“…[5,7,9 -11,33 -35] We have demonstrated that half-metallocene-diene fragments of group 5 metals are isoelectronic and isolobal to metallocene fragments of group 4 metals. [36 -40] Figure 2 shows some typical alkylidene complexes of group 4 metals [41,42] and group 5 metals [43,44] with isoelectronic fragments. This review briefly describes our studies on the synthesis and characterization of benzylidene complexes of tantalum and their stereochemistry of the benzylidene moiety, which was tunable and was highly depending on the kinds of ancillary ligands such 1,3-butadiene (1), [45,46] 2,3-dimethyl-1,3-butadiene (6), [47] o-xylylene (7), [46] 1,4-diaryl-1,4-diaza-1,3-butadiene (8), [48] and 1,4-diaryl-1-aza-1,3-butadiene (9).…”