Imido Nitrogen Research Articles

Square-planar imido complexes of cobalt: synthesis, reactivity and computational study.

Treatment of [Co(N2)(tBuPNP)] (tBuPNP = anion of 2,5-bis(di-tert-butylphosphinomethyl)pyrrole) with one equivalent of an aryl azide generates the four-coordinate imido complexes [Co(NAr)(tBuPNP)] (Ar = mesityl, phenyl, or 4-tBu-phenyl). X-ray crystallographic analysis of the compounds shows an unusual square-planar geometry about cobalt with nearly linear imido units. In the presence of the hydrogen atom donor, TEMPOH, [Co(NPh)(tBuPNP)] undergoes addition of the H atom to the imido nitrogen to generate the corresponding amido complex, [Co(NHPh)(tBuPNP)], whose structure and composition were verified by independent synthesis. Despite the observation of H atom transfer reactivity with TEMPOH, the imido complexes do not show catalytic activity for C-H amination or aziridination for several substrates examined. In the case of [Co(NPh)(tBuPNP)], addition of excess azide produced the tetrazido complex, [Co(N4Ph2)(tBuPNP)], whose bond metrics were most consistent with an anionic Ph2N4 ligand. Density Functional Theory (DFT) investigations of the imido and tetrazido species suggest that they adopt a ground state best described as possessing a low-spin cobalt(II) ion ferromagnetically coupled to an iminyl radical.

Ligands with polyfluorophenyl moieties promote a local structural rearrangement in the Spinach2 and Broccoli aptamers that increases ligand affinities.

The interaction of nucleic acids with their molecular targets often involves structural reorganization that may traverse a complex folding landscape. With the more recent recognition that many RNAs, both coding and noncoding, may regulate cellular activities by interacting with target molecules, it becomes increasingly important to understand how nucleic acids interact with their targets and how drugs might be developed that can influence critical folding transitions. We have extensively investigated the interaction of the Spinach2 and Broccoli aptamers with a library of small molecule ligands modified by various extensions from the imido nitrogen of DFHBI [(Z)-5-(3,5-difluoro-4-hydroxybenzylidene)-2,3-dimethyl-3,5-dihydro-4H-imidazol-4-one] that reach out from the Spinach2 ligand binding pocket. Studies of the interaction of these compounds with the aptamers revealed that polyfluorophenyl-modified ligands initiate a slow change in aptamer affinity that takes an extended time (half-life of ∼40 min) to achieve. The change in affinity appears to involve an initial disruption of the entrance to the ligand binding pocket followed by a gradual transition to a more defined structure for which the most likely driving force is an interaction of the gateway adenine with a nearby 2'OH group. These results suggest that polyfluorophenyl modifications might increase the ability of small molecule drugs to disrupt local structure and promote RNA remodeling.

Redox-Controlled and Reversible N-N Bond Forming and Splitting with an IronIV Terminal Imido Ligand.

Oxidation of the low-spin FeIV imido complex [{(tBupyrr)2py}Fe═NAd] (1) ((tBupyrr)2py2- = 2,6-bis(3,5-di-tert-butyl-pyrrolyl)pyridine, Ad = 1-adamantyl) with AgOAc or AgNO3 promotes reductive N-N bond coupling of the former imido nitrogen with a pyrrole nitrogen to form the respective ferric hydrazido-like pincer complexes [{(tBupyrrNAd)(tBupyrr)py}Fe(κ2-X)] (X = OAc-, 2OAc; NO3-, 2NO3). Reduction of 2OAc with KC8 cleaves the N-N bond to reform the FeIV imido ligand in 1, whereas acid-mediated demetalation of 2OAc or 2NO3 yields the free hydrazine ligand [(tBupyrrNHAd)(tBupyrrH)py] (3), the latter of which can be used as a direct entry to the iron imido complex when treated with [Fe{N(SiMe3)2}2]. In addition to characterizing these Fe systems, we show how this nitrene transfer strategy can be expanded to Co for the one-step synthesis of Co{(tBu-NHAdpyrr)(tBupyrr)py}] (4) ((tBu-NHAdpyrr)(tBupyrr)py2- = 2-(3-tBu-5-(1-adamantylmethyl-2-methylpropane-2-yl)-pyrrol-2-yl)-6-(3,5-tBu2-pyrrol-2-yl)-pyridine).

Synthesis of cyclic carbonates by ruthenium(VI) bis-imido porphyrin/TBACl-catalyzed reaction of epoxide with CO2

The catalytic activity of the ruthenium(VI) bis-imido porphyrin complex/TBACl binary system in promoting the CO[Formula: see text] cycloaddition to epoxides forming cyclic carbonates is here reported. The system was very efficient in catalyzing the conversion of differently substituted epoxides under mild experimental conditions (100 [Formula: see text]C and 0.6 MPa of CO[Formula: see text]. Even if the sole TBACl resulted active under the optimized experimental conditions, the addition of ruthenium species was fundamental to maximizing the reaction productivity both in terms of epoxide conversions and cyclic carbonate selectivities. A preliminary mechanistic study indicated a positive role of ruthenium imido nitrogen atom in activating carbon dioxide.

Molybdenum Disubstituted Alkylidene Complexes

Through relatively straightforward techniques that begin with Mo(NAr)(CH-t-Bu)[OCMe(CF3)2]2 (Ar = 2,6-i-Pr2C6H3), we have prepared Mo(NAr)(CMePh)(OMesityl)2, [Mo(NAr)(CMePh)(OC6F5)2]2, Mo(NAr)(CMePh)(OC6F5)2(MeCN), Mo(NAr)(CMePh)(OC6F5)2(bipyridyl), Mo(NAr)(CMePh)(Cl)2(bipyridyl), Mo(NAr)(CMePh)(Cl)(OHMT)(MeCN) (OHMT = O-2,6-(2,4,6-Me3C6H2)2C6H3), and Mo(NAr)(CMePh)(Pyrrolide)(OHMT). X-ray studies reveal that in five compounds the alkylidene isomer (A) is that in which the phenyl group in the alkylidene points toward the imido nitrogen. In Mo(NAr)(CMePh)(OC6F5)2(MeCN) the isomer in which the methyl group points toward the imido nitrogen (isomer B) has cocrystallized with isomer A (12%). In two 14e compounds that contain isomer A, the Mo═C–C angles differ by 30–36°, consistent with a Mo. . .C–Hβ agostic interaction. Several of the complexes reported here react readily with ethylene, 1-decene, or cyclooctene to give the expected products, thus confirming their viability as initiators or intermediates in metathesis reactions.

Carbon Dioxide Activation by a Palladium Terminal Imido Complex

We recently reported the first example of a palladium(ii) terminal imido complex. We proposed that this complex features exceptional high nucleophilicity at the nitrogen atom and a peculiar zwitterionic electronic structure with an anti-bonding highest-occupied molecular orbital (HOMO). This complex swiftly activated moderately acidic CH, OH, and NH bonds and also reacted with dihydrogen. However, unambiguous nucleophilic reactivity with substrates not featuring a hydrogen atom could not be observed. Herein, we now show that this nucleophilic complex also reacts with CO2 to give a ring-strained four-membered palladium(ii) carbamate complex. Remarkably, the same product is obtained in the reaction of the related bisamido complex, albeit at a slower reaction rate. Density functional theory calculations indicate that the addition of CO2 does not proceed via initial 1,2-addition across the Pd–N bond, but instead through nucleophilic attack by the imido (amido respectively) nitrogen atom.

Ruthenium Porphyrin Catalyzed Synthesis of Oxazolidin‐2‐ones by Cycloaddition of CO2 to Aziridines

The reaction between N‐substituted‐2‐arylaziridines and CO2 is efficiently promoted by ruthenium(VI) imidoporphyrin complexes and yields a mixture of 5‐aryl (A) and 4‐aryl (B) substituted oxazolidin‐2‐ones with a regioisomeric A/B ratio up to 99:1. Several oxazolidin‐2‐one molecules were synthesized at 100 °C and 0.6 MPa of carbon dioxide by using the low catalytic loading of 1 mol‐%. The formation of a deactivated compound, deriving from the ruthenium catalyst, suggested a possible catalytic role of imido nitrogen atoms.

Synthesis, structure, and characterization of molybdenum(VI) imido complexes with N-salicylidene-2-aminothiophenol

The di-imido complex Mo(NAr)2Cl2(dme) (dme = 1,2-dimethoxyethane; Ar = 2,6-diisopropylphenyl) reacts with the sulfur ligand N-salicylidene-2-aminothiophenol (smaH2) in methanol in the presence of two equivalents of triethylamine to form Mo(NAr)2sma (1). The structure of this molybdenum(VI) complex has been determined by X-ray crystallography. The coordination sphere of the Mo center is approximately a trigonal bipyramid. The angles of the imido linkages (Mo–N–C) are 175° and 147°. The tridentate sma ligand binds with the imine nitrogen in the axial position trans to the 175° imido linkage. 1 can be reacted with bidentate aromatic ligands to form six-coordinate complexes of the type Mo(ArN)(sma)(L) (L = catecholate, 2; 2-mercaptophenolate, 3, 1,2-benzenedithiolate, 4; 2-amidophenolate, 5; 3-amidonaphtholate, 6; 1,2-amidonaphtholate, 7; 2-amidothiophenolate, 8). The structures of compounds 2–7 have been determined by X-ray crystallography. In 2, 3, and 4 the bidentate ligand, L, binds in two equatorial positions cis to the imido linkage. In 5, 6 and 7 L binds in an axial and an equatorial position where the amido nitrogen occupies the equatorial position. All complexes have been characterized by 1H NMR spectroscopy and cyclic voltammetry. Compounds 2, 3, and 4 can be reversibly reduced with one electron to EPR-active Mo(V) complexes. The EPR spectrum of 4 shows superhyperfine splitting from the imido nitrogen. This indicates that the unpaired electron is located in the dz2 orbital that interacts with the imido nitrogen and the imine nitrogen of the sma ligand and is not influenced by the bidentate aromatic ligand which binds in two equatorial positions. This explains the similar redox potentials of the three complexes. In complexes 5–8 the reduction is not reversible and the potential is influenced by the atom of the bidentate aromatic ligand trans to the imido group.

Structural Characterization of (Diphenylhydrazido)vanadium(V) Compounds

Abstract(Diphenylhydrazido)vanadium(V) triisopropoxide was synthesized by the reaction of VO(OiPr)3 with N,N‐diphenylhydrazine. The μ‐isopropoxido‐bridged dimeric structure was observed in the molecular structure of (diphenylhydrazido)vanadium(V) triisopropoxide. The near‐linear V(1)‐N(1)‐N(2) angle of 173.7(3)° with the V(1)‐N(1) distance of 1.667(4) Å indicates that the imido nitrogen has large participation of an sp‐hybridized character. The phenyl substituents of the hydrazido moiety were found to conjugate with the N−N bond. Furthermore, CH‐π intermolecular interaction between two benzene rings was observed to induce polymeric structure in a solid state. (Diphenylhydrazido)vanadium(V) nitrilotriethoxide was obtained by the treatment of (diphenylhydrazido)vanadium(V) triisopropoxide with 2,2′,2′′‐nitrilotriethanol. The slightly increased imido angle (V(1)‐N(1)‐N(2), 176.4(5)°) was observed as compared with (diphenylhydrazido)vanadium(V) triisopropoxide probably because of the apical coordination of the nitrogen.

Decarboxylation of 5-amino-orotic acid and a Schiff base derivative by rhenium(V)

The reaction of 5-amino-orotic acid (H2aor) with trans-[ReOBr3(PPh3)2] in 2-propanol produced the complex [ReV(apd)Br(aor)(PPh3)2] (1, apd2−=5-imidopyrimidine-2,4-dione). The ligand apd2− was formed by the decarboxylation of H2aor, and it is coordinated via the dinegative imido nitrogen only. The Schiff base derivative of H2aor, salicylimine-orotic acid {5-(2-hydroxy-benzylideneamino)-1,2,3,6-tetrahydro-2,6-dioxopyrimidine-4-carboxylic acid; H2sor}, was also decarboxylated in the reaction with trans-[ReOI2(OEt)(PPh3)2] in ethanol to form [ReIII(cor)I(PPh3)2]I (2, Hcor=5-(2-hydroxybenzylideneamino)-pyrimidine-2,4(1H,3H)-dione). Decarboxylation of H2sor was not observed in its reaction with trans-[ReOCl3(PPh3)2], which led to the isolation of [ReOCl(sor)(PPh3)] (3), in which sor2− is coordinated as a tridentate ligand as expected. Spectroscopic results and the X-ray crystal structures of compounds 1–3 are also presented.

Can a pentamethylcyclopentadienyl ligand act as a proton-relay in f-element chemistry? Insights from a joint experimental/theoretical study.

Isomerisation of buta-1,2-diene to but-2-yne by (Me(5)C(5))(2)Yb is a thermodynamically favourable reaction, with the Δ(r)G° estimated from experimental data at 298 K to be -3.0 kcal mol(-1). It proceeds in hydrocarbon solvents with a pseudo first-order rate constant of 6.4 × 10(-6) s(-1) and 7.4 × 10(-5) s(-1) in C(6)D(12) and C(6)D(6), respectively, at 20 °C. This 1,3-hydrogen shift is formally forbidden by symmetry and has to occur by an alternative pathway. The proposed mechanism for buta-1,2-diene to but-2-yne isomerisation by (Me(5)C(5))(2)Yb involves coordination of methylallene (buta-1,2-diene) to (Me(5)C(5))(2)Yb, and deprotonation of methylallene by one of the Me(5)C(5) ligands followed by protonation of the terminal methylallenyl carbon to yield the known coordination compound (Me(5)C(5))(2)Yb(η(2)-MeC[triple bond, length as m-dash]CMe). Computationally, this mechanism is not initiated by a single electron transfer step, and the ytterbium retains its oxidation state (II) throughout the reactivity. Experimentally, the influence of the metal centre is discussed by comparison with the reaction of (Me(5)C(5))(2)Ca towards buta-1,2-diene, and (Me(5)C(5))(2)Yb with ethylene. The mechanism by which the Me(5)C(5) acts as a proton-relay within the coordination sphere of a metal also rationalises the reactivity of (i) (Me(5)C(5))(2)Eu(OEt(2)) with phenylacetylene, (ii) (Me(5)C(5))(2)Yb(OEt(2)) with phenylphosphine and (iii) (Me(5)C(5))(2)U(NPh)(2) with H(2) to yield (Me(5)C(5))(2)U(HNPh)(2). In the latter case, the computed mechanism is the heterolytic activation of H(2) by (Me(5)C(5))(2)U(NPh)(2) to yield (Me(5)C(5))(2)U(H)(HNPh)(NPh), followed by a hydrogen transfer from uranium back to the imido nitrogen atom using one Me(5)C(5) ligand as a proton-relay. The overall mechanism by which hydrogen shifts using a pentamethylcyclopentadienyl ligand as a proton-relay is named Carambole in reference to carom billiards.

Carbon-hydrogen bond activation, C-N bond coupling, and cycloaddition reactivity of a three-coordinate nickel complex featuring a terminal imido ligand.

The three-coordinate imidos (dtbpe)Ni=NR (dtbpe = tBu2PCH2CH2PtBu2, R = 2,6-iPr2C6H3, 2,4,6-Me3C6H2 (Mes), and 1-adamantyl (Ad)), which contain a legitimate Ni–N double bond as well as basic imido nitrogen based on theoretical analysis, readily deprotonate HC≡CPh to form the amide acetylide species (dtbpe)Ni{NH(Ar)}(C≡CPh). In the case of R = 2,6-iPr2C6H3, reductive carbonylation results in formation of the (dtbpe)Ni(CO)2 along with the N–C coupled product keteneimine PhCH=C=N(2,6- iPr2C6H3). Given the ability of the Ni=N bond to have biradical character as suggested by theoretical analysis, H atom abstraction can also occur in (dtbpe)Ni=N{2,6-iPr2C6H3} when this species is treated with HSn(nBu)3. Likewise, the microscopic reverse reaction—conversion of the Ni(I) anilide (dtbpe)Ni{NH(2,6-iPr2C6H3)} to the imido (dtbpe)Ni=N{2,6-iPr2C6H3}—is promoted when using the radical Mes*O• (Mes* = 2,4,6-tBu3C6H2). Reactivity studies involving the imido complexes, in particular (dtbpe)Ni=N{2,6-iPr2C6H3}, are also reported with small, unsaturated molecules such as diphenylketene, benzylisocyanate, benzaldehyde, and carbon dioxide, including the formation of C–N and N–N bonds by coupling reactions. In addition to NMR spectroscopic data and combustion analysis, we also report structural studies for all the cycloaddition reactions involving the imido (dtbpe)Ni=N{2,6-iPr2C6H3}.

Polyimido Sulfur(VI) Phosphanyl Ligand in Metal Complexation

Herein, new complexes containing the [Ph2PCH2S(NtBu)3](-) anion are presented, supplying three imido nitrogen atoms and a remote phosphorus atom as potential donor sites to main group and transition-metal cations. The lithiated complex [(tmeda)Li{(NtBu)3SCH2PPh2}] (1) is an excellent starting material in transmetalation reactions. Herein, the transition-metal complexes [M{(NtBu)3SCH2PPh2}2] (M=Mn (2), Ni (3), Zn (4)) were synthesized and structurally characterized. Their isotypical molecules show SN2 chelation and no employment of the adjacent phosphorus atom in coordination. The third pendent imido group is always twisted toward the vacant face of the tetrahedrally coordinated sulfur atom.

Ennobling an Old Molecule: Thiazyl Trifluoride (N≡SF3), a Versatile Synthon for Xe–N Bond Formation

The fields of sulfur-nitrogen-fluorine chemistry and noble-gas chemistry have been significantly extended by the syntheses and characterizations of four new Xe-N-bonded cations derived from N≡SF(3). The adduct-cation, F(3)S≡NXeF(+), has provided the entry point to a significant chemistry through HF solvolysis of the coordinated N≡SF(3) ligand and HF-catalyzed and solid-state rearrangements of F(3)S≡NXeF(+). The HF solvolyses of [F(3)S≡NXeF][AsF(6)] in anhydrous HF (aHF) and aHF/BrF(5) solutions yield the F(4)S═NXe(+) cation, which likely arises from an HF-catalyzed mechanism. The F(4)S═NXe(+) cation, in turn, undergoes HF displacement to form F(4)S═NH(2)(+) and XeF(2), as well as HF addition to the S═N bond to form F(5)SN(H)Xe(+). Both cations undergo further solvolyses in aHF to form the F(5)SNH(3)(+) cation. The F(4)S═NXe(+) and F(4)S═NH(2)(+) cations were characterized by NMR spectroscopy and single-crystal X-ray diffraction and exhibit high barriers to rotation about their S═N double bonds. They are the first cations known to contain the F(4)S═N- group and significantly extend the chemistry of this ligand. The solid-state rearrangement of [F(3)S≡NXeF][AsF(6)] at 22 °C has yielded [F(4)S═NXe][AsF(6)], which was characterized by Raman spectroscopy, providing the first examples of xenon bonded to an imido nitrogen and of the F(4)S═N- group bonded to a noble-gas element. The rearrangement of [F(3)S≡NXeF][AsF(6)] in a N≡SF(3) solution at 0 °C also yielded [F(4)S═NXe−N≡SF(3)][AsF(6)], which represents a rare example of a N−Xe−N linkage and the first to be characterized by X-ray crystallography. Solvolysis of N≡SF(3) in aHF was previously shown to give the primary amine F(5)SNH(2), whereas solvolysis in the superacid medium, AsF(5)/aHF, results in amine protonation to give [F(5)SNH(3)][AsF(6)]. Complete structural characterizations were not available for either species. Isolation of F(5)SNH(2)·nHF from the reaction of N≡SF(3) with HF has provided a structural characterization of F(5)SNH(2) by Raman spectroscopy. Crystal growth by sublimation of F(5)SNH(2)·nHF at -30 to -40 °C has resulted in the X-ray crystal structure of F(5)SNH(2)·2[F(5)SNH(3)][HF(2)]·4HF and structural characterizations of F(5)SNH(2) and F(5)SNH(3)(+). The redox decomposition of [F(4)S═NXe−N≡SF(3)][AsF(6)] in N≡SF(3) at 0 °C generated Xe, cis-N(2)F(2), and [F(3)S(N≡SF(3))(2)][AsF(6)].

Imidozirconocene‐Mediated Ring Cleavage of Epoxides – Evidence for Bifunctional Reactivity from DFT

AbstractThe ring cleavage of epoxides mediated by bis(cyclopentadienyl)(tert‐butylimido)zirconium (Cp2Zr=N–tBu)(THF) has been investigated using DFT calculations with a view to understand the mechanism of epoxide ring cleavage and the role of the imidozirconocene complex. Two types of epoxides have been chosen; some with and some without accessible β‐hydrogen atoms. Epoxides without accessible β‐hydrogen atoms undergo only insertion, whereas those with undergo both insertion and elimination. Although insertion is found to follow a zwitterionic mechanism, the elimination passes through a concerted intramolecular hydrogen transfer step. The role of the imidozirconocene complex has been elucidated by EDA and NBO analysis, which show that the vacant 1a1 molecular orbital of the Lewis acidic metal center of Cp2Zr=N–tBu fragment initiates the reaction as a Lewis acidic center and the Lewis basic imido nitrogen atom of the Cp2Zr=N–tBu fragment completes the reaction. The coordinate to covalent bond conversion and the involvement of the 1a1 and 2a1 molecular orbitals of the Cp2Zr=N–tBu fragment in the reaction have been examined. The formation of a five‐membered metallacycle in the insertion and the alkoxy allyl product in the elimination predicted by calculations concur with experimental observations. Topological analysis has been carried out to further elucidate the mechanism and to reveal the bifunctional reactivity of imidozirconocene in epoxide ring opening reactions.

Imidazolinone herbicides in strongly acidic media: Speciation and electroreduction

From UV-visible measurements and potentiometric titrations it follows that the lowest pK values (pK1) of imidazolinone herbicides correspond to the simultaneous protonation/dissociation equilibria of both the pyridinic (or quinolinic) nitrogen and the carboxyl group, the following pK (pK2) to the imminium nitrogen and the basic pK (pK3) to the dissociation of the imido nitrogen. Below pH 6 and down to pH c.a. 2.5, the dominant form of the herbicide is a double ion having both positive and negative charges, this being important in discussing the effect of pH in the natural dynamics of imidazolinone herbicides, especially in their soil sorption. Electrochemical studies of the reduction of the herbicides were made on mercury and carbon electrodes in strongly acidic media (0.1 to 2.7 M H2SO4) as well up to pH 7. The reduction signals were all attributed to the reduction of the imidazolinone ring except the second peak/wave that was found to have originated by the reduction of the pyridine/quinoline ring. A signal observed in strongly acidic media and at highly negative overpotentials was attributed to the reduction of the imidazolinone ring of the product of the previous reduction in a process consisting of two reversible electron transfers followed by a protonation reaction. À partir de mesures UV-visible et des titrages potentiométriques il s’ensuit que la plus basse valeur de pK (pK1) des herbicides de type imidazolinone correspond aux équilibres de dissociation/protonation simultanées d’azote pyridinique (ou quinolinique) et le groupe carboxyle, le pK suivant (pK2) à l’azote imminium et le pK basique (pK3) à la dissociation de l’azote imido. En dessous de pH 6 et pH jusqu’à C.A. 2,5, la forme dominante de l’herbicide est un ion double ayant charges positive et négative, ce qui est important dans la discussion l’effet du pH dans la dynamique naturelle des herbicides, en particulier dans leur sorption dans le sol. Des études électrochimiques de la réduction des herbicides ont été faites sur des électrodes de mercure et de charbon dans des milieux fortement acides (de 0,1 à 2,7 M H2SO4) ainsi jusqu’à pH 7. Les signaux de réduction ont été attribuées à la réduction de l’anneau de type imidazolinone, sauf le deuxième pic, les vagues causées par la réduction de l’anneau de pyridine/quinoline. La signal observé en milieu fortement acide et à surtensions très négative a été attribuée à la réduction de l’anneau d’imidazolinone du produit de la réduction précédente dans un processus composé de deux transferts d’électrons réversible suivie d’une réaction de protonation.

Synthesis and structure of mononuclear copper(II) complexes with acyclic Schiff-base ligands containing organotellurium substituents: a comparative study with selenium analogs

Tellurium-bearing acyclic Schiff bases, 2,6-bis({N-[2-(phenyltellurato)ethyl]}benzimidoyl)-4-methylphenol (HL3 ) and 2,6-bis({N-[3-(phenyltellurato)propyl]}benzimidoyl)-4-methylphenol (HL4 ) of the Te2N2O type have been prepared by condensation of 4-methyl-2,6-dibenzoylphenol (mdbpH) with the appropriate phenyltellurato(alkyl)amine. HL3 and HL4 have been characterized by mass spectrometry, IR, electronic and 1H-NMR spectroscopies and cyclic voltammetry. Their reactions with Cu(II) acetate monohydrate in a 2 : 1 molar ratio in methanol yield [(C6H2(O)(Me){(C6H5)C=N(CH2)nTe(C6H5)}{(C6H5)C=O})2Cu] (3 (n = 2), 4 (n = 3)) as suggested by analytical and spectroscopic data and single crystal X-ray crystallography of 3. In both complexes, one arm of the ligand undergoes hydrolysis at the C=N position and two molecules of the partially hydrolyzed ligand coordinate to Cu(II) through imido nitrogen and the phenolic oxygen. The telluriums do not form part of the copper(II) distorted square planar coordination sphere which has a trans-CuN2O2 core. Electrochemical studies of 3 and 4 indicate quasi-reversible reductions (E°′ = −1.113 V (3) and −1.149 V (4)) corresponding to the reduction of copper(II) to copper(I). The interactions of 3 and 4 with calf thymus DNA, investigated by spectrophotometry and cyclic voltammetry, indicate that 3 and 4 bind to DNA via intercalation, and the binding affinity of 3 is lower than that of its selenium analog.

Synthesis of (arylimido)vanadium complexes and their application for oxidative coupling reactions of silyl enol ether derivatives

(Arylimido)vanadium(v) complexes, V(NAr)(OEt)Cl(2) [Ar = C(6)H(5), p-BrC(6)H(4), p-(MeO)C(6)H(4)] or V(NAr)Cl(3) [Ar = o-BrC(6)H(4), o-(MeO)C(6)H(4)] were synthesized by the reaction of VO(OEt)Cl(2) or VOCl(3), respectively, with the corresponding aryl isocyanates. X-Ray crystal structure determination for V(NAr)(OEt)Cl(2) (Ar = C(6)H(5) and p-BrC(6)H(4)) elucidates the alkoxido-bridged dimeric building blocks [V(NAr)(OEt)Cl(2)](2), wherein the substituent on the benzene ring was found to affect the character of the imido nitrogen. The (51)V NMR spectroscopic measurements indicated that the electronic state of the vanadium metal centre depends on the ligands connecting to the vanadium and the substituents on the benzene ring. The selective oxidative cross-coupling reaction of silyl ketene acetal with silyl enol ether was achieved using V(Np-BrC(6)H(4))Cl(3) or V(No-BrC(6)H(4))Cl(3).

6-(4-(2-{2-[2-(2-Hydroxy-ethoxy)-ethoxy]-ethoxy}-ethyl)-10-oxa-4-aza-tricyclo[5.2.1.02,6]dec-8-ene-3,5-dione)

Microwave irradiation of maleimide with an excess of furan in water exclusively yields the corresponding exo-cycloadduct in good yield (87%) in 1 hour at 90 oC. Alkylation of the imido nitrogen with tetraethylene glycol under Mitsunobu conditions gives the ROMP monomer in 81% yield.

Organometallic Uranium(V)−Imido Halide Complexes: From Synthesis to Electronic Structure and Bonding

Reaction of (C5Me5)2U(=N-2,4,6-(t)Bu3-C6H2) or (C5Me5)2U(=N-2,6-(i)Pr2-C6H3)(THF) with 5 equiv of CuX(n) (n = 1, X = Cl, Br, I; n = 2, X = F) affords the corresponding uranium(V)-imido halide complexes, (C5Me5)2U(=N-Ar)(X) (where Ar = 2,4,6-(t)Bu3-C6H2 and X = F (3), Cl (4), Br (5), I (6); Ar = 2,6-(i)Pr2-C6H3 and X = F (7), Cl (8), Br (9), I (10)), in good isolated yields of 75-89%. These compounds have been characterized by a combination of single-crystal X-ray diffraction, (1)H NMR spectroscopy, elemental analysis, mass spectrometry, cyclic voltammetry, UV-visible-NIR absorption spectroscopy, and variable-temperature magnetic susceptibility. The uranium L(III)-edge X-ray absorption spectrum of (C5Me5)2U(=N-2,4,6-(t)Bu3-C6H2)(Cl) (4) was analyzed to obtain structural information, and the U=N imido (1.97(1) A), U-Cl (2.60(2) A), and U-C5Me5 (2.84(1) A) distances were consistent with those observed for compounds 3, 5, 6, 8-10, which were all characterized by single-crystal X-ray diffraction studies. All (C5Me5)2U(=N-Ar)(X) complexes exhibit U(V)/U(IV) and U(VI)/U(V) redox couples by voltammetry, with the potential separation between these metal-based couples remaining essentially constant at approximately 1.50 V. The electronic spectra are comprised of pi-->pi* and pi-->nb(5f) transitions involving electrons in the metal-imido bond, and metal-centered f-f bands illustrative of spin-orbit and crystal-field influences on the 5f(1) valence electron configuration. Two distinct sets of bands are attributed to transitions derived from this 5f(1) configuration, and the intensities in these bands increase dramatically over those found in spectra of classical 5f(1) actinide coordination complexes. Temperature-dependent magnetic susceptibilities are reported for all complexes with mu(eff) values ranging from 2.22 to 2.53 mu(B). The onset of quenching of orbital angular momentum by ligand fields is observed to occur at approximately 40 K in all cases. Density functional theory results for the model complexes (C5Me5)2U(=N-C6H5)(F) (11) and (C5Me5)2U(=N-C6H5)(I) (12) show good agreement with experimental structural and electrochemical data and provide a basis for assignment of spectroscopic bands. The bonding analysis describes multiple bonding between the uranium metal center and imido nitrogen which is comprised of one sigma and two pi interactions with variable participation of 5f and 6d orbitals from the uranium center.