C-H Activation of Methyl Vinyl Ketone in Ir(acac){eta2-CH2=CHC(O)CH3}(PCy3)

Autores: Ricardo Castarlenas, Miguel A. Esteruelas, Marta Martín y Luis A. Oro Journal of Organometallic Chemistry, 564, 241-247, (1998)

The cyclooctene complex Ir(acac)(cyclooctene)(PCy3) (1) reacts with methyl vinyl ketone to give Ir(acac){h2-
CH2=CHC(O)CH3}(PCy3) (2) and cyclooctene. In benzene at 70°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}(Pcy3) (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°C. Complex 2 also reacts with HBF4 at -78°C, to give the
five-coordinate hydrido derivative [Ir(acac)H{h2-CH2=CHC(O)CH3}(PCy3)]BF4 (5). In solution, complex 5 is only stable at
temperatures lower than 40°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.