Title

The activation of N-heterocyclic thiols and disulfides by Group VI organometallic complexes: A kinetic and thermodynamic study

Date of Award

2003

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

Carl D. Hoff, Committee Chair

Abstract

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.)

Keywords

Chemistry, Organic

Link to Full Text

http://access.library.miami.edu/login?url=http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3081267