Regioselectivity in ligand substitution reactions on diiron complexes governed by nucleophilic and electrophilic ligand properties. Academic Article uri icon


  • The discovery of a diiron organometallic site in nature within the diiron hydrogenase, [FeFe]-H2ase, active site has prompted revisits of the classic organometallic chemistry involving the Fe-Fe bond and bridging ligands, particularly of the (-SCH2XCH2S)[Fe(CO)3]2 and (-SCH2XCH2S)[Fe(CO)2L]2 (X = CH2, NH; L = PMe3, CN(-), and NHC's (NHC = N-heterocyclic carbene)), derived from CO/L exchange reactions. Through the synergy of synthetic chemistry and density functional theory computations, the regioselectivity of nucleophilic (PMe3 or CN(-)) and electrophilic (nitrosonium, NO(+)) ligand substitution on the diiron dithiolate framework of the (-pdt)[Fe(CO)2NHC][Fe(CO)3] complex (pdt = propanedithiolate) reveals the electron density shifts in the diiron core of such complexes that mimic the [FeFe]-H2ase active site. While CO substitution by PMe3, followed by reaction with NO(+), produces (-pdt)(-CO)[Fe(NHC)(NO)][Fe(CO)2PMe3](+), the alternate order of reagent addition produces the structural isomer (-pdt)[Fe(NHC)(NO)PMe3][Fe(CO)3](+), illustrating how the nucleophile and electrophile choose the electron-poor metal and the electron-rich metal, respectively. Theoretical explorations of simpler analogues, (-pdt)[Fe(CO)2CN][Fe(CO)3](-), (-pdt)[Fe(CO)3]2, and (-pdt)[Fe(CO)2NO][Fe(CO)3](+), provide an explanation for the role that the electron-rich iron moiety plays in inducing the rotation of the electron-poor iron moiety to produce a bridging CO ligand, a key factor in stabilizing the electron-rich iron moiety and for support of the rotated structure as found in the enzyme active site.

published proceedings

  • Inorg Chem

altmetric score

  • 0.75

author list (cited authors)

  • Bethel, R. D., Crouthers, D. J., Hsieh, C., Denny, J. A., Hall, M. B., & Darensbourg, M. Y.

citation count

  • 11

complete list of authors

  • Bethel, Ryan D||Crouthers, Danielle J||Hsieh, Chung-Hung||Denny, Jason A||Hall, Michael B||Darensbourg, Marcetta Y

publication date

  • April 2015