2-OXACYCLOPENTYLIDENE, 2-OXACYCLOHEXYLIDENE, AND 2-OXACYCLOHEPTYLIDENE RHENIUM COMPLEXES BY REACTION OF OMEGA-ALKYNOLS WITH THE [(MEC(CH2PPH2)(3))RE(CO)(2)](+) AUXILIARY

Various beta-, gamma-, and delta-alkynols have been reacted with the 1 6e(-) fragment [(triphos)Re(CO)(2)](+) generated in situ by H-2 elimin ation from [(triphos)Re(CO)(2)(eta(2)-H-2)]BF4 [triphos = MeC(CH2PPh2) (3)]. Irrespective of the length of the alkyl chain between the C=C an d OH functional groups in the omega-alkynol, 2-oxacyclocarbene complex es are obtained. These include the 2-oxacyclopentylidene derivatives [ (triphos)Re(CO)(2)-(=CCH2CH2CH2O)]BF4 and [(triphos)Re(CO)(2)(=CCH2CH2 CH(Me)O)]BF4, the 2-oxacyclohexylidene dervivatives [(triphos)Re(CO)(2 ){=CCH2CH2CH2CH2P}]BF4 and [(triphos)Re(CO)(2){=CCH2CH2CH2CH(Me)O}]BF4 , and the 2-oxacycloheptylidene complex [(triphos)Re(CO)(2)(=CCH2CH2CH 2CH2CH2O)]BF4. The latter compound contains a unprecedented seven-memb ered oxacarbene ring. The rhenium-assisted delta-alkynol to 2-oxacyloh eptylidene rearrangement proceeds via the hydroxybutylvinylidene kinet ic intermediate [(triphos)Re(CO)(2)(C=C(H)CH2CH2CH2CH2OH)]BF4, which h as been characterized in both the solid state and solution. An X-ray a nalysis has been carried out on a single crystal of [(triphos)Re(CO)(2 )(=CCH2CH2CH(Me)O)]BF4. The structure of this complex consists of [(tr iphos)Re(CO)(2)(= CCH2CH2CH(Me)O)](+) cations and tetrafluoroborate an ions with no interspersed solvent molecules. A facial triphos Ligand, two cis-disposed carbonyl groups and a 2-oxacyclopentylidene Ligand co ordinate the Re centre in a slightly distorted octahedral environment.