Manganese(III) Corrole-Oxidant Adduct as the Active Intermediate in Catalytic Hydrogen Atom Transfer

Hydrogen atom transfer (HAT) reactions from dihydroanthracene to ArINTs (Ar = 2-tert-butylsulfonyl)benzene and Ts = p-toluenesulfonyl) is catalyzed by Mn(tpfc) (tpfc = 5,10,15-tris(pentafluorophenyl)corrole). Kinetics of HAT was monitored by gas chromatography. Conversion to the major products anthracene, TsNH2, and ArI is too fast to be explained by direct HAT from the terminal imido complex TsN=Mn(tpfc), which forms from the reaction of Mn(tpfc) with ArINTs. Steady-state kinetics, isotope effects, and variation of the initial catalyst form (MnIII(tpfc) vs TsN=MnV(tpfc)) support a mechanism in which the active catalytic species is an adduct of manganese(III) with the oxidant, (ArINTs)MnIII(tpfc). This species was detected by rapid-scan stopped-flow absorption spectroscopy. Kinetic simulations demonstrated the viability of this mechanism in contrast to other proposals

Mechanism of Catalytic Aziridination with Manganese Corrole: The Often Postulated High-Valent Mn(V) Imido Is Not the Group Transfer Reagent

The reaction of ArINTs (Ar = 2-(tert-butylsulfonyl)benzene and Ts = p-toluenesulfonyl) and (tpfc)Mn (tpfc = 5,10,15-tris(pentafluorophenyl)corrole), 1, affords the high-valent (tpfc)MnVNTs, 2, on stopped-flow time scale. The reaction proceeds via the adduct [(tpfc)MnIII(ArINTs)], 3, with formation constant K3 = (10 ± 2) × 103 L mol−1. Subsequently, 3 undergoes unimolecular group transfer to give complex 2 with the rate constant k4 = 0.26 ± 0.07 s-1 at 24.0 °C. The complex (tpfc)Mn catalyzes [NTs] group transfer from ArINTs to styrene substrates with low catalyst loading and without requirement of excess olefin. The catalytic aziridination reaction is most efficient in benzene because solvents such as toluene undergo a competing hydrogen atom transfer (HAT) reaction resulting in H2NTs and lowered aziridine yields. The high-valent manganese imido complex (tpfc)MnNTs does not transfer its [NTs] group to styrene. Double-labeling experiments with ArINTs and ArINTstBu (TstBu = (p-tert-butylphenyl)sulfonyl) establish the source of [NR] transfer as a “third oxidant”, which is an adduct of Mn(V) imido, [(tpfc)Mn(NTstBu)(ArINTs)] (4). Formation of this oxidant is rate limiting in catalysis

Mechanism of Catalytic Aziridination with Manganese Corrole: The Often Postulated High-Valent Mn(V) Imido Is Not the Group Transfer Reagent

The reaction of ArINTs (Ar = 2-(tert-butylsulfonyl)benzene and Ts = p-toluenesulfonyl) and (tpfc)Mn (tpfc = 5,10,15-tris(pentafluorophenyl)corrole), 1, affords the high-valent (tpfc)MnVNTs, 2, on stopped-flow time scale. The reaction proceeds via the adduct [(tpfc)MnIII(ArINTs)], 3, with formation constant K3 = (10 ± 2) × 103 L mol−1. Subsequently, 3 undergoes unimolecular group transfer to give complex 2 with the rate constant k4 = 0.26 ± 0.07 s-1 at 24.0 °C. The complex (tpfc)Mn catalyzes [NTs] group transfer from ArINTs to styrene substrates with low catalyst loading and without requirement of excess olefin. The catalytic aziridination reaction is most efficient in benzene because solvents such as toluene undergo a competing hydrogen atom transfer (HAT) reaction resulting in H2NTs and lowered aziridine yields. The high-valent manganese imido complex (tpfc)MnNTs does not transfer its [NTs] group to styrene. Double-labeling experiments with ArINTs and ArINTstBu (TstBu = (p-tert-butylphenyl)sulfonyl) establish the source of [NR] transfer as a “third oxidant”, which is an adduct of Mn(V) imido, [(tpfc)Mn(NTstBu)(ArINTs)] (4). Formation of this oxidant is rate limiting in catalysis

Mechanism of Catalytic Aziridination with Manganese Corrole: The Often Postulated High-Valent Mn(V) Imido Is Not the Group Transfer Reagent

The reaction of ArINTs (Ar = 2-(tert-butylsulfonyl)benzene and Ts = p-toluenesulfonyl) and (tpfc)Mn (tpfc = 5,10,15-tris(pentafluorophenyl)corrole), 1, affords the high-valent (tpfc)MnVNTs, 2, on stopped-flow time scale. The reaction proceeds via the adduct [(tpfc)MnIII(ArINTs)], 3, with formation constant K3 = (10 ± 2) × 103 L mol−1. Subsequently, 3 undergoes unimolecular group transfer to give complex 2 with the rate constant k4 = 0.26 ± 0.07 s-1 at 24.0 °C. The complex (tpfc)Mn catalyzes [NTs] group transfer from ArINTs to styrene substrates with low catalyst loading and without requirement of excess olefin. The catalytic aziridination reaction is most efficient in benzene because solvents such as toluene undergo a competing hydrogen atom transfer (HAT) reaction resulting in H2NTs and lowered aziridine yields. The high-valent manganese imido complex (tpfc)MnNTs does not transfer its [NTs] group to styrene. Double-labeling experiments with ArINTs and ArINTstBu (TstBu = (p-tert-butylphenyl)sulfonyl) establish the source of [NR] transfer as a “third oxidant”, which is an adduct of Mn(V) imido, [(tpfc)Mn(NTstBu)(ArINTs)] (4). Formation of this oxidant is rate limiting in catalysis

Solution and Solid State Properties for Low-Spin Cobalt(II) Dibenzotetramethyltetraaza[14]annulene [(tmtaa)Co^II] and the Monopyridine Complex

The single-crystal X-ray structure of solvent-free (tmtaa)­CoII reveals three different π–π intermacrocyclic interactions between tmtaa units (tmtaa = dibenzotetramethyltetraaza[14]­annulene). Pairs of inequivalent (tmtaa)­CoII units in the unit cell link into a one-dimensional π–π stacked array in the solid state. Magnetic susceptibility (χ) studies from 300 to 2 K reveal the effects of intermolecular interactions between (tmtaa)­CoII units in the solid state. The effective magnetic moment per CoII center is constant at 2.83 μB from 300 to 100 K and begins to significantly decrease at lower temperatures. The magnetic data are fit to a singlet (S = 0) ground state with a triplet (S = 1) excited state that is 13 cm–1 higher in energy (−2J = 13 cm–1). Toluene solutions of (tmtaa)­CoII have 1H nuclear magnetic resonance (NMR) paramagnetic shifts, a solution-phase magnetic moment μeff (295 K) of 2.1 μB, and toluene glass electron paramagnetic resonance spectra that are most consistent with a low-spin (S = 1/2) CoII with the unpaired electron located in the dyz orbital. Pyridine interacts with (tmtaa)­CoII to form a five-coordinate monopyridine complex in which the unpaired electron is in the dz2 orbital. The five-coordinate complex has been structurally characterized by single-crystal X-ray diffraction, and the equilibrium constant for pyridine binding at 295 K has been evaluated by both electronic and 1H NMR spectra. Density functional theory computation using the UB3LYP hybrid functional places the unpaired electron for (tmtaa)­CoII in the dyz orbital and that for the monopyridine complex in the dz2 orbital, consistent with spectroscopic observations

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

Concerted Dismutation of Chlorite Ion: Water-Soluble Iron-Porphyrins As First Generation Model Complexes for Chlorite Dismutase

Three iron-5,10,15,20-tetraarylporphyrins (Fe(Por-Ar4), Ar = 2,3,5,6-tetrafluro-N,N,N-trimethylanilinium (1), N,N,N-trimethylanilinium (2), and p-sulfonatophenyl (3)) have been investigated as catalysts for the dismutation of chlorite (ClO2−). Degradation of ClO2− by these catalysts occurs by two concurrent pathways. One leads to formation of chlorate (ClO3−) and chloride (Cl−), which is determined to be catalyzed by O=FeIV(Por) (Compound II) based on stopped-flow absorption spectroscopy, competition with 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonicacid), 18O-labeling studies, and kinetics. The second pathway is a concerted dismutation of chlorite to dioxygen (O2) and chloride. On the basis of isotope labeling studies using a residual gas analyzer, the mechanism is determined to be formation of O=FeIV(Por)·+ (Compound I) from oxygen atom transfer, and subsequent rebound with the resulting hypochlorite ion (ClO−) to give dioxygen and chloride. While the chlorate production pathway is dominant for catalysts 2 and 3, the O2-producing pathway is significant for catalyst 1. In addition to chlorite dismutation, complex 1 catalyzes hypochlorite disproportionation to chloride and dioxygen quantitatively

Evaluation of the Rh^(II)–Rh^(II) Bond Dissociation Enthalpy for [(TMTAA)Rh]₂ by ¹H NMR T₂ Measurements: Application in Determining the Rh–C(O)– BDE in [(TMTAA)Rh]₂CO

Toluene solutions of the rhodium­(II) dimer of dibenzotetramethylaza[14]­annulene ([(TMTAA)­Rh]2; (1)) manifest an increase in the line widths for the singlet methine and methyl 1H NMR resonances with increasing temperature that result from the rate of dissociation of the diamagnetic RhII–RhII bonded dimer (1) dissociating into paramagnetic RhII monomers (TMTAA) Rh (2). Temperature dependence of the rates of RhII–RhII dissociation give the activation parameters for bond homolysis ΔH⧧app = 24(1) kcal mol–1 and ΔS⧧app = 10 (1) cal K–1 mol–1 and an estimate for the RhII–RhII bond dissociation enthalpy (BDE) of 22 kcal mol–1. Thermodynamic values for reaction of 1 with CO to form (TMTAA)­Rh–C­(O)–Rh­(TMTAA) (3) ΔH1° = −14 (1) kcal mol–1, ΔS1°= −30(3) cal K–1 mol–1) were used in deriving a (TMTAA)­Rh–C­(O)– BDE of 53 kcal mol–1

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

Synthesis of a High-Valent, Four-Coordinate Manganese Cubane Cluster with a Pendant Mn Atom: Photosystem II-Inspired Manganese–Nitrogen Clusters

High-valent, four-coordinate manganese imido- and nitrido-bridged heterodicubane clusters have been prepared and characterized by single-crystal X-ray diffraction and spectroscopic techniques. The title compound, a corner-nitride-fused dicubane with the chemical formula [Mn₅Li₃(μ₆-N)­(N)­(μ₃-N^<i>t</i>Bu)₆(μ-N^<i>t</i>Bu)₃(N^<i>t</i>Bu)] (<b>1</b>), has been prepared as an adduct with a nearly isostructural tetramanganese cluster with one Mn atom replaced by Li. An important feature of the reported chemistry is the formation of nitride from <i>tert</i>-butylamide, indicative of N–C bond cleavage facilitated by manganese