Selective C-F/C-H bond activation of fluoroarenes by cobalt complex supported with phosphine ligands

Article abstract of DOI:10.1039/c3dt33074e

The reactions of pentafluoropyridine C₅NF₅, hexafluorobenzene C₆F₆, and perfluoronaphthalene C ₁₀F₈ with cobalt(0) complex, Co(PMe₃) ₄, were investigated. The Co(i) complexes (4-C₅NF ₄)Co(PMe₃)₃ (1), (C₆F ₅)Co(PMe₃)₃ (2), (C₁₀F ₇)Co(PMe₃)₃ (3), (4-C₅NF ₄)Co(PMe₃)₄ (4) and (C₁₀F ₇)Co(PMe₃)₄ (6) were obtained by selective activation of the C-F bonds. The reactions of 1 and 2 with CO afforded dicarbonyl cobalt(i) complexes (4-C₅NF₄)Co(CO) ₂(PMe₃)₂ (7), (C₆F ₅)Co(CO)₂(PMe₃)₂ (8). Under similar reaction conditions, 2 as a C-H bond activation product was obtained from the reaction of pentafluorobenzene, C₆F₅H, with Co(PMe ₃)₄. The byproducts, hydrodefluorination product 1,2,4,5-C₆F₄H₂ and F₂PMe₃ from the reaction of C₆F₅H and Co(PMe₃) ₄ were also observed. The reaction mechanism of C₆F ₅H with Co(PMe₃)₄ is proposed and partly-experimentally verified. The reaction of C₆F₅H with Co(PMe₃)₄ under 1 bar of CO at room temperature afforded hydrido dicarbonyl cobalt(ii) complex (C₆F₅)Co(H)(CO) ₂(PMe₃)₂ (11). Treatment of the mixtures of C₆F₅H/Co(PMe₃)₄ with hexachlorobenzene, C₆Cl₆, resulted in (C₆F ₅)CoCl(PMe₃)₃ (12) via C-H bond cleavage with the hydrodechlorination product pentachlorobenzene, C₆Cl ₅H, and 1,2,4,5-tetrachlorobenzene, C₆Cl₄H ₂. The structures of complexes 1, 2, 6, 7, 8, 11 and 12 were determined by X-ray diffraction.

Full text of DOI:10.1039/c3dt33074e

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Selective C–F/C–H bond activation of fluoroarenes by
cobalt complex supported with phosphine ligands†
Cite this: Dalton Trans., 2013, 42, 5740
Junye Li,a Tingting Zheng,a,b Hongjian Sun,a Wengang Xua and Xiaoyan Li*a
The reactions of pentafluoropyridine C5NF5, hexafluorobenzene C6F6, and perfluoronaphthalene C10F8
with cobalt(0) complex, Co(PMe3)4, were investigated. The Co(I) complexes (4-C5NF4)Co(PMe3)3 (1),
(C6F5)Co(PMe3)3 (2), (C10F7)Co(PMe3)3 (3), (4-C5NF4)Co(PMe3)4 (4) and (C10F7)Co(PMe3)4 (6) were
obtained by selective activation of the C–F bonds. The reactions of 1 and 2 with CO afforded dicarbonyl
cobalt(I) complexes (4-C5NF4)Co(CO)2(PMe3)2 (7), (C6F5)Co(CO)2(PMe3)2 (8). Under similar reaction con-
ditions, 2 as a C–H bond activation product was obtained from the reaction of pentafluorobenzene,
C6F5H, with Co(PMe3)4. The byproducts, hydrodefluorination product 1,2,4,5-C6F4H2 and F2PMe3 from
the reaction of C6F5H and Co(PMe3)4 were also observed. The reaction mechanism of C6F5H with
Co(PMe3)4 is proposed and partly-experimentally verified. The reaction of C6F5H with Co(PMe3)4 under 1
bar of CO at room temperature afforded hydrido dicarbonyl cobalt(II) complex (C6F5)Co(H)(CO)2(PMe3)2
(11). Treatment of the mixtures of C6F5H/Co(PMe3)4 with hexachlorobenzene, C6Cl6, resulted in (C6F5)-
CoCl(PMe3)3 (12) via C–H bond cleavage with the hydrodechlorination product pentachlorobenzene,
C6Cl5H, and 1,2,4,5-tetrachlorobenzene, C6Cl4H2. The structures of complexes 1, 2, 6, 7, 8, 11 and 12
were determined by X-ray diffraction.
Received 17th October 2012,
Accepted 27th January 2013
DOI: 10.1039/c3dt33074e
www.rsc.org/dalton
C–F bond activation of pentafluorobenzene with a rhodium
1. Introduction
complex at room temperature.25 Recently, substantial progress
More and more fluorinated organic compounds have been has been achieved in the field of C–F bond activation and func-
applied in agriculture, leather, pharmaceutical and materials tionalization by transition metal complexes as catalysts.26–35
as well as some other industrial branches because they have Braun disclosed that the Heck cross coupling of pentafluoro-
excellent stability and some special physical and chemical pyridine was catalyzed by the C–F bond activation product of
properties.1–9 However, how to prepare efficiently polyfluori- pentafluoropyridine with Pd(II) complex supported by phos-
nated or partly-fluorinated organic compounds is still a chal- phine ligands.29 Love developed a method for the catalytic
lenge though some fluorinated methods have been developed. methylation of some polyfluoroaryl imines in high yields and
The selective C–F/C–H bond activation and functionalization of high selectivity utilizing platinum and nickel complexes.30
polyfluoro organic compounds with transition metal complexes Radius described the cross coupling reactions of perfluoro-
have gradually become an effective way to obtain the desired toluene and perfluorobiphenyl with N-heterocyclic carbene
fluorinated organic compounds.10–15 Since the mid-1990s, the (NHC) nickel complexes as the catalyst and the catalytic hydro-
activation of the C–F bond by transition metal complexes has defluorination with silanes as the hydrogen source.31,32
attracted more attention to explore effective synthesis of novel
In comparison with the studies on C–F bond activation and
organic fluorides and to develop the synthetic methodology of functionalization by nickel36 and iron15 complexes, few studies
organic fluorides via defluorination of polyfluorinated organic on C–F bond activation and functionalization with cobalt com-
compounds.16–24 Milstein reported the first example of catalytic plexes were published. Holland studied the C–F bond acti-
vation of fluorobenzene by low-coordinate cobalt complex.33
We reported the first organo cobalt(III) fluoride containing a
aSchool 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 88564464
[C–Co–F] fragment through a cyclometalation reaction invol-
ving C–F bond cleavage at a cobalt(I) center using azine as an
anchoring group.37 A synergistic effect of low-valent cobalt
complex and trimethylphosphine ligand on selective C–F bond
activation of perfluorinated toluene was explored affording a
mono-(C–F) bond cleavage product and the double-(C–F) bond
cleavage product, a benzyne cobalt complex (eqn (1)).38
bDepartment of Chemistry, Capital Normal University, 100037 Beijing, People’s
Republic of China
†Electronic supplementary information (ESI) available. CCDC 871947–871950,
846414, 718812 and 871951. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c3dt33074e
5740 | Dalton Trans., 2013, 42, 5740–5748
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(282 MHz, benzene-d6, 300 K): δ −91.4 (s, 2F), −140.0 (s, 2F).
Dec. 265 °C.
ð1Þ
Synthesis of complex 2
A solution of C6F6 (0.72 g, 3.90 mmol) in 30 mL of THF was
combined with a solution of Co(PMe3)4 (1.41 g, 3.90 mmol) in
THF (30 mL) at −80 °C. The reaction mixture was warmed to
ambient temperature and stirred for 30 h. During this period
the pale yellow mixture turned brown-yellow in color. The vola-
tiles were transferred under vacuum and the residue was
extracted with pentane (40 mL) and diethyl ether (50 mL),
respectively. Crystallization from pentane and diethyl ether at
−4 °C afforded green single crystals of 2 (0.90 g, 51.0%). Analy-
sis for 2, C15H27CoF5P3, 454.21 g mol−1, [found (calcd)]: C,
39.87 (39.66); H, 5.90 (5.99). IR (Nujol, cm−1): 1624 s, 1598 s,
ν(CvC); 947 vs., ν(PMe3). Dec. 220 °C.
In this paper we report the recent results of our study on
C–F bond activation and C–H bond activation of polyfluori-
nated aromatic compounds by tetrakis(trimethylphosphine)-
cobalt(0), Co(PMe3)4. The investigation was extended to C5NF5,
C6F6, C10F8, and C6F5H. The reaction mechanism of C6F5H
with Co(PMe3)4 via selective C–H bond activation is proposed
and partly-experimentally verified.
2. Experimental section
General procedures and materials
Synthesis of complexes 3 and 6
Standard vacuum techniques were used in manipulations of
volatile and air sensitive materials. Solvents were dried by
known procedures and distilled under nitrogen before use. Lit-
erature methods were used in the preparation of Co(PMe3)4.39
C5NF5, C6F6, C6F5H and C10F8 were obtained from ABCR. All
other chemicals were used as purchased. Infrared spectra
(4000–400 cm−1), as obtained from Nujol mulls between KBr
disks, were recorded on a Bruker ALPHA FT-IR Spectrometer.
The in situ IR was carried out on a METTLER TOLEDO React
IR IC 15. 1H, 13C, 31P and 19FNMR spectra (300, 75, 121 and
282 MHz, respectively) were recorded on a Bruker Avance 300
spectrometer. 13C and 31P NMR resonances were obtained with
broadband proton decoupling. X-ray crystallography was per-
formed with a Bruker Smart 1000 diffractometer. Elemental
analyses were carried out on an Elementar Vario EL III.
Melting points were measured in capillaries sealed under
argon and are uncorrected. GC-MS were recorded on a
TRACE-DSQ.
At −78 °C, Co(PMe3)4 (0.90 g, 2.46 mmol) was added into a solu-
tion of C10F8 (0.67 g, 2.46 mmol) in 30 mL of pentane. After
stirring for 18 h at room temperature the solution turned to
red from brown. Crystallization from the filtrate at −30 °C
afforded green crystals of 3 (0.47 g, 35.0%). Analysis for 3,
C19H27CoF7P3, 540.26 g mol−1, [found (calcd)]: C, 42.02
(42.24); H, 5.30 (5.04). IR (Nujol, cm−1): 1651 s, 1620 s, 1588 s,
ν(CvC); 935 vs., ν(PMe3). m.p.: 85 °C. The deep red single crys-
tals of 6 (0.82 g, 54.0%) were obtained by concentration of the
mother solution. Analysis for 6, C22H36CoF7P4, 616.34 g mol−1
,
[found (calcd)]: C, 42.60 (42.87); H, 5.81 (5.89). IR (Nujol mull,
cm−1): 1660 s, 1572 s, ν(CvC), 936 vs., ν(PMe3). 1H NMR
(300 MHz, benzene-d6, 297 K): δ 0.95 (br, 18H, PCH3), 1.44 (br,
18H, PCH3). 31P NMR (121.4 MHz, benzene-d6, 297 K): δ 31.0
(s, PCH3). 19F NMR (282 MHz, benzene-d6, 300 K): δ −116.89
(dd, JF1F4 = 19 Hz, JF1F8 = 65 Hz, F1, 1F), −134.61 (m, F3, 1F),
−144.93 (dt′, JF1F8 = 65 Hz, JF7F8 = 19 Hz, JF5F8 = 17 Hz, F8, 1F),
−146.39 (dt′, JF4F5 = 56 Hz, JF5F6 = JF5F8 = 15 Hz, F5, 1F),
−149.93 (dt′, JF4F5 = 56 Hz, JF3F4 = JF1F4 = 19 Hz, F4, 1F),
Synthesis of complexes 1 and 4
A solution of C5NF5 (0.39 g, 2.30 mmol) in 30 mL of THF was −154.05 (t′, JF7F8 = 22 Hz, JF6F7 = 19 Hz, F7, 1F), −156.85 (m, F6,
combined with a solution of Co(PMe3)4 (0.83 g, 2.30 mmol) in 1F).40 m.p.: 94 °C.
THF (30 mL) at −80 °C. The reaction mixture was allowed to
Synthesis of complex 7
warm to ambient temperature and stirred for 30 h. During this
period the pale yellow mixture turned brown-yellow in color. A solution of 1 (0.42 g, 0.96 mmol) in 50 mL of pentane was
The volatiles were transferred under vacuum and the residue stirred under 1 bar of CO at ambient temperature for 12 h, The
was extracted with pentane (40 mL) and diethyl ether (50 mL), color changed from red-brown to yellow. Upon filtration and
respectively. Crystallization from pentane and diethyl ether at cooling to 4 °C, complex 7 (0.30 g, 75%) was obtained as
−4 °C afforded green single crystals of 1 (0.32 g, 32.0%) suit- yellow cubic crystals. Analysis for 7, C13H18CoF4NO2P2 417.15 g
able for X-ray analysis. Analysis for 1, C14H27CoF4NP3, 437.21 g mol−1, [found (calcd)]: C, 37.67 (37.43); H, 4.20 (4.35); N, 3.25
mol−1, [found (calcd)]: C, 38.87 (38.46); H, 6.20 (6.22); N, 2.90 (3.36). IR (Nujol, cm−1): 1969, 1900 ν(CO); 1587, 1543 ν(CvC);
(3.20). IR (Nujol, cm−1): 1612, 1587 s, ν(CvC); 935 vs., ν(PMe3). 946ν (PMe3). 1H NMR (300 MHz, C6D6, 297 K): δ 0.87 (t′, 2JPH
+
Dec. 167 °C. The deep red single crystals of 4 (0.73 g, 62%) 4JPH = 8.7 Hz, PCH3). 31P NMR (121 MHz, benzene-d6, 295 K):
were obtained by concentration of the mother solution. Ana- δ 28.5 (s, PCH3). 19F NMR (282 MHz, benzene-d6, 300 K):
lysis for 4, C17H36CoF4NP4, 513.11 g mol−1, [found (calcd)]: C, δ −98.50 (m, 2F), −114.76 (m, 2F). m.p.: 135 °C.
39.88 (39.78); H, 6.90 (7.07); N, 2.67 (2.73). IR (Nujol, cm−1):
Synthesis of complex 8
1631 s, 1613, 1579 s, ν(CvC); 937 vs., ν (PMe3). 1H NMR
(300 MHz, benzene-d6, 300 K): δ 0.91 (br, PCH3). 31P NMR A solution of 2 (0.45 g, 1.0 mmol) in 50 mL of pentane was
(121.4 MHz, pentane, 297 K): δ 31.6 (s, PCH3). 19F NMR stirred under 1 bar of CO at ambient temperature for 12 h.
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The red-brown solution slowly turned yellow. Upon filtration Reaction of C6F5H with Co(PMe3)4 and C6Cl6
and cooling to 4 °C, complex 8 (0.28 g, 64%) was obtained as
A solution of C6F5H (0.50 g, 2.97 mmol) and Co(PMe3)4
yellow cubic crystals. Analysis for 8, C14H18CoF5O2P2 434.15 g
mol−1, [found (calcd)]: C, 38.66 (38.73); H, 4.32 (4.18). IR
(Nujol mull, cm−1): 1967, 1901 ν(CO); 1600, 1538 ν(CvC);
(1.08 g, 2.97 mmol) in 50 mL of THF was stirred for 12 h, then
C6Cl6 (0.85 g, 2.97 mmol) was added with stirring at −80 °C.
This reaction mixture was allowed to warm to room temp-
erature and stirred for 12 h. The solution color changed from
red-brown to green. The volatiles were transferred under vacuum
and the residue was extracted with pentane (30 mL) and
diethyl ether (30 mL). Complex 12 (1.04 g, 71%) as green crys-
tals was obtained from pentane/diethyl ether at −4 °C. Analysis
for 12, C15H27CoClF5P3 489.66 g mol−1, [found (calcd)]: C,
36.51 (36.79); H, 5.38 (5.56). IR (Nujol, cm−1): 1627 s, 1601 s
ν(CvC); 948 ν (PMe3). m.p.: 157 °C. The mother solution was
quenched with dilute HCl (1 M) and extracted by diethyl ether.
The organic phase was dried over magnesium sulfate. After fil-
tration, C6Cl5H and 1,2,4,5-C6Cl4H2 were separated by column
chromatography (silica) using petroleum ether (60–90 °C) in
the yield of 58% and 12% respectively.
942ν(PMe3). 1H NMR (300 MHz, C6D6, 297 K): δ 0.93 (t′, |2JPH
+
4JPH| = 8.4 Hz, PCH3). 31P NMR (121 MHz, C6D6, 295 K): δ 29.3
(s, PCH3). 19F NMR (282 MHz, benzene-d6, 300 K): δ −107.0 (d,
JF2F3 = 25.4 Hz, 2F), −159.9 (t, JF3F4 = JF4F5 = 20.8 Hz, 1F),
−162.05 (q, 2F). m.p.: 152 °C.
Reaction of C6F5H with Co(PMe3)4
A solution of C6F5H (0.37 g, 2.20 mmol) in 30 mL of pentane
was combined with
a solution of Co(PMe3)4 (0.80 g,
2.20 mmol) in pentane (30 mL) at −80 °C. This mixture was
allowed to warm to ambient temperature and stirred for 18 h
to form a red-brown, turbid mixture. After work-up, crystalliza-
tion from pentane at −4 °C afforded red-brown single crystals
of 2 (0.66 g, 66%). 1,2,4,5-C6F4H2 was detected by 19F NMR in
a yield of 3%. Under the same reaction conditions, a solution
of C6F5H (0.74 g, 4.40 mmol) in 60 mL of pentane was com-
bined with a solution of Co(PMe3)4 (0.80 g, 2.20 mmol) in
pentane (60 mL) at −80 °C. 1,2,4,5-C6F4H2 was detected by 19F
NMR in the yield of 14%.
Crystallographic data of complex 1
C14H27CoF4NP3, 437.21 g mol−1, 0.30 × 0.28 × 0.21 mm, mono-
clinic, P2(1)/n, a = 8.5810(10), b = 16.6960(13), c = 14.853(2) Å;
β = 99.750(12)°. V = 2097.2(4) A3, T = 140(2) K, Z = 4, Dcalc
=
1.385 Mg m−3, μ = 1.076 mm−1, data coll. range 1.85 < 2θ <
29.17°, −11 ≤ h ≤ 11, −22 ≤ k ≤ 22, −20 ≤ l ≤ 20, no. unique
data = 5626 (R(int) = 0.0294), parameters = 217, GOF on F2 =
1.077, R1 (I > 2σ(I)) = 0.0532, wR2 = 0.1485 (all data).
Experimental evidence of intermediate 9
(a) IR monitoring: a solution of C6F5H (0.37 g, 2.20 mmol) in
30 mL of pentane was combined with a solution of Co(PMe3)4
(0.80 g, 2.20 mmol) in pentane (30 mL) at −80 °C. This
mixture was allowed to warm to ambient temperature and
stirred for 10 h to form a red-brown, turbid mixture. 5 mL of
the reaction mother solution was sampled. The volatiles of
this solution were removed via vacuum. The solid residue was
used for the FTIR analysis. A vibration at 1906 cm−1 was found
to be the signal of the Co–H bond of intermediate 9. (b) In situ
1H NMR: the sample of C6F5H (0.011 g, 0.074 mmol) was
added in a solution of 0.6 mL of C6D6 with Co(PMe3)4 (0.027 g,
0.074 mmol) in a NMR tube at −80 °C. This mixture was
allowed to warm to ambient temperature and stirred for 10 h
to form a red-brown, turbid mixture. The in situ 1H NMR in
C6D6 indicates clearly the presence of the Co–H group of inter-
mediate 9 with the hydrido resonance at −17.3 ppm as a
quintet with the coupling constant of JPH = 34 Hz.
Crystallographic data of complex 2
C15H27CoF5P3, 454.21 g mol−1, 0.25 × 0.22 × 0.19 mm, mono-
clinic, P2(1)/n, a = 13.243(3), b = 11.838(2), c = 13.762(3) Å; β =
92.98(3)°. V = 2154.6(7) A3, T = 150(2) K, Z = 4, Dcalc = 1.400 Mg
m−3, μ = 1.056 mm−1, data coll. range 2.31 < 2θ < 25.00°, −15 ≤
h ≤ 7, −12 ≤ k ≤ 14, −16 ≤ l ≤ 16, no. unique data = 3582
(R(int) = 0.0173), parameters = 235, GOF on F2 = 1.044,
R1 (I > 2σ(I)) = 0.0370, wR2 = 0.1001 (all data).
Crystallographic data of complex 6
C22H36CoF7P4, 616.32 g mol−1, 0.15 × 0.12 × 0.10 mm, ortho-
rhombic, Pbca, a = 16.1878(19), b = 18.288(2), c = 18.646(2) Å;
V = 5519.9(11) A3, T = 273(2) K, Z = 8, Dcalc = 1.483 Mg m−3
,
μ = 0.911 mm−1, data coll. range 2.00 < 2θ < 25.05°, −19 ≤ h ≤ 13,
−21 ≤ k ≤ 21, −22 ≤ l ≤ 22, no. unique data = 4886 (R(int) =
0.0521), parameters = 307, GOF on F2 = 1.009, R1 (I > 2σ(I)) =
0.0384, wR2 = 0.1047 (all data).
Synthesis of complex 11
A solution of C6F5H (0.65 g, 3.86 mmol) and Co(PMe3)4
(1.40 g, 3.86 mmol) in 50 mL of pentane was stirred for 12 h,
Crystallographic data of complex 7
then stirred under 1 bar of CO for 12 h. The red-brown solu- C13H18CoF4NO2P2, 417.15 g mol−1, 0.31 × 0.25 × 0.21 mm,
tion slowly turned yellow. Upon filtration and cooling to 4 °C, monoclinic, P2(1)/c, a = 12.367(3), b = 11.760(2), c = 12.486(3)
complex 11 (1.0 g, 59.6%) was obtained as yellow cubic crys- Å; β = 93.84(3)°. V = 1811.8(6) A3, T = 293(2) K, Z = 4, Dcalc
=
tals. Analysis for 11, C14H19CoF5O2P2 435.16 g mol−1, [found 1.529 Mg m−3, μ = 1.166 mm−1, data coll. range 2.38 < 2θ <
(calcd)]: C, 38.56 (38.64); H, 4.22 (4.40). IR (Nujol, cm−1): 2002, 25.00°, −14 ≤ h ≤ 12, −13 ≤ k ≤ 10, −14 ≤ l ≤ 14, no. unique
1968 ν(CO); 1902, ν(Co–H); 1616, 1597 ν(CvC); 942 ν(PMe3). data = 2770 (R(int) = 0.0106), parameters = 214, GOF on F2 =
m.p.: 97 °C.
1.065, R1 (I > 2σ(I)) = 0.0225, wR2 = 0.0607 (all data).
5742 | Dalton Trans., 2013, 42, 5740–5748
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Crystallographic data of complex 8
vacuum conditions, the red solutions of complexes 4 and 6
turned to green. This implies an equilibrium between the
tetra-coordinate cobalt(I) complexes 1/3 and the penta-coordi-
nate cobalt(I) complexes 4/6. The stable penta-coordinate
cobalt(I) complexes 4 and 6 as red crystals were isolated and
characterized. It was found that the tetra-coordinate cobalt(I)
complex 2 was more stable in comparison with complexes 1
and 3. Complex 2 could not transform into penta-coordinate
cobalt(I) complex 5 in the presence of PMe3. It is considered
that the electrophilicity of the cobalt center in complex 2 is
weaker than that of complexes 1 and 3. From the viewpoint of
electrostatic theory, complex 2 is more stable than complexes 1
and 3. Therefore, complex 2 does not tend to combine another
phosphine ligand to form a penta-coordinate complex 5.
C14H18CoF5O2P2, 434.15 g mol−1, 0.30 × 0.22 × 0.20 mm,
monoclinic, P2(1)/c, a = 12.4005(11), b = 12.1015(10), c =
13.0277(11) Å; β = 91.942(2)°. V = 1953.9(3) A3, T = 273(2) K, Z =
4, Dcalc = 1.476 Mg m−3, μ = 1.090 mm−1, data coll. range 1.64
< 2θ < 27.46°, −16 ≤ h ≤ 8, −15 ≤ k ≤ 15, −14 ≤ l ≤ 16, no.
unique data = 4411 (R(int) = 0.0328), parameters = 227, GOF
on F2 = 1.013, R1 (I > 2σ(I)) = 0.0405, wR2 = 0.1111 (all data).
Crystallographic data of complex 11
C14H19CoF5O2P2, 435.16 g mol−1, 0.22 × 0.21 × 0.19 mm, ortho-
rhombic, Pbcn, a = 12.409(10), b = 13.286(11), c = 11.917(10) Å.
V = 1965(3) A3, T = 293(2) K, Z = 4, Dcalc = 1.471 Mg m−3, μ =
1.084 mm−1, data coll. range 2.25 < 2θ < 25.00°, −14 ≤ h ≤ 14,
−15 ≤ k ≤ 7, −14 ≤ l ≤ 14, no. unique data = 1719 (R(int) =
0.1412), parameters = 159, GOF on F2 = 1.085, R1 (I > 2σ(I)) =
0.0539, wR2 = 0.1639 (all data).
ð3Þ
Crystallographic data of complex 12
C15H27ClCoF5P3, 489.66 g mol−1, 0.30 × 0.28 × 0.25 mm, mono-
clinic, C2/c, a = 15.067(4), b = 9.121(2), c = 32.289(8) Å; β =
94.067(4)°. V = 4426.3(19) A3, T = 293(2) K, Z = 8, Dcalc = 1.470
Mg m−3, μ = 1.150 mm−1, data coll. range 1.26 < 2θ < 26.00°,
−16 ≤ h ≤ 18, −5 ≤ k ≤ 11, −39 ≤ l ≤ 36, no. unique data =
4356 (R(int) = 0.0924), parameters = 235, GOF on F2 = 1.018, R1
(I > 2σ(I)) = 0.0424, wR2 = 0.1204 (all data).
Crystallographic data for complexes 1, 2, 6, 7, 8, 11 and 12
have been deposited in the Cambridge Crystallographic Data
Centre as supplementary publications with the CCDC-871947
(1), 846414 (2), 718812 (6), 871948 (7), 871949 (8), 871950 (11)
and 871951 (12).
The molecular structures of complexes 1 and 2 are shown
in Fig. 1 and 2. The cobalt atoms of both complexes are
located at the center of a distorted tetrahedron. The Co–C
bond distance in complex 2 is 2.041(3) Å (Co1–C10), a bit
longer than that (Co1–C10 = 2.032(2) Å) in complex 1. This
could be due to the stronger electron-withdrawing power of the
nitrogen atom of the pyridinyl group. All of the Co–P bond dis-
tances are in the expected range for Co–P bonds.
In our earlier work38 a tris(trimethylphosphine)(4-trifluoro-
methyltetrafluorophenyl)cobalt(I) complex was isolated and
structurally characterized as an intermediate of the reaction of
octafluorotoluene with Co(PMe3)4. These three cobalt(I) com-
plexes belong to the same kind of cobalt(I) complexes with one
perfluorinated aromatic ligand and three neutral phosphines
as supporting ligands. Most of the bond parameters and struc-
tural characteristics of them are comparable.
3. Results and discussion
3.1 Selective C–F bond activation of perfluorinated arenes
ð2Þ
The reactions of C5NF5, C6F6 and C10F8 with Co(PMe3)4 in THF
or pentane gave rise to the corresponding tetra-coordinate
cobalt(I) complexes 1–3 and penta-coordinate cobalt(I) com-
plexes 4–6 (eqn (2)). Complexes 1 and 4 are the C–F cleavage
products at 4-position of C5NF5 while complexes 3 and 6 are
the C–F cleavage products at the β-position of C10F8. The for-
Fig. 1 Molecular structure of 1 (all the hydrogen atoms were omitted for
clarity). Selected bond distances (Å) and angles [°]: Co1–C10 2.032(2), Co1–P2
2.2276(7), Co1–P3 2.2385(8); Co1–P1 2.2412(7), C10–Co1–P2 109.34(7), C10–
Co1–P3 125.30(7), P2–Co1–P3 102.33(3), C10–Co1–P1 112.16(7), P2–Co1–P1
mation of F2PMe3 in solution was verified via 19F NMR and 31
P
NMR.41 It was found that the green solution of complexes 1
and 3 turned red with the addition of excess of PMe3 (eqn (3)).
When the amount of PMe3 of the solution was reduced under 102.39(3), P3–Co1–P1 102.72(3).
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Fig. 2 Molecular structure of 2 (all the hydrogen atoms were omitted for
clarity). Selected bond distances (Å) and angles [°]: C10–Co1 2.041(3), Co1–P3
2.2304(9), Co1–P1 2.2355(9), Co1–P2 2.2281(9); C10–Co1–P1 110.86(9), P3–
Co1–P1 100.87(4), C10–Co1–P2 120.16(10), P3–Co1–P2 103.74(4), P1–Co1–P2
101.78(4).
Fig. 4 Molecular structure of 7 (all the hydrogen atoms were omitted for
clarity). Selected bond distances (Å) and angles [°]: Co1–C13 1.7499(16), Co1–
C12 1.7585(19), Co1–C5 1.9984(15), Co1–P3 2.1869(5), Co1–P2 2.1877(5); C13–
Co1–C12 123.26(8), C13–Co1–C5 122.11(7), C12–Co1–C5 114.61(8), C13–Co1–
P3 90.43(5), C12–Co1–P3 91.62(6), C5–Co1–P3 89.08(5), C13–Co1–P2 88.79(6),
C12–Co1–P2 91.61(6), C5–Co1–P2 88.50(5), P3–Co1–P2 176.563(18).
coordinate complex 1 or penta-coordinate complex 4) was used
as the reactant. The characteristic carbonyl vibrations in the IR
spectra are at 1900/1969 cm−1 for 7 and 1901/1967 cm−1 for 8.
One singlet at 30.0 ppm (7) and 30.3 ppm (8) in the 31P NMR
spectra implies two equivalent trimethylphosphine ligands.
ð4Þ
Fig. 3 Molecular structure of 6 (all the hydrogen atoms were omitted for
clarity). Selected bond distances (Å) and angles [°]: Co1–C13 2.008(3), Co1–P4
2.1850(9), Co1–P1 2.1879(10), Co1–P3 2.1954(10), Co1–P2 2.2020(10); C13–
Co1–P4 82.61(9), C13–Co1–P1 83.87(9), P4–Co1–P1 165.43(4), C13–Co1–P3
129.35(9), C13–Co1–P2 118.84(9), P3–Co1–P2 111.78(4).
ð5Þ
The molecular structure of penta-coordinate cobalt(I)
The molecular structures of complexes 7 and 8 reveal that
complex 6 (Fig. 3) has a distorted trigonal-bipyramidal coordi- both cobalt atoms are situated at the center of a trigonal-bipyr-
nation geometry. Two axial trimethylphosphine ligands with amidal geometry (Fig. 4 and 5). They belong to the C2v space
an angle of P1–Co1–P4 (165.43(4)°) tilt toward the perfluori- group. Two trimethylphosphine ligands are located at the axial
nated naphthyl ligand due to the repulsion between the two positions with the bond angles of 176.56(18)° (7) and 176.29(4)°
equatorial trimethylphosphine ligands. The central cobalt (8). In the equatorial plane are two carbonyl ligands and one
atom deviate is 0.0157 Å from the equatorial plane. The Co1– perfluorinated aromatic ligand. The fluorinated 4-pyridinyl
C13 distance (2.008(3) Å) is shorter than those in complexes 1 ring of 7 and the pentafluorophenyl ring of 8 are in the
and 2.
equatorial planes. The four Co–CO bond distances of the two
Both complex 1 and complex 2 reacted with CO under complexes are in the range of normal Co–CO (terminal) bond
atmospheric pressure at room temperature in a pentane solu- distances.42 The Co–Cphenyl bond distances (Co1–C5 = 1.9984(15)
tion to give rise to the ligand substituted products, carbonyl Å (7); Co1–C1 = 2.013(3) Å (8)) are as expected for organo
complexes 7 and 8 (eqn (4) and (5)). Complexes 7 and 8 were cobalt complexes. The bond angles between two carbonyl
isolated as yellow crystals. The experiments showed that the ligands are 123.26(8)° (7) and 122.80(19)° (8). Similar dicarbo-
final product was penta-coordinate dicarbonyl diphosphine nyl cobalt complexes were reported with similar structural
cobalt(I) complex 7, regardless of which complex (tetra- characteristics.26,28
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Fig. 5 Molecular structure of 8 (all the hydrogen atoms were omitted for
clarity). Selected bond distances (Å) and angles [°]: C1–Co 2.013(3), C13–Co
1.743(4), C14–Co 1.741(4), Co–P1 2.1856(8), Co–P2 2.1891(8); C13–Co–C14
122.80(19), C14–Co–C1, 116.24(14), C13–Co–P1 89.93(11), C14–Co–P1 91.99(11),
C13–Co–P2 90.68(11), C14–Co–P2 90.76(11), C1–Co–P2 88.40(8), P1–Co–P2
176.29(4), C1–Co–P1 88.15(8).
Scheme 1 Proposed mechanism of reaction of C6F5H with Co(PMe3)4.
3.2 C–H bond activation of C6F5H
The C–F/C–H bond activation are competitive reactions
between polyfluoroarenes and transition metal complexes. The
reaction of Co(PMe3)4 with C6F5H in pentane was carried out
to study which bond activation is preferred. Complex 2 as a
main product was isolated from the mother solution of the
Fig. 6 The bands of the Co–H of intermediate 9 in in situ 1H NMR (a) and IR
reaction of C6F5H with Co(PMe3)4 in
a yield of 66% (b).
(Scheme 1). 1,2,4,5-C6F4H2 and F2PMe3 as byproducts were
verified via in situ 19F NMR and GC-MS (1,2,4,5-C6F4H2) and
via in situ 19F NMR and 31P NMR (for F2PMe3).41 But the yields be the possible signal of the Co–H bond of 9. The in situ H
of two byproducts were low (1,2,4,5-C6F4H2: 3%; F2PMe3; <1%). NMR in C6D6 also indicates clearly the presence of a Co–H
According to the experimental results and our early work on group with the hydrido resonance at −17.3 ppm as a quintet
C–F bond activation,15,38 the reaction sequence is proposed in with the coupling constant of JP–H = 34 Hz. In order to under-
Scheme 1. The first step is the formation of the hydrido cobalt(II) stand the existence of 1,2,4,5-C6F4H2 and F2PMe3, path b as
intermediate 9 through C–H bond activation via oxidative described in Scheme 1 was proposed. In path b, 9 reacts with
addition. Intermediate 9 is not stable. There are two possible another molecule of C6F5H to give rise to the hydrodefluorina-
paths, through which 9 can transform into end product 2. Path tion product 1,2,4,5-C6F4H2 and intermediate 10 through
a is one-electron reductive elimination of 9 to afford 2 with the ligand exchange via C–F bond activation at the 3-position of
escape of H2. A try to isolate intermediate 9 failed. 9 was veri- C6F5H. Intermediate 10 is an unstable organo cobalt(II) fluor-
1
1
fied through in situ IR and in situ H NMR spectra (Fig. 6). A ide and transforms into complex 2 with the formation of
vibration at 1906 cm−1 in the in situ IR spectrum was found to F2PMe3 in the presence of trimethylphosphine. Because of the
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strong bond energy of the C–F bond, we consider that the The distance Co1–H1 (1.62(9) Å) is in the normal range.43 Two
ligand exchange reaction via C–F bond activation in path b is carbonyl ligands tilt toward the direction of the hydrido ligand
not thermodynamically preferred. Therefore, the yield of because of the large pentafluorophenyl group and the small
1,2,4,5-C6F4H2 is very low. Even if the molar ratio of C6F5H to hydrido ligand. Therefore, the bond angle C1–Co1–C2 is 108.2(4)°
Co(PMe3)4 was increased from 1 : 1 to 2 : 1, the yield of 1,2,4,5- while the bond angle H1–Co1–C1 is 104(3)°. The bond dis-
C6F4H2 was changed only from 3 to 14%. We considered that 2 tances Co1–C1 (1.828(16) Å) is significantly shorter than Co1–
was formed mainly through path a in this reaction.
C2 (2.023(8) Å) due to the π-backbonding between the cobalt
atom and the carbonyl ligands. This also explains the multiple
bond character of the Co–CO linkage. The similar differences
can also be found in the aforementioned dicarbonyl organo
cobalt(I) complexes 7 and 8 (Fig. 4 and 5).
3.3 Further experimental study for the mechanism in
Scheme 1
In order to verify the reaction mechanism proposed in
Scheme 1, the following two experiments were designed. In
the process of isolating and confirming the hydrido intermedi-
ate 9, carbon monoxide was introduced as a supporting ligand
to catch the stability of 9 (eqn (6)). C6F5H and Co(PMe3)4 were
combined in pentane. This mixture was stirred under 1 bar of
CO for 12 h. After work-up, the hydrido dicarbonyl cobalt(II)
complex 11 was isolated as yellow crystals from the pentane
solution. In the IR spectra of complex 11 two strong absorption
bands at 1968 and 2002 cm−1 correspond to the two terminal
carbonyl ligands while the vibration of Co–H bond is located
In order to further understand the ligand exchange reaction
in Scheme 1 and to indirectly verify the existence of intermedi-
ate 10, C6Cl6 was added into the mixture of C6F5H and Co-
(PMe3)4. As expected, from the reaction solution tris(trimethyl-
phosphine)pentafluorophenylcobalt(II) chloride (12) was
obtained in a yield of 71% (eqn (7)). C6Cl5H as the second
product was also isolated in a yield of 58%. Complex 12 attains
a trigonal-bipyramidal coordination geometry with two axial
trimethylphosphine ligands (P1–Co1–P3 = 168.67(4)°) (Fig. 8).
Owing to the repulsion of the in-plane orientation of F and Cl
atoms, the bond angle (C6–Co1–Cl1 = 141.09(11)°) is much
larger than the other two bond angles (C6–Co1–P2 = 112.75(11)°
and Cl1–Co1–P2 = 106.16(4)°) in the equatorial plane. Both
axial trimethylphosphine ligands are in an eclipsed confor-
mation in the axial positions while the three equatorial
ligands are orientated in a staggered conformation with the
two axial ligands between them. The equatorial bond Co1–P2
(2.3011(10) Å) is considerably larger than both axial P–Co
bonds (P3–Co1 = 2.2179(10) Å and P1–Co1 = 2.2211(9) Å). In
addition, 1,2,4,5-C6Cl4H2 was detected as a further hydrode-
chlorination product of C6Cl5H in a yield of 12%.
at 1902 cm−1
.
ð6Þ
The molecular structure of complex 11 confirms a strongly
distorted hexa-coordinate octahedron (Fig. 7). Two trimethyl-
phosphine ligands are in the axial positions almost on a
straight line with an angle of P1–Co1–P1A = 179.79(11)°.
Fig. 7 Molecular structure of 11 (the hydrogen atoms ware omitted for
clarity). Selected distances [Å] and angles [°]: Co1–C1 1.828(16), Co(1)–C(2)
2.023(8), Co1–P1 2.222(2), Co1–H1 1.62(9); O(1)–C(1) 1.060(13), C(1)–Co(1)–C(2)
108.2(4), C(1)–Co(1)–P(1) 91.5(3), C(2)–Co(1)–P(1), 89.89(6), P1–Co1–P1A
179.79(11), C(2)–Co(1)–H(1) 147(3), P(1)–Co(1)–H(1) 95(3), C(1)–Co(1)–H(1) 104(3),
C(1)A–Co(1)–H(1) 40(3), C(1)A1–Co(1)–C(1) 143.7(9).
Fig. 8 Molecular structure of 12 (the hydrogen atoms ware omitted for
clarity). Selected distances [Å] and angles [°]: Co1–C6 1.983(3), Co1–P3 2.2179(10),
Co1–P1 2.2211(9), Co1–P2 2.3011(10), Co1–Cl1 2.3146(9); C6–Co1–P3
88.16(10), C6–Co1–P1 88.60(10), P3–Co1–P1 168.67(4), C6–Co1–P2 112.75(11),
P3–Co1–P2 95.47(4), P1–Co1–P2 95.79(4), C6–Co1–Cl1 141.09(11), P3–Co1–Cl1
88.08(4), P1–Co1–Cl1 87.63(3), P2–Co1–Cl1 106.16(4).
5746 | Dalton Trans., 2013, 42, 5740–5748
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ð7Þ
It should be noted that neither 1,2,4,5-C6F4H2 nor F2PMe3
was found in the reaction of eqn (7) with the participation of
C6Cl6. It is obvious that the ligand exchange reaction via C–Cl
bond activation is thermodynamically preferred because the
C–Cl bond in C6Cl6 is weaker than the C–F bond in C6F5H.
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In summary, the reactions of pentafluoropyridine C5NF5, hexa-
fluorobenzene C6F6, and perfluoronaphthalene C10F8 with
cobalt(0) complex, Co(PMe3)4, were investigated. The Co(I)
complexes (4-C5NF4)Co(PMe3)3 (1), (C6F5)Co(PMe3)3 (2), (C10F7)-
Co(PMe3)3 (3), (4-C5NF4)Co(PMe3)4 (4) and (C10F7)Co(PMe3)4
(6) were obtained by the selective activation of the C–F bonds.
The reactions of 1 and 2 with CO afforded dicarbonyl cobalt(I)
complexes (4-C5NF4)Co(CO)2(PMe3)2 (7), (C6F5)Co(CO)2(PMe3)2
(8). Under similar reaction conditions, 2 as a C–H bond
activation product was obtained from the reaction of penta-
fluorobenzene, C6F5H, with Co(PMe3)4. The byproducts, hydro-
defluorination product 1,2,4,5-C6F4H2 and F2PMe3 from the
reaction of C6F5H and Co(PMe3)4 were also observed. The reac-
tion mechanism of C6F5H with Co(PMe3)4 is proposed and
partly-experimentally verified. The reaction of C6F5H with Co-
(PMe3)4 under 1 bar of CO at room temperature afforded
hydrido dicarbonyl cobalt(II) complex (C6F5)Co(H)(CO)2(PMe3)2
(11). Treatment of the mixtures of C6F5H/Co(PMe3)4 with hexa-
chlorobenzene, C6Cl6, resulted in (C6F5)CoCl(PMe3)3 (12) via
C–H bond cleavage with the hydrodechlorination product
pentachlorobenzene, C6Cl5H, and 1,2,4,5-tetrachlorobenzene,
C6Cl4H2. The structures of complexes 1, 2, 6, 7, 8, 11 and 12
were determined by X-ray diffraction.
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