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High-spin and Low-spin Iron(II) Complexes with Facially Coordinated Borohydride Ligands

Mehn, M. P.; Brown, S. D.; Paine, T. K.; Brennessel, W. W.; Cramer, C. J.; Peters, J. C.; Que, L., Jr.
Dalton Trans. 2006, 1347.

Rare examples of monometallic high-spin and low-spin L3Fe(H3BH) complexes have been characterized, where the two L3 ligands are [TpPh2] and [PhBP3] ([TpPh2] = [HB(3,5-Ph2pz)3]- and [PhBP3] = [PhB(CH2PPh2)3]-). The structures are reported and the borohydride ligand is facially coordinated to the iron center in each complex. Density functional methods have been employed to explain the differences in bonding in these unusual iron(II) centers. Despite the differences in spin states, short Fe-B distances are observed in both complexes and it is believed that there is signifcant theoretical evidence to support a substantial bonding interaction between the iron and boron nuclei. In light of this interaction, we suggest these complexes can be described as (L3)Fe(η4-H3BH) complexes.

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