Reactions of acetylenes with noble-metal carbonyl halides. Part 4. The formation of a platinaoxacyclopentenone ring

Abstract

The compound [N(PPh₃)₂][cis-Pt{C(CO₂R)C(Cl)CO₂R}(CO)Cl₂](1; R = Me or Et) reacts with water in polar solvents to give [N(PPh₃)₂][graphic omitted]}(CO)Cl](2), containing a platinaoxacyclopentenone ring. In anhydrous conditions [Pt(CO)₂Cl₂] reacts with RO₂CCCCO₂R to give the insoluble polymeric species [{[graphic omitted]][(CO)}_n](7) which has been characterized both by conversion into (2) and by reaction with uni- and bi-dentate ligands to give [[graphic omitted]}L₂](L = PPh₃, PMePh₂, or PEtPh₂), [[graphic omitted]}(L–L)][L–L = 2,2′-bipyridine(bipy),4,4′-dimethyl-2,2′-bipyridine (dmbipy), or 1,2-bis(diphenylphosphino)ethane (dppe)], and [[graphic omitted]}(CO)L][L = pyridine (py), methylpyridine (mpy), or dimethylpyridine (dmpy)], where the metallo-organic ring is preserved. No breaking of the ring was observed on reaction with chlorine and hydrochloric acid; conversely alkyl iodide gave [Pt{C(CO₂R)C(Cl)CO₂R′}(CO)I] which is readily converted into salt-like compounds of type (1) by reaction with [N(PPh₃)₂]Cl. A cyclisation mechanism is proposed for both the reaction in anhydrous conditions and that in the presence of water. Crystals of [N(PPh₃)₂][[graphic omitted]}(CO)Cl](2b) are triclinic, space group P, with a= 17.144(5), b= 11.975(4), c= 10.386(4)Å, α= 106.62(8), β= 77.07(7), γ= 95.94(7)°, and Z= 2. The crystal structure has been solved by the heavy-atom method from counter data and refined by least squares to a final R of 0.041 (for 3 055 observed reflections). The structure consists of discrete anionic molecules and cationic counter ions, [N(PPh₃)₂]⁺.