We report a regiodivergent hydrosilylation of alkenes catalyzed by catalysts generated in situ from bench-stable Co­(acac)2 and phosphine- or nitrogen-based ligands. A wide range of vinylarenes and aliphatic alkenes reacted to afford either branched (45 examples) or linear (37 examples) organosilanes in high isolated yields (average: 84%) and high regioselectivities (from 91:9 to >99:1). This transformation tolerates a variety of functional groups including ether, silyloxy, thioether, epoxide, halogen, amine, ester, boronic ester, acetal, cyano, and ketone moieties. Mechanistic studies suggested that the hydrosilylation of alkenes catalyzed by the cobalt/bisphosphine system follows the Chalk–Harrod mechanism (with a Co–H intermediate), and the hydrosilylation of alkenes catalyzed by the cobalt/pyridine-2,6-diimine system follows the modified Chalk–Harrod mechanism (with a Co–Si intermediate). Systematic studies with sterically varied silanes revealed that the steric properties of silanes play a pivotal role in controlling the regioselectivity of vinylarene hydrosilylation and the chemoselectivity of the reactions of aliphatic alkenes and silanes catalyzed by the cobalt/pyridine-2,6-diimine system.

Hydrosilylation of allenes is the addition of a hydrogen atom and a silyl group to a carbon–carbon double bond of an allene molecule and represents a straightforward and atom-economical approach to prepare synthetically versatile allylsilanes and vinylsilanes. However, this reaction generally produces six possible isomeric organosilanes, and the biggest challenge in developing this reaction is to control both regioselectivity and stereoselectivity. The majorities of the developed allene hydrosilylation reactions show high selectivity towards the production of vinylsilanes or branched allylsilanes. By employing a cobalt catalyst generated from readily available and bench-stable cobalt precursor and phosphine-based ligands, here we show that this reaction proceeds under mild conditions in a regioselective and stereoselective manner, and affords synthetically challenging, but valuable linear cis-allylsilanes with excellent stereoselectivity (generally cis to trans ratios: >98:2). This cobalt-catalyzed (Z)-selective allene hydrosilylation provides a general approach to access molecules containing stereodefined (Z)-alkene units.

We report a regioselective and stereoselective hydrosilylation of terminal alkynes with catalysts generated from bench-stable Co­(acac)2 and bisphoshpine ligands. The cobalt catalyst precursors are activated by the reaction with hydrosilanes, and air-sensitive activators, such as Grignard reagents or NaBHEt3, are not required for catalyst activation. A wide range of aromatic and aliphatic terminal alkynes underwent this cobalt-catalyzed hydrosilylation, affording the corresponding (E)-vinylsilanes in high yields with high regioselectivity and stereoselectivity. These reactions show good functional group compatibility and can be readily scaled up to gram-scales without using a drybox. Deuterium-labeling experiments suggest a cis-addition of hydrosilanes to alkynes.

A cobalt-catalyzed Z-selective hydrosilylation of alkynes has been developed relying on catalysts generated from bench-stable Co(OAc) and pyridine-2,6-diimine (PDI) ligands. A variety of functionalized aromatic and aliphatic alkynes undergo this transformation, yielding Z-vinylsilanes in high yields with excellent selectivities (Z/E ratio ranges from 90:10 to >99:1). The addition of a catalytic amount of phenol effectively suppressed the Z/E-isomerization of the Z-vinylsilanes that formed under catalytic conditions.

We report the first catalytic diborylation of 1,1-disubstituted vinylarenes with pinacolborane using a cobalt catalyst generated from bench-stable Co(acac) and xantphos. A wide range of 1,1-disubstituted vinylarenes underwent this transformation to produce the corresponding gem-bis(boryl)alkanes in modest to high yields. This cobalt-catalyzed reaction can be readily conducted on a gram scale without the use of a dry box and represents a practical and effective approach to prepare a wide range of branched gem-bis(boryl)alkanes.

Polyborylated organic compounds have been emerging as versatile building blocks in chemical synthesis. Here we report a selective cobalt-catalyzed deoxygenative 1,1,3-triborylation reaction of allylic ethers with pinacolborane to prepare 1,1,3-triborylalkane compounds. With naturally abundant and/or synthetic cinnamic methyl ethers as starting materials, we have achieved the synthesis of a variety of 1,1,3-triborylalkanes (25 examples). The synthetic utility of these 1,1,3-triborylalkanes is demonstrated through site-selective allylation, protodeborylation, and consecutive carbon-carbon bond-forming reactions. Mechanistic studies including deuterium-labeling and control experiments suggest that this 1,1,3-triborylation reaction proceeds through initial cobalt-catalyzed deoxygenative borylation of allylic ethers to form allylic boronates followed by cobalt-catalyzed 1,1-diborylation of the resulting allylic boronates.

We report an asymmetric synthesis of enantioenriched gem-bis(boryl)alkanes in an enantioselective diborylation of 1,1-disubstituted alkenes catalyzed by Co(acac) /(R)-DM-segphos. A range of activated and unactivated alkenes underwent this asymmetric diborylation in the presence of cyclooctene as a hydrogen acceptor, affording the corresponding gem-bis(boryl)alkanes with high enantioselectivity. The synthetic utility of these chiral organoboronate compounds was demonstrated through several stereospecific derivatizations and the synthesis of sesquiterpene and sesquiterpenoid natural products.

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