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‐ t Bu‐salicylidene)diimine, ( 1 ‐NN)H 2 , was smoothly deprotonated by reaction with two equivalents of a metal amide M[N(SiMe 3 ) 2 ] 2 (M = Mg, Ca or Zn) to form a bimetallic metal amide complex ( 1 ‐NN)[MN(SiMe 3 ) 2 ] 2 . This heteroleptic complex was only stable in the case of Mg and ( 1‐ NN)[MgN(SiMe 3 ) 2 · thf] 2 was structurally characterized by X‐ray diffraction. For Ca and Zn homoleptic products could be obtained: ( 1 ‐NN)Ca · (thf) 2 and ( 1 ‐NN)Zn. The latter crystallized as a trimer with approximate C 3 ‐symmetry. The diprotic N–N coupled bis(β‐diketimine) ligand [RHN–C(Me)=C–C(Me)=N–N=C(Me)–C=C(Me)–NHR, R = 2,6‐di‐ i Pr‐C 6 H 3 ], which is abbreviated as ( 2 ‐NN)H 2 , can be deprotonated only under much harsher reaction conditions. Attempted synthesis of ( 2 ‐NN)[Mg( n Bu)] 2 gave after ligand exchange the homoleptic species ( 2 ‐NN)Mg and Mg( n Bu) 2 . For Ca, the complexes [( 2 ‐NN)Ca] 2 and ( 2‐ NN)[CaN(SiMe 3 ) 2 · 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(SiMe 3 ) 2 ] 2 · (thf) 2 . Reaction of ( 2 ‐NN)H 2 with excess of Et 2 Zn gave the heteroleptic complex ( 2 ‐NN)[ZnEt] 2 and is stable towards ligand exchange reactions. The complex is not active in CO 2 /cyclohexene oxide copolymerization. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)