Thermodynamic and kinetic studies of ligand binding, oxidative addition, and group/atom transfer in group VI metal complexes
Date of Award
Doctor of Philosophy (Ph.D.)
First Committee Member
Carl D. Hoff - Committee Chair
The complexes Cr(CO)3(eta5-C5Me 5), M(PR3)(CO)3 (M = Mo, W; R = iPr, Cy), and Mo(N(R)(Ar))3 (R = iPr, tBu; Ar = 3,5-C6H3Me2) were studied. First the reactions of Cr(CO)3(eta5-C5Me 5) with the phenyl dichalcogenides (PhE-EPh; E = S, Se, Te) were examined. The chalcogen-chalcogen bond strengths were found to be 46, 41, and 33 kcal/mol respectively for E = S, Se, and Te. The chalcogen-metal bond strengths in this system were found to be 38, 36, and 31 kcal/mol respectively for E = S, Se, and Te.The reactions of the phenyl dichalcogenides with the complexes M(P iPr3)(CO)3 (M = Mo, W) and Mo(N(tBu)(Ar)) 3 were then studied. The bond strengths to sulfur were found to be 38, 44, and 55 kcal/mol respectively for Mo(PiPr3)(CO) 3, W(PiPr3)(CO)3, and Mo(N( tBu)(Ar))3. The respective bond dissociation energies for selenium were 34, 39, and 52 kcal/mol, and the respective bond dissociation energies for tellurium were found to be 27, 33, and 41 kcal/mol. These bond strength data along with kinetic measurements were used to determine metal contribution to reaction order and mechanism.The enthalpies of chalcogen atom transfer to Mo(N(tBu)(Ar)) 3 were then studied and this information was used to determine the bond dissociation energies of the E=Mo bond. The bond energy to Mo(N(tBu)(Ar)) 3 was found to be 115, 87, and 64 kcal/mol respectively for E = S, Se, and Te. Also discovered was the binding of S=Mo(N(tBu)(Ar)) 3 to Mo(N(tBu)(Ar))3 forming the complex ((Ar)( tBu)N)3Mo(mu-S)Mo(N(tBu)(Ar))3. Variable temperature NMR showed this dimerization process to have DeltaH dimer = -16 kcal/mol and DeltaSdimer = -46 cal/mol K. The sulphurization/desulphurization of the P atom in the complex P≡Mo(N( tBu)(Ar))3 was also studied and found to have a S=P bond energy of 78 kcal/mol.The reactions of benzonitrile bound to Mo(N(tBu)(Ar)) 3 were studied. Benzonitrile binding to Mo(N(tBu)(Ar)) 3 produced a species with a carbon centered radical (Ph(•)CN)Mo(N( tBu)(Ar))3. This compound was shown to react with a variety of reagents, typically cleaving a reagent bond and forming a new bond between the nitrile carbon and the reagent. Some of the reagents studied included PhE-EPh (E = S, Se, Te), benzoylperoxide (BzO-OBz), and Mp-H (MP = MO(CO) 3(eta5 -C5H5)). These reactions were shown to be either stable, to insert benzonitrile, or to extrude benzonitrile, depending on the group bound to Mo or the nitrile carbon. Also examined was the difference in binding benzonitrile versus dimethyl cyanamide (NCNMe2).The last chapter discusses the activation of white phosphorous (P 4) using the compounds Mo(N(R)(Ar))3. Discussed are the bond energies, kinetics, and proposed reaction mechanisms.
Mcdonough, James Eric, "Thermodynamic and kinetic studies of ligand binding, oxidative addition, and group/atom transfer in group VI metal complexes" (2005). Dissertations from ProQuest. 2282.