Genuine Heteroleptic Complexes of Early Rare‐Earth Metals: Synthesis, X‐ray Structure, and Their Use for Stereospecific Isoprene Polymerization Catalysis

Abstract

Genuine heteroleptic neodymium and samarium complexes of formula [Cp*'Ln[(p-tol)NN](BH4)] (Cp*' = C5Me4(nPr), (p-tol)NN = (p-tol)NC(Me)CHC(Me)N(p-tol), Ln = Sm: 1a, Ln = Nd: 1b) have been synthesized for the first time. These unprecedented homologues of early lanthanocenes are prepared by a metathetic reaction between their monocyclopentadienylbisborohydrido precursors with the corresponding potassium diketiminate. Both complexes were obtained in good yields and were characterized by 1H NMR spectroscopy and elemental analysis. Complex 1 a has an non-solvated dimeric structure, as indicated by its crystallographic data. The chloroneodymium analogue [Cp*'Nd[(p-tol)NN](Cl)] (2b) was only obtained as a part of a mixture. Analysis of crystals of 2b by X-ray diffraction revealed a molecular structure very similar to that of 1a. Preliminary isoprene polymerization experiments were carried out with 1 b in the presence of an alkylmagnesium coactivator. The resulting bimetallic Nd/Mg system behaves as an efficient and highly stereospecific catalyst with the synthesis of trans-1,4-polyisoprene with more than 98% regularity. The control of the polymer structure is related to the steric hindrance around the lanthanide atom.

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, …”

Syntheses and Structures of Tris‐β‐Diketiminate Lanthanide Complexes and Their High Activity for Ring‐Opening Polymerization of ϵ‐Caprolactone and L‐Lactide

“…[1,2] A variety of derivatives, such as alkylides, [3] allylides, [4] amides, [2h,2k] borohydrides, [5] alkoxides, [6] and so on, was synthesized and found to serve as highly active initiators in homogeneous catalyses. In these catalytic reactions, β-diketiminate groups act as inert ancillary ligands to stabilize an active species.…”

Structural diversity in the borohydrido lanthanides series: First isolation and X-ray crystal structure of ionic

“…The Cp Ã0 ligand is neither bulky nor electron-rich enough to allow, like in the case of C 5 H i Pr 4 , the isolation of a non solvated compound [10,28]. With a less bulky di-substituted Cp ring [29], or a diketiminate (NRCR 0 Þ 2 CH [30], a dimeric structure is observed, whereas an anionic 'ate' complex, ðtmp 2 LnðBH 4 Þ À 2 (tmp = tetramethylphospholyl) was isolated in the electronic deficient phospholyl series [31].…”