Reactions of rhenium and manganese carbonyl complexes with 1,8-bis(diphenylphosphino)naphthalene: Ligand chelation, C-H and C-P bond-cleavage reactions

Reaction of [Re₂(CO)₈(MeCN)₂] with 1,8-bis(diphenylphosphino)naphthalene (dppn) afforded three mono-rhenium complexes fac-[Re(CO)₃(κ¹:η¹-PPh₂C₁₀H₆)(PPh₂H)] (1), fac-[Re(CO)₃{κ¹:κ¹:η¹-(O)PPh₂C₁₀H₆(O)PPh(C₆H₄)}] (2) and fac-[ReCl(CO)₃(κ²-PPh₂C₁₀H₆PPh₂)] (3). Compounds 1-3 are formed by Re-Re bond cleavage and P-C and C-H bond activation of the dppn ligand. Each of these three complexes have three CO groups arranged in facial fashion. Compound 1 contains a chelating cyclometalated diphenylnaphthylphosphine ligand and a terminally coordinated PPh₂H ligand. Compound 2 consists of an orthometalated dppn-dioxide ligand coordinated in a κ¹:κ¹:η¹-fashion via both the oxygen atoms and ortho-carbon atom of one of the phenyl rings. Compound 3 consists of an unchanged chelating dppn ligand and a terminal Cl ligand. Treatment of [Mn₂(CO)₈(MeCN)₂] with a slight excess of dppn in refluxing toluene at 72 °C, gave the previously reported [Mn₂(CO)₈(μ-PPh₂)₂] (4), formed by cleavage of C-P bonds, and the new compound fac-[MnCl(CO)₃(κ²-PPh₂C₁₀H₆PPh₂)] (5), which has an unaltered chelating dppn and a terminal Cl ligand. In sharp contrast, reaction of [Mn₂(CO)₈(MeCN)₂] with slight excess of dppn at room temperature yielded the dimanganese [Mn₂(CO)₉{κ¹-PPh₂(C₁₀H₇)}] (6) in which the diphenylnaphthylphosphine ligand, formed by facile cleavage of one of the P-C bonds, is axially coordinated to one Mn atom. Compound 6 was also obtained from the reaction of [Mn₂(CO)₉(MeCN)] with dppn at room temperature. The XRD structures of complexes 1-3, 5, 6 are reported.     

Photochromic and fluorescence properties of coumarin fulgimides

Four new fulgimides possessing a fluorescent coumarin unit were synthesized from the corresponding fulgides, and their photochromic as well as fluorescence properties were investigated. The open-ring forms of coumarin fulgimides were found to exhibit fluorescence in the visible region. Upon exposure to UV light, the fulgimides were transformed into the nonfluorescent closed-ring forms, which can be reverted to the initial fluorescent open-ring forms on exposure to visible light. The efficiency of quenching of fluorescence was as high as 95% at the photostationary state of UV irradiation.     

6,13‐Diethynyl‐5,7,12,14‐tetraazapentacene

A new relative of pentacene : The dialkynylated tetraazapentacene (see figure) was prepared by a two‐step synthesis from the corresponding quinone derivative. The heteroacene is an air‐stable, dark‐blue, crystalline material and is of great interest as a potential organic n‐electron‐transport material.

     

n‐Doping of Organic Electronic Materials Using Air‐Stable Organometallics: A Mechanistic Study of Reduction by Dimeric Sandwich Compounds

Several 19‐electron sandwich compounds are known to exist as “2×18‐electron” dimers. Recently it has been shown that, despite their air stability in the solid state, some of these dimers act as powerful reductants when co‐deposited from either the gas phase or from solution and that this behavior can be useful in n‐doping materials for organic electronics, including compounds with moderate electron affinities, such as 6,13‐bis[tri(isopropyl)silylethynyl]pentacene ( 3 ). This paper addresses the mechanisms by which the dimers of 1,2,3,4,5‐pentamethylrhodocene ( 1 b₂ ), (pentamethylcyclopentadienyl)(1,3,5‐trialkylbenzene)ruthenium (alkyl=Me, 2 a₂ ; alkyl=Et, 2 b₂ ), and (pentamethylcyclopentadienyl)(benzene)iron ( 2 c₂ ) react with 3 in solution. Vis/NIR and NMR spectroscopy, and X‐ray crystallography indicate that the products of these solution reactions are 3 ^.? salts of the monomeric sandwich cations. Vis/NIR kinetic studies for the Group 8 dimers are consistent with a mechanism whereby an endergonic electron transfer from the dimer to 3 is followed by rapid cleavage of the dimer cation. NMR crossover experiments with partially deuterated derivatives suggest that the C? C bond in the 1 b₂ dimer is much more readily broken than that in 2 a₂ ; consistent with this observation, Vis/NIR kinetic measurements suggest that the solution reduction of 3 by 1 b₂ can occur by both the mechanism established for the Group 8 species and by a mechanism in which an endergonic dissociation of the dimer is followed by rapid electron transfer from monomeric 1 b to 3 .     

Alkynoate Synthesis through the Vinylogous Reactivity of Rhodium(II) Carbenoids

Siloxy group migration: A rhodium(II) carbenoid approach has been developed for the synthesis of alkynoates. This transformation combines the addition of enol ethers at the vinylogous position of β-siloxy-substituted vinyldiazo derivatives with a siloxy group migration to give the products as single diastereomers.     

Searching for cyclin-dependent kinase inhibitors using a new variant of the cope elimination

beta-Piperidinoethylsulfides are oxidized by m-chloroperbenzoic acid to intermediates containing both N-oxide and sulfone functions. These undergo a Cope-type elimination to a vinylsulfone that can be captured by amines to afford beta-aminoethylsulfones. When a beta-aminoethylsulfone group is linked to the 4-position of a phenyl group attached at N-2 of O6-cyclohexylmethylguanine, the resulting derivatives are inhibitors of the cyclin-dependent kinase CDK2. One of the most potent inhibitors (IC50 = 45 nM) contained a N-3-hydroxypropyl group on the aminoethylsulfonyl substituent. The crystal structure of this inhibitor bound to CDK2/cyclin A was determined and shows an unusual network of hydrogen bonds. The synthetic methodology developed can be utilized in multiple-parallel format and has numerous potential applications in medicinal chemistry.     

CHARACTERIZATION OF NANOSTRUCTURES:TOOLS AND CHALLENGES

Apart from long-known and applied nanostructures like carbon black for tyres or pigments for coatings nanotechnology has created highly sophisticated structures used for nano/molecular electronics,diagnostics,drug delivery, UV-absorbers etc.Often the main question to be solved analytically is the local determination of tiny amounts of chemicals resulting in an ever increasing need for highly sensitive as well as locally resolved techniques.Applications of techniques like mass spectroscopy,transmission el...