Synthesis and oxidation of chiral rhenium phosphine methyl complexes of the formula (η5-C5Me5)Re(NO)(PR3)(CH3): in search of radical cations with enhanced kinetic stabilities
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Reactions of racemic [(η5-C5Me5)Re(NO)(NCCH 3)(CO)]+ BF-4 and phosphines PR3 (R = C6H5 a; 4-C6H4CH3 b; 4-C6H4-t-C4H9 c; 4-C6H4C6H5 d; 4-C6H4OCH3 e; C-C6H11 f) give the phosphine carbonyl complexes [(η5-C5Me5)Re(NO)(PR3)(CO)] + BF-4 (5a-5f+ BF-4; 55-95%). These are treated with LiEt3BH and then BH3·THF to give the phosphine methyl complexes (η5-C5Me5)Re(NO)(PR3)(CH 3) (2a-2f, 50-86%). Cyclic voltammetry shows that the new compounds 2b-2f undergo chemically reversible one-electron oxidations that are thermodynamically more favorable than that of 2a (ΔE○ = 0.07, 0.07, 0.01, 0.09, 0.22 V; CH2Cl2). The radical cations 2•+ X- can be generated with Ag+ X- or (η5-C5H5)2Fe•+ X- (X- = PF-6, SbF-6), as evidenced by IR and ESR spectra, but are labile and efforts to isolate pure salts fail. Reaction of 2a and TCNE give (η5-C5Me5)Re(NO)(η 2-TCNE)(CH3), which is crystallographically characterized and proposed to form by initial electron transfer followed by radical chain substitution. © 2000 Elsevier Science B.V. All rights reserved.
author list (cited authors)
Meyer, W. E., Amoroso, A. J., Jaeger, M., Le Bras, J., Wong, W., & Gladysz, J. A.