Organolead hydrides

In 1960, Becker and Cook1212 pointed out that R4 PbH (R = Me, Et n = 1, 2) reacted with diazoalkanes R CTDN (R = H, Me) with the formation of both the products of hydrides disproportionation and the insertion of the R CH group into the Pb—H bond 

In 1965, Neumann and Kuhlein1213 1366 reduced aliphatic halogens, and carbonyl, nitro and nitroso compounds, and Et3SnCl as well, by tributylplumbane at 0°C and 20 °C. A higher temperature was found unacceptable due to the decomposition of Bu3PbH. 

2R3PbH IRjPb RjPb + RjPbPbRs RjPbPbRa R + RjPbH R + RjPbPbRj 

IRsPb + H2 RsPbPbRs R4Pb + RsPbPbRz R4Pb + Pb + R RsPb + RH R4Pb + RsPb  

MeaPbCHrCHR in CsHxa rearrangement cis- to trans-form (1 4-16). Addn. Comnd. MesPbBH, (M-550), from MeaPbOMe and BaHe at -78 at -78°, rxn. with MeOH at -78° - BaHe + H (67 )-) [PbBCaHia]. 

By rxn. of PraPbCl with LiAlH in (MeOCHa)a at -60° (397, 16IO). 

IR spectrum, sensitive to air and light, stable at 0° in the dark for several days (397, I6IO), dec. slowly at -20° (67 4). 

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Organolead hydrides are prepared from the reduction of organolead halides, usually the methyl and ethyl derivatives, by KBH4 or from the reduction of trialkyllead methoxides R3PbOCH3 (R = Me, Et, w-Pr, w-Bu) with B2H6. 

Because of the lower metal-carbon and metal-hydrogen bond strength, organolead hydrides are particularly unstable species and represent the least stable of those of the group 14 elements. Triorganolead hydrides are obtained at low temperatures by reduction of the halides with LiAlH4 (equation 45), but they decompose at 0 °C. 

Hydride generation techniques for the volatilization and separation of alkyl leads have been infrequently used as the organolead hydrides are not very stable. The commonest derivatization reagents are NaBtC IRR or Grignard reagents. The normal separation systems and methods of detection are used. 

The second class includes the organolead derivatives of the various organic and inorganic acids, as well as the organolead hydrides, oxides,... 

The hydroplumbylation reaction (addition of organolead hydrides to multiple bonds) was first carried out by Becker and Cook. They showed that MesPbH added to ethylene in diglyme at 0°C under pressure of 17-35 atm to give MesPbEt in 92% yield. Further investigations were performed by Neumann and Ktihlein and by Leusink and van der Kerk " in 1965. The addition of RsPbOH or RsPbOCOR to ketene, which was studied only in 1965, was of specific interest . 

The reaction of hexaorganodileads with hydrogen halides has been observed to take place readily at room temperature (295,296,311-313,339, 351), The acid cleavage reactions are more complex since organolead hydrides are apparently not formed. From the products isolated the following series of reactions has been suggested (308,339) ... 

Many reactions have been carried out with the help of organic hydrides of the elements of the main group IV (except lead) which have resulted in the synthesis of new groups of compounds. Organotin hydrides were found to be especially versatile 189). The reactivity of organolead hydrides has presented a challenging problem that has only been recently solved. Some... 

Organolead hydrides are more reactive towards C=C and C=C bonds than are the corresponding tin hydrides. Therefore, it is very easy to add lead hydrides completely to unsaturated compounds by placing the latter into the mixture of RsPbX and organotin hydrides. Compare Section III, D,2. An analogous exchange of vinyl and hydrogen... 

All organolead hydrides are very sensitive to oxidation. Filter paper saturated with tributyllead hydride and exposed to air burns instantly. Organolead hydrides are much more reactive than the other hydrides of Group IVB. 

Halide, carbonyl, nitro, and nitroso compounds were reacted with tributyllead hydride (12, 152, 187, 188) in order to compare the reducing properties of the organolead hydrides of Group IVB more closely. The results are shown in Table IX. 

All reductions were made at 0° and 20° C respectively. Higher temperatures are not possible in view of the instabilities of the hydrides. Therefore, slow reactions cannot be accelerated by raising the temperature. The reducing ability of organolead hydrides toward halogen compounds decreases from the iodides to the chlorides (Table IX). lodobenzene... 

However, Becker and Cook 24) report addition of Me3PbH to ethylene at 0° C in diglyme at 2.5 atmospheres. They estimate a yield of 92% of Me3PbEt by gas chromatography. Later Duffy et at. 53) tried the same reaction in dimethyl ether between —78° and 0°C and at about normal pressure. The desired adduct was not formed, and ethylene was quantitatively recovered. It is of interest in this connection that a patent has been issued for the addition of organolead hydrides to ethylene, propylene, isobutylene, cyclohexene, and other a-olefins (27). 

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