Cavitand Chemistry – Towards Metallocapsular Catalysts

Abstract

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‐PtCl2” unit, was determined by single‐crystal X‐ray diffraction. Upon reaction with SnCl2, 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‐PtCl2L2, 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.