Consanguineous families of coordinated carbon: A ReC4Re assembly that is isolable in three oxidation states, including crystallographically characterized ReC CC CRe and Re-+=C=C=C=C=Re+ adducts and a radical cation in which charge is delocalized between rhenium termini
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Reaction of (5-C5Me5)Re(NO)(PPh3)(C CH) and Cu(OAc)2 (1.5 equiv, 80 C, pyridine) gives the orange-brown ReC4Re complex (5-C5Me5)Re(NO)(PPh3)(C CC C)(Ph3P)(ON)Re(5-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 +Re = C = C = C = C = Re+ 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); C = C 1.260-1.305(10) ) 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- ( = 1.74 (B); Faraday method). Edata yield a K(c) value of 1.1 x 109 (CH2Cl2, 22.5 C) for the comproportionation. ESR spectra show undecets with A(iso,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 (NO) 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; 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.
