Thomas Kottke

Low-cost conversion of a coaxial nozzle arrangement into a stationary low-temperature attachment

A stationary nozzle accessory designed for the Siemens/Nicolet LTII low-temperature device with standard ϕ-coaxial nozzle arrangement is described. The attachment is easy to assemble and its compatibility allows interchanging between both systems in less than 1 h, if required. Implementation of the stationary nozzle reduces the consumption of liquid nitrogen by more than 40% and extends the temperature range available for data collection by 60 K in the lower temperature range. Details of construction are presented, and a comparison with the ϕ-coaxial nozzle is discussed.

X-Ray Structural Analysis of a Novel Lithium Hydride/Lithium tert-Butoxide Superaggregate: Li33H17(OtBu)16

Extraordinary solubility in hydrocarbons is exhibited by the novel superaggregate Li33 H17 (OtBu)16 , which crystallizes from photolyzed solutions of lithium tert-butoxide and tert-butyllithium (ROLi:RLi≥7:3). The structure of the compound (the framework of Li, H, and O atoms without tBu groups is shown on the right) resembles a disrupted lithium hydride lattice with an inner hydride-rich core and an outer shell of lipophilic tert-butoxide groups.

Comparison of the X-ray crystal structures of the sodium and potassium 2,4,6-tris(trifluoromethyl)phenoxides (RO–) and 2,4,6-tris(trifluoromethyl)benzenethiolates (RS–); [Na(OR)(thf)2]2, [K(OR)(thf)2(µ-thf)]2, [Na(SR)(thf)2·0.25thf]x and [K(SR)(thf)]x(thf = tetrahydrofuran)

[Na(OR)(thf)2]21, [K(OR)(thf)2(µ-thf)]22, [Na(SR)(thf)2·0.25thf]x3 and [K(SR)-(thf)]x4 were formed by the reaction of the appropriate combinations of 2,4,6-tris(trifluoromethyl)phenol (ROH) or 2,4,6-tris(trifluorornethyl)benzenethiol (RSH) with NaH or KH; compounds 1-4 have been characterised by NMR spectrosccpy and single crystal X-ray structure analysis, both phenoxides being dimeric whereas two distinct polymeric structural types are observed for the thiolates.

Dimers of thf-solvated lithium anilide and lithium pentafluoroanilide: basic building blocks of lithium amide ladder structures

Representing the elementary constituents in the dis-assembling process of lithium amide ladder arrangements, the tetrasolvated dimers [C6H5H(H)Li·2thf]2 and [C6F5N(H)Li·2thf]2 are isolated and cryo-crystallographically characterised, which, based on the unexpected geometries in the solid-state structures, lead to the unaccustomed classification of nitrogen tending to sp2 hybridisation in the planar (LiN)2 four-membered rings.

endo,endo- andexo,exo-Bicyclo[1.1.0]butane-2,4-dimethanol Dimesylate: Synthesis, Structure and Solvolysis

The title compounds endo,endo-9 and exo,exo-9 were prepared from benzvalene. As determined by single-crystal X-ray diffraction, several geometrical parameters of endo,endo-9 are particularly remarkable, namely the large interflap angle of the bicyclo[1.1.0]butane system (128.2°) and the length of the C-1−C-3 bond (151.2 pm). Solvolyses of endo,endo-9 in 60% acetone/water, ethanol and 2,2,2-trifluoroethanol gave rise mainly to cis-5-substituted cyclopent-2-ene-1-methanol mesylates (cis-10, cis-11). Small quantities of the corresponding trans isomers (trans-10,trans-11) suggest a configurational conversion of the intermediate, which is proposed to be the nonclassical pseudoaxial 2-mesyloxymethyl-substituted cyclopent-3-en-1-yl cation (ax-31) formed from endo,endo-9 by heterolytic dissociation accompanied by a Wagner-Meerwein rearrangement. The solvolyses of exo,exo-9 took an entirely different course and afforded nonrearranged products (26, 27) exclusively. This is interpreted in terms of the stereochemical requirements of the Wagner−Meerwein rearrangement, which in the case of exo,exo-9 would result in a highly strained cation such as 32 or 33. In consequence, the generation of the bicyclobutylcarbinyl cation 34 seems to be the most favourable alternative. This result, together with kinetic data for solvolyses of endo,endo-9 and exo,exo-9, casts doubt on a report on solvolyses of the dimethylbicyclo[1.1.0]but-2-ylcarbinyl tosylates 6.4 Solvolyses of endo,endo-9 in several solvents are about 5 times faster than those of the ditosylate 2 (or the corresponding dimesylate), a less flexible bicyclo[1.1.0]butane derivative. That the solvolysis of exo,exo-9 takes place about 8 times more slowly than endo,endo-9 is interpreted by invoking a weaker σ-participation in the case of the former. In comparison to the stereochemically closely related exo,exo-9, the cyclobutanedimethanol ditosylate 28 solvolyses only 50 times more slowly.

Aggregation of lithium and mixed thallium(I)–lithium amides through η3- and η6-π-arene interactions in the solid

The mixed Li–Tl amide [C10H6{N[Li(thf)2]SiMe3}{N(Tl)SiMe3}] has been synthesized and shown to aggregate via η6-arene–thallium coordination in the solid; a related pattern of aggregation is found for the partially solvated homometallic Li amide [C10H6{N[Li(thf)]SiMe3}{N(Li)SiMe3}] which displays an unusual η3-arene–lithium interaction.

Self-assembly in the metallation of bis(aminoaryl) ethers

Abstract The dilithiation of 2,2′-bis(2-methoxyethylamino)diphenyl ether ( 4 ) and 2,2′-bis( N , N -dimethylethylenediamino)diphenyl ether ( 7 ) in the absence of any Lewis base donor resulted in the formation of dimeric complexes 8 and 9 , respectively, containing the unprecedented Li 4 O 2 N 4 “adamantanoid” metal core as a consequence of the self-recognition and self-assembly involving the two metallated subunits. In contrast, on monometallation using particular conditions, e.g. sodium hydride in the presence of Lewis base donor, the same ligands undergo a Smiles-type rearrangement, providing the first example of such a reaction involving an amine and a deactivated aromatic system. The conditions needed to promote this rearrangement have been investigated.

Monometallation of a di(aminoaryl) ether induces a Smiles rearrangement leading to a sodium aryloxide complex: the synthesis and crystal structure of [(MeOCH2CH2)(C6H4NHCH2CH2OMe)NC6H4O·Na]2

The title compound was synthesised by 1 : 1 reaction of sodium hydride with a di(aminoaryl) ether ligand in toluene–hexamethylphosphoramide (HMPA) solution; X-ray crystallography revealed that an in situ Smiles rearrangement of the ligand had taken place to give a dimeric aryloxide sodium complex, which is in stark contrast to previous results obtained by 2 : 1 reaction of BunLi with the ligand in the absence of HMPA.

Ionic cleavage of Ti–Co and Zr–Co bonds: the role of the nucleophilicity of the late transition metal in the reactive behaviour of early–late heterobimetallics

The ionic cleavage of Ti–Co and Zr–Co bonds occurs upon reaction with ButNC and the products [MeSi{SiMe2N(p-Tol)}3Ti(CNBut)2][Co(CO)4] 3 and[MeSi{SiMe2N(p-Tol)}3Zr(CNBut)3][Co(CO)4] 4 were characterized by single crystal X-ray diffraction; the importance of the nucleophilicity of the late transition metal fragment in reactions of the unsupported early–late heterobimetallics is demonstrated.