Unsaturation in Cyclopentadienyliron Carbonyl Fluoroborylene Derivatives: Formation of Difluorodiborene Complexes (pp. 61-160)
Authors: Liancai Xu, Qian-shu Li, R. Bruce King, and Henry F. Schaefer
Abstract: The fluoroborylene ligand (BF), isoelectronic with CO, was recently (2009) realized experimentally by Vidovi´c and Aldridge in Cp2Ru2(CO)4(µ-BF). The analogous iron derivative Cp2Fe2(CO)4(µ-BF) is predicted by density functional theory to be a viable molecule. However, the related Cp2Fe2(CO)3(BF)(µ-BF) is predicted to be disfavored with respect to CO loss. Doubly bridged structures are found for Cp2Fe2(BF)2(CO)2 and Cp2Fe2(BF)(CO)3 with BF bridges clearly preferred energetically over CO bridges. The lowest energy Cp2Fe2(BF)2(CO) structure is a singlet structure with a symmetrical bridging difluoroborylene B2F2 ligand as well as a bridging CO ligand. In a higher energy singlet Cp2Fe2(BF)2(CO) structure a BF and a CO ligand have coupled to form a bridging FB-CO ligand. For Cp2Fe2(BF)(CO)2 the lowest energy structure is a triplet triply bridged structure similar to the experimental Cp2Fe2(µ-CO)3 structure. The lowest energy Cp2Fe2(BF)2 and Cp2Fe2(BF)(CO) structures are doubly bridged structures. However, a higher energy singlet Cp2Fe2(µ-B2F2) structure is found with an unsymmetrical bridging difluorodiborene ligand.