Ferrate(ii) complexes with redox-active formazanate ligands

Abstract

The synthesis of mono(formazanate) iron complexes is described. In the presence of tetrabutylammonium halides, salt metathesis reactions afford the ferrate(ii) complexes [Bu4N][LFeX2] (L = PhNNC(p-tol)NNPh; X = Cl, Br) in good yield, and the products are characterized in detail. The high-spin ferrate(ii) complexes show cyclic voltammograms that are consistent with reversible, ligand-based one-electron reduction. The halides in these ferrate(ii) compounds are labile, and are displaced by 4-methoxyphenyl isocyanide (4 equiv.) as evidenced by formation of the low-spin, cationic octahedral complex [LFe(CNC6H4(p-OMe))4][Br]. Thus, a straightforward route to mono(formazanate) iron(ii) complexes is established.

Dinuclear Complexes of Flexidentate Pyridine‐Substituted Formazanate Ligands

“…[1][2][3] Formazanates have garnered considerable attention in coordination chemistry due to their ligand-based redox processes, which may facilitate multielectron redox transformations, [4] bond activations [5] and excited-state charge separation. [6] Av ariety of formazanate complexes of many main-group metals [7][8][9][10][11][12][13][14][15][16] andf irst-and second-row transition metals [17][18][19][20][21][22][23] have been described.T hese studies demonstrate the versatile coordination chemistry of formazanate ligandsa nd provides ignificant insight into the opticala nd redox properties of these compounds.S ome coppercomplexesc an also mediate oxygen activation, [24,25] certain cobalt and iron complexes exhibit unique magnetic characteristics, [17,26] and boronc omplexes in many cases feature not only the tunable redoxp roperties but also visible to nearinfrared photoluminescence, [9][10][11][12][13] finding applicationsa sc ellimaging agents [27,28] and electrochemiluminescence emitters. [10] Our group has expanded the coordination chemistry of formazanatest ot hird-row transition metals with as eries of hetero-leptic cyclometalated platinumc omplexes and bis-cyclometalated iridium complexes, [29][30][31] and accessed homoleptic azo-iminate platinum complexes and azo-1,2,3-triazolide iridium complexesv ia hydrogenative cleavage or [3+ +2]...…”

Highly Selective Single‐Component Formazanate Ferrate(II) Catalysts for the Conversion of CO2 into Cyclic Carbonates

“…The mono(formazanate) ferrate(II) dihalide catalysts, [(PhNNC(Ar)NNPh)FeX 2 ] − (Ar=C 6 H 4 ( p ‐Me) ( 1 ), C 6 F 5 ( 2 ), C 6 H 4 ( p ‐OMe) ( 3 ); X=Cl, Br, I) were synthesized through a modified procedure of a route previously reported by some of us . This new procedure uses a one‐pot approach that circumvents the isolation of formazanate alkali metal salts, thus allowing to use ligand substitution patterns that would otherwise lead to decomposition (for example, C 6 F 5 ‐substituents engage in nucleophilic aromatic substitution) .…”

“…Single‐crystal X‐ray diffraction of the new compounds 2Br/I and 3Br (Figure S1; Supporting Information) showed geometries close to tetrahedral (geometry index for four‐coordinate complexes τ′ 4 in the range of 0.91–0.93), similar to those of the previously reported 1Cl/Br (τ′ 4 =0.89–0.90) . The Fe−N bond lengths of 2Br/I and 3Br (see Table S2) were comparable with those of 1Cl/Br , in agreement with a high‐spin Fe II center ( S =2).…”

Formazanate coordination compounds: synthesis, reactivity, and applications

“…32 Mono(formazanate)iron(II) complexes with halide co-ligands are prone to ligand exchange reactions to the thermodynamically favored bis(formazanate) complexes (e.g., 19), but carrying out salt metathesis reactions in the presence of an additional equivalent of halide (such as [Bu 4 N][X]) allows high-yield synthesis of four-coordinate ferrate complexes 25. 33 The halide ligands in these complexes are labile, as demonstrated by the formation of octahedral, cationic complexes 26 upon treatment with isocyanide (Scheme 9a). Making use of its labile nature, 25 can be used as a source of three-coordinate Fe(II) and was shown to be an active catalyst for the synthesis of cyclic organic carbonates from CO 2 and epoxides, even in the absence of an external nucleophilic co-catalyst (Scheme 9b).…”

“…Scheme 9 (a) Synthesis of ferrate complexes 25 and subsequent halide exchange for isocyanide to give cationic complex 26. (b) Application of 25 in the catalytic conversion of CO 2 /epoxide to cyclic carbonates 33,34.…”