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]

Abstract

The mononuclear metal-alkylidyne compounds [M(C–CBu^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(CCBu^t), (CF₃CO)₂O, and L₂. The species (1a), (1c), and (1d) have been used as precursors for the synthesis of the compounds [M(C–CCBu^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–CCBu^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^tC₂CM(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–CCBu^t)(CO)₆(η-C₅H₅)₃], complex (2d) with the dimolybdenum reagent gives the µ-alkyne trimetal compound [Mo₂{µ-Bu^tC₂CW(CO)₂[HB(pz)₃]}(CO)₄(η-C₅H₅)₂]. The n.m.r. data for the new compounds are reported and discussed.