Nitric oxide reactivity of a manganese(II) complex leading to nitrosation of the ligand (original) (raw)
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Manganese (II) Coordination Complexes Involving Nitronyl Nitroxide Radicals
Inorganic Chemistry, 1999
Three new complexes involving nitronyl nitroxide and PhCOOor N 3 -ligands have been synthesized and structurally and magnetically characterized. These compounds are formulated as Mn(L) 4 (X) 2 ‚nH 2 O, L ) 2-(ppyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PNN) or 2-(p-pyridyl)-4,4,5,5-tetramethylimidazoline-1oxyl (PN) and X ) PhCOOor N 3 -. Compound A [Mn(PNN) 2 (PhCOO) 2 (H 2 O) 2 ] presents the following structural parameters:
Transition Metal Chemistry, 2005
A series of mononuclear MnII and MnIV complexes of general formulae [MnL2(NCS)2] (1a–1d) and [Mn(L′)2(NCS)2] (2a–2c) have been prepared where L are Schiff bases obtained by the condensation of pyridine-2-aldehyde with para-alkyl-substituted aniline, and L′ are the corresponding amide ligands. The room temperature magnetic susceptibility data of (1a–1d) indicate that MnII is in a high spin state. The cyclic voltammograms of (1a–1d) exhibit a one-electron quasi-reversible MnII→MnIII oxidation. A linear correlation has been found when E 0[MnIII/MnII] is plotted against Hammett σ p parameters. X-ray crystallographic data of (1b) shows that the central MnII ion adopts a distorted octahedral geometry with six different Mn–N distances. Upon oxidation of MnII complexes (1b–1d) by H2O2, the corresponding MnIV complexes (2a–2c) were obtained, and the Schiff base ligands were oxidized to the corresponding amides. The lowest energy LMCT bands of these MnIV complexes correlate linearly with Hammett σ p parameters. The redox behavior of the MnIV complexes has been investigated by cyclic voltammetry. E.p.r. spectra of the MnII and MnIV complexes are also reported.
Organometallics, 2010
In this paper we describe the synthesis of Mn(II) dialkyl compounds and their adducts with THF and pyridine. These compounds are useful precursors for the preparation of Mn complexes relevant to catalysis, such as dialkylmanganese(II) derivatives containing chelating nitrogen ligands. In contrast with previously known manganese(II) dialkyls, dibenzylmanganese can not be prepared from MnCl 2 and benzylmanganese chloride due to the formation of insoluble mixed manganesemagnesium compounds. Homoleptic manganese(II) dialkyls are highly sensitive and often quite insoluble owing to their polymeric structure. However, adducts of type MnR 2 L or MnR 2 L 2 (L = THF, pyridine) are soluble in hydrocarbon solvents and more readily isolated and stored than the homoleptic alkyls compounds. Manganese dialkyls as well as their THF or pyridine adducts react instantly with 2,2 0-bipyridyl to afford the corresponding MnR 2 (bipy) complexes. Thus, the stabilized dialkylmanganese(II) THF or Py adducts represent a practical alternative to the more reactive but less easily handled homoleptic dialkyl precursors for synthetic purposes. In addition, the reactivity of MnR 2 (bipy) derivatives with O 2 and the protic acid [H(OEt 2)][BAr 0 4 ] (Ar 0 = 3,5-C 6 H 3 (CF 3) 2) are described. The former reaction leads to the formation of a mixed-valence Mn(II)/Mn(III) alkyl complex containing a tetranuclear [Mn 4 O 2 ] core.
The Redox Chemistry of Manganese(III) and ‐(IV) Complexes
Israel Journal of Chemistry, 1985
The oxidation‐reduction thermodynamics for the manganese(III), ‐(IV), and ‐(II) ions, and their various complexes, are reviewed for both aqueous and aprotic media. In aqueous solutions the reduction potential for the manganese(III)/(II) couple has values that range from +1.51 V vs. NHE (hydrate at pH 0) to −0.95 V (glucarate complex at pH 13.5). The Mn(IV)/(III) couple has values that range from +1.0 V (solid MnIVO3 at pH 0) to −0.04 V (tris gluconate complex at pH 13.5). With anhydrous media the propensity for the Mn(III) ion to disproportionate to solid MnIVO2 and Mn(II) ion is avoided. For aprotic systems the range of redox potentials for various manganese complexes is from +2.01 V and +1.30 for the Mn(IV)/(III) and Mn(III)/(II) couples (bis terpyridyl tri‐N‐oxide complex in MeCN), respectively, to −0.96 V for the Mn(IV)/(III) couple (tris 3,5,‐di‐tert‐butylcatecholate complex in Me2SO). The redox reactions between manganese complexes and dioxygen species (O2, O2, and H2O2) also ...
Inorganica Chimica Acta, 2019
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Inorganic Chemistry, 2004
The Mn(II) and Mn(III) complexes of the pentadentate ligand N, N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2carboxamide (PaPy 3 H; H is the dissociable carboxamide H), namely, [Mn(PaPy 3 )(H 2 O)]ClO 4 (1) and [Mn(PaPy 3 )-(Cl)]ClO 4 , with bound carboxamido nitrogen have been isolated and characterized. The high-spin Mn(II) center in 1 is very sensitive to dioxygen, and this complex is rapidly converted into 2 upon reaction with Clin air. The bound carboxamido nitrogen in 1 is responsible for this sensitivity toward oxidation since the analogous Schiff base complex [Mn(SBPy 3 )Cl]ClO 4 (4) is very resistant to oxidation. Reaction of NO with 1 affords the diamagnetic {Mn−NO} 6 nitrosyl [Mn(PaPy 3 )(NO)]ClO 4 (5). Complexes with no bound carboxamido nitrogen such as 4 and [Mn(PaPy 3 H)(Cl) 2 ] (3) do not react with NO. No reaction with NO is observed with the Mn(III) complexes 2 and [Mn(PaPy 3 )(MeCN)] 2+ either. Collectively these reactions indicate that NO reacts only with the Mn(II) center ligated to at least one carboxamido nitrogen. Both the carbonyl and N−O stretching frequencies (ν CO and ν NO ) of the present and related complexes strongly suggest a {low-spin Mn(II)−NO • } formulation for 5. The alternative description {low-spin Mn(I)−NO + } is not supported by the spectroscopic and redox behavior of 5. Complex 5 is the first example of a {Mn−NO} 6 nitrosyl that exhibits photolability of NO upon illumination with low-intensity tungsten lamps in solvents such as MeCN and H 2 O. The rapid NO loss from 5 leads to the formation of the corresponding solvato species [Mn(PaPy 3 )(MeCN)] 2+ under aerobic conditions. Oxidation of 5 with (NH 4 ) 2 [Ce(NO 3 ) 6 ] in MeCN affords the highly reactive paramagnetic (S ) 1 / 2 ) {MnNO} 5 nitrosyl [Mn(PaPy 3 )(NO)](NO 3 ) 2 (6) in high yield. Spectroscopic and magnetic studies confirm a {low-spin Mn(II)−NO + } formulation for 6. The N−O stretching frequencies (ν NO ) of 5, 6, and analogous nitrosyls reported by other groups collectively suggest that ν NO is a better indicator of the oxidation state of NO (NO + , NO • , or NO -) in non-heme iron and other transition-metal complexes with bound NO.
Inorganic Chemistry, 2002
New synthesis procedures are described to tetranuclear manganese carboxylate complexes containing the [Mn 4 O 2 ] 8+ or [Mn 4 O 3 X] 6+ (X -) MeCO 2 -, F -, Cl -, Br -, NO 3 -) core. These involve acidolysis reactions of [Mn 4 O 3 (O 2 CMe) 4 -(dbm) 3 ] (1; dbm is the anion of dibenzoylmethane) or [Mn 4 O 2 (O 2 CEt) 6 (dbm) 2 ] (8) with HX (X -) F -, Cl -, Br -, NO 3 -); high-yield routes to 1 and 8 are also described. The X -) NO 3complexes [Mn 4 O 3 (NO 3 )(O 2 CR) 3 (R′ 2dbm) 3 ] (R ) Me, R′ ) H (6); R ) Me, R′ ) Et (7); R ) Et, R′ ) H (12)) represent the first synthesis of the [Mn 4 O 3 (NO 3 )] 6+ core, which contains an unusual η 1 :µ 3 -NO 3group. Treatment of known [Mn 4 O 2 (O 2 CEt) 7 (bpy) 2 ]-(ClO 4 ) with HNO 3 gives [Mn 4 O 2 (NO 3 )(O 2 CEt) 6 (bpy) 2 ](ClO 4 ) (15) containing a η 1 :η 1 :µ-NO 3group bridging the two body Mn III ions of the [Mn 4 O 2 ] 8+ butterfly core. Complex 7‚4CH 2 Cl 2 crystallizes in space group P2 1 2 1 2 1 with (at −168°C) a ) 21.110(3) Å, b ) 22.183(3) Å, c ) 15.958(2) Å, Z ) 4, and V ) 7472.4(3) Å 3 . Complex 15‚ 3 / 2 CH 2 Cl 2 crystallizes in space group P2 1 /c with (at −165°C) a ) 26.025(4) Å, b ) 13.488(2) Å, c ) 32.102(6) Å, ) 97.27(1)°, Z ) 8, and V ) 11178(5) Å 3 . Complex 7 contains a [Mn 4 (µ 3 -O) 3 (µ 3 -NO 3 )] 6+ core (3Mn III , Mn IV ) as seen for previous [Mn 4 O 3 X] 6+ complexes. Complex 15 contains a butterfly [Mn 4 (µ 3 -O) 2 ] 8+ core. 1 H NMR spectra have been recorded for all complexes reported in this work and the various resonances assigned. All complexes retain their structural integrity on dissolution in chloroform and dichloromethane. Magnetic susceptibility ( M ) data were collected on 12 in the 5−300 K range in a 10.0 kG (1 T) field. Fitting of the data to the theoretical M vs T expression appropriate for a [Mn 4 O 3 X] 6+ complex of C 3v symmetry gave J 34 ) −23.9 cm -1 , J 33 ) 4.9 cm -1 , and g ) 1.98, where J 34 and J 33 refer to the Mn III Mn IV and Mn III Mn III pairwise exchange interactions, respectively. The ground state of the molecule is S ) 9 / 2 , as found previously for other [Mn 4 O 3 X] 6+ complexes. This was confirmed by magnetization data collected at various fields and temperatures. Fitting of the data gave S ) 9 / 2 , D ) −0.45 cm -1 , and g ) 1.96, where D is the axial zero-field splitting parameter.
Inorganica Chimica Acta, 2009
Manganese(II) complexes, Mn 2 L 1 3 (ClO 4 ) 4 , MnL 1 (H 2 O) 2 (ClO 4 ) 2 , MnL 2 (H 2 O) 2 (ClO 4 ) 2 , and {(l-Cl)MnL 2 (PF 6 )} 2 based on N,N 0 -bis(2-pyridinylmethylene) ethanediamine (L 1 ) and N,N 0 -bis(2-pyridinylmethylene) propanediamine (L 2 ) ligands have been prepared and characterized. The single crystal X-ray diffraction analysis of Mn 2 L 2 3 (ClO 4 ) 4 shows that each of the two Mn(II) ion centers with a Mn-Mn distance of 7.15 Å are coordinated by one ligand while a common third ligand bridges the metal centers. Solid-state magnetic susceptibility measurements as well as DFT calculations confirm that each of the manganese centers is high-spin S = 5/2. The electronic structure obtained shows no orbital overlap between the Mn(II) centers indicating that the observed weak antiferromagentism is a result of through space interactions between the two Mn(II) centers. Under different reaction conditions, L 1 and Mn(II) yielded a one-dimensional polymer, MnL 1 (H 2 O) 2 (ClO 4 ) 2 . Ligand L 2 when reacted with manganese(II) perchlorate gives contrarily to L 1 mononuclear MnL 2 (H 2 O) 2 (ClO 4 ) 2 complex. The analysis of the structural properties of the MnL 2 (H 2 O) 2 (ClO 4 ) 2 lead to the design of dinuclear complex {(l-Cl)MnL 2 (PF 6 )} where two chlorine atoms were utilized as bridging moieties. This complex has a rhomboidal Mn 2 Cl 2 core with a Mn-Mn distance of 3.726 Å. At room temperature {(l-Cl)MnL 2 (PF 6 )} is ferromagnetic with observed l eff = 4.04 l B per Mn(II) ion. With cooling, l eff grows reaching 4.81 l B per Mn(II) ion at 8 K, and then undergoes ferromagnetic-to-antiferromagnetic phase transition.