A {Fe(NO)3}10 trinitrosyliron complex stabilized by an n-heterocyclic carbene and the cationic and neutral {Fe(NO)2}(9/10) products of its NO release.

ABSTRACT

In contrast to the instability of XFe(NO)(3) and [R(3)PFe(NO)(3)](+), the N-heterocyclic carbene (NHC)-containing trinitrosyliron complex (TNIC) [(IMes)Fe(NO)(3)][BF(4)] (1) [IMes =1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] can be readily isolated and manipulated in solution under ambient conditions. Nevertheless, in the presence of thiolates (SR(-)), this EPR-silent TNIC (denoted {Fe(NO)(3)}(10) in the Enemark-Feltham notation) releases gaseous NO, affording in the case of SR(-) = SPh(-) the EPR-active, neutral dinitrosyliron complex (DNIC) (IMes)Fe(SPh)(NO)(2) (3, {Fe(NO)(2)}(9)). Carbon monoxide enforces a bimolecular reductive elimination of PhSSPh from 3, yielding (IMes)(CO)Fe(NO)(2) (2), a reduced {Fe(NO)(2)}(10) DNIC. The NO released from TNIC 1 in the presence of SPh(-) could be taken up by the NO-trapping agent [(bme-dach)Fe](2) [bme-dach = N,N'-bis(2-mercaptoethyl)-1,4-diazacycloheptane] to form the mononitrosyliron complex (MNIC) (bme-dach)Fe(NO). In the absence of SPh(-), direct mixing of [(bme-dach)Fe](2) with 1 releases both NO and the NHC with formation of a spin-coupled, diamagnetic {Fe(NO)}(7)-{Fe(NO)(2)}(9) complex, [(NO)Fe(bme-dach)Fe(NO)(2)][BF(4)] (4). In 4, the MNIC serves as a bidentate metallodithiolate ligand of Fe(NO)(2), forming a butterfly complex in which the Fe-Fe distance is 2.7857(8) Å. Thus, 1 is found to be a reliable synthon for [{Fe(NO)(2)}(9)](+). The solid-state molecular structures of complexes 1-3 show that all three complexes have a tetrahedral geometry in which the bulky mesitylene substituents of the carbene ligand appear to umbrella the Fe(NO)(2)L [L = NO (1), CO (2), SPh (3)] motif.