On the mechanism of formation and spectral properties of radical anions generated by the reduction of -[Re(CO)3(5-nitro-1,10-phenanthroline)] and -[Re(CO)3(3,4,7,8-tetramethyl-1,10-phenanthroline)] pendants in poly-4-vinylpyridine polymers

The electrochemical reduction in aprotic media of -[Re^I(CO)₃L]⁺ pendants in poly-4-vinylpyridine polymers is compared to that of [Re^I(CO)₃L]⁺ complexes (L = 5-nitro-1,10-phenanthroline and 3,4,7,8-tetramethyl-1,10-phenanthroline). The UV-Vis absorption spectra of the reduced radical anions of 5-nitro-1,10-phenanthroline (NO₂-phen) and 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen) were obtained by spectro-electrochemistry of [Re^I(CO)₃(NO₂-phen)(CH₃CN)]⁺ and [Re^I(CO)₃(tmphen)(CH₃CN)]⁺, respectively. Similar spectra were obtained for the radical anions -phen and tmphen⁻ after pulse radiolysis experiments with -[Re^I(CO)₃L]⁺-containing polymers. The analysis of the time-resolved difference spectra was performed using “multivariate curve resolution” (MCR) techniques. Unlike , CH₂OH radicals were unable to reduce tmphen ligands. The reaction of and/or CH₂OH with -[Re^I(CO)₃(NO₂-phen)]⁺-containing polymers generates -[Re^I(CO)₃(-phen)] pendants which after disproportionation give rise to products with λ_max = 380 nm. The kinetic behavior of -[Re^I(CO)₃(-phen)] pendants under different experimental conditions is discussed.     

Bond elongation in the anion radical of coordinated tetrazine ligands: A crystallographic, spectroscopic and computational study of a reduced {Re(CO)3Cl} complex

The binuclear complex [(μ-Me₂BPTZ)(Re(CO)₃Cl)₂] (1), where Me₂BPTZ = 3,6-(5-methyl-pyridyl)-1,2,4,5-tetrazine, can be reduced by addition of bis(η⁵-pentamethylcyclopentadienyl) iron(II) (decamethylferrocene, Fc^∗), to obtain a stable radical anion form 1⁻. A single-crystal X-ray diffraction study of the radical anion (1⁻)(Fc^∗+) was conducted and compared with a computational model of the same compound in the neutral and reduced states. As such, this work presents the first structural analysis of a reduced diimine ligand that is coordinated to {Re(CO)₃Cl} moieties. Bond-length changes within the tetrazine ring system were consistent with previously reported examples of tetrazine radicals and with calculated structures that show clear elongation of the azo-type NN bond. Consistently atomic charge calculations indicate that the extra electron in the radical anion resides largely at the tetrazine core. A negligible change in the Re-Cl bond length is observed and computed.     

Platinum allenylidene complexes and formation of platinum and palladium acetonitrile alkynyl complexes

The platinum(0) complex [Pt(PPh₃)₄] reacts with brominated propargylic amides and esters in benzene by oxidative addition to give trans-[Br(PPh₃)₂Pt-CC-C(O)R] complexes whereas no reaction occurs when halogenated solvents (CH₂Cl₂, CHCl₃) are used. The cis-ligands PPh₃ can be replaced by P(ⁱPr)₃ and the bromide by trifluoroacetate. O-Alkylation of those trans-[X(PR′₃)₂Pt-CC-C(O)R] complexes (X = Br, CF₃COO; R′ = Ph, ⁱPr) derived from propargylic amides with MeOTf or [Me₃O]BF₄ in CH₂Cl₂ gives the first cationic monoallenylidene complexes of platinum, trans-[X(PR′₃)₂PtCCC(OMe)NR₂]⁺Y⁻ (Y = OTf, BF₄). In contrast, trans-[Br(PPh₃)₂Pt-CC-C(O)OMenthyl] derived from a propargylic ester does not react with MeOTf in CH₂Cl₂. However, in acetonitrile instead of O-methylation the substitution of acetonitrile for the bromide ligand to yield the cationic acetonitrile alkynyl platinum complex trans-[MeCN(PPh₃)₂Pt-CC-C(O)OMenthyl]⁺OTf⁻ is observed. The related palladium complexes trans-[X(PR′₃)₂Pd-CC-C(O)OR] (X = Br, CF₃COO; R′ = Ph, ⁱPr, R = menthyl, Et) react with MeOTf or [Et₃O]BF₄ analogously affording trans-[MeCN(PR′₃)₂Pd-CC-C(O)OR]⁺Y⁻ (Y = OTf, BF₄).     

Ferrocene- and ruthenocene-containing chalcones: A spectroscopic and electrochemical study

Chalcones of the type Mc-CO-CHCH-Ph, Ph-CO-CHCH-Mc and Mc-CO-CHCH-Mc with Mc = Fc = ferrocenyl or Rc = ruthenocenyl, and Ph = phenyl were synthesized. Synthesis was achieved by base catalyzed Claisen-Schmidt condensation of the appropriated acetyl and aldehyde in ethanol. Cyclic voltammetry in CH₃CN in the presence of 0.1 mol dm⁻³ [N(Bu)₄][PF₆] revealed chemical and electrochemical reversible behaviour for the Fc/Fc⁺ couple and irreversible electrochemistry for the two electron Rc/Rc²⁺ couple. The potential ranges for the Fc/Fc⁺ couple varied in the range 138 ? E°′ ? 302 mV while E_pa for Rc/Rc²⁺ couple was between 358 and 510 mV vs. FcH/FcH⁺, the internal standard. Chalcones with the carbonyl group adjacent to the metallocene, are more difficult to oxidize.     

Molecular and electronic structures of new iron complexes containing N,S-coordinated o-iminothionebenzosemiquinonate(1-) π radical ligands: An experimental and density functional theoretical study

Two new o-aminothiophenol type ligands have been synthesized, namely 1,3-propanediamine-N,N′-bis(benzenethiol), H₄(¹L), and 1,2-bis(2-mercapto-3,5-di-tert-butylaniline)ethane, H₄(²L). The reactions of these ligands with FeBr₂ in dry acetonitrile in the presence and absence of air (and other oxidants such as iodine) afforded seven new complexes which were characterized by single-crystal X-ray crystallography and Mössbauer spectroscopy (as well as EPR- and UV-Vis spectroscopies). Their magnetochemistry has been studied and their electronic structures have been established and verified by broken symmetry (BS) density functional theoretical (DFT) calculations using the B3LYP functional. The ligands are redox-active and the o-iminothiophenolate(2-)-o-iminothiobenzosemiquinonate(1-) oxidation levels are chemically readily accessible. The complexes characterized comprise the dimers [Fe^III(¹L)]₂ (S_T = 0) (1); [Fe^III(²L)]₂ (S_T = 0) (2), and the mononuclear, five coordinate species: [Fe^III(¹L)I] (S_T = ¹/₂) (3); [Fe^III(²L)I] (S_T = ¹/₂) (4); [Fe^II(¹L){P(CH₃)₃}] (S_T = 0) (5); [Fe^II(²L){P(C₆H₅)₃}] (S_T = 0) (6), and [Fe^III(²)(^tpy)] (S_T = 1) (7). (^tBupy) represents 4-tert-butylpyridine and (²)³⁻ is the π radical trianion of the one-electron reduced (²L_gma)²⁻ which in turn is the oxidized form of (²L)⁴⁻ (−4H⁺, −2e).     

Ferromagnetic coupling by the spin-polarization mechanism in a trinuclear V triplesalen complex

The first trinuclear vanadium complex [(talen^t-Bu₂)(V^IVO)₃] (1) of a triple tetradentate triplesalen ligand has been synthesized and characterized. The triplesalen ligand (talen^t-Bu₂)^6- provides three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone. In the electronic absorption spectrum of 1 all four ligand field transitions are detected below 21 400 cm⁻¹. The region above 23 000 cm⁻¹ is dominated by strong absorption from imine π → π^∗ and ligand-to-ligand CT transitions. The latter may also be described by a combined phenolate-to-vanadium LMCT and vanadium-to-imine MLCT through the empty metal d orbitals in a push-pull type interaction. The temperature-dependent magnetic susceptibility measurements reveal a ferromagnetic coupling of the three V^IVO units in the triplesalen complex with J = +0.44 cm⁻¹. The correlation of the electronic structure to the weakness of the ferromagnetic coupling by the spin-polarization mechanism in the trinuclear VO system is discussed.     

Spectro-electrochemical and DFT studies of a planar Cu(II)-phenolate complex active in the aerobic oxidation of primary alcohols

A square-planar compound [Cu(pyrimol)Cl] (pyrimol = 4-methyl-2-N-(2-pyridylmethylene)aminophenolate) abbreviated as CuL-Cl) is described as a biomimetic model of the enzyme galactose oxidase (GOase). This copper(II) compound is capable of stoichiometric aerobic oxidation of activated primary alcohols in acetonitrile/water to the corresponding aldehydes. It can be obtained either from Hpyrimol (HL) or its reduced/hydrogenated form Hpyramol (4-methyl-2-N-(2-pyridylmethyl)aminophenol; H₂L) readily converting to pyrimol (L⁻) on coordination to the copper(II) ion. Crystalline CuL-Cl and its bromide derivative exhibit a perfect square-planar geometry with Cu-O(phenolate) bond lengths of 1.944(2) and 1.938(2) Å. The cyclic voltammogram of CuL-Cl exhibits an irreversible anodic wave at +0.50 and +0.57 V versus ferrocene/ferrocenium (Fc/Fc⁺) in dry dichloromethane and acetonitrile, respectively, corresponding to oxidation of the phenolate ligand to the corresponding phenoxyl radical. In the strongly donating acetonitrile the oxidation path involves reversible solvent coordination at the Cu(II) centre. The presence of the dominant Cu^II-L chromophore in the electrochemically and chemically oxidised species is evident from a new fairly intense electronic absorption at 400-480 nm ascribed to a several electronic transitions having a mixed π → π^∗(L) intraligand and Cu-Cl → L charge transfer character. The EPR signal of CuL-Cl disappears on oxidation due to strong intramolecular antiferromagnetic exchange coupling between the phenoxyl radical ligand (L) and the copper(II) centre, giving rise to a singlet ground state (S = 0). The key step in the mechanism of the primary alcohol oxidation by CuL-Cl is probably the α-hydrogen abstraction from the equatorially bound alcoholate by the phenoxyl moiety in the oxidised pyrimol ligand, Cu-L, through a five-membered cyclic transition state.     

Silver(I) acetylides stabilized by η-alkynes: Synthesis, reaction chemistry and solid state structures

Individual synthetic routes to heterobimetallic Ti(IV)-Ag(I) acetylides of type {[Ti](μ-σ,π-CCR¹)₂}AgCCR² ([Ti] = (η⁵-C₅H₄SiMe₃)₂Ti: R¹ = SiMe₃: 6, R² = SiMe₃; 7, R² = Ph. R¹ = ^tBu: 8, R² = SiMe₃; 9, R² = Ph. [Ti] = (η⁵-C₅H₅)₂Ti): 10, R¹ = ^tBu, R² = SiMe₃) including (i) the reaction of {[Ti](μ-σ, π-CCR¹)₂}AgNO₃ ([Ti] = (η⁵-C₅H₄SiMe₃)₂Ti): 1, R¹ = SiMe₃; 2, R¹ = ^tBu. [Ti] = (η⁵-C₅H₅)₂Ti: 3, R¹ = ^tBu) with LiCCR² (4, R² = SiMe₃; 5, R² = Ph) and (ii) treatment of [Ti](CCSiMe₃)₂ ([Ti] = (η⁵-C₅H₄SiMe₃)₂Ti) (11) with [AgCCR²] (12, R² = SiMe₃; 13, R² = Ph) are described. The reactions of 1-3 with 4 or 5 appeared to be sensitive towards stoichiometry because an excess of 4 or 5 resulted in the formation of [(Ag(CCR²)₂)Li(OEt₂)]_n (14) and [Ti](CCR¹)₂. Coordination polymer 14 is also accessible, when, for example, [AgCCSiMe₃] (12) is treated with 1 eq. of LiCCSiMe₃ (4) in diethyl ether.The titanium(IV)-silver(I) acetylides 6-10 are stable in the dark and at low temperature, while on exposure to light and on heating they decompose to give R²CC-CCR² together with [Ti](CCR¹)₂ and elemental silver.Complexes 6-10 contain a mono-nuclear AgCCR² entity stabilized by the chelate-bonded organometallic π-tweezer molecule [Ti](CCSiMe₃)₂, which was evinced by structure determination of 7 in the solid state. In 14 linear [Me₃SiCC-Ag-CCSiMe₃]⁻ units are connected by [Li(OEt₂)]⁺ building blocks forming a coordination polymer.     

On the elusive, non-emissive yet reactive, upper excited states of [(4,4′-bpy)Re(CO)3(dppz)]PF6 (dppz = dipyridil[3,2-a:2′3′-c]phenazine)

Gradual solvation of [(4,4′-bpy)Re^I(CO)₃(dppz)]⁺ (dppz = dipyridil[3,2-a:2′3′-c]phenazine) by water molecules causes a quenching of the emission in accordance with Perrin’s model of spheres. The calculated radius of the sphere, r = 2.6 ± 0.2 ?, is therefore very close to the distance from the Re center to the oxygen atom of the CO ligands, i.e., l = 2.73 ?. In addition, excited state reactions with TEA produce [(4,4′-bpy⁻)Re^I(CO)₃(dppz)] and [(4,4′-bpy)Re^I(CO)₃(dppz⁻)]. This experimental observation is inconsistent with the formation of the products in the lowest lying and emissive dppz-centered ³ππ* excited state. Jablonski schemes based on the participation of excited states other than the lowest ³ππ* excited state are proposed.     

Benzene and heterocyclic rings formation in cycloaddition reactions catalyzed by RuCp derivatives: DFT studies

The mechanism of the RuCp(COD)Cl catalyzed cyclotrimerization of acetylene, as well as the cyclocotrimerization of two alkynes with one molecule of ethylene, R-CN (R = H, Me, Cl, COOMe), CX₂ (X = O, S, Se), and HNCX (X = O, S) investigated by means of high level DFT/B3LYP calculations, has been reviewed. The key reaction step is in all cases the oxidative coupling of two alkyne ligands to give a metallacyclopentatriene intermediate (or metallacyclopentadiene in other systems). This metallacycle adds unsaturated molecules, containing CC, CC and CX bonds, or RCN, CX₂, and HNCX, in a concerted fashion, directly to the RuC bond, forming bicyclic carbenes. The cycle is completed by a rearrangement followed by an exothermic displacement of the arene or pyridine, by two acetylene molecules regenerating the catalytically active species. Small differences are found depending on the molecules and bonds involved. These reactions are reviewed and the proposed mechanisms compared with other available studies.     

Ultrafast excited-state dynamics of photoisomerizing complexes fac-[Re(Cl)(CO)3(papy)2] and fac-[Re(papy)(CO)3(bpy)] (papy = trans-4-phenylazopyridine)

The character and dynamics of low-lying electronic excited states of the complexes fac-[Re(Cl)(CO)₃(papy)₂] and fac-[Re(papy)(CO)₃(bpy)]⁺ (papy = trans-4-phenylazopyridine) were investigated using stationary (UV-Vis absorption, resonance Raman) and ultrafast time-resolved (visible, IR absorption) spectroscopic methods. Excitation of [Re(Cl)(CO)₃(papy)₂] at 400 nm is directed to ¹ππ^∗(papy) and Re → papy ¹MLCT excited states. Ultrafast (?1.4 ps) intersystem crossing (ISC) to ³nπ^∗(papy) follows. Excitation of [Re(papy)(CO)₃(bpy)]⁺ is directed to ¹ππ^∗(papy), ¹MLCT(papy) and ¹MLCT(bpy). The states ³nπ^∗(papy) and ³MLCT(bpy) are then populated simultaneously in less then 0.8 ps. The ³MLCT(bpy) state decays to ³nπ^∗(papy) with a 3 ps time constant. ³nπ^∗(papy) is the lowest excited state for both complexes. It undergoes vibrational cooling and partial rotation around the -NN- bond, to form an intermediate with a nonplanar papy ligand in less than 40 ps. This species then undergoes ISC to the ground state potential energy surface, on which the trans and cis isomers are formed by reverse and forward intraligand papy rotation, respectively. This process occurs with a time constant of 120 and 100 ps for [Re(Cl)(CO)₃(papy)₂] and [Re(papy)(CO)₃(bpy)]⁺, respectively. It is concluded that coordination of papy to the Re center accelerates the ISC, switching the photochemistry from singlet to triplet excited states. Comparison with analogous 4-styrylpyridine complexes (M. Busby, P. Matousek, M. Towrie, A. Vl?ek Jr., J. Phys. Chem. A 109 (2005) 3000) reveals similarities of the decay mechanism of excited states of Re complexes with ligands containing -NN- and -CC- bonds. Both involve sub-picosecond ISC to triplets, partial rotation around the double bond and slower ISC to the trans or cis ground state. This process is about 200 times faster for the -NN- bonded papy ligand. The intramolecular energy transfer from the ³MLCT-excited ^∗Re(CO)₃(bpy) chromophore to the intraligand state of the axial ligand occurs for both L = stpy and papy with a comparable rate of a few ps.     

Mixed transition-metal complexes based on multitopic 1,3,5-triethynyl- and 1-diphenylphosphino-3,5-diethynyl-benzene linking units

The synthesis and reaction chemistry of heteromultimetallic transition metal complexes in which Fc, [(η⁶-C₆H₅)Cr(CO)₃], [(Ar₃P)Au], [AuCC-bpy] and [{[Ti](μ-σ,π-CCSiMe₃)₂}Cu]⁺ units (Fc = (η⁵-C₅H₄)(η⁵-C₅H₅)Fe; [Ti] = (η⁵-C₅H₄SiMe₃)₂Ti; bpy = 2,2′-bipyridyl-5-yl) are linked by alkynyl-, benzene- and phosphane- or bipyridyl-based connecting moieties is discussed. In context with this background the preparation of neutral heterotrimetallic 1-(FcCC)-3-[(CO)₃Cr(η⁶-C₆H₅CC)]-5-[(Ph₃P)AuCC]C₆H₃ (10) and ionic heteropentametallic [1-(FcCC)-3-[(CO)₃Cr(η⁶-C₆H₅CC)]-5-[(PPh₂)AuCC-bpy({[Ti](μ-σ,π-CCSiMe₃)₂}Cu)]C₆H₃](PF₆) (19) from 1-iodo-3,5-dibromobenzene (1) is reported by applying consecutive reaction methodologies including substitution, complexation and carbon-carbon cross-coupling reactions.The identities of all complexes have been confirmed by elemental analysis and IR, ¹H and ³¹P{¹H} NMR spectroscopy; heteropentametallic 19 was additionally characterized by ESI-TOF mass-spectrometry.     

Ligand redox non-innocent behaviour in ruthenium complexes of ethynyl tolans

A small series of half-sandwich bis(phosphine) ruthenium acetylide complexes [Ru(CCC₆H₄CCSiMe₃)(L₂)Cp′] and [Ru(CCC₆H₄CCC₆H₄R-4)(L₂)Cp′] (R = OMe, Me, CO₂Me, NO₂; L₂ = (PPh₃)₂, Cp′ = Cp; L₂ = dppe; Cp′ = Cp^∗) have been synthesised. One-electron oxidations of these complexes gave the corresponding radical cations, which were significantly more chemically stable in the case of the Ru(dppe)Cp^∗ derivatives. The representative complex [Ru(CCC₆H₄CCC₆H₄OMe-4)(dppe)Cp^∗] was further examined by spectroelectrochemical (IR and UV-Vis-NIR) methods. The results of the spectroelectrochemical studies, supported by DFT calculations, indicate that the hole is largely supported by the ‘RuCCC₆H₄’ moiety in a manner similar to that described previously for simple aryl ethynyl complexes, rather than being more extensively delocalized along the entire conjugated ligand.     

ortho-Carom-N bond fusion in aniline associated with electrophilic chlorination reactions at ruthenium(III) coordinated acetylacetonates

In an unusual reaction of [Ru^III(acac)₂(CH₃CN)₂](ClO₄) ([1], acac = acetylacetonate) and aniline (Ph-NH₂), resulted in the formation of ortho-semidine due to dimerisation of aniline via oxidative ortho-C_arom-N bond formation reaction. This oxidation reaction is associated with stepwise chlorination of coordinated acac ligands at the γ-carbon atom resulting in the formation of [Ru^III(acac)₂L⁻] [2a], [Ru^III(Cl-acac)(acac)L⁻] [2b], [Ru^III(acac)(Cl-acac)L⁻] [2c] and [Ru^III(Cl-acac)₂L⁻] [2d] (L⁻ = N-phenyl-ortho-semiquinonediimine) complexes, respectively. These have been characterized by ¹H NMR, UV-Vis-NIR, ESI-MS and cyclic voltammetry studies. Single crystal X-ray structures of 2c and 2d are reported. Crystallographic structural bond parameters of 2c and 2d revealed bond length equalization of C-C, C-O and M-O bonds. It has been shown that perchlorate () counter anion, present in the starting ruthenium complex, acts as the oxidizing agent in bringing about oxidation of Ph-NH₂ to ortho-semidine. The chloronium ions, produced in situ, chlorinate the coordinated acac ligands at the γ-carbon atom. Such electrophilic substitution of coordinated acac ligands indicates that the Ru-acac metallacycles in the reference compounds are aromatic. The complexes showed an intense and featureless band centered near 520 nm, and a structured band near 275 nm. These displayed one reversible cathodic response in the range, −1.1 to −0.8 V and one reversible anodic response between 0.4 and 0.6 V versus the Saturated Calomel reference Electrode, SCE. The response at the anodic potential is due to oxidation of the coordinated ligand L, while the reversible response at cathodic potential is due to reduction of the metal center.     

Probing valence and spin situations in selective ruthenium-iminoquinonoid frameworks. An experimental and DFT analysis

The ruthenium-iminoquinone complexes, [Ru(tpm)(Cl)(Q)]⁺ [tpm = tris(1-pyrazolyl)methane, Q = 3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine, where aryl = C₆H₅, [1]⁺; m-(OCH₃)₂C₆H₃, [2]⁺; m-(Cl)₂C₆H₃, [3]⁺] have been synthesized. The sensitive bond distances of “Q” in [1](ClO₄) and [2](ClO₄), C-O: 1.294(8), 1.281(2) Å; C-N: 1.352(8), 1.335(2) Å; and C-C(meta): 1.366(10)/1.367(9) Å, 1.364(2)/1.353(2) Å, respectively, and other analytical as well as theoretical (DFT) events suggest the valence configuration of [Ru^III(tpm)(Cl)(Q_Sq⁻)]⁺ for [1]⁺-[3]⁺. The paramagnetic [1]⁺-[3]⁺ show sharp ¹H NMR spectra with strikingly small J of 1.8-3.0 Hz. The DFT calculations on [1]⁺ predict that the triplet (S = 1) state exists above (1004 cm⁻¹) the singlet (S = 0) ground state. [1]⁺ exhibits μ = 2.2 BM at 300 K which diminishes to 0.3 BM near 2 K due to the steady decrease in the ratio of triplet to singlet population with the lowering of temperature. [1]⁺-[3]⁺ exhibit one oxidation and two successive reductions each in CH₃CN. Experimental and DFT analyses collectively establish the valence configurations at the non-innocent {Ru-Q} interface along the redox chain as [(tpm)(Cl)Ru^III(Q_Q^o)]²⁺ ([1]²⁺-[3]²⁺) → [(tpm)(Cl)Ru^III(Q_Sq⁻)]⁺ ([1]⁺-[3]⁺) → [(tpm)(Cl)Ru^II(Q_Sq⁻)] ↔ [(tpm)(Cl)Ru^III(Q_Cat)] (1-3) → [(tpm)(Cl)Ru^II(Q_Cat)]⁻ ([1]⁻-[3]⁻). The spectral features of [1]ⁿ-[3]ⁿ (n = +2, +1, 0) have been addressed based on the TD-DFT calculations on [1]ⁿ.     

Electron transfer. Part 169 . Delayed reduction of mononuclear manganeses(IV) using vanadium(III)

The tris-chelate formed by biguanide, H₂NC(NH)NHC(NH)NH₂, and Mn(IV) is one of the rarely encountered examples of water-stable mononuclear complexes of this oxidation state. This cation is reduced in aqueous acid by both V(II) and V(III). In contrast to the kinetically straightforward bimolecular reduction by V(II) in 0.5 M HClO₄ (k = 7.4 × 10³ M⁻¹ s⁻¹ at 22 °C), reductions by excess V(III) yield profiles which are linear (zero-order in Mn^IV) until the last few percent reaction. Analyses of these composite curves are consistent with the sequences

     

Synthesis and isocyanate insertion reactions of tungsten(IV) imido complexes formed from W(CO)(acac)(N3)(PMe3)3 with azide as the oxidant

Addition of excess trimethylphosphine and a halide source to a solution of W(CO)(acac)₂(η²-L) (L = NCPh and OCMe₂) leads to displacement of L and one acetylacetonate chelate to produce electron-rich, seven-coordinate complexes of the formula W(CO)(acac)(X)(PMe₃)₃ (X = Cl, Br, and I). Use of NaN₃ instead of a halide source leads primarily to loss of carbon monoxide and dinitrogen, and protonation from adventitious water yields the cationic imido complex [W(NH)(acac)(PMe₃)₃]⁺. Heating [W(NH)(acac)(PMe₃)₃]⁺ in aromatic isocyanates at high temperature results in isocyanate insertion into the NH imido bond to form new C-N bonds. An alternate route to related imido complexes involves heating [W(O)(acac)(PMe₃)₃]⁺ with phenyl isocyanate at high temperatures to yield the substituted imido complex [W(NPh)(acac)(PMe₃)₃]⁺.     

Complexes of [Re(CO)3Cl] with different oxidation states of the polyfunctional bmtz/H2bmtz ligand system (bmtz=3,6-bis(2-pyrimidyl)-1,2,4,5-tetrazine)

Combining fac-[Re(CO)₃Cl] with components of the ligand redox system bmtz/bmtz⁻/H₂bmtz/H₂bmtz⁻ (bmtz=3,6-bis(2-pyrimidyl)-1,2,4,5-tetrazine) has led to the isolation of the complexes (H₂bmtz)Re(CO)₃Cl, (μ-H₂bmtz)[Re(CO)₃Cl]₂ and (μ-bmtz)[Re(CO)₃Cl]₂. Other species characterized were (bmtz)Re(CO)₃Cl (UV/Vis, IR), [(H₂bmtz)Re(CO)₃Cl]⁻ (UV/Vis, IR, EPR), {(μ-H₂bmtz)[Re(CO)₃Cl]₂}⁻ (UV/Vis, IR, EPR) and {(μ-bmtz)[Re(CO)₃Cl]₂}⁻ (UV/Vis, IR, X band and high-field EPR). The results confirm bmtz as very strong and H₂bmtz as moderate π acceptor ligand versus one or two chelate-bonded low-valent metal centers. Reactivity is observed in terms of oxidative proton and reductive chloride dissociation.     

Copper(II)-mediated oxime-nitrile coupling in non-aqueous solutions: Synthetic, structural and magnetic studies of the copper(II)-salicylaldehyde oxime reaction system

The reactions of salicylaldehyde oxime (H₂salox) with Cu^II precursors yielded the known complexes [Cu(Hsalox)₂] (1) and [Cu(Hsalox)₂]_n (2), as well as complexes [Cu₃(salox)(L₁)(L₂)]·MeCN (3·MeCN), [CuCl(L₁)] (4) and [Cu₂Na(O₂CMe)₅(HO₂CMe)]_n (5), where L₁⁻ = o-O-C₆H₄-CHNO-C(CH₃)NH and L₂³⁻ = o-O-C₆H₄-CHNO-C(o-O-C₆H₄)N. L₁⁻ was formed in situ via the nucleophilic addition of the oximato O-atom of salox²⁻ to the unsaturated nitrile group of the MeCN reaction solvent. L₂³⁻ is also formed in situ probably through the nucleophilic attack of the oximato O-atom to the unsaturated nitrile group of salicylnitrile; the latter, although not directly added to the reaction mixture, can be produced via the dehydration of salox²⁻. Compounds 1 and 2 contain Hsalox⁻ bound to the metal center in two different coordination modes; they both contain the same mononuclear unit, however a 2D network is generated in 2 due to a relatively long Cu-O_oximato bond. Compound 3 contains three different ligands, i.e. salox²⁻, L₁⁻ and L₂³⁻, which act as μ₃-κ²O:κO′:κN, κO:κN:κN′ and μ₃-κ²O:κ²N:κO′:κN′, respectively, whereas 4 consists of a square planar Cu^II atom bound to a κO:κN:κN′ L₁⁻ and a chloride ion. Compound 5 consists of dinuclear [Cu₂(O₂CMe)₅(HO₂CMe)]⁻ units and Na⁺ ions assembled into an overall 3D network structure. Magnetic susceptibility measurements from polycrystalline samples of 2 and 5 gave best-fit parameters J = +0.36 cm⁻¹ (H = −J?_i?_j) and J = −360 cm⁻¹, zj = +20 cm⁻¹ (H = −J?_i?_j − zJ〈S_z〉?_z), respectively.     

NO, NO, NO! Nitrosyl siblings from [IrCl5(NO)]

Pentachloronitrosyliridate(III) ([IrCl₅(NO)]⁻), the most electrophilic NO⁺ known to date, can be reduced chemically and/or electrochemically by one or two electrons to produce the NO and HNO/NO⁻ forms. The nitroxyl complex can be formed either by hydride attack to the NO⁺ in organic solvent, or by decomposition of iridium-coordinated nitrosothiols in aqueous solutions, while NO is produced electrochemically or by reduction of [IrCl₅(NO)]⁻ with H₂O₂. Both NO and HNO/NO⁻ complexes are stable under certain conditions but tend to labilize the trans chloride and even the cis ones after long periods of time. As expected, the NO⁺ is practically linear, although the IrNO moiety is affected by the counterions due to dramatic changes in the solid state arrangement. The other two nitrosyl redox states comprise bent structures.