A series of group 6 transition metal half-sandwich complexes with 1,1-dichalcogenide ligands have been prepared by the reactions of Cp*MCl4 (Cp* = eta(5)-C5Me5; M = Mo, W) with the potassium salt of 2,2-dicyanoethylene-1,1-dithiolate, (KS)(2)C=C(CN)(2) (K-2-i-mnt), or the analogous seleno compound, (KSe)(2)C=C(CN)(2) (K-2-i-mns). The reaction of Cp*MCl4 with (KS)(2)C=C(CN)(2) in a 1:3 molar ratio in CH3CN gave rise to K[Cp*M{S2C=C(CN)(2)}(2)] (M = Mo, 1a, 74%; M = W, 2a, 46%). Under the same conditions, the reaction of Cp*MoCl4 with 3 equiv of (KSe)(2)C=C(CN)(2) afforded K[Cp*Mo{Se2C=C(CN)(2)}(2)] (3a) and K[Cp*Mo{Se2C=C(CN)(2)}{Se(Se-2)C=C(CN)(2)}] (4) in respective yields of 45% and 25%. Cation exchange reactions of 1a, 2a, and 3a with Et4NBr resulted in isolation of (Et4N)[Cp*Mo{S2C=C(CN)(2)}(2)] (1b), (Et4N)[Cp*W{S2C=C(CN)(2)}(2)] (2b), and (Et4N)[Cp*Mo{Se2C=C(CN)(2)}(2)] (3b), respectively. Complex 4 crystallized with one THF and one CH3CN molecule as a three-dimensional network structure. Inspection of the reaction of Cp*WCl4 with (KSe)(2)C=C(CN)(2) by ESI-MS revealed the existence of three species in CH3CN, [Cp*W{Se2C=C(CN)(2)}(2)](-), [Cp*W{Se2C=C(CN)(2)}{Se(Se-2)C=C(CN)(2)}](-), and [Cp*W{Se(Se-2)C=C(CN)(2)}(2)](-), of which [Cp*W{Se2C=C(CN)(2)}{Se(Se-2)C=C(CN)(2)}](-) (5) was isolated as the main product. Treatment of 2a with 1/4 equiv of S-8 in refluxing THF resulted in sulfur insertion and gave rise to K[Cp*W{S2C=C(CN)(2)}{S(S-2)C=C(CN)(2)}] (6), which crystallized with two THF molecules forming a three-dimensional network structure. 6 can also be prepared by refluxing 2a with 1/4 equiv of S-8 in THE 3a readily added one Se atom upon treatment with 1 mol of Se powder in THF to give 4 in high yield, while the treatment of 3a or 4 with 2 equiv of Na2Se in THF led to formation of a dinuclear complex [(Cp*Mo)(2)(mu-Se){mu-Se(Se-3)C=C(CN)(2)}] (7). The structure of 7 consists of two Cp*Mo units bridged by a Se2- and a [Se(Se-3)C=C(CN)(2)](2-) ligand in which the triselenido group is arranged in a nearly linear way (163degrees). The reaction of 2a with 2 equiv of CuBr in CH3CN yielded a trinuclear complex [CP*WCu2(mu-Br){mu(3)-S2C=C(CN)(2)}(2)] (8), which crystallized with one CH3CN and generated a one-dimensional chain polymer through bonding of Cu to the IN of the cyano groups.