Abstract
1‐Triphenylphosphoniobenzo[c]phospholide 1 reacts with [M(CO)~5~Br] (M = Mn, Re) and [Mn(CO)~3~(naphthalene)][BF~4~] to give complexes cis‐[M(CO)~4~(1)Br] (5 a,b) and [Mn(CO)~3~(1)][BF~4~] (6 a[BF~4~]), respectively, featuring η^1^(P)‐ and η^5^(π)‐coordination of the phosphole ring. The corresponding reactions with [M~2~(CO)~10~] proceed with conservation of the metal–metal bond and yield, depending on the reaction temperature, dinuclear complexes [M~2~(CO)~8~(1)] (M=Mn, 7 a) or [M~2~(CO)~6~(1)~2~] (M=Mn, Re, 8 a,b) with μ~2~‐bridging η^1^(P):η^2^(PC) coordination of the phosphole moiety. All complexes formed were characterized by spectroscopic data; 5 b, 6 a[BF~4~], and 8 a,b were characterized by X‐ray diffraction studies as well. The structural and ^31^P NMR data of the dinuclear manganese complex 8 a suggest that the interaction between the metal atoms and the η^2^‐bound PC double bond moieties is dominated by the L→M charge‐transfer contribution; this hints at a very low back‐donation ability of the central M~2~(CO)~6~ fragment. Investigation of the reactions of the Mn complexes 6 a and 8 a with Mg or ferrocenium hexafluorophosphate ([Fc][PF~6~]), respectively, revealed that the chemically reversible mutual interconversion between both species was feasible. Likewise, oxidation of the rhenium complex 8 b with [Fc][PF~6~] gave spectroscopic evidence for the formation of a Re analogue of 6 a. Electrochemical studies suggested that the oxidation 8 a→2 6 a involves two consecutive single‐electron‐transfer steps, the first of which is electrochemically reversible and produces a metastable radical cation that is detectable by ESR spectroscopy. The mutual interconversion between 6 a and 8 a represents the first case of a reversible coordination isomerization of a phosphaarene that is triggered by a redox process and might stimulate further studies directed at the use of dinuclear phosphaarene complexes in redox‐catalysis.