COBALT 1,2-AZABOROLYL DIENE COMPLEXES

The reaction of (1-tert-butyl-2-methyl-1H-eta-5-1,2-azaborolyl)dicarbonylcobalt [AbCo(CO)2] (1) with various di-, tri-, and tetraolefins under photolytic conditions at -40-degrees-C in pentane solution gives AbCo(eta-4-diene) complexes (diene = 1,3-butadiene (2), 2-methyl-1,3-butadiene (3a, 3b), 2,3-dimethyl-1,3-butadiene (4), 1,5-hexadiene (5), six isomers of octadiene (6a-6f), cyclopentadiene (7), 1,3-cyclohexadiene (8), norbornadiene (9), 1,3,5-cycloheptatriene (10a, 10b), 1,3,5,7-cyclooctatetraene (11)). Due to the chiral AbCo moiety, the use of prochiral olefins leads to diastereoisomers, as observed in the case of 3, 6, and 10. The use of 1,7-octadiene could lead to an immense number of isomeric complexes. Only six can be observed in the C-13 NMR spectrum. H-1, C-13, and B-11 NMR spectra of all compounds in combination with 2D and NOE techniques enable reliable structure determinations.