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

Abstract

Using [Ga(C6 H5 F)2 ](+) [Al(OR(F))4 ](-) (1) (R(F) =C(CF3)3) as starting material, we isolated bis- and tris-η(6) -coordinated gallium(I) arene complex salts of p-xylene (1,4-Me2 C6 H4), hexamethylbenzene (C6 Me6 ), diphenylethane (PhC2 H4 Ph), and m-terphenyl (1,3-Ph2 C6 H4): [Ga(1,4-Me2 C6 H4 )2.5 ](+) (2(+)), [Ga(C6 Me6 )2 ](+) (3(+)), [Ga(PhC2 H4 Ph)](+) (4(+)) and [(C6 H5 F)Ga(μ-1,3-Ph2 C6 H4)2 Ga(C6 H5 F)](2+) (5(2+)). 4(+) is the first structurally characterized ansa-like bent sandwich chelate of univalent gallium and 5(2+) 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(PhC2 H4 Ph)](+) [Al(OR(F))4](-) (4) and [(C6 H5 F)Ga(μ-1,3-Ph2 C6 H4)2 Ga(C6 H5 F)](2+) {[Al(OR(F) )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-Me3 C6 H3)2](+) [Al(OR(F))4](-) salt (6) (1,3,5-Me3 C6 H3 =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.

Exploring the Versatility of 7‐Alkynylcycloheptatriene Scaffolds Under π‐Acid Catalysis

“…The low yields observed for this transformation can be explained by polymerization side‐products detected in the crude 1 H NMR. This observation is not surprising since the intermediates to access the desired products contain an isobutylene moiety and this specific gallium(I) complex has been reported to catalyze the polymerization of isobutylene , …”

Gallium and Indium Compounds in Homogeneous Catalysis

“…60, 61 The latter complexes are highly active initiators for IB polymerization (with a catalyst loading down to 0.007 mol%) to afford highly reactive polyisobutylene (α-content > 60%, M n < 2300 g mol −1 ) in good yields (38). The nature of the arene ligands and the reaction temperature strongly affect the activity/control of the polymerization.…”

“…Thus, alkynes and indoles readily react in the presence of In(NTf 2 ) 3 (15-30 mol%) and excess methyldiphenylsilane to afford 2-or 3-alkylindoles (61). 89 A mechanistic proposal included the formation of an In(III) π-(3-indolyl)alkenyl species and a silane-water adduct as key intermediates for the reaction to occur.…”

Tris(1‐methyl‐imidazol‐2‐yl)phosphane Complexes of Pnictogen, Tetrel, and Triel Cations

“…This realization has enabled the development of complexes involving p‐block acceptors that are analogous to the vast array of transition‐metal complexes . For example, complexes of Ga + with cryptand, phosphine, pyrazine, or arene ligands, complexes of Ge 2+ with crown ethers, carbenes, ammonia, water, pyridines, phosphines, or isocyanides and complexes of As 3+ with pyridine derivatives demonstrate the diversity of this emerging coordination chemistry. Compounds containing Group 13 metals in the oxidation state +1 (M=Al, Ga, In) are susceptible to disproportionation to form M III and M 0 , as was observed for “GaI” in the presence of bipyridine to yield [Ga(bipy) 3 ][I] 3 and gallium metal .…”

“…This realizationh as enabled the development of complexes involving p-block acceptors that are analogous to the vast array of transition-metal complexes. [1] For example, complexes of Ga + with cryptand, [2] phosphine, [3] pyrazine, [4] or arene [5] ligands, complexes of Ge 2 + with crown ethers, [6] carbenes, [7] ammonia, water, [8] pyridines, [9] phosphines, [10] or isocyanides [11] andc omplexes of As 3 + with pyridine derivatives [12] demonstrate the diversity of this emerging coordination chemistry.C ompounds containing Group13 metals in the oxidation state + 1( M= Al, Ga, In) are susceptible to disproportionation to form M III and M 0 , [13] as was observed for "GaI" [14] in the presence of bipyridine to yield [Ga(bipy) 3 ][I] 3 and gallium metal. [15] Tricationic complexes of indiumh ave only been stabilized with oxygen donors, [16] such as crown ethers [17] and dimethyl sulfoxide, [18] or with 1,3,5-triaminocyclohexane, [19] and the only tricationic complexes of gallium [20] show elaborate EPR spectra.…”