A chemoselective hydroboration protocol with terminal alkene substrates is reported using an electron-rich, low-valent cobalt pincer compound. The process is catalytic and leads to exclusive formation of anti-Markovnikov products, tolerating amino groups, esters, epoxides, ketones, and other functionalities. The protocol was successfully extended toward the hydroboration of nitriles, generating the corresponding amines in moderate to good yields. Labeling studies with deuterated pinacolborane gave insights into the mechanism, establishing the intermediacy of a cobalt hydride, as well as an insertion, β-hydride elimination, and alkene isomerization pathway. These insights provide a rationale for the observed regioselectivity and allow us to propose a catalytic mechanism.

The hydrosilylation of alkene substrates bearing additional functionalities is difficult to achieve using earthabundant catalysts and has not been extensively realized with both earth-abundant transition metals and tertiary silanes or hydrosiloxanes. Reported herein is a well-defined bis(carbene) cobalt(I)-dinitrogen complex for the efficient, catalytic anti-Markovnikov hydrosilylation of terminal alkenes, featuring a broad substrate scope. Alkenes containing hydroxyl, amino, ester, epoxide, ketone, formyl, and nitrile groups are selectively hydrosilylated in this reaction sequence. Multinuclear NMR studies of reactive intermediates gave insights into the mechanism.

The synthesis and characterization of a series of nickel(II) pincer complexes of the meta-phenylene-bridged bis-N-heterocyclic DIPPCCC ligand framework are reported. Characterization of the Ni(II)Cl complex revealed a square planar species with Cl– and the anionic carbon trans to one another. Formation of Ni(II) alkyl complexes derived from complex 1 was accomplished by addition of LiR [R = CH3 (2); CH2SiMe3 (3)]. Furthermore, we report a synthetic pathway to access the catalytically relevant Ni(II)H species (DIPPCCC)NiH (4), by direct oxidative addition of an aryl C–H bond across a Ni(0) center. Complexes 1–4 have been characterized by 1H and 13C NMR and electronic absorption spectroscopies as well as X-ray crystallography.

The synthesis and characterization of a series of cobalt complexes featuring a pincer bis(carbene) ligand of the meta-phenylene-bridged bis-N-heterocyclic carbene ((Ar)CCC, Ar = 2,6-diispropylphenyl or mesityl) are reported. Cleavage of the aryl C-H bond of the ligand was achieved in a one-pot metalation procedure using Co(N(SiMe3)2)2(py)2, an equivalent of exogenous base, and trityl chloride to form the ((DIPP)CCC)CoCl2py complex. This species could be reduced to the Co(ii) and Co(i)-N2 molecules with the appropriate equivalents of reductant. Subsequent generation of ((Mes)CCC)Co(I-III) derivatives with the mesityl ligand proceeded in good yields. A suite of characterization techniques and the interconversion between all three oxidation states of the cobalt complexes is described.