Cyclopolygermanes, -stannanes and -plumbanes

The condensation of diorganotin dihydrides with diorganotin diamides is another route to cyclic polystannanes. This method is especially useful for the high-yield synthesis of the dimethyl derivative (Me2Sn)g [eqn (10.5)], which cannot be obtained by the dehydrocoupling process. 

Unexpectedly, the cyclic tetramer ( Bu2Sn)4 (rather than Bu4Sn) is obtained as bright-yellow crystals from the reaction of Bu2SnCl2 with an excess of BuMgCl in boiling Evidence for the cyclic structure of ( Bu2Sn)4 in 

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 

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