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

摘要

In contrast to the instability of XFe(NO)₃ and [R₃PFe(NO)₃]+, the N-heterocyclic carbene (NHC)-containing trinitrosyliron complex (TNIC) [(IMes)Fe(NO)₃][BF₄] (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][BF₄] (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)₂L [L = NO (1), CO (2), SPh (3)] motif.