Dedicated to Professor R. R. Schrock for his distinguished and continuous contributions to inorganic and organometallic chemistry.Abstract: This brief review discloses our studies on half-metallocene benzylidene complexes of tantalum bearing 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, oxylylene, 1,4-diaryl-1,4-diaza-1,3-butadiene, or 1-aryl-4-phenyl-1-aza-1,3-butadiene as an auxiliary ligand. These auxiliary ligands can control the stereochemistry of the benzylidene moiety and induce intriguing reactivity. Furthermore, the butadiene and o-xylylene complexes catalyze ring opening metathesis polymerization of norbornene to respectively give polymers with cisand trans-C ¼ C bonds. Such selectivity can be attributed to control of the stereochemistry of the propagating alkylidene chain end by the auxiliary ligand: the butadiene complex favors the anti-rotamer while the o-xylylene complex favors the syn-one.