Synthesis, Characterization, and Catalytic Reactivity of {CoNO}8 PCP Pincer Complexes

The reaction of coordinatively unsaturated Co­(II) PCP pincer complexes with nitric oxide leads to the formation of new, air-stable, diamagnetic mono nitrosyl compounds. The synthesis and characterization of five- and four-coordinate Co­(III) and Co­(I) nitrosyl pincer complexes based on three different ligand scaffolds is described. Passing NO through a solution of [Co­(PCPNMe-iPr)­Cl], [Co­(PCPO-iPr)­Cl] or [Co­(PCPCH2-iPr)­Br] led to the formation of the low-spin complex [Co­(PCP-iPr)­(NO)­X] with a strongly bent NO ligand. Treatment of the latter species with (X = Cl, Br) AgBF4 led to chloride abstraction and formation of cationic square-planar Co­(I) complexes of the type [Co­(PCP-iPr)­(NO)]+ featuring a linear NO group. This reaction could be viewed as a formal two electron reduction of the metal center by the NO radical from Co­(III) to Co­(I), if NO is counted as NO+. Hence, these systems can be described as {CoNO}8 according to the Enemark–Feltham convention. X-ray structures, spectroscopic and electrochemical data of all nitrosyl complexes are presented. Preliminary studies show that [Co­(PCPNMe-iPr)­(NO)]+ catalyzes efficiently the reductive hydroboration of nitriles with pinacolborane (HBpin) forming an intermediate {CoNO}8 hydride species.