ORGANOMETALLIC COMPLEXES WITH ELECTRONIC BRIDGES .7. ELECTROCHEMICAL, SPECTROSCOPIC, AND STRUCTURAL STUDIES OF MONOMETALLIC AND BIMETALLIC COMPLEXES OF IRON - X-RAY CRYSTAL-STRUCTURES OF CPFE(CO)2-C6F5, 4-CPFE(CO)2-C5F4N, AND 1,4-C6F4(CPFE(CO)2)2

The oxidative electrochemical behavior of 18 mono- and bimetallic complexes in which (eta(5)-C5H5)Fe(CO)2 (F(p)) groups are sigma-bound to arene and azine rings has been determined by cyclic voltammetry (CH2Cl2, n-Bu4NPF6, Pt electrodes) and is described. The oxidation potentials and reversibilities of these compounds are found to be very dependent on the structures of the aromatic ligands. In particular, it was found that the addition of fluorine substituents increased both the oxidation potentials and chemical reversibilities for the aryl complexes, as did the substitution of a nitrogen atom for a C-X group in the aromatic ring. For the bimetallic arene-bridged complexes, the perhydro derivatives (i.e. 1,3- and 1,4-C6H4Fp2) show low chemical reversibilities, while the fluorinated bimetallics (i.e. 1,3- and 1,4-C6F4Fp2) are reversibly oxidized in two sequential one-electron steps with separation between their first and second oxidations (i.e. DELTA-E1/2 = \E-degrees' +1/+2 - E-degrees' 0/+1\) of 280 and 200 mV for the para- and meta-substituted complexes, respectively. This is indicative of substantial long-range metal-metal electronic coupling in these compounds. The first oxidations for these complexes are much more chemically and electrochemically reversible than are the second oxidations, which are accompanied by complex electrode/electrolyte interactions. For the azine complexes, we find that those species having the Fp substituents ortho to a nitrogen atom are irreversibly oxidized at scan rates of up to 10 V s-1, while the para-substituted halopyridine complexes show excellent chemical reversibilities. The X-ray crystal structures of the title complexes CpFe(CO)2-C6F5, (C13H5F5FeO2; a = 6.993 (2) angstrom, b = 12.774 (4) angstrom, c = 13.649 (3) angstrom, V = 1219 angstrom 3; orthorhombic; Pnma; Z = 4), 4-CpFe(CO)2-C5F4N, (C12H5F4FeNO2; a = 6.948 (1) angstrom, b = 12.828 (1) angstrom, c = 13.000 (1) angstrom, V = 1159 angstrom, V = 1159 angstrom 3; orthorhombic; Pnma; Z = 4), and 1,4-C6F4(CpFe(CO)2)2 (C20H10F4Fe2O4; a = 7.714 (1) angstrom, b = 9.840 (1) angstrom, c = 12.473 (1) angstrom, beta = 107.822 (7)-degrees, V = 901 angstrom 3, monoclinic; P2(1)/c; Z = 2) have been determined. In each case, the CpFe(CO)2 group is oriented such that its mirror plane (complexes 6 and 10) or pseudo mirror plane (complex 3) is perpendicular to the arene or azine ring rather than parallel to it as predicted by molecular orbital arguments. It is suggested that these unexpected orientations minimize unfavorable steric interactions between the o-fluorine substituents on the aromatic groups and the H atoms on the C5H5 group of Fp.