Transition metal catalyzed alkene isomerization is a relatively simple concept involving the atom economical migration of carbon-carbon double bonds. Challenges to be met include achieving high positional and stereochemical selectivity, substrate tolerance and ease of catalyst use. Bifunctional catalyst 1a  developed in the Grotjahn lab provides exceptional reactivity and selectivity for movement of alkene double bonds. On a cationic CpRu fragment, a bifunctional imidazolylphosphine is thought to deprotonate coordinated alkene intermediates reversibly, facilitating isomerization between terminal and (E)-alkenes and accelerating conversions by factors of up to 1 � 104.1This catalyst offers exceptional stereocontrol to yield (E)-alkenes but positional control required certain substrate structure.In order to gain positional control, the effect of increased steric hindrance at the phosphorus, and C4 position of imidazole, was investigated with a series of imidazolylphosphines, where R1 (Cy, tBu, Ad) and R2 (tBu, Ad) were varied. Giving five new ligands and catalysts. Alkene isomerization with CpRu complexes (1b-f ) of these ligands will be discussed.Turning to the Cp ligand, modification to Cp* (C5Me5), the challenge to control of carbon-carbon double bond position and the cis/trans selectivity in isomerization of terminal alkenes to 2-alkenes have been both met with Cp*Ru complexes that bear an imidazolylphosphine  and acetonitrile(s). Catalyst comprising 2a  and 2b  can be used in 1 mol % loading to yield (E)-2-alkenes in excess of 95% with E/Z ratios >99.2 1. D. B. Grotjahn, C. R. Larsen, J. L. Gustafson, R. Nair, and A. Sharma J. Am. Chem. Soc., 2007 , 129, 9592.2. C.R. Larsen, G. Erdogan and D. B. Grotjahn J. Am. Chem. Soc., 2014 , 136, 1226.

Studies towards stereo- and regiocontrolled catalytic alkene isomerization

248th National Meeting (2014)

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