Summavy. By CNDO-CI calculations we have found that dicarbonyl compounds exhibit only two n --f n* transitions in the visible or near UV. region, instead of four as expected from simpler MO-models. The dominant features of the long-wavelength electronic spectra may be characterized by the relative energy of the two n and the two lowest n* orbitals. In general we distinguish between threc cases: i\. Large splitting (about 2 eV) both between the n and the n* orbitals. The longest-wavelength w+-n* transition is shifted to the red. The higher transition remains roughly where it would appear in the monocarbonyl compound.B. No or very small splitting between either the two n, or the two n* orbitals, or both. Both n --f n* transitions merge, roughly, in the wavelength region of the corresponding monocarbonyl compound.C. Intermediate (0.5-1.0 eV) splitting between the two n orbitals on one hand, the two n* orbitals on the other. Spectral properties between A. and B.The splitting between the two n orbitals and the two n* orbitals depends not only on the distance between the two carbonyl groups, but also very strongly on their mutual position and on the nature of the molecular fragment connecting them. As one would expect, in a-dicarbonyl compounds the splitting between the n orbitals is large, namely 1.8 eV. In some y-diketones such as p-quinone, one still finds, however, a value of 0.7 eV. The splitting between the n orbitals gets significantly lowered if the two carbonyl groups are coaxial, but their Zp, nodal planes are perpendicular to each other. In planar p-diketones the splitting between the n* orbitals is small, but may increase to an effective value of 0.4 eV when they are skewed. Our calculations agree well with measured electronic spectra and CD. data. An electrochromism experiment on camphorquinone convincingly supports our conclusions on a-dicarbonyl compounds.
Iron (2-methoxyviny1)aminocarbene complexes (Alkynoy1)iron complexes 1, Cp(C0)2Fe(O=CC=CR) (R = plexes 3, [Cp(CO),Fe(C(NHR')C=CR)+][PF,1, or (2-meth-CH,, Ph, SiMe3), were synthesized by applying a mixed an-oxyviny1)aminocarbene complexes 5. The spectroscopic prohydride procedure and transformed into the cationic meth-perties of the new complexes are discussed. The (alkyny1)-oxycarbene complexes 2, [Cp(CO) Previously we have reported on a convenient access to new alkynyl-substituted acyliron complexes l['l]. The corresponding electrophilic alkynyl-substituted methoxycarbene complexes 2 were synthesized (Scheme l), and the aminolysis with primary amines was studied. Thus, substitution at C-1 was observed exclusively at ambient temperature. A series of aminocarbene complexes 3 were obtained (Table l), and (2-methoxyviny1)aminocarbene complexes 5a, b (Scheme 2) were isolated from aniline and 2a, c, owing to the addition of the released methoxy group to the alkynyl residue. Even though a few electrophilic iron aminocarbene complexes have been prepared in the past, only very few structural data are available about this class of carbene complexes, e.g. synlunti isomer formation and ratio'6-9]. For structure determination a selected set of previously unknown simple alkyl-and aryl-substituted aminocarbene complexes 4, prepared from primary amines, was synthesized for comparison. In addition, the structures of two (alkyny1)aminocarbene complexes were assigned by X-ray crystallography. In this paper we give a detailed description of the syntheses of these complexes, published before in a preliminary communication ["], and their characterization. Results and DiscussionThe preparation of acyliron complexes 1 from carboxylic acid chlorides and the ferrates (CSH,)(C0)2FeM (M = Na, K) is well documented[l21. However, any attempts to obtain side chain-functionalized complexes in higher yield or propargylic acid derivatives failed. Therefore, we developed an alternative strategy using isobutyl chloroformate-derived mixed anhydrides of the carboxylic acids. This one-pot procedure provides access to the acyl complexes 1 in high yield after chromatographic purification. Results are given in Scheme I (see also Experimental). The spectroscopic properties of the alkynyl-substituted derivatives 1 are similar to those of other except the 13C-NMR acyliron signal [Cp(CO)2Fe-C= 0 1 being shifted upfield to about 6 = 239. In the IR spectra the iron acyl v(C0) absorptions are shifted to 1587-1583 cm-' and are about 40-50 cm-' lower than for alkyl-, aryl-, or alkenyl-substituted acyl complexes [Cp(CO)2Fe(O=CR)][61.The acyl complexes 1 were further converted into cationic methoxycarbene complexes 2 (Scheme 1). Thus, [(Me-O),CH+][PF;] was generated in CH2C12 at room temperature from trimethyl orthoformate and (Ph,CHC][PF;][lll. Solid acyl complexes were added neat to the methylating reagent, whereas oils were dissolved in CH2ClZ prior to addition to the reaction mixture by means of a cannula. The
Summary.A general review is given of the UV.-spectroscopic properties of some simple molecules containing the N-N and N-0 bond, respectively. The electronic structure of nitrosomethane, azomethane, trimethylamine oxide, azomethane N, "-dioxide, nitromethane, methyl nitrite are reinvestigated by the SCF-CI method, within the frame of thc all-valence CNDO procedure. These calculations confirm a number of older assignments, but also allow predictions concerning some not settled questions. For instance, nitroalkanes should exhibit not one but two %-n* transitions, namely a t 275 nm and around 350 nm. This prediction agrees with conclusions by Djerassi and 4-0-workers on the spectra of some nitrosteroids.Particular attention is given to the symmetry and relative energetic position of nonbonding orbitals. The question of "basicity" and "ease of protonation" is discussed in relation to it. Calculations on the overall charge distribution complement this investigation.Kein Element zeigt in der organischen Chemie eine solche Vielfalt von Bindungsarten wie der Stickstoff. Er geht Einfach-, Doppel-und Dreifachbindungen mit Kohlenstoff eiii ; er bildet Einfach-, Doppel-und Dreifachbindungen mit sich selber. Eine auffallende Mannigfaltigkeit von verschiedenen Bindungsverhaltnissen findet man in Molekeln, welche zusatzlich noch Sauerstoff enthalten, insbesondere StickstoffSauerstoff-Bindungen aufweisen. Zwar bildet die Chemie der Nitroxyle, der Nitrosoverbindungen rind ihrer Dimere, -als Oxydationsprodukte von Azoverbindungen aufzufassen -, deir Oxime, der N-Oxide, der Nitroverbindungen und Nitrile ein etwas spezielles Gebiet, fur den Biochemiker vielleicht von sekundarem Interesse. Vom Standpunkt der Bindungslehre und der Molekelspektroskopie aus aber erweist sicli dieses Feld als umso fruchtbarer. Es scheint angebracht, die Eigenschaften der Nitroxyle und Nitrosoverbindungen mit denjenigen von NO, die Merkrnale der Nitroverbindungen mit denjenigen von NO, in Zusammenhang zu bringen 111. Daher bildet eine kurze Betrachtung dieser einfachsten Molekeln den Ausgangspunkt unserer Untersuchung.
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