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

Abstract

Reaction of the neutral dihydride complexes (η-C 5 R 5 )Ir(L)H 2 (L = P(OPh) 3 , CO; R = H, Me) with triflic acid (HO 3 SCF 3 ) at ambient temperature or above affords hydrogen and the dimeric hydride bridged species {[(η-C 5 R 5 )Ir(L)H] 2 (µ-H)}O 3 SCF 3 . Deprotonation of the cationic complexes gives the neutral dimers of the form [(η-C 5 R 5 )Ir(L)H] 2 . Spectroscopic data are consistent with the presence of only terminal hydride ligands in these complexes. Variable temperature 1 H and 31 P 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-C 5 Me 4 Et)Ir(CO)H] 2 , reveals that a rapid epimerization process occurs that interconverts the two diastereomers. Thermolysis of the carbonyl complex [(η-C 5 Me 5 )Ir(CO)H] 2 affords [(η-C 5 Me 5 )Ir(CO)] 2 and dihydrogen. Keywords: iridium, hydride, bimetallic, dynamics, epimerization.