Synthesis of reactive [Al(Et)(q′)2] (q′ = 2-methyl-8-quinolinolato) serving as a precursor of light emitting aluminum complexes: Reactivity, optical properties, and fluxional behavior of the aluminum complexes

Reaction of AlEt₃ with 2-methyl-8-quinolinol gave ethylbis(2-methyl-8-quinolinolato)aluminum complex [Al(Et)(q′)₂] 1. The complex 1 provided photoluminescent Al complexes by reactions with phenols, carboxylic acid, and H₂O. The α-CH₂ hydrogens in the Et group of 1 was diastereotropic as revealed by ¹H NMR spectroscopy because of the presence of a chiral center at Al. The chirality at Al was dynamically lost at elevated temperature in CDCl₂CDCl₂ and DMSO-d₆, as indicated by temperature dependent ¹H NMR spectroscopy. This dynamic or fluxional behavior of 1 is explained by rotation of the 2-methyl-8-quinolinolato ligand. The kinetic parameters of the dynamic process were estimated at ΔH^‡ = 135 kJ mol⁻¹ and ΔS^‡ = 159 J K⁻¹ mol⁻¹ in CDCl₂CDCl₂ and at ΔH^‡ = 124 kJ mol⁻¹ and ΔS^‡ = 151 J K⁻¹ mol⁻¹ in DMSO-d₆, respectively, at 350 K. Structures of some of the obtained Al complexes were confirmed by single-crystal X-ray crystallography. These Al complexes showed photoluminescence peaks at 492-507 nm in CHCl₃ with quantum yields of 7-23%.     

Thermodynamic and kinetic parameters associated with the fluxional behavior of 2-methyl- and 2,6-dimethyltroponeiron tricarbonyl complexes

The kinetic and thermodynamic parameters for regioisomerisation of 2-methyl- and 2,6-dimethyl-derivatives of tricarbonyl[η⁴-tropone]iron complexes have been studied by ¹H NMR spectrometry over a range of 40 °C. Regioisomerisation of these complexes proceeds by an intramolecular first-order process and results in the almost complete conversion of the less stable complexes (4, 8) to more stable regioisomers (1, 5). The activation energies and half lifes for the conversion (4 → 1) and (8 → 5) were found to be ΔG^#=92 kJ mol⁻¹; τ_1/2=12.8 h, and ΔG^#=107 kJ mol⁻¹; τ_1/2=26.8 h, respectively, at 23 °C. Complex 1 reacts with (1R,2S,5R)-menthol in sulphuric acid solution, followed by neutralisation with sodium carbonate to give a separable mixture of diastereomeric tricarbonyl[(2,3,4,5-η)-(1R^′,2S^′,5R^′)-6-menthyloxy-2-methyltropone]iron complexes, 9 and 10. The corresponding dimethylated complex 5 fails to react under these conditions.     

Fluxional behavior of Al(Et)(q)2 (q=2-methyl-8-quinolinolato) studied by temperature dependent H NMR spectroscopy

Two α-CH₂ hydrogens of the Et group in Al(Et)(q^′)₂ (q^′=2-methyl-8-quinolinolato) show two ¹H NMR peaks at different positions with a separation of 0.19 ppm at 25 °C, due to the presence of a chiral center at Al. On raising the temperature, the two peaks collapsed, and coalesced above 100 °C. The ¹H NMR fluxional behavior is accounted for by simultaneous rotation of the q^′ ligands, and kinetic parameters of kJ mol⁻¹, kJ mol⁻¹, J K⁻¹ mol⁻¹ are evaluated.     

Synthesis and characterization of a planar chiral and chiral-at-metal ruthenium N-heterocyclic carbene complex

This report describes the conversion of the neutral planar chiral arene-tethered complex [Ru(η⁶:η¹-Me₂NC₆H₄C₆H₄PCy₂)Cl₂ (1), into [Ru(η⁶: η¹-Me₂NC₆H₄C₆H₄PCy₂)(1,3-dibutylimidazol-2-ylidene)Cl]BF₄ (2) via silver transmetallation. The cationic title complex is also chiral-at-metal, and forms stereoselectively as a result of the directing effect of the arene-tethered ligand. The structure in solution and in the solid state was examined; a puckered distortion of the η⁶-arene was noted in the crystal structure, along with a hindered rotation of the NHC in solution. As a comparison to the previously reported phosphine analogues, the dication derived from 2 was used to catalyze the asymmetric Diels-Alder reaction of methacrolein and cyclopentadiene.     

The rotational spectrum of the cyclopentadienylallylnickel complex

The rotational spectrum of cyclopentadienylallylnickel, C₃H₅NiC₅H₅, has been studied using a pulsed molecular beam Fourier transform microwave spectrometer. Twelve a-type transitions were analyzed to obtain rotational and centrifugal distortion constants for the parent C₃H₅⁵⁸NiC₅H₅ complex. The measured rotational constant A = 3107.603(93) MHz is about 160.0 MHz larger than the predicted DFT value, providing evidence for possible fluxional motion in the complex. The large distortion constants, on the order of 100 kHz, provide further evidence for fluxional motion. The experimental constants B = 1302.38(22) and C = 1276.40(15) MHz are in good agreement with the DFT calculated values and confirm the η³-bonding of the allyl ligand to the Ni–C₅H₅ moiety. DFT calculations provide a V₅ barrier for internal rotation about the Ni–C₅H₅ axis of 53 cm⁻¹, with the lowest energy conformation having the central allyl c-atom eclipsed with respect to two C₅H₅ carbon atoms. Several additional rotational lines, possibly those of an exited torsional state, were observed but not assigned.     

Fluxional behavior of methyl-substituted tricarbonyl(tropone)iron complexes and their different reactivity

The compositions of regioisomeric mixtures of tricarbonyliron complexes of 2-methyltropone (1a,b), 3-methyltropone (2a,b) and 2,6-dimethyltropone (3a,b) are studied and compared with the results of ab initio computations. The structures, frontier orbitals, and population analysis are evaluated by means of density functional theory. The thermodynamic and kinetic parameters of regioisomerizations are determined using dynamic ¹H NMR technique. The influence of methyl-substituent(s) on the equilibrium ratio of regioisomers resulting from the haptotropic rearrangement is discussed. Significant differences in the reactivity of C-protonized methyl- and dimethyl-substituted tricarbonyl(tropone)iron complexes 4–6 in nucleophilic additions and corresponding O-trimethylsilylated complexes 7–9 in [3+2] cycloadditions are explained in terms of electronic and steric effects of the methyl group(s). Various hydroazulenone cycloadducts of tricarbonyl(η⁴-2,6-dimethyltropone)iron 3a,b have been prepared by stereoselective [3+2] cycloaddition with Fp-reagents 12–14 and characterized. Formerly proposed mechanism of [3+2] cycloaddition was approved.     

二苯基膦基锂与富烯的反应—取代茂铁衍生物的合成与表征

二苯膦基锂与６，６－二甲基富烯发生环外双键的加成反应，生成含膦取代环戊二烯基负离子（Ⅰ），它与ＦｅＣｌ２络合，生成１，１＇，二（１－二苯膦基－异丙基）茂铁（Ⅱ）。（Ⅱ）与ＰｄＣｌ２（ＰｈＣＮ）２反应，生成杂双核络合物（Ⅲ）。茂铁（Ⅱ）为单斜晶系，空间群Ｐ２１／ｃ，晶胞参数ａ＝１．３３８２（５）ｎｂ，ｂ＝０．８５５０（１）ｎｍ，ｃ＝１．７３０９（４）ｎｍ，β＝１０９．１６（２）°，Ｖ＝１．８７０８２     

Synthesis, Characterization, and Fluxional Behaviour of Binuclear Palladium Complexes with a Half-A-Frame Structure

Summary.  Partial removal of chloride anions from the dimer [Pd(η³-2-CH₃*C₃H₄)(μ-Cl)]₂ with AgTf(Tf = CF₃SO₃) followed by addition of dppm affords [Pd₂(η³-Me*C₃H₄)₂(μ-Cl)(μ-dppm)]Tf (1). The substitution of Cl⁻ by X⁻ (X = pz, SC₆F₅, S _py ) using the appropriate salts yields the new derivatives [Pd₂(η³-Me*C₃H₄)₂(μ-X)(μ-dppm)]Tf (2–4). All complexes exhibit a dinuclear half-A-frame structure with two isomers present in solution. The isomers differ in the relative orientation of the two allyl groups (cis or trans). The isomer interconversion was studied by variable temperature ¹H NMR spectroscopy. The molecular structures of 2 and 4 were solved by X-ray diffraction studies. A distorted boat conformation of the seven- or six-membered metallacycle was found in both cases. Received June 7, 2000. Accepted June 20, 2000     

The synthesis of heteronuclear clusters containing cyclopentadienyl- or pentamethylcyclopentadienyliridium and ruthenium or osmium

The reaction of Cp*Ir(CO)₂ or CpIr(CO)₂ with Ru₃(CO)₁₂ under a hydrogen atmosphere afforded the heterometallic clusters Cp*IrRu₃(μ-H)₂(CO)₁₀ and CpIrRu₃(μ-H)₂(CO)₁₀, respectively, in moderate yields. In the former reaction, the tetrahydrido cluster Cp*IrRu₃(μ-H)₄(CO)₉ was also formed in trace amounts, although this cluster can be obtained in high yields by the hydrogenation of Cp*IrRu₃(μ-H)₂(CO)₁₀; the Cp analogue was not obtainable. The reaction of Os₃(μ-H)₂(CO)₁₀ with Cp*Ir(CO)₂ afforded the osmium analogue Cp*IrOs₃(μ-H)₂(CO)₁₀ in 70% yield, along with a trace amount of the pentanuclear cluster Cp*IrOs₄(μ-H)₂(CO)₁₃. Hydrogenation of Cp*IrOs₃(μ-H)₂(CO)₁₀ afforded Cp*IrOs₃(μ-H)₄(CO)₉ in excellent yield. The reaction of Cp*Ir(CO)₂ with Os₃(CO)₁₀(CH₃CN)₂ afforded the known trinuclear cluster Cp*IrOs₂(CO)₉ and the novel cluster Cp*IrOs₃(CO)₁₁. Solution-state NMR studies show that the hydrides in the iridium-ruthenium clusters are highly fluxional even at low temperatures while those in the iridium-osmium clusters are less so.