867. Mesityl and phenyl derivatives of lead

Abstract

Lead chloride or bromide reacts rapidly with phenyl-lithium or phenylor mesityl-magnesium bromide in tetrahydrofuran at -40". Deeply coloured solutions result which involve equilibrium mixtures, PbAr, + ArLi(MgX) Ar,Pb*Li(MgX) . Evidence is presented that diaryl-leads are rapidly hydrolysed even a t low temperatures, giving a basic lead bromide. Bromination studies indicate that dimesityl-lead is produced by carbonation of (Mesityl),Pb-MgBr.THE isolation of diplienyl-and di-p-tolyl-lead was reported by Krause and Reissaus in 1922. They treated anhydrous lead chloride with ethereal phenylmagnesium bromide a t +2" and obtained a deep red-brown solution from which, after hydrolysis at 0", they isolated diphenyl-lead by extraction into benzene and precipitation with ethanol. Diphenyl-lead obtained in this way (4-57; yield) is described as a blood-red, air-sensitive, amorphous powder which is decolorised when heated above 100" and is monomeric in benzene solution. More recently Gilman and his co-workers investigated the apparently analogous reaction between lead chloride and phenyl-lithium in ether. They obtained evidence for the equilibrium, Ph,Pb*Ei PbPh, + PhLi, based on the appearance of a positive Gilman colour test when more than 2-8 moles of phenyl-lithium were used per mole of lead chloride. Hydrolysis of such solutions (which might have been expected to produce diphenyl-lead) gave a heavy yellow precipitate and a red or yellow ether solution. Attempts to isolate diphenyl-lead were unsuccessful. In contrast to the deep red solutions (presumably of diphenyl-lead) obtained by Krause and Reissaus, Gilman et al. found that using two moles of phenyl-lithium and one of lead chloride in ether at -10" led to a yellow solution that gave a negative colour test, deposited lead when boiled, and on hydrolysis afforded hexaphenyldilead in 70% yield :

Functionalization of Potassium Graphite

“…26 Biphenyl is formed in high yield when phenyl halides are treated with C 8 K,27 whereas reactions of C 8 K with alkyl halides lead to products ranging from alkanes to typical Wurtz‐type coupling products 26. 28 Novel ring‐closure reactions leading to the coupling of α‐diketones and nitrogen‐containing heterocyclic compounds have also been reported 29. 30 Ebert studied reductive alkylations, as well as potassium intercalation, with soot 31…”

Functionalization of Potassium Graphite

“…[23,24] Bergbreiter and Killough studied the Lewis basicity and the electron-transfer properties of C 8 K. [25,26] Biphenyl is formed in high yield when phenyl halides are treated with C 8 K, [27] whereas reactions of C 8 K with alkyl halides lead to products ranging from alkanes to typical Wurtz-type coupling products. [26,28] Novel ring-closure reactions leading to the coupling of a-diketones and nitrogencontaining heterocyclic compounds have also been reported. [29,30] Ebert studied reductive alkylations, as well as potassium intercalation, with soot.…”

Tris(triphenylplumbyl)plumbate: an anion with three stretched lead–lead bonds

“…7 The mechanism of the latter reaction was assumed to involve the initial formation of diphenylplumbylene which should then oligomerise with subsequent disproportionation of the lead chain affording the dilead compound and lead. 7,8 Addition of a solution of phenylmagnesium bromide in THF to solid PbBr 2 at 2110 °C and slow warming resulted in a reaction starting at 280 °C, recognisable from a yellow coloration of the suspension, that intensified to orange-brown until it was complete at 0 °C. After exchange of THF and separation of the magnesium salt, crystallisation at 230 °C gave in 38% yield yellow needles that were not only thermally labile but also sensitive to light and air, and which disproportionate rapidly to leave lead and tetraphenylplumbane (Scheme 2).…”