Synthesis and Oxidation of Dirhenium C4, C6, and C8Complexes of the Formula (η5-C5Me5)Re(NO)(PR3)(C⋮C)n(R3P)(ON)Re(η5-C5Me5) (R = 4-C6H4R‘, c-C6H11): In Search of Dications and Radical Cations with Enhanced Stabilities

The racemic methyl complexes (η 5 -C 5 Me 5 )Re(NO)(PR 3 )(CH 3 ) (R: b, 4-C 6 H 4 CH 3; c, 4-C 6 H 4 - t -C 4 H 9; d, 4-C 6 H 4 C 6 H 5; e, c-C 6 H 11 ), which feature phosphines that are more electron rich and/or bulkier than P(C 6 H 5 ) 3, are elaborated by reactions with HBF 4 ·OEt 2 /chlorobenzene, HC⋮CH or HC⋮CC⋮CSiMe 3, and t- BuOK to give the alkynyl complexes (η 5 -C 5 Me 5 )Re(NO)(PR 3 )(C⋮CH) ( 3b, c ) and (η 5 -C 5 Me 5 )Re(NO)(PR 3 )(C⋮CC⋮CSiMe 3 ) ( 7b − e ). The latter are converted (K 2 CO 3 /MeOH or wet n -Bu 4 N + F - ) to butadiynyl complexes ( 8b − e ). Homo- or cross-couplings ( 3b, 8b − e; Cu(OAc) 2 /pyridine) lead to the μ-butadiynediyl complex (η 5 -C 5 Me 5 )Re(NO)(PR 3 )(C⋮C) n (R 3 P)(ON)Re(η 5 -C 5 Me 5 ) ( 4b; n = 2) and analogous μ-hexatriynediyl ( 10b; n = 3) and μ-octatetraynediyl ( 9b − e; n = 4) species. Oxidation of 4b by AgSbF 6 (ca. 1:1 or 1:2) gives the radical cation 4b • + SbF 6 - or the dication 4b 2+ (SbF 6 - ) 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(C 6 H 5 ) 3 analogues. However, these longer chain systems decompose rapidly at −78 °C and could not be isolated or spectroscopically characterized.