570
Organometallics 1995, 14, 570-573
Preparation of (Aminocarbene)tetracarbonyliron(O) Complexes by the Reaction of Tertiary Amides with Fe(C0)42-and Chlorotrimethylsilane Dalimil DvoEakl Department of Chemistry, Prague Technical University, 166 28 Prague 6, Czech Republic Received July 26, 1994@ Scheme 1 0
Summary: (Amimcarbem)tetracarbonyliron(O) complexes without hydrogen atoms at the position a to the carbene atom can easily be prepared by the reaction of formamides or aromatic and heteroaromatic tertiary amides with sodium or potassium tetracarbonylferrate and chlorotrimethylsilane in THF solution. While the chemistry of chromium aminocarbene complexes has been intensively explored during the last years, resulting in development of many synthetically useful methods,2 the chemistry of analogous iron aminocarbene complexes remains almost untouched. To the best of our knowledge, there is only one paper dealing with the reactivity of neutral iron aminocarbene complexese3 This is apparently due to the relative inaccessibility of these compounds. Several iron aminocarbene complexes have been prepared to date. The method most used for the preparation of chromium aminocarbene complexes (aminolysis of alkoxycarbene complexes) can, in principle, be used also for the preparation of iron aminocarbene ~omplexes.~ However, the preparation of the starting iron alkoxycarbenes is not as easy as the synthesis of chromium alkoxycarbene complexes.4a Furthermore, the exchange reaction with amines has been reported to give satisfactory results only with carbene complexes without hydrogen at the position a to the carbene atom.3 Other methods described for the preparation of iron aminocarbene complexes include a photochemical exchange and the reaction of NazFe(C0)r with (chloromethy1ene)dialkylammonium ~hlorides.~ However, these methods are either complicated or not general. A very efficient and relatively general method for preparation of chromium aqinocarbene complexes 1, based on the reaction of Na%C1@0)5or K2Cr(C0)5with amides and chlorotrimethylsilane, was developed by Imwinkelried and Hegedus.6 This reaction is believed to proceed via nucleophilic addition of Cr(C0)52- (prepared by reduction of Cr(CO)6with sodium or potassium Abstract published in Advance ACS Abstracts, November 15,1994. (1) Temporary address: University of Leicester, Department of Chemistry, University Road, Leicester, LE1 7RH, U.K. (2) For a review, see: Schwindt, M. A.; Miller, J. R.; Hegedus, L. S . J. Organomet. Chem. 1991,413, 143. (3) Semmelhack,M. F.;Park, J. Organometallics 1986,5,2550. For a review of the reactivity of Fischer iron carbene complexes; see: Semmelhack, M. F.; Park, J.; Schnatter, W.;Tamura, R.; Steigerwald, M. Chem. Scr. 1987,27, 509. (4) Preparation of (alkoxycarbene)iron(O) complexes by Fischer procedure: (a) Semmelhack, M. F.; Tamura, R. J.Am. Chem. SOC.1983, 105,4099. (b) Park, J.; Kang, S.; Whang, D.; Kim, K. Organometallics 1991, 10, 3413. (c) Fischer, E.0.; Beck, H.-J.;Kreiter, C. G.; Lynch, J.; Muller, J.; Winkler, E . Chem. Ber. 1972, 105, 162. For aminolysis of (a1koxycarbene)ironcomplexes, see: References 2 and 3c. ( 5 ) Hartshorn, A. J.;Lappert, M. F.; Turner, K. J.Chem. SOC., Dalton Trans. 1978,348. (6) Imwinkelried, R.; Hegedus, L. S . Organometallics 1988, 7, 702. @
-- --
0-
.
M Cr, n 5 M Fe, n 4
,.,
SiMel
-- -
1, M Cr, n 5 2, M Fe, n = 4
naphthalenide) to the carbonyl group of an amide followed by the 0-silylation of the adduct and subsequent reaction with an excess of chlorotrimethylsilane and elimination of hexamethyldisiloxane (Scheme 1). The drawback of this procedure-the necessity of separating 2 equiv of naphthalene formed from the sodium naphthalenide from the product by means of chromatography on silica-can be avoided by using CsK as a reducing agent.7 A similar concept was used by Hossain, who treated aldehydes with FeCp(C0)z- and chlorotrimethylsilane to produce unstabilized cationic iron carbene complexes.s Fe(C0)42-is known as a very strong nucleophile. We reasoned that it can react with amides and chlorotrimethylsilane in the same way as Cr(C0)S2-,forming the desired iron aminocarbene complexes. To verify this hypothesis, we chose dimethylformamide, which should give the known product5 2a, for the first experiments. However, the treatment of DMF with the dioxane solvate of NazFe(CO14 and chlorotrimethylsilane in THF solution gave only traces of the expected [(Nfl-dimethylamino)methyleneltetracarbonyliron(O) (2a). This might be due to the low solubility of the dioxane solvate of NasFe(C0)r in THF. Therefore, for further experiments, we generated NazFe(C0)a free of dioxane in situ by reduction of iron pentacarbonyl with sodium naphthalenideg in THF. With this reagent the desired iron aminocarbene complex 2a was obtained in high yield. The product 2a (61%)was separated from the naphthalene byproduct by chromatography on aluminium oxide.1° The scope of this method was explored using other substrates with the aim of preparing iron aminocarbene (7) Schwindt, M. A.; Lejon, T.;Hegedus, L. S. Organometallics 1990, 9 , 2814.
(8)Vargas, R. M.; Theys, R. D.; Hossain, M. M. J.Am. Chem. SOC. 1992,114, 777. (9) Strong, H.; Krusic, P. J.; Filippo, J. S. Inorg. Synth. 1986, 24, 157. (10) Aluminium oxide turned out to be the adsorbent of choice, since chromatography on silica gel is accompanied by partial decomposition of the product.
0276-733319512314-0570$09.00/0 0 1995 American Chemical Society
Notes
Organometallics, Vol. 14, No. 1, 1995 571 Table 1. PreDaration of (Aminocarbene)tetracrbkyliron(O)Complexes R R' % yield complex
1 2
2a
2b 2c
2d 2e
2f 2g
2h 2i
H Ph 4-MeOPh 3-ClPh 4-BrPh 4-CNPh 3-pyridyl 2-furyl 3-thienyl
61.7" 63.1"; 76.w; 74.3c 48.6"
39.0" 26.3"; 54.7b 29.2" 28.7" 67.0" 65.2"
Method A. Method B. Method C.
complexes bearing hydrogen (2a), aromatic (2b-f9, or heteroaromatic (2g-i) substituents at the carbene atom. The yield wa$ modest to high (Table 1). However, this method failed.in the case of amides bearing a-hydrogens such as NJV-dimethylacetamide or N-methylpyrrolidone. Also NJV-dimethylamidesor cinnamic and pivalic acids failed to give aminocarbene complexes, the latter probably as a result of a steric hindrance. Iron aminocarbene complexes are yellow crystalline solids with IR absorption characteristic for the Fe(C0)4 moiety. The lH NMR spectra of dimethylamino carbenes show characteristic signals of NCH3 groups at d -3.10 and 4.00, only slightly influenced by the aromatic substituent. The complexes are infinitely stable at 8 "C under nitrogenll and can be handled in air as solids for a limited time without oxidation, but are readily oxidized in solution, especially in the light. If K2Fe(C0)4 prepared by reduction of Fe(C0)5 with potassium naphthalenide or C& in THF is used instead of NazFe(CO)r, the yields of iron aminocarbene complexes are generally higher (Table 1, entries 2 and 5 ) . In this case, it is crucial to keep the THF solution of KzFe(C0)4 below -30 "C, otherwise an insoluble THF solvate of K2Fe(C0)4 is formed and the yield of aminocarbene complex drops to zero. It is known that Cr(C0)s2-does not tolerate aromatic iodo12 and bromo13compounds, presumably because of the electron transfer processes. Fe(C0h2- behaves differently in this respect: [(4-Bromophenyl)-(NJV-dimethylamino)methyleneltetracarbonyliron(O)was readily formed by the reaction of 4-bromo-NJV-dimethylbenzamide with potassium tetracarbonylferrate in 54% yield (Table 1, entry 5). The reaction of 4-iodo-NJV-dimethylbenzamide with sodium tetracarbonylferrate appeared to be more complicated. Besides the two singlets at 6 3.11 and 4.00 characteristic for the carbene dimethylamino group, the 'H NMR spectrum of the reaction product indicated the presence of two different 4-substituted phenyl groups in 60.5:39.5 ratio and an intensive singlet at d 0.27 (a trimethylsilyl group belonging t o the compound with less intensive phenyl signals). This spectrum can be interpreted as that of a mixture of two carbene complexes [(4-iodophenyl)-(NJV-dimethylamino)carbene]tetracarbonyliron(0) (2j) and [4-(trim-
(11)The only exception is 2-furylderivative 2h, which slowly decomposes even a t -18 "C.
ethylsilyl)phenyll-(NJV-dimethylamino)carbeneltetracarbonyliron(0) (2k). This was confirmed by mass spectrometry showing molecular ions of low intensity for both compounds together with the character is ti^^^ stepwise lose of CO ligands. The silylated product 2k is likely to be formed by reductive splitting of iodine followed by silylation of the resulting carbanion by Me3SiC1.14 In conclusion, the reaction of Fe(C0)42- with tertiary amides without a-hydrogens provides a useful new route to (aminocarbene)tetracarbonyliron(O)complexes. The chemistry of these compounds is currently under study in our laboratory. Experimental Section Methods. Melting points were taken on a Kofler block and are uncorrected. Unless otherwise noted, all 'H NMR spectral data were recorded in CDC13 at 100 MHz and chemical shifts are reported relative to TMS. All IR spectra were recorded as CCh solutions. Elemental analyses were performed by the analytical departments of UOCHB-CSAV and Prague Technical University. The yields are based on starting amides. All experiments were carried out under argon. Materials. Tetrahydrofuran was distilled from benzophenone ketyl under a nitrogen atmosphere just prior to use. Ethyl acetate was distilled over CaH2; diethyl ether was dried over sodium metal and distilled. Iron pentacarbonyl, chromium hexacarbonyl, and chlorotrimethylsilane were obtained from Aldrich and used without further purification. Neutral aluminium oxide (Brockman I11 grade) was obtained from Lachema. Dimethylformamide and dimethylacetamide were obtained from Aldrich; the other amides were prepared from appropriate acid chlorides and dimethylamine or morpholine in ether. General Procedure for the Preparation of the Iron Aminocarbene Complexes 2a-i. Method A. In a 250 mL, round-bottomed flask equipped with a magnetic stirring bar and a septum inlet was placed a solution of iron pentacarbonyl (1.4 mL, 10.5 mmol) in THF (50 mL). The solution was cooled to -78 "C, and the flask was evacuated and filled with argon. This procedure was repeated five times. Then an -0.8 M stock solution of sodium naphthalenide in THF (35 mL, 28 mmol) was added via a double-ended needle over several minutes. The reduction of iron pentacarbonyl proceeds almost immediately with evolution of CO gas. The reaction mixture was than allowed to warm to 0 "C, and the amide (5 mmol) in THF (10 mL) was added through a double-ended needle. The solution was stirred at 0 "C for 10 min and then cooled to -78 "C; chlorotrimethylsilane (2.5mL, 19.7 mmol) was added via a syringe. The solution was stirred a t -78 "C for 0.5 h, then the cooling bath was removed, the mixture was allowed to warm to 0 "C, and neutral alumina (8 g) was added. The solvent was removed under reduced pressure on a rotatory evaporator, and the residue was dried for several hours under high vacuum to remove all the THF. n-Hexane (50 mL) was added, and the mixture was stirred vigorously for several minutes under argon atmosphere. The suspension formed was then transferred to the top of a column filled with neutral alumina (150 9). Naphthalene and green FedC0)12 were eluted with hexane, and further elution with hexane-CHzClz (51)gave the crude iron carbene complex as a brown-yellow solid. The crude product was dissolved in a small amount of dichloromethane, and the solution was diluted with n-hexane and filtered under argon atmosphere. Evaporation of dichloromethane in vacuum a t 0 "C and filtration under argon gave the pure iron aminocarbene complex. (12) Semmelhack, M.F.;Lee, G. R. 0rganometaUic.s 1987,6,1839. (13)D v o f a , D.Unpublished results. (14)All attempts a t separation of z j and 2k by chromatography or crystallization have failed.
572 Organometallics, Vol. 14, No. 1, 1995 Method B. To a solution prepared by dissolving potassium (1.20g, 30 mmol) and naphthalene (4.3g, 33.5mmol) in THF
Notes cooling in refrigerator. Recrystallization gave pure product
(0.737g, 39.0%) as yellow crystals: mp 89-93 "C; lH NMR 6 3.44-3.74(m, 4,CHz), 3.94-4.15(m, 2,CHz), 4.58-4.74(m, (80 mL) in an argon atmosphere was added iron pentacarbonyl 2,CHz), 6.65-6.89(m, 2, ArH), 7.10-7.42(m, 2,ArH); IR v (1.4mL, 10 mmol) at -78 "C via a syringe. Fe(C015 was 2045 (s), 1976 (s), 1946 (s), 1920 (9) cm-l. Anal. Calcd for reduced almost instantaneously, forming a yellow-brown soluH, 3.20;C1, 9.39; N, 3.71. Found: C15HlzClFeN05: C, 47.72; tion of Kz[Fe(C0)4]. After 15 min at -78 "C, the amide (5 C, 47.94;H, 3.26;C1, 9.52;N, 3.65. mmol) in THF (10mL) was added. After 0.5 h at -78 "C, the (4-Bromophenyl)-NJV-dimethylamino)methyleneltettemperature was allowed to rise slowly (in -0.5 h) to -40 "C, racarbonyliron(0) (2e). Method A. Reaction of sodium and the mixture was than kept at this temperature for another naphthalenide [Na (0.74g, 32.2mmol), naphthalene (4.6g, 0.5 h. The resulting solution was cooled again t o -78 "C, and chlorotrimethylsilane (2.5mL, 19.7mmol) was added. The 35.9mmol) in THF (100mL)] with Fe(C0)5(1.4mL, 10mmol), reaction mixture was stirred at -78 "C for 0.5 h and let t o 4-bromo-NJV-dimethylbenzamide(1.76g, 7.72mmol), and chlorotrimethylsilane (2.6mL, 20.5mmol) gave 1.53g (52%) warm gradually to 0 "C over 1 h. Neutral alumina (10g) was of crude 2e. Crystallization from ethyl acetate-n-heptane then added, and further workup was identical to that described under (A). mixture afforded 0.771 g (26.3%)of the pure compound: decomposes above 100 "C; IH NMR (300MHz) 6 3.10(6, 3, Method C. To C8K,7 prepared from graphite (2.5g, 208 NCH3), 4.00(s, 3,NCH3), 6.73-6.75(m, 2,ArH), 7.51-7.53 mmol) and potassium (1.06g, 26 mmol), was added THF (50 (m, 2,ArH); IR v 2045 (s), 1974 (s), 1945 (s), 1922 ( 8 ) cm-'. mL) under argon. The resulting suspension was cooled to -78 Anal. Calcd for Cl3HloBrFeNO4: C, 41.09;H, 2.65;N, 3.69; "C, and Fe(C0)5(1.4mL, 10 mmol) was added via a syringe, H, 2.75;N, 3.80;Br, 21.04. Br, 21.03.Found: C, 41.35; while CO evolved. The resulting mixture was stirred 0.5 h at -78 "C, and then a solution of the amide (8 mmol) in THF (15 Method B. A 2.08 g (54.7%)sample of pure 2e was mL) was added by syringe. Further procedure was identical obtained from potassium naphthalenide (66mmol), Fe(C0)5 to that described for method A, except that only 50 g of (2.8mL, 20 mmol), 4-bromo-NJV-dimethylaminobenzamide (2.2g, 10mmol), and chlorotrimethylsilane (5.2mL, 41mmol) alumina was used for chromatography. [(NJV-Dimethylamino)methyleneltetracarbonyliron- in THF (150mL) upon chromatography (150 g A l 2 0 3 ) and crystallization. (0) (2a). Procedure A using Fe(C0)5 (3.95g, 20 mmol), a 0.71 M THF solution of sodium naphthalenide (76mL), dimethyl[(4-Cyanophenyl)morpholinomethyleneltetracarformamide (0.790g, 10.8mmol), and chlorotrimethylsilane (4.0 bonyliron(0) (20. The reaction of Fe(C0)5 (1.4mL, 10.3 mL, 31.5mmol) gave 1.99g (82%) of the crude product. Pure mmol), a 0.75M THF solution of sodium naphthalenide (36 compound was obtained from crystallization as fawn needles: mL), N-(4-cyanobenzoyl)morpholine(1.10g, 5.09mmol), and 1.50g (61.7%),mp 58-60 "C (lit.5mp 55-56 "C). 'H NMR chlorotrimethylsilane (2.5mL, 19.7mmol) according to method A gave 1.08 g (57.8%) of yellow solid. Pure product was and IR spectra were identical with those in ref 4. obtained by crystallization: 0.548g (29.2%),mp 123 "C dec; [(NJV-Dimethy1amino)phenylmethyleneltetracarlH NMR 6 3.60(m, 4,CHZ),4.07(m, 2,CHZ),4.67(m, 2,CHZ), bonyliron(0) (2b). Method A. Crude carbene 2b (1.03g, 6.96(m, 2,ArH), 7.70(m, 2,ArH); IR v 2047 (m), 1979 (m), 68.5%)was obtained from NJV-dimethylbenzamide (0.745g, 1947 (s), 1925 (s) cm-'. Anal. Calcd for C ~ ~ H I ~ F ~ NC,Z O ~ : 5 mmol), Fe(C0)5 (2.033g, 10.4mmol), a 0.71M THF solution 52.20;H, 3.29;N, 7.61.Found: C, 52.53; H, 3.22;N, 7.54. of sodium naphthalenide (42mL), and chlorotrimethylsilane (2.5mL, 19.75mmol). Crystallization gave 0.95g (63.1%)of [(NJV-Dimethylamino)-3-pyridylmethylenel tetracaryellow crystalline solid: mp 96-102 "C (ref.4cmp 106 "C); 'H bonyliron(0) (2g). Procedure A using Fe(C0)6 (1.4mL, 10.3 NMR 6 3.10(8, 3,NCHs), 4.00(s, 3,NCHs), 6.64-6.80(m, 2, mmol), a 0.8 M THF solution of sodium naphthalenide (34mL), ArH), 7.00-7.50(m, 3,ArH); IR v 2043 (s), 1972(s), 1943 (s), NJV-dimethylnicotinamide(0.850 g, 5.66mmol), and chlorot1921 (9) cm-l [from ref 3c: IR (n-hexane) v 2045 (m), 1968 rimethylsilane (2.5mL, 19.7mmol) gave 0.60g (35.1%)of (m), 1955 (m), 1945 (s), 1923 (s) cm-l]. crude product as a dark brown oil and 0.490g (28.7%)of pure yellow crystalline compound after recrystallization: mp 87"C Method B. Pure 2b (0.65g, 76.0%) was obtained by dec; lH NMR 6 3.15( 8 , 3,NCHz), 4.07(s, 3,NCHs), 7.13-7.33 starting from potassium naphthalenide [K (3.1g, 77.5mmol), (m, 1,Py-H), 7.36-7.60(m, 1,Py-H), 8.53-8.77(m, 1,Py-H), naphthalene (10.25g, 80 mmol), and THF (180mL)], Fe(C0)5 (4.2mL, 30 mmol), NJV-dimethylbenzamide (3.03g, 20.31 8.87-9.13(m, 1,Py-H); IR v 2045 (s), 1974(s), 1945 (s), 1923 (s) cm-l. Anal. Calcd for C12HloFeN204: C, 47.71;H, 3.34; mmol), and chlorotrimethylsilane (7.5mL, 59.1mmol) in THF N, 9.27.Found: C, 47.76; H, 3.41;N, 9.06. (180mL) after chromatography (250g A12031 and crystallization. [(NJV-Dimethylamino)-2-furfurylmethylenel tetracarbonyliron(0) (2h). The reaction of Fe(C0)5 (1.40g, 10.3 Method C. The reaction of C8K (26.5mmol), Fe(C0)b (1.4 mmol), a 0.8 M THJ? solution of sodium naphthalenide (34mL), mL, 10mmol), NJV-dimethylbenzamide (1.2g, 8.05 mmol), and NJV-dimethyl-2-furfUcarboxamide(0.700g, 5.03mmol), and chlorotrimethylsilane (3mL, 23.6mmol) gave 1.80g (74.3%) chlorotrimethylsilane (2.5mL, 19.7mmol) gave, according t o of 2b after chromatography (50g of A l 2 0 3 ) and crystallization. method A, 1.18g (80.56%)of crude product, which afforded [(4-Methoxyphenyl)morpholinomethylenel tetracarafter recrystallization 0.981g (67.0%)of orange crystals: mp bonyliron(0) (2c). The reaction of Fe(C0)5 (1.4mL, 10.3 46-48.5"C; 'H NMR 6 3.23(5, 3,NCH3), 3.96(s, 3,NCH3), mmol), a 0.8 M THF solution of sodium naphthalenide (34mL), 6.32-6.48(m, 2,ArH), 7.44(br s, 1,ArH); IR Y 2044 (s), 1972 N-(4-methoxybenzoyl)morpholine(1.12g, 5 mmol), and chlo(s), 1945(s), 1925(6). Anal. Calcd for C11HgFeN05: C, 45.40; rotrimethylsilane (2.5mL, 19.75mmol) according to method H, 3.12;N, 4.81.Found: C, 45.09;H, 3.06;N, 4.78. A gave 1.28g (68.0%)of yellow solid. Crystallization afforded 0.907g (48.6%)of pure carbene complex 2c: mp 121 "C dec; [(NJV-Dimethylamino)-3-thienylmethylenel tetracar'H NMR 6 3.59(s, 4,CHz), 3.82(9, 3,CH3), 3.96-4.10(m, 2, bonyliron(0) (2i). Method A gave by the reaction of Fe(C0)b CHz), 4.58-4.74(m, 2,CHz), 6.68-7.00(m, 4,ArH); IR v 2043 (1.40mL, 10.3 mmol), a 0.8 M THF solution of sodium (s), 1972(s), 1942 (s), 1918(s) cm-'. Anal. Calcd for C16H16naphthalenide (36mL), NJV-dimethyl-3-thienylcarboxamide FeN06: C, 51.50;H, 4.05; N, 3.75.Found: C, 51.61;H, 4.05; (0.860g, 5.55 mmol), and chlorotrimethylsilane (3.0mL, 23.6 N, 3.87. mmol), 1.353g (79.5%) of crude product. Crystallization afforded 1.10g (64.5%)of yellow solid: mp 82-85 "C; 'H NMR [(3-Chlorophenyl)morpholinomethylene] tetracar6 3.16(s,3,NCH& 3.98(s,3,NCH3), 6.73(s, l,ArH), 6.77(d, bonyliron(0)(2d). Procedure A was used to produce 1.472 J = 0.7Hz, 1,ArH), 7.24-7.40 (m, 1,ArH); IR v 2043 (s), 1972 g (77.5%)of carbene 2d from N-(3-chlorobenzoyl)morpholine (s), 1943 (s), 1917(s). Anal. Calcd for C11HgFeN04S: C, 43.02; (1.135g, 5 mmol), Fe(CO)5 (1.4mL, 10.3mmol), a 0.8 M THF H, 2.95;N, 4.56; S,10.44.Found: C, 42.68;H, 2.94;N, 4.73; solution of sodium naphthalenide (34mL), and chlorotrimS,10.50. ethylsilane (2.5mL, 19.75mmol) as an oil which solidified after
Organometallics, Vol. 14, No. 1, 1995 573
Notes Reaction of 4-Iodo-NJV-dimethylbemamidewith NapFe(C0)s. The reaction of sodium naphthalenide [naphthalene (4.5 g, 35.1 mmol), Na (0.70 g, 30.4 mmol) in THF (70 mL)] with Fe(C0)E (1.4 mL, 10.3 mmol), Ciodophenyl-NJVdimethylbenzamide (1.37 g, 5 mmol), and chlorotrimethylsilane (3 mL, 23.6 "01) according to method A afforded after chromatography (150 g of A&) and crystallization 0.324 g of a mixture of the [(NJV-dimethylamino)-(4-iodophenyl)methyleneltetracarbonyliron(0)(2j)and [(NJV-dimethylamino)[(4-trimethylsilyl)phenyl]methylene]~trac~bonyliron(O) (2k) in -60.5:39.5 ratio (based on IH NMR). All attempts t o separate 2j and 2k by chromatography and crystallization were unsuccessful. For Zj: lH NMR (300 MHz) 6 3.11 ( 8 , 3, NCHs), 4.00 ( 8 , 3, NCH3), 6.55-6.65 (m, 2, ArH), 7.65-7.78 (m, 2, ArH); MS (C13HloFeIN04) 427 (M+), 399 (M+ - CO),
371 (M+ - 2CO), 343 (M+- 3CO). For 2 k IH NMR (300 MHz) 6 0.27 ( 8 , 9, Si(CH3)3), 3.11 (s, 3, NCHd, 4.00 ( 8 , 3, NCH3), 6.75-6.85 (m, 2, ArH), 7.45-7.55 (m, 2, ArH); MS (CleHleFeNO4Si)373 (M+), 345 (M+ - CO), 317 (M+ - 2CO), 289 (M+ - 3CO), 261 (M+ - 4CO). For the mixture of Zj and 2k IR Y 2044 (s), 1973 (m), 1944 (s), 1920 ( 8 ) . Elemental analysis of the mixture gave 18.78%I, which corresponds t o a 63.15%content of 2j in the mixture of 2j and 2k. This value is in good agreement with that obtained from lH NMR.
Acknowledgment. We thank t h e Prague Technical University and Institute of Organic Chemistry a n d Biochemistry-AVCR for their support of our program. OM940596X
