THE PREPARATION AND REACTIONS OF BIS(PYRAZOLYL)PHENYLMETHANE COMPLEXES OF RHODIUM(I)

Article abstract of DOI:10.1016/S0022-328X(00)90026-3

The complexes <(LL)Rh(C2H4)Cl>x (I), <(LL)(Rh(cod)Cl)2> (II), <(MeLL)Rh(C2H4)2Cl> (III) and <(MeLL)Rh(cod)>⁺Cl^- (IV) have been prepared via the reactions of the bis-(pyrazolyl)phenylmethane ligands PhCH(H2pz)2 (LL; H2pz = pyrazolyl) and PhCH(Me2pz)2 (MeLL; Me2pz = 3,5-dimethylpyrazolyl) with 2 and 2 (cod = cyclooctadiene).Complex IV reacts with NaBPh4 to form <(MeLL)Rh(cod)>⁺BPh4^- (V).III and IV react with carbon monoxide to give <(MeLL)Rh(CO)2>^+- (VI).Complexes I and III give neutral solutions in methanol, while II and IV behave as 1:2 and 1:1 electrolytes, respectively.The rhodium(I) centre is typically four-coordinate in I, II, IV-VI, and five-coordinate in III.The ligands LL and MeLL show bidentate chelating behaviour in all of the above complexes, with the exception of II, where LL bridges two different Rh^I moieties.Reactions with H2, HCl and Ph3P are described.Complex III functions as a homogeneous catalyst, in neutral methanolic solution, for the hydrogenation of olefins, but is ineffective for the hydrogenation of α,β-unsaturated aldehydes and ketones.