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Potassium and Well-Defined Neutral and Cationic Calcium Fluoroalkoxide Complexes: Structural Features and Reactivity

Abstract : The fluorinated aminoether alcohols (1-aza-12-crown-4)CH2C(CF3)2OH ({RO1F}H), (MeOCH2CH2)2NCH2C(CF3)2OH ({RO2F}H), and (MeOCH2CH2)(Me)NCH2C(CF3)2OH ({RO3F}H) have been synthesized and used to prepare the heteroleptic calcium amido complexes {ROxF}Ca(N(SiMe2R)2) (4–7; x = 2, 3, R = H, Me). The ability to form stable complexes varies with the chelating and electron-donating ability of the aminoether alkoxide ligand, as exemplified by our failure to isolate cleanly the elusive {RO1F}Ca(N(SiMe2R)2). X-ray diffraction studies show that, in the solid state, intramolecular Ca···F interactions help reach coordinative saturation in the dimeric [{RO2F}Ca(N(SiMe3)2)]2 ([4]2), [{RO2F}Ca(N(SiMe2H)2)]2 ([5]2), [{RO3F}Ca(N(SiMe3)2)]2 ([6]2), and [{RO3F}Ca(N(SiMe2H)2)]2 ([7]2), which crystallized free of solvent coligands. Similar stabilizing K···F patterns were found in the polymetallic potassium fluoroalkoxides [{RO1F}K]2 ([1]2), [{RO2F}K]4 ([2]4), and [{RO3F}K]4 ([3]4); [2]4 and [3]4 form heterocubanes in the solid state. Examination of the XRD data for [1]2–[7]2 shows that metal···F interactions can be favored over binding of Oether atoms for calcium and potassium. Pulse-gradient spin–echo NMR spectroscopy shows that the complexes remain aggregated in aromatic solvents. The solvent-free salts [{ROxF}Ca+]·[H2N{B(C6F5)3}2–] (x = 1 (8), 2 (9), 3 (10)) are obtained by treating 4–7 with [H(OEt2)2+]·[H2N{B(C6F5)3}2–] or by reacting Ca(N(SiMe3)2)2 with [{ROxF}HH+]·[H2N{B(C6F5)3}2–]; the solid-state structures of [8·H2O]2 and [9·H2O]2 again showed the presence of Ca···F contacts. Complexes 5–7 are promising catalysts for the regiospecific anti-Markovnikov hydrophosphination of styrene with diphenylphosphine, affording TOF values as high as 52 molsubst molCa–1 h–1 with up to 400 equiv of substrates within 1–2 h at 60 °C.
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https://hal-univ-rennes1.archives-ouvertes.fr/hal-01114341
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Submitted on : Monday, February 9, 2015 - 11:40:53 AM
Last modification on : Friday, July 10, 2020 - 4:24:46 PM

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Sorin-Claudiu Roşca, Thierry Roisnel, Vincent Dorcet, Jean-François Carpentier, Yann Sarazin. Potassium and Well-Defined Neutral and Cationic Calcium Fluoroalkoxide Complexes: Structural Features and Reactivity. Organometallics, American Chemical Society, 2014, 33 (20), pp.5630-5642. ⟨10.1021/om500343w⟩. ⟨hal-01114341⟩

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