Catalyse et Organométalliques, UMR CNRS 6226 Sciences Chimiques de Rennes, Université de Rennes 1, Campus de Beaulieu, Avenue du Général Leclerc, 35042 Rennes Cedex, France.
Chemistry. 2012 May 14;18(20):6289-301. doi: 10.1002/chem.201103666. Epub 2012 Apr 11.
The factors governing the stability and the reactivity towards cyclic esters of heteroleptic complexes of the large alkaline earth metals (Ae) have been probed. The synthesis and stability of a family of heteroleptic silylamido and alkoxide complexes of calcium [{LO(i)}Ca-Nu(thf)(n)] supported by mono-anionic amino ether phenolate ligands (i = 1, {LO(1)}(-) = 4-(tert-butyl)-2,6-bis(morpholinomethyl)phenolate, Nu(-) = N(SiMe(2)H)(2)(-), n = 0, 4; i = 2, {LO(2)}(-) = 2,4-di-tert-butyl-6-{[2-(methoxymethyl)pyrrolidin-1-yl]methyl}phenolate, Nu(-) = N(SiMe(2)H)(2)(-), n = 0, 5; i = 4, {LO(4)}(-) = 2-{[bis(2-methoxyethyl)amino]methyl}-4,6-di-tert-butylphenolate, Nu(-) = N(SiMe(2)H)(2)(-), n = 1, 6; Nu(-) = HC≡CCH(2)O(-), n = 0, 7) and those of the related [{LO(3)}Ae-N(SiMe(2)H)(2)] ({LO(3)}(-) = 2-[(1,4,7,10-tetraoxa-13-azacyclopentadecan-13-yl)methyl]-4,6-di-tert-butylphenolate Ae = Ca, 1; Sr, 2; Ba, 3) have been investigated. The molecular structures of 1, 2, [(4)(2)], 6, and [(7)(2)] have been determined by X-ray diffraction. These highlight Ae⋅⋅⋅H-Si internal β-agostic interactions, which play a key role in the stabilization of [{LO(i)}Ae-N(SiMe(2)H)(2)] complexes against ligand redistribution reactions, in contrast to regular [{LO(i)}Ae-N(SiMe(3))(2)]. Pulse-gradient spin-echo (PGSE) NMR measurements showed that 1, 4, 6, and 7 are monomeric in solution. Complexes 1-7 mediate the ring-opening polymerization (ROP) of L-lactide highly efficiently, converting up to 5000 equivalents of monomer at 25 °C in a controlled fashion. In the immortal ROP performed with up to 100 equivalents of exogenous 9-anthracenylmethanol or benzyl or propargyl alcohols as a transfer agent, the activity of the catalyst increased with the size of the metal (1<2<3). For Ca-based complexes, the enhanced electron-donating ability of the ancillary ligand favored catalyst activity (1>6>4≈5). The nature of the alcohol had little effect over the activity of the binary catalyst system 1/ROH; in all cases, both the control and end-group fidelity were excellent. In the living ROP of L-LA, the HC≡CCH(2)O(-) initiating group (as in 7) proved superior to N(SiMe(2)H)(2)(-) or N(SiMe(3))(2)(-) (as in 6 or [{LO(4)}Ca-N(SiMe(3))(2)] (B), respectively).
已探究了大碱土金属（Ae）杂配位配合物对环状酯的稳定性和反应性的影响因素。合成并稳定了一系列具有单阴离子氨甲醚酚氧配体的钙 [{LO(i)}Ca-Nu(thf)(n)] 杂硅酰胺和烷氧基配合物（i = 1，{LO(1)}(-) = 4-(叔丁基)-2,6-双（吗啉甲基）苯酚，Nu(-) = N(SiMe(2)H)(2)(-)，n = 0,4；i = 2，{LO(2)}(-) = 2,4-二叔丁基-6-{[2-(甲氧基甲基)吡咯烷-1-基]甲基}苯酚，Nu(-) = N(SiMe(2)H)(2)(-)，n = 0,5；i = 4，{LO(4)}(-) = 2-{[双(2-甲氧基乙基)氨基]甲基}-4,6-二叔丁基苯酚，Nu(-) = N(SiMe(2)H)(2)(-)，n = 1,6；Nu(-) = HC≡CCH(2)O(-)，n = 0,7) 及其相关的 [{LO(3)}Ae-N(SiMe(2)H)(2)] ({LO(3)}(-) = 2-[(1,4,7,10-四氧杂-13-氮杂环十五烷-13-基)甲基]-4,6-二叔丁基苯酚 Ae = Ca,1；Sr,2；Ba,3)。通过 X 射线衍射确定了 1、2、[(4)(2)]、6 和 [(7)(2)] 的分子结构。这些突出了 Ae⋅⋅⋅H-Si 内部β-桥联相互作用，这在稳定 [{LO(i)}Ae-N(SiMe(2)H)(2)] 配合物方面发挥了关键作用，使其免受配体重排反应的影响，而不是常规的 [{LO(i)}Ae-N(SiMe(3))(2)]。脉冲梯度自旋回波 (PGSE) NMR 测量表明，1、4、6 和 7 在溶液中均为单体。配合物 1-7 高效地介导 L-丙交酯的开环聚合（ROP），在 25°C 下以可控方式将高达 5000 个当量的单体转化。在使用高达 100 当量的外源 9-蒽甲醇或苄醇或炔丙醇作为转移剂进行的不朽 ROP 中，催化剂的活性随金属尺寸的增加而增加（1<2<3）。对于基于 Ca 的配合物，辅助配体的增强供电子能力有利于催化剂活性（1>6>4≈5）。醇的性质对二元催化剂体系 1/ROH 的活性影响不大；在所有情况下，控制和端基保真度都非常出色。在 L-LA 的活性 ROP 中，HC≡CCH(2)O(-)引发基团（如 7 中的基团）比 N(SiMe(2)H)(2)(-)或 N(SiMe(3))(2)(-)（如 6 或 [{LO(4)}Ca-N(SiMe(3))(2)] (B)）优越。
