Reactions of Tris(oxazolinyl)phenylborato Rhodium(I) with C−X (X = Cl, Br, OTf) Bonds: Stereoselective Intermolecular Oxidative Addition

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2010-08-25
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Ho, Hung-An
Dunne, James
Ellern, Arkady
Sadow, Aaron
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Ames National Laboratory

Ames National Laboratory is a government-owned, contractor-operated national laboratory of the U.S. Department of Energy (DOE), operated by and located on the campus of Iowa State University in Ames, Iowa.

For more than 70 years, the Ames National Laboratory has successfully partnered with Iowa State University, and is unique among the 17 DOE laboratories in that it is physically located on the campus of a major research university. Many of the scientists and administrators at the Laboratory also hold faculty positions at the University and the Laboratory has access to both undergraduate and graduate student talent.

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The Department of Chemistry was founded in 1880.

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Abstract

The achiral and enantiopure chiral compounds ToMRh(CO)2 (3) and ToPRh(CO)2 (4) (ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate; ToP = tris(4S-isopropyl-2-oxazolinyl)phenylborate) were prepared to investigate stereoselective oxidative addition reactions and develop new catalytic enantioselective bond functionalization and cross-coupling chemistry. Reactivity at the rhodium center is first shown by the substitution of the carbonyl ligands in 3 and 4 in the presence of the appropriate ligand; thus treatment of ToMRh(CO)2 with P(OMe)3 provides ToMRh(CO)[P(OMe)3] (5). However, reaction of ToMRh(CO)2 and MeOTf (Tf = SO2CF3) affords the complex [{N-Me-κ2-ToM}Rh(CO)2]OTf (6), resulting from N-oxazoline methylation rather than oxidative addition to rhodium(I). In contrast, ToMRh(CO)2 reacts with allyl bromide and chloroform, forming the rhodium(III) species (κ3-ToM)Rh(η1-C3H5)Br(CO) (7) and (κ3-ToM)Rh(CHCl2)Cl(CO) (8), respectively. Interestingly, the chiral ToPRh(CO)2 and CHCl3 react to give one diastereomer of (κ3-ToP)Rh(CHCl2)Cl(CO) (9; 100:3 dr) almost exclusively. To evaluate the reactivity of these rhodium(I) compounds, the carbonyl stretching frequencies have been examined. The data for the mono- and trivalent rhodium oxazolinylborate compounds indicate that the electron-donating ability of [ToM]− is slightly greater than that of [ToP]−, and both ligands provide electronic environments that can be compared to the tris(pyrazolyl)borate ligand family.

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Reprinted (adapted) with permission from Organometallics 29 (2010): 4105, doi: 10.1021/om100515u. Copyright 2010 American Chemical Society.

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Fri Jan 01 00:00:00 UTC 2010
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