Reactivity of permethylscandocene derivatives with acetylene. Structure of acetylenediylbis(permethylscandocene), (η^5-C_5Me_5)_2Sc-C≡C-Sc(η^5-C_5Me_5)_2
Excess acetylene reacts with Cp*_2Sc-R (Cp* = η-C5Me_5; R = H, alkyl, aryl, alkenyl, alkynyl, amide) below -78 °C to yield R-H and Cp*_2Sc-C≡CH; the latter then reacts with excess C_2H_2 to form polyacetylene. Cp*_2Sc-C≡CH cleanly decomposes to Cp*_2Sc-C≡C-ScCp*_2, most likely via u bond metathesis involving the Sc-acetylide and terminal C-H bonds for two molecules of Cp*_2Sc-C≡CH. The structure of this unusual acetylenediyl-bridged dimer has been determined by X-ray diffraction methods. It crystallizes with a half-molecule of toluene per scandium dimer in the tetragonal system, space group P42_1c (No. 114), with a = 15.057 (3) Å, c = 18.617 (6) Å, V = 4220.7 (18) Å^3, and z = 4
