ARTÍCULO CIENTÍFICO

New diazaphospholidine terminated Polyhedral Oligomeric Silsesquioxane (POSS) molecules have been synthesized and tested in styrene and vinyl acetate hydroformylation. Some of them have been shown to precipitate upon mixing with rhodium precursors, whilst others remain in solution and show activity. These latter are more compact and rigid in comparison to the former, which are more flexible and hence more prone to

been able to rationalise these observations. PP distance calculations show that the ligands, for which precipitation occurs upon mixing with the rhodium precursor, have PP distances too big to promote bidentate coordination, whereas the two active ligands display more rigid and compact structures with PP distance falling in the range of possible bidentate coordination. We have, therefore succeeded in using macromolecular design to induce a dendritic effect by sufficiently crowding SemiEsphos units at the periphery of a dendrimer like molecule that the properties of ESPHOS (a bidentate analogue of monodentate SemiEsphos) are at least partially reproduced. The activity, branched selectivity and even the activity for subsequent aldehyde hydrogenation to alcohol of ESPHOS are reproduced, but not the enantioselectivity. This suggests that despite the crowding initiating bidentate binding, the exact chiral environment provided by ESPHOS has not been achieved.

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