Synthesis and Characterization of Crotyl Intermediates in Rh-Catalyzed Hydroformylation of 1,3-Butadiene

Crotyl rhodium complexes like (κ2-L)­Rh­(η3-crotyl) and (κ2-L)­Rh­(η3-crotyl)­(CO) (L = chelating
phosphorus ligand) are important
intermediates in hydroformylation catalysis of butadiene and related
reactions. They are assumed to be responsible for the specific reactivity
patterns of conjugated dienes. We prepared and characterized by X-ray
crystallography several of these complexes with novel chelating bisphosphite
ligands. (κ2-L)­Rh­(η3-crotyl)
complexes exhibit a square-planar geometry, while their CO adducts
(κ2-L)­Rh­(η3-crotyl)­(CO)
are trigonal-bipyramidal with the bisphosphite ligand in ee-bonding
mode. Typically, the η3-crotyl unit can be oriented
in several diastereomeric ways, of which oftentimes two or more are
present in solution and in the solid state.