A Computational and Experimental Study of Interesting Organometallic Complexes

The novel complexes, h⁶-1,2-dehydrobenzenetricarbonylchromium(0), h⁵-1,2-dehydrocyclo-pentadienyltricarbonylmanganese(I), and h⁴-1,2-dehydrocyclobutadiene-tricarbonyliron(0) (shown below), have not yet been synthesized and/or isolated, even though each of these examples is a straightforward derivative of a known and stable transition metal complex. Semmelhack, et al., reported the possible existence of h⁶-1,2-dehydrobenzenetricarbonylchromium(0), however this was based on degradation products, not direct observation of the metal complex or a derived metal complex. We are carrying out density functional theory calculations on the three complexes to determine their stability. Calculations thus far have shown that the dehydrobenzene and the dehydrocyclopentadienyl complexes are local minima, i.e. it may be possible to synthesize them, and trap them. It was also found that the dehydrocyclobutadiene complex is not at a potential energy minimum, i.e. it may not be possible to synthesize it.

Attempts are being made to synthesize, and, perhaps, directly observe the novel small ring alkynes bound to the metals. These complexes are expected to open new routes to a new class of substituted aromatic metal complexes by reactions with nucleophiles and to allow novel entries into the synthesis of new and interesting bicyclic ring systems after trapping with dienes in situ.

We are also working on a route to simple, yet unknown synthetically, cyclobutadieneiron tricarbonyl compounds. Both fluoro- and hydroxycyclobutadieneiron tricarbonyl have not been synthesized. We are currently developing a route to the parent, cyclobutadieneiron tricarbonyl that does not use cyclooctatetraene. This will then be converted to the fluoro derivative, which will in turn be transformed into the hydroxy derivative.