Cobalt‐Mediated Cyclooligomerization Reactions of Borylacetylenes

Abstract

AbstractReaction of bis(diethylamino)acetylene (1) with lithium and chlorobis(dimethylamino)borane yields 1‐[bis(dimethylamino)boryl]‐2‐(diethylamino)acetylene (2). Treatment of 1‐aryl‐2‐(trimethylstannyl)acetylenes 3 with chlorobis(diisopropylamino)borane results in the quantitative formation of 1‐aryl‐2‐[bis(diisopropylamino)boryl]acetylene compounds 4. The 1‐aryl‐2‐borylacetylene derivatives 5, 6, and 7 are obtained by the reaction of 3 with the appropriate haloborane, or by reacting 4 with two equivalents of HCl and one equivalent of catechol, dithiocatechol and 2‐hydroxythiophenol. The catalytic cyclotrimerizations of 5a−d with [CpCo(CO)2] or [Co2(CO)8] lead to isomeric mixtures of the triborylbenzene derivatives 8a−d and 8a′−d′, whereas 6a−d and 7a−b undergo cyclotrimerization only with catalytic amount of [Co2(CO)8], to give isomeric mixtures of the triborylbenzene derivatives 12a−d/12a′−d′ and 13a−b/13a′−b′, respectively. The reaction of 2 with a stoichiometric amount of (η5‐cyclopentadienyl)bis(ethene)cobalt leads to (η5‐cyclopentadienyl)(η4‐cyclobutadiene)cobalt complexes 9. The analogous complexes 10 and 11 are obtained by the reactions of 6 and 7 with a stoichiometric amount of (η5‐cyclopentadienyl)dicarbonylcobalt. Treatment of Co2(CO)8 with 5a, 6a, and 7a yields the dicobaltatetrahedranes 14a, 15a and 16a. Compound 15a reacts with two equivalents of diphenylacetylene and 1‐(1,3,2‐benzodioxaborolyl)‐2‐phenylacetylene (5a), to furnish (1,3,2‐benzodithiaborolyl)pentaphenylbenzene (17) and bis(1,3,2‐benzodioxaborolyl)(1,3,2‐benzodithiaborolyl)triphenylbenzene (18), respectively. The new compounds have been characterized by NMR spectroscopy and mass spectrometry, as well as by X‐ray structural analyses for 4a, 5a, 6a, and 10a. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)