Syntheses and characterizations of iron complexes of bulky o-phenylenediamide ligand

Abstract

We report the syntheses a family of tetrahedral iron complexes bearing a bulky redox active o-phenylenediamide ligand. The electronic structures of these complexes have been investigated by Mössbauer spectroscopy, magnetic...

[2Fe–2S] Cluster Supported by Redox-Active o-Phenylenediamide Ligands and Its Application toward Dinitrogen Reduction

“…The precursor [Fe­( Xyl pda •– )­(η 6 -toluene)] [ 1 ; Xyl pda = N , N ′-bis­(2,6-dimethylphenyl)- o -phenylenediamide] was prepared from N , N ′-bis­(2,6-dimethylphenyl)­phenylenediamine and Fe­(HMDS) 2 (HMDS = hexamethyldisilazide) in toluene at room temperature. The spectroscopic data and metric parameters of 1 are similar to those of the previously reported Fe­( Dipp pda •– )­(η 6 -toluene) [ Dipp pda = N , N ′-bis­(2,6-diisopropylphenyl)- o -phenylenediamide]. , The reaction of 1 with 1 / 8 equiv of S 8 in tetrahydrofuran (THF) at room temperature affords dark-purple complex 2 in 78% yield (Scheme ). The 1 H NMR spectrum of complex 2 in THF- d 8 at 25 °C shows five paramagnetically broadened and shifted resonances between +14 and +4 ppm.…”

“…The spectroscopic data and metric parameters of 1 are similar to those of the previously reported Fe( Dipp pda •− )(η 6 -toluene) [ Dipp pda = N,N′-bis(2,6-diisopropylphenyl)-o-phenylenediamide]. 66,67 The reaction of 1 with 1 / 8 equiv of S 8 in tetrahydrofuran (THF) at room temperature affords dark-purple complex 2 in 78% yield (Scheme 1). The 70 The solution magnetic moment of 2 is 1.2 μ B in THF-d 8 at 25 °C using the Evans method, 71 close to an S Total = 0 ground state.…”

“…Redox-active ligands have multiple energetically accessible oxidation states. − Their coordination to metal centers induces radical reactivity and electron reservoir behavior, which is often utilized to develop exciting new examples of catalysis. − The N,N-chelating o -phenylenediamide (pda) is a classic example of a redox-active ligand, whose coordination chemistry has been explored toward a large number of transition metals and main-group elements. − It has been clearly established that the pda ligand exists in three different redox states in coordination compounds: the closed-shell dianion, open-shell π-radical monoanion ( S = 1 / 2 ), and closed-shell neutral form. − We have been investigating the coordination chemistry of the pda ligand toward transition metals and main-group elements. − Our group is interested in coordinating redox-active pda ligands to the diferric [2Fe–2S] 2+ cluster. We envision that the resulting complex can store multiple electrons (i.e., reduction equivalents) and mediate multielectron redox processes.…”

Redox-Neutral Transformations of Carbon Dioxide Using Coordinatively Unsaturated Late Metal Silyl Amide Complexes

“…This provides an Osilylcarbamate ligand, which has previously been found to rapidly eject TMSNCO, affording a metal siloxide complex (III). In the case of the reported Fe-formazanate 24 and Fephenylenediamide 23 complexes shown in Figure 1, this is the terminal step of the reaction, providing isolable bridging siloxide complexes along with TMSNCO. In contrast, rhodium, 29 zinc, 27,28 and cadmium 25,26 examples (Figure 1) form metal siloxides which react further with the released TMSNCO to generate the final metal-cyanate complex.…”

“…However, in most cases, these reactions are slow with rates on the order of hours to days (Figure ). − Notably, most of these reported examples contain electron-rich late transition metals. This property is particularly suited for channeling the desired reactivity because the higher d-electron count prevents π-donation from the lone pair on the amide ligand into an empty d-orbital, which would quench its nucleophilicity.…”