Iodine Oxidative Addition to Isomeric Platinum(II) Phosphine Complexes

The reaction between cis and trans isomers of (Et3P)2PtAr2 (Ar = 4-FC6H4) (1a and 1b,
respectively) with I2 was studied in detail. At low temperatures, the clean formation of an
intermediate was observed for each of the isomers. Upon warming, both intermediates
provided the single thermodynamic product trans-(Et3P)2PtAr2(I)2 (2), where each of the iodo
ligands is located trans to the aryl group in the equatorial plane. The reactions followed
first-order kinetics with the intermediate formed from 1b converting into 2 at a faster rate
than that from 1a. The conversion was significantly faster in toluene than in acetone, with
the reaction in toluene giving a very large negative activation entropy (ca. −40 cal/mol·K-1). On the basis of the NMR analysis and kinetic data, both intermediates are proposed
to be the corresponding products of the trans oxidative addition. Subsequent iodide
dissociation and rearrangement of the resulting pentacoordinate Pt(IV) complex provides
complex 2.

本研究详细探究了(Et₃P)₂PtAr₂（Ar=4-FC₆H₄）的顺式（1a）与反式（1b）异构体分别与碘单质（I₂）的反应。低温条件下，两种异构体均可干净地生成对应中间体；升温后，两个中间体均转化为单一热力学产物反式-(Et₃P)₂PtAr₂I₂（2），该产物中两个碘配体均位于赤道平面内，且各自与芳基配体呈反式配位。该反应遵循一级动力学规律，由1b生成的中间体转化为产物2的速率快于由1a生成的中间体。甲苯溶剂中的反应速率显著高于丙酮体系，且甲苯体系下反应的活化熵为绝对值较大的负值（约-40 cal/(mol·K)）。基于核磁共振（NMR）分析与动力学数据，本研究提出两种中间体均为对应反式氧化加成产物；后续经碘离子解离及生成的五配位铂(IV)配合物重排，最终得到产物2。