Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99354, USA.
Dalton Trans. 2013 Jan 21;42(3):615-9. doi: 10.1039/c2dt31628e.
Calorimetry is used to measure the reaction enthalpies of hydrogen (H(2)) activation by 2,6-lutidine (Lut), 2,2,6,6-tetramethylpiperidine (TMP), N-methyl-2,2,6,6-tetramethylpiperidine (MeTMP), and tri-tert-butylphosphine (TBP) with tris(pentafluorophenyl)borane (BCF). At 6.6 bar H(2) the conversion of the Lewis acid Lewis base pair to the corresponding ionic pair in bromobenzene at 294 K was quantitative in under 60 min. Integration of the heat release from the reaction of the Frustrated Lewis Pair (FLP) with H(2) as a function of time yields a relative rate of hydrogenation in addition to the enthalpy of hydrogenation. The half-lives of hydrogenation range from 230 s with TMP, ΔH(H2) = -31.5(0.2) kcal mol(-1), to 1400 s with Lut, ΔH(H2) = -23.4(0.4) kcal mol(-1). The (11)B nuclear magnetic resonance (NMR) spectrum of B(C(6)F(5))(3) in bromobenzene exhibits three distinct traits depending on the sterics of the Lewis base; (1) in the presence of pyridine, only the dative bond adduct pyridine-B(C(6)F(5))(3) is observed; (2) in the presence of TMP and MeTMP, only the free B(C(6)F(5))(3) is observed; and (3) in the presence of Lut, both the free B(C(6)F(5))(3) and the Lut-B(C(6)F(5))(3) adduct appear in equilibrium. A measure of the change in K(eq) of Lut + B(C(6)F(5))(3) ⇔ Lut-B(C(6)F(5))(3) as a function of temperature provides thermodynamic properties of the Lewis acid Lewis base adduct, ΔH = -17.9(1.0) kcal mol(-1) and a ΔS = -49.2(2.5) cal mol(-1) K, suggesting the Lut-B(C(6)F(5))(3) adduct is more stable in bromobenzene than in toluene.
量热法用于测量 2,6- 二甲基吡啶（Lut）、2,2,6,6- 四甲基哌啶（TMP）、N- 甲基-2,2,6,6- 四甲基哌啶（MeTMP）和三（五氟苯基）硼烷（BCF）与三（五氟苯基）硼烷（BCF）对氢气（H2）的反应焓。在 6.6 巴 H2 的条件下，路易斯酸路易斯碱对在 294 K 下溴苯中的相应离子对的转化率在 60 分钟内达到定量。反应热的积分从 Frustrated Lewis Pair（FLP）与 H2 的反应作为时间的函数，除了加氢焓外，还产生加氢的相对速率。加氢的半衰期范围从 230 s（TMP，ΔH（H2）=-31.5（0.2）kcal mol-1）到 1400 s（Lut，ΔH（H2）=-23.4（0.4）kcal mol-1）。溴苯中 B（C6F5）（3）的（11）B 核磁共振（NMR）谱取决于路易斯碱的空间位阻，具有三个明显的特征；（1）在吡啶存在下，只观察到配位键加合物吡啶-B（C6F5）（3）；（2）在 TMP 和 MeTMP 的存在下，只观察到游离的 B（C6F5）（3）；（3）在 Lut 的存在下，游离的 B（C6F5）（3）和 Lut-B（C6F5）（3）加合物都处于平衡状态。测量 Lut+B（C6F5）（3） ⇔ Lut-B（C6F5）（3）平衡常数随温度的变化可以提供路易斯酸路易斯碱加合物的热力学性质，ΔH=-17.9（1.0）kcal mol-1，ΔS=-49.2（2.5）cal mol-1 K，表明 Lut-B（C6F5）（3）加合物在溴苯中的稳定性比在甲苯中高。
