Reductive Cleavage of the N−N Bond: Synthesis of Imidoiron(III) Cubanes

Reductive Cleavage of the N−N Bond:  Synthesis of Imidoiron(III) Cubane

A Polymeric Binary Titanium(IV) Sulfide and Its Conversion to Molecular Lewis Base Adducts

A Polymeric Binary Titanium(IV) Sulfide and Its Conversion to Molecular Lewis Base Adduct

Sulfido−Persulfido Equilibria in Sulfur-Rich Metal Clusters: The Case of (C₅Me₅)₃RhRu₂S₄²⁺

The reaction of [(C5Me5)M(MeCN)3](PF6)2 with (C5Me5)2Ru2S4 gives the cluster compounds [(C5Me5)3MRu2S4(MeCN)](PF6)2, 1(PF6)2 (M = Rh) and 3(PF6)2 (M = Ir). Crystallographic studies of 1(PF6)2 show that the dication consists of an asymmetric RhRu2S4 core containing an isosceles triangle of metal atoms with a Ru−Ru bond of 2.88 Å. The three metal atoms are joined by two μ3-η1:η2:η1-S2 units, each persulfide being monodentate toward Rh. NMR studies show that 12+ is stereochemically nonrigid such that the two Ru(C5Me5) resonances coalesce at higher temperatures. The dynamic processes involving 12+ are unaffected by added (C5Me5)Rh(MeCN)32+, ruling out dissociation of the (C5Me5)Rh center. Exchange of the (C5Me5)Ru sites in [(C5Me5)2(C5Me4Et)RhRu2S4(MeCN)](PF6)2, 2(PF6)2, is associated with coalescence of the pairs of C5Me4Et resonances, suggesting that the dynamics in 12+ involve racemization. It is proposed that these dynamics proceed via the “base-free” intermediate [(C5Me5)3RhRu2S4]2+, wherein one S−S bond has been cleaved. Solutions of 12+ react with acetone to give the S-acetonyl derivative [(C5Me5)3RhRu2S3(SCH2COCH3)]PF6, 4(PF6). This species, which is not fluxional on the NMR time scale, is a rare example of a metal sulfido cluster with a trigonal prismatic M3S3 core. There is one metal−metal bond of 2.75 Å between the two Ru atoms, spanned by the acetonylthio ligand. The M−S distances are nearly equivalent at 2.33 Å while the S−S bonding distance is 2.12 Å. This reaction is reversed by acid to give 12+ and acetone

Iron Sulfido Derivatives of the Fullerenes C₆₀ and C₇₀

Toluene solutions of C60 react upon UV irradiation with Fe2S2(CO)6 to give C60[S2Fe2(CO)6]n where n = 1−6. C60[S2Fe2(CO)6]n where n = 1−3 have been isolated and characterized. Crystallographic studies of C60S2Fe2(CO)6 show that the S−S bond of the Fe2 reagent is cleaved to give a dithiolate with idealized C2v symmetry. The addition occurred at a 6,6 fusion, and the metrical details show that the Fe2 portion of the molecule resembles C2H4S2Fe2(CO)6. IR spectroscopic measurements indicate that the Fe2(CO)6 subunits in the multiple-addition species (n > 1) interact only weakly. UV−vis spectra of the adducts show a shift to shorter wavelength with addition of each S2Fe2(CO)6 unit. Photoaddition of the phosphine complex Fe2S2(CO)5(PPh3) to C60 gave C60[S2Fe2(CO)5(PPh3)]n, where n = 1−3. 31P{1H} NMR studies show that the double adduct consists of multiple isomers. Photoaddition of Fe2S2(CO)6 to C70 gave a series of adducts C70[S2Fe2(CO)6]n where n = 1−4. HPLC analyses show one, four, and three isomers for the adducts, respectively

Reactivity of a Sterically Hindered Fe(II) Thiolate Dimer with Amines and Hydrazines

The sterically hindered Fe(II) thiolate dimer Fe2(μ-STriph)2(STriph)2 (1; [STriph]− = 2,4,6-triphenylbenzenethiolate) reacts with primary amines (tBuNH2, aniline) and N2H4 to form the structurally characterized addition complexes Fe(STriph)2(NH2tBu)2, Fe2(μ-STriph)2(STriph)2(NH2Ph)2, and Fe2(μ-η1:η1-N2H4)2(N2H4)4(STriph)4 in high yield. Chemical and NMR spectroscopic evidence indicate that the binding of these nitrogen donors is labile in solution and multispecies equilibria are likely. With arylhydrazines, 1 catalytically disproportionates 1,2-diphenylhydrazine to aniline and azobenzene, and it rearranges 1-methyl-1,2-diarylhydrazines to give, after treatment with alumina, mononuclear, trigonal bipyramidal Fe(III) complexes of composition Fe(ISQ)2(STriph), where [ISQ]− denotes an appropriately substituted bidentate o-diiminobenzosemiquinonate ligand. Complex 1 shows no reaction with hindered 1,2-dialkylhydrazines (isopropyl or tert-butyl) or tetrasubstituted 1,2-dimethyl-1,2-diphenylhydrazine

Sulfido−Persulfido Equilibria in Sulfur-Rich Metal Clusters: The Case of (C₅Me₅)₃RhRu₂S₄²⁺

The reaction of [(C5Me5)M(MeCN)3](PF6)2 with (C5Me5)2Ru2S4 gives the cluster compounds [(C5Me5)3MRu2S4(MeCN)](PF6)2, 1(PF6)2 (M = Rh) and 3(PF6)2 (M = Ir). Crystallographic studies of 1(PF6)2 show that the dication consists of an asymmetric RhRu2S4 core containing an isosceles triangle of metal atoms with a Ru−Ru bond of 2.88 Å. The three metal atoms are joined by two μ3-η1:η2:η1-S2 units, each persulfide being monodentate toward Rh. NMR studies show that 12+ is stereochemically nonrigid such that the two Ru(C5Me5) resonances coalesce at higher temperatures. The dynamic processes involving 12+ are unaffected by added (C5Me5)Rh(MeCN)32+, ruling out dissociation of the (C5Me5)Rh center. Exchange of the (C5Me5)Ru sites in [(C5Me5)2(C5Me4Et)RhRu2S4(MeCN)](PF6)2, 2(PF6)2, is associated with coalescence of the pairs of C5Me4Et resonances, suggesting that the dynamics in 12+ involve racemization. It is proposed that these dynamics proceed via the “base-free” intermediate [(C5Me5)3RhRu2S4]2+, wherein one S−S bond has been cleaved. Solutions of 12+ react with acetone to give the S-acetonyl derivative [(C5Me5)3RhRu2S3(SCH2COCH3)]PF6, 4(PF6). This species, which is not fluxional on the NMR time scale, is a rare example of a metal sulfido cluster with a trigonal prismatic M3S3 core. There is one metal−metal bond of 2.75 Å between the two Ru atoms, spanned by the acetonylthio ligand. The M−S distances are nearly equivalent at 2.33 Å while the S−S bonding distance is 2.12 Å. This reaction is reversed by acid to give 12+ and acetone

Reactivity of a Sterically Hindered Fe(II) Thiolate Dimer with Amines and Hydrazines

The sterically hindered Fe(II) thiolate dimer Fe2(μ-STriph)2(STriph)2 (1; [STriph]− = 2,4,6-triphenylbenzenethiolate) reacts with primary amines (tBuNH2, aniline) and N2H4 to form the structurally characterized addition complexes Fe(STriph)2(NH2tBu)2, Fe2(μ-STriph)2(STriph)2(NH2Ph)2, and Fe2(μ-η1:η1-N2H4)2(N2H4)4(STriph)4 in high yield. Chemical and NMR spectroscopic evidence indicate that the binding of these nitrogen donors is labile in solution and multispecies equilibria are likely. With arylhydrazines, 1 catalytically disproportionates 1,2-diphenylhydrazine to aniline and azobenzene, and it rearranges 1-methyl-1,2-diarylhydrazines to give, after treatment with alumina, mononuclear, trigonal bipyramidal Fe(III) complexes of composition Fe(ISQ)2(STriph), where [ISQ]− denotes an appropriately substituted bidentate o-diiminobenzosemiquinonate ligand. Complex 1 shows no reaction with hindered 1,2-dialkylhydrazines (isopropyl or tert-butyl) or tetrasubstituted 1,2-dimethyl-1,2-diphenylhydrazine

Iron-Mediated Hydrazine Reduction and the Formation of Iron-Arylimide Heterocubanes

The reaction of Fe(N{SiMe3}2)2 (1) with 1 equiv of arylthiol (ArSH) results in material of notional composition Fe(SAr)(N{SiMe3}2) (2), from which crystalline Fe2(μ-SAr)2(N{SiMe3}2)2(THF)2 (Ar = Mes) can be isolated from tetrahydrofuran (THF) solvent. Treatment of 2 with 0.5 equiv of 1,2-diarylhydrazine (Ar′NH−NHAr′, Ar′ = Ph, p-Tol) yields ferric-imide-thiolate cubanes Fe4(μ3-NAr′)4(SAr)4 (3). The site-differentiated, 1-electron reduced iron-imide cubane derivative [Fe(THF)6][Fe4(μ3-N-p-Tol)4(SDMP)3(N{SiMe3}2)]2 ([Fe(THF)6][4]2; DMP = 2,6-dimethylphenyl) can be isolated by adjusting the reaction stoichiometry of 1/ArSH/Ar′NHNHAr′ to 9:6:5. The isolated compounds were characterized by a combination of structural (X-ray diffraction), spectroscopic (NMR, UV−vis, Mössbauer, EPR), and magnetochemical methods. Reactions with a range of hydrazines reveal complex chemical behavior that includes not only N−N bond reduction for 1,2-di- and trisubstituted arylhydrazines, but also catalytic disproportionation for 1,2-diarylhydrazines, N−C bond cleavage for 1,2-diisopropylhydrazine, and no reaction for hindered and tetrasubstituted hydrazines

Iron-Mediated Hydrazine Reduction and the Formation of Iron-Arylimide Heterocubanes

The reaction of Fe(N{SiMe3}2)2 (1) with 1 equiv of arylthiol (ArSH) results in material of notional composition Fe(SAr)(N{SiMe3}2) (2), from which crystalline Fe2(μ-SAr)2(N{SiMe3}2)2(THF)2 (Ar = Mes) can be isolated from tetrahydrofuran (THF) solvent. Treatment of 2 with 0.5 equiv of 1,2-diarylhydrazine (Ar′NH−NHAr′, Ar′ = Ph, p-Tol) yields ferric-imide-thiolate cubanes Fe4(μ3-NAr′)4(SAr)4 (3). The site-differentiated, 1-electron reduced iron-imide cubane derivative [Fe(THF)6][Fe4(μ3-N-p-Tol)4(SDMP)3(N{SiMe3}2)]2 ([Fe(THF)6][4]2; DMP = 2,6-dimethylphenyl) can be isolated by adjusting the reaction stoichiometry of 1/ArSH/Ar′NHNHAr′ to 9:6:5. The isolated compounds were characterized by a combination of structural (X-ray diffraction), spectroscopic (NMR, UV−vis, Mössbauer, EPR), and magnetochemical methods. Reactions with a range of hydrazines reveal complex chemical behavior that includes not only N−N bond reduction for 1,2-di- and trisubstituted arylhydrazines, but also catalytic disproportionation for 1,2-diarylhydrazines, N−C bond cleavage for 1,2-diisopropylhydrazine, and no reaction for hindered and tetrasubstituted hydrazines

Iron−Arylimide Clusters [Fe<i>_m</i>(NAr)<i>_n</i>Cl₄]^2- (<i>m</i>, <i>n</i> = 2, 2; 3, 4; 4, 4) from a Ferric Amide Precursor: Synthesis, Characterization, and Comparison to Fe−S Chemistry

Tetrahedral FeCl[N(SiMe3)2]2(THF) (2), prepared from FeCl3 and 2 equiv of Na[N(SiMe3)2] in THF, is a useful ferric starting material for the synthesis of weak-field iron−imide (Fe−NR) clusters. Protonolysis of 2 with aniline yields azobenzene and [Fe2(μ-Cl)3(THF)6]2[Fe3(μ-NPh)4Cl4] (3), a salt composed of two diferrous monocations and a trinuclear dianion with a formal 2 Fe(III)/1 Fe(IV) oxidation state. Treatment of 2 with LiCl, which gives the adduct [FeCl2{N(SiMe3)2}2]- (isolated as the [Li(TMEDA)2]+ salt), suppresses arylamine oxidation/iron reduction chemistry during protonolysis. Thus, under appropriate conditions, the reaction of 1:1 2/LiCl with arylamine provides a practical route to the following Fe−NR clusters:  [Li2(THF)7][Fe3(μ-NPh)4Cl4] (5a), which contains the same Fe−NR cluster found in 3; [Li(THF)4]2[Fe3(μ-N-p-Tol)4Cl4] (5b); [Li(DME)3]2[Fe2(μ-NPh)2Cl4] (6a); [Li2(THF)7][Fe2(μ-NMes)2Cl4] (6c). [Li(DME)3]2[Fe4(μ3-NPh)4Cl4] (7), a trace product in the synthesis of 5a and 6a, forms readily as the sole Fe−NR complex upon reduction of these lower nuclearity clusters. Products were characterized by X-ray crystallographic analysis, by electronic absorption, 1H NMR, and Mössbauer spectroscopies, and by cyclic voltammetry. The structures of the Fe−NR complexes derive from tetrahedral iron centers, edge-fused by imide bridges into linear arrays (5a,b; 6a,c) or the condensed heterocubane geometry (7), and are homologous to fundamental iron−sulfur (Fe−S) cluster motifs. The analogy to Fe−S chemistry also encompasses parallels between Fe-mediated redox transformations of nitrogen and sulfur ligands and reductive core conversions of linear dinuclear and trinuclear clusters to heterocubane species and is reinforced by other recent examples of iron− and cobalt−imide cluster chemistry. The correspondence of nitrogen and sulfur chemistry at iron is intriguing in the context of speculative Fe-mediated mechanisms for biological nitrogen fixation