CARBORANE TO ENHANCE CHELATING CAPACITY S,S'-THIOETHER-THIOESTER COORDINATION AND ITS TRANSITION-METAL STABILITY

An S,S'-thioether-thioester chelating ligand [7,8-mu-SCH2C(O)S-7,8-C2B 9H10](-) (L-1), incorporating the unit [-(C)(2)B9H10](-) has been synt hesized. Reactions have been conducted with RhCl(PPh3)(3) and PdCl2(PP h3)(2) complexes in ethanol. With Rh, L-1 maintains its original cycli c nature and most probably chelation via thioether-thioester takes pla ce. The carborane negative charge may stabilize this original thioethe r-thioester complex. The other two Rh positions are occupied by two PP h3 ancillary ligands forming [Rh(L-1)(PPh3)(2)]. The reaction of L-1 w ith Pd induces ligand modifications and the cyclic nature of L-1 is lo st. A transesterification process leading to a dianionic ligand L-2, [ 7-S-8-SCH2C(O)OCH2CH3-7,8-C2B9H10](2-) has taken place. In this way L- 2 is capable of compensating the dipositive Pd charge. The other two P d positions are occupied by two PPh3. This reaction has been extended to methanol and isopropanol solvents. The crystal structure of [Pd(L-2 )(PPh3)(2)] has been determined.