METALLOCENE ANALOGS WITH SPLIT (2+4)-PI-ELECTRON LIGANDS
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After reaction of the split (2 + 4)--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[5.2.1.0 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 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 0.230.26 or 0.530.56 V more negative than ferrocene, depending on whether one or both Cp's were replaced by split (2 + 4)--electron ligands. The Mssbauer 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 5 bonding of BCOD to iron and showed a gauche-eclipsed arrangement of the two ligands (orthorhombic, space group Fddd, a = 16.228(2) , b = 16.481 (2) , c = 17.016(2) , 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)--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.
