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Carboxylate Ligand Executes Fluxional Behavior in Dimeric
Tetraorganodicarboxylato Stannoxanes
Muhammad Danisha and Saqib Alib
a
Department of Chemistry, University of Sargodha, 40100-Sargodha, Pakistan
[email protected], Fax: +92 48 3222 121
b
Department of Chemistry, Quaid-e-Azam University, 45320-Islamabad, Pakistan
Dimeric tetraorganodicarboxylatostannoxanes comprise one of the most interesting
class of organotin compounds as they show different sets of 1H and 13C-NMR signals for Rgroups attached to Sn(IV) and only one set of signals for carboxylate ligand. A similar
dichotomy is observed 119Sn-NMR spectra1,2. Two types of signals are only possible if there
are two environments for the R-groups and Sn(IV) atoms. When two type of signals are
observed for R-groups and tin atoms then, why only one for carboxylate ligand. It is
suggested that one set of signals for carboxylate ligand is possible only if it executes fluxional
behavior in the molecule. This process is too fast to be observed on NMR time scale even at 100oC. It is proposed that the ease of fluxional process depends upon the nature of R-groups
as well as the carboxylate ligands. It is recommended that fluxional process can be stopped if
there is another donor group in the ligand in close vicinity of the tin atom. The attachment of
this donor group to tin centre may stop the fluxionating ability of the carboxylate ligand.
Figure: 500 MHz 1H NMR spectra, (in CDCl3 (40%) at 298K). 2J[119/117Sn-1H] are marked
with * and $ for endo- and exocyclic methyl groups respectively; solvent is marked with S.
References
1. Fluxional Behavior in Dimeric Tetraorganodicarboxlato Stannoxanes. Danish M.;Ali S. and
Mazhar M. Heteroatom Chem., 1996, 7, 233-237.
2. Organotin Ester of 3-(2-Furanyl)-2-Propenoic Acid: Their Characterization & Biological Activity.
Danish M.;Alt H.G.; Ali S.; Badshah A.; Mazhar M. and Islam N. J. Organomet. Chem., 1995, 486,
51-56.