Reaction of Cyclooctatetraenechromium

Indian Journal of Chemistry Vol. 24A. December 1985, pp. 1052-1053

Reaction of Cyclooctatetraenechromium• chromiumhexacarbonyl in acetonitrile and further tricarbonyl with Dimethylacetylene refluxing this product in cyclooctatetraene (COT). Dicarboxylate in Presence of Reaction of cyclooctatetraenechromiumtricarbonyl with Triirondodecacarbonyl-Exchange dimethyl acetylenedicarboxylate and triirondodeca• of Chromium by Iron & Contraction carbonyl of Cyclooctatetraene Ring A mixture of cyclooctatetraenechromiumtri•

carbonyl (0.5g, 2.08 >< 1O~3mol), dimethyl acetylene• s S ULLAH*, 1 AHMED, S E KABIR, M M KARIM & dicarboxylate (DMAD, 0.5g, 2.08 x 10-3 mol) and A H MOLLA FeiCO)12 (1.05g, 2.08 x 10-3 mol) in tetrahydrofuran Department of Chemistry, Jahangirnagar University, Savar, was refluxed for 1 hr under nitrogen atmosphere. Dhaka, Bangladesh Removal of solvent under reduced pressure afforded a Received I March 1985; revised and accepted 24 June 1985 solid mass which was extracted with pet ether (40-60°). The organic extract was chromatographed over a Metal. exchange and ring contraction reactions occur when cyclooctatetraenechromiumtricarbonyl is relluxed for I hr with column of silica gel (60-120 mesh) employing pet ether Fe3(CO)12 in the presence of dimethyl acetylenedicarboxylate in (60_80°)as an eluent. Removal of solvent from eluate tetrahydrofuran under nitrogen atmosphere, as revealed by the under reduced pressure gave rise to red crystals of the formation of two complexes, viz. cyclooctatetraenetricarbonyl known2 complex, COT Fe(COh (complex-I) (0.417g, iron(l) (a metal exchange product) and (COh Cr 82% based on cyclooctatetraenechromiumtri• C6H,C .•H3(C02Me)2 Fe(CO).•(II) (a ring contraction product). The structures of the complexes have been established by spectral data carbonyl), m.p. 93-95°; IR 2045, 1995 and 1985 em-I (JR, PMR and mass) and elemental analyses. (CO); PMR (CDCh) : b 4.8 (s,8H); MS: m/z244(M.+), 216 (M-CO), 188 (M-2CO), 160 (M-3CO), 104 [M• (3Co + Fe)] and 78 (C6H6) (Found C,54.2; H, 5.5. Cl1HsFe03 requires e, 54.1; H, 3.3%). The complex, The objective of the present work was to examine the COT Fe(COh(I) was obtained in 90~1oyield by carrying reaction of cyclooctatetraenechromiumtricarbonyl out the reaction between COTCr(COh and Fe3(CO)t2 with dimethyl acetylenedicarboxylate in the presence in the absence of DMAD. of Fe3(CO)12 and to identify the product(s) of this The second band on removal of solvent resulted in reaction. The product analysis revealed that the the isolation of a reddish yellow crystalline compound reaction took an unusual course in which the complex (complex 11), 0.12g (l0.48% based on cyclooctate• cycloocta tetraenechromiumtricarbony 1 underwent traenechromiumtricarbonyl), m.p. 142-45"(Found: e, metal exchange to give the known complex2, 45.5; H, 2.5. Reqd: e, 45.3; H, 2.3'%). cyclooctatetraeneirontricarbonyl(I) and another The structure of the complex (II) has been proposed complex(II). The structures of the complexes(l) and (II) on the basis of its spectral data (IR, PMR and mass) have been confirmed on the basis of spectral data (IR, and elemental analyses. The complex (II) exhibited in PMR and mass) and elemental analyses. its IR spectrum bands at 2060, 2040, 2015 and 1990 All reactions and subsequent manipulations were em -I. Its PMR spectrum displayed three peaks at b 4.5 carried out under nitrogen atmosphere. Infrared (s,5H), 8.5 (m,3H) and 7.5 (s,6H). The signal at b 4.5 is spectra were recorded on a Beckman IR 4220 due to the protons of the aromatic moiety bonded to spectrophotometer in cyclohexane, PMR spectra in the Cr(COh and that at b 8.5 (m,3H) is due to the Sp3_ CDCl3 on a Varian EM-390(90 MHz) spectrometer protons of cyclobutene group coordinated to the and mass spectra on an MS-12 high resolution Fe(CO)4 group. The signal at b 7.5 has been attributed spectrometer. Elemental analyses were carried out at to the methyl protons of the ester groups. Its mass the microanalytical laboratory of Tohoku University, spectrum showed the parent molecular ion at m/z Japan. Melting points were taken on a Fisher-Johns 556(M +) and other peaks at 219.(M+-CI2HgOsFe), electrothermal melting point apparatus and are 336(M + -C9HS03). The mass spectrum also exhibited uncorrected. Tetrahydrofuran (THF) was freshly peaks due to successive loss of four CO units from the distilled from sodium and benzophenone immediately CI2Hg04 Fe group and three CO from the C9HS03 Cr before use. group. Cyclooctatetraenechromiumtricarbonyl was pre• On the basis of the above spectral evidences we pared by the known procedure 1 by refluxing believe that the reaction between COTCr (COh and 1052

Ii .1'1;'1 NOTES

DMAD in the presence of FeiCO)12 follows the of reaction with cyclooctatetraene to finally end-up in pathway outlined in Scheme I. a cyclobutene moiety. The cyclobutene moiety is stabilized by an Fe(CO)4 group supplied by FeiCO) 12 to give the complex (II) in 26% yield. In the reaction , + F.(CO)4 H COOCH3 Scheme I, metal exchange reaction predominates over Q

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