Formation and reactions of cyanocyclohexadienyl complexes of manganese(I)

Abstract

Reactions of the cationic arene complexes [(C₆H_{6 –n}Me_n)Mn(CO)₃]⁺ with cyanide ion under mild conditions yield exo-cyanocyclohexadienyl complexes (C₆H_{6 –n}Me_nCN)Mn(CO)₃ in which the cyano-group is attached to an unsubstituted carbon atom: the hexamethylbenzene complex reacts differently to form (C₆Me₆)Mn(CO)₂CN. The preference for addition to an unsubstituted carbon atom is (at least in part) kinetic rather than thermodynamic in origin, since the compound formed by cyanide addition to the mesitylene complex rearranges in chloroform solution to give some of the isomer in which the cyano-group is attached to a methyl-substituted carbon atom.

Decomposition of the cyanocyclohexadienyl complexes in the solid state or in solution yields either (C₆H_{6 –n}Me_n)Mn(CO)₂CN or free arene and a polymeric manganese complex according to the reaction conditions used. Conventional hydride-abstracting reagents remove the cyano-group from the complexes, regenerating [(C₆H_{6 –n}Me_n)Mn(CO)₃]⁺, but oxidation with cerie ion liberates the cyano-arene C₆H_{5 –n}Me_nCN uncontaminated by C₆H_{6 –n}Me_n

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