Synthesis and Reactivity of NHC-Supported Ni2(μ2‑η2,η2‑S2)‑Bridging Disulfide and Ni2(μ-S)2‑Bridging Sulfide Complexes

The (IPr)Ni scaffold stabilizes low-coordinate, mononuclear and dinuclear complexes with a diverse range of sulfur ligands, including μ2-η2,η2-S2, η2-S2, μ-S, and μ-SH motifs. The reaction of {(IPr)­Ni}2(μ-Cl)2 (1, IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazolin-2-ylidene) with S8 yields the bridging disulfide species {(IPr)­ClNi}2(μ2-η2,η2-S2) (2). Complex 2 reacts with 2 equiv of AdNC (Ad = adamantyl) to yield a 1:1 mixture of the terminal disulfide compound (IPr)­(AdNC)­Ni­(η2-S2) (3a) and trans-(IPr)­(AdNC)­NiCl2 (4a). 2 also reacts with KC8 to produce the Ni–Ni-bonded bridging sulfide complex {(IPr)­Ni}2(μ-S)2 (6). Complex 6 reacts with H2 to yield the bridging hydrosulfide compound {(IPr)­Ni}2(μ-SH)2 (7), which retains a Ni–Ni bond. 7 is converted back to 6 by hydrogen atom abstraction by 2,4,6-tBu3-phenoxy radical. The 2,6-diisopropylphenyl groups of the IPr ligand provide lateral steric protection of the (IPr)Ni unit but allow for the formation of Ni–Ni-bonded dinuclear species and electronically preferred rather than sterically preferred structures.