Iridium Models of Rhodium Intermediates in Hydroformylation Catalysis: Isolation and Molecular Structures of Fluxional ae and ee Isomers

We
report the synthesis and single-crystal molecular structures
of two stereoisomers of trigonal-bipyramidal hydrido dicarbonyl Ir
complexes [(L2)­Ir­(H)­(CO)2] with ae (axial–equatorial)
and ee (equatorial–equatorial) ligand P coordination and fluxional
behavior in solution. L2 is a new chelating bisphosphite
with unprecedented high selectivity in Rh-catalyzed bis-hydroformylation
of butadiene to adipic aldehyde. These Ir analogues are ideal stabilized
structural models for nonseparable ae and ee Rh-hydroformylation resting
state isomers [(L2)­Rh­(H)­(CO)2]. With Ir, both
stereoisomers with the same ligand could be characterized independently
for the first time.