Experimental and DFT Study of the [AuAr(AsPh3)]-Catalyzed cis/trans Isomerization of [PdAr2(AsPh3)2] (Ar = C6F5 or C6Cl2F3): Alternative Mechanisms and Its Switch upon Pt for Pd Substitution

The aryl transmetalation processes between cis-[PdRf2(AsPh3)2] (Rf = C6Cl2F3) and [AuPf­(AsPh3)] (Pf = C6F5) has been studied experimentally and by DFT calculations. Aryl exchange with or without isomerization of the Pd geometry occurs by ligand displacement of one AsPh3 ligand by an [AuAr­(AsPh3)] molecule, which coordinates using the Au–Ar bond electron density, followed or not by a second switch to the next aryl (Ar) group. The transition states are bridged Ar–Au­(AsPh3)–Ar′ structures with fairly planar geometries. Alternatively, a direct switch of the Au­(AsPh3) fragment to either cis or trans Ar groups on Pd can be achieved from a square-pyramidal [(AsPh3)­Au-PdAr3(AsPh3)] intermediate or transition state. The later pathway is less favorable for the case studied (M = Pd), but it is preferred for the same chemical system with M = Pt. The study provides some clues on exchanges that can be relevant in organic syntheses catalyzed by bimetallic systems.