Synthetic, kinetic and thermodynamic studies of the complexes phosphorus tricyanogen tricyclohexyl phosphine metal tricarbonyl, M = chromium, molybdenum, and tungsten

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)



First Committee Member

Carl D. Hoff - Committee Chair


The substitution reactions of $\rm (PCy\sb3)\sb2M(CO)\sb3,$ M = Cr, Mo and W, with small donor ligands (py, CH$\sb3$CN, H$\sb2,$ N$\sb2,$ P(OMe)$\sb3,$ etc.) have been studied by conventional and stopped-flow kinetics. These results are combined with thermodynamic measurements to give a complete picture of ligand substitution in these complexes. The relative rates of dissociation of the M-py bond are in the order Cr $>$ Mo $>$ W in the approximate ratio 4,800/300/1. The relative rates of reaction of $\rm (PCy\sb3)\sb2M(CO)\sb3$ with P(OMe)$\sb3$ is Mo $>$ W $>$ Cr in the ratio 80/36/1. The chromium complex does not obey simple steady-state kinetics. Calorimetric studies show the enthalpies of binding of py and P(OMe)$\sb3$ to be: W = $-$19 and $-$26 kcal/mol, Mo = $-$17 and $-$24 kcal/mol, and Cr = $-$16 and $-$11 kcal/mol. The enthalpies of activation for dissociation of py are: W = $-$23.4 kcal/mol, Mo = $-$22.2 kcal/mol, and Cr = $-$15.8 kcal/mol. The synthesis of the Cr analogue, previously unknown, is reported. Equilibrium experiments to determine the entropy and enthalpy of binding H$\sb2$ and N$\sb2$ show a preference for binding of H$\sb2$ over N$\sb2$ which is due to entropic factors.


Chemistry, Inorganic; Chemistry, Organic

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