Synthesis and reactivity of [(thiomethoxy)methyl]- and [(dimethylsulfonio)methyl]nickel(II) complexes

Article abstract of DOI:10.1021/om00126a007

The new complexes [NiCp(L)CH₂SCH₃] (L = PPh₃, PPhMe₂, P(OCH₃)₃ were prepared by substitution of halide in [NiCp(L)X] and, in the case of L = PPh₃, by reaction of chloromethyl methyl sulfide with [Ni(PPh₃)₂(C₂H₄)], to give [Ni(PPh₃)₂(Cl)(η¹-CH₂SCH ₃)] or [Ni(PPh₃)(Cl)(η²-CH₂SCH₃)] depending upon reaction conditions, followed by reaction with sodium cyclopentadienide. Addition of ammonium hexafluorophosphate to [Ni(PPh₃)₂(Cl)(η¹-CH₂SCH ₃)] in acetone produced [Ni(PPh₃)₂(η²-CH₂SCH ₃)]PF₆. S-methylation of the cyclopentadienyl complexes yielded the sulfonium ions [NiCp(L)CH₂S(CH₃)₂]⁺. [NiCp(PPh₃)CH₂S(CH₃)₂]⁺ was also prepared from [NiCp(L)X] and dimethylsulfonium methylide, but the dinuclear species {[NiCp(PPh₃)CH₂]₂S(CH₃)}⁺ was formed in comparable amounts. The structure of the dinuclear complex (PF₆^- salt, acetone solvate) was determined by a single-crystal X-ray structure: C₅₂H₅₃F₆Ni₂OP₃S; space group Pbcm; a = 11.20 (1) A?, b = 18.814 (6) A?, c = 24.40 (1) A?; Z = 4; R = 0.11 and R_w = 0.096 for 2100 data with F > 3σ_F. The sulfur and methyl carbons of the cation lie on a mirror plane. The mononuclear sulfonium salts reacted with charged nucleophiles (X = Br^-, I^-, and CN^-) to produce [NiCp(L)X]. That these reactions occurred by substitution of the CH₂S(CH₃)₂ group was suggested by the fact that [NiCp(PPh₃)CH₂CN], prepared from the halide and LiCH₂CN, was stable under the reaction conditions. The nickelated sulfonium salts were found to have limited utility as reagents for the cyclopropanation of cyclooctene in acetonitrile solution.