Three-Coordinate Nickel Carbene Complexes and Their One-Electron Oxidation Products

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{η2-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°
and 180° (155.7(3)° and 152.3(3)°, 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(I) alkyl [{κ2-P,C-di-tert-butylphosphino-di-tert-butyl-PCH­(dmp)­ethane}­Ni]­[BArF4] (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)]­[BArF4] (6). Both oxidations are chemically
reversible and the respective reductions lead to the neutral carbene
complexes, 1 and 2.