Synthesis of pyridazinyl ligands for multimetallic complexes

Abstract

A family of ligands based upon the linking of two or three bis-(2-pyridyl)pyridazine (dppz) moieties via the 4- or 4,5-positions of the pyridazine rings has been synthesised using an inverse electron demand Diels–Alder pathway. Thus, reaction of 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (dptz) with a series of dienes (1,4-divinylbenzene, 1,5-cyclooctadiene, norbornadiene, 1,5-hexadiene or 1,4-cyclohexadiene), diketones (1,4-diacetylbenzene), or trienes (trans,trans,cis-1,5,9-cyclododecatriene or trans,trans,trans-1,5,9-cyclododecatriene) has been studied and seven ligands isolated, namely 4,4′-(1,4-phenylene)bis(3,6-dipyridin-2-ylpyridazine) (L¹), 5,6,11,12-tetrahydro-1,4,7,10-tetrapyridin-2-ylcycloocta[1,2-d:5,6-d′]dipyridazine (L²), 5,10-methano-1,4,6,9-tetrapyridin-2-ylpyridazino[4,5-g]phthalazine (L³), 4,4′-ethane-1,2-diylbis(3,6-dipyridin-2-ylpyridazine) (L⁴), 1,4,6,9-tetrapyridin-2-ylpyridazino[4,5-g]phthalazine (L⁵), cyclododeca[1,2-d:5,6-d′]dipyridazine-(11Z)-5,6,11,12,15,16-hexahydro-1,4,7,10-tetrapyridin-2-yl (L⁶) and 5,6,11,12,17,18-hexahydro-1,4,7,10,13,16-hexapyridin-2-ylcyclododeca[1,2-d:5,6-d′:9,10-d″]tripyridazine (L⁷). Compounds L¹, L² and L⁴ have been characterised by single crystal X-ray diffraction revealing the formation of molecular stacking in the solid-state via π–π interactions between dppz moieties. The potential of these ligands to form multimetallic complexes has been demonstrated by the successful synthesis and structural characterisation of {[Cu₄(L¹)(NO₃)₆(MeO)₂(MeOH)₂]}, {[Cu₄(L¹)(NO₃)₆(MeO)₂(EtOH)₂]}, {[Cd(NO₃)(EtOH)₃][Cd(NO₃)₃(L²)]} and {[Cd(NO₃)₂]₂(L⁵)₃}.