Stabilization of β‐Diketiminato Nickel(I) with Alkaline Metal Halide Entities for Small Molecule Activation

The reduction of the β‐diketiminato nickel(II) halide complex [L t Bu Ni II Br] [L t Bu = CH(C t BuNdipp) 2 – , dipp = 2,6‐diisopropylphenyl] with potassium sources proceeds via the initial formation of [(L t Bu Ni I ) x (μ‐Br) x K x ] aggregates, which could be isolated and characterized for x = ∞ and 6. The KBr equivalents readily give way to external donors or substrates to be activated at the central nickel(I) atoms. To test, in how far the steric bulk induced by the residues at [L t Bu ] – influences the formation of the KBr adducts β‐diketiminato ligands with less steric congestion, namely L Me6 and L Me7 [L Me6 = CH(CMeNdmp) 2 – , L Me7 = CMe(CMeNdmp) 2 – , dmp = 2,6‐dimethylphenyl] were employed. Through deprotonation of HL Me6 with n BuLi followed by treatment with NiBr 2 (dme) the nickel(II) precursor compound [L Me6 Ni II (μ‐Br) 2 Li(THF) 2 ] was prepared and shown to enter an equilibrium with [(L Me6 Ni II Br) 2 ] and LiBr in solution; [(L Me6 Ni II Br) 2 ] could be accessed also independently. Syntheses of the complexes [L Me7 Ni II (μ‐Br) 2 Li(THF) 2 ] and [(L Me7 Ni II Br) 2 ] could be achieved analogously. To test the potential of nickel complexes with the L Me6 and L Me7 ligands for the activation of N 2 the thf‐free [(L Me6/7 Ni II Br) 2 ] complexes were reduced with potassium in an N 2 atmosphere. This led neither to a KBr adduct nor to an N 2 complex but to the dimer [(L Me6 Ni I ) 2 ], as the smaller ligands allow an efficient interaction of the central nickel atoms with the aryl rings.