The reaction of the lithium dithioacetate derivative [Li(bdmpzdta)(THF)] [bdmpzdta = bis(3,5-dimethylpyrazol-1-yl)dithioacetate] with 1 equiv. of C3H5MgCl proceeds in high yield to give the first alkaline-earth-metal complex bearing an asymmetrical gem-dithiolato moiety, namely, [Mg(κ3-NNS-μ-S-bppbte)]3 (1) [bppbte = 1,1-bis(3,5-dimethyl-1H-pyrazol-1-yl)pent-4-ene-2,2-bis(thiolate)]. This is achieved through an unprecedented insertion reaction of the allyl group into the C=S bond. In contrast, the reaction with the Grignard reagents MeMgCl or EtMgCl leads to the formation of the six-coordinate sandwich species [Mg(κ3-bdmpzdta)2] (2), as a result of a rapid ligand redistribution. The molecular structures of 1 and 2 in the solid state have been unambiguously established by single-crystal X-ray diffraction studies, which reveal a trinuclear entity with a twisted six-membered core for 1, in which all magnesium centers are arranged in a distorted trigonal bipyramidal geometry, whereas in 2 the magnesium center has an octahedral coordination environment with two heteroscorpionato ligands, which bind in a κ3-NNS fashion with a relative trans disposition.