Diastereoselective formation of calcium and ytterbium ansa-metallocenes via recombination of guaiazulene (Gaz) radical anions. Molecular structure of ansa-(η5-Gaz)2Ca(THF)2 and ansa-(η5-Gaz)2Yb(Py)2 (Gaz = 1,4-dimethyl-7-isopropylazulene) complexes

ansa-Metallocene derivative (⁵-Gaz)₂Ca(THF)₂ (1) (Gaz = 1,4-dimethyl-7-isopropylazulene) was synthesized by the reaction of CaI₂(THF)₂ with two equivalents of potassium and two equivalents of guaiazulene in THF. The ytterbium analog ansa-(⁵-Gaz)₂Yb(THF)₂ (2a) was synthesized by the reduction of guaiazulene with ytterbium naphthalenide in THF. The recrystallization of 2a from pyridine leads to the exchange of the coordinated solvent molecules and gives ansa-(⁵-Gaz)₂Yb(NC₅H₅)₂ (2b). The molecular structures of 1, 2a, and 2b were determined by X-ray diffraction analysis. The crystals of 1, 2a, and 2c consist of a racemic mixture of both R,R- and S,S-enantiomers. The calcium and ytterbium atoms ⁵-coordinate the five-membered rings of the guaiazulene ligands. The ¹H NMR spectroscopic and X-ray diffraction data unambiguously confirm the exclusive formation of N₂-symmetric ansa-metallocenes in these reactions. The reaction of compound 1 with Me₃SiCl in THF occurs with retention of the N—N bond between two guaiazulene moieties and affords bis(1,4-dimethyl-3-trimethylsilyl-7-isopropylazulene) (3) in high yield.     

Molecular structure and fluxional behaviour of the iron-rhodium methoxymethylidyne cluster complex Fe2 Rh(μ-H)(μ3-COCH3)(CO)7(η-C5H5)

The complex Fe₂Rh(μ-H)(μ₃-COCH₃)(CO)₇(η-C₅H₅) prepared by treatment of Fe₃(μ-H)(μ-COCH₃)(CO)₁₀ with Rh(CO)₂ (η-C₅H₅), has been examined by single crystal X-ray diffraction. The compound crystallises in the monoclinic space group C2/c (No. 15) with a 25.409(2), b 8.129(1), c 17.044(1) Å, β 103.744(6)°, V 3419.6(6) ų and D_c 2.02 g cm⁻³ for Z = 8 and M = 519.8. Data were collected for 2° ⩽ θ ⩽ 30° with graphite monochromated X-radiation (Mo-K_α) using an Enraf-Nonius CAD4-F diffractometer. The structure was refined to R = 0.025 (R_itw = 0.037) for 3557 observed [I ⩾ 3(σI)], absorption corrected data. The complex contains an asymmetrically bonded methoxymethylidyne ligand capping an Fe₂Rh triangular face (Fe(1)-C(8) 1.863(3), Fe(2)-C(8) 1.881(3), Rh-C(8), 2.211(3) Å). The terminal carbonyl ligand on the rhodium atom shows slight semi-bridging interactions with the two iron atoms (Fe(1) … C(7) 2.888(4), Fe(2) … C(7), 2.769(4) Å, Rh-C(7)-O(7) 169.1(4)°. The iron—iron vector is spanned by a (directly located) μ-hydride ligand. Variable temperature ¹³C NMR studies reveal fluxional behaviour, including a temperature dependence both of the alkylidyne carbon chemical shift (δ 323.5 at +80°C, δ 319.2 at −90°C) and its ¹⁰³Rh coupling constant (¹J(Rh-C) 23 Hz at −90°C, 26 Hz at +80°C). These data suggest an increased interaction of the ‘semi-μ₃’ alkylidyne ligand with the rhodium centre at higher temperatures, primarily associated with the highest energy fluxional process. Extended Hückel MO calculations on this complex allow a rationalisation of the ‘semi-μ₃’ nature of the COCH₃ group.     

Lithium and lanthanum complexes with acenaphthylene dianion. Molecular structure of [Li(Et2O)2]2μ2:η3[Li(η3:η3-C12H8)]2 complex

The lithium complex with the acenaphthylene dianion [Li(Et₂O)₂]₂₂:³[Li(³:³-C₁₂H₈)]₂ (1) was synthesized by the reduction of acenaphthylene with lithium in diethyl ether. According to the X-ray diffraction data, compound 1 has a reverse-sandwich structure with the bridging dianion ₂:³[Li(³:³-C₁₂H₈)]₂. Two lithium atoms in complex 1 are located between two coplanar acenaphthylene ligands of the ₂:³[Li(³:³-C₁₂H₈)]₂ ^2– dianion and are ³-coordinated with the five- and six-membered rings. The lanthanum complex with the acenaphthylene dianion [LaI₂(THF)₃]₂(₂-C₁₂H₈) (2) was synthesized by the reduction of acenaphthylene in THF with the lanthanum(iii) complex [LaI₂(THF)₃]₂(₂-C₁₀H₈) containing the naphthalene dianion. The ¹H NMR spectrum of complex 2 in THF-d₈ exhibits four signals of the acenaphthylene dianion, whose strong upfield shifts compared to those of free acenaphthylene indicate the dianionic character of the ligand. The highest upfield chemical shift belongs to the proton bound to the C atom on which, according to calculation, the maximum negative charge is concentrated.     

Analysis of the Rydberg structure in the vapor-phase electronic absorption spectrum of (η7-cycloheptatrienyl)(η5-cyclopentadienyl) chromium

Parameters of the Rydberg transitions in the vapor-phase absorption spectrum of (η⁷-C₇H₇)(η⁵-C₅H₅)Cr were analyzed in detail. A correspondence between the three Rydberg series in the short-wavelength region of the spectrum and low-frequency Rydberg bands was established. Vibronic structure of the observed transitions to the lowest Rydberg s, p _x,y , p _z , and d _xz,yz levels was interpreted. The long-wavelength and short-wavelength series, respectively characterized by quantum defect (σ) values of 1.26 and 0.82, were unambiguously assigned to the Rydberg p _x,y and d _xz,yz excitations, respectively. Transitions from the 3d _z 2 orbital to theR(n−1)f,Rnd _z 2, andRnp _z levels can contribute to the series characterized by a σ value of 1.04. The assignment was made of Rydberg bands in the spectral region corresponding to the principal quantum number (n) values of 5, 6, and 7 (in this region, interpretation of the spectral pattern is complicated because of the band shifts and broadening). Atn>5, changes in the σ values of the Rydberg excitations with increase in then value are due to configuration interaction. The electronic-excited states, which can be responsible for the observed changes in the Rydberg parameters, were determined. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1677–1684, September, 1999.     

Structural properties of the trimetallic acetylide complex [{Ru(CO)2(η5C5H5)}3(η1:η1:η2:-CC)]+

The purpose of this Note is the study of the structure and fluxional behavior of the complex [{Ru(CO)₂(η⁵C₅H₅)}₃(η¹:η¹:η²:-CC)]⁺, using density functional methods. The molecular geometry of this complex will be optimized, the transition state (TS) of the fluxional process will be determined and the origin of the energy barrier will be analyzed.     

Calcium tetramethylheptanedionate adducts with N-donor ligands. Molecular structure of a dimeric and volatile adduct Ca2(η2-thd)(μ,η2-thd)3(η2-bipy)

Decomplexation of Ca₃(thd)₆ by mono- and bidentate N-donors [morpholine, dimorpholinoethane (DIMOE), TMEDA, bipyridine] afforded the corresponding adducts Ca(thd)₂L [L=morpholine (1a), DIMOE (1b), TMEDA (2)] and {Ca(thd)₂}₂(bipy) (3). All complexes have been fully characterised by elemental analysis, FT-IR and ¹H NMR spectroscopy. Compounds 1b and 3 have also been characterised by X-ray crystallography. The structure of 3 is based on six- and seven-coordinated Ca centres; it is the first dimeric volatile Lewis base adduct of Ca(thd)₂. The thermal behaviour of all derivatives has been studied by thermal gravimetric analysis.     

Molecular structure of ansa-compound (η5-C5H4)CMe2(η5-C9H6)TiCl2

The structure of a new ansa compound, (⁵-C₅H₄)CMe₂(⁵-C₉H₆)TiCl₂ (1), was studied by X-ray analysis:a = 15.00(1),b =15.500(5),c = 13.032(4) Å, = 92.66°(4),V = 3025.1(1) ų, space groupP2₁/.,R = 0.038. The distorted tetrahedral coordination sphere of the Ti atom is formed by two Cl atoms and two -ligands. It was proposed that the angle () between theC-M direction and the line normal to M-Cp can be considered as one of the geometric parameters characteristic of the structure-properties correlation.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 305–308, February, 1995.     

Structure and reactivity of substituted di-η5-cyclopentadienyl metal dihalides. Crystal structure of dichlorobis(η5-t-butylcyclopentadienyl)zirconium(IV)

A new approach to the synthesis of t-butylcyclopentadienyl and related anions, via the addition of methyl- or other alkyl-lithium compounds to dimethylfulvene, is reported and details are given for the preparation of (η⁵-t-BuCp)₂ZrCl₂ and (η⁵-t-BuCp)₂TiCl₂. The zirconium compound is orthorhombic, P2₁2₁2, a 13.003(17), b 10.761(10), c 6.703(8) Å. A crystal structure determination (R = 0.037, 980 reflections) shows that the t-butyl groups are directed away from each other on opposite sides of the molecule: this structure appears to be adopted only in molecules in which the substituent groups are too bulky to be accommodated directly above and below the MCl₂ group.     

Crystal structure of (η5-pentamethylcyclo-pentadienyl)(methyldiphenylphosphite-P)dichlororhodium(III)

The molecule (η⁵-pentamethylcyclopentadienyl)(methyldiphenylphosphinite-P)dichlororhodium(III), [(η⁵-C₅Me₅)RhCl₂(PPh₂OMe)], crystallizes in the monoclinic crystal system in space group P2₁/c with unit cell parameters a = 16.056(3) Å, b = 9.4331(18) Å, c = 15.745(3) Å, β = 108.330(4)°, V = 2263.8(7) ų and Z = 4. There is three-legged piano stool geometry about Rh. The Rh-P distance of 2.278(2) Å is shorter than those of [(η⁵-C₅Me₅)RhCl₂(PPh₂OR)] where R is an aryl group, and longer than those found in [(η⁵-C₅Me₅)RhCl₂{PPh(OR)₂}]. The structure reveals significant distortion of the pentamethylcyclopentadienyl towards ′η³,η²-enyl-ene′ coordination.     

Mixed cyclopentadienyl-naphthalene complexes of rare-earth elements: mono- and binuclear derivatives. Molecular structure of (η5-C5H5)YC10H8(DME)

Reaction of CpLnCl₂(THF)₃ (Ln = Y, Gd, Er, and Tm) with sodium naphthalenide in 1,2-dimethoxyethane (DME) gives mononuclear complexes CpLnC₁₀H₈(DME). Binuclear complexes (CpLn)₂C₁₀H₈(THF)₄ (Ln = Sm and Yb) containing the Ln atoms in the oxidation state +2 are formed in similar reactions of Sm and Yb complexes. The structure of CpYC₁₀H₈(DME) was determined by the X-ray diffraction method. The coordinated naphthalene ring linked to the Y atom is nonplanar: it is bent by an angle 26.1° over the C(1)...C(4) line. The existence of two short, Y(1)-C(1) and Y(1)-C(4) (2.438(6) and 2.452(6) Å), and two long, Y(1)-C(2) and Y(1)-C(3) (2.599(7) and 2.598(7) A), Y-C(C₁₀H₈) bonds testifies to the 2 ¹:²-interaction of the Y atom with the naphthalene dianion. The same yttrium complex in a mixture with Cp₃Y is formed in the reaction of Cp₂YCl with sodium naphthalenide.Deceased.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 993–997, April, 1996.     

Reaction of NiBr2(DME) with 2-pyridinal-methyl-N-2,6-diisopropylphenylimine. The first crystal structure of an α-diimine nickel(II) complex of the NiL2X2 type

NiBr₂ (DME) (DME = ethylene glycol dimethyl ether) reacts with 2-pyridinal-methyl-N-2,6-diisopropylphenylimine (L) in a 1:1 molar ratio in CH₂Cl₂ to give NiBr₂(L) and [NiBrL₂]Br · 4CH₂Cl₂ in 52% and 14% yield, respectively. The crystal of [NiBrL₂]Br · 4CHCl₃ obtained from CHCl₃ was structurally characterized.     

The reactions of phenylacetylene with naphthalene complexes of europium and ytterbium. Molecular structure of [IYbC≡CPh(DME)2]2

Reactions of naphthaleneeuropium and naphthaleneytterbium, C₁₀H₈Ln(DME) (Ln = Eu or Yb), with phenylacetylene are accompanied by the formation of the C-C bond and yield the complexes of composition Ph₂C₄H₂Ln(DME)₂. Hydrolysis of the Ph₂C₄H₂Ln(DME)₂ complexes affords a mixture of isomers of 1,4-diphenyl-1,3-butadiene. Reactions of C₁₀H₈[LnI(DME)₂]₂ with PhCCH yield mixed iodine-ethynyl complexes [ILn(-CCPh)(DME)₂]₂. According to the data of X-ray diffraction analysis, the ytterbium complex consists of two YbI(DME)₂ units bonded through two bridging CCPh groups. The crystals of this complex belong to the space groupP2₁/c. The central cyclic Yb-C-Yb-C fragment is planar; the C(I)-Yb(I)-C(I) angle is 86.4(3)°. The Yb-C bond lengths are 2.584(8) and 2.603(9) Å.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 2101–2104, August, 1996.     

Crystal structure of the complex Zn(2,2′-Bipy)(C2H5OCS2)2 with mono- and bidentate ethylxanthate ligands

While seeking molecular precursors for ZnS films obtained by gas phase chemical deposition [1, 2] we synthesized mixed-ligand compounds ZnL(ROCS₂)₂ [R = i-Pr. /-Bu; L = 2,2′-bipyridyl (2,2′-Bipy), 1,10-phenanthroline (Phen)] [3]. The volatile complex Zn(2,2′-Bipy)(i-PrOCS₂)₂ was used as a precursor to obtain electroluminescent ZnS:Mn films [4]. According to XRD data, the compound Zn(Phen)(i-BuOCS₂)₂ is monomeric. The c.n. of zinc is six. The Phen and 1-B11OCS₂ ions behave as cyclic bidentate ligands [3, 5]. It was assumed that other mixed-ligand complexes with Phen and 2,2′-Bipy have an analogous structure [3]. Here we report on the structure of the known mixed-ligand complex of zinc(II) ethylxanthate with 2,2′-bipyridyl [6, 7]. It was found that the behavior of alkylxanthate ligands in mixed-ligand complexes of zinc(II) is more complex. Translated from Zhumal Stmktumoi Khimii, Vol. 41, No. 1, pp. 196-201, January–February, 2000.     

Synthesis of a Mo–Ru/Carbon Nanocomposite Using (η-C7H7)(OC)2MoRu(CO)2(η-C5H5) as a Single-Source Molecular Precursor

Degradation of a (-C₇H₇)(OC)₂MoRu(CO)₂(-C₅H₅)/carbon powder composite under appropriate thermal conditions affords a nanocomposite containing crystalline nanoclusters of Mo–Ru alloy highly dispersed on the carbon support. The alloy nanoparticles have an average diameter of 2.2 nm and crystallize as a fully disordered fcc lattice having a cell constant of 4.09 Å. When tested as an cathode catalyst in a direct methanol fuel cell, this nanocomposite shows significant methanol tolerance but affords current production too low to be of practical importance.     

A new route to iron(0) thiocarbonyl complex involving desulphurization of the Fe(η2-CS2R)+ cation with P-n-Bu3. Crystal structure of Fe(CS)(CO)2(PPh3)2

Reaction of [Fe(η²-CS₂R)(CO)₂(PPh₃)₂][X] (R = CH₃, CH₂Ph; X⁻ = PF₆⁻, I⁻) with P-n-Bu₃ or PEt₃ gives Fe(CS)(CO)₂(PPh₃)₂ (3a); (ν(CS) 1235 cm⁻¹; δ(¹³C) 324.28 ppm). The structure of 3a has been determined by X-ray diffraction. Crystal data are: a 18.821(5), b 12.113(3), c 18.149(5) Å, β 117.76(6)°, monoclinic, space group P2₁, Z = 4. The structure is a trigonal-bypyramid with equatorial CS group, trans PPh₃ ligands, a FeC(S) bond distance of 1.768(8) and a CS bond distance of 1.563(8) Å.     

An exceptionally stable cis-(hydride)(η2-dihydrogen) complex of iron

The cis-(H)(H₂ complex [(PP₃)Fe(H)(H₂)]BPh₄ (PP₃  P(CH₂CH₂PPh₂)₃) has been made by reaction of the chloride [(PP₃)FECl]BPh₄ in THF with NaBH₄ under 1 atm of H₂. In the solid state and in solution at low temperature the complex is octahedral, and the hydride and dihydrogen ligands occupy mutually cis positions. At ambient temperature in solution the complex is trigonal-bipyramidal, and an “H₃” unit occupies an axial position trans to the bridgehead phosphorus atom of PP₃; this results in exceptional thermal and chemical stability of the complex.     

Synthesis and conversions of metallocycles. 9. Synthesis of polycyclic aluminocyclopentanes with the participation of (η5-C5H5)2ZrCl2

The Cp₂ZrCl₂-catalyzed (Cp=⁵-C₅H₅) stereoselective cyclometalation of norbornenes and norbornadienes with AlEt₃ was carried out. It led in one stage to the preparation of polycyclic aluminocyclopentanes (ACP). It was shown that the ACP synthesized can be converted into polycyclic thiophanes under the action of elementary sulfur.For previous communication, see [1].Institute of Chemistry, Bashkir Scientific Center, Ural Branch, Academy of Sciences, 450054 Ufa. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 386–391, February, 1992.     

Theoretical exploration of structure-reactivity relationships in organometallic chemistry: butadiene insertion into the organyltransition-metal bond and conversion of the allyltransition-metal fragment in the [Ni(η-Cp)(η-phenyl)(η-butadiene)] complex

We have theoretically examined the reaction course of the butadiene insertion into the arylNi^II bond in the [Ni^II(η⁵-Cp)(η¹-phenyl)(η²-butadiene)] complex (1), by employing a gradient-corrected DFT method. Critical elementary processes have been scrutinized, viz. monomer insertion, rotational allylic isomerization and allylic η¹-σ→η³-π rearrangement. The first mechanism suggested by Lehmkuhl et al. was refined and supplemented with important details. The critical factors that determine the generation of anti-η³- and syn-η³-allyl isomers of the [Ni^II(η⁵-Cp)(1-benzyl-allyl)] product have been elucidated. This let us to rationalize the experimentally observed, almost exclusive formation of the anti-η³-allyl isomer. Butadiene preferably inserts in η²-mode into the η¹-phenylNi^II bond, initially giving rise to the η¹(C³)-allyl product species, 3σ. The direct formation of the η³-allyl product species, 3π, along the alternative path for η⁴-butadiene insertion, however, is found to be almost entirely disabled kinetically. The thermodynamically favorable η²-trans form of 1 is also shown to be more reactive in accomplishing CC bond formation. Species 3σ is indicated to be a metastable intermediate, occurring in an appreciable stationary concentration. Its respective anti and syn isomeric forms are likely to be in equilibrium, due to the facile rotational isomerization. The subsequent allylic rearrangement into the thermodynamically strongly favorable η³-allylNi^II coordination mode is shown to be the crucial elementary step that discriminates which of the isomeric η³-allyl forms is preferably generated. The higher reactivity of the anti isomer in this process decisively determines the almost exclusive formation of the anti-η³-allyl product species under kinetic control. The requirement of elevated temperatures for the anti-η³-allyl→syn-η³-allyl isomerization to occur, as revealed from experiment, is attributed to the pronounced thermodynamic stability of the η³-allylNi^II coordination.     

Reactions of (η6-diphenylacetylene) chromiumtricarbonyl complexes with polynuclear carbonyls I. Synthesis of Cr(CO)3(η6-diphenylacetylene) complex and its reaction with Co2(CO)8. Crystal and molecular structure of Cr(CO)3(η6:η2-diphenylacetylene)Co2(CO)6

The reaction of Cr(CO)₃(NH₃)₃ with diphenylacetylene affords as a main product the complex with Cr(CO)₃ moiety bound to a phenyl ring of diphenylacetylene; Cr(CO)₃(η⁶-PhC₂Ph) (I). Complex I readily reacts with Co₂(CO)₈ yielding the mixed metal complex Cr(CO)₃(η⁶:η²-PhC₂Ph)Co₂(CO)₆ (II). The reaction proceeds with retention of the Cr(CO)₃ (η⁶-arene) structural unit, the Co₂(CO)₆ fragment being bound to the triple bond of diphenylacetylene in μ₂,η²-mode. The structure of II was determined by single crystal X-ray analysis. The complex crystallizes in space group P2₁/c with unit cell parameters a 8.666(3) Å, b 18.046(3) Å, c 15.155(6) Å. β 97.57(3)°, V 2349(2) ų, Z = 4, D_x = 1.70 g/cm³. The structure was solved by direct methods and refined by full-matrix least-squares technique to R and R_w values of 0.032 and 0.034, respectively, for 3655 observed reflections. The data obtained show that two structural units in II, Cr(CO)₃(η⁶-Ph-) and Co₂(CO)₆(μ₂,η²-CC), are distorted due to steric repulsion between these metal carbonyl moieties. The Cr(CO)₃ fragment is shifted from the centre of the phenyl ring and slightly tilted with respect to the phenyl ring plane. The Co₂C₂ tetrahedron in the Co₂(CO)₆(μ₂,η²-CC) moiety is distorted in such a way that two of the four Co_iC_j bonds are elongated.