Calcium Amido Complexes Coordinated by Tridentate Amidinate Ligands: Synthesis, Structures and Catalytic Activity in Olefin Hydrophosphination and Polymerization of Cyclic Esters

The reactions of [(Me3Si)2N]2Ca(thf)2 with amidines 2‐(Ph2P=NPh)C6H4NHC(tBu)=N(2,6‐R2C6H3) {R = iPr (L1H); R = Me (L2H)} afford heteroleptic calcium amido complexes [2‐(Ph2P=NPh)C6H4NC(tBu)=N(2,6‐R2C6H3)]Ca[N(SiMe3)2](thf) {R = iPr (1); R = Me (2)} featuring tridentate coordination of the amidinate ligands. Complexes 1 and 2 proved to be efficient catalysts for intermolecular hydrophosphination of styrene, α‐methylstyrene, divinylbenzene and phenylacetylene with Ph2PH and PhPH2. Compounds 1 and 2 exhibit high catalytic activity in the ring‐opening polymerization of ε‐caprolactone and enable quantitative conversion of 500 equiv. of monomer in 5 seconds (22 °C). Polymerization of rac‐lactide initiated by 1 and 2 proceeds much slower: 52–72 % conversion ([M]0/[Ca]0 = 100) was reached in 12 h (20 °C). The obtained polymers are characterized by narrow polydispersities (Mw/Mn = 1.22–1.28). Catalytic activity of complexes 1 and 2 in rac‐lactide polymerization increases significantly in the presence of 1–3 equiv. of iPrOH. Nearly quantitative (86–98 %) conversion of 100 equiv. of monomer was reached in 1 h and the obtained polymer samples were characterized by relatively narrow polydispersity (Mw/Mn = 1.51–1.68).