The unsaturated trinuclear iron fluoroborylene complexes Fe3(BF)3(CO) n (n = 7, 6) have been studied using density functional theory (DFT). Relatively complicated potential energy surfaces are found with nine and eight structures within 15 kcal mol-1 of the lowest energy structures for the Fe3(BF)3(CO)7 and Fe3(BF)3(CO)6 systems, respectively. In each of these low-energy structures all three BF groups are either edge-bridging or face-bridging but never terminal groups. Some, but not all, of the low-energy structures also have edge-bridging and/or face-bridging CO groups leading to some structures with as many as five bridging groups. The relatively narrow range of Fe-Fe distances in the central Fe3 triangles of the Fe3(BF)3(CO) n (n = 7, 6) structures, mainly between 2.37 and 2.55 Å, suggests considerable delocalization in these unsaturated systems. Graphical Abstract The lowest energy Fe3(BF)3(CO)7 and Fe3(BF)3(CO)6 structures have a face-bridging μ3-BF group with the two remaining BF groups bridging edges. The lowest energy Fe3(BF)3(CO)6 structure also has one four-electron donor bridging η2-μ-CO group.
Keywords: Density functional theory; Fluoroborylene; Iron; Metal carbonyls; Metal-metal bonding.