Stable triply bonding silyl cation prepared A long-sought new form of silicon bearing three bonds rather than the usual two, four, or five has been characterized by a Northwestern University research group. Chemistry professor Joseph B. Lambert says that discovery of triply bonding silicon offers some new synthesis routes for chemists. The new material also is being considered as a possible catalyst for certain types of silicones. The silicon is contained in the crystal structure of a stable silyl cation, triethylsilylium, in the form of its tetrakis(pentafluorophenyDborate salt. The work was carried out by Lambert, along with postdoctoral researcher Shizhong Zhang and crystallographers Charlotte L. Stern of Northwestern and John C. Huffman of Indiana University, and is described in last week's Science [260, 1917 (1993)1. Silicon is carbon's close kin in the periodic table and displays many of the same characteristics. In the synthesis of some of the new organosilicon compounds, one of the more sought after species of silicon has been tricoordinate silicon, R3Si+, which is analogous to carbocarions, R3C+. This search has been in progress for about 50 years, Lambert notes. His work during the past 10 years has included three important discoveries that led to tricoordinate silicon. First was the realization that, in generating tricoordinate silicon, it is necessary to remove a "fourth" group from a silicon atom, and the best such candidate is hydrogen. Hydrogen readily moves from silicon to carbon because the C-H bond is stronger. The second discovery was finding an appropriate solvent for the chemistry. The silicon cation would be destroyed immediately if the solvent reacts with it. The best solvents turned out to be aromatics, particularly toluene. The third step was selecting the anion species. This was particularly difficult. Anions that are compatible with carbocations react with silicon cations, and the silicon returns to the tetracoordination form as the positive and negative charges cancel each other. The anion finally chosen was (C6FS)4B~, which is stable in toluene and does not react with silicon cations. The compound the team eventually
Three components essential +3 to generate Si in stable form
Solvent (toluene)
Silyl cation
Borate anion
Note: £rtvn = fluorine; blue = hydrogen; yellow = silicon; orange = boron; black = carbon.
synthesized was (C2Hs)3Si+(C6Fs)4B~, which it crystallized from mixtures of hexane and toluene. The research team examined the crystals by x-ray diffraction. The silicon cation is not planar because of the influence of the toluene solvent. The team is now carrying out experiments similar to those with silicon, but with germanium and tin in its place. Both elements are in the same periodic family as silicon and carbon.
Moreover, Lambert says he has already found that silicon cations can catalyze formation of silicones that are commercially important. However, comments a spokesman for Dow Corning Corp., exact uses for the silicon cations are still speculative. Patent protection has been obtained for the discoveries. The work was supported by the National Science Foundation, with additional funding by Dow Corning. Joseph Haggin
Space station barely survives House vote Big science found itself under the gun last week in Congress. In a dramatic vote on June 23, the House of Representatives barely rejected a move to kill the proposed U.S. space station Freedom. By a vote of 216 to 215, House members turned down an amendment offered by Rep. Tim Roemer (D.-Ind.) to the bill authorizing the National Aeronautics & Space Administration's budget for fiscal 1994. The next day, the House approved at press time, 280 to 150, a motion by Rep. Jim Slattery (D.-Kan.) to kill the Superconducting Super Collider (SSC), presented as an amendment to the bill authorizing the Department of Energy's fiscal 1994 budget. The House also denied SSC funding last year, by a smaller margin, 232 to 181. However, the Senate and then a House-Senate conference committee restored SSC funding last year (C&EN, Aug. 10, 1992, page 3).
House members' votes broadly cut across party lines, with supporters' concern for scientific progress, world technological leadership, and jobs pitted against opponents' concern for cutting the federal budget and for giving greater priority to other U.S. needs. The Clinton Administration strongly supports both the space station and the SSC—legacies of the Reagan Administration—and actively lobbied for them. However, about 60% of the Democrats voted against the space station, r e jecting it 153 to 104. Two thirds of the Republicans favored the space station, 112 supporting it and 61 opposing. The vote on the space station followed hours of impassioned debate. Opponents called it "pork in space," a "bigticket scientific boondoggle" that returns little on a massive investment, "waste in space," "technologically indefensible and fiscally unjustifiable," and "a flying turkey." Proponents noted that the space JUNE 28, 1993 C&EN
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