Cavitand Chemistry – Towards Metallocapsular Catalysts

Two diphosphanes with widely separated P centres and cores that consists of two covalently linked resorcinarene cavitands were synthesised. Their ability to bind transition‐metal ions in a chelating fashion with the concomitant formation of capsular complexes was shown in their reactions with metal centres with two available binding sites. The solid‐state structure of one of the complexes, a capsule with a partially embedded “ trans ‐PtCl 2 ” unit, was determined by single‐crystal X‐ray diffraction. Upon reaction with SnCl 2 , this complex developed good activity for the hydroformylation of styrene. Its activity and selectivity towards the branched aldehyde were significantly superior to those observed for the reference complex trans ‐PtCl 2 L 2 , in which L is a monophosphane monocavitand ligand. The higher activity is likely to reflect the initial formation of a hydrido intermediate with a somewhat distorted trigonal‐bipyramidal structure that facilitates the intracapsular olefin/PtH insertion step. The observed aldehyde selectivity is probably controlled by the shape of the capsule, which is sterically better suited for hosting a branched Pt–alkyl unit than a linear one.