Diverse and Selective Metal-Ligand Cooperative Routes for Activating Non-Functionalized Ketones

The rhodium and iridium complexes [Cp*M(κ³N,N',N″-L)][SbF₆] (Cp* = η⁵-C₅Me₅; M = Rh, 1; Ir, 2; HL = pyridinyl-amidine ligand) exhibit three different cooperative metal-ligand reactivity modes when interacting with nonfunctionalized ketones. With the methyl ketones CH₃COR (R = CH₃, Ph, CF₃), activation of the ketone methyl C(sp³)-H bond yields ketonyl compounds of formula [Cp*M(CH₂COR)(κ²N,N'-HL)][SbF₆]. With the ketones (CF₃)₂CO and CF₃COPh, the complexes add to the C═O double bond of the ketone. The addition of the iridium compound 2 occurs across the metal atom and the exocyclic carbon of the dearomatized pyridinyl moiety, and that of the rhodium analogue 1 takes place through the rhodium atom and the exocyclic methylene carbon of the Cp* ligand of the intermediate fulvene complex. In the rhodium case, the resulting metal-alkoxide derivative evolves to give rise to rhodium derivatives containing up to four added ketone molecules. In all of these processes, no additives are required, rendering them atom 100% efficient procedures for bond activation. From a mechanistic point of view, DFT calculation reveals that the diverse and selective behavior of 1 and 2 toward ketones can be explained by invoking three different intermediates, each driving the process through distinct reaction pathways.