Selenium-capped trimolybdenum and tritungsten carbonyl clusters [Se2M3(CO)10]2− (M = Mo, W)

A facile synthesis of the novel selenium-capped trimolybdenum and tritungsten ring carbonyl clusters [Se2M3(CO)10]2− (M = Mo, 1; W, 4) have been achieved. The selenium-capped trimolybdenum cluster compound [Et4N]2[Se2Mo3(CO)10] ([Et4N]2[1]) can be obtained from the reaction of the trichromium cluster compound [Et4N]2[Se2Cr3(CO)10] with 4 equiv. of Mo(CO)6 in refluxing acetone. On the other hand, when [Et4N]2[Se2Cr3(CO)10] reacted with 4 equiv. of W(CO)6 in refluxing acetone, the planar cluster compound [Et4N]2[Se2W4(CO)18] ([Et4N]2[3]) was isolated, which could further transform to the tritungsten cluster compound [Et4N]2[Se2W3(CO)10] ([Et4N]2[4]) in good yield. Alternatively, clusters 1 and 4 could be formed from the reactions of the monosubstituted products [Et4N]2[Se2Cr2M(CO)10] (M = Mo; W, [Et4N]2[2]) with 3 equiv. of M(CO)6 in acetone, respectively. Complexes 1–4 are fully characterized by IR, 77Se NMR spectroscopy, and single-crystal X-ray analysis. Clusters 1, 2, and 4 are isostructural and each display a trigonal bipyramidal structure with a homometallic M3 ring (M = Mo, 1; W, 4) or a heterometallic Cr2W ring that is further capped above and below by μ3-Se atoms. Further, the intermediate planar complex 3 exhibits a Se2W2 square with each Se atom externally coordinated to one W(CO)5 group. This paper describes a systematic route to a series of selenium-capped trimetallic carbonyl clusters and the formation and the structural features of the resultant clusters are discussed.