Synthesis and reactivity of platinum complexes of cyclic alkynes and tropynes

Article abstract of DOI:10.1021/om00006a039

Platinum complexes of dibenzannelated didehydrotropone 5, didehydrooxepin 6, and didehydrocycloheptatriene 7 have been synthesized in good yields by base-induced dehydrobromination from the corresponding bromoalkenes in the presence of Pt(PPh₃)₃. Complex 5 crystallizes in triclinic space group P1: a = 11.221(2) ?, b = 11.318(2) ?, c = 16.621(4) ?, α = 74.22(2)°, β = 78.86(2)°, γ = 73.56(2)°, V = 2445.0(9) ?³, Z = 2, R = 5.79%. Reaction of 5 with tert-butyl isocyanide gives a single phosphine displacement product 11, and reaction with HBF₄ and HBr gives oxidative addition products 8 and 12, respectively. Bis-(dicyclohexylphosphino)ethane displaces triphenylphosphine from 5 and 6 to give 9 and 10. Complex 5 reacts with tetracyanoethylene to give the highly distorted substituted benzene 14 which was characterized by X-ray diffraction. Crystal data for 14: Space group P1, a = 11.274(2) ?, b = 11.826(1) ?, c = 13.474(2) ?, α = 111.79(1)°, β = 106.34(1)°, γ = 98.54(1)°, V = 1534.9(4) ?³, Z = 2, R = 6.17%. Complex 6 reacts with TCNE to give the platinacyclopent-2-ene 15 (55%). Complex 15 crystallizes in monoclinic space group Ia: a = 17.175(3) ?, b = 15.411(2) ?, c = 18.661(2) ?, β = 91.86(1)°, V = 4915(2) ?³, R = 4.74%. Reaction of 7 with triphenylcarbenium tetrafluoroborate gives the dibenzannelated tropyne complex 16 which can be converted back to 7 with KBEt₃H. Reaction of 16 with bis(dicyclohexylphosphino)ethane gives 17 (60%), and reaction with HBr gives the oxidative addition product 18 which slowly isomerizes to 19.