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

Abstract The dichlorotantalum metallacarborane CpCl 2 Ta(Et 2 C 2 B 4 H 4 ) ( 1 ) on treatment with LiAlH 4 in THF gave a hydridotantalum dimer [CpTa(H)(Et 2 C 2 B 4 H 4 )] 2 ( μ -Cl) 2 ( 2 ), which was found to undergo alkyne insertion with p -tolyl acetylene to generate exclusively trans -CpCl( p -MeC 6 H 4 -CHCH)Ta(Et 2 C 2 B 4 H 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 2 CH 2 Ph)(Et 2 C 2 B 4 H 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.