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

The reactions of [(Me 3 Si) 2 N] 2 Ca(thf) 2 with amidines 2‐(Ph 2 P=NPh)C 6 H 4 NHC( t Bu)=N(2,6‐R 2 C 6 H 3 ) {R = i Pr ( L 1 H ); R = Me ( L 2 H )} afford heteroleptic calcium amido complexes [2‐(Ph 2 P=NPh)C 6 H 4 NC( t Bu)=N(2,6‐R 2 C 6 H 3 )]Ca[N(SiMe 3 ) 2 ](thf) {R = i Pr ( 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 Ph 2 PH and PhPH 2 . 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 ( M w /M n = 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 i PrOH. 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 (M w /M n = 1.51–1.68).