Unsupported gallatabenzene via rare-earth-metal pentadienyl complexes

Abstract

The treatment of rare-earth-metal aluminata/gallata complexes with the Lewis acids AlMe₃ and ECl₃ (E = Al, Ga) gives access to new group 13 metallacyclic fragments. The reaction of the mixed yttrocene (C₅Me₅)Y(μ-Me)(AlC₅H₃Me-1-tBu₂-3,5) with AlMe₃ produced the bis(heteroaluminato) complex (C₅Me₅)Y[(3,5-tBu₂C₅H₃AlMe₂)(AlMe₃)]. The reaction of (C₅Me₅)Y(μ-Me)(AlC₅H₃Me-1-tBu₂-3,5) with AlCl₃ gave an organoaluminium entity with a central chair conformation of alternating aluminium and carbon atoms. Alternatively, the new Al₃ entity can be interpreted as a monoanionic aluminatabenzene moiety [(1-Me-3,5-tBu₂-C₅H₃Al)(THF)], which is stabilized by the cationic dialuminium fragment [3,5-tBu₂-C₅H₃(AlMe)₂]. The donor (THF) free Ga₃ homologue was obtained from bis(gallata) “open” lutocene (1-Me-3,5-tBu₂C₅H₃Ga)(μ-Me)Lu(1-Me-3,5-tBu₂C₅H₃Ga) and GaCl₃. The reaction of the bis(gallata) lutetium sandwich complex with KOtBu gave the potassium coordination polymer [K(1-Me-3,5-tBu₂C₅H₃Ga)(THF)]_n, which can be converted to the separated ion pair [(1-Me-3,5-tBu₂C₅H₃Ga)][K([2.2.2]crypt)] by addition of the [2.2.2]cryptand. The isolated compounds were analyzed by ¹H, ¹³C, ⁸⁹Y, and variable temperature ¹H NMR spectroscopy, SC-XRD, IR spectroscopy, and elemental analysis. The bonding of the unsupported gallatabenzene moiety was further investigated by DFT calculations.