Catalytic olefin cyclopropanation and oxidation using (salen)iron(III) complexes

(Salen)iron(III) complexes were developed and investigated for their use as group-transfer catalysts for olefin cyclopropanation and oxidation reactions. A series of air-stable mu-oxo-bis[(salen)iron(III)] complexes and (salen)iron(III) chloride were synthesized, characterized, and found to be efficient olefin cyclopropanation catalysts. The catalytic activity of the (mu-oxo)-dimers, in the cyclopropanation of styrene with ethyl diazoacetate (EDA), was examined as a function of the diamine backbone and the substituents in the 3, 3' and 5, 5' positions of the phenyl rings on the ligands. Solvent variation, catalyst loading, and styrene concentration were investigated to determine the optimal reaction conditions to obtain the highest cyclopropane yields. Complex [Fe(3,3 ',5,5'-tBu 4salen)]2O was identified as the most efficient catalyst in the series (85% EDA-styrene cyclopropane yield). We were also able to successfully cyclopropanate various internal (19%--28% cyclopropane yields) and terminal olefins (72%--97% cyclopropane yields) with EDA and other diazo carbene sources.;(Salen)iron(III) complexes were the first iron-based catalysts that were capable of cycloproponating internal olefins with EDA as the carbene source. In contrast to many existing catalytic systems where olefin formation from the dimerization of the diazoester carbene source is a major side reaction, this non-productive coupling was not observed for our system when terminal olefins were used. Additionally, unlike other iron-based cyclopropanation catalysis, our system did not require an inert atmosphere during the catalysis.;Detailed mechanistic investigations and supporting kinetic studies were also carried out to better understand the mode of operation of (salen)iron(III) catalysts. Based on these studies, we proposed a mechanistic model with (salen)iron(II) as the active species for our catalytic system. Using this knowledge, we attempted to reduce several (salen)iron(III) catalysts in situ so that the catalytic cyclopropanation reactions could be carried out under ambient room temperature and yield better stereoselectivity. A variety of reducing agents were screened for this purpose and Super-Hydride was gauged as the most effective reductant yielding cyclopropanes at room temperature and with higher enantioselectivity when used in conjunction with a chiral (salen)iron(III) catalyst.;Since the utility of (salen)iron(III) catalysts in carbene-transfer reactions was successfully demonstrated, we extended the scope to other group transfer reactions. Several investigations were also carried out to assess the feasibility of these catalysts for several other transformations such as olefin epoxidation and oxidative cleavage.