Imine-assisted C-F bond activation using low-valent cobalt compounds supported by trimethylphosphine ligands and formation of novel organic fluorides

Article abstract of DOI:10.1039/c0dt00526f

A cyclometalation reaction involving C-F bond activation at a cobalt(i) center with an aldazine-N atom as anchoring group affords ortho-chelated cobalt(iii) complexes containing a [C-Co-F] fragment [CoFMe(PMe ₃)₂{(C₆H₃F-ortho)CHN-R}] 5-8. Under similar reaction conditions π-coordinated cobalt(0) complexes [Co(PMe ₃)₃((C₆H₃F-ortho)CHN-R)] 12-14 were formed when [Co(PMe₃)₄], instead of [CoMe(PMe ₃)₄], was applied. C-F bond activation did not occur. Carbonylation of complexes 6-8 delivered novel organic fluorides 15-17. A proposed formation mechanism of the novel organic fluorides with demetallation and carbonylation of complexes 6-8 by CO is discussed with experimental support. As important intermediates, an acetyl cobalt complex, [CoFMeCO(PMe ₃)₂{(C₆H₃F-ortho)CHN-R}] 20, and a 19-electron cobalt(0) complex, Co(CO)₃(PMe₃) ₂21, were structurally characterized. The crystal and molecular structures of complexes 5, 6, 8, 12, 20 and 21 were determined by X-ray diffraction.

Full text of DOI:10.1039/c0dt00526f

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PAPER
www.rsc.org/dalton | Dalton Transactions
Imine-assisted C–F bond activation using low-valent cobalt compounds
supported by trimethylphosphine ligands and formation of novel organic
fluorides†
Zhe Lian, Xiaofeng Xu, Hongjian Sun, Yue Chen, Tingting Zheng and Xiaoyan Li*
Received 22nd May 2010, Accepted 15th July 2010
DOI: 10.1039/c0dt00526f
A cyclometalation reaction involving C–F bond activation at a cobalt(I) center with an aldazine-N
atom as anchoring group affords ortho-chelated cobalt(III) complexes containing a [C–Co–F] fragment
[CoFMe(PMe3)2{(C6H3F-ortho)CH N–R}] 5–8. Under similar reaction conditions p-coordinated
cobalt(0) complexes [Co(PMe3)3((C6H3F-ortho)CH N–R)] 12–14 were formed when [Co(PMe3)4],
instead of [CoMe(PMe3)4], was applied. C–F bond activation did not occur. Carbonylation of
complexes 6–8 delivered novel organic fluorides 15–17. A proposed formation mechanism of
the novel organic fluorides with demetallation and carbonylation of complexes 6–8 by CO
is discussed with experimental support. As important intermediates, an acetyl cobalt complex,
[CoFMeC O(PMe3)2{(C6H3F-ortho)CH N–R}] 20, and a 19-electron cobalt(0) complex,
Co(CO)3(PMe3)2 21, were structurally characterized. The crystal and molecular structures of
complexes 5, 6, 8, 12, 20 and 21 were determined by X-ray diffraction.
the fluorinated aromatic imines 1–4. Carbonylation of complexes
1. Introduction
6–8 afforded novel organic fluorides 15–17 with demetallation. A
The activation of carbon–fluorine bonds is of great importance in
mechanism is proposed on the basis of the experimental results.
organometallic chemistry and catalyst development because this
type of reaction contributes to the fundamental understanding
2. Experimental
of the reactivity of stable bonds and the selective replacement of
fluorine atoms.1–4 There have been some reports on C–F bond
2.1 General procedures and materials
activation by first-row transition metals.5 We reported a cyclomet-
Standard vacuum techniques were used in manipulations of
volatile and air-sensitive materials. Literature methods were used
in the preparation of methyltetrakis(trimethylphosphine)cobalt(I)
and tetrakis(trimethylphosphine)cobalt(0).7 Schiff bases were ob-
tained by condensation of 2,6-difluorobenzaldehyde with amines.
Other chemicals were used as purchased. Infrared spectra (4000–
400 cm-1), as obtained from Nujol mulls between KBr disks, were
recorded on a Nicolet 5700. 1H and 31P NMR (300 and 121
MHz respectively) spectra were recorded on a Bruker Avance 300
spectrometer. 31P NMR resonances were obtained with broadband
proton decoupling. Melting points were measured in capillaries
sealed under argon and are uncorrected. X-Ray crystallography
was performed with a Bruker Smart 1000 diffractometer. MS
were obtained from Agilent 6510 Accurate-Mass Q-TOF LC/MS
system
alation reaction involving carbon–fluorine bond activation at a
cobalt(I) center with an azine donor as anchoring group which,
for the first time, afforded an ortho-chelated cobalt(III) complex
containing a [C–Co–F] fragment (eqn (1)).6
(1)
Herein we report on progress in the research of cyclometalation
reactions involving C–F bond activation at electron-rich low valent
cobalt centers with imine as pre-chelate ligands. The novel cobalt
complexes 5–8 containing the [C–Co–F] fragment formed by
oxidative addition of an aromatic C–F bond to cobalt(I) centers
were isolated and characterized. p-Coordinated imine cobalt(0)
complexes 12–14 were obtained by reactions of Co(PMe3)4 with
2.2 Syntheses
Complex 5.
A solution of 1.07 g (2.83 mmol) of
[CoMe(PMe3)4] in 30 mL of pentane was combined with a solution
of 1 0.59 g (2.83 mmol) in 20 mL of pentane at -80 ◦C. The
reaction mixture was allowed to warm to ambient temperature
and stirred for 18 h. During this period, the reaction mixture
turned yellow–brown in color. After filtering, the solid residue was
extracted with diethyl ether (40 mL). Crystallization from pentane
and diethyl ether at 4 ◦C yielded red single crystals 5 suitable for X-
ray structure analysis. Yield: 0.38 g (35.3%). Decomp. >135 ◦C. IR
(Nujol): 1595 n(C N), 1581, 1567 n(C C), 940 n(PMe3) cm-1.
School of Chemistry and Chemical Engineering, Shandong University,
Shanda Nanlu 27, 250100, Jinan, People’s Republic of China. E-mail:
xli63@sdu.edu.cn; Fax: +86 531 88361350
† CCDC reference numbers 761542 (5), 761539 (6), 761538 (8), 761541
(12), 761540 (20) and 761543 (21). For crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0dt00526f
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The Royal Society of Chemistry 2010
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1H NMR (300 MHz, C6D6, 296 K): d 0.64 (m, 3H, CH3), 0.80 (br,
18H, PCH3), 3.46 (br, 3H, CH3), 6.50–7.50 (m, 3H, Ar–H), 8.46 (s,
1H, CH N). 31P NMR (121 MHz, C6D6, 300 K): d 28.9 s. Anal.
Calc. for C15H28CoF2NP2: C 47.25, H 7.40, N 3.67%. Found: C
47.01, H 7.67, N 3.46%.
6.9–7.4 (m, 8H, Ar–H), 8.83 (s, 1H, CH N). Anal. Calc. for
C15H12FNO: C 74.68, H 5.01, N 5.81%. Found: C 74.49, H 5.03,
N 5.55%.
Complexes 16 and 17 were synthesized according to the method
given above for 15.
Complexes 6–8 were synthesized according to the method given
above for 5.
Complex 16. Yield: 62.4%. IR (Nujol): 1699 n(C O), 1624
n(C N), 1557 n(C C) cm-1. 1H NMR (300 MHz, C6D6, 296 K):
d 2.86 (s, 3H, CH3), 6.99–8.32 (m, 10H, Ar–H), 8.97 (s, 1H,
CH N). Anal. Calc. for C19H14FNO: C 78.34, H 4.84, N 4.81%.
Found: C 78.48, H 5.01, N 4.73%.
Complex 6. Yield: 38.6%. Decomp. >135 ◦C. IR (Nujol): 1592
n(C N), 1566 n(C C), 945 n(PMe3) cm-1. 1H NMR (300 MHz,
C6D6, 296 K): d 0.64 (m, 3H, CH3), 0.81 (br, 18H, PCH3), 6.59–
8.04 (m, 8H, Ar–H), 9.10 (s, 1H, CH N). 31P NMR (121 MHz,
C6D6, 300 K): d 31.0 s. Anal. Calc. for C20H30CoF2NP2: C 54.18,
H 6.82, N 3.16%. Found: C 54.01, H 7.12, N 3.46%.
Complex 17. Yield: 72.1%. IR (Nujol): 1699 n(C O), 1624
n(C N), 1557 n(C C) cm-1. 1H NMR (300 MHz, C6D6, 296 K):
d 2.37 (s, 3H, Ar–CH3), 2.70 (s, 3H, –COCH3), 6.99–8.32 (m, 7H,
Ar–H), 8.97 (s, 1H, CH N). Anal. Calc. for C16H14FNO: C 75.28,
H 5.53, N 5.49%. Found: C 75.47, H 5.33, N 5.56%.
Complex 7. Yield: 46.1%. Decomp. >128 ◦C. IR (Nujol): 1597
n(C N), 1567 n(C C), 946 n(PMe3) cm-1. 1H NMR (300 MHz,
C6D6, 296 K): d 0.64 (m, 3H, CH3), 0.82 (m, 18H, PCH3), 6.10–
8.50 (m, 10H, Ar–H), 8.58 (s, 1H, CH N). 31P NMR (121 MHz,
C6D6, 300 K): d 30.5 s. Anal. Calc. for C24H32CoF2NP2: C 58.42,
H 6.54, N 2.84%. Found: C 58.11, H 6.82, N 3.00%.
Complexes 21 and 20. A solution of 1.52 g (3.32 mmol) of
complex 8 in pentane was stirred under 1 atm of CO for 3 h.
Complex 21 as yellow crystals was obtained from the yellow
filtrate at -20 ◦C. Yield: 0.32 g (65%). IR (Nujol): 2095, 1969,
1924 n(CO), 947 n(PMe3) cm-1. Anal. Calc. for C9H18CoO3P2:
C 45.77, H 7.68. Found: C 45.47, H 7.73%. At the same time
a few fine red crystals of intermediate 20 were separated from
the mother-liquor. The molecular structure of 20 was confirmed
through X-ray diffraction.
Complex 8. Yield: 30.4%. Decomp. >120 ◦C. IR (Nujol): 1603
n(C N), 1565 n(C C), 938 n(PMe3) cm-1. 1H NMR (300 MHz,
C6D6, 296 K): d 0.64 (m, 3H, CH3), 0.82 (m, 18H, PCH3), 2.09 (3H,
CH3), 6.10–8.50 (m, 7H, Ar–H), 9.01 (s, 1H, CH N). 31P NMR
(121 MHz, C6D6, 300 K): d 30.9 s. Anal. Calc. for C21H32CoF2NP2:
C 55.15, H 7.05, N 3.06%. Found: C 55.01, H 7.12, N 3.26%.
2.3 X-Ray structure determinations
Complex 12. A solution of 1.00 g (2.75 mmol) of [Co(PMe3)4]
in 30 mL of pentane was combined with a solution of 2 0.60 g
(2.75 mmol) in 20 mL of pentane at -80 ◦C. The reaction mixture
was allowed to warm to ambient temperature and stirred for 18 h.
During this period, the reaction mixture turned yellow–brown in
color. After filtering, the solid residue was extracted with diethyl
ether (40 mL). Crystallization from pentane at 4 ◦C yielded red–
brown single crystals 12 suitable for X-ray structure analysis. Yield:
0.48 g (30.4%). Decomp. >130 ◦C. IR (Nujol): 1624 n(C N), 1581
n(C C), 945 n(PMe3) cm-1. Anal. Calc. for C22H36CoF2NP3: C
52.39, H 7.19, N 2.78%. Found: C 52.03, H 7.12, N 3.05%.
Complexes 13 and 14 were synthesized according to the method
given above for 12.
Intensity data were collected on a Bruker SMART diffractometer
with graphite-monochromated Mo-Ka radiation (l = 0.71073
˚
A). Crystallographic data for complexes 5, 6, 8, 12, 20 and 21
are summarized in Table 1. The structures were solved by direct
methods and refined with full matrix least-squares on all F2
(SHELXL-97) with non-hydrogen atoms anisotropic.
3. Results and discussion
3.1. Reactions of [CoMe(PMe3)4] with fluorinated benzalimines
Reactions of [CoMe(PMe3)4] with ortho-fluorinated substrates
(1–4) containing an imine donor as anchoring group proceed
by oxidative addition of the C–F bond to give rise to the
ortho-metalated diorganocobalt(III) fluorides 5–8 (eqn (2)). Initial
coordination of the N-donor appears to be the key step. With
the HC N-moiety as an anchoring group the oxidative addition
reactions of the C–F bond at cobalt centers are favored by the
chelate effect. Stable diorganocobalt(III) complexes 5–8 with [C–
Co–F] fragments were isolated and characterized.
Complex 13. Yield: 37.5%. Decomp. > 153 ◦C. IR (Nujol):
1625 (C N), 1557 (C C), 946 (PMe3) cm-1. Anal. Calc. for
C26H38CoF2NP3: C 56.32, H 6.91, N 2.53%. Found: C 56.01, H
7.03, N 2.56%.
Complex 14. Yield: 31.3%. Decomp. > 120 ◦C. IR (Nujol):
1622 (C N), 1570 (C C), 945 (PMe3) cm-1. Anal. Calc. for
C23H38CoF2NP3: C 53.29, H 7.39, N 2.70%. Found: C 53.01, H
7.33, N 2.66%.
Complex 15. A solution of 1.00 g (2.26 mmol) 6 in 50 mL of
pentane was stirred under 1 atm of CO for 24 h. The solution
was filtered, freezing at 4 ◦C afforded 0.07 g of orange crystals
of Co(CO)3(PMe3)2. The solution was washed with 100 mL of
saturated solution of NH4Cl and dried over anhydrous magnesium
in air. Column chromatographic separation using petroleum
ether–ethyl acetate as eluent leads to analytically pure 15. Yield:
59%. IR (Nujol): 1699 n(C O), 1624 n(C N), 1557 n(C C)
1
cm-1, H NMR (300 MHz, C6D6, 296 K): d 2.71 (s, 3H, CH3),
(2)
9524 | Dalton Trans., 2010, 39, 9523–9529
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Table 1 Crystallographic data for complexes 5, 6, 8, 12, 20 and 21
5
6
8a
12
20b
21
Formula
C15H28CoF2NP2
0.17 ¥ 0.16 ¥ 0.12
381.25
Orthorhombic
Cmc21
13.136(12)
12.813(17)
11.417(10)
90
90
90
1921.6
4
1.318
C20H30Co F2NP2
0.30 ¥ 0.28 ¥ 0.25
443.32
C47H64CoF4N3P2
0.15 ¥ 0.15 ¥ 0.10
867.88
Monoclinic
P21/c
12.7602(13)
22.376(2)
17.1926(18)
90
102.235(7)
90
4797.3(8)
4
1.202
C22H36CoF2NP3
0.23 ¥ 0.15 ¥ 0.14
504.36
Monoclinic
P21/n
8.5130(17)
16.009(3)
18.999(4)
90
94.35(3)
90
2581.8(9)
4
C22H34CoF2NO2P2
0.35 ¥ 0.32 ¥ 0.28
503.39
Monoclinic
P21/n
8.9511(6)
31.208(2)
9.0569 (2)
90
95.8310(10)
90
2516.9(3)
4
1.328
C9H18CoO3P2
0.15 ¥ 0.15 ¥ 0.10
295.12
Orthorhombic
Pnma
9.9363(7)
10.6261(8)
13.7536(9)
90
Size/mm3
Mr/g mol-1
Crystal system
Space group
Triclinic
¯
P1
˚
a/A
8.7532(18)
13.961(3)
18.876(4)
87.60(3)
89.85(3)
75.58(3)
2232.0(8)
4
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
90
90
3
˚
V/A
1452.16(18)
4
1.350
1.389
8191
1756
83
Z
Dc/g cm-3
m/mm-1
1.319
0.932
36864
10236
1.298
0.870
6781
4795
1.070
10489
2273
120
0.473
22121
8448
514
0.841
12455
4428
324
Rflns collected
Indep. rflns
Parameters
483
272
Rint
0.0440
27.53
0.0232 0
0.0584
0.985
0.0205
27.54
0352 0
0.0991
1.020
0.0329
25.05
0474 0
0.1416
0.0729
27.14
0699
0.2035
0.984
0.0374
25.00
0.0555
0.1591
0.0353
27.68
0.0307
0.0796
1.024
◦
qmax
/
R1 (I > 2s(I))
wR2 (all data)
GOF
1.047
1.019
a Diamine–pentane solvate. b Water solvate.
Complexes 5–8 were isolated from the pentane or diethyl ether
solutions as red crystals in yields of 30–40%. In the infrared
spectra of complexes 5–8, the characteristic n(C N) bands are
found in the region of 1592–1603 cm-1. The imine-H proton
resonances of 5–8 are recorded at 8.46–9.70 ppm, while Co-methyl
protons resonate between 0.30–0.37 ppm. All spectroscopic data
are compatible with an octahedral configuration around the cobalt
atom in solution, consisting of a P–Co–P axis and equatorial
coordination of C, C, F and N donor atoms. The crystal structures
of complexes 5, 6 and 8 were elucidated by X-ray diffraction
analysis.
The molecular structures of complexes 5, 6 and 8 (Fig. 1, 2 and
3) confirm the octahedral coordination geometry of cobalt. A five-
membered metallacycle is formed through the coordination of the
N atom of the imine group and the ortho-chelated C atom. The sum
of internal bond angles (540◦) of this chelate ring indicates ideal
planarity. Typically, the F atom is trans-oriented to the phenyl-C
atom, which is well understood in terms of mutual trans-influence.
The bite angle of the chelating ligand in complex 6 (C26–Co1–N2
83.29(8)◦) is close to those in complexes 5 (C1–Co1–N2 83.17(11)◦)
and 8 (C1–Co1–N1 83.36(12)◦), but significantly larger than that
found in a related compound,8 The two axial trimethylphosphine
ligands are slightly displaced (P2–Co1–P1 173.91(3)◦) towards the
Co–methyl group for steric reasons. The C N bond lengths (N2–
Fig. 1 Molecular structure of 5 with 30% probability ellipsoids. A-labelled
atoms are related to the corresponding atoms by the symmetry operation
◦
˚
(1 - x, +y, +z). Selected bond distances (A) and angles ( ): N2–Co1
1.966(2), P1–Co1 2.2068(5), F200–Co1 1.9285(14), Co1–P1A 2.2068(5),
C1–Co1 1.906(3), C100–Co1 2.016(3), C7–N2 1.284(3), C1–C2 1.418(3);
C1–C2–C7 114.7(2), P1–Co1–P1 173.51(4), F200–Co1–C100 89.77(12),
C1–Co1–N2 83.17(11), C7–N2–Co1 115.62(18), C2–C1–Co1 112.07(19),
N2–C7–C2, 114.5(2), N2–Co1–C100 178.91(13).
˚
˚
˚
C7 1.284(3) A, 5; N2–C23 1.294(3) A, 6 and N1–C7 1.290(4) A,
˚
8) are comparable with that (1.293(8) A) in the ortho-metalated
cobalt(III) fluoride,6 but a bit larger than in the uncoordinated
˚
these three complexes (Co1–C100 2.016(3) A, 5; Co1–C3 2.004(2)
˚
˚
imine molecules.
The Co–F bond lengths in complex 5 (Co1–F200 1.9285(14) A)
and in complex 6 (Co1–F3 1.926(1) A) are shorter than in complex
8 (Co1–F1 1.9584(17) A). Co–Cphenyl bond lengths in complex 5
A, 6 and Co1–C14 2.004(3) A, 8) because of the trans-influence of
the fluorine atoms with strong electron-withdrawing ability. There
are two independent molecules in the asymmetric unit and only
one of them is shown in Fig. 2.
˚
˚
˚
˚
˚
(Co1–C1 1.906(3) A), 6 (Co1–C26 1.910(2) A) and 8 (Co1–C1
CoMe(PMe3)4 did not react with fluoroaromatic imines (9, 10
and 11) that contain bulky groups at the imine–N atom (eqn (3)).
˚
1.899(3) A) are remarkably shorter than Co–Cmethyl bond lengths in
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(3)
3.2. Reaction of Co(PMe3)4 with fluorinated benzalimine
When Co(PMe3)4 instead of CoMe(PMe3)4 was used under similar
reaction conditions, no C–F activation was observed via route a
of Scheme 1. Unexpectedly the p-coordinated cobalt(0) complexes
12–14 were obtained (route b, Scheme 1).
Fig. 2 Molecular structure of 6 with◦ 30% probability ellipsoids, se-
˚
lected bond lengths (A) and angles ( ): C26–Co1 1.910(2), Co1–F3
1.926(1), C3–Co1 2.004(2), Co1–N2 2.040(2), Co1–P1 2.214(1),
Co1–P2 2.212(1), N2–C23 1.294(3), C24–C26 1.414(3); C26–Co1–F3
175.29(1), C26–Co1–C3 96.88(10), F3–Co1–C3 87.72(9), C23–N2–Co1
112.06(13), N2–C23–C24 116.90(18), C26–Co1–N2 83.29(8), F3–Co1–N2
92.11(6), P1–Co1–P2 173.91(3), C26–C24–C23 115.12(17), C24–C26–Co1
112.57(14).
Scheme 1 Preparation of p-coordinated cobalt(0) complexes 12–14.
The reaction of N-phenyl-2,6-difluorobenzalimine 2 with
Co(PMe3)4 afforded complex 12 as brown–red crystals (from
◦
pentane solution at 0 C). Complex 12 is paramagnetic and was
characterized by single-crystal X-ray diffraction.
Complex 12 has a tetrahedral coordination geometry with
a p-coordinated imine (C7–N1) group and three s-coordinated
trimethylphosphine ligands with normal Co–P distances (Fig. 4)
which makes complex 12 a formal cobalt(0) complex. The Co1–
Fig. 3 Molecular structure of 8 with 30% probability ellipsoids, only
one of the three components in the crystal cell is shown. Selected bond
˚
N1 distance (1.919(4) A) is a bit shorter than Co1–C7 distance
◦
˚
lengths (A) and angles ( ): Co1–C1 1.899(3), Co1–F1 1.9584(17), Co1–C14
2.004(3), Co1–N1 2.047(2), Co1–P2 2.2157(10), Co1–P1 2.2234(10),
N1–C7 1.290(4), C2–C7 1.429(4); N1–Co1–P2 92.43(7), N1–Co1–P1
93.92(7), P2–Co1–P1 173.60(4), F1–Co1–N1 92.43(8), C1–Co1–C14
94.98(16), C1–Co1–N1 83.36(12), C7–N1–Co1 111.5(2), C2–C1–Co1
112.6(2), C1–C2–C7 115.2(3), N1–C7–C2 117.3(3).
˚
(2.015(4) A) as expected for the smaller covalent radius of the
nitrogen atom. Owing to the p-coordination of C N, the C
N
˚
bond length (N1–C7 1.396(5) A) is remarkably longer than those
in the complexes 5, 6 and 8 (average: 1.289 A) and is between a
˚
C–N single bond and C N double bond, while s-N coordination
of the C N group is indicated in complexes 5, 6 and 8.
Compared with the reaction of Co(PMe3)4 and N-phenyl-
2-chlorobenzalimine, in which C–Cl bond activation occurred
with the formation of a five-membered chelate ring,9 no C–F
cleavage was observed (Scheme 1). Because the C–F bond energy
is larger than that of C–Cl bond, the coordination of nitrogen
It is proposed that the spatial hindrance of the bulky groups makes
the coordination of nitrogen atom to cobalt centre difficult. This
coordination is a necessary pre-condition for the activation and
cleavage of the C–F bond.
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3.3. Formation of novel organic fluorides with demetallation and
carbonylation of complexes 6–8 by CO
The carbonylation of aryl chlorides and bromides is of particular
interest. In these carbonylations carbon monoxide is widely used as
a cheap and readily available reagent for C–C coupling reaction.10
Pentane solutions of complexes 6–8 were stirred under 1 bar of
CO for 24 h (eqn (4)). After work-up, column chromatographic
separation using petroleum ether–ethyl acetate as eluent led to
organic fluorides 15–17. Compounds 15–17 were characterized by
IR, NMR and MS. Co(CO)3(PMe3)2 was confirmed by single-
crystal X-ray diffraction.
(4)
Fig. 4 Molecular structure of 12 with 30% probability ellipsoids, Selected
◦
˚
bond lengths (A) and angles ( ): N1–Co1 1.919(4), Co1–C7 2.015(4),
Co1–P2 2.1933(14), Co1–P3 2.2338(16), Co1–P4 2.2093(14), N1–C7
1.396(5); N1–Co1–C7 41.47(16), N1–Co1–P2 138.04(11), C7–Co1–P2
102.92(12), N1–Co1–P3 107.47(13), C7–Co1–P3 100.39(14), P2–Co1–P3
99.28(6), N1–Co1–P4 102.69(12), C7–Co1–P4 142.35(13), P2–Co1–P4
102.16(6), P3–Co1–P4 102.75(6).
A proposed mechanism is described in Scheme 2. Substitution
of one trimethylphosphine ligand by a carbonyl ligand is likely
to be the first step. Subsequent insertion of the carbonyl ligand
into the Co–methyl bond gives an acetyl cobalt complex as an
important intermediate. With complex 8 the intermediate 20, an
acetyl cobalt complex, was isolated and structurally characterized
(Fig. 5). The novel organic fluorides 15–17 form through reductive
elimination with C, C-coupling. The unstable cobalt(I) complex,
[Co(CO)2(PMe3)2F], disproportionates to insoluble cobalt diflu-
oride and the soluble cobalt(0) complex Co(CO)3(PMe3)2 (21).
Complex 21 was structurally characterized by X-ray single-crystal
diffraction (Fig. 6). The characterization of [CoF2]n was not
successful.
atom and the formation of the chelate ring can not compensate
the energy, which is necessary for the C–F bond cleavage. In
addition, the p-coordination of C N to cobalt(0) centre makes
a great contribution to the backbonding which is beneficial for
the stability of complexes 12–14. The p-coordinated cobalt(0)
complexes 12–14 are likely to be kinetic products, compared with
the expected cyclometalated products that arise from C–F bond
activation.
Under similar conditions complex 13 and 14 were isolated
through the reaction of 3 and 4 with Co(PMe3)4. In the IR spectra
the n(C N) vibrations for complexes 13 (1625 cm-1) and 14
(1622 cm-1) are comparable with that of complex 12 (1624 cm-1).
Scheme 2 Proposed formation mechanism for organic fluorides 15–17.
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The crystal of complex 21 belongs to the Pnma space group
in the orthorhombic crystal system with D3h symmetry for the
molecular structure. Co(CO)3(PMe3)2 has a trigonal bipyramidal
configuration with two axial trimethylphosphine ligands, while
three carbonyl ligands are oriented in the equatorial plane.
From the axial view the two trimethylphosphine ligands are in
eclipsed conformation, while three carbonyl ligands are located
in staggered positions with respect to the two axial phosphine
ligands. The bond angle of P–Co–P is 178.97(4)◦. The Co–C and
carbonyl C O bond lengths are in the normal region.11
Complex 21 is a neutral complex with cobalt in zero oxidation
state.12–14 To our knowledge, this is one of a small number of five-
coordinated 19-electron cobalt(0) complexes without support of
a chelate ligand or other auxiliary reagent.12,13 Zhuang reported a
19-electron cobalt(0) complex, Co(CO)2(PPh3)2(CO–BEt3), which
is stabilized by terminal linking of the carbonyl ligand to
BEt3.11 Tyler presented a formal 19-electron cobalt(0) complex,
Co(CO)3L2 (L2 = 2,3-bis(diphenylphosphino)maleic anhydride),
which was referred to as an (18 + d) cobalt(0) complex and was
applied as a catalyst in cyclooligomerization of acetylenes.13 The
IR bands at 2095, 1969 and 1924 cm-1 of complex 21 are assigned
to the C O stretches, by comparison to those of Co(CO)3L2
complexes.15
Fig. 5 Molecular structure of 20 with 30% probability ellipsoids,
the water molecule in the crystal cell is omitted for the clar-
◦
˚
ity. Selected bond lengths (A) and angles ( ): Co01–F1 1.928(3),
Co01–C007 1.930(4), Co01–N1 2.092(3), Co01–P1 2.2115(15), Co01–P2
2.2162(17), Co01–C016 1.904(5), C012–N1 1.275(5), C010–C012
1.435(6), C10–N1 1.438(5), C016–O1 1.194(5), C016–C025 1.541(7);
N1–Co01–C007 82.5(7), N1–C012–C010 117.5(4), P1–Co1–P2 173.49(6),
F1–Co01–C007 170.78(15), N1–Co01–C016 178.56(18), C025–C016–O1
115.2(5), Co01–C016–O1 127.7(4), Co01–C016–C025 117.2(4).
4. Conclusion
A cyclometalation reaction involving C–F bond activation at a
cobalt(I) center with aldazine–N atom as an anchoring group
affords ortho-chelated cobalt(III) complexes containing a [C–
Co–F] fragment [CoFMe(PMe3)2{(C6H3F-ortho)CH N–R}] 5–
8. Under similar reaction conditions p-coordinated cobalt(0) com-
plexes [Co(PMe3)3((C6H3F-ortho)CH N–R)] 12–14 were formed
when [Co(PMe3)4], instead of [CoMe(PMe3)4], was applied. No
C–F bond activation was then observed. Carbonylation of
complexes 6–8 delivered novel organic fluorides 15–17 with
demetallation. As important intermediates, an acetyl cobalt
complex, [CoFMeC O(PMe3)2{(C6H3F-ortho)CH N–R}] 20,
and a cobalt(0) complex, Co(CO)3(PMe3)2 19, were structurally
characterized by X-ray diffraction. The crystal and molecular
structures of complexes 5, 6, 8, 12, 20 and 21 were determined
by X-ray diffraction.
Acknowledgements
We gratefully acknowledge support by NSF China No.
20972087/20772072. and kind assistance from Prof. Dr Dieter
Fenske (Karlsruhe, Germany) for X-ray diffraction analysis.
Fig. 6 Molecular structure of 21 with 30% probability ellipsoids. A-la-
belled atoms are related to the corresponding atoms by the symmetry
◦
˚
operation (+x, 1/2 - y, +z). Selected bond lengths (A) and angles ( ):
C1–O1 1.114(3), C1–Co1 1.843(3), Co1–C1A 1.843(3), Co1–P3 2.1825(9),
Co1–P2 2.1908(9), C2–Co1 1.762(4), O2–C2 1.129(4); C1–Co1–C1A
115.69(16), C2–Co1–C1 122.15(8), C2–Co1–C1A 122.15(8), P3–Co1–P2
178.97(4), O1–C1–Co1 178.5(2), O2–C2–Co1 180.0(4).
Notes and references
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