An expanded series of pi-bound molybdenum-quinonoid complexes supported by pendant phosphines has been synthesized. These compounds formally span three protonation-oxidation states of the quinonoid fragment (catechol, semiquinone, quinone) and two different oxidation states of the metal (Mo-0, Mo-II), notably demonstrating a total of two protons and four electrons accessible in the system. Previously, the reduced Mo-0-catechol complex 1 and its reaction with dioxygen to yield the two-proton/two-electron oxidized Mo-0-quinone compound 4 was explored, while, herein, the expansion of the series to include the two-electron oxidized Mo-II-catechol complex 2, the one-proton/two-electron oxidized Mo-semiquinone complex 3, and the two-proton/four-electron oxidized Mo-II-quinone complexes 5 and 6 is reported. Transfer of multiple equivalents of protons and electrons from the Mo-0 and Mo-II catechol complexes, 1 and 2, to H atom acceptor TEMPO suggests the presence of weak O-H bonds. Although thermochemical analyses are hindered by the irreversibility of the electrochemistry of the present compounds, the reactivity observed suggests weaker O-H bonds compared to the free catechol, indicating that proton-coupled electron transfer can be facilitated significantly by the pi-bound metal center.