Helicates as Versatile Supramolecular Complexes.

Synthetic organic chemists enjoy the luxury of having a large collection of reliable reactions at their disposal for preparing small molecules, mesoscopic structures, and polymers. Coordination chemists, on the other hand, are faced with the fact that transition metal chemistry, when normalized for the number of transition metals, has relatively few high-yielding reactions, when compared to the chemistry of carbon, for preparing even small molecule structures. This lack of control is manifested, in large part, in the weak metal-ligand interactions found in coordination complexes as compared with the strong covalent bonds in organic compounds. Weak bonding often translates into many reaction pathways that are not substantially different from an energetic point of view, and therefore, results in poor selectivity. As a result, many coordination chemists in recent years have come to the realization that it may be easier and more productive to develop straightforward and reliable routes to mesoscopic supramolecular structures by capitalizing on the modest collection of high-yielding reactions in coordination chemistry, the directional bonding afforded by metal centers, and strategies aimed at taking advantage of the weak metal bonds found in coordination complexes. Three emerging synthetic strategies, the symmetry-interaction, directional-bonding, and weak-link synthetic approaches, all use metal centers as structural building blocks to rationally assemble molecular components into supramolecular metallocyclophanes. These three approaches are discussed herein, and the fundamental principles underlying each as well as their capabilities are compared and contrasted.

Strategies for the Construction of Supramolecular Compounds through Coordination Chemistry

Living polymerization of alpha -olefins by chelating diamide complexes of titanium

Converting carbon dioxide into carbamato derivatives.

This Dalton Perspective deals with solvent-free reactions taking place within solids or between solids or involving a solid and a vapour. The focus is on reactions involving organometallic and coordination compounds and occurring via reassembling of non-covalent bonding, e.g. hydrogen bonds, and/or formation of ligand-metal coordination bonds. It is argued that reactions activated by mechanical mixing of solid reactants as well as those obtained by exposing a crystalline solid to a vapour can be exploited to "make crystals", which is the quintessence of crystal engineering. It is demonstrated through a number of examples that solvent-free methods, such as co-grinding, kneading, milling of molecular solids, or reactions of solid with vapours represent viable alternative, when not unique, routes for the preparation of novel molecular and supramolecular solids as well as for the preparation of polymorphic or solvate modifications of a same species. The structural characterization of the products requires the preparation of single crystals suitable for X-ray diffraction, a goal often achieved by seeding.

Mechanochemical preparation of molecular and supramolecular organometallic materials and coordination networks.

The new ligand 4′-ferrocenyl-2,2′:6′,2″-terpyridine L has been prepared in good yield from ferrocenecarbaldehyde by two different routes. The crystal and molecular structure of L has been determined [monoclinic, space group P21/c, a= 7.905(2), b= 22.045(4), c= 11.394(2)A, β= 107.10(3)°, Z= 4, R= 0.034 for 2486 independent reflections]. The co-ordination behaviour of L has been studied and the homoleptic complexes [ML2][PF6]2(M = Co, Fe or Ru) prepared and characterised. In addition, the heteroleptic complex [RuL(terpy)][PF6]2(terpy = 2,2′:6′,2″-terpyridine) has been prepared. All of these complexes are redox active.

Complexes containing ferrocenyl groups as redox spectators; synthesis, molecular structure and co-ordination behaviour of 4′-ferrocenyl-2,2′:6′,2″-terpyridine

A New Method for the Synthesis of Heterometallic Complexes: Syntheses and Structures of [(PhCH2CH2NLi)3Sb(thf)]2 and [Sb3(cyN)4(NMe2)2]Li

Neue Methode zur Synthese von Heterometallkomplexen – Synthesen und Strukturen von [(PhCH2CH2NLi)3Sb(thf)]2 und [Sb3(cyN)4(NMe2)2]Li

Preparation of copper organometallics via nucleophilic substitution of CpCuPPh3: syntheses and x-ray structure determinations of [Li(THF)4]+[(fluorenyl)2CuPPh3]- and [Cy3PCu(.mu.-C.tplbond.CtBu)2Cu(PPh3)2] (THF = tetrahydrofuran, fluorenyl = C13H9)

Andrew J. Edwards

Papers

Complexes containing ferrocenyl groups as redox spectators; synthesis, molecular structure and co-ordination behaviour of 4′-ferrocenyl-2,2′:6′,2″-terpyridine

A New Method for the Synthesis of Heterometallic Complexes: Syntheses and Structures of [(PhCH2CH2NLi)3Sb(thf)]2 and [Sb3(cyN)4(NMe2)2]Li

Neue Methode zur Synthese von Heterometallkomplexen – Synthesen und Strukturen von [(PhCH2CH2NLi)3Sb(thf)]2 und [Sb3(cyN)4(NMe2)2]Li

Preparation of copper organometallics via nucleophilic substitution of CpCuPPh3: syntheses and x-ray structure determinations of [Li(THF)4]+[(fluorenyl)2CuPPh3]- and [Cy3PCu(.mu.-C.tplbond.CtBu)2Cu(PPh3)2] (THF = tetrahydrofuran, fluorenyl = C13H9)

Lithium Intermediates during the α-Lithiation and Subsequent α-Substitution of Heterocyclic Amines in the Presence of CO2†