Hollfelder CO, Meermann-Zimmermann M, Spiridopoulos G, Werner D, Törnroos KW, Maichle-Mössmer C, Anwander R. C-H-Bond Activation and Isoprene Polymerization Studies Applying Pentamethylcyclopentadienyl-Supported Rare-Earth-Metal Bis(Tetramethylaluminate) and Dimethyl Complexes.
Molecules 2019;
24:molecules24203703. [PMID:
31618971 PMCID:
PMC6832758 DOI:
10.3390/molecules24203703]
[Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Revised: 10/02/2019] [Accepted: 10/03/2019] [Indexed: 11/29/2022] Open
Abstract
As previously shown for lutetium and yttrium, 1,2,3,4,5-pentamethylcyclopentadienyl (C5Me5 = Cp*)-bearing rare-earth metal dimethyl half-sandwich complexes [Cp*LnMe2]3 are now also accessible for holmium, dysprosium, and terbium via tetramethylaluminato cleavage of [Cp*Ln(AlMe4)2] with diethyl ether (Ho, Dy) and tert-butyl methyl ether (TBME) (Tb). C–H-bond activation and ligand redistribution reactions are observed in case of terbium and are dominant for the next larger-sized gadolinium, as evidenced by the formation of mixed methyl/methylidene clusters [(Cp*Ln)5(CH2)(Me)8] and metallocene dimers [Cp*2Ln(AlMe4)]2 (Ln = Tb, Gd). Applying TBME as a “cleaving” reagent can result in both TBME deprotonation and ether cleavage, as shown for the formation of the 24-membered macrocycle [(Cp*Gd)2(Me)(CH2OtBu)2(AlMe4)]4 or monolanthanum complex [Cp*La(AlMe4){Me3Al(CH2)OtBu}] and monoyttrium complex [Cp*Y(AlMe4)(Me3AlOtBu)], respectively. Complexes [Cp*Ln(AlMe4)2] (Ln = Ho, Dy, Tb, Gd) and [Cp*LnMe2]3 (Ln = Ho, Dy) are applied in isoprene and 1,3-butadiene polymerization, upon activation with borates [Ph3C][B(C6F5)4] and [PhNHMe2][B(C6F5)4], as well as borane B(C6F5)3. The trans-directing effect of AlMe3 in the binary systems [Cp*Ln(AlMe4)2]/borate is revealed and further corroborated by the fabrication of high-cis-1,4 polybutadiene (97%) with “aluminum-free” [Cp*DyMe2]3/[Ph3C][B(C6F5)4]. The formation of multimetallic active species is supported by the polymerization activity of pre-isolated cluster [(Cp*Ho)3Me4(CH2)(thf)2].
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