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, R3Si(CHB11X11), has been extended to the heavier group 14 elements. Et3Ge(CHB11H5Br5) was prepared from Et3GeH and trityl CHB11H5Br6-. 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(CHB11H5Br6). 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 nu GeHGe 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.