Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 92. Synthesis of alkynylmethylidyne-molybdenum and -tungsten complexes and their reactions with [Co₂(CO)₈] and [Mo₂(CO)₆(η-C₅H₅)₂]

The mononuclear metal-alkylidyne compounds [M(≡C-C≡Bu^t)(O₂CCF₃)(CO) ₂L₂][L₂ = tmen (N,N,N′,N′-tetramethylethylenediamine), M = Mo (1a) or W (1b); L₂ = bipy (2,2′-bipyridine), M = Mo (1c); L₂ = 2 × py (py = pyridine), M = W (1d)] have been prepared by treating the complexes [M(CO)₆] in thf (tetrahydrofuran) successively with Li(C≡CBu^t), (CF₃CO)₂O, and L₂. The species (1a), (1c), and (1d) have been used as precursors for the synthesis of the compounds [M(≡C-C≡CBu^t)(CO)₂L] {L = η-C₅H₅, M = Mo (2a) or W (2b); L = HB(pz)₃ [hydrotris(pyrazol-1-yl) borate], M = Mo (2c) or W (2d); L = HB(dmpz)₃ [tris(3,5-dimethylpyrazol-1-yl)hydroborate], M = MO (2e). Treatment of the complexes (2a) and (2b), respectively, with [Co₂(CO)₈] in light petroleum gives the trimetallatetrahedrane clusters [MCo₂(μ₃-C-C≡CBu^t)(CO) ₈(η-C₅H₅)] (M = Mo or W) in quantitative yield. In contrast, (2d) and (2e) with [Co₂(CO)₈] afford, respectively, the μ-alkyne trimetal compounds [Co₂{μ-Bu^tC₂C≡M(CO) ₂L}(CO)₆][M = W, L = HB(pz)₃; M = Mo, L = HB(dmpz)₃]. Similarly, whereas (2b) reacts with [Mo₂(CO)₆(η-C₅H₅)₂] to yield a trimetallatetrahedrane cluster [Mo₂W(μ₃-C-C≡CBu^t)(CO) ₆(η-C₅H₅)₃], complex (2d) with the dimolybdenum reagent gives the μ-alkyne trimetal compound [Mo₂{μ-Bu^tC₂C≡W(CO) ₂[HB(pz)₃]}(CO)₄(η-C₅H ₅)₂]. The n.m.r. data for the new compounds are reported and discussed.