Template-Free Synthesis of a Macrocyclic Bis(pyridine-dienamine) Proligand and Metal Complexes of Its Bis(pyridine-diimine) and Bis(pyridine-dienamido) Forms.

We describe the template-free synthesis of the bis(pyridine-dienamine) proligand [4,5-(m-xylylenediamine)NH-C═(CH)(9-butyl-octahydroacridine)]2 (2'), a variant of Burrows's macrocyclic bis(pyridine-diimine) (bis-PDI) ligand [2,6-(m-xylylenediamine)N═C(py)]2 (A), using octahydroacridine as the ligand backbone. The octahydroacridine backbone favors macrocyclization by constraining the PDI units in the (s-cis)2 conformation. The template-free synthesis of 2' enables facile access to a wide array of bis-PDI and bis(pyridine-dienamido) (bis-PDE) metal complexes. Five-coordinate binuclear bis-PDI (2)M2Cl4 complexes {2 = [4,5-(m-xylylenediamine)N═C(9-butyl-octahydroacridine)]2; M = Zn, Co, or Fe} and a four-coordinate bis-PDI [(2)Pd2Br2][B(3,5-(CF3)2-Ph)4]2 complex were synthesized and characterized. (2)Zn2Cl4 undergoes macrocyclic ring inversion on the nuclear magnetic resonance (NMR) time scale with a free energy barrier ΔG⧧ of 15.5(3) kcal/mol at 295 K. In contrast, (2)Fe2Cl4 and (2)Co2Cl4 undergo slow ring inversion on the NMR chemical shift time scale at 295 K. The amine elimination reaction of 2' with Zr(NMe2)4 yields the bis-PDE complex (2'-4H)Zr2(NMe2)4, which was alkylated with AlMe3 and Al(CH2SiMe3)3 to generate (2'-4H)Zr2Me4 and (2'-4H)Zr2(CH2SiMe3)2(NMe2)2, respectively.