Electrochemistry of bis(indenyl)dimethylzirconium complex—the precursor of the olefin polymerization catalyst

The reduction in THF and oxidation in CH₂Cl₂ of the bent-sandwich complex (η⁵-lnd)₂ZrMe₂ (1) (Ind=C₉H₇, indenyl) were studied by cyclic voltammetry. Complex1 in THF undergoes one-electron reduction to radical anion1 ⁻, which partially decomposes with the liberation of the Ind⁻ anion. Even at −45°C the one-electron oxidation leads to the formation of an unstable 15-electron radical cation undergoing fast heterolytic decomposition to the Me^• radical and (η⁵-lnd)₂ZrMe² cation, which is the key reaction center in the catalytic polymerization of olefins. Comparative analysis of electron-transfer-induced transformations of bent-sandwich dimethyl and dichloride zirconocenes of the general formula L₂ZrX₂ (L=η⁵-lnd, η⁵-Cp: X=Xl, Me) was performed. The material of the paper was first reported at the 195th Meeting of the Electrochemical Society (see Ref. 1). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 59–62, January, 2000.     

Synthesis, crystal structure, and reduction of bis(2-phenylindenyl)hafnium dichloride

Reduction of the bent-sandwich [·⁵-(Ph)Ind]₂HfCl₂ complex (1) (where (Ph) Ind is the 2-phenylindenyl anion) in a THF medium was studied by low-temperature cyclic voltammetry. Complex1 is stable in THF at a temperature lower than −50°C and undergoes reversible one-electron reduction to radical anion1 ^{. −}. Further one-electron reduction of1 ^{. −} to dianion1 ²⁻ is accompanied by the elimination of two Cl⁻ ions to form the bisindenyl sandwich [·⁵-(Ph)Ind]₂Hf complex (2). This complex can undergo reversible one-electron reduction to the corresponding radical anion2 ^{. −}, which is stable within the cyclic voltammetry time scale. AtT=−30°C in a THF solution, complex1 was reduced to a diamagnetic (apparently, binuclear) Hf^III complex, which was characterized by cyclic voltammetry. Synthesis and the crystal structure of complex1 are reported. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2161–2165, December, 1997.     

Reaction of a naphthalene complex C10H8Yb(THF)2 with cyclopentadienyl-substituted alcohols and amines as a convenient synthetic route to the half-sandwich complexes of divalent ytterbium

The reactions of ytterbium naphthalene complex C₁₀H₈Yb(THF)₂ with 2-cyclopentadienylethanol, 1-cyclopentadienylpropan-2-ol, 3-cyclopentadienyl-1-butoxypropan-2-ol, and cyclopentadienyldimethylsilyl-tert-butylamine were studied. The bivalent ytterbium complexes with chelate bifunctional cyclopentadienyl ligands [(η⁵−C₅H₅)CH₂CH₂(η¹−O)]Yb(THF), [(η⁵−C₅H₅)CH₂CH₂(η¹−O)]Yb(DME). [(η⁵−C₅H₅)CH₂CH(Me)(η¹−O)]Yb(THF), [(η⁵−C₅H₅)CH₂CH(CH₂OC₄H₉)(η¹−O)]Yb(THF), and [(η⁵−C₅H₅)SiMe₂(η¹−N(Bu¹))]Yb(THF) were obtained and characterized. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 742–745, April, 2000.     

Synthesis,crystal structures,and redox behavior of bis(2-phenylindenyl) nickel and bis(2-phenylindenyl)zirconium dichloride

Redox reactions of the sandwich jn⁵-(Ph)Ind]₂Ni complex (1) (where (Ph)Ind is the 2-plrenylindenyl anion) in CH₂CI₂ and of the bent-sandwich (⁵-(Plr)Ind]₂ZrCl₂ complex (2) in THF have been studied by low-temperature cyclic voltammetry. Complex ( undergoes quasi-reversible two-step oxidation to cation i+ and dication 12+, which are stable at room temperature within the cyclic voltammetry time scale. Two-electron reduction of complex 1 is irreversible up to -50 °C, and this process is accompanied by destruction of the sandwich structure of the complex. Redaction of complex 2 is described by the conventional scheme for bent-sandwich complexes. According to this scheme, further one-electron reduction of radical anion 2- generates dianion 2^2–, which eliminates two CI^– ions to afford bisindcnyl sandwich complex (⁵-(Ph)lnd]₂Zr (3). This complex is stable at T < -45 °C within the cyclic voltammetry time scale and is capable of undergoing one-electron reduction to the corresponding radical anion 3-. Synthesis and crystal structures of complexes 1 and 2 are reported.Translated fromIzvestiya Akademii Nauk. Seriya Kidmicheskaya, No. 6, pp. 1529–1536, June, 1996.     

Reaction of cyclopentadienyllutetium anthracenide with azobenzene. Synthesis and molecular and crystal structure of the binuclear complex [C5H5(THF)Lu(μ−η2:η2−PhN—NPh)]2(THF)2 and its dynamic behavior in solution

The reaction of the cyclopentadienyllutetium anthracenide, C₅H₅Lu(C₁₄H₁₀)²⁻(THF)₂ (1), with azobenzene yielded the [C₅H₅(THF)Lu(μ−η²:η²−PhN—NPh)]₂(THF)₂ (2) binuclear complex. The structure of the reaction product was established by X-ray structural analysis. The dynamic behavior of complex2 in a THF-d₈ solution was studied by¹H NMR spectroscopy in the temperature range of 265–330 K. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1667–1671, September, 1997.     

Reduction of bis[(2-phosphinoethyl)tetramethyl-cyclopentadienyl]zirconium dichlorides: intramolecular C-H activation <Emphasis Type="Italic">vs.</Emphasis> stabilization of the low-valence metal center

Reduction of the R₂P-functionalized zirconocene dichlorides [C₅Me₄(CH₂)₂PR₂] (C₅Me₅)ZrCl₂ (R = Me (1) and Ph (2)) and [C₅Me₄(CH₂)₂PMe₂][C₅Me₄(CH₂)₂PR₂]ZrCl₂ (R = Me (3) and Ph (4)) with amalgamated magnesium was studied. In the reduction of compounds 1 and 2, intramolecular C-H activation highly selectively afforded the fulvene hydride complexes Zr(H)(η⁵−C₅Me₅)[η⁵:η²(C,P)−(CH₂)C₅Me₃CH₂CH₂PR₂] (R = Me (7), Ph (8)); in the case of compound 2, the aryl hydride Zr(H)(η₅:C₅Me₅)[η⁵:η¹(C)−C₅Me₄CH₂CH₂PPh(o−C₆H₄)] (9) was also formed. The reduction of complexes 3 and 4 gave the Zr^II derivatives Zr[η⁵:η¹(P)− C₅Me₄CH₂CH₂PMe₂]₂ (12) and Zr[η⁵:η₁(P)−C₅Me₄CH₂CH₂PMe₂][η⁵:η¹(P)−C₅Me₄CH₂ CH₂PPh₂] (14) stabilized by two phosphine groups. The second product in the reduction of compound 4 was the fulvene hydride complex Zr(H)(η⁵−C₅Me₄CH₂CH₂PPh₂)[η⁵:η²(C,P)−(CH₂)C₅Me₃CH₂CH₂PMe₂] (15). The reaction of compound 7 with an excess of MeI resulted selectively in replacement of the hydride ligand by iodide to give the complex ZrI(η⁵−C₅Me₅)[η⁵:η²(C,P)−(CH₂)C₅Me₃CH₂CH₂PMe₂] (10). In contrast, in the reaction of compound 7 with Me₂Si(H)Cl, the Zr-CH₂ bond underwent cleavage to give the chloride hydride complex Zr(H)Cl(η₅−C₅Me₅)[η⁵:η¹(P)−C₅Me₃(CH₂SiMe₂H)CH₂CH₂PMe₂] (11). In the reaction of complex 12 with CO, a phosphine group was replaced by CO to form the complex Zr(CO)(η5−C₅Me₄CH₂CH₂PMe₂)[η⁵:η¹(P)−C₅Me₄CH₂CH₂PMe₂] (13). The results obtained were compared with analogous reduction reactions of MeO-, MeS-, and Me₂N-functionalized zirconocene dichlorides. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 65–74, January, 2008.     

Ab initio MO LCAO SCF simulation of molecular and electronic structure of η5-π-C60H5XCp (X=Fe, Si) complexes

The problem of existence of η⁵-π-complexes of unsubstituted fullereneI _h -C₆₀ and its cyclopentadienyl type derivative C₆₀H₅ ^. is discussed.Ab initio MO LCAO SCF calculations of hypothetical sandwich systems η⁵-π-C₆₀H₅XCp (X=Fe (1a), Si (1b)), the cationic complex C₆₀FeCp⁺ of unsubstituted C₆₀, and the C₆₀H₅ ^. radical were performed in the STO-3G and 3-21G basis sets. In the1a, 1b, and C₆₀H₅ ^. systems, hydrogen atoms are attached to carbon atoms of fullerenei _h -C₆₀ at α-positions relative to the same pentagonal face (pent ^*). In η⁵-complexes, XCp species are also coordinated to this face. According to calculations in the 3-21G basis set, the Fe-pent ^* bond energy in complex1a is much higher than those of similar bonds in1b and in the η⁵-π-C₆₀FECp⁺ cation (117 kcal mol⁻¹ vs. 37 and 64 kcal mol⁻¹, respectively) and is 7 kcal mol⁻¹ higher than the Fe−Cp bond energy in the classical sandwich system FeCp₂. The Fe…C _pent* and Fe…C_Cp distances in complex1a are slightly shorter than the Fe…C distance in the ferrocene molecule. The spin populations in the C₆₀H₅ ^. radical are almost completely localized on the atoms of thepent ^* face, which must favor the formation of η⁵-π-complexes of this radical. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1657–1662, September, 1999.     

Reactivity of 17- and 19-electron organometallic complexes. Formation of bent sandwich 19-electron radical cation complexes of ruthenium and osmium

The redox behavior of sandwich indenyl complexes of the general formula (⁵-C₉H₇)ML (M=Ru and L=⁵-C₉H₇ (1), ⁵-C₅H₅ (2), ⁵-C₅Me₅ (3); M=Os, L=⁵-C₉H₇ (4)) has been studied in THF, MeCN, and CH₂Cl₂ by cyclic voltammetry and controlled potential electrolysis on a Pt electrode in the –85 to +20 °C temperature range. The title complexes have been found to undergo reversible one-electron oxidation to the corresponding radical cations, whose stabilities and reactivities depend on the nature of both the metal and °-ligands and of the nucleophilic properties of the solvent. The fast interaction of the electrogenerated 17-electron radical cations with nucleophiles yields bent sandwich 19-electron radical cations, [(⁵-C₉H₇)M(L)(Nu)]⁺ (Nu = Cl^–, MeCN, or THF), the latter undergoing one-electron oxidation to the corresponding [(⁵-C₉H₇)M(L)(Nu)]²⁺ dications. In the case of Nu=THF, the reaction of the electrogenerated 17-electron radical cations with nucleophiles appears to be reversible. Radical cations [(⁵-C₉H₇)₂M]^+· (M=Ru, Os) have been characterized by ESR spectra.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2394–2399, December, 1995.     

π-dimerization of pleiadiene radical cations at low temperatures revealed by UV–vis spectroelectrochemistry and quantum theory

One-electron oxidation of the non-alternant polycyclic aromatic hydrocarbon pleiadiene and related cyclohepta[c,d]pyrene and cyclohepta[c,d]fluoranthene in THF produces corresponding radical cations detectable in the temperature range of 293–263 K only on the subsecond time scale of cyclic voltammetry. Although the EPR-active red-coloured pleiadiene radical cation is stable according to the literature in concentrated sulfuric acid, spectroelectrochemical measurements reported in this study provide convincing evidence for its facile conversion into the green-coloured, formally closed shell and, hence, EPR-silent π-bound dimer dication stable in THF at 253 K. The unexpected formation of the thermally unstable dimeric product featuring a characteristic intense low-energy absorption band at 673 nm (1.84 eV; logε _max = 4.0) is substantiated by ab initio calculations on the parent pleiadiene molecule and the PF₆⁻ salts of the corresponding radical cation and dimer dication. The latter is stabilized with respect to the radical cation by 14.40 kcal mol⁻¹ (DFT B3LYP) [37.64 kcal mol⁻¹ (CASPT2/DFT B3LYP)]. An excellent match has been obtained between the experimental and TD-DFT-calculated UV–vis spectra of the PF₆⁻ salt of the pleiadiene dimer dication, considering solvent (THF) effects.     

Photochemical substitution of benzene in the iron cyclohexadienyl complex [(η<Superscript>5</Superscript>-C<Subscript>6</Subscript>H<Subscript>7</Subscript>)Fe(η-C<Subscript>6</Subscript>H<Subscript>6</Subscript>)]<Superscript>+</Superscript>

The visible light irradiation of the [(η⁵-C₆H₇)Fe(η-C₆H₆)]⁺ cation (1) in acetonitrile resulted in the substitution of the benzene ligand to form the labile acetonitrile species [(η⁵-C₆H₇)Fe(MeCN)₃]⁺ (2). The reaction of 1 with Bu^tNC in MeCN produced the stable isonitrile complex [(η⁵-C₆H₇)Fe(Bu^tNC)₃]⁺ (3). The photochemical reaction of cation 1 with pentaphosphaferrocene Cp*Fe(η-cyclo-P₅) afforded the triple-decker cation with the bridging pentaphospholyl ligand, [(η⁵-C₆H₇)Fe(μ-η:η-cyclo-P₅)FeCp*]⁺ (4). The latter complex was also synthesized by the reaction of cation 2 with Cp*Fe(η-cyclo-P₅). The structure of the complex [3]PF₆ was established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2088–2091, November, 2007.