Metallocene analogs with split (2+4)-.pi.-electron ligands
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After reaction of the split (2 + 4)-π-electron ligands bicyclo[3.2.1]octa-2,6-dien-4-yl (BCOD), bicyclo[3.2.2]nona-2,6,8-trien-4-yl (BCNT), and tricyclo[220.127.116.11 2,6 ]deca-3,8-dien-5-yl (DICP) anion with iron(II) and chromium(II) chloride the orange diamagnetic compounds (BCNT) 2 Fe (5), (BCOD) 2 Fe (11), (DICP)FeCp (16; Cp = cyclopentadienyl), and red paramagnetic (BCOD) 2 Cr (13) have been isolated. When the reactions were carried out in the presence of CpNa, the mixed-ligand species (BCNT)FeCp (7) and (BCOD)FeCp (12) were obtained, while (BCNT)-SnMe 3 and (CO) 5 MnBr gave (BCNT)Mn(CO) 3 (8) and (BCOD)K and Cp*Ni(acac) (Cp* = pentamethylcyclopentadienyl, acac = acetylacetonate) gave green diamagnetic (BCOD)NiCp* (14). The 1 H and 13 C NMR data, including 57 Fe- 13 C and 13 C- 13 C coupling constants for 16, were consistent with the bonding of both the olefin and the allyl part of BCOD, BCNT, and DICP to the metal, except for 14, which contains a Cp*Ni fragment bound in a η 3 fashion to the exo face of BCOD. Temperature-dependent magnetic measurements for 13 established two unpaired electrons per molecule and a close resemblance to chromocene. In cyclic voltammetry 5, 7, 11, and 16 underwent chemically reversible one-electron oxidations which occurred 0.23–0.26 or 0.53–0.56 V more negative than ferrocene, depending on whether one or both Cp's were replaced by split (2 + 4)-π-electron ligands. The Mössbauer spectrum of 16 showed an isomer shift and a quadrupole splitting which were smaller than previously known for ferrocenes. The X-ray crystal analysis of 11 confirmed the η 5 bonding of BCOD to iron and showed a gauche-eclipsed arrangement of the two ligands (orthorhombic, space group Fddd, a = 16.228(2) Å, b = 16.481 (2) Å, c = 17.016(2) Å, Z = 16, R w = 0.027 for 114 refined parameters and 951 unique structure factors). Comparison of the X-ray results of 11, 5, and 16 disclosed a strong, but similar, distortion of the split (2 + 4)-π-electron ligands: The two systems have moved together, the allyl plane is bent away from the metal up to 27°, and the olefinic and allylic protons are bent away from and toward the metal, respectively. © 1993, American Chemical Society. All rights reserved.
author list (cited authors)
Bluemel, J., Hertkorn, N., Kanellakopulos, B., Koehler, F. H., Lachmann, J., Mueller, G., & Wagner, F. E.