This study probes the impact of electronic asymmetry of diiron(I) dithiolato carbonyls. Treatment of Fe-2(S2Cn,H-2n)(CO)(6-x)(PMe3)(x). compounds (n = 2, 3; x = 1, 2, 3) with NOBF4 gave the derivatives [Fe-2(S2CnH2n)(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 [Fe-2(S2C3H6)(CO)(3)(PMe3)(2)(NO)]BF4 were characterized spectroscopically and crystallographically. Each isomer features electron-rich Fe(CO)(2)PMe3 and electrophilic Fe(CO)(PMe3)(NO)(+) subunits. These species are in equilibrium with an unobserved isomer that reversibly binds CO (Delta H = -35 kJ/mol, Delta S = -139 J mol(-1) K-1) to give the symmetrical adduct [Fe-2(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 similar to 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, M., Bruschi, M., DE GIOIA, L., Rauchfuss, T., Wilson, S. (2008). Nitrosyl derivatives of diiron(I) dithiolates mimic the structure and lewis acidity of the [FeFe]-hydrogenase active site. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 130(36), 12021-12030 [10.1021/ja802268p].
Nitrosyl derivatives of diiron(I) dithiolates mimic the structure and lewis acidity of the [FeFe]-hydrogenase active site
BRUSCHI, MAURIZIO;DE GIOIA, LUCA;
2008
Abstract
This study probes the impact of electronic asymmetry of diiron(I) dithiolato carbonyls. Treatment of Fe-2(S2Cn,H-2n)(CO)(6-x)(PMe3)(x). compounds (n = 2, 3; x = 1, 2, 3) with NOBF4 gave the derivatives [Fe-2(S2CnH2n)(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 [Fe-2(S2C3H6)(CO)(3)(PMe3)(2)(NO)]BF4 were characterized spectroscopically and crystallographically. Each isomer features electron-rich Fe(CO)(2)PMe3 and electrophilic Fe(CO)(PMe3)(NO)(+) subunits. These species are in equilibrium with an unobserved isomer that reversibly binds CO (Delta H = -35 kJ/mol, Delta S = -139 J mol(-1) K-1) to give the symmetrical adduct [Fe-2(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 similar to 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.