Perfluorinated Taddol Phosphoramidite as an L,Z-Ligand on Rh(I) and Co(-I): Evidence for Bidentate Coordination via Metal-C6F5 Interaction.

Perfluorinated Taddol-based phosphoramidite, CKphos, is a highly selective ligand for formation of the vinylogous amide cycloadduct in the Rh(I) catalyzed [2+2+2] cycloaddition of alkenyl isocyanates and alkynes. CKphos overrides substrate bias of product selectivity in the cycloaddition, providing indolizinones in excellent product and enantioselectivities. Excellent selectivities are attributed to a shortened Rh-P bond and coordination of one C6F5 to rhodium via a Z-type interaction, making the phosphoramidite a bidentate L,Z-ligand on rhodium. Evidence for the shortened Rh-P and C6F5 coordination is provided by X-ray, NMR and DFT computation analyses. Additionally, an anionic cobalt complex with CKphos was synthesized and two Co-C6F5 interactions are seen. Rh(C2H4)Cl•CKphos catalyst in the [2+2+2] cycloaddition of alkenyl isocyanates and alkynes represents a rare example of metal-C6F5 Z-type interaction affecting selectivity in transition metal catalysis.