NNN-Cobalt(II) Pincer Complexes: Paramagnetic NMR Spectroscopy in Solution and Application as Hydrosilylation Catalysts

The tridentate, monoanionic bis(oxazolinylmethylidene)-isoindolate pincer ligand was utilized for the synthesis of various cobalt(II)high-spincomplexes. Employing standard complexation procedures, the corresponding acetato and chlorido complexes were isolated in good yields and thoroughly characterized in the solid-state and in solution. In particular, a density functional theory (DFT) supported paramagnetic NMR analysis revealed a strong correlation between observed(13)C NMR shifts and calculated spin-density distributions, allowing for an unambiguous signal assignment in all(1)H and(13)C NMR spectra. An acetato-bridged trinuclear cobalt species as well as the hexacoordinate "homoleptic" complex [((R)boxmi)(2)Co] were further identified as side products generated in the complex synthesis. The chlorido complexes were applied as catalysts for the cobalt-catalyzed hydrosilylation of acetophenone, producing the chiral secondary alcohol with moderate enantioselectivities.