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

Abstract

The (IPr)Ni scaffold stabilizes low-coordinate, mononuclear and dinuclear complexes with a diverse range of sulfur ligands, including μ(2)-η(2),η(2)-S2, η(2)-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(μ(2)-η(2),η(2)-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(η(2)-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-(t)Bu3-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.

Progress toward the Isolation of Late Metal Terminal Sulfides

“…The solid‐state structures of 32 and 33 feature Y‐shaped coordination environments at Ni (Figure ). Surprisingly, the Ni–S distances in 32 (2.064(2) Å) and 33 (2.084(1) Å) are comparable to those observed for a variety of Ni 2 (µ‐S)‐type complexes (Table ),, , suggesting that the π‐bonds in 32 and 33 are no stronger than those of bridging sulfides. In addition, both 32 and 33 feature interactions (albeit weak) between the sulfide ligand and the potassium counterion, despite the use of either 18‐crown‐6 or 2.2.2‐cryptand to sequester the K + ion.…”

“…For example, reaction of excess S 8 with [Co(PMe 3 ) 4 ] results in formation of the bridging sulfide complex, [(PMe 3 ) 3 Co] 2 (µ‐S) 2 , in excellent yields, along with Me 3 PS, but not a terminal sulfide . This result is typical of elemental sulfur additions to the late metals . Similary, Sacconi and co‐workers reported that deprotonation of [(np 3 )Co(SH)][BPh 4 ] ( 17 , np 3 = tris(2‐diphenylphosphinoethyl)amine) with NaOEt also resulted in formation of a Co I bridged sulfide, [(np 3 )Co] 2 (µ‐S) ( 18 ), according to the stoichiometry shown in Scheme a .…”

“…[70] This result is typical of elemental sulfur additions to the late metals. [71][72][73][74][75] Similary, Sacconi and co-workers reported that deprotonation of [(np 3 )Co(SH)][BPh 4 ] (17, np 3 = tris(2-diphenylphosphinoethyl)amine) with NaOEt also resulted in formation of a Co I bridged sulfide, [(np 3 )Co] 2 (μ-S) (18), according to the stoichiometry shown in Scheme 6a. [76] The authors did not comment on the intermediacy of a terminal sulfide complex; however, its 20(Scheme 6b).…”

Dinuclear Nickel(I) and Palladium(I) Complexes for Highly Active Transformations of Organic Compounds

“…Tatsumi et al reported that substitution of the bridging halide ligands with sulfide anions resulted in efficient formation of the corresponding μ-sulfide Ni(I) dimer 16a [ 47 ]. Olechnowicz et al also synthesized the NHC analogue 16b , in which the bridging thiolate was μ–SH, from Sigman’s dimer [ 48 ]. Interestingly, this complex was also obtained from the heterolytic cleavage of H 2 in the presence of the sulfido-bridged Ni(II) dimer [Ni(IPr)(μ-S)] 2 [ 49 ].…”

Synthesis of a “Masked” Terminal Nickel(II) Sulfide by Reductive Deprotection and its Reaction with Nitrous Oxide

“…[29][30][31]34] TheN i ÀSb ond lengths in complexes 3, 4,a nd 5 are amongst the shortest known, and are intermediate between the additive covalent radii projected for nickel-sulfur single (2.13 ) and double bonds (1.95 ). [23,24,35] Forc omparison, [{L tBu Ni} 2 (m-S)], [30] [{(IPr)Ni} 2 (m-S) 2 ]( IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), [36] and [{PhB-(CH 2 StBu) 3 }Ni] 2 (m-S) [32] display comparable NiÀSb ond lengths of 2.0651(7), 2.0972(6), and 2.0714(4) , respectively, despite each possessing ab ridging S 2À ligand. Overall, this suggests similar magnitudes of p-bonding in both classes of materials.…”