Heterobimetallic Silver–Iron Complexes Involving Fe(CO)₅ Ligands

Iron­(0) pentacarbonyl is an organometallic compound with a long history. It undergoes carbonyl displacement chemistry with various donors (L), leading to molecules of the type Fe­(CO)x(L)5–x. The work reported here illustrates that Fe­(CO)5 can also act as a ligand. The reaction between Fe­(CO)5 with the silver salts AgSbF6 and Ag­[B­{3,5-(CF3)2C6H3}4] under appropriate conditions resulted in the formation of [(μ-H2O)­AgFe­(CO)5]2­[SbF6]2 and [B­{3,5-(CF3)2C6H3}4]­AgFe­(CO)5, respectively, featuring heterobimetallic {Ag–Fe­(CO)5}+ fragments. The treatment of [B­{3,5-(CF3)2C6H3}4]­AgFe­(CO)5 with 4,4′-dimethyl-2,2′-bipyridine (Me2Bipy) and Fe­(CO)5 afforded a heterobimetallic [(Me2Bipy)­AgFe­(CO)5]­[B­{3,5-(CF3)2C6H3}4] species with a Ag–Fe­(CO)5 bond and a heterotrimetallic [{Fe­(CO)5}2(μ-Ag)]­[B­{3,5-(CF3)2C6H3}4] with a (CO)5Fe–Ag–Fe­(CO)5 core, respectively, illustrating that it is possible to manipulate the coordination sphere at silver while keeping the Ag–Fe bond intact. The chemistry of [B­{3,5-(CF3)2C6H3}4]­AgFe­(CO)5 with Et2O and PMes3 (Mes = 2,4,6-trimethylphenyl) has also been investigated, which led to [(Et2O)3Ag]­[B­{3,5-(CF3)2­C6H3}4] and [(Mes3P)2Ag]­[B­{3,5-(CF3)2­C6H3}4] with the displacement of the Fe­(CO)5 ligand. X-ray structural and spectroscopic data of new molecules as well as results of computational analyses are presented. The Fe–Ag bond distances of these metal-only Lewis pairs range from 2.5833(4) to 2.6219(5) Å. These Ag–Fe bonds are of primarily an ionic/electrostatic nature with a modest amount of charge transfer between Ag+ and Fe­(CO)5. The ν̅(CO) bands of the molecules with Ag–Fe­(CO)5 bonds show a notable blue shift relative to those observed for free Fe­(CO)5, indicating a significant reduction in Fe→CO back-bonding upon its coordination to silver­(I).五羰基合铁(0)（Iron(0) pentacarbonyl）是一类拥有悠久研究历史的有机金属化合物。它可与各类给体配体（L）发生羰基取代反应，生成通式为Fe(CO)ₓ(L)₅₋ₓ的配合物。本研究工作表明，五羰基合铁(0)还可作为配体参与配位。 在适宜反应条件下，五羰基合铁(0)分别与银盐AgSbF₆和Ag[B{3,5-(CF₃)₂C₆H₃}₄]反应，分别得到[(μ-H₂O)AgFe(CO)₅]₂[SbF₆]₂和[B{3,5-(CF₃)₂C₆H₃}₄]AgFe(CO)₅，二者均含有异双金属{Ag–Fe(CO)₅}⁺结构片段。 将[B{3,5-(CF₃)₂C₆H₃}₄]AgFe(CO)₅分别与4,4'-二甲基-2,2'-联吡啶（Me₂Bipy）和五羰基合铁(0)反应，可得到含Ag–Fe(CO)₅键的异双金属物种[(Me₂Bipy)AgFe(CO)₅][B{3,5-(CF₃)₂C₆H₃}₄]，以及以(CO)₅Fe–Ag–Fe(CO)₅为核心的异三金属配合物[{Fe(CO)₅}₂(μ-Ag)][B{3,5-(CF₃)₂C₆H₃}₄]，该结果证明，在保持Ag–Fe键完整的前提下，可对银中心的配位环境进行精准调控。 本研究还考察了[B{3,5-(CF₃)₂C₆H₃}₄]AgFe(CO)₅分别与乙醚（Et₂O）和三(2,4,6-三甲基苯基)膦（PMes₃，Mes=2,4,6-三甲基苯基）的反应，最终得到了[Fe(CO)₅]配体被取代的产物[(Et₂O)₃Ag][B{3,5-(CF₃)₂C₆H₃}₄]和[(Mes₃P)₂Ag][B{3,5-(CF₃)₂C₆H₃}₄]。 本文报道了上述新型配合物的X射线晶体结构、光谱表征数据以及计算分析结果。这类纯金属路易斯酸碱对（metal-only Lewis pairs）的Fe–Ag键长介于2.5833(4)至2.6219(5) Å之间。此类Ag–Fe键主要以离子/静电相互作用为主要成键方式，同时在Ag⁺与Fe(CO)₅之间存在一定程度的电荷转移。 与游离态的五羰基合铁(0)相比，含Ag–Fe(CO)₅键的配合物的ν̅(CO)谱带呈现显著蓝移，表明其与银(I)配位后，Fe→CO的反馈π键作用发生了显著减弱。