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The N-heterocyclic carbene supported three-coordinate Ni(I) complex (IPr)Ni(κ1-N-N(iPr)C(O)tBu)(CNXyl) ([2-CNXyl]; CNXyl = 2,6-dimethylphenyl isocyanide) undergoes disproportionation with 1 equiv of CNXyl to afford an equimolar mixture of Ni(0) and Ni(II) complexes (IPr)Ni(CNXyl)3 ([3-CNXyl]) and (IPr)Ni(κ2-N,O-N(iPr)CO(tBu))2 ([4]), respectively. Complexes [3-CNXyl] and [4] are also produced when 2 equiv of the isonitrile CNXyl is added to (IPr)Ni(κ3-N,bis(H2CMe)-N(iPr)C(O)tBu) ([1]). Furthermore, we show that reactions with p-acceptors CO and select alkenes also result in disproportionation. In the case of CO we show that reactions in the solid state afford selectivity for and isolation of the reaction intermediate (IPr)Ni(κ1-N-N(iPr)C(O)tBu)(CO) ([2-CO]), which is not isolable by solution methods. Kinetic analysis of the disproportionation reaction with alkenes suggests that the reaction is first order in both nickel and alkene. Preliminary trapping experiments rule out amidyl radicals as intermediates in these reactions. We propose instead that a bimolecular ligand transfer is operative, in part due to the hemilabile nature of amidate ligands. [ABSTRACT FROM AUTHOR]

Reduction of the group 4 transition metal precursors [(PN)2MCl2] (M = Zr (1), and Hf (2)); PN− = (N-(2-(diisopropylphosphino)-4-methylphenyl)-2,4,6-trimethylanilide), both readily prepared by transmetallation of 2 LiPN with [MCl4(THF)2], with a slight excess of KC8, resulted in the isolation of the trivalent complexes [(PN)2MCl] (M = Zr (3), and Hf (4)). Complexes 1–4 were all identified by solid-state X-ray diffraction analysis, whereas in the case of 3 and 4 low temperature X-band EPR spectroscopy allowed for the identification of these metal-centered d1 radicals. A comparison with the isostructural and isoelectronic but more stable [(PN)2TiCl] is also presented. [ABSTRACT FROM AUTHOR]

The syntheses and characterization of new nitro complexes of Ru(II) with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) and different substituted bipyridines are reported. A disproportionation reaction can occur after applying an oxidation potential corresponding to the couple Ru II /Ru III forming the nitrate and the nitrosyl complexes, which were detected by cyclic voltammetry. This reaction was confirmed by IR-spectroelectrochemistry with an OTTLE cell, for the first time. Additionally, for 2,2′-bipyridine we have obtained as ClO 4 − salt a new nitrosyl-complex which presents an elevated IR stretching frequency. [ABSTRACT FROM AUTHOR]

Two mononuclear Mn III complexes [Mn(3,5-F 2 salpn)(H 2 O) 2 ][B(C 6 H 5 ) 4 ]·2H 2 O ( 1 ·2H 2 O) and [Mn(3,5-Cl 2 salpn)(OAc)(H 2 O)]·H 2 O ( 2 ·H 2 O), where H 2 salpn = 1,3-bis(salicylidenamino)propane, have been prepared and characterized. The crystal structure of 1 ·H 2 O shows that this complex forms μ -aqua dimers with a short Mn ⋯ Mn distance of 4.93 Å. Under anaerobic conditions, the two complexes are stable in solution and possess trans -diaxial symmetry with the tetradentate Schiff base ligand symmetrically arranged in the equatorial plane. When left in air, these complexes slowly dimerize to yield high-valent [Mn IV 2 (3,5-X 2 -salpn) 2 ( μ -O) 2 ] in which each X 2 -salpn ligand wraps the two Mn ions. This process is favored in basic medium where the deprotonation of the bound water molecule is concomitant with air oxidation. The two complexes catalyze the dismutation of superoxide (superoxide dismutase (SOD) activity) and peroxide (catalase (CAT) activity) in basic medium. The phenyl-ring substituents play an important role on the CAT reaction but have little effect on SOD activity. Kinetics and spectroscopic results indicate that 1 and 2 catalyze H 2 O 2 disproportionation through a cycle involving Mn III 2 and Mn IV 2 dimers, unlike related complexes with a more rigid and smaller chelate ring, which employ Mn III /Mn V O monomers. [ABSTRACT FROM AUTHOR]

A series of dinuclear copper(I) oxalate complexes was synthesized by the direct acid-base reaction of Cu 2 O with oxalic acid in ethanol with a ligand, or in neat ligand. The complexes incorporated a variety of ligands L (L = triphenylphosphine, 1,2-bis(diphenylphosphino)ethane, triphenylphosphite, diisopropyl sulfide, cyclooctadiene and cyclohexylisocyanide) and had the general formula L n Cu(μ 2 -C 2 O 4 )CuL n ( n = 1 or 2). The Cu I /Cu II mixed-valence trinuclear compound (iPr 2 S) 2 Cu I (C 2 O 4 )Cu II (C 2 O 4 )Cu I (iPr 2 S) 2 was formed concomitantly with the target dinuclear Cu 2 C 2 O 4 (iPr 2 S) 4 complex, shedding light on the mechanism of disproportionation of this family of complexes. With norbornadiene (nbd) as a ligand, however, a coordination polymer Cu 2 C 2 O 4 (nbd) was formed. Also, the same reaction with L = 2,9-dimethyl-1,10-phenanthroline or pyridine resulted in the known tetrahedral complex ions [CuL m ] + ( m = 2 or 4). Lastly, the ligand di-2-(1-di-(2-picolyl)amino)propyl disulfide produced not the expected Cu(I) oxalate complex, but a Cu(II) picolylamine oxalate coordination polymer. All products were structurally characterized by single-crystal X-ray diffraction if soluble, and by powder X-ray diffraction methods if not. [ABSTRACT FROM AUTHOR]

Two manganese(V)-oxo corroles [Mn V (Cor)O] that differ in their electronic environments were produced by visible light irradiation of highly photo-labile corrole-manganese(IV) bromates. The corrole ligands under study include 5,10,15-tris(pentafluorophenyl)corrole (TPFC), and 5,10,15-triphenylcorrole (TPC). The kinetics of oxygen transfer atom (OAT) reactions with various organic reductants by these photo-generated Mn V (Cor)O were also studied in CH 3 CN and CH 2 Cl 2 solutions. Mn V (Cor)O exhibits remarkable solvent and ligand effect on its reactivity and spectral behavior. In the more electron-deficient TPFC system and in the polar solvent CH 3 CN, Mn V (Cor)O returned Mn III corrole in the end of oxidation reactions. However, in the less polar solvent CH 2 Cl 2 or in the less electron-deficient TPC system, Mn IV product was formed instead of Mn III . Furthermore, with the same substrates and in the same solvent, the order of reactivity of Mn V (Cor)O was TPC> TPFC, which is inverted from that expected based on the electron-demand of corrole ligands. Our spectral and kinetic results in this study provide compelling evidence in favor of multiple oxidation pathways, where Mn V (Cor)O may serve as direct two-electron oxidant or undergo a disproportionation reaction to form a manganese(VI)-oxo corrole as the true oxidant. The choice of pathways is strongly dependent on the nature of the solvent and the corrole ligand. [ABSTRACT FROM AUTHOR]

The synthesis of the first linear coordinated CuII complex Cu{N(SiMe3)Dipp}2 ( 1 Dipp=C6H5-2,6Pr i2) and its CuI counterpart [Cu{N(SiMe3)Dipp}2]− ( 2) is described. The formation of 1 proceeds through a dispersion force-driven disproportionation, and is the reaction product of a CuI halide and LiN(SiMe3)Dipp in a non-donor solvent. The synthesis of 2 is accomplished by preventing the disproportionation into 1 by using the complexing agent 15-crown-5. EPR spectroscopy of 1 provides the first detailed study of a two-coordinate transition-metal complex indicating strong covalency in the Cu−N bonds. [ABSTRACT FROM AUTHOR]

Iron(II) hydride complexes of the "piano-stool" type, Cp*(P-P)FeH (P-P = dppe (1H), dppbz (2H), dppm (3H), dcpe (4H)) were examined as hydride donors in the reduction of N-benzylpyridinium and acridinium salts. Two pathways of hydride transfer, "single-step H-" transfer to pyridinium and a "two-step (e-/H•)" transfer for acridinium reduction, were observed. When 1-benzylnicotinamide cation (BNA+) was used as an H- acceptor, kinetic studies suggested that BNA+ was reduced at the C6 position, affording 1,6-BNAH, which can be converted to the more thermally stable 1,4-product. The rate constant k of H- transfer was very sensitive to the bite angle of P-Fe-P in Cp*(P-P)FeH and ranged from 3.23 × 10-3 M-1 s-1 for dppe to 1.74 × 10-1 M-1 s-1 for dppm. The results obtained from reduction of a range of N-benzylpyridinium derivatives suggest that H- transfer is more likely to be charge controlled. In the reduction of 10-methylacridinium ion (Acr+), the reaction was initiated by an e- transfer (ET) process and then followed by rapid disproportionation reactions to produce Acr2 dimer and release of H2. To achieve H• transfer after ET from [Cp*(P-P)FeH]+ to acridine radicals, the bulkier acridinium salt 9-phenyl-10-methylacridinium (PhAcr+) was selected as an acceptor. More evidence for this "two-step (e-/H•)" process was derived from the characterization of PhAcr• and [4H]+ radicals by EPR spectra and by the crystallographic structure confirmation of [4H]+. Our mechanistic understanding of fundamental H- transfer from iron(II) hydrides to NAD+ analogues provides insight into establishing attractive bio-organometallic transformation cycles driven by iron catalysis. [ABSTRACT FROM AUTHOR]

Chemical one-electron oxidation of [PtII(3,5-DTBCat)(DTBbpy)] (1) (3,5-DTBCat = 3,5-di-tert-butyl catecholato, DTBbpy = 4,4′-di-tert-butyl-2,2′-bipyridine) afforded the corresponding paramagnetic complex, [PtII(3,5-DTBSQ)(DTBbpy)]+PF6− (1(PF6)), as a result of ligand-centred oxidation. While complex 1 is relatively stable in common organic solvents, the present study demonstrates that cationic [1]+ is subject to an unprecedented solvent-induced disproportionation in highly polar solvents such as DMSO and DMF, which results in the formation of 1 and a free benzoquinone. [ABSTRACT FROM AUTHOR]

A Re(I) fac-tricarbonylcomplex with a 2-(2-cyclohexyl-1-methyl)-methylimino-pyridineligand is found to electrocatalyze the reductive disproportionationof two equivalents of CO2to CO and CO32–. Electrochemical and spectroelectrochemical experiments,supplemented by stoichiometric reactions with chemically reduced species,indicate that this reaction is catalyzed via a process that is first-orderin [Re]. These findings show that the decreased aromaticity of pyridinemonoimine ligands (relative to that of previously studied bipyridinesystems) has mechanistic implications for the electrocatalytic reductionof CO2with Re complexes. NMR experiments indicate thatthis is also manifested in a competing pathway where CO2undergoes a reductive insertion reaction into the monoamine ligand. [ABSTRACT FROM AUTHOR]

A stable trigonal bipyramidal copper(III) complex, [PPN][Cu(TMSPS3)Cl] (1, wherein PPN represents bis(triphenylphosphine)iminium), was synthesized from CuCl2/PPNCl via intramolecular copper(II) disproportionation. Under ambient conditions, the axial chloride of 1 is exchangeable in solution thus making 1 serve as an intermediate to prepare trigonal bipyramidal copper(III) derivatives, e.g., [PPN][Cu(TMSPS3)(N3)] (2) and [Cu(TMSPS3)(DABCO)] (3). Diamagnetic complexes 1-3 were fully characterized by X-ray crystallography, NMR, UV-vis, and Cu K-edge absorption spectroscopy. A series of UV-vis titrations were performed to investigate the relative ligand affinity toward the [Cu(TMSPS3)] moiety, verifying the 1:1 binding equilibrium between various ligands. Compared to known copper(III) compounds, Cu K-edge absorptions of 1-3 possess lower pre-edge energy and higher shakedown transition energy, which, respectively, attribute to the electron donation from TMSPS33- ligand and their trigonal ligand field. [ABSTRACT FROM AUTHOR]

A three-coordinate cobalt species, IPrCoCl{N(SiMe3)2} [1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene], was synthesized by the reaction of {IPrCoCl2}2 with NaN(SiMe3)2. Compound 1 is a useful starting material for low-coordinate (IPr)Co species. 1 reacts with 2,6-di-tert-butyl-4-methylphenol (BHT-H) via aminolysis of the Co–N bond to generate a three-coordinate phenoxide complex, IPrCoCl(O-2,6-tBu2-4-MeC6H2) (2). The reaction of 1 with 2,6-diisopropylaniline (NH2DIPP) generates IPrCoCl(NHDIPP) (4), which undergoes disproportionation to form a mixture of 4, {IPrCoCl2}2, and IPrCo(NHDIPP)2 (3). The same product mixture is formed by the reaction of 1 with Li[NH(DIPP)], which unexpectedly proceeds by amide exchange. Compound 3 was synthesized independently by the reaction of {IPrCoCl2}2 with 4 equiv of Li[NH(DIPP)]. The reaction of 1 with the bulkier lithium 2,6-dimesitylanilide (LiNHDMP) also proceeds by amide exchange to generate IPrCoCl(NHDMP) (5), which is stable toward disproportionation. Compounds 1 and 2 exhibit trigonal-planar geometries at cobalt in the solid state. The solid-state structure of 3 also contains a trigonal-planar cobalt center and exhibits close Co---H contacts involving the methine hydrogen atoms of the NH(DIPP) groups in the axial positions. The solid-state structure of 5 features an interaction between cobalt and a flanking aryl group of the anilide ligand, resulting in pyramidalization of the cobalt center. [ABSTRACT FROM AUTHOR]

Theligand effect on CuIdisproportionation is investigatedthrough operando IR. It is found that the CuIcomplexesformed from the reaction of CuI with β-diketone enolate, β-ketoester enolate, and β-keto amide enolate could disproportionateto CuIIand Cu0species, respectively. The distinctdisproportionation rates of CuIcomplexes chelated by differentβ-dicarbonyl ligands provide a useful insight into the natureof copper catalytic reactions, which will be helpful for designingligands and understanding the mechanism of Cu-catalyzed coupling reactions. [ABSTRACT FROM AUTHOR]

Redoxbehavior of Fe(I) complexes bearing a PNP-pincer-type phosphaalkeneligand, 2,6-bis[1-phenyl-2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyl]pyridine(BPEP-Ph), is reported. The four-coordinate Fe(I) complex [FeBr(BPEP-Ph)](1) readily reacts with 1 equiv of tBuNC in toluene at −35 °C to give [FeBr(tBuNC)(BPEP-Ph)] (2) with a 17e configuration. Complex 2is fairly stable in neat benzene at room temperature, butsmoothly undergoes disproportionation in the presence of added tBuNC to afford the Fe(0) complex [Fe(tBuNC)2(BPEP-Ph)] (3) and the Fe(II) complex[FeBr2(tBuNC)4] (4) along with free BPEP-Ph. The single-crystal X-ray diffraction studiesof 3and 4reveal distorted trigonal bipyramidaland square pyramidal arrangements around Fe, respectively. The yieldof 3increases up to 50%/2when 2 equivof tBuNC is added to the system. A disproportionationprocess involving a 19e intermediate is proposed. [ABSTRACT FROM AUTHOR]

A wide variety of 2,5-di(2-pyridyl)pyrroles (dppHs) substituted at the C3 and C4 positions of the pyrrole core were obtained by direct condensation of a 2-pyridylcarboxaldehyde (2 equiv), an α-methylene ketone with at least one electron-withdrawing substituent and ammonium acetate. A novel 2,5-di(1,10-phenanthrolin-2-yl)pyrrole was also characterised. The dppHs provide a direct, quick entry to dipyridylpyrrolato (dpp−)-metal complexes. The meridial tridentate dpp− ligand is a useful anionic analogue of the terpyridyl ligand. The first (dpp)Ru complexes are described; the 3,4-substitution of the central pyrrole significantly perturbs the potentials of the redox processes of these complexes. A [(dpp)Ru(bpy)(MeCN)]+ (bpy=2,2′-bipyridine) complex is an electrocatalyst for the reductive disproportionation of carbon dioxide to carbon monoxide and the carbonate ion. [ABSTRACT FROM AUTHOR]

The oxidation of the earlier synthesized [4,6-di- tert-butyl- N-(2,6-diisopropylphenyl)- o-amidophenolato]methylgallium( iii) ( 1a) and [4,6-di- tert-butyl- N-(2,6-diisopropylphenyl)- o-amidophenolato]iodogallium( iii) ( 1b) by different reagents, such as mercury( ii) salts, molecular iodine, and tetramethylthiuram disulfide, was studied. The oxidation of the starting diamagnetic compounds gives pentacoordinated gallium( iii) bis- o-iminosemiquinolates 4-7 as the major products, which are generated as a result of the further disproportionation of intermediate monoradical tetracoordinated metal complexes. [ABSTRACT FROM AUTHOR]

Reaction of [Ni(NO)(bipy)(Me2phen)][PF6] with 1 equiv of nitric oxide (NO) in CH2Cl2 results in the formation of N2O and [{(Me2phen)Ni(NO)}2(µ-η¹-N:η¹-O)-NO2)][PF6] (3), along with the known complex, [Ni(bipy)3][PF6]2 (4). The isolation of complex 3, which contains a nitrite ligand, demonstrates that the reaction of [Ni(NO)(bipy)(Me2phen)][PF6] with exogenous NO results in NO disproportionation and not NO reduction. Complex 3 could also be accessed by reaction of [Ni(NO)(Me2phen)][PF6] (5) with (Me2phen)Ni(NO)(NO2) (7) in good yield. Complexes 3, 5, and 7 were fully characterized, including analysis by X-ray crystallography in the case of 3 and 7. Furthermore, addition of 0.5 equiv of bipy to [Ni(NO)(bipy)][PF6] results in formation of the hyponitrite complex, [{(bipy)Ni(η2-O2N2)}η¹:η¹-N,N-{Ni(NO)(bipy)}2][PF6]2 (9), in modest yield. Importantly, the hyponitrite ligand in 9 is thought to form via coupling of two NO- ligands and not by coupling of a nucleophilic nitrosyl ligand (NO-) with an electrophilic nitrosyl ligand (NO+). X-ray crystallography reveals that complex 9 features a new binding mode of the cis-hyponitrite ligand. [ABSTRACT FROM AUTHOR]

Hydroxylamine (NH2OH) is an important molecule in biology that serves as an intermediate in the nitrogen cycle, and that can also be utilized as a nitric oxide donor in mammals under certain conditions. In light of this, the interaction of NH2OH with hemes in proteins and model systems has gained much attention recently. In this study, we use the more stable, oxygen substituted O-benzylhydroxylamine (NH2OBn) as a model for NH2OH. Here, the reactivity of the ferric bis-picket fence porphyrin complexes [Fe(3, 5-Me-BAFP)(ClO4)] ( 1) and [Fe(3, 5-Me-BAFP)(PF6)] ( 2) (3,5-Me-BAFP2- = dianion of tetra(2, 6-bis(3,5-dimethylphenoxy)phenyl)porphyrin)) with NH2OBn is investigated. The product of these reactions is characterized by UV/Vis and EPR spectroscopy and X-ray crystallography. We found that addition of excess NH2OBn to our ferric porphyrin complexes results in reduction of the heme to the ferrous oxidation state. This is followed by disproportionation of additional NH2OBn to yield the ferrous complex [Fe(3,5-Me-BAFP)(NH3)2] ( 3) as the final product. The crystal structure of ( 3) constitutes the first structural characterization of a bis-ammonia complex of a ferrous heme. The stability of this complex may be facilitated by the picket fences of the porphyrin ligand used here. [ABSTRACT FROM AUTHOR]

Interaction of NO (15NO) with amorphous layers of Ru(II) carbonyl porphyrin (Ru(TPP)(CO), TPP2- = meso-tetraphenylporphyrinato dianion) was monitored by FTIR spectroscopy from 80 K to room temperature. An intermediate spectrally characterized at very low temperatures (110 K) with ν(CO) at 2001 cm-1 and ν(NO) at 1810 cm-1 (1777 cm-1 for 15NO isotopomer) was readily assigned to the mixed carbonyl--nitrosyl complex Ru(TPP)(CO)(NO), which is the logical precursor to CO labilization. Remarkably, Ru(TPP)-mediated disproportionation of NO is seen even at 110 K, an indication of how facile this reaction is. By varying the quantity of supplied NO, it was also demonstrated that the key intermediate responsible for NO disproportionation is the dinitrosyl complex Ru(TPP)(NO)2, supporting the conclusion previously made from solution experiments. [ABSTRACT FROM AUTHOR]

Pentaammineruthenium(III) complexes of deoxyinosine (dIno) and xanthosine (Xao) ([Ru(NH)(L)], L is dIno, Xao) in basic solution were studied by UV-vis spectroscopy, liquid chromatography/electrospray ionization mass spectrometry, and high-performance liquid chromatography. Both Ru complexes disproportionate to Ru and Ru. Disproportionation followed the rate law d[Ru]/d t = ( k + k[OH])[Ru]. k and k of disproportionation at 25 °C were 2.1 (±0.1) × 10 s and 21.4 ± 3.2 M s, respectively, for [Ru(NH)(dIno)], and 3.5 (±0.7) × 10 s and 59.7 ± 3.6 M s, respectively, for [Ru(NH)(Xao)]. The [Ru(NH)(Xao)] complex disproportionates at a faster rate than [Ru(NH)(dIno)] owing to the stronger electron-withdrawing effect of exocyclic oxygen in Xao. The activation parameters Δ H and Δ S for k of [Ru(NH)(dIno)] were 80.2 ± 15.2 kJ mol and 47.6 ± 9.8 J K mol, respectively, indicating that the disproportionation of Ru to Ru and Ru is favored owing to the positive entropy of activation. The final products of both complexes in basic solution under Ar were compared with those under O. Under both conditions [Ru(NH)(8-oxo-L)] was produced, but via different mechanisms. In both aerobic and anaerobic conditions, the deprotonation of highly positively polarized C8-H of Ru-L by OH initiates a two-electron redox reaction. For the next step, we propose a one-step two-electron redox reaction between L and Ru under anaerobic conditions, which differentiates from Clarke's mechanism of two consecutive one-electron redox reactions between L, Ru, and O. [ABSTRACT FROM AUTHOR]

Abstract: A new MnIV dinuclear complex [MnIV 2(μ-O)2(L′)4].2CH3OH (HL′=(E)-N′-(1-(thiophen-2-yl)ethylidene)benzohydrazide) was obtained from MnIII(acetate)3.2H2O by an unusual MnIII disproportionation reaction. This compound exhibits a strong antiferromagnetic coupling with a J value of −149(5) cm−1. Moreover, a new MnIII mononuclear complex bearing L′ named [MnIII(acac)(L′)2] (acac = acetylacetonate) was obtained from [MnIII(acac)3] and is described as a part of a systematic research work around manganese complexes of magnetic interest. [Copyright &y& Elsevier]

To design new metal string complexes, several naphthyridyl group modulated oligo-α-pyridylamido ligands have been synthesized in the past five years. Because these ligands are less anionic than pyridylamido ligands, the resulting metal string complexes tend to form reduced mixed-valence [Ni2(napy)4]3+ dinuclear units which contain a delocalized unpaired electron and thus significantly enhance the conductance of metal string complexes. Furthermore, the asymmetric naphthyridyl group modulated oligo-α-pyridylamido ligands can stabilize the central heteronuclear or charge disproportionational metal frameworks, providing a plausible strategy to build inorganic molecular rectifiers. [ABSTRACT FROM AUTHOR]