FORMATION OF DIARYLS BY THERMAL DECOMPOSITION OF RHODIUM(I) TRIARYLPHOSPHINE COMPLEXES

Article abstract of DOI:10.1016/S0022-328X(00)83492-0

Chlorotris(triphenylphosphine)rhodium, RhCl(PPh3)3 undergoes thermal decomposition above 140 deg C in solution and in the solid state to yield biphenyl.Rhodium complexes with para-substituted triphenylphosphine ligands form exclusively 4,4'-disubstituted biphenyls.Mixtures of two complexes RhCl(PAr3)3 and RhCl(PAr'3)3 form the crossed diaryl ArAr' and two non-crossed compounds (Ar)2 and (Ar')2.The mechanism is assumed to involve dissociation of RhCl(PPh3)3 into PPh3 and solvated RhCl(PPh3)2 followed by oxidative addition of the liberated phosphine to the latter bis-triphenylphosphine compound.Evidence for a phenyl-rhodium intermediate has been provided by phenylation of styrene by RhCl(PPh3)3.In an independent process, RhCl(PPh3)3 forms benzene by an ortho-metallation route.