Ruthenium Vinylidene Complexes Generated by Selective 1,2-Migration of P- and S-Substituents: Synthesis, Structures, and Dichromism Arising from an Intramolecular CH···O Hydrogen Bond

Abstract

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{CC(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 EO 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.

Retro-Vinylidene Rearrangements of P- and S-Substituted Ruthenium Vinylidene Complexes

“…When a reaction of complex 1aa-13 C α or 1ca-13 C α with PPh 3 was performed, alkyne A was obtained with exclusive selectivity, indicating that the P-substituent served as a migration group with >99% selectivity (entries 1 and 2). Thus, combined with our previous reports on the vinylidene rearrangements, 12 it is revealed that both forward and backward alkyne/vinylidene isomerizations are mediated by the selective migration of the P-substituents.…”

“…In our preceding study, it was confirmed that the vinylidene rearrangements of S-substituted alkynes at 70 °C proceed via the exclusive 1,2-migration of the heteroatom group. 12 Thus, it seems that the present less selective migration in the case of the SPh-substituted complex is somewhat contradictory.…”

“…Following our previously reported procedures, 12 . With these complexes in hand, we at first examined a reaction of complex 1aa [E = PO(OMe) 2 , R = Ph] with PPh 3 , the latter of which serves as a trapping agent for the unsaturated ruthenium complex generated by retro-vinylidene rearrangement (Table 1).…”

“…When a reaction of complex 1aa coordinated by dppe was carried out in toluene at 70 °C, at which the corresponding alkyne-to-vinylidene transformation smoothly proceeds, 12 only 6% of [Ru(PPh 3 )(dppe)Cp]BAr F 4 (2) was obtained. However, a reaction at 100 °C for 2 h provided complex 2 and the alkyne [PhC�CPO(OMe) 2 ] in 54 and 47% yields, respectively (entry 1).…”

“…In this context, even unactivated internal alkynes with alkyl or aryl substituents have been demonstrated to participate in vinylidene rearrangements by us and other researchers, and these findings led to the development of novel catalytic alkyne transformations . More recently, we have reported that vinylidene rearrangements of various P- and S-substituted internal alkynes were also feasible by using cationic metal complexes like Ru­(dppe)­Cp + [Cp = cyclopentadienyl, dppe = 1,2-bis­(diphenylphosphino)­ethane] and Mo­(dppe)­(η 7 -C 7 H 7 ) + . , As a result, the vinylidene rearrangement of alkynes is now recognized to have considerable tolerance and generality with respect to the alkyne substrate.…”