Binuclear Magnesium, Calcium, and Zinc Complexes Based on Nitrogen-Nitrogen-Coupled Salicylaldiminate and β-Diketiminate Ligands

The diprotic bis(salicylaldimine) ligand N,N'-bis(3,5-di-tBu-salicylidene)diimine, (1-NN)H-2, was smoothly deprotonated by reaction with two equivalents of a metal amide M[N(SiMe3)(2)](2) (M = Mg, Ca or Zn) to form a bimetallic metal amide complex (1-NN)[MN(SiMe3)(2)](2). This heteroleptic complex was only stable in the case of Mg and (1-NN)[MgN(SiMe3)(2)center dot thf](2) was structurally characterized by Xray diffraction. For Ca and Zn homoleptic products could be obtained: (1-NN)Ca center dot(thf)(2) and (1-NN)Zn. The latter crystallized as a trimer with approximate C-3-symmetry. The diprotic N-N coupled bis(beta-diketimine) ligand [RHN-C(Me)=C-C(Me)=N-N=C(Me)-C=C(Me)-NHR, R = 2,6-di-iPr-C6H3] which is abbreviated as (2-NN)H-2, can be deprotonated only under much harsher reaction conditions. Attempted synthesis of (2-NN)[Mg(nBu)](2) gave after ligand exchange the homoleptic species (2-NN)Mg and Mg(nBU)(2). For Ca, the complexes [(2-NN)Ca](2) and (2-NN)[CaN(SiMe3)(2)center dot thf](2) both have been prepared and structurally characterized by X-ray diffraction. The latter heteroleptic complex is in benzene solution in equilibrium with [(2-NN)Ca](2) and Ca[N(SiMe3)(2)](2)center dot(thf)(2). Reaction of (2-NN)H-2 with excess of Et2Zn gave the heteroleptic complex (2-NN)[ZnEt](2) and is stable towards ligand exchange reactions. The complex is not active in CO2/cyclohexene oxide copolymerization. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)