Jörg Glatthaar

Structural Analyses of N‐Acetylated 4‐(Dimethylamino)pyridine (DMAP) Salts

We have studied the formation of several N-acetyl-4-(dimethylamino)pyridine (DMAP) salts (with Cl(-), CH(3)COO(-), and CF(3)COO(-) counterions), which are considered to be the catalytically active species in DMAP-catalyzed acetylation reactions of alcohols. Combined crystal structure analyses, variable temperature matrix IR and NMR spectroscopy as well as computational techniques at the UAHF-PCM-B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) level were utilized to examine the structures and dynamics of salt formation. We found clear evidence for the formation of tight ion pairs that are stabilized by dynamic hydrogen-bonding interactions. In nonpolar solvents, the nucleophilicity of acetate in its N-acetyl-DMAP salt only allows a steady-state concentration smaller 1% at room temperature. Thus, we propose additional hydrogen-bonding interactions with alcohols to be the key stabilization factor in subsequent acetylations.

Reaction of Silicon Atoms with Hydrogen Cyanide: Generation and Matrix-Spectroscopic Identification of CHNSi and CNSi Isomers

Cocondensation of thermally generated silicon atoms with hydrogen cyanide in an argon matrix can be used as an access to compounds of the composition CHNSi and CNSi. Isolation, matrix-spectroscopic identification and photo-chemical behavior of these species are described. Structural assignments are made by the comparison of experimental with calculated IR spectra.

Reactions of Silicon Atoms with Methane and Silane in Solid Argon: A Matrix‐Spectroscopic Study

The reaction of silicon atoms with methane (1) and silane (7) in argon at 10 K has been studied. Methane (1) is found to be inert to silicon atoms, but reaction occurs upon photochemical excitation under formation of methylsilylene (2). On the contrary, silane (7) is spontaneously converted into a mixture of silylsilylene (10) and disilene (12). Subsequent irradiation generates the butterfly-type disilyne Si(2)H(2) (14), together with a third photoproduct, which we assume to be the doubly bridged Si(2)H(4) isomer 13. The structural elucidation of the new species is based on the comparison of the experimental IR and UV/Vis spectra with data from density functional theory calculations. The results are supported by isotopic labeling studies.

Dihalodimethylsilanes from silicon atoms and methyl halides: a combined matrix-spectroscopic and density functional theory study☆

Abstract The reaction of silicon atoms with methyl halides 6a–d has been studied in an argon matrix at 10 K. It is shown that the product formation depends on the relative methyl halide/argon ratio. In the initial step triplet n-adducts T-5 are formed. T-5a–c can be identified spectroscopically. The next step can be induced photochemically. The primary photoproducts are the halomethylsilylenes S-1a–c. In case of methyl iodide 6d the reaction with silicon atoms leads spontaneously to silylene S-1d. In a diluted argon matrix all silylenes 1a–d can further be photoisomerized to the corresponding halosilenes 2a–d. In the presence of an excess of a methyl halide complexes of type 7a–d are formed. Longer irradiation transforms these adducts into the dihalodimethylsilanes 8a–d. The generation of the silanes 8a–d starting from silicon and a methyl halide images the results of the Rochow-Muller synthesis. The relevance of our findings to this important technical process is discussed. The structural elucidation of all new species is based on the comparison of the experimental observations with density functional theory calculations.