The terminal (diphenylalkenyl)alkylidene complexes (C5Me4R)Ta(CHCHCPh2)X2 (R=Me, Et; X=Cl, Br) are formed in moderate yields from the ring-opening reaction of 3,3-diphenylcyclopropene with the organoditantalum(III) halides (η-C5Me4R)2Ta2(μ-X)4. Potassium amalgam reduction of these alkenylalkylidene complexes afforded the alkylidene-tethered tantallanorbornadienes (C5Me4R)Ta[CHCHCPh(σ2-C6H5)], which possess a bent, boat conformation σ2-arene ligand with a fold angle of 19.24(46)° (R=Me) in the solid state. 13C and 1H NMR spectroscopies are consistent with a rapid flip-flop motion that averages the resonances of the σ2-phenyl group to fewer resonances than expected from the solid-state structure.
