Diastereoselective Transformations on Heterometal Clusters

Abstract

Table 2. Relative rate of conversion of n-hexyl bromide 2b into n-hexyl azide 3b with the polymer 1 (after 4 h in various solvents; determined by GC). ~~ ~~ Solvent Conversion [No] to I u e n e 23 chloroform 26 methanol 32 tetrahydrofuran 38 pentane 52 Solvent Conversion [%] diethyl ether 54 acetone 82 acetonitrile > 95 dimethylformamide > 95even the more sluggishly reacting hexyl bromide 2b are converted into their azides 3a and 3b, respectively, by reaction with 1 at 20°C Within 3 h in acetonitrile o r within 24 h in dichloromethane.Most remarkably, this method allowed us, for the first time, to convert dibromomethane 2k or, more slowly, dichloromethane into diazidomethane 3k, a n explosive com-Although dichloromethane is a convenient, lowboiling solvent for reactions of 1 with alkyl halides (usually complete within 4-24 h), the above results indicate caution when employing this solvent (conversion into 3k requires over two weeks). The relative rate of reactivity with the polymer 1 is R-I>R-Br>R-OTos>R-CI, which is in accord with a nucleophilic substitution process. Experimental ProcedurePolymer 1 : Amberlite IR-400 was washed with 20% sodium azide soiution, then with water, methanol, and chloroform or ether. The polymer was dried at room temperature in vacuum and found to contain 2.55 mmol of azide per gram. The friction parameter of 1 as measured on a Julius-Peter apparatus was 14.4 kg, indicative of high friction stability. Reaction of 1 with Ze: To 4.9 g of 1 (12.5 mmol of azide) was added 4 mL of CH2Cl2 and 0.265 g (1.06 mmol) of p-bromobenzyl bromide 2e. After 2 h of mixing, the polymer was filtered and washed with CHZCIZ. Evaporation of the combined solvent mixture gave purep-bromobenzyl azide 3e as an oil in 93% yield: 'H-NMR: 6=7.5 and 7.2 (AA'BB', 4 H ) ; 4.29 (s, 2H). m / z 212.74, 210.84.

A S8‐like [Sb8]8− Zintl Anion in the Ammoniate [K17(Sb8)2(NH2)] · 17.5NH3

“…As is to be expected, the homoatomic bonds in antimony polyanions with a lesser charge-per-atom ratio like [Sb 11 ] 3Ϫ (mean value 2.803 Å [11,12]) or [Sb 7 ] 3Ϫ (mean value 2.82 Å [13]) are considerably shorter. This charge-induced effect is virtually nonexistent for the As 8 -containing complex anions mentioned above; the mean As-As bond lengths of [NbAs 8 ] 3Ϫ (2.434 Å [9]) and MoAs 8 2Ϫ 2.429 Å [10]) are exactly the same as those in [As 11 ] 3Ϫ (2.432 Å [12]) and [As 7 ] 3Ϫ (2.420 Å [14]). This observation alone demonstrates that the structural properties of the As 8 ring in those complexes differ markedly from the properties expected for a free [As 8 ] 8Ϫ anion.…”