Catalytic oxidations using cobalt(II) complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 304

Kinetic studies reveal first order dependence on both the catalyst
concentration and dioxygen pressure. The dependence of the initial rate on
the substrate concentration shows a saturation type behavior, indicating
reversible initial coordination of the substrate to (A), with
subsequent coordination of to the catalyst, producing intermediate X ,
which is oxidized in the subsequent rate-determining step (Figure 48).
The proposed structure of intermediate X is shown in Figure 49.