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 (HC≡CCO2Me) at ambient temperature leads to MeCpCo(S2C2B10H9)(CH=CHCO2Me) (2), MeCpCo(S2C2B10H8)(CH=CHCO2Me)2 (3), MeCpCo-(S2C2B10H9)[MeO2CC=CH(MeO2C)C=CH)](CH=CHCO2Me) (4) and MeCpCo(S2C2B10H9)-(CH2CCO2Me) (5). The reaction of Me4CpCo(S2C2B10H10) (1c; Me4Cp = tetramethylcyclopentadienyl) and the alkyne gives rise to Me4CpCo(S2C2B10H10)[MeO2CC=CH(MeO2C)C=CH] (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(CH=CHCO2Me)][S2CCH(CH3)2] [Cp# = Cp (10a), MeCp (10b) and Me4Cp (10c)], [S2CCH(CH3)2]2Co(S2C2B10H10)(CH=CCO2Me){CpCo[S2CCH(CH3)2]} (11a), Cp#Co[S2C2B10H10(CH=CHCO2Me)][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.