The synthesis and characterization of two new carbene complexes, (dtbpe)Ni=CH(dmp) (1; dtbpe = 1,2-bis(di-tert-butylphosphino)ethane; dmp = 2,6-dimesitylphenyl) and (dippn)Ni=CH(dmp) (2; dippn = 1,8-bis(di-iso-propylphosphino)naphthalene), are described. Complexes 1 and 2 were isolated by photolysis of the corresponding side-bound diazoalkane complexes, exemplified by (dtbpe)Ni{eta(2)-N2CH(dmp)} (3). The carbene complexes feature Ni-C distances that are short and Ni-C-C angles at the carbene carbon that are intermediate between 120 degrees and 180 degrees (155.7(3)degrees and 152.3(3)degrees, respectively). The difference between the two carbenes became obvious when their reactivity toward 1-electron oxidizing agents was studied: the oxidation of 1 led to an internal rearrangement and the formation of a nickel(1) alkyl [{kappa(2)-P,C-di-tert-butylphosphino-di-tert-butyl-PCH(dmp)ethane}Ni][BAr4F](4), while the oxidation of 2 allowed the isolation of an unrearranged product, formulated as the cationic nickel(III) carbene complex[(dippn)Ni=CH(dmp)][BAr4F] (6). Both oxidations are chemically reversible and the respective reductions lead to the neutral carbene complexes, 1 and 2.