Binuclear iron boronyl carbonyls isoelectronic with the well-known decacarbonyldimanganese

The recent (2010) synthesis of the boronylplatinum halide (R3P)2Pt(BO)Br by Braunschweig and coworkers makes interesting the chemistry of metal carbonyl boronyls isoelectronic with the binary metal carbonyls Mx(CO)y. In this connection, theoretical studies on Fe2(BO)2(CO)8 isoelectronic with the known Mn2(CO)10 predict symmetrical unbridged structures consisting of Fe(BO)(CO)4 units linked by an iron–iron single bond of ∼2.9 A length. These Fe2(BO)2(CO)8 structures with a staggered arrangement of the BO and CO ligands are similar to the experimental structure of Mn2(CO)10. Three such structures are found within ∼3 kcal mol−1 of energy differing only in the locations of the terminal BO groups. Related higher energy unbridged eclipsed Fe2(BO)2(CO)8 structures are found with small imaginary vibrational frequencies of around 30i cm−1. Following the corresponding normal modes leads to the corresponding staggered structures. Even higher energy symmetrical Fe2(μ-CO)2(BO)2(CO)8 structures are found with two bridging carbonyl groups lying 15 to 21 kcal mol−1 above the global minimum, again similar to the isoelectronic Mn2(CO)10 system. In addition to the above structures higher energy unsymmetrical Fe2(BO)2(CO)8 structures are found, which have no analogues in Mn2(CO)10 chemistry. These include structures in which an Fe(CO)4 unit is connected to an Fe(BO)(CO)4 unit through a bridging BO group without an iron–iron bond as well as a structure in which an Fe(CO)5 unit is connected to an Fe(BO)2(CO)3 unit by an Fe–Fe dative bond. The lowest energy Fe2(BO)2(CO)8 structure is viable towards symmetric dissociation into two Fe(BO)(CO)4 radicals as well as unsymmetrical dissociation into Fe(CO)5 + Fe(BO)2(CO)3 with dissociation energies in excess of 15 kcal mol−1.