Indian Journal of Chemistry Vol. 41B. August 2002. pp 1736-1737

Note.

Synthesis of 1 , 1 , 4, 4-tetraryl- l , 3-diazabuta­dienes by oxidation of hydrazones using

bis( acety lacetonato )copper (II) G S Singh* & K Kopo

Chemistry Department. University of Botswana. Private Bag 0022. Gaborone. Botswana

e-mail: singhgs@mopipi.ub.bw

Received 23 November 2000; accepted (revised) 1 1 June 2001

The treatment of benzophenone hydrazones with bis(acety­lacetonato)copper(II) affords 1 . 1 . 4. 4-tetraryl- l . 3-diaza-buta­dienes in good yields. The formation of diazabutadienes is ex­plained by the intermediacy of carbenoids generated by the Cu(acac)z-catalyzed decomposition of diaryldiazomethanes which in tum are formed initially by oxidation of the corresponding hy­drazones.

Transition metal salts and complexes occupy a central place in an organic chemist's arsenal of oxidants. Several transition metal salts and complexes have been employed in oxidative reactions of different or­ganic substrates 1 .9. It has been observed for the first time by our group that bis(acetylacetonato)copper(II) serves as a catalyst in the oxidation of benzil mono­hydrazoneslO• u-Diazoketones and azines were iso­lated under different reaction conditions. In continua­tion of this study the present paper reports the synthe­sis of diaryldiazabutadienes via oxidation of benzo-

. phenone hydrazones using bis(acetylacetonato)copper (II). The products have been characterized on the ba­sis of satisfactory elemental analysis and spectro­scopic (IR, IH NMR and MS) data. Such compounds have drawn wider interest which is evident from the fact that their various uses have been the subject of patents l l . 13. The most common method to prepare di­aryldiazabutadienes appears to be the preparation of hydrazones first followed by the reaction of latter with an excess of ketone for 10 to 15 hrl4. Some other methods for their synthesis involve the reaction of benzophenone hydrazones with an excess of poly­phosphoric acid at 150°C and the reaction of alde­hydes with thiosemicarbazide in N,N-dimethyl­fonnamide in the presence of zinc chloride at 152°CI5.16.

The treatment of benzophenone hydrazones la-d with an equimolar amount of bis(acetylacetonato) copper(lI) in dichloromethane yielded light yellow

crystalline compounds characterized as diazabutadie­nes 2a-d on the basis of satisfactory analytical and spectral data (see Experimental Section).

It was observed by TLC monitoring of the reaction progress that all the hydrazones disappeared com­pletely in comparatively lesser times in dichloro­methane than that in benzene. The reaction was also affected by temperature and amount of catalyst. The maximum yield was obtained at reflux temperature by taking an equimolar amount of the catalyst.

The IR spectra of the compounds showed a sharp and strong absorption band in the region of 1600-1 635 cm·1 which is characteristic of the C-N=N-C linkage. The mass spectra showed the peak corre­sponding to M+. The other main fragments observed are due to cleavage of either one or two aromatic rings and N-N bond. The signals in the NMR spectra are also in agreement with the assigned structures.

The plausible mechanism for the formation of products is shown in Scheme I. It involves an initial oxidation of hydrazones to diaryldiazomethanes. The diaryldiazoalkanes could not be isolated as the reac­tion required reflux temperature which has been re­ported in our previous communication 10. However, their intervention is ascertained by isolation of u­diazoketones from the controlled oxidation of benzil monohydrazoneslO• The diazoalkanes decompose and react in usual way as copper-carbenoids do with an­other molecule of diazoalkanes to give diazabutadie­nes 2a-d17•

Experimental Section Melting points have been recorded on a Stuart

Scientific melting point SMPI apparatus and are uncorrected. IR spectra were recorded on a Perkin­Elmer 781 spectrophotometer, NMR spectra on a Bruker™ 300 MHz spectrometer in a CDCh solution and mass spectra on a Mat SSQ 7000 spectrometer using EI method. Benzophenone hydrazones were prepared by the reaction of benzophenones with hydrazine hydrate in n-butanol according to reported methodl8.

General reaction procedure A solution containing 1 mmole each of benzophe­

none hydrazones la-c and bis(acetylacetonato)

NOTES 1737

Ar " /C=N-NH2

Ar' la-d

Cu(acac}z ' � [Ar ] " E9 e

/C=N=N Ar'

Cu(acac}z � rComplex of A &] LCu(acac}z

A 2a. Ar = Ar' = Phenyl 2b. Ar = Ar' = p -Anisyl 2c. Ar = Ar' = p -Tolyl 2d. Ar = Phenyl

Ar Ar " / C=N -N=C

A [ Complex of ArAr'C:] ..... 1--- & Cu(acac}z

Ar' = p -Chlorophenyl / "Ar' Ar'

2a-d

Scheme I

copper(II) in 15 mL of benzene or dichloromethane was heated to reflux for 3-4 hr. After cooling down to room temperature the reaction mixture was subjected to filtration through a silica gel column ( lOg, 1 .2xlOcm

2) using a mixture of n-hexane and ethyl

acetate as eluant. The evaporation of solvent under reduced pressure afforded the products 2a-d as light yellow solids which were recrystallized with ethanol. The physical and spectral data are given below:

2a: Yield 80 %; m.p. 164°C; IR (KBr): 1 600 cm-I ; IH NMR (CDCh: 8 7.33 (m, 20H, arom); MS: mJz (r. i .) 360 (80, M+), 283 (64, M+ - Ph), 1 80 ( 100, Ph2C=N+), 77 ( 14) (Found: C, 86.25; H, 5.69; N, 7.55. C26H2oN2 requires C, 86.66; H, 5.55; N, 7.77%).

2b: Yield 63 %; m.p. 180°C; IR (KBr): 1635 cm-I ; IH NMR (CDCb): 8 6.94 - 6.81 (m, 8H, arom), 7.50 - 7.27 (m, 8H, arom) , 3 .90 & 3.82 (two S, 12H, four OCH3); MS: mJz (r. i .) 480 (52, M+), 373 ( 100, M+ -C6�.OCH3-P), 266 (8, C6H4.OCH3-P2C=N-N=C), 264 (48), 240 (70, C6H4.OCH3-P2C=N), 210 (98), 1 67 (44), 1 5 1 (48), 138 (42) (Found: C, 74.64; H, 6.09; N, 5.55. C30H2SN202 requires C, 75.00; H, 5.83; N, 5.83%).

2c: Yield 67 %; m.p. 206°C; IR (KBr): 1 6 1 9 cm-I ; IH NMR (CDCh): 8 7.70 - 7. 10 (m, 16H, arom), 2.29 & 2.20 (two S, 1 2H, four CH3); MS: mJz (r. L) 416 (100, M+), 325 (86, M+ - C6�.CH3-P), 299 (24), 284 (20), 208 (54, C6�.CH3-p2C=N), 1 93 ( 16, Ar2C), 178 (44) (Found: C,86.40; H, 7.02; N, 6.42. C30H2SN2 re­quires C, 86.50; H, 6.73; N, 6.73%).

2d: Yield 86 %; m.p. 1 88°C; IR (KBr): 1605 cm-I ; IH NMR (CDCh) : 8 7.50 - 6.80 (m, 1 8H, arom);

MS: ,mJz (r. i.) 428 (84, M+), 35 1 (92, M+ - Ph), 3 17 ( 100, M+ - C6�.CI-p), 2 17 (98), 214 (30, M+/2), 1 65 (52) (Found: C, 72.59; H, 4.42; N,6.35. C26HI SN2Ch

requires C, 72.89; H, 4.20; N, 6.54%).

Authors are grateful to Professor B. M. Abegaz, Head, Chemistry Department, University of Botswana for providing the necessary research facilities.

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