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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis of the Germanium(I) Compounds [Ge2Hal4]2- and Their Reductive Condensation to Octahedral [Ge6]2- Clusters in an Organometallic Environment (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 879-887 
    Details
    ISSN: 1434-1948
    Keywords: Germanium(I) ; Tetrahalgenodigermanate(2-) ; Octahedral [Ge6]2- clusters ; Organometallic derivatives ; Carbonyl complexes ; Chromium ; Tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: GeI2 reacts with [M2(CO)10]2- (M = Cr, W) leading to reductive coupling of two GeI2 units to produce the [Ge2I4]2- ligands of [{(OC)5M}I2Ge-GeI2{M(CO)5}]2- (1a and 2a). The [Ph4P] salts of these anions have been characterised by X-ray structure analyses as have the [Ph4P] salts of [{(OC)5M}Cl2Ge-GeCl2{M(CO)5}]2- (1b and 2b) obtained from the iodo derivatives 1a and 2a by halide metathesis with [Ph4P]Cl. Treatment of GeI2 with [W2(CO)10]2- in the presence of 2,2′-bipyridine leads to [{(OC)5W}I2Ge-Ge(bipy){W(CO)5}] (3). The digermanium ligands in 1-3 contain germanium in the unconventional formal oxidation state +I. Reductive condensation of [{(OC)5Cr}I2Ge-GeI2{Cr(CO)5}]2- (1a) by addition of [Cr2(CO)10]2- leads to the octahedral cluster [{(OC)5Cr}6Ge6]2- (4) in a yield of 40%. The sequence of reactions as reported describes the first systematic approach to the synthesis of [E6]2- clusters.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Electron Transfer in Dinuclear Cobalt Complexes with “Non-innocent” Bridging LigandsPart of this work was presented at the 31st International Conference on Coordination Chemistry, Vancouver (Canada), August 1996. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 732-743 
    Details
    ISSN: 0947-6539
    Keywords: bridging ligands ; charge transfer ; cobalt ; quinones ; tripodal ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of tripod cobalt(II) templates [{CH3C(CH2PAr2)3}CoII] with potentially bridging ligands L generates the dinuclear compounds [(tripod)-Co-L-Co(tripod)]2+. With L = oxalate (C2O2-4) a biscobalt(II) complex (1) is formed, while with L = C6H2O2-4, the dianion derived from 2,5-dihydroxy-1,4=benzoquinone (anilic acid), two-electron transfer within the dimetallic unit occurs and a biscobalt(III) charge distribution results (2a), as shown by X-ray structural analyses of 1 and 2a, NMR spectroscopy, and theoretical investigations by the INDO method. Complex 2a exhibits an unusually intense, low-energy absorption in its electronic spectrum; this is explained with a simple MO model. One-electron reduction of 2a generates the corresponding mixed-valence complex, which is highly stabilised through extensive electron delocalisation. Substituents at the 3,6 positions of the bridging ligand (Cl, Br, I, NO2, Me, iPr, Ph; 2b-h) as well as alkyl substitution at the aromatic rings of the tripod ligands (3, 4) influence the optical and electrochemical properties consistent with the proposed model of charge distribution. Formal replacement of one [(tripod)CoIII]3+ moiety by [CH2]2+ leads to the mononuclear complex 6, which is shown to be a typical [(tripod)CoIII=(catecholato)]+ complex. Therefore the substantially different optical and electrochemical properties of the dinuclear complexes with respect to those of 6 result from strong metal-metal interactions mediated by the bridging ligand.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030513
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetic Interaction in Dinuclear Triphos-Cobalt Complexes with Co···Co Separations of 8 and 10 Å (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 183-189 
    Details
    ISSN: 1434-1948
    Keywords: Tripodal ligands ; Cobalt complexes ; Bridging ligands ; Exchange coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Weak antiferromagnetic exchange interactions are observed in two CoII dimers of the general formula [{(triphos)Co}2(μ-dicarboxylato)](BF4)2 where the dicarboxylate is the dianion of fumaric acid [3 ·(BF4)2] or terephthalic acid [4 ·(BF4)2] and triphos is the tridentate phosphorus ligand 1,1,1-tris(diphenylphosphanomethyl)ethane. In these complexes the metal ions are separated by 8 and 10 Å, as determined by X-ray crystallography. Insight into the interaction pathway is gained through molecular orbital calculations performed on model compounds. The influence of bridging-ligand distortions and the stereochemistry around the two cobalt centres is discussed.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Four-Coordinate Group-14 Elements in the Formal Oxidation State of Zero - Syntheses, Structures, and Dynamics of [{(CO)5Cr}2Sn(L2)] and Related Species (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 703-720 
    Details
    ISSN: 1434-1948
    Keywords: Germanium ; Tin ; Lead ; 119Sn NMR ; Dynamic NMR ; Salt metathesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sodium salts Na2[{(CO)5M}2EX2] (M = Cr, Mo, W; E = Ge, Sn, Pb; X = Cl, I, OOCCH3) react with 2,2′-bipyridine (bipy) to form neutral compounds [{(CO)5M}2E(bipy)] (E = Sn: 1a-1c; E = Ge: 3a; E = Pb: 4). 1,10-Phenanthroline (phen) analogues of compounds 1a-1c and 3a [{(CO)5M}2E(phen)] (E = Sn: 1d-1f, E = Ge: 3b) are as well accessible. The 2,2′-bipyridine ligand in 1 may be formally replaced by two pyridine (py) ligands resulting in [{(CO)5M}2Sn(py)2] (1g: M = Cr, 1h: M = W). The bis-bidentate ligand 2,2′-bipyrimidine (bpmd) is found to coordinate just one [{(CO)5M}2Sn] entity in [{(CO)5M}2Sn(bpmd)] (2b: M = Cr, 2c: M = W). The biimidazolato (biim) ligand binds two [{(CO)5Cr}2Sn] moieties in [{(CO)5Cr}2Sn(biim)Sn{Cr(CO)5}2]2-, 2a. It is shown by 1H-NMR that the pyrimidine entities in these compounds (2b, 2c) are able to rotate by a full 180° turn-around with respect to one another. This process must involve complete de-coordination of at least one of the two nitrogen donors in again at least one of the chelate cycles, the activation energy for this process being around 60 kJ/mol. By 119Sn-NMR spectroscopy of almost all of the tin compounds described it is shown that equilibria between [{(CO)5M}2Sn(L2)] and [{(CO)5M}2Sn(L)] + L exist in all cases. From the temperature dependence of the δ values it is concluded that the activation barriers for this association/dissociation process is below 10 kJ/mol. The structures of all new compounds are documented by X-ray analyses and all compounds are characterized by the usual analytical and spectroscopical techniques.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    The 1,3-Sn2O2-Heterocycle as a Ligand in Organometallic Compounds - Dimerization of the Inidene Species [{(CO)5M}2SnOR]- (M = Cr, W) (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1057-1066 
    Details
    ISSN: 1434-1948
    Keywords: Pentacarbonylmetal-tin bonding ; Alkoxytin compounds ; Inidene compounds ; 119Sn NMR ; Bonding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dimerized inidene complexes [(CO)5M-Sn(OR)-M(CO)5]22- (M = Cr, W; R = Et, iPr), 1, are obtained from [{(CO)5M}2SnCl2]2- by different routes. Dimerization occurs via alkoxy-donor tin-acceptor bonding by which a planar Sn2O2 ring is formed. The Sn-{M(CO)5} bonds are made in a plane vertical to this ring such that, with the R-O groups being almost coplanar with the Sn2O2 ring, the overall geometry of the compounds shows idealized D2h symmetry. - The 119Sn-NMR resonances of 1 are found at rather low fields (M = Cr: δ ≈ 1400; M = W: δ ≈ 1170) indicating a low-lying tin-centered orbital in the LUMO range. Correspondingly EHT analyses show that the 3-center-4π system, which characterizes monomeric inidene species [LnM-E(X)-MLn]n, is still prevalent in the dimeric species 1. The low-lying π*-type LUMOs of 1 are the rationale for the observed 119Sn-NMR low-field shifts of 1. The dimeric compounds 1 react with 2,4-pentanedione to form chelate compounds of the same type as those characteristically obtained from monomeric inidene complexes: [{(CO)5Cr}2SnOEt]22- (1a) reacts to give [{(CO)5Cr}2Sn(acac)]- (2). The experimental results are verified by X-ray analyses in addition to the usual spectroscopic and analytical investigations.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Functionalized Ether Derivatives of HOCH2C(CH2PPh2)3 and Related Tripod Ligands - Synthesis and Coordination Chemistry (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1407-1415 
    Details
    ISSN: 1434-1948
    Keywords: Functionalized tripod ligands ; Mixed donor set ligands ; Solubilized tripod ligands ; Molybdenum ; Iron ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Neopentane-derived tripod ligands of the general type HOCH2C(CH2PPh2)(CH2Y)(CH2Z) (1; Y, Z = PPh2, SR) are notoriously resistant to ether formation at their hydroxy group. Two routes have been found, which allow the transformation of 1 into ether functionalized tripod ligands ROCH2C(CH2PPh2)(CH2Y)(CH2Z) (Y = Z = PPh2: 5, Y = Z = SR: 8). One of these strategies relies upon the η3 coordination of 1 in 1·Mo(CO)3 (2). By this way the donor groups are efficiently protected and the steric encumbrance of the CH2OH group at the backbone of the ligands is greatly reduced by fixing three arms of the neopentane scaffolding to the metal center. After deprotonation, reaction with electrophiles will produce the corresponding ether derivatives ROCH2C(CH2PPh2)(CH2Z)2 (3). Mesylation of 2 leads to MeSO2OCH2C(CH2PPh2)3·Mo(CO)3 (4), which reacts with alkoxides to produce 3 in a sequence of reversed polarity. Ligands 5 [ROCH2C(CH2PPh2)3] are liberated from 3 by UV irridation of their solutions in the presence of pyridine N-oxide. Direct etherification of 1 is also possible in some cases after deprotonation of 1 by KOtBu and subsequent reaction with an electrophile RX in the narrow temperature range between -10 and +20 °C. By this way, ω-methyl polyglycol ether functions are easily introduced resulting in H3C(OC2H4)nOCH2C(CH2PPh2)3 (5g, h).
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Preparation of Enantiomerically Pure Chelate Ligands L2 = XCH2CH(OH)CH2Y from Epichlorohydrin - Conformation of Their L2Rh(COD)+ Derivatives and Enantioselective Hydrogenation by L2Rh(COD)+ (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 405-420 
    Details
    ISSN: 1434-1948
    Keywords: Epichlorohydrin ; Chiral diphos ligands ; Diphos rhodium complexes ; Conformation analysis ; Chelates ; Asymmetric synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiomerically pure chelate ligands L2 = XCH2CH(OH)CH2Y (1) are obtained from epichlorohydrin in a two-step synthesis. × and Y may be different types of R2P donor groups, NR2 or SR donors. The OH function of 1 may be transformed into an ether function under specialized conditions. Ligands 1 react with [Rh(COD)Cl]2 in the presence of KPF6 to give the coordination compounds 2, [L2Rh(COD)]+PF6-, as orange, microcrystalline salts. The structures adopted by compounds 2 in the solid state have been analysed by X-ray crystallography in selected cases, and it has been found that the six-membered chelate cycles adopt twist as well as chair conformations depending on the nature of × and Y. In solution, compounds 2 generally show dynamic behaviour, which is in part due to the conformational flexibility of the six-membered cycles. In cases where one of the PR2 donor groups contains ortho-substituted phenyl substituents, rotational isomerism of these groups is an additional dynamic process. For some of these compounds, the nature of the dynamic behaviour has been analysed by variable-temperature NMR experiments. Compounds 2 are found to be precatalysts in the hydrogenation of (Z)-2-acetamidocinnamic acid. The rate of conversion is strongly influenced by the steric bulk of the substituents, with smaller substituents leading to higher rates. Enantiomeric discrimination is high only for those ligands that contain ortho-substituted aryl groups at their PR2 donors. The maximum enantiomeric excess observed was 85% for × = PPh2, Y = P(2-MeOPh)2.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Metal-Metal Interactions in Dinuclear (triphos)Cobalt Complexes Exhibiting Mixed Valency (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 593-600 
    Details
    ISSN: 1434-1948
    Keywords: Tripodal ligands ; Cobalt ; Bridging ligands ; Mixed-valence compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The spectroscopic and electrochemical properties of a series of dinuclear mixed-valence complexes containing two (triphos)Co units are reported: [(triphos)Co(L)Co(triphos)]+ (L = C6O4X2; × = H, Cl, Br, I, Me: 2a-e+; L = C14H4O4Me2: 4+). Complexes 2a-e+ are bridged by tetraoxybenzene ligands and exhibit very strong metal-metal interaction leading to delocalized class-III behaviour while in 4+ the extended tetraoxoanthracence bridging ligand leads to a partial electron localization. Additionally, the different oxidation behaviour of the parent dicationic complexes 1a-e2+ and 32+ have been investigated and are explained on the basis of a qualitative MO model.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Dinuclear Cobalt(II) Complexes of Pyrazole Ligands with Chelating Side ArmsDedicated to Prof. Dr. Walter Siebert on the occasion of his 60th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 605-613 
    Details
    ISSN: 0009-2940
    Keywords: Pyrazolate complexes ; Dinuclear complexes ; Bridging ligands ; Cobalt ; Conformational analysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of pyrazole-based potential ligands bearing polydentate amine substituents in the 3- and 5-positions of the heterocycle has been synthesized [3,5-bis(R2NCH2)-pyzH R2N = Me2N(CH2)3NMe (2aH), [Me2N(CH2)3]2N (2bH), (Et2NCH2CH2)2N (2cH)]. Upon reaction with two equivalents of CoCl2 they form complexes LCo2Cl3 (3a-c; L = 2a-c, respectively) which are shown crystallographically to contain a dinuclear metal core bridged by both the pyrazolate unit and a chlorine atom, with each cobalt center carrying a further terminal chlorine atom. Two of the ligand side arms in 3b, c are dangling, thus leading to five-coordination of the cobalt(II) centers in all cases. Addition of two equivalents of NaBPh4 to solutions of 3b, c induced coordination of the formerly dangling side arms to the metal centers by substitution of the terminal chlorine atoms. The resulting compounds [LCo2Cl](BPh4)2 (4b, c, respectively) were characterized by X-ray structure analyses. They can be viewed as dinuclear linked versions of tran-type complexes [(tran = tris(aminoalkyl)amine] with distorted trigonal-bipyramidal coordination spheres around cobalt(II). Conformational analyses employing force-field calculations were carried out for 4b, c in order to rationalize the conformations observed in the solid state with regard to the accessible conformational space.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971300511
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  • 10
    Electronic Resource
    Electronic Resource
    Divalent Tin and Lead Compounds EX2 Acting as Bridging Ligands in [{(CO)5M}2EX2]2- (E = Sn, Pb; M = Cr, Mo, W): Preparation and PropertiesDedicated to Professor G. E. Herberich on the occasion of his 60th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 687-699 
    Details
    ISSN: 0009-2940
    Keywords: Tin ; Lead ; 119Sn NMR ; Salt metathesis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of Na2[M2(CO) 10] (M = Cr, Mo, W) with SnHal2 (Hal = Cl, Br) is a well established procedure for the synthesis of anions of type A, [{(CO)5M)SnHal3]-. Conditions are described which, for the same type of procedure, result in the additional formation of dianions of type B, [{(CO)5M}2SnHal2]2-. Procedures for separating these two types of anions in the form of their stable [Ph4P]+ or [nBu4N]+ salts by appropriate salt metathesis are presented. The structures of theses species have been characterized by X-ray analysis of three salts containing type A anions and two salts containing type B anions. The reactivity of the type B salts containing the bulky cations [Ph4P]+ or [nBu4N]+, respectively, is remarkably low; the salts are, however, transformed into highly reactive sodium salts by further metathesis with Na[BPh4]. In such salts the halide substitutents are easily exchanged as shown by the synthesis of ]})CO(5Cr}2oxinato]- (4)- from [Na-(THF)x]2[{(CO)5Cr}2SnCl2] and sodium 8-oxoquinolate, Na[C9H6NO]. The structure of the anion, 4 is compared to the structure of [[(CO)5Cr)SnCl2· THF] and sodium 8-oxochinolate. The preparation of the dinuclear anions [{(CO)5Cr}2E(OOCCH3)2]2- (E = Sn, 2g; E = Pb, 3) is accomplished by the reaction of [Ph4P]2[Cr2(CO)10] with the corresponding acetates E(OOCCH3)2. While 2g and 3 are formal analogues of the type-B anions, their structures reveal an asymmetrical η2-coordination of the two acetato ligands, in each case ending up in a 4+2 coordination for the main group centres, instead of the four-coordination observed for [{(CO)5M}2SnHal2]2-, All compounds have been characterized by usual spetroscopic and analytical techniques. X-ray analyses have been performed for selected examples. 119Sn-NMR data are presented for all of the compounds which contain tin-centred ligands.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971300604
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