Chemistry - A European Journal
Chemistry - A European Journal
4 years ago

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

Metal Complexes of a Redox-Active [1]Phosphaferrocenophane: Structures, Electrochemistry and Redox-Induced Catalysis
Karin Fink, Frank Breher, Markus K. Armbruster, Alexander Feyrer
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(κ1P-1)(cod)Cl] (M=Rh: 2; M=Ir: 4), [Rh(κ1P-1)2(CO)Cl] (3) and [AuCl(κ1P-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. Redox-induced catalysis: Bimetallic complexes of a [1]phosphaferrocenophane are reported featuring a good electronic communication between the metal atoms. A rhodium(I) complex was employed as redox-active catalyst in the hydrosilylation of terminal alkynes. Oxidatively induced reductive elimination facilitates higher activity and markedly different selectivity for the oxidised complex.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201700868

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