Synthetic, structural, and catalytic studies on ethylene and carbonyl complexes of rhodium(I) containing 2-alkoxy-1, 3-dioxa-6, 9-diaza-2-phosphacycloundecane ligands

The title compounds are produced by addition of [Rh(CO)₂(μ-Cl)]2 or [Rh(C₂H₄₎₂(M-Cl)]₂to the appropriate, potentially tridentate, macrocyclic ligand. Crystallographic study of [Rh(CO)(Cl)(6,9-Me₂-2-OMe-1, 3, 6, 9, 2-0₂N₂PC₆H₁₂)] reveals that while all three donor atoms of the 11-membered macrocycle are formally associated with the rhodium center, one Rh-N bond is extremely long, 2.570 (5) Å, affording a geometry at the metal center that is intermediate between 4-and 5-coordinate. The origin of such distortion is traced to congestion within the macrocycle. It is suggested that the intermediacy of the structure between a planar 16e and trigonal-bipyramidal 18e configuration is related to the catalytic activity of these complexes. Crystals are orthorhombic, space group Pbca, with a = 13.5964 (15) Å, b = 15.367 (2) Å, c = 14.621 (2) Å, and Z = 8. With use of 2108 diffracted intensities recorded at 268 ± 1 K on an Enraf-Nonius CAD₄diffractometer the structure has been refined to R = 0.0548, Rw = 0.0580. The title complexes are shown to be good precursors for the catalytic hydroformylation of olefins. Catalytic asymmetric induction during styrene hydroformylation has given only 0.6% enantiomeric excess of hydratropaldehyde with the neomenthyl-substituted ligand in the presence of [Rh(H)(Cl)(PPh₃)₃], However, these new ligands give complexes that are more effective than the classical 2, 3-isopropylidene-2, 3-dihydroxyl, 4-bis(diphenylphosphino)butane ligand (DIOP) for aldehyde production under very mild conditions.