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4721262 
Journal Article 
Fluorenyl Half-Sandwich Bis(tetramethylaluminate) Complexes of the Rare-Earth Metals: Synthesis, Structure, and Isoprene Polymerization 
Diether, D; Tyulyunov, K; Maichle-Moessmer, C; Anwander, R 
2017 
1 
Organometallics
ISSN: 0276-7333
EISSN: 1520-6041 
36 
23 
4649-4659 
WOS:000418109700019 
Aiming at half-sandwich complexes of the type (Flu(R))Ln(AlMe4)(2), homoleptic tetramethylaluminates Ln(AlMe4)(3) (Ln = Y, La, Nd, and Lu) were treated with equimolar amounts of R-substituted potassium fluorenyls. The salt metathesis reaction of La(AlMe4)(3) with K(Flu) (Flu = fluorenyl = C1(3)H(9)) and K(Flu(tBu)) (Flu(tBu) = di(tert-butyl) fluorenyl) selectively gave the desired half-sandwich complexes (Flu(R))La(AlMe4)(2). The corresponding reactions of Y(AlMe4)(3) with K(Flu)/K(Flu(tBu)) and Lu(AlMe4)(3) with K(Flu(tBu)) gave mixtures of half-sandwich and sandwich complexes, while treatment of Lu(AlMe4)(3) with K(Flu) produced only the lutetocene complex (Flu)(2)Lu(AlMe4). Sterically more demanding 1-trimethylsilyl fluorenyl (Flu(Si)) allowed for the isolation of half-sandwich complexes for the entire Ln(III) size range (Ln = La, Nd, Y, and Lu), in crystalline yields up to 94%. Upon activation with routinely employed borate or borane activators [Ph3C][B(C6F5)(4)], [PhNMe2H][B(C6F5)(4)], and B(C6F5)(3), highly active initiators for isoprene polymerization were obtained. The catalyst activity as well as molecular weight (distribution) and stereoregularity of the obtained polyisoprenes are governed by the rare-earth metal size, fluorenyl ligand, and cocatalyst: highest activity for La/Flu(Si)/[Ph3C][B(C6F5)(4)], lowest M-w/M-n = 1.11 for La/Flu/[PhNMe2H][B(C6F5)(4)], maximum trans-1,4 selectivity = 85% for La/Flu(tBu)/[PhNMe2H][B(C6F5)(4)], maximum cis-1,4 selectivity = 78% for Lu/Flu(Si)/[Ph3C][B(C6F5)(4)]. The formations of the active species were investigated by NMR spectroscopy revealing not only established cationization pathways but also fluorenyl abstraction in lanthanum complexes (Flu)La(AlMe4)(2) and (Flu(tBu))La(AlMe4)(2) by trityl borate [Ph3C][B(C6F5)(4)]. The reaction of half-sandwich complexes (Flu(R))Ln(AlMe4)(2) with equimolar amounts of Me2AlCl did not give access to catalytically active species. Crystallization of binary mixtures (Flu(Si))Y(AlMe4)(2)/Me2AlCl in distinct molar ratios of 1:1 and 1:1.7 yielded complexes [(Flu(Si))Y(AlMe4)(mu-Cl)](2) and (Flu(Si))(6)Y6Cl12, respectively.