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.     

Oxidation of isomeric η6- and η5-fluorenylchromiumtricarbonyl anions

The oxidation of the carbon-centered [(⁶-C₁₃H₉)Cr(CO)₃]^– anion (1 ^–) results in formation of (-⁶:⁶-9,9-bifluorenyl)bis-chromiumtricarbonyl (3) due to coupling of the intermediate carbon-centered radical (1^.). The oxidation of the metal-centered anion [(⁵-C₁₃H₉)Cr(CO)₃]^– (2 ^–), which is isomeric to the 1^– anion, gives an equilibrium mixture of the chromium-centered radical {(⁵-C₁₃H₉)Cr(CO)₃}^. (2 ^.) and its dimer [(⁵-C₁₃H₉)Cr(CO)₃]₂ (6). Radical2 ^. readily reacts with MeI and the solvent (THF); the resulting derivatives, (⁵-C₁₃H₉)Cr(CO)₃R (R=Me (10); R=H (7)), undergo fast ricochet inter-ring ⁵⁶ rearrangements into (⁶-9R-C₁₃H₉)Cr(CO)₃ (R=CH₃ (9); R=H (4)).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1354–1358, July, 1995.The authors are grateful to D. V. Zagorevskii who recorded the mass spectra. This study was financially supported by the Russian Foundation for Basic Research (Grant No. 94-03-05209) and the International Science Foundation (Grant Nos. MQ 4000 and REV 000).     

The interconversion of η5 and η3 hapticities in cycloheptadienyl complexes of molybdenum and tungsten

[Mo(CO)₄(η⁵-C₇H₉)]⁺ (1) reacts with acetonitrile to give [Mo(CO)₂(NCMe)₃(η³-C₇H₉)]⁺ (3), which is precursor of a wide reange of η⁵-cycloheptadienyl complexes [Mo(CO)₂L₂(η⁵-C₇H₉)]⁺ [6, L = PPH₃; 7, L₂ = Ph₂PCH₂PPh₂; 8, L₂ = 1,3-cyclohexadiene; 9, L₂ = 2,2′-dipyridyl]; 9 reacts reversibly with NCMe to give [Mo(CO)₂(NCMe)(dipy)(η³-C₇H₉)]⁺ (10).     

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).     

Bonding situation and stability of η1- and η6-bonded heteroarene complexes M(η1-EC5H5)6 and M(η6-EC5H5)2 (M = Cr,Mo, W; E = N,P, As,Sb, Bi)

Density functional calculations at the BP86/TZ2P level are reported for the pseudo-octahedral heteroarene complexes M(η¹-EC₅H₅)₆ and for the sandwich complexes M(η⁶-EC₅H₅)₂ (M = Cr, Mo, W; E = N, P, As, Sb, Bi). The complexes M(CO)₆ and M(η⁶-C₆H₆)₂ have been calculated for comparison. The nature of the metal–ligand interactions was analyzed with the EDA (energy decomposition analysis) method. The calculated bond dissociation energies (BDE) of M(η¹-EC₅H₅)₆ have the order for E = P > As > N > Sb ? Bi and for M = Cr < Mo < W. All hexaheteroarenes bind more weakly than CO in M(CO)₆. Except for pyridine, which is the weakest η⁶-bonded ligand, the trend in the BDE of the M(η⁶-EC₅H₅)₂ complexes is opposite to the trend of the M(η¹-EC₅H₅)₆ complexes NC₅H₅ < PC₅H₅ < AsC₅H₅ < SbC₅H₅ < BiC₅H₅. The opposite trend is explained with the different binding modes in M(η⁶-EC₅H₅)₂ and M(η¹-EC₅H₅)₆. The bonding in the former complexes mainly takes place through the π electrons of the ligand which are delocalized over the ring atoms while the bonding in the latter takes place through the lone-pair electrons of the heteroatoms E. The Lewis basicity of the group-15 heterobenzenes EC₅H₅ becomes weaker for the heavier elements E. The occupied π orbitals of the heterobenzene ring become gradually more polarized toward the five carbon atoms in the heavier arenes EC₅H₅ which induces stronger metal-carbon bonds in M(η⁶-EC₅H₅)₂ and weaker metal-E bonds. The EDA calculations show that the nature of the M-EC₅H₅ bonding in M(η¹-EC₅H₅)₆ is similar to the M–CO bonding in M(CO)₆. Both types of bonds have a slightly more covalent than electrostatic character. The π orbital interactions in the chromium and molybdenum complexes of CO and heterobenzene are more important than the σ interactions. This holds true also for the tungsten complexes of CO and the lighter heteroarenes while the σ- and π-bonding in the heavier W(η¹-EC₅H₅)₆ species have similar strength. The EDA results also show that the nature of the bonding in the sandwich complexes M(η⁶-EC₅H₅)₂ is very similar to the bonding in the bisbenzene complexes M(η⁶-C₆H₆)₂. The orbital interactions contribute for all metals and all arene ligands about 60% of the attractive interactions while the electrostatic attraction contributes about 40%. The largest contribution to the orbital term comes always from the δ orbitals. The calculations predict that the relative stability of the sandwich complexes M(η⁶-EC₅H₅)₂ over the octahedral species M(η¹-EC₅H₅)₆ increases when E becomes heavier and it increases from W to Mo to Cr when E = N, P, As.     

Synthesis,characterization, and reactivity of ruthenium(II) complexes containing η6-arene-η1-pyrazole ligands

New ruthenium(II) complexes containing η⁶-arene-η¹-pyrazole ligands were synthesized and characterized by elemental analysis and spectroscopic methods. In addition, the molecular structure of dichloro-3,5-dimethyl-1-(pentamethylbenzyl)-pyrazole–ruthenium(II), [Ru]L_3b, was determined by X-ray diffraction studies. These complexes were applied in the transfer hydrogenation of acetophenone by isopropanol in the presence of potassium hydroxide. The activities of the catalysts were monitored by NMR.     

Acetylation of α- and β-cyclodextrines

Applying acetyl chloride and versatile bases and solvents per- and regioacetylated derivatives of α- and β-cyclodextrines were prepared. Conditions were established for performing regiodirected acetylation of the primary hydroxy groups of α- and β-cyclodextrines in the presence of free secondary hydroxy groups.     

The formation,crystal and molecular structures of bis(η5-indenyl)dicarbonyltitanium and bis(η5-indenyl)dicarbonylzirconium

Bis(η⁵-indenyl)dicarbonyltitanium has been produced in 47% yield by reduction of bis(η⁵-indenyl)dichlorotitanium with activated aluminum in THF solution under a carbon monoxide atmosphere. Bis(η⁵-indenyl)dicarbonylzirconium can similarly be prepared in 45% yield by the reductive carbonylation of bis(η⁵-indenyl)dichlorozirconium using activated magnesium turnings. IR spectral evidence has been obtained for the corresponding hafnium analog, although it could not be isolated. Detailed syntheses for the precursors (η⁵-indenyl)₂MCl₂ (M = Ti, Zr, Hf) have been developed. Bis(η⁵-indenyl)dicarbonyltitanium crystallizes in the monoclinic space group C2/c with unit cell parameters a 30.435(8), b 7.357(5), c 28.279(8) Å and β 90.93(5)°. Refinement of 3530 observed reflections lead to final agreement indices of R = 0.052 and R_w = 0.049. Bis(η⁵-indenyl)dicarbonylzirconium crystallizes in the monoclinic space group P2₁/n with unit cel parameters of a 7.288(5), b 14.398(8), c 15.273(7) Å and β 89.84(5)°. Refinement of 2253 observed reflections lead to final agreement indices of R = 0.049 and R₂ = 0.055.     

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.     

Synthesis and structures of the η5-C5H5Cl(CO)2W-η1,η5-(PPh2)C5H4(CO)2Fe-η1,η5-C5H4Mn(CO)3 and MeSi[C5H4(CO)2Fe-η1,η5-C5H4Mn(CO)2PPh3]3 complexes

The metallation of the η⁵-C₅H₅(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₃ complex with BuⁿLi (THF, ?78 °C) followed by the treatment of the lithium derivative with Ph₂PCl afforded the η⁵-Ph₂PC₅H₄(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₃ complex. The reaction of the latter with η⁵-C₅H₅(CO)₃WCl in the presence of Me₃NO produced the trinuclear complex η⁵-C₅H₅Cl(CO)₂W-η¹,η⁵-(Ph₂P)C₅H₄(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₃. The structure of the latter complex was established by IR, UV, and 1H and ³¹P NMR spectroscopy and X-ray diffraction. The reaction of MeSiCl₃ with three equivalents of LiC₅H₄(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₂PPh₃ gave the hexanuclear complex MeSi[C₅H₄(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₂PPh₃]₃.     

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.     

Acid-catalysed ketone rearrangements of t-butanoyl substituted η6-arene-η5-cyclopentadienyliron(II) cations

The t-butanoyl substituent of η⁶-benzene-η⁵-t-butanoylcyclopentadienyliron(II) hexafluorophosphate rearranges to a 3-methylbutan-2-oyl group under the influence of electrophilic catalysts such as AlCl₃ or CF₃SO₃H. This typical rearrangement of α-branched ketones has been studied in several acids, and the rates are compared to those for the analogous rearrangement of the uncomplexed t-butyl phenyl ketones. The presence of the C₆H₆Fe⁺ group markedly increases the rate of reaction. η⁶-t-Butanoylbenzene-η⁵-cyclopentadienyliron(II) hexafluorophosphate was also found to undergo a similar rearrangement, but there was a major competing reaction involving loss of the t-butanoyl substituent. The presence of the (arene)Fe⁺(cp) group causes a 10⁴–10⁵ fold increase in the rate of the rearrangement.     

Redox-induced η5 ⇔ η3 haptotropy of the fluorenyl ligand in 9-substituted η5-fluorenylmanganesetricarbonyl complexes

It has been shown by cyclic voltammetry in THF within the –90 to 40 °C temperature range that fluorenyl (⁵-9-R-C₁₃H₈)Mn(CO)₃ complexes (R=Bu^t (3) and Ph (4)) undergo two-electron reduction to form allyl type [(³-9-R-C₁₃H₈)Mn(CO)₃]^2– dianions as final products. At low temperatures complexes3 and4 are reduced in two one-electron steps according to the EEC-scheme. The first step is reversible and corresponds to the formation of 19-radical anions 3^–. and 4^–.. TheE ⁰ values for redox pairs3 ^0/–. and4 ^0/–. are –1.88 and –1.73 V, respectively. The further reduction of radical anions3 ^–. and4 ^–. at more negative potentials is accompanied by fast ^{5 3} haptocoordination of the fluorenyl ligand to form 18-dianions [(³-9-R-C₁₃H₈)Mn(CO)₃]^2–. These dianions obtained by the reduction of complexes3 and4 by the radical anion of pyrene are stable at –80 °C and are characterized by their IR spectra. At room temperature the ^{5 3} hapticity change is a fast and reversible process occurring at the step of 19-radical anions3 ^–. and4 ^–. and leading to the electron deficient 17-species [(³-9-R-C₁₃H₈)Mn(CO)₃]^–., which are reduced easier than the initial complexes. As a result, complexes3 and4 are reduced to the corresponding dianions [(³-9-R-C₁₃H₈)Mn(CO)₃]^2– at room temperature in one reversible two-electron step according to the ECE-scheme. Reactivities of 19e^–-species of the isomeric ⁵- and ⁶-fluorenylmanganesetricarbonyl complexes are compared.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1347–1353, July, 1995.The work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-05209) and the International Science Foundation (Grant No. REV 000).     

New preparation of alkyl- and aryl-mono-η5-cyclopentadienylphosphine compounds or iron,cobalt and nickel

Tertiary phosphine stabilized homoleptic alkyl and aryl compounds of Fe, Co and Ni undergo protonolysis of their MC bonds with cyclopentadiene to produce the corresponding mono-η⁵-cyclopentadienyl complexes. Initial low reaction temperatures and the presence of phosphine ligands prevent the formation of metallocenes. This method allows the easy introduction of various achiral and chiral ligands into complexes of this class.     

Migration of the η1:η6-C6H5Cr(CO)3 ligand into the cyclopentadienyl ring during metallation of the η5-C5H5(CO)2Fe η1:η6-C6H5Cr(CO)3 binuclear complex

It was found that the ¹⁶-C₆H₅Cr(CO)₃ ligand migrates into the cyclopentadienyl ring when the ⁵-C₅H₅(CO)₂Fe ¹⁶-C₆H₅Cr(CO)₃ binuclear complex is metallated with BuⁿLi. Under the same conditions, no migration of the phenyl ligand in the ⁵-C₅H₅(CO)₂Fe ¹-C₆H₅ complex was observed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 325–326, February, 1994.     

Synthesis,Structure,and Ring-opening Metathesis Polymerization of η~5-Pentamethylcyclopentadienyl-(η~5-exo-tricyclo [5.2.1.0~(2,6)]deca-2,5,8-trien-6-yl) Iron

η5-Pentamethylcyclopentadienyl-(η5-exo-tricyclo[5.2.1.02,6]deca-2,5,8-trien-6-yl) iron(3) was synthesized and characterized by 1H NMR, 13C NMR, MS, elemental analysis, IR, UV and X-ray diffraction analysis. Compound 3 was polymerized with ring-opening metathesis polymerization(ROMP) initiator (PCy3)2Cl2Ru=CHPh. 1H NMR and IR spectra revealed the presence of CH=CH units in the polymer and supported the ROMP mechanism. GPC analysis of the polymer showed that the weight-average molecular weights(Mw) was 5967, ...     

Synthesis, NMR and quantum chemical studies of the [Cp3Rh3Se2]2+ clusters (Cp = η5-C5Me5, η5-C5Me4Et, η5-C5H3 t Bu2)

Reactions of [CpRhCl₂]₂ (Cp = η⁵-C₅Me₅ (Cp*), η⁵-C₅Me₄Et (Cp′), η⁵-C₅H₃ ^t Bu₂(Cp″)) with in situ generated H₂Se give triangular [Cp₃Rh₃Se₂]²⁺ clusters. These clusters were isolated as PF₆ salts and characterized with ESI-MS, ⁷⁷Se, ¹H NMR and DFT calculations. [Cp₃Rh₃Se₂] undergoes two reversible two-electron reduction steps. Quantum-chemical calculations reveal non-trivial bonding situation in the cluster core and changes in the hapticity of the Cp* ligand upon reduction. Crystal structure of [Cp ₃ ^* Rh₃Se₂][Re₂(μ-Cl)₃(CO)₆]Cl · 3.3H₂O has been determined.     

Studies on nucleophilic substitution reactions with η6-o-dichlorobenzene-η5-cyclopentadienyliron hexafluorophosphate

Reaction of η⁶-o-dichlorobenzene-η⁵-cyclopentadienyliron hexafluorophosphate (IPF₆) with an excess of phenol or p-thiocresol in the presence of K₂CO₃ could give disubstitution of both chloro groups of I, while a similar reaction with one equivalent of the nucleophile, and under conditions of high dilution, monosubstitution of only one of the chloro groups of I could be obtained. Similarly, di- or monosubstitution could be brought about under appropriate conditions with benzyl or methyl alcohol as the source of the nucleophile. While no reaction could take place between IPF₆ and aniline, a reaction did occur between IPF₆ and o-anisidine (o-methoxyaniline), but only the monosubstitution product was obtained, even in the presence of an excess of o-anisidine. Similar results of monosubstitution were observed with other nucleophiles containing the NH₂ group, including NH₃, NH₂NH₂, CH₃NH₂ and C₆H₅CH₂NH₂. These findings are consistent with the reported differences in yields when IPF₆ was treated with two nucleophilic groups (OH, SH and/or NH₂) located in the 1,2-positions of a benzene ring to give CpFe complexes of heterocyclic systems related to 9,10-dihydroanthracene with two hetero-atoms at the 9,10-positions [15]. Reactions were also carried out between IPF₆ and the carbanion-enolate anion derived from acetylacetone, α-benzoylacetophenone, diethyl malonate or ethyl acetoacetate. In these cases, only monosubstitution of one of the chloro groups of I was observed, leading to the formation of a CC bond. A possible explanation for the formation of only monosubstitution products in reactions with N- or C-containing nucleophiles is discussed.     

Synthesis and structure of η6-(biphenyl)-η5- (cyclopentadienyl)iron(II) hexaflourophosphates

A series of η⁶-(biphenyl)-η⁵-(cyclopentadienyl)iron(II) hexafluorophosphates have been prepared. Demethylation occured during the synthesis of the 2′-OMe derivatives to yield the correspoding 2′-OH product. The mechanism of this process is discussed. In all cases the complexation involved the unsubstituted phenyl ring. From ¹³C NMR data, values of Hammett resonance parameters σ_R, were calculated which show that the [CpfeC₆H₅]⁺ group behaves as an electron-withdrawing substituent comparable in strength to the cyano group. Approximate values of the biphenyl interplanar angle (θ) were obtained. θ appeared to be significantly lower when electron-releasing substituents were present. ⁵⁷ Fe Mössbauer data support the strong electron acceptor properties of the [CpFe⁺C₆H₅] moiety. In particular the quadrupole splitting (QS) shows a marked increase for the 4-OMe derivative relative to the unsubstituted comples. This is in direct contrast to the aryl ferrocenes. Here, the ferrocenyl and OMe substituents are electronically and so there is no (QS) enhancement.