Effect of Different Bases and Phosphorus Ylide on the Selective Deprotonation of Phosphorus Ylide Adduct Cp*TaCl₄(CH₂PPh₃)

Abstract

The effect of different bases and phosphorus ylide on the selective deprotonation of phosphorus ylide adduct Cp*TaCl4(CH2PPh3) (4) was studied. The acidity of the methylene hydrogen atoms in ylide adduct complex 4, [Cp*TaCl4(CH2PPh3)], is weaker than those in the derivative complex [CpTaCl4(CH2PPh3)]. Under the same conditions complex 4 cannot transylidate. With the strong, but weakly coordinating base bis(trimethylsilyl)amide a double deprotonation of two methyl groups on the pentamethylcyclopentadienyl ring occurs, and the novel ylide adduct complex 6, with an η3-ally-η4-butadiene ligand, is obtained. Only when elimination of three chloride ligands is compensated by at least three coordinating ylide molecules can the strong base bis(trimethylsilyl)amide selectively deprotonate in a Ta−CH position, affording the expected carbyne complex 5.