Amino Ether–Phenolato Precatalysts of Divalent Rare Earths and Alkaline Earths for the Single and Double Hydrophosphination of Activated Alkenes

Abstract

A range of stable ytterbium(II) amino ether–phenolato amido complexes of the type {LONxOy}Yb{N(SiMe3)2}, together with a congeneric samarium(II) and two calcium and strontium amido and alkyl derivatives, have been synthesized. They constitute very active, fully regioselective (anti-Markovnikov), and chemoselective precatalysts for the intermolecular hydrophosphination of styrene derivatives with PhPH2, achieving TONs up to 2150, TOFs up to 30 h–1 and chemoselectivities in the region of 95–99%. The ytterbium(II) precatalysts, among which is most prominently {LONO4}Yb{N(SiMe3)2} (3), where the ligand possesses a 15-c-5-aza-crown ether side arm, outperform their related calcium analogues, and the activity of the catalyst increases substantially with the denticity of the ligand. The rate law rate = k[p-tBu-styrene][3] was established following kinetic monitoring of the hydrophosphination of p-tBu-styrene and PhPH2 catalyzed by 3. The kinetic studies also revealed that the reactions are entropically driven and...