Cyclohexadienyl Complexes Research Articles

Lewis acidity of benzene in half-sandwich ruthenium arene complex. A computational study

Abstract [Ru(benzene)(en)Cl]+ (en = ethylenediamine) is a very active anticancer drug like cisplatin. It has been shown that upon coordination to metal in half sandwich ruthenium complex the benzene ring becomes electron deficient. A library of Lewis bases: Tetrahydrofuran (THF), Acetonitrile (MeCN), Diethyl ether (Et2O), Water (H2O), Trimethylamine (Me3N), Ammonia (NH3), Pyridine (Py), Benzene (Bz), Furan, Adenine, Carbon monoxide (CO), Thiophene and Phosphine (PH3) are considered to study the Lewis acid character of the metal bound benzene. The binding energies of the bases are calculated at M06-2X/LanL2DZ(Ru), 6-31+G∗(C, H, N, O, P, S, Cl) level using Density Functional Theory (DFT) and the values are compared with free benzene. A conformational sampling analysis is carried out to get the most stable supermolecul. It is found that the binding energy is significantly higher in case of coordinated benzene in [Ru(benzene)(en)Cl]+ (e.g., interaction energy of Py is −5.56 Kcal mol−1 more in [Ru(benzene)(en)Cl]+ than that of free benzene). An Energy Decomposition Analysis shows that for the coordinated benzene the stability of the acid-base adduct comes from the combination of electrostatic and dispersion term. From the Quantum Theory of Atoms in Molecules (QTAIM) a cage critical point (CCP) is found in between the donor atom of base and centroid of the benzene ring. The values of electron density of the bond critical point (BCP) in the supermolecule are higher in coordinated benzene than that of the free one. Moreover, a change in the electron density and its Laplacian of the ring critical point (RCP) and bond critical points of the benzene ring in metal bound and free state have been observed. Nucleus Independent Chemical Shift (NICS) calculations also show change in the values of NICS(0) and NICS(1) upon interaction of benzene with Lewis base. An interesting experimental observation of the formation of substituted cyclohexadienyl complex of ruthenium(II) from the reaction of [Ru(benzene)Cl2]2 with nucleophilic reagents hydride, hydroxide and cyanide have been justified from DFT calculations. Thermochemical parameters; enthalpy (ΔH) and free energy (ΔG) of the reactions suggest the adduct formation follows the order: H− > OH− > CN−. This is because of the electron deficient nature of coordinated benzene and hence the nucleophilic reagent undergoes addition reaction. Global and local reactivity parameters such as chemical potential, hardness, electrophilicity index and Fukui function are calculated to understand the electronic properties.

Thioether Iron Complexes [(X‐SMe‐7,8‐C2B9H10)Fe(C6H6)] (X = 9 or 10) as Synthons of Neutral Ferracarborane Fragments

The demethylation reactions of the cyclohexadienyl complexes [(η‐X‐SMe2‐7,8‐C2B9H10)Fe(η5‐C6H7)] {X = 9 (1a), 10 (1b); X is the number of the substituent position} with PhCH2SNa in N,N‐dimethylformamide (DMF) and subsequent protonation by acetic acid lead to the iron–benzene complexes [(η‐X‐SMe‐7,8‐C2B9H10)Fe(η‐C6H6)] (2a and 2b). The visible‐light irradiation of 2a in the presence of tBuNC or [Cp*Fe(η‐cyclo‐P5)] (Cp* = pentamethylcyclopentadienyl) affords the neutral half‐sandwich complex [(η‐9‐SMe‐7,8‐C2B9H10)Fe(tBuNC)3] (3) or the triple‐decker complex [(η‐9‐SMe‐7,8‐C2B9H10)Fe(µ‐η:η‐cyclo‐P5)FeCp*] (4). The reaction of 2b with (THF)W(CO)5 (THF = tetrahydrofuran) selectively gives the iron–tungsten dinuclear complex [(η‐10‐SMe{W(CO)5}‐7,8‐C2B9H10)Fe(η‐C6H6)] (5). The structures of 2a, 4, and 5 were determined by X‐ray diffraction. Electrochemistry revealed that the redox processes of the SMe‐substituted ferracarboranes are cathodically shifted (by ca. 350 mV) with respect to the corresponding redox changes of the SMe2 analogs. The Fe–C6H6 bonding in 2a and the related benzene complexes [(η‐9‐SMe2‐7,8‐C2B9H10)Fe(η‐C6H6)]+ and [(η‐7,8‐C2B9H11)Fe(η‐C6H6)] was analyzed by energy‐decomposition analysis.

Click Chemistry of an Ethynylarene Iron Complex: Syntheses, Properties, and Redox Chemistry of Cationic Bimetallic and Dendritic Iron-Sandwich Complexes

The functionalization of dendrimers and other macromolecules with cationic redox-active organometallics remains a target toward metal-containing dendrimers and polymers that can serve in particular as polyelectrolytes and multielectron redox reagents. Along this line, we report the click functionalization of organometallics and dendrimers with a redox-active ethynylarene iron complex, [FeCp(η6-ethynylmesitylene)][PF6], 3, easily available from [FeCp(η6-mesitylene)][PF6], 1. Complex 3 reacts with azidomethylferrocene upon catalysis by copper sulfate and sodium ascorbate (CuAAC reaction) to give a bimetallic complex that is reduced on the mesitylene ligand to a mixture of isomeric cyclohexadienyl complexes. Complex 3 also reacts according to the same click reaction with zeroth- and first-generation metallodendrimers containing, respectively, 9 and 27 azido termini to provide new polar polycationic metallodendrimers that are reversibly reduced, on the electrochemical time scale, to 19-electron FeI species.

High-yield synthesis of osmium complexes [(η6-C6H6)OsCl2]2, [CpOs(η6-C6H6)]+ and CpOs(η5-cyclohexadienyl)

The benzene complex [(η6-C6H6)OsCl2]2 (1) was obtained in 97% yield from thermal or microwave-assisted reaction of Na2OsCl6 with 1,3-cyclohexadiene in aqueous ethanol. Further reaction of 1 with TlCp gives [CpOs(η6-C6H6)]PF6 in 75% yield. Treatment of [CpM(η6-C6H6)]PF6 (M = Ru and Os) with NaBH4 in wet THF affords the cyclohexadienyl complexes CpM(η5-C6H7) in almost quantitative yields. The structure of [CpOs(η6-C6H6)]BArF (BArF = [B((3,5-(CF3)2)C6H3)4]) was confirmed by X-ray diffraction.

Valuable New Cyclohexadiene Building Blocks from Cationic η5‐Iron–Carbonyl Complexes Derived from a Microbial Arene Oxidation Product

Biooxidation of benzoic acid by Ralstonia eutropha B9 provides an unusual cyclohexadiene carboxy diol that contains a quaternary stereocentre. Tricarbonyliron derivatives of this chiron, on treatment with acid, give two isomeric η(5)-cyclohexadienyl complexes as observed by NMR spectroscopy. Both of these can be subjected to the addition of nucleophiles to provide isomeric cyclohexadiene complexes with new substituent patterns, several of which have been characterised crystallographically. De-metallation of these provides a versatile library of cyclohexadiene building blocks, the utility of which is demonstrated by formal syntheses of oseltamivir. The mechanism of product formation and its stereochemical implications are discussed, as are the procedures undertaken to establish the enantiopurity of a representative cyclohexadiene product.

Synthesis of Polycyclic Cyclohexadienyl Ruthenium(II) Complexes from η6-Arene Precursors via Phosphine-Promoted Intramolecular Nucleophilic Aromatic Addition

An experimentally straightforward procedure for the synthesis of structurally elaborate cyclohexadienyl ruthenium(II) complexes has been developed along the lines of the Morita−Baylis−Hillman reaction. Coordination of (cyclopentadienyl)Ru(II) fragments to N-benzyl and N-phenethyl acrylamides was found to facilitate conversion to stable cyclohexadienyl complexes via Bu3P-mediated intramolecular cyclization. An ipso cyclization was observed in all but one case, resulting in formation of five- or six-membered spirolactams at C6 positions of cyclohexadienyl ligands. Acrylamides prepared from dihydroindene and tetrahydronaphthalene precursors were suitable substrates for this transformation, affording access to novel tricyclic cyclohexadienyl complexes. One such complex was characterized by X-ray crystallography.

Synthesis, structure, electrochemistry, and Mössbauer effect studies of (ring)Fe complexes (ring = Cp, Cp ∗, and C 6H 7). Photochemical replacement of benzene in the cyclohexadienyl complex [(η 5-C 6H 7)Fe(η-C 6H 6)] +

Visible light irradiation of cation [(η 5-C 6H 7)Fe(η-C 6H 6)] + ( 1 + ) in acetonitrile results in substitution of the benzene ligand giving the labile acetonitrile derivative [(η 5-C 6H 7)Fe(MeCN) 3] + ( 2a + ). The stable isonitrile and phosphite complexes [(η 5-C 6H 7)FeL 3] + [L = t BuNC ( 2b + ), P(OMe) 3 ( 2c + ), P(OEt) 3 ( 2d + )] were obtained by reaction of 1 with L in MeCN. The structures of 2cPF 6, [CpFe(η-C 6H 6)]PF 6 ( 3PF 6), and Cp ∗Fe(η-C 6H 6)]PF 6 ( 4PF 6) were determined by X-ray diffraction. The redox activity of the cyclohexadienyl complexes 1 + , 2b + − 2d + has been investigated by electrochemical techniques and compared with that of the related cyclopentadienyl complexes 3 + and 4 + . DFT calculations of the redox potentials and the respective geometrical changes were performed. Variable temperature Mössbauer (ME) spectroscopy has elucidated the relationship between structure and formal oxidation state of the iron atom in these complexes. In the case of 3 + an unexpected pair of crystallographic changes has been observed and interpreted in terms of both a second and first order phase transition. The mean-square-amplitude-of-vibration of the metal atom has been compared between the ME and X-ray data. ME measurements in a magnetic field have shown that in 4 + the quadrupole splitting is positive as it is in ferrocene.

Relative stability of half-sandwich η 6-benzene Ru(II) complexes of tridentate (2-pyridyl)alkylamine ligands of varying chelate ring-size: Nucleophilic addition of hydride ion onto the benzene ring

A full account of half-sandwich complexes of ruthenium(II) having three-legged “piano-stool” geometry supported by tridentate (2-pyridyl)alkylamine ligands is presented. Reaction of the dimer [{(η 6-C 6H 6)RuCl(μ-Cl)} 2] with N-methyl- N, N-bis(2-pyridylmethyl)amine (MeL ∗) in CH 3OH in the presence of NH 4PF 6 affords the complex [(η 6-C 6H 6)Ru(MeL ∗)][PF 6] 2 ( 1). A similar reaction with N-methyl- N, N-bis(2-pyridylethyl)amine (MeL ∗∗), however, affords a non-organometallic Ru(III)-dimeric complex [ ( MeL ∗ ∗ ) 2 Ru 2 III ( μ -O ) ( μ -Cl ) Cl 2 ] [ PF 6 ] ( 5) (the composition of this complex has been established by physicochemical method). Nucleophilic addition reaction on 1 with NaBH 4 leads to the isolation of a cyclohexadienyl complex [(η 5-C 6H 7)Ru(MeL ∗)][PF 6] ( 3). The molecular structure of 1 · 2CH 3CN, 3, and previously reported cyclohexadienyl complex [(η 5-C 6H 7)Ru(MeL)][PF 6] ( 4) [MeL = N-methyl-[(2-pyridyl)ethyl(2-pyridyl)-methyl]amine], obtained from the reaction between NaBH 4 and previously reported “piano-stool” complex [(η 6-C 6H 6)Ru(MeL)][PF 6] 2 ( 2), has been confirmed by X-ray crystallography. Solution-state structure of new complexes 1 and 3 has been elucidated by their 1H NMR spectra in CD 3CN. The behavior of complex 3 has been investigated with the aid of two-dimensional 1H NMR spectroscopy, as well. An attempt has been made to provide a rationale for the effect of supporting tridentate N-donor ligand [MeL, MeL ∗, and MeL ∗∗], varying in the chelate ring-size on (i) the relative stability of half-sandwich η 6-benzene Ru(II) complexes and (ii) the electrophilicity of Ru(II)-coordinated benzene ring on the nucleophilic addition reactions.

Carbon−Carbon and Carbon−Heteroatom Bond Formation on Solid Phase Using Cationic Iron Carbonyl Complexes

Iron-mediated methodology for the formation of carbon-carbon and carbon-heteroatom sp(3) bonds on solid phase has been developed. Treatment of a polymer-bound cationic iron cyclohexadienyl complex with carbon, oxygen, nitrogen, and phosphorus nucleophiles, followed by cleavage with amines and subsequent decomplexation, yielded 18 different cyclohexadienoic acid amides of high purity. [reaction: see text]

Hydrogenolysis of [PhBP3]Fe[triple bond]N-p-tolyl: probing the reactivity of an iron imide with H2.

This paper describes the reductive hydrogenolysis of a low-spin (S = 1/2) iron(III) imide. Pseudotetrahedral [PhBP3]FeIIIN-p-tolyl is reduced by hydrogen at ambient temperature and pressure in benzene solution. The reduction appears to proceed in a stepwise fashion. An intermediate S = 2 iron(II) anilide, [PhBP3]Fe(N(H)-p-tolyl), is observed and has been independently generated and structurally characterized. Prolonged hydrogenolysis in benzene results in the complete hydrogenolysis of the Fe-N linkage to release H2N-p-tolyl. The major iron-containing product formed from this step is the diamagnetic cyclohexadienyl complex, [PhBP3]Fe(eta5-cyclohexadienyl), which has also been independently prepared and structurally characterized. Evidence is presented to suggest that the final [PhBP3]Fe(eta5-cyclohexadienyl) product is formed via benzene insertion into a reactive [PhBP3]FeII-H intermediate.

Synthesis of some substituted 5,6,11,12-tetrahydro-dibenzo[ a, e]cyclooctene derivatives through the intermediacy of tricarbonyl(η 6-arene)chromium complexes

5,6,11,12-Tetrahydrodibenzo[ a, e]cyclooctene derivatives with α- and β-substituents are readily accessible from [Cr(CO) 3(5,6,11,12-tetrahydrodibenzo[ a, e]cyclooctene)] 2 via a two-step sequence, which involves addition of a nucleophile and oxidation of the intermediate anionic cyclohexadienyl complex. Nucleophiles used included LiCMe 2CN ( A ), LiCH 2CN ( B ), and ▪ ( C ). The results show that the primary carbanion LiCH 2CN and the S-stabilized carbanion ▪ give mixtures of α- and β-substituted products and in both cases α-isomers were major, whereas the opposite regioselectivity was obtained with the tertiary carbanion LiCMe 2CN.

Reductive Dimerization of the Cyclohexadienyl Complex [Mn(CO)3(η5-C6H7)] through a Radical Pathway

Slow naphthalenide reduction of [Mn(η5-C6H7)(CO)3] (1) generates the transient anionic radical [Mn(η5-C6H7)(CO)3]•- (4•-), which adds as a nucleophile to 1 to form, after further reduction, [Mn(CO)3{η4-C6H7−CO−Mn(η5-C6H7)(CO)2}]2-, while fast reduction of 1 at low temperature gives [{Mn(CO)3}2(μ2-η4:η4-C6H7−C6H7)]2-, a dimer of 4•-. Both reactions suggest that formation of transient 4•- allows access to new reaction manifolds in which the cyclohexadienyl ligand of the classic complex 1 has been activated to further reactions.

Oxidative Demetalation of Cyclohexadienyl Ruthenium(II) Complexes: A Net Ru‐Mediated Dearomatization.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Oxidative demetalation of cyclohexadienyl ruthenium(II) complexes: a net Ru-mediated dearomatization.

[reaction: see text] An experimentally simple method for the demetalation of spirocyclic cyclohexadienylruthenium(II) complexes has been developed. Treatment of an alkoxy-substituted cyclohexadienyl complex with CuCl(2) affords either azaspiro[4.5]decane derivatives or heavily functionalized tetrahydroisoquinolines. The former reaction manifold completes a net Ru-mediated dearomatization as the organometallic starting materials are prepared from (eta(6)-arene)Ru(II) precursors. Both of these heterocyclic products are well suited for further synthetic elaboration.

Spirocyclic and Bicyclic Cyclohexadienyl Complexes from Intramolecular Nucleophilic Addition Reactions in Dicationic Arene Complexes

The dicationic arene complexes [(p-cymene)Ru(PhCH2CH2[CH2]nOH)][OTf]2 and [Cp*Ir(PhCH2CH2[CH2]nOH)][OTf]2 (n = 1−2) react with K2CO3 to cleanly generate spirocyclic cyclohexadienyl complexes through intramolecular nucleophilic addition of the alkoxide at the ipso carbon of the arene ligand. When the internal nucleophile is the bulkier benzenesulfonamide group, cyclohexadienyl complexes derived from both ipso and ortho intramolecular nucleophilic addition are formed.

Reversible intramolecular hydride transfer between tantalum and an aromatic ring: an eta(5)-cyclohexadienyl complex as a masked hydride.

The methyl triflate complex (2,6-Mes2C6H3N=)(2,6-Mes2C6H3NH)TaMe(OSO2CF3) reacts cleanly with H2 to give the eta5-cyclohexadienyl complex 3. Complex 3 therefore results from the insertion of an arene ring into an M-H bond, which has been proposed as the first step in catalytic arene hydrogenations. This insertion is reversible, such that 3 behaves as a "masked hydride" in its reaction chemistry.

Single and double nucleophilic addition to methylated podocarpic acid coordinated to manganese tricarbonyl

Coordination of the Mn(CO) 3 + moiety to the arene ring in dimethylated podocarpic acid ( 1) occurs with similar probability to both α and β faces ( 2). The nucleophile MeMgCl adds predominantly to the ortho C-13 site when the metal is situated β and to the meta C-14 site when the metal is α, to afford cyclohexadienyl complexes 3(β) and 4(α). The minor isomers 3(α) and 4(β) (Nu=Me) were isolated and characterized by X-ray diffraction, from which it is concluded that the diterpenoid Me-17 group interacts sterically with a carbonyl ligand when the metal is β and the nucleophile is at the meta C-14 position. Complexes 3(β) and 4(α) are readily converted into cationic Mn(CO) 2NO + salts 5(β) and 6(α), which add hydride ion to afford cyclohexadiene complexes.

Reactivity patterns in cationic tricarbonyliron complexes: crystallographic proof of stereoselectivity in long range asymmetric induction in the 1,3/1?,2? series

The analysis of patterns of regioselectivity in cyclohexadienyl complexes illustrates the versatility and power of the iron-based methodology in reaction sequences that make multiple use of the metal to establish a series of chiral centres, The conversion of tricarbonyl(eta (4)-cyclohexadienone)iron(0) into the dimethyl malonate adduct 4, which contains two chiral centres at carbon besides the controlling chirality of the tricarbonyliron complex itself, provides an example of long-range asymmetric induction. The relative stereochemistry of the 1,3/1',2' product has been defined as S,S,R*,R*. Copyright (C) 2001 John Wiley & Sons, Ltd.

Electronic Factors for Protonation of an Organometallic Molecule. Photoelectron Spectroscopy and Electron Paramagnetic Resonance Study of [(η6-C6H6)Mo(TRIPOD)]0/+

We have previously shown that the arene complex (η6-C6H6)Mo(TRIPOD), where TRIPOD = 1,1,1-tris((diphenylphosphino)methyl)ethane, is protonated by exo addition of H+ to the arene ring to give the transient cyclohexadienyl complex [(η5-C6H7)Mo(TRIPOD)]+, which eventually yields the thermodynamic molybdenum hydride [(η6-C6H6)Mo(TRIPOD)(H)]+. The present study is a combined experimental and theoretical investigation that reveals the fundamental basis for this mechanism. Photoelectron spectroscopy (PES) is used to probe the electronic structure of (η6-C6H6)Mo(TRIPOD) and the production of the [(η6-C6H6)Mo(TRIPOD)]+ cation in the gas phase. The initial ionizations of (η6-C6H6)Mo(TRIPOD) are from energetically closely spaced orbitals of predominantly metal d character (2A1 and 2E cation states using C3v symmetry) that are shifted over 2 eV to lower energy with respect to the comparable ionizations of (η6-C6H6)Mo(CO)3. The oxidized species [(η6-C6H6)Mo(TRIPOD)]+ is also prepared in solution by electrochemical means and through the use of chemical oxidants. The electron paramagnetic resonance (EPR) spectrum of this cation shows arene-proton hyperfine coupling that indicates substantial arene character in the highest occupied orbital. The photoelectron and EPR spectra both provide evidence for Jahn−Teller distortion of the 2E positive ion states. Electronic structure calculations show that this distortion involves opening of one L−Mo−L angle, which effectively creates an open coordination site on the metal for the hydride to occupy in the final thermodynamic product. These experimental and computational results show that, in terms of their energy, the e symmetry and a1 symmetry metal-based orbitals are similarly favored for oxidative protonation directly at the metal. The e symmetry orbital has a portion of its density on the arene ring, making access to this orbital by proton approach to the exo position of the arene ring possible. For (η6-C6H6)Mo(TRIPOD), exo attack at the arene is favored because the TRIPOD ligand shields the e symmetry orbital from direct attack at the metal by the solvated proton. Thus, exo attack is not initiated by proton interaction with an arene-based orbital but is initiated by proton interaction with the arene portion of the same e symmetry orbital that directs attack at the metal. Calculations predict low barriers for both direct attack at the metal and exo attack at the arene, with attack at the arene favored for longer metal−proton distances.

Models for the Homogeneous Hydrodesulfurization of Benzothiophenes. Carbon−Sulfur Bond Cleavage, Hydrogenolysis, and Desulfurization Reactions Mediated by Coordination of the Carbocyclic Ring to Manganese and Ruthenium

Chemical reduction of a series of (η6-benzothiophene)Mn(CO)3+ complexes (10a−c) under CO affords neutral dimanganese metallathiacyclic complexes (12a−c), which have a Mn(CO)4 moiety inserted into the C(aryl)−S bond. Reduction of (η6-benzothiophene)Ru(C6Me6)2+ in the presence of CO and (η6-1-Me-naphthalene)Mn(CO)3+ affords an analogous cationic bimetallic (15), which is converted to a neutral cyclohexadienyl complex (16) by hydride addition to the carbocyclic benzothiophene ring. The sulfur atom in the metallathiacyclic ring in 12 and 16 is nucleophilic and reacts with electrophiles CF3SO3Me, HBF4, and W(CO)5(THF) to afford complexes such as 6, 14, and 17. Treatment of 12 with H2 results in hydrogenolysis of the Mn−C σ bond and formation of the bimetallic Mn2(CO)8(H)(SCHCHPh) (8), which contains a Mn−Mn bond and bridging hydride and thiolate ligands. Reaction of 6 and 17 with H2 results in desulfurization of the benzothiophene and formation of a mixture of Mn(CO)5SR and [Mn(CO)4SR]2 (R = H, Me). Crystal st...