A Co(II) complex, (PPHP)CoI2, was synthesized and evaluated as a pre-catalyst for the hydrogenation and hydroboration of various alkenes. Initial results have shown that (PPHP)CoI2, when activated with KBEt3H (4 mol%) is capable of selective reduction of terminal alkenes in nearly quantitative yields under mild conditions. Interestingly, saturated frameworks bearing a terminal olefin were found to produce a mixture of the fully saturated product and internal olefins via a chain-walk mechanism. This chain-walking phenomenon was not observed when pyridine was used as an additive (6 mol%). We hypothesize that a pyridine-cobalt adduct generated in-situ slows the process of catalyst deactivation and may play a part in this observed selectivity. Additionally, this catalyst was shown to effectively hydroborylate terminal alkenes with high selectivity for the anti-markovnikov products with low catalyst loading (1 mol%) in three hours. The sole metal-containing product observed upon completion of catalytic reactions, [(PPP)CoH]2, suggests a monomeric (PPP)CoIIH active species that is deactivated by dimerization when substrates are depleted.

Catalytic hydrogenation and hydroboration of terminal alkenes by a pincer-ligated cobalt (II) complex

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