Homoleptic Hexa and Penta Gallylene Coordinated Complexes of Molybdenum and Rhodium

The reactions of molybdenum(0) and rhodium(I) olefin containing starting materials with the carbenoid group 13 metal ligator ligand GaR (R = Cp*, DDP; Cp* = pentamethylcyclopentadienyl, DDP = HC(CMeNC₆H₃-2,6-ⁱPr₂)₂) were investigated and compared. Treatment of [Mo(η⁴-butadiene)₃] with GaCp* under hydrogen atmosphere at 100 °C yields the homoleptic, hexa coordinated, and sterically crowded complex [Mo(GaCp*)₆] (1) in good yields ≥50%. Compound 1 exhibits an unusual and high coordinated octahedral [MoGa₆] core. Similarly, [Rh(GaCp*)₅][CF₃SO₃] (2) and [Rh(GaCp*)₅][BAr^F] (3) (BAr^F = B{C₆H₃(CF₃)₂}₄) are prepared by the reaction of GaCp* with the rhodium(I) compound [Rh(coe)₂(CF₃SO₃)]₂ (coe = cyclooctene) and subsequent anion exchange in case of 3. Compound 2 features a trigonal bipyramidal [RhGa₅] unit. In contrast, reaction of excess Ga(DDP) with [Rh(coe)₂(CF₃SO₃)]₂ does not result in a high coordinated homoleptic complex but instead yields [(coe)(toluene)Rh{Ga(DDP)}(CF₃SO₃)] (4). The common feature of 2 and 4 in the solid state structure is the presence of short CF₃SO₂O···Ga contacts involving the GaCp* or rather the Ga(DDP) ligand. Compounds 1, 2, and 4 have been fully characterized by single crystal X-ray diffraction, variable temperature ¹H and ¹³C NMR spectroscopy, IR spectroscopy, mass spectrometry, as well as elemental analysis.