New strategy to mixed-group 6 metal carbonyl telluride complexes: Completion of the trigonal bipyramidal clusters [Te₂CrM ₂(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, la; 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 Te ₂M₂ 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, ¹²⁵Te 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, le), and the interesting transformations and structural features of the new complexes 1b-2c are systematically studied as well.