Heck, Jurgen; Lange, Gerhard; Malessa, Maik; Boese, Roland; Blaser, Dieter:

Cooperative effects in p-ligand bridged dinuclear complexes. Part XXI. Synfacially structured [(CpRu)2m-cot] - what a difference the coordination side makes!

In: Chemistry--A European Journal, Jg. 5 (1999) ; Nr. 2, S. 659-668
ISSN: 0947-6539
Zeitschriftenaufsatz / Fach: Chemie
By reaction of the neutral mononuclear complex [CpRu(1,2,3-h:6,7-h-C8H9)] (1) with [(C5R5)Ru(MeCN)3]PF6 (R = H, Me) the synfacial cationic m-cyclooctatetraene-m-hydridodiruthenium complexes [(CpRu){(C5R5)Ru}(m-H)(m-cot)]PF6 (cot = cyclooctatetraene; R = H: 2a; R = Me: 2b) are formed. Deprotonation of 2a and 2b with lithium diisopropylamide yields the synfacial homodinuclear complexes [(CpRu){(C5R5)Ru}m-cot] (R = H: 3a; R = Me: 3b). Cyclic voltammetry studies of 3a and 3b show two clearly sepd., electrochem. reversible one-electron redox waves 0/ + 1 and + 1/ + 2 (0/ + 1: E1/2(3a) = -0.79 V; E1/2 (3b) = -0.89 V; + 1/ + 2: E1/2 (3a) = -0.17 V; E1/2 (3b) = -0.27 V vs. [FeCp2]/[FeCp2]+). Chem. oxidn. of 3a with [FeCp2]+ affords the monocation [3a]+ and the dication [3a]2+, depending on the stoichiometry. X-ray structure detn. was performed on all dinuclear complexes. The complex 2a and the neutral complex 3a crystallize in the space groups Cmcm and P1, resp., and the monocationic species [3a]PF6 in the space group C2/c. The dication [3a]2+ crystallizes as the mixed salt [3a](BF4)(PF6) in the space group Pnma. In all the dinuclear complexes, the two metal centers are synfacially coordinated at the cot ligand. Complexes 2a and 3a show a h4:h4 bonding mode of the cot moiety, whereas, upon oxidn., the cot ligand in 3a changes its hapticity to h5:h5. Results from 1H NMR spectroscopic studies of 2a, 2b and [3a]2+ are in accordance with the crystallog. findings, in contrast to the neutral complex 3a, which shows a fast rotation of the cot entity even at 200 K. The Ru-Ru distances in the dinuclear complexes decrease dramatically from 307.8 pm in 2a to 266 pm in [3a]2+; complexes 3a and [3a]+ have Ru-Ru bond lengths of 295.6 and 282.2 pm, resp. The Ru-Ru interaction in 2a and 2b can best be described as a three-center, two-electron RuHRu bond, whereas in 3a and [3a]2+ a Ru-Ru single bond must be considered. For the paramagnetic complex cation [3a]+, a Ru-Ru s* semi-occupied MO is postulated based on EPR and UV/Vis spectroscopic results, which indicate that [3a]+ is a mixed-valent class III compd.