The $C_{60}$-triosmium complexes, $Os_3(CO)_{11}(\eta^2-C_{60})$ (1) and $Os_3(CO)_{10}(PPh_3)(\eta^2-C_{60})$ (2), have been chemically reduced and the reduced species were characterized by various spectroscopic (MS, $^1H$ NMR, IR, vis-NIR and EPR) methods. Reduction of 1 with $NiCp^*_2(Cp^*$=$\eta^5-C_5Me_5)$ gives a dark green salt, $NiCp^*_2^+[Os_3(CO)_{11}(\eta^2-C_{60})]^-$ (3). Metathesis of (3) with PPNCl affords $PPN^+[Os_3(CO)_{11}(\eta^2-C_{60})]^-$ (4) which has better solubility in THF than 3. $CoCp_2^+[Os_3(CO)_{10}(PPh_3) (\eta^2-C_{60})]^-$ (5) has been prepared from the reaction of 2 and $CoCp_2(Cp=\eta^5-C_5H_5)$.
The red-shift of IR carbonyl bands (νco) of 3, 4 $(ca. 40 \sim 50 cm^{-1}$ and 5 $(ca. 60 \sim 70 cm^{-1})$ compared to the corresponding neutral complexes indicates that the electron in the anionic species may be localized in the triosmium center. The vis-NIR spectra of 3 and 5 show no absorption in the NIR region, which also suggests the electron localization in the metal center. The X-band EPR spectra of the frozen solution of 4 and 5 at 77K reveal a sharp signal (ΔH = 2.0 G with g = 2.0018 and 2.0015, respectively. This is believed to originate from the unpaired electron in the triosmium center.
