The reactivity of the gallium(I) compound NacNacGa (4) to a variety of unsaturated compounds has been studied. Whereas 4 proved surprisingly unreactive toward olefins, ketones, guanidines, and thioureas, it reacts with isocyanates and carbodiimides to furnish the products of coupling of two heterocumulenes. With isothiocyanate, the C=S cleavage occurs, leading to the dimer (NacNacGa)(2)(mu-S)(mu-CNPh) and the cyclization product NacNacGa(S2C=NPh). These compounds were characterized by multinuclear NMR spectroscopy and X-ray crystal structure analyses. Oxidative addition of S=PPh3 occurs at elevated temperatures and results in the known dimer [NacNacGa(mu-S)](2).