Metal Lewis acid bonding

Over the past few years, the coordination of preformed ambiphilic ligands, especially PBs, has been shown to afford straightforward access to complexes featuring metal-Lewis acid interactions. As discussed hereafter, this approach has allowed the significant extension of the scope of M-Z interactions, and to gain better understanding of their bonding situation. 

The osmium carbyne complex 115 reacts with elemental sulfur, selenium, and tellurium to afford the complexes 135 in which the element atoms "bridge the metal-carbon triple bond [Eq. (123)] (56). Complex 115 also reacts with transition metal Lewis acids such as AgCl or Cul to give dinuclear compounds with bridging carbyne ligands. Reaction with elemental chlorine results in addition across the metal-carbon triple bond to generate the chlorocarbene osmium complex 136 [Eq. (124)]. 

Molecular orbital interaction between a metal (Lewis acid) and a ligand (Lewis base) to form a coordinate covalent bond. 

The versatile utility of transition-metal Lewis acids in catalytic organic synthesis has been thereby demonstrated in this decade to show high synthetic performance in a variety of reactions with high stereoselection and enantioselection, for example, for asymmetric Diels-Alder reactions, 1,3-dipolar cycloadditions, and other carbon-carbon or hetero atom bond-formation reactions. We hope that this review will stimulate further developments of this category Lewis acid catalyst and its application in a truly efficient chemical process in the future. 

The microencapsulation technique has been developed by Kobayashi for the immobilization of metal Lewis acid catalyst in polymer [57]. The catalysts were immobilized on to polymers using physical environment by polymer backbones and interaction between 71 electrons of benzene rings of the polystyrenes and vacant orbitals of the catalysts. Microencapsulated scandium trifiuoromethanesul-fonate was easily prepared from polystyrene and Sc(OTf)3 in cyclohexane, which was successfully used in several important Lewis acid catalyzed carbon-carbon bond-forming reactions [57]. 

Their polar carbon-oxygen bonds and the presence of unshared electron pairs at oxygen contribute to the ability of ethers to form Lewis acid Lewis base complexes with metal ions... 

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