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

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.

氟化氨基醚醇类化合物(1-氮杂-12-冠-4)­CH₂C­(CF₃)₂OH（记作{RO1F}­H）、(MeOCH₂CH₂)₂NCH₂C­(CF₃)₂OH（记作{RO2F}­H）以及(MeOCH₂CH₂)­(Me)­NCH₂C­(CF₃)₂OH（记作{RO3F}­H）已成功合成，并用于制备杂配位型钙氨基配合物{ROₓF}­Ca­(N­(SiMe₂R)₂)（4~7；x=2、3，R=H、Me）。该类配合物的稳定合成能力随氨基醚烷氧基配体的螯合能力与给电子能力的变化而改变，例如我们未能分离得到纯净的、难以获取的{RO1F}­Ca­(N­(SiMe₂R)₂)。
X射线衍射（X-ray diffraction）研究表明，在固态下，分子内Ca···F相互作用可帮助二聚体[{RO2F}­Ca­(N­(SiMe₃)₂)]₂（记作[4]₂）、[{RO2F}­Ca­(N­(SiMe₂H)₂)]₂（记作[5]₂）、[{RO3F}­Ca­(N­(SiMe₃)₂)]₂（记作[6]₂）以及[{RO3F}­Ca­(N­(SiMe₂H)₂)]₂（记作[7]₂）达到配位饱和，上述二聚体可在无溶剂共配体的条件下结晶析出。
类似的稳定化K···F相互作用模式也存在于多金属氟烷氧基配合物[{RO1F}­K]₂（记作[1]₂）、[{RO2F}­K]₄（记作[2]₄）以及[{RO3F}­K]₄（记作[3]₄）中；其中[2]₄与[3]₄在固态下可形成杂立方烷结构。
对[1]₂~[7]₂的X射线衍射数据进行分析后发现，对于钙与钾而言，金属···F相互作用相较于醚氧原子的配位结合更具优势。脉冲梯度自旋回波核磁共振（Pulse-gradient spin–echo NMR）光谱研究显示，这些配合物在芳香族溶剂中仍保持聚集状态。
通过将4~7与[H­(OEt₂)₂⁺]·[H₂N­{B­(C₆F₅)₃}₂⁻]反应，或是使Ca­(N­(SiMe₃)₂)₂与[{ROₓF}­HH⁺]·[H₂N­{B­(C₆F₅)₃}₂⁻]发生反应，可得到无溶剂盐[{ROₓF}­Ca⁺]·[H₂N­{B­(C₆F₅)₃}₂⁻]（x=1对应8，x=2对应9，x=3对应10）。[8·H₂O]₂与[9·H₂O]₂的固态结构同样显示存在Ca···F接触。
配合物5~7是一类极具应用潜力的催化剂，可催化苯乙烯与二苯基膦发生区域专一性反马氏加成氢磷化反应；在60℃、底物用量高达400当量的条件下，于1~2小时内即可达到最高52 mol底物·mol_Ca⁻¹·h⁻¹的转换频率（Turnover Frequency, TOF）。