Reactions of Transition Metal Carbonyl Dianions with (Organo)gallium Chlorides: Anionic Gallium Complexes of Chromium, Iron, and Manganese. Structure of [PPN]2{[(CO)4Fe−Ga(CH3)−Fe(CO)4]}

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Abstract
Salt elimination reactions between the divalent transition carbonyl metalates [L(CO)nM]2- (M = Cr, Mn, Fe; L = CO, NO; n = 3, 4) and the (organo)gallium halides ClaGaR3-a (R = CH3, CH2CH3; a = 1, 2, 3) as well as the intramolecularly donor stabilized species ClGa[(CH2)3NMe2](R) (R = Cl, Me, tBu) have been studied in some detail. Novel stable anionic (organo)gallium and chlorogallium metal complexes of the types {[L(CO)nM]Ga[(CH2)3NMe2](R)}- (1−6), {[L(CO)nM]GaCl2}- (7, 8), {[L(CO)nM]Ga(Cl)(R)}- (9, 10), and {[L(CO)nM]2Ga(CH3)}2- (11−13) have been prepared in high yields and were fully characterized by means of elemental analysis, infrared ν(CO) data, and NMR spectroscopy. The effect of substituents at the Ga center on the Lewis acidity was studied by temperature-dependent NMR (inversion at the N atom of the alkylamine ligand) using the compounds 1−6. The compounds 7−10 are supposed to be dimeric. The dianionic complex [PPN]2{[(CO)4Fe−Ga(CH3)−Fe(CO)4]} (11a) was also characterized by single-crystal X-ray diffraction: monoclinic, C2/c, a = 2699.1(3) pm, b = 1411.2(2) pm, c = 2392.8(3) pm, β = 127.45(1)°, V = 7236 × 106 pm3, Z = 4, and R = 0.038 (Rw = 0.097). The diminished Lewis acidity of the compounds 1−13 is explained by an electrostatic effect, which also stabilizes low-coordinate Ga centers without steric shielding.