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

The compound [N(PPh3)2][cis-Pt{C(CO2R)=C(Cl)CO 2R}(CO)Cl2] (1; R = Me or Et) reacts with water in polar solvents to give [N(PPh3)2][Pt{C(CO2R)=C(Cl)COO}(CO)Cl]}(2), containing a platinaoxacyclopentenone ring. In anhydrous conditions [Pt(CO)2Cl2] reacts with RO2CC≡CCO2R to give the insoluble polymeric species [{Pt[C(CO2R]=C(Cl)COO](CO)}n] (7) which has been characterized both by conversion into (2) and by reaction with uni- and bi-dentate ligands to give [Pt{C(CO2R)=C(Cl)COO}L2] (L = PPh3, PMePh2, or PEtPh2), [Pt{C(CO2R)=C(Cl)COO}(L-L)] [L-L = 2,2′-bipyridine(bipy),4,4′-dimethyl-2,2′-bipyridine (dmbipy), or 1,2-bis(diphenylphosphino)ethane (dppe)], and [Pt{C(CO2R)=C(Cl)COO}(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][Pt{C(CO)2Me]}=C(Cl)COO}(CO)Cl(2b) are triclinic, space group P1, 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]+.