Tuning rare-earth hydride reactivity with a reductive diazabutadienyl ligand beyond insertion

Abstract

A new strategy for tuning rare-earth hydride reactivity has been developed using a reductive ligand. The reaction of diazabutadienyl-supported rare-earth hydride [(DAD)Y·THF]₂(μ-H)₂ (DAD = N,N′-di(2,6-diisopropylphenyl)-1,4-diazabutadienyl dianion), (1) with two equiv. of Ph₂CO gave a reduced Ph₂CO-coupled product (DAD′Y)₂(μ-H)₂(μ-η²:η¹-Ph₂C(O)C(O)Ph₂)(THF) (DAD′ = N,N′-di(2,6-diisopropylphenyl)-1,4-diazabutadienyl radical-anion, 2), in which active Y–H bonds were retained, while 1 reacted with PhC(O)Cy to yield a Y–H bond insertion product [(DAD)Y(μ-OC(H)PhCy)]₂ (3). Complex 3 further reacted with PhC(O)Cy and lithium metal to give a C–C coupled product (DAD′)Y(PhCyC(O)C(O)PhCy)(OC(H)PhCy)Li(THF) (4). An investigation of the scope of reactivity of 1 found it reacted with PhNNPh to produce a two-electron reduced product (DAD′Y)₂(μ-N(Ph)NPh)₂(THF) (5), accompanied by the elimination of H₂. The reaction of 1 with acridine afforded two structurally characterized yttrium 9-H acridinyl complexes (DAD)Y(NC₁₃H₁₀)(THF)₂ (6) and (DAD′)Y(NC₁₃H₁₀)₂(THF) (7). Investigations into the reactivity of 2 showed that 2 facilely reacted with PhCCH to give an unusual hydride H⁻ and radical-anionic DAD ligand coupled product (DAD)Y(μ-Ph₂C(O)C(O)Ph₂)(μ-η²:η¹-CCPh)Y(HDAD) (8), while 2 reacted with Me₃SiCCH to afford the mono Me₃SiCCH protolysis product (DAD′)Y(μ-Ph₂C(O)C(O)Ph₂)(CCSiMe₃)(μ-H)Y(DAD′) (9), in which no hydride H⁻ migration occurred. These results indicated that the electronic properties of the reductive DAD ligand strongly modified the reactivity of rare-earth hydrides.