Investigation of the vinylidene rearrangement of phosphorus-and sulfur-substituted internal alkynes at a ruthenium center unveiled selective 1,2-migration of P-and S-substituents and unexpected dichromatic behaviors of a part of the resulting vinylidene complexes. Reactions of [CpRu(dppe)Cl] and R 1 C CR 2 , where R 1 = alkyl, Ar and R 2 = P(O)(OR) 2 , P(O)R 2 , SR, SO 2 R, in the presence of NaBAr F 4 afforded the corresponding vinylidene complexes [CpRu{CC(R 1 )(R 2 )}(dppe)][BAr F 4 ], which were fully characterized by NMR and elemental analysis and, in some cases, X-ray diffraction analysis. 13 C-labeling experiments disclosed selective migration of the P-and Ssubstituents. To our surprise, some of the products displayed dichromatic characters: although solutions of all the vinylidene products are yellow, several products were obtained as yellow and red crystals, others as red-purple crystals, and the rest as yellow crystals. UV−vis absorption spectra for the complexes displaying a dichromatic nature were recorded both in solution and in the solid state. X-ray diffraction analysis revealed that an intramolecular CH•••O hydrogen bond between one of the methylene CH bonds in the dppe ligand and the EO group (E = P, S) is present in the red and the red-purple crystals, which affects the conformation of the vinylidene ligand. In contrast, such hydrogen bonds were not observed in the yellow crystals. Time-dependent density functional theory (TD-DFT) analysis based on the crystal structures revealed that the structural changes of the vinylidene ligand upon the hydrogen bonding account for the dichromism.
Vinylidene rearrangement of internal acylalkynes and sulfonylalkynes at a d6 molybdenum center is presented. Treatment of [(η7-C7H7)MoBr(dppe)] with various acylalkynes R–CC–COR′ in the presence of NaBArF 4 afforded the corresponding vinylidene complexes [(η7-C7H7)Mo[CCR(COR′)](dppe)][BArF 4], which exist as mixtures of two rotamers, with respect to the MoCα bond at room temperature, as evidenced by NMR studies. This provides the first example of vinylidene rearrangement of internal alkynes at a Mo center. X-ray diffraction studies revealed that the vinylidene ligand :CCR(COR′) coordinates almost perpendicularly toward the C7H7 plane. A 13C-labeling experiment unveiled selective migration of the acyl group, which is in agreement with a nucleophilic 1,2-migration mechanism. When sulfonylakynes R–CC–SO2R′ were used as substrates, three types of productsη2-alkyne, vinylidene, and unexpected η2-phosphonioalkyne complexeshave been isolated, depending on the R group. The η2-phosphonioalkyne complex is considered to be generated through nucleophilic substitution of the sulfonyl group by a phosphine.
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