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Treatment of a fresh acetonitrile solution of [{Ru(η 6 -arene)Cl 2 } 2 ] with poly(pyrazolyl)borates and methanes such as [HXR 3 ] n- [X = B, R = pyrazolyl (pz); X = C, R = 3,5-dimethylpyrazolyl (dmpz)] resulted in formation of novel ruthenium compounds of the following type [Ru(η 6 -arene){κ 2 -HXR 3 }Cl] n+ (X = B, n = 0, R = pz, arene = p-xylene 2, mesitylene 3 or hexamethylbenzene 6; X = C, n = 1, R = pz 7, dmpz 8, arene = benzene; R = dmpz, arene = p-xylene 9). Syntheses of the mixed-sandwich complexes of the type [Ru(η 6 -arene){κ 3 -HB(pz) 3 }][PF 6 ] (arene = p-xylene 1a, mesitylene 4 or hexamethylbenzene 5a) are also reported from aged solutions. The hapticity change of the tridentate ligand from κ 2 to κ 3 can be affected by either warming the bis-chelated compounds in a polar solvent such as MeCN or by treatment with methanolic [NH 4 ][PF 6 ]. Crystal structures of [Ru(η 6 -C 6 Me 6 ){κ 2 -HB(pz) 3 }Cl] and [Ru(η 6 -C 6 H 6 ){κ 2 -HC(dmpz) 3 }Cl][PF 6 ] have been determined.

The chemistry of interactions of 2-(2,6-diisopropylphenylaminomethylene)indole ligand (1) with europium and ytterbium amides is described. Reaction of 2-(2,6-diisopropylphenylaminomethylene)indole 2-(2,6-i-Pr2C6H3NHCH2)C8H5NH (1) with europium amide [(Me3Si)2N]3Eu(III)(μ-Cl)Li(THF)3 afforded a novel europium(II) complex formulated as {[μ-η(6):η(1):η(1)-2-(2,6-i-Pr2C6H3N═CH)C8H5N]Eu[2-(2,6-i-Pr2C6H3N═CH)C8H5N]}2 (2), having a bridged indolyl ligand in the novel μ-η(6):η(1):η(1) hapticities with the reduction of europium(III) to europium(II) and the oxidation of amino to imino group. Reaction of 2-(2,6-diisopropylphenylaminomethylene)indole 2-(2,6-i-Pr2C6H3NHCH2)C8H5NH (1) with ytterbium(III) amide [(Me3Si)2N]3Yb(III)(μ-Cl)Li(THF)3 produced the only deprotonated ytterbium(III) complex formulated as [2-(2,6-i-Pr2C6H3NCH2)C8H5N]Yb[N(SiMe3)2](THF)2 (3), having an η(1) hapticity indolyl ligand. Reaction of 2 with formamidine [(2,6-Me2C6H3)NCHNH(C6H3Me2-2,6)] produced {[μ-η(3):η(1):η(1)-2-(2,6-i-Pr2C6H3N═CH)C8H5N]Eu[(2,6-Me2C6H3)NCHN(C6H3Me2-2,6)](THF)}2 (4), which has a bridged indolyl ligand in the novel μ-η(3):η(1):η(1) hapticities, whereas the reaction of 2 with the more sterically bulky formamidine [(2,6-i-Pr2C6H3)NCHNH(C6H3i-Pr2-2,6)] afforded complex {[μ-η(2):η(1):η(1)-2-(2,6-i-Pr2C6H3N═CH)C8H5N]Eu[(2,6-i-Pr2C6H3)N═CHN(C6H3i-Pr2-2,6)](THF)}2 (5), having the indolyl ligand in the novel μ-η(2):η(1):η(1) hapticities. The results represent the first example of organometallic complexes having indolyl ligands in the novel μ-η(6):η(1):η(1), μ-η(3):η(1):η(1), and μ-η(2):η(1):η(1) bonding modes with metal.

A series of alkylated phenols (phenol, 3,5-dimethylphenol and 3,4-dimethylphenol) were complexed by the [Cp*Ir(solvent)3][BF4]2 (1) unit prepared in situ; subsequent treatment with NEt3 produced the (oxo-η5-cyclohexadienyl)iridium complexes [Cp*Ir(η5-C6H3R2O)][BF4] [R = H (2); R = Me (3, 4)]. The X-ray molecular structure of 3 was determined. These (oxo-η5-cyclohexadienyl)iridium derivatives react with NaOMe in methanol to give the novel iridium cyclohexadienone complexes [Cp*Ir{η4-C6H3R2O(OMe)}] [R = H (5); R = Me (6, 7)] in 75−90% yield with nucleophilic attack occurring exclusively at the ortho-position relative to the CO function. Addition of HBF4·Me2O to these iridium cyclohexadienone complexes 5−7 affords the starting material (oxo-η5-cyclohexadienyl)iridium derivatives 2−4 with MeOH. Further exposure to HBF4·Me2O produces the corresponding phenolic compounds [Cp*Ir(η6-C6H3R2OH)][BF4]2 (8−10); these chemical reactions are accompanied with hapticity changes η4 → η5 → η6 of the coordinated π-hydrocarb...

Reaction of the seven-coordinate [Mo(I)2(CO)3(CH3CN)2] with an equivalent amount of the hydrotris(3, 5-dimethylpyrazol-1-yl)borate (TpMe2) ligand has been studied. The reaction course and the isolated products depend on the solvent and the initial concentration of the starting compound. Degradation of the TpMe2 ligand to produce derivatives containing 3, 5-dimethylpyrazole (HpzMe2) has been observed in all the experimental conditions used. So, in acetonitrile the reactions yield [Mo4O8(OH)2(HpzMe2)6]I2·4CH3CN and, only if a concentration of the starting complex greater than 0.01 M is used, the compound [Mo(I)( k 3-TpMe2)(CO)2]·2CH3CN is isolated together the above oxo-tetramer. When a less coordinating solvent like dichloromethane is used the complex [Mo(μ-I) (CO)2(HpzMe2)2]2I2·2CH3CN is always obtained independent of the initial concentration. Intermediate compounds in which the TpMe2 ligand is implicated with different hapticity are proposed to explain the different results. The molecular structure of [Mo4O4(μ3-O)2(μ2-O)2 (μ2-OH)2(HpzMe2)6]I2·4CH3CN has been crystallographically determined. The complex can be described as having a tetrametallic framework with a skeleton of edge-linked MoL6 (L = HpzMe2, O, OH) octahedra, which makes a compact closed structure. In each dimeric unit the Mov centres participate in a metal-metal single bond with an average Mo-Mo bond length of 2.568(1)A˚. This complex is the first structurally characterized cationic polyoxo tetrametallic Mov-containing the cluster described.

Extended Huckel and ab initio calculations based on the density functional theory were carried out onto the model complexes [(benzene)Ni I (OH) 3 ] 2− and [(benzene)Ni I (OH) (OH 2 ) 2 ] in order to investigate the bonding mode of benzene to silica-supported Ni I ions. In these model complexes, the contribution of the silica support is restricted to hydroxyl groups or water molecules. Both calculation methods are consistent in predicting an η 2 -coordination of benzene that was previously observed by infrared spectroscopy. The calculations allow a better geometrical description of the stable dihaptobenzene complexes and are discussed in terms of interaction of molecular orbitals.

The biscyclopentadienyldicarbonyl derivatives of zirconium(II) and hafnium(II) ([MCp2(CO)2]; MZr, Hf) promote the reductive coupling of coordinated carbon monoxide to give, in the presence of N,N-dialkylcarbamtes of the tetravalent metals [M(O2CNR2)4], the ketenylidene complexes [M3Cp2(μ2-CCO)-(μ3-O)(O2CNR2)6] (1 a: MZr, REt; 1 b: MZr, RiPr; 2: MHf, RiPr). The yields of the isolated zirconium complexes are as high as 60%, while that of the hafnium derivative is 40%. The X-ray crystal structure analysis of 1 b shows that it consists of trinuclear molecules, with the three zirconium atoms held together by the bidentate C2O ligand, by the tridentate bridging oxide and by the bidentate carbamato groups. Labelling experiments with [ZrCp2(13CO)2] show that the ketenylidene ligand originates from the coordinated CO groups. These ketenylidene complexes, which are rare examples of compounds containing a CCO but no CO ligand, are characterized by an intense IR band at about 2015 cm−1, associated with the bridging C2O ligand. The ketenylidene group of 1 b was readily removed and replaced by a bidentate μ-oxo ligand of the same hapticity by reaction with carbon dioxide or acetone or by thermal decomposition. The resulting product [Zr3Cp2(μ-O)(μ3-O)-(O2CNiPr2)6] (3) crystallizes in the same space group as 1 b and with similar cell constants and bond parameters.

A series of reactions of the general type [MX(CO)2(η7-C7H6R)]n++ 2L′→[MX(CO)2L′2(η3-C7H6R)]n+ involving η7→η3 hapticity conversion at a molybdenum or tungsten co-ordinated cycloheptatrienyl ring have been examined with the objective of determining the effects of variation of X, M and R on the reactivity of [MX(CO)2(η7-C7H6R)]n+ towards adduct formation with ligands L′= NCMe, L′2= Ph2PCH2CH2PPh2(dppe) or 2,2′-bipyridyl (bipy). The complexes [MoX(CO)2(η7-C7H7)] exhibit a markedly X-dependent reactivity. The derivatives with X = NCO or NCS form adducts [MoX(CO)2(dppe)(η3-C7H7)]1 and 2, [MoX(CO)2(bipy)(η3-C7H7)]3 and 4 and [MoX(CO)2(NCMe)2(η3-C7H7)]{as an equilibrium mixture with [MoX(CO)2(η7-C7H7)] in NCMe}. By contrast [MoX(CO)2(η7-C7H7)](X = CCPh, C6F5 or SnPh3) do not react with dppe, bipy or NCMe at room temperature. Tungsten complexes [WX(CO)2(η7-C7H7)]n+ are activated towards adduct formation with L′= NCMe by comparison with the molybdenum analogues. Thus [WX(CO)2(η7-C7H7)](X = NCO or Br) react with NCMe to form [WX(CO)2(NCMe)2(η3-C7H7)](X = NCO 5 or Br 6). The composition of equilibrium mixtures of [Mo(CO)2(NCMe)(η7-C7H6R)]+ and [Mo(CO)2(NCMe)3(η3-C7H6R)]+ in NCMe is dependent upon R and temperature; the % composition of the η7-C7H6R component is enhanced by electron-donating ring substituents (R = Me) and by an increase in temperature. The crystal structures of 4 and [MoCl(CO)2(dppe)(η3-C7H6C6H4F-4)] have been determined. Both exhibit a pseudo-octahedral ligand arrangement at the Mo but, whilst 4 possesses a symmetrical structure with NCS located trans to the η3-C7H7 ring, the latter complex adopts an asymmetric ligand arrangement with one phosphorus of the dppe ligand positioned trans to the cycloheptatrienyl ring.

[EN] The phenomenological approach in Juhani Pallasmaa’s (Hämeenlinna, Finland, 1936) theory of architecture derives from his criticism of the dominant pan-visual model. Architecture, understood as a constructive amendment of the immediate spatial reality, is grounded on hapticity. In contrast with the traditional oculocentrism –and its conceptual premises: the moral hierarchy of the senses, the predominance of analysis, the legitimacy of instrumental rationality, technophilia, objectivity...– Pallasmaa stresses the value of holistic, comprehensive and simultaneous perception –a perception which does not merely correspond to an expanded sense of the scopic. Because of this, the author proposes a multi-sensory re-use in the architectural and urbanistic field, enabling, from a de-visualized approach, a tactilized reading of this field. Perceiving is not just seeing, but also apprehending “the flesh of the world”: the retina –on which focuses a model which recalls the panoptic vision analyzed by Foucault– generates, in the words of Merleau-Ponty, “a Cartesian perspective scopic regime” that facilitates the disembodiment of the subject –a subject which, in an idealistic fashion, tears itself from the world, splits from it. This entails the reduction of architecture to a retinal imposition, to image. A constraint that suppresses the materiality of the world and, in doing so, transforms us into consumers of urban icons and bulimic custodians of a false memory, [ES] El planteamiento fenomenológico en el ámbito de la teoría arquitectónica de Juhani Pallasmaa (Hämeenlinna, Finlandia, 1936) deriva de su crítica al modelo panvisual dominante. La arquitectura, concebida como modificación constructiva de la realidad espacial más inmediata, se asienta en la hapticicidad. Frente al tradicional oculocentrismo –y sus presupuestos conceptuales: jerarquización moral de los sentidos, predominio de lo analítico, legitimación de una racionalidad instrumental, tecnofilia, objetividad...–, Pallasmaa incide en el valor de una percepción holista, global y simultánea que no responde restrictivamente al sentido expandido de lo escópico. Debido a ello, este autor propone una reutilización multisensorial en el ámbito arquitectónico y urbanístico que posibilite, desde una aproximación desvisualizada, una lectura tactilizada del mismo. Percibir no sólo es ver, sino aprehender “la carne del mundo”: la retina –cuyo modelo remite a la visión panóptica analizada por Foucault– genera, en palabras de Merleau-Ponty, “un régimen cartesiano perspectivo escópico” que facilita la acorporalización de un sujeto que, de forma idealista, se desgaja del mundo y se desintegra del mismo. Este hecho trae consigo la reducción de la arquitectura a una imposición retiniana, así como la constricción de lo arquitectónico a la imagen. Una constricción que elimina la materialidad del mundo y que, al hacerlo, nos transforma en consumidores icónicos urbanos y en bulímicos depositarios de una falsa memoria

The molecular structure and dynamics of beryllocene are investigated using the Car–Parrinello projector augmented wave method. In the ground state, the molecule prefers a η1–η5‐coordinated conformation of CS symmetry. At finite temperature, beryllocene undergoes rapid hapticity changes with a frequency of 1–5×1012 s−1. This occurs by means of two mechanisms, each corresponding to a saddle point of the potential surface elevated 5 and 8 kJ mol−1 above the minimum, respectively. The saddle points have CS and C2h symmetry, respectively. The geometric and electronic structure at finite temperature are discussed.

It has been shown by cyclic voltammetry in THF within the −90 to 40 °C temperature range that fluorenyl (η5-9-R-C13H8)Mn(CO)3 complexes (R=But (3) and Ph (4)) undergo two-electron reduction to form allyl type [(η3-9-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 19ē-radical anions 3−. and 4−.. TheE0 values for redox pairs30/−. and40/−. are −1.88 and −1.73 V, respectively. The further reduction of radical anions3−. and4−. at more negative potentials is accompanied by fast η5 → η3 haptocoordination of the fluorenyl ligand to form 18ē-dianions [(η3-9-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 η5 ⇔ η3 hapticity change is a fast and reversible process occurring at the step of 19ē-radical anions3−. and4−. and leading to the electron deficient 17ē-species [(η3-9-R-C13H8)Mn(CO)3]−., which are reduced easier than the initial complexes. As a result, complexes3 and4 are reduced to the corresponding dianions [(η3-9-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 η5- and η6-fluorenylmanganesetricarbonyl complexes are compared.

Cp 2 Cd.TMEDA 1 and Cp 2 Cd.PMDETA 2 have been synthesized and characterized by spectroscopic studies and by X-ray diffraction studies at low-temperature (153 K). The adducts are present in the crystals as mononuclear complexes. When the denticity of the Lewis base ligands in these adducts is increased (from two in 1 to three in three in 2 ) the Cd 2+ centre requires less electron density from the Cp ligands and the hapticity changes from η 2 − in 1 to η 1 − in 2 . Complexes 1 and 2 are the first compounds for which π-bonding of Cp ligands to Cd 2+ has been observed in the solid state.

Thermal rearrangement of bicycloheptatriene, C14H14, followed by reaction with 1 equivalent of [CPh3][PF6] at –20 °C afforded the cycloheptatriene-substituted cycloheptatrienyl cation, [C14H13][PF6] as a mixture of two isomers differing in the position of the CH2 group on the cycloheptatriene ring. Treatment of [C14H13][PF6] with a further equivalent of [CPh3][PF6] afforded the bicycloheptatrienyl dication [C14H12][PF6]2 which reacts with [Mo(CO)3(NCMe)3] to give the bicycloheptatrienyl bridged bimetallic [Mo2(CO)6(µ-η7 : η7-C14H12)][PF6]21. Reaction of [C14H13][PF6] with [Mo(CO)3(NCMe)3] leads to co-ordination at the cycloheptatrienyl ring and formation of [Mo(CO)3(η7-C14H13)][PF6]2 which is the precursor to [MoI(CO)2(η7-C14H12)][PF6]5 which contains an unco-ordinated, pendant cycloheptatrienyl ring. Complex 5 reacts with [Mo(CO)3(NCMe)3] to give doubly bridged [Mo2(CO)4(µ-I)(µ-η7 : η7-C14H12)][PF6]7. X-Ray crystallographic characterisation of 7 reveals two crystallographically distinct cations both of which exhibit a twisted conformation of the bicycloheptatrienyl ligand. Reaction of 1 with Na[Mn(CO)5] results in conversion of the carbon–carbon bond which links the bridgehead carbons, from a single to a double bond and isolation of heptafulvalene-bridged [Mo2(CO)6(µ-η6 : η6-C14H12)]8. The acetonitrile derivative [Mo2(CO)4(NCMe)2(µ-η7 : η7-C14H12)][BF4]211, formed in a two-step synthesis from 1, is activated towards η7→η3 hapticity interconversion by comparison with [Mo(CO)2(NCMe)(η7-C7H7)][BF4], and when 11 is dissolved in acetonitrile at room temperature, the major product is [Mo2-(CO)4(NCMe)6(µ-η3 : η3-C14H12)][BF4]213. Cyclic voltammetric investigations on [Mo2(NCMe)2(Ph2PCH2CH2PPh2)2(µ-η7 : η7-C14H12)][PF6]215 reveal two discrete, reversible oxidations with ΔE°= 130 mV, indicating a limited degree of intermetallic electronic communication through the bicycloheptatrienyl ligand.

This habilitation addresses the issues of Art and Geography from a grounded and lively practice of the fieldwork experience. On the edge of the subject- ever-searching-with-space, attentive to the relationality and corporeality of this practice and using transitional psychoanalytic tools, it develops the idea of a haptic regime of spatial knowledge in these two disciplines. It engages a dialogue with the geographies of identity, of creativity and publicness elaborated in the English-Speaking world. It questions the epistemological divide between Art and Geography., Cette Habilitation à diriger des recherches traite d'art et de géographie à partir de la pratique et de l'expérience vivante du terrain. A fleur du sujet-cherchant-avec-l'espace, par une attention portée à la relationnalité et à la corporalité de cette pratique, à l'aide d'outils psychanalytiques transitionnels, elle élabore l'idée d'un régime haptique de connaissance spatiale dans ces deux disciplines. Elle dialogue avec les géographies anglophones de l'identité, et de l'art (ville créative, art public). Elle interroge la ligne de démarcation épistémologique entre art et géographie.

A mechanism for the rearrangement of oxiranylpropargylic esters to cyclopentenones catalyzed by PtCl(2) is proposed based on DFT calculations (M06/6-31++G(d,p)). Although the basic steps are coincidental with those proposed by Sarpong et al., who characterized a 2H-pyran as intermediate, calculations have revealed other intricate details of this complex rearrangement. The 2H-pyran is proposed to result from the ring-opening of a bicyclic oxonium ion that follows the nucleophilic capture by the epoxide of a platinum carbene generated by an initial Pt-mediated 1,2-propargylic rearrangement. The key steps in the evolution of this system are the electrocyclic ring-opening of the 2H-pyran to a α-methoxycarbonyl dienone and an iso-Nazarov ring closure. Prior to those, changes in hapticity and in the conformation of the dienone are required in order to produce the helical conformation needed to generate a single diastereomer of the cyclopentenone product obtained experimentally. The metal is needed well beyond the first step of the mechanism, and both electrocyclic reactions are favored by coordination to the metal when compared to their uncomplexed counterparts. Moreover, we have experimentally demonstrated that the rearrangement is stereoconvergent, a feature that is traced back to the initial configuration of the epoxide, which determines the somewhat counterthermodynamic placement of the metal syn to the methyl group of the stereogenic center in the 2H-pyran intermediate. Finally, starting from enantiopure oxiranylpropargylic ester 13, a racemate of cyclopentenone (R*,S*)-16 was obtained. Thus, the sequence does not proceed with memory of chirality, and the absolute stereochemical information is already lost at the stage of the 2H-pyran 14.

Recently, our lab has developed monoanionic tridentate ligand, To{sup R}, showing the corresponding coordination chemistry and catalyst reactivity of magnesium, zirconium, zinc and iridium complexes. This thesis details synthetic chemistry, structural study and catalytic reactivity of the To{sup R}-supported rhodium compounds. Tl[To{sup R}] has been proved to be a superior ligand transfer agent for synthesizing rhodium complexes. The salt metathesis route of Tl[To{sup M}] with [Rh({mu}-Cl)(CO)]{sub 2} and [Rh({mu}- Cl)(COE)]{sub 2} gives To{sup M}Rh(CO){sub 2} (2.2) and To{sup M}RhH({eta}{sup 3}-C{sub 8}H{sub 13}) (3.1) respectively while Tl[To{sup P}] with [Rh({mu}-Cl)(CO)]{sub 2} affords To{sup P}Rh(CO){sub 2} (2.3). 2.2 reacts with both strong and weak electrophiles, resulting in the oxazoline N-attacked and the metal center-attacked compounds correspondingly. Using one of the metal center-attacked electrophiles, 2.3 was demonstrated to give high diastereoselectivity. Parallel to COE allylic C-H activation complex 3.1, the propene and allylbenzene allylic C-H activation products have also been synthesized. The subsequent functionalization attempts have been examined by treating with Bronsted acids, Lewis acids, electrophiles, nucleophiles, 1,3-dipolar reagents and reagents containing multiple bonds able to be inserted. Various related complexes have been obtained under these conditions, in which one of the azide insertion compounds reductively eliminates to give an allylic functionalization product stoichiometrically. 3.1 reacts with various primary alcohols to give the decarbonylation dihydride complex To{sup M}Rh(H){sub 2}CO (4.1). 4.1 shows catalytic reactivity for primary alcohol decarbonylation under a photolytic condition. Meanwhile, 2.2 has been found to be more reactive than 4.1 for catalytic alcohol decarbonylation under the same condition. Various complexes and primary alcohols have been investigated as well. The proposed mechanism is based on the stochiometric reactions of the possible metal and organic intermediates. Primary amines, hypothesized to undergo a similar reaction pathway, have been verified to give dehydrogenative coupling product, imines. In the end, the well-developed neutral tridentate Tpm coordinates to the rhodium bis(ethylene) dimer in the presence of TlPF{sub 6} to give the cationic complex, [TpmRh(C{sub 2}H{sub 4}){sub 2}][PF{sub 6}] (5.1). 5.1 serves as the first example of explicit determination of the solid state hapticity, evidenced by X-ray structure, among all the cationic Tpm{sup R}M(C{sub 2}H{sub 4}){sub 2}{sup +} (Tpm{sup R} = Tpm, Tpm*, M = Rh, Ir) derivatives. The substitution chemistry of this compound has been studied by treating with soft and hard donors. The trimethylphosphine-sbustituted complex activates molecular hydrogen to give the dihydride compound.

The electron distribution and orbital interactions of C 60 with metals coordinated at different sites on the outside of the fullerene are evaluated. These sites include the position of a metal atom directly above a carbon atom (η 1 site), the metal atom centered above two carbons of a pentagon or above two carbons between two pentagons (both η 2 sites), the metal atom centered above a pentagon (η 5 site), and the metal atom centered above a hexagon (η 6 site). The frontier orbitals of C 60 are illustrated first with three-dimensional orbital contour plots. A palladium atom is then used to probe the bonding at the different sites on the C 60 surface. The results with Pd 0 are compared to our earlier study with the harder Ag + ion in order to examine the effects of metal electron richness and size. In addition, these results are compared with the bonding to more traditional ligands that represent the hapticity of these sites, such as methyl (η 1 ), ethylene (η 2 ), cyclopentadienyl (η 5 ), and benzene (η 6 ). The strength of the metal-C 60 interaction and the amount of charge delocalized from the metal to C 60 is sensitive to the site of coordination, the electron richness of the metal, and distortions in the geometry of C 60 . As discussed in our previous work, the frontier orbitals of C 60 are well-suited for synergistic bonding of a metal atom to a carbon-carbon pair in an alkene-like fashion, in which the HOMO of C 60 donates carbon-carbon π bonding electron density to the metal, and the LUMO of C 60 accepts electron density from the metal into a carbon-carbon π* antibonding orbital. Although the HOMO and LUMO of C 60 describe the basic interaction, many frontier orbitals are involved. The site above the CC bond between two pentagons is favored over the site above the CC bond within a pentagon, and the interaction above the other sites is indicated to be net repulsive by these calculations. The differentiation between these sites increases with the electron richness of the metal center. The bonding of the metal to C 60 is generally weaker than to the small ligands, except for very electron rich metal centers where the bonding to the η 2 site between pentagons apparently becomes stronger than the bonding to ethylene.

Solutions containing copper(II) and an -S-S- bridged cyclic oligopeptide (general formula Cys-(Gly)n-Cys, CG(n)C, 0 less-than-or-equal-to n less-than-or-equal-to 4) in aqueous KCl (0.1 mol dm-3) were studied at 25-degrees-C by potentiometric titration methods and absorption spectrometry. The ligands studied were found to give rise to a number of complexes ; besides several (3 to 5) monoligand complexes, the formation of at least one (up to 5) bis-ligand species was detected for each ligand. Stability constants of all detected complex species (4 to 11 per ligand) were determined. From the acidity constants of individual complexes (computed from stability constants) the hapticities of the ligands were inferred. Visible absorption spectra of all examined solutions contain one peak whose position shifts hypsochromically (almost- equal-to 740 nm ... 540 nm) with increasing deprotonation and hapticity, indicating changes in the coordination geometry of the copper(II) ion, probably from tetragonal towards distorted tetrahedral. With CG2C, and additional absorption peak (588 nm) was osbserved.

A series of reactions of the general type [Mo(CO)2L2(η5-C7H9)]++ L′→[Mo(CO)2(L′)L2(η3-C7H9)]+, involving η5→η3 hapticity conversion at a molybdenum co-ordinated Cycloheptadienyl ring, have been examined. The specific examples investigated comprise reactions of [Mo(CO)2L2(η5-C7H9)]+[L2= 2,2′-bipyridyl (bipy)1, Ph2PCH2PPh2(dppm)6, Ph2PCH2CH2PPh2(dppe)7; L = CNBut17 or PPh318] with NCMe or CNBut. Complex 1 reacts reversibly with NCMe to give [Mo(CO)2(NCMe)(bipy)(η3-C7H9)]+2 and, in NCMe, 7 exists as an equilibrium mixture with [Mo(CO)2(NCMe)(dppe)(η3-C7H9)]+8. The complexes 6, 17 and 18 do not react with NCMe at ambient temperature. Treatment of 1, 6 and 7 with CNBut affords [Mo(CO)2(CNBut)L2(η3-C7H9)]+(L2= bipy 4, dppm 9 or dppe 11) although 4 is better prepared by reaction of [Mo(CO)2(CNBut)(NCMe)2(η3-C7H9)]+5 with bipy. Complex 4 is resistant to carbonyl elimination but 9 and 11 undergo facile loss of CO to give [Mo(CO)(CNBut)L2(η5-C7H9)]+(L2= dppm 10 or dppe 12) so establishing examples of associative ligand-substitution processes which proceed with η5→η3→η5 hapticity interconversion at the C7H9 dienyl ligand. The reaction between 17 and CNBut affords [Mo(CO)(CNBut)3(η5-C7H9)]+19 with no observable η3-C7H9 intermediate but 19 reacts with further CNBut to yield [Mo(CO)(CNBut)4(η3-C7H9)]+20. The crystal structures of complexes 1 and 4 have been determined. Complex 1 adopts an asymmetric ligand arrangement similar to that previously described for 6. Complex 4 has a pseudo-octahedral molecular geometry in which CNBut is located trans to the η3-bonded C7H9 ligand.

Condensation of ruthenium or osmium atoms with mixtures of hexafluorobenzene and a second arene at –196 °C has given the novel compounds [M(η6-arene)(η4-C6F6)](M = Ru or Os; arene = C6H3Me3-1,3,5, C6H4Me2-1,3 or C6H6), these being further examples of compounds with a partially co-ordinated hexafluorobenzene ligand. The hapticity of the arene rings was determined from their proton and fluorine NMR spectra. This was confirmed for the specific case of [Ru(η6-C6H3Me3-1,3,5)(η4-C6F6)] by an X-ray crystallographic study. The bis(hexafluorobenzene) compounds could not be prepared.

Bis(hexamethylbenzene) complexes of the group 8 metals (Fe, Ru, Os) show surprising diversity in their electron-transfer mechanisms and associated thermodynamics for the M(II) → M(I) → M(0) redox series. In electrochemical experiments, the Fe complex exhibits normally ordered potentials separated by ∼1 V, the Ru system shows nearly overlapping one-electron redox events, and Os demonstrates a one-step, two-electron transfer with a peak potential separation suggestive of highly inverted potentials. It has been conjectured that the sequential one-electron transfers observed for Fe are due to the lack of an accessible η(4):η(6) Fe(0) state, destabilizing the fully reduced species. Using an established model chemistry based on DFT, we demonstrate that the hapticity change is a consequence of the bonding throughout this transition metal triad and that apparent multielectron behavior is controlled by the vertical electron attachment component of the M(II) → M(I) redox event. Furthermore, the η(6):η(6) Fe(0) triplet state is more favorable than the hypothetical η(4):η(6) singlet state, emphasizing that the hapticity change is not sufficient for multielectron behavior. Despite both displaying two-electron redox responses, Ru and Os traverse fundamentally different mechanisms based on whether the first (Os) or second (Ru) electron transfer induces the hapticity change. While the electronic structure analysis is limited to the Fe triad here, the conceptual model that we developed provides a general understanding of the redox behavior exhibited by d(6) bis(arene) compounds.

Binuclear Cp(2)M(2)(μ-C(8)H(8)) derivatives have been synthesized for M = V, Cr, Co, and Ni and have now been studied theoretically for the entire first row of transition metals from Ti to Ni. The early transition metal derivatives Cp(2)M(2)(μ-C(8)H(8)) (M = Ti, V, Cr. Mn) are predicted to form low-energy cis-Cp(2)M(2)(μ-C(8)H(8)) structures with a folded C(8)H(8) ring (dihedral angle ∼130°) and short metal-metal distances suggesting multiple bonding. These predicted structures are close to the experimental structures for M = V, Cr with V≡V and Cr≡Cr bond lengths of ∼2.48 and ∼2.36 Å, respectively. The middle to late transition metals form trans-Cp(2)M(2)(μ-C(8)H(8)) structures (M = Mn, Fe, Co, Ni) with a twisted μ-C(8)H(8) ring and no metal-metal bonding. The hapticity of the central μ-C(8)H(8) ring in such structures ranges from five for Mn and Fe to four for Co and three for Ni and thus depend on the electronic requirements of the central metal atom. This leads to the favored 18-electron configuration for both metal atoms in the singlet Fe, Co, and Ni structures but only 17-electron metal configurations in the triplet Mn structure. In addition, the late transition metals form trans-Cp(2)M(2)(μ-C(8)H(8)) structures (M = Fe, Co, Ni), with the tub conformation of the μ-C(8)H(8) ring functioning as a tetrahapto (M = Fe, Co) or trihapto (M = Ni) ligand to each CpM group. A μ-C(8)H(8) ring in the tub conformation also bonds to two CpFe units as a bis(tetrahapto) ligand in both singlet and triplet cis-Cp(2)Fe(2)(μ-C(8)H(8)) structures.

The syntheses and spectroscopic properties (IR and 1H and 13C NMR spectra) of tris(methylcyclopentadienyl)-scandium and -ytterbium are described. The vapour pressure of Yb(MeCP)3 has been determined over the range 70–90°C. The gas phase electron diffraction data for M(MeCP)3 (M  Sc or Yb) have been recorded with nozzle temperatures of about 160°C. The data for M  Yb are consistent with a model containing three pentahapto cyclopentadienyl rings; Yb(η5-MeCp)3, a mean Yb to ring-centre distance of YbZ = 236.6(6) pm, and a mean YbC bond distance of 265.5(7) pm. The gas phase electron diffraction data for M  Sc are incompatible with models containing three η5-MeCp rings, but consistent with models containing two η5 rings and one ring with a hapticity of 2 or 3; η2/3-MeCp. The distance from Sc to the centres of the two η5-MeCp rings is 222.3(6) pm, corresponding to a mean Sc C(η5) bond distance of 253.0(6) pm. The third ring is at a greater distance from the Sc atom, SCZ(η2/3) = 252(5) pm, but is tilted, the angle between the ScZ(μ2/3) vector and the ring normal being 22(4)°. As a result two or three carbon atoms of the ring are in a position to form strong bonds to the metal atom. Molecular mechanics calculations indicate that interligand interactions in M(η5-C5H4)3 or M(η5-MeCP)3 molecules are strongly repulsive when MZ(η5) is less than 225 pm, and that the strain is eliminated on rearrangement to M(η5-C5H5)2(η2/3-C5H5) or M(η5-MeCP)2(η 2/3-MeCp) configurations.

The review covers the results of studies on the reactions of iron, ruthenium, and osmium carbonyls with olefins having functional group substituents, the behaviour of which differs significantly from that of simple olefins. Such studies have made it possible to create a new aspect of the chemistry of olefin complexes. The development of this field has led to the synthesis of previously unknown mononuclear and polynuclear complexes and to the discovery of unusual rearrangements of the complex compounds. The reactions of iron carbonyls differ from those of ruthenium and osmium carbonyls. In the last case, the hapticity of the unsaturated ligands increases and the ligands are found to be capable of giving rise to extremely unexpected structures. The present review surveys mainly the results of studies by the authors, who made a significant contribution to the development of this field. The bibliography includes 73 references.

Cooperative Effects in π1-Ligand-Bridged Dinuclear Complexes, XIII[1]. – Unexpected Weak d-d Interactions in Synfacial Heterodinuclear μ1-Cyclooctatetraene Complexes of the Type {(CpCr)[(CO)3M′]}μ1-Cot (M′Fe, Cr, W) The heterodinuclear complexes {(CpCr)[(CO)3M′]}μ1-Cot (CotC8H8; M′Fe, Cr, W) (5 – 7) and {(Cp*Cr)[(CO)3Cr]}μ1-Cot (Cp*C5Me5) (9) are synthesized by the reaction of the corresponding mononuclear Cot complexes CpCr(η61-Cot) (4) and Cp*Cr(η61-Cot) (8), respectively, with M′(CO)3(EtCN)3 (M′Cr, W) and with Fe2(CO)9. The CrFe compound 5 is obtained in very low yield only. However, much better yields of 5 are achieved in the reaction of CrCl2 and CrCp2 with (CO)3Fe(η41-Cot) (10) in the presence of an excess of Zn. X-ray structure determinations of 5 and 6 reveal synfacial configurations of the CpCr and M′(CO)3 units with a μ1-η5:3- and μ1-η4:51-Cot bonding mode for 5 and 6, respectively. The metal – metal distances are 2.9369(13) A for 5 and 2.81(2) A for 6 indicating metal – metal single bonds. 5 contains 33 valence electrons (ve) and is paramagnetic with one unpaired electron. A well-resolved fluid-solution ESR spectrum of 5 shows a 53Cr and 1H hyperfine structure (hfs). The 1H hfs can be calculated with three different 1H hyperfine coupling constants (1H hfcc) indicative of protons in α1-position with respect to the paramagnetic metal center: one 1H hfcc of the five Cp protons (1.68 G), one of three (3.32 G) and one of two protons of the Cot ligand (5.04 G). This agrees with the Cot bonding mode of the CpCr unit in the crystalline phase. The ratio of 3:2 protons for the Cot ligand prove the rigidity of the Cot ligand on the ESR time scale. The excellent agreement of the ESR data of the liquid and frozen solution ESR spectra of 5 with the ESR data of the mononuclear complex CpCr(η61-Cot) leads to the conclusion that the unpaired electron in 5 must predominantly be chromium-centered. 6, 7, and 9 have 31 ve and are paramagnetic with three unpaired electrons as shown by means of ESR spectroscopy and magnetic measurements. The calculations of the quartet ESR spectra of 6, 7, and 9 reveal zero-field splitting parameters D ranging from 3.6 to 4.8 cm–1 which are similar to that of the mononuclear quartet compound vanadocene. The small range in the parameters D prove the minor influence of the second metal on going from Cr to W. Hence, the three unpaired electrons are assumed to be mainly localized on the Cr center of the CpCr unit. Cyclic voltammetry studies result in the redoxcascade − 2 ⇄ − 1 ⇄ 0 ⇄ + 1 for 5 and 7 at +20°C and for 6 at –35°C. However, at +20°C 6 and 9 only show one electrochemically reversible reduction wave 0/–1, whereas the oxidation 0/+1 and the second reduction –1/–2 are irreversible. The redox potentials indicate a considerable influence of the metal combinations. On the strength of the ESR spectroscopic results and according to the results of crystal structure determinations, an isolobal relationship is drawn between the (CO)3M′(η8 – ×1-Cot) fragment and a cyclic organic π1-ligand with the hapticity × + 1.

Azulene is reported to react with Mn(2)(CO)(10) to give trans-C(10)H(8)Mn(2)(CO)(6), which has been shown by X-ray crystallography to have a bis(pentahapto) structure with no metal-metal bond. This structure is found by density functional theory to be the lowest energy C(10)H(8)Mn(2)(CO)(6) structure. However, a corresponding bis(pentahapto) cis-C(10)H(8)Mn(2)(CO)(6) structure, also without an Mn···Mn bond, lies within ~1 kcal mol(-1) of this global minimum. The lowest energy C(10)H(8)Mn(2)(CO)(5) structure is singlet cis-η(5),η(5)-C(10)H(8)Mn(2)(CO)(5) with an Mn→Mn dative bond from the Mn(CO)(3) group to the Mn(CO)(2) group. However, a singlet cis-η(6),η(4)-C(10)H(8)Mn(2)(CO)(5) structure with a normal Mn-Mn single bond lies within ~6 kcal mol(-1) of this global minimum. The lowest energy structures of the more highly unsaturated C(10)H(8)Mn(2)(CO)(n) (n = 4, 3, 2) systems all have cis geometries and manganese-manganese bonds of various orders. The corresponding global minima are triplet cis-η(5),η(3)-C(10)H(8)Mn(2)(CO)(3)(η(2)-μ-CO) for the tetracarbonyl with a four-electron donor bridging carbonyl group, singlet cis-η(5),η(5)-C(10)H(8)Mn(2)(CO)(3) for the tricarbonyl, and triplet cis-η(6),η(4)-C(10)H(8)Mn(2)(CO)(η(2)-μ-CO) for the dicarbonyl.

The coordination chemistry of alkenes is among the fundamentals of organometallic chemistry. However, despite the beneficial effects of fluorination to organic molecules, their fluorinated counterparts are rarely found in transition-metal complexes and most examples are limited to simple monoalkenes like tetrafluoroethene. The paucity of fluorodiene complexes is contrasted by their structural diversity. Seemingly similar dienes containing conjugated, isolated or cumulated double bonds exhibit largely different ligand properties. While the most prominent group, the conjugated fluorodienes, is very flexible in hapticity, their analogues bearing isolated double bonds behave more like monoalkenes. Fluorinated cumulenes in contrast are thermally labile, their chemistry is dominated by the stabilising effect of metal coordination. This review outlines the synthesis, structure and reactivity of transition-metal complexes derived from fluorinated dienes.

In the realm of atropochiral ligands initiated by the BINOL and BINAP paradigms and extended by modifications of the 1,1′-binaphthyl backbone and the coordinating heteroatoms (O, P, N, S,..), the emerging domain of the carbon versions serving as spectator ligands in catalysis is reviewed. These atropochiral C,X-chelating ligands are classified according to their coordinating mode (monodentate or bidentate), to the nature of the auxiliary donor X (a heteroatom or a carbon atom), to the overall charge of the coordinating carbon function (neutral or anionic C-ligands), and to the hapticity of the coordinating carbon function (η1 for NHCs and ylides, or η2 for alkenes). Emphasis is put on both synthetic aspects and applications in catalysis, and especially in asymmetric catalysis. This survey suggests that the “carbon ligands” should continue to provide surprises not only in coordination chemistry and in stereoselective synthesis and catalysis, but also in fundamental molecular chemistry by pushing farther the stability limits of the metal–ligand interactions, thus reconciliating further the fields of organic and inorganic chemistry.

Cyclopentadienylaluminum compounds have been a curiosity due to the ring-slipped structures they exhibit and due to their highly fluxional nature, which has prevented the freezing out of discrete solution structures on the NMR time scale. Lately, increased attention toward these compounds in the form of molecular structure determinations, theoretical calculations, and 27Al-NMR spectroscopic measurements is providing a clearer picture of the bonding between the aluminum and its cyclopentadienyl ring(s). A variety of ring coordination geometries (η1, η2, η3, η5) have been identified in molecular structures of these compounds, and although theoretical calculations reveal very small energy differences between different haptotropes, consistent with their highly fluxional behavior in solution, there is close agreement between the calculated ground state geometries for the compounds and the geometries they exhibit in the solid state and in solution. Theory and experiment reveal a delicate balance of covalent π-interactions and ionic interactions between the aluminum and its cyclopentadienyl ring. Although the balance is easily tipped by steric effects, some structural trends are emerging. The solution 27Al-NMR chemical shifts of cyclopentadienylaluminum compounds are surprisingly diagnostic of their geometries, exhibiting a strong correlation with coordination numbers that take into account the hapticity of the cyclopentadienyl ring.

[reaction: see text] The in situ generation of a copper-poly(pyrazolyl)borate complex from copper chloride and a sodium poly(pyrazolyl)borate salt results in a catalyst that is effective for the aziridination of olefins. A significant influence of the combination of the starting copper oxidation state and the hapticity of the poly(pyrazolyl)borate ligand on the efficiency of the reaction has been observed.

Addition of a nucleophile to an (η6-arene)tricarbonylchromium or a tricarbonyl(η5-cyclohexadienyl)manganese complex substituted with a leaving group X (X = F, Cl, OMe, OPh, NR2) affords (after treatment with acid) new complexes with the same η6 or η5 hapticity. The overall reaction involves addition of the nucleophile ortho, meta, or para with respect to the leaving group and HX elimination. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Novel [Rh(η-diene)Tp(x)] complexes of sterically encumbered Tp(x) ligands (Tp(x) = Tp(4Bo), diene = cod, 1; nbd, 2; Tp(x) = Tp(4Bo,5Me), diene = cod, 3; nbd, 4; Tp(x) = Tp(a,3Me), diene = cod, 5; nbd, 6; Tp(x) = Tp(a*,3Me), diene = cod, 7; nbd, 8) have been prepared by treatment of [Rh(η-diene)(μ-Cl)](2) with TlTp(x) (Tp(x) in general, in detail: Tp(4Bo) = hydrotris(indazol-1-yl)borate, Tp(4Bo,5Me) = hydrotris(5-methyl-indazol-1-yl)borate, Tp(a,3Me) = hydrotris(3-methyl-2H-benz[g]-4,5-dihydroindazol-2-y1)borate, Tp(a*,3Me) = hydrotris(3-methyl-2H-benz[g]indazol-2-yl)borate), and characterized by analytical and spectral data (IR, (1)H, (11)B, and (13)C NMR solution). The structures adopted by [Rh(nbd)Tp(4Bo)] 2, [Rh(cod)Tp(4Bo,5Me)] 3, [Rh(nbd)Tp(a,3Me)] 6, [Rh(nbd)Tp(a*,3Me)] 8, and [Rh(nbd)Tp(a*,3Me*)] 8* (incorporating a borotropomeric ligand), have been investigated. Low steric hindrance between the ligands in 2 and 3 permits κ(3) coordination of the pyrazolylborate while the high steric encumbrance present in 6, 8, and 8* results in κ(2) ligands. The coordination modes of the ligands to the metal have also been established by (15)N CPMAS studies of selected ligands and their corresponding Rh complexes. These spectroscopic data are in agreement with the (15)N chemical shifts obtained by using quantum-chemical methods to assist reliable assignments of the experimental values, affording new insights into the extraction of structural information concerning the hapticity (κ(2) or κ(3)) of the poly(pyrazolyl)borate ligands to the Rh metal.

The ligands 8-diphenylphosphanylquinoline (DPPQ) and 8-diphenylphosphanyl-2-methylquinoline (DPPQ-Me) react in chlorinated solvents with the allyl dimers [Pd(μ-Cl)(η3-C3H5)]2 and [Pd(μ-Cl)(η3-C3H3M...

The sigma-bond metathesis reaction between PhSiH(3) and the heteroleptic metal pentafluorophenyl compounds [Dmp(Tph)N(3)MC(6)F(5)(thf)(n)] (Dmp = 2,6-Mes(2)C(6)H(3) with Mes = 2,4,6-Me(3)C(6)H(2); Tph = 2-TripC(6)H(4) with Trip = 2,4,6-(i)Pr(3)C(6)H(2); n = 1, 2; M = Sr, Ba, Eu) supported by sterically crowded, biphenyl- and terphenyl-substituented triazenido ligands afforded the first homoleptic stontium, barium, and europium triazenides [M{N(3)Dmp(Tph)}(2)] {M = Sr (2), Ba (4), Eu (5)}. Crystallization of 2 from an n-heptane/1,2-dimethoxyethane mixture gave the complex [Sr{N(3)Dmp(Tph)}(2)(dme)] (3). All new compounds have been characterized by (1)H and (13)C NMR spectroscopy (not 5), elemental analysis, IR spectroscopy (5 only), and X-ray crystallography. In the solid-state structures, the first coordination sphere of the metal cations consists of four nitrogen atoms of the two bidentate triazenide ligands. Additional metal-eta(n)-pi-arene-interactions of different hapticity n (n = 3-6) are observed to the flanking arms of the terphenyl substituents.

International audience; By employing high-resolution electron energy loss spectroscopy (HREELS), temperature-programmed desorption (TPD), and low-energy electron diffraction (LEED), we have studied the adsorption and thermal decomposition of crotonaldehyde (2-butenal) on Pt(111) as well as Pt3Sn/Pt(111) and Pt2Sn/Pt(111) surface alloys. In order to understand the adsorption structures and the vibrational properties, an extensive theoretical study of the possible adsorption geometries and vibrational spectra on the three considered surfaces has been carried out using density functional theory (DFT). A careful analysis of the variety of possible adsorption configurations of crotonaldehyde allowed structural identification by correlating their vibrational fingerprints with the measured HREELS peaks. The mixed phases of crotonaldehyde formed on the model catalysts turned out to be even more complex than those we found in previous studies for prenal. The set of stable configurations identified by combination of HREELS with DFT consists of η2, η3, and η4 flat adsorption structures, which exhibit adsorption energies from −69 to −80 kJ/mol. Nonetheless, the thermal decomposition measured with TPD and the general adsorption behavior show similarities to prenal and acrolein. Starting from a strongly adsorbed state on Pt(111) at low temperatures, crotonaldehyde decomposes at temperatures close to 300 K. On the surface alloys, a high-coverage phase with structures of low hapticity such as η2-diσ(CC) is measured at low temperatures (∼160 K), and a low-coverage situation of high hapticity η2, η3, and η4 configurations is formed at higher temperatures (∼200 K). On Pt3Sn/Pt(111), two energetically competitive η1-top-E-(s)-trans-OSn forms cannot be excluded at low temperatures.

The preparation of novel alkali metal chalcogenides supported by multidentate nitrogen rich ligands is reported. Treatment of the ligand precursors [H{(4,5-(P(E)Ph(2))(2)tz}] (E = S (1a), Se (1b)) with organolithium reagents or elemental sodium and potassium in tetrahydrofuran (THF) leads to the isolation of 2-7 in high yields. These compounds were characterized by elemental analysis, IR spectroscopy, mass spectrometry, solution and solid-state multinuclear NMR spectroscopy, and single crystal X-ray diffraction analysis. In the solid state, 2, 4, and 5 are dimers that contain bimetallic six-membered (M(2)N(4)) rings (M = Li, Na). In 3, the discrete monomer [Li{4,5-(P(Se)Ph(2))(2)tz}(thf)(2)] (tz = 1,2,3-triazole) contains a five-membered CPSeLiN ring which adopts an envelope conformation. The polymeric arrangement [K{4,5-(P(S)Ph(2))(2)}tz](infinity) in 6 displays different bonding modes based on the hapticity of the ligand upon binding to the potassium atom. In compounds 2-6, the presence of secondary bonding features the alkali metal chalcogen bonds.

Coordination of diazines such as quinoxaline to transition metals stabilizes radical anions generated by chemical or electrochemical cathodic reduction. However, even though various sorts of radical anionic diazines have been subjected to spectroscopic investigations in the recent past, reports combining structural, solid-state electron paramagnetic resonance (EPR) and computational investigations of kinetically stable species are still missing. In this study, four radical anions derived from tricarbonylmanganese- and tricarbonylrhenium-bound quinoxaline chelates, embedded within a triple-decker architecture, have been prepared from neutral substrates by chemical reduction over alkaline metals (K, Rb); the electronic structure of the latter metalloorganic paramagnetic salts was investigated by the means of structural X-ray diffraction analysis, electrochemistry, solution and crystal EPR spectroscopy, and density functional theory (DFT). Unprecedented structures of three manganese-bound and one rhenium-bound quinoxaline-derived paramagnetic salts were obtained from solutions of the corresponding radical anions crystallized in the presence of cryptand 222. It is inferred from a comparative study of the structures of anionic and neutral quinoxaline complexes that reduction does not have any significant impact over the coordination mode of the metal centers and over the overall geometry of the triple-decker architecture. The most notable changes in the radical-anionic metalloorganic species, as compared to the neutral parent molecules, comprise a slight hapticity shift of the metal-bound benzyl moiety and a weak intraannular distortion of the quinoxalyl core. Single-crystal EPR experiments carried out with the rhenium and manganese compounds produced the respective anisotropic g tensor, which was found in each case to be essentially located at the quinoxalyl fragment. Computations, carried out using DFT methods (B3LYP-LANL2DZ and Becke-Perdew-TZP), corroborated the features suggested by structural analysis. Single-point calculation using the B3LYP functional and various basis sets [LANL2DZ, 6-31G(d), 6-311+G(d), and 6-311+G(2d,p)] provided us with values of anisotropic g tensors and hyperfine coupling constants consistent with those determined experimentally. It is inferred from this study that the two metal centers bound to the nitrogen atoms of the quinoxalyl core contribute in the lowering of the HOMO-LUMO gap in the neutral species. The triple-decker arrangement, which combines chelation of the metal, steric protection, and encapsulation of the central quinoxalyl core, is a stabilizing factor that provides a long-lived character to the radical-anionic species.

The synthesis and structural characterization of lanthanum(III) and uranyl(VI) complexes coordinated by tridentate diglycolamide (DGA) ligands O(CH2C(O)NR2)2[R=i-Pr (L1), i-Bu (L2)] are described. Reaction of L with UO2Cl2(H2O) n forms the uranyl(VI) cis-dichloride adducts UO2Cl2L [L=L1 (1a), L2 (1b)], while reaction of excess L with the corresponding metal nitrate hydrate produces [LaL3][La(NO3)6] [L=L1 (2a), L2 (2b)] for lanthanum and UO2(NO3)2L [L=L1 (3a), L2 (3b)] for uranium. Compounds 2b and 3a have been structurally characterized. The solid-state structure of the cation of 2b shows a triple-stranded helical arrangement of three tridentate DGA ligands with approximate D3 point-group symmetry, while the counteranion consists of six bidentate nitrate ligands coordinated around a second La center. The solid-state structure of 3a shows a tridentate DGA ligand coordinated along the equatorial plane perpendicular to the OUO unit as well as two nitrate ligands, one bidentate and oriented in the equatorial plane and the other monodentate and oriented parallel to the uranyl unit with the oxygen donor atom situated above the mean equatorial plane. Ambient-temperature NMR spectra for 3a and 3b indicated an averaged chemical environment of high symmetry consistent with fluxional nitrate hapticity, while spectroscopic data obtained at -30 degrees C revealed lower symmetry consistent with the slow-exchange limit for this process.

The adsorption and thermal decomposition of the α,β-unsaturated aldehyde prenal (3-methyl-2-butenal) have been studied on Pt(111), the Pt3Sn/Pt(111) and Pt2Sn/Pt(111) surface alloys, and the corresponding terminations of the Pt3Sn(111) bulk alloy by means of high-resolution electron energy loss spectroscopy (HREELS), temperature-programmed desorption (TPD), and low-energy electron diffraction (LEED). By comparing the experimental results with extensive theoretical calculations of the multitude of possible adsorption configurations of prenal using density functional theory (DFT), the adsorption configurations actually present on all model catalysts have been identified. This approach, thus, reveals a new way to identify complex, multifunctional molecules adsorbed on model catalyst surfaces. On Pt(111), prenal is strongly adsorbed and decomposes at approximately 300 K. By the aid of density functional theory (DFT), five flat-lying adsorption structures of η2, η3, and η4 hapticity, which exhibit similar adso...

The crystal and molecular structures of [(η-C9H7)2M] (M = Fe, 1; Co, 2; Ni, 3) and [(η-C9Me7)2Fe], 4, are reported, along with a discussion of the correlation between hapticity and the 13C chemical shift of the indenyl ring-junction carbons (C(3a), C(7a)). Single crystals of both 1 and 2 undergo non-destructive and reversible phase changes upon cooling below ca. 240–245 K. The room-temperature structures are disordered; however, the low temperature ones (150 K) are essentially ordered. Crystals of 3 do not display this behavior on cooling to 150 K, and residual anisotropy in certain carbon atoms is ascribed to a minor twinning problem. Crystals of 4 were only examined at ambient temperature, where an ordered structure was obtained. In contrast to the analogous Cp2M series (Cp = η5-C5H5; M = Fe, Co, Ni), which display a gradual symmetric increase in MC distances in the order Fe < Co < Ni, the distortions in the indenyl series are of a fundamentally different nature. Thus, there is a gradual increase in the degree of slip-fold distortion from η5- toward η3-coordination which involves (a) slippage of the metal away from C(3a),C(7a), and (b) folding of the ring system (particularly at C(1),C(3)), in the order Fe < Co < Ni. The slip values (Δ = avg d(MC(3a),C(7a)) − avg d(MC(1),C(3)) are 0.043(4), 0.124(4), 0.418(6), and 0.030(4) A for 1–4, respectively. For a “true η5”-complex, Δ should be ca. 0 A, whereas values of ca. 0.69–0.79 A have been reported for “true η3-”indenyl complexes such as [(η3-C9H7)Ir(PMe2Ph)3]. Therefore, complexes 1 and 4 are clearly η5, as predicted on the basis of the 18-electron rule, whereas 2 and 3 display increasing degrees of distortion in both rings to avoid 19- and 20-electron counts, respectively. The two indenyl rings in 3 are half-way between η5- and η3-coordination modes. Crystal data for 1 at 295 K are: monoclinic, P21n, a 8.030(2), b 7.806(2), c 10.779(2) A, β 107.39(1)°, V 648.9(2) A3, Z = 2, structure not refined; at 150 K: monoclinic, Cc, a 16.021(4), b 15.510(5), c 11.187(3) A, β 115.53(2)°, V 2509(1) A3, Z = 8, R = 0.0306, Rw = 0.0332. For 2 at 295 K: monoclinic, P21n, a 8.027(2), b 7.838(2), c 10.936(3) A, β 107.57(2)°, V 655.9(2) A3, Z = 2, structure not refined; at 150 K: monoclinic, P21c, a 11.258(3), b 7.824(3), c 15.256(6) A, β 108.07(2)°, V 1277.7(7) A3, Z = 4, R = 0.0397, Rw = 0.0447. For 3, at 150 K: monoclinic, P21n, a 6.063(1), b 20.056(3), c 10.703(2) A, β 94.27(1)°, V 1297.9(3) A3, Z = 4, R = 0.0413, Rw = 0.0493. For 4, at 295 K: orthorhombic, Pbcn, a 14.211(2), b 9.284(2), c 19.289(4) A, V 2544.8(8) A3, Z = 4, R = 0.0410, Rw = 0.0421.

Infrared spectroscopic evidence, including 13CO labelling and energy-factored force-field fitting, is presented to show that once a CO ligand has been photochemically ejected from [Mn(C7H7CO)(CO)5] to yield [Mn(σ-C7H7)(CO)5]via a 16-electron species, [Mn(C7H7CO)(CO)4], subsequent photolyses of [M (σ-C7H7)(CO)5] complexes (M = Mn or Re) leads to sequential formation of the 18-electron species [M(η3-C7H7)(CO)4], [M(η5-C7H7)(CO)3], and [M(η-C7H7)(CO)2] in Ar, CH4, N2, and CO matrices at ca. 12 K. The fact that no 16-electron species were observed prior to ring slippage even at such low temperatures indicated that such ring slips occur extremely readily or that they occur as a concerted process with CO ejection. The facility of the ring-slippage process was demonstrated by the failure of intermediate species [M(σ-C7H7)(CO)5] and [M(η3-C7H7)(CO)4] to undergo exchange with 13CO in doped matrices or to take up a N2 ligand when photolyses are carried out in nitrogen matrices. Exchange with 13CO and substitution of CO by N2 does, however, occur once the ring-slippage process is nearing completion for Mn affording [Mn(η5-C7H7)(12CO)n(13CO)3 –n] and [Mn(η5-C7H7)(CO)2(N2)]. The electronic spectra of [Mn(η7-C7H7)(CO)2] shows vibrational splitting which indicates a symmetric structure, cf.[Co(η5-C5H5)(CO)2], rather than a bent geometry. The photophysical and photochemical processes associated with the observed reactions are discussed.

This contribution reviews the structural and dynamical properties of mononuclear transition metal complexes with tetrahydroborate ligands. Three different coordination modes involving one (η1), two (η2) or three (η3) bridging hydrogen atoms are possible for the BH4 – ligand. A structural classification of the X-ray characterised complexes is presented. The metal-boron distances and the vibrational frequencies of the coordinated borohydrides, which are the key experimental data usually used to determine the hapticity of tetrahydroborate binding, have been surveyed and trends along the Periodic Table established. Electronic factors governing the coordination mode have been rationalized by means of simple orbital arguments supported by quantitative calculations. In solution, most of the transition metal tetrahydroborate complexes show fluxional behaviour, displaying a single resonance for the four B–H hydrogens in the 1H NMR spectrum at ambient temperature. This fast intramolecular exchange between bridging and terminal hydrogens has been analysed. Experimental and computational data for these processes have been collected and the exchange mechanisms are discussed. In summary, several examples illustrating the perspectives on the field are presented.

The first homoleptic anions of hydroxylaminato ate-complexes of yttrium and samarium of the formulae K[M((ONPr2)-Pr-i)(4)] (M=Y, Sm) have been prepared and structurally characterised featuring variations of the hapticity of their (ONPr2)-Pr-i ligands leading to different chain connectivities in their solid state aggregates.

This review covers in detail the chemistry of manganese compounds without carbonyl or isonitrile ligands from 1993 through 2005. Recent developments in the chemistry of manganocene and its derivatives are well the extensive manganese centers linked by conjugated carbon bridges, with linkages of 2, 4 and even 8 carbons. The material in the chapter is organized by ligand type, and when two or more ligand types are present the reactions are listed under that with the lower hapticity.

Using density functional theory within the generalized gradient approximation, I analyzed the electronic structure of a C60–ferrocene hybrid [= C FeCp] around HOMO in comparison with that of ferrocene, where C and Cp denote C60(CH3)5 and a cyclopentadienyl ring. HOMO–LUMO gap is significantly smaller than that of ferrocene because of the intervention of π(C) states below LUMO. In addition, geometrical and electronic structures of N@C FeCp are also investigated. I find that there are two isomers with the energy difference of 0.13 eV. In one of the two, the encased nitrogen atom is located at the center of the fullerene cage. The Fe atom is η5-coordinated to both Cp and R*, where R* is a five-membered ring of C cage. On the other hand, the atom is coordinated to R* with η4-hapticity, and the nitrogen atom is bonded to a carbon atom of the R* ring in the other isomer. Upon the isomerization between the two isomers, there occurs a partial transfer of spin density between the nitrogen and Fe atoms as well as the creation and breaking of a CN bond. © 2006 Wiley Periodicals, Inc. J Comput Chem 28: 594–600, 2007

Studies involving the preparation, reactivity, and properties of the organometallic complexes of iron (compounds possessing a FeC bond) have played a central role in the growth of organometallics as a major subdiscipline with chemistry. From the discovery of ferrocene in the 1950s to the present day, interest and research activity remain high. This entry provides a survey of this large and diverse area of organometallic chemistry, and is arranged by increasing hapticity of the organic ligand of interest that is bound to iron. Included are discussions of the chemistry of iron σ-alkyl, acyl, alkynyl, and vinyl complexes, iron carbenes, η1- and η3-allyl iron complexes, η2-alkene and η4-diene iron complexes, trimethylenemethane and cyclobutadiene complexes of iron, cationic iron pentadienyl, cyclohexadienyl, and arene complexes, and ferrocenes and heteroferrocenes. Keywords: iron organometallics; iron carbene; tricarbonyliron complex; ferrocene; iron diene complex; iron alkene; iron alkyl; iron acyl; iron allyl; iron pentadienyl cation