Scandium terminal imido complex induced intramolecular C–N bond cleavage and transformation

<正>1 X-ray crystallography Suitable single crystal of 2 was sealed in a thin-walled glass capillary, and data collection was performed at 293(2) K on a Bruker SMART diffractometer with graphite-monochromated Mo Kα radiation(λ = 0.71073 ). Suitable single crystals of 3and 4 were mounted under nitrogen atmosphere on a glass fiber, and data collection was performed at 133(2) K on a Bruker APEX2 diffractometer with graphite-monochromated Mo Kα radiation(λ = 0.71073 ). The SMART program package was used to determine the unit cell parameters. The absorption correction was applied using SADABS. The structures were solved     

Synthesis of a first-row transition metal parent amido complex and carbon monoxide insertion into the amide N-H bond

The parent amido iron complex (dmpe)2Fe(H)(NH2) (dmpe = 1,2-bis(dimethylphosphino)ethane), the first such first-row transition metal complex, has been synthesized and characterized spectroscopically and crystallographically. This complex has been found to insert carbon monoxide into the amide N-H bond (rather than the M-N bond) to give trans-(dmpe)2Fe(H)(NHCHO). The mechanism of this transformation has been studied and is believed to occur through an unusual mechanism in which CO behaves as an apparent electrophile.     

Disulfide bond cleavage induced by a platinum(II) methionine complex

The cleavage of a disulfide bond and the redox equilibrium of thiol/disulfide are strongly related to the levels of glutathione (GSH)/oxidized glutathione (GSSG) or mixed disulfides in vivo. In this work, the cleavage of a disulfide bond in GSSG induced by a platinum(II) complex [Pt(Met)Cl2] (where Met = methionine) was studied and the cleavage fragments or their platinated adducts were identified by means of electrospray mass spectrometry, high-performance liquid chromatography, and ultraviolet techniques. The second-order rate constant for the reaction between [Pt(Met)Cl2] and GSSG was determined to be 0.4 M(-1) s(-1) at 310 K and pH 7.4, which is 100- and 12-fold faster than those of cisplatin and its monoaqua species, respectively. Different complexes were formed in the reaction of [Pt(Met)Cl2] with GSSG, mainly mono- and dinuclear platinum complexes with the cleavage fragments of GSSG. This study demonstrated that [Pt(Met)Cl2] can promote the cleavage of disulfide bonds. The mechanistic insight obtained from this study may provide a deeper understanding on the potential involvement of platinum complexes in the intracellular GSH/GSSG systems.     

Comparing a mononuclear Zn(II) complex with hydrogen bond donors with a dinuclear Zn(II) complex for catalysing phosphate ester cleavage

Introducing ligand based hydrogen bond donors to increase the activity of a mononuclear Zn(II) complex for catalysing phosphate ester cleavage can be a more effective strategy than making the dinuclear analogue.     

Scandium terminal imido complex induced C-H bond selenation and formation of an Sc-Se bond

The reaction between scandium terminal imido complexes and elemental selenium showed an unprecedented C-H bond selenation and the formation of an Sc-Se bond.     

Oxidative C-H and C-C bond cleavage by a (2,2'-bipyridine)copper(I) chloride complex

Acetonitrile is easily oxygenated at ambient reaction conditions to copper(II) oxalate [Cu(bpy)(ox)] n mediated by copper(I) chloride in the presence of 3,5-di-tert-butylcatechol and 2,2'-bipyridine. In the case of other nitriles (e.g., propionitrile), instead, the unusual and selective 1,4-extradiol cleavage of 3,5-di-tert-butylcatechol occurs to give copper(II) tert-butylmaleate [Cu(bma)(bpy)(H2O)]n in good yield.     

Reactivity of mononuclear alkylperoxo copper(II) complex. O-O bond cleavage and C-H bond activation

A detailed reactivity study has been carried out for the first time on a new mononuclear alkylperoxo copper(II) complex, which is generated by the reaction of copper(II) complex supported by the bis(pyridylmethyl)amine tridentate ligand containing a phenyl group at the 6-position of the pyridine donor groups and cumene hydroperoxide (CmOOH) in CH3CN. The cumylperoxo copper(II) complex thus obtained has been found to undergo homolytic cleavage of the O-O bond and induce C-H bond activation of exogenous substrates, providing important insights into the catalytic mechanism of copper monooxygenases.     

Distinct thermodynamics for the formation and cleavage of N-H bonds in aniline and ammonia. Directly-observed reductive elimination of ammonia from an isolated amido hydride complex

The reactions of aryl and alkylamines with the (PCP)Ir fragment (PCP = 1,3-di-tert-butylphosphinobenzene) were studied to determine the reactivities and stabilities of amine and amido hydride complexes relative to C-H activation products. Reaction of aniline with the (PCP)Ir unit generated from (PCP)IrH2 and norbornene resulted in the N-H oxidative addition product (PhNH)(H)Ir(PCP) (1a). In contrast, reaction of this fragment with ammonia gave the ammonia complex (NH3)Ir(PCP) (2). The amido hydride complex that would be formed by oxidative addition of ammonia, (PCP)Ir(NH2)(H) (1b), was generated independently by deprotonation of the ammonia complex (NH3)Ir(H)(Cl)(PCP) (3) with KN(SiMe3)2 at low temperature. This amido hydride complex underwent reductive elimination at room temperature to form the ammonia complex 2. Addition of CO to anilide complex 1a gave (PCP)Ir(PhNH)(H)(CO) (4a). Addition of CNtBu to terminal amido complex 1b formed (PCP)Ir(NH2)(H)(CNtBu) (4b), the first structurally characterized iridium amido hydride. Complexes 4a and 4b underwent reductive elimination of aniline and ammonia; parent amido complex 4b reacted faster than anilide 4a. These observations suggest distinct thermodynamics for the formation and cleavage of N-H bonds in aniline and ammonia. Complexes 1a, 2, 4a, and 4b were characterized by single-crystal X-ray diffraction methods.     

N-H and alpha(C-H) bond dissociation enthalpies of aliphatic amines

Bond dissociation enthalpies (BDEs) of a large series of aliphatic amines (21) were measured by means of photoacoustic calorimetry. Despite the different structures studied in the primary, secondary, and tertiary amine series, the alpha(C-H) BDEs were found to be very similar for unconstrained amines with values very close to 91 kcal/mol. alphaC- and N-alkylation or introduction of an hydroxy group only slightly affect the BDEs, a fact in perfect agreement with calculations performed at different CBS levels. This demonstrates the predominance of the two-orbital-three-electron interaction involving the N and alphaC(*) orbitals. On the other hand, the N-H BDE decreases when going from primary to secondary amines. This result is interpreted in term of a hyperconjugation in sigmaC-C bonds, which leads to a stabilization of the aminyl radical. For cyclized amines, the BDEs depend on the relative geometry of the singly occupied alphaC(*) orbital with respect to that of the N atom, disfavoring the two-orbital-three-electron interaction. However, such structures can exhibit through-bond interaction. For a crowded structure such as triisopropylamine, for which the alphaC(*) orbital is not coplanar with the nitrogen one, the relaxation of a strain energy allows the BDE to be comparable to flexible structures.     

Rhodium complexes of 1,3-diaryltriazenes: Usual coordination, N-H bond activation and, N-N and C-N bond cleavage

Reaction of 1,3-diaryltriazenes (R-C₆H₄-NN-(NH)-C₆H₄-R, R = OCH₃, CH₃, H, Cl, NO₂ at the para position) with [Rh(PPh₃)₃Cl] in ethanol in the presence of a base (NEt₃) affords a family of yellow complexes (1-R) containing a PPh₃, two de-protonated triazenes coordinated as bidentate N,N-donors, and an aryl (C₆H₄-R) fragment coordinated in the η¹-fashion. A similar reaction in toluene yields a group of reddish-orange complexes (2-R) containing a PPh₃, two N,N-coordinated triazenes, and a chloride. Structures of the 1-CH₃ and 2-CH₃ complexes have been determined by X-ray crystallography. All the 1-R and 2-R complexes are diamagnetic, and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. The 1-R and 2-R complexes also fluoresce in the visible region under ambient condition while excited at around 400 nm. Cyclic voltammetry on these complexes shows a Rh(III)-Rh(IV) oxidation (within 0.76-1.68 vs. SCE), followed by an oxidation of the coordinated triazene ligand (except the R = NO₂ complexes). An irreversible reduction of the coordinated triazene is also observed for all the complexes below −0.96 V vs. SCE. In the 1-R and 2-R complexes potential of the Rh(III)-Rh(IV) oxidation correlates linearly with the electron-withdrawing nature of the para-substituent (R).     

Mono(sulfido)-bridged mixed-valence nitrosyl complex: protonation and oxidative addition of iodine across the Ir(II)-Ir(0) bond

Treatment of [Cp*IrH(SH)(PMe3)] (Cp* = eta5-C5Me5) with [IrCl2(NO)(PPh3)2] in the presence of triethylamine yielded the sulfido-bridged Ir(II)Ir0 complex [Cp*Ir(PMe3)(mu-S)Ir(NO)(PPh3)], which further reacted with I2 and triflic acid to give the diiodo complex [Cp*Ir(PMe3)(mu-I)(mu-S)IrI(NO)(PPh3)] and the hydrido complex [Cp*Ir(PMe3)(mu-H)(mu-S)Ir(NO)(PPh3)][OSO2CF3], respectively.     

Phosphine-free palladium-catalyzed C-H bond arylation of free (N-H)-indoles and pyrroles

This paper describes a phosphine-free palladium-catalyzed method for direct C-arylation of free (N-H)-indoles and pyrroles with iodo- and bromoarene donors. Employing commercially available materials, this new and operationally simple procedure provides a rapid entry to a wide range of C-arylated (N-H)-indoles including derivatives of tryptamine. In the course of this study, a profound halide effect was uncovered, affecting both the efficiency and regioselectivity of indole arylation.     

N-H bond activation by palladium(ii) and copper(i) complexes featuring a reactive bidentate PN-ligand

The first examples of reactivity at the backbone of a bidentate PN-ligand L1H relevant to N-H activation are described, leading to novel Pd(II) and Cu(I) amido complexes. Activation of the PN-ligand backbone led to selective dearomatization of the pyridyl ring structure. In the case of Pd(II), the intermediate could be efficiently stabilized using PMe(3). Selective N-H bond cleavage of e.g. trifluorosulfonylamide resulted in facile formation of mononuclear metal-amido species 2 and 4, which have been crystallographically characterized. Hydrogen-bonding dimerization is observed in these solid state structures. The results obtained with these structurally versatile and reactive scaffolds likely open up new avenues in cooperative catalysis.     

Stoichiometric aerobic PtII-Me bond cleavage in aqueous solutions to produce methanol and a PtII(OH) complex

Di(2-pyridyl)methanesulfonate ligand allows for facile aerobic oxidation of a PtIIMe complex into PtIVMe(OH)2 species and clean C-O reductive elimination of methanol from the latter in either acidic or basic aqueous solutions.     

Isocyanate and carbodiimide synthesis by nitrene-group-transfer from a nickel(II) imido complex

The imido complex (dtbpe)Ni(N(2,6-(CHMe2)2C6H3)) reacts with CO and CNCH2Ph with addition at the Ni-N bond to give (dtbpe)Ni(C,N:eta 2-C(O)N(2,6-(CHMe2)2C6H3)) and (dtbpe)Ni(C,N:eta 2-C(NCH2Ph)N(2,6-(CHMe2)2C6H3)); both complexes react further with CO to liberate the isocyanate and carbodiimide ligands with formation of (dtbpe)Ni(CO)2.     

Activation of atmospheric nitrogen and azobenzene N=N bond cleavage by a transient Nb(III) complex

Atmospheric N2 is activated by two transient Nb(III) "(PNP)NbCl2" (PNP- = N[2-P(CHMe2)2-4-methylphenyl]2) fragments to form the bridging diimido [(PNP)NbCl2]2(mu-N2) (1). Complex 1 can also be independently synthesized from Nb(IV) and Nb(V) precursors via one-electron and transmetalation reactions, respectively. In the presence of azobenzene, the transient Nb(III) intermediate, prepared from Li(PNP) and NbCl3(DME) (DME = dimethoxyethane) under Ar, cleaves the N=N bond via a metal-ligand cooperative four-electron reduction to form niobium imide and phosphoranimine functionalities. Structural studies are presented and discussed for various Nb systems bearing the pincer-type framework PNP as well as the N2 and azobenzene activated products. Theoretical studies addressing the Nb-N2-Nb core in 1 are also presented.     

Synthesis and structure of amido- and imido(pentafluorophenyl)borane zirconocene and hafnocene complexes: N-H and B-H activation

Treatment of Me(2)S·B(C(6)F(5))(n) H(3-n) (n=1 or 2) with ammonia yields the corresponding adducts. H(3)N·B(C(6)F(5))H(2) dimerises in the solid state through N-H···H-B dihydrogen interactions. The adducts can be deprotonated to give lithium amidoboranes Li[NH(2)B(C(6)F(5))(n)H(3-n)]. Reaction of the n=2 reagent with [Cp(2)ZrCl(2)] leads to disubstitution, but [Cp(2)Zr{NH(2)B(C(6)F(5))(2)H}(2)] is in equilibrium with the product of β-hydride elimination [Cp(2)Zr(H){NH(2)B(C(6)F(5))(2)H}], which proves to be the major isolated solid. The analogous reaction with [Cp(2)HfCl(2)] gives a mixture of [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)] and the N-H activation product [Cp(2)Hf{NHB(C(6)F(5 )(2)H}]. [Cp(2)Zr{NH(2)B(C(6)F(5))(2)H}(2)]·PhMe and [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)]·4(thf) exhibit β-B-agostic chelate bonding of one of the two amidoborane ligands in the solid state. The agostic hydride is invariably coordinated to the outside of the metallocene wedge. Exceptionally, [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)]?PhMe has a structure in which the two amidoborane ligands adopt an intermediate coordination mode, in which neither is definitively agostic. [Cp(2)Hf{NHB(C(6)F(5))(2)H}] has a formally dianionic imidoborane ligand chelating through an agostic interaction, but the bond-length distribution suggests a contribution from a zwitterionic amidoborane resonance structure. Treatment of the zwitterions [Cp(2)MMe(μ-Me)B(C(6)F(5))(3)] (M=Zr, Hf) with Li[NH(2)B(C(6)F(5))(n)H(3-n)] (n=2) results in [Cp(2) MMe{NH(2)B(C(6)F(5))(2)H}] complexes, for which the spectroscopic data, particularly (1)J(B,H), again suggest β-B-agostic interactions. The reactions proceed similarly for the structurally encumbered [Cp'(2)ZrMe(μ-Me)B(C(6)F(5))(3)] precursor (Cp'=1,3-C(5)H(3)(SiMe(3))(2) , n=1 or 2) to give [Cp'(2)ZrMe{NH(2)B(C(6)F(5))(n)H(3-n)}], both of which have been structurally characterised and show chelating, agostic amidoborane coordination. In contrast, the analogous hafnium chemistry leads to the recovery of [Cp'(2)HfMe(2)] and the formation of Li[HB(C(6)F(5))(3)] through hydride abstraction.     

An intramolecular N-H...(mu-H)Re2 dihydrogen bond and a novel mu 3-eta 2 coordination mode of the pyrazolate anion on a triangular cluster face

The quantitative addition of pyrazole (Hpz) to the 44 valence-electron, triangular cluster anion [Re3(mu 3-H)-(mu-H)3(CO)9]- gives the novel unsaturated anion [Re3(mu-H)4(CO)9(Hpz)]- (1, 46 valence electrons), which contains a pyrazole molecule that is terminally coordinated on a cluster vertex. Solidstate X-ray and IR analyses reveal a rather weak hydrogen-bonding interaction between the NH proton and one of the hydrides bridging the opposite triangular cluster edge (delta H degree = -3.1 kcal mol-1 from the Iogansen equation). Both IR and NMR data indicate that such a proton-hydride interaction is maintained in the major conformer present in CD2Cl2, but also provide evidence of the presence of minor conformers of 1 in which the NH proton is involved in an intermolecular hydrogen bond with the solvent. The mu-H...HN bond length evaluated in solution through the T1 minimum value (2.07 A) and that determined in the solid state by X-ray diffraction (2.05 A) are in good agreement. NMR experiments show that, in acetone, intermolecular N-H...solvent interactions replace the intramolecular dihydrogen bond. At room temperature in CH2Cl2, the pyrazole ligand in 1 is labile and 1 slowly "disproportionates" to [Re3(mu 3-H)-(mu-H)3(CO)9]- and [Re3(mu-H)3(CO)9-(mu-eta 2-pz)(Hpz)]-, with H2 evolution. Slow H2 evolution also leads to the formation of the anion [Re3(mu-H)3-(CO)9(pz)]- (5), in which the pyrazolate anion adopts a novel mu 3-eta 2-coordination mode, as revealed by a single-crystal X-ray analysis. The analysis of the bond lengths indicates that the pyrazolate anion in 5 acts as a six-electron donor, with loss of the aromaticity. The formation of 5 from 1 is much faster in solvents with a high dielectric constant, such as acetone or DMF. Anion 5 was also obtained from the reaction of pyrazole with [Re3(mu-H)3(CO)9(mu 3-CH3)]- through the intermediate formation of two isomeric addition derivatives and following CH4 evolution.