Investigating Pentamethycyclopentadienyl Rhenium(I) Reactivity with Cycloaklane: Synthetic Strategies Toward Crystalline Metal-Alkane Complexes

Investigating Pentamethycyclopentadienyl Rhenium(I) Reactivity with Cycloaklane: Synthetic Strategies Toward Crystalline Metal-Alkane Complexes

Ironically, in nearly thirty years since Bergman and Graham first observed organoiridium activate methane in hydrocarbon solutions, there are today no productive ways to catalytically convert smaller alkanes to more energetically useful ones, or selectively oxidize them to alcohols for fuel or commodity purposes. This is unfortunate since natural petrol supplies are dwindling while the global demand on them continues to rise. A high-yielding methane to methanol conversion, however, still remains science fiction. One reason for the paucity of productive C—H transformations today, is an unclear understanding of the reaction's initial step; metal-alkane ligation. We describe below our efforts to elucidate C—H activation by investigating model organo-rhenium systems designed to enhance metal- alkane binding energies such that metal-alkane complexes become isolable in the solid state for the first time. Preliminary infrared data collected on a photoinduced reaction involving (C5Me5)ReC03 and methylcyclohexane is presented and discussed within the context of IR spectra reported for putative metal-alkane complexes present in the literature. A semi-empirical molecular orbital study illustrating the allowable overlap an MLS fragment undergoes in a pseudo-octahedral ligand environment with an interested sp hybridized C—H bond as a function of both alkane size and approach to the metal center, is preSented for discussion along with our strategies to increase metal-alkane binding energies based upon the diagramed energetics.