Phosphine oxide adducts of tin(IV) chloride: Experimental NMR and DFT computational study

The stereochemistry of four octahedral complexes SnCl4·2(O)PCl(NR2)2 (R = Me (1); R = Et (2)) and SnCl4·2(O)PCl2NR2 (R = Me (3); R = Et (4)) was studied by both multinuclear (1H, 31P and 119Sn) NMR spectroscopy in solution and density functional theory (DFT) calculation. The NMR data suggest the presence in dichloromethane solutions of a mixture of cis and trans isomers for 1 and 2, whereas only the cis isomer is observed for 3 and 4. Moreover, the latter complexes showed partial ligand dissociation in solution. The assignment of the cis and trans isomers was based on the NMR chemical shifts and particularly on the magnitude of the 2J(31P–119Sn) coupling constant obtained in both solution NMR and DFT studies. In addition, the stereochemistry observed was shown to be highly dependent on the steric hinderance and/or the Lewis basicity of the phosphine oxide ligand. DFT/B3LYP calculations which compared favourably with the experimental data provided further insight into the coordination at the tin atom. The results obtained for both complexes are compared with those of the hexamethylphosphoramide complex.