“Click”‐Like η⁶‐Metalation/Demetalation of Aryl Iodides as a Means of Turning “ON/OFF” Halogen Bond Donor Functionality

Abstract

η6‐Metalated aryl halides are recognized as a class of halogen bond (XB) donors. Click‐like η6‐metalation/demetalation of aryl iodides by cyclopentadienylruthenium(II) ([CpRuII]+) is shown to turn ON/OFF (amplify/suppress) XB donor functionality. [CpRu(MeCN)3][PF6] is shown to react quantitatively with iodobenzenes (ArIn, n=1,2) to yield [CpRu(η6‐ArIn)][PF6] compounds. Photochemical demetalation (405 nm) quantitatively reverts these compounds to ArIn and [CpRu(MeCN)3][PF6]. Crystal structures of [CpRu(ArXn)]+ salts show that the [CpRu(ArIn)]+ cations are strong, charge‐assisted XB donors analogous to iodopyridinium cations. XB‐induced association of [CpRu(C6H5I)]+ with diazobicyclo[2.2.2]octane (DABCO) is established by NMR spectroscopy. [CpRu(C6H5I)][BPh4] and [CpRu(1,4‐C6H4I2)][BPh4] co‐crystallize with DABCO and the structure of [CpRu(1,4‐C6H4I2)][BPh4]⋅DABCO⋅Et2O is reported. DFT calculations support amplification of the XBing capabilities of aryl iodides upon [CpRu]+‐metalation.