Selective metalation of phenol-type proligands for preparative organometallic chemistry

The selective C-metalation of phenol ester derived proligands is a readily applicable addition to state-of-the-art protocols toward cyclometalated structures, in particular of the base metals.

Stabilization of different redox levels of a tridentate benzoxazole amidophenoxide ligand when bound to Co(iii) or V(v)

The electronic structure of Co and V complexes of a tridentate benzoxazole-containing aminophenol ligand NNOH2 were characterized by both experimental and theoretical methods.

Bio-inspired approaches to accelerating metal ion-promoted reactions: enzyme-like rates for metal ion mediated phosphoryl and acyl transfer processes

Intense efforts by many research groups for more than 50 years have been directed at biomimetic approaches to understand how enzymes achieve their remarkable rate accelerations. Nevertheless, it was noted in 2003 that, despite numerous efforts to design models for catalyzing the cleavage of such species as phosphate diesters, “none of the several models so far described approaches the enormous catalytic efficiency of natural enzymes”. The same could be said for biomimetics of other enzymes promoting acyl or phosphoryl transfer reactions, particularly those mediated by metal ions such as Zn(II). Clearly other important factors were being overlooked or awaiting discovery. In this manuscript we describe two important effects that we have implemented to accelerate metal ion catayzed phosphoryl and acyl transfer reactions. The first of these relates to a medium effect where the polarity of the solution, as measured by dielectric constant, is reduced from that of water (ε = 78) to values of 31.5 and 24.3 when the solvent is changed to methanol or ethanol. Among organic solvents these light alcohols are closest to water in terms of structure and properties as well as retaining important H-bonding properties. The second important effect involves a known but difficult to demonstrate mode of catalysis where the leaving group (LG) in a solvolysis reaction is accelerated as it becomes progressively poorer. In the cases described herein, the LG’s propensity to depart from a substrate during the course of reaction is accelerated by coordination to a metal ion in a process known as leaving group assistance, or LGA. These two effects can each impart accelerations of 109–1017 for certain metal ion catalyzed reactions relative to the corresponding solvent, or base induced reactions.

A modular approach for molecular recognition by zinc dipicolinate complexes

Recognition of 4-nitrophenol guest molecules by stacking and H-bonding interactions with a 4,4′-bipyridinium zinc dipicolinate host was found and investigated in detail.

Synthesis, Characterization and Copper Chemistry of a Non-symmetric Ligand: 2-Methyl-9-(3,5-dimethyl-N-pyrazolylmethyl)-1,10-phenanthroline

The synthesis of an unsymmetrical phenanthroline based ligand, 2-methyl-9-(3,5-dimethylpyrazolylmethyl)-1,10-phenanthroline (L), and its cupric [Cu(II)] (1) and cuprous [Cu(I)] (2) complexes, are reported. The X-ray structures of each of these Cu complexes show distinct changes in coordination environments consistent with the geometrical preferences of the two oxidation states. In the solid state the Cu(II) complex (1) adopts a geometry best described as trigonal bipyramidal, while the Cu(I) complex (2) consists of a single dicationic dimer in which the ligand bridges between two copper ions, separated by 4.26 Å. The two Cu(I) coordination sites differ in 2 with one copper center complexed in a trigonal planar geometry and the other copper in a distorted tetrahedral environment; the latter coordination results from an additional CH(3)CN ligand. Complex 1 exhibits a reversible redox process at -0.34 V vs. Fc/Fc(+) in CH(3)CN, attributable to the Cu(2+)/Cu(+) couple, while the dimeric Cu(I) complex (2) is resistant to oxidation on the CV timescale. Over minutes however, complex 1 does oxidize in the presence of dioxygen to 2 in CH(3)CN.

The synthesis and structure of terpyridine-N-oxide complexes of copper(II) perchlorate

The co-ordination of a series of terpyridine-N-oxide ligands to the Cu(ii) ion is reported. Addition of two equivalents of ligand results in the formation of the expected 2 : 1 six co-ordinate product, while the addition of one equivalent of ligand allows the isolation of 1 : 1 species if the ligand has a meridonal binding mode. The five complexes isolated were characterised in the solid state by X-ray crystallography while they are studied in solution using EPR, UV-vis spectroscopy and IR spectroscopy.

On the Tacticity of Polynorbornenes with 5,6-endo Pendant Groups That Contain Substituted Aryl Chromophores

Two dimers and a series of polymers with 5,6-endo pendant aryl groups that contain different substituents at the para positions were synthesized. The conformation and stereochemistry of the dimers and polymers were determined by nonlinear optical analysis (EFISH) as well as UV/Vis and 13C NMR spectroscopy. The chemical shifts of C7 for the polymers appeared as two peaks in the 13C NMR spectra when the substituents are electron-withdrawing groups. The percentage decrease in the relative extinction coefficient of the polymers, epsilon(d), was linearly related to the Hammett constant sigma. Polynorbornenes with electron-withdrawing substituents may adopt isotactic stereochemistry with all pendant groups aligned in one direction. The nature of the interactions between neighboring chromophores may be one of the most important factors in directing the stereoregularity and conformation of these polymers. The corresponding polymers derived from the exo isomers appeared to be less stereoregular.