Irradiation (254, 300, 355 nm) of [CH 3N(PF 2) 2] 3Co 2(CO) 2, 1, [CH 3N(PF 2) 2] 3Co 2(PPh 3) 2, 2, and [CH 3N(PF 2) 2] 2Fe 2(CO) 5, 3, at room temperature in the presence of acetophenone and triethylsilane leads to photoassisted hydrosilation with moderate quantum yields (0.037, 0.004, and 0.07 at 355 nm, respectively). The quantum yields (Φ) vary as a function of the irradiation wavelength (Φ300 > Φ254 > Φ355) and are drastically reduced when the reaction is conducted in the presence of either CO or PPh 3. The wavelength dependence and external ligand quenching is consistent with dissociative CO loss from an upper excited state. UV spectral analyses suggest that the σ → σ ∗ electronic transition is responsible for the observed quantum yield trends. Photocatalyzed 1-pentene isomerization was observed with 1 but not with 2 or 3 at 355 nm. Variable temperature studies of the photocatalyzed 1-pentene isomerization catalyzed by 1 show that a thermally active catalytic species is present. Photocatalyzed hydrogenation of 1-pentene was achieved with 1, but only at high hydrogen pressure (1̃00 psi). Attempted 1-pentene hydrosilation with triethylsilane, catalyzed by 1, led only to olefin isomerization. UV irradiation of 1 in the presence of trichlorosilane led to the oxidative addition of silane to one cobalt atom, to afford [CH 3N(PF 2) 2] 3Co 2(CO)H(SiCl 3). Dimer fragmentation was not observed with [CH 3N(PF 2) 2] 3Co 2(CO) 2 or [CH 3N(PF 2) 2] 3Co 2-(PPh 3) 2 due to the geometrical constraints imposed by the three bridging ligands. Plausible catalytic mechanisms are presented herein, based on experimental data.