Phosphine-assisted C-H bond activation in Schiff bases and formation of novel organo cobalt complexes bearing Schiff base ligands

Article abstract of DOI:10.1039/c7nj03480f

Two novel cobalt Schiff base complexes 3 and 4, ((2-PPh₂)C₆H₄)CN(C₁₀H₇)Co(PMe₃)₂ (3) and ((2-PPh₂)C₆H₄)CHN(C₆H₅)Co(PMe

Full text of DOI:10.1039/c7nj03480f

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Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
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Phosphine-assisted C-H Bond Activation in Schiff Base and Formation of Novel
Organo Cobalt Complexes Bearing Schiff Base Ligand
Hua Zhang,a Junyang Xing,a Yanhong Dong,a Shangqing Xie,a Shishuai Ren,a
Xinghao Qi,a Hongjian Sun,a Xiaoyan Li,a,* Olaf Fuhr,b Dieter Fenskeb
a
School of Chemistry and Chemical Engineering, Key Laboratory of Special
Functional Aggregated Materials, Ministry of Education, Shandong University,
Shanda Nanlu 27, 250199 Jinan, People’s Republic of China
b
Institut für Nanotechnologie (INT) und Karlsruher Nano-Micro-Facility (KNMF),
Karlsruher Institut für Technologie (KIT), Hermann-von-Helmholtz-Platz 1, 76344
Eggenstein-Leopoldshafen, Germany
E-mail: xli63@sdu.edu.cn; Fax: +86 531 88361350
Abstract
Two
novel
cobalt
Schiff
base
complexes
3
and
4,
((2ꢀPPh2)C6H4)C=N(C10H7)Co(PMe3)2
(3)
and
((2ꢀPPh2)C6H4)CH=N(C6H5)Co(PMe3)2(4) with η2(CꢀH) coordination, were
synthesized by the reactions of Schiff base preligands ((2ꢀPPh2)C6H4)CH=N(C10H7)
(1) and ((2ꢀPPh2)C6H4)CH=N(C6H5) (2) with CoMe(PMe3)4 via sp2 CꢀH bond
activation. Under similar reaction conditions, the reactions of Co(PMe3)4 with 1 and 2
gave
rise to the simple πꢀ(C=N)ꢀcoordinated cobalt(0) complexes
((2ꢀPPh2)C6H4)CH=N(C10H7)Co(PMe3)2
((2ꢀPPh2)C6H4)CH=N(C6H5)Co(PMe3)2
(5)
(6).
and
Complex
((2ꢀPPh2)C6H4)C=N(C10H6)CoI(PMe3)2 (7) was obtained through the reaction of 3
with iodomethane via the activation of the second CꢀH bond in 1. The substitution
reaction of complex 3 with carbon monoxide afforded the dicarbonyl cobalt(I)
complex ((2ꢀPPh2)C6H4)C=N(C10H7)Co(CO)2(PMe3) (8). The molecular structures of
4, 5, 7 and 8 were determined by single crystal Xꢀray diffraction.
Keywords: C-H activation / cobalt /Schiff base / Trimethylphosphine
1

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Introduction
The CꢀH bond activation mediated by transition metal complexes is of great
interest due to its importance in organic synthesis1 and catalytic reaction2. As an early
example, Chatt and Davidson obtained hydrido Ru(II) complex by CꢀH activation via
oxidative addition.3 Since then, more and more research groups made efforts in the
field of CꢀH bond activation mediated by transition metals. Our research interest
focuses on CꢀH bond activation by electronꢀrich Fe, Co and Ni complexes supported
by trimethylphosphine ligands because Fe, Co and Ni as abundant metals are
inexpensive and ecoꢀfriendly in comparison with the precious metals such as Ru4, Pd5,
Rh6, It7 and etc. Secondly, the publications on Fe, Co and Ni are less than those on
noble metals. Finally, trimethylphosphine as a strong σꢀdonor ligand benefits the inert
bond activation.
Schiff base as a kind of ligands plays an important role in coordination chemistry.
ImineꢀN donor was utilized as anchoring group in the study of CꢀCl, CꢀF and CꢀH
bond
activation.8ꢀ9
In
2015,
we
disclosed
the
reaction
of
Nꢀbenzylideneꢀ1ꢀnaphthylꢀamine with CoMe(PMe3)4 to afford the hydrido
[CNC]ꢀpincer cobalt complex CoH((C6H4)CH=N(C10H6)) via double CꢀH bond
activation.10 It was found that this hydrido cobalt(III) complex is an efficient catalyst
for hydrosilylation of aldehydes and ketones.
Over the past few years, our group has published several reports on CꢀH bond
activation promoted by iron, cobalt and nickel complexes.11 In 2017, we reported the
synthesis of three novel unsymmetrical η3ꢀ2ꢀazaallyl cobalt(I) complexes through
C(sp3)ꢀH bond activation in Schiff base ligands under a mild condition without
additives.12 As continuation of this study, in this paper, two novel cobalt Schiff base
complexes 3 and 4 were synthesized by the reactions of Schiff base preligands
((2ꢀPPh2)C6H4)CH=N(C10H7) (1) and ((2ꢀPPh2)C6H4)CH=N(C6H5) (2) with
CoMe(PMe3)4 via sp2 CꢀH bond activation. The reactions of 1 and 2 with Co(PMe3)4
afforded πꢀ(C=N)ꢀcoordinated Co(0) complexes 5 and 6. The chemical reactivity of
complex 3 with MeI, HCl and carbon monoxide was investigated. The cobalt(III)
iodide 7 was obtained from the reaction of 3 with MeI. Dicarbonyl cobalt(I) complex
2

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8 was formed through the substitution reaction of complex 3 with carbon monoxide.
The molecular structures of 4, 5, 7 and 8 were determined by single crystal Xꢀray
diffraction.
Results and Discussion
Reactions of CoMe(PMe3)4 with diphenylphosphino benzalimines 1-2
The reaction of Schiff base preligands 1 or 2 with CoMe(PMe3)4 in THF afforded
cobalt(I) complexes 3 or 4 as red cubic crystals in the yield of 65% and 68%
respectively via sp2 CꢀH bond activation of the HC=Nꢀmoiety with the elimination of
methane (Eq. (1)).
In the infrared spectra of complexes 3 and 4, the characteristic ρ(PMe3) bands
were found at 946 and 932 cmꢀ1. In the 1H NMR spectra of 3 and 4, the imineꢀH proton
resonance disappeared. The signals of the two PMe3 ligands were recorded at 0.55,
1.00 (3) and 0.65, 1.00 (4) ppm respectively. The resonance of one aromatic proton
was registered at 8.78 (3) and 8.75 (4) ppm as doublet with the coupling constant J =
9Hz. For aromatic proton this is a special downfield shift. This indicates that there is
one aromatic proton in both 3 and 4 which is specially positioned. The chemical shifts
of aromatic protons were recorded in normal range of the chemical shifts of aromatic
protons (7.97 – 7.04 (3) and 8.05 – 7.08 (4) ppm). In comparison with the 1H NMR of
complex 7, this assignment is reasonable because after reaction (3) the signal at 8.78
ppm (3) disappeared. It is considered that this is an indirect evidence for this
3

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assignment. This conjecture is confirmed by single crystal XꢀRay diffraction (Fig.1).
In the 31P NMR spectra of 3 and 4 there are three different phosphorus signals as
singlet appearing at 78.3, 12.4, 10.6 for 3, at 69.1, 5.2, 0.94 ppm for 4 respectively.
No expected splitting was observed. Possibly, this result was caused by rapid
exchange between the phosphorus ligands at room temperature.
Fig.1 Molecular structure of complex 4. Most of the hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and angles (deg): Co1ꢀP1 2.1610(5)，
Co1ꢀP2 2.2272(5)， Co1ꢀP3 2.1801(6), Co1ꢀC1 2.1387(19), Co1ꢀC7 1.9310(18),
C7ꢀN1 1.307(2), C2ꢀN1 1.387(2), C1ꢀC2 1.423(3), C1ꢀC6 1.410(3), C2ꢀC3 1.400(3),
C3ꢀC4 1.384(3), C4ꢀC5 1.392(4), C5ꢀC6 1.384(3); C7ꢀCo1ꢀP2 175.47(6), P1ꢀCo1ꢀP3
114.04(2), P3ꢀCo1ꢀC1 100.15(6)，C1ꢀCo1ꢀP1 139.20(6).
Complexes 3 and 4 should have the similar structures and all the spectroscopic
data are compatible with a trigonal biyramid geometry around the cobalt atom. The
molecular structure of complex 4 was elucidated by Xꢀray diffraction analysis (Fig. 1).
The cobalt atom is centered in a trigonal biyramid geometry with P2–Co1–C7
(175.47(6)o) in the axial direction. The four atoms Co1, P1, P3and C1 are in the
equatorial plane. The chelate ring [Co1P1C9C8C7] is formed through the coordination
of the P atom of the –PPh2 group and the C atom of the C=N group. The sum of the
4

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internal bond angles (531.26o) of this fiveꢀmembered metallacycle indicates that it does
not have ideal planarity. The bite angle of this chelate ring (P1ꢀCo1ꢀC7 = 81.98(6)o) is
smaller than in the related cobalt complex.9 This chelate ring is almost perpendicular to
the equatorial plane. The imine bond length (C7ꢀN1 = 1.307(2) Å) is significantly
longer than those (1.28 – 1.29 Å) in the related cobalt complexes.9 It must be pointed
out that there is an η2ꢀ(C1ꢀH1)ꢀcoordination to the cobalt center but Co1ꢀC1 (2.1387(19)
Å) is obviously longer than the normal CoꢀC distances (
∼
1.9 Å)9 and C1ꢀH1 distance
(1.13(3) Å) is also longer than other CꢀH distances ( 0.95 Å) in this complex. Co1ꢀH1
∼
distance (1.67 Å) is remarkably longer than the normal CoꢀH distances (1.40 ꢀ 1.50 Å)13.
These data illustrate that C1ꢀH1 bond was activated via η2ꢀ(C1ꢀH1)ꢀcoordination. The
uniqueness of H1 is also indicated by its significant downfield chemical shift. C1ꢀC2
(1.423(3) Å) and C1ꢀC6 (1.410(3) Å) are longer than C3ꢀC4 (1.384(3) Å), C4ꢀC5
(1.392(4) Å) and C5ꢀC6 (1.384(3) Å) due to this η2ꢀ(C1ꢀH1)ꢀcoordination. Co1ꢀP2
(2.2272(5) Å) is longer than Co1ꢀP1 (2.1610(5) Å) and Co1ꢀP3 (2.1801(6) Å) because
of the strong transꢀinfluence of the negativelyꢀcharged carbon atom (C7) of the imine
group.
Scheme 1 Formation mechanism of 3 and 4
The mechanism of formation of complexes 3 and 4 is proposed in Scheme 1.
5

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The reaction begins with the ligand replacement of one PMe3 by 1 and 2 to form
intermediate A1,2. The coordination of ꢀPPh2 group as an anchoring group makes the
oxidative addition of the CꢀH bond of the imine group at Co(I) center possible to
afford hydrido Co(III) species B1,2 via CꢀH bond activation with the formation of the
fiveꢀmembered chelate ring. B1,2 transforms to C1,2 through reductive elimination
between CoꢀH and CoꢀMe bond with the escape of CH4. After the coordination of the
carbon atom of the imine group, the η2ꢀ(CꢀH)ꢀcoordination to the cobalt atom is
formed. However, the second CꢀH bond cleavage is not realized.
Reactions of Co(PMe3)4 with diphenylphosphino benzalimines 1-2
Instead of CoMe(PMe3)4, Co(PMe3)4 reacted with Schiff base preligands 1 and 2
under similar reaction conditions to give rise to Co(0) complexes 5 and 6 as red
crystals in the yield of 68% (5) and 60% (6) respectively (Eq. (2)). No CꢀH bond
activation occurred. 5 and 6 are paramagnetic complexes. The EPR spectra of
fourꢀcoordinated Schiff base cobalt(0) complexes 5 and 6 were obtained in solid state
at 298 K (Fig. 2 and Fig. 3). The EPR spectrum of complex 5 exhibits three separated
signals corresponding to three
EPR spectrum of complex 6 (fwhh ≈ 170 G) exhibits only a slightly broad line (
2.112), ordinarily assigned to the rotated cobalt(0) atom. Hyperfine couplings are not
resolved in the EPR spectra. The values of complexes 5 and 6 are similar to those of
g values (g1 = 2.038, g2 = 2.109, g3 = 2.209). And the
g
=
g
the previously reported cobalt(0) complexes.14,15 This indicates that the rotated cobalt
6

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is cobalt(0) atom.
Fig 2. EPR spectrum of complex 5 recorded in solid state.
Fig. 3 EPR spectrum of complex 6 recorded in solid state.
7

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Fig. 4 Molecular structure of complex 5. Hydrogen atoms have been omitted for
clarity. Selected bond lengths (Å) and angles (deg): Co1ꢀP1 2.2085(4), Co1ꢀP2
2.2174(4), Co1ꢀP3 2.2105(4), C7ꢀN1 1.394(2), Co1ꢀC7 1.9879(13), Co1ꢀN1
1.9994(11); C7ꢀCo1ꢀP2 151.04(4), P1ꢀCo1ꢀP2 106.061(14), P3ꢀCo1ꢀP2 102.468(14),
C7ꢀCo1ꢀN1 40.91(5).
The molecular structure of 5 was confirmed by single crystal Xꢀray diffraction
(Fig. 4). The cobalt(0) center in complex 5 has a tetrahedral coordination geometry
with a πꢀcoordinated imine (C7=N1) group and three coordinated P atoms of the
phosphine ligands. Owing to the πꢀcoordination of the imine group C7=N1 bond
(1.394(2) Å) is remarkably longer than that (1.307(2) Å) in complex 4. This shows
that the C=N bond becomes weaker after its coordination. The similar πꢀ(C=N)
coordinated Co(0) complexes were also obtained from the reactions of fluorinated
imines with Co(PMe3)4.9
Reactions of complex 3 with MeI and HCl
8

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N
PMe3
N
(3)
MeI
+
Co
Ph2P
- CH4
Co
H
I
P
PMe3
PMe3
Ph2
PMe3
3
7
The combination of complex 3 and iodomethane afforded the [PCC]ꢀpincer
cobalt(III) iodide 7 as yellow crystals in the yield of 40% (Eq. (3)). In this process, the
orthoꢀ(CꢀH) bond of the naphthalene ring was cleaved. In the IR spectrum of complex
7, the signal of ρ(PMe3) appeared at 940 cm−1. In the 1H NMR spectrum of complex 7,
the proton resonances of the two PMe3 ligands were recorded at 0.32 and 0.77 ppm as
2
doublet peaks with the coupling constant J(PH) = 6 and 9 Hz. In comparison with
complex 3, the signal of one specific aromatic proton with downfield shift
disappeared and 20 aromatic protons were registered between 7.76 – 6.81 ppm. This
explains that the CꢀH cleavage occurred. In addition, three phosphorus signals at 71.1,
13.4 and 11.0 were recorded for the –PPh2 group and two PMe3 ligands.
Fig. 5 Molecular structure of complex 7. Hydrogen atoms have been omitted for
clarity. Selected bond lengths (Å) and angles (deg): Co1ꢀI1 2.7147(3), Co1ꢀC9
1.9543(2), Co1ꢀC7 1.9047(2), Co1ꢀP1 2.2653 (5), Co1ꢀP2 2.2550 (5), Co1ꢀP3 2.2789
(5); P1ꢀCo1ꢀP2 99.86(2), P3ꢀCo1ꢀP1 96.80(2), P3ꢀCo1ꢀP2 162.63(2), P3ꢀCo1ꢀC9
80.35(5), P2ꢀCo1ꢀC9 82.31(5), C7ꢀCo1ꢀI1 176.57(5).
9

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The molecular structure of complex 7 was determined by single crystal
Xꢀdiffraction (Fig. 5). The cobalt atom is centered in a distorted octahedral geometry. If
P2–Co1–P3 (162.63(2)o) is identified as the axial direction, the five atoms
[Co1C7C9P1I1] are in the equatorial plane. The two fiveꢀmembered chelate rings, the
phenyl ring [C1ꢀC6] and the naphthalene plane are almost in the same plane. The bond
angle P2ꢀCo1ꢀP3 is bent away from the –PPh2 group owing to the steric effect. The
structural characteristics of 7 are similar to those of the [CNC]ꢀpincer cobalt(III) iodide
while Co1ꢀI1 (2.7147(3) Å) in complex 7 is longer than CoꢀI distance (2.621(9) Å) in
the [CNC]ꢀpincer cobalt(III) iodide because of the strong transꢀinfluence of the C atom
of the imine group in complex 7.10
Scheme 2. The Formation Mechanism of 7
A plausible formation mechanism of 7 is proposed in Scheme 2. The oxidative
addition of MeI at the Co(I) center of 3 delivering methyl cobalt(III) iodide
intermediate 3a is the first step. The combination of methyl ligand with the orthoꢀH
atom of the naphthalene group gives rise to cobalt(III) complex 7 via CꢀH bond
activation with the formation of the second fiveꢀmembered chelate ring as the driving
force. The escape of methane also contributes to the activation of CꢀH bond.
10

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However, complex 3 did not react with EtBr under the similar reaction conditions
because the oxidation ability of EtBr is weaker than that of MeI. In the presence of HCl,
complex 3 decomposed into the free ligand 1 and CoCl(PMe3)3 as violet crystals (Eq.
(4)). Both ligand 1 and CoCl(PMe3)3 were confirmed by spectroscopic methods.
Subsitution Reaction of Complex 3 with Carbon Monoxide
A THF solution of complex 3 was stirred under 1 bar of carbon monoxide
atmosphere for 24 h to afford dicarbonyl cobalt(I) complex 8 as substitution product
(Eq. (5)). In this process, one PMe3 ligand and the η2ꢀ(CꢀH)ꢀcoordination were
replaced by two CO ligands. Complex 8 was isolated as yellow crystals in the yield of
60%.
In the IR spectrum of complex 8, two strong signals of two terminal carbonyl
ligands were registered at 1906 and 1969 cm−1. The signal of ρ(PMe3) appeared at 947
cm−1. In addition, the signal of the PMe3 is situated at 0.63 ppm as doublet with the
coupling constant J = 9 Hz in the 1H NMR spectrum of 8. In the 31P NMR spectrum of 8
two dublets were found at 61.5 and 16.1 ppm with the coupling constant of 36.5 Hz for
11

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–PPh2 group and PMe3 ligand respectively.
Fig. 6 Molecular structure of complex 8. Hydrogen atoms have been omitted for
clarity. Selected bond lengths (Å) and angles (deg): Co1ꢀC1 1.763(4), Co1ꢀC2
1.735(3), Co1ꢀC3 2.000(3), Co1ꢀP1 2.2063(9), Co1ꢀP2 2.1966 (9); P2ꢀCo1ꢀC1
118.33(10), C1ꢀCo1ꢀC2 126.17(14), C2ꢀCo1ꢀP2 115.07(11), C3ꢀCo1ꢀP1 175.69(9).
Single crystal Xꢀray diffraction confirmed the molecular structure of complex 8
(Fig. 6). The cobalt atom is centered in a fiveꢀcoordinate trigonal biyramidal geometry
with C3–Co1–P1 (175.69(9)o) identified as the axial direction. Co1, P2 and two CO
ligands formed the equatorial plane. The sum (359.57o) of three bond angle
(P2ꢀCo1ꢀC1 = 118.33(10)o, C1ꢀCo1ꢀC2 = 126.17(14)o and C2ꢀCo1ꢀP2 = 115.07(11)o)
indicates that the four atoms [Co1P2C1C2] are almost in one plane. Both Co1ꢀC1
(1.763(4) Å) and Co1ꢀC2 (1.735(3) Å) are significantly shorter than Co1ꢀC3 (2.000(3)
Å) due to the πꢀbackbonding from the Co(I) atom to the CO ligands.
Conclusions
Two
novel
Schiff
base
cobalt(I)
complexes
((2ꢀPPh2)C6H4)C=N(C10H7)Co(PMe3)2 (3) and ((2ꢀPPh2)C6H4)C=N(C6H5)Co(PMe3)2
(4) were synthesized by the reactions of Schiff base preligands
((2ꢀPPh2)C6H4)CH=N(C10H7) (1) and ((2ꢀPPh2)C6H4)CH=N(C6H5) (2) with
12

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CoMe(PMe3)4 via sp2 CꢀH bond activation. Under similar reaction conditions, the
reactions of Co(PMe3)4 with 1 and 2 gave rise to the simply πꢀ(C=N)ꢀcoordinated
cobalt(0)
complexes
((2ꢀPPh2)C6H4)C=N(C10H7)Co(PMe3)2
(6). Cobalt(III)
(5)
and
((2ꢀPPh2)C6H4)CH=N(C6H4)Co(PMe3)2
iodide
((2ꢀPPh2)C6H4)C=N(C10H6)CoI(PMe3)2 (7) was obtained through the reaction of 3
with iodomethane with the activation of the second CꢀH bond in ligand 1. The
substitution reaction of complex 3 with carbon monoxide afforded the dicarbonyl
cobalt(I) complex ((2ꢀPPh2)C6H4)C=N(C10H7)Co(CO)2(PMe3) (8). The molecular
structures of 4, 5, 7 and 8 were determined by single crystal Xꢀray diffraction.
Experimental
General procedures and materials: Standard vacuum techniques were used in the
manipulations of volatile and airꢀsensitive materials. Solvents were dried by distillation
16
from Naꢀbenzophenone under nitrogen before use. CoMe(PMe3)416, Co(PMe3)4 and
the Schiff base preligands 1-217 were prepared by the literature methods. Infrared
spectra (4000 ꢀ 400 cm−1), as obtained from Nujol mulls between KBr disks, were
recorded on a Bruker ALPHA FTꢀIR instrument. 1H, 31P{H} and 13C{H} NMR spectra
(300, 121.5 and 75 MHz, respectively) were recorded on a Bruker Avance 300
spectrometer with C6D6 as the solvent without an internal reference at room
temperature. The 13C{H} and 31P{H} NMR resonances were obtained with broadband
proton decoupling. Elemental analyses were carried out on an Elementar Vario ELIII.
The EPR spectra were recorded using Jeol Resonance X320 at 8K, 9.24 GHz and 1
mW. Melting points were measured in capillaries sealed under nitrogen and are
uncorrected.
Synthesis of complex 3: A solution of ligand 1 (0.65 g, 1.57 mmol) in THF (30 mL)
was added to a solution of CoMe(PMe3)4 (0.59 g, 1.57 mmol) in THF (30 mL) at ꢀ78 °C.
The reaction mixture was warmed to 25°C and stirred for 24 h to get a red solution.
THF was removed under reduced pressure. The residue was extracted with pentane (60
mL) and diethyl ether (60 mL) in turn to give red solution. Complex 3 was obtained as
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red crystals from the nꢀpentane solution and diethyl ether solution at –10 °C, yield 0.64
g (1.02 mmol, 65 %). m.p.: 156 ꢀ 160 . Anal. Calcd for C35H39CoNP3 (625.55
℃
g/mol): C, 67.20; H, 6.28; N, 2.24. Found: C, 66.89; H, 6.51; N, 2.07. IR (Nujol, mull,
1
cmꢀ1): 1609 ν(C=N), 1574 ν(C=C), 945 ρ(PMe3). H NMR (300 MHz, C6D6, 298K,
ppm): 8.78 (d, J = 9 Hz, 1H, ArꢀH), 7.97 ꢀ 7.04 (m, 20H, ArꢀH), 1.01 (d, 2JP,H = 6.0 Hz,
9H, PMe3), 0.56 (d, 2JP,H = 6.0 Hz, 9H, PMe3). 31P NMR (121.5 MHz, C6D6, 298K, ppm):
78.4 (s, 1P, PPh2), 12.4 (s, 1P, PMe3), 10.6 (s, 1P, PMe3). 13C{H} NMR (75 MHz, C6D6,
298K, ppm):159.1 (C=N), 149.1 (CAr), 141.4 (CAr), 134.8 (CAr), 134.3 (CAr), 133.6
(CAr), 133.4 (CAr), 133.2 (CAr), 133.1 (CAr), 132.2 (d, J = 10 Hz, CAr), 131.9 (CAr),
131.6 (CAr), 129.6 (CAr), 129.5 (CAr), 129.4 (CAr), 129.0 (CAr), 128.9 (CAr), 128.6 (d, J
= 9 Hz, CAr), 126.2 (d, J = 7 Hz, CAr), 125.5 (CAr), 124.4 (CAr), 113.3 (CAr), 22.9 (d, J =
18 Hz, P(CH3)3), 21.5 (d, J = 17Hz, P(CH3)3).
Synthesis of complex 4: A solution of ligand 2 (0.60 g, 1.64 mmol) in THF (30 mL)
was added to a solution of CoMe(PMe3)4 (0.62 g, 1.64 mmol) in THF (30 mL) at ꢀ78 °C.
The reaction mixture was warmed to 25°C and stirred for 24 h to get a red solution.
THF was removed under reduced pressure. The residue was extracted with pentane (60
mL) and diethyl ether (60 mL) in turn to give red solution. Complex 4 was obtained as
red crystals from the nꢀpentane solution and diethyl ether solution at ꢀ10 °C, yield 0.64
g (1.12 mmol, 68 %). m.p.: 165 ꢀ 166
℃. Anal. Calcd for C31H37CoNP3 (575.45
g/mol): C, 64.70; H, 6.48; N, 2.43. Found: C, 65.14; H, 6.69; N 2.55. IR (Nujol, mull,
cmꢀ1): 1574 ν(C=C), 932 ρ(PMe3). 1H NMR (300 MHz, C6D6, 298K, ppm): 8.75 (d, J =
9 Hz, 1H, ArꢀH), 8.05 ꢀ 7.08 (m, 18H, ArꢀH), 1.01 (s, 9H, PMe3), 0.65 (s, 9H, PMe3).
31P{H} NMR (121.5 MHz, C6D6, 298K, ppm): 69.1 (s, 1P, PPh2), 5.2 (s, 1P, PMe3),
0.94 (s, 1P, PMe3). 13C{H} NMR (75 MHz, C6D6, 298K, ppm): 167.8 (C=N), 156.9 (d,
J = 12 Hz, CAr), 154.6 (CAr), 147.5 (d, J = 10 Hz, CAr), 139.8 (CAr), 138.3 (CAr), 133.2
(CAr), 132.5 (CAr), 130.8 (CAr), 128.7 (CAr), 126.3 (CAr), 122.2 (CAr),120.4 (CAr), 117.1
(CAr), 115.8 (CAr), 111.7 (CAr), 20.7 (d, J = 14 Hz, P(CH3)3), 19.4 (d, J = 14 Hz,
P(CH3)3).
Synthesis of complex 5: A solution of ligand 1 (0.50 g, 1.20 mmol) in THF (30 mL)
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was added to a solution of Co(PMe3)4 (0.44 g, 1.20 mmol) in THF (30 mL) at ꢀ78 °C.
The reaction mixture was warmed to 25°C and stirred for 24 h to get a red solution.
THF was removed under reduced pressure. The residue was extracted with nꢀpentane
(60 mL) and diethyl ether (60 mL) in turn to give red solution. Complex 5 was obtained
as red crystals from the nꢀpentane solution and diethyl ether solution at ꢀ10 °C, yield
0.51 g (0.82 mmol, 68 %). m.p.: 125 ꢀ 127
℃. Anal. Calcd for C35H40CoNP3 (626.55
g/mol): C, 67.09; H, 6.43; N, 2.24. Found: C, 67.41; H, 6.77; N 2.01. IR (Nujol, mull,
cmꢀ1): 1584 ν(C=C), 939 ρ(PMe3). EPR spectra: g1 = 2.038, g2 = 2.109, g3 = 2.209
Synthesis of complex 6: A solution of ligand 2 (0.55 g, 1.51 mmol) in THF (30 mL)
was added to a solution of Co(PMe3)4 (0.55 g, 1.51mmol) in THF (30 mL) at ꢀ78 °C.
The reaction mixture was warmed to 25°C and stirred for 24 h to get a red solution.
THF was removed under reduced pressure. The residue was extracted with nꢀpentane
(60 mL) and diethyl ether (60 mL) in turn to give red solution. Complex 6 was obtained
as red crystals from the nꢀpentane solution and diethyl ether solution at ꢀ10 °C, yield
0.52 g (0.90 mmol, 60 %). m.p.: 120 ꢀ 122
℃. Anal. Calcd for C31H38CoNP3 (576.49
g/mol): C, 64.59; H, 6.64; N, 2.43. Found: C, 64.10; H, 6.29; N, 2.61. IR (Nujol, mull,
cmꢀ1): 1582ν(C=C), 942 ρ(PMe3). EPR spectra: g = 2.094
Synthesis of complex 7: A solution of complex 3 (0.65 g, 1.04 mmol) in THF (20 mL)
was added to a solution of iodomethane (0.15 g, 1.04 mmol) in THF (20 mL) at ꢀ78 °C.
The reaction mixture was warmed to 25 °C and stirred for 24 h to give a muddy orange
solution. THF was removed under reduced pressure. The residue was extracted with
nꢀpentane (60 mL) and diethyl ether (60 mL) in turn to give orange solution. Complex 7
was obtained as orange crystals from the nꢀpentane solution and diethyl ether solution
at ꢀ10 °C, yield 0.31 g (0.42 mmol, 40 %). m.p.: 170 ꢀ 172
℃. Anal. Calcd for
C35H38CoINP3 (751.44 g/mol): C, 55.94; H, 5.10; N, 1.86. Found: C, 55.67; H, 4.90;
N, 2.07. IR (Nujol, mull, cmꢀ1): 1609 ν(C=N), 1577 ν(C=C), 940 ρ(PMe3). 1H NMR
(300 MHz, C6D6, ppm): 7.76 – 6.81 (m, 20H, PhꢀH), 0.77 (d, 2JP.H = 6.0 Hz, 9H, PMe3),
0.32 (d, 2JP.H = 9.0 Hz, 9H, PMe3). 31P{H} NMR (121.5 MHz, C6D6, ppm): 71.1 (d, 2JP.P
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= 62 Hz, 1P, PPh2), 13.7 (s, 1P, PMe3), 11.0 (m, 1P, PMe3). 13C{H} NMR (75 MHz,
C6D6, 298K, ppm):141.4 (C=N), 137.8 (CAr), 137.4 (CAr), 136.5 (CAr), 136.0 (CAr),
134.8 (CAr), 134.4 (CAr), 133.5 (d, J = 8 Hz, CAr), 132.5 (CAr), 131.8 (d, J = 10 Hz, CAr),
129.5 (CAr), 129.2 (d, J = 5 Hz, CAr), 126.0 (CAr), 125.7 (CAr), 125.5 (CAr), 125.1 (CAr),
124.3 (CAr), 124.2 (CAr), 123.9 (CAr), 122.6 (CAr), 119.4 (CAr), 100.0 (CAr), 18.1 (d, J =
15 Hz, P(CH3)3), 17.1 (d, J = 14 Hz, P(CH3)3).
Reactions of complex 3 with HCl: PMe3 (0.10 g, 1.31 mmol) and HCl (2.6 mL of
0.31 M solution in diethyl ether, 0.80 mmol) was respectively added to a solution of
complex 3 (0.50 g, 0.80 mmol) in 20 mL of THF at ꢀ78 °C. The solution was stirred
for 10 min at this temperature and then was allowed to reach room temperature slowly.
The solution was stirred for 2 h, and a light blue solution was obtained. After removal
of the solvent under vacuum, the residue was extracted with 20 mL of diethyl ether.
Co(PMe3)3Cl (0.19 g, 74% yield) as blue crystals was isolated from the diethyl ether
solution at ꢀ20 °C. The existence of ligand 1 in diethyl ether solution was further
identified with in situ 31P NMR spectrum.
Synthesis of complex 8: A solution of complex 3 (0.65 g, 1.04 mmol) in THF (40 mL)
was stirred in the atmosphere of carbon monoxide for 24 h at 25 °C to give a light
yellow solution. The THF was removed under reduced pressure. The residue was
extracted with nꢀpentane (60 mL) and diethyl ether (60 mL) in turn to give light yellow
solution. Complex 8 was obtained as yellow crystals from the nꢀpentane solution and
diethyl ether solution at ꢀ10 °C, yield 0.38 g (0.62 mmol, 60 %). m.p.: 144 ꢀ 146
℃.
Anal. Calcd for C34H30CoNO2P2 (605.49 g/mol): C, 67.44; H, 4.99; N, 2.31. Found: C,
67.92; H, 5.20; N, 2.11. IR (Nujol, mull, cmꢀ1): 1969, 1906 ν(C=O), 1667 ν(C=N),
1
1566 ν(C=C), 947 ρ(PMe3). H NMR (300 MHz, C6D6, ppm): 8.49 (d, 1H, J = 9Hz,
2
ArꢀH) 7.92 ꢀ 7.00 (m, 20H, ArꢀH), 0.63 (d, JP,H = 9.0 Hz, 9H, PMe3). 31P{H} NMR
(121.5 MHz, C6D6, 298K, ppm): 61.5 (d, 2J = 36.5 Hz, 1P, PPh2), 16.2 (d, 2J = 36.5 Hz,
1P, PMe3). 13C{H} NMR (75 MHz, C6D6, 298K, ppm):157.5 (C=N), 156.7 (CAr), 153.3
(CAr), 137.3 (CAr), 136.9 (CAr), 134.7 (CAr), 134.3 (CAr), 134.0 (CAr), 133.0 (d, J = 13
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Hz, CAr), 131.9 (d, J = 10 Hz, CAr), 130.3 (CAr), 129.5 (CAr), 128.8 (CAr), 128.6 (CAr),
128.5 (CAr), 128.4 (CAr), 126.2 (CAr), 125.7 (CAr), 125.5 (d, J = 5 Hz, CAr), 124.6
(CAr), 122.5 (CAr), 112.1 (CAr), 18.1 (d, J = 23 Hz, P(CH3)3).
X-ray Crystal Structure Determinations: Single crystal Xꢀray diffraction data are
listed In the Table SI of ESI. Single crystal Xꢀray diffraction data of the complexes 4, 5,
7 and 8 were collected on a STOE STADIVARI Cu or Stoe IPDS2 diffractometer.
Using Olex218, the structure was solved with ShelXS19 structure solution program
using Direct Methods and refined with the ShelXL20 refinement package using Least
Squares minimization. CCDCꢀ1547326 (4), ꢀ1539739 (5), ꢀ1490872(7), ꢀ1534556 (8)
contain supplementary crystallographic data for this paper. Copies of the data can be
obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK (fax: (+44)1223ꢀ336ꢀ033; eꢀmail: deposit@ccdc.cam.ac.uk).
Acknowledgements. This work was supported by NSFC No. 21372143.
Notes and references
1 T. Gensch, M. N. Hopkinson, F. Glorius and J. WencelꢀDelord, Chem. Soc. Rev.
2016, 45, 2900ꢀ2936.
2 (a) I. Bauer and H.ꢀJ. Knoelker, Chem. Rev. 2015, 115, 3170ꢀ3387; (b) F. Huang, Z.
Liu and Z. Yu, Angew. Chem. Int. Ed. 2016, 55, 862ꢀ875; (c) L. Huang, M. Arndt,
K. Goossen, H. Heydt and L. J. Goossen, Chem. Rev. 2015, 115, 2596ꢀ2697.
3 V. J. Shiner and D. Whittaker, J. Am. Chem. Soc. 1965, 87, 843ꢀ846.
4 (a) J. Jeschke, T. B. Engelhardt and H. Lang, Eur. J. Org. Chem. 2016, 1548ꢀ1554;
(b) L. Zhang, Z. Han, X. Zhao, Z. Wang and K. Ding, Angew. Chem. Int. Ed. 2015,
54, 6186ꢀ6189.
5 (a) A. GutierrezꢀBonet, F. JuliaꢀHernandez, B. de Luis and R. Martin, J. Am. Chem.
Soc. 2016, 138, 6384ꢀ6387; (b) A. Luquin, N. Castillo, E. Cerrada, F. L. Merchan,
J. Garrido and M. Laguna, Eur. J. Org. Chem. 2016, 789ꢀ798; (c) S.ꢀL. Zhang and
Z.ꢀL. Yu, J. Org. Chem. 2016, 81, 57ꢀ65.
17

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6 J. Cheng, M. Zhu, C. Wang, J. Li, X. Jiang, Y. Wei, W. Tang, D. Xue and J. Xiao,
Chem. Sci. 2016, 7, 4428ꢀ4434.
7 (a) X. Jia and Z. Huang, Nat. Chem. 2016, 8, 157ꢀ161; (b) L.ꢀJ. Song, S. Ding, Y.
Wang, X. Zhang, Y.ꢀD. Wu and J. Sun, J. Org. Chem. 2016, 81, 6157ꢀ6164.
8 Y. Chen, H. Sun, U. Flörke and X. Li, Organometallics 2008, 27, 270–275.
9 (a) Z. Lian, X. Xu, H. Sun, Y. Chen, T. Zheng and X. Li, Dalton Trans. 2010, 39,
9523–9529; (b) H.ꢀF. Klein, R. Beck, U. Floerke, H.ꢀJ. Haupt, Eur. J. Inorg. Chem.
2002, 3305ꢀ3312.
10 H. Zhou, H. Sun, S. Zhang and X. Li, Organometallics 2015, 34, 1479−1486.
11 (a) S. F. Huang, H. Zhao, X. Y. Li, L. Wang and H. J. Sun, RSC Adv. 2015, 5,
15660ꢀ15667; (b) L. Wang, H. J. Sun and X. Y. Li, Eur. J. Inorg. Chem. 2015,
2732ꢀ2743; (c) H. Zhao, H. J. Sun and X. Y. Li, Organometallics 2014, 33,
3535ꢀ3539; (d) H. Zhou, H. Sun, S. Zhang and X. Li, Organometallics 2015, 34,
1479ꢀ1486; (e) G. Zhu, L. Wang, H. Sun and X. Li, RSC Adv. 2015, 5,
19402ꢀ19408.
12 J. Xing, H. Sun, B. Xue, X. Li, O. Fuhr and D. Fenske, Organometallics 2017, 36,
975ꢀ980.
13 S. Wu, X. Li, Z. Xiong, W. Xu, Y. Lu and H. Sun Organometallics 2013, 32,
3227−3237.
14 S. Deblon, L. Liesum, J. Harmer, H. Schonberg, A. Schweiger, and H.
Grutzmacher Chem. Eur. J. 2002, 8, 601−611.
15 P. Pietrzyk, and Z. Sojka Chem. Commun. 2007, 1930–1932.
16 H.ꢀF. Klein and H. H. Karsch, Chem. Ber. 1975, 108, 944ꢀ955.
17 S. M. Nobre and A. L. Monteiro, J. Mol. Catal. A-Chemical 2009, 313, 65ꢀ73.
18 O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard and H. J.
Puschmann, Appl. Crystallogr. 2009, 42, 339−341.
19 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, A64,
112−122.
20 G. M. Sheldrick, Acta Crystallogr., Sect. C: Struct. Chem. 2015, C71, 3−8.
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TOC
The sp2 CꢀH bond activation of the HC=Nꢀmoiety in diphenylphosphino benzalimines
was realized using CoMe(PMe3)4 with the elimination of methane.
19