Westerhausen, M. Organocalcium compounds with catalytic activity for the ring-opening polymerization of lactones

Westerhausen, M., Schneiderbauer, S., Kneifel, A.N., Söltl, Y., Mayer, P., Nöth, H., Zhong, Z., Dijkstra, P.J. and Feijen, J

European journal of inorganic chemistry, 18, 3432-3439

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)(THF)3] (1). A similar reaction in toluene with a stoichiometric ratio of 2:3 gives the dinuclear complex [2(tmhd)2(µ-tmhd)] (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.