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].

Adduct complexes Ga6(μ-CH2)9(DMAP)3(THF) and Ga8(μ-CH2)12(PEt3) x (x = 4 and 6) could be obtained upon crystallization of Ga8(CH2)12 from THF/DMAP (hard Lewis bases) and PEt3 (soft Lewis base), respectively. Mixed methyl/methylene {Ga4} species with either bridging aryloxy, thiophenolato, or arylamido ligands were accessible via the treatment of Ga8(CH2)12 with phenols (HOC6H2Me3-2,4,6 and HOC6H3Me2-2,6), thiophenol HSC6H2Me3-2,4,6, and anilines (H2NC6H2Me3-2,4,6 and H2NC6H3Me2-2,6). Such tetrametallic complexes Ga4(μ2-CH2)2(CH3)4(μ2-XAr)4 (X = O, S, NH) are isostructural, displaying an adamantane-like core structure. The sterically more demanding phenol HOC6H3 tBu2-2,6 afforded the {Ga5} cluster Ga5(μ2-CH2)6(OC6H3 tBu2-2,6)3(THF)2 with the gallium centers exclusively bridged by methylene groups. Treatment of Ga8(CH2)12 with other protic substrates HOR/H2NR′, including HOCH2 tBu, HOSi­(OtBu)3, H2NC6H3 iPr2-2,6, and H2NSiPh3 point to a pronounced stereoelectronic dependency and intricacy of such transformations but provided helpful information about potential side products such as [(CH3)2Ga­(μ-X)]2 (X = OR, HNR′) and reaction intermediates. Efficient methylene → imido transformations using Ga8(CH2)12/aniline mixtures could not be implemented.