The mononuclear σ-aryl complexes of the type trans-[Pt(σ-C 6 H 4 R)(4,7-phen)(PPh 3 ) 2 ]OTf (R=4-CO 2 Si t BuPh 2 , 4-CONHMe, 3-CO 2 Si t BuPh 2 , 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(PPh 3 ) 4 to yield the key iodoplatinum(II) precursors trans-[PtI(σ-C 6 H 4 R)(PPh 3 ) 2 ], followed by halogen metathesis with one equivalent of 4,7-phen. The reaction of trans-[Pt(σ-C 6 H 4 R)(4,7-phen)(PPh 3 ) 2 ]OTf with labile complexes of the type trans-[Pt(OTf)L 2 (σ-C 6 H 4 R ' )] (L=PEt 3 , R ' =H; L=PPh 3 , R ' =4-CO 2 Si t BuPh 2 , 3-CO 2 Si t BuPh 2 , 3-CONHMe) afforded the asymmetric dinuclear complexes of the type trans-[Pt(σ-C 6 H 4 R)L 2 (μ-4,7-phen)Pt(σ-C 6 H 4 R ' )L ' 2 ](OTf) 2 (L=PPh 3 , R=4-CO 2 Si t BuPh 2 , L ' =PEt 3 , R ' =H; L=L ' =PPh 3 , R=4-CONHMe, R ' =4-CO 2 Si t BuPh 2 ; R=4-CO 2 Si t BuPh 2 , R ' =3-CONHMe; R=3-CONHMe, R ' =3-CO 2 Si t BuPh 2 ) 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-[PtL 2 (σ-aryl)] units in the equilibrium mixture.