Covalently Bonded Bis(phosphane)gold(I) Cations in a Cross-Linked Phosphazene Polymeric Matrix as Recyclable Supported Catalysts for Thermal and Microwave-Assisted Hydration of Alkynes

The unexpected finding that the complex [Au(PPh3)(2)]PF6 (C1) catalyses the specific hydration of 1-octyne, (p-phenoxyphenyl) acetylene, phenylacetylene, (p-chlorophenyl)acetylene and benzylacetylene at 100 degrees C in the presence of H2SO4 and THF or methanol as solvents, specially using microwave radiation, led to the first gold(I) recyclable catalysts for this reaction. The phosphazene polymeric framework of idealised formula {[NP(O2C12H8)](0.85)[NP(OC6H4PPh2)(2) (AuPF6)(0.5)](0.15)}(n) (C2), and the newly synthesised cyclomatrix material of idealised formula {[N3P3(OC6H4PPh2)(6)]-(AuPF6)(3.5)}(n) (C3), both having cationic [-Ph2P-Au+-PPh2-] cross-linking sites, catalysed the complete hydration of terminal alkynes at 100 degrees C and 150 degrees C and could be used six and four times respectively without significant loss of activity. The mechanism of the catalytic system is based on the initial reversible displacement of one anchoring O-C6H5-PPh2 group from the [-Ph2P-Au+-PPh2-] cross-linking sites by an alkyne molecule. Using microwave radiation, the hydration of (p-phenoxyphenyl) acetylene, phenylacetylene, (p-chlorophenyl) acetylene and benzylacetylene can be completed in 5 min to 2 h in the absence of any gold(I) catalyst.