Selective and catalytic carbon dioxide and heteroallene activation mediated by cerium N-heterocyclic carbene complexes

Abstract

A series of rare earth complexes of the form Ln(LR)3 supported by bidentate ortho-aryloxide–NHC ligands are reported (LR = O(o-C6H2–tBu2-2,6-CN(C2H2)NR); R = iPr, tBu, Mes; Ln = Ce, Sm, Eu).

Dicerium letterbox-shaped tetraphenolates: f-block complexes designed for two-electron chemistry

“…Anionic oxygen-donor alkoxide and aryloxide ligands have shown most use in stabilising the higher oxidation state in the Ce III/IV redox couple, 7,12,[17][18][19][20][21] and applications of cerium reagents in molecular chemistry have largely been focused on mononuclear cerium complexes. 6,20,22 We have used functionalised aryloxide ligands to support cerium(III) catalysts [Ce(L R ) 3 ] (L R = ortho-NHC-aryloxide = O(o-C 6 H 2 -t Bu 2 -2,6-CN(C 2 H 2 ) NMes)) for the formation of cyclic carbonates from CO 2 and epoxides, 23 and cerium(IV) catalysts [Me 3 SiOCe(OArP) 3 ], (OArP = ortho-phosphino-aryloxide = OC 6 H 2 -6-t Bu-4-Me-2-PPh 2 ) for the ring-opening polymerisation (ROP) of the bio-renewable ester L-lactide. 3 The development of systems that can combine two cerium cations in a molecule has received considerably less attention.…”

Recent Advances in Rare Earth Complexes Containing N-Heterocyclic Carbenes: Synthesis, Reactivity, and Applications in Polymerization

“…On the other hand, activation of CS 2 by 30 solely involved the NHC moiety. Another class of homoleptic Ln-tris(aryloxotethered NHC) complexes, Ln(Arylo-NHC) 3 (Ln = Ce, Sm, and Eu) (31)(32)(33)(34)(35), were also synthesized by treatment of the corresponding ortho-aryloxide imidazolium salt proligand with KN(SiMe 3 ) 2 followed by salt metathesis with LnCl 3 (THF) n (Figure 9) [61]. The Ce complexes 31 and 34 were capable of activating CO 2 and its isoelectronic heteroallenes using the Ce-C(NHC) bonds.…”

“…A series of CCC-pincer 2,6-xylenyl bis(carbene)-ligated Ln dibromides (60)(61)(62)(63)(64)(65)(66)(67)(68)(69) were synthesized via the treatment of imidazolium dibromide proligands and LnCl 3 with dropwise addition of n BuLi (Figure 15) [79,80]. The Y, Nd, Gd, Dy, and Ho complexes exhibited high activity and cis-1,4 selectivity (99.6%, 25 • C) in the polymerization of isoprene under activation with AlR 3 (R = Me, Et, i Bu) and [Ph 3 C][B(C 6 F 5 ) 4 ], while the others were inactive.…”

Effective and Reversible Carbon Dioxide Insertion into Cerium Pyrazolates

“…[16] Recently, cerium, the most abundant rare-earth element, has gained attention for CO 2 activation. [8,[17][18][19] For example, while the hydrogen-bonded Ce IV oxo complex [(L OEt ) 2 [17] ortho-NHC-substituted aryloxide Ce III complexes (NHC = N-heterocyclic carbene) insert CO 2 into the Ce À C NHC bond in a semireversible manner, and catalytically form propylene carbonate from propylene oxide. [18,19] Bulky cyclopentadienyl (Cp) derivatives (e.g.…”

“…[8,[17][18][19] For example, while the hydrogen-bonded Ce IV oxo complex [(L OEt ) 2 [17] ortho-NHC-substituted aryloxide Ce III complexes (NHC = N-heterocyclic carbene) insert CO 2 into the Ce À C NHC bond in a semireversible manner, and catalytically form propylene carbonate from propylene oxide. [18,19] Bulky cyclopentadienyl (Cp) derivatives (e.g. Ln-(C 5 Me 5 ) 3 ) were shown to accommodate CO 2 insertion in a unidirectional manner, thereby forming very stable carboxylato moieties through a h 5 -to-h 1 switch in the C 5 Me 5 coordination (cf.…”