The use of macrocyclic and polydentate ligands in ruthenium organometallic chemistry

This report deals with two stereochemically different tridentate N3-ligands suitable as ancillary ligands in the organometallic chemistry of ruthenium. [{Ru(p-cymene)(Cl)}2(μ-Cl)2] assisted the template synthesis of a tridentate N3-macrocycle derived from 2-aminobenzaldehyde, thus forming [Ru(η3-C21H15N3)Ru(p-cymene)]2+2Cl−, 1. The ligand 2, PyrPic·H, derived from the condensation of pyrrole-2-aldehyde and 2-picolylamine, functions as a monoanionic tridentate ligand in the reaction with [{Ru(COD)(Cl)}2(μ-Cl)2] leading to [Ru(COD)(Cl)(PyrPicH2)], 4, which undergoes the ionization of the RuCl bond both in pyridine or in THF in the presence of AgTf, leading to [Ru(PyrPicH)Py3]+Cl−, 5 and [Ru(COD)(PyrPicH)Tf], 6, respectively. The alkylation of 4 using LiMe led to [(RuMe)(PyrPicH)(COD)], 7, which undergoes a methane elimination to yield [Ru2(μ-PyrPic)2(COD)2], 8. The reaction of potassiumpyren [pyren=N,N′-ethylenebis(2-pyrrolyliminato)dianion], 10, with [{Ru(COD)(Cl)}2(μ-Cl)2] led to the Ru-macrocyclic derivative [Ru(Pyren)(COD)], 11, where COD fills two cis-positions around ruthenium. Extended Hückel calculations have been carried out on the two stereochemically different RuN3 fragments having a facial (see complex 1) and a meridional (4, 5, 6, 7 and 8) arrangements in order to identify the difference in the frontier orbitals for the metal reactivity.