Ernst Koerner von Gustorf

Photochemische synthese von 1,3-dientetracarbonylchromkomplexen und ihre rolle bei der photokatalytischen hydrierung von diene mit Cr(CO)6

The photochemical synthesis of butadienetetracarbonylchromium (I) and trans,trans-2,4-hexadienetetracarbonylchromium (II) is described. II is shown to be an intermediate in the photocatalytic hydrogenation of trans,trans-2,4-hexadiene with Cr(CO)6.

Aspects of Organo-Transition-Metal Photochemistry and their Biological Implications

Publisher Summary Photochemistry is the study of chemical changes brought about by light. It encompasses all processes “participating in the formation and deactivation of electronically excited molecules”. Some of its aspects may be considered as photophysics, some as photobiology; however, any arbitrary demarcation would not be in accord with the interdisciplinary character of this field. It is considered that organmetallic chemistry is the chemistry of compounds, in which metals are bound to groups or molecules that are under the regime of organic chemistry. One does make any distinction whether bonding occurs via carbon or another element, as for instance N, P, O, or S. In many transformations of organic material involving metals, the site of bonding and the primary reactive steps remain obscure anyhow. Organometallic compounds are often made from “inorganic’’ starting materials, are applied in organic syntheses, and play a significant role in biochemistry.

Photochemische synthese von H2Fe3-komplexen und ihre aktivität bei der photokatalytischen hydrierung von olefinen und dienen

Abstract The photochemical reaction of the trinuclear complex Fe 3 (CO) 10 NSi(CH 3 ) 3 under hydrogen leads to substitution of the bridging carbonyl group by two hydrogens. The resulting complex H 2 Fe 3 (CO) 9 NSi(CH 3 ) 3 acts as a catalyst in the photochemical hydrogenation of olefins and dienes.

The mechanism of photoinsertion of haloalkenes into FeC bonds of dieneiron tricarbonyls

Abstract 1,1-Dichloro-2,2-difluoroethylene (like other fluoroalkenes) and dieneiron tricarbonyls react photochemically to give products in which the haloalkene has inserted into the FeC(1) bond of the diene complex. The reaction is regiospecific with respect to both diene and haloalkene. The reaction is shown to occur by (a) photodissociation of a CO ligand from iron; (b) π-complexation of haloalkene; (c) π → σ ligand rearrangements accompanied by CO reattachment. The adducts undergo hydrolysis on silica gel chromatography, to give substituted 2-chlorocyclohexadienoneiron tricarbonyls.

(Diethyl muconate)(1,4-diaza-1,3-diene)carbonyliron complexes: syntheses, spectra, and structure

Three examples of a new type of mixed (1,3-diene)(1,4-diaza-1,3-diene)carbonyliron complexes have been prepared. The diene ligand is diethyl muconate, trans , trans -H 5 C 2 OOCCHCHCHCHCOOC 2 H 5 , and the 1,4-diaza-1,3-diene (DAD) ligands are 2,2′-bipyridyl (BIPY) and the Schiff bases 2-benzoylpyridineanil (BPA) and 2-benzoylpyridine- p -methoxyanil (BPpMA). The complexes were made by thermal substitution of one diene ligand of bis(muconate)carbonyliron by the respective DAD ligands, and photochemically from (muconate)tricarbonyliron and DAD by substitution of two CO ligands. The structure of (muconate)(BIPY)Fe(CO) (I) was established by an X-ray analysis (cell data: a = 9.648(2) », b = 11.422(2) », c = 19.080(2) », β = 100.77(2)°; space group P2 1 / n , R = 0.048). The complex approximates to a square pyramid with one of the BIPY nitrogen atoms occupying the apical position. IR, UV, and mass spectra are reported. The 1 H and 13 C NMR spectra reveal the unsymmetrical structure. The complexes II (with BPA) and III (with BPpMA) are mixtures of isomers. The spectral data indicate structures analogous to I.

Chemische und biologische Aspekte der Fixierung und Reduktion molekularen Stickstoffs

The fixation and reduction of molecular nitrogen in transition-metal complexes is one of the most fascinating areas of current research. In the hope of cata!yzing further progress, a brief survey is given of some aspects of this rapidly developing field: historical background; methods of preparation of metal-N~ complexes; bonding in metal-N2 complexes; reactivity of complexed N2; models for nitrogenase; further routes for the reduction of complexed N v A few speculative suggestions are put forward to stimulate further discussion.

Chemical synthesis with metal atoms: preparation and X-ray structure of (η5-cycloheptadienyl)-(η5-cycloheptatrienyl) iron. A bifluxional molecule

[Fe(η5-C7H7)(η5-C7H9)] has been prepared by cocondensation of iron vapour with cycloheptatriene; an X-ray analysis shows a sandwich structure with open faces of the two η5-systems skew to each other, and in solution two types of fluxional behaviour are exhibited.

The Comparative Photochemical Behaviour of Dibenzenechromium and Benzenetricarbonyl Chromium

In comparison with (C6H6)Cr(CO)3, (C6H6)2Cr is relatively light stable. The major part of the light energy absorbed by (C6H6)2Cr leads neither to its decomposition or ligand exchange, nor can it be transferred to common low energy triplet acceptors. Internal dissipation of energy, either by rapid conversion to the ground state or by rapid reversible isomerization, must be an important process. In the case of (C6H6)Cr(CO)3, the main pathway to the previously reported lightinduced exchange of benzene involves an intermediate which is suggested to be (benzene)-dicarbonylchromium (1) and not a one-step dissociation of the excited molecule, to give Cr(CO)3 and benzene1b: 1 is also of major importance for the exchange of CO.

Chemical synthesis with metal atoms. The preparation and structure of cyclo-octadiene trifluorophosphine complexes of chromium. The crystal structure of (η5-cyclo-octa-1,3-dienyl)hydridotris(trifluorophosphine) chromium

The reaction of cyclo-octa-1,5-diene (1,5-cod), PF3, and chromium atoms produces [Cr(1,5-cod)(PF3)4](1) and [Cr(C8H11)(PF3)3H](2). The use of 1,3- rather than 1,5-cod produces only (2) under the same conditions. Complex (1) is readily converted into (2) by heating (90 °C, in toluene). The preparation of [Cr(1,5-cod)(CO)4](3) from 1,3- or 1,5-cod is also described. The structure of (2) was determined by X-ray crystallography. The compound crystallizes in the orthorhombic space group Pbca with a= 13.452(3), b= 14.419(4), c= 15.268(3)A, and Z= 8. The final R value was 0.065 9 for 1 699 observed reflections. The structure is retained in solution below –80 °C, but is shown by 13C and 1H n.m.r. spectroscopy to become fluxional upon warming. There are two distinct exchange processes; one results in pairwise coalescence of the 13C and 1H resonances; the other finally leads to a set of only two 1H signals with an intensity ratio of 8 : 4, thus indicating equivalence of the eight ring positions.

Low-Temperature Matrix Photochemistry of (η4 -Diene)tetracarbonylchromium Complexes

Photolysis of (η4-diene)Cr(CO)4 complexes (diene = butadiene, trans,trans-2A-hexadiene, 2,3-dimethylbutadiene) in Ar, N2, and CO matrices at 10-12 K was monitored by infrared and UV-Vis spectroscopy. In argon and dinitrogen matrices loss of CO ist the predominant photoreaction. The resulting fac-(η4-diene)Cr(CO)3 can take up N2 from the matrix to form (η4-diene)Cr(CO)3(N2). In the case of the hexadiene complex this process requires matrix annealing subsequent to photolytic loss of CO. Photolysis in CO matrices, by contrast, results in stepwise displacement of the diene ligand, yielding (η2-diene)Cr(CO)5 and ultimately Cr(CO)6.