Univalent Gallium Complexes of Simple and ansa-Arene Ligands: Effects on the Polymerization of Isobutylene.
Using [Ga(C6H5F)2]+[Al(ORF)4]-(1) (RF=C(CF3)3) as starting material, we isolated bis- and tris-η6-coordinated gallium(I) arene complex salts of p-xylene (1,4-Me2C6H4), hexamethylbenzene (C6Me6), diphenylethane (PhC2H4Ph), and m-terphenyl (1,3-Ph2C6H4): [Ga(1,4-Me2C6H4)2.5]+(2+), [Ga(C6Me6)2]+(3+), [Ga(PhC2H4Ph)]+(4+) and [(C6H5F)Ga(μ-1,3-Ph2C6H4)2Ga(C6H5F)]2+(52+). 4+is the first structurally characterized ansa-like bent sandwich chelate of univalent gallium and 52+the first binuclear gallium(I) complex without a GaGa bond. Beyond confirming the structural findings by multinuclear NMR spectroscopic investigations and density functional calculations (RI-BP86/SV(P) level), [Ga(PhC2H4Ph)]+[Al(ORF)4]-(4) and [(C6H5F)Ga(μ-1,3-Ph2C6H4)2Ga(C6H5F)]2+{[Al(ORF)4]-}2(5), featuring ansa-arene ligands, were tested as catalysts for the synthesis of highly reactive polyisobutylene (HR-PIB). In comparison to the recently published 1 and the [Ga(1,3,5-Me3C6H3)2]+[Al(ORF)4]-salt (6) (1,3,5-Me3C6H3=mesitylene), 4 and 5 gave slightly reduced reactivities. This allowed for favorably increased polymerization temperatures of up to +15 °C, while yielding HR-PIB with high contents of terminal olefinic double bonds (α-contents=84-93 %), low molecular weights (Mn=1000-3000 g mol-1) and good monomer conversions (up to 83 % in two hours). While the chelate complexes delivered more favorable results than 1 and 6, the reaction kinetics resembled and thus concurred with the recently proposed coordinative polymerization mechanism.
Albert-Ludwigs-Universität Freiburg, Institut für Anorganische und Analytische Chemie and Freiburger Materialforschungszentrum (FMF), Albertstr. 21, 79104 Freiburg (Germany).
Martin R
MR
Lichtenthaler
Steffen
S
Maurer
Robert J
RJ
Mangan
Florian
F
Stahl
Florian
F
Mönkemeyer
Julian
J
Hamann
Ingo
I
Krossing
NMR spectroscopy; density functional calculations; gallium; ligand effects; polymerization