Preparation and reactivity of a square-planar PNP cobalt(ii)-hydrido complex: isolation of the first {Co-NO}8-hydride.

The synthesis of a square-planar cobalt(ii) hydrido complex supported by a pyrrole-based PNP ligand has been reinvestigated and its reactivity with various small molecules examined. Preparation of the complex was accomplished by treatment of the corresponding chloride complex, [CoCl(tBuPNP)] (tBuPNP = anion of 2,5-bis((di-tert-butylphosphino)methyl)pyrrole), with di-iso-butylaluminum hydride (DIBAL). Reaction of [CoCl(tBuPNP)] with other hydride sources such as NaEt3BH and LiAlH4 resulted in mixtures of the desired Co(ii) hydride along with the reduced Co(i) species, [Co(N2)(tBuPNP)], as the primary product. The hydride complex exhibits facile migratory insertion chemistry with CO2 producing the corresponding Co(ii) formate complex. When the Co-H complex is reacted with nitric oxide, the first example of a cobalt nitrosyl hydride complex is produced.