Cp2ZrCl2 – Et3Al Reagent System in the Homo-Coupling of Trimethylsilyl-Substituted Alkynes

The reaction of homo-coupling of alkynes using zirconocene reagents is an important basis for the efficient synthesis of polymer, oligomers and macrocycles. The most widely used reagents include Negishi reagent (“Cp2ZrBu2”), Takahashi reagent (“Cp2ZrEt2”), and Rosenthal reagent (Cp2Zr(py)TMSC≡CTMS). Despite detailed studies of the reaction of Et3Al with Cp2ZrCl2, the resulting zirconocene complexes could not be successfully used for intramolecular coupling of alkynes. We found that the reaction of trimethylsilyl-substituted alkynes with 0.5 equivalents of Cp2ZrCl2, 1 equivalents of Et3Al in toluene at room temperature for 18 hours gives, after hydrolysis/deuterolysis or iodination, functionalized products of the homocoupling of silyl-substituted alkynes in good yield. We assume that the reaction proceeds through the stage of intermediate formation of the metalcyclopentadiene, which can be of a ziconocene or organoaluminum nature. The detected reaction is of a general nature and allows the synthesis of previously difficult to obtain and practically important unsaturated bis-trialkylsilanes connected by a conjugated hydrocarbon spacer. The first positive results open the way for the synthesis of macrocyclic polyene compounds through the combination of diyne molecules.