Alkyl dehydrogenation in iridium tri-cyclopentyl phosphines

The iridium cyclooctadiene complex incorporating a tricyclopentyl phosphine ligand (PCyp3), Ir(η2:η2-C8H12)(PCyp3)Cl, has been prepared. Removal of the chloride from this complex using Na [ BAr F 4 ] [ Ar F = C 6 H 3 ( CF 3 ) 2 ] in CH2Cl2/arene solvent results in dehydrogenation (C–H activation followed by β-H transfer) of one of the alkyl phosphine rings and formation of the complexes [ Ir ( η 6 - C 6 H 5 X ) { PCyp 2 ( η 2 - C 5 H 7 ) } ] [ BAr F 4 ] (X = H, F) which contain a hybrid phosphine–alkene ligand. These complexes are formed alongside another product (5–20% yield) that has been identified as [ Ir ( η 2 : η 2 - C 8 H 12 ) { PCyp 2 ( η 2 - C 5 H 7 ) } ] [ BAr F 4 ] , which can be prepared in high yield by an alternative, and slightly modified, route. This complex is with a minor isomer that has been tentatively identified as [ Ir ( η 2 : η 3 - C 8 H 11 ) ( H ) { PCyp 2 ( η 2 - C 5 H 7 ) } ] [ BAr F 4 ] , which results from allylic C–H activation of cyclooctadiene. Addition of H2 to [ Ir ( η 2 : η 2 - C 8 H 12 ) { PCyp 2 ( η 2 - C 5 H 7 ) } ] [ BAr F 4 ] and its isomer in arene solvent (C6H5X, X = F, H) forms the dihydrido η6-arene Ir(III) complexes [ Ir ( H ) 2 ( η 6 - C 6 H 5 X ) ( PCyp 3 ) ] [ BAr F 4 ] . In contrast, hydrogenation in CH2Cl2 alone results in the formation of Ir ( H ) 2 ( PCyp 3 ) { η 6 - ( C 6 H 3 ( CF 3 ) 2 ) BAr F 3 } in which the [ BAr F 4 ] - anion is now acting as a ligand through one of its aryl rings. The fluorobenzene complex [ Ir ( H ) 2 ( η 6 - C 6 H 5 F ) ( PCyp 3 ) ] [ BAr F 4 ] can be cleanly converted to [ Ir ( η 6 - C 6 H 5 F ) { PCyp 2 ( η 2 - C 5 H 7 ) } ] [ BAr F 4 ] by addition of the hydrogen acceptor tert-butylethene (tbe).