Conformationally locked pentadentate macrocycles containing the 1,10-phenanthroline unit. Synthesis and crystal structure of 5-oxa-2,8-dithia[9](2,9)-1,10-phenanthrolinophane (L) and its coordination properties to NiII, PdII, PtII, RhIII and RuII

Abstract

The complexation of the new mixed thia–aza–oxa macrocycle 5-oxa-2,8-dithia[9](2,9)-1,10-phenanthrolinophane (L) containing the 1,10-phenanthroline unit with Ni^II, Pd^II, Pt^II, Rh^III and Ru^II has been investigated. The results have been compared with those obtained with the structurally related ligand 2,5,8-trithia[9](2,9)-1,10-phenanthrolinophane (L′). The most stable conformations of both ligands have been calculated in order to understand their change upon metal complexation and for L good agreement has been found with the conformations observed in the crystal structure of L·½H₂O. The single-crystal structures of [Ni(L)Cl]BF₄ and [Ru(L)(PPh₃)][PF₆]₂·1//₄MeCN reveal a N₂S₂O coordination sphere about Ni^II and Ru^II, with the macrocyclic ligand in a folded conformation and with the sixth coordination site taken up by Cl⁻ or PPh₃, respectively. For [Pd(L)][BF₄]₂ an [N₂S₂ + O] coordination is observed, with the O-donor interacting weakly with the metal centre at the apical position of a square-based coordination sphere. ¹³C and ¹H NMR spectroscopic studies indicate that the complexes are not fluxional in solution, with the ligand imposing the same coordination sphere as observed in the solid state. ¹³C NMR spectroscopy has also helped in elucidating the stereochemistry of [Rh(L)Cl₂]BF₄ for which no suitable crystals could be grown: the two Cl⁻ ligands are mutually trans with the N₂S₂ donor set of the macrocyclic ligand occupying the equatorial positions of an octahedral coordination sphere and with the O-donor atom left un-coordinated. The redox properties of all the complexes in MeCN have been studied.