Synthesis and redistribution reactions of asymmetric σ-arylplatinum(II) complexes containing 4,7-phenanthroline

The mononuclear σ-aryl complexes of the type trans-[Pt(σ-C₆H₄R)(4,7-phen)(PPh₃)₂]OTf (R=4-CO₂Si^tBuPh₂, 4-CONHMe, 3-CO₂Si^tBuPh₂, 3-CONHMe; OTf=trifluoromethanesulfonate) containing a monodentate 4,7-phenanthroline (4,7-phen) ligand were prepared by an oxidative addition reaction of an aryl iodide with Pt(PPh₃)₄ to yield the key iodoplatinum(II) precursors trans-[PtI(σ-C₆H₄R)(PPh₃)₂], followed by halogen metathesis with one equivalent of 4,7-phen. The reaction of trans-[Pt(σ-C₆H₄R)(4,7-phen)(PPh₃)₂]OTf with labile complexes of the type trans-[Pt(OTf)L₂(σ-C₆H₄R′)] (L=PEt₃, R′=H; L=PPh₃, R′=4-CO₂Si^tBuPh₂, 3-CO₂Si^tBuPh₂, 3-CONHMe) afforded the asymmetric dinuclear complexes of the type trans-[Pt(σ-C₆H₄R)L₂(μ-4,7-phen)Pt(σ-C₆H₄R′)L′₂](OTf) ₂ (L=PPh₃, R=4-CO₂Si^tBuPh₂, L′=PEt₃, R′=H; L=L′=PPh₃, R=4-CONHMe, R′=4-CO₂Si^tBuPh₂; R=4-CO₂Si^tBuPh₂, R′=3-CONHMe; R=3-CONHMe, R′=3-CO₂Si^tBuPh₂) in which the 4,7-phen acts as a bridging bidentate ligand. The novel dinuclear species undergo an unusual redistribution reaction that is essentially thermoneutral at 298 K. The exchange process involves facile cleavage of a Pt-N bond and the rapid exchange of trans-[PtL₂(σ-aryl)] units in the equilibrium mixture.