Reversible pyranyl complex formation and the mechanism of rearrangement to (η5-6-oxocycloheptadienyl)Mn(CO)3 complexes in the reaction of β-cyclomanganated 1,5-diarylpenta-1,4-dien-3-ones and alkynes; the crystal structure of [2,4-diphenyl-6-(2-phenylethe

[1-Phenyl-2-[(E)-3-phenylprop-2-en-1-oyl-κO]ethenyl-κC1]tetracarbonylmanganese (1a) reacts with PhCCH in CCl4 at room temperature to form [2,4-diphenyl-6-(2-phenylethenyl)pyranyl-η5]tricarbonylmanganese (2a), whose X-ray crystal structure is reported to complement that of its isomer [6-oxo-2,4,7-triphenylcyclohepta-1,4-dienyl-1,2,3,4,5-η]tricarbonylmanganese (3a), previously obtained from the reaction under reflux; but for 1a and PhCCPh the pyranyl complex cannot be isolated before rearrangement to the 3a analogue occurs. More forcing reaction conditions for 1a with Me3SiCCH and for [1-(2-trifluoromethylphenyl)-2-[(E)-3-(2-trifluoromethylphenyl)prop-2-en-1-oyl-κO]ethenyl-κC1]tetracarbonylmanganese (1b) with Me3SiCCH and PhCCH give new analogues of 3a where previously only 2a analogues had been isolated.The reaction in CCl4 under reflux of PhCCH and the β-deuterio analogue of 1a, [1-phenyl-2-[(E)-3-phenylprop-2-en-1-oyl-3d-κO]ethenyl-κC1]tetracarbonylmanganese, gave deuteriated 3a with exo-D at the α-carbon, C7. This is inconsistent with the Mn-mediated Ph migration mechanism originally proposed to accommodate the endo position of Ph in 3a, and instead it implicates a cyclopropyl carbonyl-addition intermediate or a cyclopropyl acyl-substitution transition state in the key rearrangement step for 2a → 3a.

[1-Phenyl-2-[(E)-3-phenylprop-2-en-1-oyl-3d-κO]ethenyl-κC1]tetracarbonylmanganese reacts with phenylacetylene to form the endo-7-Ph isomer of [6-oxo-2,4,7-triphenyl-7d-cyclohepta-1,4-dienyl-1,2,3,4,5-η]tricarbonylmanganese, implicating a cyclopropyl carbonyl-addition intermediate or a cyclopropyl acyl-substitution transition state in the key rearrangement step from the initially formed pyranyl complex. Also reported are some new (oxocycloheptadienyl)Mn(CO)3 and (pyranyl)Mn(CO)3 complexes from other alkynes and cyclomanganated dienones.Figure optionsDownload as PowerPoint slide