Coordination geometry | EPFL Graph Search

The term coordination geometry is used in a number of related fields of chemistry and solid state chemistry/physics. Molecules Molecular geometry The coordination geometry of an atom is the geometrical pattern formed by atoms around the central atom. Inorganic coordination complexes In the field of inorganic coordination complexes it is the geometrical pattern formed by the atoms in the ligands that are bonded to the central atom in a molecule or a coordination complex. The geometrical arrangement will vary according to the number and type of ligands bonded to the metal centre, and to the coordination preference of the central atom, typically a metal in a coordination complex. The number of atoms bonded, (i.e. the number of σ-bonds between central atom and ligands) is termed the coordination number. The geometrical pattern can be described as a polyhedron where the vertices of the polyhedron are the centres of the coordinating atoms in the ligands. The coordinatio

Creating Tertiary and Quaternary Carbon Centers by Nickel and Copper-Catalyzed Cross-Coupling Reactions of Alkyl Electrophiles

Peng Ren

Transition-metal-catalyzed C-C coupling reactions have been extensively studied in the past three decades. These reactions have become invaluable to fundamental research and industrial applications, because they can be used construct complicated molecules from simple precursors. Among them, the coupling systems of aryl, alkenyl, and alkynyl halides have been well-optimized, while the coupling of non-activated alkyl halides, especially secondary alkyl halides, is still difficult. In the first chapter, the development of the transition-metal-catalyzed alkyl-alkyl cross-coupling reactions is introduced and summarized, and the difficulties and potential improvements are discussed. In chapter 2, a structure-activity study is described for Ni-catalyzed alkyl-alkyl Kumada- type cross coupling reactions. A series of new nickel(II) complexes bearing bidentate and tridentate amino-amide ligands were synthesized and structurally characterized. The coordination geometries of these complexes include square planar, tetrahedral, and square pyramidal. The complexes had been examined as pre-catalysts for the cross coupling of non- activated alkyl halides, particularly secondary alkyl iodides, with alkyl Grignard reagents. Comparison was made to the results obtained with the previously reported Ni pincer complex [(MeN2N)NiCl] (1). A transmetalation site in the pre-catalysts is necessary for the catalysis. The coordination geometries and spin-states of the pre-catalysts have little or no influence. The work led to the discovery of several well-defined Ni catalysts that are significantly more active and efficient than the pincer complex (1) for the coupling of secondary alkyl halides. The best catalysts are [(HNN)Ni(PPh3)Cl] (24) and [(HNN)Ni(2,4-lutidine)Cl] (27). The improved activity and efficiency were attributed to the fact that the phosphine and lutidine ligands in these complexes could dissociate from the Ni center during catalysis. The activation of alkyl halides was shown to proceed via a radical mechanism. After investigating how secondary alkyl halides could couple with primary Grignard reagents in high yields using nickel catalysts, the complementary methodology, the coupling of non-activated alkyl electrophiles with secondary and tertiary alkyl nucleophiles, is described in chapter 3. It was found that simple copper(I) chloride could catalyze the cross- coupling of non-activated primary alkyl halides and tosylates with secondary and tertiary alkyl Grignard reagents. The method is highly efficient, practical, and general. A wide range of functional groups can be tolerated, such as ester, ketone, amide, nitrile, and heterocylic groups. In chapter 4, a series of new copper complexes bearing hemilabile ligands were synthesized and structurally characterized. Among them, the copper complex [(MeN2N)Cu(PPh3)] (36) was shown to have the highest catalytic activity towards alkylation of benzoxazoles with secondary alkyl halides. The higher efficiency of 36 relative to other copper catalysts might result from a hemilabile property of the pincer ligand. An important additive, bis[2-(N,N-dimethylamino)ethyl] ether (BDMAEE) is also identified. This is the first time that non-activated secondary alkyl halides have been used as electrophiles in the alkylation of benzoxazoles.

EPFL2012

A Structure-Activity Study of Ni-Catalyzed Alkyl-Alkyl Kumada Coupling. Improved Catalysts for Coupling of Secondary Alkyl Halides

Xile Hu, Peng Ren, Rosario Scopelliti, Oleg Vechorkin, Kim Dimuth Von Allmen

A structure–activity study was carried out for Ni catalyzed alkyl–alkyl Kumada-type cross coupling reactions. A series of new nickel(II) complexes including those with tridentate pincer bis(amino)amide ligands (RN2N) and those with bidentate mixed amino-amide ligands (RNN) were synthesized and structurally characterized. The coordination geometries of these complexes range from square planar, tetrahedral, to square pyramidal. The complexes had been examined as precatalysts for cross coupling of nonactivated alkyl halides, particularly secondary alkyl iodides, with alkyl Grignard reagents. Comparison was made to the results obtained with the previously reported Ni pincer complex [(MeN2N)NiCl]. A transmetalation site in the precatalysts is necessary for the catalysis. The coordination geometries and spin-states of the precatalysts have a small or no influence. The work led to the discovery of several well-defined Ni catalysts that are significantly more active and efficient than the pincer complex [(MeN2N)NiCl] for the coupling of secondary alkyl halides. The best two catalysts are [(HNN)Ni(PPh3)Cl] and [(HNN)Ni(2,4-lutidine)Cl]. The improved activity and efficiency was attributed to the fact that phosphine and lutidine ligands in these complexes can dissociate from the Ni center during catalysis. The activation of alkyl halides was shown to proceed via a radical mechanism.

2011

Syntheses, structures and properties of silver(I) complexes constructed from nitrogenous aromatic heterocyclic carboxylic acids and N-donor ligands

Chi Wai Cheung, Hong-Ling Gao

Four new coordination complexes with silver(I) ions and nitrogenous aromatic heterocyclic carboxylic ligands, namely [AB(4)(Pac)(Phen)(4)]center dot 8H(2)O (1), {[AB(4)(Pztc)(bPe)(3)] center dot 5H(2)O}(n) (2), [Ag-4(Hmptc)(2)(4,4'-bPY)(3)] center dot 4.5H(2)O (3), and [Ag-2(H(2)mPtc)(2)(2,2'-bPY)(2)] (4) (H(4)Pztc = pyrazine-2,3,5,6-tetracarboxylic acid, H(3)mptc = 6-methyl2,3,5-pyridine-tricarboxylic acid, phen = 1,10-phenanthroline, bpe = trans-1,2-bis(4-pyridyl)ethylene, 4,4'bpy = 4,4'-bipyridine, 2,2'-bpy = 2,2'-bipyridine), have been synthesized by the self-assembly reactions and characterized by X-ray diffraction single crystal structure analysis, elemental analysis, IR, PXRD, fluorescence and thermal analysis. In I, four crystallographically independent silver(l) atoms are found to coordinate with only one pztc(4-) ligand. Complex 2 is a 2D grid structure. Complexes 3 and 4 are extended from OD to 2D or 1D by the Ag center dot center dot center dot O interactions. (C) 2014 Elsevier B.V. All rights reserved.

Elsevier2014

Creating Tertiary and Quaternary Carbon Centers by Nickel and Copper-Catalyzed Cross-Coupling Reactions of Alkyl Electrophiles

Peng Ren

EPFL2012