bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chromophore in binuklearen ringförmigen Gold(I)‐Komplexen
Authors: Ludwig Werner , Meyer Walter 
Published: December 2004

AbstractAnnular compounds containing two PAuP‐entities are prepared by reaction of (trialkylphosphine)gold (I) halogenides with diphosphines. With bis (dimethyl‐phosphino)methane (DMPM), 1,2‐bis(dimethylphosphino)ethane (DMPE) and 1,3‐bis(dimethylphosphino)propane (DMPP) we obtained the following 8‐, 10‐and 12‐membered annular binuclear complexes: [Au(DMPM)]2Cl2 H2O, [Au(DMPM)]2(SbF6)2, [Au(DMPE)]2Cl2 2H2O, [Au(DMPE)]2(SbF6)2, [Au‐(DMPP)]2Cl2 and [Au(DMPP)]2(SbF6)2 as identified by conductivity measurements, 1H‐ and 31P‐NMR. spectra and extinction curves. Their absorption spectra differ from those of the isolated linear PAuP‐complexes mainly by a very strong band at low energy which is absent in the latter. There is a strong interaction between the PAuP‐entities only in certain excited electronic states and an understanding of all transitions is only possible, if both chromophores PAuP and (PAuP)2 are taken as a basis of interpretation. Bands of the same spectrum belong apparently to two different electronic systems.The absorption spectra of isolated linear and annular ylide‐complexes containing one and two CAuC‐entities, respectively, show quite the same behaviour.
Synthesis and Properties of 1, 1‐Dihalogenocycloprop[b]Anthracenes
Authors: M¨︁ller Paul , Rey Michel 
Published: December 2004

AbstractThe synthesis of 1, 1‐difluoro‐1H‐cycloprop[b]anthracene (3) is described. The key step of the synthesis is the cycloaddition of 1,2‐dichloro‐3,3‐difluorocyclo‐propene (6) to 2,3‐dimethylidene‐1,2,3,4‐tetrahydronaphthalene (5). The 13C‐NMR. spectrum of 3 is assigned on the grounds of C,F‐coupling constants, selective H‐decoupling and the resulting residual C,H‐coupling. The 1, 1‐dichloro derivative 4 was synthesized by the same route, but could not be isolated pure. Experiments for the reduction to 1H‐cycloprop[b]anthracene (2) and for the ionization of 3 or 4 to the cation 16 failed.
Ergebnisse der Verfahrensforschung, I. Synthese von o‐{(+)‐D‐2‐[4‐(4‐(Trifluormethyl)phenoxy)phenoxy]propionyl}‐aceton‐oxim
Authors: Imfeld Marquard , Suchý Miloš , Vogt Peter , Lukáč Teodor , Schlageter Markus , Widmer Erich , Boguth Walter 
Published: December 2004

Results of process Research I. Synthesis of O‐{(+)‐D‐2‐[4‐(4‐(triluoromethyl)phenoxy)phenoxy]propionyl}‐acetone oximeEfficient and simple procedures for the preparation of O‐{L‐[(sulfonyl)oxy]‐propionyl}‐oxime derivatives 7b‐e have been developed. The alleviation of 4‐[4‐(trifluoromethyl)phenoxy]phenol (11) with 7d, the final step of a technical synthesis of 1, has been studied in detail.
Alkaloid Production in Catharanthus Roseus Cell Cultures. XI. Biotransformation of 3′, 4′‐Anhydrovinblastine to Other Bisindole Alkaloids
Authors: Kutney James P. , Aweryn Barbara , Choi Lewis S. L. , Kolodziejczyk Pawel , Kurz Wolfgang G. W. , Chatson Kenneth B. , Constabel Friedrich 
Published: December 2004

AbstractBiotransformation studies of 3′,4′‐anhydrovinblastine (1) in Calharanthus roseus cell suspension cultures are reported. A detailed study of one cell line, coded at „916”︁, has revealed that 1 is transformed to the natural bisindole alkaloids leurosine (2) and Catharine (3) in approximately 25–30 and 9–16% yield, respectively. In 24–48 h, about 40% of 1 is utilized by the cells. Conditions for biotransformation of 1 have not been optimized so the above yields quoted are not final.
Reaktionen von o‐Chinonen mit Aminen und Proteinen. 4. Mitteilung. 7a‐Methyl‐5,6‐dioxo‐5,6,7,7a‐tetrahydroindol‐Derivate aus 4‐Methylbrenzcatechin und Enaminen
Authors: Peter Martin G. , Speckenbach Fritz 
Published: December 2004

Reactions of o‐Quinones with Amines and Proteins. 7a‐Methyl‐5,6,7,7a‐tetrahysroindole Derivatives from 4‐Methylcatechol and EnaminesMethyl l‐[2′‐(methoxycarbonyl)ethyl]‐7a‐methyl‐5,6‐dioxo‐5.6.7,7a‐tetrahydro‐indole‐3‐carboxylate (1) was isolated after the oxidation of 4‐methylcatechol with silver (1) oxide in the presence of b̃‐alanine methyl ester in glacial acetic acid. The formation of 1 requires in situ dehydrogenation of the b̃‐aminocarboxylate and addition of the resulting enamine to 4‐methyl‐1,2‐benzoquinone. Reaction of ethyl 3‐(phenylamino)crotonate with 4‐methyl‐1,2‐benzoquinone afforded ethyl 2,7a‐dimethyl‐5,6‐dioxo‐1‐phenyl‐5,6,7,7a‐tetrahydroindole‐3‐carboxylate (6). Despite the fact that the yields are low, the addition of enamines to o‐quinones represents an interesting novel extension of the Nenitzescu‐reaction which is well known in the p‐quinone series. Compound 1 may be considered as a novel model for the crosslinking of proteins by o‐quinones. Formation of 1 was, however, not observed under physiological conditions.
N, N, N′,N′‐Tetrabutyl‐3,6‐dioxaoctan‐dithioamid, ein ionophor mit Cd2+‐Selektivität, Röntgenstrukturanalyse des Cd2+‐Komplexes
Authors: Sauter Hansjürg , Dobler Max 
Published: December 2004

N, N, N′,N′‐Tetrabutyl‐3,6‐dioxaoctan‐dithioamid, an Ionophore with Cd2+‐SelectivityThe CdCl2‐complex of N, N, N′, N′‐tetrabutyl‐3, 6‐dioxaoctanedithioamide crystallizes with the composition [Ligand. Cd2Cl4] in space group P1, a= 14.140, b= 10.025, c= 12.173 Å, α = 95.59°. β = 102.06°. γ = 85.50° Z= 2. Each ligand coordinates two Cd2+‐ions. Adjacent cations are bridged by two Cl+‐ions such that infinite bands along the b‐axis are formed.
Structures cristallines et moléculaires des muscs macrocycliques III. La muscone et sa 2,4‐dinitrophénylhydrazone
Authors: Bernardinelli Gérald , Gerdil Raymond 
Published: December 2004

Crystal and Molecular Structure of Macrocyclic Musks. III. Muscone and its 2, 4‐DiuitrophenylhydrazoneMuscone (3‐methylcyclopentadecanone C16H30O) forms orthorhombic plastic‐crystals with Z = 2 (a = 5.560(4), b = 8.176(6), c = 17,168(20) Å). Single crystals are obtained by zone melting at 258 °K. The high degree of disorder and the ambiguity of space group have precluded a structural determination by X‐ray diffraction methods.The crystal structure of muscone 2,4‐dinitrophenylhydrazone (DNPHM; C22H34N4O4, triclinic, space group P¯, a = 8.015 (4), b = 8.235 (2), c = 17.409 (4) Å. α = 102.69 (4), β; = 93.86 (3), γ = 96.03 (3)° Z = 2) was solved by direct methods and refined to a final R of 0.155 (Rω = 0.102). The macrocycle shows static disorder, which could be partially resolved by analysis of the anisotropy of the atomic vibrational parameters. Eight possible conformers with reasonable geometries emerged from the subsequent refinements and were used as starting models in force‐field calculations, which converged to four quinquangular conformations ([25233]; [34233]; [21423*4]; [3423*4]) with similar energies. In the molecular packing, the interactions between macrocycles and substituents are minimized. They are comparable to those described for the cis‐ and trans‐civetone DNPH derivatives [1] [2].
Enrichment of Potassium Isotopes with Macrocyclic Polyether Potassium Complexes
Authors: Schmidhaltcr Beat , Schumacher Ernst 
Published: December 2004

AbstractEnrichment of the potassium isotopes is achieved by means of the chemical exchange reaction

Where L represents a macrocyclic polyether. Dicyclohexyl‐18‐crown‐6 ((cis‐syn‐cis)‐isomer) was investigated. The single stage‐separation factor a=1+ε was determined according to the method of Glueckauf from the elution curve and iso‐topic assays. One obtains ε‐values of 1.18, 0.84. and 0.74 × 10−3(±5×10−5) at −10, 0 and 10° respectively, in favor of the heavy isotope, indicating an enthalpy of isotopic exchange of −13 ± 4 Joule mol−1.The technical feasibility of a pre‐enrichment process for 40K starling with basic laboratory data is discussed.
Serine‐Protease‐Assisted Synthesis of Peptide Substrates for α‐Chymotrypsin
Authors: Bizzozero Spartaco A. , Rovagnati Bruno A. , Dutler Hans 
Published: December 2004

Abstractδ‐Chymotraypsin catalyzes peptide‐bond formation between acylated amino‐acid and peptide esters as the carboxyl component and amino‐acid and peptide amides as the amino component. The conditions under which enzyme‐catalyzed coupling can be used for fragment condensation in peptide synthesis is investigated. To illustrate the method the synthesis of tetra‐, penta‐ and hexapeptides of the structure Ac‐Lxn …︁ LxlLyl …︁ LymNH2 with Lxl  Tyr, designed as substrates for α‐chymotrypsin, is described.
The Conformation of 1,6‐Diaza‐2,7‐cyclodecadione in Solution
Authors: Winkler Tammo , Leutert Thomas 
Published: December 2004

AbstractFrom 1H‐ and 13C‐NMR. data, a crown conformation with trans amide bonds is deduced for 1,6‐diaza‐2,7‐cyclodecadione (1) in solution. Compound 1 was obtained by reaction of 2‐pyrrolidone with POCl3.
A case of highly diastereoselective addition to unsymmetrical ketones: lk‐addition of (2‐alkenyl)triphenoxytitanium derivatives
Authors: Seebach Dieter , Widler Leo 
Published: December 2004

Abstract(2‐Butenyl)‐, (4‐methyl‐2‐pentenyl)‐, and (2‐heptenyl)triphenoxytitanium (2a–c) add to dialkyl, alkyl aryl‐, and alkinyl aryl ketones to give high yields of tertiary homoallylic alcohols (5–12), which are diastereomerically enriched up to 98%. Configurational assignment by degradation of two of the products to olefins 15 and 18 ‐ through β‐hydroxy acids 13 and 16 and β‐lactones 14 and 17 ‐ leads to the proposal of a general mechanism and of a specification of the relative topicity lk of the process (Scheme 5). The allylic Ti‐compounds 2 can serve as d2‐reagents (see the d2‐synthon II and the aldol‐type structures 1).
Interaction of Ca2+ and Mg2+ with Ionophores Studied by Using a Pair‐Potential Model Based on ab initio Calculations
Authors: Welti Martin , Pretsch Ernö , Clementi Enrico , Simon Wilhelm 
Published: December 2004

AbstractAtom pair potentials are obtained from ab initio SCF‐LCAO‐MO calculations for model complexes of Mg2+ and Ca2+ with N, N‐dimethylacetamide, and malonamide. The SCF‐LCAO‐MO interaction energies for 271 complexes of Mg2+ and 271 complexes of Ca2+ with these amides were fitted with a simple analytical potential by a least‐square procedure. Interaction energies and optimal ion locations obtained by pair‐potential calculations are compared with values obtained by ab initio calculations for some related amides. The application of the atom pair potentials to the structure of the Mg2+‐complex [MgCl2 (C3H7ON)6] of N‐ethylacetamide is discussed.
On Cardioactive Steroids. VIII. The Synthesis of Bufalin and Resibufogenin Isomers
Authors: Wiesner Karel , Tsai Thomas Y. R. , Jäggi Franz J. , Tsai Connie S. J. , Gray Glenna D. 
Published: December 2004

Abstractα‐IsobufalinSystematic names are given at the titles of the Exper. Part.
(1) and β‐isoresibufogenin (3) have been synthesized from testosterone by a method which features a novel oxidative furan to pyrone transformation.
Polar versus steric effects in the solvolysis of 6endo‐substituted 2endo‐norbornyl p‐toluenesulfonates. Norbornanes, Part 8
Authors: Grob Cyril A. , Günther Bettina , Hanreich Reinhard 
Published: December 2004

AbstractThe solvolysis rates and products of the 6endo‐R‐substituted 2endo‐norbornyl toluenesulfonates 6a–6i have been determined. The rates of 6a–6g correlate with the inductive constants σ the 6endo‐substituents and are not related to the size of the latter. It is therefore concluded that polar rather than steric effects control the exo/endo‐rate ratios of norbornyl sulfonates. Products are derived mainly from rearranged 6exo‐R‐norbornyl cations when the substituent is an electron donor and from unrearranged 6endo‐R‐substituted cations when the substituent is an electron acceptor.
Partialsynthesen und Reaktionen von Abietanderivaten (Lanugonen) aus Plectranthus lanuginosus und verwandten Verbindungen
Authors: Schmid Jean Martin , Uchida Masaaki , Rüedi Peter , Eugster Conrad Hans 
Published: December 2004

Partial Syntheses and Reactions of Abietanoid Derivatives (Lanugones) from Plectranthus lanuginosus and of Related CompoundsInterconversions by partial syntheses of several lanugones establish their absolute configuration at C(15). Unexpected reactions exemplify the unique reactivity of these abietanoic diterpenes, ‐ Lanugone O (4) was prepared in several steps from (15S)‐coleon C (8a; Scheme 2) thus establishing its (15S)‐configuration. One of the intermediates, the 12‐O‐acetyl‐6‐oxoroyleanone 12, through acetyl‐migration sets up an equilibrium with the vinylogous quinone 13 (Scheme 3). ‐ The chirality at C(15) in the dihydrofuran moiety of lanugone Q (16) was proven by acid‐catalyzed conversion of lanugone O (4) to 16. ‐ Instead of the usual nucleophilic attack shown by quinomethanes, lanugone L (1) is electrophilically substituted at C(7) by acetic anhydride/pyridine (Scheme 1). ‐ In a homosigmatropic [1,5]‐H‐shift, lanugone G (17) in solution is converted to the corresponding allyl substituted royleanone 18 (Scheme 4). ‐ Methanolysis of lanugone J (19) leads to the expected royleanone 20 having the 2‐methoxypropyl side chain (Scheme 5). Similar reactions were found in acetolytic reactions. However, treatment‐of spirocoleons with SOCl2/DMF produces mainly 12‐deoxyroyleanones with allyl‐ and 2‐chloropropyl groups, i. e. 19→26 and 27; 28 → 29. The possible natural occurrence of these compounds is emphasized.
The chemistry of thujone. VI. Thujone as a chiral synthon for the synthesis of optically active steroid analogues
Authors: Kutney James P. , Grice Peter , Pascoe Keith O. , Piotrowska Krystyna , Rettig Steven J. , Szykula Jerzy , Trotter James 
Published: December 2004

AbstractThe thujone derived enone 1 is converted in one step to the pentacyclic compound 4. The structure of 4 was determined by X‐ray diffraction analysis. The acid‐catalyzed cyclopropane‐ring opening of 4 and of the model compound 9 are described.
Water Relaxation Measurements on Semiquinones of Various Flavoproteins
Authors: Visser Antonie J. W. G. , De Wit Jan L. , Müller Franz , Berendsen Herman J. C. 
Published: December 2004

AbstractThe water relaxation rates of several flavoproteins in the semiquinone state have been investigated by the spin echo technique. The results indicate a rather unspecific interaction between water and the protein‐bound flavosemiquinones. An average interaction distance of 0.3‐0.5 nm has been estimated. From the temperature dependence of the rate constants the free energy of activation for proton exchange is calculated to be about 17 kJ/mol. The rate of proton exchange is around 1011 s−1 for the flavosemiquinones investigated are accessible to water regardless of their ionic state.The large difference in relaxation rates of water protons between D‐ and L‐ amino‐acid oxidases is noticeable. Oxynitrilase exhibits the highest whereas Azotobacter vinelandii flavodoxin shows the lowest water relaxation rate of the flavoproteins studied. The results are discussed in relation to the visible‐light absorption properties of the flavoproteins.
Alkoxycarbonyl‐ and Carboxylate‐Group Migrations in the Benzilic Acid Rearrangement of Ethyl Cyclopropane‐2, 3‐dioxopropionate
Authors: Dahn Hans , Dao Lê H. , Hunma Rannoo 
Published: December 2004

AbstractIn alkaline medium C3H5COC (OH)2COOEt (1b) is transformed into C3H5C (OH)(COOH)2 (2a). Labelling experiments show that the cyclopropyl group is not shifted, but only ROOC and/or −O2C groups. GC./MS. and NMR. analysis after incomplete reaction show that both ROOC‐ and −O2C‐groups Migrate; at higher pH (ca. 14) the ester group rearrangement seems to be more important than at pH ca.9‐10.
Rearrangements Involving C8H8F‐Cations of the Cage Type
Authors: Jefford Charles W. , Mareda Jiri , Blaudzun Jean‐Pierre , Burger Ulrich 
Published: December 2004

AbstractThe homo‐l, 4 adduct obtained from difluorocarbene and bicyclo [2.2.1]hepta‐2, 5‐diene (1) was treated successively with HCl, FSO3H and SbF5 in SO2ClF at low temperature. The protic acids underwent electrophilic addition to the cyclopropane part of 1, giving the corresponding derivatives. However, in FSO3H at − 50°, protonation of the gem‐difluoro grouping also occurred to give the 2‐fluoro‐6‐fluorosulfonylbicyclo [3.2.1]oct‐2‐en‐3‐yl cation. The reaction of 1 with SbF5 at −78° led initially to the formation of the 2‐fluorobicyclo [3.2.1 ]octa‐2, 6‐dien‐4‐yl cation, which rearranged to 4‐fluorotricyclo [5.1.0.05,8]oct‐3‐en‐2‐yl cation at −40°. These rearrangements are discussed in the light of those expected for C8H8F square pyramidal cations.
On the Mechanism of the α‐Alkynone Cyclization: A Theoretical Study
Authors: Kaneti José , Karpf Martin , Dreiding André S. 
Published: December 2004

AbstractThe acetylene → carbene rearrangement of three model a‐alkynones, namely propynal (1a), 2‐butynal (1b) and butynone (1c) is studied by ab initio double‐zeta, double‐zeta plus polarization and double‐zeta plus self‐consistent electron pairs calculations. Transition states are located by force‐gradient geometry optimization. Calculated minimum energy reaction paths reveal substituent effects on the activation parameters, which indicate that a H‐atom or an alkyl group competes favorably with an acyl group in the [1,2]‐shift from a‐alkynones 1 to the corresponding acylvinylidenes 5.
Dass Hydrierprodukt eines β‐Nitro‐N‐nitrosoamins ist kein 1,2,3‐Triazolidin, sondern ein β‐Hydroxylamino‐N‐nitrosoamin
Authors: Egger Notker , Hoesch Lienhard , Dreiding André S. 
Published: December 2004

The Product of Hydrogenation of a β‐Nitro‐N‐nitrosoamine Is Not a 1,2,3‐Triazolidine, but a β‐Hydroxylamino‐N‐nitrosoamineIt is shown, by spectroscopy, that the product of catalytic hydrogenation of N, 2‐dimethyl‐2‐nitro‐N‐nitrosopropylamine (1) consists of a 5:1 mixture of (E)‐ and (Z)‐2‐hydroxylamino‐N, 2‐dimethyl‐N‐nitrosopropylarnine (3) and does not contain ‐ as had been claimed ‐ any l, 2‐dihydroxy‐1, 2, 3‐triazolidine (2). Thus there is still no evidence for the existence of the N(OH)N(OH) functionality. The structure of intermediates on the way to 1 are also revised.
Additionsreaktionen von 2‐Thiazolin‐5‐thionen mit Acetylenen Vorläufige Mitteilung
Authors: Jenny Christjohannes , Obrecht Daniel , Heirngartner Heinz 
Published: December 2004

Addition Reactions of 2‐Thiazolin‐5‐thiones with AcetylenesThe reaction of the 2‐thiazolin‐5‐thiones 1 and 5, respectively, with acetylen carboxylates yields mainly 1, 4‐dithiafulvenes of type 3. In the presence of the acetylenic compounds, the 1, 4‐dithiafulvenes undergo an isomerization to give the corresponding 2, 3‐dihydrothiophene‐2‐thiones 4.
Geometrisch enantiomorphe Cyclobutan‐Derivate
Authors: Prelog Vladimir , Thix Jean , Srikrishnan Tamarapu 
Published: December 2004

Geometrically Enantiomorphic Cyclobutane DerivativesThe concept of geometrical enantiomorphism of unsaturated molecules is generalized to cover other planar rectangular arrangements of four ligands of which two are enantiomorphic.Three pairs of geometrically enantiomorphic cyclobutane derivatives were prepared, their configurations were established, and their CD. was investigated.The construction of a catalogue of possible stereoisomers from ligands of different types attached to an achiral core is discussed using a rectangle as example of such a core.
Calf Intestinal Alkaline Phosphatase I. Improved Isolation Method and Molar Composition of the Purified Phosphatase
Authors: Portmann Plato , Jörg Andreas , Furrer Kurt , Walker Hans‐Sepp , Leuthard Peter , Sudan Jean‐François , Perriard FrançOis , Comment Jean‐François , Leva Geneviève , Nell Jean‐pierre 
Published: December 2004

AbstractA modified and improved method for isolation of calf intestinal alkaline phosphatase is described. By this method 300 to 400 mg of pure enzyme was prepared in a relatively short time. On the basis of the results of ultracentrifugation and of the free, polyacrylamide and immunoelectrophoresis the phosphatase obtained is found to be a homogenous glycoprotein, containing firmly bound zinc, magnesium and phosphoric acid. The molar composition of the enzyme and the catalytic activity were determined with different substrates and buffers.
Nicht‐Berry Pseudorotation beim Carbonylgruppenaustausch von Tetracarbonyl(η‐(Z)‐cycloalken)eisen‐Komplexen
Authors: Cosandey Marcel , von Büren Martin , Hansen Hans‐Jürgen 
Published: December 2004

Exchange of Carbonyl Group Sites in Tetracarbonyl(η‐(Z)‐cycloalkene)iron Complexes via Non‐Berry PseudorotationThe tetracarbonyliron complexes of cyclobutene, cyclopentene, 4,4‐dimethyl‐cyclopentene, 2,5‐dihydrofurane, cyclohexen, (Z)‐cyclohepten, ‐octene, ‐nonene, and ‐decene were prepared by thermal or photochemical reaction of the corresponding olefins with nonacarbonyldiiron and pentacarbonyliron, respectively. The low‐temperature behaviour of the mostly new complexes which can be stored over a longer period only below 250 K and which exhibit four C,O‐stretching frequencies in the IR. spectra (cf. Table 2), indicative for a trigonal bipyramidal structure with the olefin ligand in an equatorial position, was studied in CCl2F2 by 13C‐NMR. spectroscopy between 200 and 115 K. In this temperature range all complexed olefin ligands with the exception of (Z)‐cyclooctene (cf. [11]) show an averaged Cs‐symmetry on the NMR. time scale. About 115 K the tetracarbonyliron group gives rise to three 13C‐signals in a ratio of 1:1:2 for the complexes of (Z)‐cycloheptene, (Z)‐cyclodecene and 2,5‐dihydrofurane (Cf. Table 3). This is an agreement with the fixed equatorial position of the non‐rotating olefin ligands. The complexes of cyclooctene and cyclononene give only two 13C‐signals in a ratio of 1:1 for the carbonyl groups. The temperature dependence of the signals indicates that in these cases the two axial carbonyl groups exhibit accidentally the same chemical shift. In all cases a complete line shape analysis of the 13C‐signals of the carbonyl groups could only be accomplished by using two exchange constants (cf. Tables 4 and 5 as well as Fig. 2–5 and Fig. 8). The same is true for the cyclobutene complex, but only one exchange constant could be determined (at 120 K: two 13C‐signals in a ratio of 1:3 with the beginning of a further coalescence). The cyclopentene and cyclohexene complexes showed only one 13C‐signal even at 115 K. The observed temperature‐dependent line shapes of the 13C‐signals can be interpreted in terms of a Non‐Berry pseudorotation mechanism involving a three site exchange with each of the two diastereotopic axial carbonyl groups and the two equatorial carbonyl groups (for activation parameters see Table 4). The differences in the activation parameters can be explained on steric grounds by assuming a transition state (cf. Fig. 8) similar to the C3b‐structure of tetracarbonyliron which lies about 27 kJmol−1 above its C2v‐structure (cf. [30]) comparable with the ground state of our complexes with weak dπ(Fe),pπ(Olefin) back bonding. The transition state model implies that the reorganization process involving the axial carbonyl group in exo‐position possesses the higher exchange barrier (cf. Fig. 8).