Intramolekularer Carbonylgruppenaustausch in Tetracarbonyleisen‐Komplexen von Äthylen und einfachen (<i>E</i>)‐konfigurierten Olefinen

SummaryElectron transmission measurements yield vertical electron affinities of -1.93 eV for (Z)-and of -1.79 eV for (4-cyclooctene (Z and E, respectively). It is concluded that the 'out of plane' bending effect in torsioned E does not influence its LUMO-energy to a larger degree than its HOMO-energy (as determined by photoelectron (PE.) spectroscopy) with respect to non-torsioned Z.Twisting the C, C-double bond in R' R2C= C R3 R4 around the angle 13 leads to a decrease of the resonance integral ,!I and therefore to a change of the bonding n-orbital energy [2]:It has been predicted theoretically [3] that this twist is coupled to an 'out of plane'-bending (oop-bend) motion of R'/R2 and R3/R4 with respect to the original plane defined by the three o-bonds attached to each of the CSpZ-centers. This motion admixes s-character to the n-basis functions of originally pure 2 pz-type, resulting in a change of the basis energy (effect a) in addition to a change of the resonance integral ,!I (effect b) expressed by Equation 1. The 'oop-bend' should therefore manifest itself as a deviation from Equation 1, although its explicit incorporation into the equation is not straightforward due to its complex nature.Photoelectron spectroscopy (PE.) is used to measure approximately the 'experimental' orbital energies via Kooprnans' theorem. PE. spectra of twisted olefines therefore provided the means to test experimentally the effect of twisting a double bond on occupied orbital energies [2]. The ionization energy (IE.) of (E)-cyclooctene (E) was found to lie 0.29 eV lower than the IE. of (2)-cyclooctene (Z). This small change was found to be consistent with Equation I using a torsion

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Nicht‐Berry Pseudorotation beim Carbonylgruppenaustausch von Tetracarbonyl(η‐(Z)‐cycloalken)eisen‐Komplexen

Cosandey¹,

Büren²,

Hansen³

1983

Helvetica Chimica Acta

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Exchange of Carbonyl Group Sites in Tetracarbonyl(q-(2)-cycloa1kene)iron Complexesvia Non-Berry Pseudorotation SummaryThe tetracarbonyliron complexes of cyclobutene, cyclopentene, 4,4-dimethylcyclopentene, 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, 0-stretching frequencies in the IR. spectra (cJ Table 2), indicative for a trigonal bipyramidal structure with the olefin ligand in an equatorial position, was studied in CC12F2 by I3C-NMR. spectroscopy between 200 and 115 K. In this temperature range all complexed olefin ligands with the exception of (Z)-cyclooctene (cf. [ 1 11) show an averaged C,-symmetry on the NMR. time scale. About 115 K the tetracarbonyliron group gives rise to three l3C-signa1s in a ratio of 1 : 1 : 2 for the complexes of (a-cycloheptene, (2)-cyclodecene and 2,5-dihydrofurane (CJ 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 I3C-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 ( c ! 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 I3C-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 ') 2,

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Intramolekularer Carbonylgruppenaustausch in Tetracarbonyleisen‐Komplexen von Äthylen und einfachen (E)‐konfigurierten Olefinen

Cited by 4 publications

References 23 publications

ChemInform Abstract: INTRAMOLECULAR EXCHANGE OF CARBONYL GROUP IN TETRACARBONYLIRON COMPLEXES OF ETHYLENE AND SIMPLE (E)‐OLEFINS

ChemInform Abstract: INTRAMOLECULAR EXCHANGE OF CARBONYL GROUP IN TETRACARBONYLIRON COMPLEXES OF ETHYLENE AND SIMPLE (E)‐OLEFINS

The electron affinities of (E)‐ and (Z)‐cyclooctene. Preliminary communication

Nicht‐Berry Pseudorotation beim Carbonylgruppenaustausch von Tetracarbonyl(η‐(Z)‐cycloalken)eisen‐Komplexen

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