1,2-AZABOROLYL COMPLEXES .31. CYCLOOLIGOMERIZATION OF ALKYNES AT THE 1,2-AZABOROLYLCOBALT MOIETY

1-tert-Butyl-2-methyl-eta(5)-1H-1,2-azaboro-bis(eta(2)-ethene)cobalt (AbCo(C2H4)(2)) (1) reacts with 2-butyne to give AbCo(eta(4)-1,2,3,4-tetramethyl-1,3-cyclohexadiene) (2) and catalytically generated free hexamethylbenzene. With diphenylethyne, 3-hexyne and 4-octyne the formation of 1,3-cyclohexadiene complexes 3, 5 and 7 is observed as well as the cyclodimerization of the alkynes with formation of cyclobutadiene complexes 4, 6 and 8. The separation of corresponding cyclohexadiene and cyclobutadiene complexes is possible by high performance liquid chromatography, as is exemplified with the combination 3-4. Two-dimensional NMR techniques enable the characterization of the product mixtures 5-6 and 7-8.