Siloxide

Abstract: The synthesis of the unsymmetrically substituted β-diketimine, 2-(2-methoxyphenylimino)-4-(2,6-diisopropylphenylamido)pent-2-ene, (BDI-2)H, is described and its complexation chemistry with magnesium and zinc is explored. Emphasis is placed on the preparation of alkoxide and amide derivatives for the ring-opening polymerisation of lactide; their behaviour as polymerisation initiators is compared to analogous compounds supported by the N,N′-bis(2,6-diisopropylphenyl) β-diketiminate ligand, BDI-1. (BDI-2)H reacts with Me2Mg to give the bis(chelate) complex, (BDI-2)2Mg, 3. Magnesium alkyls supported by BDI-2 may be prepared by increasing the size of the alkyl group. Hence, lithiation of (BDI-2)H affords [(BDI-2)Li]2, 4; its subsequent treatment with iPrMgCl produces (BDI-2)MgiPr, 5. Aminolysis of complex 5 using iPr2NH yields the amide complex, (BDI-2)MgNiPr2, 6. Zn(NTMS2)2 and ZnEt2 react with (BDI-2)H to give (BDI-2)Zn(NTMS2), 7, and (BDI-2)ZnEt, 8, respectively. The former is converted into the siloxide complex,(BDI-2)Zn(OSiPh3), 9, upon reaction with Ph3SiOH. The chloride derivative, (BDI-2)ZnCl, 10, has also been prepared via the reaction of ZnCl2 with 4. Crystallographic analysis of compounds 3, 4, 7 and 8 reveals that the potential for (BDI-2) to bind in a tridentate manner is only realised with the more electrophilic metals Li and Mg. Compared to their (BDI-1) counterparts, complexes 6, 7 and 9 are more active, but less well-controlled, initiators for the ring-opening polymerisation of rac-lactide, a consequence of the diminished steric protection afforded by (BDI-2) relative to (BDI-1).

Abstract: The complexes [Ln(AlMe 4 ) 3 ] (Ln=Y, La, Ce, Pr, Nd, Sm, Ho, Lu) have been synthesized by an amide elimination route and the structures of [Lu{(μ-Me) 2 AlMe 2 } 3 ], [Sm{(μ-Me) 2 -AlMe 2 } 3 ], [Pr{(μ-Me) 2 AlMe 2 } 3 ], and [La((μ-Me) 2 AlMe 2 } 2 {(μ-Me) 3 AlMe}] determined by X-ray crystallography. These structures reveal a distinct Ln 3+ cation size-dependency. A comprehensive insight into the intrinsic properties and solution coordination phenomena of [Ln(AlMe 4 ) 3 ] complexes has been gained from extended dynamic 1 H and 13 C NMR spectroscopic studies, as well as 1D 89 Y, 2D 1 H/ 89 Y, and 27 Al NMR spectroscopic investigations. [Ce-(AlMe 4 ) 3 ] and [Pr(AlMe 4 ) 3 ] have been used as alkyl precursors for the synthesis of heterobimetallic alkylated rare-earth metal complexes. Both carboxylate and siloxide ligands can be introduced by methane elimination reactions that give the heterobimetallic complexes [Ln{(O 2 CAr iPr )2(μ-AlMe 2 )} 2 -(AlMe 4 )(C 6 H 14 ) n ) and [Ln{OSi-(OtBu) 3 }(AlMe3)(AlMe4)2], respectively. [Pr{OSi(OtBu)3}(AlMe3)(AlMe4)2] has been characterized by X-ray structure analysis. All of the cerium and praseodymium complexes are used as precatalysts in the stereospecific polymerization of isoprene (1-3 equivalents of Et 2 AlCl as co-catalyst) and compared to the corresponding neodymium-based initiators reported previously. The superior catalytic performance of the homoleptic complexes leads to quantitative yields of high-cis-1,4-polyisoprene (>98%) in almost all of the polymerization experiments. In the case of the binary catalyst mixtures derived from carboxylate or siloxide precatalysts quantitative formation of polyisoprene is only observed for n Ln :n Cl = 1:2. The influence of the metal size is illustrated for the heterobimetallic lanthanum, cerium, praseodymium, neodymium, and gadolinium carboxylate complexes, and the highest activities are observed for praseodymium as a metal center in the presence of one equivalent of Et 2 AlCl.