Co2(CO)8-promoted Dihydrogen Activations under Unusually Mild Conditions by Highly Polarizing Co2+ Cations

The reaction between Co2(CO) 8 and CoX2 (X = C1, I, O2CC2H5) in THF involves in a P(CO)-dependent disproportionation of the neutral carbonyl: 3 2Co2(CO) 8 + CoX2 ⇆ 2[Co(CO) 4]- + 2[CoX]+ + 4CO For X- = I-, a stable CoII, Co-I homonuclear ion-pair (HNIP) is the only product at room temperature, while for X- = C1- and O2CC2H5- is also formed. For X = C1- or O2CC2H5- the solutions obtained activate dihydrogen under unusually mild conditions; highly polarizing Co2+ cations, insufficiently stabilized by [Co(CO)]- and the X ligand, are suggested to be the active species in this activation. This picture would also account for the catalytic effect of small amounts of pyridine on the formation of HCo(CO) 4 from Co2(CO)8 and dihydrogen in toluene.