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Addition of Inorganic and Organic Nucleophiles to the Vinylidene Ligand of the Cluster FeCo2(CO)9(μ3-CCH2) The CCH2 ligand of the cluster FeCo2(CO)9(μ3-CCH2) (1) is electrophilic at the terminal C atom. Soft inorganic nucleophiles [Nu – PR3, (CH3)2SO, CN−, SCN−] are added to form the zwitterionic complexes FeCo2(CO)9(μ3-C–CH2–Nu) (4, 7, 8), as proved by the structure determination of FeCo2(CO)9(μ3-CCH2 – PMe3) (4a). The products are of low thermal stability. Upon heating, the PR3 derivatives rearrange to the CO substitution products FeCo2(CO)8(PR3)(μ3-CCH2) (5, 6). C–C coupling is achieved by addition of malonic ester anion derivatives [X – CH – CO2Me] (XMeO2C, CN, Br). The anionic addition product for XMeO2C (10a) can be protonated to form HFeCo2(CO)9[μ3 CCH2 – CH(COOMe)2] (11) which liberates H2 upon warming resulting in FeCo2(CO)9[μ3-CCH – CH(COOMe)2] (12). Thus, a substitution of a vinylidene H atom has been performed by an HX addition/H2 elimination sequence. Phosphorus ylides R3PCHX [XH, SiMe3, Cl, CHO, C(O)Ph, COOR] are also added with CC coupling to yield the complexes FeCo2(CO)9(μ3-CCH2 – CHX – PR3) (15, 16). The structure determination of the compound with XEtO2C and RPh (16c) proves that these complexes differ from the complexes 4 just by insertion of one methylene unit. |
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