Federico Franceschi

Molecular Batteries Based on Carbon–Carbon Bond Formation and Cleavage in Titanium and Vanadium Schiff Base Complexes

A novel mode of storing and releasing electrons, based on the reversible formation and cleavage of C−C bonds, has been created. The C−C bonds formed by the reductive coupling of imino groups across two [M(salophen)] complexes (see structure) function as shuttle for two electrons, permitting long-range electron transfer to a variety of substrates (e.g. quinone, dioxygen, and azides). This electron transfer is mediated by the metal, which becomes the reactive site, while the C–C functionality is never directly involved.

The use of macrocyclic and polydentate ligands in ruthenium organometallic chemistry

Abstract 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 (μ-Cl) 2 ] assisted the template synthesis of a tridentate N 3 -macrocycle derived from 2-aminobenzaldehyde, thus forming [Ru(η 3 -C 21 H 15 N 3 )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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 (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 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.

GEOMETRICAL ISOMERISM AND REDOX BEHAVIOUR IN ZIRCONIUM-SCHIFF BASE COMPLEXES : THE FORMATION OF C-C BONDS FUNCTIONING AS TWO-ELECTRON RESERVOIRS

Two model compounds have been used for exploring the ligand-based redox chemistry of zirconium–Schiff base complexes, namely [Zr(salophen)Cl 2 (thf)] 1 and [Zr(salophen) 2 ] 2 [salophen = N,N′-bis (salicylidene)-o-phenylenediamine dianion, thf = tetrahydrofuran]. The latter occurs in two thermally non-interconvertible isomeric forms, 2A and 2B. Both contain eight-co-ordinate zirconium in a dodecahedral, 2A, and in a square-antiprismatic environment, 2B. The reduction of 1 with either Na or Mg led to the isolation of [Zr 2 LL′ 2 ] (L′ = thf 3 or pyridine 4). The centrosymmetric dinucleating octaanionic ligand L, which contains two-fold coupled salophen units joined by two C–C bonds, arises from the intermolecular reductive coupling of four imino groups belonging to two Zr(salophen) units. In an attempt to perform intramolecularly the same transformation, complexes 2A and 2B were reduced with sodium. Both isomers gave complex [ZrL″Na 4 (dme) 4 ] 5 (dme = 1,2-dimethoxyethane) containing a novel form of an hydrogenated coupled salophen ligand, L″, where the two salophen units are joined by a single C–C bond. The C–C bonds in the ligand L have been exploited as two-electron reservoirs in the reaction of 3 with PhICl 2 and 9,10-phenanthrenequinone. In this reaction the original salophen moiety is restored in its original form and the Zr(salophen) moiety present in 3 behaves as a source of masked zirconium(II).