Synthesis, Molecular Structure, and Solution Stereochemistry of Hypercoordinated Bis(3-(dimethylamino)propyl)tin Compounds. Dissociative (Nonregular) and Nondissociative (Regular) Isomerization Pathways

The syntheses of [Me 2 N(CH 2 ) 3 ] 2 Sn(EAr) 2 ( 1, E = O, Ar = C 6 H 5; 2, E = O, Ar = p- t -BuC 6 H 4; 3, E = O, Ar = p-NO 2 C 6 H 4; 4, E = O, Ar = o-FC 6 H 4; 7, E = S, Ar = C 6 H 5 ), [Me 2 N(CH 2 ) 3 ] 2 Sn( o -O 2 C 6 H 3 R-3) ( 5, R = H; 6, R = OCH 3 ), and {[Me 2 N(CH 2 ) 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 1 H, 13 C, and 119 Sn NMR investigations reveal the compounds to have similar structures in solution. The coalescence phenomena observed in the 1 H and 13 C 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.