Synthesis, molecular structure, and solution stereochemistry of hypercoordinated bis(3-(dimethylamino)propyl)tin compounds.: Dissociative (nonregular) and nondissociative (regular) isomerization pathways

The syntheses of [Me2N(CH2)(3)](2)Sn(EAr)(2) (1, E = O Ar = C6H5; 2 E O Ar p-t-BuC6H4 3, E = O, Ar = p-NO2CsH4; 4, E = O, Ar = o-FC6H4; 7, E = S, A = C6H5), [Me2N(CH2)(3)](2)-Sn(o-O2C6H3R-3) (5, R = H; 6, R = OCH3), and {[Me2N(CH2)(3)](2)SnPh}I-+(-) (8) are reported. X-ray diffraction analyses reveal distorted-octahedral geometries for the tin atoms in compounds 1-7 with, except for the stannaindane derivative 5, the carbon atoms in mutually trans positions, while the nitrogen and oxygen atoms are cis. In compound 5, the carbon atoms are cis, whereas the nitrogen atoms are trans. Compound 8, in contrast, is ionic and consists of an intramolecularly pentacoordinated triorganotin cation and an iodide anion. Variable-temperature H-1, C-13, and Sn-119 NMR investigations reveal the compounds to have similar structures in solution. The coalescence phenomena observed in the H-1 and C-13 NMR spectra are explained both in terms of Sn-O bond cleavage (1-4) and chirality inversion through a sequence of five intramolecular Berry-type pseudorotations (1-4, 8), interconverting the enantiomers with propeller-like geometry. The dynamic behavior in solution of the stannaindane derivatives 5 and 6 and of the thiophenolate derivative 7 is interpreted in terms of intramolecular Sn-N bond dissociation.