ORGANOTRANSITION-METAL METALLACARBORANES .37. PARAMAGNETIC IRON-COBALT AND DICOBALT TRIPLE-DECKER SANDWICH COMPLEXES

A series of 2,3-C2B3-bridged iron-cobalt and dicobalt triple-decker co mplexes having Cp or Cp end rings was examined in detail via several techniques, including correlated H-1 and C-13 NMR spectra, which allow complete assignment of the resonances of paramagnetic species. The 29 valence electron (ve) complexes CpFe(Et(2)C(2)B(3)H(2)-5-R)CoCp* (1a , R = H; 1b, R = Cl; 1c, R = Br) were prepared from nido-CpCo(Et(2)C( 2)B(3)H(4)-5-R) by bridge-deprotonation and treatment with (CpFeCl)(2 ) and examined by cyclic voltammetry, ESR, and Mossbauer spectra and N MR correlation experiments. In the latter studies, paramagnetic neutra l species were progressively reduced to the diamagnetic monoanions 1a( -)-1c(-) via repeated contact with a potassium mirror in the NMR tube or oxidized to the diamagnetic cations by treatment with AgBF4. The da ta consistently support a model in which the unpaired electron in the neutral species 1a is primarily associated with Fe; in the paramagneti c 31 ve dianion 1a(2-), the unpaired electron resides mainly on cobalt . Correlated H-1 and C-13 NMR studies on the mixed-ligand 29 ve FeCo c omplex CpFe(Et(2)C(2)B(3)H(3))CoCp (2) and the diamagnetic 30 ve dico balt complexes CpCo(R'2C2B3H3)COCP* (3a, R' = Et; 3b, R' = Me; 3c, R' = H) and CpCo(Et(2)C(2)B(3)H(3))CoCp (4), together with their associ ated cationic and anionic species, afforded additional information on the electronic structures of these systems. The preparation and spectr oscopic characterization of the new complexes 1a-1c, 2, 3a, and 3a(-) are reported, as well as X-ray crystal structure determinations on a K (THF)(crown ether)(+) salt of 3a(-) acid neutral 4. Crystal data for [ K(THF)(crown ether)(+)][3a(-)]: Co2KO7C42B3H75, space group P2(1)2(1)2 (1) (orthorhombic); a = 15.252(14), b = 15.54(2), c = 20.25(2) Angstro m; Z = 4; R = 0.046 for 6641 independent reflections. Crystal data for 4: Co2C21B3H33, space group P2(1)/c (monoclinic); a = 8.694(4), b = 2 1.049(11), c = 11.870(8) Angstrom; beta = 101.15(4) Angstrom; Z = 4; R = 0.039 for 4653 independent reflections.