The first examples of a new class of main-group metallacycles, 4,5-didehydro-2-thiastibolanes, have been synthesized. These compounds were prepared via transmetalation from zirconocene metallacycles. The X-ray crystal structures of the 1-chloro-4,5-dimethyl-4,5-didehydro-2-thiastibolane (4a) and the 1-bromo-4,5-diphenyl-4,5-didehydro2-thiastibolane (5b) are reported.