Journal
ORGANOMETALLICS
Volume 38, Issue 7, Pages 1627-1639Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.organomet.9b00068
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Funding
- Fonds der Chemischen Industrie (FCI)
- Deutsche Forschungsgemeinschaft (DFG) [TA 189/12-1]
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The molybdenum and tungsten 2,4,6-trimethylbenzylidynes [MesC M{OC(CF3)(2)Ph}(3)] (12a, M = Mo; 12b, M = W) were prepared and structurally characterized as related complexes to already known [MesC M{OC(CF3)(2)Me}(3)] (MoF6, M = Mo; WF6, M = W). While treatment of 12a with 3-hexyne yielded the propylidyne complex [EtC Mo{OC(CF3)(2)Ph}(3)] (13), the tungsten congener 12b formed isolable metallacyclobutadiene (MCBD) species 14-16 by reaction with 3-hexyne, 1-phenyl-1-propyne, and 2,4-hexadiyne, which can be correlated with the higher electrophilicity of the tungsten complex. Furthermore, the labile MCBD [(C3Et3 )Mo{OC(CF3)(2)Me}(3)] (17) was isolated at low temperature from the reaction of the highly active MoF6 catalyst with 3-hexyne and could be characterized by X-ray diffraction analysis. At room temperature, the same reaction afforded [EtC Mo{OC(CF3)(2)Me}(3)] (18), and the equilibrium reaction with 3-hexyne to form 17 was additionally studied by variable temperature NMR spectroscopy, which allowed determining Delta H degrees and Delta S degrees for the formation of MCBD 17. The experimental thermodynamic data were used to set the benchmark for DFT calculations. Moreover, the deprotiometallacyclobutadiene complex (DPMCBD) [C-3(Mes)(Ph)}Mo{OC(CF3)(3)}(2)] (19), prepared from [MesC Mo{OC(CF3)(3)}(3)] (MoF9) and phenylacetylene, was isolated and structurally characterized as a decomposition product of terminal alkyne metathesis and employed in the polymerization of phenylacetylenes.
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