The reactivity of bromoform with [Au(CH2)2PPh2]2. The completion of the halomethane series CHyX4−y (y=3,2,1,0; X=Cl,Br, I) and reactivity with [Au(CH2)2PPh2]2

The reaction of [Au(CH₂)₂PPh₂]₂ with excess CHBr₃ in benzene initially gives [Au(CH₂)₂PPh₂]₂₋ (CHBr₂)Br. This observation establishes that halomethanes, CH_yX_4−y (y=3,2,1,0; X=Cl, Br, I), react with [Au(CH₂)₂PPh₂]₂ to initially give Au(II) adducts of the general form [Au(CH₂)₂PPh₂]₂₋(CH_yX_3−y)X (y=3,2,1,0) via oxidative addition across the carbon-halogen bond. The order of reactivity inversely follows the order of carbon-halogen bond dissociation energies of haloalkanes. Methyl chloride is the only halomethane of the series that does not give a Au(II) adduct under similar reaction conditions.     

M?ssbauer, EPR, and magnetization studies of the Azotobacter vinelandii Fe protein. Evidence for a [4Fe-4S]1+ cluster with spin S = 3/2

We have studied the Fe protein (Av2) of the Azotobacter vinelandii nitrogenase system with M?ssbauer and EPR spectroscopies and magnetic susceptometry. In the oxidized state the protein exhibits M?ssbauer spectra typical of diamagnetic [4Fe-4S]2+ clusters. Addition of Mg.ATP or Mg.ADP causes a pronounced decline in the quadrupole splitting of the M?ssbauer spectra of the oxidized protein. Our studies show that reduced Av2 in the native state is heterogeneous. Approximately half of the molecules contain a [4Fe-4S]1+ cluster with electronic spin S = 1/2 and half contain a [4Fe-4S]1+ cluster with spin S = 3/2. The former yields the characteristic g = 1.94 EPR signal whereas the latter exhibits signals around g = 5. The magnetization of reduced Av2 is dominated by the spin S = 3/2 form of its [4Fe-4S]1+ clusters. These results explain a long standing puzzle, namely why the integrated spin intensity of the g = 1.94 EPR signal is substantially less than 1 spin/4 Fe atoms. In 50% ethylene glycol, 90% of the clusters are in the spin S = 1/2 form whereas, in 0.4 M urea, 85% are in the S = 3/2 form. In 0.4 M urea, the EPR spectrum of reduced Av2 exhibits well defined resonances at g = 5.8 and 5.15, which we assign to the S = 3/2 system. The EPR and M?ssbauer studies yield a zero-field splitting of 2D approximately equal to -5 cm-1 for this S = 3/2 state.     

Iridium(I) dimers with bridging N,N′-di-p-tolylformamidine. X-ray molecular structure of Ir2(μ-p-CH3C6H4NCHN-p-C6H4CH3)(μ-NH-p-C6H4CH3)(C8H14)2

The reaction of [IrCl(COD)]₂ with K[CH(N-p- C₆H₄CH₃)₂] (K⁺form⁻) has been carried out in both neat toluene and in the presence of Bu^tOH. In the first case [Ir(form)(COD)]₂ (1) was obtained in good yields. The other reaction follows a somewhat different course with partial alcoholysis of the formamidine ligand and formation of Ir₂(μ-form)(μ-NH-p-C₆H₄CH₃)(COD)₂ (2). Crystal data for compound 2: space group P2₁/c, a = 9.389(2), b = 21.083(4), c = 16.810(2) Å, β = 91.54(1)° V=3326(2) ų, Z = 4, R = 0.0343 for 3707 data with F_o² > 3σ(F_o²).     

Analysis of [2H7]methionine, [2H4]methionine,methionine, [2H4]homocysteine and homocysteine in plasma by gas chromatography–mass spectrometry to follow the fate of administered [2H7]methionine

Homocysteine plays a key role in several pathophysiological conditions. To assess the methionine–homocysteine kinetics by stable isotope methodology, we developed a simultaneous quantification method of [²H₇]methionine, [²H₄]methionine, methionine, [²H₄]homocysteine and homocysteine in rat plasma by gas chromatography–mass spectrometry (GC–MS). [¹³C]Methionine and [¹³C]homocysteine were used as analytical internal standards to account for losses associated with the extraction, derivatization and chromatography. For labeled and non-labeled homocysteine measurements, disulfide bonds between homocysteine and other thiols or proteins were reduced by dithiothreitol. The reduced homocysteine and methionine species were purified by cation-exchange chromatography and derivatized with isobutyl chlorocarbonate in water–ethanol–pyridine. Quantification was carried out by selected ion monitoring of the molecular-related ions of N(O,S)-isobutyloxycarbonyl ethyl ester derivatives on the chemical ionization mode. The intra- and inter-day precision of the assay was less than 6% for all labeled and non-labeled methionine and homocysteine species. The method is sensitive enough to determine pharmacokinetics of labeled methionine and homocysteine.     

DFT study on the reactions of ClO–/BrO– with RCl (R = CH3, C2H5, and C3H7) in gas phase

Gas-phase reactions of ClO^–/BrO^– with RCl (R = CH₃, C₂H₅, and C₃H₇) have been investigated in detail using the popular DFT functional BHandHLYP/aug-cc-pVDZ level of theory. As a result, our findings strongly suggest that the type of reaction is firstly initiated by a typical S_N2 fashion. Subsequently, two competitive substitution steps, named as S_N2-induced substitution and S_N2-induced elimination, respectively, would proceed before the initial S_N2 product ion-dipole complex separates, in which the former exhibits less reactivity than the latter. Those are consistent with relevant experimental results. Moreover, we have also explored reactivity difference for the title reactions in term of some factors derived from methyl group, p-π electronic conjugation, ionization energy (IE), as well as molecular orbital (MO) analysis.

Chiroptical properties of diastereomeric five-coordinate Pt(II)–olefin complexes. Molecular structure of [PtCl2{(S,S)-(E)-CNCHCHCN}(R,R)-{C6H5CH(CH3)N(CH3)CH2}2]·C6H6

The chiroptical properties of five-coordinate diastereomeric complexes of general formula [PtCl₂(R,R)-{C₆H₅CH(CH₃)N(CH₃)CH₂}₂{olefin}], with olefin ligands having electron-withdrawing substituents, have been investigated. The sign of CD bands in the 28 000–30 000 cm⁻¹ region appears to be correlated to the absolute configuration of the prochiral coordinated alkene. Single-crystal X-ray diffraction structure determination has been performed on the single diastereomer [PtCl₂(E-but-2-enedinitrile)(R,R)-{C₆H₅CH(CH₃)N(CH₃)CH₂}₂]· C₆H₆. The compound crystallizes in the monoclinic space group C2 with a = 17.842(2), b = 8.466(1), c = 10.464(1) Å, β = 109.34(1)°, Z = 2. The number of observed reflections was 1943 and the final R and R_w values were 0.020 and 0.028 respectively. Trigonal-bipyramidal geometry is observed around the Pt atom, with the two Cl atoms in axial positions. The unsaturated ligand lies in the equatorial plane disclosing S,S absolute configuration.     

Structures and aromaticity of X2Y 2 − (X = C, Si, Ge and Y = N, P, As) anions

The equilibrium geometries, total energies, and vibrational frequencies of anions X₂Y₂ ⁻ (X = C, Si, Ge and Y = N, P, As) are theoretically investigated with density functional theory (DFT) method. Our calculation shows that for C₂N₂ ⁻ species, the D _2h isomer is the most stable four-membered structure, and for other species the C _2v isomer in which two X atoms are contrapuntal is the most stable structure at the B3LYP/6-311 +G_* level. Wiberg bond index (WBI) and negative nucleus-independent chemical shift (NICS) value indicate the existence of delocalization in stable X₂Y₂ ⁻ structures. A detailed molecular orbital (MO) analysis further reveals that stable isomers of these species have strongly aromatic character, which strengthens the structural stability and makes them closely connected with the concept of aromaticity.     

Further studies on the copper(II) complexes of lysine: [Cu(II)(H3N·C5H10·CH·NH2·COO)2] [HgI3]2

Spontaneous resolution in the formation of the [HgI₃]⁻ salts of the copper complex of racemic lysine was previously reported. X-ray and IR studies were used to support this conclusion. Gas chromatographic studies using a chiral phase on the crystals originally studied, and on newly formed crystals using D,L-lysine, do not substantiate the suggestion that spontaneous resolution occurs.     

Ab initio study of mechanism of forming a spiro-heterocyclic ring compound with Si and Ge between dimethylsilylene germylidene (Me2Si?=?Ge:) and acetone

The mechanism of the cycloaddition reaction between singlet state dimethylsilylene germylidene (Me(2)Si?=?Ge:) and acetone has been investigated with CCSD(T)//B3LYP/6-31G* method. From the potential energy profile, it could be predicted that the reaction has one dominant reaction pathway. The reaction rules presented are that the two reactants first form a Si-heterocyclic four-membered ring germylene through the [2?+?2] cycloaddition reaction. Because of the 4p unoccupied orbital of Ge atom in the Si-heterocyclic four-membered ring germylene and the π orbital of acetone forming a π→p donor-acceptor bond, the Si-heterocyclic four-membered ring germylene further combines with acetone to form an intermediate. Because the Ge atom in the intermediate happens sp(3) hybridization after transition state, then, the intermediate isomerizes to a spiro-heterocyclic ring compound with Si and Ge via a transition state.     

Syntheses and michael additions to vinylidene diphosphine complexes of type [M(CO)4{(Ph2P)2CCH2}] (MCr,Mo or W)

Treatment of [M(CO)₄Ph₂PCHPPh₂]⁻ with CH₃- OCH₂Cl at 20 °C gave the methoxymethyl derivations [M(CO)₄{Ph₂PCH(CH₂OCH₃)PPh₂}] (MCr or W), but a similar treatment at 80 °C gave derivatives of a vinylidene diphosphine [M(CO)₄(Ph₂P)₂C CH₂]. Treatment of [M(CO)₄Ph₂PCHPPh₂]⁻with CH₃CHClOCH₃ at 20 or 80 °C gave only [M(CO)₄- (Ph₂P)₂CHCH(CH₃)OCH₃] (MCr or W). The vinylidene diphosphine complexes [M(CO)₄(Ph₂P)2- CCH₂] (MCr, Mo or W) were even more easily prepared by treating [M(CO)₆] with (Ph₂P)₂CCH₂ (vdpp) in hot solvents such as CH₃OCH₂CH₂OCH₂- CH₂OCH₃.Treatment of [W(CO)₄vdpp] with LiBuⁿ followed by methanol gave [W(CO)₄(Ph₂P)₂CHCH₂Buⁿ] (1c), i.e. conjugate addition to the CCH₂ occurs. 1c was also made by treating [W(CO)₄(Ph₂P)₂CH]⁻ with n-pentyl-iodide. Similarly LiMe was added to [W(CO)₄(Ph₂P)₂CCH₂]. Treatment of [M(CO)₄- vdpp] with NaCH(COOEt)₂ gave [M(CO)₄(Ph₂- P)₂CHCH₂CH(COOEt)₂] (MW or Mo). Pyrrolidine added to the CCH₂ bonds of [M(CO)₄vddp] to give [M(CO)₄(Ph₂P)₂CHCH₂NC₄H₈]. ³¹p and ¹H NMR and IR data are given.     

Structural chemistry of lanthanidedicyclopentadienidehalides. Part 1. Two modifications of gadoliniumdicyclopentadienidebromide, [Gd(C5H5)2Br]2 and 1∞[Gd(C5H5)2Br]

The crystal structures of two modifications of gadoliniumdicyclopentadienidebromide, [Gd(C₅H₅)₂Br]₂ (I) and ¹_∞[Gd(C₅H₅)₂Br] (II) have been determined from X-ray diffraction data. I crystallizes in the [Sc(C₅H₅)₂Cl]₂-type structure, space group P2₁/c, with a=14.110(3), b=16.488(3), c= 13.765(3) Å, β=93.25(2)°, V=3197(2) ų, and D_c= 2.289 g cm⁻³ for Z=6 molecules. II crystallizes in space group P2₁/c with a=5.946(7), b=8.447(5), c=20.239(9) Å, β=90.11(4)°, V=1020(2) ų, D_c=2.392 g cm⁻³ for Z=4 formula units. The structures have been refined by full matrix least-squares techniques to conventional R factors of 0.034 for 3014 (I) and 1964 (II) reflections (with I>2σ(I)). I consists of dimers with two bromine bridges (mean GdBr 2.872 Å). II has a double chain structure with alternating juxtaposition of gadolinium and bromine atoms (GdBr 2.912 Å (once) and 3.133 Å (twice)). The arrangement of the C₅H₅ groups with regard to the metal η⁵ fashion) is nearly identical in I and II (mean GdC 2.63(1) Å (I) and 2.62(1) Å (II)). Single crystals of I and II are obtained by sublimation at different temperatures. The formation of both modifications is discussed as to its dependence on the state of the gaseous phase equilibrium [Gd(C₅H₅)₂Br]₂ ⇄ 2Gd(C₅H₅)₂Br. Obviously, I crystallizes from gaseous phase dimers while II forms from the monomers.     

Solution behaviour and relative stability of the complexes [MCl2(RNCHCHNR)] and [MCl2(py-2-CHNR)] (M=Pd,Pt;R=C6H4OMe-p)

Even though the α-diimino complexes [MCl₂(RNCHCHNR)] and [MCl₂(py-2-CHNR)] (M=Pd, Pt;R=C₆H₄OMe-p) are poorly soluble in chlorinated solvents, such as chloroform and 1,2-dichloroethane, or in acetonitrile, the electronic and ¹H NMR spectra indicate that these compounds are generally present as undissociate monomers with σ, σ′-N,N′ chelate N-ligands in dilute solutions. Only for [PdCl₂(RNCHCHNR)], some dissociation of the α-diimine occurs in acetonitrile. In dimethylsulfoxide, where the solubility is much higher, no dissociation is observed for the pyridine-2-carbaldimine complexes [MCl₂(py-2-CHNR)], whereas the 1,2-bis(imino) ethane derivatives [MCl₂(RNCHCHNR)] are extensively dissociated through a step-wise process involving intermediates with a σ-N monodentate α-diimino group. As is shown by the course of substitution reactions with 2,2′-bipyridine, the higher stability of [MCl₂(py-2-CHNR)] in dimethylsulfoxide is mainly due to thermodynamic factors (ground state stabilization for the presence of stronger MN bonds) rather than by kinetic factors (higher activation energy for steric strain in the activation states or transients).