Understanding the Early Stages of Nickel Sulfide Nanocluster Growth: Isolation of Ni₃, Ni₄, Ni₅, and Ni₈ Intermediates

Abstract

Addition of sub‐stoichiometric quantities of PEt3 and diphenyl disulfide to a solution of [Ni(1,5‐cod)2] generates a mixture of [Ni3(SPh)4(PEt3)3] (1), unreacted [Ni(1,5‐cod)2], and [(1,5‐cod)Ni(PEt3)2], according to 1H and 31P{1H} NMR spectroscopic monitoring of the in situ reaction mixture. On standing, complex 1 converts into [Ni4(S)(Ph)(SPh)3(PEt3)3] (2), via formal addition of a “Ni(0)” equivalent, coupled with a CS oxidative addition step, which simultaneously generates the Ni‐bound phenyl ligand and the μ3‐sulfide ligand. Upon gentle heating, complex 2 converts into a mixture of [Ni5(S)2(SPh)2(PEt3)5] (3) and [Ni8(S)5(PEt3)7] (4), via further addition of “Ni(0)” equivalents, in combination with a series of C–S oxidative addition and CC reductive elimination steps, which serve to convert thiophenolate ligands into sulfide ligands and biphenyl. The presence of 1–4 in the reaction mixture is confirmed by their independent syntheses and subsequent spectroscopic characterization. Overall, this work provides an unprecedented level of detail of the early stages of Ni nanocluster growth and highlights the fundamental reaction steps (i.e., metal atom addition, CS oxidative addition, and CC reductive elimination) that are required to grow an individual cluster.

[Ni30S16(PEt3)11]: an open-shell nickel sulfide nanocluster with a “metal-like” core

“…Previous work by our group suggests that the first step in APNC formation involves formation of [Ni(1,5-cod)(PEt 3 ) 2 ] by ligand substitution. 30 Thus, we surmise that a large excess of PEt 3 is required to completely form [Ni(1,5-cod)(PEt 3 ) 2 ], which is much more thermally stable than [Ni(1,5-cod) 2 ], and subsequently functions as a better Ni(0) source at these elevated temperatures. However, the excess PEt 3 unavoidably sequesters some of the S 8 (see below), which likely contributes to the low isolated yield.…”

“…For comparison, the average Ni–S distances observed in [Ni 5 S 2 (SPh) 2 (PEt 3 ) 5 ] and [Ni 8 S 5 (PEt 3 ) 7 ] are shorter (2.04 and 2.19 Å, respectively), perhaps reflecting the lower average coordination number of their S 2− ligands. 30 For further comparison, the average Ni–S distance in β-NiS is 2.31 Å, 36 whereas the Ni–S distances in Ni 3 S 2 are 2.2914(5) and 2.2534(5) Å. 37 Finally, the average Ni–P distance in 1 is 2.18 Å, which is similar to Ni–P distances in [Ni 8 S 5 (PEt 3 ) 7 ], [Ni 21 Se 14 (PEt 2 Ph) 12 ], and [Ni 23 Se 12 Cl 3 (PEt 3 ) 10 ].…”

“…27 Additionally, past work by Jin and co-workers has shown that NaBH 4 cannot reduced Ni 2+ salts to Ni(0). [28][29][30] Given these considerations, we chose PEt 3 as our supporting ligand and [Ni(1,5-cod) 2 ] as our Ni source. Thus, heating a mixture of [Ni(1,5-cod) 2 ] (30 equiv.…”

“…For comparison, the average Ni-S distances observed in [Ni 5 S 2 (SPh) 2 (PEt 3 ) 5 ] and [Ni 8 S 5 (PEt 3 ) 7 ] are shorter (2.04 and 2.19 Å, respectively), perhaps reecting the lower average coordination number of their S 2À ligands. 30 For further comparison, the average Ni-S distance in b-NiS is 2.31 Å, 36 whereas the Ni-S distances in Ni 3 S 2 are 2.2914(5) and 2.2534(5) Å. 37 20,30,33 The average Ni oxidation state in 1 is 1.067, making it among the most reduced Ni chalcogenide clusters yet isolated, and highlighting its high "metal-like" character.…”

“…30 For further comparison, the average Ni-S distance in b-NiS is 2.31 Å, 36 whereas the Ni-S distances in Ni 3 S 2 are 2.2914(5) and 2.2534(5) Å. 37 20,30,33 The average Ni oxidation state in 1 is 1.067, making it among the most reduced Ni chalcogenide clusters yet isolated, and highlighting its high "metal-like" character. For comparison, and 1.17, respectively.…”