Synthesis and oxidation of dirhenium C-4, C-6, and C-8 complexes of the formula (eta(5)-C5Me5)Re(NO)(PR3)(C C)(n)(R3P)(ON)Re(eta(5)-C5Me5)(R=4-C6H4R ', c-C6H11): In search of dications and radical cations with enhanced stabilities
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abstract
The racemic methyl complexes (5-C5 Me5)Re(NO)(PR3)(CH3) (R: b, 4-C6H4CH3; c, 4-C6H4-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 HBF4OEt2/chlorobenze, HCCH or HCCCCSiMe3, and t-BuOK to give the alkynyl complexes (5-C5Me5)Re(NO) (PR3)(CCH) (3b,c) and (5-C5Me5)Re(NO)(PR3) (CCCCSiMe3) (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 -butadiynediyl complex (5-C5Me5)Re- (NO)(PR3)(CC)n(R3P)(ON)Re (5-C5Me5) (4b; n = 2) and analogous -hexatriynediyl (10b; n = 3) and -octatetraynediyl (9b-e; n = 4) species. Oxidation of 4b by AgSbF6 (ca. 1:1 or 1:2) gives the radical cation 4b+SbF6- or the dication 4b2+(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 -78C and could not be isolated or spectroscopically characterized.
