Tin-119 NMR studies on diorganoyltin(IV)dihalides and triorganoyltin(IV)halides; Formation and stereochemistry of adducts

Abstract The reactions of R 2 SnX 2 (R = Ph, Me; X = Cl, Br) with excess halide, tributylphosphine, tricyclohexylphosphine and tributylphosphine oxide have been investigated in dichloromethane solution by tin-119 and phosphorus-31 NMR techniques. R 2 SnX 2 form five coordinate 1:1 adducts with halide and phosphine (phos) ligands whilst both 1:1 and 1:2 adducts are formed with tributylphosphine oxide (L). Tin-119 spectra imply that Ph 2 SnX 2 (phos) has the phosphine in the equatorial position of a trigonal bipyramid. At low temperature there is evidence for a slow intramolecular twist mechanism between octahedral isomers of Ph 2 SnCl 2 L 2 . The stereochemistry of the complexes Ph 2 SnX 2 L 2 differ between chloro and bromo compounds and no mixed halide complex is observed. In the case of the bromo system only, the 1:3 adduct [Ph 2 SnBrL 3 ] + Br − is formed. Ph 3 SnCl does not react with phosphines but it does give 1:1 adducts with Cl − , L and pyridine. All the adducts have similar tin-119 chemical shifts which is consistent with the phenyl groups being equatorial in the five coordinate trigonal bipyramidal adducts. Ph 4 Sn does not form adducts with X − , L or phosphine.