The use of macrocyclic and polydentate ligands in ruthenium organometallic chemistry

This report deals with two stereochemically different tridentate N-3-ligands suitable as ancillary ligands in the organometallic chemistry of ruthenium. [{Ru(p-cymene)(Cl)}(2)(mu-Cl)(2)] assisted the template synthesis of a tridentate N-3-macrocycle derived from 2-aminobenzaldehyde, thus forming [Ru(eta(3)-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)(mu-Cl)(2)] leading to [Ru(COD)(Cl)(Pyr-Pic-H-2)], 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)Py-3](+) 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 [Ru-2(mu-Pyr-Pic)(2)(COD)(2)], 8. The reaction of potassium-pyren [pyren = N,N'-ethylenebis(2-pyrrolyliminato)dianion], 10, with [{Ru(COD)(Cl)}(2)(mu-Cl)(2)] led to the Ru-macrocyclic derivative [Ru(Pyren)(COD)], 11, where COD fills two cis-positions around ruthenium. Extended Huckel calculations have been carried out on the two stereochemically different Ru-N-3 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. (C) 2000 Elsevier Science S.A. All rights reserved.