RESUMO

We report a synthetic strategy that allows for the preparation of sterically encumbered heteroleptic Ru(II)porphyrinates with the desired configuration of stable/inert and weak/labile axial ligands to direct reactions between substrates to exclusively occur at the sterically encumbered face. To demonstrate the method, we describe the synthesis of a strapped-Ru(II)porphyrinate bearing a stable/inert triphenylphosphine (PPh3) bulky axial ligand coordinated exo to the central cavity and a weak/labile methanol molecule coordinated at the internal axial position. With this axial ligand configuration, the reported Ru(II)porphyrinate exclusively promotes carbene transfer reactions to olefins through the central cavity, which has been verified by the selective formation of cycloprane-linked [2]rotaxanes.

Assuntos

Alcenos , Ligantes , Modelos Moleculares

RESUMO

Selectivity in N-H and S-H carbene insertion reactions promoted by Ru(II)porphyrinates currently requires slow addition of the diazo precursor and large excess of the primary amine and thiol substrates in the reaction medium. Such conditions are necessary to avoid the undesirable carbene coupling and/or multiple carbene insertions. Here, the authors demonstrate that the synergy between the steric shielding provided by a Ru(II)porphyrinate-based macrocycle with a relatively small central cavity and the kinetic stabilization of otherwise labile coordinative bonds, warranted by formation of the mechanical bond, enables single carbene insertions to occur with quantitative efficiency and perfect selectivity even in the presence of a large excess of the diazo precursor and stoichiometric amounts of the primary amine and thiol substrates. As the Ru(II)porphyrinate-based macrocycle bears a confining nanospace and alters the product distribution of the carbene insertion reactions when compared to that of its acyclic version, the former therefore functions as a nanoreactor.

RESUMO

A 5,15-bis(1,1'-biphenyl)porphyrin-based molecular clip covalently connected to a ditopic aliphatic ester loop moiety yields a semi-rigid macrocycle with a well-defined cavity. The resulting macrocycle fits the structural requirements for the preparation of porphyrinates capable of promoting formation of C-C bonds. To demonstrate the usefulness of porphyrin-based macrocycles, an active-metal-template synthesis of rotaxanes through a redox non-innocent carbene transfer reaction is described. Coordination of CoII ions into the porphyrin subunit followed by addition of appropriate monodentate nitrogen-based additives to function as axial ligands enables the radical carbene transfer reactions to styrene derivatives to occur exclusively through the cavity of the macrocycle to afford cyclopropane-linked rotaxanes in excellent 95 % yield. Investigation of the product distribution afforded from the rotaxane assembly reaction reveals how the redox cooperative action between the carbene species and the CoII ions can be manipulated to gain control over the radical-type mechanism to favor the productive rotaxane forming process.

RESUMO

A CoII /porphyrinate-based macrocycle in the presence of a 3,5-diphenylpyridine axial ligand functions as an endotopic ligand to direct the assembly of [2]rotaxanes from diazo and styrene half-threads, by radical-carbene-transfer reactions, in excellent 95 % yield. The method reported herein applies the active-metal-template strategy to include radical-type activation of ligands by the metal-template ion during the organometallic process which ultimately yields the mechanical bond. A careful quantitative analysis of the product distribution afforded from the rotaxane self-assembly reaction shows that the CoII /porphyrinate subunit is still active after formation of the mechanical bond and, upon coordination of an additional diazo half-thread derivative, promotes a novel intercomponent C-H insertion reaction to yield a new rotaxane-like species. This unexpected intercomponent C-H insertion illustrates the distinct reactivity brought to the CoII /porphyrinate catalyst by the mechanical bond.