Ligand-Template Directed Assembly: An Efficient Approach for the Supramolecular Encapsulation of Transition-Metal Catalysts

Facile Isolation of Bisimines Based on 3,3‘-Diaminobenzidine: Direct Access to Unsymmetrical Bimetallic Salphen Building Blocks

Diimines obtained from 3,3'-diaminobenzidine and tert-butyl-substituted salicylaldehydes in MeOH can be readily isolated in 60-90% yield and were obtained as a mixture of geometrical isomers. Two distinct diimine intermediates (4 and 5) with a higher molecular symmetry as related to the other isomeric diimine products were both isolated by crystallization of which 5 was subsequently used to demonstrate that nonsymmetrical bis-salphen complexes with different functional groups and metal centers can be assembled via a three-component one-pot procedure.

Expedient Method for the Transmetalation of Zn(II)-Centered Salphen Complexes

Various mono- and bis-ZnII complexes derived from salphen ligands have been conveniently transmetalated with a number of transition metal (TM) acetates (M=Ni, Pd, Mn) in THF to afford their respective TM-salphen counterparts in excellent isolated yields (80-100%). This new transmetalation procedure allows in situ switching between supramolecular and catalytic functions of the metallosalphen complex.

Enantioselective Hydrogenation with Self-Assembling Rhodium Phosphane Catalysts: Influence of Ligand Structure and Solvent

Three sets of new and related chiral phospholane and phosphepine ligands have been prepared for Rh-catalyzed enantioselective hydrogenation. The size and substitution pattern of the cyclic monophosphanes were varied. More importantly, the ligands differ in the nature of the heterocyclic group linked to the trivalent phosphorus atom: 2-pyridone or 2-alkoxypyridine. In the corresponding Rh complexes, the pyridone units of two monodentate P ligands can assemble by hydrogen bonding and form chelates. In contrast, synthetic precursors bearing alkoxypyridine appendages are not able to aggregate via intramolecular hydrogen bonds. The nature of self-assembly is dependent on the nature of the P ligand and the solvent used for the hydrogenation (CH2Cl2 vs. MeOH). These features affect the rate of the reaction as well as the enantioselectivity, which varied in the range of 0-99 % ee Complexation studies and DFT calculations were performed to explain these differences.

Bisphosphine based hetero-capsules for the encapsulation of transition metals

Just mixing of solutions of tetracationic diphosphine ligands and tetraanionic calix[4]arene building blocks leads to the formation of supramolecular heterocapsules that coordinate a palladium metal within the cavity of the assembly, giving rise to a new class of potential supramolecular transition metal catalysts.