Acidity of benzoic acids bearing the (CO)5Cr=CN(CH 3)2 group

Article abstract of DOI:10.1021/om100608x

Benzoic acids 2a and 2b, bearing the (CO)₅Cr=CN(CH ₃)₂ group in the p- and m-position, and the corresponding benzoic acids 2c and 2d, in which the rotation of the aminocarbene moiety was blocked by the presence of a methyl group, were prepared together with the corresponding N,N-dimethylamido acids 3a-d. The measurement of pK_a values in EtOH and DMF revealed that the (CO)₅Cr=CN(CH ₃)₂ group is a very weak electron acceptor (δ_p = 0; δ_m = 0.14). The restriction of the rotation of the aminocarbene moiety did not significantly influence its electronic properties. The obtained results are in accordance with earlier findings that the relatively strong acidity of carbene complexes bearing hydrogens at the ±-position to the carbene atom is due to the resonance stabilization of the anion.

Full text of DOI:10.1021/om100608x

Organometallics 2010, 29, 4135–4138 4135
DOI: 10.1021/om100608x
Acidity of Benzoic Acids Bearing the (CO)5CrdCN(CH3)2 Group
†
†
†
‡
‡
ꢀ
ꢀ
ꢁ
Patrik Parık, Jirı Kulhanek, Miros^lav Ludwig, Roman Wagner, Ivan Rotrekl,
‡
ꢀ
ꢀ
ꢀ
ꢁ §
Dusan Drahonovsky, Ludek Meca, Marketa Smıdkova, Tomas Tobrman, and
ꢀ
ꢁ
ꢁ ‡
ꢁꢀ
,‡
ꢀꢁ
Dalimil Dvorak*
†
ꢁ
Institute of Organic Chemistry and Technology, University of Pardubice, Studentska 573, 532 10 Pardubice,
‡
ꢁ
Czech Republic, Department of Organic Chemistry, Institute of Chemical Technology Prague, Technicka 5,
166 28 Prague 6, Czech Republic, §Department of Organic and Nuclear Chemistry, Charles University,
Hlavova 2030, 128 40 Prague 2, Czech Republic, and ^Zentiva k.s., U Kabelovny 130, 102 37 Praha 10,
Czech Republic
Received June 23, 2010
Benzoic acids 2a and 2b, bearing the (CO)5CrdCN(CH3)2 group in the p- and m-position, and the
corresponding benzoic acids 2c and 2d, in which the rotation of the aminocarbene moiety was
blocked by the presence of a methyl group, were prepared together with the corresponding N,N-
dimethylamido acids 3a-d. The measurement of pKa values in EtOH and DMF revealed that the
(CO)5CrdCN(CH3)2 group is a very weak electron acceptor (σp = 0; σm = 0.14). The restriction of
the rotation of the aminocarbene moiety did not significantly influence its electronic properties. The
obtained results are in accordance with earlier findings that the relatively strong acidity of carbene
complexes bearing hydrogens at the R-position to the carbene atom is due to the resonance
stabilization of the anion.
Introduction
considerably stronger C-acid compared with N,N-dimethyl-
acetamide (pKa of 29.4 in H2O).5 By contrast, this lower
acidity is connected with the higher nucleophilicity of the
corresponding aminocarbene anions, which makes possible
the synthesis of a variety of aminocarbene complexes by
alkylation and aldolization.6
The fact that hydrogen atoms in the R-position to the
carbene carbon atom in Fischer carbene complexes are acidic
was first reported by Kreiter1 in 1968. The pKa of pentacar-
bonylchromium methoxymethylcarbene was first estimated
by Casey and Anderson,2 who found that this compound is
roughly as strong an acid as p-cyanophenol in THF, which is
a relatively strong acid in water (pKa = 8). However, Gandler
and Bernasconi3 later showed that in water the acidity of
pentacarbonylchromium methoxymethylcarbene is much
lower (12.3) than that of p-cyanophenol. This difference
was attributed to the different degrees of stabilization of
the corresponding anions by solvation. The phenolate anion
with a negative charge localized on the oxygen atom is
solvated more efficiently than the methoxymethylcarbene
anion, where the negative charge is delocalized over carbonyl
ligands. The electron properties of the Cr(CO)5 group are
considered similar to those of oxygen in the carbonyl group
(super oxygen). Therefore, the properties of Fischer carbenes
are often compared to those of carboxylic acid derivatives.
Accordingly, aminocarbene complexes, owing to the higher
electron-donating properties of the nitrogen atom, are con-
siderably less acidic than the corresponding alkoxycarbene
complexes. Thus, the reported pKa of (CO)5CrdC(CH3)-
N(CH3)2 in DMSO (20.4)4 shows that this compound is less
acidic than the corresponding alkoxycarbene, but still a
Probably the simplest way to quantify the electronic
properties of the (CO)5CrdC(NMe2) group is to measure
the pKa of carbene-substituted benzoic acid and, thus, obtain
its Hammett σ-constant. Therefore, pentacarbonyl[(N,N-
dimethylamino)(4-(methoxycarbonyl)phenyl)carbene]chro-
mium(0) (1a)7 and pentacarbonyl[(N,N-dimethylamino)-
(3-(methoxycarbonyl)phenyl)carbene]chromium(0) (1b) were
prepared and hydrolyzed to the corresponding acids 2a and 2b.
We have recently shown that the methyl group in the o-position
to the N,N-dimethylaminocarbene moiety completely blocks
its rotation, and the π-plane of the carbene ligand becomes
orthogonal to the plane of the aromatic ring.8 In such com-
plexes, the π-systems of the aminocarbene group and the
aromatic ring are not in conjugation. Therefore, benzoic acids
2c and 2d, bearing the methyl group ortho to the aminocarbene
moiety, were also included in the study. To compare the
influence of the (CO)5CrdC(NMe2) andOdC(NMe2) groups,
the corresponding amido acids 3a-d were also prepared and
subjected to pKa measurement. The obtained pKa values were
(5) Richard, J. P.; Williams, G.; O’Donoghue, A. C.; Amyes, T. L.
J. Am. Chem. Soc. 2002, 124, 2957.
*To whom correspondence should be addressed. E-mail: dvorakd@
vscht.cz.
(6) (a) Wulff, W. D.; Anderson, B. A.; Isaacs, L. D. Tetrahedron Lett.
1989, 30, 4061. (b) Wulff, W. D.; Anderson, B. A.; Toole, A. J. J. Am. Chem.
Soc. 1989, 111, 5485.
(1) Kreiter, C. G. Angew. Chem., Int. Ed. Engl. 1968, 7, 390.
(2) Casey, Ch. P.; Anderson, R. L. J. Am. Chem. Soc. 1974, 96, 1230.
(3) Gandler, J. R.; Bernasconi, C. F. Organometallics 1989, 8, 2282.
(4) Wulff, W. D.; Anderson, B. A.; Toole, A. J.; Xu, Y.-C. Inorg.
Chim. Acta 1994, 220, 215.
ꢀ
ꢀꢁ
ꢁ
ꢁ
ꢀꢁ
(7) Tobrman, T.; Meca, L.; Dvorakova, H.; Cerny, J.; Dvorak, D.
Organometallics 2006, 25, 5540.
ꢀ
ꢁ
(8) Meca, L.; Cısarova, I.; Drahonovsky, D.; Dvorak, D. Organome-
ꢀ
ꢁ
ꢀꢁ
tallics 2008, 27, 1850.
r
2010 American Chemical Society
Published on Web 08/25/2010
pubs.acs.org/Organometallics

ꢀ´
Parık et al.
4136 Organometallics, Vol. 29, No. 18, 2010
Scheme 1. Preparation of the Aminocarbene-Bearing Benzoic Acids
Table 1. pKa Values of the Carbene-Substituted Benzoic Acids 2, the Corresponding Amidobenzoic Acids 3, and the Benzoic Acids 4a
a Obtained by potentiometric titration (standard deviations were max. 0.10).
then compared with those reported for benzoic and m- and
p-methyl benzoic acids.
Unexpectedly, the obtained pKa value for 2a in ethanol
(10.06) was only very slightly lower than that reported for
benzoic acid (4a) in the same solvent (10.25).11 In DMF, the
pKa of 2a was exactly the same as that reported for benzoic
acid (12.27).12 By contrast, the corresponding amide 3a was a
slightly stronger acid than the carbene 2a (the difference of
pKa was 0.29 in EtOH and 0.19 in DMF). When the coplana-
rity of the benzene ring and the aminocarbene group was not
possible because of the introduction of the methyl group into
the ortho position of the aminocarbene moiety (2c),8 the
situation does not change significantly. The differences in
acidity between the carbene acid 2c, the corresponding
amido acid 3c, and 3-methylbenzoic acid (4c) were very
similar to the case of 2a (Table 1). This is probably because
Results and Discussion
The aminocarbene-bearing benzoic acids were prepared
by the reported procedure,9 by the reaction of the corre-
sponding amido esters with Na2Cr(CO)5 and (CH3)3SiCl
followed by the hydrolysis of the obtained ester-carbenes
(Scheme 1).8
To avoid potential problems with the hydrolysis of the
carbene group,10 the pKa measurements were taken in etha-
nol and DMF. The obtained values are summarized in Table
1 together with the pKa values of the corresponding N,N-
dimethylamidobenzoic 3a-c, benzoic 4a, and 3-methylben-
zoic acid 4c.
(11) Kolthoff, I. M. J. Phys. Chem. 1931, 35, 2732.
(12) Kolthoff, I. M.; Chantooni, M. K. J. Am. Chem. Soc. 1971, 93,
3843.
(9) Imwinkelried, R.; Hegedus, L. S. Organometallics 1988, 7, 702.
(10) Bernasconi, C. F.; Flores, F. X.; Kittredge, K. W. J. Am. Chem.
Soc. 1997, 119, 2103.
ꢀ ꢀ
(13) Ludwig, M.; Baron, V.; Kalfus, K.; Pytela, O.; Vecera, M.
Collect. Czech. Chem. Commun. 1986, 51, 2135.

Article
Organometallics, Vol. 29, No. 18, 2010 4137
the aminocarbene group prefers an orthogonal arrangement
to the aromatic ring even if the substituent in the ortho
position is not present.7
When the aminocarbene moiety was in a meta position to
the carboxylic group, the influence on the acidity of the
corresponding benzoic acid 2b was somewhat higher than in
2a, but still small (Table 1). Other trends were similar to the
previous case. Amide 3b was a stronger acid than 2b, and the
ortho substitution had little influence on it.
Besides these results, it was observed that the introduc-
tion of the methyl group to the skeleton of amido acids
or aminocarbene acids led to the lowering of acidity in
each case and in both solvents. This decrease in acidity
roughly corresponded with the electronic effects of the
methyl group.
acid methyl ester,15 5-methoxycarbonyl-N,N,2-trimethyl-
benzamide,8 pentacarbonyl[(N,N-dimethylamino)(4-methoxy-
carbonylphenyl)carbene]chromium(0) (1a),7 pentacarbonyl[(N,N-
dimethylamino)(4-carboxy-2-methylphenyl)carbene]chromium(0)
(2c),8 and pentacarbonyl[(N,N-dimethylamino)(5-carboxy-2-
methylphenyl)carbene]chromium(0) (2d)8 were prepared according
to published procedures. 4-Methoxycarbonyl-N,N,2-trimethyl-
benzamide was prepared in several steps from commercially avail-
able 3-methyl-4-nitrobenzoic acid as described below.
4-Amino-3-methylbenzoic Acid. A mixture of 3-methyl-4-
nitrobenzoic acid (50 g, 0.276 mol), granulated tin (100 g, 1.187
mol), and concentrated hydrochloric acid (400 mL) was heated in a
boiling water bath for 4 h. The hot reaction mixture was filtered,
and after cooling to room temperature, the separated yellow solid
was filtered off and dissolved in 15% aqueous NaOH (300 mL).
The solution was filtered, and the pH of the filtrate was adjusted to 7
by the addition of concentrated hydrochloric acid and then to 5.5
by the addition of acetic acid. The precipitated solid was filtered
off, washed with water, and air-dried. Yield: 24.5 g (59%), mp
160-163 ꢀC (169 ꢀC16).
Conclusions
The above results show that the chromium pentacarbonyl-
aminocarbene group itself is a very weak electron acceptor,
with the values of Hammett constants σp roughly 0 and σm =
0.14. These values are about the same as for the CH3S group.
This is in accordance with the earlier findings of Gandler and
Bernasconi3 that the relatively strong acidity of carbene
complexes bearing hydrogens at the R-position to the car-
bene atom is due to the resonance stabilization of the anion.
There is no direct conjugation between the carboxylate anion
and the carbene in carbene-bearing benzoic acids 2a-d, and
therefore, such stabilization is not possible. The perpendi-
cular arrangement of the aminocarbene moiety to the aro-
matic ring also plays an important role by intercepting the
conjugation of the carbene moiety with the aromatic ring.
From this point of view the corresponding alkoxycarbene
benzoic acid is interesting, since the rotation of the alkoxy
group is far less hindered and the alkoxycarbene group can
more easily adopt a coplanar arrangement with an aromatic
ring. Another interesting example would be the phenol-
bearing carbene group, in which the direct conjugation of
carbene with negatively charged oxygen of the phenolate
anion is possible. The synthesis of these types of compounds
is now in progress in our laboratory.
4-Iodo-3-methylbenzoic Acid. A suspension of 24.5 g (0.162
mol) of 4-amino-3-methylbenzoic acid in a mixture of water (210
mL) and concentrated H2SO4 (25 mL) was cooled to 0 ꢀC using
an external ice bath, and a solution of NaNO2 (13.8 g, 0.162 mol)
in water (50 mL) was slowly added, keeping the temperature
below 5 ꢀC. Then, a solution of KI (44.4 g, 0.267 mol) in 10%
H2SO4 (85 mL) was added, and the mixture was heated to reflux
for 20 min. After cooling, the crude product (28.3 g) was sepa-
rated by filtration and crystallized from a mixture of ethanol
(350 mL) and water (150 mL). Yield: 18.9 g (45%), mp 208-
214 ꢀC17 and 223-224 ꢀC.18 1H NMR (DMSO-d6, 360 MHz): δ
2.41 (s, 3H, CH3), 7.43 (dd, J = 8.2, 2.3 Hz, 1H, Ar-H), 7.83 (d,
J = 2.1 Hz, 1H, Ar-H), 7.94 (d, J = 8.2 Hz, 1H, Ar-H). 13C
NMR (DMSO-d6, 90.55 MHz): δ 27.5, 107.6, 128.3, 130.3,
131.0, 139.1, 141.5, 167.1. Anal. Calcd (%) for C8H7IO2: C
36.67, H 2.69. Found: C 36.64, H 2.79.
4-Iodo-3-methylbenzoic Acid Methyl Ester. This compound
was prepared from 4-iodo-3-methylbenzoic acid according to
the previously published procedure.19
4-Methoxycarbonyl-2-methylbenzoic Acid. This compound
was prepared according to the procedure previously used for
the preparation of 5-methoxycarbonyl-2-methylbenzoic acid.8
A dry 100 mL round-bottomed flask, equipped with a magnetic
stirring bar, was charged with methyl 4-iodo-3-methylbenzoate
(1.3 g, 4.71 mmol) and THF (7 mL) under argon and cooled to
-20 ꢀC. i-PrMgCl (2 M in THF; 2.6 mL; 5.18 mmol) was slowly
added, and the suspension was stirred for 1 h at -20 ꢀC. Dry ice
(0.88 g) was then quickly added, and the resulting yellow
solution was stirred for 1 h at room temperature. Solvents were
evaporated, and water (3 mL) and 10% HCl (3 mL) were added.
The precipitated product was then filtered and washed with
water. Drying in air afforded a yellowish solid (0.88 g, 96%).
Mp: 138-140 ꢀC. 1H NMR (CDCl3, 300 MHz): δ 2.70 (s, 3H,
Ph-CH3), 3.68 (s, 3H, O-CH3), 7.92 (d, J = 8.2 Hz, 1H, Ph-H), 7.95
(s, 8.10, 1H, Ph-H), (d, J = 8.2 Hz, 1H, Ph-H). 13C NMR (CDCl3,
75 MHz): δ 21.9 (Ph-CH3), 52.4 (O-CH3), 126.8, 131.5, 132.2,
132.8, 133.6, 141.3 (Ph-C), 166.3, 172.5 (CdO). Anal. Calcd (%)
for C10H10O4: C 61.85, H 5.19. Found: C 61.57, H 5.17.
Experimental Section
Melting points were determined on a Kofler block and are
uncorrected. NMR spectra were measured on a Varian Gemini
300, Bruker AMW 360, or Bruker DRX 500 Avance spectro-
meter at 25 ꢀC. Infrared spectra were recorded on a Nicolet 740
instrument. Dissociation constants were determined by poten-
tiometric titration using an Titralab 3 (Radiometer) automatic
titrator under the same experimental conditions and using the
same electrodes as in previous work.14 All experiments were
carried out under argon. Tetrahydrofuran was distilled from
benzophenone ketyl under Ar prior to use. Chromium hexacar-
bonyl, chlorotrimethylsilane, 2 M i-PrMgCl in THF, and
3-chlorocarbonylbenzoic acid methyl ester were purchased from
commercial suppliers and were used without purification. Neu-
tral aluminum oxide (Brockmann grades II-III) and silica gel
were obtained from Merck. Dimethylamine (1 M) in diethyl ether
was prepared by bubbling gaseous dimethylamine (from commer-
cial dimethylammonium chloride and NaOH) to diethyl ether at 0
ꢀC. The resulting solution was stored over solid NaOH ina freezer.
Unless stated otherwise, products were used in their crude states
without further purification. N,N-Dimethylterephthalamic
4-Methoxycarbonyl-N,N,2-trimethylbenzamide. 4-Methoxycar-
bonyl-2-methylbenzoic acid (0.568 g, 2.93 mmol), benzene (5 mL),
DMF (0.03 mL), and SOCl2 (0.34 mL, 4.7 mmol) were stirred at
80 ꢀC for 2 h with the exclusion of air and moisture. The solvents
were evaporated, and the residue was dissolved in diethyl ether
(15) Kikugawa, Y. Chem. Pharm. Bull. 1976, 24, 1059.
€
(16) Muller, E. Chem. Ber. 1909, 42, 423.
(17) Edinger, A.; Goldberg, P. Chem. Ber. 1900, 33, 2883.
(18) Gore, P. H.; Thorburn, S.; Weyell, D. J. J. Chem. Soc., Perkin
Trans. 1 1973, 2940.
ꢀ ꢀ
(14) Ludwig, M.; Pytela, O.; Vecera, M. Collect. Czech. Chem. Com-
(19) Blaszykowski, C.; Aktoudianakis, E.; Bressy, C.; Alberico, D.;
mun. 1984, 49, 2593.
Lautens, M. Org. Lett. 2006, 8, 2043.

ꢀ´
Parık et al.
4138 Organometallics, Vol. 29, No. 18, 2010
(15 mL). An ethereal solution of dimethylamine (1 M, 12 mL) was
slowly added at 0 ꢀC, and the resulting suspension was stirred for
24 h at room temperature. The evaporation of solvents afforded the
crude product, which was purified by chromatography on silica
(EtOAc-hexane, 2:1). Yield: 0.60 g (93%) of a yellow oil. 1H NMR
(CDCl3, 300 MHz): δ 2.29 (s, 3H, Ph-CH3), 2.77 (s, 3H, N-CH3),
3.10 (s, 3H, N-CH3), 3.88 (s, 3H, O-CH3), 7.21 (d, J = 7.9 Hz, 1H,
Ph-H), 7.84 (m, 2H, Ph-H). 13C NMR (CDCl3, 75 MHz): δ 18.7
(Ph-CH3), 34.4(N-CH3), 38.1(N-CH3), 52.1(O-CH3), 125.9, 127.2,
130.3, 131.4, 134.4 (C-Ph), 141.1 (C-Ph), 166.5 (CdO), 170.4
(CdO). IR: ν 2951, 2929, 1723, 1639, 1510, 1437, 1407, 1395,
1300, 1288, 1258, 1220, 1198, 1110, 1067, 778 cm-1. HR-MS (ES):
calcd for C12H16NO3 222.1130; found 222.1149.
Pentacarbonyl[(N,N-dimethylamino)(3-carboxyphenyl)carbene]-
chromium(0) (2b). The same method as that used for the prepara-
tion of 2a starting from pentacarbonyl[(N,N-dimethylamino)(3-
methoxycarbonylphenyl)carbene]chromium(0) (1b) (377 mg; 0.98
mmol) afforded a yellow solid of the product (308 mg; 85%).
Mp > 110 ꢀC (dec). 1H NMR (CDCl3, 300 MHz): δ 3.08 (s, 3H,
N-CH3), 4.03 (s, 3H, N-CH3), 6.97 (d, J = 8.2 Hz, 1H, Ar-H), 7.45
(s, 1H, Ar-H), 7.51 (t, J = 8.0 Hz, 1H, Ar-H), 7.92 (d, J = 8.2 Hz,
1H, Ar-H). 13C NMR (CDCl3, 75 MHz): δ 47.3 (CH3), 52.4
(CH3), 121.1 (Ar-CH), 124.5 (Ar-CH), 127.5 (Ar-CH), 129.9
(Ar-CH), 131.9 (Ar-Cq), 153.4 (Ar-Cq), 167.9 (CO2H), 218.0
(CO), 224.8 (CO), 265.1 CdCr). IR (CHCl3): ν 2055, 1976, 1992
cm-1. Anal. Calcd (%) for C15H11CrNO7: C 48.79, H 3.00, N 3.79.
Found: C 48.65, H 3.27, N 3.65.
N,N-Dimethylisophthalamic Acid Methyl Ester. This com-
pound was prepared by a reaction of 3-chlorocarbonylbenzoic
acid methyl ester with dimethylamine in diethyl ether. 1H NMR
(CDCl3, 300 MHz): δ 2.99 (bs, 3H, N-CH3), 3.11 (bs, 3H,
N-CH3), 3.92 (s, 3H, OCH3), 7.49 (t, J = 8.2 Hz, 1H, Ar-H),
7.62 (d, J = 7.6 Hz, Ar-H), 8.06 (m, 2H, Ar-H). 13C NMR
(CDCl3, 75 MHz,): δ 35.2 (N-CH3), 39.4 (N-CH3), 52.1
(O-CH3), 128.0 (Ar-CH), 128.5 (Ar-CH), 130.1 (Ar-Cq), 130.4
(Ar-CH), 131.4 (Ar-CH), 136.5 (Ar-Cq), 166.2 (CO), 170.4
(CO). HR-MS: calcd for C11H13NO3 207.0895; found 207.0894.
Pentacarbonyl[(N,N-dimethylamino)(3-methoxycarbonylphenyl)-
carbene]chromium(0) (1b). To a suspension of chromium hexa-
carbonyl (2.2 g, 10 mmol) in THF (50 mL) was added at -78 ꢀC via
a syringe a solution of sodium naphthalenide prepared from sodium
(0.6 g, 26 mmol) and naphthalene (3.4 g, 26.5 mmol) in THF
(50 mL). The reaction mixture was then allowed to warm to 0 ꢀC,
stirred at this temperature for 30 min, and cooled to -78 ꢀC, and
3-methoxycarbonyl-N,N-dimethylbenzamide (1.45 g, 7 mmol) in
THF (5 mL) was added via a syringe. The solution was allowed to
warm to 0 ꢀC, stirred for 30 min at 0 ꢀC, and then cooled to -78 ꢀC,
and trimethylchlorosilane (2.5 mL, 20 mmol) was added via a
syringe. The solution was stirred at -78 ꢀC for 30 min, and then the
cooling bath was removed. The mixture was stirred for an addi-
tional 1 h without cooling, and neutral alumina (8 g) was added.
THF was removed under reduced pressure, and the residue was
dried under high vacuum to remove all solvents. Hexane (15 mL)
was then added, and the suspension formed was transferred to the
top of a column filled with silica gel (60 g). Naphthalene was eluted
with hexane, and further elution with hexane-dichloromethane
General Procedure for the Preparation of Amido Acids 3a-d.
Esteramide (0.5 mmol) and potassium hydroxide (56 mg,
1 mmol) were dissolved in a mixture of CH3OH (1 mL) and
water (0.5 mL), and the mixture was stirred and heated to 50 ꢀC
for 1 h. The methanol was then evaporated in a vacuum, the
residue was acidified by several drops of concentrated hydro-
chloric acid, extracted with dichloromethane (2Â 1 mL), and
dried over Na2SO4, and the solvent was evaporated.
N,N-Dimethylterephthalamic Acid (3a). Yield: 83%. 1H NMR
(CDCl3, 300 MHz): δ 2.98 (s, 3H, CH3), 3.16 (s, 3H, CH3), 7.51
(d, J = 8.2 Hz, 2H, Ar-H), 8.13 (d, J = 8.2 Hz, 2H, Ar-H), 10.05
(bs, 1H, CO2H), in accordance with ref 20. 13C NMR (CDCl3, 75
MHz): δ 35.5 (CH3), 39.5 (CH3), 127.0 (Ar-CH), 130.1 (Ar-CH),
130.4 (Ar-Cq), 140.9 (Ar-Cq), 170.3 (CO), 170.6 (CO).
N,N-Dimethylisophthalamic Acid (3b). Yield: 47%. Mp:
102-103 ꢀC (acetone). 1H NMR (CDCl3, 300 MHz): δ 2.99 (s,
3H, N-CH3), 3.14 (s, 3H, N-CH3), 7.50 (t, J = 7.6 Hz, 1H,
Ar-H), 7.67 (d, J = 7.6 Hz, 1H, Ar-H), 8.11 (d, J = 7.6 Hz, 1H,
Ar-H), 8.13 (s, 1H, Ar-H). 13C NMR (CDCl3, 75 MHz): δ 35.5
(CH3), 39.6 (CH3), 128.6 (Ar-CH), 128.7 (Ar-CH), 129.9
(Ar-Cq), 131.2 (Ar-CH), 132.1 (Ar-CH), 136.3 (Ar-Cq), 170.0
(CO), 170.7 (CO). IR: ν 2961, 2929, 1739, 1708, 1614, 1596,
1573, 1453, 1412, 1401, 1300, 1277, 1258, 1205, 742 cm-1. HR-
MS: calcd for C10H11NO3 193.0739; found 193.0734.
3,N,N-Trimethylterephthalamic Acid (3c). Yield: 89%. Mp:
200-202 ꢀC. 1H NMR (CDCl3, 300 MHz): δ 2.34 (s, 3H, CH3),
2.83 (s, 3H, N-CH3), 3.16 (s, 3H, N-CH3), 7.27 (d, J = 8.0 Hz,
1H, Ar-H), 7.95 (m, 2H, Ar-H), 10.55 (bs, 1H, CO2H). 13C
NMR (CDCl3, 75 MHz): δ 18.8 (CH3), 34.6 (N-CH3), 38.3
(N-CH3), 126.0 (Ar-CH), 127.8 (Ar-CH), 129.9 (Ar-Cq), 132.0
(Ar-CH), 134.5 (Ar-Cq), 141.4 (Ar-Cq), 170.69 (CO), 170.75
(CO). IR: ν 2926 (m), 2801 (m), 2586 (m), 1705 (s), 1614 (s), 1587
(s), 1515 (m), 1485 (m), 1416 (s), 1399 (s), 1276 (s), 1257 (s), 1223
(s), 1196 (s), 1114 (m), 1069 (m), 962 (w), 856 (w), 780 (m), 746
(m), 704 (w), 660 (m). Anal. Calcd (%) for C11H13NO3: C 63.76,
H 6.32, N 6.76. Found: C 64.20, H 6.19, N 6.72.
1
mixture (2:1) gave a product as a yellow oil (0.377 g, 14%). H
NMR (CDCl3, 300 MHz,): δ 3.06 (s, 3H, N-CH3), 3.92 (s, 3H,
O-CH3), 4.02 (s, 3H, N-CH3), 6.92 (d, J = 7.6 Hz, 1H, Ar-H), 7.39
(s, 1H, Ar-H), 7.48 (t, J = 7.6 Hz, 1H, Ar-H), 7.87 (d, J = 7.6 Hz,
1H, Ar-H). 13C NMR (CDCl3, 75 MHz): δ 46.2 (CH3), 51.4 (CH3),
52.3 (CH3), 120.0 (Ar-CH), 123.4 (Ar-CH), 127.0 (Ar-CH), 128.9
(Ar-CH), 130.5 (Ar-Cq), 152.40 (Ar-Cq), 166.5 (CO2), 216.9 (CO),
223.5 (CO), 274.2 (CdCr). IR (CHCl3): ν 2058, 1978, 1992 cm-1
.
Anal. Calcd (%) for C16H13CrNO7: C 50.14, H 3.42, N 3.65.
Found: C 50.48, H 3.62, N 3.27.
4,N,N-Trimethylisophthalamic Acid (3d). Yield: 85%. Mp:
155-157 ꢀC. 1H NMR (CDCl3, 300 MHz): δ 2.36 (s, 3H,
CH3), 2.85 (s, 3H, N-CH3), 3.16 (s, 3H, N-CH3), 7.30 (d, J =
7.7 Hz, 1H, Ar-H), 7.90 (s, 1H, Ar-H), 7.96 (d, J = 7.7 Hz, 1H,
Ar-H), 9.50 (bs, 1H, CO2H). 13C NMR (CDCl3, 75 MHz): δ 19.4
(CH3), 34.8 (N-CH3), 38.6 (N-CH3), 127.4 (Ar-Cq), 127.6
(Ar-CH), 130.3 (Ar-CH), 130.6 (Ar-CH), 136.6 (Ar-Cq), 140.5
(Ar-Cq), 170.3 (CO), 170.4 (CO). IR: ν 2923, 1716, 1597, 1399,
1286, 1248, 1214, 1129, 1118, 765 cm-1. HR-MS: calcd for
C11H13NO3 207.0895; found 207.0891.
Pentacarbonyl[(N,N-dimethylamino)(4-carboxyphenyl)carbene]-
chromium(0) (2a). Pentacarbonyl[(N,N-dimethylamino)(4-methoxy-
carbonylphenyl)carbene]chromium(0) (1b) (200 mg; 0.52
mmol), powdered KOH (112 mg; 2 mmol), water (5 mL), THF
(5 mL), and methanol (2 mL) were stirred under argon at 50 ꢀC for
5 h (starting compound quantitatively disappeared during that
time). Volatile solvents were then evaporated in a vacuum, and
nonacidic impurities were extracted with CH2Cl2. The pH of the
mixture was adjusted to 1-2 with diluted H3PO4, and the product
was extracted with diethyl ether. Extracts were dried over Na2SO4
and evaporated to afford a product as a yellow solid (180 mg;
92%), which decomposes without melting. 1H NMR (DMSO-d6,
300 MHz): δ 3.03 (s, 3H, N-CH3), 3.94 (s, 3H, N-CH3), 6.87 (d,
J = 8.4 Hz, 2H, Ar-H), 7.97 (d, J = 8.1 Hz, 2H, Ar-H), 12.94 (bs,
1H, COOH). 13C NMR (DMSO-d6, 75 MHz): δ 47.4, 52.3, 120.3,
128.8, 130.8, 156.7, 167.8, 217.9, 224.8, 265.1. IR (CHCl3): ν 2056,
Acknowledgment. This project was supported by the
Research Centre “The Structure and Synthetic Applica-
tions of Transition Metal Complexes-LC06070” of the
Ministry of Education, Youth and Sports of the Czech
Republic and by the MSM6046137301 and the MSM-
0021627501 research projects of the same Ministry.
1976, 1932 cm-1. Anal. Calcd (%) for C15H11CrNO7 0.5H2O: C
ꢁ
(20) Pytela, O.; Kulhanek, J. Collect. Czech. Chem. Commun. 2002,
67, 596.
3
47.62, H 3.17, N 3.70. Found: C 47.58, H 3.53, N 3.46.