Synthesis of Molybdenum and Tungsten Alkylidene Complexes
that Contain a <i>tert</i>-Butylimido Ligand
- Publication date
- Publisher
Abstract
A variety
of molybdenum or tungsten complexes that contain a <i>tert</i>-butylimido ligand have been prepared. For example, the <i>o</i>-methoxybenzylidene complex W(N-<i>t</i>-Bu)(CH-<i>o</i>-MeOC<sub>6</sub>H<sub>4</sub>)(Cl)<sub>2</sub>(py)
was prepared through addition of pyridinium chloride to W(N-<i>t</i>-Bu)<sub>2</sub>(CH<sub>2</sub>-<i>o</i>-MeOC<sub>6</sub>H<sub>4</sub>)<sub>2</sub>, while Mo(N-<i>t</i>-Bu)(CH-<i>o</i>-MeOC<sub>6</sub>H<sub>4</sub>)(OR<sub>F</sub>)<sub>2</sub>(<i>t</i>-BuNH<sub>2</sub>) complexes
(OR<sub>F</sub> = OC<sub>6</sub>F<sub>5</sub> or OC(CF<sub>3</sub>)<sub>3</sub>) were prepared through addition of two equivalents
of R<sub>F</sub>OH to Mo(N-<i>t</i>-Bu)<sub>2</sub>(CH<sub>2</sub>-<i>o</i>-MeOC<sub>6</sub>H<sub>4</sub>)<sub>2</sub>. An X-ray crystallographic study of Mo(N-<i>t</i>-Bu)(CH-<i>o</i>-MeOC<sub>6</sub>H<sub>4</sub>)[OC(CF<sub>3</sub>)<sub>3</sub>]<sub>2</sub>(<i>t</i>-BuNH<sub>2</sub>) showed that the methoxy oxygen is bound to the metal and that two
protons on the <i>tert</i>-butylamine ligand are only a
short distance away from one of the CF<sub>3</sub> groups on one of
the perfluoro-<i>tert</i>-butoxide ligands (H···F
= 2.456(17) and 2.467(17) Å). Other synthesized tungsten <i>tert</i>-butylimido complexes include W(N-<i>t</i>-Bu)(CH-<i>o</i>-MeOC<sub>6</sub>H<sub>4</sub>)(pyr)<sub>2</sub>(2,2′-bipyridine) (pyr = pyrrolide), W(N-<i>t</i>-Bu)(CH-<i>o</i>-MeOC<sub>6</sub>H<sub>4</sub>)(pyr)(OHMT)
(OHMT = O-2,6-(mesityl)<sub>2</sub>C<sub>6</sub>H<sub>3</sub>), W(N-<i>t</i>-Bu)(CH-<i>t</i>-Bu)(OHMT)(Cl)(py)
(py = pyridine), W(N-<i>t</i>-Bu)(CH-<i>t</i>-Bu)(OHMT)(Cl), W(N-<i>t</i>-Bu)(CH-<i>t</i>-Bu)(pyr)(ODFT)(py), W(N-<i>t</i>-Bu)(CH-<i>t</i>-Bu)(OHMT)<sub>2</sub>, and W(N-<i>t</i>-Bu)(CH-<i>t</i>-Bu)(ODFT)<sub>2</sub> (ODFT = O-2,6-(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>C<sub>6</sub>H<sub>3</sub>). Interestingly, W(N-<i>t</i>-Bu)(CH-<i>t</i>-Bu)(OHMT)<sub>2</sub> does not react with ethylene or 2,3-dicarbomethoxynorbornadiene.
Removal of pyridine from W(N-<i>t</i>-Bu)(CH-<i>t</i>-Bu)(Biphen<sub>CF3</sub>)(pyridine) (Biphen<sub>CF3</sub> = 3,3′-di-<i>tert</i>-butyl-5,5′-bistrifluoromethyl-6,6′-dimethyl-1,1′-biphenyl-2,2′-diolate)
with B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> led to formation of
a five-coordinate 14<i>e</i> neopentyl complex as a consequence
of CH activation in one of the methyl groups in one <i>tert</i>-butyl group of the Biphen<sub>CF3</sub> ligand, as was proven in
an X-ray study. An attempted synthesis of W(N-<i>t</i>-Bu)(CH-<i>t</i>-Bu)(Biphen<sub>Me</sub>) (Biphen<sub>Me</sub> =
3,3′-di-<i>tert</i>-butyl-5,5′,6,6′-tetramethyl-1,1′-biphenyl-2,2′-diolate)
led to formation of a 1:1 mixture of W(N-<i>t</i>-Bu)(CH-<i>t</i>-Bu)(Biphen<sub>Me</sub>) and a neopentyl complex
analogous to the one characterized through an X-ray study. The metallacyclobutane
complexes W(N-<i>t</i>-Bu)(C<sub>3</sub>H<sub>6</sub>)(pyrrolide)(ODFT)
and W(N-<i>t</i>-Bu)(C<sub>3</sub>H<sub>6</sub>)(ODFT)<sub>2</sub> were prepared in reactions involving W(N-<i>t</i>-Bu)(CH-<i>t</i>-Bu)(pyr)<sub>2</sub>(bipy), ZnCl<sub>2</sub>(dioxane), and one or two equivalents of DFTOH, respectively,
under 1 atm of ethylene
