The synthesis of a cobalt dihydrogen Co(I)-(H2) complex prepared from a Co(I)-(N2) precursor supported by a monoanionic pincer bis(carbene) ligand, (Mes)CCC ((Mes)CCC = bis(mesityl-benzimidazol-2-ylidene)phenyl), is described. This species is capable of H2/D2 scrambling and hydrogenating alkenes at room temperature. Stoichiometric addition of HCl to the Co(I)-(N2) cleanly affords the Co(III) hydridochloride complex, which, upon the addition of Cp2ZrHCl, evolves hydrogen gas and regenerates the Co(I)-(N2) complex. Furthermore, the catalytic olefin hydrogenation activity of the Co(I) species was studied by using multinuclear and parahydrogen (p-H2) induced polarization (PHIP) transfer NMR studies to elucidate catalytically relevant intermediates, as well as to establish the role of the Co(I)-(H2) in the Co(I)/Co(III) redox cycle.

The reactivity of a Co-H complex was extended toward the semihydrogenation of internal alkynes. Under ambient temperatures and moderate pressures of H, a broad scope of alkynes were semihydrogenated using a Co-N precatalyst, resulting in the formation of trans-alkene products. Furthermore, mechanistic studies using H,H, and para-hydrogen induced polarization (PHIP) transfer NMR spectroscopy revealed cis-hydrogenation of the alkyne occurs first. The Co-mediated alkene isomerization afforded the E-selective products from a broad group of alkynes with good yields and E/Z selectivity.

The selective hydrogenation of nitriles to primary amines using a bench-stable cobalt precatalyst under 4 atm of H is reported herein. The catalyst precursor was reduced in situ using NaHBEt, and the resulting Lewis acid formed, BEt, was found to be integral to the observed catalysis. Mechanistic insights gleaned from para-hydrogen induced polarization (PHIP) transfer NMR studies revealed that the pairwise hydrogenation of nitriles proceeded through a Co(I/III) redox process.

Treatment of 1,3-bis(3'-butylimidazolyl-1'-yl)benzene diiodide with elemental sulfur in the presence of a base produced a bis(N-heterocyclic thione) (NHT) pincer ligand precursor. Its reaction with PdCl2(CH3CN)2 produced chloro[1,3-bis(3'-butylimidazole-2'-thione-κ-S)benzene-κ-C]palladium(ii), a 6,6-fused ring SCS-NHT palladium pincer complex. This air stable compound is, to our knowledge, the first SCS pincer complex that utilizes N-heterocyclic thione (NHT) donor groups. The molecular structures of the ligand precursor and the palladium complex were determined by X-ray crystallography and computational studies provided insight into the interconversion between its rac and meso conformations. The photophysical properties of the complex were established, and its catalytic activity in Suzuki, Heck, and Sonogashira cross-coupling reactions was evaluated.