New strategy to mixed-group 6 metal carbonyl telluride complexes:: Completion of the trigonal bipyramidal clusters [Te2(CrM2(CO)10]2- (M = Cr, Mo, W)

The new series of tellurium-containing trigonal bipyramidal clusters [Te2CrM2(CO)(10)](2-) (M = Cr, 2a; Mo, 2b; W, 2c) has been synthesized from the ring closure reactions of the ring complexes [Te2Cr2M2(CO)(18)](2-) (M = Cr, 1a; Mo, 1b; W, 1c) in refluxing acetone solutions. The mixed-metal ring complexes [Te2Cr2M2(CO)(18)](2-) (M = Mo, 1b; M = W, 1c) can be obtained readily from the metal expansion reactions of the dichromium complex [Te{Cr(CO)(5)}(2)](2-) with M(CO)(6) (M = Mo, W) in MeCN. The ring complexes [Te2Cr2M2(CO)(18)](2-) (M = Mo, 1b; W, 1c) each display a Te2M2 ring with each Te atom externally coordinated with one Cr(CO)5 group, while the new group 6-containing trigonal bipyramidal clusters [Te2CrM2(CO)(10)](2-) (M = Cr, 2a; Mo, 2b; W, 2c) each consist of a CrM2 trigonal plane capped above and below by two tellurides. Complexes 1b-2c are fully characterized by IR, Te-125 NMR spectroscopy, and single-crystal X-ray analysis. This paper describes a new methodology to the highly strained group 6 metal clusters [Te2CrM2(CO)(10)](2-) (M = Cr, 2a; Mo, 2b; W, 2c) from the ring closure reactions of their corresponding ring complexes [Te2Cr2M2(CO)(18)](2-) (M = Cr, 1a; Mo, 1b; W, 1c), and the interesting transformations and structural features of the new complexes 1b-2c are systematically studied as well.