Observations on the Stereodynamic Behavior of Mono‐ and Polynuclear Iron Carbonyl Compounds Including a Survey of M(CO)3 Scrambling Processes

Abstract

AbstractIt has been shown conclusively by the observation of 57Fe–13C coupling (J = 8.3 Hz) that in Fe3(CO)12 the scrambling is intramolecular and that all of the CO groups have equal access to all three of the iron atoms. This result is fully in accord with the scrambling mechanism proposed in an earlier paper from this laboratory. We have found that for axially substituted amine derivatives of iron pentacarbonyl, AmFe(CO)4, the activation energy for CO scrambling is raised from the extremely low value (ca. 2 kcal mol−1) characteristic of Fe(CO)5 to a range (ca. 5.0–5.5 kcal mol−1) such that the coalescence temperatures are at, or very near, the threshold (ca. – 150°C) of experimental observation. The crystal and molecular structures of (1,2‐C4H4N2)Fe(CO)4 are also reported. The molecular structure is very similar to those of the (C5H5N)Fe(CO)4 and (1,4‐C4H4N2)Fe(CO)4 compounds. The space group is P21/n with unit cell dimensions a = 6.487(1)Å, b = 11.331(3)Å, c = 14.226(3)Å, β = 107.85(2)Å, V = 995.3(4)Å3. Finally, in the compound (C9H8O)Fe(CO)3, where C9H8O is derived from barbaralone, the scrambling of the three CO groups proceeds in a concerted manner with an activation energy of 16.5(3) kcal mol−1. The available data for CO scrambling in M(CO)3 moieties in general is summarized and discussed.