Dinuclear Mn Complexes Featuring Formal Metal–Metal Double Bonds

Dimanganese complexes featuring formal metal–metal multiple (MMM) bonds are scarce. Here, we examine the 32-e– bis-μ-phosphido complex [{Mn(CO)3(μ-PtBu2)}2] (1), which has a formal bond order (fBO) of two. But does 1 actually possess Mn–Mn multiple bonding? In a previous study, we answered this question through assessment of its short Mn–Mn distance and unusual low-energy absorption in the UV–vis spectrum. Herein, we further address the question through sequential reduction, UV–vis, and resonance Raman spectroscopic analysis, and computational methods. Reduction of 1 resulted in several new complexes, some with fBO = 2; only those with fBO = 2 exhibit the characteristic low-energy MM→MM* transition predicted by TD-DFT, whereas species with fBO = 1 do not. This work addresses the broader hypothesis that MMM bonds in low-coordinate dimanganese complexes may act as spectators or participants in reactions. This view aligns with prior observations that CO dissociation from dimanganese carbonyls is required for alkyne and H2 activation (Lacy; ; Abhyankar Chem. - Eur. J. 2023, e202300518). These results suggest that the elusive Mn–Mn multiple bond is more than just an esoteric curiosity but a plausible hidden participant in the landscape of dinuclear manganese catalysis.