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Reactions of Half-Sandwich Ethene Complexes of Rhodium(I) toward Iodoperfluorocarbons: Perfluoro-alkylation or -arylation of Coordinated Ethene versus Oxidative Addition

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posted on 27.02.2012, 00:00 by Juan Gil-Rubio, Juan Guerrero-Leal, María Blaya, José Vicente, Delia Bautista, Peter G. Jones
Perfluoroalkylation or perfluoroarylation of coordinated ethene takes place when complexes [Rh­(η5-Cp*)­(η2-C2H4)2] or [Rh­(η5-Cp*)­(η2-C2H4)­(PR3)] react with IRF, to give complexes [Rh­(η5-Cp*)­(CH2CH2RF)­(μ-I)]2 (RF = CF­(CF3)2 (1a), CF­(CF3)­CF2CF3 (1b), or C­(CF3)3 (1c)) and [(η5-Cp*)­IRh­(μ-I)2Rh­(η5-Cp*)­(CH2CH2RF)] (2ac), or [Rh­(η5-Cp*)­(CH2CH2RF)­I­(PR3)] (R = Me, RF = CF­(CF3)2 (3a), C­(CF3)3 (3c), C6F5 (3d); R = Ph, RF = CF­(CF3)2 (3a′), CF2C6F5 (3e′)), respectively. Bridge splitting reactions of 1a, 1b, or 1c with phosphines afford complexes [Rh­(η5-Cp*)­(CH2CH2RF)­I­(PR3)] (3a, 3a′, 3c; RF = CF­(CF3)2, R = iPr (3a″); RF = CF­(CF3)­CF2CF3, R = Me (3b), Ph (3b′)). In contrast, oxidative addition dominates over addition to ethene in the reactions of [Rh­(η5-Cp*)­(η2-C2H4)­(PMe3)] with IRF (RF = CF2C6F5, nC3F7, nC4F9, CFCF2) and in the reaction of [Rh­(η5-Cp)­(η2-C2H4)­(PMe3)] with InC4F9, affording complexes of the type [Rh­(η5-C5R5)­(RF)­I­(PMe3)] (4eh and 5, respectively). The reaction of [Rh­(η5-Cp*)­(η2-C2H4)­(PR3)] with ICF­(CF3)­CF2CF3 gives a mixture of cis- and trans-octafluoro-2-butene as the main fluoroorganic reaction product. Evidence for the intermediacy of RF anions in these reactions has been obtained. 3a′ reacts with AgOTf (OTf = O3SCF3) and XyNC or CO to give complexes [Rh­(η5-Cp*)­{CH2CH2CF­(CF3)2}­(CNXy)­(PPh3)]­OTf (6) or [Rh­(η5-Cp*)­{C­(O)­CH2CH2CF­(CF3)2}­(CO)­(PPh3)]­OTf (7), respectively. Complex [Rh­(η5-Cp*)­I­(py)­(PMe3)]­BF4 (8) was obtained either by reaction of (1) [Rh­(η5-Cp*)­(η2-C2H4)­(PMe3)] with [I­(py)2]­BF4 or (2) [Rh­(η5-Cp*)­I2(PMe3)] with AgBF4 and py. The crystal structures of 1a, 1b, 3c, 4g, 7, and 8 have been determined.