ИСТИНА

The activity of manganese phenylvinylidene Cp(CO)(Ph3P)Mn=С=С(H)Ph and diphenylallenylidene Cp(CO)2Mn=С=С=СPh2 complexes in catalyzing the electrochemical reduction of proton in an acidic medium,1 as we have described earlier, gives promise that a similar activity can be exhibited by other transition metal complexes, the protonated forms of which contain a C–H bond conjugated with the metal–carbon multiple bond. Therefore, we studied the activity of the iron σ-phenylethynyl complex Ср(СО)(Ph3P)Fe–C≡CPh (1), the rhenium vinylidene complex Cp*(CO)2Re=С=С(H)Ph (2), and the manganese isonitrile complexes Cp(CO)2Mn=С=NR (3, R=Me; 4 R = But) in such a catalysis. Complexes 1 and 2 were found to be active in the ERP: they are quantitatively protonated by HBF4•OEt2 in СH2Cl2 to form a cationic iron vinylidene [Ср(СО)(Ph3P)Fe=C=C(H)Ph]BF4 (1H+) and a cationic rhenium carbyne [Cp*(CO)2Re≡С‒СH2Ph]BF4 (2H+), respectively (see Scheme 1). Catalytic currents were observed upon the electrochemical reduction of (1H+) and (2H+) to corresponding 19e radicals (1H▪) and (2H▪); the current magnitudes were governed by the structure of the catalyst and the acid content in a solution (see data in Scheme 1). The key step in these catalytic cycles is the homolysis of Cβ-H bonds in 19e radicals (1H▪) and (2H▪), which is accompanied by hydrogen evolution and regeneration of the starting complexes 1 and 2.