REDOX-INDUCED ETA(5)DOUBLE-LEFT-RIGHT-ARROW-ETA(3) HAPTOTROPY OF THE FLUORENYL LIGAND IN 9-SUBSTITUTED ETA(5)-FLUORENYLMANGANESETRICARBONYLCOMPLEXES

It has been shown by cyclic voltammetry in THF within the -90 to 40 de grees C temperature range that fluorenyl (eta(5)-9-R-C13H8)Mn(CO)(3) c omplexes (R = Bu(t) (3) and Ph (4)) undergo two-electron reduction to form allyl type [(eta(3)-9-R-C13H8)Mn(CO)(3)](2-) dianions as final pr oducts. At low temperatures complexes 3 and 4 are reduced in two one-e lectron steps according to tie EEC scheme. The first step is reversibl e and corresponds to the formation of 19 (e) over bar-radical anions 3 (-.) and 4(-.). The E(0) values for redox pairs 3(0/-.) and 4(0/-.) ar e -1.88 and -1.73 V, respectively. The further reduction of radical an ions 3(-.) and 4(-.) at more negative potentials is accompanied by fas t eta(5) --> eta(3) haptocoordination of the fluorenyl ligand to form 18 (e) over bar-dianions [(eta(3)-9-R-C13H8)Mn(CO)(3)](2-). These dian ions obtained by the reduction of complexes 3 and 4 by the radical ani on of pyrene are stable at -80 degrees C and are characterized by thei r IR spectra. At room temperature the eta(5) double left right arrow e ta(3) hapticity change is a fast and reversible process occurring at t he step of 19 (e) over bar-radical anions 3(-.) and 4(-.) and leading to the electron deficient 17 (e) over bar-species [(eta(3)-9-R-C13H8)M n(CO)(3)](-.), which are reduced easier than the initial complexes. As a result, complexes 3 and 4 are reduced to the corresponding dianions [(eta(3)-9-R-C13H8)Mn(CO)(3)](2-) at room temperature in one reversib le two-electron step according to the ECE-scheme. Reactivities of 19 ( e) over bar-species of the isomeric eta(5)- and eta(6)-fluorenylmangan esetricarbonyl complexes are compared.