Anionic Roussin's red esters (RREs) syn-/anti-[Fe(mu-SEt)(NO)(2)](2)(-): the critical role of thiolate ligands in regulating the transformation of RREs into dinitrosyl iron complexes and the anionic RREs

摘要

The anionic syn-/anti-(Fe(mu-SEt)(NO)(2)](2)(-) (2a) were synthesized and characterized by IR, UV-vis, EPR, and X-ray diffraction. The geometry of the [Fe(mu-S)(2)Fe] core is rearranged in going from [{Fe(NO)(2)}(9)-{Fe(NO)(2)}(9)] Roussin's red ester [Fe(mu-SEt)(NO)(2)](2) (1a) (Fe center dot center dot center dot Fe distance of 2.7080(5) angstrom) to the [(Fe(NO)(2)}(9)-{Fe(NO)(2)}(10)] complex 2a (Fe center dot center dot center dot Fe distance of 2.8413(6) angstrom) to minimize the degree of Fe center dot center dot center dot Fe interaction to stabilize complex 2a. On the basis of X-ray absorption (Fe K- and L-edge), EPR and SQUID, complex 2a is best described as the anionic [{Fe(NO)(2)}(9)-{Fe(NO)(2)}(10)] Roussin's red ester with the fully delocalized mixed-valence core. The complete bridgedthiolate cleavage yielded DNIC [(EtS)(2)Fe(NO)(2)](-) (3a) in the reaction of 2 equiv of [EtS](-) and complex la, whereas reaction of 2 equiv of [(BuS)-Bu-t](-) with [Fe(mu-(SBu)-Bu-t)(NO)(2)](2) (1b) gave DNIC [((BuS)-Bu-t)(2)Fe(NO)(2)](-) (3b) and the anionic Roussin's red ester [Fe(mu-(SBu)-Bu-t)(NO)(2)](2)(-) (2b) through bridged-thiolate cleavage in combination with reduction. In contrast to the inertness of DNIC 3b toward complex 1b, nucleophile DNIC 3a induces the reduction of complex la to produce the anionic Roussin's red ester 2a. Interestingly, dissolution of complex 3a in MeOH at 298 K finally led to the formation of a mixture of complexes 2a and 3a, in contrast to the dynamic equilibrium of complexes 3b and 1b observed in dissolution of complex 3b in MeOH. These results illustrate the aspect of how the steric structures of nucleophiles ([EtS](-) vs [(BuS)-Bu-t](-) and [(EtS)(2)Fe(NO)(2)](-) vs [(tBuS)(2)Fe(NO)(2)](-)) function to determine the reaction products.