Coordination and Reactivity Diversity ofN-Piperidineethyl-Functionalized Indenyl Ligands:  Synthesis, Structure, Theoretical Calculation, and Catalytic Activity of Organolanthanide Complexes with the Ligands

Abstract

The interactions of N-piperidineethyl-functionalized indene compounds 1-R-3-C 5 H 10 NCH 2 CH 2 C 9 H 6 (R ) H-(1), Me 3 Si-( 2)) with lanthanide(III) amides [(Me 3 Si) 2 N] 3 Ln(µ-Cl)Li(THF) 3 (Ln ) Yb, Eu, Sm, Nd) were studied. The results indicated that the ligands and reductive potentials of Ln 3+ /Ln 2+ have an influence on the reaction patterns and the coordination mode of the indenyl ligands with the central metals. Reactions of [(Me 3 Si) 2 N] 3 Ln(µ-Cl)Li(THF) 3 (Ln ) Yb, Eu) with 2 equiv of corresponding indene compounds 1-R-3-C 5 H 10 NCH 2 CH 2 C 9 H 6 (R ) H-(1), Me 3 Si-(2)) produced organolanthanide(II) complexes [η 5 :η 1 -C 5 H 10 NCH 2 CH 2 C 9 H 6 ] 2 Ln II (Ln ) Yb (3), Eu (5)) and novel organolanthanide(II) complexes with general formula [η 4 :η 4), Eu ( 6)), and a new highly conjugated bis(N-piperidineethyl)dibenzofulvalene, (C 5 H 10 NCH 2 CH 2 C 9 H 5 ) 2 ( 9), was unexpectedly isolated as a byproduct in the preparation of 6, indicating the ligands' effects on the coordination and reactivity patterns. Theoretical calculations on ytterbium(II) complexes having indenyl ligands indicated that the indenyl hapticity depends on the strain, steric, and electronic effects. Treatment of lanthanide(III) amides [(Me 3 Si) 2 N] 3 Ln(µ-Cl)Li(THF) 3 (Ln ) Sm, Nd) with 2 equiv of C 5 H 10 NCH 2 CH 2 C 9 H 7 (1) afforded indenyl lanthanide(III) complexes with general formula [η 3 -C 5 H 10 NCH 2 CH 2 C 9 H 6 ] 2 Ln III [η 3 :η 1 -C 5 H 10 NCH 2 CH 2 C 9 H 6 ] (Ln ) Sm (7), Nd (8)). The shortest distances involving the nonbridging atoms of the C 5 portions of the indenyl groups indicated an allyl-like nature of the ligand-to-metal coordination. The interaction of [(Me 3 Si) 2 N] 3 Sm III (µ-Cl)Li-(THF) 3 with 2 equiv of 1-Me 3 Si-3-C 5 H 10 NCH 2 CH 2 C 9 H 6 (2) produced an unexpected bis(N-piperidineethyl)dibenzofulvalene (C 5 H 10 NCH 2 CH 2 C 9 H 5 ) 2 (9) and other unidentified solids, suggesting the ligands' influence on the reactivity patterns. All the compounds were fully characterized by spectroscopic methods and elemental analyses. The structures of compounds 4, 7, 8, and 9 were additionally determined by X-ray diffraction study. The catalytic activity of the organolanthanide complexes 3-8 on MMA polymerization was examined. It was found that the π-bonded tris(N-piperidineethylindenyl)lanthanide(III) complexes 7 and 8 exhibit unexpected good catalytic activity on MMA polymerization, and complex 7 also showed an unexpected high catalytic activity on ε-caprolactone polymerization. It was found that the catalytic activity of the complexes depended on the polymerization conditions. The solvents, temperatures, substituted groups, and lanthanide ionic radii effects on the catalytic activity of the complexes were examined.

New Insights into the Polymerization of Methyl Methacrylate Initiated by Rare‐Earth Borohydride Complexes: A Combined Experimental and Computational Approach

“…[21] Other complexes, which include allyl, [22] alkyl, [23][24][25] lanthanocene, silylene-bridged azaallyl, [26] indenyl, [27] amido, [24,[28][29][30][31] thiolato, [32] halogeno, [33][34][35] or divalent [31,36,37] derivatives, have been reported as efficient initiators for MMA polymerization. Noteworthy is the bimetallic bisA C H T U N G T R E N N U N G (enolato)samariumA C H T U N G T R E N N U N G (III) initiator, generated in situ from the coupling of a radical anion species formed by one-electron transfer from a samarocene catalyst, such as [SmA C H T U N G T R E N N U N G (Cp*) 2 …”

Differences in the cyclometalation reactivity of bisphosphinimine-supported organo-rare earth complexes

“…hydroamination, 8-16 hydrosilylation, 10,[16][17][18][19][20] hydrophosphination, [21][22][23][24] hydroboration, 25,26 and hydroalkoxylation [27][28][29][30] ), and especially polymerization chemistry. [31][32][33][34][35][36][37][38][39][40][41][42][43][44] However, compared to research on organotransition-metal species, the study of rare earth complexes remains much less explored. For instance, stabilization of rare earth organometallic complexes has traditionally focused on simple carbocyclic frameworks, 45 particularly cyclopentadienyl motifs.…”

Mixed ligands supported yttrium alkyl complexes:

“…Indene (Ind-H) has been demonstrated to be a more sterically demanding yet planar p ligand [15]. The differences of the steric and electronic properties between indenyl and cyclopentadienyl moieties would be reflected in the molecular structure and reactivity of the corresponding complexes.…”