ABSTRACT
In this study, the importance of anion-pi interactions in four-membered rings has been evidenced. Two kinds of rings have been found to be suitable for participation in anion-pi interactions: first, in different salts of cyclobuten-1,2-dione derivatives and, second, in eta(4)-cyclobutadiene complexes with transition metals.
Subject(s)
Cyclobutanes/chemistry , Models, Molecular , Anions , Crystallography, X-Ray , Cyclobutanes/chemical synthesis , Molecular Conformation , Molecular StructureABSTRACT
The combination of the square-planar cis-protected [Pt(dppp)(O 3SCF 3) 2] (M) with the ditopic N, N'-bis(3,5-dimethyl-4-pyridinyl)-4-ethoxy-2,6-pyridinedicarboxamide ligand (L) leads both in solution and in the solid state to the quantitative self-assembly of a M 2L 2 metallocycle. We also report crystallographic evidence derived from the solid-state structure of the dinuclear metallocycle in support of the existence of anion-pi-pi interactions.
ABSTRACT
A detailed DFT (B3LYP/6-31+G*) study upon alpha-oxybenzylorganolithium compounds such as alpha-carbamoyloxybenzyllithium 1 has revealed two relevant issues concerning the outcome of electrophilic substitutions (1) lithium salts catalyze these reactions, and (2) some pi lithium complexes can provide an extra position to which electrophiles can anchor and thus drive invertive (at the carbanionic carbon) processes. Calculations have shown that carboxylation, alkylation, and acylation should take place with inversion at the original C-Li bond.
ABSTRACT
A dinuclear self-assembled cationic macrocycle based on Pt(II)-N(pyridine) coordinative bonds and having competitive triflate anions, as metal counterions, is used in the construction of [2]rotaxane and [2]pseudorotaxane architectures assisted by hydrogen bonding. The kinetic lability of the Pt(II)-N(pyridine) coordinative bond controls the dynamics of the [2]rotaxane.
Subject(s)
Organoplatinum Compounds/chemistry , Pyridines/chemistry , Rotaxanes/chemistry , Hydrogen Bonding , Kinetics , Magnetic Resonance Spectroscopy , Models, Chemical , Molecular StructureABSTRACT
A series of tripodal amidopyridine receptors capable of selective recognition of methylmethanetriacetic acid (MMTA) in organic solvents is described. Intramolecular hydrogen-bonding groups, built into some of the receptors, were designed as preorganization devices. Binding was studied by NMR titration, variable temperature NMR experiments, 2D-NMR, isothermal titration calorimetry, and single-crystal X-ray crystallography. The results reveal that a balancing act between inter- and intramolecular hydrogen-bonding interactions in the complexes governs both the dynamics and the geometry of binding. Receptor 1b (without intramolecular hydrogen-bonding groups) features a simple symmetric MMTA binding geometry with optimal enthalpic interactions. In sharp contrast, receptor 1a (with intramolecular hydrogen-bonding groups) reveals a temperature-dependent dual binding mode where MMTA can bind in two completely different geometries. The two solution binding geometries of 1a.MMTA were unraveled by NMR experiments and correlated to the X-ray structures.
ABSTRACT
A new three nuclear triple-stranded helicate complex M3L3 containing Na+/Li+ ions has been synthetized and characterised by 1H, 23Na, 7Li solution NMR, ESI-MS and X-ray crystallography.
