Low-Coordinate Iron Chalcogenolates and Their Complexes with Diethyl Ether and Ammonia

Abstract

Treatment of Fe­{N­(SiMe3)2}2 with 2 equiv of the appropriate phenol or thiol affords the dimers {Fe­(OC6H2-2,6-Bu t 2-4-Me)2}2 (1) and {Fe­(OC6H3-2,6-Bu t 2)2}2 (2) or the monomeric Fe­{SC6H3-2,6-(C6H3-2,6-Pr i 2)2}2 (3) in moderate to excellent yields. Recrystallization of 1 and 2 from diethyl ether gives the corresponding three-coordinate ether complexes Fe­(OC6H3-2,6-Bu t 2-4-Me)2(OEt2) (4) and Fe­(OC6H3-2,6-Bu t 2)2(OEt2) (5). In contrast, no diethyl ether complex is formed by the dithiolate 3. The 1H NMR spectra of 4 and 5 show equilibria between the ether complexes and the base-free dimers. A comparison of these spectra with those of the dimeric 1 and 2 allows an unambiguous assignment of the paramagnetically shifted signals. Treatment of 1 with excess ammonia gives the tetrahedral diammine Fe­(OC6H2-2,6-Bu t 2-4-Me)2(NH3)2 (6). Ammonia is strongly coordinated in 6, with no apparent loss of ammine ligand either in solution or upon heating under low pressure. In contrast, significantly weaker ammonia coordination is observed when dithiolate 3 is treated with excess ammonia, which gives the diammine Fe­{SC6H3-2,6-(2,6-Pr i 2-C6H3)2}2(NH3)2 (7). Complex 7 readily loses ammonia either in solution or under reduced pressure to give the monoammine complex Fe­{SC6H3-2,6-(2,6-Pr i 2-C6H3)2}2(NH3) (8). The weak binding of ammonia by iron thiolate 7 reflects the likely behavior of the proposed iron–sulfur active site in nitrogenases, where release of ammonia is required to close the catalytic cycle.

Mn(II), Fe(II), and Co(II) Aryloxides: Steric and Dispersion Effects and the Thermal Rearrangement of a Cobalt Aryloxide to a Co(II) Semiquinone Complex

“…The predicted bond length for a Fe–O single bond is 1.79 Å, and the distances observed for the terminal Fe–O bonds [av. 1.81(39) Å] match known 2-coordinate Fe­(II) aryloxide monomers , and dimers, while the bridging Fe–O bonds [av. 1.96(4) Å] are shorter than those in recently reported Fe­(II) aryloxide dimers using similar ligands, such as 2,6-di- t -butylphenol (Table ).…”

“…The UV–vis spectrum features an LMCT band at 282 nm and a d–d transition at 310 nm. IR spectroscopy in Nujol mulls shows two bands that can be assigned to the O–Fe and μ 2 -O–Fe stretching modes at 525 and 460 cm –1 , respectively, consistent with previously reported data for iron­(II) phenoxide dimers. , A magnetic moment of 3.9 μ B was obtained via Evans’ method and indicates strong antiferromagnetic coupling between the irons in 2 , in contrast to the predicted spin-only moment of two noninteracting nuclei of 9.80 μ B . The magnetic moment of 1 is notably higher than that of 2 , consistent with the greater number of unpaired electrons in the Mn­(II) species.…”

“…For example, reactions of [M­(N­(SiMe 3 ) 2 ) 2 ] 2 (M = Mn, Fe, Co) with 2,4,6-tri- t -butylphenol, HOC­(C 6 H 11 ) 3 , HOC­(4-MeC 6 H 4 ) 3 , or HOSiPh 3 yielded the corresponding neutral, dimeric metal phenoxides or siloxides, while the use of trityl alcohol produced mononuclear, distorted tetrahedral metal coordination in the presence of Lewis bases. , Further examples using boryloxides (−OBR 2 ) as ligands also produced products with M 2 O 2 core structures . Additionally, the use of adamantyl-substituted aryloxides afforded monomeric products, and substituted di- t -butylphenols formed dimers unless coordinated by ethereal solvents or ammonia . In parallel work, the reaction of [Co­(N­(SiMe 3 ) 2 ) 2 ] 2 with 3,5-di- tert -butylcatechol resulted in the formation of a tetrameric Co­(II) catecholate, featuring a cubane-like Co 4 O 4 core which was spectroscopically and structurally characterized …”

“…In fact, just ca. 10 compounds of the type [M­(OR) 2 ] n (M = Mn, Fe, Co, n = 2,3) of any kind have been structurally characterized, although a number of such complexes stabilized by σ-donor Lewis bases or solvent molecules such as ether, pyridine, ammonia, or THF are known. − Herein, we report the synthesis and characterization of six neutral metal­(II) aryloxides (M = Mn, Fe, Co) synthesized from 2,4,6-tricyclohexylphenol or 2,6-di-isopropylphenol and the respective bissilylamides [M­(N­(SiMe 3 ) 2 ) 2 ] 2 (M = Mn, Fe, Co) as synthons to demonstrate how dispersion energy donor stabilization affects physical properties and structures.…”

Polynuclear Iron(II) Pyridonates: Synthesis and Reactivity of Fe4 and Fe5 Clusters

“…The high basicity and monodentate binding mode of the terminal hexamethyldisilazido ligands N­(SiMe 3 ) 2 may enable rapid protolytic ligand exchange. Initial attempts were directed at substitutions with alkoxides . Reaction of the Fe 5 cluster 1 with 4 equiv 2,6-di- tert -butyl- p -cresol (HOAr) led to the isolation of single crystals of the structurally different higher nuclearity μ 4 -oxido-heptairon cluster Fe 7 (L H ) 9 (μ 4 -O)­(OAr) 3 ( 3 , Scheme , top).…”