METALLOCENE ANALOGS WITH SPLIT (2-PI-ELECTRON LIGANDS(4))

After reaction of the split (2 + 4)-pi-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) 2Fe (5), (BCOD)2Fe (11), (DICP)FeCp (16; Cp = cyclopentadienyl), and r ed paramagnetic (BCOD)2Cr (13) have been isolated. When the reactions were carried out in the presence of CpNa, the mixed-ligand species (BC NT)FeCp (7) and (BCOD)FeCp (12) were obtained, while (BCNT)SnMe3 and ( CO)5MnBr gave (BCNT)Mn(CO)3 (8) and (BCOD)K and CpNi(acac) (Cp* = pen tamethylcyclopentadienyl, acac = acetylacetonate) gave green diamagnet ic (BCOD)NiCp (14). The H-1 and C-13 NMR data, including Fe-57-C-13 a nd C-13-C-13 coupling constants for 16, were consistent with the bondi ng of both the olefin and the allyl part of BCOD, BCNT, and DICP to th e metal, except for 14, which contains a CpNi fragment bound in a eta 3 fashion to the exo face of BCOD. Temperature-dependent magnetic meas urements for 13 established two unpaired electrons per molecule and a close resemblance to chromocene. In cyclic voltammetry 5, 7, 11, and 1 6 underwent chemically reversible one-electron oxidations which occurr ed 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)-pi-electron l igands. The Mossbauer spectrum of 16 showed an isomer shift and a quad rupole splitting which were smaller than previously known for ferrocen es. The X-ray crystal analysis of 11 confirmed the eta5 bonding of BCO D to iron and showed a gauche-eclipsed arrangement of the two ligands (orthorhombic, space group Fddd, a = 16.228(2) angstrom, b = 16.481(2) angstrom, c = 17.016(2) angstrom, z = 16, R(w) = 0.027 for 114 refine d parameters and 951 unique structure factors). Comparison of the X-ra y results of 11, 5, and 16 disclosed a strong, but similar, distortion of the split (2 + 4)-pi-electron ligands: The two systems have moved together, the allyl plane is bent away from the metal up to 27-degrees , and the olefinic and allylic protons are bent away from and toward t he metal, respectively.