A new synthetic methodology applied to the preparation of some novel, alkyl-substituted, cyclic carbene complexes of ruthenium, tungsten, and rhenium

It has been shown that 1-carbonyl(h{dollar}sp5{dollar}-cyclopentadienyl) (2-methoxy)-1-ferracyclopentene can be formed by a 1,2 alkyl migration reaction through the decarbonylation of (dicarbonyl) (h{dollar}sp5{dollar}-cyclopentadienyl) (1-methoxy-1-cyclobutyl)iron. This novel rearrangement has also been found with similar compounds of manganese.; With the intent to observe this reaction in complexes with metal centers in the second and third row of the periodic table, the synthesis of (dicarbonyl) (h{dollar}sp5{dollar}-cyclopentadienyl) (1-methoxybenzocyclobutenoyl-1-carbonyl)ruthenium was attempted. Subsequent decarbonylation of this acyl complex was unsuccessful, therefore the carbene complex had to made by an alternative method. The migratory insertion reaction from the carbene complex to the alkyl could then be studied.; A new synthetic methodology was developed for the synthesis of (carbonyl) (h{dollar}sp5{dollar}-cyclopentadienyl) (1-methoxy)ruthenacyclopentene. This series of reactions represents a new approach to the preparation of these types of carbene complexes.; The carbene migratory insertion reaction was studied using PPh{dollar}sb3{dollar} and CO to trap the sixteen electron alkyl intermediate formed by the rearrangement. These experiments indicated that under the same conditions in which the iron analog was chosen to rearrange the ruthenium compound was unreactive. Labeling the carbene complex with deuterium and following the reaction in situ by NMR spectroscopy confirmed these results. An minimum activation energy of 32 kcal/mol was calculated for the migratory insertion reaction with the ruthenium carbene complex. This compares to a 20 kcal/mol activation barrier for the analogous iron complex. The differences in the energies for these reactions can be attributed to the respective M=C double bonds strengths. Going from iron to ruthenium, the bond strength has increased, therefore the energy requirements for rearrangement to occur are more demanding.; With this in mind, it was hoped we could observe the same trend by looking at carbene complexes with metal centers from the third row of the periodic table. Applying the new synthetic methodology to the preparation of (dicarbonyl) (h{dollar}sp5{dollar}-cyclopentadienyl) (1-methoxy)tungstacyclopentene was not successful due to unexpected side reactions. Although the preparation of the carbene complex was not successful, useful information was obtained concerning the limitations of the synthesis which will be helpful in selecting the appropriate metal ligand systems in the future.