Why are SiX5(-) and GeX5(-) (X = F, Cl) stable but not CF5(-) and CCl5(-)?

The possible existence of the CF(5)(-), CCl(5)(-), SiF(5)(-), SiCl(5)(-), GeF(5)(-), and GeCl(5)(-) anions has been investigated using ab initio methods. The species containing Si and Ge as central atoms were found to adopt the D(3h)-symmetry trigonal bipyramidal equilibrium structures whose thermodynamic stabilities were confirmed by examining the most probable fragmentation channels. The ab initio re-examination of the electronic stabilities of the SiF(5)(-), SiCl(5)(-), GeF(5)(-), and GeCl(5)(-) anions [using the OVGF(full) method with the 6-311+G(3df) basis set] led to the very large vertical electron detachment (VDE) energies of 9.316 eV (SiF(5)(-)) and 9.742 eV (GeF(5)(-)), whereas smaller VDEs of 6.196 and 6.452 eV were predicted for the SiCl(5)(-) and GeCl(5)(-) species, respectively. By contrast, the high-symmetry and structurally compact anionic CF(5)(-) and CCl(5)(-) systems cannot exist due to the strongly repulsive potential predicted for the X(-) (F(-) or Cl(-)) approaching the CX(4) (CF(4) or CCl(4)). The formation of weakly bound CX(4)···X(-) (CF(4)···F(-) and CCl(4)···Cl(-)) anionic complexes (consisting of pseudotetrahedral neutral CX(4) with the weakly tethered X(-)) might be expected at low temperatures (approaching 0 K), whereas neither CX(5)(-) (CF(5)(-), CCl(5)(-)) systems nor CX(4)···X(-) (CF(4)···F(-) and CCl(4)···Cl(-)) complexes can exist in the elevated temperatures (above 0K) due to their susceptibility to the fragmentation (leading to the X(-) loss).     

Nature of M-Ga bonds in dihalogallyl complexes (η5-C5H5)(Me3P)2M(GaX2) (M = Fe, Ru, Os) and (η5-C5H5)(OC)2Fe(GaX2) (X = Cl, Br, I): a DFT study

Density functional theory (DFT) calculations have been performed on the terminal dihalogallyl complexes of iron, ruthenium, and osmium (η(5)-C(5)H(5))(Me(3)P)(2)M(GaX(2)) (M = Fe, Ru, Os; X = Cl, Br, I) and (η(5)-C(5)H(5))(OC)(2)Fe(GaX(2)) (X = Cl, Br, I) at the BP86/TZ2P/ZORA level of theory. On the basis of analyses suggested by Pauling, the M-Ga bonds in all of the dihalogallyl complexes are shorter than M-Ga single bonds; moreover, on going from X = Cl to X = I, the optimized M-Ga bond distances are found to increase. From the perspective of covalent bonding, however, π-symmetry contributions are, in all complexes, significantly smaller than the corresponding σ-bonding contribution, representing only 4-10% of the total orbital interaction. Thus, in these GaX(2) complexes, the gallyl ligand behaves predominantly as a σ donor, and the short M-Ga bond lengths can be attributed to high gallium s-orbital character in the M-Ga σ-bonding orbitals. The natural population analysis (NPA) charge distributions indicate that the group 8 metal atom carries a negative charge (from -1.38 to -1.62) and the gallium atom carries a significant positive charge in all cases (from +0.76 to +1.18). Moreover, the contributions of the electrostatic interaction terms (ΔE(elstat)) are significantly larger in all gallyl complexes than the covalent bonding term (ΔE(orb)); thus, the M-Ga bonds have predominantly ionic character (60-72%). The magnitude of the charge separation is greatest for dichlorogallyl complexes (compared to the corresponding GaBr(2) and GaI(2) systems), leading to a larger attractive ΔE(elstat) term and to M-Ga bonds that are stronger and marginally shorter than in the dibromo and diiodo analogues.     

Crystal structure of twinned (η5-C5(CH3)4CF3) (η5-C5(CH3)5)Ru

The substituted sandwich complex crystallizes in monoclinic space groupP2₁/m withZ=2. Twinning to the (001) direction with the special conditionc ^*/4a ^* = cos ^* causes systematic superposition of the reciprocal lattices of both domains and results in an apparent unit cell with double volume and the reflection condition (2h)kl, l=2n. The structure solution was obtained with the subset of intensity data for the predominant individuum and converged atR = 0.040,R _w =0.046 for 832 independent observations and 122 variables. The molecules show disorder with respect to the crystallographic mirror plane. The structure is closely related to that of decamethylruthenocene.     

Synthesis of (3S,5R)-cis- and (3S,5S)-trans-3,5-Dimethylvalerolactones and Their Conversion to Biotransformation Products of (S)-5-Ethyl-5-(2′-pentyl)barbituric Acid

(R,S)-5-Ethyl-5-(2′-pentyl)barbituric acid (I)^1,2 is metabolized in vivo to give all four possible optical isomers of 5-ethyl-5-(3′-hydroxy-1′-methylbutyl)barbituric acid (II). ^3,4 From metabolism studies of pure (1′S)- I and (1′3)-I, Palmer and co-workers^4,5 were able to determine the relative amounts of each of the four isomers formed. These studies showed that (1′S)-I gave mainly one enantiomer of (1′S)-II, whereas (1′R)-I gave approximately equal amounts of both (1′R)-II enantiomers.     

Asymmetric Conjugate Addition of Alcohols to (R)-(-)-5-[(1R,2S,5R)-Menthyloxy]-2-(5H)-Furanone

(R)-(-y5-[(IR,2S,5R)-menthyloxy](1)isausefulchiralsynthonreadilypreparedonatWo-stepprocedure-l']FindingsoffuranoneringsexistingascomponentSofsomenaturalproductSI'laswellastheiractivereactivityl']havestimu1atedeXtensiveresearchofitSasymmetricreactionswhichincludeDiels-Alderreactions,l']l,3-dipo1arcycloadditions,['1Michaelauditionsl5]andconjugateedditionsofaminesl']andmercaPtans.g4:,::7f:7':theseadductsledtovariousmultifunctionalhomochiralbuildingblockssuchas2-alkyl-l,4-butanediols,I'l2-aI…     

(η~5-C_5H_5)Ln(η~8-C_8H_8)(THF)_n(Ln=Pr,Nd,Gd)的合成及(η~5-C_5H_5)Pr(η~8-C_8H_8)(THF)_2的晶体结构

自1969年首次报道稀土环辛四烯基化合物Eu(C_8H_8)和Yb(C_8H_8)的合成以来,相继合成K[Ln(C_8H_8)_2],[Ln(C_8H_8)Cl·2THF]_2和[Ln(C_8H_8)·2THF]等,还报     

A mild,phosphine-assisted synthesis of (η-C5Me5)Ta(CO)4. Isolation and crystal structure of intermediate (η-C5Me5)TaCl2(CO)2(PMe3)

Mild, reductive carbonylation of (C₅Me₅)TaCl₄ in the presence of trimethylphosphine gives (C₅Me₅)Ta(CO)₄ in 47% yield. The intermediate (C₅Me₅)TaCl₂- (CO)₂(PMe₃) has been isolated from the reaction of (C₅Me₅)TaCl₂(PMe₃)₂ with carbon monoxide and its crystal structure determined (space group P2₁2₁2₁).     

Synthesis and structures of the η5-C5H5Cl(CO)2W-η1,η5-(PPh2)C5H4(CO)2Fe-η1,η5-C5H4Mn(CO)3 and MeSi[C5H4(CO)2Fe-η1,η5-C5H4Mn(CO)2PPh3]3 complexes

The metallation of the η⁵-C₅H₅(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₃ complex with BuⁿLi (THF, ?78 °C) followed by the treatment of the lithium derivative with Ph₂PCl afforded the η⁵-Ph₂PC₅H₄(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₃ complex. The reaction of the latter with η⁵-C₅H₅(CO)₃WCl in the presence of Me₃NO produced the trinuclear complex η⁵-C₅H₅Cl(CO)₂W-η¹,η⁵-(Ph₂P)C₅H₄(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₃. The structure of the latter complex was established by IR, UV, and 1H and ³¹P NMR spectroscopy and X-ray diffraction. The reaction of MeSiCl₃ with three equivalents of LiC₅H₄(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₂PPh₃ gave the hexanuclear complex MeSi[C₅H₄(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₂PPh₃]₃.     

ELECTRONIC STRUCTURE OF(C_5H_5)_aCe(OCMe_a)

The electronic structure of(C_σH_σ)_σCe(OCMe_a)have beenstudied by INDO method.Some interesting results hays been obtained.     

The reactions of (η5-C5H5)NiO(s)3(μ-H)3(CO)9 with group V donor ligands. Spectroscopic characterization of the disubstituted derivatives,and crystal structure of (η5-C5H5)NiO(s)3(μ-H)3(CO)7(PMe2Ph)2

The complex (η⁵-C₅H₅NiO(s)₃(μ-H)₃(CO)₉ (1 reacts with phosphines in the presence of Me₃NO to give monosubsituted derivatives, the main products, along with smaller amounts of disubstituted derivatives. The IR and NMR spectroscopic characterizations of two representative disubstituted derivatives are described.The crystal structure of (η⁵-C₅H₅)NiO(s)(μ-H)₃(CO)₇(PMe₂Ph)₂ has been determined by X-ray diffraction. The crystals are monoclinic, space group P2₁/a with Z = 4 in a unit cell of dimensions a 18.198(8), b 20.865(8), c 8.656(5) Å, β 99.67(2)°. The structure was solved by direct and Fourier methods and refined by full-matrix least-squares to R = 0.061 for 3139 observed reflections. The structure can be regarded as derived from that of 1 (which has a tetrahedral NiO(s) core with three hydride hydrogen atoms bridging the OsOs edges, a cyclopentadienyl group coordinated to the Ni atom,and nine terminal carbonyls bound to the Os atoms, three for each Os atom) by replacing two axial carbonyls by two PMe₂Ph ligands.     

Tantalocene complexes as bidentate métalloligands: (C5Me5)(C5H4X)Ta(H2)(PPh2) (C5Me5) (C5H4X)Ta(CO) (PPh2) (X = PPh2, CH2CH2NMe2)

The synthesis of new bidentate métalloligands derived from tantalocene(C₅Me₅)(C₅H₄X)Ta(H₂)(PPh₂) (X = PPh₂, 2P; X = CH₂CH₂NMe₂2N) and (C₅Me₅)(C₅H₄X)Ta(CO)(PPh₂) 4(P,N) is described. When opposed to chromium unsaturated fragments the phosphino functionalised complexes 2P and 4P act as chelating bidentate ligands affording Ta(V) (C₅Me₅)(C₅H₄PPh₂)Ta(CH₂) (μ-PPh₂)Cr(CO)₄ or Ta(III) (C₅Me₅)(C₅H₄PPh₂)Ta(CO)(μ-PPh₂)Cr(CO)₄ bimetallic complexes. The same reaction carried out starting from 2N gives rise to a μ-phosphido, μ-hydrido dibridged complex Cp*(C₅H₄CH₂CH₂NMe₂)TaH(μ-H)(μ-PPh₂)Cr(CO)₄.     

Triphospha-Ferrocenes as Ligands. Crystal Structures of [Fe(η5-C5Me5)(η5-C2 TBu2P3)M(CO)5)], (M= Cr,MO, W) and the Novel ruthenium and Nickel Complexes [Fe(η5-C5Me5) (η5-C2 TBu2P3)Ru3(CO)9] and [Fe(η5-C5Me5)(η5-C2 tBu2P3)Ni(Co)2]2

Abstract

Syntheses and structures of penta- and hexaphosphorus analogues of ferrocene have been described recently¹. Unlike their simple ferrocene analogues, these complexes have further ligating potential towards other transition metal centres by virtue of the availability of the ring phosphorus lone-pair electrons that are not involved in the η⁵-coordination. We now describe the first examples of coordination compounds of the triphospha-ferrocene [Fe(η⁵-C₅Me₅) (η⁵-C₂ ^tBu₂P₃]. In the ruthenium complex [Fe(η⁵-C₅Me₅)(η⁵-C₂ ^tBu₂P₃) Ru₃(CO)₉] ² two adjacent phosphorus atoms of the η⁵-C₂ ^tBu₂P₃ ring are interlinked by a ruthenium carbonyl cluster in which all three ruthenium atoms interact with the phosphorus atoms. The tetrametallic nickel complex [Fe(η⁵-C₅Me₅)(η⁵-C₂ ^tBu₂P₃)Ni(CO)₂]₂ ³ represents the first example of intermolecular interlinkage of two phospha-ferrocene systems by two metal centres.     

Die indikatoreigenschaften des vicinalen m-Xylenolphthaleins (3′ ,5′ ,3′' ,5′'-Tetramethylphenolphthalein)

Ohne ZusammenfassungMit 1 Abbildung     

Concerning the silicon-germanium bond: mass spectral fragmentations of isomeric SiGe compounds R3EE′R3 (E  Si,E′  Ge,R  Ph,Me,(η5-C5H4)Fe (C5H5), (η5-C5H5)Fe(CO)2 and (η5-C9H7) Fe(CO)2)

Isomeric pairs of silicon-germanium compounds containing a SiGe bond (Me₃SiGePh₃ (I) and Ph₃SiGeMe₃ (II); FpSiMe₂GeMe₃ (III) and FpGeMe₂SiMe₃ (IV) (Fp = (η⁵-C₅H₅)Fe(CO)₂); IFpSiMe₂GeMe₃ (V) and IFpGeMe₂SiMe₃ (VI) (IFp = (η⁵-C₉H₇)Fe(CO)₂); IFpSiMe₂GePh₃ (VII) and IFpGeMe₂SiPh₃ (VIII) and the complex FcSiMe₂GeMe₂Fc (IX) (Fc = ferrocenyl) have been synthesized and examined by mass spectrometry.The R₃SiGeR′₃ compounds I and II exhibit considerable exchange of R groups to produce [R_3-nR′_nSi]⁺ and [R′_3-nR_nGe]⁺ ion in progressively lesser amounts as n = 1 → 2 → 3. For the metal-substituted complexes containing the grouping FeSiGe fragmentation occurs predominantly via SiGe bond cleavage with formation of ions containing the silylene ligand [FeSiR₂]⁺. Complexes with the FeGeSi backbone undergo preferential scission of the FeGe bond, illustrating the general bond strength trend FeSi > SiGe. Upon direct cleavage of the SiGe bond in R₃SiGeR₃ compounds, the percentage of the charge carried by [R₃Si]⁺ ions significantly exceeds that carried by [R₃Ge]⁺ ions, reflecting the greater electronegativity of Ge polarizing the SiGe bond.