[252554-72-6]  · C20H25OP  · (MW 312.39)

(monophosphine ligand for asymmetric catalysis;1 nickel(II) complexes are effective catalyst precursors for enantioselective hydrovinylation with non-coordinating counterions)

Solubility: soluble in THF, diethyl ether, hydrocarbons, and chlorinated solvents.

Analysis of Reagent Purity: 1H NMR, 13C NMR, 31P NMR, and GLC analysis.

Preparative Methods: prepared by the reaction of potassium dianion of 2-(benzyloxymethyl)phenylphosphane1 and (2S,5S)-hexane-2,5-diol cyclic sulfate. The preparation of the latter reagent is described in the literature.2

Purification: by column chromatography under an inert atmosphere.

Handling, Storage, and Precautions: readily oxidizes to the phospholane oxide upon exposure to atmospheric oxygen. The corresponding (allyl)Ni(BARF) complex is stable upon storage at room temperature for several days under a nitrogen atmosphere.

Asymmetric Hydrovinylation

Heterodimerization of olefins is a reaction of enormous synthetic potential, since it has been demonstrated that excellent yields and selectivities can be achieved under exceptionally mild conditions in many cases (2, 1).3,4 In 2, the catalytically active species is thought to be [Ni-H]+ generated via b-hydride elimination from a nickel precursor. In this reaction, the steric environment provided by ligand as well as the appropriate positioning of possible hemilabile coordinating group (OR) in the ligand are critical factors in yield, regioselectivity, and enantioselectivity.

Effect of Counterions on the Hydrovinylation

In the hydrovinylation of styrene using a ligand with a hemilabile atom (e.g. OBn in 1a, 1b), the choice of appropriate counter anion is very important. For example, when 2 and a weakly coordinating anion such as AgOTf is used in the reaction of styrene, the yield of hydrovinylation product is 94%. However, with phospholane ligands having a hemilabile coordinating group (-OR), the externally added coordinating anion (AgOTf) suppresses the reaction, while a non-coordinating anion (NaBAr4, Ar = 3,5-(CF3)2C6H3) completely restores the activity and selectivity (2).1

1. Nandi, M.; Jin, J.; RajanBabu, T. V., JACS 1999, 121, 9899.
2. Burk, M. J., JACS 1991, 113, 8518.
3. (a) Jolly, P. W.; Wilke, G., In Applied Homogeneous Catalysis with Organometallic Compounds, Cornils, B. and Herrmann, W. A., Eds; VCH: New York, 1996; p. 1024-1048. (b) RajanBabu, T. V.; Nomura, N.; Jin, J.; Radetich, B.; Park, H.; Nandi, M., Chem. Eu. J. 1999, 5, 1963.
4. Nomura, N.; Jin, J.; Park, H.; RajanBabu, T. V., JACS 1998, 120, 459.

Seunghoon Shin & T. V. RajanBabu

The Ohio State University, Columbus, Ohio, USA

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