Synthesis and Reactions of Group 6 Metal Half-Sandwich Complexes of 2,2-Dicyanoethylene-1,1-dichalcogenolates [(Cp*)M{E₂CC(CN)₂}₂]^- (M = Mo, W; E = S, Se)

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* = η5-C5Me5; M = Mo, W) with the potassium salt of 2,2-dicyanoethylene-1,1-dithiolate, (KS)2CC(CN)2 (K2-i-mnt), or the analogous seleno compound, (KSe)2CC(CN)2 (K2-i-mns). The reaction of Cp*MCl4 with (KS)2C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)2CC(CN)2 afforded K[Cp*Mo{Se2CC(CN)2}2] (3a) and K[Cp*Mo{Se2CC(CN)2}{Se(Se2)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)2C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(Se2)CC(CN)2}]-, and [Cp*W{Se(Se2)CC(CN)2}2]-, of which [Cp*W{Se2CC(CN)2}{Se(Se2)CC(CN)2}]- (5) was isolated as the main product. Treatment of 2a with 1/4 equiv of S8 in refluxing THF resulted in sulfur insertion and gave rise to K[Cp*W{S2CC(CN)2}{S(S2)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 S8 in THF. 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(μ-Se){μ-Se(Se3)CC(CN)2}] (7). The structure of 7 consists of two Cp*Mo units bridged by a Se2- and a [Se(Se3)CC(CN)2]2- ligand in which the triselenido group is arranged in a nearly linear way (163°). The reaction of 2a with 2 equiv of CuBr in CH3CN yielded a trinuclear complex [Cp*WCu2(μ-Br){μ3-S2CC(CN)2}2] (8), which crystallized with one CH3CN and generated a one-dimensional chain polymer through bonding of Cu to the N of the cyano groups.