Equilibrium and Kinetic Studies of Isomerization of (OC)5M[η1-PPh2CH2CH(PPh2)2] and (OC)5M[η1-PPh2CH(PPh2)CH2PPh2] (M=Cr, Mo, W)

Author

Weiying Lin, Eastern Illinois University

Degree Name

Master of Science (MS)

Semester of Degree Completion

1995

Thesis Director

Richard L. Keiter

Abstract

It has been found that (OC)₅M[η¹-PPh₂CH₂CH(PPh₂)₂] and (OC)₅M[η¹-PPh₂CH(PPh₂)CH₂PPh₂] (M=Cr, Mo, W) exist in equilibrium in solution. This linkage isomerization is the first experimental evidence for the exchange of terminal and coordinated phosphorus groups in pentacarbonyl complexes of group 6 metals.

(OC)₅M[η¹-PPh₂CH₂CH(PPh₂)₂] ⇌ (OC)₅M[η¹-PPh₂CH(PPh₂)CH₂PPh₂]

(M = Cr, Mo, W)

In this work, equilibrium constants (K) at several temperatures were measured in order to obtain the values for the change of enthalpy (ΔH°), the change of entropy (ΔS°), and the change of free energy (ΔG°) for the isomerization. The relative stabilities of the two linkage isomers were determined. Rate constants (k) at several temperatures were also measured for the isomerization of W and Cr complexes. From these, the half reaction time (t_1/2), activation energy (E_a), enthalpy of activation (ΔH^≠), entropy of activation (ΔS^≠), and free energy of activation (ΔG^≠) were calculated. A mechanism was proposed for the isomerization. Energy diagrams were also plotted from the equilibrium and kinetic data. Phosphorus-31 nuclear magnetic resonance spectroscopy was applied to monitor the change of concentration of the isomers.

Recommended Citation

Lin, Weiying, "Equilibrium and Kinetic Studies of Isomerization of (OC)5M[η1-PPh2CH2CH(PPh2)2] and (OC)5M[η1-PPh2CH(PPh2)CH2PPh2] (M=Cr, Mo, W)" (1995). Masters Theses. 1975.
https://thekeep.eiu.edu/theses/1975