"Click"-Like η 6 -Metalation/Demetalation of Aryl Iodides as a Means of Turning "ON/OFF" Halogen Bond Donor Functionality.

η 6 -Metalated aryl halides are recognized as a class of halogen bond (XB) donors. Click-like η 6 -metalation/demetalation of aryl iodides by cyclopentadienylruthenium(II) ([CpRu II ] + ) is shown to turn ON/OFF (amplify/suppress) XB donor functionality. [CpRu(MeCN) 3 ][PF 6 ] is shown to react quantitatively with iodobenzenes (ArI n , n=1,2) to yield [CpRu(η 6 -ArI n )][PF 6 ] compounds. Photochemical demetalation (405 nm) quantitatively reverts these compounds to ArI n and [CpRu(MeCN) 3 ][PF 6 ]. Crystal structures of [CpRu(ArX n )] + salts show that the [CpRu(ArI n )] + cations are strong, charge-assisted XB donors analogous to iodopyridinium cations. XB-induced association of [CpRu(C 6 H 5 I)] + with diazobicyclo[2.2.2]octane (DABCO) is established by NMR spectroscopy. [CpRu(C 6 H 5 I)][BPh 4 ] and [CpRu(1,4-C 6 H 4 I 2 )][BPh 4 ] co-crystallize with DABCO and the structure of [CpRu(1,4-C 6 H 4 I 2 )][BPh 4 ]⋅DABCO⋅Et 2 O is reported. DFT calculations support amplification of the XBing capabilities of aryl iodides upon [CpRu] + -metalation.