Synthesis of phosphido-bridged phosphinito platinum(I) complexes by reaction of cis-PtCl2(PHCy2)2 with oxygenated bases - Crystal structure of [(PCy2OMe)Pt(μ-PCy2)] 2(Pt-Pt)

Reaction of cis-PtCl2(PHCy2)2 (1) with oxygenated bases leads to phosphido-bridged dinuclear complexes. The product obtained using sodium hydroxide is the asymmetric Pt1 complex [(Cy2PH)Pt(μ-PCy2)(κ2P,O-μ-Cy 2PO)Pt(Cy2PH)](Pt-Pt) (2), which represents a rare example of a complex containing a Pt-Pt-P-O cycle. The reaction products between 1 and NaOR (R = Me, Et) depend on experimental conditions: lack of base results in the formation of trans-[Pt(PHCy2) Cl(μ-PCy2)]2 (3) as the main product. Using an excess of base at 50°C allowed the isolation of the symmetric PtI dimers [(PCy2OR)P(μ- PCy2)]2(Pt-Pt) (5, R = Me; 7, R = Et) containing two alkyl dicyclohexylphosphinito ligands. The asymmetric compounds [(PCy 2H)Pt(μ-PCy2)2Pt(PCy2OR)](Pt-Pt) (4, R = Me; 8, R = Et) form after work-up of the reaction of 1 with excess NaOR (8 equiv.) in toluene/methanol at room temperature. Investigations on the mechanism of formation of phosphinito PtI complexes (carried out also employing NaOtBu and NaOPh as oxygenated bases) show that the first two steps of the overall reaction are the metathesis leading to cis-Pt(OR) 2(PHCy2)2 and the subsequent formation of terminal phosphido complexes through ROH elimination. Single crystal X-ray diffraction showed that molecules of 5 are located on cristallographic inversion centres; hence their necessarily planar Pt2P2 core contains a Pt-Pt bond.