Ligand Recognition Processes in the Formation of Homochiral C₃‐Symmetric LnL₃ Complexes of a Chiral Alkoxide

Abstract

The reaction of a chiral racemic bidentate ligand HL1 (tBu2P(O)CH2CH(tBu)OH) with mid to late trivalent lanthanide cations affords predominantly homochiral lanthanide complexes (RRR)-[Ln(L1)3] and (SSS)-[Ln(L1)3]. A series of reactions are reported that demonstrate that the syntheses are under thermodynamic control, and driven by a ligand 'self-recognition' process, in which the large asymmetric bidentate L1 ligands pack most favourably in a C3 geometry around the lanthanide cation. The synthesis of bis(L1) adducts [Ln(L1)2X] (X=N(SiMe3)2, OC6H3tBu-2,6) is also reported. Analysis of the diastereomer mixtures shows that homochiral (L1)2 complexes are favoured but to a lesser extent. The complexes Ln(L1)3 and [Ln(L1)2(OC6H3tBu-2,6)] have been studied as initiators for the polymerization of epsilon-caprolactone and its copolymer with lactide, glycolide and its copolymer with lactide, and epsilon-caprolactam.

Lanthanide phosphine oxide complexes

“…The structure has a 2-dimensional pore network and the DMF and two water molecules are located in the void spaces. The hydrogen uptake was particularly high (1.96%wt) for this compound and similarly high values for the uptake of Tris-chelate phosphine oxide-alkoxide complexes [Ln( t Bu 2 P(O) CH 2 CHO t Bu) 3 ] with Ln = Y, Eu, Er and Yb have been synthesised by reaction of the alcohol with Ln(N(SiMe 3 ) 2 ) 3 at À80°C [80]. The smaller lanthanides required longer for the reaction to proceed to completion.…”

Making a Right or Left Choice: Chiral Self-Sorting as a Tool for the Formation of Discrete Complex Structures

“…The question of whether the distribution of products is thermodynamically or kinetically controlled has also been addressed. 109 Thus, the (R,R,R)-(Y(50) 3 ) complex has been equilibrated in the presence of the racemic ligand rac-50 and exchange of ligands has been observed, indicating a thermodynamically controlled process. rac-Y(50) 3 has been applied as a catalyst of the polymerization of rac-lactide, leading to highly isotactic (composed of monomers of the same chirality) polymeric chains.…”

Ring opening polymerisation of lactide with uranium(iv) and cerium(iv) phosphinoaryloxide complexes

“…6 Although often overlooked due to misconceptions of scarcity and excessive oxophilicity, the f-block cations possess a unique capability to tune the ROP performance due to the available range of size and Lewis acidity. [7][8][9][10] This variability is difficult for other metals; the propensity of In III to adopt a coordination number of 5 limited the scope in our system. 11 While rare, both Ce III and Ce IV are known to initiate ROP reactions, and judicious choice of ligands can dramatically alter activity.…”