C-Cl bond activation of ortho-chlorinated benzamides by nickel and cobalt compounds supported with phosphine ligands

Article abstract of DOI:10.1039/c2dt12395a

The C-Cl bonds of ortho-chlorinated benzamides Cl-ortho-C₆H ₄C(O)NHR (R = Me (1), nBu (2), Ph (3), (4-Me)Ph (4) and (4-Cl)Ph (5)) were successfully activated by tetrakis(trimethylphosphine)nickel(0) and tetrakis(trimethylphosphine)cobalt(0). The four-coordinate nickel(ii) chloride complexes trans-[(C₆H₄C(O)NHR)Ni(PMe₃) ₂Cl] (R = Me (6), nBu (7), Ph (8) and (4-Me)Ph (9)) as C-Cl bond activation products were obtained without coordination of the amide groups. In the case of 2, the ionic penta-coordinate cobalt(ii) chloride [(C ₆H₄C(O)NHnBu)Co(PMe₃)₃]Cl (10) with the [C_phenyl, O_amide]-chelate coordination as the C-Cl bond activation product was isolated. Under similar reaction conditions, for the benzamides 3-5, hexa-coordinate bis-chelate cobalt(iii) complexes (C ₆H₄C(O)NHR)Co(Cl-ortho-C₆H₄C(O)NR) (PMe₃)₂ (11-13) were obtained via the reaction with [Co(PMe₃)₄]. Complexes 11-13 have both a five-membered [C,N]-coordinate chelate ring and a four-membered [N,O]-coordinate chelate ring with two trimethyphosphine ligands in the axial positions. Phosphonium salts [Me₃P⁺-ortho-C₆H₄C(O)NHR]Cl ^- (R = Ph (14) and (4-Me)Ph (15)) were isolated by reaction of complexes 8 and 9 as a starting material under 1 bar of CO at room temperature. The crystal and molecular structures of complexes 6, 7 and 9-12 were determined by single-crystal X-ray diffraction.

Full text of DOI:10.1039/c2dt12395a

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PAPER
C–Cl bond activation of ortho-chlorinated benzamides by nickel and cobalt
compounds supported with phosphine ligands†
Junye Li, Chenggen Wang, Xiaoyan Li and Hongjian Sun*
Received 12th December 2011, Accepted 28th May 2012
DOI: 10.1039/c2dt12395a
The C–Cl bonds of ortho-chlorinated benzamides Cl-ortho-C6H4C(vO)NHR (R = Me (1), nBu (2), Ph (3),
(4-Me)Ph (4) and (4-Cl)Ph (5)) were successfully activated by tetrakis(trimethylphosphine)nickel(0) and
tetrakis(trimethylphosphine)cobalt(0). The four-coordinate nickel(II) chloride complexes trans-
[(C6H4C(vO)NHR)Ni(PMe3)2Cl] (R = Me (6), nBu (7), Ph (8) and (4-Me)Ph (9)) as C–Cl bond
activation products were obtained without coordination of the amide groups. In the case of 2, the ionic
penta-coordinate cobalt(II) chloride [(C6H4C(vO)NHnBu)Co(PMe3)3]Cl (10) with the [Cphenyl, Oamide]-
chelate coordination as the C–Cl bond activation product was isolated. Under similar reaction conditions,
for the benzamides 3–5, hexa-coordinate bis-chelate cobalt(III) complexes (C6H4C(vO)NHR)Co-
(Cl-ortho-C6H4C(vO)NR)(PMe3)2 (11–13) were obtained via the reaction with [Co(PMe3)4].
Complexes 11–13 have both a five-membered [C,N]-coordinate chelate ring and a four-membered
[N,O]-coordinate chelate ring with two trimethyphosphine ligands in the axial positions. Phosphonium
salts [Me3P+-ortho-C6H4C(vO)NHR]Cl− (R = Ph (14) and (4-Me)Ph (15)) were isolated by reaction of
complexes 8 and 9 as a starting material under 1 bar of CO at room temperature. The crystal and
molecular structures of complexes 6, 7 and 9–12 were determined by single-crystal X-ray diffraction.
[CoBr(PMe3)3], by activation of the C–Cl bond.8 Reactions of
mono- and di-ortho-chlorinated compounds containing imine
1. Introduction
Chloroarenes play an important role in many fields, especially in
industry and agriculture. At the same time, the application of
them also leads to environmental problems. They are commonly
found as soil and groundwater contaminants because most of
them are toxic and thermally stable.1 How to cope with these
issues has driven several research groups to examine practical
and effective methods to transform toxic and inert chloroarenes
into useful and/or environment-friendly substances. Activation
of the comparatively inert C–Cl bond seems to be a feasible
approach using transition metal complexes under stoichiometric
or catalytic conditions.2 Related studies could be found in cross-
coupling reactions such as Heck reaction, Suzuki coupling and
Stille coupling. Catalytic activation of the C–Cl bond by palla-
dium,3 nickel,4 cobalt,5 rhodium6 and iron7 complexes is the key
step in these reactions.
groups as directing groups with Fe(PMe3)4 delivered cyclo-
metalated complexes in octahedral coordination geometry via the
C–Cl bond activation.9 The reaction of ortho-chlorinated phenyl-
imine with tetrakis(trimethylphosphine)nickel(0) under a CO
atmosphere (1 bar) at room temperature provides bis(isoindolin-
ones) via carbonylative cyclization and dimerization through
C–Cl bond cleavage.10
As a part of our continuing interest in the C–Cl bond acti-
vation of chlorinated aromatic molecules, we prefer to produce
the C–Cl bond activation product through cyclometalation reac-
tions with an ortho-chlorinated benzamide-O atom or N atom
as an anchoring group, by nickel(0) and cobalt(0) complexes
supported with phosphine ligands. The C–Cl bond of the ortho-
chlorinated benzamides 1–5 were successfully activated by tetra-
kis(trimethylphosphine)nickel(0) and tetrakis(trimethylphos-
phine)cobalt(0). The four-coordinate nickel(II) chloride
complexes (6–9) as C–Cl bond activation products were
obtained. In the case of benzamide 2, the cobalt(II) chloride 10
as a C–Cl bond activation product was isolated. Instead of the
n-butyl group on the amide-N atom, if the substituent on the
amide-N atom is phenyl or its derivatives, the hexa-coordinate
bis-chelate cobalt(III) complexes 11–13 could be obtained via the
reaction of the amides 3–5 with [Co(PMe3)4]. The phosphonium
salts 14 and 15 were isolated by reaction of complexes 3 and 4
as starting material under 1 bar of CO at room temperature. The
crystal and molecular structures of complexes 6, 7 and 9–12
were determined by single-crystal X-ray diffraction.
We reported C–Cl bond activation at a cobalt(I), iron (0) and
nickel(0) center with imine as an anchoring group through cyclo-
metalation reactions.8–10 Novel ortho-chelated cobalt(III) com-
plexes were obtained through reactions of ortho-chlorinated
aromatic compounds bearing imine groups as anchoring groups
with cobalt(I) complexes, [CoMe(PMe3)4], [CoCl(PMe3)3] or
School of Chemistry and Chemical Engineering, Shandong University,
Shanda Nanlu 27, 250100 Jinan, People’s Republic of China.
E-mail: hjsun@sdu.edu.cn; Fax: +86 531 88361350
†CCDC 806080–806085. For crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c2dt12395a
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 8715–8722 | 8715

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(m, 2H, CH2), 1.62 (m, 2H, CH2), 1.32 (m, 2H, CH2), 0.88
(t, 3H, 3J(HH) = 7.5 Hz, CH3), 0.78 (t′, 18H, |2J(PH) +
4J(PH)| = 7.8 Hz, PCH3). 31P NMR (121.5 MHz, C6D6, 294 K,
ppm): δ −13.3 (s, PCH3).
2. Experimental section
2.1 General procedures and materials
Standard vacuum techniques were used in manipulations of vola-
tile and air-sensitive materials. Solvents were dried by known
Synthesis of 8. A solution of 3 (0.50 g, 2.14 mmol) in 30 mL
of THF was combined with a solution of Ni(PMe3)4 (0.78 g,
2.14 mmol) in THF (20 mL) at −78 °C. The reaction mixture
was warmed to ambient temperature and stirred for 30 h. During
this period the pale yellow mixture turned yellow-brown in
color. After filtering, the yellow-brown residue was extracted
with pentane (40 mL) and diethyl ether (50 mL), respectively.
Repeated re-crystallization from diethyl ether at 4 °C yielded
red-brown crystals. Yield: 0.60 g (64%). m.p.: >136 °C. Analysis
for 8, C19H28ClNNiOP2 (442.53 g mol−1), found (calcd): C,
51.42 (51.57); H, 6.29 (6.38); N, 3.00 (3.17)%. IR (Nujol mull):
procedures and distilled under nitrogen before use. Literature
11a
methods were used in the preparation of Ni(PMe3)4
and
Co(PMe3)4.11b ortho-Chlorinated benzamides were obtained by
refluxing mixtures of ortho-chlorobenzoyl chloride and amine in
diethyl ether solution. Infrared spectra (4000–400 cm−1), as
obtained from Nujol mulls between KBr disks, were recorded on
1
an ALPHA FT-IR Spectrometer. H, 13C and 31P NMR spectra
(300, 75, and 121 MHz, respectively) were recorded on a Bruker
Avance 300 spectrometer. 13C and 31P NMR resonances were
obtained with broadband proton decoupling. X-ray crystallo-
graphy was performed with a Bruker Smart 1000 diffractometer.
3302 ν(N–H), 1631 ν(CvO), 937 ρ(PMe3) cm−1 1H NMR
.
(300 MHz, C6D6, 297 K, ppm): δ 12.8 (s, 1H, NH), 8.67 (m,
3H, Ar–H), 7.66 (m, 1H, Ar–H), 7.30 (m, 2H, Ar–H), 6.96 (m,
2.2 Syntheses
4
1H, Ar–H), 6.87 (m, 2H, Ar–H), 0.67 (t′, |2J(PH) + J(PH)| =
Synthesis of 6. A solution of 1 (0.39 g, 2.34 mmol) in 30 mL
of THF was combined with a solution of Ni(PMe3)4 (0.85 g,
2.34 mmol) in THF (20 mL) at −78 °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. After filtering, the yellow-brown residue was extracted
with pentane (40 mL) and diethyl ether (50 mL), respectively.
Repeated re-crystallization from diethyl ether at 4 °C yielded
yellow crystals suitable for single-crystal X-ray diffraction
analysis. Yield: 0.57 g (64%). m.p.: >136 °C. Analysis for 6,
C14H26ClNNiOP2 (380.44 g mol−1), found (calcd): C, 44.15
(44.20); H, 6.78 (6.89); N, 3.70 (3.68)%. IR (Nujol mull): 3400
7.8 Hz, 18H, PCH3). 13C NMR (75 MHz, C6D6, 297 K. ppm):
δ 165.6 (s, CvO), 119.4–140.5 (s, Carom), 12.3 (t, |1J(PC) +
3J(PC)| = 28.6 Hz, PCH3). 31P NMR (121.5 MHz, C6D6, 294 K,
ppm): δ −12.33 (s, PCH3).
Synthesis of 9. A solution of 4 (0.43 g, 1.76 mmol) in 30 mL
of THF was combined with a solution of Ni(PMe3)4 (0.64 g,
1.76 mmol) in THF (20 mL) at −78 °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. After filtering, the yellow-brown residue was extracted
with pentane (40 mL) and diethyl ether (50 mL), respectively.
Repeated re-crystallization from diethyl ether at 4 °C yielded
yellow crystals suitable for single-crystal X-ray diffraction analy-
sis. Yield: 0.50 g (61%). m.p.: >145 °C. Analysis for 9,
ν(N–H), 1626 ν(CvO), 946 ρ(PMe3) cm−1
.
1H NMR
(300 MHz, C6D6, 297 K, ppm): δ 8.06 (br, 1H, NH), 6.81 (t,
3J(HH) = 7.4 Hz, 1H, Ar–H), 6.88 (t′, J(HH) = 7.2 Hz, 1H,
3
3
3
Ar–H), 7.66 (d, J(HH) = 7.5 Hz, 1H, Ar–H), 7.86 (d, J(HH) =
C20H30ClNNiOP2 (456.53
56.58 (56.61); H, 6.60 (6.62); N, 3.22 (3.07)%. IR (Nujol mull):
3458 ν(N–H), 1651 ν(CvO), 946 ρ(PMe3) cm−1 1H NMR
(300 MHz, C6D6, 297 K, ppm): δ 12.72 (s, 1H, NH), 8.68 (dd,
g
mol−1), found (calcd): C,
3
9 Hz, 1H, Ar–H), 2.94 (d, J(HH) = 4.8 Hz, 3H, CH3), 0.77 (t′,
4
|2J(PH) + J(PH)| = 7.8 Hz, 18H, PCH3). 13C NMR (75 MHz,
.
C6D6, 297 K, ppm): δ 169.3 (s, CvO), 121.8–135.0 (s, Carom),
3
3
4
23.0 (s, 3H, CH3) 12.7 (t, |1J(PC) + J(PC)| = 27.8 Hz, PCH3).
1H, J(HH) = 6.9 Hz, J(HH) = 2.7 Hz, Ar–H), 8.60 (d, 2H,
3J(HH) = 8.4 Hz, Ar–H), 7.65 (dd, 1H, 3J(HH) = 6.3 Hz,
4J(HH) = 2.1 Hz, Ar–H), 7.09 (m, 2H, Ar–H), 6.89 (m, 2H,
31P NMR (121.5 MHz, C6D6, 294 K, ppm): δ −13.1 (s, PCH3).
4
Synthesis of 7. A solution of 2 (0.42 g, 1.98 mmol) in 30 mL
of THF was combined with a solution of Ni(PMe3)4 (0.72 g,
1.98 mmol) in THF (20 mL) at −78 °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. After filtering, the yellow-brown residue was extracted
with pentane (40 mL) and diethyl ether (50 mL). Repeated re-
crystallization from pentane at 4 °C yielded yellow crystals suit-
able for single-crystal X-ray diffraction analysis. Yield: 0.57 g
(68%). m.p.: >109 °C. Analysis for 7, C17H32ClNNiOP2
(422.54 g mol−1), found (calcd): C, 48.52 (48.32); H, 7.60
(7.63) ; N, 3.29 (3.31)%. IR (Nujol mull): 3283 ν(N–H), 1651
Ar–H), 2.10 (s, 3H, CH3), 0.68 (t′, 18H, |2J(PH) + J(PH)| =
7.6 Hz, PCH3). 13C NMR (75 MHz, C6D6, 297 K, ppm): δ
165.6 (s, CvO), 119.4–138.1 (s, Carom), 20.8 (s, CH3), 12.3 (t,
|1J(PC) + 3J(PC)| = 29.4 Hz, PCH3). 31P NMR (121.5 MHz,
C6D6, 294 K, ppm): δ −12.3 (s, PCH3).
Synthesis of 10. A solution of 2 (0.42 g, 1.98 mmol) in
30 mL of THF was combined with a solution of Co(PMe3)4
(0.72 g, 1.98 mmol) in 20 mL of THF at −78 °C. The reaction
mixture was warmed to ambient temperature and stirred for 16 h.
During this period the yellow-brown mixture turned red-brown
in color. After filtering, the red-brown residue was extracted with
diethyl ether (50 mL). Repeated re-crystallization from diethyl
ether at −12 °C yielded red crystals. Yield: 0.36 g (36%). m.p.:
>148 °C. Analysis for 10, C20H41ClCoNOP3 (498.83 g mol−1),
found (calcd): C, 47.80 (48.16); H, 8.30 (8.28) %. IR (Nujol
ν(CvO), 947 ρ(PMe3) cm−1
.
1H NMR (300 MHz, C6D6,
297 K, ppm): δ 8.57 (br, 1H, NH), 8.02 (dd, 1H, 3J(HH) =
4
3
7.8 Hz, J(HH) = 1.5 Hz, Ar–H), 7.65 (d, 1H, J(HH) = 7.8 Hz,
3
4
Ar–H), 6.90 (dt′, 1H, J(HH) = 6 Hz, J(HH) = 1.8 Hz, Ar–H),
3
4
6.83 (dt′, 1H, J(HH) = 7.2 Hz, J(HH) = 1.5 Hz, Ar–H), 3.62
8716 | Dalton Trans., 2012, 41, 8715–8722
mull): 3229 ν(N–H), 1595 ν(CvO), 941 ρ(PMe3) cm−1
.
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Synthesis of 11. A solution of 3 (0.80 g, 3.48 mmol) in
30 mL of THF was combined with a solution of Co(PMe3)4
(0.63 g, 1.74 mmol) in 20 mL of THF at −78 °C. The reaction
mixture was warmed to ambient temperature and stirred for 16 h.
During this period the yellow-brown mixture turned red-brown
in color. After filtering, the red-brown residue was extracted with
diethyl ether (50 mL). Repeated re-crystallization from diethyl
ether at −12 °C yielded red crystals. Yield: 0.91 g (82%). m.p.:
>142 °C. Analysis for 11, C32H36ClCoN2O2P2 (636.95 g
mol−1), found (calcd): C, 60.70 (60.34); H, 5.88 (5.70) %. IR
Synthesis of 15. A solution of 9 (1.36 g, 2.97 mmol) in
40 mL of diethyl ether was stirred under 1 bar of CO at −80 °C.
The reaction mixture was warmed to ambient temperature and
stirred for 24 h. During this period the brown mixture turned
single yellow, and a great deal of white powder was obtained.
The white powder was washed by diethyl ether. Yield: 0.84 g
(88%). m.p.: >119 °C. (M − Cl)+ = 286.1. Analysis for 15,
C17H21ClNOP (321.78 g mol−1), found (calcd): C, 63.79
(63.45); N, 4.32(4.35); H, 6.50 (6.58)%. IR (Nujol mull): 3388
ν(N–H), 1656 ν(CvO), 954 ρ(PMe3) cm−1
.
1H NMR
(Nujol mull): 1608 ν(CvO), 944 ρ(PMe3) cm−1
.
1H NMR
(300 MHz, D2O, 297 K, ppm): δ 7.10–7.86 (m, 8H, Ar–H), 2.14
2
(300 MHz, C6D6, 298 K, ppm): δ 6.74–8.85 (m, 18H, Ar–H),
0.80–1.02 (m, 18H, PCH3). 31P NMR (121.5 MHz, C6D6,
298 K, ppm): δ 4.3 (s, PCH3).
(s, 3H, CH3), 1.97 (d, JPH = 14.1 Hz, 9H, PCH3). 31P NMR
(121.5 MHz, D2O, 294 K, ppm): δ 22.8 (s, PCH3).
X-Ray structure determinations. Intensity data were collected
on a Bruker SMART diffractometer with graphite-monochro-
mated Mo-Kα radiation (λ = 0.71073 Å). The crystallographic
data for complexes 6, 7 and 9–12 are summarized in Table 1.
The structures were solved by direct methods and refined with
the full-matrix least-squares method on all F2 (SHELXL-97)
with non-hydrogen atoms anisotropic. CCDC 806080 (6),
806081 (7), 806084 (9), 806082 (10), 806083 (11) and 806085
(12) contain the supplementary crystallographic data for this
paper.†
Synthesis of 12. A solution of 4 (0.65 g, 2.51 mmol) in
30 mL of THF was combined with a solution of Co(PMe3)4
(0.46 g, 1.25 mmol) in 20 mL of THF at −78 °C. The reaction
mixture was warmed to ambient temperature and stirred for 16 h.
During this period the yellow-brown mixture turned red-brown
in color. After filtering, the red-brown residue was extracted with
diethyl ether (50 mL). Repeated re-crystallization from diethyl
ether at −12 °C yielded red crystals. Yield: 0.67 g (80%). m.p.:
>184 °C. Analysis for 12, C34H40ClCoN2O2P2 (665.0 g mol−1),
found (calcd): C, 61.20 (61.41); H, 6.31 (6.06) %. IR (Nujol
1
mull): 1607 ν(CvO), 947 ρ(PMe3) cm−1. H NMR (300 MHz,
3. Results and discussion
C6D6, 298 K, ppm): δ 6.62–8.36 (m, 16H, Ar–H), 1.90–2.49 (m,
6H CH3), 0.74–0.91 (m, 18H, PCH3). 31P NMR (121.5 MHz,
C6D6, 298 K, ppm): δ 4.4 (t, PCH3).
3.1. Reaction of [Ni (PMe3)4] with ortho-chlorinated
benzamides
The reaction of ortho-chlorinated benzamides 1–4 with
Ni(PMe3)4 afforded four-coordinate Ni(II) complexes 6–9 via
C–Cl bond activation (eqn (1)).
Synthesis of 13. A solution of 5 (0.65 g, 2.46 mmol) in
30 mL of THF was combined with a solution of Co(PMe3)4
(0.45 g, 1.23 mmol) in 20 mL of THF at −78 °C. The reaction
mixture was warmed to ambient temperature and stirred for 16 h.
During this period the yellow-brown mixture turned red-brown
in color. After filtering, the red-brown residue was extracted with
diethyl ether (50 mL). Repeated re-crystallization from diethyl
ether at −12 °C yielded red crystals. Yield: 0.50 g (88%). m.p.:
>190 °C. Analysis for 13, C32H34Cl3CoN2O2P2 (705.93 g
mol−1), found (calcd): C, 54.63 (54.45); H, 4.59 (4.85)%. IR
ð1Þ
(Nujol mull): 1596 ν(CvO), 947 ρ(PMe3) cm−1 1H NMR
.
(300 MHz, C6D6, 298 K, ppm): δ 6.47–8.42 (m, 16H, Ar–H),
0.74–0.88 (m, 18H, PCH3). 31P NMR (121.5 MHz, C6D6,
298 K, ppm): δ 5.2 (s, PCH3).
Complexes 6–9 were isolated as crystals in yields of 64–68%.
Complexes 6–9 were characterized by elemental analysis, IR and
NMR spectroscopy. In the infrared spectra of complexes 6–9 the
characteristic ν(CvO) bands were recorded at 1626, 1651, 1631
and 1651 cm−1, while the corresponding ν(CvO) bands of the
free ortho-chlorinated benzamides ligands (1–4) are located at
1650, 1659, 1643, 1659 cm−1. The characteristic ν(N–H) band
changes from 3287 to 3400 cm−1. These substantial red shifts
upon coordination of the CvO and N-donor atoms indicate a
weakening of these bonds.
Synthesis of 14. A solution of 8 (1.26 g, 2.8 mmol) in 40 mL
of diethyl ether was stirred under 1 bar of CO at −80 °C. The
reaction mixture was warmed to ambient temperature and stirred
for 24 h. During this period the brown mixture turned single
yellow, and a great deal of white powder was obtained. The
white powder was washed by diethyl ether. Yield: 0.74 g (85%).
m.p.: >89 °C. (M − Cl)+ = 272.1. Analysis for 14, C16H19-
ClNOP (307.75 g mol−1), found (calcd): C, 62.69 (62.44); N,
4.22 (4.55); H, 6.47 (6.22)%. IR (Nujol mull): 3508 ν(N–H),
1
In the H NMR spectra, the proton resonances of the N–H
groups in complexes 6–9 are recorded as a singlet between
8.06 and 12.77 ppm, while those of the free ligands are at
8.18–10.80 ppm. Only one 31P NMR signal is observed between
−13.1 and −12.3 ppm as a singlet. This suggests that the two
phosphorus atoms are in trans-orientation. Spectroscopic data
1
1650 ν(CvO), 968 ρ(PMe3) cm−1. H NMR (300 MHz, D2O,
2
297 K, ppm): δ 7.29–8.00 (m, 9H, Ar–H), 2.15 (d, JPH
=
14.1 Hz, 9H, PCH3). 31P NMR (121.5 MHz, D2O, 294 K, ppm):
δ 48.8 (s, PCH3).
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 8715–8722 | 8717

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Table 1 Crystallographic data for complexes 6, 7 and 9–12
6
7
9
10
11
12
Empirical formula C14H26ClNNiOP2 C17H32ClNNiOP2 C20H30ClNNiOP2 C20H41ClCoNOP3 C32H36ClCoN2O2P2 C34H40ClCoN2O2P2
Fw
380.44
422.54
456.53
498.83
636.95
665.00
Crystal size/mm
Crystal system
Space group
a/Å
b/Å
c/Å
0.15 × 0.10 × 0.10 0.15 × 0.15 × 0.10 0.28 × 0.25 × 0.20 0.15 × 0.15 × 0.10 0.15 × 0.15 × 0.10
0.28 × 0.25 × 0.20
Monoclinic
P2(1)/c
9.9389(6)
28.7709(17)
11.8115(7)
90
Monoclinic
P2(1)/c
13.607(2)
24.405(4)
16.845(3)
90
Orthorhombic
Pbca
9.6040(19)
19.709(4)
22.573(5)
90
Monoclinic
P2(1)/c
13.506(3)
14.564(3)
12.115(2)
90
Monoclinic
P2(1)/c
16.4434(11)
9.1090(6)
18.6041(13)
90
Monoclinic
P2(1)/c
10.989(2)
14.336(3)
19.780(4)
90
α (°)
β (°)
91.232(3)
90
5592.9(16)
12
1.355
26 057
90
90
106.80(3)
90
2281.3(8)
4
1.329
10 503
108.4464(10)
90
2643.4(3)
4
1.253
14 855
93.90(3)
90
3108.1(11)
4
1.361
23 633
93.90(3)
90
3343.5(3)
4
1.321
17 944
γ (°)
V/Å3
4272.7(15)
8
1.314
Z
Dcalcd/g cm−3
No. of rflns
collected
18 755
No. of independent 9255
4417
4562
5754
6313
6570
rflns
Rint
θmax (°)
0.0633
24.45
0.0609
26.73
0.0606
26.70
0.0414
27.12
0.0237
26.80
0.0400
26.00
R1 (I > 2σ(I))
wR2 (all data)
0.0633
0.1814
0.0389
0.1141
0.0424
0.1174
0.0475
0.1318
0.0357
0.0921
0.0675
0.1953
Fig. 1 Molecular structure of 6 (all hydrogen atoms were omitted for
clarity). Selected distances (Å) and angles (°): Ni1–C1 1.883(6), Ni1–P1
2.1909(1), Ni1–P2 2.2035(1), Ni1–Cl1 2.2570(1), O1–C7 1.219(7), C7–
N1 1.358(8), N1–C8 1.453(8); C1–Ni1–P1 89.72(18), C1–Ni1–P2
87.02(18), P1–Ni1–P2 175.76(8), C1–Ni1–Cl1 175.63(19), P1–Ni1–Cl1
90.05(7), P2–Ni1–Cl1 93.41(7).
Fig. 2 Molecular structure of 7 (all hydrogen atoms were omitted for
clarity). Selected distances (Å) and angles (°): O1–C13 1.238(3), N1–
C13 1.343(4), N1–C14 1.455(4), Ni1–C7 1.885(2), Ni1–P2 2.1868(7),
Ni1–P1 2.1887(7), Ni1–Cl1 2.2412(7); C7–Ni1–P2 88.45(7), C7–Ni1–
P1 91.91(7), P2–Ni1–P1 177.67(3), C7–Ni1–Cl1 174.25(8), P2–Ni1–
Cl1 90.12(3), P1–Ni1–Cl1 89.30(3).
are otherwise in accordance with the expected molecular
configurations and are comparable with those in the literature.10
The molecular structures of complexes 6, 7 and 9 are shown
in Fig. 1–3. The selected bond distances and angles are listed
under the figures. The complexes show distorted square planar
structures with two trans-phosphine ligands. This is consistent
with the observation in the 31P NMR spectra. The nickel atom is
centered in a square planar geometry with the trans-orientated Cl
and phenyl-C atoms due to the trans-effect. The C–O distances
(1.224(3), 1.238(3) and 1.219(7) Å for 6, 7 and 9) are in the
region of a CvO double bond. This also implies that there is no
bonding interaction between the O atom and the central nickel
atom. In addition, the coordination of the N atom to the nickel
atom does not exist because the distances between both atoms
are much larger than those of the normal coordination bond of
Ni–N (1.861–1.981 Å).12 Therefore, treatment of [Ni(PMe3)4]
with 1–4 produced the coordinately unsaturated four-coordinate
nickel(II) chloride complexes 6–9. The expected cyclometalation
reactions with an ortho-chlorinated benzamide-O atom or -N
atom as an anchoring group did not occur. The possible expla-
nation is that most of the nickel(II) complexes are apt to form
square planar coordination geometry and the amide-N atom has
weak coordination ability in comparison with the imine-N atom.
8718 | Dalton Trans., 2012, 41, 8715–8722
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Fig. 3 Molecular structure of 9 (all hydrogen atoms were omitted for
clarity). Selected distances (Å) and angles (°): Ni1–C7 1.895(2), Ni1–P1
2.1992(8), Ni1–P2 2.2012(7), Ni1–Cl1 2.2096(7), O1–C13 1.224(3),
N1–C13 1.363(3), N1–C14 1.417(3); C7–Ni1–P1 88.17(7), C7–Ni1–P2
88.91(7), P1–Ni1–P2 176.66(3), C7–Ni1–Cl1 172.91(7), P1–Ni1–Cl1
92.29(3), P2–Ni1–Cl1 90.42(3).
Fig. 4 Molecular structure of 10 (all hydrogen atoms were omitted for
clarity). Selected distances (Å) and angles (°): Co–C1 1.957(3), Co–O1
2.228(2), Co–P1 2.2380(10), Co–P2 2.2422(10), Co–P3 2.2572(9); C1–
Co–O1 80.27(10), C1–Co–P1 84.31(10), O1–Co–P1 94.91(7), C1–Co–
P2 86.62(10), O1–Co–P2 93.33(7), P1–Co–P2 166.54(4), C1–Co–P3
166.54(9), O1–Co–P3 86.32(6), P1–Co–P3 95.78(4), P2–Co–P3
95.36(4).
In other words, an amide group is not a good anchoring group
for cyclometallation.
band is changed from 3304 cm−1 for benzamide 2 to 3230 cm−1
for complex 10 owing to the coordination of the CvO to the Co
atom and the weakening of the N–H band.
It was found that the amide-O atoms in complexes 6 and 7
have different orientations from that of the amide-O atom in
complex 9. It is considered that there are weak coordination
interactions between the oxygen atoms and the nickel centers in
6 and 7 (6: Ni1–O1 = 2.686 Å; 7: Ni1–O1 = 2.856 Å), while a
hyperconjugation between the phenyl group in one molecule of
9 and a methyl group of the trimethylphosphine ligand of
another molecule of 9 in the crystal cell of 9 exists. It can also
be understood as a result of crystal packing effect. In all of the
three crystal lattices (6, 7 and 9) no hydrogen bond related to the
amide group was observed.
The molecular structure of complex 10 (Fig. 4) confirms a dis-
torted square-pyramidal coordination of the cobalt(II) center with
an O atom in the apical position and three PMe3 groups as well
as a phenyl-C atom in the equatorial plane. The P1–Co–P2 angle
is 166.54°. This is equal to the angle C1–Co–P3. The long dis-
tance of 2.8182(10) Å between Co and the Cl atom in complex
10 indicates that no covalent interaction between the cobalt and
chlorine atoms exists because the average Co(II)–Cl length is
much shorter.13 The chloride ion is located as a counter-ion
outside the chelate cobalt cation. The bite angle C1–Co–O1 of
80.27(10)° is in the normal region. The sum (362.0°) of the four
angles [C1–Co–P1 = 84.31(10), C1–Co–P2 = 86.62(10), P1–
Co–P3 = 95.78(4) and P2–Co–P3 95.36(4)°] around the central
cobalt atom proves that the co-planarity of the five atoms
[CoC1P1P2P3] is poor. The five-membered chelate ring and the
phenyl ring are in one plane. The butyl group is almost perpen-
dicular to this plane due to the packing effect in the crystal cell.
Under similar reaction conditions the reaction of Co(PMe3)4
with the ortho-chlorinated benzamides 3–5 (R = Ph (3); (4-Me)Ph
(4) and (4-Cl)Ph (5)) containing a phenyl group on the N atom
did not afford the analogous complexes to penta-coordinate Co(II)
complex 10, but hexa-coordinate bis-chelate cobalt(III) complexes
11–13 were obtained via the C–Cl bond cleavage of one benza-
mide molecule (eqn (3)). The deprotonation of the (NH)-group of
the second benzamide supports this transformation with the
escape of HCl. This benzamide coordinates to the cobalt atom
with [N, O]-coordination to form a four-membered chelate ring.
The five-membered chelate ring with [C, N]-coordination is
formed through C–Cl bond activation and N–H bond cleavage.
The IR spectra of cobalt(III) complexes 11–13 clearly indicates
the disappearance of the N–H bond. This shows us that both of
the NH-groups of the amides are deprotonated in the reaction. In
the 31P NMR spectra two phosphorus nuclei resonate at 4.3 ppm
3.2. Reaction of [Co(PMe3)4] with ortho-chlorinated
benzamides
The reaction of N-nbutyl-ortho-chlorinated benzamide 2 with
Co(PMe3)4 afforded the cobalt(II) chloride complex 10 via C–Cl
bond activation (eqn (2)).
ð2Þ
With the carbonyl-O atom as an anchoring group, the oxi-
dative addition reaction of the C–Cl bond on the cobalt(0) center
proceeds. Product 10 is a penta-coordinate cation with the cobalt
(II) center and the counter-ion is the chlorine anion. In the infra-
red spectrum of complex 10 the characteristic ν(CvO) band is
found at 1595 cm−1 showing a bathochromic shift by 67 cm−1
comparing with that of the free ligand, while the typical
vibration of a PMe3 ligand is recorded at 940 cm−1. The ν(N–H)
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ð3Þ
Fig. 6 Molecular structure of 12 (all hydrogen atoms were omitted for
clarity). Selected distances (Å) and angles (°): Co–N1 1.953(4), Co–N2
2.021(4), Co–O2 2.055(3), Co–P1 2.2430(13), Co–P2 2.2489(12) C1–
Co–N1 83.64(17), N1–Co–N2 168.41(16), N1–Co–O2 103.65(14), C1–
Co–P1 90.58(13), N1–Co–P1 86.54(11), N2–Co–P1 94.11(11), O2–Co–
P1 89.93(10), C1–Co–P2 86.43(13), N1–Co–P2 91.41(11), N2–Co–P2
88.45(11), N2–Co–O2 64.80(14), O2–Co–P2 93.25(10), P1–Co–P2
176.55(5).
effect the three phenyl groups, phenyl-[C8-C13], phenyl-[C14-
C19] and phenyl-[C21-C26] are neither in the equatorial plane
nor in the same plane. They have different dihedral angles
among them. The sum of the angles around the two N-atoms are
360° [for N1 atom: C7–N1–C8 (118.4(2)°) + C7–N1–Co1
(116.16(16)°) + C8–N1–Co1 (125.46(16)°) = 360.02°; for N2
atom: C20–N2–C21 (123.30(19)°) + C20–N2–Co1 (86.63(14)°)
+ C21–N2–Co1 (150.01(15)°) = 359.94°], which indicates that
both N atoms nearly have planar configuration. The sp3-hybrid
state of the N atom in the “free” benzamides changed to the
sp2-hybrid state of the N atom in the cobalt(III) complexes. This
transformation is supported by the phenyl group on the N atom
because of the “large” π-conjugation.
The molecular structure of complex 12 is similar to that of 11,
the only difference is that two N-atoms are trans-situated
in complex 12, while the two N-atoms in complex 11 are cis-
orientated. The reason of this difference is not unclear. Owing to
the strong trans-effect of the coordinated phenyl-C atom, Co–N2
bond distance (Co1–N2 = 2.1187(18) Å) in complex 11 is con-
siderably longer than that (Co–N2 = 2.021(4) Å) in complex 12,
while the Co–O2 bond distance (Co–O2 = 2.055(3) Å) in
complex 12 is also longer than that (Co1–O2 = 1.9712 Å) in
complex 11 for the same reason.
Fig. 5 Molecular structure of 11 (all hydrogen atoms were omitted for
clarity). Selected distances (Å) and angles (°): Co1–C1 1.902(2), Co1–
N1 1.9410(17), Co1–O2 1.9712(14), Co1–N2 2.1187(18), Co1–P1
2.2449(7), Co1–P2 2.2540(6), C1–Co1–N1 83.52(8), N1–Co1–O2
179.13(7), C1–Co1–P1 89.02(6), N1–Co1–P1 92.73(6), O2–Co1–P1
87.36(5), N2–Co1–P1 93.01(5), C1–Co1–P2 84.52(6), N1–Co1–P2
89.59(6), O2–Co1–P2 90.41(5), N2–Co1–P2 92.18(5), P1–Co1–P2
172.84(2).
in complex 11, at 4.5 ppm in complex 12 and at 5.2 ppm in
complex 13 as a singlet. This illustrates that two PMe3 ligands
have the same chemical environment in the solution.
The molecular structures of complexes 11 and 12 (Fig. 5 and
6) confirm the hexa-coordinate octahedral geometry of these two
complexes. In the molecular structure of complex 11 a five-mem-
bered metallacycle [C1C6C7N1Co1] is formed through the
coordination of the N1 atom of the amide group and the ortho-
metalated phenyl-C1 atom, while a four-membered chelate ring
[N2C20O2Co1] is formed with the amide as an anion ligand
through deprotonation of the NH group. Both the five-membered
and the four-membered chelate rings are coplanar. Two tri-
methylphosphine ligands are in the axial position with the angle
of P1–Co1–P2 of 172.84(2)°. The bite angle (N2–Co1–O2 =
64.67(7)°) of the four-membered chelate ring is much smaller
than that (C1–Co–N1 = 83.52(8)°) of the five-membered chelate
ring, as expected. Because of the repulsion and the packing
The formation mechanism of complexes 11–13 is suggested in
Scheme 1. The first step is C–Cl bond cleavage to form a
cobalt(II) cation intermediate a, as complex 10. This process is
supported and compensated through cyclometalation with an
O-atom as an anchoring group. The deprotonation of the
NH-group of the second benzamide molecule affords the inter-
mediate b with the escape of HCl. The N–H bond activation of
the coordinated benzamide generates the hydrido intermediate c.
Intermolecular elimination of H2 delivers the end products 11–13
(path A). The alternative route from intermediate c to end pro-
ducts 11–13 is path B. The reaction of intermediate c with
Co(PMe3)4 gives rise to end products 11–13 with the formation
of HCo(PMe3)4, but HCo(PMe3)4 was not observed by in situ
IR. The precipitation of the trimethylphosphonium chloride,
8720 | Dalton Trans., 2012, 41, 8715–8722
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Scheme 1
[Me3PH]Cl, from the mother solution is an evidence of the for-
mation of HCl. In these three reactions the deprotonation of the
amide-NH group is possibly supported by the phenyl (11) or the
phenyl derivatives (aromatic group) on the N-atom (12 and 13)
because the deprotonated amide is a “larger” conjugated system with
the anion [NCO]-moiety containing two phenyl groups, one attached
to the carbon atom and the other linked to the nitrogen atom. For
this reason no deprotonation product of the NH-group was found
with the butyl group (aliphatic) on the amide-N atom in eqn (2).
3.3. Reaction of complexes 6–9 with CO
In 2008 we synthesized a series of bis(isoindolinone) through
carbonylative cyclization and dimerization of phenylimine with
Ni(PMe3)4 stoichiometric amounts via C–Cl bond activation
under a CO atmosphere at room temperature (eqn (4)).10 Under
the same conditions, metal amide complexes 6–9 could not
transform to heterocyclic compounds 2-alkylisoindoline-1,3-
dione via cyclization as expected (eqn (5)).
Scheme 2
14 and 15 (eqn (6)). The byproduct Ni(CO)3(PMe3) was
confirmed by IR.14
ð4Þ
ð5Þ
ð6Þ
The proposed mechanism of the formation of phosphonium
salts 14 and 15 is shown in Scheme 2. The ligand replacement
of trimethylphosphine by carbon monoxide in complexes 8 and
Complexes 8 and 9 as starting materials under 1 bar of CO at
room temperature unexpectedly converted to phosphonium salts
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9 to form the mono-carbonyl intermediate d is the first step. The
further carbonylation of the intermediate d gives rise to the inter-
mediate e with the dissociation of the chlorine ligand and the
formation of the positively-charged nickel center. The unstable
intermediate e transforms to the end products 14 and 15 via
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The phosphonium salt, as a Lewis acid, can be used in
organocatalysis. The most prominent catalytic application of this
kind of compound is as a phase-transfer catalyst.15 Several
related catalytic systems were developed using phosphonium
salts as catalysts.16–19
4. Conclusion
In summary the C–Cl bonds of ortho-chlorinated benzamides
1–5 were successfully activated by tetrakis(trimethylphosphine)-
nickel(0) and tetrakis(trimethylphosphine)cobalt(0). The trans-
four-coordinate nickel(II) chloride complexes 6–9, as C–Cl bond
activation products, were obtained without coordination of
the amide groups. In the case of benzamide 2, ionic cobalt(II)
chloride 10, as a C–Cl bond activation product, was isolated.
If, instead of the n-butyl group on the amide-N atom (as in 2),
the substituent on the amide-N atom is phenyl or its derivatives
(as in 3–5), the hexa-coordinate bis-chelate cobalt(III) complexes
11–13 could be obtained via the reaction of the amides 3–5 with
[Co(PMe3)4]. The phosphonium salts 14 and 15 were obtained
by reaction of complexes 3 and 4, respectively, as a starting
material under 1 bar of CO at room temperature. The crystal and
molecular structures of complexes 6, 7, 9, 10, 11 and 12 were
determined by single-crystal X-ray diffraction.
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Acknowledgements
We gratefully acknowledge the supports by NSF China No.
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