-Heterocyclic Carbene-Coordinated M(II) (M = Yb, Sm, Ca) Bisamides: Expanding the Limits of Intermolecular Alkene Hydrophosphination.

A series of NHC-stabilized amido compounds (NHC)M[N(SiMe)] (M = Yb(II), Sm(II), Ca(II); = 1, 2) showed remarkable catalytic efficiency in addition of PhPH and PH to alkenes under mild conditions and low catalyst loading. The effect of σ-donor capacity of NHCs on catalytic activity in hydrophosphination of styrene with PhPH and PH was revealed. For the series of three-coordinate complexes , a tendency to increase the catalytic activity with growth of σ-donating strength of the carbene ligand was clearly demonstrated. The complex (NHC)Sm[N(SiMe)] (NHC = 1,3-diisopropyl-2-imidazole-2-ylidene) () proved to be the most efficient catalyst, which enabled hardly realizable transformations such as PhPH addition across internal C═C bonds of norbornene and - and -stilbenes, providing the highest reaction rate for addition of PH to styrene. Excellent regio- and chemoselectivities of alkylation of PH with styrenes allow for a selective and good-yield synthesis of desired organophosphines─either primary, secondary, or tertiary. Stepwise alkylation of PH with various substituted styrenes can be efficiently applied as an approach to nonsymmetric secondary phosphines. The rate equation of the addition of styrene to PH promoted by was found: rate = [styrene][5Sm].