Nitrosyl derivatives of diiron(I) dithiolates mimic the structure and Lewis acidity of the [FeFe]-hydrogenase active site.
This study probes the impact of electronic asymmetry of diiron(I) dithiolato carbonyls. Treatment of Fe2(S2C(n)H(2n))(CO)(6-x)(PMe3)x compounds (n = 2, 3; x = 1, 2, 3) with NOBF4 gave the derivatives [Fe2(S2C(n)H(2n))(CO)(5-x)(PMe3)x(NO)]BF4, which are electronically unsymmetrical because of the presence of a single NO(+) ligand. Whereas the monophosphine derivative is largely undistorted, the bis(PMe3) derivatives are distorted such that the CO ligand on the Fe(CO)(PMe3)(NO)(+) subunit is semibridging. Two isomers of [Fe2(S2C3H6)(CO)3(PMe3)2(NO)]BF4 were characterized spectroscopically and crystallographically. Each isomer features electron-rich Fe(CO)2PMe3 and electrophilic Fe(CO)(PMe3)(NO)(+) subunits. These species are in equilibrium with an unobserved isomer that reversibly binds CO (DeltaH = -35 kJ/mol, DeltaS = -139 J mol(-1) K(-1)) to give the symmetrical adduct [Fe2(S2C3H6)(mu-NO)(CO)4(PMe3)2]BF4. In contrast to Fe2(S2C3H6)(CO)4(PMe3)2, the bis(PMe3) nitrosyl complexes readily undergo CO substitution to give the (PMe3)3 derivatives. The nitrosyl complexes reduce at potentials that are approximately 1 V milder than their carbonyl counterparts. Results of density functional theory calculations, specifically natural bond orbital analysis, reinforce the electronic resemblance of the nitrosyl complexes to the corresponding mixed-valence diiron complexes. Unlike other diiron dithiolato carbonyls, these species undergo reversible reductions at mild potentials. The results show that the novel structural and chemical features associated with mixed-valence diiron dithiolates (the so-called H(ox) models) can be replicated in the absence of mixed-valency by the introduction of electronic asymmetry.
Olsen
Matthew T
MT
Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
Bruschi
Maurizio
M
De Gioia
Luca
L
Rauchfuss
Thomas B
TB
Wilson
Scott R
SR
D001665:Binding Sites; D040761:Biomimetic Materials / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D005290:Ferric Compounds / Q000737:chemistry* / Q000378:metabolism; D006864:Hydrogenase / Q000737:chemistry* / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D009589:Nitrogen Oxides / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular; D013438:Sulfhydryl Compounds / Q000737:chemistry* / Q000378:metabolism
D005290:Ferric Compounds; D007506:Iron-Sulfur Proteins; D009589:Nitrogen Oxides; D013438:Sulfhydryl Compounds; C002007:dithiol-iron(III)-sulfide complex; C118830:iron hydrogenase; D006864:Hydrogenase