Asymmetric cobalt catalysts for hydroboration of 1,1-disubstituted alkenes

Abstract

The chiral iminopyridine oxazoline (IPO) ligands were designed, synthesized and utilized for the first cobalt-catalyzed highly regio-and enantioselective anti-Markovnikov hydroboration of 1,1-disubstituted aryl alkenes. This novel IPO ligands will likely be of high value for asymmetric transformations with first-row transition metals.

Visible‐Light Controlled Divergent Catalysis Using a Bench‐Stable Cobalt(I) Hydride Complex

“…We elected to investigate the visible‐light promoted hydroboration of alkenes: an atom‐economical, value‐adding transformation which has provoked substantial research. Examples of both Markovnikov and anti‐Markovnikov cobalt‐catalysed hydroborations have been reported previously. Many of these examples, however, rely on complex ligand systems or use an air sensitive cobalt complex that must be manipulated in a glovebox .…”

Cobalt‐Catalyzed Alkyne Hydrosilylation and Sequential Vinylsilane Hydroboration with Markovnikov Selectivity

“…More interestingly,t he a-vinylsilanes react with pinacolborane (HBpin) to form geminal borosilanes 10 with excellent regioselectivity.T he formation of the sterically crowded tetrasubstituted carbon center through Markovnikov hydroboration is remarkable because Lu and co-workers [19] and our group [10g] previously demonstrated that IPO Co precatalyst 3a gave exclusively the anti-Markovnikov hydroboration products when 1,1-disubstituted aryl alkyl alkenes were used as the substrates.Incontrast, acatalyst screen revealed that the Co and Fe complexes of IPO (3a, 3b), PDI (5a, 5b), and Pybox (6a, 6b)w ere all selective for the formation of geminal borosilane 10 a in the reaction of 2a with HBpin (see the Supporting Information). Among them, PDI Co complex 5a was most effective;i nt he presence of this precatalyst (2 mol %) and NaBHEt 3 (4 mol %), 10 a was formed in 90 % yield.…”

Cobalt‐Catalyzed Regio‐ and Stereoselective Hydroboration of Allenes

“…Although cobalt complexes have been reported to catalyze the hydroboration of alkenes, under the optimized conditions, allenes exhibit a much higher reactivity than both terminal and internal alkenes as demonstrated by the formation of Z ‐ 4 q , Z ‐ 4 r , and Z ‐ 4 s in high yields with exclusive chemoselectivity.…”