Complexes of new chiral terpyridyl ligands. Synthesis and characterization of their ruthenium(II) and rhodium(III) complexes

Abstract

Enantiomerically pure, chiral terpyridyl-type ligands L¹ (‘dipineno’-[5,6∶5″,6″]-fused 2,2′∶6′,2″-terpyridine) and L² (‘dipineno’-[4,5∶4″,5″]-fused 2,2′∶6′,2″-terpyridine) have been synthesized in high yields starting from 2,6-diacetylpyridine and enantiopure α-pinene. Complexes of L¹ and L² with Rh^III and Ru^II have been prepared and studied spectroscopically. The complexes [Ru(L)₂][PF₆]₂ (L = L¹ or L²) were obtained in high yields using microwave heating in ethylene glycol as solvent. The rhodium(III) and ruthenium(II) complexes of L¹ and L² have a helically distorted terpyridyl moiety, as shown by the considerable optical activity in the ligand centered and metal to ligand charge transfer transitions. Crystal structures of [Rh(L¹)Cl₃] and [Ru(L¹)Cl₃] show a considerable out of plane distortion of the terpyridyl moiety, whereas free L² and [Ru(trpy)(L²)][PF₆]₂ have a more planar arrangement of the pyridyl units.

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