scholarly journals C–H-Bond Activation and Isoprene Polymerization Studies Applying Pentamethylcyclopentadienyl-Supported Rare-Earth-Metal Bis(Tetramethylaluminate) and Dimethyl Complexes

Molecules ◽  
2019 ◽  
Vol 24 (20) ◽  
pp. 3703 ◽  
Author(s):  
Christoph O. Hollfelder ◽  
Melanie Meermann-Zimmermann ◽  
Georgios Spiridopoulos ◽  
Daniel Werner ◽  
Karl W. Törnroos ◽  
...  

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].

2019 ◽  
Vol 25 (30) ◽  
pp. 7298-7302 ◽  
Author(s):  
Christoph O. Hollfelder ◽  
Lars N. Jende ◽  
Hans‐Martin Dietrich ◽  
Klaus Eichele ◽  
Cäcilia Maichle‐Mössmer ◽  
...  

2008 ◽  
Vol 41 (24) ◽  
pp. 9565-9569 ◽  
Author(s):  
Andrea Ravasio ◽  
Cristina Zampa ◽  
Laura Boggioni ◽  
Incoronata Tritto ◽  
Julia Hitzbleck ◽  
...  

2010 ◽  
Vol 695 (25-26) ◽  
pp. 2794-2797 ◽  
Author(s):  
Waldemar Fegler ◽  
Teruhiko Saito ◽  
Kazushi Mashima ◽  
Thomas P. Spaniol ◽  
Jun Okuda

Polymers ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 836
Author(s):  
Ge Guo ◽  
Xiaolu Wu ◽  
Xiangqian Yan ◽  
Li Yan ◽  
Xiaofang Li ◽  
...  

A series of fluorenyl-based constrained-geometry-configuration (CGC) allyl-type rare earth metal monoalkyl complexes bearing the divalent anionic η3:η1-tert-butyl(dimethylfluorenylsilyl)amido (η3:η1-FluSiMe2NtBu) ligand (η3:η1-FluSiMe2NtBu)Ln(CH2SiMe3)(THF)2 (1–3) have been synthesized via the alkane elimination reaction between the FluHSiMe2NHtBu ligand and rare earth metal tri(trimethylsilylmethyl) complexes Ln(CH2SiMe3)3(THF)n. Their structures are characterized by means of NMR spectrum, elemental analyses, and X-ray diffraction. These complexes 1–3 are isostructural and isomorphous, and each of them adopts a distorted-trigonal-bipyramidal configuration containing one η3:η1-FluSiMe2NtBu ligand, one CH2SiMe3 ligand, and two THF molecules. Unlike traditional CGC allyl-type rare earth metal complexes showing no or low activity and regio-/stereoselectivity in styrene or MMA polymerization, these complexes 1–3 exhibit high catalytic activities and/or high regio-/stereoselectivities in the cis-1,4-polymerization of isoprene and myrcene or in the syndiotactic polymerization of styrene under the aid of different activators (borate or borane) and AlR3. The in situ 1H NMR spectra suggest that the exchanges of chelating ligands such as alkyl groups and divalent anionic η3:η1-FluSiMe2NtBu ligands between rare earth metal centers and Al centers result in the formation of a heterobimetallic tetraalkylaluminate complex R2Al(μ-R)2Ln(R)(μ-R)2AlR2, which is activated by activators to form a divalent cationic species [Ln(μ-R)2AlR2]2+ as a catalytically active species in the coordination–insertion polymerization of olefins.


2019 ◽  
Vol 25 (18) ◽  
pp. 4821-4832 ◽  
Author(s):  
Damir Barisic ◽  
Dennis A. Buschmann ◽  
David Schneider ◽  
Cäcilia Maichle‐Mössmer ◽  
Reiner Anwander

2020 ◽  
Vol 49 (6) ◽  
pp. 2004-2013 ◽  
Author(s):  
Dominic Diether ◽  
Melanie Meermann-Zimmermann ◽  
Karl W. Törnroos ◽  
Cäcilia Maichle-Mössmer ◽  
Reiner Anwander

Steric pressure enforces the formation of dianionic and trianionic pincer-type ligands involving a rare alkylidene moiety in the latter case.


Sign in / Sign up

Export Citation Format

Share Document