Regioselective Mono-, Di-, and Trifunctionalization of Iridabenzofurans through Electrophilic Substitution Reactions

Reaction between the cationic iridacyclopentadiene complex [Ir(C4H4)(NCMe)(CO)(PPh3)2][CF3SO3] (1) and methylpropiolate produces the cationic iridabenzofuran [Ir(C7H5O{OMe-7})(CO)(PPh3)2][CF3SO3] (2) in high yield. On treatment of 2 with chloride, the carbonyl ligand is displaced and the corresponding neutral iridabenzofuran Ir(C7H5O{OMe-7})Cl(PPh3)2 (3) is formed. The fused metallacyclic rings of the iridabenzofurans 2 and 3 bear only one substituent (OMe), and therefore these compounds are well suited for studies of electrophilic aromatic substitution reactions. Bromination of cationic 2 with pyridinium tribromide proceeds to give the monobrominated iridabenzofuran [Ir(C7H5O{OMe-7}{Br-6})(CO)(PPh3)2][CF3SO3] (4) exclusively. Bromination of neutral 3 with the same reagent gives the dibrominated iridabenzofuran Ir(C7H5O{OMe-7}{Br-6}{Br-2})Br(PPh3)2 (5) exclusively. Treatment of compound 3 with mercury(II) trifluoroacetate followed by excess bromide (to displace coordinated trifluoroacetate) produces the trimercurated iridabenzofuran Ir(C7H5O{OMe-7}{HgBr-6}{HgBr-4}{HgBr-2})Br(PPh3)2 (6). The three Hg−C bonds in 6 are readily cleaved on addition of pyridinium tribromide, and the resulting product is the tribrominated iridabenzofuran Ir(C7H5O{OMe-7}{Br-6}{Br-4}{Br-2})Br(PPh3)2 (7). These regioselective mono-, di-, and trifunctionalization reactions of iridabenzofurans have been studied by DFT calculations, and the derived condensed Fukui functions have been used to rationalize the preferred sites for electrophilic attack. The crystal structures of 2−7 have been obtained.

阳离子型铱杂环戊二烯配合物[Ir(C₄H₄)(NCMe)(CO)(PPh₃)₂][CF₃SO₃]（化合物1）与丙炔酸甲酯发生反应，以高产率得到阳离子型铱苯并呋喃配合物[Ir(C₇H₅O{OMe-7})(CO)(PPh₃)₂][CF₃SO₃]（化合物2）。用氯化物处理化合物2时，其羰基配体发生取代反应，生成相应的中性铱苯并呋喃配合物Ir(C₇H₅O{OMe-7})Cl(PPh₃)₂（化合物3）。铱苯并呋喃2和3的稠合金属杂环仅带有一个取代基（OMe），因此这类化合物非常适合用于亲电芳香取代反应的研究。以三溴化吡啶鎓为溴代试剂对阳离子型配合物2进行反应，专一性得到单溴代铱苯并呋喃配合物[Ir(C₇H₅O{OMe-7}{Br-6})(CO)(PPh₃)₂][CF₃SO₃]（化合物4）。使用相同试剂对中性配合物3进行溴代反应，专一性得到二溴代铱苯并呋喃配合物Ir(C₇H₅O{OMe-7}{Br-6}{Br-2})Br(PPh₃)₂（化合物5）。用三氟乙酸汞(II)处理化合物3，再加入过量溴化物以取代配位的三氟乙酸根配体，得到三汞取代的铱苯并呋喃配合物Ir(C₇H₅O{OMe-7}{HgBr-6}{HgBr-4}{HgBr-2})Br(PPh₃)₂（化合物6）。配合物6中的三条Hg−C键在加入三溴化吡啶鎓后可轻易断裂，所得产物为三溴代铱苯并呋喃配合物Ir(C₇H₅O{OMe-7}{Br-6}{Br-4}{Br-2})Br(PPh₃)₂（化合物7）。本研究通过密度泛函理论（DFT）计算对铱苯并呋喃的这些区域选择性单、双、三官能化反应进行了探究，并利用推导得到的凝聚型福井函数（condensed Fukui functions）阐释了亲电进攻的优先位点。目前已获得配合物2至7的晶体结构。