A Back‐to‐Back Ligand with Dipyrazolylpyridine and Dipicolylamine Metal‐Binding Domains

Abstract

Reaction of 4-bromomethyl-2,6-bis(pyrazol-1-yl)pyridine with dipicolylamine yields 4-bis(pyrid-2-ylmethyl)aminomethyl-2,6-bis(pyrazol-1-yl)pyridine (L). Treatment of L with [MCl 2 (NCPh) 2 ] (M = Pd, Pt) in the presence of AgPF 6 affords [MCl(L)]PF 6 , whose palladium or platinum centre is bound exclusively by the dipicolylamino moiety of L, as established by NMR spectroscopy. The pendant dipyrazolylpyridine residue in these compounds is complexed by iron(II) to form [Fe{MCl(μ-L)} 2 ][PF 6 ] 4 (M = Pd, 1; M = Pt, 2·nH 2 O). The nitromethane solvate crystal of 1 contains low-spin iron centres at 150 K. However, dried 1 and 2·nH 2 O are predominantly high-spin at room temperature, undergoing very gradual thermal spin transitions upon cooling to ≤ 50 % completeness. The platinum compound also undergoes a thermal spin transition in CD 3 NO 2 solution, with T 1/2 = 253 K.