Manganese carbonyl fluorides: are they viable molecules?

Abstract

The mononuclear Mn(CO)₅X and binuclear Mn₂(CO)₈(μ-X)₂ manganese carbonyl halides have long been known for the halogens Cl, Br, and I. However, the corresponding manganese carbonyl fluorides (X = F) remain unknown. The structures and thermochemistry of such manganese carbonyl fluorides and their decarbonylation products have now been investigated using density functional theory. In all cases singlet structures were found to have lower energies than the corresponding triplet structures. The expected octahedral structure is predicted for Mn(CO)₅F. Decarbonylation of Mn(CO)₅F is predicted to give trigonal bipyramidal Mn(CO)₄F with equatorial fluorine. Further, decarbonylation gives tetrahedral Mn(CO)₃F. All of the binuclear Mn₂(CO)_nF₂ structures (n = 8, 7, 6) are predicted to have a central Mn₂F₂ unit with two bridging F atoms, a non-bonding Mn⋯Mn distance of ∼3.1 Å, and exclusively terminal CO groups. The thermochemistry of these manganese carbonyl fluorides indicates that they are viable species. This suggests that the failure to date to synthesize the simple manganese carbonyl fluorides arises from a lack of a suitable synthetic method rather than from the instability of the desired products.