Synthesis and reactivity of dichloroboryl complexes of platinum(ii)

Abstract

The reaction between [Pt(nbe)₃] (nbe = norbornene), two equivalents of the phosphines PPh₃, PMePh₂ or PMe₂Ph and 1 equivalent of BCl₃ affords the platinum dichloroboryl species [PtCl(BCl₂)(PPh₃)₂], [PtCl(BCl₂)(PMePh₂)₂] and [PtCl(BCl₂)(PMe₂Ph)₂]. All three complexes were characterised by X-ray crystallography and reveal that the boryl group lies trans to the chloride. With PMe₃ as the phosphine, the complex [PtCl(BCl₂)(PMe₃)₂] is isolated in high yield as a white crystalline powder although crystals suitable for X-ray crystallography were not obtained. Crystals were obtained of a product shown by X-ray crystallography to be the unusual dinuclear species [Pt₂(BCl₂)₂(PMe₃)₄(µ-Cl)][BCl₄] which reveals an arrangement in which two square planar platinum(II) centres are linked by a single bridging chloride which is trans to a BCl₂ group on each platinum centre. The reaction of [PtCl(BCl₂)(PMe₃)₂] with NEt₃ or pyridine (py) affords the adducts [PtCl{BCl₂(NEt₃)}(PMe₃)₂] and [PtCl{BCl₂(py)}(PMe₃)₂], respectively, both characterised spectroscopically. The reaction between [PtCl(BCl₂)(PMe₃)₂] and either 4 equivalents of NHEt₂ or piperidine (pipH) results in the mono-substituted boryl species [PtCl{BCl(NEt₂)}(PMe₃)₂] and [PtCl{BCl(pip)}(PMe₃)₂], respectively, the former characterised by X-ray crystallography. Treatment of either [PtCl(BCl₂)(PMe₃)₂] (in the presence of excess NEt₃) or [PtCl{BCl(NEt₂)}(PMe₃)₂] with catechol affords the B(cat) (cat = catecholate) derivative [PtCl{B(cat)}(PMe₃)₂] which is also formed in the reaction between [Pt(PMe₃)₄] and ClB(cat) and also from the slow decomposition of [Pt{B(cat)}₂(PMe₃)₂] in dichloromethane over a period of months. The compound [Pt{B(cat)}₂(PMe₃)₂] was prepared from the reaction between [Pt(PMe₃)₄] and B₂(cat)₂.