Cobalt N-heterocyclic carbene alkyl and acyl compounds: Synthesis, molecular structure and reactivity

Article abstract of DOI:10.1039/b604200g

The N-heterocyclic-carbene containing cobalt carbonyl compound [Co(IMes)(CO)₃(Me)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)-imidazol- 2-ylidene), 1, has been synthesised by tertiary phosphine displacement from [Co(PPh₃)(CO)₃(Me)]. Subsequent carbonylation afforded the acyl derivative [Co(IMes)(CO)₃(COMe)], 2. Similarly, the compound [Co(IMes)(CO)₃(COEt)], 3, has been synthesised. The compounds 2 and 3 have been shown to react with dihydrogen to form the cobalt hydride compound [Co(IMes)(CO)₃(H)], 4. The molecular structures of compounds 1 and 2 have been determined. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b604200g

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PAPER
www.rsc.org/dalton | Dalton Transactions
Cobalt N-heterocyclic carbene alkyl and acyl compounds: synthesis,
molecular structure and reactivity
Simon A. Llewellyn,* Malcolm L. H. Green and Andrew R. Cowley
Received 21st March 2006, Accepted 18th May 2006
First published as an Advance Article on the web 6th June 2006
DOI: 10.1039/b604200g
The N-heterocyclic-carbene containing cobalt carbonyl compound [Co(IMes)(CO)
,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene), 1, has been synthesised by tertiary phosphine
displacement from [Co(PPh )(CO) (Me)]. Subsequent carbonylation afforded the acyl derivative
Co(IMes)(CO) (COMe)], 2. Similarly, the compound [Co(IMes)(CO) (COEt)], 3, has been
synthesised. The compounds 2 and 3 have been shown to react with dihydrogen to form the cobalt
3
(Me)] (IMes =
1
3
3
[
3
3
hydride compound [Co(IMes)(CO)
determined.
3
(H)], 4. The molecular structures of compounds 1 and 2 have been
Introduction
displacement of tertiary phosphine ligands by stronger r-donor
N-heterocyclic carbenes. The displacement of triphenylphos-
phine/trimethylphosphine by IMes in cobalt half-sandwich com-
Imidazole-derived N-heterocyclic carbenes (NHCs) were first
¨
1
2–8
20
reported by Ofele and Wanzlick et al. Subsequent work by
pounds has been reported.
9
–11
Arduengo et al.,
in isolating the first NHC by deprotonation
This paper describes the synthesis, characterisation and reactiv-
ity of N-heterocyclic carbene bearing complexes of cobalt.
of 1,3 diadamantylimidazolium chloride, helped to establish the
use of imidazole-derived NHCs in organometallic chemistry. A
large body of subsequent research has centred on NHC complexes
of transition metals. In particular, the replacement of tertiary
phosphine ligands by NHCs in Grubb’s olefin metathesis catalyst
has led to a series of extremely potent catalysts. N-heterocyclic
carbenes show similarities with tertiary phosphines, both being
strong r-donor ligands. It is widely accepted that NHCs are
Results and discussion
Synthesis of compounds
12
Treatment of the compound [Co(PPh
3
)(CO) (Me)] with 1,3-
3
bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene, (IMes), in di-
ethyl ether at room temperature led to the formation of
13
stronger r-donor ligands than are tertiary phosphines.
Transition metal complexes of N-heterocyclic carbenes have
been synthesised by a number of different synthetic routes,
[Co(IMes)(CO)
3
(Me)], 1, by displacement of PPh . Recrystalli-
3
sation from diethyl ether–pentane gave yellow crystals of 1 in
80% yield. Passing carbon monoxide through an ethereal solution
of 1 gave a quantitative yield of [Co(IMes)(CO)
1,2
including deprotonation of the imidazolium salt by metal anions,
1
4
15
ligand displacement, oxidative addition, and silver carbene
3
(COMe)], 2
16
transmetallation. Transition metal N-heterocyclic carbene com-
pounds have been synthesised by carbonyl group displacement.
(Scheme 1). The compounds 1 and 2 have been characterised by
1
13
1
H, C{ H} NMR and IR spectroscopies, by elemental analysis,
and by X-ray crystal structure determination.
Thus the reaction of the simple carbonyl compounds Fe(CO)
Ni(CO) , M(CO)
gave the corresponding monosubstituted carbene complexes.
5
,
4
6
(M = Cr, Mo, W) with N-heterocyclic carbenes
1
4
We recently reported the synthesis of the complexes [Fe(g-
)(IMes)(CO)(Me)], and [Fe(g-C )(L)(CO)(COMe)], by
CO displacement from [Fe(g-C )(CO)
C
5
H
5
5
H
5
17
5
H
5
2
(Me)]. Replacement
of transition metal carbonyl ligands by N-heterocyclic car-
benes has also been demonstrated for the dimeric cobalt
compound [Co(CO) ] . Thus, treatment of dicobalt octacar-
4
2
bonyl with one equivalent of 1,3-bis(2,4,6-trimethylphenyl)-
imidazol-2-ylidene (IMes) followed by one equivalent of triph-
enylphosphine, gave the mixed phosphine–carbene complex
18
[Co(CO)
3
(PPh
3
)Co(CO) (IMes)]. Van Rensburg et al. subse-
3
Scheme
1
3
Synthesis of [Co(IMes)(CO) (Me)] 1 and [Co(IMes)-
quently reported the synthesis of the bis-carbene compound
19
(CO) (COMe)] 2.
[Co(CO)
3
(IMes)]
2
,
which was stable only when maintained
3
under an atmosphere of carbon monoxide. Transition metal N-
heterocyclic carbene complexes have also been synthesized by
It was found more convenient to synthesise [Co(IMes)-
CO) (COEt)] from [Co(PPh )(CO) (Et)] directly. Thus treatment
of [Co(PPh )(CO) (Et)] with IMes in diethyl ether at room
(
3
3
3
Inorganic Chemistry Laboratory, University of Oxford, South Parks Road,
Oxford, UK OX1 3QR
3
3
temperature, followed by the passing of CO through the reaction
4
164 | Dalton Trans., 2006, 4164–4168
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mixture for 1 h, led to the formation of 3, by ligand exchange
and CO-induced migratory-insertion. The compound 3 has been
Table 2 Crystallographic data for compounds 1 and 2
1
13
1
1
2
characterised by H, C{ H} NMR and IR spectroscopies, and
by elemental analysis.
Chemical formula
Formula weight
Crystal system
C
462.43
Triclinic
P1
820.3(7)
2161.3(17)
18.9876(7)
101.1593(12)
90.3479(13)
109.8209(16)
150
1171.71(7)
2
25
H
27CoN
2
O
3
26 2 4
C H27CoN O
490.44
Monoclinic
P2 /c
8.6117(2)
33.0497(5)
9.2569(2)
90
112.0508(6)
90
150
2441.92(9)
4
The compound [Co(IMes)(CO)
stirring a solution of [Co(IMes)(CO)
under a 1 atm pressure of dihydrogen for 17 h. [Co(IMes)(CO)
may also be synthesised from [Co(IMes)(CO) (COEt)] under
3
(H)], 4, was synthesised by
(COMe)] in diethyl ether
(H)]
3
¯
Space group
1
3
a/A˚
3
b/A˚
c/A˚
1
analogous conditions. Compound 4 has been characterised by H,
1
3
1
◦
C{ H} NMR and IR spectroscopies, and by elemental analysis.
a/
b/
◦
[Co(IMes)(CO) (H)], 4, decomposed slowly at room temperature
3
◦
c /
in solution—an NMR sample showed ca. 15% decomposition
after 7 d. However, in the solid form, the compound 4 may be
stored in the absence of moisture and oxygen without apparent
decomposition. The stability of 4 with respect to dimerisation
T/K
V/A˚
3
Z
Reflections measured
Unique reflections
16259
5289
20344
5632
is notable, as the hydride compounds [Co(L)(CO)
PBu , PPh , P(OPh) , PF ) show low thermal stability at room
temperature.
3
(H)] (L =
R
int
0.045
3655
0.041
3569
3
3
3
3
Observed reflections
21
Parameters refined
R
wR
292
0.0377
0.0439
298
0.0344
0.0383
Characterisation of complexes
The solid state structure of [Co(IMes)(CO)
3
◦
(Me)], 1, is shown
25
2
-ylidene), and [Co(NO)(PPh
3
)(L)(CO)] (L = 1,3,4-trimethyl-
˚
26
in Fig. 1. Bond lengths (A) and angles ( ) are given in Ta-
ble 1. Selected crystal parameters are presented in Table 2.
The compound 1 shows a distorted trigonal bipyramidal ge-
imidazolin-2-ylidene), the Co–Ccarbene bond lengths are 1.875(8)
A, 1.888(3) A, and 1.974(14) A respectively.
˚
˚
˚
The molecular structure of [Co(IMes)(CO)
˚
3
(COMe)], 2, is
22,23
ometry, typical for cobalt (1) alkyl compounds,
in which
◦
shown in Fig. 2. Selected bond lengths (A) and angles ( ) are
given in Table 3. Selected crystal parameters are presented in
Table 2. The compound 2 shows the expected distorted trigonal
bipyramidal geometry that is closely related to that of 1, with
the acyl and carbene occupying the axial positions, and with the
the alkyl and carbene ligands occupy mutually axial positions,
and the three terminal carbonyl groups occupy the equato-
rial positions. The Co–Ccarbene (i.e. Co–C(1)) bond length of
˚
.961(2) A is in the range typical for other reported cobalt (1)
1
24
compounds; in the complexes [Co(g-C
5
5
H )(IMes)(CO)], [Co(g-
C
5
H
5
)(IPr)(CO)] (IPr = 1,3-bis(2,6-diisopropylphenyl)-imidazol-
Fig. 1 The molecular structure of 1. Thermal ellipsoids are drawn at 40%
Fig. 2 The molecular structure of 2. Thermal ellipsoids are drawn at 40%
probability. Hydrogen atoms have been omitted for clarity.
probability. Hydrogen atoms have been omitted for clarity.
◦
◦
Table 1 Selected bond lengths ( A˚ ) and angles ( ) for 1
Table 3 Selected bond lengths ( A˚ ) and angles ( ) for 2
Co(1)–C(1)
Co(1)–C(22)
Co(1)–C(23)
Co(1)–C(24)
Co(1)–C(25)
C(1)–N(1)
1.961(2)
2.071(2)
1.770(2)
1.790(3)
1.774(3)
1.367(3)
1.368(3)
1.444(3)
C(23)–O(1)
C(24)–O(2)
C(25)–O(3)
N(1)–C(2)
N(1)–C(4)
C(2)–C(3)
C(3)–N(2)
1.145(3)
1.148(3)
1.154(3)
1.389(3)
1.440(3)
1.351(3)
1.387(3)
Co(1)–C(1)
Co(1)–C(22)
Co(1)–C(24)
Co(1)–C(25)
Co(1)–C(26)
C(1)–N(1)
2.004(2)
2.016(2)
1.770(3)
1.788(3)
1.815(2)
1.365(3)
1.369(3)
1.390(3)
C(24)–O(2)
C(25)–O(3)
C(26)–O(4)
N(1)–C(4)
C(2)–C(3)
C(3)–N(2)
N(2)–C(13)
C(22)–O(1)
1.151(3)
1.142(3)
1.138(3)
1.446(3)
1.335(4)
1.390(3)
1.441(3)
1.205(3)
C(1)–N(2)
N(2)–C(13)
C(1)–N(2)
N(1)–C(2)
C(1)–Co(1)–C(22)
C(22)–Co(1)–C(23)
C(22)–Co(1)–C(25)
Co(1)–C(23)–O(1)
Co(1)–C(25)–O(3)
176.3(11)
82.5(11)
82.8 (11)
173.2(2)
170.8(2)
C(22)–Co(1)–C(24)
C(3)–N(2)–C(13)
C(2)–N(1)–C(4)
81.1(11)
121.3(19)
120.7(19)
168.7(2)
C(1)–Co(1)–C(22)
C(22)–Co(1)–C(24)
C(22)–Co(1)–C(25)
C(22)–Co(1)–C(26)
Co(1)–C(24)–O(2)
172.3(9)
81.9(10)
86.76(10) C(2)–N(1)–C(4)
86.08(10) C(3)–N(2)–C(13)
177.3(2)
Co(1)–C(25)–O(3) 173.5(2)
Co(1)–C(26)–O(4) 171.8(2)
120.9(18)
121.9(19)
Co(1)–C(24)–O(2)
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three terminal carbonyl groups occupying the equatorial positions.
mutually trans positions, whilst three terminal carbonyl groups
occupy the equatorial positions
22,27
This geometry is typical of cobalt (1) acyl compounds.
The
˚
Co–Ccarbene (C(1)–Co) bond length of 2.004(2) A represents a
˚
lengthening of 0.0431 A when compared with the parent alkyl
Preliminary hydroformylation investigations
compound 1. The 2,4,6-trimethylphenyl substituents are rotated
out of the plane of the heterocyclic ring in compound 2 as was
The unexpected stability of the compound [Co(IMes)(CO) (H)]
3
observed for compound 1. This is shown by C(carbene)–N–C(ipso)
–
with respect to dimerisation, suggests that it may be an ideal
◦
◦
C
(ortho) torsional angles of −85.9 and 83.2 .
candidate for the homogeneous hydroformylation of alkenes.
Cobalt-based hydroformylation catalyst precursors are typically
1
The H NMR spectra of compounds 1 and 2 show two singlet
1
9,30–35
peaks corresponding to the mesityl methyl substituents. The C
s
dimers of the type [Co(L)(CO)3]2
(L = tertiary phosphine).
symmetry of the cobalt carbene complexes results in magnetic
equivalence of the 2,6 methyl groups. Similarly, a single resonance
attributable to the Ar–H resonances is seen. In compound 1, the
methyl group was observed at d 0.70. By contrast, the methyl
Under reaction conditions of high pressures of syngas (50–80 atm)
and high temperatures (ca. 150 C), these dimers form hydride pre-
◦
catalysts of the type [Co(L)(CO) (H)].
3
Rhodium-based hydroformylation catalysts are generally more
1
3
1
protons of the acyl group in 2 were observed at d 2.78. C{ H}
NMR spectra were assigned with the help of HMBC and HMQC
experiments, and the carbene carbons were observed at d 187.2
active and more selective than are cobalt-based catalysts. However,
these rhodium-based catalysts tend to decompose under reaction
conditions needed for the hydroformylation of long chain alkenes
1
19
and d 185.0 respectively. The H NMR spectra of compound 3
(C > 10). Consequently, cobalt-based catalytic systems employ-
showed resonances characteristic of the [COEt] moiety. A triplet
resonance was observed at d 0.82, and a quartet resonance was
observed at d 2.92. The resonances attributable to the IMes ligand
were analogous to those recorded for the compounds 1 and 2, the
ing the strong r-donor tertiary phosphine PBu and [Co(CO) ]
3
4 2
are favoured for the hydroformylation of long chain alkenes (C
> 10). The use of strong r-donor tertiary phosphine ligand has
been shown to increase the linear/branched selectivity of the
1
36
carbene carbon was observed at d 186.5. The H NMR spectrum
catalytic system. Thus knowing that N-heterocyclic carbenes
of the compound 4 showed a singlet resonance at d −13.12 that
was due to the Co–H hydrogen. Two resonances assignable to the
methyl mesityl protons were observed at ca. d 2.0 (12H) and ca.
d 2.1 (6H). Two further resonances were observed at d 6.18 and
d 6.79 and were assigned to the imidazole backbone protons and
aromatic mesityl protons respectively. Resonances consistent with
are generally stronger r-donors than are tertiary phosphines,
then [Co(IMes)(CO) (H)] may be expected to show good product
3
selectivity.
19
Van Rensburg et al. have tested the related compound
[Co(IMes)(CO) ] . They showed that when heated at 170 C under
◦
3 2
60 bar of synthesis gas in a 50 ml autoclave, no hydroformylation of
1-octene was observed. Decomposition of the pre-catalyst to give
1
3
1
a metal coordinated IMes ligand were observed in the C{ H}
NMR spectra, the carbene carbon was observed at d 187.8.
The IR spectrum of the compound 1 in Nujol shows three bands:
+
−
[1,3-bis(2,4,6-trimethylphenyl)imidazolium] [Co(CO) ] was sug-
4
gested. Having shown that the compound, [Co(IMes)(CO) (H)]
3
−
1
−1
two strong bands at 1940 cm and 1926 cm , and a weaker
is stable with respect to dimerisation at room temperature, it was
hoped that it would be an active hydroformylation catalyst under
much milder conditions.
−
1
band at 2018 cm . The weak band may be assigned to the A
1
m(CO)terminal totally symmetric stretch, while the two strong bands
may be assigned to the m(CO)terminal E mode. This contrasts with
The compound [Co(IMes)(CO) (H)] was tested for the hydro-
3
compounds of the type [Co(L)(CO)
which typically exhibit 2 m(CO)terminal bands corresponding to the
and E modes, as expected for a molecule of C3v symmetry.
The IR spectrum of the compound 2 shows a weak band at
3
(R)] (L = tertiary phosphine),
formylation of 1-octene. In a typical experiment an autoclave was
vacuum dried and purged with synthesis gas. Samples were then
analysed by GC at the indicated time. Products were identified
by comparison of retention times. The conditions employed and
product distribution observed are summarised in Table 4.
A
1
−
1
−1
2038 cm , and a pair of stronger bands at 1964 and 1930 cm .
These three bands may be attributed to m(CO)terminal. A further
band, observed at 1652 cm , corresponds to m(CO)acyl. The IR
Inspection of Table 4 shows selectivity for the more highly sub-
stituted 2-methyl-octanal product, rather than the linear nonanal.
Only small amounts of alcohol were recorded, presumably due to
the low temperature used. This high selectivity for the branched
aldehyde product in unusual, and may indicate that the alkene
first isomerises to give an internal alkene before hydroformyla-
tion occurs. These preliminary results show that the compound
−
1
−
1
spectrum of the compound 3 showed two absorptions at 1600 cm
−
1
and 1648 cm , assigned to m(CO)acyl. The observation of two
absorptions suggests the presence of two distinct [COEt] groups.
For the compound 4 the principle m(CO) IR absorptions were
recorded at 1936 cm , 1944 cm and 2023 cm . This pattern
was analogous to that recorded for both [Co(IMes)(CO) (Me)]
and [Co(IMes)(CO) (COMe)] and suggests that the compound
shares the same symmetry as these compounds. This supports
a structure in which the IMes ligand and hydride ligand are in
−
1
−1
−1
3
[Co(IMes)(CO) (H)] can catalyse the hydroformylation of 1-
3
3
octene under very mild conditions. By contrast the cobalt tertiary
4
phosphine analogues [Co(PR )(CO) (H)] are typically formed in
3
3
19,30–35
situ from the precursor dimers [Co(L)(CO) ] ,
3
2
under higher
3
Table 4 Hydroformylation results for 1-octene using [Co(IMes)(CO) (H)]
Reaction conditions
Conversion (%)
47.3
Nonanal (%)
4.5
1-Nonanol (%)
3.5
2-Methyl-octanal (%)
39.3
◦
8
atm syngas, 50 C, 1 mol% catalyst, toluene, 17 h
4
166 | Dalton Trans., 2006, 4164–4168
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−
1
pressures of synthesis gas. The low thermal stability of compounds
[s, Co(CO)
2018w (C≡O).
3
]. mmax/cm (Nujol, KBr) 1926s (C≡O), 1940s (C≡O),
21
of the type [Co(PR
3
)(CO)
3
(H)] at lower pressures, has resulted
in more forcing conditions being used in reported tests, which are
not directly comparable with the data reported here.
Preparation of [Co(IMes)(CO) (COMe)] (2)
3
Carbon monoxide was passed through
a
solution of
Conclusion
[Co(IMes)(CO) (Me)] (100 mg, 0.216 mmol) in diethyl ether
3
(20 ml) at rt for 20 min. Solvents were then removed under reduced
In the system [Co(L)(CO)
N-heterocyclic carbene results in a less labile [Co(L)(CO)
system and increased stability of the hydride [Co(L)(CO)
IMes. This hydride compound is an active hydroformylation
catalyst.
3
(R)], the replacement of L = PR
3
by L =
(R)]
(H)], L =
pressure to give 2 as a yellow solid, which was isolated by filtration
and dried in vacuo (105 mg, 99%). Crystals of 2 suitable for X-
ray crystal structure determination were grown from a saturated
diethyl ether–pentane solution. (Found: C, 62.6; H, 5.7; N, 5.2
3
3
C
26
H
27CoN
2
O
4
requires C, 63.7; H, 5.6; N, 5.7); d
Si) 1.99 [12H, s, o-CH ], 2.10 [6H, s, p-CH
], 6.10 [2H, s, NCHCHN], 6.77 [4H, s, ArH];
:Me Si) 17.77 [s, o-CH ], 20.93 [s, p-
], 47.41 [s, COCH ], 123.78 [s, NCHCHN], 129.30 [s,
Mes C3.5], 135.85 [s, Mes C2.6], 137.85 [s, Mes C ], 139.52 [s, Mes
], 238.74 [s, COCH ].
H
(500.0 MHz,
C
6
D
6
:Me
4
3
C
6
H
2
3
C
6
H
2
],
Experimental
2.48 [3H, s, COCH
(75.5 MHz, C
CH
3
d
C
6
D
6
4
3
C
6
H
2
All manipulations of air- and/or moisture-sensitive compounds
were carried out under an inert atmosphere of dinitrogen, in
either an inert-atmosphere box or using standard Schlenk line
techniques. Solvents used in the preparation of air- and/or
moisture-sensitive compounds were dried by passage through
an alumina column under a positive pressure of dinitrogen.
Dinitrogen was passed through the dried solvents for 20 min
before use. Deuterated solvents were degassed using three freeze–
pump–thaw cycles and were vacuum distilled from potassium or
3
C
6
H
2
3
4
C
1
], 184.96 [s, NCN], 201.78 [s, Co(CO)
3
3
−1
mmax/cm (Nujol, KBr) 1652m, 1930s, 1964s, 2038w.
Preparation of [Co(IMes)(CO) (COEt)] (3)
3
Asolution of [Co(PPh
3
)(CO)
3
(Et)] (220 mg, 0.507 mmol) and IMes
(150 mg, 0.500 mmol) in diethyl ether (20 ml) was stirred at rt for
1
h. CO was then passed through the resulting yellow/orange
sodium (d
6
-benzene). Solution NMR spectra were recorded with
1
13
solution at rt for 30 min. Solvents were then removed in vacuo
to leave a yellow solid, which was washed with cold pentane
(2 × 20 ml), and vacuum dried (145.5 mg, 56.8%). (Found: C,
either a Varian UNITYplus ( H: 500.0 MHz, C: 125.7 MHz,
3
1
1
13
P: 202.4 MHz) or a Varian Mercury 300 ( H: 300.2 MHz, C:
3
1
7
5.5 MHz, P: 121.5 MHz). The spectra were either internally
1
64.5; H, 6.3; N, 5.1 C H CoN O requires C, 64.3; H, 5.8;
referenced relative to the residual protio-solvent ( H) and solvent
27
32
2
4
3
1
3
1
13
N, 5.5); dH (500.0 MHz, C D Me Si) 0.84 [t, J = 7.28 Hz,
2 3 3 6 2
(
C) resonances relative to tetramethylsilane ( H, C, d = 0
ppm), or were referenced externally, relative to H PO
( P, d =
ppm). Infrared spectra were recorded on either a Perkin-
Elmer 1710 FTIR spectrometer or a Perkin-Elmer 1600 FTIR
6
6:
4
HH
3
1
3H, COCH CH ], 2.01 [s, 12H, o-CH C H ], 2.10 [s, 6H, p-
3
4
3
CH
3
C
6
H
2
], 2.95 [q, JHH = 7.24 Hz, 2H, COCH
2
CH
3
], 6.08 [s,
Si)
0
2
H, NCHCHN], 6.78 [s, 4H, ArH]; d
C
(75.5 MHz, C
6
D
6:Me
4
−
1
8.69 [s, COCH CH ], 16.27 [s, o-CH C H ], 19.45[s, p-CH C H ],
instrument in the range 4000–400 cm . Samples were prepared
as Nujol mulls between KBr plates. Data are quoted in wave
numbers (cm ). The following compounds were synthesised
2
3
3
6
2
3
6
2
5
4.28 [s, COCH
2
CH ], 123.77 [s, NCHCHN], 129.64 [s, Mes C3.5],
3
−
1
136.00 [s, Mes C ], 137.24 [s, Mes C ], 139.68 [s, Mes C ], 186.48
2.6
4
1
−
1
37
[s, NCN], 203.10 [s, Co(CO) ], 242.98 [s, COCH CH ]. mmax/cm
by modifications of literature methods: [Co(PPh
3
)(CO)
3
(Me)],
3
2
3
37
38,39
(Nujol, KBr) 1600w, 1648m, 1830m, 1928s, 1966s, 2050w.
[
Co(PPh
Preparation of [Co(IMes)(CO)
A solution of 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene
3
)(CO)
3
(Et)], IMes.
Preparation of [Co(IMes)(CO) (H)] (4)
3
3
(Me)] (1)
A
yellow solution of [Co(IMes)(CO)
3
(COMe)] (100 mg,
0
.216 mmol) in diethyl ether (20 ml) was stirred under a 1 atm
(
72 mg, 0.238 mmol) in diethyl ether (10 ml) was added to a
dihydrogen atmosphere for 17 h. During this time the solution
darkened to an orange/brown colour. Removal of solvents under
solution of [Co(PPh )(CO) (Me)] (100 mg, 0.238 mmol), in diethyl
3
3
ether (10 ml). The resulting solution was stirred for 3 h during
which a small amount of precipitate formed. This mixture was
filtered, and the resulting yellow solution was concentrated to ca.
reduced pressure afforded [Co(IMes)(CO)
solid, which was dried in vacuo (85 mg, 88.5%). (Found: C, 62.8;
H, 6.3; N, 5.6 C24 requires C, 64.3; H, 6.2; N, 5.6); d
500.0 MHz, C
Si) −13.12 [H, s, Co–H], 2.03 [12H, s, o-
CH ], 2.11 [6H, s, p-CH ], 6.18 [2H, s, NCHCHN], 6.79
4H, s, ArH]; d (75.5 MHz, C Si) 17.88 [s, 12H, o-CH ],
1.07 [s, 6H, p-CH ], 47.41 [s, COCH ], 123.21 [s, NCHCHN],
29.57 [s, Mes C3.5], 135.71 [s, Mes C2.6], 137.52 [s, Mes C ],
3
(H)] as a yellow orange
H
25CoN
2
O
3
H
1
0 ml. Pentane (10 ml), was then added, and the resultant solution
(
6
D
6:Me
4
◦
cooled to −80 C. The compound 1 then formed as a yellow
3
C
6
H
2
3
C
6
H
2
crystalline solid, which was isolated by filtration and dried in vacuo
[
C
6
D
6:Me
4
3
(
89.9 mg, 81.8%). Crystals suitable for X-ray crystal structure
determination were grown from a saturated diethyl ether–pentane
solution. (Found: C, 65.2; H, 6.4; N, 5.8 C25 requires
C, 64.9; H, 5.9 N; 6.1); d (500.0 MHz, C Si) 0.70 [3H, s,
CH ], 2.05 [12H, s, o-CH ], 2.10 [6H, s, p-CH ], 6.13
2H, s, NCHCHN], 6.79 [4H, s, ArH]. d (75.5 MHz, C :Me Si)
7.76 [s, Co–CH ], 17.98 [s, o-CH ], 21.08 [s, p-CH ],
23.53 [s, NCHCHN], 129.64 [s, Mes C3.5], 135.84 [s, Mes C2.6],
37.50 [s, Mes C ], 139.36 [s, Mes C ], 187.23 [s, NCN], 204.39
2
1
1
3
3
4
−
H
27CoN
2
O
3
1
39.31 [s, Mes C
1
], 188.80 [s, NCN], 201.67 [s, Co(CO) ]. mmax/cm
3
H
6
D
6
:Me
4
(Nujol, KBr) 1936s, 1944s, 2023w.
3
3
C
6
H
2
3
C
6
H
2
[
C
6
D
6
4
Reactivity of [Co(IMes)(CO) (H)] towards hydroformylation
3
−
3
3
C
6
H
2
3
C
6
H
2
1
1
Catalytic runs were performed using a Buchi Ag Miniclave reactor
fitted with a glass jacket. Heating and stirring was facilitated
4
1
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Dalton Trans., 2006, 4164–4168 | 4167

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by immersing the glass jacket in a paraffin oil bath, placed
on a stirrer hotplate. The autoclave was dried under vacuum,
and purged three times with syngas before introduction of the
test solution. Test solutions were introduced into the autoclave
using an over pressure of dinitrogen, via a vacuum/nitrogen
manifold. The autoclave was then purged three times with syngas,
before introducing the final test pressure into the autoclave.
3 H. W. Wanzlick, B. Lachmann and E. Schikora, Chem. Ber., 1965, 98,
3
170–3177.
4
5
H. W. Wanzlick and H. Ahrens, Chem. Ber., 1964, 97, 2447–2450.
H. W. Wanzlick and E. Schikora, Chem. Ber., 1961, 94, 2389–2393.
6 H. W. Wanzlick and H. J. Kleiner, Angew. Chem., 1961, 73, 493.
7 H. W. Wanzlick, Angew. Chem., Int. Ed. Engl., 1962, 74, 129–134.
8
9
H. W. Wanzlick and E. Schikora, Angew. Chem., 1960, 72, 494.
A. J. Arduengo, III, M. Kline, J. C. Calabrese and F. Davidson, J. Am.
Chem. Soc., 1991, 113, 9704–9705.
The compound [Co(IMes)(CO)
3
(H)] (3.5 mg. 0.0078 mmol) was
10 A. J. Arduengo, III, WO Pat., 9114678, 1991.
1 A. J. Arduengo, III, R. L. Harlow and M. Kline, J. Am. Chem. Soc.,
1
dissolved in 10 ml of toluene. 1-Octene (114 ll, 0.726 mmol) was
then added to the solution. The resulting yellow solution was
then introduced into the autoclave, and a pressure of 8 atm of
1
991, 113, 361–363.
1
2 A. F u¨ rstner, O. R. Thiel, L. Ackermann, H.-J. Schanz and S. P. Nolan,
J. Org. Chem., 2000, 65, 2204–2207.
◦
syngas introduced. The solution was then heated at 50 C for
13 W. A. Herrmann, Angew. Chem., Int. Ed. Engl., 2002, 41, 1290–1309.
¨
1
4 K. Ofele, W. A. Herrmann, D. Mihalios, M. Elison, E. Herdtweck, W.
1
7 h under stirring. The autoclave was then allowed to cool,
Scherer and J. Mink, J. Organomet. Chem., 1993, 459, 177–184.
5 D. S. McGuinness, K. J. Cavell, B. F. Yates, B. W. Skelton and A. H.
White, J. Am. Chem. Soc., 2001, 123, 8317–8328.
and depressurised. Visual inspection of the solution at the end
of the reaction showed a homogeneous yellow solution. An
aliquot was then analysed by GC. Conversions were estimated by
integration, assuming that all species had the same sensitivity in the
FID detector. The conditions employed and product distribution
observed are summarised in Table 4.
1
16 H. M. J. Wang and I. J. B. Lin, Organometallics, 1998, 17, 972–975.
1
1
1
2
2
7 S. A. Llewellyn, M. L. H. Green and A. R. Cowley, Dalton Trans.,
006, 1776–1783.
2
8 S. E. Gibson, C. Johnstone, J. A. Loch, J. W. Steed and A. Stevenazzi,
Organometallics, 2003, 22, 5374–5377.
9 H. Van Rensburg, R. P. Tooze, D. F. Foster and A. M. Z. Slawin, Inorg.
Chem., 2004, 43, 2468–2470.
0 V. K. Dioumaev, D. J. Szalda, J. Hanson, J. A. Franz and R. M. Bullock,
Chem. Commun., 2003, 1670–1671.
1 J. S. Leigh and K. H. Whitmire, Acta Crystallogr., Sect. C: Cryst. Struct.
Commun., 1989, C45, 210–212.
22 S. A. Llewellyn, M. L. H. Green and A. R. Cowley, J. Organomet.
Chem., 2005, 690, 2358–2364.
3 V. Galamb and G. Palyi, Coord. Chem. Rev., 1984, 59, 203–238.
4 E. Fooladi, B. Dalhus and M. Tilset, Dalton Trans., 2004, 3909–
3917.
Crystallography
Data collections were performed by Dr A. R. Cowley, us-
ing an Enraf-Nonius KappaCCD diffractometer (graphite-
˚
monochromated Mo-Ka radiation, k = 0.71073 A). Intensity data
40
were processed using the DENZO-SMN package. The crystal
structures were solved using direct-methods program SIR92,
which located all non-hydrogen atoms. Subsequent full-matrix
2
2
41
42
2
2
5 R. W. Simms, M. J. Drewitt and M. C. Baird, Organometallics, 2002,
least-squares refinement was carried out using the CRYSTALS
2
1, 2958–2963.
program suite. Coordinates and anisotropic thermal parameters
of all non-hydrogen atoms were refined. Hydrogen atoms were
positioned geometrically after each cycle of refinement. A 3-
term Chebychev polynomial weighting scheme was applied. The
hydrogen atoms were all positioned geometrically. For the ortho-
methyl groups a difference Fourier map suggested that they were
oriented with one CH pointing away from the bulky imidazole
substituents (and hence in the plane of the phenyl ring) and
they were positioned accordingly. The para-methyl hydrogens were
poorly defined in the Fourier map, possibly as a result of disorder
and were positioned geometrically at what appeared to be the
preferred orientation. Crystal structure diagrams were produced
6 A. W. Coleman, P. B. Hitchcock, M. F. Lappert, R. K. Maskell and
J. H. Muller, J. Organomet. Chem., 1985, 296, 173–196.
27 I. Kovacs and F. Ungvary, Coord. Chem. Rev., 1997, 161, 1–32.
2
2
8 C. A. Tolman, Chem. Rev., 1977, 77, 313–348.
9 D. J. Darensbourg, A. L. Phelps, N. Le Gall and L. Jia, J. Am. Chem.
Soc., 2004, 126, 13808–13815.
30 M. Haumann, R. Meijboom, J. R. Moss and A. Roodt, Dalton Trans.,
2004, 1679–1686.
3
3
3
3
1 R. Meijboom, M. Haumann, A. Roodt and L. Damoense, Helv. Chim.
Acta, 2005, 88, 676–693.
2 M. J. Chen, R. J. Klingler, J. W. Rathke and K. W. Kramarz,
Organometallics, 2004, 23, 2701–2707.
3 C. Dwyer, H. Assumption, J. Coetzee, C. Crause, L. Damoense and M.
Kirk, Coord. Chem. Rev., 2004, 248, 653–669.
4 A. Polas, J. D. E. T. Wilton-Ely, A. M. Z. Slawin, D. F. Foster, P. J.
Steynberg, M. J. Green and D. J. Cole-Hamilton, Dalton Trans., 2003,
4669–4677.
42
using the CRYSTALS program suite.
CCDC reference numbers 291790 and 291791.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b604200g
3
3
3
3
5 C. D. Wood and P. E. Garrou, Organometallics, 1984, 3, 170–174.
6 E. R. Tucci, Ind. Eng. Chem. Proc. Des. Dev., 1968, 7, 32–38.
7 C. C. Tso and A. R. Cutler, Polyhedron, 1993, 12, 149–158.
8 A. J. Arduengo, III, H. V. R. Dias, R. L. Harlow and M. Kline, J. Am.
Chem. Soc., 1992, 114, 5530–5534.
Acknowledgements
3
4
4
9 L. Jafarpour, E. D. Stevens and S. P. Nolan, J. Organomet. Chem., 2000,
6
06, 49–54.
We thank the EPSRC for a grant (S.A.L).
0 Z. Otwinowski and W. Minor, Methods Enzymol., 1997, 276, 307–
3
26.
1 A. Altomare, G. Carascano, C. Giacovazzo and A. Guagliardi, J. Appl.
Crystallogr., 1993, 26, 343.
42 D. J. Watkin, C. K. Prout, J. R. Carruthers, P. W. Betteridge and R. I.
Cooper, CRYSTALS, Chemical Crystallography Laboratory, Oxford,
UK, 2001.
References
¨
1
2
K. Ofele, J. Organomet. Chem., 1968, 12, P42–P43.
H. W. Wanzlick and H. J. Schoenherr, Angew. Chem., Int. Ed. Engl.,
968, 7, 141–142.
1
4
168 | Dalton Trans., 2006, 4164–4168
This journal is © The Royal Society of Chemistry 2006