Lanthanide Metallocene Reactivity with Dialkyl Aluminum Chlorides:  Modeling Reactions Used to Generate Isoprene Polymerization Catalysts

Abstract

The well-defined coordination environment of trivalent [(C5Me5)2Ln]+ complexes has been used to examine the reaction chemistry of the lanthanide carboxylate and R2AlCl (R = Me, Et, iBu) components used in the preparation of lanthanide-based diene polymerization catalysts. Each of the R2AlCl reagents can replace a carboxylate ligand with chloride in reactions with [(C5Me5)2Sm(O2CC6H5)]2, but instead of forming a simple chloride complex like [(C5Me5)2SmCl]3, bimetallic lanthanide aluminum dichloro complexes (C5Me5)2Sm(μ-Cl)2AlR2 are generated by ligand redistribution. These bis(chloride)-bridged complexes are also readily formed from the divalent precursor (C5Me5)2Sm(THF)2 and R2AlCl. However, the analogous reaction between (C5Me5)2Sm(THF)2 and Et3Al gives (C5Me5)2Sm(THF)(μ-η2-Et)AlEt3, which contains the first Ln(III)−(η2-Et) linkage, a coordination mode that differentiates Et from Me. To determine if mixed mono-chloride/alkyl-bridged (C5Me5)2Ln(μ-Cl)(μ-R)AlR2 complexes can be isolated, (C5Me5)2Y(μ-Cl)YCl(C5Me5)2 was reacted with R3Al. These reactions form [(C5Me5)2Y(μ-Cl)(μ-R)AlR2] x complexes, but again there is a differentiation on the basis of R: the Me complex is a dimer and the others are monomers. (C5Me5)2Y(μ-Cl)2AlR2 complexes were similarly prepared for comparison with the mixed ligand species and for additional Me, Et, and iBu comparisons.

1,3-Diene Polymerization Mediated by Homoleptic Tetramethylaluminates of the Rare-Earth Metals

“…It is presumed, that R2AlCl replaces AlMe3 in the aluminate precursors and that larger clusters form by chlorido bridging, as it has been observed for lanthanide half-sandwich complexes carrying tetramethylaluminate moieties and for lanthanidocene model systems for Ziegler-Natta catalysis [4,32,[34][35][36], as well as for lanthanide mixed silylamide/chloride complexes [13]. With release of R2AlMe multimetallic species are formed (Scheme 2) [4,13,35].…”

1,2 Enriched polymerization of isoprene by cobalt complex carrying aminophosphory fused (PN3) ligand

“…The mechanism for the catalytic result is proposed in Scheme and can be explained in the light of some of the more relevant studies presented in the literatures . Activated by Mg n‐ Bu 2 , a heterobimetallic intermediate M1 stabilized by F and butyl bridges well known for Ziegler‐Natta system could be formed, whose analogues were also reviewed for transition metals catalyzed organic transformation reactions . The monomer is then activated on the cobalt center probably via η 4 ‐1,4 coordination and then inserted to Co‐C( n‐ Bu), forming anionic allylic polymer end.…”

Reactivity of Yttrium Carboxylates Toward Alkylaluminum Hydrides

“…Metallocene‐based carboxylates have been successfully exploited as model systems for probing the reactivity of rare‐earth‐metal carboxylates toward alkylaluminum chlorides7 and trialkylaluminum compounds 8. As part of our ongoing interest in the reactivity of alkylaluminum hydrides toward rare‐earth‐metal carboxylates, herein, we present the utilization of a Cp*‐supported yttrocene‐benzoate complex as another model system (Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl).…”