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

Abstract

The reduction of the β‐diketiminato nickel(II) halide complex [LtBuNiIIBr] [LtBu = CH(CtBuNdipp)2–, dipp = 2,6‐diisopropylphenyl] with potassium sources proceeds via the initial formation of [(LtBuNiI)x(μ‐Br)xKx] 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 [LtBu]– influences the formation of the KBr adducts β‐diketiminato ligands with less steric congestion, namely LMe6 and LMe7 [LMe6 = CH(CMeNdmp)2–, LMe7 = CMe(CMeNdmp)2–, dmp = 2,6‐dimethylphenyl] were employed. Through deprotonation of HLMe6 with nBuLi followed by treatment with NiBr2(dme) the nickel(II) precursor compound [LMe6NiII(μ‐Br)2Li(THF)2] was prepared and shown to enter an equilibrium with [(LMe6NiIIBr)2] and LiBr in solution; [(LMe6NiIIBr)2] could be accessed also independently. Syntheses of the complexes [LMe7NiII(μ‐Br)2Li(THF)2] and [(LMe7NiIIBr)2] could be achieved analogously. To test the potential of nickel complexes with the LMe6 and LMe7 ligands for the activation of N2 the thf‐free [(LMe6/7NiIIBr)2] complexes were reduced with potassium in an N2 atmosphere. This led neither to a KBr adduct nor to an N2 complex but to the dimer [(LMe6NiI)2], as the smaller ligands allow an efficient interaction of the central nickel atoms with the aryl rings.