RESUMO
Results of kinetic experiments and quantum chemical computations on a series of platinum-promoted polycyclization reactions are described. Analyses of these results reveal a reactivity model that reaches beyond the energetics of the cascade itself, incorporating an ensemble of pre-cyclization conformations of the platinum-alkene reactant complex, only a subset of which are productive for bi- (or larger) cyclization and lead to products. Similarities and differences between this scenario, including reaction coordinates for polycyclization, for platinum- and enzyme-promoted polycyclization reactions are highlighted.
Assuntos
Alcenos/química , Platina/química , Polienos/química , Alcenos/síntese química , Biomimética , Catálise , Ciclização , Modelos Moleculares , Conformação Molecular , Polienos/síntese química , Esqualeno/análogos & derivados , Esqualeno/síntese química , Esqualeno/química , EstereoisomerismoRESUMO
Reaction of a complex Pt organometallic species with electrophilic halogen sources in the presence of X- ligands changes the mechanism of reductive elimination from a concerted reductive coupling type to an SN2 type reductive elimination. In the absence of the added X- ligand the reductive elimination is stereoretentive; in its presence, the process is stereoinvertive. This selectivity hinges on the reactivity of a key five-coordinate Pt(IV) intermediate with the X- ligand.
RESUMO
Application of a tridentate NHC containing pincer ligand to Pt catalyzed cascade cyclization reactions has allowed for the catalytic, diastereoselective cycloisomerization of biogenic alkene terminated substrates to the their polycyclic counterparts.
Assuntos
Compostos Organometálicos/química , Platina/química , Compostos Policíclicos/síntese química , Polienos/química , Catálise , Ciclização , Cinética , Estrutura Molecular , Estereoisomerismo , TermodinâmicaRESUMO
Catalytic systems based on Ni and Pd complexes modified with chiral P-P ligands can be used in a convenient strategy for enantioselectively adding a boron unit to the beta-position of alpha,beta-unsaturated esters.