Ligand and metal effects on the heats of protonation of organometallic compounds

dc.contributor.advisor Robert J. Angelici Rottink, Mary
dc.contributor.department Chemistry 2018-08-23T15:56:41.000 2020-06-30T07:02:27Z 2020-06-30T07:02:27Z Wed Jan 01 00:00:00 UTC 1992 1992
dc.description.abstract <p>Titration calorimetry has been used to determine the heats of protonation ([delta]H[subscript] HM) of transition metal complexes. These protonation studies have been performed in 1,2-dichloroethane (DCE) solution with CF[subscript]3SO[subscript]3H at 25.0°C (eq 1). ML[subscript]n + CF[subscript]3SO[subscript]3H DCE [over] 25.0° C HML[subscript]n[superscript]+CF[subscript]3SO[subscript]3[superscript]-; [delta] H[subscript]HM\eqno(1);In the CpOs(PPh[subscript]3)[subscript]2X (X = I, Br, Cl, H) series, it was determined that the basicity ([delta]H[subscript] HM) of the osmium center increases in the order: I[superscript]- < Br[superscript]- < Cl[superscript]- << H[superscript]-. The hydride complex is 23 kcal/mol more basic than the iodide complex; in terms of an equilibrium constant, the hydride complex is 10[superscript]17 times more basic than the iodide complex. There is an excellent linear correlation between the basicities ([delta]H[subscript] HM) of the CpOs(PPh[subscript]3)[subscript]2X complexes and the gas phase proton affinities of the anions, X[superscript]-, toward the H[superscript]+. Changing the phosphine ligands in the CpOs(PR[subscript]3)[subscript]2Br complexes results in a linear increase in the basicity (-[delta]H[subscript] HM) from 16.3 kcal/mol to 29.4 kcal/mol in the order: PPh[subscript]3 < PPh[subscript]2Me < PPhMe[subscript]2 < PMe[subscript]3. Osmium complexes are 6.0-8.5 kcal/mol more basic ([delta]H[subscript] HM) than the analogous ruthenium complexes, and Cp* raises the basicity ([delta]H[subscript] HM) of a complex by 5.5-9.0 kcal/mol over the analogous Cp complexes;Studying multihydrido complexes ((H)[subscript]2Os(PR[subscript]3)[subscript]4, (H)[subscript]4Os(PR[subscript]3)[subscript]3, HIr(CO)(PPh[subscript]3)[subscript]3 and CpIr(ER[subscript]3)(H)[subscript]2] has shown that the basicity ([delta]H[subscript] HM) of the metal in (H)[subscript]4Os(PR[subscript]3)[subscript]3 (PR[subscript]3 = PPh[subscript]2Me, PPhMe[subscript]2) increases by ~15 kcal/mol when two hydride ligands are replaced by a PR[subscript]3 ligand to give (H)[subscript]2Os(PR[subscript]3)[subscript]4. Replacement of the two hydride ligands in CpIr(PPh[subscript]3)(H)[subscript]2 to give CpIr(PPh[subscript]3)(CO) results in a 10.4 kcal/mol increase in the basicity ([delta]H[subscript] HM) of the metal. Thus, comparison of the two electron donor ligand sets (H)[subscript]2, CO and PR[subscript]3 has illustrated that the basicity ([delta]H[subscript] HM) of the metals increase in the order: (H)[subscript]2 < CO < PPh[subscript]2Me < PPhMe[subscript]2. It has also been determined that the basicities of the CpIr(ER[subscript]3)(H)[subscript]2 complexes increase with ER[subscript]3 in the order: P(OPh)[subscript]3 << AsPh[subscript]3 ≈ PPh[subscript]3;In contrast to the above complexes protonation occurs at uncoordinated phosphorus atom of the [eta][superscript]1-dppm (Ph[subscript]2PCH[subscript]2PPh[subscript]2) ligand in M(CO)[subscript]5([eta][superscript]1-dppm) (M = Cr, Mo, W) and fac-M(CO)[subscript]3(N N)([eta][superscript]1-dppm) (M = Mo, N N = bipy, phen; M = W, N N = bipy). For dppm, its monoprotonated form (dppmH[superscript]+) and these complexes, the basicity (-[delta]H[subscript] HM) increases from 14.9 kcal/mol to 23.1 kcal/mol in the order: dppmH[superscript]+ < Cr(CO)[subscript]5([eta][superscript]1-dppm) < Mo(CO)[subscript]5([eta][superscript]1-dppm) < W(CO)[subscript]5([eta][superscript]1-dppm) < dppm ≤ fac-Mo(CO)[subscript]3([eta][superscript]2-bipy)([eta][superscript]1-dppm) < fac-Mo(CO)[subscript]3([eta][superscript]2-phen)([eta][superscript]1-dppm) ≈ W(CO)[subscript]3([eta][superscript]2-bipy)([eta][superscript]1-dppm). Thus, the H[superscript]+ is more electron with-drawing than M(CO)[subscript]5 (M = Cr, Mo, W) and M(CO)[subscript]3([eta][superscript]2-phen) and W(CO)[subscript]3([eta][superscript]2-bipy) actually enhance the basicity ([delta]H[subscript] HM) of the dangling phosphorus as compared to dppm itself.</p>
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dc.identifier archive/
dc.identifier.articleid 11149
dc.identifier.contextkey 6385201
dc.identifier.s3bucket isulib-bepress-aws-west
dc.identifier.submissionpath rtd/10150
dc.language.iso en
dc.source.bitstream archive/|||Fri Jan 14 18:14:52 UTC 2022
dc.subject.disciplines Analytical Chemistry
dc.subject.disciplines Inorganic Chemistry
dc.subject.disciplines Physical Chemistry
dc.subject.keywords Chemistry
dc.subject.keywords Inorganic chemistry
dc.title Ligand and metal effects on the heats of protonation of organometallic compounds
dc.type article
dc.type.genre dissertation
dspace.entity.type Publication
relation.isOrgUnitOfPublication 42864f6e-7a3d-4be3-8b5a-0ae3c3830a11 dissertation Doctor of Philosophy
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