Consanguineous Families of Coordinated Carbon: A ReC₄Re Assembly That Is Isolable in Three Oxidation States, Including Crystallographically Characterized ReC⋮CC⋮CRe and+ReCCCCRe+Adducts and a Radical Cation in Which Charge Is Delocalized between Rhenium Termini

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Abstract

Reaction of (η5-C5Me5)Re(NO)(PPh3)(C⋮CH) and Cu(OAc)2 (1.5 equiv, 80 °C, pyridine) gives the orange-brown ReC4Re complex (η5-C5Me5)Re(NO)(PPh3)(C⋮CC⋮C)(Ph3P)(ON)Re(η5-C5Me5) (2, 88%) as a 50:50 diastereomer mixture. Crystallization affords (SS,RR)-2·2CH2Cl2 and solutions enriched in (SR,RS)-2 (meso). Addition of Ag+PF6- (≥2 equiv) yields deep blue (SS,RR)- and (SR,RS)-22+2PF6- (86%), which give two geometric isomers (62:38, 89:11; CD2Cl2, −93 °C) about the +ReCCCCRe+ linkages. Crystal structures of (SS,RR)-2·2CH2Cl2 and (SS,RR)-22+2PF6- show ReC4Re units with bond angles (169−178°) and lengths (C⋮C, 1.202(7); C−C 1.398(5); CC 1.260−1.305(10) Å) near those of butadiyne or cumulenes. Natural bond order analysis and topological electron density calculations confirm the valence formulations. Reactions of (SS,RR)-2 with (SS,RR)-22+2PF6- or Ag+PF6- (1 equiv) give a green radical cation (SS,RR)-2•+PF6- (μ = 1.74 μB; Faraday method). E° data yield a Kc value of 1.1 × 109 (CH2Cl2, 22.5 °C) for the comproportionation. ESR spectra show undecets with Aiso,Re values (98 G) half those of related monorhenium radical cations, indicating spin delocalization over two rheniums (I = 5/2). Accordingly, IR spectra give only one υNO band, positioned between those of 2 and 22+2PF6- (CH2Cl2, 1665 vs 1623/1719 cm-1). Near IR spectra show unique solvent-independent bands (883, 1000, 1200 nm; ε 15000, 9400, 3200 M-1 cm-1). Sodium naphthalenide reduces (SS,RR)- or (SR,RS)-2•+PF6- to (SS,RR)- or (SR, RS)-2, establishing configurational stability. These and related data are analyzed in detail.

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