Hydride chiral clusters

NMR studies have shown the reactions of the chiral hydrido clusters [(At3-RC)RuCoM(Cp)(CO)8H] (R = Me, Ph M = Mo, W) with the prochiral alkene H2C=C(C02Me)NHC0Me to be diastereoselective. This formal insertion process produces only one enantiomeric pair of the possible four diastereomeric products, in which the terminal CH2 of the intermediate alkene complex becomes a CH3 group via Markownikow-type addition of the coordinated hydride. This preferred product stereochemistry may arise from the mutual approach during olefin coordination of the two most polar units, the MoCp and C02Me groups, on the same side of the molecule. 

In ketones having a chiral cluster next to the carbonyl carbon reduction with lithium aluminum hydride gave one of the two possible diastereomers, erythro or threo, in larger proportions. The outcome of the reduction is determined by the approach of the reducing agent from the least hindered side (steric control of asymmetric induction) [828]. With lithium aluminum hydride as much as 80% of one diasteromer was obtained. This ratio is higher with more bulky reducing hydrides [837]. 

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