Palladium End-Capped Polyynes via Oxidative Addition of 1-Haloalkynes to Pd(PPh₃)₄

Abstract

Reported here is the use of 1-haloacetylenes and 1-halopolyynes as synthons for the preparation of new palladium(II) end-capped polyynes. The 1-haloalkynes were obtained in a series of transformations from para-substituted bromoarenes that included Sonogashira coupling followed by halogenation and chain elongation via Cadiot–Chodkiewicz protocol. The key step for the synthesis of metal complexes was oxidative addition of 1-haloalkynes to Pd(PPh3)4, which allowed obtaining a series of metal compounds 1–5-C n X with carbon chains up to hexatriyne in 75–100% yield. All the compounds were characterized by NMR and HRMS or elemental analysis. The 13C spectra of the 1-haloalkynes showed interesting, although expected, shifts of the carbon chain atoms close to the halogen termini. X-ray crystal structures were obtained for three polyynestwo butadiynes (2-C4[Pd]Br and 3-C4[Pd]Br) and one hexatriyne (1-C6[Pd]Br)and the latter is the first reported X-ray crystal structure of palladium end-capped hexatriyne.

Reactivity of Polyynes: Complex Molecules from Simple Carbon Rods

“…[135,136] Such complexes are inaccessible with the use of more traditional approaches Scheme 29. In our group, we developed the methodology that leads to metal-end caped polyynes through oxidative addition.…”

Reactivity of 3-halopropynols: X-ray crystallographic analysis of 1,1-dihalocumulenes and 2+2 cycloaddition products

“…1,1-Dibromo-or 1,1-diiodo-cumulenes have a significant potential as building blocks for more complex, all-carbon scaffolds and may be obtained from 1-halobutadiynes. In our group, we have been conducting continuous studies on the syntheses and reactivity of 1-haloalkynes and 1-halopolyynes [11][12][13][14][15][16] and we attempted to use them as precursors of 1,1-dihalocumulenes. On the other hand, (2+2) cycloaddition of allenes has been intensively explored for many years.…”

Direct synthesis of butadiynyl-substituted pyrroles under solvent- and transition metal-free conditions

“…21 Moreover 1-halopolyynes are used as substrates in the synthesis of symmetric polyynes, 22 glycosylated polyynes, 23 natural products, 24 and as precursors of organometallic polyynes. 25 In this work we describe the application of pyrroles 1a-e and 1halobutadiynes 2a-d-X (X = Cl or Br or I) as useful precursors of butadiynyl-substituted heterocycles. The scope of the known coupling reaction was extended to butadiynes that possess a great potential for further modification.…”