Cobalt-bis(imino)pyridine complexes as catalysts for hydroalumination–isomerisation of internal olefins

The insertion of α- and internal octenes (hydroalumination) and chain walking isomerisation at di-n-octylaluminium hydride [Al(Oct)₂H], catalysed by bis(imino)pyridine–Co complexes has been investigated by NMR spectroscopy. The Co-based catalysts promote efficient hydroalumination of 1-octene. Internal olefins are partially hydroaluminated, with isomerisation to the primary alkyls, but the catalyst responsible appears to deactivate rapidly. The reaction between the Co precatalysts and [Al(Oct)₂H] generates a Co-hydride species, likely to be a hydride bridged dinuclear Co and Al complex. This species is reactive towards α-olefins but inert towards internal olefins. In contrast to hydroalumination, the catalysts promote efficient hydroboration, where insertion and isomerisation of internal octenes goes to completion. The differences between the systems may be partially ascribed to formation of an active mononuclear Co catalyst in the borane system versus a less active Co/Al dinuclear complex in hydroalumination.