Synthesis and reactivity of dichloroboryl complexes of platinum(II)

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(micro-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.