Binding interactions between transition metal cations and organic molecules

为了阐明过渡金属阳离子与有机分子相互作用的本质，研究了结构对结合能的影响。用FT-ICR质谱仪测定了一系列苯乙酮和吡啶的配体交换平衡，得到了CuL_2^+ = Cu^+ + 2L反应的气相自由能变化。为了比较，本研究还确定了苯乙酮系列中静电相互作用起重要作用的锂阳离子碱度。取代基对Cu阳离子GB（Cu）气相碱性的影响分析表明，对π供体取代基对苯乙酮的GB（Cu）的影响比GB(H)降低29%，比GB（Li）降低37%。取代基对GB（Cu）的影响比相应的GB(H)小38%，但比GB（Li）大。对吡啶碱也观察到类似的结果。这些结果表明，cu -配合物离子中羰基氧原子处的正电荷大于li -配合物离子。研究了Cu和Li阳离子与一系列具有两个结合位点的MeO(CH_2)_nOMe在气相中的反应。当n大于4时，Cu离子呈1:1加合。从n=4到n=9， GB（Cu）随n的增加而增加，即10 kcal/mol。另一方面，当n=2时，虽然观察到与Li阳离子呈1:1的加合，但GB（Li）的变化远小于GB（Cu）。这一结果表明，O-Cu-O键的线性度是决定GB（Cu）的重要因素，与DFT计算得到的优化几何形状一致。这些事实表明，除了静电相互作用外，O-Cu和N-Cu键的性质还受共价相互作用的控制。

To elucidate the intrinsic nature of interaction between transition metal cation and organic molecule structural effects on the binding energy was investigated. The free energy changes for the reaction CuL_2^+ = Cu^+ + 2L were obtained in the gas phase for a series of acetophenones and pyridines by measuring ligand exchange equilibria using a FT-ICR mass spectrometer. For comparison lithium cation basicities in which electrostatic interaction plays a important role were also determined for acetophenone series in this sudy.Analysis of substituent effects on gas-phase basicity toward Cu cation, GB(Cu), showed that the effect of para-π-donor substituents on the GB(Cu) of acetophenone is reduced by 29% than that of GB(H) while that of GB(Li) is reduced by 37%. The magnitude of substituent effects on GB(Cu) is smaller than the corresponding GB(H) by 38% but is larger than the GB(Li). The similar results were observed for the pyridine bases. These results suggest that the positive charge developed at the carbonyl oxygen atom in the Cu-complex ion is larger than that of Li-complex ion.Reaction of Cu and Li cations with a series of MeO(CH_2)_nOMe that has two binding sites was studied in the gas phase. Cu cation gave a 1 : 1 adduct ion when n is larger than 4. The GB(Cu) increased with n, i.e., 10 kcal/mol from n=4 to n=9. On the other hand, although a 1 : 1 adduct ion with Li cation was observed when n=2, the change of GB(Li) is much smaller than the GB(Cu). This result suggests that the linearity of the O-Cu-O bond is an important factor to determine the GB(Cu), being in consistent with the optimized geometries obtained by DFT calculations.These facts suggests that the nature of O-Cu and N-Cu bonds are controlled by covalent interactions in addition to electrostatic interactions.