C-H activation of methyl vinyl ketone in Ir(acac){η2-CH2=CHC(O)CH3}(PCy3)

The cyclooctene complex Ir(acac)(cyclooctene)(PCy3) (1) reacts with methyl vinyl ketone to give Ir(acac){eta(2)-CH2=CHC(O)CH3}(PCy3) (2) and cyclooctene. In benzene at 70 degrees C, complex 2 affords by means of an intramolecular C-H activation process the thermodynamically favored alkenyl derivative Ir(acac)H{(Z)-CH=CHC(O)CH3}(Pcy(3)) (3), which was isolated as a mixture of the isomers 3a (PCy3 trans to carbonyl group of alkenyl ligand) and 3b (PCy3 trans to acac). Isomers 3a and 3b do not react with tricyclohexylphosphine. However, the complex Ir(acac)H{(E)-CH=CHC(O)CH3}(PCy3)(2) (4) can be obtained by treatment of 2 with the phosphine in benzene at 70 degrees C. Complex 2 also reacts with HBF4 at -78 degrees C, to give the five-coordinate hydride derivative [Ir(acac)H{eta(2)-CH2=CHC(O)CH3} (PCy3)]BF4 (5). In solution, complex 5 is only stable at temperatures lower than - 40 degrees C. At room temperature and in the presence of acetonitrile, it evolves into the alkyl compound [Ir(acac){CH2CH2C(O)CH3}(NCCH3)(PCy3)]BF4 (6), as a result from the selective anti-Markovnikov insertion of the carbon-carbon bond of the activated olefin into the Ir-H bond of the 5. (C) 1998 Elsevier Science S.A. All rights reserved.