Monomeric plumbylenes

Pb- -Pb interaction is formed. The reaction of the more crowded aryllead bromide [Pb(/r-Br)R]2, R = 2,6-(2,4,6-/Pr3C6H2)C6H3, with 4-isopropylbenzylmagnesium bromide or LiSi(SiMe3)3, yielded strictly monomeric plumbylenes.91... 

However, reaction of the sterically congested arylcopper compound 89 with the disilylplumbylene 66 yielded the strictly monomeric plumbylene 90 (Equation (30)).100... 

The successful synthesis of a cyclic oligoplumbane was not reported until 2003. The outcome of reactions of lead(II) halides with aryl Grignard reagents ArMgBr depends on both the steric requirements of the ligand and the reaction conditions. When Ar = 2- Bu-4,5,6-Me3C6H a monomeric plumbylene... 

In the solid state, both 46 and 47 exist as bent monomeric sandwich complexes with ring centroid-lead-ring centroid angles of 152.2° in 46 and 144.2° in 47. Interestingly, if the reaction between PbCl2 and [Li(dme)2][/Bu2G2P3] is carried out in tmen rather than DME, the product formed is not a homoleptic plumbylene but rather the novel heterobimetallic compound 48.73... 

In contrast, the structurally similar molecules 66 and 67 are strictly monomeric in the solid state, with large distances to the lead atoms of neighboring plumbylene molecules. The same holds for the diarylplumbylene 6885 and for the sterically extremely overcrowded plumbylenes 69,86 70,87 as well as 71.88... 

In the solid state, the adducts are monomeric and the three-coordinate carbene C atom is essentially planar and the Pb atom is pyramidalized with a relatively long carbene C-Pb bond, 2.586(7) A. In solution, the adducts dissociate to free carbenes and plumbylenes. 

There is only one report of a carbene-plumbylene adduct. Addition of carbene (1) (R = i-Pr, R = Me) to a toluene solution of PbR (R = 2,4,6-i-Pr3C6H2) afforded the 1 1 adduct (87). An X-ray structure determination revealed that (87) is monomeric with an unusually long Pb-C(carbene) distance of 2.540(5) A. The structure of (87) is similar to the silylene- (80) and stannylene-carbene (86) adduct such that the carbene carbon is almost planar with a pyramidal lead atom. Therefore, of the two possible electronic forms of (87) (the plumbene (87a) and the zwitterionic (87b)), the latter dominates. 

Fig. 13. 52.3 MHz 2

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