Synthesis of Phosphido-Bridged Phosphinito Platinum(I) Complexes by Reaction of cis-PtCl_2(PHCy_2)_2 with Oxygenated Bases-Crystal Structure of [(PCy_2OMe)Pt(mu-PCy_2)]_2(Pt-Pt)

摘要

Reaction of cis-PtCl_2(PHCy_2)_2 (1) with oxygenated bases leads to phosphido-bridged dinuclear complexes.The product obtained using sodium hydroxide is the asymmetric Pt~I complex [(Cy_2PH)Pt(mu-PCy_2)(K~2P,O-mu-Cy_2PO)Pt(Cy_2PH)](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(PHCy_2)Cl(mu-PCy_2)]_2 (3) as the main product.Using an excess of base at 50 deg C allowed the isolation of the symmetric Pt~I dimers [(PCy_2OR)Pt(mu-PCy_2)]_2(Pt-Pt) (5,R=Me;7,R=Et) containing two alkyl dicyclohexylphosphinito ligands.The asymmetric compounds [(PCy_2H)Pt(mu-PCy_2)_2Pt(PCy_2OR)](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 Pt~I complexes (carried out also employing Na-OtBu and NaOPh as oxygenated bases) show that the first two steps of the overall reaction are the metathesis leading to cis-Pt(OR)_2(PHCy_2)_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 crystallographic inversion centres;hence their necessarily planar Pt_2P_2 core contains a Pt-Pt bond.