MIGRATION OF A HYDRIDE LIGAND TO A DIFLUOROCARBENE LIGAND BOUND TO RHODIUM - THE SYNTHESIS AND CRYSTAL-STRUCTURE OF RHCL2(CF2H)(PPH3)2

Rh(CF3)(CO)(PPh3)2 has been made by treating RhH(CO)(PPh3)3 with Hg(CF3)2, and found to display reactivity consistent with a 16 e-, d8 complex, in that it undergoes addition of a number of small molecules, including O2, X2 (X = Cl, Br, I) and MeI. Treatment of Rh(CF3)(CO)(PPh3)2 with aqueous acids results in hydrolysis of the trifluoromethyl group to a carbonyl ligand. Confirmation that this reaction proceeds via a difluorocarbene intermediate came from the reaction with dry HCl, which gave RhCl2(CF2H)(CO)(PPh3)2. A study of this reaction, by multinuclear NMR spectroscopy and 2H-labelling experiments led to the proposal of a mechanism for the formation of RhCl2(CF2H)(CO)(PPh3)2 that involves hydride migration to a cationic difluorocarbene ligand bound to rhodium. Another difluoromethyl complex RhCl2(CF2H)(PPh3)2 is formed when RhHCl2(PPh3)3 is treated with Hg(CF3)2. The crystal structure of this complex has been determined, and displays square pyramidal geometry with the CF2H ligand occupying the apical position. © 1990.