Syntheses of cyclic imine complexes of the chiral rhenium Lewis acid [(ν5-C5H5) Re(NO)(PPh3)]+ by hydride ion abstraction from amido complexes
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Reactions of (η5-C5H5)Re(NO)(PPh3)(OTf) and the cyclic amines HNCH2CH2(CH2)n-4 give adducts [(η5-C5H5)-Re(NO)(PPh3)(HNCH2CH2CH2(CH2)n-4)]+ TfO-; (3a-e+ TfO-; n =a, 3; b, 4; c, 5; d, 6; e, 7) in 98-88% yields. Reactions of 3a-e+ TfO- and tBuO- K+ give the labile amido complexes (η5-C5H5)Re(NO)(PPh3) (NCH2CH2CH2(CH2)n-4) (4a-e), which are characterized in situ at -20°C. Subsequent reactions of 4b-e with Ph3C+ PF6-, and metatheses with NH+6, give the cyclic imine complexes [(η5-C5H5)Re(NO)(PPh3)(η1-NCHCH2CH2(CH2)n-4)]+ PF6- (5b-e+ PF6-). However, 5d,e+ PF6- are difficult or impossible to separate from byproducts (up to 30%). In order to circumvent these and other complications, 3a-e+ TfO- and NH4+ PF6- are first allowed to react to give 3a-e+ PF6-(94-76%). Additions of tBuO- K+ and then Ph3C+ PF6- give, under carefully optimized conditions, 5b-e+ PF6- of > 98% purities. All attempts to prepare the three-membered cyclic imine complex 5a+ PF6-, and phenyl-substituted analogs, are unsuccessful. The IR and NMR properties of the preceding compounds are analyzed in detail. © 1994.
author list (cited authors)
Cantrell, W. R., Richter-Addo, G. B., & Gladysz, J. A.