Highly stereoselective reduction of methyl ketone complexes of the chiral Lewis acid [(η-C5H5)Re(NO)(PPh3)] by K(s-C4H9)3BH; synthesis of optically active secondary alcohols and derivatives

Reaction of optically active ketone complexes (+)-(R)-[(η⁵-C₅H₅)Re(NO)-(PPh₃)(η¹-O=C(R)(CH₃)]⁺ BF₄⁻ (R = CH₂CH₃, CH(CH₃)₂m C(CH₃)₃, C₆H₅) with K(s-C₄H₉)₃BH gives alkoxide complexes (+)-(RS)-(η⁵-C₅H₅)Re(NO)(PPh₃)-(OCH(R)CH₃) (73–90%) in 80–98% de. The alkoxide ligand is then converted to Mosher esters (93–99%) of 79–98% de.     

Structures of propionaldehyde, butyraldehyde, and pivalaldehyde complexes of the chiral rhenium fragment [(η-C5H5)Re(NO)(PPh3)]

The crystal structures of propionaldehyde complex (RS,SR)-(η⁵-C₅H₅)Re(NO)(PPh₃)(η²-O=CHCH₂CH₃)]⁺ PF₆⁻ (1b⁺ PF₆^s−; monoclinic, P2₁/c (No. 14), a = 10.166 (1) Å, b = 18.316(1) Å, c = 14.872(2) Å, β = 100.51(1)°, Z = 4) and butyraldehyde complex (RS,SR)-[(η⁵-C₅H₅)Re(NO)(PPh₃)(η²-O=CHCH₂CH₂CH₃)]⁺ PF₆⁻ (1c⁺PF₆⁻; monoclinic, P2₁/a (No. 14), a = 14.851(1) Å, b = 18.623(3) Å, c = 10.026(2) Å, β = 102.95(1)°, Z = 4) have been determined at 22°C and −125°C, respectively. These exhibit C O bond lengths (1.35(1), 1.338(5) Å) that are intermediate between those of propionaldehyde (1.209(4) Å) and 1-propanol (1.41 Å). Other geometric features are analyzed. Reaction of [(η⁵-C₅H₅)Re(NO)(PPh₃)(ClCH₂Cl)]⁺ BF₄⁻ and pivalaldehyde gives [(η⁵-C₅H₅)Re(NO)(PPh₃)(η²-O=CHC(CH₃)₃)]⁺BF₄⁻ (81%), the spectroscopic properties of which establish a π C O binding mode.     

Microwave spectrum and rotational isomers of ethyl fluoroformate

The microwave spectrum of ethyl fluoroformate displays strong a-type R branch transitions from two rotameric forms. One species (extended form) has rotational constants A₀ = 9191.3(9) MHz, B₀ = 2112.61(1) MHz, C₀ = 1756.73(1) MHz which are consistent with a syn-anti (τ₁(OCOC) = 0°, r₂(cocc) = 180°) planar heavy atom structure. The second species (compact form) has rotational constants A₀ = 7760(3) MHz, B₀ = 2388.38(4) MHz, C₀ = 2102.47(3) MHz which are consistent with a syn-gauche (τ₁(ococ) = 0°, τ₂(cocc) ˜ 90°) structure. The two conformational forms have approximately equal energy (0 ± 40 cm⁻¹). Four vibrational satellites of the extended species have been analyzed yielding a torsional frequency around the O-ethyl bond of 70(10) cm⁻¹. Three vibrational satellites attributed to the O-ethyl torsion of the compact species have been analyzed yielding a vibrational frequency of 90(10) cm⁻¹. Approximate Fourier coefficients of a three term potential function for internal rotation about the O-ethyl bond have been determined. Vibrational satellites attributed to the first excited states of the O-ester torsion have been analyzed for both conformers. The torsional vibrational frequency around the O-ester bond is 110(15) cm⁻¹ for the extended conformers and 120(20) cm⁻¹ for the compact.     

Homo- and hetero-bridged mixed-valence dinuclear complexes which contain the fragment ‘Rh(C6F5)3’

The reaction of the anionic mononuclear rhodium complex [Rh(C₆F₅)₃Cl(Hpz)]^t- (Hpz = pyrazole, C₃H₄N₂) with methoxo or acetylacetonate complexes of Rh or Ir led to the heterodinuclear anionic compounds [(C₆F₅)₃Rh(μ-Cl)(μ-pz)M(L₂)] [M = Rh, L₂ = cyclo-octa-1,5-diene, COD (1), tetrafluorobenzobarrelene, TFB (2) or (CO)₂ (4); M = Ir, L₂ = COD (3)]. The complex [Rh(C₆F₅)₃(Hbim)]⁻ (5) has been prepared by treating [Rh(C₆F₅)₃(acac)]⁻ with H₂bim (acac = acetylacetonate; H₂bim = 2,2′-biimidazole). Complex 5 also reacts with Rh or Ir methoxo, or with Pd acetylacetonate, complexes affording the heterodinuclear complexes [(C₆F₅)₃Rh(μ-bim)M(L₂)]⁻ [M = Rh, L₂ = COD (6) or TFB (7); M = Ir, L₂ = COD (8); M = Pd, L₂ = η³-C₃H₅ (9)]. With [Rh(acac)(CO)₂], complex 5 yields the tetranuclear complex [{(C₆F₅)₃Rh(μ-bim)Rh(CO)₂}₂]₂₋. Homodinuclear Rh^III derivatives [{Rh(C₆F₅)₃}₂(μ-L)₂]^·- [L₂ = OH, pz (11); OH, S^tBu (12); OH, SPh (13); bim (14)] have been obtained by substitution of one or both hydroxo groups of the dianion [{Rh(C₆F₅)₃(μ-OH)}₂]²⁻ by the corresponding ligands. The reaction of [Rh(C₆F₅)₃(Et₂O)_x] with [PdX₂(COD)] produces neutral heterodinuclear compounds [(C₆F₅)₃Rh(μ-X)₂Pd(COD)] [X = Cl (15); Br (16)]. The anionic complexes 1–14 have been isolated as the benzyltriphenylphosphonium (PBzPh₃⁺) salts.     

Relative thermodynamic stabilities of isomeric alkyl allyl and alkyl (Z)-propenyl ethers

The relative thermodynamic stabilities of ten allyl ethers (ROCH₂CH=CH₂) and the corresponding isomeric (Z)-propenyl ethers (where R is an alkyl group, or a methoxysubstituted alkyl group) have been determined by chemical equilibration in DMSO solution with t-BuOK as catalyst. From the variation of the equilibrium constant with temperature, the values of the thermodynamic parameters ΔGΘ, ΔHΘ and ΔSΘ of isomerization at 298.15 K were evaluated. The propenyl ethers are highly favored at equilibrium, the values of both ΔGΘ and ΔHΘ for the allyl → propenyl reaction being ca. −18 to −25 kJ mol⁻¹. The favor of the propenyl ethers is increased by bulky alkyl substituents, and decreased by methoxy-substituted alkyl groups. In most cases the entropy contribution is negligible; however, for R = (MeO)₂CH and R = (MeO)₃C the values of ΔSΘ are ca. −5 J K⁻¹ mol⁻¹.     

Synthesis of ferrocenyl-1,2-diketones and related compounds: Crystal and molecular structures of 1,2-diferrocenylethanedione and 1-ferrocenyl-2-(4-biphenylyl) ethanedione

Ferrocenyl-1,2-diketones FcCOCOR, 3, [Fc = (C₅H₅)Fe(C₅H₄)] can be prepared by oxidation of acylferrocenes FcCOCH₂R or, more efficiently, by oxidation of the isomeric ketones FcCH₂COR, 2. The ketones 2 are in turn readily synthesized from the salt (FcCH₂PPh₃)⁺I⁻ via the acylated salts [FcCH(COR)PPh₃]⁺I⁻. The haloacylferocenes FcCOCCl_x H_3−x (x = 1, 2, 3, of which the x = 2 example is synthetically equivalent to a diketone) are synthesized by Friedel—Crafts acylation of ferrocene using CCl_xH_3−xCOCl/AlCl₃, but the reaction proceeds via two parallel pathways, one giving the normal acyl derivatives FcCOCCl_xH_3−x and the other giving the reduced products FcCOCCl_x−1H_4−x. Two diketones FcCOCOFc 3b and FcCOCOC₆H₄Ph 3c have been structurally characterised by single-crystal X-ray diffraction.     

La-NMR-spektroskopie an allyllanthan(III)-komplexen

¹³⁹La-NMR chemical shifts were measured for several anionic complexes of formulae Li(C₄H₈O₂)_3/2 [La(ν³-C₃H₅)₄], [Li(C₄H₈O₂)₂][Cp′_nLa(ν³-C₃]H₅)_4−n] (Cp′ = Cp(ν⁵-C₅H₅); n = 1, 2 and Cp′ = Cp * (ν⁵-C₅Me₅); N = 1) and Li[R_nLa(ν³-C₃H₄)₄−n] (R = N(SiMe₃)₂; n = 1, 2 and R = CCsIMe₃; n = 4), as well as for neutral compounds for formulae La(ν³-C₃H₅)₃L_n (L = (C₄H₈O₂)_1.5, (HMPT)₂, TMED), Cp′_nLa(ν³-C₃H₅)_3−n (Cp′= Cp(ν⁵-Cp₅H₅), Cp *(ν⁵-C₅Me₅); n = 1, 2) and La(ν³-C₃H₂)₂X(THF)₂ X = Cl, Br, I). Typical ranges of the ¹³⁹La-NMR chemical shifts were found for the different types of complex independent of number and kind of organyl groups directly bonded to lanthanum.

Zusammenfassung

¹³⁹La-NMR-Spektroskopie wurde an einer Reihe anionischer Allyllanthanat(III)-Komplexe der Zusammensetzung ]- [La)ν³-C₃H₅)₄, [Li(C₄H₈)₂][Cp′_nLa(ν³-C₃H₅)_4−n(Cp′ = Cp(ν⁵-C₅H₅); n = 1, 2 und Cp′ = Cp * (ν⁵-C₅Me₅); N = 1) und Li[R_nLa(ν³-C₃H₅)_4−n (R = B(SiMe₃)₂; n = 1, 2 und R = CCSiMe₃; n = 4 sowie neutraler Allyllanthan(III)-Komplexe der Zusammensetzung La(ν³-C₃H₅)₃L_n (L_n = (C₄H₈O₂)_1.5, (HMPT)₂, TMED), Cp′_n, La(ν³-C₃H₅)_3−n (Cp′ = Cp(ν⁵-C₅H₅), Cp * (ν⁵- Cp₅Me₅); n = 1, 2) und La(ν³-Cp₃H₅)₂X(THF)₂ (X = Cl, Br, I) durchgefürt. In Abhängikeit von der Anzahl und der Art der am Lanthan gebundenen Gruppen wurden für die verschieden Komplextypen charakteristische Resonanzbereiche ermittelt.     

Synthesis and molecular structure of the optically active organoaluminium dimer (S)-(—)-(S)-(—)- [(C6H5)CH(CH3)NHA1(CH3)2]2

Reaction of the optically active primary amine (S)-(—)--methylbenzylamine with trimethylaluminium in heptane affords the crystalline organoaluminium dimer (S)-(—)-(S)-(—)-[(C₆H₅)CH(CH₃)NHA1(CH₃)₂]₂. Isolated as large, colourless, extremely air-sensitive prismatic crystals, the title compound crystallizes in the orthorhombic space group P2₁2₁2₁ with unit cell parameters a = 8.406(3), b = 15.505(4), c = 17.547(5) Å, V = 2287 ų and p = 1.03 g cm⁻³ for Z = 4. Least-squares refinement based on 1477 observed reflections converged at R = 0.056, R_w = 0.058. Methane was eliminated during the course of the reaction due to cleavage of A1---C and N---H bonds resulting in an asymmetric A1₂N₂ fragment at the core of the organoaluminium dimer. The mean A1---C bond distance in the dimethylaluminium units is 1.930(8), while the mean A1---N bond distance is 1.950(5) Å. Specific rotation ([]_D²⁵ in CH₂C1₂)of the dimer is determined to be - 20.6°.     

Metallorganische lewissäuren : XX. Reaktionen von (π-C5H5)(CO)2LM-X (L = CO, PR3; M = Mo, W; X = BF4, PF6, AsF6, SbF6) mit Schwefel-haltigen liganden

The compounds (π-C₅H₅)(CO)₂LM-X (L = CO, PR₃; M = Mo, W; X = BF₄, PF₆, AsF₆, SbF₆) react with H₂S, p-MeC₆H₄SH, Ph₂S and Ph₂SO(L′) to give ionic complexes [(π-C₅H₅)(CO)₂LML′]⁺ X⁻. Also sulfur-bridged complexes, [(π-C₅H₅)(CO)₃W---SH---W(CO)₃(π-C₅H₅)]⁺ AsF₆⁻ and [(π-C₅H₅)(CO)₃M-μ-S₂C=NCH₂Ph-M(CO)₃(π-C₅H₅)], have been obtained. Reactions with SO₂ and CS₂ have been examined.     

Studies on organolanthanide complexes : LXIII. Synthesis, spectroscopic and X-ray crystallographic characterization of new early organolanthanide, organoyttrium hydride and organoholmium hydroxide complexes

Organolanthanide chloride complexes [(CH₃OCH₂CH₂C₅H₄)₂Ln(μ-Cl)]₂ (Ln = La, Pr, Ho and Y) react with excess NaH in THF at 45°C to give the dimeric hydride complexes [(CH₃OCH₂CH₂C₅H₄)₂Ln(μ-H)]₂, which have been characterized by IR, ¹H NMR, MS and XPS spectroscopy, elemental analyses and X-ray crystallography. [(CH₃OCH₂CH₂C₅H₄)₂Y(μ-H)]₂ crystallizes from THF/n-hexane at −30°C, in the triclinic space group P1 with a = 8.795(2) Å, b = 11.040(1) Å, c = 16.602(2) Å, = 93.73(1)°, β = 91.82(1)°, γ = 94.21(1)°, D_c = 1.393 gcm⁻³ for Z = 2 dimers. However, crystals of [(CH₃OCH₂CH₂C₅H₄)₂Ho(μ-OH)]₂ were obtained by recrystallization of holmium hydride in THF/n-hexane at −30°C, in the orthorhombic space group Pbca with a = 11.217(2) Å, b = 15.865(7) Å, c = 17.608(4) Å, D_c = 1.816 gcm⁻³ for Z = 4 dimers. In the complexes of yttrium and holmium, each Ln atom of the dimers is coordinated by two substituted cyclopentadienyl ligands, one oxygen atom and two hydrogen atoms (for the Y atom) or two hydroxyl groups (for the Ho atom) to form a distorted trigonal bipyramid if the C(η⁵)-bonded cyclopentadienyl is regarded as occupying a single polyhedral vertex.     

The rovibrational analysis of the high-resolution IR spectrum of CD2HF below 1200 cm: an interacting tetrad of vibrational levels

The spectrum of CD₂HF was measured by high-resolution interferometric Fourier-transform IR (FTIR) spectroscopy (apodised instrumental band with:0.004 cm⁻¹ fwhm) between 800 and 1200 cm⁻¹ covering the four lowest fundamentals. A complete rotational analysis using a semi-automatic assignment procedure yields accurate band centres (ν₉: 912.2028 cm⁻¹, ν₆:964.4994 cm⁻¹, ν₅: 1050.5104 cm⁻¹, ν₄: 1093.8632 cm⁻¹) and a complete set of first-order Coriolis coupling constants. The most important couplings occur between ν₉ and ν₆ (ξ_a= 1.069 cm⁻¹, ξ_c= −0.3535 cm⁻¹) and between ν₅ and ν₄ (ξ_b= −0.80606 cm⁻¹). The analysis was guided by and compared with results from our ab initio calculations for Coriolis constants and transition moments using CADPAC at TZP/MP2 level.     

Recent studies on metal and metalloid bis(trimethylsilyl)methyls and the transformation of the bis(trimethylsilyl)methyl into the azaallyl and β-diketinimato ligands

Recent results (post-1990) on the synthesis and structures of bis(trimethylsilyl)methyls M(CHR₂)_m (R = SiMe₃) of metals and metalloids M are described, including those of the crystalline lipophilic [Na(μ-CHR₂)]_∞, [Rb(μ-CHR₂)(PMDETA)]₂, K₄(CHR₂)₄(PMDETA)₂, [Mg(CHR₂)(μ-CHR₂)]_∞, P(CHR₂)₂ (gaseous) and P₂(CHR₂)₄, [Yb(CHR₂)₂(OEt₂)₂] and [{Yb(CR₃)(μ-OEt)(OEt₂)}₂]; earlier information on other M(CHR₂)_m complexes and some of their adducts is tabulated. Treatment of M(CHR₂) (M = Li or K) with four different nitriles gave the X-ray-characterized azaallyls or β-diketinimates , and (LL′ = N(R)C(^tBu)CHR, L′L′ = N(R)C(Ph)C(H)C(Ph)NR, LL″ = N(R)C(Ph)NC(H)C(Ph)CHR, R = SiMe₃ and Ar = C₆H₃Me₂-2,5). The two lithium reagents were convenient sources of other metal azaallyls or β-diketinimates, including those of K, Co(II), Zr(IV), Sn(IV), Yb(II), Hf(IV) and U(VI)/U(III). Complexes having one or more of the bulky ligands [LL′]⁻, [L′L′]⁻, [LL]⁻, [LL″]⁻, [L″L]⁻, [LL]⁻ and [{N(R)C(^tBu)CH}₂C₆H₄-2]²⁻ are described and characterized (LL = N(H)C(Ph)C(H)C(Ph)NH, L″L = N(R)C(^tBu)C(H)C(Ph)NR, LL = N(R)C(^tBu)CHPh). Among the features of interest are (i) the contrasting tetrahedral or square-planar geometry for and , respectively, and (ii) olefin-polymerization catalytic activity of some of the zirconium(IV) chlorides.     

Synthesis of metallocenes of zirconium, hafnium, manganese, iron, tin, lead and half-sandwich complexes of rhodium and iridium containing the ligands (η-C5R4CR′2PMe2), where R and R′ may be H or Me

The dimethylphosphino substituted cyclopentadienyl precursor compounds [M(C₅Me₄CH₂PMe₂)], where M=Li⁺ (1), Na⁺ (2), or K⁺ (3), and [Li(C₅H₄CR′₂PMe₂)], where R′₂=Me₂ (4), or (CH₂)₅ (5), [HC₅Me₄CH₂PMe₂H]X, where X⁻=Cl⁻ (6) or PF₆⁻ (7) and [HC₅Me₄CH₂PMe₂] (8), are described. They have been used to prepare new metallocene compounds, of which representative examples are [Fe(η-C₅R₄CR′₂PMe₂)₂], where R=Me, R′=H (9); R=H and R′₂=Me₂ (10), or (CH₂)₅ (11), [Fe(η-C₅H₄CMe₂PMe₃)₂]I₂ (12), [Fe{η-C₅Me₄CH₂P(O)Me₂}₂] (13), [Zr(η-C₅R₄CR′₂PMe₂)₂Cl₂], where R=H, R′=Me (14), or R=Me, R′=H (15), [Hf(η-C₅H₄CMe₂PMe₂)₂]Cl₂] (16), [Zr(η-C₅H₄CMe₂PMe₂)₂Me₂] (17), {[Zr(η-C₅Me₄CH₂PMe₂)₂]Cl}{(C₆F₅)₃BClB(C₆F₅)₃} (18), [Zr{(η-C₅Me₄CH₂PMe₂)₂Cl₂}PtI₂] (19), [Mn(η-C₅Me₄CH₂PMe₂)₂] (20), [Mn{(η-C₅Me₄CH₂PMe₂B(C₆F₅)₃}₂] (21), [Pb(η-C₅H₄CMe₂PMe₂)₂] (23), [Sn(η-C₅H₄CMe₂PMe₂)₂] (24), [Pb{η-C₅H₄CMe₂PMe₂B(C₆F₅)₃}₂] (25), [Pb(η-C₅H₄CMe₂PMe₂)₂PtI₂] (26), [Rh(η-C₅Me₄CH₂PMe₂)(C₂H₄)] 29, [M(η,κP-C₅Me₄CH₂PMe₂)I₂], where M=Rh (30), or Ir, (31).     

Diastereoselective synthesis of a resolved secondary arsine complex: asymmetric synthesis of (R-(−)589-ethylmethylphenylarsine

The reaction of [R-(R,R)]-(+)₅₈₉-[(η⁵-C₅H₅){1,2-C₆H₄(PMePh)₂}Fe(NCMe)]PF₆ with (±)-AsHMePh in boiling methanol yields crystalline [R-[(R)-(R,R)]-(+)_{589)-[(η⁵-C5H5){1,2-C6H4(PMePh)2}Fe(AsHMePH)}PF₆, optically pure, in ca. 90% yield, in a typical second-order asymmetric transformation. This complex contains the first resolved secondary arsine. Deprotonation of the secondary arsine complex with KOBu^t at −65°C gives the diastereomerically pure tertiary arsenido-iron complex [R-[(R),(R,R)]]-[((η⁵-C₅H₅){1,2-C₆H₄(PMePh)₂}FeAsMePh] · thf, from which optically pure [R-[(S),(R,R)]]-(+)₅₈₉-[(η⁵-C₅H₅){1,2-C₆H₄(PMePh)₂}Fe(AsEtMePh)PF₆ is obtained by reaction with iodoethane. Cyanide displaces (R)-(−)₅₈₉-ethylmethylphenylarsine from the iron complex, thereby effecting the asymmetric synthesis of a tertiary arsine, chiral at arsenic, from (±)-methylphenylarsine and an optically active transition metal auxiliary.     

Structure cristalline et conformation en solution aqueuse de la carnosine (β-alanyl-L-histidine)

Carnosine (β-alanyl-L-histidine) is a biologically active molecule involved in muscular metabolism. It crystallises in the C; space group with a = 24.725 Å b = 5,427 Å c = 8,004 Å β = 100,2° (Z = 4)

In the crystal, acid and basic groups are engaged in hydrogen bonds whose strength is evaluated through IR frequencies. Molecular conformation in the solid state is defined by τ₁ = /t-177° τ₂ = −38° φ = −96° ψ = +131° χ₁ = 181° χ₂₁ = 62°

NMR study of carnosine in aqueous solution indicates that rotation about CH₂-CH₂ is free and that the other angles take the following values: Ø −150° or −90° and X₁ = 165° or 315°. Infrared and Raman spectra suggest that τ₂ undergoes small changes when going from crystal to solution while ψ is close to +150°.     

Übergangsmetall-Carben-Komplexe : CXXXXI. Untersuchungen zum Reaktionsverhalten der Carben-Komplexe cis-(CO)4(SnPh3)Re[C(OEt)NR2] (R = pr, hex) gegenüber Lewis-Säuren

In the reaction of cis-(CO)₄(SnPh₃)Re[C(OEt)NR₂] (R = ⁱpr (isopropyl), ^chex (cyclohexyl)) with BI₃ the Lewis acid attacks the triphenylstannyl ligand. Substitution of a phenyl for a iodine group leads to equilibrium mixtures of rhenium carbene complexes of general formula cis-(CO)₄(SnPh_3−χI_χ)Re[C(OEt)NR₂] (χ = 1−3; R = ⁱpr, ^chex). By changing the solvent and ratio of can be shifted such that only one major product is formed. Thus this reaction pathway can be used for the preparation of cis-(CO)₄(SnPhI₂)Re[C(OEt)NR₂] (R = ⁱpr, ^chex). Even when a large excess of BI₃ is present electrophilic attack by the Lewis acid on the carbene ligand is not observed.

Synthesis of cis-(CO)₄(SnPh_3−χI_χ)Re[C(OEt)NR₂] (χ = 1−3; R --- ⁱpr, ^chex) can be achieved in high yield by reaction of cis-(CO)₄(SnPh₃)Re[C(OEt)NR₂] (R = ⁱpr, ^chex) with one, two or three equivalents of HI. This reaction, with successive rupture of the tin-carbon bonds in the triphenylstannyl ligand and the simultaneous formation of benzene, affords the desired substitution product irreversibly. Reaction of cis-(CO)₄(SnPh₃)Re[C(OEt)NR₂] (R = ⁱpr, ^chex) with I₂ gives the compounds, cis-(CO)₄(SnI₃)Re[C(OEt)NR₂] (R = ⁱpr, ^chex), in relatively low yields.     

Si-Kernresonanzspektren und synthese von bromdisilanen und ioddisilanen

The syntheses of Bromodisilanes Br_nSi₂H_6−n and Iododisilanes I_nSi₂H_6−n (n = 1, 2, 3, 4, 5), starting from caryldisilanes Ar_nSi₂H_6−n (Ar = phenyl, -naphthyl, mesityl) are reported. The ²⁹Si-NMR-spectra of all compounds, including ²⁹Si²⁹Si-coupling constants, have been measured.

Zusammenfassung

Ausgehend von Aryldisilanen ArS₂H_6−n, (Ar = Phenyl, -Naphthyl, Mesityl) wurden die Bromdisilane Br_nSi₂H_6−n, und Ioddisilane I_nSi₂H_6−n, (n = 1, 2, 3, 4, 5) synthetisiert. Die ²⁹Si-NMR-Spektren aller Verbindungen, (eingeschlossen ²⁹Si²⁹Si-Kopplungskonstanten) wurden vermessen.     

Direct observation of weak state mixing in highly vibrationally excited acetylene

A pulsed-laser double-resonance technique probes the mixing of zero-order states in the 3ν_CH vibrational overtone (ε_vib ≈ 9640 cm⁻¹) of acetylene (C₂H₂), where the calculated vibrational state density is about three states/cm⁻¹. Vibrational overtone excitation populates and laser induced fluorescence via the ùA_u electronic state detects the molecular eigenstates, which have slightly mixed vibrational character because of weak interactions between the zero-order optically bright C---H stretching state and optically dark background states. Observing the interacting states at low state density in the weak perturber limit dramatically simplifies the assignment and interpretation of the spectra. A two-state model recovers the important features of the experimental data including our prior observations of surprisingly intense electronic transitions originating from 3ν_CH, the anomalous rotational-level dependence of the electronic absorption cross sections, and small perturbations in the 3ν_CH line positions. A multi-state deperturbation analysis gives coupling matrix elements of 0.01–0.05 cm⁻¹ that are consistent with those measured for weak interactions in other polyatomic molecules at higher state densities.     

An ab initio close-coupling calculation of the lower vibrational energies of the HCl dimer

We have previously determined an analytical ab initio six-dimensional potential energy surface for the HCl dimer, and in the present paper we use this potential, with the HCl bond lengths held fixed, in a full (four-dimensional) close-coupling calculation to determine the energies of the lowest 24 vibrational states. These vibrational states involve the intermolecular stretch ν₄, the trans-bend tunneling vibration ν₅, and the torsion ν₆. The highest of the 24 levels is the (ν₄ν₅ν₆)=(111) state, for which we calculate an energy of 200 cm⁻¹ above the (000) state. As well as determining tunneling energies up to 5ν₅=183 cm⁻¹, we determine ν₄=49 cm⁻¹, 2ν₄=93 cm⁻¹, 3ν₄=134 cm⁻¹, 4ν₄=172 cm⁻¹, ν₆=137 cm⁻¹ and ν₄+ν₆=178 cm⁻¹, together with tunneling energies in all these states. Making allowance for the HCl stretching zero-point energy we determine the dissociation energy D₀ as 390 cm⁻¹ on this analytical surface. We determine that below 300 cm⁻¹ there are 72 vibrational (J=K=0) states, and below dissociation there are 162 vibrational (J=K=0) states, for this potential surface.     

Electron paramagnetic resonance study of the reactions of tetrathiomolybdate with roussin salts and esters, and with some related iron nitrosyls

The tetrathiomolybdate ion [MoS₄]²⁻ reacts in DMF solution with Roussin esters Fe₂(SR)₂(NO)₄ (R = Me, Et, n-Pr, i-Pr, n-Bu,t-Bu, n-C₅H₁₁) to yield the paramagnetic iron nitrosyls [Fe(NO)₂(SR)₂]⁻ (1), [Fe(NO)₂(S₂MoS₂]⁻ (2) and [Fe(NO)(S₂MOS₂)₂]⁻ (3). The new complexes (2) and (3) have been characterized by EPR spectroscopy and the assignment to them of constitutions based respectively upon tetrahedral and square pyramidal iron is supported by EHMO calculations. Fe₂(SPh)₂(NO)₄ with [MoS₄]²⁻ yields only [Fe(NO)₂(SPh)₂]⁻, and preformed (3) reacts with PhS⁻ to give firstly EPR-silent species, and then [Fe(NO)₂(SPh)₂]⁻. The mononitrosyl (3) can also be formed by reaction of [MoS₄]²⁻ with [Fe₄S₃(NO)₇]⁻, Fe₄S₄(NO)₄, or Fe₂I₂(NO)₄.