Synthesis and Reactivity of N‑heterocyclic Carbene Stabilized Lanthanide(II) Bis(amido) Complexes
journal contribution
posted on 2021-05-31, 20:14 authored by Zexiong Pan, Dongjing Gao, Chunqi Zhang, Lulu Guo, Jianfeng Li, Chunming CuiLanthanide amides are some of the
most important reagents and catalysts
in lanthanide organometallic chemistry because of their high stability.
Nevertheless, the readily available homoleptic Ln[N(SiMe3)2]n (n =
2, 3) complexes lack feasible strategies to modulate their reactivity
and selectivity. In this paper, monodentate N-heterocyclic carbenes
(NHCs) were applied to synthesize the divalent lanthanide bis(amido)
adducts 3,4Sm and 2–4,7,8Eu. σ-bond metathesis
reactions of (IiPr)2Yb[N(SiMe3)2]2 (2Yb; IiPr = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) with alkyne,
aniline, and phenol yielded alkynyl-bridged [(IiPr)Yb[N(SiMe3)2](μ-CCtBu)]2 (9), monomeric (IiPr)2Yb[N(SiMe3)2](NHAr1) (10; Ar1 = 2,6-iPr2C6H3), and (IiPr)2Yb(OAr2)2 (11; Ar2 = 2,6-tBu2-4-MeC6H2), respectively.
All of the NHC adducts of lanthanide(II) complexes were structurally
characterized by X-ray diffraction analysis. Moreover, 4Sm has high activity in the ROP of rac-LA without
an alcohol initiator. Preliminary mechanism studies reveal that the
ROP by 4Sm was initiated through a coordination–insertion
mechanism, which involves electrophilic activation of the monomer
by the metal center and nucleophilic attack of the amido group on
the activated monomer. These studies demonstrate that the diverse
NHCs could be potential ligands to not only suppress the ligand redistribution
of heteroleptic Ln(II) complexes but also modulate the reactivity
of lanthanide amide catalysts.
