Single X-ray structures

The same group also reported the first isolation and characterization of the corresponding sulfenium cation salt 173, as shown in Equation (47) <1998TL2593>. A single X-ray structure determination revealed that the two amino groups coordinate direct to the cationic sulfur atom. 

A few attempts to brominate C70 were undertaken by reaction with bromine either neat or in solution. The only derivative whose composition could be confirmed is CyoBrjo. A single X-ray structure of this compound revealed its structure (Figure 9.9), which is identical to that of C70CI10 (see Figure 9.8) [95]. 

Combination with a second C3BN ring leads to diastereoisomers which can be separated (46a,b). In the diastereoisomer (46a) the metal M uses the same ring sites, whereas in (46b) different sites are coordinated. Many examples have been described by Schmid where both isomers are formed and could be separated and characterized by single x-ray structure analysis <85MI 317-01 >. This chiral property of 1,2-azaborolyl rings in combination with metal atoms has some interesting consequences with respect to stereoselective reactions. 

A convenient synthesis of the triethylamine-sulphur trioxide complex Et3NS03 (129) has been reported by Nair and Bernstein177. A 75% yield of 129 was obtained by the reaction of triethylamine with chlorosulphonic acid. Reaction of quinuclidine N-oxide with SO2 yield a stable colourless, non-hygroscopic material which was identified by X-ray and elemental analysis to be the quinuclidine-sulphur trioxide complex 130178. The complex was exceedingly stable and its hydrolysis in water even at 86 °C was very slow, 280 times slower than the analogous rate for triethylamine-sulphur trioxide (129). A single X-ray structure determination of the complex showed a sulphamic acid type coordination of SO3 to the quinuclidine nucleus [N-S =1.831 (6) A]. 

The intra- and intermolecular arrangements of the DPP molecules in a DPP crystal have been investigated by single X-ray structure analysis ". Angles and bond distances in the diphenyl DPP 2 are shown in Figure 11-3. 

Exemplary, the solid state structure of 85a was determined by single X-ray structure analysis. The result thereof is shown in Figure 6 [14a, 48],... 

The molecular solid state structures of 98a - 98c were established by single X-ray structure analyses showing that constraint Pt(C=CP)2M rings (M = Mo, Pd, Pt) are present. This corresponds with the observation made that 98a is a very efficient catalyst in Heck reactions showing very high activities [40]. 

Several structures of the transition state have been proposed (I. D. Williams, 1984 K. A. Jorgensen, 1987 E.J. Corey, 1990 C S. Takano, 1991). They are compatible with most data, such as the observed stereoselectivity, NMR measuiements (M.O. Finn, 1983), and X-ray structures of titanium complexes with tartaric acid derivatives (I.D. Williams, 1984). The models, e. g., Jorgensen s and Corey s, are, however, not compatible with each other. One may predict that there is no single dominant Sharpless transition state (as has been found in the similar case of the Wittig reaction see p. 29f.). 

Bahar et al. [46] have used this kind of approach to predict the B-factors of 12 X-ray structures. Elements in the Hessian corresponding to atom pairs separated by a distance of less than 7 A are set to zero, and the remainder have the same value dependent on a single adjustable parameter. Generally B-factor predictions for the a-carbons compare very well with the B-factors measured by X-ray crystallography. Figure 1 shows the result for the subunit A of endodeoxyribonuclease I complexed with actin. 

By diluting HF by means of multiple additions of water, followed by the evaporation of a solution initially prepared by the dissolution of NaF and Nb205 in HF, Stomberg [58] obtained Na3NbOF6 in the form of small single crystals that were suitable for X-ray structure investigations. 

Diazotization of 5-amino[l, 2,3]triazole 692 afforded (88BSB179) triaz-olo[l, 5-i>][l, 2,4]triazine 694 as a result of a Dimroth rearrangement of the initially formed isomeric structure triazolo[5,l-c][l,2,4]triazine 693. Molecular structure of 694 was determined by single X-ray diffraction (Scheme 146). 

Addition of lithiated Ar-(4-methylphenylsulfonyl)-S-phenyl-S -(2-propenyl)sulfoximine to acyclic enones gives exclusively 1,4-a-adducts in high diastereomeric purity. The configuration of the adduct (R2 = R3 = C6H5) has been determined by a single crystal X-ray structure determination27. 

From single-crystal X-ray structural analysis the ground-state conformation of (.S )-2-(4-meth-ylphenylsulfinyl)-2-cyclopentenone was shown to have the sulfoxide bond orientated anti to the carbonyl bond, as expected for minimization of electrostatic interactions13. 

Very recently, synthesis and structure of molybdenum and tungsten complexes of the relatively unhindered disilene Si2Me4 were reported. The x-ray structure of 84 shows a metallacyclosilane structure with W — Si = 2.606(2) A and Si —Si = 2.260(3) A. The W — Si bond length is within the range of various estimates of the Si and W covalent radii and the Si —Si distance falls midway between the expected values for a single (2.35 A) and a double bond (2.14 A) (Fig. 13). 

---