Univalent Gallium Complexes of Simple and ansa-Arene Ligands: Effects on the Polymerization of Isobutylene.

Using [Ga(C H F) ] [Al(OR ) ] (1) (R =C(CF ) ) as starting material, we isolated bis- and tris-η -coordinated gallium(I) arene complex salts of p-xylene (1,4-Me C H ), hexamethylbenzene (C Me ), diphenylethane (PhC H Ph), and m-terphenyl (1,3-Ph C H ): [Ga(1,4-Me C H ) ] (2 ), [Ga(C Me ) ] (3 ), [Ga(PhC H Ph)] (4 ) and [(C H F)Ga(μ-1,3-Ph C H ) Ga(C H F)] (5 ). 4 is the first structurally characterized ansa-like bent sandwich chelate of univalent gallium and 5 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(PhC H Ph)] [Al(OR ) ] (4) and [(C H F)Ga(μ-1,3-Ph C H ) Ga(C H F)] {[Al(OR ) ] } (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-Me C H ) ] [Al(OR ) ] salt (6) (1,3,5-Me C H =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 (M =1000-3000 g mol ) 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.