From Functional Phospholide Ions to Bifunctional 1,1′-Diphosphaferrocenes

Both the 2-ethoxycarbonyl and the 2-benzoyl phospholides (1 and 2) react with FeCl2 in the presence of ZnCl2 to give the corresponding 2,2′-difunctional 1,1′-diphosphaferrocenes as mixtures of meso and rac diastereomers. Stable rotamers are also detected by 1H and 13C NMR spectroscopy. Under the same conditions, the 2,5-bis(ethoxycarbonyl)phospholide (3) gives the tetrafunctional 1,1′-biphospholyl (6). The diphosphaferrocenes and the 1,1′-biphospholyl are probably formed from a common type of intermediates with a bis(η1-phospholyl)iron structure. DFT computations indicate that this kind of intermediate is pyramidal at P and only weakly aromatic.