Bis(oxazolinyl)phenylrhodium(III) Aqua Complexes:  Synthesis, Structure, Enantioselective Allylation of Aldehydes, and Mechanistic Studies

Yukihiro Motoyama, Masanori Okano, Hiroki Narusawa, Nobuyuki Makihara, Katsuyuki Aoki, and Hisao Nishiyama*
School of Materials Science, Toyohashi University of Technology, Tempaku-cho, Toyohashi, Aichi 441-8580, Japan
Organometallics, 2001, 20 (8), pp 1580–1591
DOI: 10.1021/om010018y
Publication Date (Web): March 22, 2001
Copyright © 2001 American Chemical Society
*

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

Abstract

Abstract Image

The reaction of (Phebox)SnMe3 (4; Phebox = 2,6-bis(oxazolinyl)phenyl) and [(cyclooctene)2RhCl]2 in the presence of CCl4 provided the air-stable and water-tolerant (Phebox)RhCl2(H2O) complexes 5. These neutral (noncationic) aqua complexes 5 acted as asymmetric catalysts for enantioselective allylation of aldehydes with allyltin reagents in the presence of 4 Å molecular sieves (MS 4A). Furthermore, these aqua complexes could be recovered quantitatively from the reaction media. Detailed mechanistic studies of this catalytic system using X-ray and NMR spectroscopy revealed that the (Phebox)RhCl2 fragment, generated by releasing H2O from aqua complex 5, is an active catalyst and the reaction proceeds by a Lewis acid catalyzed mechanism. The relative stereochemistry of the major adduct of the reaction of benzaldehyde with crotyltin reagents was anti (threo). The observed anti diastereoselectivity and si-face attack of allyltins on the carbonyl carbon of aldehydes were explained by the inverse antiperiplanar transition-state model.

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History

  • Published In Issue April 16, 2001
  • Received January 9, 2001

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