Alkali metal compounds 1–12, with terpene-derived oximate ligands, have been prepared and fully spectroscopically characterized. For derivatives 1–9 aggregation processes are observed in solution. To disfavor these processes and decrease the nuclearity, derivatives 10–12 with crown ethers or cryptands were prepared, which are mononuclear in solution. The activity as ring-opening polymerization (ROP) promoters was assessed for compounds 1–12. In these studies, Na and K compounds proved to be very active and polymerized rac-lactide within minutes. In their activity, the aggregation processes have a clear effect and polymers with molecular weights higher than the theoretical weights are obtained, as a reflection of fewer accessible active centers. This effect is more pronounced at lower temperatures; however, the potassium compound 11, with a crown ether coordinated plus an extra anchoring point in the terpenoid ligand via a pyridine group, is not as heavily affected by the aggregation and is active even at −70 °C. In fact, this potassium compound can promote rac-lactide isoselective polymerization to give highly isotactic polymers, being one of the very few alkali-metal compounds reported that is able to induce such an isoselective process.

中文翻译：

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碱金属化合物与生物基配体作为等选择性丙交酯聚合的催化剂：催化剂聚集对聚合控制的影响

碱金属化合物1 - 12，用萜烯衍生的配体的肟酸，已经制备并完全光谱表征。对于衍生物1 – 9，在溶液中观察到聚集过程。到不利于这些过程和降低核性，衍生物10 - 12，制备与冠醚或穴状配体，这是在单核溶液。评估了化合物1 – 12作为开环聚合（ROP）促进剂的活性。在这些研究中，Na和K的化合物被证明是非常活跃并聚合外消旋-丙交酯在几分钟内。在其活性方面，聚集过程具有明显的效果，并且获得分子量高于理论重量的分子量的聚合物，这是较少可及的活性中心的反映。在较低温度下，这种影响更为明显。然而，具有冠醚配位并通过吡啶基团在萜类配体中具有额外锚固点的钾化合物11不受聚集的影响很大，甚至在-70°C时仍具有活性。实际上，该钾化合物可以促进外消旋-丙交酯的选择性聚合，以得到高度全同立构的聚合物，是报道的极少数能够诱导这种等选择过程的碱金属化合物之一。