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, Se-77 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 M-3 ring (M = Mo, 1; W, 4) or a heterometallic Cr2W ring that is further capped above and below by mu(3)-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. (c) 2005 Elsevier B.V. All rights reserved.