Synthesis and oxidation of dirhenium C4, C6, and C8 complexes of the formula (η5-C5Me5)Re(NO)(PR3)(CC)n(R3P)(ON)Re(η5-C5Me5)(R=4-C6H4R′, c-C6H11):: In search of dications and radical cations with enhanced stabilities

he racemic methyl complexes (eta (5)-C5Me5)Re(NO)(PR3)(CH3) (R: b, 4-C6H4CH3; c, 4-C(6)H(4)t-C4H9; d, 4-C6H4C6H5; e, c-C6H11), which feature phosphines that are more electron rich and/or bulkier than P(C6H5)(3), are elaborated by reactions with HBF4. OEt2/chlorobenzene, HC drop CH or HC drop CC drop CSiMe3, and t-BuOK to give the alkynyl complexes (eta (5)-C5Me5)Re(NO)(PR3)(C drop CH) (3b,c) and (eta (5)-C5Me5)Re(NO)(PR3)(C drop CC drop CSiMe3) (7b-e). The latter are converted (K2CO3/MeOH or wet n-Bu4N+F-) to butadiynyl complexes (8b-e). Homo- or cross-couplings (3b, 8b-e; Cu(OAc)(2)/pyridine) lead to the mu -butadiynediyl complex (eta (5)-C5Me5)Re(No)(PR3)(C C)(n)(R3P)(ON)Re(eta (5)-C5Me5) (4b; n = 2) and analogous mu -hexatriynediyl (10b; n = 3) and mu -octatetraynediyl (9b-e; n = 4) species. Oxidation of 4b by AgSbF6 (ca. 1:1 or :2) gives the radical cation 4b(.+)SbF(6)(-) or the dication 4b(2+)(SbF6-)(2). These isolable compounds exhibit delocalized mixed-valence and cumulenic electronic ground states, respectively. The cyclic voltammograms of 9b-e and 10b show oxidations to analogous species, with much better chemical reversibilities than for the P(C6H5)(3) analogues. However, these longer chain systems decompose rapidly at -78 degreesC and could not be isolated or spectroscopically characterized.