Perfluorinated Taddol phosphoramidite as an L,Z-ligand on Rh(i) and Co(−i): evidence for bidentate coordination via metal–C6F5 interaction

Abstract

Perfluorinated Taddol-based phosphoramidite, CKphos, is a highly selective ligand for formation of vinylogous amide cycloadducts 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 indolizidinones in excellent yields and enantioselectivities. The 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 computational analyses. Additionally, an anionic cobalt complex with CKphos was synthesized and two Co–C₆F₅ interactions are seen. The 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.