Stoichiometric and catalytic C–F bond activation by the trans-dihydride NHC complex [Ru(IEt₂Me₂)₂(PPh₃)₂H₂] (IEt₂Me₂= 1,3-diethyl-4,5-dimethylimidazol-2-ylidene)

Abstract

The room temperature reaction of C6F6 or C6F5H with [Ru(IEt2Me2)2(PPh3)2H2] (; IEt2Me2 = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene) generated a mixture of the trans-hydride fluoride complex [Ru(IEt2Me2)2(PPh3)2HF] () and the bis-carbene pentafluorophenyl species [Ru(IEt2Me2)2(PPh3)(C6F5)H] (). The formation of resulted from C-H activation of C6F5H (formed from C6F6via stoichiometric hydrodefluorination), a process which could be reversed by working under 4 atm H2. Upon heating with C6F5H, the bis-phosphine derivative [Ru(IEt2Me2)(PPh3)2(C6F5)H] () was isolated. A more efficient route to involved treatment of with 0.33 eq. of TREAT-HF (Et3N·3HF); excess reagent gave instead the [H2F3](-) salt () of the known cation [Ru(IEt2Me2)2(PPh3)2H](+). Under catalytic conditions, proved to be an active precursor for hydrodefluorination, converting C6F6 to a mixture of tri, di and monofluorobenzenes (TON = 37) at 363 K with 10 mol% and Et3SiH as the reductant.

Room Temperature Regioselective Catalytic Hydrodefluorination of Fluoroarenes with trans‐[Ru(NHC)4H2] through a Concerted Nucleophilic Ru−H Attack Pathway

“…This also accounts for the high selectivity observed experimentally,incontrast to earlier mixed NHC/PR 3 catalysts. [9] Our findings corroborate earlier work that predicted the effects of the presence of other F-substituents on selectivity. [7b] Thus controlling the mechanism also controls the synthetic outcome and this insight will hopefully allow the development of new HDF catalysts that have greater utility in synthesis.…”

“…[9] Our findings corroborate earlier work that predicted the effects of the presence of other F-substituents on selectivity. Experimental studies indicate that 3 acts directly in catalysis and that alternative pathways based on initial ligand loss are not relevant.…”

“…[9,10] This did indeed give higher activity,w ith C 6 F 6 being converted to difluorobenzene through four HDF cycles at 90 8 8C. [9,10] This did indeed give higher activity,w ith C 6 F 6 being converted to difluorobenzene through four HDF cycles at 90 8 8C.…”

“…Having identified hydride nucleophilicity as akey element in these Ru-catalyzed HDF reactions we turned to the more electron-rich, trans-dihydride complex [Ru(IEt 2 Me 2 ) 2 -(PPh 3 ) 2 H 2 ]( 2). [9,10] This did indeed give higher activity,w ith C 6 F 6 being converted to difluorobenzene through four HDF cycles at 90 8 8C. However,this was counterbalanced by poorer regioselectivity,with both the 1,2-and 1,4-isomers of C 6 F 2 H 4 being formed.…”

Room Temperature Regioselective Catalytic Hydrodefluorination of Fluoroarenes with trans‐[Ru(NHC)4H2] through a Concerted Nucleophilic Ru−H Attack Pathway

“…Having identified hydride nucleophilicity as a key element in these Ru‐catalyzed HDF reactions we turned to the more electron‐rich, trans ‐dihydride complex [Ru(IEt 2 Me 2 ) 2 (PPh 3 ) 2 H 2 ] ( 2 ) . This did indeed give higher activity, with C 6 F 6 being converted to difluorobenzene through four HDF cycles at 90 °C.…”