Exploring the reactivity of a tungsten(II) aryloxide
Abstract
One continuing problem with the development of the early transition metal chemistry of sterically demanding aryloxides is the sometimes facile intramolecular activation (cyclometalation) of CH bonds that are a part of the ligand itself. A new series of phenols containing meta substituents was prepared by condensing an $\alpha, \beta$-unsaturated ketone (e.g., trans-chalcone, trans-3-penten-2-one or 2,6-dimethyl-4-hepten-3-one) with 1,3-diphenylacetone. The 2,6-diphenyl-3,5-disubstituted phenols were found to be much more cyclometalation resistant than the parent compound, 2,6-diphenylphenol. This same condensation reaction was used to prepare asymmetric phenols by utilizing several asymmetric ketones. Room temperature sodium amalgam reduction of $\rm\lbrack W(OC\sb6HPh\sb4$-$\rm 2,3,5,6)\sb2Cl\sb4\rbrack$ (4 Na per W) in the presence of a tertiary phosphine (L) leads to the deep emerald green, 16 electron complex, $\rm\lbrack W(OC\sb6HPh\sb3$-$\eta\sp6$-$\rm C\sb6H\sb5)(OC\sb6HPh\sb4$-2,3,5,6)(L)). Structural studies of $\rm\lbrack W(OC\sb6HPh\sb3$-$\eta\sp6$-$\rm C\sb6H\sb5)(OC\sb6HPh\sb4$-2,3,5,6)(L)) (L = PMe$\sb2$Ph or PBu$\sb3)$ show a significant amount of distortion within the $\eta\sp6$-bound arene ring leading to a tungstanorbornadiene type resonance structure. This compound will reduce dioxygen or diazo compounds to produce the corresponding bis(oxo) and bis(imido) complexes. Kinetic and mechanistic studies conclusively prove the reductive cleavage of a diazo compound takes place a single tungsten metal center. A wide variety of additional substrates (e.g. elemental chalcogens, ketones, aldehyde and imines) can also be reduced to yield a variety of new organometallic complexes, all of which are characterized by a four electron oxidation at the tungsten metal center. The same complex, $\rm\lbrack W(OC\sb6HPh\sb3$-$\eta\sp6$-$\rm C\sb6H\sb5)(OC\sb6HPh\sb4$-2,3,5,6)(L)), will also mediate the four-electron reductive coupling of two alkyne units to yield a tungstacyclopentatriene complex.
Degree
Ph.D.
Advisors
Rothwell, Purdue University.
Subject Area
Chemistry
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