Electronic communication in homobimetallic anthracene-bridged, eta(5)-cyclopentadienyl derivatives of rhodium(I): Generation and characterization of the average-valence species [L2Rh{C5H4CH2(9,10-anthrylene)CH2C5H4}RhL2](+)

9,10-Bis(cyclopentadienylmethyl)anthracene (1) is obtained by reacting 9,10 -bis(bromo-methyl)anthracene with cyclopentadienylsodium and transformed in to its dithallium(I) derivative 3 on reaction with thallium ethoxide. The r eaction of 3 with the chloro derivatives of rhodium(I) of formula [RhClL2]( 2) (L = eta (2)-C2H4 or CO; L-2 = eta (4)-C7H8) leads to the corresponding bimetallic complexes [L2Rh{C5H4CH2(9,10-anthrylene)CH2C5H4}RhL2], 4 (L = et a (2)-C2H4), 5 (L = CO), and 6 (L-2 = eta (4)-C7H8), in 13, 22, and 55% yie lds, respectively. All complexes have been characterized by elemental analy sis, particle beam mass spectrometry, H-1 NMR, and FT-IR. The UV-vis spectr a (280-800 nm) of 4-6 are indicative of the existence of strong electronic interactions among the anthrylic chromophore and the two cyclopentadienylRh L(2) moieties. When excited at ca. 370 nm, 1 becomes an efficient light-emi tting molecule, while 4-6 are poorly luminescent compounds. The fluorescenc e spectra of all the complexes present the vibrational structure typical of the anthrylic fluorophore but have low intensity: 6, 3, and 15% of the one observed for 9-methylanthracene, taken as the reference compound, respecti vely for 4, 5, and 6. The study of the electrochemical behavior of 4-6 in s trictly aprotic conditions allows a satisfactory interpretation of the obse rved electrode processes and furnishes information about the location of th e redox sites along with the thermodynamic characterization of the correspo nding redox processes. These data show that the occurrence of an intramolec ular charge-transfer process between the photoexcited 9,10-anthrylenic moie ty and the cyclopentadienylRhL(2) unit is a possible route for the observed quenching of emission in the compounds 4-6. The one-electron oxidation of compounds 4-6 by thallium(III) trifluoroacetate in a 1:1 dichloromethane/1, 1,1,3,3,3-hexafluoropropan-2-ol mixture leads to the formation of the corre sponding radical cations [L2Rh{C5H4CH2(9,10-anthrylene)CH2C5H4}RhL2](+) Two of them, i.e., 4(+) (L = eta (2)-C2H4) and 5(+) (L = CO), give rise to hig hly resolved EPR spectra which allow one to describe such species as averag e-valence [Rh+1/2, Rh+1/2] complexes. DFT calculations of spin density dist ribution confirm the EPR results and allow a further insight into the struc ture of 4+ and 5. complexes.