Edward W. Abel

Bio: Edward W. Abel is an academic researcher from Queen's University Belfast. The author has contributed to research in topics: Denticity & Crystal structure. The author has an hindex of 19, co-authored 127 publications receiving 1210 citations. Previous affiliations of Edward W. Abel include University College London & University of Leicester.

2,2′:6′,2″-Terpyridine (terpy) acting as a fluxional bidentate ligand. Part 2. Rhenium carbonyl halide complexes, fac-[ReX(CO)3(terpy)](X = Cl, Br or I): NMR studies of their solution dynamics, synthesis of cis-[ReBr(CO)2(terpy)] and the crystal structure of [ReBr(CO)3(terpy)]

Abstract: Under mild conditions pentacarbonylhalogenorhenium(I) complexes react with 2,2′:6′,2″-terpyridine (terpy) to form stable octahedral tricarbonyl complexes fac-[ReX(CO)3(terpy)](X = Cl, Br or I) in which the terpyridine acts as a bidentate chelate ligand. Under more severe reaction conditions fac-[ReBr(CO)3(terpy)] can be converted to cis-[ReBr(CO)2(terpy)]. In solution the tricarbonyl complexes are fluxional with the terpyridine oscillating between equivalent bidentate bonding modes. At low temperatures rotation of the unco-ordinated pyridine ring is restricted and in CD2Cl2 solution two preferred rotamers exist in approximately equal abundances. Rotational energy barriers have been estimated for the X = Cl and I complexes. The X-ray crystal structure of fac-[ReBr(CO)3(terpy)] confirms the bidentate chelate bonding of terpy with a N–Re–N angle of 74.3°. The pendant pyridine ring is inclined at an angle of 52.9° to the adjacent co-ordinated ring and the unco-ordinated nitrogen is directed towards the axial carbonyl and trans to Br.

2,2′:6′,2″-Terpyridine (terpy) acting as a fluxional bidentate ligand. Part 4. cis-[M(C6F5)2(terpy)](M = Pd or Pt): nuclear magnetic resonance studies of their solution dynamics and crystal structure of cis-[Pd(C6F5)2(terpy)]

Abstract: 2,2′:6′,2″-Terpyridine reacted with trans-[M(C6F5)2(diox)2](M = Pd or Pt, diox = 1,4-dioxane) to form the square-planar complexes cis-[M(C6F5)2(terpy)] in which the terpyridine acts as a bidentate chelate ligand. In solution these complexes are fluxional with the terpyridine oscillating between equivalent bidentate modes by a mechanism consisting of a ‘tick-tock’ twist of the metal moiety through an angle equal to the N–M–N angle of the metal centre. Rates of this fluxion were measured by NMR spectroscopy from the exchange effects on the 1H signals of the aromatic hydrogens and in the 19F signals of two C6F5 groups. The ΔG‡ values for the fluxion were ca. 71 and 94 kJ mol–1 for the complexes of PdII and PtII respectively. At below-ambient temperatures further changes in the 19F NMR spectra of both complexes were interpreted in terms of varying rates of rotation of the unco-ordinated pyridine ring, with the rates of rotation of the C6F5 rings being substantially slower at all temperatures and not separately measurable. The lowest-temperature spectra suggested the presence of a pair of degenerate rotamers each having the planes of both C6F5 rings and the unco-ordinated pyridine ring closely parallel and orthogonal to the remainder of the ligand ring system. The crystal structure of [Pd(C6F5)2(terpy)] confirms the bidentate chelate bonding of terpy with a N–Pd–N angle of 77.9°, and the pendant ring oriented at an angle of 46° to the adjacent co-ordinated ring.

2,2′:6′,2″-Terpyridine (terpy) acting as a fluxional bidentate ligand. Part 1. Trimethylplatinum(IV) halide complexes [PtXMe3(terpy)](X = Cl, Br or I): nuclear magnetic resonance studies of their solution dynamics and crystal structure of [PtIMe3(terpy)]

Abstract: 2,2′:6′,2″-Terpyridine (terpy) reacts with trimethylplatinum halides [(PtXMe3)4](X = Cl, Br or I) to form stable octahedral complexes fac-[PtXMe3(terpy)](X = Cl, Br or I) in which the terpy molecule is acting as a bidentate chelate ligand. In solution the complexes are fluxional with the ligand oscillating between equivalent bidentate bonding modes by a mechanism consisting of ‘tick-tock’ twists of the metal moiety through an angle equal to the N–Pt–N angle of the octahedral centre. At below-ambient temperatures rotation of the unco-ordinated pyridine ring is severely restricted with the most favoured rotamers having the plane of the pendant pyridine ring at an angle of ca. 52° with respect to the adjacent co-ordinated pyridine ring plane. The X-ray crystal structure of [PtIMe3(terpy)] depicts the pendant pyridine N atom cis to iodine and this is the predominant species in solution at low temperatures. At above-ambient temperatures the complexes exhibit intramolecular Pt–Me exchange of axial and equatorial environments. Energy data based on accurate dynamic NMR fittings are reported for the three dynamic processes, namely pendant pyridine rotation, 1,4-Pt–N metallotopic shifts and Pt–Me scramblings.

The first examples of 2,2′:6′,2″-terpyridine as a fluxional bidentate ligand

Abstract: 2,2′:6′,2″-Terpyridine (terpy) forms octahedral complexes fac-[ReBr(CO)3(terpy)], cis-[W(CO)4(terpy)] and fac-[PtClMe3(terpy)] in which the ligand oscillates between equivalent bidentate forms by a mechanism involving a ‘tick-tock’ twist of the metal moiety through an angle equal to the N–M–N angle of the octahedral centre and involving a seven-coordinate metal intermediate.

Hemilability of Hybrid Ligands and the Coordination Chemistry of Oxazoline‐Based Systems

Abstract: Ligand design is becoming an increasingly important part of the synthetic activity in chemistry. This is of course because of the subtle control that ligands exert on the metal center to which they are coordinated. Ligands which contain significantly different chemical functionalities, such as hard and soft donors, are often called hybrid ligands and find increasing use in molecular chemistry. Although the interplay between electronic and steric properties has long been recognized as essential in determining the chemical or physical properties of a complex, predictions remain very difficult, not only because of the considerable diversity encountered within the Periodic Table-different metal centers will behave differently towards the same ligand and different ligands can completely modify the chemistry of a given metal-but also because of the small energy differences involved. New systems may-even through serendipity-allow the emergence of useful concepts that can gain general acceptance and help design molecular structures orientated towards a given property. The concept of ligand hemilability, which finds numerous illustrations with hybrid ligands, has gained increased acceptance and been found to be very useful in explaining the properties of metal complexes and in designing new systems for molecular activation, homogeneous catalysis, functional materials, or small-molecule sensing. In the field of homogeneous enantioselective catalysis, in which steric and/or electronic control of a metal-mediated process must occur in such a way that one stereoisomer is preferentially formed, ligands containing one or more chiral oxazoline units have been found to be very valuable for a wide range of metal-catalyzed reactions. The incorporation of oxazoline moieties in multifunctional ligands of increasing complexity makes such ligands good candidates to display hemilabile properties, which until recently, had not been documented in oxazoline chemistry. Herein, we briefly recall the definition and scope of hemilabile ligands, present the main classes of ligands containing one or more oxazoline moieties, with an emphasis on hybrid ligands, and finally explain why the combination of these two facets of ligand design appears particularly promising.

Square-planar Pd(II), Pt(II), and Au(III) terpyridine complexes: their syntheses, physical properties, supramolecular constructs, and biomedical activities.

Abstract: 5.1.2. Viscosity and Thermal Denaturation 1874 5.1.3. Induced Circular Dichroism 1875 5.1.4. Competitive Fluorescence Spectroscopy 1875 5.1.5. Closed Circular DNA 1876 5.1.6. Stereochemical Changes in DNA 1876 5.1.7. Site-Specific Intercalation 1877 5.1.8. Other Mononuclear Intercalators 1877 5.1.9. Multinuclear Intercalators 1878 5.2. Covalent Binding to Biomolecules 1881 5.3. Labeling Biomolecules 1882 5.4. Cytotoxicity 1885 5.4.1. Chemotherapeutic Agents 1886 5.4.2. Radiotherapeutic Agents 1892 6. Conclusion 1892 7. Acknowledgments 1892 8. References 1893