The preparation of 2H-1,4-benzoxazin-3-(4H)-ones via palladium-catalyzed intramolecular C-O bond formation

Pd/PtBu(3)-catalyzed intramolecular C-O bond formation has been used to access aryl- and alkyl-substituted benzoxazinones.     

Oxidative aromatic C-N bond formation: convenient synthesis of N-amino-3-nitrile-indoles via FeBr3-mediated intramolecular cyclization

A variety of functionalized N-amino-3-nitrile-indole derivatives are obtained via an intramolecular hetero-cyclization of 2-aryl-3-substituted hydrazono-alkylnitriles using FeBr(3) as a single electron oxidant. This approach allows the N-moiety on the side-chain to be annulated to the benzene ring during the final synthetic step via direct oxidative aromatic C-N bond formation.     

Iron(II)-catalyzed direct CH cyanoalkylation of 2H-indazoles and coumarins via radical CC bond cleavage

An iron-catalyzed C-3 cyanoalkylation of 2H-indazole and coumarin derivates with cyclobutanone oxime esters has been accomplished, which proceeds efficiently in a high regioselective manner to construct diverse alkylated 2H-indazole and coumarin derivates in moderate to good yields. Preliminary mechanistic studies reveal that a distal cyanosubstituted alkyl radicals intermediate would be formed through radical-involved CC bond cleavage of cyclobutanone oximes ester.     

DNA cleavage by the photolysis of cyclopentadienyl metal complexes: mechanistic studies and sequence selectivity of strand scission by CpW(CO)3CH3

[Reaction: see text]. The photolysis of CpW(CO)3Me has been shown to produce methyl radicals and to cleave DNA in a single-stranded manner, and preliminary evidence implicated a carbon-centered radical in this process. In this work, the mechanism of strand scission in this reaction was determined to occur by hydrogen atom abstraction from the 4'- and 5'-positions of the deoxyribose moiety of the backbone of DNA. Additionally, in a side reaction that does not lead to frank strand scission, all four bases of DNA are methylated under these conditions; however, none of these base or backbone modifications lead to the formation of abasic sites.     

Nickel(0)-catalyzed isomerization of an aryne complex: formation of a dinuclear Ni(I) complex via C-H rather than C-F bond activation

The reaction of the aryne complex (PEt3)2Ni(eta2-C6H2-4,5-F2) with a catalytic amount of Ni(PEt3)2 results in a dinuclear Ni(I) complex from the coupling of the isomer (PEt3)2Ni(eta2-C6H2-3,4-F2), obtained via rearrangement of the aromatic C-H bonds, which demonstrates that Ni(PEt3)2 is kinetically capable of C-H bond activation, even in the presence of C-F bonds. The intermediate [(PEt3)2Ni]2(mu-eta2:eta2-C6H2-4,5-F2) was isolated and crystallographically characterized; the mu-eta2:eta2-bonding mode observed is unprecedented in aryne chemistry.     

P-C versus C-H bond cleavage in coordinated bis(dimethylphosphino)methane: controlled access to either phosphinite or functionalized diphosphine complexes

Treatment of fac-[Mn(CNPh)(CO)3(dmpm)]ClO4 (1) with KOH affords neutral phosphinite complex fac-[Mn(PMe2O)(CNPh)(CO)3(PMe3)] (2) as a result of P-C bond cleavage on the dmpm ligand, whereas when carrying out the reaction in the presence of iodine the diphosphinoketenimine derivative fac-[MnI(CO)3[(PMe2)2C=C=NPh]] (4) is obtained after deprotonation and further functionalization of the central carbon atom of the diphosphine.     

一氯甲烷同步辐射光电离研究: 离子生成焓与键能的测定

本文报道超音速射流冷却条件下, 用同步辐射光研究CH3Cl光电离及其解离电离的动力学, 测得CH3Cl的电离能(IP)为11.28±0.01eV。通过测定CH3Cl光解离电离碎片的出现势(AP), 并结合有关已确认的热力学数据, 获得了它们的标准生成焓、离子型分子中的键能、中性分子或自由基中的键能及母体离子的解离能等热力学数据。对CH3Cl分子VUV光解离电离通道进行了分析。     

Crossed-beam dynamics studies of the radical-radical combustion reaction O((3)P) + CH3 (methyl)

The dynamics of the radical-radical reaction O((3)P) + CH(3), a prototypical case for the reactions of atomic oxygen with alkyl radicals of great relevance in combustion chemistry, has been investigated by means of the crossed molecular beam technique with mass spectrometric detection at a collision energy of 55.9 kJ mol(-1). The results have been examined in the light of previous kinetic and theoretical work. From product angular and velocity distribution measurements, the dynamics of the predominant H-displacement channel leading to formaldehyde formation has been characterized. This channel has been found to proceed via the formation of an osculating complex; a significant coupling between the product centre-of-mass angular and translational energy distributions has been noted. Experimental attempts to characterize the dynamics of the channel leading to HCO + H(2) have failed and it remains unclear whether HCO is formed by the reaction and/or, if formed, a part of HCO does not dissociate quickly into CO + H.     

Palladium-catalyzed synthesis of benzosilolo[2,3-b]indoles via cleavage of a C(sp3)-Si bond and consequent intramolecular C(sp2)-Si coupling

An efficient process involving Pd-catalyzed selective cleavage of a C(sp(3))-Si bond and consequent intramolecular C(sp(2))-Si coupling has been developed, affording benzosilolo[2,3-b]indoles as a new type of silicon-bridged polyheteroarene in excellent yields. Aldehyde was found for the first time to be able to promote the efficiency of the catalytic process remarkably.     

Cu(I)/Fe(III) promoted dicarbonylation of aminopyrazole via oxidative CH coupling with methyl ketones

Cu(I)/Fe(III) promoted C4-dicarbonylation of 5-aminopyrazole is developed. The strategy involved radical triggered direct oxidative coupling of 5-aminopyrazoles with methyl ketones using aerial oxygen as a source of oxygen in newly generated carbonyl group. CuI is used as catalyst and FeCl₃·6H₂O is used as additive and the reaction proceeded at 120?°C in DMSO for 9–12?h. It is found that use of Cu(II) catalyst gives the thiomethylated product by reacting with DMSO instead of oxidative coupling. A plausible mechanism is also given.     

A reaction for sp(3)-sp(3) C-C bond formation via cooperation of Lewis acid-promoted/Rh-catalyzed C-H bond activation

A new method for intermolecular sp3-sp3 C-C bond formation between primary aliphatic alcohol and olefin by use of a RhCl(PPh3)3 (cat.)/BF3.OEt2 (2.5 equiv)/BuBr (0.5 equiv)/toluene system was first disclosed, which possessed quite significant utilities for organic synthesis, especially for that of secondary alcohols. The most significant aspect is the discovery that rhodium-catalyzed C-H bond activation of alcohols is feasible under Lewis acid-promoted conditions.     

Ni(0)/ZnCl(2)-promoted coupling of enones and enynes. Domino process via formation of three C-C bonds and cleavage of one C-C bond

Domino coupling of enones and enynes, which proceeds via the formation of three carbon-carbon bonds and the cleavage of one carbon-carbon bond, was developed using a Ni(0) and ZnCl2 system.     

Synthesis, photophysics, electrochemistry, theoretical, and transient absorption studies of luminescent copper(I) and silver(I) diynyl complexes. X-ray crystal structures of [Cu3(micro-dppm)3(micro3-eta1-C triple bond CC triple bond CPh)2]PF6 and [Cu3(micro-dppm)3(micro3-eta1-C triple bond CC triple bond CH)2]PF6

A series of soluble trinuclear copper(I) and silver(I) complexes containing bicapped diynyl ligands, [M(3)(micro-dppm)(3)(micro(3)-eta(1)-C triple bond CC triple bond CR)(2)]PF(6) (M = Cu, R = Ph, C(6)H(4)-CH(3)-p, C(6)H(4)-OCH(3)-p, (n)C(6)H(13), H; M = Ag, R = Ph, C(6)H(4)-OCH(3)-p), has been synthesized and their electronic, photophysical, and electrochemical properties studied. The X-ray crystal structures of [Cu(3)(micro-dppm)(3)(micro(3)-eta(1)-C triple bond CC triple bond CPh)(2)]PF(6) and [Cu(3)(micro-dppm)(3)(micro(3)-eta(1)-C triple bond CC triple bond CH)(2)]PF(6) have been determined.     

Reactions of alkali metal and yttrium alkyls with a sterically demanding bis(aryloxysilyl)methane: Formation of aryloxide complexes by Si-O bond cleavage

Reaction of bis(bromodimethylsilyl)methane (BrSiMe₂)₂CH₂ (1) with two equivalents of 2,6-diisopropylphenol (Ar′OH) in the presence of the auxiliary base NEt₃ affords the bis(aryloxysilyl)methane (Ar′OSiMe₂)₂CH₂ (2) as a colourless oil following work-up. The reaction of 2 with [Li(Buⁿ)] in the presence of [K(OBu^t)] promoted Si-O bond cleavage and the sole isolable product from this reaction was found to be the colourless, crystalline heterobimetallic complex [{Li(OAr′)}₂{K(OAr′)}₂(THF)₄] (3). The in situ reaction of 2 with one equivalent of [Li(Buⁿ)] in the presence of one equivalent of [K(OBu^t)] and subsequent addition to one equivalent of [Y(I)₃(THF)_3.5] afforded colourless, crystalline [Y(OAr′)(I)₂(THF)₃] (4) as the only isolable product. No reaction was observed between [Y(Bn)₃(THF)₃] (Bn = CH₂C₆H₅) and one equivalent of 2 in toluene at room temperature; heating solutions led to decomposition and recovery of 2. In THF, the reaction between 2 and one equivalent of [Y(Bn)₃(THF)₃] resulted in Si-O bond cleavage with concomitant Si-C bond formation to give (BnSiMe₂)₂CH₂ (5) as a colourless oil and the colourless, crystalline compounds [Y(OAr′)₂(Bn)(THF)] (7), and [Y(OAr′)₃(THF)₂] (8) which were separated by fractional crystallisation. In an attempt to prepare 7 by a rational route, [Y(OAr′)₂(I)(THF)₂] (6) was prepared from the reaction of [Y(I)₃(THF)_3.5] with two equivalents of [K(OAr′)]. However, although 6 could be prepared by a rational salt elimination route, attempts to convert it to 7 resulted instead in 8 being recovered as the only isolable product. This is proposed to be the result of Schlenk-type equilibria, which is supported by the observation that dissolution of pure 6 in benzene results in the additional presence of 8 in the ¹H NMR spectrum over 12 h. Compound 7 was prepared rationally from the reaction between [Y(Bn)₃(THF)₃] and two equivalents of HOAr′. However, although crystalline 7 could be isolated in sufficient quantities for analysis, NMR spectra were consistent with the formation of 8 in solution from Schlenk-type equilibria. Compounds 2–8 have been variously characterised by X-ray diffraction, NMR and FTIR spectroscopy, and CHN microanalyses.     

Theoretical study of the strong intramolecular hydrogen bond and metal-ligand interactions in group 10 (Ni, Pd, Pt) bis(dimethylglyoximato) complexes

The structural and bonding characteristics of the bis(dimethylglyoximato) complexes of group 10 transition metals ([M(dmg)₂], where M = Ni, Pd and Pt) were investigated by means of quantum chemical computations. The equilibrium geometries, energetic and bonding properties were computed using the B3P86 exchange-correlation density functional in conjunction with a 6-311+(+)G^∗∗ basis set. The computations revealed that the strong O⁻?H-O hydrogen bond exists only in the presence of the metal cations. The free (dmg)₂²⁻ ligand has significantly different geometry in which the O⁻?H-O interaction is replaced by N?O-H bonds. The characteristics of the metal-ligand interactions were determined by natural bond orbital analysis.     

NMR studies of mononuclear octahedral Ni(II) complexes supported by tris((2-pyridyl)methyl)amine-type ligands

The recent discovery of acireductone dioxygenase (ARD), a metalloenzyme containing a mononuclear octahedral Ni(II) center, necessitates the development of model systems for evaluating the role of the metal center in substrate oxidation chemistry. In this work, three Ni(II) complexes of an aryl-appended tris((2-pyridyl)methyl)amine ligand (6-Ph(2)TPA, N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine), [(6-Ph(2)TPA)Ni(CH(3)CN)(CH(3)OH)](ClO(4))(2) (1), [(6-Ph(2)TPA)Ni(ONHC(O)CH(3))]ClO(4) (3), and [(6-Ph(2)TPA)Ni-Cl(CH(3)CN)]ClO(4) (4), and one Ni(II) complex of tris((2-pyridyl)methyl)amine, [(TPA)Ni(CH(3)CN)(H(2)O)](ClO(4))(2) (2), have been characterized in acetonitrile solution using conductance methods and NMR spectroscopy. In acetonitrile solution, 1-4 have monomeric cations that exhibit isotropically shifted (1)H NMR resonances. Full assignment of these resonances was achieved using one- and two-dimensional (1)H NMR techniques and (2)H NMR of analogues having deuteration of the supporting chelate ligand. COSY cross peaks were observed for pyridyl protons of the 6-Ph(2)TPA ligand in 1 and 3. This study lays the groundwork for using NMR methods to examine chemical reactions of 1 and 2 with model substrates of relevance to ARD.     

Theoretical studies on the molecular dependence of bond dissociation after core excitations II: CH(3)CO(CH(20)(n)CN,n = 0-3

Approximate theoretical normal and resonant Auger spectra for a series of methylcyano ketones were calculated. Compared with our previous procedure, a set of initial molecular orbitals (MOs) for Auger decay probability calculations of the normal Auger process was modified by changing from a set of ground state MOs to a set of core-holed MOs. For the resonant Auger process, a set of MOs was also modified in the same manner. Furthermore, the bond dissociation factor, which we introduced in the previous article, was also calculated to estimate the bond strength after Auger decay. The site-selectivity for a series of methylcyano ketones was qualitatively explained, but a significant state-specificity was not observed. Molecular size dependence after Auger decay was also discussed.