Synthesis, characterization and structural studies of new heterometallic alkynyl complexes of platinum and Group 11 metals with chelating bis(diphenylphosphino)ferrocene ligand

Reaction of the platinum bis(alkynyl) complex [Pt(dppf)(C ≡ CPh)₂] (1) (dppf = bis(diphenylphosphino)ferrocene) with an equimolar amount of Group 11 metal salts [Cu(NCMe)₄]BF₄ and AgBF₄ initially gives 1:1 mixed-metal complexes [Pt(dppf)(C ≡ CPh)₂Cu(NCMe)]BF₄ (2) and [Pt(dppf)(C ″ CPh)₂Ag]BF₄ (3) in good yields. Upon standing in solution at room temperature, compounds 2 and 3 rearrange and aggregate to the corresponding diplatinum complexes [{Pt(dppf)(C ≡ CPh)₂}₂M]BF₄ (M = Cu (4), Ag (5)) which exhibit an intense molecular ion envelope for the respective cation in their electrospray mass spectra. Compounds 4 and 5 can also be formed when the reaction is performed using a 2:1 molar ratio of 1 and the Group 11 salts. The X-ray crystal structures of 1, 4 and 5 have been determined. Structures of 4 and 5 reveal that the two square-planar platinum coordination planes in the cation are approximately orthogonal an 2-fashion to four carbon-carbon triple bonds to afford heterometallic pentanuclear Fe₂Pt₂M complexes (M = Cu, Ag) in which each platinum center is stabilized by a dppf ligand. Each of the new complexes displays a reversible oxidation couple corresponding to the ferrocenyl unit of dppf and there is less stabilization of the silver in the mixed-metal complex than in the copper congeners.