From gallium hydride halides to molecular gallium sulfides

Complexes of the type (L)GaHCl₂, with L =tertiary phosphines or pyridines, have been prepared from (HGaCl₂)₂ and the ligands in diethyl ether. The products are stable crystalline solids soluble in common organic solvents. The presence of the Ga-H function has been confirmed by IR and NMR spectroscopy and by single crystal X-ray diffraction, carried out for the 1:1 adducts with L = PCy₃ and PPh₃ (two polymorphs) and for the 2:1 adduct with L = (CH₂PPh₂) ₂ (dppe, two different solvates). The reaction of PVi₃ with (HGaCl₂)₂ gives an insoluble polymer owing to the hydrogallation of vinyl groups by the gallium hydride units (no Ga-H functions are left in the product).Treatment of the complexes (R₃P)GaHCl ₂ with H₂S, metal sulfides or (Me₃Si) ₂S gave only insoluble, ill-defined products. - The 1:1 adduct (L′)GaHCl₂, with L′ = 4-dimethylamino-pyridine, reacts with (Me₃Si)₂S in acetonitrile at ambient temperature to give an only partially sulfur-substituted product of the net formula (L′)GaSH_0.66Cl_0.34. With excess ligand L′, under reflux conditions and after longer reaction times, a pyridine complex of the tetranuclear, molecular gallium sulfide Ga₄S₆ is obtained in low yield. The core of the compound with the composition (L′)₄Ga₄S₆ has an adamantane structure resembling a cluster unit of the binary gallium sulfide polymorphs Ga ₂S₃. The edge-sharing Ga₃S₃ six-membered rings are all in a chair conformation as found previously for the pyridine complexes of the ternary compounds [(L)GaEX]₃(with E = S, Se and X = Cl, Br) and for the bicyclic dication [(L)₆Ga ₄S₅]²⁺. Thermolysis and degradation under mass spectrometry conditions lead to sublimation of L′ and leave amorphous Ga₂S₃. The reaction of (L′)GaCl₃ with (Me₃Si)₂S did not afford any molecular gallium sulfide complex. A comparison of the structural data for (L′)GaCl₃ and (L′)₄Ga₄S₆ suggests a much poorer acceptor character of the gallium sulfide cluster.