A HYDRIDOTANTALUM(V)-CARBORANE ANALOG OF SCHWARTZ REAGENT - SYNTHESISAND REACTIVITY

The dichlorotantalum metallacarborane CpCl2Ta(Et2C2B4H4) (1) on treatm ent with LiAlH4 in THF gave a hydridotantalum dimer [CpTa(H)(Et2C2B4H4 )](2)(mu-Cl)(2) (2), which was found to undergo alkyne insertion with p-tolyl acetylene to generate exclusively trans-CpCl(p-MeC6H4-CH=CH)Ta (Et2C2B4H4) (3); the reaction of the latter complex with anhydrous HCl afforded p-tolylstyrene and 1. In contrast, reaction of 2 with diphen yl acetylene or methyl phenyl acetylene gave hydridotantalum-alkyne co mplexes, which are apparently the first examples of alkyne pi-coordina tion to a formal d(0) metal. Treatment of 2 with styrene produced the alkyl-tantalum species CpTaCl(CH2CH2Ph)(Et2C2B4H4) (5), but no reactiv ity was observed between 2 and the sterically hindered olefins cis-sti lbene, trans-stilbene, and cyclohexene. Addition of anhydrous HCl to 5 generates 1 and styrene via an apparent beta-elimination mechanism. ( C) 1998 Elsevier Science S.A.