Kinetics of η6→η5 isomerization of (η6-fluorenyl)(η5-cyclopentadienyl)iron

The kinetics of the reversible isomerization of the zwitterionic complex [(⁶-C₁₃H₉)Fe(⁵-C₅H₅)] (1) into dibenzoferrocene (2) was studied by electronic spectroscopy in the temperature range from 70 to 103 °C. The activation parameters of the reaction 1 2 were determined, E _a = 22.5 kcal mol^–1.     

Nature of low-lying electron excited states of (η5-cyclopentadienyl) (η7-cycloheptatrienyl)niobium

Electron absorption spectra of (⁵-cyclopentadienyl)(⁷-cycloheptatrienyl)niobium in solution and in the vapor phase have been measured for the first time. Possible variants of the band assignment for the spectrum of the complex in a solution have been considered. In the spectrum of the vaporous compound the bands at 29570, 31730, and 34630 cm^–1 correspond to the electron transitions from the 4d(⁺) orbital to the lowest Rydberg p- and d-levels. The values of Rydberg transition terms and symmetry of p-states have been determined.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 634–638, April, 1994.The author is grateful to I. L. Fedyushkin for the synthesis of complex 1.     

Exo-H- andendo-H-η4-pentamethylcyclopentadiene complexes of platinum

A mixture ofendo-H andexo-H isomers (1a and1b) of the (⁴-C₅Me₅H)PtCl₂ complex was prepared by the reaction of K₂PtCl₄ with C₅Me₅H in MeOH. The mixture of isomers reacts with CpTl in the presence of TiBF₄ to give a novel complex, [(⁴-C₅Me₅H)Pt(⁵-C₅H₅)]⁺BF₄ ^–, as a mixture ofendo-H- andexo-H-isomers (2a and2b). The data of¹H and¹³C NMR spectroscopy of the resulting complexes are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 514–517, March, 1994.     

Synthesis and reactions of dicarbonyl (η2-indene)-η5-indenyl complexes of manganese and rhenium

Photochemical reactions of M(CO)₃(⁵-C₉H₇), where M=Mn (1) or Re (2), with indene have produced ²-indene complexes M(CO)₂(²-C₉H₈)(⁵-C₉H₇), where M=Mn (3) or Re (4). Deprotonation of complex3 witht-BuOK in THF at –60 °C gives the anion [Mn(CO)₂(¹-C₉H₇)(⁵-C₉H₇)^– (5), in which there occurs a rapid interchange of the Mn(CO)₂(⁵-C₉H₇) group between positions 1 and 3 in the ¹-indenyl ligand. The reaction of complex4 with Ph₃CPF₆ in CH₂Cl₂ at 0 °C leads to the complex [Re(CO)₂(³-C₉H₇)(⁵-C₉H₇)PF₆, whereas the similar reaction of complex3 gives only decomposition products even at –20 °C.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1280–1285, July, 1993.     

Vapor-phase electronic absorption spectrum of (η5-cyclopentadienyl)(η5-cycloheptatrienyl)chromium

The UV and visible absorption spectra of (Cp)(Ch)Cr (Cp = η⁵-C₅H₅, Ch = η⁷-C₇H₇) vapor show surprisingly well-resolved Rydberg structure. The first ionization potential (5.603 ± 0.007 eV) has been determined as a convergence limit of three Rydberg series. (Cp)(Ch)Cr is the first sandwich complex in which the lowest Rydberg transitions terminating at ns and np(σ) orbitals have vibrational structure.     

Synthesis and molecular structure of (η-pentamethyl-cyclopentadienyl) (η-cyclopentadienyl) hexacarbonyl molybdenum tungsten

The metathesis reaction of Cp*(CO)₃MoBr and NaW(CO)₃Cp produced Cp*(CO)₃Mo-W(CO)₃Cp (1), featuring an unsupported Mo-W bond. Exposure of solutions of 1 to light leads to the quantitative formation of the corresponding homometallic dimers. In the solid state, the title complex exhibits an anti-arrangement of the η⁵-cyclopentadienyl and the η⁵-pentamethyl-cyclopentadienyl ligands and six terminal carbonyls. Comparison to corresponding complexes of molybdenum and tungsten reveals that the Mo-W distance is dictated by the presence of a Cp and a Cp* ligand. This is the first time that an unsupported Mo-W single bond distance is reported.     

μ-η6,η6-Arene-bridged diuranium hexakisketimide complexes isolable in two states of charge

Diuranium μ-η(6),η(6)-arene complexes supported by ketimide ligands were synthesized and characterized. Disodium or dipotassium salts of the formula M(2)(μ-η(6),η(6)-arene)[U(NC(t)BuMes)(3)](2) (M = Na or K, Mes = 2,4,6-C(6)H(2)Me(3)) and monopotassium salts of the formula K(μ-η(6),η(6)-arene)[U(NC(t)BuMes)(3)](2) (arene = naphthalene, biphenyl, trans-stilbene, or p-terphenyl) were both observed. Two different salts of the monoanionic, toluene-bridged complexes are also described. Density functional theory calculations have been employed to illuminate the electronic structure of the μ-η(6),η(6)-arene diuranium complexes and to facilitate the comparison with related transition-metal systems, in particular (μ-η(6),η(6)-C(6)H(6))[VCp](2). It was found that the μ-η(6),η(6)-arene diuranium complexes were isolobal with (μ-η(6),η(6)-C(6)H(6))[VCp](2) and that the principal arene-binding interaction was a pair of δ bonds (total of 4e) involving both metals and the arene lowest unoccupied molecular orbital. Reactivity studies have been carried out with the mono- and dianionic μ-η(6),η(6)-arene diuranium complexes, revealing contrasting modes of redox chemistry as a function of the system's state of charge.     

Synthesis and H NMR spectroscopic properties of substituted (η-tetraarylcyclobutadiene)(η-cyclopentadienyl)cobalt metallocenes

The reaction of diarylacetylenes with CoCl(PPh₃)₃ and sodium cyclopentadienylide or sodium carbomethoxycyclopentadienylide gave (η⁴-tetra-arylcyclobutadiene)(η⁵-cyclopentadienyl)cobalt and (η⁴-tetra-arylcyclobutadiene)(η⁵-carbomethoxycyclopentadienyl)cobalt, respectively, where aryl = para-XC₆H₄ (X = CF₃, F, MeO). The reaction was unsuccessful for the synthesis of (η⁴-tetra(para-methoxyphenyl)cyclobutadiene)(η⁵-cyclopentadienyl)cobalt, which was synthesised instead from dicarbonyl(η⁵-cyclopentadienyl)cobalt. In all of the examples starting with CoCl(PPh₃)₃ an intermediate (η⁵-cyclopentadienyl)- or (η⁵-carbomethoxycyclopentadienyl)(triphenylphosphine)-2,3,4,5-tetraarylcobaltacyclopentadiene complex was isolated, and two examples were characterised by X-ray crystallography. Heating the (η⁵-cyclopentadienyl)- or (η⁵-carbomethoxycyclopentadienyl)(triphenylphosphine)-2,3,4,5-tetraarylcobaltacyclopentadiene complexes resulted in clean conversion to the corresponding metallocenes. The influence of the para-aryl substituents on the ¹H NMR of the cyclopentadienyl moiety is tabulated, together with the influence of a range of R substituents in (η⁴-tetraphenylcyclobutadiene)(η⁵-RC₅H₄)cobalt (R = CO₂Me, CH₂OH, Me, CHO, CCH, CO₂H, CN, CONHR¹, 2-oxazolinyl, NH₂, NHAc, HgCl, Br, I, SiMe₃, SnMe₃, Ph).     

Nitroxide-mediated photo-living radical polymerization of methyl methacrylate in the presence of (η6-benzene)(η5-cyclopentadienyl)FeII hexafluorophosphate

The photoradical polymerization of methyl methacrylate (MMA) was performed at room temperature using (2RS,2’RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) as the initiator and 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MTEMPO) as the mediator in the presence of (η⁶-benzene)(η⁵-cyclopentadienyl)Fe^II hexafluorophosphate (BzCpFe^II). The bulk polymerization provided narrower molecular weight distributions (Mw/Mn = 1.4 − 1.5) than the solution polymerization in acetonitrile, although BzCpFe^II was insoluble in MMA. The polymerization rate was retarded by an increase in the amount of BzCpFe^II. BzCpFe^II, which had no ability to control the molecular weight by itself, could control it through the interaction with MTEMPO. The interaction of BzCpFe^II and MTEMPO was attributed to the electron transfer involving the MTEMPO–aminoxy anion redox system and the iron redox system. The polymerization was confirmed to occur in accordance with a living mechanism because linear correlations were obtained for both the plots of the first order time–conversion and the conversion–molecular weight.     

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.     

Synthesis, reactivity and structural studies of (η-methylcyclopentadienyl)(η-tetraphenylcyclobutadiene)cobalt and its derivatives

(η⁵-methylcyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt (1) and its derivatives, [(1-acetyl-2-methyl)η⁵-cyclopentadienyl](η⁴-tetraphenylcyclobutadiene)cobalt (2) [(1-acetyl-3-methyl)η⁵-cyclopentadienyl](η⁴-tetraphenylcyclobutadiene)cobalt (3) [(1-carbomethoxy-2-methyl)η⁵-cyclopentadienyl](η⁴-tetraphenylcyclobutadiene)cobalt (4) and [(1-carbomethoxy-3-methyl)η⁵-cyclopentadienyl](η⁴-tetraphenylcyclobutadiene) cobalt (5) have been prepared in yields varying from 11% to 28% by introducing the substituents on the cyclopentadienyl ring of methylcyclopentadienyl sodium and then reacting with diphenylacetylene and CoCl(PPh₃)₃. The carboxylic acids [(1-carboxy-2-methyl)η⁵-cyclopentadienyl](η⁴-tetraphenylcyclobutadiene)cobalt (6), [(1-carboxy-3-methyl)η⁵-cyclopentadienyl](η⁴-tetraphenylcyclobutadiene)cobalt (7) have been prepared after ester hydrolysis of compounds 4 and 5 using KOH/ethanol. [(1-dimethylaminomethyl-3-methyl)η⁵-cyclopentadienyl](η⁴-tetraphenylcyclobutadiene) cobalt (8), was prepared selectively by direct substitution on the cyclopentadienyl ring of (η⁵-methylcyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt in 65% yield. The 1,2-isomer was formed only in traces in this reaction. Reactivity of (η⁵-methylcyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt and its carbomethoxy derivative have been compared with (η⁵-cyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt. All new compounds were characterized by ¹H and ¹³C NMR, FT-IR, mass spectra and CHN analysis. Compounds 2, 4, 6 and 8 have also been structurally characterized by single crystal X-ray structural analysis.     

Acetylation and benzoylation of η5,η5-fulvalenedimanganesehexacarbonyl

⁵,⁵-Fulvalenedimanganesehexacarbonyl (dicymantrenyl) was acetylated and benzoylated by RC(O)Cl+AlCl₃ in CH₂Cl₂, under conditions of the Friedel-Crafts reaction. The reaction involves both nonequivalent positions of the cyclopentadienyl rings to give mixtures of two isomeric ketones. When using an excess of the acetylating mixture, diacetyl derivatives of dicymantrenyl were obtained.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2017–2020, October, 1995.The authors are grateful to P. V. Petrovsky and E. V. Vorontsov (the NMR laboratory of the Institute of Organoelement Compounds, Russian Academy of Sciences) for recording¹H NMR spectra.     

Diastereoselectivity of the formation of planar chiral ruthenocenol in reactions of chiral tertiary phosphines with the (η4-cyclopentadienone)(η5-cyclopentadienyl)ruthenium cation

The reactions of chiral benzyl- and ethyl(phenyl)ferrocenylphosphines with (acetonitrile)(⁴-cyclopentadienone)(⁵-cyclopentadienyl)ruthenium trifluoromethylsulfonate proceed diastereoselectively through the attack on the cyclopentadienone ring to form planar chiral 2-phosphonioruthenocenols as mixtures of two diastereomers in ratios of 1.7 : 1 and 2 : 1, respectively.     

Reactions of [η-carboxycyclopentadiene][η-tetraphenylcyclo butadiene] cobalt with alkyl and aryl tin oxides: Synthesis, structural studies and electrochemistry of novel monomeric and dimeric [η-carboxycyclopentadiene][η-tetraphenylcyclobutadiene]cobalt based stannoxanes

Reactions of [η⁵-carboxycyclopentadienyl][η⁴-tetraphenylcyclobutadiene] cobalt, Ph₄C₄CoC₅H₄COOH (1), with (Ph₃Sn)₂O, [(n-Bu)₂SnO]_n and (Ph₂SnO)_n in refluxing toluene resulted in the formation of the monomeric compound Ph₃SnOC(O)C₅H₄CoC₄Ph₄ (2) and dimeric compounds n-Bu₂Sn[OC(O)C₅H₄CoC₄Ph₄]₂ (3) and Ph₂Sn[OC(O)C₅H₄CoC₄Ph₄]₂ (4), respectively. Reactions carried out in the solid state by mechanical grinding also yielded same results. Crystal structure determination and cyclic voltammetric studies of compounds 1, 2, 3 and 4 have been carried out and compared with similar ferrocene carboxylic acid derivatives. The structures and electrochemistry of these compounds are compared with analogous organotin ferrocene carboxylates. The results obtained from the reaction of 1 with alkyl and aryl tin oxides suggest that the formation of stannoxanes assemblies having more than two carboxylate units are not favored indicating that 1 is a highly sterically hindered metallocene carboxylic acid.     

Insertion of alkynes into the heterocycle of (η-pentaalkyl-2,3-dihydro-1,3-diborolyl)(η-pentamethylcyclopentadienyl)ruthenium: Formation and characterization of 4-borataborepine ruthenium complexes

The violet ruthenium complex [(η⁵-C₅Me₅)Ru(η⁵-C₃B₂Me₄R¹)] (2a, R¹ = Me) reacts with terminal alkynes R²CCH to give yellow 4-borataborepine compounds [(η⁵-C₅Me₅)Ru{η⁷-(MeC)₃(R¹B)₂(R²C₂H)}] (4c, R¹ = Me, R² = Ph; 4d, R¹ = Me, R² = SiMe₃; 4e, R¹ = Me, R² = H). The insertion of alkynes into the folded C₃B₂ heterocycle of 2a causes some steric hindrance, which yields with elimination of the distant boranediyl group the corresponding boratabenzene complexes 5 as byproducts. The analogous reactions with internal alkynes R²CCR² proceed slowly and afford predominantly the boratabenzene complexes [(η⁵-C₅Me₅)Ru{η⁶-(MeC)₃(MeB)(R²C)₂}] (5f, R² = Et, 5g, R² = p-tolyl), respectively. In the latter case, three byproducts are formed: methylboronic acid and 1,2,3,4-tetra-p-tolyl-1,3-butadiene (9) due to hydrolysis of the postulated 2,3,4,5-tetra-p-tolyl-1-methylborole (10) and unexpectedly, the cationic triple-decker complex [{(η⁵-C₅Me₅)Ru}₂{μ,η⁷-(MeC)₃(MeB)₂(CH)₂}]Cl (11) having two separated CH groups. The new compounds were characterized by NMR, MS, and single-crystal X-ray studies of 4c, 5f, 9 and 11.     

Inter-ring η6⇌η5 haptotropic rearrangements of 18ē and 19ē (η5-pentamethylcyclopentadienyl)(η6-9-methylfluorenyl)iron complexes

New cationic complexes [(⁶-C₁₃H₁₀)Fe(⁵-Cp^*)]PF₆ and [(⁶-9-CH₃-C₁₃H₉)Fe(⁵-Cp^*)]PF₆ were obtained by the reaction of Cp^*Fe(CO)₂Br with fluorene and 9-methylfluorene, respectively. Deprotonation of these complexes byt-BuOK in THF affords zwitter-ionic compounds (⁶-C₁₃H₉)Fe(⁵-Cp^*) and (⁶-9-CH₃-C₁₃H₈)Fe(⁵-Cp^*) (A). WhenA is heated in nonane at 150 °C it undergoes ⁶⁵ inter-ring rearrangement with the formation of hexamethyldibenzoferrocene (B). The electrochemical behavior ofA andB was studied by cyclic voltammetry. One-electron reduction ofA andB to the corresponding radical anions induces inter-ring haptotropic rearrangementA ^.–B ^.–. The equilibrium in the 19 state is shifted to the ⁶-isomeric radical anionA ^.–, while in the 18 precursors, it shifts to the ⁵-isomerB.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 319–324, February, 1994.The authors are grateful to D. V. Zagorevskii (A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences) for recording and interpreting the mass spectra, and to A. A. Borisenko (Moscow State University) for recording the NMR spectra.This work was financially supported by the Russian Foundation for Basic Research (Grant 93-03-5209).     

Oxidative dinuclear addition of a PdI-PdI moiety to arenes: generation of μ-η3:η3-arene-Pd(II)2 species

We report the oxidative dinuclear addition of a Pd(I)-Pd(I) bond to arenes. The oxidative dinuclear addition products, which have a bi-π-allyl-type arene dipalladium(II) structure, were obtained from [2.2]paracyclophane, anthracene, tetracene, and pentacene. A systematic study of the reaction of [Pd(2)(CH(3)CN)(6)][BF(4)](2) with benzene and polyacenes showed that the larger polyacenes, tetracene and pentacene, afforded the oxidative dinuclear addition products, while benzene, naphthalene, and anthracene gave the π-sandwich Pd(I)-Pd(I) complexes.     

η3-Propargyl complexes of molybdenum, tungsten, and rhenium

The reactions of the Me _n C₆H_6−n M(CO)₃ (M=Cr, Mo, W;n=3, 5, 6) and C₅R₅M(CO)₃ (M=Mn, Re; R=H, Me) complexes with propargyl alcohol in acidic media under UV irradiation were studied. Novel Me _n C₆H_6−n M(CO)₂(η³-C₃H₃)BF₄ (M=Mo, W;n=3, 5, 6) and C₅R₅Re(CO)₂(η³-C₃H₃)CF₃SO₃ complexes with the 3ē-propargyl ligand were synthesized, and their properties compared with those of similar η³-allyl derivatives. The structure and dynamic propeties of the compounds obtained are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1796–1803, September, 1999.     

Regioselective, stereoselective, and conformationally controlled synthesis of (η4-tetraarylcyclobutadiene)(η5-carbomethoxycyclopentadienyl)cobalt metallocenes

The Friedel-Crafts reaction of (η(4)-tetraphenylcyclobutadiene)(η(5)-carbomethoxycyclopentadienyl)cobalt with acid chlorides/aluminum chloride resulted exclusively in para-phenyl acylation. Both monoacylated (1.1 equiv of RCOCl/AlCl(3)) and tetraacylated products (>4 equiv of RCOCl/AlCl(3)) were synthesized. Reaction of PhCC(o-RC(6)H(4)) (R = Me, i-Pr) with Na(C(5)H(4)CO(2)Me) and CoCl(PPh(3))(3) gave predominantly (η(4)-1,3-diaryl-2,4-diphenylcyclobutadiene)(η(5)-carbomethoxycyclopentadienyl)cobalt metallocenes (1,3-[trans] vs 1,2-[cis] selectivity up to 6:1). Conformational control of Friedel-Crafts reactions on the major isomers gave exclusively para-acylation of the unsubstituted phenyl groups.     

Kinetics and Mechanism of Thermal Decomposition of Bis(η3-Allyl)Nickel Complexes

Kinetics and Catalysis - The kinetics of thermal decomposition of bis(η3-allyl) nickel complexes in various media is studied. The specific features of the mechanism are determined, including...