Thioether, Dinitrogen, and Olefin Complexes of (PNP)Rh: Kinetics and Thermodynamics of Exchange and Oxidative Addition Reactions

A variety of (PNP)Rh−L complexes (where L = organic sulfide or sulfoxide, dinitrogen, or tert-butylethylene) have been synthesized by trapping transient (PNP)Rh (1) in situ. Equilibrium studies established the relative affinity of the (PNP)Rh fragment (1) for various L in the following order (of decreasing affinity): Ph2SO > SBun2 > SPhMe > dibenzothiophene > SPh2 > benzothiophene > SPri2 > thiophene ≈ SButMe > SBus2 ≈ H2CCHCMe3 ≫ SBut2. Dinitrogen reacted with 1 to yield a mixture of terminal and bridging N2 complexes and was found to bind more strongly than SPri2. Reaction of (PNP)Rh(SPri2) (10) with PhHal led to the corresponding oxidative addition products (PNP)Rh(Ph)(Hal) (Hal = Cl, 18a; Hal = Br, 18b; Hal = I, 18c). The relative rates of oxidative addition of PhHal to 10 were found to be in the order PhI > PhBr > PhCl. Kinetic studies of the reaction of 10 with PhBr were consistent with the reaction proceeding via reversible dissociation of SPri2, followed by irreversible addition of PhBr. Evidence for a similar dissociative mechanism for the conversion of 10 to (PNP)Rh(S(O)Ph2) in a ligand exchange reaction was also discovered. Solid-state structures of [(PNP)Rh]2(N2) (19a) and (PNP)Rh(H2CCHCMe3) (21) were determined using X-ray crystallography. Approximately square-planar geometry about Rh was registered.

通过原位捕获瞬态(PNP)铑（1），合成了一系列(PNP)Rh−L配合物（其中L为有机硫化物、亚砜、二氮（dinitrogen）或叔丁基乙烯（tert-butylethylene））。通过平衡研究确定了(PNP)铑片段（1）对各类配体L的相对亲和性，亲和性由高到低排序如下：二苯亚砜（Ph₂SO）> 二正丁基硫醚（SBun₂）> 苯基甲基硫醚（SPhMe）> 二苯并噻吩 > 二苯硫醚（SPh₂）> 苯并噻吩 > 二异丙基硫醚（SPri₂）> 噻吩 ≈ 叔丁基甲基硫醚（SButMe）> 二仲丁基硫醚（SBus₂）≈ 叔丁基乙烯（H₂C=CHCMe₃）≫ 二叔丁基硫醚（SBut₂）。二氮（dinitrogen）与1发生反应，生成端基和桥联二氮配合物的混合物，且其结合强度高于二异丙基硫醚（SPri₂）。(PNP)Rh(SPri₂)（10）与卤代苯（PhHal）发生反应，得到相应的氧化加成（oxidative addition）产物(PNP)Rh(Ph)(Hal)（其中Hal为Cl时为18a、Hal为Br时为18b、Hal为I时为18c）。研究发现，卤代苯与10发生氧化加成（oxidative addition）的相对反应速率顺序为：碘苯（PhI）> 溴苯（PhBr）> 氯苯（PhCl）。针对10与溴苯反应的动力学研究结果表明，该反应遵循如下路径：先发生二异丙基硫醚（SPri₂）的可逆解离，随后进行不可逆的溴苯加成。同时还发现，在配体交换（ligand exchange）反应中，10转化为(PNP)Rh(S(O)Ph₂)的过程同样遵循类似的解离机制（dissociative mechanism）。通过X射线晶体学（X-ray crystallography）测定了[(PNP)Rh]₂(N₂)（19a）与(PNP)Rh(H₂C=CHCMe₃)（21）的固态结构。结果显示，铑中心周围具有近似平面正方形几何构型（square-planar geometry）。