Tailoring Reactivity of Molecular Gallium Hydroxides via Chalcogen Bridging

Abstract

Abstract We studied the influence of bridging chalcogen atoms (μ-E; E = S, Se) on the structure and reactivity of digallium dihydroxide complexes [{MeLGa(OH)}2(μ-E)] [E = S (4), Se (5); MeL = CH{CMe(NAr)}2–, Ar = 2,4,6-Me3C6H2]. Compounds 4 and 5 were synthesized from MeLGaCl2 and sodium chalcogenide (Na2E) in THF-NH3(l), followed by controlled hydrolysis. For the sulfur system, the intermediates [{MeLGa(Cl)}2(μ-S)] (2) and [{MeLGa(NH2)}2(μ-S)] (3) were isolated and characterized, whereas the corresponding selenium derivatives proved too reactive for isolation. The reactivity of 4 and 5 toward Group 4 metal amides, M(NR2)4 (M = Ti, R = Me; M = Zr, Hf, R = Et), revealed a chalcogen effect, affording both monocyclic and spirocyclic complexes from 4, while 5 selectively yielded spirocyclic complexes. Likewise, the milder amide Me2Si(NMe2)2 reacted exclusively with 5 to produce a siloxide-bridged derivative. Distinct borane-dependent pathways were also observed. Treatment of 4 and 5 with BH3·THF resulted in the Ga–OH protonolysis to form cyclic borates, whereas BH3·SMe2 promoted hydride attack at gallium, yielding gallium hydrides. These results provide an insight into the ambiphilic character of 4 and 5 and establish chalcogen bridging as a strategy for tuning their bonding and reactivity.