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.     

Synthesis of (η-arene)(η-cyclopentadienyl) iron (II) complexes with heteroatom and carbonyl substituents. Part I: Oxygen and carbonyl substituents

A series of reactions have been used to introduce oxygen substituents into (η-arene)(η-cyclopentadienyl) iron (II) complexes. Photochemical ligand exchange led to the formation of the first recorded trioxygenated complex as well as mono- and di-oxygenated species. Using microwave techniques, reaction times for S_NAr displacement reactions of halobenzene complexes by phenols were reduced from several hours to a few minutes. Phenols protected by either t-butylation or trimethylsilylation were found to give modest yields of the corresponding phenol complexes, using conventional thermal ligand exchange reactions. Without such protection, yields were extremely low. The above method led to the synthesis of the first example of a dihydroxybenzene complex. Some miscellaneous syntheses are also reported.The Nef reaction has been adapted to convert (η⁶-α-nitroalkylarene)(η⁵-Cp) iron (II) salts to corresponding aldehyde and ketone complexes. The α-nitroalkyl arene complexes were synthesised in good yields from (η⁶-halobenzene)(η⁵-Cp) iron (II) complexes using NaOtBu in DMSO. H/D exchange reactions with ²[H]₆-DMSO in the presence of K₂CO₃ showed partial D incorporation in the methyl group for the unreacted α-nitroethylbenzene complex and complete exchange for the carbanion generated by deprotonation. Conversion of the α-nitroalkylarene complexes to the corresponding aldehyde and ketone complexes was accomplished in moderate yields using three methods:

(A)

H₂O₂ and NaOtBu in DMSO followed by reaction with CF₃CO₂H.

(B)

SnCl₂/aq. HCl.

(C)

K₂CO₃ in DMF using microwave-mediated reactions.

In addition, two one-pot syntheses are reported using methods B and C.     

Oxidation of theexo- andendo-phenylcyclohexadienyl iron complexes Fe(η5-6-PhC6H6) (η5- C5H5)

The roe of oxidatively induced homolyhc scission a the C(sp³)-H bonds in the iron phenykychhexadienyl complexes Fe(⁵-6-PhC₆H₆)(⁵-C₅H₅) (1) depends on the spatial orientation of the Ph substitutent. In the case of the (1 _endo ⁺) radical cation this process, resulting in the cationic biphenyl complex (Fe(⁶ -C₆H₅C₆H₅)(⁵-C₅H₅)]⁺ (2 ⁺), is fast and proceeds for several minutes. In the case of the more stable radical cation (1 _exo ⁺) the formation of 2⁺ is slow and takes tens minutes to complete.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1698–1700, July, 1996.     

Stereocontrolled acylation of (η4-cycloheptatriene)iron tricarbonyl

The anion derived by deprotonating (cycloheptatriene)Fe(CO)₃ reacts with acid chlorides to give exo C-7 substitution. The acyl group is readily isomerized to C-5 on treatment with base. The C-7 acylated products can be deprotonated; the resulting anions react at oxygen with acyl chlorides and Me₃SiCl, and at carbon with MeI.     

Reaction of Mercury(II) Trifluoroacetate with Deprotonated (η6-Toluene)-, (η6-Diphenylmethane)-, and (η6-Triphenylmethane)(η5-cyclopentadienyl)iron(II) Complexes. Mercuration of Some Cationic (Arene)(cyclopentadienyl)iron(II) Complexes

Treatment with mercury(II) trifluoroacetate of deprotonated (⁶-toluene)- and (⁶-diphenyl- methane)(⁵-cyclopentadienyl)iron(II) complexes gave mono-, di-, and trisubstituted [from (⁶-toluene)(⁵-cyclopentadienyl)iron(II) cation] mercury-containing salts. The reaction of mercury(II) trifluoroacetate with deprotonated (⁶-triphenylmethane)(⁵-cyclopentadienyl)iron(II) afforded only the corresponding sym- metric mercury derivative. The same product was obtained by direct mercuration with mercury(II) trifluoroacetate of (⁶-triphenylmethane)(⁵-cyclopentadienyl)iron(II) on heating the reactants in boiling unhydrous ethanol. Reactions of the resulting mercury-containing compounds with acids, symmetrizing bases, and acylating agents were studied.     

Mercuration with Mercury(II) Trifluoroacetate of (η6-Aniline)- or (N,N-dimethylaniline)(η5-cyclopentadienyl)iron(II)

The reaction of mercury(II) trifluoroacetate with the hexafluorophosphate of the ⁶-aniline-⁵cyclopentadienyliron(II) cation under reflux in dry ethanol gives rise to N-mono- and N,N-disubstituted mercury-containing salts of this cation. The same mercury-containing salts have been synthesized by the action of mercury(II) trifluoroacetate on the deprotonation product of the (⁶-aniline)(⁵-cyclopentadienyl)iron(II) cation. Direct mercuration of the [⁶-(N,N-dimethylaniline)](⁵-cyclopentadienyl)iron(II) cation into the para position of the benzene ring of the arene ligand has been performed. The reactivity of the compounds obtained has been studied.     

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.     

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).     

Crystal structure of twinned (η5-C5(CH3)4CF3) (η5-C5(CH3)5)Ru

The substituted sandwich complex crystallizes in monoclinic space groupP2₁/m withZ=2. Twinning to the (001) direction with the special conditionc ^*/4a ^* = cos ^* causes systematic superposition of the reciprocal lattices of both domains and results in an apparent unit cell with double volume and the reflection condition (2h)kl, l=2n. The structure solution was obtained with the subset of intensity data for the predominant individuum and converged atR = 0.040,R _w =0.046 for 832 independent observations and 122 variables. The molecules show disorder with respect to the crystallographic mirror plane. The structure is closely related to that of decamethylruthenocene.     

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.     

(η6-Anisole) (η2-benzene) dicarbonylchromium(0): an intermediate in the photochemical carbonyl substitution of (η6-anisole)tricarbonylchromium(0) in benzene

The photochemical carbonyl substitution of (η⁶-anisole)Cr(CO)₃ has been investigated by laser flash photolysis. Both transient spectra and second-order rate constants for the reactions of transients with nucleophiles are found to be extremely variable depending upon solvents used. The coordination of benzene to the transient in cyclohexane forms the transient in benzene, indicating two discrete chemical species: (η⁶-anisole)Cr(CO)₂ and (η⁶-anisole)Cr(CO)₂(η²-benzene). The latter type of transient was observed also for fluorobenzene and mesitylene, leading to the assignment of a weak band in the visible region as η²-arene → Cr charge transfer. The existence of (η⁶-arene)Cr(CO)₂(η²-arene′) may throw light on what have been described as solvent effects in organometallic reactions.     

Regiospecific substitution of carbonyl by phosphine ligands in hydrocarbyl-substituted carbonyl clusters. Synthesis and spectroscopic characterization of Fe3(CO)8(PPh3)(μ3-η2- ⊥ -EtC2Et) and (η5-C5H5)NiFe2(CO)5(PPh3)(η3-η2- ⊥-C2But)

The complexes Fe₃(CO)₈(PPh₃)(μ₃-η²- ⊥ -EtC₂Et) and (η⁵-C₅H₅)NiFe₂(CO)₅(PPh₃)(η₃-η²- ⊥-C₂Bu^t) have been obtained by treating Fe₃(CO)₉(C₂Et₂) or (Cp)NiFe₂(CO)₆(C₂Bu^t) with PPh₃ under mild conditions; the substituted clustes have been characterized spectroscopically. Structures are proposed in which the phosphine is on the unique metalatom σ-bonded to the alkyne or acetylide moiety. Replacement of CO by PPh₃ ligands rather than by addition, is observed for the formally unsaturated Fe₃(CO)₉(C₂Et₂). Reorientation of the acetylide was expected for (Cp)NiFe₂(CO)₆(C₂Bu^t) upon substitution, but was not observed.     

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.     

Insertion reactions of t-Bu(η5-C5H5)Fe(CO)2

The complex t-Bu(η⁵-C₅H₅)FE(CO)₂ has been treated with triphenylphosphine in refluxing THF to produce t-BuCO(η⁵-C₅H₅)Fe(CO)(PPh₃). The large steric bulk of the t-butyl group suggests that this reaction should be faster than the reaction involving the methyl group, and a kinetic investigation illustrates this to be the case. The same steric bulk predicts that the reaction with SO₂ should be slow, and indeed we have been unable to effect the related SO₂ insertion reaction. Attempts to prepare the corresponding t-Bu(η⁵-C₅H₅)W(CO)₃ led to formation of the related isobutyl complex.     

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.     

The reactivity of cyclopentadienyl dicarbonyl complexes of iron, η5-C5H5(CO)2Fe-η1-R (R = alkyl or aryl). Synthesis of novel derivatives substituted in the cyclopentadienyl ring

The results of the study of the reactivity of the cyclopentadienyl ligand in Cp(CO)₂Fe-¹-R (R=Alk or Ar) iron complexes have been summarized. The methods for preparation of mono-, bi-, and trinuclear homo- and heterometallic complexes containing a Cp(CO)₂Fe moiety are presented.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1367–1373, August, 1994.