Carbon–carbon and carbon–chlorine bond formation on reaction of iodine(III) reagents with the bis(alkynyl)palladium(II) motif, and structural chemistry of trans-Pd(CC-o-Tol)2(PMe2Ph)2] and trans-[PdCl(CC-o-Tol)(PMe2Ph)2]

Trans-di(ortho-tolylethynyl)bis(dimethylphenylphosphine)palladium(II) reacts above −20 °C with the iodonium reagent IPhCl2 to give predominantly o-Tol–CC–Cl, above 15 °C with IPh2(OTf) (OTf = triflate) to give o-Tol–CC–Ph and (o-Tol–CC)2 in ca. 3:1 ratio, and above 10 °C with IPh(CCR)(OTf) (R = But, SiMe3) to give predominantly o-Tol–CC–CC–R and (o-Tol–CC)2. 31P NMR spectra provide evidence for detection of intermediates. The complexes trans-[Pd(CC-o-Tol)2(PMe2Ph)2] and trans-[PdCl(CC-o-Tol)(PMe2Ph)2] are obtained on reaction of trans-[PdCl2(PMe2Ph)2] with Li(CC-o-Tol) and o-Tol-CCH/Et3N, respectively, and have been characterised by X-ray crystallography.

The complex trans-[Pd(CC-o-Tol)2(PMe2Ph)2] reacts with iodonium reagents IPh2+ and IPh(CCR)+ to give organic products showing alkynyl-alkynly coupling, and with IPhCl2 to undergo alkynyl-chlorine coupling to form o-Tol–CC–Cl and trans-[PdCl(CC-o-Tol)(PMe2Ph)].Figure optionsDownload as PowerPoint slideHighlights
► trans-[Pd(CC-o-Tol)2(PMe2Ph)2] reacts with iodonium reagents IPh2(OTf), IPh(CCR)(OTf) (OTf = triflate).
► C–C coupling occurs to give o-Tol–CC–CC–R, (o-Tol–CC)2 and o-Tol–CC–Ph.
► trans-[Pd(CC-o-Tol)2(PMe2Ph)2] reacts with IPhCl2 to give o-Tol–CC–Cl and trans-[PdCl(CC-o-Tol)(PMe2Ph)2].
► Intermediates are detected by NMR spectroscopy and visible spectroscopy, but the nature of intermediates not determined.
► Intermediates are assumed to arise by transfer of Ph+, [CCR]+ or Cl+ in oxidation of Pd(II) to form Pd(III) or Pd(IV) species that reductively eliminate C–C or C–Cl.
► Synthesis and X-ray structures are reported for trans-[Pd(CC-o-Tol)2(PMe2Ph)2] and trans-[PdCl(CC-o-Tol)(PMe2Ph)2].