Mononuclear CoIIand NiIIcomplexes [L1CoIIH2O2][ClO4]21 and [L1NiIIMeCN2][BPh4]23 L1= 2,2′[propane1,3diylbis1Hpyrazole1,3diyl]dipyridine display a quasireversible MIIMIredox process E12= –0.96 V vs. SCE, ΔEp= 110 mV for 1; E12= –0.71 V vs. SCE, ΔEp= 90 mV for 3. The dinuclear CoIIcomplex [L12CoII2μO2CMe2][BPh4]22 displays a quasireversible reductive response E12= –1.46 V vs. SCE, ΔEp= 120 mV, supposedly due to CoII2CoI2redox process. For these complexes chemical NaBH4 and electrochemical reduction generate CoIand NiIspecies. The existence of dark purple NiIspecies has been authenticated by its UVVis spectral feature crystalfield transition at 901 nm and metaltoligand chargetransfer transition at 537 nm and axial EPR spectrum g= 2.27 and g⊥= 2.08. Dark greenish bluebright green CoIspecies were characterized by absorption spectroscopy. Reaction of chemically generated CoIspecies with CH3I resulted in the formation of dimethylCoIIIcomplexes. Notably, CoIspecies generated from monomeric complex 1led to the formation of two products: a mononuclear complex [L1CoIIICH32][ClO4] 4 minor and a dinuclear complex [L12CoIII2CH34][ClO4]25 major. In contrast, when the dimeric complex 2was reduced with NaBH4and reacted with CH3I the monomeric complex [L1CoIIICH32][BPh4] 6 was isolated in reasonable yield. All three organometallic dialkylCoIIIcomplexes 4–6have been characterized by elemental analysis, 1H NMR spectroscopy, and Xray crystallography.© WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009