Dinuclear dihydride complexes of iridium: a study of structure and dynamics

Abstract

Reaction of the neutral dihydride complexes (η-C5R5)Ir(L)H2(L = P(OPh)3, CO; R = H, Me) with triflic acid (HO3SCF3) at ambient temperature or above affords hydrogen and the dimeric hydride bridged species {[(η-C5R5)Ir(L)H]2(µ-H)}O3SCF3. Deprotonation of the cationic complexes gives the neutral dimers of the form [(η-C5R5)Ir(L)H]2. Spectroscopic data are consistent with the presence of only terminal hydride ligands in these complexes. Variable temperature 1H and 31P NMR studies indicate that a rapid dynamic process exchanges the two terminal hydride ligands and that the complexes exist as unequal mixtures of the racemic and meso diastereomers. Synthesis of a lower symmetry derivative, [(η-C5Me4Et)Ir(CO)H]2, reveals that a rapid epimerization process occurs that interconverts the two diastereomers. Thermolysis of the carbonyl complex [(η-C5Me5)Ir(CO)H]2 affords [(η-C5Me5)Ir(CO)]2 and dihydrogen. Keywords: iridium, hydride, bimetallic, dynamics, epimerization.