Synthesis and Multinuclear NMR Properties of Sixmembered Heterocyclic Organolead Compounds

Abstract

Several six-membered heterocyclic organolead compounds were synthesized from the appropriate di-Grignard resp. organodilithio compounds and a (diorgano)lead dihalide. The compounds were investigated by multinuclear NMR spectroscopy. Variable temperature 1 H NMR measurements revealed a conformational equilibrium. In the 13 C and 207 Pb NMR spectra specific effects caused by the presence of a lead atom in the ring system could be observed. IntroductionIn several previous studies we had investigated some aspects of the chemistry of cyclic organolead compounds, including five-membered ring compounds, in particular [2,3]. Subsequently we studied several six-membered cyclic organolead compounds of the general type (1) and the results are presented here. We were particularly interested in the effects of variation of the element Ε on the multinuclear NMR properties. Results on 10,10-dimethylphenoxaplumbin, in which Ε denotes an oxygen atom and R is CH 3 , have been previously published [1]. Materials and Methods1 H and 13 C NMR spectra were recorded on a JEOL-PFT-100 NMR spectrometer. 207 Pb NMR spectra were recorded on a Bruker WH 90 multinuclear spectrometer. Experimental details on the recording and assignments of the various spectra have been published elsewhere [24,36]. All synthetic reactions were carried out under dry nitrogen. The solvents diethylether (ether) and tetrahydrofuran (THF) were distilled from lithiumaluminiumhydride before use. For more experimental details see ref.[39]. Synthesis of bis-(o-bromophenyl)methane [6]A solution of 25.0 g of o-dibromobenzene (0.106 mol) and 19.9 g of 1,2-dibromoethane (0.106 mol) in 125 ml of ether was added dropwise to 5.15 g of magnesium (0.212 mol) in 15 ml of ether which was stirred magnetically. External cooling was applied by means of an ice bath and the reagents were added at such a rate that the temperature of the reaction mixture did not exceed 10°C. After the reaction was completed (ca. 3 h) the mixture was stirred for another 10 min. and at 0°C 19.7 g of o-bromobenzaldehyde (0.106 mol) was added dropwise. After refluxing for 2 h the mixture was cooled down to room temperature and hydrolysed with an aqueous ammonium chloride solution. The ether layer was isolated and the water layer was extracted with a 100 ml portion of ether. The combined ether fractions were dried over anhydrous magnesium sulfate. After filtration and evaporation, a yellow oil of 2,2'-dibromodiphenylmethanol was obtained. ©Part III, see ref.[1] Abstract R' R (1) 37 Brought to you by | Purdue University Libraries