Synthetic and spectroscopic studies of some organotin(iv) complexes
(^119)Sn NMR and IR data are presented for Me(_2)SnX(_2) (X = C1. NCS,N(_3), NCO). Three series of mixed dimethyltin chloro-pseudohalide complexes (Et(_4)N(^+))(_2) Me(_2)SnCl(_n)X(^2-)(_4-n) (X = NCS. N(_3). Partial success obtained for X = NCO) have been prepared from them, and IR, Mossbauer (determined by Dr. P. J. Smith) and (^119)Sn NMR data are presented for the first two series of complexes. The results show them to be formed discretely, to contain regular octahedral anions with linear trans Me-Sn-Me units, and to dissociate in solution. The crystal structure of (Ph(_4)P(^+)(_2) Me(_2)Sn(N(_3))(^2-)(_4) (determined by Dr.J. Halfpenny) is also presented. δ((^119)Sn) changes across the series in the opposite direction to that expected on the basis of substituent electronegativity. The change is tentatively ascribed to polarisability differences between CI and pseudohalide ligands. A rough correlation between δ(mms(^-1)) and substituent electronegativity is observed, and the AE(_q) values correlate fairly well with those expected on the basis of the additivity model. The corresponding series of diphenyltin complexes has been prepared for X = NCS. C(^+)(_2) Ph(_2)Sn(NCS)(_n)C1(^2-)(_4-n). as has the series of five-coordinate complexes Et(_4)N(^+) Me(_2)Sn(NCS)(_n)C1(^-)(_3-n) (except for Me(_2)Sn(NCS)(^-)(_3)). Mossbauer data for the former compounds again show that the anions take up a trans octahedral arrangement. The dissociation of the dimethyltin tetrahalo/pseudohalo complexes (Et(_4)N(^+)(_2) Me(_2)SnCl(^2-)(_4)(^.) (Pr(_4)N(^+))(_2) Me(_2)Sn(NCS)(^2-)(_4) and (Et(_4)N(^+))(_2) Me(_2)Sn(N_3)(^2-)(_4) has been investigated in acetonitrile solution by (^119)Sn NMR, and equilibrium constants for the dissociation were derived. These show the tetra-azide complex to be considerably less dissociated in solution than are the chloride and thiocyanate complexes, although K is quite large for all three. When the same reaction was investigated in DMSO solution, it was deduced that the solvent completely replaces two of the anionic ligands of the complex. Addition of X(^-) to Me(_2)SnCl(^-)(_3) (X = C1), Me(_2)SnCl(_2) (X = C1) and Me(_2)Sn(NCS)(_2) (X = C1.NCS) in acetonitrile has also been studied. Addition is observed in all cases, followed by substitution for Me(_2)Sn(NCS)(_2) + C1(^-). and the limiting shift of the appropriate six-coordinate complex is ultimately obtained. Substitution reactions have been followed for the systems Me(_2)Sn(NCS)(^2-)(_4) + Cl and Me(_2)SnCl(^-2)(_4) + NCS(^-) (both in acetonitrile). The reaction was found to be more facile in the former case. The synthesis of some compounds containing hexacoordinate heterocyclic tin has been attempted, for testing as possible anti-cancer reagents. Preparation via ylide or dilithium reagents did not lead to useful products, but a series of bis(pyridine) or (bidentate pyridine ligand).1.1-dibromostannacyclohexanes has been successfully prepared. The (^1)H. (^13)C and (^119)Sn NMR and infra-red data for these compounds are presented and discussed.