Siloxy ligand

The properties of siloxide as ancillary ligand in the system TM-O-SiRs can be effectively utilized in molecular catalysis, but predominantly by early transition metal complexes. Mono- and di-substituted branched siloxy ligands (e.g., incompletely condensed silsesquioxanes) have been employed as more advanced models of the silanol sites on silica surface for catalytically active centers of early TM (Ti, W, V) that could be effectively used in polymerization [5], metathesis [6] and epoxidation [7] of alkenes as well as dehydrogenative coupling of silanes [8]. 

We have shown that alanes substituted with alkoxy and siloxy ligands can be used very efficiently in CVD processes, either producing single ceramic phases or mixtures of several phases using only one single precursor molecule. As the processes discussed above are driven by chemical reactions within distinct molecules or in between two molecules, the phases formed are... 

All zirconium based solids synthesized share in common a number of features which are responsible for their catalytic properties and their stability. Thus, zirconium is anchored to a silica surface via a Zr-Oj bond, known to be a strong bond. This bond intervenes in two ways it stabilizes Zr as a mononuclear species (dimerization is further prevent from by the fact that the hydroxyl groups on the surface are isolated) it leads to a very reactive species, formally an 8e species. Thus the siloxy ligand shows an immobilizing effect and an electronic effect. 

Facile replacement of the hydroxy ligand in Os3(GO)io(/x-H)(/x-OH) by siloxy ligands furnishes Os3(GO)io(/i-H)-(/x-OSiR2R ) (R=Et, Ph R = Et, Ph, OH, SiPh20H). These clusters have been examined as models to better understand the reactivity of osmium carbonyls on silica surfaces. The X-ray crystal structures of Os3(GO)io(/i-H)-(//-0SiPh20H) and Os3(GO)io(/i-H)(/ -OSiPh20SiPh20H) have been determined.The thermal and chemical stabilities of these clusters have also been examined. 

DFT study of interception of the allenyl enolate intermediate of Meyer-Schuster rearrangement using aldehydes and imines has shown that the active form of the vanadium catalyst bears two triphenyl siloxy ligands and that vanadium enolate is directly involved in the C-C bond formation." DFT calculations have elucidated the mechanisms and diastereoselectivities of phosphine-catalysed [4-1-2] annulations between allenoates and ketones or aldimines (Scheme 44). 

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