Alkyne complexes of platinum. Part 6. The synthesis of compounds containing platinacyclopenta-2,4-diene and diplatinacyclohexa-2,5-diene rings

Abstract

The triplatinum compound [Pt₃(CNBu^t)₆] reacts with the alkynes RCCR (R = Ph, C₆H₄Me-4, or C₆F₄OMe-4) in toluene at 100 °C to give platinacyclopenta-2,4-diene complexes [[graphic omitted](R)}(CNBu^t)₂], and with C₂(CO₂Me)₂ at 40 °C to afford the diplatinacyclohexa-2,5-diene compound [[graphic omitted](CO₂Me)}(CNBu^t)₄]. Bis(cyclo-octa-1,5-diene)platinum reacts with RCCR (R = C₆F₄OMe-4 or CO₂Me) to afford the compounds [[graphic omitted](R)}(cod)](cod = cyclo-octa-1,5-diene). The unsymmetrical alkyne MeCCCO₂Me reacts at 25 °C with [Pt₃(CNBu^t)₆] to give [[graphic omitted](CO₂Me)}(CNBu^t)₄], and with [Pt(cod)₂] to yield a mixture of platinacyclopentadiene isomers [[graphic omitted](R⁵)}(cod)](R²= R⁴= Me, R³= R⁵= CO₂Me; R²= R⁵= CO₂Me, R³= R⁴= Me). At 100 °C in toluene, the compound [Pt(RC₂R)(cod)](R = C₆F₄OMe-4) affords [[graphic omitted](R)}(cod)], whereas in acetone at ambient temperatures it is slowly converted into [[graphic omitted](R)](cod)₂]. The latter in hot toluene affords the platinacyclopenta-2,4-diene derivative and platinum metal. Moreover, treatment of [[graphic omitted](R)}(CNBu^t)₄](R = CO₂Me) with C₂(CO₂Me)₂ affords [[graphic omitted](R)}(CNBu^t)₂] in high yield. Hydrogen-1 and ¹³C n.m.r. data for the new compounds are reported, and the observed interconversion of the various metallacycles is discussed.