When activated with fluorinated borate cocatalysts the trimetallic complexes [Cp*LnMe2]3 (Ln=Y, Lu; Cp*=C5Me5) promote efficiently the formation of high‐cis polybutadiene. Respective polyisoprenes instead bear much less pronounced microstructures, but reveal crosslinked products at lower polymerization temperatures. Varying the amount of cocatalyst, the emerging active species were examined by NMR spectroscopic techniques (incl. 1H DOSY). The occurrence of donor‐solvent and thermally induced degradation products of the highly reactive precatalyst [Cp*YMe2]3 and derived catalyst species was revealed by the elucidation of methylidene clusters [Cp*3Y3Me4(CH2)(thf)2] and [Cp*6Y6Me4(CH2)4], as well as [(Cp*Y)2Me2(N(Me)2(C6H4)]n[B(C6F5)4]n, implying a multimetallic active species.

[(C5Me5)­LnMe2]3 (Ln = Y, Lu) dissolve readily in a n-hexane/toluene mixture upon addition of 3 equiv of the organoaluminum boryl compound [Me2Al­{B­(NDippCH)2}]2 (Dipp = C6H3 iPr2-2,6). The half-sandwich complexes (C5Me5)­Ln­[(AlMe3)­{B­(NDippCH)2}]2 thus formed display unsymmetrical heteroaluminate coordination not only in the solid state but also at lower temperatures in solution, which is distinct from the behavior of the homoaluminate congeners (C5Me5)­Ln­(AlMe4)2. The effect of homo- versus heteroaluminate coordination is assessed in the coordinative polymerization of isoprene.

During the past two decades homoleptic tetramethylaluminates of the trivalent rare-earth metals, Ln(AlMe 4 ) 3 , have emerged as useful components for efficient catalyst design in the field of 1,3-diene polymerization. Previous work had focused on isoprene polymerization applying Ln

Rare-earth-metal half-sandwich allyl complexes bearing an amino-functionalized cyclopentadienyl ligand (Cp NMe2 = 1-[2-(N,N-dimethylamino)ethyl]-2,3,4,5-tetramethylcyclopentadienyl) were synthesized in a two-step saltmetathesis reaction. Treatment of LnCl 3 (THF) x with LiCp NMe2 , followed by an in situ reaction with the Grignard reagent C 3 H 5 MgCl, generated the bis(allyl) half-sandwich complexes Cp NMe2 Ln(η 3 -C 3 H 5 ) 2 only for the smaller rare-earth metals (Ln = Y, Ho, Lu) in good yields (82−88%). In case of the larger neodymium, the dimeric mono(allyl) chlorido half-sandwich complex [Cp NMe2

No 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].

No abstract