Bis(imino)carbazolide Complexes of Rhodium: Highly Nucleophilic Ligands Exerting a Dramatic Accelerating Effect on MeI Oxidative Addition

Rhodium(I) complexes bearing a bis(imino)carbazolide ligand L and an additional neutral
donor [LRh(C2H4), 2; LRh(CO), 3] have been prepared via a salt metathesis reaction between
NaL and the dimeric rhodium precursors [RhCl(C2H4)2]2 and [RhCl(CO)2]2, respectively.
Complex 3 was also prepared by reaction of the free ligand with [RhCl(CO)2]2, whereas a
related reaction with [RhCl(C2H4)2]2 afforded the dinuclear RhI−RhIII ethyl complex 4. The
X-ray crystal structure of 4 showed octahedral [bis(imino)carbazolide]RhIII(Cl)Et linked to
square-planar bis(ethylene)RhICl via chloride bridges. Kinetic studies on the oxidative
addition of MeI to 3 to form the LRhIIII(CO)Me complex 5 revealed a second-order rate
constant of 1.66 M-1 s-1 in CH2Cl2 at 25 °C, which corresponds to a reaction rate
approximately 50 000 times faster than that observed for [RhI2(CO)2]-.

带有双(亚氨基)咔唑基配体(bis(imino)carbazolide ligand) L及额外中性给体的一价铑配合物(rhodium(I) complexes) [LRh(C₂H₄), 2；LRh(CO), 3]，分别经由NaL与二聚铑前驱体(dimeric rhodium precursors) [RhCl(C₂H₄)₂]₂和[RhCl(CO)₂]₂之间的复分解反应(salt metathesis reaction)制得。配合物3亦可通过游离配体与[RhCl(CO)₂]₂的反应制备，而与之对应的与[RhCl(C₂H₄)₂]₂的反应则得到了双核Rh(I)-Rh(III)乙基配合物4。配合物4的X射线晶体结构(X-ray crystal structure)显示，八面体构型(octahedral)的[双(亚氨基)咔唑基]Rh(III)(Cl)Et通过氯桥(chloride bridges)与平面正方形构型(square-planar)的双(乙烯)Rh(I)Cl相连。针对甲基碘(methyl iodide, MeI)与配合物3发生氧化加成(oxidative addition)以生成LRh(III)(CO)Me配合物5的动力学研究表明，在25 ℃的二氯甲烷(dichloromethane, CH₂Cl₂)溶剂中，其二级速率常数(second-order rate constant)为1.66 M⁻¹·s⁻¹，该反应速率约比[RhI₂(CO)₂]⁻所对应的反应速率快50000倍。