Alexander von Zelewsky

Synthesis, structure and chemistry of a twisted olefinic bis-didentate proligand: 5,5 '-bi-5H-cyclopenta[2,1-b : 3,4-b ']dipyridinylidene

The elusive chiral twisted alkene, 5,5-bi-5H-cyclopenta[2.1-b : 3,4-b]dipyridinylidene, known also as 9,9-bi-4,5-diazafluorenylidene (BDAF), has been prepared in racemic form from 9-bromo-4,5-diazafluorene and from 9,9-bi-4,5-diazafluorenyl and fully characterised. X-Ray measurements show that there is a twist of 37.8 degrees about the double bond between the 4,5-diazafluorenylidene units. A 1:1 charge-transfer compound with 7,7,8,8-tetracyanoquinodimethane (TCNQ) contains an unusual packing arrangement which is centred around the formation of spiral stacks. Each BDAF molecule contributes one 4,5-diazofluorenylidene unit to the backbone of the stack, while the second half is involved in hydrogen-bonding interactions and additional stacking with TCNQ. Examples of complexes containing the axially symmetric tetradentate ligand binding to one and to two metal ions. [M(bdaf)Cl-2] and [(MCl2)(2)(bdaf)] (M = Co, Ni, Zn), are reported.

Platinum(II) Compounds with Enantiomerically Pure Bis(pinene)-Fused Bipyridine Ligands − Diimine-Dichloro Complexes and Their Substitution Reactions

The synthesis of chiral square-planar PtII complexes using symmetrical and unsymmetrical bis(pinene)-fused 2,2′-bipyridine is described. The neutral diimine dichloro complexes show a strong deviation of the coordination sphere from planarity if the pinene groups are attached at the 5- and 6-positions of the pyridine rings. However, this distortion does not occur in parallel with the chiral configuration at the diimine ligands. The substitution of the two cis-chloro ligands with diamines to form five-membered chelate rings shows little diastereoselectivity when racemic mixtures of chiral diamines are used. Also, ligands that are prochiral at the ligating centers show little selectivity upon coordination.

Stereoselectivity in the formation of tris-diimine complexes of Fe(II), Ru(II), and Os(II) with a C2-symmetric chiral derivative of 2,2'-bipyridine.

A C2-symmetric enantiopure 4,5-bis(pinene)-2,2-bipyridine ligand (-)-L was used to investigate the diastereoselectivity in the formation of [ML3]2+ coordination species (M = Fe(II), Ru(II), Os(II), Zn(II), Cd(II), Cu(II), Ni(II)), and [ML2Cl2] (M = Ru(II), Os(II)). The X-ray structures of the [ML3]2+ complexes were determined for Delta-[FeL3](PF6)2, Delta-[RuL3](PF6)2, Lambda-[RuL3](PF6)2, Delta-[OsL3](PF6)2, and Lambda-[OsL3](TfO)2. All of these compounds were also characterized by NMR, CD and UV/VIS absorption spectroscopy. The [FeL3]2+ diastereoisomers were studied in equilibrated solutions at various temperatures and in several solvents. The [RuL3]2+ complexes, which are thermally stable up to 200 degrees C, were photochemically equilibrated.

Diastereoselective preparation of Cu(I) and Ag(I) double helices by the use of chiral bis-bipyridine ligands

Chiral bis-5,6-pinene bipyridine type ligands have been used to form, through self-assembly reaction, dinuclear coordination compounds which show a highly diastereoselective formation of double helices with copper(I) and silver(I) as coordination centers.

New Ruthenium(II) Complexes with Enantiomerically Pure Bis- and Tris(pinene)-Fused Tridentate Ligands. Synthesis, Characterization and Stereoisomeric Analysis

A new set of Ru-Cl complexes containing either the pinene[5,6]bpea ligand (L1) or the C3 symmetric pinene[4,5]tpmOMe (L2) tridentate ligand in combination with the bidentate (B) 2,2-bipyridine (bpy) or 1,2-diphenylphosphinoethane (dppe) with general formula [RuCl(L1 or L2)(B)](+) have been prepared and thoroughly characterized. In the solid state, X-ray diffraction analysis techniques have been used. In solution, cyclic voltammetry (CV) and 1D and 2D NMR spectroscopy have been employed. DFT calculations have been also performed on these complexes and their achiral analogues previously reported in our group, to interpret and complement experimental results. Whereas isomerically pure complexes ([Ru(II)Cl(L2)(bpy)](BF4), 5 and [Ru(II)Cl(L2)(dppe)](BF4), 6) are obtained when starting from the highly symmetric [Ru(III)Cl3(L2)], 2, isomeric mixtures of cis, fac-[Ru(II)Cl(L1)(bpy)](BF4) (3b/3b), trans,fac- (3a) and up/down,mer- (3c, 3d) isomers are formed when bpy is added to the less symmetric [Ru(III)Cl3(L1)], 1, in contrast to the case of the bulky dppe ligand that, upon coordination to 1, leads to the trans,fac-[Ru(II)Cl(L1)(dppe)](BF4) (4a) complex as a sole isomer due to steric factors.

Novel HEXOL-type cyclometallated iridium(III) complexes: stereoselective synthesis and structure elucidation.

Two diastereoisomers of tetranuclear cyclometallated iridium complexes, either having an inner core of HEXOL-type [Ir(IrCl2)3]6+ unit and a surface of six chiral, didentate, cyclometallated ligands, are stereoselectively synthesized from an enantiopure pinenopyridine derivative.

New chiral pyrazine-based ligands for self-assembly reactions

The syntheses of two families of ditopic N-heterocyclic ligands are described. All the compounds contain a central pyrazine ring connected to peripheral pyridine or bipyridine moieties, providing bipyridine- and terpyridine-like binding sites, respectively. Annellated terpene fragments render these metal chelators chiral. Thus they face the challenge of introducing stereoselectivity into the formation of chiral, multinuclear co-ordination species.

Synthetic routes for a new family of chiral tetradentate ligands containing pyridine ringsElectronic supplementary information (ESI) available: experimental details. See http://www.rsc.org/suppdata/ob/b2/b210625f/

A series of new tetradentate ligands containing two bipyridine groups or two pyridine moieties carrying amine substituents has been synthesised either from 5- and 6-substituted chiral bipyridines, or from chiral pyridine derivatives. These precursors have been prepared from (-)-alpha-pinene or (-)-myrtenal, respectively. The structures of three tetradentate-, and of five chiral bipyridine ligands have been determined by X-ray diffraction.