The Structure of ([W₃Q₄X₃(dmpe)₃]⁺, Y^-) Ion Pairs (Q = S, Se; X = H, OH, Br; Y = BF₄, PF₆, dmpe = Me₂PCH₂CH₂PMe₂) in Dichloromethane Solution and the Effect of Ion-Pairing on the Kinetics of Proton Transfer to the Hydride Cluster [W₃S₄H₃(dmpe)₃]⁺

The 1H,19F HOESY spectra of the title compounds in CD2Cl2 solution indicate that the cluster cations form ion pairs with the BF4- and PF6- anions with a well-defined interionic structure that appears to be basically determined essentially by the nature of the X- ligand. For the clusters with X = H and OH, the structure of the ion pairs is such that the counteranion (Y-) and the X- ligands are placed close to each other. However, when the size and electron density of X- increase (X = Br), Y- is forced to move to a different site, far away from X-. The relevance of ion-pairing on the chemistry of these compounds is clearly seen through a decrease in the rate of proton transfer from HCl to the hydride cluster [W3S4H3(dmpe)3]+ in the presence of an excess of BF4-. The kinetic data for this reaction can be rationalized by considering that the ([W3S4H3(dmpe)3]+, BF4-) ion pairs are unproductive in the proton-transfer process. Theoretical calculations indicate that the real behavior can be more complex. Although the cluster can still form adducts with HCl in the presence of BF4-, the structures of the most-stable BF4--containing HCl adducts show H···H distances too large to allow the subsequent release of H2. In addition, the effective concentration of HCl is also reduced because of the formation of adducts as ClH···BF4-. As a consequence of both effects, the proton transfer takes place more slowly than for the case of the dihydrogen-bonded HCl adduct resulting from the unpaired cluster.标题化合物在氘代二氯甲烷（CD2Cl2）溶液中的1H、19F异核Overhauser效应谱（1H,19F HOESY）结果表明，簇阳离子与四氟硼酸根阴离子（BF4-）、六氟磷酸根阴离子（PF6-）形成离子对，其离子间结构明确，且该结构本质上主要由X-配体的性质所决定。对于X为H或OH的簇体系，其离子对结构表现为抗衡阴离子（Y-）与X-配体相互靠近。但当X-的尺寸与电子密度增大时（如X=Br），抗衡阴离子Y-会被推移至远离X-的另一位置。离子配对对该类化合物化学行为的影响，可通过过量BF4-存在时，氯化氢（HCl）向氢化物簇[W3S4H3(dmpe)3]+的质子转移速率降低的现象直观体现。该反应的动力学数据可通过以下思路得到合理解释：([W3S4H3(dmpe)3]+, BF4-)离子对无法参与质子转移过程。理论计算结果显示，实际反应过程可能更为复杂。尽管在BF4-存在下簇阳离子仍可与HCl形成加合物，但含BF4-的最稳定HCl加合物的氢-氢（H···H）间距过大，无法发生后续的氢气释放步骤。此外，由于ClH···BF4-型加合物的形成，HCl的有效浓度也会有所降低。受上述两种因素共同影响，该质子转移反应的速率较未配对簇与HCl形成的双氢键合HCl加合物体系更为缓慢。