| Summary: | This study probes the impact of electronic asymmetry of diiron(l) dithiolato carbonyls. Treatment of Fe(SCH)(CO)(PMe) compounds (n = 2, 3; x = 1, 2, 3) with NOBF gave the derivatives [Fe(SCH)(CO)(PMe)(NO)]BF, which are electronically unsymmetrical because of the presence of a single NO ligand. Whereas the monophosphine derivative is largely undistorted, the bis(PMe) derivatives are distorted such that the CO ligand on the Fe(CO)(PMe)(NO) subunit is semibridging. Two isomers of [Fe(SCH)(CO)(PMe)(NO)]BF were characterized spectroscopically and crystallographically. Each isomer features electron-rich Fe(CO)PMe and electrophilic Fe(CO)(PMe)(NO) subunits. These species are in equilibrium with an unobserved isomer that reversibly binds CO (ΔH = -35 kJ/mol, ΔS = -139 J mol K) to give the symmetrical adduct [Fe(SCH)(μ-NO)(CO)(PMe)]BF. In contrast to Fe(SCH)(CO)(PMe), the bis(PMe) nitrosyl complexes readily undergo CO substitution to give the (PMe) derivatives. The nitrosyl complexes reduce at potentials that are ~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 models) can be replicated in the absence of mixed-valency by the introduction of electronic asymmetry.
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