¹H NMR Studies of Ligand and H/D Exchange Reactions of <i>cis</i>- and <i>trans</i>-([14]aneN₄)(H₂O)RhH²⁺ in Aqueous Solutions

Substitution and exchange reactions of cis- and trans-L1(H2O)RhH2+ (L1 = 1,4,8,11-tetraazacyclotetradecane = [14]aneN4) were studied in aqueous solutions by UV−vis and 1H NMR spectroscopies. At pH 1 and 25 °C, the substitution of SCN- for the coordinated molecule of water is rapid and thermodynamically favorable. Spectrophotometric determinations yielded the equilibrium constants K = 1.49 × 103 M-1 (cis) and 1.44 × 103 (trans). 1H NMR studies in D2O revealed a rapid dynamic process, interpreted as the exchange between coordinated water and X- (X = Cl, Br, or I). On the other hand, no line broadening was observed for the strongly bound ligands CN- and SCN-. The complex trans-L1(D2O)RhH2+ undergoes a base-catalyzed H/D exchange of the hydride in D2O with a rate constant of (1.45 ± 0.02) × 103 M-1 s-1. The exchange in the cis isomer is very slow under similar conditions. The complex cis-[L1ClRhH](ClO4) crystallizes in the centrosymmetric P1̄ space group, unit cell dimensions a = 8.9805(11) Å, b = 9.1598(11) Å, c = 10.4081(13) Å, α = 81.091(2)°, β = 81.978(2)°, γ = 88.850(2)°. The rhodium atom resides in a slightly distorted octahedral environment consisting of the four N atoms of the cyclam, a stereochemically active hydrogen, and a chlorine atom.本研究采用紫外-可见（UV−vis）光谱与质子核磁共振（1H NMR）波谱法，在水溶液中探究了顺式与反式L1(H2O)RhH2+（其中L1为1,4,8,11-四氮杂环十四烷（[14]aneN4））的取代与交换反应。在pH=1、25 ℃条件下，硫氰根（SCN-）取代配位水分子的反应速率较快且热力学上有利。分光光度法测定得到平衡常数K：顺式异构体为1.49×10³ M⁻¹，反式异构体为1.44×10³ M⁻¹。在重水（D2O）中开展的1H NMR研究揭示了一种快速动态过程，该过程可归因为配位水与X-（X=Cl、Br或I）之间的配体交换。而对于结合能力较强的配体氰根（CN-）与硫氰根（SCN-），未观察到谱线宽化现象。反式L1(D2O)RhH2+配合物在重水中发生碱催化氢氘（H/D）交换反应，速率常数为(1.45±0.02)×10³ M⁻¹·s⁻¹。在相似条件下，顺式异构体的氢氘交换反应速率极慢。顺式-[L1ClRhH](ClO4)配合物以中心对称空间群P1̄结晶，晶胞参数为a=8.9805(11) Å，b=9.1598(11) Å，c=10.4081(13) Å，α=81.091(2)°，β=81.978(2)°，γ=88.850(2)°。铑原子处于略微畸变的八面体配位环境中，该环境由环胺配体cyclam的四个氮原子、一个立体化学活性氢原子与一个氯原子构成。