Bis(guanidinate) Alkoxide Complexes of Lanthanides: Synthesis, Structures and Use in Immortal and Stereoselective Ring‐Opening Polymerization of Cyclic Esters

Abstract

A series of new bis(guanidinate) alkoxide Group 3 metal complexes [Ln((Me3Si)2NC(NiPr)2)2(OR)] (R=OtBu, Ln=Y, Nd, Sm, Lu; R=OiPr, Ln=Y, Nd, Lu) has been synthesized. X-ray structural determinations revealed that bis(guanidinate) tert-butoxides are monomeric complexes. The isopropoxide complex [Y((Me3Si)2NC(NiPr)2)2(OiPr)] undergoes slow decomposition in solution, to afford the unusual dimeric amido complex [(Y((Me3Si)2NC(NiPr)2)2(mu-N(iPr)C triple chemical bond N))2]. Complexes [Ln((Me3Si)2NC(NiPr)2)2(OR)] (R=OtBu, Ln=Y, Nd, Sm, Lu; R=OiPr, Ln=Y, Nd, Lu) are active catalysts/initiators for the ROP of rac-lactide and rac-beta-butyrolactone under mild conditions. Most of those polymerizations proceed with a significant degree of control. Bis(guanidinate) alkoxides appear to be well suited for achieving immortal polymerization of lactide, through the introduction of large amounts of isopropanol as a chain-transfer agent. The synthesized complexes are able to promote the stereoselective ROP of rac-beta-butyrolactone to afford syndiotactic poly(hydrobutyrate) through a chain-end control mechanism, while they are surprisingly non-stereoselective for the ROP of lactide under strictly similar conditions.

Bis(phosphinimino)methanide Borohydride Complexes of the Rare‐Earth Elements as Initiators for the Ring‐Opening Polymerization of ε‐Caprolactone: Combined Experimental and Computational Investigations

“…[21] In the 1980s Mirsaidov and co-workers developed a more convenient approach starting from LnCl 3 (Ln = La, Ce, Pr, Nd, Sm) and NaBH 4 . [22][23][24] Later on, greater value was given to these original species in the promotion of rare-earth borohydride organometallic chemistry [25][26][27][28] and in their use as efficient catalysts for the (co)polymerization of ethylene, [29][30][31] isoprene, [31][32][33][34][35] styrene, [34,36] and some polar monomers such as lactide, [37][38][39][40][41][42] e-caprolactone, [37][38][39][43][44][45][46][47][48][49][50][51][52] trimethylene carbonate, [52] and methyl methacrylate. [53][54][55][56][57] Also, some rare-earthmetal borohydride derivatives such as metallocenes, [31,46] mono-cyclopentadienyl complexes, …”

Lactide Polymerisation with Air‐Stable and Highly Active Zinc Complexes with Guanidine–Pyridine Hybrid Ligands

“…[19] The anionic guanidinate ligands have already been shown to stabilise lactide-polymerising complexes, but they are sensitive to moisture and air. [20,21] A related ligand class is represented by the 2-iminoimidazolines [22] which offer good donor properties and stabilise catalytically active complexes as well. [23] To improve the activity of guanidine-based zinc complexes we modified the ligand system by substituting one guanidine moiety by an amine group.…”

One‐Pot Synthesis of Lactide–Styrene Diblock Copolymers via Catalytic Immortal Ring‐Opening Polymerization of Lactide and Nitroxide‐Mediated Polymerization of Styrene

“…The so-called immortal ROP (iROP) pioneered by Inoue in the 1980s, which exploits the efficient chain transfer between growing polymer chains and an external protic agent, offers an efficient alternative route towards this goal. [28] A line of our current research focuses on the development of such productive and versatile catalytic systems, and we have reported effective two-component catalysts for the iROP of LA, [7,10,29] b-butyrolactone, [30] and trimethylene carbonate. [31] In this report, we describe the ready sequential synthesis of S-LA diblock copolymers via catalytic iROP of LA directly in styrene, acting first as a solvent and then as a reagent.…”

“…[1,4] Although tin(II) compounds are the industries' first choice of initiators for the ROP of cyclic esters because of their robustness and ease of use, drawbacks include a slow, poorly controlled mechanism and growing concerns revolving around the heavy tin element. These issues were partly circumvented by introduction of well-defined metallic initiators (based mostly on non-toxic zinc, [5][6][7] aluminum, [8] or group III metals [9][10][11] ) or organocatalysts [12] for the controlled, living ROP of LA. [13] Although PLLA is a highly versatile material with a good balance of physical and mechanical properties, its wide utilization as a commodity material has so far been hampered by limited availability and high production costs in comparison to traditional polyolefins.…”