AbstractN‐heterocyclische Phosphane reagieren unter UV‐Bestrahlung in einer hochselektiven Dehydrokupplungsreaktion zu Diphosphanen und H2. Computerchemische Studien legen nahe, dass die Produktbildung durch die Entstehung dimerer molekularer Assoziate eingeleitet wird, deren elektronische Anregung H2 und ein Diphosphan liefert. Kombination der Dehydrokupplung sterisch anspruchsvoller Phosphane mit einer Mg‐Reduktion der gebildeten Diphosphane erlaubt die Konstruktion eines Reaktionszyklus zur photokatalytischen Erzeugung von H2 aus Et3NH+.

This paper focuses on the investigation of the role of catalytic and molecular factors determining the optical yield in the enantioselective hydrogenation of C=C double bonds in prochiral unsaturated ketones and in the kinetic resolution of racemates of chiral cyclic ketones with proline mediated reductive alkylation. The hydrogenation of two unsaturated methyl cyclohexenones, and the kinetic resolution of two saturated methyl cyclohexanones with proline were studied with different Pd catalysts. The aim was to find out the effects of catalyst modifiers and chiral auxiliary, beside that of the structure and the degree of substitution of the substrates on the stereochemical outcome and yield of these reactions.

The effect of the substituents on the planarity and aromaticity of the silolide anion was studied computationally. It was revealed that π-electron acceptor groups (e.g., silyl or trimethylsilyl) at the α position of the ring reduce substantially the inversion barrier about the central silicon increasing the aromaticity according to isomeric stabilization energy (ISE) and NICS values. In the planar and highly aromatic silolide anions, the mesomeric structures with the largest weight exhibit a Si=C double bond and a negative charge which is located at the α or β carbons based on NRT calculations. 2,5-disilylsilacyclopentadienides coordinated by naked Li+ have planar minima, however, further coordination by THF molecules (as in a solution) reduces somewhat the flattening of the silicon pyramid. NMR calculations were carried out to understand the connection between the 29Si chemical shift and the aromaticity of the ring. It was revealed that the commonly accepted charge transfer–chemical shift relationship is strongly influenced by the substituents and the counter cation. THF complexation of the Li counter cation has a small influence on the NMR shift.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The mass spectral fragmentation of different 1-chloroalkanes (of the 1-chlorohexane-1-chlorooctadecane series) has been investigated, quantifying the relative abundance of the fragment ions. The base peak is dominantly at m/z 91, 93 in each investigated case, although with the increasing chain length, its contribution to the total ion current exhibits some reduction. Among the possible fragmentation products, the five-membered chloronium containing ring is the most stable as measured by an isodesmic reaction, although the six-and seven-membered rings exhibit only slightly reduced stability. The most stable structure of the 1-chlorohexane radical cation has a hydrogen bonded structure with the involvement of chlorine and the HC(δ), pre-forming the five-membered cationic ring. Accordingly, among the reactions leading to alkyl (or H) radical and a chloronium containing ring, this transition structure has the lowest energy, providing explanation for the experimental observations.

Metalation of the aminophosphaalkene (iPrMe(2)Si)(2)C=PN(H)SiMe3 (2) with lithium diisopropylamide (LDA) in THIF solution, followed by the reaction of the lithium salt 3 with the P-chlorophosphaalkenes (RMe2Si)(2)C=PCl (1a, R = Me; 1b, R = iPr; 1c, R = Ph), furnishes the first N-silylimmo-bridged bis(phosphaalkenes) [(iPrMe(2)Si)(2)C=P](2)NSiMe3 (4a) and [(iPrMe(2)Si)(2)C=P][(RMe2Si)(2)C=P]NSiMe3 (4b, R = Me; 4c, R = Ph). The N-Si bond cleavage of 4a under very mild conditions with AuCl(THT) and with [RhCl(COD)](2) provides binuclear Au-1 and Rh-1 complexes 5, 6 of the P, P'-coordinated imidobis(phosphaalkene) anion [(iPrMe(2)Si)(2)C=P](2)N-, the first case of elusive P=C-unsaturated congeners of the "classic" bis(phosphanyl)amide ligands. Solid 4a exists in a helically distorted S-shaped structure with two inequivalent P=C groups, but P-31-NMR reveals the equivalence of both P=C groups in solution at the NMR time scale. The P=C and P-N bonds distances in 4a do not indicate significant conjugation within the C=P-N-P=C moieties whereas in complexes 5 and 6 the W-shaped CPNPC heteropentadienide anion exhibits strong 5-center-6-pi conjugation according to DFT calculations and to the experimental P=C and P=N bond lengths.

Hydrolytic cleavage of the P-chlorophosphaalkenes (RMe2Si)2C=PCl (R = Me: 1a; R = iPr: 1b) in the presence of triethylamine leads to di(phosphavinyl) ethers (2,4-diphospha-3-oxapentadienes) [(RMe2Si)2C=P]2O (2a, 2b) as main products, accompanied by alkylphosphinic acids (RMe2Si)2(H)CP(H)(O)OH (3a, 3b). The hydrolysis of (PhMe2Si)2C=PCl (1c) proceeds less selectively. Reactions with metal oxides under aprotic conditions provide 2a [impure, from 1a with (nBu3Sn)2O] and 2b [from iodophosphaalkene (iPrMe2Si)2C=PI with Ag2O] as oils. 1H, 13C, 29Si and 31P NMR spectra, however, allow unambiguous characterisation of 2a and 2b. Formation mechanisms, structure, and C=P-O π stabilisation of the oxabisphosphaalkene [(H3Si)2C=P]2O (2ʹ) were studied with DFT methods. The double [2+4] cycloaddition reaction of 2a with two equivalents of cyclopentadiene leads to the phosphinous anhydride 7 as a mixture of diastereomers whereas the addition of two equivalents of tetrachloro-o-benzoquinone proceeds in a diastereoselective fashion. An X-ray crystal structure determination of the resulting oxo-bridged bis(2-phospha-2,5-dioxa-3,4-benzophospholene) derivative 8 revealed the presence of a racemic mixture of (R,R)- and (S,S)-configurated molecules. The solid state structure of a by-product, bisylphosphonic tetrachlorocatechol monoester (Me3Si)2CH-P(=O)(OH)-o-OC6Cl4OH 9, was also determined crystallographically.