Potassium and Well-Defined Neutral and Cationic Calcium Fluoroalkoxide Complexes: Structural Features and Reactivity
dataset
posted on 2014-10-27, 00:00 authored by Sorin-Claudiu Roşca, Thierry Roisnel, Vincent Dorcet, Jean-François Carpentier, Yann SarazinThe
fluorinated aminoether alcohols (1-aza-12-crown-4)CH<sub>2</sub>C(CF<sub>3</sub>)<sub>2</sub>OH ({RO<sub>1</sub><sup>F</sup>}H),
(MeOCH<sub>2</sub>CH<sub>2</sub>)<sub>2</sub>NCH<sub>2</sub>C(CF<sub>3</sub>)<sub>2</sub>OH ({RO<sub>2</sub><sup>F</sup>}H), and (MeOCH<sub>2</sub>CH<sub>2</sub>)(Me)NCH<sub>2</sub>C(CF<sub>3</sub>)<sub>2</sub>OH ({RO<sub>3</sub><sup>F</sup>}H) have been synthesized and used
to prepare the heteroleptic calcium amido complexes {RO<sub><i>x</i></sub><sup>F</sup>}Ca(N(SiMe<sub>2</sub>R)<sub>2</sub>)
(<b>4</b>–<b>7</b>; <i>x</i> = 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 {RO<sub>1</sub><sup>F</sup>}Ca(N(SiMe<sub>2</sub>R)<sub>2</sub>). X-ray diffraction
studies show that, in the solid state, intramolecular Ca···F
interactions help reach coordinative saturation in the dimeric [{RO<sub>2</sub><sup>F</sup>}Ca(N(SiMe<sub>3</sub>)<sub>2</sub>)]<sub>2</sub> (<b>[4]</b><sub><b>2</b></sub>), [{RO<sub>2</sub><sup>F</sup>}Ca(N(SiMe<sub>2</sub>H)<sub>2</sub>)]<sub>2</sub> (<b>[5]</b><sub><b>2</b></sub>), [{RO<sub>3</sub><sup>F</sup>}Ca(N(SiMe<sub>3</sub>)<sub>2</sub>)]<sub>2</sub> (<b>[6]</b><sub><b>2</b></sub>), and [{RO<sub>3</sub><sup>F</sup>}Ca(N(SiMe<sub>2</sub>H)<sub>2</sub>)]<sub>2</sub> (<b>[7]</b><sub><b>2</b></sub>), which crystallized free of solvent coligands. Similar stabilizing
K···F patterns were found in the polymetallic potassium
fluoroalkoxides [{RO<sub>1</sub><sup>F</sup>}K]<sub>2</sub> (<b>[1]</b><sub><b>2</b></sub>), [{RO<sub>2</sub><sup>F</sup>}K]<sub>4</sub> (<b>[2]</b><sub><b>4</b></sub>), and
[{RO<sub>3</sub><sup>F</sup>}K]<sub>4</sub> (<b>[3]</b><sub><b>4</b></sub>); <b>[2]</b><sub><b>4</b></sub> and <b>[3]</b><sub><b>4</b></sub> form heterocubanes in the solid
state. Examination of the XRD data for <b>[1]</b><sub><b>2</b></sub>–<b>[7]</b><sub><b>2</b></sub> shows
that metal···F interactions can be favored over binding
of O<sub>ether</sub> atoms for calcium and potassium. Pulse-gradient
spin–echo NMR spectroscopy shows that the complexes remain
aggregated in aromatic solvents. The solvent-free salts [{RO<sub><i>x</i></sub><sup>F</sup>}Ca<sup>+</sup>]·[H<sub>2</sub>N{B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>}<sub>2</sub><sup>–</sup>] (<i>x</i> = 1 (<b>8</b>), 2 (<b>9</b>), 3
(<b>10</b>)) are obtained by treating <b>4</b>–<b>7</b> with [H(OEt<sub>2</sub>)<sub>2</sub><sup>+</sup>]·[H<sub>2</sub>N{B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>}<sub>2</sub><sup>–</sup>] or by reacting Ca(N(SiMe<sub>3</sub>)<sub>2</sub>)<sub>2</sub> with [{RO<sub><i>x</i></sub><sup>F</sup>}HH<sup>+</sup>]·[H<sub>2</sub>N{B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>}<sub>2</sub><sup>–</sup>]; the solid-state structures of
[<b>8·H</b><sub><b>2</b></sub><b>O]</b><sub><b>2</b></sub> and [<b>9·H</b><sub><b>2</b></sub><b>O]</b><sub><b>2</b></sub> again showed the presence
of Ca···F contacts. Complexes <b>5</b>–<b>7</b> are promising catalysts for the regiospecific anti-Markovnikov
hydrophosphination of styrene with diphenylphosphine, affording TOF
values as high as 52 mol<sub>subst</sub> mol<sub>Ca</sub><sup>–1</sup> h<sup>–1</sup> with up to 400 equiv of substrates within
1–2 h at 60 °C.
