The small-scale preparation and NMR characterization of isotopically enriched organotin compounds

Synthetic methods for the small-scale laboratory preparation of isotopicall y enriched dibutyltin dichloride, dibutyltin di-iodide, tributyltin chlorid e, tributyltin iodide, diphenyltin dichloride, triphenyltin chloride and tr iphenyltin iodide have been successfully established. Organotin iodides wer e prepared from redistribution reactions between tin(IV) iodide and the cor responding tetraorganotin, with the exception of dibutyltin di-iodide, whic h was prepared directly from the reaction between tin metal and iodobutane. The development of novel procedures for the dealkylation/dearylation of te traorganotins by acid hydrolysis produced superior yields of tributyltin ch loride and diphenyltin dichloride in comparison with redistribution reactio ns. Organotin iodide redistribution reaction products were converted to the ir chloride analogues via the fluoride salts using an aqueous ethanolic sol ution of potassium fluoride. The insolubility of organotin fluoride salts w as exploited to isolate and purify the isotopically enriched compounds, and to prevent losses during the purification procedure. The nuclear magnetic resonance (NMR) spectroscopic study of 'natural abunda nce' and isotopically enriched organotin compounds gave proton (H-1) and ca rbon-13 (C-13) spectra for butyltins, Bu4-nSnXn, and phenyltins, Ph4-n SnXn (X = I, CI), allowing the assignment of C-13 chemical shifts, and Sn-119-C -13 and Sn-117-C-13 coupling constants. The C-13 NMR spectroscopic analysis of Sn-117-enrichcd organotin compounds has allowed the assignment of certa in resonances and tin-carbon coupling constants which were previously unobs ervable. The spectral patterns show that delta(H-1) and delta(C-13) values are sensi tive to structural changes, and that C-13 shielding decreases with an incre ase in the electronegativity of the substituent. The tin-carbon coupling co nstants are also sensitive to structural changes, and for alkyl and aryl co mpounds the couplings decrease in the order (1)J > (3)J > (2)J > (4)J. The C-13 chemical shift values and the magnitude of tin-carbon coupling constan ts are shown to be solvent-dependent. The C-13 spectra of the isotopically enriched compounds show that the degree of isotopic enrichment and the natu re of the isotope used (magnetic or non-magnetic) are reflected in the spec tral pattern obtained. Copyright (C), 2000 John Wiley & Sons, Ltd.