Solution and solid state conformation of Fischer carbene complexes vis-à-vis conformation of aryl carboxamides: Complexation of the aromatic ring by tricarbonylchromium makes a difference

Article abstract of DOI:10.1016/S0022-328X(00)00728-2

Crystallography and proton NMR spectroscopy were used to compare the conformations of aryl amino Fischer carbene complexes with structurally analogous aryl carboxamides. The similarity disappears when the aromatic rings were complexed with tricarbonylchro

Full text of DOI:10.1016/S0022-328X(00)00728-2

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Journal of Organometallic Chemistry 617–618 (2001) 709–722
Solution and solid state conformation of Fischer carbene
complexes vis-a`-vis conformation of aryl carboxamides:
complexation of the aromatic ring by tricarbonylchromium makes
a difference
K.N. Jayaprakash a, Debasis Hazra a, Karl S. Hagen b, Uttamkumar Samanta c,
Mohan M. Bhadbhade a, Vedavati G. Puranik a, Amitabha Sarkar a,*
a National Chemical Laboratory, Pune 411 008, India
b Department of Chemistry, Emory Uni6ersity, Atlanta GA 30322, USA
c Structure and Analysis group, Department of Biochemistry, P-1/12 CIT Scheme VIIM, Bose Institute, Calcutta 700 054, India
Received 22 September 2000; accepted 9 October 2000
Abstract
Crystallography and proton NMR spectroscopy were used to compare the conformations of aryl amino Fischer carbene
complexes with structurally analogous aryl carboxamides. The similarity disappears when the aromatic rings were complexed with
tricarbonylchromium groups. Details of synthesis, spectral and analytical data for all new compounds are provided. © 2001
Elsevier Science B.V. All rights reserved.
Keywords: Fischer carbene complexes; Aryl carboxamides; Arene chromium complexes
1. Introduction
In our earlier study on the solution conformation of
Fischer carbene complexes [2], we have shown that the
aromatic ring attached to the carbene carbon is ori-
ented orthogonal to the metal–carbene p-plane, as
commonly observed in solid state [3]. The two possible
conformers differ in the orientation of the hetero atom
substituent which is either syn or anti with respect to
the M (CO)5 group (structures I and II, Chart 2).
In the anti orientation (as in I), the substituent is
placed in the anisotropic shielding zone of the aromatic
ring, so that its protons experience an upfield shift of
about 0.9–1.0 ppm compared to the same protons in
the syn conformer (II). When X is oxygen, the two
conformers can be observed at low temperatures (below
−40°C). If X is nitrogen, relatively high barrier of
rotation about the CcarbeneꢀN bond allows observation
of distinct signals of syn and anti substituents in the
1H-NMR spectra at ambient temperature. When the
aromatic ring attached to the carbene carbon is unsym-
metrically substituted, the methylene protons of a ben-
zyl group on X (in the anti conformer I) show clear
A deviation from coplanarity has often been ob-
served for sterically constrained, ortho-substituted aryl
carboxamides [1]. The amide plane is twisted away
from the plane of the aromatic ring, as presented in
Chart 1, giving rise to an axial disymmetry. Since the
N-substituent of the amide group faces the aromatic
ring in such a structure, the relevant set of protons are
likely to be shielded by the aromatic ring current
anisotropy.
Chart 1.
* Corresponding author.
E-mail address: sakar@ems.ncl.res.in (A. Sarkar).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00728-2

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mined in open capillary tubes on a Thermonik Camp-
bell melting point apparatus and are uncorrected.
2.1. General procedure for the preparation of
pentacarbonyl (ethoxy aryl)-chromium (0) complexes
1a–f
All alkoxy carbene complexes were prepared accord-
ing to Fischer’s original procedure [9]. Appropriate
aryllithiums (1.5 n mmol) were treated with chromium
hexacarbonyl (1 n mmol) in diethyl ether at 0°C. The
temperature was raised to 20–25°C in about 30 min.
The solvent was evaporated to dryness under reduced
pressure and the residue was dissolved in a small
amount cold water. A dichloromethane solution of
triethyloxonium tetrafluoroborate (1.5 n mmol) was
added to the aqueous solution and the complexes were
extracted with petroleum ether. Pure product was ob-
tained after filtration through a small plug of flash
silica. For 1a, 1b, 1c see ref. [2].
Chart 2.
diastereotopicity, and this feature was indeed used as a
corroborative evidence for the conformation assign-
ment. If the conformation of the molecule undergoes no
significant change upon complexation of the aromatic
ring with a Cr (CO)3 group, one could monitor the
relative magnitude of the anisotropic effect of the aro-
matic ring on hetero atom substituent in presence or in
absence of Cr (CO)3 complexation to the aromatic ring
(III versus I, Chart 2). Complexation of Cr (CO)3 to an
aromatic ring is likely to perturb the ring current [4]
which is responsible for its anisotropic shielding effect.
It was of interest, therefore, to compare the struc-
tural details of ortho-substituted phenyl carboxamides
with analogous Fischer carbene complexes (CꢁO re-
placed by CꢁCr (CO)5 group), and examine the fate of
anisotropic shielding of N-substituents when the aro-
matic ring is coordinated to a tricarbonyl chromium
group.
2.1.1. Preparation of complex 1d
2-Methylanisole (0.86 ml, 6.81 mmol) was treated
with n-butyllithium (4.68 ml, (1.6 M solution in hex-
ane), 7.5 mmol) at 10–20°C in diethyl ether (20 ml) and
the reaction mixture stirred at room temperature (r.t.)
for 20 h. After treatment with Cr (CO)6 (1 g, 4.54
mmol) and triethyl oxoniumtetrafluoroborate (6.8 ml,
6.8 mmol) as described before, the product was ob-
tained (1.1 g, 65%) as a red liquid, IR w (CO) 2069.2
(m), 1974 (sh), 1930 (s) cm−1 1H-NMR (CDCl3) l 1.6
(t, J=6 Hz, 3H, ethyl-CH3), 2.35 (s, 3H, CH3), 3.75 (s,
3H, OCH3), 4.45 (bs, 2H, ethyl-CH2), 6.75–7.3 (m, 3H,
Phenyl). 13C-NMR (CDCl3) l 14.81 (ethyl-CH3), 16.39
(CH3), 55.25 (OCH3), 60.71 (ethyl-CH2), 110.92, 120.30,
123.74, 128.23, 131.85, 145.25 (each as for phenyl ring),
216.29, 224.66 (CO), 359.2 (ꢁC).
2. Experimental
2.1.2. Preparation of complex 1e
3,4-Dimethylanisole (0.95 ml, 6.81 mmol) was treated
with n-Butyllithium (4.68 ml, (1.6 M in hexane), 7.5
mmol) at 10–20°C in diethyl ether (20 ml) and the
reaction mixture stirred at r.t. for 20 h. This solution
was treated with Cr (CO)6 (1 g, 4.54 mmol) and triethyl
oxoniumtetrafluoroborate (6.8 ml, 6.8 mmol) yielded
the product (1.20 g, 69%) as a red liquid, IR w (CO)
All reactions were performed under an inert atmo-
sphere of argon. Solvents were dried using standard
procedures and distilled under an inert atmosphere
prior to use. Methylamine was used as commercially
available aqueous solutions as received (40% in water).
Infrared spectra were obtained on a Perkin–Elmer
599B spectrometer in chloroform solution. The 1H-
NMR spectra were recorded on Bruker AC-200 spec-
trometer whereas 13C-NMR spectra were recorded on a
Bruker AC-200 and Bruker AMX 300 spectrometers at
50.3 and 75.8 MHz, respectively using CDCl3 as the
solvent and reported as parts per million downfield of
tetramethylsilane. Elemental analyses of compounds
were carried out on a Carlo–Erba 1100 automatic
analyzer. Melting points in the Celsius scale were deter-
2068.2 (m), 1972 (sh), 1942.5 (s) cm−1 1H-NMR
,
(CDCl3) l 1.52 (t, J=6 Hz, 3H, ethyl-CH3), 2.20 (s,
3H, CH3), 2.30 (s, 3H, CH3), 3.8 (s, 3H, OCH3), 4.38
(bs, 2H, ethyl-CH2), 6.55 (s, 1H, phenyl meta proton),
6.7 (s, 1H, phenyl ortho proton).13C-NMR (CDCl3) l
15.34 (ethyl-CH3), 19.34 (CH3), 20.60 (CH3), 55.85
(OCH3), 75.71 (ethyl-CH2), 112.95, 122.85, 129.04,
130.61, 137.28, 147.27 (each as for phenyl ring), 216.98,
226.12 (CO), 355.12 (ꢁC).

K.N. Jayaprakash et al. / Journal of Organometallic Chemistry 617–618 (2001) 709–722
711
2.1.3. Preparation of complex 1f
3.74 (d, J=5 Hz, 3H, NꢀCH3), 8.69 (bs, 1H, NꢀH),
overlap regions: 2.38 (s, 3H, CH3), 6.4-7.45 (m, 4H,
phenyl protons). 13C-NMR (CDCl3) l syn-3b 37.42
(NꢀCH3), 280.0 (ꢁC) anti-3b 39.02 (NꢀCH3), 283.32 (ꢁC)
overlap regions 21.31 (CH3), 115.82, 117.52, 119.18,
122.13, 127.33, 128.38, 138.42, 149.04, 154.54 (each as for
phenyl ring), 216.99, 223.92 (CO). Anal. Calc. for
C14H11CrO5N: C, 51.70; H, 3.40; N, 4.307. Found C,
51.72; H, 3.35; N, 4.32%.
4-Trimethylsilyl anisole (1.25 g, 6.81 mmol) was
treated with n-butyllithium (4.68 ml, (1.6 M in hexane),
7.5 mmol) at 10–20°C in diethyl ether (20 ml) and the
reaction mixture stirred at r.t. for 20 h. This solution was
treated with Cr (CO)6 (1g, 4.54 mmol) and triethyloxo-
niumtetrafluoroborate (6.8 ml, 6.8 mmol) yielded the
product (1.25 g, 63%) as a red liquid, IR w (CO) 2070 (m),
1
1976 (sh), 1935 (s) cm−1, H-NMR (CDCl3) l 0.35 (s,
9H, SiMe3), 1.58 (t, J=6 Hz, 3H, ethyl-CH3), 3.88 (s,
3H, OCH3), 4.42 (bs, 2H, ehtyl-CH2), 6.95 (m, 2H,
phenyl meta and para proton), 7.5 (m, 1H, phenyl ortho
proton). 13C-NMR (CDCl3) l −1.25 (SiMe3), 14.69
(ethyl-CH3), 55.03 (OCH3), 75.24 (ethyl-CH2), 110.33,
113.52, 125.96, 131.75, 134.72, 149.18 (each as for phenyl
ring), 216.20, 225.32 (CO), 360.23 (ꢁC).
2.1.7. Preparation of complex 3c
Reaction of the complex 1c (1 g, 2.80 mmol) in diethyl
ether (8 ml) and methylamine (0.286 ml, 3.36 mmol)
afforded the product (0.87 g, 90%) as yellow solid, m.p.
113°C IR w (CO) 2056.5 (m), 1975.3 (sh). 1932.6 (s) cm−1
,
1H-NMR (CDCl3) l syn:anti=25:75, syn-3c 3.73 (d,
J=6 Hz, 3H, NꢀCH3), 3.77 (s, 3H, OCH3), 8.69 (bs, 1H,
NꢀH), anti-3c 2.93 (d, J=6 Hz, 3H, NꢀCH3), 3.82 (s,
3H, OCH3), 9.13 (bs, 1H, NꢀH), overlap regions 6.74 (t,
J=8 Hz, 1H, ), 6.90–7.06 (m, 2H), 7.22 (t, J=8 Hz, 1H)
(each as for 4 phenyl protons). 13C-NMR (CDCl3) l
anti-3c 37.48 (NꢀCH3), 223.85 (CO), 280.50 (ꢁC) syn-3c
39.30 (NꢀCH3), 224.05 (CO), 280.01 (ꢁC) overlap regions
55.45 (OCH3), 111.24, 120.99,123.45, 128.53, 137.94,
140.25, 149.06, 151.43 (each as for phenyl ring), 217.52
(CO). Anal. Calc. for C14H11CrO6N: C, 49.28; H, 3.25;
N, 4.11. Found: C, 49.38; H, 3.06; N, 4.01%.
2.1.4. General procedure for the preparation of amino
carbene complexes 3a–f
All amino carbene complexes were prepared according
to the literature procedure [10]. Corresponding pentacar-
bonyl (ethoxy aryl) chromium (0) complexes (n mmol)
in diethyl ether (3 n ml) was treated with methylamine
(1.2 n mmol) at room temperature under argon until the
color changed from red to yellow. The reaction mixture
was diluted with water, extracted with dichloromethane,
and the organic extract was dried over anhydrous
Na2SO4 and concentrated under reduced pressure. The
pure product was isolated by flash chromatography using
dichloromethane (10–20%) in petroleum ether as the
eluent.
2.1.8. Preparation of complex 3d
Reaction of the complex 1d (0.95 g, 2.70 mmol) in
diethyl ether (8 ml) and methylamine (0.275 ml, 3.24
mmol) afforded the product (0.79 g, 85%) as a yellow
liquid IR w (CO) 2066.4 (m), 1965.8 (sh). 1933.5 (s) cm−1
1H-NMR (CDCl3) l syn:anti=40:60, syn-3d 2.32 (s, 3H,
CH3), 8.87 (bs, 1H, N-H), anti-3d 2.29 (s, 3H, CH3), 2.98
(d, J=5 Hz, 3H, NꢀCH3), 3.67 (s, 3H, OCH3), 9.11 (bs,
1H, NꢀH), overlap regions 3.70–3.80 (m, 6H, NꢀCH3
and OCH3), 6.6–7.1 (m, 3H, phenyl protons).
2.1.5. Preparation of complex 3a
Reaction of the complex 1a (0.90 g, 2.76 mmol) in
diethyl ether (8 ml) and methylamine (0.280 ml, 3.31
mmol) afforded the product (0.791 g, 92%) as a yellow
solid, m.p. 121°C, IR w (CO) 2052.1 (m), 1971.1 (sh),
1
1926.8 (s) cm−1, H-NMR l (CDCl3) syn:anti=30:70,
syn-3a 3.75 (d, J=6 Hz, 3H, NꢀCH3), 8.76 (bs, 1H,
NꢀH), anti-3a 2.96 (d, J=6 Hz, 3H, NꢀCH3), 9.13 (bs,
1H, NꢀH) overlap regions 6.65–7.55 (m, 5H, phenyl
protons). 13C-NMR l (CDCl3), syn-3a 39.78 (NꢀCH3),
223.40 (CO), 280.02 (ꢁC), anti-3a 37.48 (NꢀCH3), 223.16
(CO), 282.92 (ꢁC) overlap regions 118.73, 120.77, 126.63,
127.60, 128.26, 128.50, 149.17, 155.27 (each as for phenyl
ring), 216.92 (CO). Anal. Calc. for C13H9CrO5N: C,
50.17; H, 2.91; N, 4.50. Found: C, 50.58; H, 2.68; N,
4.46%.
2.1.9. Preparation of complex 3e
Reaction of the complex 1e (0.90 g, 2.60 mmol) in
diethyl ether (7 ml) and methylamine (0.265 ml, 3.13
mmol) afforded the product (0.81 g, 94%) as a yellow
solid, m.p. 118°C, IR w (CO) 2057 (m), 1980 (sh), 1930
(s) cm−1. 1H-NMR (CDCl3) l syn:anti 45:55 syn-3e, 8.85
(bs, 1H, Nꢀh), anti-3e 2.96 (d, J=6 Hz, 3H, NꢀCH3),
9.15 (bs, 1H, NꢀH) overlap regions 2.17 (s, 3H), 2.25 (s,
3H) (each as for CH3), 3.60–3.85 (m, 6H) (NꢀCH3,
OCH3) 6.4–6.7 (m, 2H, phenyl protons). 13C-NMR
(CDCl3) l syn-3e 39.51 (NꢀCH3), 224.08 (CO), 279.93
(ꢁC), anti-3e 37.08 (NꢀCH3), 223.49 (CO), 280.57 (ꢁC),
overlap regions 18.47, 18.62, 19.72 (each as for CH3),
55.02 (OCH3), 112.08, 121.74, 122.77, 127.73, 128.37,
134.98, 136.29, 140.54, 146.51, 148.07 (each as for phenyl
ring), 217.25 (CO). Anal. Calc. for C16H15CrO6N: C,
52.04; H, 4.10; N, 3.79. Found: C, 52.28; H, 4.50; N,
3.68%.
2.1.6. Preparation of complex 3b
Reaction of the complex 1b (0.85 g, 2.5 mmol) in
diethyl ether (7 ml) and methylamine (0.25 ml, 3 mmol)
afforded the product (0.75 g, 92.5%) as a yellow solid,
m.p. 115°C, IR w (CO) 2056 (m), 1980 (sh), 1930 (s)
cm−1, 1H-NMR (CDCl3) l syn:anti=25:75, anti-3b 2.96
(d, J=5 Hz, 3H, NꢀCH3), 9.15 (bs, 1H, NꢀH), syn-3b

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2.1.10. Preparation of complex 3f
6.45–6.55 (m, 2H), 6.97 (d, J=6 Hz, 1H), 7.23 (d,
J=6 Hz, 1H) (for 4 phenyl protons). 13C-NMR
Reaction of the complex 1f (0.90 g, 2.32 mmol) in
diethyl ether (7 ml) and methylamine (0.24 ml, 2.78
mmol) afforded the product (0.82 g, 95%) as a yellow
solid, m.p. 100°C IR w (CO) 2054 (m), 1973 (sh), 1926
(CDCl3)
l
21.46 (CH3), 45.77 (NꢀCH3), 51.22
(NꢀCH3), 115.95, 119.41, 126.47, 128.42, 138.34, 152.
86 (each as for phenyl ring), 217.28, 223.95 (CO),
274.72 (ꢁC). Anal. Calc. for C15H13CrO5N: C, 53.10; H,
3.86; N, 4.12. Found: C, 53.40; H, 3.78; N, 4.08%.
1
(s) cm−1, H-NMR (CDCl3) l syn:anti=45:55 syn-3f
3.00 (d, J=6 Hz, 3H, NꢀCH3), 9.2 (bs, 1H, NꢀH),
anti-3f 3.75 (d, J=6 Hz, 3H, NꢀCH3), 8.8 (bs, 1H,
NꢀH), overlap regions 0.30 (s, 9H, SiMe3), 3.80 (s, 3H,
OCH3), 6.9–7.00 (m , 2H), 7.4 d, J=6 Hz, 1H) (for 3
phenyl protons). 13C-NMR (CDCl3) l syn-3f 37.19
(NꢀCH3), 54.80 (OCH3), 223.39 (CO), 280.89 (ꢁC),
anti-3f 39.55 (NꢀCH3), 54.93 (OCH3), 223.94 (CO),
280.43 (ꢁC), overlap regions −1.38 (SiMe3), 110.03,
110.22, 125.58, 126.4, 131.04, 131.73, 133.32, 133.46,
142.20, 149.08, 150.68 (each as for phenyl ring), 217.14
(CO). Anal. Calc. for C17H19CrO6NSi: C, 49.39; H,
4.63; N, 3.39. Found: C, 49.50; H, 4.50; N, 3.42%.
2.2.3. Preparation of complex 5c
Complex 3c (0.40 g, 1.12 mmol), TBAB (36 mg,
0.112 mmol), 50% aq. NaOH (1 ml) and methyl iodide
(0.35 ml, 5.6 mmol) in benzene (11ml) were stirred for
2 h yielded the product (0.381 g, 91.5%) as yellow solid,
m.p. 82°C, IR w (CO) 2051.1 (m), 1971.1 (sh), 1922.9 (s)
1
cm−1, H-NMR (CDCl3) 3.06 (s, 3H, NꢀCH3), 3.79 (s,
3H, OCH3), 3.97 (s, 3H, NꢀCH3), 6.67 (d, J=8 Hz,
1H), 6.87 (d, J=8 Hz, 1H), 6.99 (t, J=8 Hz, 1H), 7.15
(t, J=8 Hz, 1H) (for 4 phenyl protons). 13C-NMR
(CDCl3) l 45.02 (NꢀCH3), 50.67 (NꢀCH3), 54.87
(OCH3), 110.57, 120.47, 127.16, 140.94, 147.92 (each as
for phenyl ring), 217.17, 223.83 (CO), 271.72 (ꢁC).
Anal. Calc. for: C15H13CrO5N: C, 50.71; H, 3.68; N,
3.94. Found: C, 51.06; H, 3.97; N, 3.94%.
2.2. General procedure for the alkylation of amino
carbene complexes
The carbene complex (n mmol) and tetrabutylammo-
nium bromide (0.1 n mmol) in benzene (10 n ml) was
treated with 50% aqueous NaOH and methyl iodide (5
n mmol) or benzyl bromide (1.5 n mmol). The mixture
was stirred at r.t. under argon until the starting mate-
rial was consumed (TLC, 2 h). The reaction mixture
was diluted with water, extracted with dichloro-
methane, dried, and concentrated under reduced pres-
sure. The pure product was isolated by flash chro-
matography.
2.2.4. Preparation of complex 5d
Complex 3d (0.45 g, 1.22 mmol), TBAB (39 mg,
0.122 mmol), 50% aq. NaOH (1 ml) and methyl iodide
(0.38 ml, 6.08 mmol) in benzene (12 ml) were stirred for
2 h yielded the product (0.32 g, 68.5%) as a yellow
liquid. IR w (CO) 2054.1 (m), 1970.5 (sh), 1928.2 (s)
1
cm−1. H-NMR (CDCl3) l 2.30 (s, 3H, CH3), 3.13 (s,
3H, NꢀCH3), 3.75 (s, 3H, OCH3), 4.03 (s, 3H, NꢀCH3),
6.65 (m, 1H), 6.85–7.25 (m, 2H) (for 3 phenyl protons).
2.2.1. Preparation of complex 5a
Complex 3a (0.50 g, 1.60 mmol), TBAB (51 mg, 0.16
mmol), 50% aq. NaOH (1 ml) and methyl iodide (0.5
ml, 8 mmol) in benzene (15 ml) were stirred for 2 h
yielded the product (0.455 g, 87%) as yellow solid, m.p.
82°C, IR w (CO) 2056 (m), 1971 (sh), 1930 (s) cm−1
1H-NMR (CDCl3) l 3.04 (s, 3H, NꢀCH3), 3.99 (s, 3H,
NꢀCH3), 6.70 (d, J=8 Hz, 2H), 7.05–7.45 (m, 3H)
(each as for 5 phenyl protons). 13C-NMR (CDCl3) l
45.69 (NꢀCH3), 51.10 (NꢀCH3), 118.67, 125.62,
128.36,152.62 (each as for phenyl ring), 217.01, 223.79
(CO), 273.94 (ꢁC), Anal. Calc. for C14H11CrO5N: C,
51.72; H, 3.40; N, 4.307. Found: C, 52.02; H, 3.54; N,
4.39%.
2.2.5. Preparation of complex 5e
Complex 3e (0.50 g, 1.36 mmol), TBAB (43 mg,
0.136 mmol), 50% aq. NaOH (1 ml) and methyl iodide
(0.42 ml, 6.8 mmol) in benzene (13 ml) were stirred for
2 h yielded the product (0.463 g, 89.2%) as a yellow
solid, m.p. 96°C. IR w (CO) 2056 (m), 1976.9 (sh),
1932.5 (s) cm−1 1H-NMR (CDCl3) l 2.17 (s, 3H,
.
CH3), 2,27 (s, 3H, CH3), 3.05 (s, 3H, NꢀCH3), 3.75 (s,
3H, OCH3), 3,95 (s, 3H, NꢀCH3), 6.43 (s, 1H), 6.65 (s,
1H) (for 2 phenyl protons). 13C-NMR (CDCl3) l 18.60,
19.60 (CH3) 44.83, 50.61 (NꢀCH3), 54.87 (OCH3),
111.93, 121.52, 128.08, 135.11, 138.64, 145.82 (each as
for phenyl ring) 217.27, 223.87 (CO), 272. 60 (ꢁC).
Anal. Calc. for C17H17CrO6N: C, 53.27; H, 4.47; N,
3.65. Found: C, 53.61; H, 4.80; N, 3.80%.
2.2.2. Preparation of complex 5b
Complex 3b (0.50 g, 1.54 mmol), TBAB (49 mg,
0.154 mmol), 50% aq. NaOH (1 ml) and methyl iodide
(0.48 ml, 7.7 mmol) in benzene (15 ml) were stirred for
2 h yielded the product (0.472 g, 90.5%) as a yellow
solid, m.p. 83°C, IR w (CO) 2054 (m), 1973.0 (sh),
2.2.6. Preparation of complex 5f
Complex 3f (0.45 g, 1.08 mmol), TBAB (35 mg, 0.108
mmol), 50% aq. NaOH (1 ml) and methyl iodide (0.34
ml, 5.4 mmol) in benzene (11 ml) were stirred for 2 h
yielded the product (0.432 g, 93%) as a yellow solid,
m.p. 87°C IR w (CO) 2080 (m), 2000 (sh), 1955 (s)
1928.7 (s) cm−1 1H-NMR (CDCl3) l 2.35 (s, 3H,
.
CH3), 3.05 (s, 3H, NꢀCH3), 3.98 (s, 3H, NꢀCH3),

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713
1
cm−1. H-NMR (CDCl3) l 0.25 (s, 9H, SiMe3), 3.08 (s,
and stirred for 2 h at −78°C. Cr (CO)6 (n mmol) was
introduced at −78° C to the reaction mixture. 3 n ml
of diethyl ether was added after 30 min. The reaction
mixture was slowly warmed to 0°C (3 h). To this a
dichloromethane solution of triethyloxonium tetra-
fluoroborate (1.5 n mmol) was added. The reaction
mixture was filtered through a small plug of neutral
alumina and the solvent was removed under vacuum at
low temperature. The residue was purified by flash
chromatography (20% dichloromethane in petroleum
ether).
3H, NꢀCH3), 3.8 (s, 3H, OCH3), 4.0 (s, 3H, NꢀCH3),
6.8 (s, 1H), 6.9 (d, J=7.5 Hz, 1H), 7.28–7.35 (m, 1H)
(for 3 phenyl protons). 13C-NMR (CDCl3) l −1.37
(SiMe3), 44.95, 50.64 (NꢀCH3), 54.76 (OCH3), 109.99,
125.09, 131.41, 132.419, 140.48, 148.62 (each as for
phenyl ring), 217.15, 223.86 (CO), 272.31 (ꢁC). Anal.
Calc. for C18H21CrO6NSi: C, 50.58; H, 4.95; N, 3.28.
Found: C, 50.53; H, 4.90; N, 3.20%.
2.2.7. Preparation of complex 5g
Complex 3a (0.50 g, 1.6 mmol), TBAB (52 mg, 0.16
mmol), 50% aq. NaOH (1 ml) and benzyl bromide
(0.274 ml, 2.4 mmol) in benzene (16 ml) were stirred for
2 h yielded the product (0.506 g, 84%) as yellow solid,
m.p. 85°C, IR w (CO) 2066 (m), 1979 (sh), 1934 (s)
2.3.1. Preparation of complex 2a
Benzene tricarbonylchromium complex (1 g, 4.77
mmol) in THF ꢀ15 ml treated with butyllithium (3.24
ml (1.6M in hexane), 5.19 mmol) at −78°C for 2 h.
After reaction with Cr(CO)6 (0.943 g, 4.28 mmol) and
triethyloxoniumtetrafluoroborate (6.5 ml, 6.5 mmol)
yielded the product (1.51 g, 69%) as a dark red solid,
cm−1 1H-NMR (CDCl3) l syn:anti=30:70 syn-5g.
.
2.78 (s, 3H NꢀCH3), 5.51 (s, 2H, NꢀCH2ꢀ), anti-5g.
3.77 (s, 3H, NꢀCH3), 4.51 (s, 2H, NꢀCH2ꢀ), overlap
regions 6.74 (d, J=8 Hz, 2H), 7.00–7.37 (m, 8H) (for
10 phenyl protons). 13C-NMR (CDCl3) l 43.25, 48.35
(NꢀCH3), 61.65, 67.08 (NꢀCH2ꢀ), 118.66, 125.78,
127.00, 127.19, 128.49, 128.59, 129.11, 134.01, 152.92
(each as for phenyl rings), 216.83, 223.83 (CO), 276.32
(ꢁC). Anal. Calc. for C20H15CrO5N: C, 59.86; H, 3.76;
N, 3.49. Found: C, 59.76; H, 3.80; N, 3.50%.
IR w (CO) 2061.8 (m), 1980 (sh), 1946 (s) cm−1. H-
1
NMR (CDCl3) l 1.74 (t, J=7 Hz, 3H, ethyl CH3),
5.10–5.40 (m, 4H, 2-OCH2, 2-aromatic protons), 5.71
(t, J=6 Hz, 1H, phenyl H), 6.01 (d, J=6Hz, 2H,
phenyl H), 13C-NMR (CDCl3) l 15.70 (CH3), 78.39
(CH2), 89.36, 93.47, 95.83, 113.25 (each as for aromatic
carbons), 216.70, 223.61, 231.63 (each as for COs),
335.48 (ꢁC).
2.2.8. Preparation of complex 5h
Complex 3b (0.5 g, 1.54 mmol), TBAB (49 mg, 0.154
mmol), 50% aq. NaOH (1 ml) and benzyl bromide (0.26
ml, 2.3 mmol) in benzene (15 ml) were stirred for 2 h
yielded the product (0.475 g, 79%) as yellow solid, m.p.
2.3.2. Preparation of complex 2b
3-Trimethyltin toluene tricarbonylchromium complex
(1 g, 2.56 mmol) in THF ꢀ8 ml treated with butyl-
lithium (1.76 ml (1.6M in hexane), 2.82 mmol) at
−78°C for 2 h. After reaction with Cr (CO)6 (0.512 g,
2.33 mmol) and triethyloxoniumtetrafluoroborate (3.5
ml, 3.5 mmol) yielded the product (0.892 g, 73%) as a
dark red solid. IR w (CO) 2061.8 (m), 1976 (sh), 1948 (s)
93°C. IR w (CO) 2054.0 (m), 1970.1 (sh), 1928 (s) cm−1
.
1H-NMR (CDCl3) l syn:anti=4060, anti-5h 2.25 (s, 3H
CH3), 3.76 (s, 3H, NꢀCH3), 4.52 (d, J=5 Hz, 2H,
NꢀCH2ꢀ), syn-5h 2.30 (s, 3H, CH3), 2.79 (s, 3H,
NꢀCH3), 5.50 (s, 2H, NꢀCH2ꢀ), overlap regions 6.52–
7.37 (m, 9H) (for phenyl ring). 13C-NMR (CDCl3) l
21.37 (CH3), 42.87, 48.39 (NꢀCH3), 61.40, 66.98
(NꢀCH3), 115.64, 115.86, 119.09, 119.40, 126.36, 126.93,
127.12, 128.09, 128.37, 129.02, 133.85, 138.29, 152.82
(each as for phenyl rings), 216.70, 217.08, 223.46 (CO),
277.36 (ꢁC), Anal. Calc. for C21H17CrO5N: C, 60.72;
H, 4.13; N, 3.37. Found C, 60.72; H, 4.07; N, 3.30%.
1
cm−1. H-NMR (CDCl3) l 1.75 (t, J=6 Hz, 3H, ethyl
CH3), 2.26 (s, 3H, CH3), 5.10–5.40 (m, 3H, 2-OCH2, 1
aromatic proton), 5.59 (d, J=6 Hz, 1H), 5.77 (s, 1H),
5.83 (d, J=6 Hz, 1H) (each as for aromatic protons)
13C-NMR (CDCl3) l 15.72 (ethyl CH3), 21.57 (CH3),
78.55 (OꢀCH2), 90.70, 93.54, 95.39, 95.95, 106.18,
113.91 (each as for aromatic carbons), 216.72, 223.41,
232.41 (each as for COs), 336.75 (ꢁC).
2.3. General procedure for the preparation of
pentacarbonyl {ethoxy
2.3.3. Preparation of complex 2c
Anisole tricarbonylchromium complex (1 g, 4.1
mmol) in THF ꢀ12 ml treated with butyllithium (1.76
ml (1.6M in hexane), 4.5 mmol) at −78°C for 2 h.
After reaction with Cr(CO)6 (0.82 g, 3.72 mmol) and
triethyloxonium tetrafluoroborate (6.2 ml, 6.2 mmol)
yielded the product (1.431 g, 71%) as a dark red solid.
IR w (CO) 2067.7 (s), 2016 (sh), 1959.5 (s), 1890.5 (s)
[(tricarbonylchromium)-p6-aryl]carbene}chromium (0)
complexes 2a–f
All alkoxy carbene complexes were prepared accord-
ing to Fischer’s original procedure [9]. Arene tricabonyl
chromium complex (1.1 n mmol) was dissolved in (3 n
ml) THF under argon, the reaction mixture was cooled
to −78°C using acetone–dry ice bath. The reaction
mixture was treated with butyllithium (1.21 n mmol)
1
cm-1, H-NMR (CDCl3) l 1.60 (t, J=6 Hz, 3H, ethyl
CH3), 3.45 (s, 3H, OꢀCH3), 4.82 (t, J=6 Hz, 1H, aro-
matic proton), 5.02 (d, J=6 Hz, 1H, aromatic proton),

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K.N. Jayaprakash et al. / Journal of Organometallic Chemistry 617–618 (2001) 709–722
5.15–5.35 (m, 3H, 2-OCH2, 1 aromatic H), 5.65 (t,
J=6 Hz, 1H, aromatic H).
matography using dichloromethane (30–40%) in
petroleum ether as the eluent.
2.3.4. Preparation of complex 2d
2.4.1. Preparation of complex 4a
2-Methylanisole tricarbonylchromium complex (1 g,
3.88 mmol) in THF ꢀ12 ml treated with butyllithium
(2.66 ml (1.6M in hexane), 4.26 mmol) at −78°C for 2
h. After reaction with Cr (CO)6 (0.776 g, 3.53 mmol)
and triethyloxonium-tetrafluoroborate (5.3 ml, 5.3
mmol) yielded the product (1.33 g, 68%) as a dark red
solid. IR w (CO) 2065.7 (s), 2012 (sh), 1950.5 (s), 1885
Reaction of the complex 2a (1 g, 2.16 mmol) in
diethyl ether (6 ml) and methylamine (0.221 ml, 2.59
mmol) afforded the product (0.91 g, 94%) as a yellow
solid: m.p. 168°C. IR w (CO) 2080 (m), 2000 (sh), 1950
(s), 1900 (m), 1860 (sh) cm−1. 1H-NMR (CDCl3) l 3.82
(d, J=5Hz, 3H, NCH3), 5.13 (d, J=6 Hz, 2H), 5.25 (t,
J=6 Hz, 2H), 5.70 (t, J=6 Hz, 1H) (each as for
aromatic protons), 9.44 (bs, 1H, NH). 13C-NMR
(CDCl3) l 40.97 (NCH3), 88.62, 90.85, 96.48 (each as
for aromatic protons), 217.19, 223.02, 232.45 (each as
for COs), 270.12 (ꢁC). Anal. Calc. for C16H9Cr2O8N:
C, 42.97; H, 2.02; N, 3.13. Found: C, 43.30; H, 1.87; N,
3.27%.
1
(s) cm−1. H-NMR (CDCl3) l 1.82 (t, J=6 Hz, 3H,
ethyl CH3), 2.24 (s, 3H, CH3), 3.69 (s, 3H, OꢀCH3),
4.80–4.90 (m, 1H, aromatic proton), 5.19–5.35 (m, 4H,
2-OCH2, 1 aromatic proton).
2.3.5. Preparation of complex 2e
3,4-Dimethylanisole tricarbonylchromium complex (1
g, 3.68 mmol) in THF ꢀ12 ml treated with butyl-
lithium (2.52 ml (1.6 M in hexane), 4.04 mmol) at
−78°C for 2 h. After reaction with Cr(CO)6 (0.736 g,
3.35 mmol) and triethyloxonium tetrafluoroborate (5
ml, 5 mmol) yielded the product (1.412 g, 74%) as a
dark red solid. IR w (CO) 2063.7 (s), 2010 (sh), 1959.5
2.4.2. Preparation of complex 4b
Reaction of the complex 2b (0.6 g, 1.26 mmol) in
diethyl ether (4 ml) and methylamine (0.130 ml, 1.512
mmol) afforded the product (0.513 g, 88.5%) as a
yellow solid, m.p. 165°C. IR w (CO) 2080 (m), 1990
1
(sh), 1950 (s) cm−1. H-NMR (CDCl3) l 2.22 (s, 3H,
(s), 1880.5 (s) cm−1
.
1H-NMR (CDCl3) l 1.75 (t,
CH3), 3.82 (d, J=6 Hz, 3H, NꢀCH3), 4.91–5.05 (m,
2H), 5.32 (t, J=6 Hz, 1H), 5.54 (d, J=6 Hz, 1H (each
as for aromatic protons), 9.48 (bs, 1H, NꢀH). 13C-
NMR (CDCl3) l 21.51 (CH3), 40.95 (NꢀCH3), 88.59,
91.59, 93.49, 95.03, 96.63, 106.60 (each as for aromatic
carbons), 217.30, 223.20, 233.95 (each as for COs),
272.16 (ꢁC), Anal. Calc. for C17H11Cr2O8N: C, 44.27;
H, 2.40; N, 3.04. Found: C, 44.62; H, 2.02; N, 2.96%.
J=6Hz, 3H, ethyl CH3), 2.08 (s, 3H, CH3), 2.30 (s, 3H,
CH3), 3.75 (s, 3H, OCH3), 4.97 (s, 1H, aromatic pro-
ton), 5.1–5.3 (m, 3H, 2-OCH2, 1 aromatic proton).
2.3.6. Preparation of complex 2f
4-Trimethylsilylanisole tricarbonylchromium com-
plex (1 g, 3.13 mmol) in THF ꢀ10 ml treated with
butyllithium (2.15 ml (1.6 M in hexane), 3.44 mmol) at
−78°C for 2 h. After reaction with Cr(CO)6 (0.626 g,
2.84 mmol) and triethyloxonium tetrafluoroborate (4.25
ml, 4.25 mmol) yielded the product (1.26 g, 71%) as a
dark red solid. IR w (CO) 2063.7 (m), 2023.2 (sh),
2.4.3. Preparation of complex 4c
Reaction of the complex 2c (1 g, 2.03 mmol) in
diethyl ether (6 ml) and methylamine (0.208 ml, 2.44
mmol) afforded the product (0.895 g, 92.5%) as a
yellow solid, m.p. 160°C. IR w (CO) 2057.9 (m), 1971.1
1
1961.5 (s), 1882.4 (s) cm−1. H-NMR (CDCl3) l 0.28
1
(s, 9H, SiMe3), 1.77 (t, J=6 Hz, 3H, ethyl CH3), 3.71
(s, 3H,OCH3), 5.01 (d, J=5Hz, 1H), 5.10 (d, J=5Hz,
1H) (each as for aromatic protons), 5.23 (q, J=6Hz,
2H, OCH2ꢀ), 5.55–5.65 (s, 1H, aromatic proton).
(sh), 1932.5 (s) cm−1. H-NMR (CDCl3) l 3.69 (s, 3H,
OꢀCH3), 3.82 (d, J=6 Hz, 3H, NꢀCH3), 4.84 (t, J=6
Hz, 1H), 5.08 (d, J=6 Hz, 1H), 5.27 (d, J=6 Hz, 1H),
5.78 (t, J=6 Hz, 1H) (each as for aromatic protons),
9.48 (bs, 1H, NꢀH). 13C-NMR (CDCl3) l 40.89
(NꢀCH3), 56.34 (OꢀCH3), 73.13, 82.57, 92.67, 96.73,
122.01, 138.00 (each as for aromatic carbons), 217.45,
223.65, 232.97 (each as for COs), 270.67 (ꢁC). Anal.
Calc. for C17H11Cr2O9N: C, 42.78; H, 2.32; N, 2.94.
Found: C, 42.35; H, 2.35; N, 2.80%.
2.4. General procedure for the preparation of amino
carbene complexes 4a–h
All amino carbene complexes were prepared accord-
ing to the literature procedure [10]. Pentacarbonyl {eth-
oxy [(tricarbonylchromium)-h6-aryl]carbene}chromium
complexes (n mmol) in diethyl ether (3 n ml) was
treated with methylamine/benzylamine (1.2 n mmol) at
room temperature under argon until the color changes
from red to yellow. The reaction mixture was diluted
with water, extracted with dichloromethane, dried over
anhydrous Na2SO4 and concentrated under reduced
pressure. The pure product was isolated by flash chro-
2.4.4. Preparation of complex 4d
Reaction of the complex 2d (1 g, 1.98 mmol) in
diethyl ether (6 ml) and methylamine (0.202 ml, 2.37
mmol) afforded the product (0.88 g, 90.5%) as a yellow
solid, m.p. 158°C. IR w (CO) 2057.9 (m), 1971.1 (sh),
1934.5 (s) cm−1 1H-NMR (CDCl3) l 2.25 (s, 3H,
.
CH3), 3.75 (s, 3H, OꢀCH3), 3.85 (d, J=5Hz, 3H,

K.N. Jayaprakash et al. / Journal of Organometallic Chemistry 617–618 (2001) 709–722
715
NꢀCH3), 5.00–5.2 (m, 2H), 5.55–5.65 (m, 1H) (each as
2.4.8. Preparation of complex 4h
for aromatic protons), 9.6 (bs, 1H, NꢀH). 13C-NMR
(CDCl3) l 17.04 (CH3), 40.31 (NꢀCH3), 63.18 (OꢀCH3),
78.02, 86.01, 89.08, 96.88, 102.10, 128.85 (each as for
aromatic carbons), 216.69, 224.75, 232.42 (each as for
COs), 270.02 (ꢁC) Anal. Calc. for C18H13Cr2O9N: C,
44.01; H, 2.67; N, 2.85. Found: C, 44.30; H, 2.85; N,
2.95%.
Reaction of the complex 2b (0.5 g, 1.05 mmol) in
diethyl ether (3 ml) and benzylamine (0.137 ml, 1.26
mmol) afforded the product (0.53 g, 94 %) as a yellow
solid, m.p. 105°C. IR w (CO) 2057.9 (m), 1973 (sh),
1
1934 (s) cm−1. H-NMR (CDCl3) l 2.21 (s, 3H, CH3),
5.0–5.10 (m, 2H, NꢀCH2), 5.15–5.35 (m, 3H, Cr(CO)3-
aromatic protons)), 5.56 (d, J=8Hz, 1H, aromatic
protons), 7.47 (s, 5H, phenyl protons), 9.57 (bs, 1H,
NꢀH)). 13C-NMR (CDCl3) l 21.33 (CH3), 30.42
(NꢀCH2), 58.49, 89.17, 92.10, 97.12, 105.02, 128.99,
130.00, 130.30, 130.52, 134.11 (aromatic carbons),
217.57, 223.37, 232.63 (each as for COs), 270.27 (ꢁC).
Anal. Calc. for C23H15Cr2O8N: C, 51.22; H, 3.12; N,
2.60. Found: C, 51.35; H, 3.07; N, 2.51%.
2.4.5. Preparation of complex 4e
Reaction of the complex 2e (1 g, 1.93 mmol) in
diethyl ether (6 ml) and methylamine (0.198 ml, 2.32
mmol) afforded the product (0.875 g, 90%) as a yellow
solid, m.p. 126°C, 2058.0 (m), 1963 (sh), 1932 (s), 1894
1
(s) cm−1. H-NMR (CDCl3) l 2.04 (s, 3H, CH3), 2.36
(s, 3H, CH3), 3.65 (s, 3H, OꢀCH3), 3.8 (d, J=5Hz, 3H,
NꢀCH3), 5.00 (s, 1H), 5.24 (s, 1H) (each as for aromatic
protons), 9.47 (bs, 1H, NꢀH). 13C-NMR (CDCl3) l
17.66 (CH3), 19.13 (CH3), 39.84 (NꢀCH3), 55.31
(OꢀCH3), 75.28, 94.08, 96.91, 110.24, 119.04, 135.32
(each as for aromatic protons), 216.57, 222.75, 232.79
(each as for COs), 269.30 (ꢁC), Anal. Calc. for
C19H15Cr2O9N: C, 45.16; H, 2.99; N, 2.77. Found: C,
45.30; H, 3.15; N, 2.45%.
2.5. General procedure for the alkylation of amino
carbene complexes
The carbene complex (n mmol) and tetrabutylammo-
nium bromide (0.1 n mmol) in benzene (10 n ml) was
treated with 50% aqueous NaOH and methyl iodide (5
n mmol). The mixture was stirred at r.t. under argon
until the starting material was consumed (TLC, 2–3 h).
The reaction mixture was diluted with water and ex-
tracted with dichloromethane. The organic extract was
dried, and concentrated under reduced pressure. The
pure product was isolated by flash chromatography
(30% dichloromethane in petroleum ether).
2.4.6. Preparation of complex 4f
Reaction of the complex 2f (1 g, 1.76 mmol) in
diethyl ether (5 ml) and methylamine (0.18 ml, 2.12
mmol) afforded the product (0.92 g, 94.5%) as a yellow
solid, m.p. 117°C. IR w (CO) 2075 (m), 1995 (sh), 1950
2.5.1. Preparation of complex 6a
1
(s) cm−1. H-NMR (CDCl3) l 0.26 (s 9H, SiMe3), 3.69
Complex 4a (0.50 g, 1.12 mmol), TBAB (37 mg,
0.112 mmol), 50% aq. NaOH (1 ml) and methyl iodide
(0.348 ml, 5.6 mmol) in benzene (11 ml) were stirred for
2.5 h yielded the product (0.451 g, 87.5%) as an or-
ange–yellow solid, m.p. 126°C. IR w (CO) 2055.0 (m),
(s, 3H, OꢀCH3), 3.83 (d, J=6Hz), 3H, NꢀCH3), 5.12
(d, J=6Hz, 1H), 5.18 (s, 1H), 5.76 (d, J=6Hz, 1H)
(each as for aromatic protons), 9.4 (bs, 1H, NꢀH).
13C-NMR (CDCl3) l 1.37 (SiMe3), 40.05 (NꢀCH3),
55.43 (OꢀCH3), 72.71, 91.25, 96.10, 100.44, 120.59,
137.22 (each as for aromatic carbons), 216.80, 223.04,
232.79 (each as for COs), 270.17 (ꢁC). Anal. Calc. for
C20H18Cr2O9NSi: C, 43.80; H, 3.31; N, 2.55. Found: C,
44.14; H, 3.47; N, 2.41%.
1
1965 (sh), 1926 (s) cm−1. H-NMR (CDCl3) l 4.03 (s,
3H, NꢀCH3), 4.05 (s, 3H, NꢀCH3), 5.12 (d, J=6 Hz,
2H), 5.34 (t, J=6 Hz, 2H), 5.70 (t, J=6 Hz, 1H) (each
as for aromatic protons). 13C-NMR (CDCl3) l 44.43
(NꢀCH3), 54.39, 88.81, 89.61, 96.34 (each as for aro-
matic carbons), 217.10, 223.88, 233.34 (each as for
COs), 270.21 (ꢁC) Anal. Calc. for C17H11Cr2O8N: C,
44.27; H, 2.40; N, 3.04. Found: C, 44.16; H, 2.80; N,
2.70%.
2.4.7. Preparation of complex 4g
Reaction of the complex 2a (0.5 g, 1.08 mmol) in
diethyl ether (3 ml) and benzylamine (0.141 ml, 1.30
mmol) afforded the product (0.525 g, 92.5%) as a
yellow solid, m.p. 120°C. IR w (CO) 2057.9 (m), 1976
2.5.2. Preparation of complex 6b
1
(sh), 1934.5 (s) cm−1. H-NMR (CDCl3) l 5.12–5.31
Complex 4b (0.30 g, 0.650 mmol), TBAB (20 mg,
0.065 mmol), 50% aq. NaOH (1 ml) and methyl iodide
(0.202 ml, 3.25 mmol) in benzene (7 ml) were stirred for
2 h yielding the product (0.272 g, 88%) as an orange–
yellow solid, m.p. 132°C. IR w (CO) 2080 (m), 2000
(sh), 1940 (s), 1920 (sh), 1860 (sh) cm-1, 1H-NMR
(CDCl3) l 2.24 (s, 3H, CH3), 4.02 (s, 3H, NꢀCH3), 4.04
(s, 3H, NꢀCH3), 4.99 (d, J=6 Hz, 1H), 5.07 (s, 1H),
5.37 (t, J=6 Hz, 1H), 5.58 (d, J=6 Hz, 1H) (each as
(m, 6H, 5Cr(CO)3-aromatic protons, 1 NꢀCH2ꢀH),
5.65–5.73 (m, 1H, NꢀCH2ꢀH), 7.47 (s, 5H, phenyl
protons)), 9.51 (bs, 1H, NꢀH). 13C-NMR (CDCl3) l
30.41 (NꢀCH2), 58.41, 87.94, 91.48, 96.97, 128.91,
130.01, 130.33, 134.13 (each as for aromatic carbons),
217.24, 223.33, 232.09 (each as for COs), 270.33 (ꢁC).
Anal. Calc. for C22H13Cr2O8N: C, 50.30; H, 2.88; N,
2.67. Found: C, 50.01; H, 2.71; N, 2.47%.

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K.N. Jayaprakash et al. / Journal of Organometallic Chemistry 617–618 (2001) 709–722
for aromatic protons). 13C-NMR (CDCl3) l 21.44 (CH3),
44.47(NꢀCH3), 54.56(NꢀCH3), 88.09, 89.38, 91.16, 97.13,
105.17, 121.08 (each as for aromatic carbons), 217.20,
223.81, 233.75 (each as for COs), 269.68 (ꢁC). Anal. Calc.
for C18H13Cr2O8N: C, 45.48; H, 2.75; N, 2.94. Found: C,
45.15; H, 2.56; N, 2.82%.
2.5.6. Preparation of complex 6f
Complex 4f (0.50 g, 0.91 mmol), TBAB (29 mg, 0.091
mmol), 50% aq. NaOH (1 ml) and methyl iodide (0.280
ml, 4.52 mmol) in benzene (9 ml) were stirred for 2 h,
yielding the product (0.438 g, 85.4%) as an orange–yellow
solid, m.p. 104°C. IR w (CO) 2054.0 (m), 1967.3 (sh),
1930.6 (s) cm−1. 1H-NMR (CDCl3) l 0.29 (s, 9H, SiMe3),
3.78 (s, 3H, OꢀCH3), 4.00 (s, 3H, NꢀCH3), 4.03 (s, 3H,
NꢀCH3), 5.20 (d, J=6 Hz, 1H), 5.30 (s, 1H), 5.67 (d, J=6
Hz, 1H) (each as for aromatic protons). 13C-NMR
(CDCl3) l 1.28 (SiMe3), 29.26 (NꢀCH3), 53.48 (NꢀCH3),
55.51 (OꢀCH3), 74.14, 91.75, 94.72, 99.53, 111.83, 132.80
(each as for aromatic carbons), 216.63, 223.17, 233.61
(each as for COs), 266.27 (ꢁC). Anal. Calc. for
C21H20Cr2O9NSi: C, 44.84; H, 3.58; N, 2.49. Found C,
44.80; H, 3.43; N, 2.34%.
2.5.3. Preparation of complex 6c
Complex 4c (0.50 g, 1.05 mmol), TBAB (34n mg, 0.105
mmol), 50% aq. NaOH (1 ml) and methyl iodide (0.325
ml, 5.25 mmol) in benzene (11 ml) were stirred for 2.25
h yielding the product (0.472 g, 92%) as an orange–yellow
solid, m.p. 125°C. IR w (CO) 2054 (m), 1965 (sh), 1924
(s) cm−1. 1H-NMR (CDCl3) l 3.79 (s, 3H, OꢀCH3), 4.02
(s, 3H, NꢀCH3), 4.04 (s, 3H, NꢀCH3), 4.98 (t, J=6 Hz,
1H), 5.24 (d, J=6 Hz, 1H), 5.36 (d, J=6 Hz, 1H), 5.73
(t, J=6 Hz, 1H) (each as for aromatic protons). 13C-
NMR (CDCl3) l 44.59 (NꢀCH3), 54.27 (NꢀCH3), 56.48
(OꢀCH3), 74.73, 83.23, 91.01, 96.61, 111.54, 132.93 (each
as for aromatic carbons), 217.29, 223.91, 233.94 (each as
for COs), 266. 21 (ꢁC). Anal. Calc. for C18H13Cr2O9N:
C, 44.01; H, 2.67; N, 2.85. Found: C, 43.96; H, 2.35; N,
2.69%.
2.5.7. Preparation of complex 6g
Complex 4g (0.25 g, 0.47 mmol), TBAB (15 mg, 0.047
mmol), 50% aq. NaOH (1 ml) and methyl iodide (0.145
ml, 2.35 mmol) in benzene (5 ml) were stirred for 2 h,
yielding the product (0.215 g, 84%) as an orange–yellow
solid, m.p. 110°C,. IR w (CO) 2056.0 (m), 1971.1 (sh),
1930.6 (s) cm−1 1H-NMR (CDCl3) l 3.80 (s, 3H,
.
NꢀCH3), 5.22 (d, J=8 Hz, 2H, aromatic protons), 5.38
(t, J=8 Hz, 2H, aromatic protons), 5.63 (s, 2H, NꢀCH2),
5.67–5.79 (m, 1H, aromatic proton), 7.25–7.46 (m, 5H,
phenyl protons). 13C-NMR (CDCl3) l 30.30 (NꢀCH3),
42.14 (NꢀCH2ꢀ), 70.63, 88.63, 89.87, 96.31, 127.96,
129.79, 130.23, 133.93 (each as for aromatic carbons),
216.85, 223.74, 233.19 (each as for COs), 277.26 (ꢁC).
Anal. Calc. for C23H15Cr2O8N: C, 51.41; H, 2.82; N, 2.60.
Found: C, 51.35; H, 3.07; N, 2.51%.
2.5.4. Preparation of complex 6d
Complex 4d (0.50 g, 1.02 mmol), TBAB (33 mg, 0.102
mmol), 50% aq. NaOH (1 ml) and methyl iodide (0.320
ml, 5.1 mmol) in benzene (10 ml) were stirred for 2.75
h, yieldingtheproduct(0.443g, 86%)asanorange–yellow
solid, m.p. 141°C. IR w (CO) 2054 (m), 1967 (sh), 1931
1
(s) cm−1. H-NMR (CDCl3) l 2.29 (s, 3H, CH3), 3.76
(s, 3H, OꢀCH3), 4.02 (s, 3H, NꢀCH3), 4.06 (s, 3H,
NꢀCH3), 5.06 (t, J=6Hz, 1H), 5.27 (d, J=6Hz, 1H), 5.66
(d, J=6Hz, 1H) (each as for aromatic protons). 13C-
NMR (CDCl3) l 17.33 (CH3), 45.27 (NꢀCH3), 53.80
(NꢀCH3), 60.72 (OꢀCH3), 79.23, 84.79, 97.54, 100.20,
113.74 (each as for aromatic carbons), 216.57, 22.72,
232.97 (each as for COs), 282.62 (ꢁC). Anal. Calc. for
C19H15Cr2O9N: C, 45.16; H, 2.99; N, 2.77. Found C,
45.60; H, 3.05; N, 2.83%.
2.5.8. Preparation of complex 6h
Complex 4h (0.25 g, 0.46 mmol), TBAB (15 mg, 0.046
mmol), 50% aq. NaOH (1 ml) and methyl iodide (0.140
ml, 2.30 mmol) in benzene (5 ml) were stirred for 2 h,
yielding the product (0.225 g, 87.5%) as an orange–yellow
liquid. IR w (CO) 2057.0 (m), 1969.1 (sh), 1929.6 (s) cm−1
.
1H-NMR (CDCl3) l 2.27 (s, 3H, CH3), 3.79 (s, 3H,
NꢀCH3), 5.01–5.50 (m, 4H, aromatic protons), 5.64 (s,
2H, NꢀCH2) 7.25–7.50 (m, 5H, phenyl protons), 13C-
NMR (CDCl3) l 21.48 (CH3), 30.42 (NꢀCH3), 42.15
(NꢀCH2), 70.66, 88.48, 89.35. 91.53, 97.22, 105.05, 127.97,
129.76, 130.21, 134.02 (each as for aromatic carbons),
216.94, 223.81, 233.66 (each as for COs) 271.35 (ꢁC).
2.5.5. Preparation of complex 6e
Complex 4e (0.50 g, 0.99 mmol), TBAB (32 mg, 0.099
mmol), 50% aq. NaOH and methyl iodide (0.31 ml, 4.95
mmol) in benzene (10 ml) were stirred for 3 h, yielding
the product (0.46 g, 90%) as an orange–yellow solid, m.p.
95°C. IR w (CO) 2054.0 (m), 1950 (sh), 1903. (s),1880 (s),
1
1840 (m) cm−1. H-NMR (CDCl3) l 2.09 (s, 3H, CH3),
2.6. X-ray structure solution of complex Ib, IIb, 5c and
6c
2.35 (s, 3H, CH3), 3.76 (s, 3H, OꢀCH3), 3.97 (s, 3H,
NꢀCH3), 4.02 (s, 3H, NꢀCH3), 5.18 (s, 1H), 5.35 (s, 1H)
(eachasforaromaticprotons). 13C-NMR(CDCl3)l17.97
(CH3), 19.07 (CH3), 44.05 (NꢀCH3), 53.44 (NꢀCH3),
55.61 (OꢀCH3), 78.85, 93.21, 98.06, 109.75, 131.11 (each
as for aromatic carbons), 216.76, 223.15, 232.92 (each as
for COs), 265.87 (ꢁC). Anal. Calc. for C20H17Cr2O9N: C,
46.25; H, 3.30; N, 2.68. Found C, 46.44; H, 3.12; N, 2.64%.
The crystals of the complex Ib were grown from a
petroleum ether–dichloromethane mixture as colorless
prisms. Diffraction data were collected on an Enraf–No-
nius CAD-4 single-crystal X-ray diffractometer. Unit cell
dimensions were determined using 25 machine centered
reflections in the range 135q521. The structure was

K.N. Jayaprakash et al. / Journal of Organometallic Chemistry 617–618 (2001) 709–722
717
solved using SHELXS-86. Least-squares refinement of scale
factors and positional and anisotropic thermal parame-
ters for non-hydrogen atoms were carried out using
SHELXL-93 [16]. The weighting scheme was w=1/
[|2(Fo2)+(0.0914 P)2+0.9733P] where P=(Fo2 +2F2c)/
3. The refinement converged to R=0.0594 for 2578
observed reflections.
The crystals of the complex IIa were grown from
petroleum ether–dichloromethane mixture as pale yellow
prisms. Diffraction data were collected on a crystal of size
0.2×0.24×0.4 mm3 on an Enraf–Nonius CAD-4 single-
crystal X-ray diffractometer, using MoKa radiation. Unit
cell dimensions were determined using 25 machine cen-
tered reflections in the range 85q516. The compound,
C13H13CrNO4, M=299.4, crystallizes in the monoclinic
space group P21/n with 4 molecules per unit cell. a=
thermal parameters for non-hydrogen atoms were carried
out using SHELXL-97 [17]. The weighting scheme was
ꢀ=1/[|2(F0)2+(0.920P)2+0.3958P] where P=(F20+
2Fc2)/3. The refinement converged to R=0.0553 for 2139
observed reflections.
The crystals of the complex 6c were grown from
petroleum ether–dichloromethane mixture as orange
blocks. Unit cell dimensions were determined using 25
machine centered reflections in the range 2.935q5
56.75. The structure was solved using SHELXS-93. Least-
squares refinement of scale factors and positional and
anisotropic thermal parameters for non-hydrogen atoms
were carried out using SHELXL-97. The weighting scheme
was ꢀ=1/[|2(F0)2+(0.1224P)2+0.5297P] where P=
(F20+2Fc2)/3. The refinement converged to R=0.0632
for 2433 observed reflections.
,
10.259 (5), b=12.391 (13), c=10.708 (6) A, i=100.04
3
(5)°, V=1340.3 (17) A , Z=4, Dcalc=1.483 Mg m−3
.
,
3. Synthesis
The structure was solved by direct methods using SHELXS
and subsequent difference Fourier synthesis and refined
by full-matrix least squares on F2 using SHELXL-97 [17].
All the atoms were refined anisotropically and the
refinement converged with a reliability criteria for the
structure of R1=0.0433, Rw=0.1069, w=1/|2[(Fo2)+
(0.0731P)2+0.0000P] where P=(Fo2+2Fc2)/3 from
2352 unique reflections ([I\2|(I)]), from a total of 2591
collected. The residual density in the difference map for
3.1. Preparation of amides
The amides Ia [5] and Ib [6] were readily synthesized
from the corresponding acids. While amide Ia is a liquid
at ambient temperature, amide Ib is a crystalline solid.
Complexation with tricarbonyl chromium was accom-
plished by thermolysis of amide Ia under standard
conditions [7] (Scheme 1). The metal complex IIa is
crystalline solid and provided satisfactory spectral and
analytical data [8].
peak and hole is 0.443 and −0.332 e A−3, respectively.
,
The crystals of the complex 5c were grown from
petroleum ether–dichloromethane mixture as yellow
needles. Diffraction data were collected on a Brucker P4
single-crystal X-ray diffractometer for both crystals. Unit
cell dimensions were determined using 25 machine cen-
tered reflections in the range 4.815q556.76. The struc-
ture was solved using SHELXS-93. Least-squares
refinement of scale factors and positional and anisotropic
3.2. Preparation of amino carbene complexes
The requisite Fischer carbene complexes were synthe-
sized in three steps: Fischer’s original preparation [9] of
alkoxy carbene complexes, displacement of alkoxy group
by methylamino group, and finally methylation of the me-
thylamino carbene complexes, as depicted in Scheme 2.
The alkoxy carbene complexes bearing ortho-OMe
substituent on the aromatic ring are relatively unstable,
they provided satisfactory NMR data but not accurate
elemental analysis. These were immediately converted to
the more stable amino carbene complexes [10] (Chart 3
Scheme 1.
Scheme 2.
Chart 3.

718
K.N. Jayaprakash et al. / Journal of Organometallic Chemistry 617–618 (2001) 709–722
Chart 6.
4. Comparison of structures
1
The H-NMR spectrum of the amide Ia reveals that
Fig. 1. ORTEP diagram of amide Ib.
the chemical shifts of the methyl groups on nitrogen
differ by 0.3 ppm. The lines are slightly broad at 25°C
due to onset of a slow site exchange. For the dibenzy-
lamino group in amide Ib, the methylene protons ap-
pear as four two line signals indicating extensive
chemical shift nonequivalence, the spectra being
recorded at −40°C to obtain clearly resolved lines (two
protons are shielded relative to their expected position
by 0.35 ppm). Since the amide Ia was a liquid, crystal
structure was determined for amide Ib to gain an
insight into the molecular conformation. The ORTEP
diagram is depicted in Fig. 1, Table 1.
and 4). In Scheme 2, the complex 4a-f and 6a-h contain
aromatic rings complexed with tricarbonylchromium.
The structure reveals that one NꢀCH2ꢀ group is
located above the aromatic ring plane (C2ꢀC1ꢀNꢀC16=
0.1°) and thus can experience anisotropic shielding ef-
fect of the aromatic ring current. The chemical shift
difference between two sets of methylene protons is
moderate (0.3 ppm). It may be due to the orientation of
the aromatic ring is not entirely orthogonal
(C3ꢀC2ꢀC1ꢀO=102.4°, C3ꢀC2ꢀC1ꢀN= −77.1°, C7ꢀ
C2ꢀC1ꢀO= −72.9°, C7ꢀC2ꢀC1ꢀN=107.6°).
Chart 4.
When the aromatic ring of the amide Ia is complexed
by Cr (CO)3 moiety, the difference in chemical shift
between two methyl signals diminishes from 0.30 ppm
ppm to 0.03 ppm. This would reflect depletion of the
p-electron density of the aromatic ring. Crystal struc-
ture of complex IIa confirms this explanation (Fig. 2,
Table 2).
The orientation of the amide function with respect to
the aromatic ring is maintained in the same way as the
amide Ia, one methyl group still tilted towards the ring
from a near perpendicular direction. The distance
parameters remaining just about the same, the absence
of anisotropic shielding can be attributed to metal
coordination to the ring [4].
Based on our earlier experience of C-alkylation [11],
alkylation of monoalkylamino complexes was carried
out by a biphasic protocol [12] using 50% aq. NaOH as
base, benzene as the solvent and tetrabutylammonium
bromide as the phase-transfer catalyst (Chart 5 and 6).
Barring three, all amino carbene complexes were iso-
lated as crystalline solids, and their structural character-
ization was validated by spectral and analytical data.
The anti conformer predominates for all the methyl-
amino carbene complexes (3a–3f), as was earlier ob-
served for the benzylamino complexes [2]. The methyl
doublets corresponding to the two conformers appear
between 2.90 (anti ) and 3.76 (syn) ppm for all com-
plexes except 3d. For 3d, the ꢀNCH3 signal appears at
2.30 (anti ) and 2.98 (syn) ppm.
Chart 5.

K.N. Jayaprakash et al. / Journal of Organometallic Chemistry 617–618 (2001) 709–722
719
Table 2
In dimethylamino carbene complexes (5a–5f) two
Crystal data and structure refinement for IIa
signals for Nꢀ (CH3)2 (syn and anti ) are observed at
3.05 and 4.00 ppm. This difference in chemical shift is
typical, the anti Me group is shielded compared to the
syn Me group. A comparison of NꢀMe signals in
monomethylamino complexes (3a–3f) with dimethyl-
amino complexes (5a–5f) is presented in Table 3.
Empirical formula
Formula weight
Temperature (K)
C13H13CrNO4
299.24
293 (2)
Mo−Ka radiation,
u=0.7093
Monoclinic
P21/n
,
Wavelength (A)
Crystal system
Space group
Unit cell dimensions
,
a (A)
10.259 (5)
12.391 (13)
10.708 (6)
100.04 (5)
1340.3 (17)
4
1.483
0.862
616
0.2×0.24×0.4
2.53–24.98
−125h512, 05k514,
05l512
,
b (A)
Table 1
,
c (A)
i (°)
V (A )
Crystal data and structure refinement for Ib
3
,
Empirical formula
Formula weight
Temperature (K)
C22H21NO
315.40
293 (2)
Z
Dcalc (Mg m−3
)
Absorption coefficient (mm−1
F (000)
)
,
Wavelength (A)
Mo−Ka radiation,
u=0.7093
Monoclinic
P21/n
Crystal size (mm3)
Crystal system
Space group
q range for data collection (°)
Index ranges
Unit cell dimensions
,
a (A)
7.339 (2)
12.997 (3)
18.348 (4)
94.53 (2)
1744.7 (7)
4
1.201
0.073
Reflections collected/unique
Refinement method
2591/2352 [Rint=0.0000]
,
b (A)
Full-matrix least-squares on
F2
1.011
,
c (A)
i (°)
V (A )
Goodness-of-fit on F2
Final R indices [R[I\2| (I)]
R indices (all data)
3
,
R1=0.0433, wR2=0.1069
R1=0.0657, wR2=0.1157
0.443 and −0.332
Z
Dcalc (Mg m−3
)
Largest difference peak and hole
Absorption coefficient (mm−1
F (000)
)
(e A−3
)
498
Crystal size (mm)
q max (°)
0.63×0.45×0.25
23.44
Index ranges
−85h58, 05k514,
05l520
2578/2331
Crystal structure determination of a representative
complex, 5c was undertaken, and the ORTEP diagram is
displayed in Fig. 3. As is evident from the structure,
one of the methyl groups attached to the nitrogen, the
C-9 carbon, is placed in the expected region above the
aromatic ring [defined by C (2) to C (7)] to experience
a shielding effect due to aromatic ring current an-
isotropy. The dihedral angle defined by C (9), N (1), C
(1) and C (2) is only 5.3°, while the dihedral angle
defined by C (10), N (1), C (1) and C (2) is −174.7°.
This indicates planarity of the nitrogen substituents-a
consequence of extensive delocalization of the non-
bonded pair of electrons from nitrogen to the metal.
Reflections collected/unique
Refinement method
Full-matrix least-squares on
F2
1.010
Goodness-of-fit on F2
Final R indices R[I\2| (I)]
R1=0.0594, wR2=0.1537
0.140 and −0.315
Largest difference peak and hole
−3
,
(e A
)
,
The bond length [C (1)ꢀN (1) 1.307 A] is thus much
,
shorter than [N (1)ꢀC (10) 1.464 A] and [N (1)ꢀC (9)
,
1.456 A]. The dihedral angle of N (1)ꢀC (1)ꢀC (2)ꢀC (7)
94.4° ascertain that the plane of NMe2 is perpendicular
to the aromatic ring. This establishes the orientation of
the shielded methyl group unequivocally. The dihedral
angles C (15)ꢀCR (1)ꢀC (1)ꢀN (1)ꢀ 34.9° and C
(15)ꢀCR (1)ꢀC (1)ꢀC (2)ꢀ 143.2° further reveal that the
aminocarbene group has a staggered conformation with
respect to the Crꢀ (CO)5 groups, as predicted by theory
[13]. The molecular structure of 5c, therefore, confirms
the relative orientation of groups [14] as deduced from
NMR data (see Tables 4 and 5).
Fig. 2. ORTEP diagram of amide IIa.

720
K.N. Jayaprakash et al. / Journal of Organometallic Chemistry 617–618 (2001) 709–722
Table 3
Compound No.
NꢀCH3 peak position in ppm
Compound No.
NꢀCH3 peak position in ppm
syn
anti
Dl
syn
anti
Dl
3a
3b
3c
3d
3e
3f
3.76
3.75
3.72
2.98
3.73
3.73
2.96
2.96
2.94
2.30
2.96
2.94
0.80
0.79
0.78
0.68
0.77
0.79
5a
5b
5c
5d
5e
5f
3.99
3.98
3.97
4.00
3.97
3.95
3.77
3.76
3.04
3.05
3.06
3.12
3.05
3.05
2.78
2.79
0.95
0.93
0.91
0.88
0.92
0.90
0.99
0.97
5g
5h
recalled that methyl and methylene signals shielded by
aromatic ring anisotropy in 5g appear at 2.78 and 4.51
ppm respectively. Thus, the data indicate that an an-
isotropic effect is practically absent in complexes with
ArꢀCr (CO)3 group. In this respect, the result is consis-
tent with expectations based on the results of chromium
complexed amide 2a described above. The absence of
aromatic ring current could be manifested in the dimin-
ished Dl of syn/anti Me groups. The crystal structure
however revealed a different story.
The crystal structure of a representative complex 6c
was determined by the usual method and has been
described in the Section 3. The ORTEP diagram is
represented in Fig. 4 (see Tables 7 and 8).
Table 5
Fig. 3. ORTEP diagram of complex 5c.
Crystal data and structure refinement for 5c
Table 4
Empirical formula
Formula weight
Temperature (K)
C15H13CrNO6
355.26
300 (2)
,
Selected Bond lengths [A] and angles [°] for 5c
,
Cr(1)ꢀC(11)
Cr(1)ꢀC(1)
N(1)ꢀC(1)
N(1)ꢀC(9)
N(1)ꢀC(10)
C(1)ꢀC(2)
1.856(6)
2.133(5)
1.307(6)
1.456(7)
1.464(7)
1.499(7)
178.3(2)
94.0(2)
C(14)ꢀCr(1)ꢀC(1)
C(12)ꢀCr(1)ꢀC(1)
C(1)ꢀN(1)ꢀC(9)
C(1)ꢀN(1)ꢀC(10)
C(9)ꢀN(1)ꢀC(10)
N(1)ꢀC(1)ꢀC(2)
N(1)ꢀC(1)ꢀCr(1)
C(2)ꢀC(1)ꢀCr(1)
89.3(2)
91.7(2)
Wavelength (A)
1.54178
Orthorhombic
P212121
Crystal system
Space group
125.0(5)
123.6(4)
111.4(5)
114.0(4)
130.1(3)
115.9(3)
Unit cell dimensions
,
a (A)
9.4463 (5)
11.3796 (12)
15.5903 (17)
1675.9 (3)
,
b (A)
,
C(11)ꢀCr(1)ꢀC(1)
C(15)ꢀCr(1)ꢀC(1)
c (A)
3
,
V (A )
Z
4
Calculated density (Mg m−3
)
1.408
5.884
728
Absorption coefficient (mm−1
F (000)
)
In analogous Fischer carbene complexes 6a–f, where
the aromatic ring is complexed with tricarbonylchrom-
ium, the chemical shift difference between syn and anti
Me groups decrease dramatically; the difference in
chemical shift is barely 0.02–0.05 ppm indicating a
drastic reduction in anisotropic shielding effect of the
aromatic ring [15] (see Table 6).
The complexes 6g and 6h illustrate this point vividly.
The chemical shift of NꢀCH3 (syn) signal is 3.80 ppm
for 6g and 3.79 ppm for 6h, while the methylene signal
of NꢀCH2ꢀPh appears at 5.63 and 5.64 ppm. It may be
Crystal size (mm3)
0.10×0.30×0.50
4.81–56.76
−105h510, −125k512,
−155l516
2501/2139 [Rint=0.0334]
Full-matrix least-squares on
F2
q range for data collection (°)
Index ranges
Reflections collected/unique
Refinement method
Goodness-of-fit on F2
Final R indices [R[I\2| (I)]
R indices (all data)
1.068
R1=0.0553, wR2=0.1351
R1=0.0580, wR2=0.1376
Largest difference peak and hole 0.453 and −0.316
−3
,
(e A
)

K.N. Jayaprakash et al. / Journal of Organometallic Chemistry 617–618 (2001) 709–722
721
Table 6
Table 8
Crystal data and structure refinement for 6c
Compound No.
NꢀCH3 peak position in ppm
Empirical formula
Formula weight
Temperature (K)
C18H13Cr2NO9
491.29
299 (2)
Syn
anti
Dl
,
Wavelength (A)
1.54178
6a
6b
6c
6d
6e
6f
4.05
4.04
4.04
4.06
4.02
4.03
3.80
3.79
4.03
4.02
4.01
4.02
3.97
4.00
0.02
0.02
0.03
0.04
0.05
0.03
Crystal system,
Space group
Unit cell dimensions
Monoclinic
P21/c
,
a (A)
15.4039 (5)
10.0630 (3)
13.3601 (8)
101.607 (4)
2028.59 (15)
4
1.609
9.294
,
b (A)
,
c (A)
6g
6h
i (°)
3
,
V (A )
Z
Dcalc (Mg m−3
)
Absorption coefficient (mm−1
F (000)
)
992
Crystal size (mm3)
0.20×0.26×0.30
2.93–56.75
q range for data collection (°)
Index ranges
−165h516, −105k51,
−15l514
Reflections collected/unique
Refinement method
3061/2433 [Rint=0.0594]
Full-matrix least-squares on
F2
Goodness-of-fit on F2
Final R indices [R[I\2| (I)]
R indices (all data)
1.042
R1=0.0632, wR2=0.1636
R1=0.0722, wR2=0.1731
Largest difference peak and hole 0.477 and −0.220
−3
,
(e A
)
accommodated in the vicinity of the Cr(CO)5 group.
The amino group is coplanar (as expected) as seen from
the dihedral angles: C (9)ꢀN (1)ꢀC (7)ꢀC (1) −6.3° and
C (8)ꢀN (1)ꢀC (7)ꢀC (1) −172.4°. One of the N-methyl
group (C-9) is twisted (about 80° with respect to the
aromatic plane) towards the chromium tricarbonyl
moiety.
Fig. 4. ORTEP diagram of the complex 6c.
Table 7
Selected bond lengths (A) and angles (°) for 6c
,
5. Conclusions
Cr(1)ꢀC(14)
Cr(1)ꢀC(7)
N(1)ꢀC(7)
N(1)ꢀC(8)
N(1)ꢀC(9)
C(1)ꢀC(7)
C(2)ꢀO(1)ꢀC(10)
C(7)ꢀN(1)ꢀC(8)
1.861(7)
2.146(5)
1.289(7)
1.471(7)
1.473(8)
1.495(7)
118.0(5)
122.8(5)
C(7)ꢀN(1)ꢀC(9)
C(8)ꢀN(1)ꢀC(9)
C(2)ꢀC(1)ꢀC(6)
C(2)ꢀC(1)ꢀC(7)
C(6)ꢀC(1)ꢀC(7)
N(1)ꢀC(7)ꢀC(1)
N(1)ꢀC(7)ꢀCr(1)
C(1)ꢀC(7)ꢀCr(1)
126.6(5)
110.6(5)
116.8(5)
117.8(4)
123.3(4)
118.6(4)
129.3(4)
112.0(3)
In summary, we have described synthesis and charac-
terization of new and structurally related sets of aryl
amino carbene complexes. The aryl group of one set is
complexed with tricarbonylchromium. We compared
the conformation of these complexes with amide com-
pounds of similar structure and sought to use chemical
shift of NꢀCH3 groups as a convenient conformational
probe. We surmized that absence of anisotropic shield-
ing of these methyl signals is a reflection of electron-
density withdrawal from arene ring by Cr(CO)3 group,
and hence should represent similarity of conformation
between isostructural amides and carbene complexes.
The crystal structures of representative compounds re-
vealed that such correlation would have been in great
error since the conformation of a carbene complex
bearing an areneꢀCr(CO)3 group is vastly different
from the expected structure.
Evidently, the molecular structure of 6c is consider-
ably different in the terms of orientation of the ꢀNMe2
group with respect to the aromatic ring. The Cr(CO)3
group and one of the NꢀMe group are actually on the
same side, instead of occupying opposite faces of the
plane containing the aromatic group! This explains,
albeit in a disappointing way, why the chemical shifts
of the methyl groups on the nitrogen are similar. The
bulk of the Cr(CO)3 group is perhaps too large to be

722
K.N. Jayaprakash et al. / Journal of Organometallic Chemistry 617–618 (2001) 709–722
[7] C.A.L. Mahaffy, P.L. Pausen, Inorg. Synth. 19 (1979) 154. (b) S.
Acknowledgements
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Financial support by the Department of Science and
Technology, Government of India, New Delhi, is grate-
fully acknowledged. The authors (K.N.J., D.H. and
U.K.S.) thank CSIR, New Delhi, for research
fellowships.
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