R3E+ carborane salts of the heavier group 14 elements: E = Ge, Sn, and Pb

The synthetic and structural chemistry of catalytically useful trialkylsilylium salts with weakly coordinating carborane anions, R 3Si(CHB11X11), has been extended to the heavier group 14 elements. Et3Ge(CHB11H5Br 5) was prepared from Et3GeH and trityl CHB 11H5Br6-. Its X-ray crystal structure shows ion-like character very similar to its Si congener. The heavier element analogues, Et3E(CHB11H5Br6) (E = Sn, Pb), were prepared by chloride ion abstraction from Et3SnCl and Et3PbCl, respectively, using Et3Si(CHB 11H5Br6). Their crystal structures differ from those of the four-coordinate lighter elements by adopting five-coordinate trigonal-bipyramidal stereochemistries, reflecting the periodic table transition of these elements from semi-metals to metals. The carborane anions are weak, bridging, axial ligands connecting trigonal Et3E+ cation-like moieties in polymeric chain structures. When the less coordinating CHB11Cl11- anion is used, excess germane competes with the carborane anion for coordination to Ge and a salt of the new hydride-bridged cation [Et3Ge-H-GeEt3]+ can be isolated. It has a distinctive αGeHGe IR band at ca. 1740 cm-1 analogous to the 1875 cm-1 band of the [Et3Si-H-Si-Et 3]+ cation. Comparable chemistry is not observed for the Sn and Pb congeners. © 2010 American Chemical Society.