Browsing by Author "Stezowski, John J."
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Item Open Access Crystal and molecular structures of novel (arene)chromium tricarbonyl complexes (Aminobenzenes ; 18)(1985) Schöllkopf, Klaus; Stezowski, John J.; Effenberger, FranzSeveral new (1,3,5-tris(dialkylamino)benzene)chromium tricarbonyl (chromium tricarbonyl = TCC) complexes (2) were prepared and crystal structures for two of them, 2a ((1,3,5-tripyrrolidinobenzene)TCC) and 2b ((1,3,5-tripyrrolidino-2-methylbenzene)TCC), were determined to high precision with X-ray data collected from cooled crystals (T ≈ 120 K). Complex 2a crystallizes in space group symmetry P1 with a = 8.7670 (5) A, b = 10.6023 (8) A, c = 11.6337 (8) A, α = 66.724 (6)°, β = 72.560 (6)°, γ = 79.651 (7)°, and Z = 2. For 2b the space group is P2 l/c with a = 12.323 (1) A, b = 8.2651 (8) A, c = 23.902 (2) A, β = 123.114 (7)°, and Z = 4. The model for 2a was refined with 13 110 contributing reflections to give Rw = 0.053; for 2b refinement with 9154 reflections gave Rw = 0.058. A crystal structure was also determined for the [(phenyl(trimethylsiloxy)methyl)benzene]TCC complex (3) for which the space groups is P2 1/c with a = 6.282 (1) A, b = 11.319 (4) A, c = 26.962 (12) A, β = 93.82 (2)°, and Z = 4 (room temperature). All three complexes display a close approximation to the syn-e conformation for the (arene)TCC moiety. The rotational barriers for compounds 2 could not be established because of their low solubility. The application of conclusions from crystal structures to reaction behavior in solution was proved in the case of the [(phenyl)trimethylsiloxy)methyl)benzene]TCC complex (3). The experimental results are in agreement with the reactivity pattern calculated for the crystal structure determined for 3.Item Open Access Dimeric σ-complexes : intermediates in the oxidative dimerization of aromatics (Aminobenzenes ; 19)(1988) Effenberger, Franz; Mack, Karl-Ernst; Niess, Rolf; Reisinger, Friedrich; Steinbach, Adalbert; Stohrer, Wolf-Dieter; Stezowski, John J.; Rommel, Ilse; Maier, AndreasDimeric σ-complexes 2, postulated intermediates in the oxidative dimerization of aromatics, were obtained by oxidation of tripprolidin-1-ylbenzenes 1a-f with silver nitrate. Treatment of 2 with strong base gave biphenyls 4. In solution, especially under the influence of light, compounds 2 dissociate to radical cations 1o+,which react irreversibly with solvent under H abstraction to give σ-complexes 3. Crystal structures were determined by X-ray diffraction methods for compounds 2a and 2c. Reactions of triaminobenzenes 8 and 9 with bromine and halocyanogens gave mixtures of substitution (10/ 11) and dimerization products (12/ 13). This product formation can be plausibly explained in terms of known steric and electronic factors of both reaction partners.Item Open Access Ein neuer Weg zu Phloroglucinen - Synthese, Struktur und Reaktionen von [n](2,4)Phloroglucinophanen(1982) Effenberger, Franz; Schönwälder, Karl-Heinz; Stezowski, John J.-Item Open Access Ein neuer Weg zu Phloroglucinen : Synthese, Struktur und Reaktionen von [n](2,4)Phloroglucinophanen(1982) Effenberger, Franz; Schönwälder, Karl-Heinz; Stezowski, John J.-Item Open Access A novel route to phloroglucinols : synthesis, structure, and reactions of [n](2,4)phloroglucinophanes(1982) Effenberger, Franz; Schönwälder, Karl-Heinz; Stezowski, John J.-Item Open Access Structure and reactivity of aromatic σ-complexes (cyclohexadienylium ions) : a correlated experimental and theoretical study(1987) Effenberger, Franz; Reisinger, Friedrich; Schönwälder, Karl-Heinz; Bäuerle, Peter; Stezowski, John J.; Jogun, Kurt H.; Schöllkopf, Klaus; Stohrer, Wolf-DieterSteric and electronic properties for a series of σ-complexes have been examined by experimental and theoretical techniques. Crystal structures for three 2,4,6-tripyrrolidinocyclohexadienylium salts 3a, 3b, and 4a and for l-methyl-2,4,6-tripyrrolidinobenzene 5 are reported. With respect to the cyclohexadienylium ring, the H,H σ-complexes, 3, display a planar conformation whereas σ-complexes 4 and 6 are bent. Steric interactions force the larger substituents of the tetrahedral carbon atom in 4 and 6 into the pseudoaxial position. The results of EH, MNDO, and 3-21G calculations are in agreement with the crystal structure determinations for σ-complexes 3,4, and 6. Calculations performed for other σ-complexes indicate that the ring conformation for σ-complexes with small substituents in the 2- and 6-positions should be planar even in cases with different substituents on the tetrahedral carbon atom; with larger substituents, a bent conformation is favored with the larger substituent at C1 axial. The activation energy for planarization of the bent structure is fairly high, and it is even higher for inversion. For stereoelectronic reasons, only the ligand in the axial position of bent σ-complexes can dissociate during rearomatization. Thus the stability and reactivity of σ-complexes are strongly dependent on their conformation. The large differences in pKa values of planar and nonplanar σ-complexes, as well as the unexpectedly high stability of phloroglucinophane σ-complexes, can be explained by the high inversion energy for the formation of the σ-complexes with the proton as the leaving group in the axial position.Item Open Access Synthese und Struktur von [n](2,4)Phloroglucinophanen (Enolether ; 15)(1984) Schönwälder, Karl-Heinz; Kollat, Petra; Stezowski, John J.; Effenberger, FranzEnolether cyclischer Ketone 1 reagieren mit Malonyldichlorid (2) in Ether unter zweifacher Acylierung zu [n](2.4)Phloroglucinophanen bzw. deren Tautomeren oder Derivaten (Acetale, Ether); nach nichtwäßriger Aufarbeitung resultieren die Bicyclen 5, 6, nach wäßriger Aufarbeitung die Bicyclen 7-10. Die unterschiedliche Produktbildung läßt sich mit den Kenntnissen der Struktur- und Bindungsverhältnisse in ungesättigten bicyclischen Systemen bzw. Metacyclophanen plausibel deuten. Aus der nachgewiesenen benzoiden Struktur der tautomeriefähigen Metacyclophane 9f und 10g ist zu folgern, daß auch noch [8]- bzw. [7]Metacyclophane relativ spannungsfrei sind. Mittels 18O-Markierung konnte für die Etherspaltung am Beispiel der Methylarylether 6d und 6h ein Additions-Eliminierungs-Mechanismus nachgewiesen werden. Für die Verbindungen 7b, d und 10h wurden Röntgenstrukturanalysen durchgeführt.Item Open Access Synthesis, structure, and spectral behavior of donor acceptor substituted biphenyls(1983) Effenberger, Franz; Agster, Wolfgang; Fischer, Peter; Jogun, Kurt H.; Stezowski, John J.; Daltrozzo, Ewald; Kollmannsberger- von Nell, GeorgReaction of the activated halonitrobenzenes 2a-f with the bis- and tris(dialkylamino)benzenes 1a-e affords, via a direct nucleophilic substitution, the highly substituted biphenyls 3a-o; the lesser substituted biphenyls 5 and 6 were prepared by an Ullmann reaction. All these biphenyls are deeply colored; the dark red color can be assigned to an intramolecular charge transfer. A crystal structure determination was carried out for 2,4,6-tripyrrolidino-2',4',6'-trinitrobiphenyl (3a): space group C2/c, a = 16.071 (2) A, b = 14.545 (1) A, c = 20.177 (2) A, {3 = 91.361 (9)°, Z = 8 (temperature ≈ 120 K). The dihedral angle between the two arene rings was found to be only 52.5°, despite the four bulky substituents in the o,o'-positions. With this far-from-orthogonal torsional angle about the biphenyl linkage, the strong intramolecular charge transfer from the π system of the donor into the π system of the acceptor arene becomes easily understandable. A PPP calculation with the torsional angles taken from the X-ray structure analysis satisfactorily reproduces the experimental absorption spectrum of 3a. The shift of the long-wavelength absorption between the individual biphenyls 3a-o, 5, and 6 likewise is accounted for satisfactorily by the calculation; it depends primarily on the intrinsic donor strength of the different NR2 moieties (pyrrolidino > dimethylamino > piperidino > morpholino). The IH NMR spectra (in dilute solution) likewise mirror this gradation in Nr2 donor capacity; they also show that steric hindrance at the biphenyl linkage is mainly the result of interaction between the o-dialkylamino groups and the C6 skeleton of the acceptor arene. This is borne out by the crystal structure analysis.