Metal Complexes of a Redox‐Active [1]Phosphaferrocenophane: Structures, Electrochemistry and Redox‐Induced Catalysis

The synthesis and characterisation of several metal complexes of a redox‐active, mesityl(Mes)‐substituted [1]phosphaferrocenophane, FcPMes ( 1 ), are reported. Cyclic voltammetry studies on the bimetallic complexes [M(κ 1 P ‐ 1 )(cod)Cl] (M=Rh: 2 ; M=Ir: 4 ), [Rh(κ 1 P ‐ 1 ) 2 (CO)Cl] ( 3 ) and [AuCl(κ 1 P ‐ 1 )] ( 5 ), in conjunction with DFT calculations, provided indications for a good electronic communication between the metal atoms. To confirm that the ferrocenophane unit might be able to electrochemically influence the reactivity of the coordinated transition metal, the rhodium complex 2 was employed as stimuli‐responsive catalyst in the hydrosilylation of terminal alkynes. All reactions were greatly accelerated with in situ generated 2 + as a catalyst as compared to 2 . Even more importantly, a markedly different selectivity was observed. Both factors were attributed to different mechanisms operating for 2 and 2 + (alternative Chalk–Harrod and Chalk–Harrod mechanism, respectively). DFT calculations revealed relatively large differences for the activation barriers for 2 and 2 + in the reductive elimination step of the classical Chalk–Harrod mechanism. Thus, the key to the understanding is a cooperative “oxidatively induced reductive elimination” step, which facilitates both a higher activity and a markedly different selectivity.