Skeletal Rearrangement during Rhodium-Promoted Ring Opening of 1,2-Diphenyl-3-vinyl-1-cyclopropene. Preparation and Characterization of 1,2- and 2,3-Diphenyl-3,4-pentadienediyl Rhodium Complexes and Their Ring Closure to a 1,2-Diphenylcyclopentadienyl Complex

Abstract

Under conditions of kinetic control, 1,2-diphenyl-3-vinyl-1-cyclopropene undergoes ring opening with the [Rh(Cl)(PMe3)2] fragment to give two isomeric η3:η1-1,3-pentadienediyl compounds: the expected 1,2-diphenyl isomer, and the 2,3-diphenyl isomer resulting from an apparent skeletal rearrangement reaction. The latter complex has been characterized by X-ray crystallography. Both complexes underwent ring closure to give the same 1,2-diphenylcyclopentadienyl complex on treatment with silver ion. Addition of a third equivalent of trimethylphosphine to the 2,3-diphenyl isomer produced two meridional rhodacyclohexadienes, which exhibit facile solvent-dependent chloride dissociation. In contrast, phosphine added reversibly to the 1,2-diphenyl isomer to give only the chloride-dissociated compound, and the tris(phosphine) product could only be isolated after anion exchange with hexafluorophosphate. No deprotonation to give rhodabenzene complexes could be achieved. The mechanism of rearrangement is proposed to involve a carbocation rearrangement during the ring-opening reaction and is compared to other metal-promoted reactions of vinylcyclopropenes.

Recent Advances in Metallabenzene Chemistry

“…In solution, a third compound, 119, was detected. [85] There is a striking similarity between cation 119 and 120, [29] the precursor to Bleekes iridabenzene 4, which suggested that deprotonation may lead to a rhodabenzene. Complex 119, however, either decomposed or failed to react with several strong bases.…”

Iridium-Promoted Reactions of Carbon−Carbon Bonds. Skeletal Rearrangement of a Vinylcyclopropene during Iridacyclohexadiene Formation and Subsequent Isomerization of Iridacyclohexadienes via α,α‘-Substituent Migrations

“…For example, reductive elimination of bonds cd affords the vinylcyclopropene complex, elimination of bonds bc yields a metallacyclohexadiene, and coupling of bonds ad generates a coordinated cyclopentadiene; examples of all these reactions have been observed previously. [2][3][4][5][6][7][8][9][10][11][12][13][14][15] We believe this model is useful for understanding the chemistry described in this paper, in which we describe other skeletal contortions and substituent gymnastics observed in these systems. Skeletal rearrangements have been observed previously during the reactions of vinylcyclopropenes with transition metal complexes.…”

“…The ring opening of vinylcyclopropenes by transition metal complexes to give metallacyclohexadienes and related compounds is now well-established. [2][3][4][5][6][7][8][9][10][11][12][13][14][15] Metallacyclohexadienes are compounds of considerable interest, yet few isolated examples exist, and their reaction chemistry is poorly defined. They have been invoked as key intermediates in the Do ¨tz reaction, 16 and iridacyclohexadiene species, obtained by a different route, 17 were shown to undergo a facile deprotonation at the R-carbon to afford the first examples of iridabenzene complexes, leading to an extensive chemistry for these compounds.…”

Metallabenzenes and Valence Isomers. 5. Synthesis and Structural Characterization of a Rhodabenzvalene: A Rare η2-Cyclopropene/σ-Vinylrhodium(I) Complex

“…The weaker coordination also translates into a much larger P1−M−P2 angle, which is nearly 7° greater in 5 . Regardless, formation of the η 2 -cyclopropene−Rh moiety is unique, as oxidative addition to the strained σ-bond is the exclusive reactivity observed in previous studies of cyclopropenes with Rh …”