COMPLEXES WITH 2 (ARENE)CHROMIUM TRICARBONYL MOIETIES SEPARATED BY RIGID SPACERS - PREPARATION, X-RAY STRUCTURES, AND OXIDATIVE VOLTAMMETRY

Chromium tricarbonyl complexes with arenes bonded to rigid polynorbornyl-type spacers [1], [2], and [3] (structures are given in the text) have been prepared. The dinuclear complexes, e.g., [1][Cr(CO)3]2, which is the bis(chromium tricarbonyl) derivative of ligand [1], all adopt an exo,exo configuration. The structures of [1][Cr(CO)3], [1][Cr(CO)3]2, and [3][Cr(CO)3]2.(CH3)2CO were determined by X-ray crystallography: for [1][Cr(CO)3], C18H12CrO3, triclinic, P1BAR, a = 8.143 (3) angstrom, b = 8.356 (4) angstrom, c = 11.116 (6) angstrom, alpha = 75.76 (4)-degrees, beta = 78.06 (3)-degrees, gamma = 87.060, V = 717.8 angstrom3, Z = 2, (R(F) = 3.40%; for [1][Cr(CO)3]2, C2lHl2Cr2O6, orthorhombic, P2(1)2(1)2(1), a = 8.090 (1) angstrom, b = 10.,568 (2) angstrom, c = 22.336 (3) angstrom, v = 1909.9 (5) angstrom3, Z = 4, R(F) = 4.47 %; for [3] [Cr(CO)3]2.(CH3)2CO, C32H28Cr2O6.C3H6O, Orthrohombic Pnma, a = 23.807 (10) angstrom, b = 10.568 (5) angstrom, c = 12.409 (5) angstrom, V = 3121 (2) angstrom3, Z = 4, R(F) = 5.38%. Oxidations of the new complexes were studied by cyclic voltammetry and controlled-potential coulometry and through reaction with tris(p-bromophenyl)ammoniumyl ion. Each dinuclear complex oxidizes by two electrons to a dication: in a single process for the complex of [31, within a single oxidation wave for that of [2], and in two resolved one-electron steps for [1][Cr(CO)3]2. The E-degrees separation of 140 mV for the last compound is large, considering that the two metals are separated by 6.48 angstrom. The interaction between the two redox sites is ascribed to efficient through-bond coupling through the bicyclic spacer. Some characterization of the cation radicals was accomplished by low-temperature IR and ESR studies.