Understanding an old dog’s old tricks: The coupling of selective C–H activation with O₂ activation by Co(salen).

Accompanied by a change in color from red to black, the enantiomorphic phases of the cobalt complexes of a chiral salen ligand (L²⁻, Co(L)·CS₂, and Co(L) (L = L^S,S or L^R,R)) chemisorb NO (g) at atmospheric pressure and rt over hours for the CS₂ solvated phase, and within seconds for the desolvated phase. NO is installed as an axial nitrosyl ligand. Aligned but unconnected voids in the CS₂ desorbed Co(L^R,R)·CS₂ structure indicate conduits for the directional desorption of CS₂ and reversible sorption of NO, which occur without loss of crystallinity. Vibrational circular dichroism (VCD) spectra have been recorded for both hands of LH₂, Zn(L), Co(L)·CS₂, Co(L), Co(NO)(L), and Co(NO)(L)·CS₂, revealing significant differences between the solution-state and solid-state spectra. Chiral induction enables the detection of the ν_NO band in both condensed states, and surprisingly also the achiral lattice solvent (CS₂ (ν_CS at 1514 cm⁻¹)) in the solid-state VCD. Solution-state spectra of the paramagnetic Co(II) complex shows a nearly 10-fold enhancement and more extensive inversion of polarity of the vibrations of dominant VCD bands compared to the spectra of the diamagnetic compounds. This enhancement is less pronounced when there are fewer polarity inversions in the solid state VCD spectra.

A bridging nitrite and a nitrate counter anion per Co₂ site are generated in-crystal and an arylamine group on the ligand scaffold is oxidised to a nitro group when nitric oxide (NO) is chemisorbed by molecular crystals of cobalt complexes.

This tutorial review provides a practical guide for solid/gas in crystallo solid-state molecular organometallic chemistry (SMOM).