A hydridotantalum(V)-carborane analogue of Schwartz's reagent: synthesis and reactivity

Abstract

The dichlorotantalum metallacarborane CpCl 2Ta(Et 2C 2B 4H 4) ( 1) on treatment with LiAlH 4 in THF gave a hydridotantalum dimer [CpTa(H)(Et 2C 2B 4H 4)] 2( μ-Cl) 2 ( 2), which was found to undergo alkyne insertion with p-tolyl acetylene to generate exclusively trans-CpCl( p-MeC 6H 4-CHCH)Ta(Et 2C 2B 4H 4) ( 3); the reaction of the latter complex with anhydrous HCl afforded p-tolylstyrene and 1. In contrast, reaction of 2 with diphenyl acetylene or methyl phenyl acetylene gave hydridotantalum–alkyne complexes, which are apparently the first examples of alkyne π-coordination to a formal d 0 metal. Treatment of 2 with styrene produced the alkyl–tantalum species CpTaCl(CH 2CH 2Ph)(Et 2C 2B 4H 4) ( 5), but no reactivity was observed between 2 and the sterically hindered olefins cis-stilbene, trans-stilbene, and cyclohexene. Addition of anhydrous HCl to 5 generates 1 and styrene via an apparent β-elimination mechanism.