Formation of (Alkenylphosphonio)phenylruthenium Complexes from Diphenylacetylene and a [CpRu(dppm)] Cation: Experimental Evidence for the Equilibrium between η¹-Disubstituted Vinylidene and η²-Internal Alkyne

Abstract

The reaction of diphenylacetylene at a cationic ruthenium complex with a dppm (Ph2PCH2PPh2) ligand, [CpRu(dppm)]+, has been studied to reveal essentially for the first time the existence of an equilibrium between an η2-internal alkyne and η1-disubstituted vinylidene at a transition metal center. The reaction mixture at 70 °C for 69 h unexpectedly afforded a coupling product of diphenylacetylene and the dppm ligand, an (alkenylphosphonio)phenyl complex [CpRu{Ph2PCH2P(C6H4)Ph(η2-C(Ph)CHPh)}]+ with the extremely rare coordination mode of κ1 P,η1 C,η2 C,C′. The (alkenylphosphonio)phenyl complex further undergoes inversion of the coordination face of the alkene moiety at p-xylene reflux temperature. Both isomers of (alkenylphosphonio)phenyl complexes as well as the intermediary η2-internal alkyne and η1-disubstituted vinylidene complexes were fully characterized spectroscopically and crystallographically. By considering the structure of the (alkenylphosphonio)phenyl complexes obtained, the coupling reaction has been proposed to involve the attack of a phosphorus atom on the coordinated diphenylacetylene, which is in equilibrium with an η1-diphenylvinylidene ligand, and the C–H bond activation of a phenyl group on the cationic phosphorus atom leading to the products. Theoretical calculations support the proposed mechanism.

DFT Study of Internal Alkyne-to-Disubstituted Vinylidene Isomerization in [CpRu(PhC≡CAr)(dppe)]+

“…The product ratios of the reaction suggest that the migration reaction is electrophilic. Therefore, in our previous papers, we suggested that the alkyne/vinilydene rearrangement was more likely to occur via electrophilic reaction from the results of migratory aptitude . However, the reaction mechanism that the migrating groups move as a nucleophilic reagent is elucidated by the minute NBO analysis in the present study.…”

“…The conversion reaction from internal alkynes to vinylidenes is an unusual process, and it has been reported only for heteroatom-substituted alkynes such as trimethylsilyl alkynes . Recently, the migration of acyl and hydrocarbyl substituents in internal alkynes has been reported by three groups independently. − Shaw and co-workers described that internal alkynones can participate in such interconversion to give disubstituted vinylidene complexes [CpRu{CCR 1 (COR 2 )}(PPh 3 ) 2 ] + . According to the reports by us, aryl- or alkyl-disubstituted vinylidene compounds have been obtained by the reaction of [CpRu(dppe)] + and [CpFe(dppe)] + with PhCCC 6 H 4 R- p (R = OMe, Me, H, Cl, and CO 2 Et), revealing the migratory activity of the substituents.…”

Reactivity of a Cationic (C5Me5)IrIII-Cyclometalated Phosphine Complex with Alkynes

“…In addition, vinylidene units derived from silyl-, stannyl-, and other heteroatom-substituted alkynes have been recognized as well . However, the analogous redistribution of internal alkynes is a less common, albeit interesting reaction, which has flourished only in the last few years following its discovery by the Ishii group in 2008. − With reference first to the reaction system based on the internal alkyne PhCCMe, the nature of the allylic functionality of complex 9 + (Scheme ), in which the Ph and Me substituents are bound to different carbon atoms, rules out the vinylidene path and hints at the insertion route, as depicted in Scheme . The C–C bond formation step implicates in a regioselective manner the less hindered alkyne carbon atom, forming the undetected alkenyl intermediate C- Ph,Me + .…”

Migration of Condensed Aromatic Hydrocarbons During Alkyne‐Vinylidene Rearrangements

“…The half‐sandwich complexes [MCl(dppe)Cp] (dppe=1,2‐bis(diphenylphosphino)ethane, Cp = η 5 ‐C 5 H 5 , M = Ru, 1 a ; Fe, 1 b ) were chosen as metal frameworks from which to explore rearrangement reactions of 1,2‐disubstituted acetylenes. This particular combination of (di)phosphine and η 5 ‐motif avoids the complications of side‐reactions, which are known to occur for η 5 ‐indenyl [21] and dppm [22] auxiliary ligands. From 1 a and 1 b , generation of the reactive 16‐valence electron (VE) coordinatively unsaturated {M(dppe)Cp} + species is achieved by halide abstraction with sodium salts of weakly coordinating tetraarylborates Na[BAr F 4 ] ([BAr F 4 ] − =[B(3,5‐(CF 3 ) 2 ‐C 6 H 3 ) 4 ] − ) or Na[BAr Cl 4 ] ([BAr Cl 4 ] − =[B(3,5‐Cl 2 ‐C 6 H 3 ) 4 ] − in non‐coordinating solvents, such as toluene or 1,2‐dichloroethane [23] .…”