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 biph asic. Plots of absorbance (lambda = 400 nm) vs. time show two consecut ive 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 a t 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 s tudies 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 mecha nism, whereas the second part of the biphasic process is best describe d as an associative interchange mechanism.