New chiral cyclopentadienylrhenium Lewis acids featuring fluorinated triarylphosphanes and enhanced acceptor abilities - An unusual carbon-fluorine bond activation in a metal coordination sphere

The acetonitrile complex [(5-C5H5)Re(NO)(NCCH3)(CO)] +BF4- (1) and P(4-C6H4CF3)3 slowly react (2 d, room temperature) to give the substitution product [(5-C5H5)Re(NO){P(4-C6H 4CF3)3}(CO)]+BF4- (3, 85%). The reaction of 1 and less nucleophilic P(C6F5)3 must be conducted in a melt at 140C, but [(5-C5H5)Re(NO){P(C6F 5)3}(CO)]+BF4- (11) is isolated in 90% yield. Reduction of 3 by NaBH4 gives the methyl complex (5-C5H5)Re(NO){P(4-C6H 4CF3)3}(CH3), which is treated with TfOH and H3CN=C(H)C6H5 to give the imine complex [(5-C5H5)Re(NO)(PPh3){N(CH 3)=C(H)C6H5}]+TfO- (9). Complex 9 was, like the non-fluorinated analog, unreactive towards allyltin nucleophiles. Complex 11 should lead to a more reactive imine complex, but NaBH4 gave a methyl complex that was difficult to purify. However, NaOCH3 or NaSCH3/methanol gave easily purified (5-C5H5)Re(NO){P(4-C6F 4OCH3)3}(CO2CH3) (85%) or (5-C5H5)Re(NO){P(4-C6F 4SCH3)3}(CO2CH3) (51%), in which all para-fluorine atoms have undergone nucleophilic displacements, and the carbonyl ligands methoxide additions. This suggests that catalytic chemistry of the chiral Lewis acid [(5-C5H5)Re(NO){P(C6F 5)3}]+(I-F15) will be complicated by nucleophilic degradation. Nonetheless, density functional calculations show that I-F15 is a much stronger acceptor and weaker donor than less fluorinated analogs.

New chiral cyclopentadienylrhenium Lewis acids featuring fluorinated triarylphosphanes and enhanced acceptor abilities - An unusual carbon-fluorine bond activation in a metal coordination sphere Academic Article