The activation of N-heterocyclic thiols and disulfides by Group VI organometallic complexes: A kinetic and thermodynamic study
Date of Award
Doctor of Philosophy (Ph.D.)
First Committee Member
Carl D. Hoff - Committee Chair
The reaction of 2,2'-pyridine disulfide (2-mpd) and 2-mercaptopyridine (2-pyridine thione, H-2mp) with Group VI (Cr, Mo, and W) L3M(CO)3 complexes were studied in comparison to their phenyl analogues: phenyl disulfide and thiophenol. Where L = Py or 1/3 CHPT (CHPT = cycloheptatriene), 18-electron complexes of the type (CHPT)M(CO) 3 or (Py)3M(CO)3 showed oxidative addition of the disulfide bond of 2-mpd to form chelated complexes Cr(eta2-2mp) 3, [(eta2-2mp)Mo(eta2,mu- S-2mp)(CO)]2, and (eta2-2mp)2W(CO) 3. Synthesis and crystal structures of all 3 products are reported. The 7-coordinate W(II) complex (eta2-2mp)2W(CO) 3 undergoes further oxidative addition with additional 2-mpd yielding W(eta2-2mp)4. Whilst the reaction of (eta 2-2mp)2W(CO)3 with •NO forms solely (eta 2-2mp)2W(NO)2, the reaction of (eta 2-2mp)2W(CO)3 with 2-mpd in the presence of •NO yields a mixture of (eta2-2mp)3W(NO) and (eta2-2mp)2W(NO)2, the crystal structures of which are reported. The rate of nitrosylation of (eta 2-2mp)2W(CO)3 was found to be within the rate of substitution with P(Ph2Me), which forms the complex (eta 2-2mp)2W(CO)2(PPh2Me) as characterized by X-ray diffraction.With two moles of the 17-electron organometallic radical •Cr(CO) 3Cp* (where Cp* = C5Me5), 2-Pyridine thione undergoes rapid oxidative addition yielding hydride H-Cr(CO)3Cp* and thiolate (eta1-2mp)Cr(CO)3Cp*.Reaction of 4-pyridine thione (4-mercaptopyridine, H-4mp) with •Cr(CO) 3Cp* in CH2Cl2 also follows second-order kinetics and occurs 2--4 times more rapidly than that of H-2mp under the same conditions.Finally, reaction of the unsaturated 16-electron complex (PiPr 3)2W(CO)3 (referred to as iprW k) with H-2mp in toluene almost instantaneously forms the complex iprWk(H-2mp). This adduct undergoes slow, first-order oxidative addition to yield the W(II) thiolate iprWk(H)(2mp): rate = k[iprWk] where k (288 K) = 3.22 x 10 -5 s-1; DeltaH⁁ = +25.7 kcal/mol, DeltaS⁁ = +10.7 cal/mol K.The gas phase and solvent dependent preference of the tautomerization between 2-pyridine thiol and 2-pyridine thione was assessed using variable temperature FTIR experiments and 1H NMR spectroscopy. (Abstract shortened by UMI.)
Sukcharoenphon, Kengkaj, "The activation of N-heterocyclic thiols and disulfides by Group VI organometallic complexes: A kinetic and thermodynamic study" (2003). Dissertations from ProQuest. 2023.