Phosphorus stabilized carbene complexes: bisphosphonate dianion synthesis, reactivity and DFT studies of O∼C∼O zirconium(iv) complexes

Abstract

The reactivity of the geminal dianion of tetraisopropyl methylenediphosphonate, 3, with [ZrCl₄(THF)₂] affords a trinuclear structure 5 in which an unprecedented triscarbene–Zr dianionic fragment is found. The overall trinuclear arrangement is assembled by PO bridging moieties. The X-ray crystal structure of 5 is presented. The reaction of complex 5 with stoichiometric amounts of pyridine affords a dinuclear complex 6 whose formulation was ascertained by an X-ray crystal structure. Complexes 5 and 6 cleanly react with aldehydes (R¹)(H)CO to afford the corresponding olefin of general formula [((OiPr)₂PO)₂CC(R¹)(H)]. DFT calculations which were carried out on the model complex of 5t and a hypothetical monometallic Zr complex [Zr(3)Cl₂(OMe₂)₂] 8t indicate that the Zr–C bond only features a weak π-interaction between the carbon atom and a vacant orbital at the metal. The polarization of the orbital towards the carbon center is consistent with the observed nucleophilic character of the carbene complexes described here.