Configurational equilibria in amido and lithioamido complexes of formulas ({eta}{sup 5}-C{sub 5}H{sub 5})Re(NO)(PAr{sub 3})(NHCHRR`) and ({eta}{sup 5}-C{sub 5}H{sub 5})Re(NO)(PAr{sub 3})(NLiR``): Epimerization occurs at rhenium via phosphine dissociation
- Univ. of Utah, Salt Lake City, UT (United States)
The diastereometrically and enantiomerically pure amido complex (SR)-({eta}{sup 5}-C{sub 5}H{sub 5})Re(NO)(PPh{sub 3})(NHCH(CH{sub 3}) Ph) ((SR)-5) converts to (RR)-5 (inversion at rhenium, retention at carbon) in THF-d{sub 8} at 49.4{degree}C with k{sub 1} = 2.34 x 10{sup -4}s{sup -1} and k{sub -1} = 0.90 x 10{sup -4} s{sup -1}. Similarly, (SS)-5 converts to (RS)-5 with k{sub 1} = 0.90 x 10{sup -4}s{sup -1} and k{sub -1} = 2.30 x 10{sup -4}s{sup -1}. Both epimerizations give equilibrium ratios (RR/SR or SS/RS) of 70:30. Enantiomeric purities and absolute configurations are assayed by chiral NMR shift reagents and (-)-menthyl chloroformate derivatives, respectively, establishing configurations of epimerized 5. The results are best modeled by mechanisms involving initial and rate determining PPh{sub 3} dissociation, with anchimeric assistance by the amido lone pair, to give an intermediate that is trigonal planar at rhenium and combines with PAr{sub 3} without significant diastereoselectivity. Reactions of n-BuLi with 5 and related complexes give NLiR species from which PPh{sub 3} is lost at lower temperatures, and are presumed to be much less configurationally stable. 40 refs., 8 figs., 1 tab.
- OSTI ID:
- 420750
- Journal Information:
- Organometallics, Journal Name: Organometallics Journal Issue: 22 Vol. 15; ISSN ORGND7; ISSN 0276-7333
- Country of Publication:
- United States
- Language:
- English
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