Displacement of piperidine (pip) from cis-(tricyclohexylphosphine) (pip)tetracarbonyl tungsten(0)

Displacement of piperidine (pip) from cis-eta(1)-(P(cy)(3))(pip)W(CO)(4) (cy=cyclohexyl) to produce eta(2)-(P(cy)(3)(pip)W(H)(CO)(4) is biphasic. Plots of absorbance (lambda = 400 nm) vs. time show two consecutive first order reactions. The first reaction involves dissociation of pip to produce the chelate complex eta(2)-(P(cy)(3))W(CO)(4), where P(cy)(3) forms a five-membered ring bonded to tungsten via phosphorus at one end and via hydrogen (agostic bond) at the other end. The second reaction involves intramolecular oxidative addition (cyclometalation) of cy to produce eta(2)-(P(cy)(3))W(H)(CO)(4). Results from kinetic studies suggest that departure of pip from cis-eta(1)-(P(cy)(3))(pip)W(CO)(4) is assisted by the solvent via a dissociative interchange mechanism, whereas the second part of the biphasic process is best described as an associative interchange mechanism.