A. Tekkaya et al., DISPLACEMENT KINETICS OF 1,5-CYCLOOCTADIENE FROM MO(CO)4(ETA(2-2)-1,5-CYCLOOCTADIENE) BY BIS(DIPHENYLPHOSPHINO)METHANE, Inorganic chemistry, 33(11), 1994, pp. 2439-2443
The kinetics of the thermal substitution of 1,5-cyclooctadiene (COD) f
rom [Mo(CO)4(eta2:2-COD)] (1) by bis-(diphenylphosphino)methane (DPPM)
and the formation of [Mo(CO)4(DPPM)] (6) was studied by quantitative
FT-IR spectroscopy. The reaction rate exhibits first-order dependence
on the concentration of 1, and the observed rate constant, k(obs), dep
ends on the concentrations of both leaving COD and entering DPPM ligan
d. From the evaluation of data collected, one can propose a mechanism
in which the rate-determining step is the cleavage of one of two Mo-ol
efin bonds. A rate law is derived from the proposed mechanism. The eva
luation of the kinetic data gives the enthalpy of activation DELTAH =
80 (+/-1) kJ.mol-1 and the entropy of activation DELTAS = -55 (+/-2)
J.mol-1.K-1. The negative entropy value obtained tends to suggest an
associative mechanism in transition states. Material balance and yield
of product do not show any significant depletion implying that there
is no decomposition in noticeable amounts during the substitution reac
tion.