Heavier carbon subchalcogenides C3E2 (E = S, Se) can bind to transition metals through either a C═C or a C═E double bond. These two binding modes on a reactive tungsten (PMe3)4WCl2 site have been explored by density functional theory methods (M06-L/DZP+Lanl2DZ). The important step controlling the reaction direction is the initial binding of the C3E2 ligand. Of particular significance is the M═C═C═C═E fragment resulting from the C═E coordination mode. This fragment can bind to additional C3E2 molecules or bridge to other metals. Ultimately C3E2 serves as a source of C3 units for building C3n carbon sp-hybridized allotropes.