The treatment of [(IPr)Ni(mu-Cl)](2) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with NaOt -Bu and then pinB-Bpin (bis (pinacolato)diboron) gives rise to a mono-NHC-Ni(0) complex, which dimerizes upon crystallization. The same product is prepared by the treatment of [(IPr)Ni(mu-Cl)](2) with Li(BEt)(3)H, or with NaOt -Bu and then HSi(OEt)(3). The treatment of [(IPr)Ni](2) or its monomer with CO2 reduces CO2 to CO generating [(IPr)Ni](2)(mu-CO)(mu eta(2),eta(2)-CO2). This compound represents an unprecedented symmetric double-bridging mode Of CO2.