Summary: 270 J. Am. Chem. SOC.1986, 108, 270-284
A Theoretical Survey of Unsaturated or Multiply Bonded and
Divalent Silicon Compounds. Comparison with Carbon
Brian T. Luke,laJohn A. Pople,'"Mary-Beth Krogh-Jespersen,'bYitzhak Apeloig,"
Miriam Karni,lCJayaraman Chandrasekhar,ldand Paul von Ragu6 Schleyer*Id
Contributionfrom the Department of Chemistry, Carnegie-Mellon University, Pittsburgh,
Pennsylvania 15213, Department of Chemistry, Pace University, New York, New York 10038,
Department of Chemistry, Technion-Israel Institute of Technology, 32000 Haifa, Israel, and
Institut fur Organische Chemie der Friedrich-Alexander- Universitat Erlangen-Nurnberg.
0-8520 Erlangen, Federal Republic of Germany. Received July 5, 1984
Abstract: Multiply bonded Si molecules, H2SiX (X = Be, BH, CH2,SiH2,NH, 0),HSiY (Y = B, CH, SiH, N), and SiZ
(Z = 0,02),along with their carbon analogues, have been investigatedby ab initio methods. All structural parameters were
optimized by use of the 3-21G basis set and the higher 3-21G(*)basis set for silicon. In addition, the isomeric substituted
silyleneswhich result from 1,2-hydrogenshifts were also considered. In many cases, the substituted silylenestructures were
energetically favored. The effect of all first-rowsubstituentson the singlet-triplet energy separationof divalent silicon molecules
was assessed and compared with the corresponding carbenes.
Though many molecules involving silicon singly bonded to first-
and second-row elements are known,2 multiply bonded silicon
analogues of carbon compounds, until recently, were experi-