalytic system
based on nickel and palladium diimine complexes has
been proposed in [7, 8]. An undoubted advantage of
such systems is that lower olefins can be transformed
into linear polymers with a considerable
αꢀform conꢀ
tent. This type of catalytic systems holds promise as
In this work, we studied in detail complexation
precursors of cationic or electrically neutral allyl between bisallylnickel(II) and bis(2,6ꢀdiisopropylꢀ
phenyl)diazabutadiene (DAB) by NMR, EPR, and IR
spectroscopy; DAB is an efficient, abundant, and synꢀ
thetically accessible diimine ligand.
nickel and palladium complexes with various diimine
ligands including the diazabutadiene fragment [8].
Although such catalytic systems are currently under
intensive study, a question is still open as to whether
Nꢀcontaining ligands themselves can be transformed
in organometallic complexes. As a result, almost all
the mechanisms proposed in the literature for the catꢀ
EXPERIMENTAL
All manipulations were performed using standard
alytic cycle ignore possible changes in the nature of the Schlenk ware with an argon–vacuum double manifold
glass line. Solvents and volatile components were admitꢀ
ted into the systems by recondensation; solid components
were added from evacuated tubes fused to the systems.
NMR spectra were recorded on a Bruker AVANCE
500 spectrometer in sealed evacuated tubes. For reliꢀ
able assignments of NMR signals and interpretation of
the spectra, we employed the APT, DEPT,
metal–ligand bond and in the structure of the diimine
ligand itself [9–15]. One can state that this ligand is
most often regarded as an unchangeable entity
involved in the catalytic cycle as a “guest” that can
either be coordinated to the metal center or quit its
coordination sphere intact. Thus, possible transforꢀ
mations of the ligand itself are usually left out. In addiꢀ
tion, the catalytic cycle mechanisms considered in the COSY, NOESY, TOCSY, HMQC, HSQC, and
416

NICKEL(I) COMPLEX AS THE FINAL PRODUCT OF THE SEQUENCE
of the signals in the NMR spectra of the nickel allyl complexes
417
Chemical shifts
δ
Complex δH15anti δH17anti δH16 δH15syn δH17syn δC15
δC16
δC17
δC26
δC25
δC24
δC8
δC7
I
(THFꢀ d8) 1.41
1.43
= 12.0
5.34
5.46
1.59
1.62 53.6
= 6.8
106.39 50.6 119.48 132.44 37.65 191.36 72.82
J
= 13.0
J
J
J
= 6.0
J
J
II (C6D6)
1.83
= 13.0
1.79
= 13.0
1.62
= 6.0
2.0 53.75 106.43 50.75 18.47 139.49 123.46 183.13 69.4
= 4.3
J
J
II (THFꢀd8) 1.61
1.43
5.35
4.9
1.41
1.59 53.97 106.7 50.71 19.26 140.88 124.18 184.13 69.56
Ni(Allyl)2
1.67
3.76
J = 7.6
[2, 20]
J
= 14.3
HMBC techniques. IR spectra were recorded on an filled with glass beads lined with a K–Na alloy. Solꢀ
Infralyum FTꢀ801 FTIR spectrometer (in KBr pellets vents were stored over a Na–K mirror.
pressed in an inert atmosphere or in Nujol between
ZnSe windows). Mass spectra were measured on a
Varian MAT spectrometer (direct inlet probe). Eleꢀ
mental analysis was carried out on a FLACH 1112
(EA series) analyzer in sealed crucibles filled and
encapsulated in an inert atmosphere.
The complex Ni(Allyl)2 and DAB were prepared as
described in [2] and [18], respectively.
Synthesis of complex I [19]. A solution of DAB
(1.50 g, 4 mmol) in diethyl ether (100 mL) was slowly
(for 30 min) added dropwise at –5 C to a vigorously
°
stirred solution of Ni(Allyl)2 (0.564 g, 4 mmol) in
diethyl ether (100 mL). The bright red reaction mixꢀ
An experimental set of Xꢀray diffraction data for
ture was stirred at about –5°C for 2 h, filtered, and
the imino amide allyl nickel(II) complex (
lected with its red single crystal (0.22
I
) was colꢀ
concentrated in vacuo. The bright red powder that
×
0.18
×
formed was dissolved in pentane (50 mL) at –5
the solution was kept in a freezer at –30
°
C
and
for
0.05 mm) on a Smart Apex II automated diffractomeꢀ
ter (Mo radiation, = 240 K, 2.30° ≤ θ ≤ 28.05 ,
°C
K
Т
°
α
five days. The bright red crystals that formed as thin
plates were filtered off at –30 and dried in vacuo
= 10–2 mm Hg) at
= 20–25 for 6 h. The crysꢀ
tals are stable under argon, yet rapidly decomposing
with selfꢀignition in air. The yield of complex was
1.07 g (2.08 mmol, 52.0%); no melting was observed
7168 independent reflections out of 20928 measured
ones, Rint = 0.1354). The monoclinic unit cell of comꢀ
°C
(
Р
Т
°C
plex
10.939(4),
3044.7(19) Å3
0.658 mm–1). Structure
I
has the following parameters:
= 18.470(7) = 116.46(2)
21/
= 4, ρcalcd = 1.129 g/cm3
a
= 16.832(6),
b
=
=
=
c
Å
,
β
°, V
I
,
P
с,
Z
,
μ
I
was solved by the direct
up to 60–65
°
C
(decomp.).
methods and refined by the fullꢀmatrix leastꢀsquares
method in the anisotropic approximation for all nonꢀ
hydrogen atoms. The H atoms were located geometriꢀ For C32H46N2Ni
cally and refined together with the nonꢀhydrogen
atoms using a riding model. The final residuals are
Anal. calcd. (%): C, 74.28,
H, 8.96,
H, 8.20,
N, 5.41.
N, 4.92.
Found (%):
C, 75.16,
R
1 = 0.0520 and wR2 = 0.1056 (
I
> 2σ(I)),
R
1 = 0.1784, wR2 = 0.1377 for all reflections. The
HRMS: for C32H46N2Ni anal. calcd.: –516.3014,
measured –516.2994 (–2 mmu).
comprehensive tables of the coordinates of the basic
atoms and the bond lengths and bond angles in strucꢀ
ture
tallographic Data Collection (no. 819771;
deposit@ccdc.cam.ac.uk or http://www.ccdc.
cam.ac.uk) and can be made available from the
authors upon request.
MS (70 eV, m/z, %): 476 (100.0), 516 (74.8).
I have been deposited with the Cambridge Crysꢀ
IR (KBr,
532 (CCC).
ν
, cm–1): 1602
ν
(C=N), 1105
ν
(CCC),
δ
1H NMR (500 MHz, THFꢀd8, 297 K,
δ, ppm):
6.95 (d, 1H, CH(3), 3JH3–H4 = 7.12 Hz), 6.86 (m, 1H,
CH(4)), 6.98 (d, 1H, CH(5), 3JH5–H4 = 6.87 Hz), 4.38
(d, 1H, CH27, 2JH7'–H7 = 26.5 Hz), 4.56 (d, 1H, CH27',
All (including deuterated) solvents were purchased
from Merck. Before use, solvents were placed in stanꢀ
dard Schlenk flasks with Teflon valves by recondensaꢀ CH(13)), 1.67 (d, 1H, CH215, JH15–H16 = 5.98 Hz),
2JH7–H7' = 27 Hz), 7.20 (m, 3H, CH(11), CH(12),
3
3
tion in a vacuum manifold through a Uꢀshaped seal 1.61 (d, 1H, CH215', JH15–H16 = 13.2 Hz), 5.35 (d,
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
No. 6
2012

418
KRAIKIVSKII et al.
3
1H, CH(16)), 1.48 (d, 1H, CH217, JH17–H16 = 5.98 1H, CH(30)), 1.11 (m, 3H, CH331), 1.16m, 3H,
3
Hz), 1.40 (d, 1H, CH217', JH17–H16 = 14.3 Hz), 4.50 CH332).
13C NMR (125 MHz, THFꢀd8, 297 K,
, ppm):
δ
(d, 1H, CH(18)), 1.38 CH319, CH320), 3.86 (m, 1H,
CH(21)), 1.31 (m, 6H, CH322, CH323), 2.88 (m, 2H,
CH224'), 5.73 (m, 1H, CH(25)), 5.01 (m, 2H,
CH226), 3.32 (m, 1H, CH(27)), 1.29 (m, 6H, CH328,
CH329), 3.67 (m, 1H, CH(30)), 1.22 (m, 6H, CH331,
CH332).
158.17 (C(1)), 123.02 (C(3)), 123.53 (C(4)), 123.43
(C(5)), 146.54 (C(6)), 69.56 (C(7)), 184.13 (C(8)),
147.17 (C(9)), 139.71 (C(10)), 124.17 (C(11)), 127.13
(C(12)), 124.43 (C(13)), 140.20 (C(14)), 53.97
(C(15)), 106.7 (C(16)), 50.71 (C(17)), 28.45 (C(18)),
26.10 (C(19)), 26.26 (C(20)), 28.28 (C(21)), 24.89,
25.15 (C(22), C(23)), 124.18 (C(24)), 140.88 (C(25)),
19.26 (C(26)), 29.22 (C(27)), 23.78 (C(28)), 24.00
(C(29)), 29.42 (C(30)), 24.28 (C(31)), 24.62 (C(32)).
13C NMR (125 MHz, THFꢀd8, 297 K,
, ppm):
δ
157.84 (C(1)), 147.87 (C(2)), 123.06 (C(3)), 123.54
(C(4)), 123.43 (C(5)), 146.33 (C(6)), 72.82 (C(7)),
191.36 (C(8)), 146.67 (C(9)), 124.41 (C(11)), 127.33
(C(12)), 124.67 (C(13)), 53.61 (C(15)), 106.39
(C(16)), 50.62 (C(17)), 28.44 (C(18)), 26.16, 26.34
(C(19), C(20)), 28.30 (C(21)), 24.49, 25.16 (C(22),
C(23)), 37.65 (C(24)), 132.44 (C(25)), 119.48
(C(26)), 29.09 (C(27)), 24.23, 24.14 (C(28), C(29)),
29.29 (C(30)), 24.42, 24.57 (C(31), C(32)).
1H NMR (500 MHz, C6D6, 297 K,
δ, ppm): 7.28
3
(d, 1H, CH(3), JH3–H4 = 7.3 Hz), 7.23 (m, 1H,
CH(4)), 1.62 (d, 1H, CH(5), 3JH5–H4 = 7.2 Hz), 4.67
2
(d, 1H, CH27, JH7'–H7 = 25.30 Hz), 4.90 (d, 1H,
2
CH27', JH7–H7' = 25.0 Hz), 7.06 (m, 3H, CH(11),
Synthesis of the complex C32H46N2Ni (II) [19].
solution of complex (2.58 g, 5 mmol) in diethyl ether
(100 mL) was kept in a Schlenk flask at 20–25 for
A
CH(12), CH(13)), 1.83 (d, 1H,
anti 15, 3JH15–H16
=
CH2
I
13 Hz, COSY 5.46, NOESY 1.62–, HSQC 53.75,
°С
syn15, JH15–H16
=
3
5 h. The solvent was removed in vacuo. The resulting
reddish brown powder was dissolved in pentane
HMBC 50.75), 1.62 (d, 1H,
6.0 Hz, COSY 2.00, 5.46, NOESY 1.83–
CH2
,
2.00+ 5.46–
, ,
(50 mL) and kept in a freezer at –30
amorphous reddish brown powder that formed was filꢀ
tered off and dried in vacuo (
= 10–2 mm Hg) at 20–
25 for 6 h. According to Xꢀray powder diffraction
°C for 5 days. The
HSQC 53.75, HMBC 50.75), 5.46 (m, 1H, CH(16),
COSY 1.62, 1.79, 1.83, 2.00, NOESY 1.62, 2.00,
HSQC 106.43, HMBC 50.75, 53.75), 2.00 (d, 1H,
P
°C
syn17, JH17–H16 = 4.3 Hz, COSY 1.62, 5.46,
3
CH2
data, the product is Xꢀray amorphous. The product is
stable under argon, yet rapidly decomposing with selfꢀ
ignition in air. The yield of complex II was 1.99 g
NOESY 1.62+ 1.79–; 5.46⎯ , HSQC 50.75, HMBC
,
anti
3
53.75), 1.79 (d, 1H,
17, JH17–H16 = 13.0 Hz,
CH2
(3.85 mmol, 77.0%),
Т
m = 97–10 C.
°
COSY 5.46, NOESY 2.00–, HSQC 50.75, HMBC
53.75), 4.81 (m, 1H, CH(18)), 1.47 (d, 3H, CH319,
3
3JH19–H18 = 6.7 Hz), 1.53 (d, 3H, CH320, JH20–H18
=
For C32H46N2Ni
6.7 Hz), 4.14 (m, 1H, CH(21)), 1.41 (m, 6H, CH322,
CH323), 5.64 (d, 1H, CH(24), JH24–H25 = 16.0 Hz,
Anal. calcd. (%): C, 74.28,
Found (%): C, 73.42,
H, 8.96,
H, 8.05,
N, 5.41.
N, 4.70.
3
HSQC 123.46, HMBC 18.47), 5.87 (dq, 1H, CH(25),
3
3JH25–H26 = 6.45 Hz, JH25–H24 = 16.2 Hz, HSQC
MS (70 eV,
IR (KBr,
532 (CCC).
1H NMR (500 MHz, THFꢀd8, 297 K,
m/z, %): 476 (100.0), 516 (65.2).
ν
, cm–1): 1641
ν
(C=N), 1076
ν
(CCC), 134.49, HMBC 18.47, 183.13), 0.94 (d, 2H, CH226,
3JH26–H25 = 6.54 Hz, HSQC 18.47), 3.46 (m, 1H,
δ
δ, ppm):
CH(27)), 1.1 (m, 3H, CH328), 1.28 (m, 3H, CH329),
3.75 (m, 1H, CH(30)), 1.27 (m, 3H, CH331), 1.15 (m,
3H, CH332).
6.97 (m, 1H, CH(3), HSQC 123.01), 6.84 (m, 1H,
CH(4)), 6.94 (m, 1H, CH(5)), 4.79 (d, 1H, CH(7),
2JH7–H7' = 25.0 Hz), 4.57 (d, 1H, CH(7'), JH7'–H7
=
2
13C NMR (125 MHz, C6D6, 297 K,
, ppm):
δ
25.0 Hz), 7.18 (m, 6H, CH(11), CH(12), CH(13)),
1.61 (d, 1H, CHanti15, JH15–H16 = 12.7 Hz, COSY
3
157.63 (C(1)), 123.23 (C(3)), 123.25 (C(5)), 146.0
(C(6)), 69.4 (C(7)), 183.13 (C(8)), 146.47 (C(9)),
139.06 (C(10)), 123.84 (C(13)), 139.53 (C(14)), 53.75
(C(15)), 106.43 (C(16)), 50.75 (C(17)), 28.02
(C(18)), 24.74 (C(19)), 26.07 (C(20)), 27.88 (C(21)),
25.02–25.9 (C(22), C(23)), 123.46 (C(24)), 139.49
(C(25)), 18.47 (C(26)), 28.48 (C(27)), 23.95 (C(28)),
23.55 (C(29)), 28.67 (C(30), HSQC 3.75), 23.37
(C(31)), 24.28 (C(32)).
5.35, HMBC 53.97), 1.41 (d, 1H, CHsyn15, 3JH15–H16
=
6.0 Hz, HSQC 53.97), 5.35 (m, 1H, CH(16), COSY
1.43, 1.61, HSQC 106.7), 1.43 (d, 1H, CHanti17,
3JH17–H15 = 14.3 Hz, COSY 1.61, 5.35, NOESY 1.59,
HSQC 50.71), 1.59 (d, 1H, CHsyn17, JH17–H16
=
3
6.0 Hz, NOESY 1.43), 4.51 (m, 1H, CH(18)), 1.26
(m, CH319), 1.29 (m, 3H, CH320), 3.88 (m, 1H,
CH(21)), 1.2 (m, 6H, CH322, CH323), 5.7 (m, 1H,
3
CH(24), JH24–H25 = 16.4 Hz, HSQC 124.18), 6.51
A solution of complex in THFꢀd8 was kept in a
I
3
3
(dq, 1H, CH(25), JH25–H26 = 7.0 Hz, JH25–H24
=
sealed NMR tube at 25 C while monitoring its transꢀ
°
13
16.1 Hz, HSQC 140.88, HMBC 184.13), 1.64 (d, 3H, formation by the DEPTꢀ135 C NMR technique.
3
CH326, JH26–H24 = 7.0 Hz, HSQC 19.26), 3.37 (m, The characteristic signals for the C(26) atom were
1H, CH(27)), 1.35 (m, 3H), 1.37 CH329), 3.66 (m, watched. After 3 h, the signal at δ 119.48 (complex I)
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
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NICKEL(I) COMPLEX AS THE FINAL PRODUCT OF THE SEQUENCE
419
was completely replaced by the signal at δ 19.27 (comꢀ
plex II). The degree of conversion of complex
complex II is nearly 100%.
I into
C(16)
C(17)
C(15)
Ni(1)
The atomic numbering in structures
given below:
I and II is
26
N(1)
23
N(2)
29
25
28
27
21 22
7
24
8
10 11
5
C(8)
6
C(7)
12
N
N
1
9
C(24)
Ni
15
17
14 13
31
3
2
C(25)
C(26)
16
30
18
19
32
20
(I
)
26
23
29
25
Fig. 1. Molecular structure of complex I (Xꢀray diffraction
28
27
data). Selected bond lengths and bond angles: Ni–N(1),
1.845(3) Å; Ni–N(2), 1.922(3) Å; Ni–C(15), 1.955(4) Å;
Ni–C(16), 1.955(9) Å; Ni–C(17), 1.947(13) Å; C(25)–
C(26), 1.13ÅA; C(24)–C(25), 1.320(4) Å; C(8)–C(24),
1.557(3) Å; N(1)–C(7), 1.437(9) Å; N(2)–C(8),
1.287(9) Å; C(7)–C(8), 1.478 Å; N(1)NiN(2),
21 22
7
24
8
10 11
5
6
12
N
N
1
9
Ni
15
17
14 13
31
3
2
84.93(12)
104.01(3)
113.92(3)
121.16(2)
°
°
°
°
; N(2)NiC(17), 102.76(16)
°
; N(1)NiC(15),
NiN(1)C(7),
°; C(17)C(16)C(15),
16
;
C(17)NiC(15), 68.30(6)°;
30
18
19
32
; NiN(2)C(8), 114.92(4)
20
.
(II)
A reaction of Ni(Allyl)2 with DAB does not occur
as a simple ligand metathesis; it is accompanied by a
complex iminoꢀamide rearrangement in the diazabꢀ
utadiene fragment of the ligand.
RESULTS AND DISCUSSION
A reaction of a yellow solution of Ni(Allyl)2 with an
equimolar amount of DAB in diethyl ether at –5
produces a bright red solution. The reaction product
was precipitated with pentane and cooled to –30 for
crystallization. The resulting bright red platelike crysꢀ
tals are unstable in air; when finely divided, they
decompose with selfꢀignition.
°C
Complex I has a molecular structure. The planes of
the phenyl rings of the diisopropylphenyl ligands are
nearly perpendicular to the plane of the chelate ring:
°C
the respective dihedral angles are 88.1
°
and 82.4 . The
°
Ni–N distances differ substantially (1.846(3) and
1.921(3) Å): for the N atom at the double C=N bond,
this distance is noticeably longer. The allyl ligand is
disordered over two positions.
According to Xꢀray diffraction data (Fig. 1), the
product is an imino amide
Its formation can be represented by the scheme
π
ꢀallyl nickel(II) complex (I).
To get comprehensive information on the structure
of the product of such an unusual reaction, we thoroughly
examined complex I using 2D homoꢀ and heteronuꢀ
clear NMR experiments.
Pri
Pri
Pri
Pri
+
Ni
N
N
In the1H NMR spectrum of complex
I, the multipꢀ
let at 5.35 characteristic of the central proton of the
δ
nickelꢀcoordinated allyl group is well resolved [2]. In
the HSQC experiment, this signal shows a cross peak
δ
with a signal for the 13C nucleus at
106.39. According
Pri
Pri
to DEPTꢀ135 data, this carbon atom is bound to only
one proton. In the COSY spectrum, the cross peaks at
N
N
Ni
δ
5.35–1.40, 5.3–1.48, 5.35–1.61, and 5.35–1.67 are
resolved. In the HSQC spectrum, the signals at 1.40
and 1.48 correlate with the signal at 50.62 and the
signals at 1.61 and 1.67 correlate with the signal at
Pri
Pri
δ
(
I
)
δ
δ
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
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2012

420
KRAIKIVSKII et al.
δ
53.61. According to DEPTꢀ135 data, these signals According to the DEPTꢀ135 data, this carbon atom is
can unambiguously be assigned to the 13C nuclei in the quaternary.
СH2 groups. When analyzing the degrees of shielding
and the coupling constants, one can identify the sigꢀ
The IR spectrum of complex
I
shows a band at
1602 cm–1
(
ν
(C=N)imine). This band is shifted by
~24 cm–1 to the lower frequencies compared to an
analogous band in the spectrum of the free ligand,
which agrees with the literature data [21] on the vibraꢀ
tional frequency changes upon the metal–nitrogen
coordination bonding in diimine ligands. The carbon
nals for the synꢀ and antiꢀprotons of the ꢀcoordinated
π
allyl group and the corresponding carbon atoms
(table). The signals for the terminal protons of the
πꢀallyl group of complex I are substantially shifted
downfield compared to the analogous signals for
Ni(Allyl)2 (table). The fragment of a conventional
molecule with atomic numbering is shown below:
framework of the
(CCC)) and 532 cm–1 (
The mass spectrum of complex
nounced molecular ion peak with
π
ꢀallyl group absorbs at 1105
(CCC)) [22, 23].
shows a proꢀ
516 ( rel > 70%).
(
ν
δ
I
m
/
z
I
26
In mass spectra recorded for ethyl complexes of nickel
under comparable conditions, the molecular ion peak
intensities do not exceed 5% [24]. A comparative analꢀ
25
24
8
7
ysis allows one to state that the
πꢀallyl group in comꢀ
N Ph(Pri)2
17
(Pri)2Ph
plex is coordinated to the metal atom more strongly
I
N
15
than in other organometallic nickel complexes and is
less prone to dissociation under electron impact.
Ni
16
Thus, the Xꢀray diffraction data fully agree with the
data from 2D NMR and IR spectroscopy and mass
spectrometry.
All the hydrogen and carbon atoms of the
π
ꢀallyl
group in complex are nonequivalent, in contrast to
I
In the crystalline state, complex
least 90 days. In sealed evacuated tubes, its bright red
solutions in THF and benzene at 20–25 turn redꢀ
I is stable for at
those in Ni(Allyl)2 [2, 20]. The considerable nonꢀ
equivalence of the 13C and 1H nuclei in the CH2 fragꢀ
°C
ments of the allyl group of complex I can be associꢀ
π
dish brown in 3 to 4 h. The NMR spectra show considꢀ
erable changes suggesting a “migration” of the double
bond. In this respect, the DEPTꢀ135 13C NMR specꢀ
tra are most illustrative (Fig. 2). The signals at 119.48
ated with a considerable difference between the
shielding abilities of the imine and amide moieties of
the ligand. It is difficult to locate the atoms of the
π
ꢀallyl group relative to the ligand because the TOCSY
and NOESY spectra show no selective cross peaks
between the protons of the ꢀallyl group and the proꢀ
(H2C=), 132.44
penyl fragment with the terminal CH2 group of comꢀ
plex are replaced by the signals at 19.26 (terminal
(HC=), and 37.65 (CH2) for the proꢀ
π
I
δ
tons of the imino amide ligand.
CH3), 140.88 (HC=), and 124.16 (HC=) for the proꢀ
penyl fragment with the terminal methyl group of
complex II (Fig. 2).
13
The DEPTꢀ135 C NMR spectrum of complex
I
contains one signal at
carbon atom of the CH2 group, which correlates in the
HSQC spectrum with the signal at 5.01. These sigꢀ
δ
119.48 for the sp2ꢀhybridized
According to the NMR data obtained, one can
state that complex
I in solution undergoes a spontaneꢀ
δ
ous transformation into complex II
:
nals belong to the terminal CH2 group at the double
bond of the 1ꢀpropenyl substituent. Analysis of the
HSQC, HMBC, COSY, NOESY, and DEPTꢀ135 data
allowed us to assign the signals for the other nuclei of
the propenyl fragment (table).
Pri
Pri
Pri
The CH2 group at the N atom covalently bonded to
N
N
nickel can unambiguously be identified since the
Ni
1H NMR spectrum exhibits doublets at
δ
4.56 and 4.38
for two nonequivalent protons. In the NOESY specꢀ
trum, the doublet a 4.56 shows a cross peak with the
signal at 3.86 for the proton at the tertiary C atom of
Pri
(I)
δ
δ
the isopropyl substituent of the phenyl ring of the
ligand. We used this signal to determine the relative
positions of the substituted phenyl rings and the other
Pri
Pri
Pri
fragments in complex
Experimental). In the HMBC spectrum, the signals at
4.56 and 4.38 correlate with the signal at 191.36 for
the carbon atom at the nickelꢀcoordinated N atom.
I (for detailed assignments, see
N
N
Ni
II
Pri
δ
δ
(
)
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
No. 6
2012

NICKEL(I) COMPLEX AS THE FINAL PRODUCT OF THE SEQUENCE
421
26
25
24
(а)
iPr
Pri
Pri
7
8
С16
С25
N
17
N
15
iPr
Ni
16
30
28
26
24
f1, ppm
22
20
18
26
25
С7
С17
С15
24
8
iPr
Pri
(b)
7
С26
N
17
N
15
iPr
Ni
16
С24
С26
Pri
С25
С16
30
28
26
24
f1, ppm
22
20
18
С7
С15
С17
140
130
120
110
100
90
80
f1,
70
60
50
40
30
20
δ
13
Fig. 2. DEPTꢀ135 C NMR spectra of complex I (a) immediately upon its dissolution and (b) after 4 h (THFꢀd , a sealed evacꢀ
8
uated tube).
All our attempts to obtain complex II in the crystalꢀ For the doublets at
δ
1.62 (
13 Hz), the COSY spectrum shows an intense cross
peak at 5.46. In combination with the values of the
J = 13 Hz) and 1.79 (J =
line state failed. Both bulk crystallization and zone
refining gave only reddish brown Xꢀray amorphous
powders that are extremely unstable in air. Because of
this, the structure of complex II is mainly concluded
from 2D NMR data.
δ
coupling constants, this allows unambiguous assignꢀ
ment of these doublets to the antiꢀprotons of the allyl
group (Fig. 4).
The multiplet for the central proton of the
group in complex II appears at 5.46 and correlates in
the HSQC spectrum with the signal at 106.43,
which, according to the DEPTꢀ135 data, belongs to
the carbon atom bound to only one proton. In the
π
ꢀallyl
Accordingly, the doublets at
δ
1.83 (J = 6 Hz) and
δ
2.0 ( = 4.3 Hz) correspond to the synꢀprotons. The
J
δ
COSY experiment reveals spinꢀspin couplings of these
protons with each other and with the central proton of
the ꢀallyl group. These cross peaks are much less
π
HMBC spectrum, the signal at
δ
5.46 correlates with
50.75 and 53.75 for the terminal carbon
ꢀallyl group, either of which is bound to
intense than those in the COSY spectrum between the
central and antiꢀprotons.
the signals at
atoms of the
δ
π
Analysis of the NMR data for the ꢀallyl fragment
π
two protons (DEPTꢀ135 data). The HSQC spectrum
contains cross peaks at 53.75–1.83, 53.7–1.62,
50.7–1.79, and 50.75–2.0. Thus, the signals in the 1H
NMR spectrum at 1.83, 1.62, 1.79, and 2.0 can
of complex II reveals an unusual inversion of the
chemical shifts of the signals for its synꢀ and antiꢀproꢀ
tons. As a rule, the antiꢀprotons in allyl complexes of
transition metals are more strongly shielded than the
synꢀprotons [2, 20]. In complex II, the opposite is
observed for the protons at the C(15) atom (the atomic
δ
δ
unambiguously be assigned to the terminal protons of
the allyl group (Fig. 3).
According to the HSQC and HMBC data, the proꢀ numbering is the same as in table): the signal for the
tons with the signals at 1.83 and 1.62 are bound to the synꢀproton is shifted upfield compared to the signal
carbon atom with the signal at 53.75, while the proꢀ for the antiꢀproton. The NOESY spectrum shows disꢀ
tons with the signals at 1.79 and 2.0 are bound to the tinct cross peaks for all the four terminal protons of the
carbon atom with the signal at 50.75. All the four sigꢀ ꢀallyl group (Fig. 4), including exchange cross peaks
nals for the terminal protons are split into doublets. for the synꢀ and antiꢀprotons [25]. This exchange can
δ
δ
δ
δ
π
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
No. 6
2012

422
KRAIKIVSKII et al.
HSQC
HMBC
20
30
50
52
54
40
50
60
70
HSQC
5.50 5.45 5.40
80
50
52
54
90
100
110
120
130
140
150
160
170
180
HMBC
50
52
54
56
HMBC
182
184
2.0 1.9 1.8 1.7 1.6
5.8 5.6 5.4 5.2 5.0 4.8
7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0
f2,
δ
Fig. 3. HSQC and HMBC spectra of complex II in C D . The insets in the main spectrum are placed in the areas free from cross
6
6
peaks.
be effected only by rotation of the terminal CH2 1076 cm–1
ν
(CCC)) due to the vibrations of the
ꢀforms carbon framework is broadened and shifted by 29 cm–1 to
of the allyl group in complex II are in equilibrium:
the lower frequencies compared to that for complex I.
π
ꢀallyl
3
1
σ
groups, which is possible if the
η
–πꢀ
and
η
–
The position of the band
δ
(CCC) remains virtually
unchanged (532 cm–1).
The mass spectrum of complex II shows a proꢀ
nounced molecular ion peak with 516 ( rel = 65%),
which also suggests insignificant dissociation of the
N
N
N
N
N
N
m/z
I
Ni
Ni
Ni
15
17
15
17
17
15
πꢀallyl group under electron impact.
16
16
16
In a sealed evacuated NMR tube, a solution of
complex II remains stable for several hours (NMR
Our data agree well with data on such an exchange
in allyl complexes of palladium thoroughly examined
by NOESY NMR spectroscopy [4, 5]. Therefore,
1
data), whereupon the H and 13C NMR signals
broaden and disappear in 24 h (except the signals for
the solvent). The reddish brown solution turns dark
brown. The EPR spectrum of the resulting dark brown
solution shows an intense signal (Fig. 5) characteristic
of Ni(I) complexes [26].
3
1
complex II exists in solution as both the
ꢀallyl forms.
In the IR spectrum of complex II, the band
(C=N)imine is shifted by 39 cm–1 to the higher freꢀ
quencies (1641 cm–1) compared to an analogous band
for complex
η
–π
and
η
–
σ
ν
Therefore, allyl complex II in solution spontaneꢀ
. This is consistent with the formation of ously decomposes with time, Ni(II) being reduced to
I
a conjugated system of double bonds during the Ni(I). It is worth noting that the resulting paramagꢀ
isomerization of the propenyl substituent. The band at netic complex remains stable in a sealed tube at room
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
No. 6
2012

NICKEL(I) COMPLEX AS THE FINAL PRODUCT OF THE SEQUENCE
423
NOESY
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
COSY
1.5
1.8
2.0
1.9 1.7
NOESY
1.6
1.8
2.0
2.0 1.9 1.8 1.7 1.6
7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0
f2,
δ
Fig. 4. NOESY and COSY spectra of complex II in C D . The insets in the main spectrum are placed in the areas free from cross
6
6
peaks.
temperature for more than a year. The nickel oxidation
state can change through cleavage of both the covalent
Ni–C bond and the Ni–N bond. Because the 14N
nuclei show no hyperfine structure, it is impossible to
specify the type of the Ni–N bond in the paramagꢀ
netic complex. Some structural information for the
g
tensor for the complex under study. The aforesaid
data suggest that the spontaneous decomposition of
complex II and the reduction of Ni(II) to Ni(I) are
due to the transformation of the Ni–N bond from the
covalent bond to a coordination one without eliminaꢀ
tion of the allyl group from the coordination sphere. In
complex can be obtained by analyzing the
x = 2.186, gy = 2.143, and gz = 2.024). The ratio of
the components of the tensor (gx gy gz) suggests a
trigonal structure of the complex [27]. While comparꢀ
ing the greatest component of the tensor (2.186) with
g tensor
(g
g
,
>
g
analogous parameters for typical amide complexes of
nickel(I) of the formula (Nacnac)NiL (where Nacnac
is
βꢀdiketiminate and L is bis(diphenylphosꢀ
phino)methane [28], tricyclohexylphosphine [28],
and THF [29]), one should note that the greatest comꢀ
ponents of the
g
tensor for ꢀdiketiminate complexes
β
of nickel(I) (2.43–2.54) differ greatly from the pure
spin value, though these complexes contain spectroꢀ
chemically “strong” ligands such as bis(diphenylphosꢀ
phino)methane or tricyclohexylphosphine. On the
other hand, the same parameter, e.g., for a cyclopenꢀ
tadienyl complex of Ni(I) with bipyridyl CpNi(Bipy)
(2.184 [30]), is nearly as great as the component of the
2800 2900 3000 3100 3200 3300 3400 3500 3600
G
Fig. 5. EPR spectrum of Ni(I) complex III in THFꢀd , at
8
77 K.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
No. 6
2012

424
KRAIKIVSKII et al.
this case, the paramagnetic complex can be formuꢀ
According to the above scheme, the first step of the
reaction of the nickel bis( ꢀallyl) complex with DAB
involves the formation of an intermediate complex ( ),
lated as the most plausible structure III
:
π
a
3
1
in which at least one
η
–πꢀallyl group exists in the
η
–
σꢀallyl form. The coordination sphere of complex (a)
H
undergoes a rearrangement that can formally be
regarded as insertion of the activated double C=N
bond into the metal–carbon bond. This rearrangeꢀ
(Pri)2Ph
N
N Ph(Pri)2
Ni
III
ment gives intermediate imino amide ꢀallyl complex I,
π
which isomerizes with time into 2ꢀpropenyl complex II
containing a stable system of conjugated double bonds.
In the final step of the process, a spontaneous reduction
(
)
The transformation of diamagnetic nickel(II)
complex II into paramagnetic nickel(I) complex III
retaining the allyl group is suggested by the absence of
the NMR signals (except those for the solvent) in the
system after the intensity of the EPR signal reaches a
maximum value. If the allyl fragment were eliminated,
the NMR spectrum would contain the signals for proꢀ
pene or its transformation products (the transformaꢀ
tion of complex II into complex III was studied in a
sealed NMR tube).
of Ni(II) to Ni(I) leads to nickel(I) complex III
.
ACKNOWLEDGMENTS
This work was supported by the Federal Target Proꢀ
gram “Scientific and Pedagogical Personnel of
an Innovative
Russia”
(State
Contract
no. 14.740.11.0619).
Thus, diamagnetic nickel complex
I in THF in a
sealed tube rapidly isomerizes into diamagnetic comꢀ
plex II, which is completely transformed in 48 h into
paramagnetic complex III as the final product.
Despite the thermodynamic stability of nickel(I) comꢀ
plex III, we failed to isolate it in the individual state.
Concentration of a solution of complex III resulted in
the formation of a resinous product extremely suscepꢀ
tible to oxygen and moisture traces. Elemental analyꢀ
sis data for the resinous product are close to
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2012