Dihydroxylation osmium

Figure 5.2 The use of hollow PDMS thimbles to achieve site separation ofGrubbs catalyst and an osmium dihydroxylation catalyst [34], The solution of the Grubbs catalyst was placed on the interior of the PDMS thimble in which a metathesis reaction was then performed. After...

Bowden and co-workers demonstrated the utility of such a system in multiple cascade reactions, including the use of an otherwise incompatible combination of a Grubbs catalyst and an osmium dihydroxylation catalyst (Figure 5.2) [34],... 

Abstract The applications of hybrid DFT/molecular mechanics (DFT/MM) methods to the study of reactions catalyzed by transition metal complexes are reviewed. Special attention is given to the processes that have been studied in more detail, such as olefin polymerization, rhodium hydrogenation of alkenes, osmium dihydroxylation of alkenes and hydroformylation by rhodium catalysts. DFT/MM methods are shown, by comparison with experiment and with full quantum mechanics calculations, to allow a reasonably accurate computational study of experimentally relevant problems which otherwise would be out of reach for theoretical chemistry. 

The computational study of the osmium dihydroxylation of aliphatic al-kenes is much more complicated than the case of aromatic alkenes due to the large number of conformations that the former could adopt. To overcome this issue, we considered the system to be composed of two different parts the catalyst and the olefin. For the catalyst, the conformation considered is that from the X-ray structure. As already shown in the study of styrene [95], and in some experimental works [98], the catalyst is a fairly rigid molecule. For the aliphatic alkenes under study, there is a large number of possible conformations in addition, the stability of an olefin conformation is also affected by the interactions between the olefin substituent and the catalyst. Therefore, the catalyst must be included in the conformational search. The conformational analysis was done using a scheme based on the systematic search approach [99]. The strategy consisted of two parts first we developed a method to identify all of the possible conformations afterwards, we screened all of the possible conformations at MM level to select the most stable. Finally, we only carried out the relatively expensive QM/MM calculations on these selected conformations. 

Pandit and coworkers also prepared a functionahzed tricyclic core (148) by a different version of the intramolecular Diels-Alder reaction (Scheme 13). For further introduction of an alkenyl group, the trisubstituted alkene in 148 was subjected to osmium dihydroxylation followed by dehydration imder... 

---