Tailoring Reactivity of Molecular Gallium Hydroxides via Chalcogen Bridging

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.