Activation of Molecular Hydrogen and Oxygen by PSiP Complexes of Cobalt

The syntheses of Co II halide complexes supported by κ 3 ‐(2‐Cy 2 PC 6 H 4 ) 2 SiMe (Cy‐PSiP) ligation are detailed. Reduction of (Cy‐PSiP)Co(PMe 3 )I could be achieved under mild conditions using magnesium metal to generate the Co I complex (Cy‐PSiP)Co(PMe 3 )N 2 in high yield. When this reaction was carried out under an atmosphere of CO, (Cy‐PSiP)Co(CO) 2 was obtained. Unlike the facile reduction of Co II to Co I , attempts to access Co III species supported by Cy‐PSiP ligation proved challenging. Attempted oxidative addition reactions involving (Cy‐PSiP)Co(PMe 3 )N 2 were generally unsuccessful, with the sole exception of H 2 , which reacted to afford the dihydride complex (Cy‐PSiP)Co(PMe 3 )(H) 2 . The dihydride complex undergoes Co‐H site exchange in solution and readily eliminates H 2 . The Co I precursor (Cy‐PSiP)Co(PMe 3 )N 2 is a competent precatalyst for the hydrogenation of terminal alkenes. Exposure of (Cy‐PSiP)CoI to O 2 gas under anhydrous conditions led to rapid ligand oxidation at Si and P, with no evidence observed at low temperature for a Co III superoxo or peroxo intermediate. Exclusive oxidation at Si to afford a Co II ‐siloxy complex was observed upon treatment of (Cy‐PSiP)CoI with one equiv. Me 3 NO. While this siloxy complex did not react further with O 2 , treatment with a second equiv. of Me 3 NO led to subsequent oxidation involving one phosphino donor. This observation supports the notion that in the ligand oxidation reactivity observed with O 2 , the O atoms incorporated at both Si and P are likely derived from the same O 2 molecule.