Reactivity of 16-electron half-sandwich cobalt compounds containing a chelating 1,2-dicarba-closo-dodecaborane-1,2-dithiolate ligand towards methyl propiolate and dithio ligands

Abstract

The reaction of the 16-electron half-sandwich complex MeCpCo(S₂C₂B₁₀H₁₀) (1b; MeCp = methylcyclopentadienyl) and methyl propiolate (HCCCO₂Me) at ambient temperature leads to MeCpCo(S₂C₂B₁₀H₉)(CHCHCO₂Me) (2), MeCpCo(S₂C₂B₁₀H₈)(CHCHCO₂Me)₂ (3), MeCpCo(S₂C₂B₁₀H₉)[MeO₂CCCH(MeO₂C)CCH)](CHCHCO₂Me) (4) and MeCpCo(S₂C₂B₁₀H₉)(CH₂CCO₂Me) (5). The reaction of Me₄CpCo(S₂C₂B₁₀H₁₀) (1c; Me₄Cp = tetramethylcyclopentadienyl) and the alkyne gives rise to Me₄CpCo(S₂C₂B₁₀H₁₀)[MeO₂CCCH(MeO₂C)CCH] (6) and Me₄CpCo (S₂C₂B₁₀H₉)(CH₂CCO₂Me) (7). Both 2 and 3 are 16-electron complexes but containing a B(3)-substituted o-carborane-1,2-dithiolate ligand in 2 and a B(3,6)-disubstituted o-carborane-1,2-dithiolate ligand in 3, respectively. In 4 and 6, two alkynes are inserted into one Co–S bond to meet an 18 electron configuration at metal, however, 4 has one B-substitution at carborane. Both 5 and 7 have the same structural type bearing a B–CH₂ unit. The reactions of Cp^#Co(E₂C₂B₁₀H₁₀) [Cp^# = Cp (1a), MeCp (1b), Me₄Cp (1c) and Me₅Cp (1d); E = S, Se] with 2-methylpropanedithioic acid (L1) or pyrrolidine-1-carbodithioic acid (L2) lead to Co[S₂CCH(CH₃)₂]₃ (8) or Co[S₂CN(CH₂)₄]₃ (9), respectively, in an octahedral geometry. The three-component reactions of 1a–1d, methyl propiolate and L1 or L2 afford seven new compounds Cp^#Co[S₂C₂B₁₀H₁₀(CHCHCO₂Me)][S₂CCH(CH₃)₂] [Cp^# = Cp (10a), MeCp (10b) and Me₄Cp (10c)], [S₂CCH(CH₃)₂]₂Co(S₂C₂B₁₀H₁₀)(CHCCO₂Me){CpCo[S₂CCH(CH₃)₂]} (11a), Cp^#Co[S₂C₂B₁₀H₁₀(CHCHCO₂Me)][S₂CN(CH₂)₄] [Cp^# = Cp (12a), MeCp (12b) and Me₄Cp (12c)]. All 10a–10c and 12a–12c contain one deprotonated L1 or L2 ligand and one reduced alkyne. 11a has two 18-electron Co centers linked by one reduced alkyne. One metal is coordinated by an o-carborane-1,2-dithiolate and two L1 ligands, and the other is coordinated by one L1 ligand and one η⁵-Cp unit. In both two- and three-component reactions the reactivity of the 16-electron half-sandwich complexes Cp^#Co(S₂C₂B₁₀H₁₀) is dependent on the size of the Cp^# unit. All compounds were fully characterized by spectroscopic techniques and elemental analysis. The solid-state structures of 4, 5, 7, 10a and 11a were further determined by X-ray crystallographic analysis.