SYNTHESIS OF NOVEL DIVALENT ORGANOTIN COMPOUNDS CONTAINING THE CHIRAL C,N [2-(DIMETHYLAMINO)PHENYL]-(TRIMETHYLSILYL)METHYL OR 2-[1-(DIMETHYLAMINO)ETHYL]-PHENYL CHELATING LIGAND

The novel chiral, divalent organotin compounds bis{]2-(dimethylamino)phenyl]-(trimethylsilyl)methyl}tin (II) 1 and bis{2-]1-(dimethylamino)ethyl]phenyl}tin (II) 2 have been synthesised from their corresponding racemic lithium compounds and SnCl2. Similarly enantiomerically pure bis{2-[1-dimethylamino)ethyl]phenyl}tin(II) 2a has been prepared from the enantiomerically pure organolithium analog. Whereas the formation of the benzylic tin (II) compound 1 is completely diastereoselective (only one diastereomeric pair is formed in which the two chiral carbon atoms have the same configuration, either (R) or (S), the formation of the phenyl tin(II) compound 2 is not diastereoselective (all possible diastereoisomers are formed in a statistical ratio). The H-1 and C-13 NMR spectra of 1 and 2, recorded at - 40-degrees-C, indicate that a Sn - N coordinate bond is present which is inert at this temperature. This results in a psi-trigonal bipyramidal coordination geometry at Sn in both 1 and 2. As a result of this intramolecular coordination the Sn atoms become additional chiral centers. The presence of specific diastereoisomeric pairs in solution at low temperature is explained by the steric requirements of the substituents in the five-membered chelate rings.