Silylidyne, HSi≡MoH3 and HSi≡WH3, and Silyl Metal Hydride, SiH3—CrH, Products in Silane Reactions

Laser-ablated group 6 metal atoms react with silane to form inserted SiH 3-MH hydride intermediates, which are identified from M-H and Si-H stretching modes. Following two successive alpha-H-transfers, the HSiMH 3 (M = Mo, W) silylidyne molecules are produced. These silicon-metal triple-bonded species are identified as major products from the strong M-H stretching modes through deuterium substitution and comparison with frequencies and intensities from density functional calculations and from the analogous methylidynes. The silylidynes have calculated C 3 v structures and longer Si-H bonds than silane, but the C 3 v methylidyne analogues have shorter C-H bonds than methane. The SiMo and SiW bonds are polarized differently and have slightly lower effective bond orders than their carbon analogues. In addition, calculations for the group 6 silylidene molecules reveal C s structures with no evidence of agostic distortion, in contrast to the corresponding methylidene molecules.