Preparation of hydrido [CNC]-pincer cobalt complexes via selective C-H/C-F bond activation and their catalytic performances

Article abstract of DOI:10.1039/C8NJ02979B

Polyfluorinated aryl imines 2,4,5-R₁,R₂,R₃-C₆H₂-HC═N-1-C₁₀H₇ (R₁ = F, R₂ = F, R₃ = H (1); R₁ = F, R₂ = H, R₃ = F (2) and R₁ = F, R₂ = F, R₃ = F (3)) and F₅C₆-HC═N-1-C₁₀H₇ (7) reacted with CoMe(PMe₃)₄ to give rise to hydrido [CNC]-pincer cobalt(iii) complexes (2,4,5-R₁,R₂,R₃-C₆H-HC═N-1-C₁₀H₆)Co(H)(PMe₃)₂ (R₁ = F, R₂ = F, R₃ = H (4); R₁ = F, R₂ = H, R₃ = F (5); R₁ = F, R₂ = F, R₃ = F (6)) and (F₄C₆-HC═N-1-C₁₀H₆)Co(H)(PMe₃)₂ (8) via selective C-F/C-H bond activation. Penta-coordinate dicarbonyl cobalt(i) complexes (2,4,5-R₁,R₂,R₃-C₆H-HC═N-1-C₁₀H₇)Co(CO)₂(PMe₃) (R₁ = F, R₂ = H, R₃ = F (9); R₁ = F, R₂ = F, R₃ = F (10)) were obtained from reactions of hexa-coordinate cobalt(iii) complexes 5 and 6 with carbon monoxide through reductive elimination. Cobalt(iii) halides (2,4,5-R₁,R₂,R₃-C₆H-HC═N-1-C₁₀H₆)Co(i)(PMe₃)₂ (R₁ = F, R₂ = F, R₃ = H (11); R₁ = F, R₂ = H, R₃ = F (12); R₁ = F, R₂ = F, R₃ = F (13)) and (2,4,5-R₁,R₂,R₃-C₆H-HC═N-1-C₁₀H₆)Co(Br)(PMe₃)₂ (R₁ = F, R₂ = F, R₃ = H (14); R₁ = F, R₂ = H, R₃ = F (15); R₁ = F, R₂ = F, R₃ = F (16)) were prepared by the interaction between hydrido cobalt(iii) complexes 4-6 and MeI or EtBr. The molecular configurations of complexes 4, 8, and 11 were determined by single crystal X-ray diffraction. We then confirmed that the four hydrido cobalt(iii) complexes 4-6 and 8 could be used as catalysts for reduction of aldehydes and ketones. Complex 8 is the best catalyst among the four complexes and can selectively catalyze the carbonyl groups of α,β-unsaturated aldehydes and ketones.

Full text of DOI:10.1039/C8NJ02979B

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Preparation of hydrido [CNC]-pincer cobalt
complexes via selective C–H/C–F bond activation
and their catalytic performances†
Cite this:DOI: 10.1039/c8nj02979b
Fei Yang,a Yangyang Wang,ab Faguan Lu,a Shangqing Xie,a Xinghao Qi,a
a
Hongjian Sun,
Xiaoyan Li, *a Olaf Fuhrc and Dieter Fenskec
Polyfluorinated aryl imines 2,4,5-R1,R2,R3-C6H2-HCQN-1-C10H7 (R1 = F, R2 = F, R3 = H (1); R1 = F,
R2 = H, R3 = F (2) and R1 = F, R2 = F, R3 = F (3)) and F5C6-HCQN-1-C10H7 (7) reacted with CoMe(PMe3)4
to give rise to hydrido [CNC]-pincer cobalt(III) complexes (2,4,5-R1,R2,R3-C6H-HCQN-1-
C10H6)Co(H)(PMe3)2 (R1 = F, R2 = F, R3 = H (4); R1 = F, R2 = H, R3 = F (5); R1 = F, R2 = F, R3 = F (6)) and
(F4C6-HCQN-1-C10H6)Co(H)(PMe3)2 (8) via selective C–F/C–H bond activation. Penta-coordinate
dicarbonyl cobalt(I) complexes (2,4,5-R1,R2,R3-C6H-HCQN-1-C10H7)Co(CO)2(PMe3) (R1 = F, R2 = H,
R3 = F (9); R1 = F, R2 = F, R3 = F (10)) were obtained from reactions of hexa-coordinate cobalt(III)
complexes 5 and 6 with carbon monoxide through reductive elimination. Cobalt(III) halides (2,4,5-
R1,R2,R3-C6H-HCQN-1-C10H6)Co(I)(PMe3)2 (R1 = F, R2 = F, R3 = H (11); R1 = F, R2 = H, R3 = F (12);
R1 = F, R2 = F, R3 = F (13)) and (2,4,5-R1,R2,R3-C6H-HCQN-1-C10H6)Co(Br)(PMe3)2 (R1 = F, R2 = F,
R3 = H (14); R1 = F, R2 = H, R3 = F (15); R1 = F, R2 = F, R3 = F (16)) were prepared by the interaction
between hydrido cobalt(III) complexes 4–6 and MeI or EtBr. The molecular configurations of complexes
4, 8, and 11 were determined by single crystal X-ray diffraction. We then confirmed that the four
hydrido cobalt(III) complexes 4–6 and 8 could be used as catalysts for reduction of aldehydes
and ketones. Complex 8 is the best catalyst among the four complexes and can selectively catalyze the
carbonyl groups of a,b-unsaturated aldehydes and ketones.
Received 15th June 2018,
Accepted 6th August 2018
DOI: 10.1039/c8nj02979b
rsc.li/njc
cobalt-induced C–H bond activation and functionalization.1
Glorius evaluated a Co-based catalytic system with mild C–H
Introduction
Recently, great progress has been made on transition-metal- bond activation.2 The C–H functionalization has been an
induced C–H bond activation and functionalization because efficient method for selective derivatization of C–H bonds
this method provides a green and sustainable way to various and has been broadly used in synthetic chemistry.3 At the same
new organic compounds. In many reactions, chemists mainly time, more and more fluorinated compounds are being applied
use the second and third transitional series of precious metals. in agrochemicals, drugs, and new materials. Not only the
The C–H bond functionalization catalyzed by more abundant formation of C–F bonds, but also the activation of C–F bonds,
and cost-efficient 3d metals, such as Fe, Co, and Ni, is used has been used to prepare organic fluorides because selective
less. Ackermann summarized stoichiometric and catalytic defluorinated reactions of per- or polyfluorinated compounds
are applicable to syntheses of partially fluorinated compounds.
a School of Chemistry and Chemical Engineering, Key Laboratory of Special
Functional Aggregated Materials, Ministry of Education, Shandong University,
Shanda Nanlu 27, 250100 Jinan, People’s Republic of China.
E-mail: xli63@sdu.edu.cn
This strategy is often better than direct fluorination since it is
not easy to control selectivity using direct fluorination.4 C–F
bond activation of aliphatic fluorides by Lewis acids, Brønsted
superacids, and hydrogen bonding or metal complexes provides
new methodologies for synthesis of new fluorinated building
blocks.5
If there are both C–F and C–H bonds within a molecule, it is
a selective problem to give priority to C–F or C–H activation
when a metal center interacts with the molecule. Although the
average bond energy of a C–H bond is smaller than that of a
C–F bond, bond energy will vary when the chemical bond is
b College of Chemistry and Chemical Engineering, Northwest Normal University,
730070 Lanzhou, P. R. China
c
¨
Institut fur Nanotechnologie (INT) und Karlsruher Nano-Micro-Facility (KNMF),
¨
Karlsruher Institut fur Technologie (KIT), Hermann-von-Helmholtz-Platz 1,
76344 Eggenstein-Leopoldshafen, Germany
† Electronic supplementary information (ESI) available: Table of selected crystal-
lographic data, original IR, 1H NMR and 19F NMR spectra of the compounds and
CIF files. CCDC 1840080–1840082. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c8nj02979b
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within a specific molecule. The priority of C–F/C–H bond activation cobalt(III) complexes 4–6 via dual C–H bond activation with
is related to many factors, such as the kind of metal center, its the release of a CH4 molecule (eqn (1)). In this process, no
oxidation state, coordination number, spatial configuration, and ortho-(C–F) bond activation was observed. We think that the
type of supporting ligands in the metal complex.6 Therefore, first step of reaction (1) is ortho-(C–H) bond activation of the
selective activation of a C–F/C–H bond is still a great challenge. phenyl ring because this C–H bond activation is easier than
In 2010, we studied the competitive cleavage of a C–F or C–H activation of the C–H bond at the 8-position of the naphthyl
bond with an imine or carbonyl group as an anchoring group group. This is caused by the F atoms in the phenyl ring. The
and found that both the anchoring group and the valence of the formation of CH4 and cyclometalation are the driving forces.
cobalt atom effect the preference of C–F/C–H bond activation.7 Activation of a C–H bond at the 8-position of the naphthyl
A similar conclusion was drawn from the reactions of fluori- group gives rise to a Co–H bond with formation of a second
nated imines with Fe(PMe3)4.8 The experimentally observed 5-membered chelate ring.
(1)
C–F and C–H cyclometalation products by cobalt complexes were
In the IR spectra of complexes 4–6, typical Co–H stretching
rationalized by analyzing the thermodynamic and kinetic properties bands at 1889 (4), 1892 (5), and 1894 (6) cmÀ1 were found.
of C–H and C–F activation pathways.9 A further investigation of the The hydrido resonances of complexes 4–6 were recorded at
reactions of different 2,6-difluorophenylarylimines with Fe(PMe3)4 À18.88 (4), À17.75 (5), and À17.90 (6) ppm as triplets with a
indicates that C–H bond activation products were obtained if coupling constant J(PH) = 69.0 Hz in the 1H NMR spectra of
the aryl rings of fluoroarylimines were substituted by electron- complexes 4–6. The singlets at 9.17 (4), 9.27 (5), and 9.10 (6)
withdrawing groups. And, C–F bond activation products were ppm belong to the hydrogen atoms of the imine groups. In the
formed if aromatic rings of fluoroarylimines were substituted 19F NMR spectra of complexes 4–6, the coupling patterns are in
by electron-donating groups. Surprisingly, both the C–H and accord with structural characteristics of the corresponding
C–F bond activation products are hydrido iron complexes.10 complexes. One signal at 10.4 (4), 11.2 (5), and 10.5 (6) ppm
The reaction of Fe(PMe3)4 with 2,3,5,6-tetrafluoropyridine in for two PMe3 ligands was registered in the 31P NMR spectra of
pentane selectively resulted in the C–H bond activation product complexes 4–6. This demonstrates that two P atoms in each
with the release of hydrogen.11 Fluoroarylimine-stabilized iron complex have the same chemical environment in the molecular
hydrides formed via selective C–F/C–H bond activation could be structure of the complex.
used for activating CO2 and CS212 and the activation preference
of the C–F/C–H bond could be changed with an auxiliary strong diffraction were obtained from its n-pentane solution at 0 1C.
Lewis acid. The molecular structure of complex 4 has a hexa-coordinate
Red crystals of complex 4 suitable for single crystal X-ray
As a continuation in the field of selective C–F/C–H bond configuration (Fig. 1). It is clear that two trimethylphosphine
activation, in this work, we have realized selective activation of ligands are symmetrical about the [CNC]-pincer plane. This
the C–F and C–H bond from a reaction of CoMe(PMe3)4 with result confirms that the conclusion drawn from the 31P NMR
polyfluorinated aryl imines. Four hydrido [CNC]-pincer cobalt spectra is correct. Both the phenyl and the naphthyl ring are in
complexes were synthesized and characterized and the properties the chelate plane. If P1–Co1–P2 (161.11(2)1) is alleged to be
and catalytic activities of these cobalt hydrides were explored. The axial, then the other four coordination atoms [H100C7C13N1]
cobalt hydrides showed excellent catalytic activity in the hydro- are in the equatorial plane. Co1–H100 (1.41(2) Å) is in the
silylation of aldehydes, especially for selective hydrosilylation of region of the known Co–H bonds (1.40–1.50 Å).14 The sum
the carbonyl groups of a,b-unsaturated aldehydes and ketones.
of the four coordination bond angles (N1–Co1–C7 = 83.40(7);
C7–Co1–H100 = 99.3(10); H100–Co1–C13 = 94.8(10), and
C13–Co1–N1 = 82.48(7)1) around the central cobalt atom in
the equatorial plane is 359.981. This shows that coplanarity of
the coordination atoms and Co atom is very good.
Results and discussion
Selective C–F/C–H bond activation
The combination of pre-ligand 7 and CoMe(PMe3)4 (or
In order to study selective C–F/C–H bond activation in a phenyl Co(PMe3)4) in diethyl ether gave rise to the hydrido [CNC]-pincer
ring, reactions of fluorophenylimines 1–313 with CoMe(PMe3)4 cobalt complex 8 via both C–F and C–H bond activation with the
were carried out to afford hydrido bischelate [CNC]-pincer formation of MeF (or F2PMe3 in the case of Co(PMe3)4) (eqn (2)).
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Fig. 1 Molecular structure of complex 4 (most of the hydrogen atoms
were omitted for clarity). Selected bond distances (Å) and angle (1): Co1–
N1 1.9306(15), Co1–C13 1.9416(17), Co1–C7 1.9661(18), Co1–P2 2.1619(6),
Co1–P1 2.1637(6), Co1–H100 1.41(2), N1–C11 1.303(2); N1–Co1–C13
82.48(7), N1–Co1–C7 83.40(7), C13–Co1–C7 165.87(8), N1–Co1–P2
100.17(5), C13–Co1–P2 94.24(5), C7–Co1–P2 88.80(5), N1–Co1–P1
98.21(5), C13–Co1–P1 92.47(5), C7–Co1–P1 88.98(5), P2–Co1–P1 161.11(2),
N1–Co1–H100 177.1(10), C13–Co1–H100 94.8(10), C7–Co1–H100 99.3(10),
P2–Co1–H100 81.0(11), and P1–Co1–H100 80.9(11).
Fig. 2 Molecular structure of complex 8 (most of the hydrogen atoms
were omitted for clarity). Selected bond distances (Å) and angle (1): Co1–
N1 1.936(2), Co1–C8 1.953(3), Co1–C20 1.965(3), Co1–P1 2.1666(11), Co1–
P2 2.1674(12), Co1–H100 1.33(3), N1–C13 1.295(3); N1–Co1–C8 81.75(10),
N1–Co1–C20 83.54(10), C8–Co1–C20 165.26(12), N1–Co1–P1 99.01(6),
C8–Co1–P1 92.53(8), C20–Co1–P1 89.04(8), N1–Co1–P2 100.60(6),
C8–Co1–P2 95.12(8), C20–Co1–P2 88.29(7), P1–Co1–P2 159.78(3),
N1–Co1–H100 174.3(11), C8–Co1–H100 94.3(11), C20–Co1–H100
100.3(11), and P1–Co1–H100 77.0(12), P2–Co1–H100 83.8(12).
(2)
MeF and F2PMe3 in solution could be confirmed by in situ 19F and location of C–F bonds on the aromatic ring, but also to the
31P NMR.15,16 The n(Co–H) band in the IR spectrum of complex 8 number of C–F bonds on the aromatic ring. Based on our early
was recorded at 1893 cmÀ1. The hydrido hydrogen was found at report on C–F/C–H bond activation of polyfluoroaryl imine,19
À17.86 ppm as a triplet with a coupling constant of 69.0 Hz while we propose a mechanism for reaction (2) (Scheme 1).
the signal of imine hydrogen was registered at 8.97 ppm as a
The reaction of CoMe(PMe3)4 with pre-ligand 7 begins with
1
singlet in the H NMR spectrum of complex 8. In the 19F NMR coordination of the N atom of the imine group and the
spectrum of complex 8, there are four groups of F signals with the oxidative addition of the C–F bond at the Co(I) center to afford
same integral intensity. This implies that one C–F bond of the five Co(III) intermediate 7A, an organo cobalt(III) fluoride. The reaction
C–F bonds in 7 was cleaved.
of Co(PMe3)4 with pre-ligand 7 also starts with coordination of
Single crystal X-ray diffraction confirmed that complex 8 is hexa- the N atom of the imine group and the oxidative addition of the
coordinate with an octahedral geometry (Fig. 2). The structural C–F bond at the Co(0) center to give rise to Co(II) intermediate 7B,
characteristics of cobalt complex 8 are similar to those of complex 4. an organo cobalt(II) fluoride. The reductive elimination between
We have known that the reaction of CoMe(PMe3)4 with an Co–Me and Co–F bond of intermediate 7A delivers intermediate
imine derived from 2,6-difluorobenzaldehyde and naphthalene- 7C, a Co(I) species, with the escape of MeF. 7B, which reacts
1-amine provides only C–F activation products without C–H with PMe3 ligand to give intermediate 7C and difluorotrimethyl-
bond activation (eqn (3)).17 This result is similar to the C–Cl phosphine, F2PMe3. After dissociation of one PMe3 ligand,
bond activation by cobalt complex.18
oxidative addition of the C–H bond of the naphthyl group at
the unstable Co(I) center of intermediate 7C generates the final
hydrido [CNC]-pincer cobalt(III) complex 8 via a second cyclo-
metalation. Even though the intermediates 7A, 7B, and 7C were
not isolated, the existence of these complexes could be indirectly
verified by our early work.17,19
Chemical properties of hydrido cobalt(III) complexes 4–6
(3)
Hydrido cobalt complexes are important compounds in many
From the results of eqn (1)–(3) it can be concluded that fields of synthetic chemistry. Therefore, we further studied the
selective C–F/C–H bond activation is related not only to the chemical properties of hydrido cobalt complexes. Hydrido cobalt
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Scheme 1 A proposed mechanism for reaction (2).
complexes 5 and 6 reacted with CO to generate cobalt(I) complexes 10 with coordination of the second CO ligand. These experi-
9 and 10 (eqn (4)).
mental results show that the ligand has an important influence
on the configuration of the complexes.
The C–X bonds of MeI and EtBr are active and can interact with
many transition metal complexes. The reactions of MeI and EtBr
with hydrido complexes 4–6 were carried out (eqn (5) and (6)).
(4)
(5)
In the IR spectra of cobalt(I) complexes 9 and 10, two bands
for carbonyl ligands at 2019/1934 (9) and 1979/1913 (10) cmÀ1
were recorded. The Co–H vibrations of complexes 5 and 6
disappeared. When comparing the 1H NMR spectra of complexes
9 and 10, with those of complexes 5 and 6, one more aromatic
hydrogen atom was found. Resonances of the imine hydrogen
atom are situated at 8.42 (9) and 8.26 (10) ppm. The hydrido
signals of complexes 5 and 6 in upfield disappeared. In the 31P
NMR spectra of complexes 9 and 10, only one singlet for PMe3 at
8.8 (9) and 9.2 (10) ppm was detected. From this experimental
information, it can be concluded that reaction (4) is not a simple
replacement of PMe3 by CO.
(6)
Complexes 11–13 have similar structures with complexes
We consider that the first step is ligand replacement of PMe3 14–16. They are hexa-coordinate di-organo cobalt(III) halides.
by CO to form intermediate A5,6 (Scheme 2). Intermediate A5,6 In the IR spectra of complexes 11–16, the n(CQN) vibrations
as a carbonyl cobalt(III) species is not stable because of the weak appeared at 1599–1605 cmÀ1. In the 1H NMR spectra of complexes
p-backbond between cobalt(III) and CO ligands. After reductive 11–16, the H atom of the imine group was registered at 8.65–
elimination between Co–H and Co–Cnaphthyl occurs it gives rise 9.10 ppm. In the 31P NMR spectra of complexes 11–16, only one
to stable penta-coordinate dicarbonyl cobalt(I) complexes 9 and singlet was found at 16.3–18.4 ppm. This result shows that
Scheme 2 Pathway of formation of complexes 9 and 10.
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Table 2 Hydrosilylation of aldehydes catalyzed by 8a
Entry
1
Substrate
Conversionb (%)
99
Yieldc (%)
92
2
3
92
90
87
84
Fig. 3 Molecular structure of complex 11 (all the hydrogen atoms were
omitted for clarity). Selected bond distances (Å) and angles (1): I1–Co1 2.6090(8),
Co1–N1 1.894(4), Co1–C6 1.957(5), Co1–C17 1.976(5), Co1–P1 2.2210(15), Co1–
P2 2.2246(16), N1–C7 1.274(6); N1–Co1–C6 82.47(19), N1–Co1–C17 83.65(19),
C6–Co1–C17 166.1(2), N1–Co1–P1 92.43(12), C6–Co1–P1 91.02(15),
C17–Co1–P1 88.68(15), N1–Co1–P2 91.13(12), C6–Co1–P2 91.30(15),
C17–Co1–P2 89.86(15), P1–Co1–P2 175.98(6), N1–Co1–I1 179.41(13),
C6–Co1–I1 97.03(15), C17–Co1–I1 96.86(14), P1–Co1–I1 87.88(4), and
P2–Co1–I1 88.58(5).
4
5
85
83
81
78
6
7
92
87
85
77
these two trimethylphosphine ligands are in the same chemical
environments. The molecular structure of complex 11 deter-
mined by single crystal X-ray diffraction has a hexa-coordinate
coordination geometry (Fig. 3). This iodo cobalt(III) complex 11
has the same structural characteristics as its hydrido cobalt(III)
complex 4. Two chelate rings are in the same plane with both
the phenyl and naphthyl ring. Two PMe3 ligands are symmetrically
placed about the chelate ring, so they have the same chemical
environments.
8
93
88
a
b
c
2 mol% 8, (EtO)3SiH, THF, 80 1C, 4 h. GC conversion. Isolated
yield.
4–6 and 8, could catalyze the reduction of benzaldehyde to a
silyl benzyl ether with silanes as hydrogen sources (Table 1).
The control experiment showed that the catalytic reaction did
Catalytic applications of hydrido cobalt complexes 4–6 and 8
It has been reported that hydrido cobalt(III) complexes as catalysts not occur without a catalyst (Table 1, entry 1). Under the same
could be used in the reduction of aldehydes and ketones.20,21 conditions, complex 8 had the best catalytic activity among the
In this work, we found that four hydrido cobalt(III) complexes, four hydrido cobalt complexes (Table 1, entries 2–5). When the
Table 1 Hydrosilylation of benzaldehyde catalyzed by cobalt hydride under different conditionsa
Entry
Catalyst
Loading (mol%)
Silane
Solvent
Temp. (1C)
Time (h)
Conversionb (%)
1
2
3
4
5
6
7
8
None
0
2
2
2
2
2
1
2
2
2
2
2
2
2
(EtO)3SiH
(EtO)3SiH
(EtO)3SiH
(EtO)3SiH
(EtO)3SiH
(EtO)3SiH
(EtO)3SiH
(EtO)3SiH
(EtO)3SiH
(EtO)3SiH
Et3SiH
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
Toluene
80
80
80
80
80
80
80
60
50
30
80
80
80
80
24
4
4
4
4
2
4
4
4
4
4
4
4
4
0
71
67
80
99
85
76
68
54
11
24
0
4
5
6
8
8
8
8
8
8
8
8
8
8
9
10
11
12
13
14
Ph3SiH
Me(EtO)2SiH
(EtO)3SiH
59
88
a
b
Reaction conditions: PhCHO (1.0 mmol), R3SiH (1.2 mmol), solvent (2 mL). Determined by GC with n-dodecane as an internal standard.
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Table 4 Selective reduction of a,b-unsaturated carbonyls catalyzed by 8a
reaction temperature was lower than 80 1C, the conversion
became low (Table 1, entries 8–10). It was found that (EtO)3SiH is
the best hydrogen source among the tested four silanes (Table 1,
entries 5 and 11–13). If the catalyst loading was decreased to
1 mol%, then the conversion became 76% from 99% (Table 1,
entries 5 and 7). If the reaction time was shortened to 2 hours,
then the conversion decreased to 85% (Table 1, entry 6). We also Entry
confirmed that THF is a better reaction medium than toluene for
Substrate
Conversionb (%)
91
Yieldc (%)
85
this catalytic reaction (Table 1, entries 5 and 14).
1
2
3
To expand the scope of the substrates, more aldehydes were
tested under the optimized conditions: 2 mol% catalyst loading,
(EtO)3SiH, THF, 4 h, 80 1C (Table 2). Whether the phenyl group
of the substrate has an electron-withdrawing group or electron-
donating group, the catalytic reaction could take place and the
isolated yields were between 77–92%. With 1-naphthaldehyde as
substrate, the conversion reached 93% and the isolated yield
was 88%. In general, ketones are less active than aldehydes for
these reduction reactions. Some aromatic ketones were selected
as substrates for this catalytic system (Table 3, entries 1–5). The
results show that both conversions and the isolated yields are
lower than those with the aldehydes (Table 2). The conversion
of an aliphatic ketone is significantly lower than that of an aromatic
ketone (Table 3, entries 6 and 7). Interestingly, a,b-unsaturated
aldehydes could selectively transfer to the corresponding
a,b-unsaturated alcohols (Table 4, entries 1–5). In this process, the
CQC bond remained unchanged. Under the catalytic conditions,
chalcone transformed to 1,3-diphenyl-pro-2-en-1-ol in an isolated
85
58
80
55
4
5
96
86
95
94
88
87
6
a
Cinnamaldehyde (1.0 mmol), (EtO)3SiH (1.2 mmol), 8 (0.02 mmol) in
2 mL THF, 80 1C, 4 h. GC conversion. Isolated yield.
b
c
yield of 87% with a conversion of 94%. In comparison with the
data in Table 3, it can be concluded that an a,b-unsaturated
ketone is more active than a normal ketone.
Table 3 Hydrosilylation of ketones catalyzed by 8a
Conclusions
Hydrido [CNC]-pincer cobalt(III) complexes 4–6 and 8 were
prepared from reactions of polyfluorinated aryl imines 1–3
and 7 with CoMe(PMe3)4 via selective C–H/C–F bond activation.
Hydrido complexes 5 and 6 reacted with CO to give rise to
dicarbonyl cobalt(I) complexes 9 and 10 via reductive elimination
and in this process the hexa-coordinate cobalt(III) complexes
transformed to penta-coordinate cobalt(I) complexes. Complexes
4–6 interacted with MeI or EtBr afforded iodo cobalt(III) complexes
11–13 or bromo cobalt(III) complexes 14–16. The molecular
structures of complexes 4, 8, and 11 were determined by single
crystal X-ray diffraction. It was found that these four hydrido
cobalt(III) complexes 4–6 and 8 could catalyze the reduction
reactions of aldehydes and ketones. Among them, complex 8
has the strongest catalytic activity. Complex 8 selectively catalyzed
the carbonyl group of a,b-unsaturated aldehydes and ketone with
an unchanged CQC bond.
Entry
1
Substrate
Conversionb (%)
85
Yieldc (%)
77
2
3
88
77
78
70
4
5
6
85
82
60
75
72
57d
71d
Experimental section
General procedures and materials
Standard vacuum techniques were applied to the preparation of
all air-sensitive materials in this paper. Solvents were dried
with sodium on the basis of known procedures and distilled in
nitrogen atmosphere before use. Schiff bases were prepared by
7
76
a
b
c
2 mol% 8, (EtO)3SiH, THF, 80 1C, 4 h. GC conversion. Isolated yield.
GC yield.
d
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condensation of polyfluorobenzaldehyde with amines by refluxing 31P NMR (121 MHz, C6D6, 298 K, d/ppm): 10.5 (s, PMe3). 19F
in alcohol solution. CoMe(PMe3)4 and Co(PMe3)4 were prepared NMR (282 MHz, C6D6, 298 K, d/ppm): À117.5 (d, J = 22.6 Hz,
according to literature methods.22 Infrared spectra (4000–400 cmÀ1
)
1F), À120.9 (dd, J = 30.0, 22.6 Hz, 1F), À131.0 (d, J = 30.0 Hz, 1F).
were obtained with a Bruker ALPHA FT-IR instrument used with Anal. calc. For C23H27CoF3NP2 (495.34 g molÀ1): C, 54.77;
Nujol mulls between KBr disks to display the characteristic peaks of H, 5.49; N, 2.83. Found: C, 55.82; H, 5.48; N, 2.74.
substances. NMR data were recorded on a Bruker Avance 300 MHz
Preparation of complex 8. A solution of imine 7 (0.64 g,
spectrometer. GC was collected with a Fuli 9790 instrument 2.0 mmol) in 20 mL of diethyl ether was added to a solution of
with n-dodecane as an internal standard. All the aldehydes CoMe(PMe3)4 (0.95 g, 2.5 mmol) or Co(PMe3)4 (0.91 g, 2.5 mmol)
and ketones were purchased and some of them were freshly in 40 mL of diethyl ether at À78 1C. After stirring for 24 h at
distilled before use.
room temperature, the reaction mixture turned red. Then the
Preparation of complex 4. A solution of imine 1 (0.54 g, diethyl ether was transferred, and n-pentane was used to extract
2.0 mmol) in 20 mL of diethyl ether was added into a solution the residual solid. After filtering, the product (0.48 g, 47% yield)
of CoMe(PMe3)4 (0.95 g, 2.5 mmol) in 40 mL of diethyl ether at was obtained as red crystals from the n-pentane at 0 1C.
À78 1C. After stirring for 24 h at room temperature, the reaction Dec. 4280 1C. IR (Nujol mull, KBr, cmÀ1): 1893 n(Co–H),
mixture turned red. Then the diethyl ether was transferred, and 1628 n(CQN), 1599, 1531 n(CQC), 940 r(PMe3). 1H NMR
n-pentane was used to extract the residual solid. After filtering, (300 MHz, C6D6, 298 K, d/ppm): 8.97 (s, 1H, CHQN), 7.59–
the product (0.67 g, 72% yield) was obtained as red crystals 7.27 (m, 4H, Ar-H), 7.13–7.06 (m, 2H, Ar-H), 0.50 (t, J = 3.0 Hz,
from n-pentane at 0 1C. Dec. 4135 1C. IR (Nujol mull, KBr, cmÀ1): 18H, PMe3), À17.86 (t, J = 69.0 Hz, 1H, Co-H). 31P NMR
1889 n(Co–H), 1559 n(CQN), 1528 n(CQC), 942 r(PMe3). 1H NMR (121 MHz, C6D6, 298 K, d/ppm): 10.9 (s, PMe3). 19F NMR
(300 MHz, C6D6, 298 K, d/ppm): 9.17 (s, 1H, CHQN), (282 MHz, C6D6, 298 K, d/ppm): À116.2 (dd, J = 22.6, 19.7 Hz,
7.59–7.16 (m, 7H, Ar-H), 6.49 (t, J = 9.0 Hz, 1H, Ar-H), 0.53 1F), À141.2 (t, J = 19.7 Hz, 1F), À153.4 (dd, J = 33.8, 19.7 Hz, 1F),
(s, 18H, PMe3), À18.88 (t, J = 69.0 Hz, 1H, Co-H). 31P NMR À164.6 (t, J = 19.7 Hz, 1F). Anal. calc. For C23H26CoF4NP2
(121 MHz, C6D6, 298 K, d/ppm): 10.4 (s, PMe3). 19F NMR (513.33 g molÀ1): C, 53.81; H, 5.11; N, 2.73. Found: C, 53.73;
(282 MHz, C6D6, 298 K, d/ppm): À108.7 (d, J = 8.5 Hz, 1F), H, 5.08; N, 2.82.
À113.0 (d, J = 8.5 Hz, 1F). Anal. calc. For C23H28CoF2NP2
(477.35 g molÀ1): C, 57.87; H, 5.91; N, 2.93. Found: C, 57.74; solution of complex 5 (0.48 g, 1.0 mmol) in 40 mL of THF. After
H, 5.95; N, 2.88. stirring for 48 h at room temperature, the reaction mixture
Preparation of complex 9. CO (1 bar) was bubbled into a
Preparation of complex 5. A solution of imine 2 (0.54 g, turned light red. Then the THF was transferred, and n-pentane
2.0 mmol) in 20 mL of diethyl ether was added to a solution of was used to extract the residual solid. After filtering, the product
CoMe(PMe3)4 (0.95 g, 2.5 mmol) in 40 mL of diethyl ether at (0.29 g, 63% yield) was obtained as yellowish red crystals from
À78 1C. After stirring for 24 h at room temperature, the reaction the n-pentane at 0 1C. Dec. 4258 1C. IR (Nujol mull, KBr, cmÀ1):
mixture turned red. Then the diethyl ether was transferred, and 2019, 1934 n(CQO), 1614 n(CQN), 1543 n(CQC), 946 r(PMe3).
n-pentane was used to extract the residual solid. After filtering, 1H NMR (300 MHz, C6D6, 298 K, d/ppm): 8.42 (s, 1H, CHQN),
the product (0.73 g, 78% yield) was obtained as red crystals 7.67 (d, J = 6.0 Hz, 1H, Ar-H), 7.54 (d, J = 6.0 Hz, 1H, Ar-H), 7.42
from the n-pentane at 0 1C. Dec. 4135 1C. IR (Nujol mull, KBr, (d, J = 9.0 Hz, 1H, Ar-H), 7.16 (m, 1H, Ar-H), 7.10–6.99 (m, 2H,
cmÀ1): 1892 n(Co–H), 1600 n(CQN), 1539 n(CQC), 942 r(PMe3). Ar-H), 6.77 (m, 1H, Ar-H), 6.61 (d, J = 9.0 Hz, 1H, Ar-H), 6.52–6.45
1H NMR (300 MHz, C6D6, 298 K, d/ppm): 9.27 (s, 1H, CHQN), (m, 1H, Ar-H), 0.43 (d, J = 9.0 Hz, 9H, PMe3). 31P NMR (121 MHz,
7.68–7.32 (m, 4H, Ar-H), 7.15–6.52 (m, 4H, Ar-H), 0.61 (t, C6D6, 298 K, d/ppm): 8.8 (s, PMe3). 19F NMR (282 MHz, C6D6,
J = 3.0 Hz, 18H, PMe3), À17.77 (t, J = 69.0 Hz, 1H, Co-H). 298 K, d/ppm): À100.1 (s, 1F), À120.7 (s, 1F). Anal. calc. For
31P NMR (121 MHz, C6D6, 298K, d/ppm): 11.2 (s, PMe3). C22H19CoF2NO2P (457.30 g molÀ1): C, 57.78; H, 4.19; N, 3.06.
19F NMR (282 MHz, C6D6, 298 K, d/ppm): À97.3 (d, J = 25.4 Hz, Found: C, 57.87; H, 4.29; N, 3.04.
1F), À122.2 (d, J = 25.4 Hz, 1F). Anal. calc. For C23H28CoF2NP2
(477.35 g molÀ1): C, 57.87; H, 5.91; N, 2.93. Found: C, 57.77; solution of complex 6 (0.50 g, 1.0 mmol) in 40 mL of THF. After
H, 5.89; N, 2.80. stirring for 48 h at room temperature, the reaction mixture
Preparation of complex 10. CO (1 bar) was bubbled into a
Preparation of complex 6. A solution of imine 3 (0.57 g, turned light red. Then the THF was transferred, and n-pentane
2.0 mmol) in 20 mL of diethyl ether was added to a solution of was used to extract the residual solid. After filtering, the product
CoMe(PMe3)4 (0.95 g, 2.5 mmol) in 40 mL of diethyl ether at (0.27 g, 56% yield) was obtained as yellowish red crystals from
À78 1C. After stirring for 24 h at room temperature, the reaction the n-pentane at 0 1C. Dec. 4136 1C. IR (Nujol mull, KBr, cmÀ1):
mixture turned red. Then the diethyl ether was transferred, and 1979, 1913 n(CQO), 1614 n(CQN), 1540 n(CQC), 951 r(PMe3).
n-pentane was used to extract the residual solid. After filtering, 1H NMR (300 MHz, C6D6, 298 K, d/ppm): 8.26 (s, 1H, CHQN),
the product (0.84 g, 85% yield) was obtained as red crystals 7.66 (d, J = 9.0 Hz, 1H, Ar-H), 7.56 (d, J = 9.0 Hz, 1H, Ar-H),
from the n-pentane at 0 1C. Dec. 4167 1C. IR (Nujol mull, KBr, 7.43 (d, J = 6.0 Hz, 1H, Ar-H), 7.21–7.17 (m, 1H, Ar-H), 7.13–7.01
cmÀ1): 1894 n(Co–H), 1602 n(CQN), 1527 n(CQC), 940 r(PMe3). (m, 2H, Ar-H), 6.55 (d, J = 24.0 Hz, 1H, Ar-H), 6.43–6.34 (m, 1H,
1H NMR (300 MHz, C6D6, 298 K, d/ppm): 9.10 (s, 1H, CHQN), Ar-H), 0.41 (d, J = 9.0 Hz, 9H, PMe3). 31P NMR (121 MHz, C6D6,
7.59–7.28 (m, 4H, Ar-H), 7.16–7.12 (m, 2H, Ar-H), 6.54–6.46 (m, 298 K, d/ppm): 9.2 (s, PMe3). 19F NMR (282 MHz, C6D6, 298 K,
1H, Ar-H), 0.64 (s, 18H, PMe3), À17.90 (t, J = 69.0 Hz, 1H, Co-H). d/ppm): À115.4 (d, J = 19.7 Hz, 1F), À123.4 to À123.6 (m, 1F),
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À129.8 (d, J = 25.4 Hz, 1F). Anal. calc. For C22H18CoF3NO2P À78 1C. After stirring for 24 h at room temperature, the reaction
(475.29 g molÀ1): C, 55.60; H, 3.82; N, 2.95. Found: C, 55.52; mixture turned light red. After filtering, the product (0.38 g,
H, 3.88; N, 2.86.
69% yield) was obtained as light red crystals from the n-pentane
Preparation of complex 11. A solution of MeI (0.22 g, at 0 1C. Dec. 4240 1C. IR (Nujol mull, KBr, cmÀ1): 1599 n(CQN),
1.5 mmol) in 10 mL of diethyl ether was added to a solution 1576, 1524 n(CQC), 943 r(PMe3). 1H NMR (300 MHz, C6D6,
of complex 4 (0.48 g, 1.0 mmol) in 40 mL of diethyl ether at 298 K, d/ppm): 8.73 (s, 1H, CHQN), 8.16 (s, 1H, Ar-H), 8.04 (d,
À78 1C. After stirring for 24 h at room temperature, the reaction J = 9.0 Hz, 1H, Ar-H), 7.65 (d, J = 6.0 Hz, 1H, Ar-H), 7.44 (m, 3H,
mixture turned light red. After filtering, the product (0.39 g, Ar-H), 7.24–7.23 (m, 1H, Ar-H), 6.55 (t, J = 9.0 Hz, 1H, Ar-H), 0.73
65% yield) was obtained as light red crystals from the n-pentane (s, 18H, PMe3). 31P NMR (121 MHz, C6D6, 298 K, d/ppm): 17.3
at 0 1C. Dec. 4248 1C. IR (Nujol mull, KBr, cmÀ1): 1599 n(CQN), (s, PMe3). 19F NMR (282 MHz, C6D6, 298 K, d/ppm): À104.1 (d,
1548, 1528 n(CQC), 944 r(PMe3). 1H NMR (300 MHz, C6D6, J = 8.5 Hz, 1F), À112.4 (d, J = 8.5 Hz, 1F). Anal. calc. For
298 K, d/ppm): 8.80–8.74 (m, 2H, CHQN and Ar-H), 8.61 (t, C23H27CoF2BrNP2 (556.25 g molÀ1): C, 49.66; H, 4.89; N, 2.52.
J = 6.0 Hz, 1H, Ar-H), 7.54 (d, J = 9.0 Hz, 1H, Ar-H), 7.45 (m, 2H, Found: C, 49.52; H, 4.78; N, 2.46.
Ar-H), 7.01 (t, J = 9.0 Hz, 1H, Ar-H), 6.76 (d, J = 9.0 Hz, 1H, Ar-H),
Preparation of complex 15. A solution of EtBr (0.16 g,
6.52–6.45 (m, 1H, Ar-H), 0.61 (t, J = 6.0 Hz, 18H, PMe3). 31P NMR 1.5 mmol) in 10 mL of diethyl ether was added to a solution
(121 MHz, C6D6, 298 K, d/ppm): 16.3 (s, PMe3). 19F NMR of complex 5 (0.48 g, 1.0 mmol) in 40 mL of diethyl ether at
(282 MHz, C6D6, 298 K, d/ppm): À103.7 (d, J = 8.5 Hz, 1F), À78 1C. After stirring for 24 h at room temperature, the reaction
À112.0 (d, J = 8.5 Hz, 1F). Anal. calc. For C23H27CoF2INP2 mixture turned light red. After filtering, the product (0.35 g,
(603.25 g molÀ1): C, 45.79; H, 4.51; N, 2.32. Found: C, 45.57; 63% yield) was obtained as light red crystals from the n-pentane
H, 4.48; N, 2.46.
at 0 1C. Dec. 4238 1C. IR (Nujol mull, KBr, cmÀ1): 1601 n(CQN),
Preparation of complex 12. A solution of MeI (0.22 g, 1578, 1541 n(CQC), 939 r(PMe3). 1H NMR (300 MHz, C6D6,
1.5 mmol) in 10 mL of diethyl ether was added to a solution 298 K, d/ppm): 8.67 (t, J = 3.0 Hz, 1H, CHQN), 8.14–8.10 (m, 1H,
of complex 5 (0.48 g, 1.0 mmol) in 40 mL of diethyl ether at Ar-H), 7.55 (d, J = 9.0 Hz, 1H, Ar-H), 7.37–7.27 (m, 3H, Ar-H),
À78 1C. After stirring for 24 h at room temperature, the reaction 7.16–7.11 (m, 1H, Ar-H), 6.88–6.82 (m, 1H, Ar-H), 6.66–6.59 (m,
mixture turned light red. After filtering, the product (0.36 g, 1H, Ar-H), 0.73 (t, J = 6.0 Hz, 18H, PMe3). 31P NMR (121 MHz,
59% yield) was obtained as light red crystals from the n-pentane C6D6, 298 K, d/ppm): 18.4 (s, PMe3). 19F NMR (282 MHz, C6D6,
at 0 1C. Dec. 4273 1C. IR (Nujol mull, KBr, cmÀ1): 1599 n(CQN), 298 K, d/ppm): À99.2 (d, J = 22.5 Hz, 1F), À121.7 (d, J = 22.6 Hz,
1575, 1540 n(CQC), 941 r(PMe3). 1H NMR (300 MHz, C6D6, 1F). Anal. calc. For C23H27CoF2BrNP2 (556.25 g molÀ1): C, 49.66;
298 K, d/ppm): 9.10–9.07 (m, 1H, CHQN), 8.66 (t, J = 6.0 Hz, 1H, H, 4.89; N, 2.52. Found: C, 49.52; H, 4.78; N, 2.46.
Ar-H), 7.55–7.43 (m, 3H, Ar-H), 6.97 (t, J = 9.0 Hz, 1H, Ar-H),
Preparation of complex 16. A solution of EtBr (0.16 g,
6.85–6.79 (m, 1H, Ar-H), 6.70 (d, J = 9.0 Hz, 1H, Ar-H), 6.55–6.49 1.5 mmol) in 10 mL of diethyl ether was added to a solution
(m, 1H, Ar-H), 0.78 (t, J = 6.0 Hz, 18H, PMe3). 31P NMR (121 MHz, of complex 6 (0.50 g, 1.0 mmol) in 40 mL of diethyl ether at
C6D6, 298 K, d/ppm): 17.5 (s, PMe3). 19F NMR (282 MHz, C6D6, À78 1C. After stirring for 24 h at room temperature, the reaction
298 K, d/ppm): À90.4 (d, J = 22.5 Hz, 1F), À121.5 (d, J = 22.6 Hz, mixture turned light red. After filtering, the product (0.42 g, 73%
1F). Anal. calc. For C23H27CoF2INP2 (603.25 g molÀ1): C, 45.79; yield) was obtained as light red crystals from the n-pentane at
H, 4.51; N, 2.32. Found: C, 45.68; H, 4.45; N, 2.27.
0 1C. Dec. 4280 1C. IR (Nujol mull, KBr, cmÀ1): 1605 n(CQN),
Preparation of complex 13. A solution of MeI (0.22 g, 1538 n(CQC), 942 r(PMe3). 1H NMR (300 MHz, C6D6, 298 K,
1.5 mmol) in 10 mL of diethyl ether was added to a solution d/ppm): 8.68–8.65 (m, 1H, CHQN), 8.36 (t, J = 3.0 Hz, 1H, Ar-H),
of complex 6 (0.50 g, 1.0 mmol) in 40 mL of diethyl ether at 7.55–7.44 (m, 3H, Ar-H), 6.97–6.90 (m, 1H, Ar-H), 6.62 (d,
À78 1C. After stirring for 24 h at room temperature, the reaction J = 6.0 Hz, 1H, Ar-H), 6.52–6.44 (m, 1H, Ar-H), 0.62 (t,
mixture turned light red. After filtering, the product (0.48 g, J = 6.0 Hz, 18H, PMe3). 31P NMR (121 MHz, C6D6, 298 K,
77% yield) was obtained as light red crystals from the n-pentane d/ppm): 17.8 (s, PMe3). 19F NMR (282 MHz, C6D6, 298 K,
at 0 1C. Dec. 4268 1C. IR (Nujol mull, KBr, cmÀ1): 1605 n(CQN), d/ppm): À117.2 (dd, J = 22.6, 5.6 Hz, 1F), À122.6 (dd, J = 28.2,
1581, 1534 n(CQC), 940 r(PMe3). 1H NMR (300 MHz, C6D6, 22.6 Hz, 1F), À126.4 (dd, J = 28.2, 5.6 Hz, 1F). Anal. calc. For
298 K, d/ppm): 9.03–9.00 (m, 1H, CHQN), 8.51 (t, J = 3.0 Hz, 1H, C23H26CoF3BrNP2 (574.24 g molÀ1): C, 48.11; H, 4.56; N, 2.44.
Ar-H), 7.55–7.43 (m, 3H, Ar-H), 6.97 (t, J = 9.0 Hz, 1H, Ar-H), Found: C, 48.22; H, 4.48; N, 2.46.
6.67 (d, J = 6.0 Hz, 1H, Ar-H), 6.51–6.44 (m, 1H, Ar-H), 0.73 (t,
Representative experimental procedure of catalytic reduction
J = 6.0 Hz, 18H, PMe3). 31P NMR (121 MHz, C6D6, 298 K, d/ppm): of aldehydes and ketones. A 25 mL Schlenk tube was charged
17.4 (s, PMe3). 19F NMR (282 MHz, C6D6, 298 K, d/ppm): À115.9 with a mixture of PhCHO (1.0 mmol), HSi(OEt)3 (1.2 mmol) and
(dd, J = 28.2, 22.6 Hz, 1F), À116.9 (dd, J = 5.6, 22.6 Hz, 1F), complex 8 (0.02 mmol) in 2 mL of THF. The reaction vessel was
À126.1 (dd, J = 28.2, 5.6 Hz, 1F). Anal. calc. For C23H26CoF3INP2 stirred at 80 1C for 4 h and reaction progress was monitored by
(621.24 g molÀ1): C, 44.47; H, 4.22; N, 2.25. Found: C, 44.38; GC. After cooling to room temperature, CH3OH (3 mL) and 10%
H, 4.48; N, 2.46.
NaOH (5 mL) were added to the tube. After stirring for 24 h at
Preparation of complex 14. A solution of EtBr (0.16 g, 60 1C, the product was extracted with Et2O (30 mL Â 2). The
1.5 mmol) in 10 mL of diethyl ether was added to a solution combined organic phases were dried over anhydrous Na2SO4,
of complex 4 (0.48 g, 1.0 mmol) in 40 mL of diethyl ether at filtered, and the solvent was evaporated under reduced pressure.
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The product was purified by column chromatography on silica References
gel (petroleum ether (60–90 1C)/ethyl acetate 5 : 1, v/v) to afford
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PhCH2OH as a colorless liquid (0.098 g, 92%).
Representative experimental procedure of catalytic reduction
of a,b-unsaturated aldehydes. A 25 mL Schlenk tube was charged
with a mixture of cinnamaldehyde (1.0 mmol), HSi(OEt)3 (1.2 mmol),
and complex 8 (0.02 mmol) in 2 mL of THF. The reaction vessel was
stirred at 80 1C for 4 h and the progress of the reaction was
monitored by TLC. After cooling to room temperature, CH3OH
(3 mL) and 10% NaOH (5 mL) were added to the tube. After stirring
for 24 h at 60 1C, the product was extracted with Et2O (30 mL Â 2).
The combined organic phases were dried over anhydrous Na2SO4,
filtered, and the solvent was evaporated under reduced pressure.
The product was purified by column chromatography on silica
gel (petroleum ether (60–90 1C)/ethyl acetate 3 : 1, v/v) to afford
cinnamyl alcohol as pale yellow crystals (0.113 g, 85.0%).
X-ray crystal structure determinations. Single crystal X-ray
diffraction data of the complexes (4, 8, 11) were collected on a
Bruker SMART Apex II CCD diffractometer equipped with
graphite-monochromated Mo Ka radiation (l = 0.71073 Å).
During collection of the intensity data, no significant decay was
observed. The intensities were corrected for Lorentz-polarization
effects and empirical absorption with the SADABS program. The
structures were resolved by direct or Patterson methods with the
SHELXS-97 program and were refined on F2 with SHELXTL. All
non-hydrogen atoms were refined anisotropically. Hydrogen
atoms were included in calculated positions and were refined
using a riding model. A residual Q peak with peak value greater
than 1 around the cobalt center was theoretically defined as a
hydrido hydrogen atom. Then the structure was constantly
refined and optimized to determine the location of the hydrido
hydrogen. CCDC 1840081(4), 1840080 (8), 1840082 (11) contain
the supplementary crystallographic data for this paper.†
¨
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Conflicts of interest
There are no conflicts to declare.
¨
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21 H. Zhou, H. Sun, S. Zhang and X. Li, Organometallics, 2015,
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Acknowledgements
This work was supported by the NSF China (no. 21372143).
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