Binuclear fluoroborylene manganese carbonyls

The lowest energy structure for Mn2(BF)(CO)10 is predicted to consist of two Mn(CO)5 groups bridged by a BF group without a manganese–manganese bond. This structure is related to the stable compounds Mn2(μ-BX)(CO)10 (X = Cl, Br) and [(η5-C5H5)Ru(CO)2]2(μ-BF), which have been synthesized and characterized by X-ray crystallography. The following principles determine the lowest energy structures of the Mn2(BF)(CO)n (n = 9, 8, 7, 6) derivatives: (1) two-electron donor bridging μ-BF groups are highly favorable; (2) four-electron donor bridging η2-μ-BF groups are not found and thus appear to be highly unfavorable. Thus the lowest energy structure of Mn2(BF)(CO)9 is a doubly bridged structure with bridging CO and BF groups, in contrast to the experimentally observed unbridged structure of Mn2(CO)10. The lowest energy structures of Mn2(BF)(CO)8 have either a four-electron donor η2-μ-CO group or a two-electron donor bridging BF group. Similarly the lowest energy structures of the more highly unsaturated Mn2(BF)(CO)n (n = 7, 6) are singlet (for n = 7) or triplet (for n = 6) states in which the BF group is a bridging rather than a terminal ligand.