No abstract

A chiral, tetradentate polyether ligand with a trans-1,2-cyclohexanediyl backbone, bis(methoxyethoxy)-trans-1,2-cyclohexane (5), was synthesized as both a racemate and the (S,S) enantiomer. 5 was found to form stable adducts with alkaline earth metal amides [M{N(SiMe(3))(2)}(2)(thf)(x)] (M = Mg (x = 0), Ca (x = 2) and Sr (x = 2/3)), [Ca{N(SiHMe(2))(2)}(2)(thf)] as well as with hydrocarbyl compounds [Mg(CH(2)SiMe(3))(2)] and [Ca(η(3)-C(3)H(5))(2)]. X-ray diffraction study of the bis(amide) [((S,S)-)Ca{N(SiMe(3))(2)}(2)] and of the bis(allyl) [(rac-5)Ca(η(3)-C(3)H(5))(2)] was performed. The complexes obtained were tested as initiators for the ring-opening polymerization of meso-, racemic and L-lactide.

Cyclic tetra-amine 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane, (Me 3 TACD)H (= Me 3 [12]aneN 4 ) was reacted with [M{N(SiMe 3 ) 2 } 2 (thf) x ] (M = Mg, x = 0; M = Ca, x = 2) in n-pentane to give thf-free complexes [{Me 3 TACD}M{N(SiMe 3 ) 2 }] (M = Mg (1); M = Ca (2)). Both compounds are monomeric in solution and X-ray diffraction studies showed the metal centers to be five-coordinated. The proligand (Me 3 TACD)H reacted with [Ca{N(SiHMe 2 ) 2 } 2 (thf) 2 ] in benzene-d 6 to give [{(Me 3 TACD)SiMe 2 N(SiHMe 2 )}Ca{N(SiHMe 2 ) 2 }] (3) with hydrogen evolution. Single-crystal X-ray diffraction showed 3 to be monomeric with a six-coordinated calcium center in the solid state. The alkaline earth metal amide complexes 1 to 3 catalyzed the ring-opening polymerization of lactide monomers to give syndiotactic-rich polylactides from meso-lactide and isotactic-rich polylactides from rac-and L-lactide.Scheme 1 Synthesis of complexes [{Me 3 TACD}M{N(SiMe 3 ) 2 }], M = Mg (1) and M = Ca (2).

The synthesis and attempted isolation of neutral bis(allyl)strontium [Sr(C(3)H(5))(2)] (1) resulted in the isolation of potassium tris(allyl)strontiate K[Sr(C(3)H(5))(3)] (2). In situ generated 1 shows a pronounced Brønsted basicity, inducing polymerisation of THF. Ate complex 2 crystallises as [K(THF)(2){Sr(C(3)H(5))(3)}(THF)](∞) (2·(THF)(3)). The salt-like solid state structure of 2·(THF)(3) comprises a two-dimensional network of (μ(2)-η(3):η(3)-C(3)H(5))(-) bridged potassium and strontium centres. Synthesis of allyl complexes 1 and 2 utilised SrI(2), [Sr(TMDS)(2)] (3) (TMDS = tetramethyldisilazanide), and [Sr(HMDS)(2)] (HMDS = hexamethyldisilazanide) as strontium precursors. The solid state structure of previously reported [Sr(TMDS)(2)] (3) was established by X-ray single crystal analysis as a dissymmetric dimer of [Sr(2)(TMDS)(4)(THF)(3)] (3·(THF)(3)) with multiple Si-HSr agostic interactions. The presence of ether ligands (THF, 18-crown-6) influenced the Si-HSr resonances in the NMR spectra of the amido complex 3.

Gut abgeschirmt: Kationische Calciumhydridkomplexe mit einem [Ca3(μ3‐H)2]‐Kern wurden ausgehend von verschiedenen Organocalcium‐Vorstufen und Ph2SiH2 synthetisiert. Die Hydridkomplexe katalysieren die Hydrosilylierung und Hydrierung von 1,1‐Diphenylethen.