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

Abstract

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.

Earth-abundant transition metal catalysts for alkene hydrosilylation and hydroboration

“…It is important to note, however, that the ( Ar PDI)Fe(N 2 ) 2 compounds, which contain the same large aryl substituents, can effectively catalyze the hydroboration of these cyclic internal olefins presumably due to the decreased steric penalty in the interception of iron-secondary alkyl intermediates by HBPin by virtue of the larger atomic radius of iron than cobalt. This olefin isomerization-functionalization strategy was applied in the synthesis of linear alpha olefins (LAOs), 117 which find use as high-value chemical intermediates in the petrochemical industry, 118 from internal olefins. Using cobalt complex 7 , chain-walking isomerization-hydroalumination followed by thermolysis allows the net transformation of internal olefins to LAOs.…”

“…Using cobalt complex 7 , chain-walking isomerization-hydroalumination followed by thermolysis allows the net transformation of internal olefins to LAOs. 117…”

Walking Metals for Remote Functionalization

“…Recently, the generality of cobalt bis(imino)pyridine complexes in chain-walking scenarios was extended by showing the viability to conduct hydroaluminations of internal olefins via an initial isomerization prior to C–Al bond formation. 56 …”

“…While the role of the ligand still remains unclear, the differences on both t BuCH 2 MgBr and CyMgBr are likely attributed to the presence of β-hydrogens in the latter, thus setting the basis for the generation of cobalt hydride species. Recently, the generality of cobalt bis­(imino)­pyridine complexes in chain-walking scenarios was extended by showing the viability to conduct hydroaluminations of internal olefins via an initial isomerization prior to C–Al bond formation …”

“…Recently, the generality of cobalt bis(imino)pyridine complexes in chain-walking scenarios was extended by showing the viability to conduct hydroaluminations of internal olefins via an initial isomerization prior to C−Al bond formation. 56 Palladium Catalysis. Despite the rapid development of a range of catalytic systems to induce remote functionalization via "chain-walking", this area of research is largely dominated by palladium-based catalysts.…”