Organocalcium Compounds with Catalytic Activity for the Ring‐Opening Polymerization of Lactones

The equimolar reaction of calcium bis[bis(trimethylsilyl)amide] with 2,2,6,6‐tetramethylheptane‐3,5‐dione (Htmhd) in THF yields liquid mononuclear [Ca(tmhd){N(SiMe 3 ) 2 }(THF) 3 ] ( 1 ). A similar reaction in toluene with a stoichiometric ratio of 2:3 gives the dinuclear complex [{(THF)Ca} 2 (tmhd) 2 (µ‐tmhd){µ‐N(SiMe 3 ) 2 }] ( 2 ). The calcium atoms of these complexes are in a distorted octahedral environment. In 2 the complex consists of two octahedra connected by a common face of one nitrogen base and two oxygen atoms; the bridging Ca−N bond lengths are extremely large. The metalation of the tetradentate Jacobsen reagent with calcium bis[bis(trimethylsilyl)amide] in 1,2‐dimethoxyethane (DME) gives the corresponding calcium complex 3 , nearly quantitatively, as its DME adduct. The calcium atom is in an unusual trigonal prismatic coordination sphere. The metathesis reaction of 3 with tin( II ) chloride yields the corresponding yellow tin( II ) complex with the metal atom in a distorted square‐pyramidal environment. Complexes 2 and 3 show catalytic reactivity in the ring‐opening polymerization of cyclic esters such as lactones and lactides. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)