Selective Solubility of Organometallic Complexes in Saturated Fluorocarbons. Synthesis of Cyclopentadienyl Ligands with Fluorinated Ponytails

Abstract

Cyclopentadienes bearing varying length fluorinated “ponytails”, C5H5[(CH2)n(CF2)mF] ([n.m] = [0.8], [0.10], [0.12], [2.6], [2.8], and [2,10]) have been prepared by reaction of the corresponding fluoroalkyl iodides and triphenylphosphine with nickelocene. From these, the 1,1‘-bis[2.6]-, 1,1‘-bis[2.8]-, and 1,1‘-bis[2.10]-disubstituted ferrocenes and [2.10]-substituted [Mn(CO)3L], [Re(CO)3L], and [Co(CO)2L] derivatives (L = η5-C5H4[2.10]) were prepared. Although the anions of the [0.m] compounds were thermally unstable, the corresponding [0.8], [0.10], and [0.12] cobalt dicarbonyl complexes were prepared directly from the cyclopentadienes. The solubilities of these compounds in both saturated fluorocarbon (fluorous) and conventional solvents was found to depend strongly on the length of the fluoroalkyl tail and on the temperature. These compounds all dissolve in fluorous solvents, and the 1,1‘-bis[2.10]ferrocene partitions selectively into the fluorous layer of a biphasic perfluoro(methylcyclohexane)/toluene system. The oxidation potentials of the 1,1‘-, bis[2.6]-, and 1,1‘-bis[2.10]ferrocenes are only very slightly more positive than ferrocene itself, demonstrating that the C2H4 spacer effectively insulates the electron-withdrawing effect of the fluoroalkyl part of the ponytail from the metal. A similar insulating effect is noted in the carbonyl stretching frequencies of [Mn(CO)3L], [Re(CO)3L], and [Co(CO)2L] derivatives (L = η5-C5H4[2.10]), which are slightly to low energy of those in the corresponding parent cyclopentadienyl analogues. In contrast, the corresponding frequencies in [Co(CO)2L] derivatives (L = η5-C5H4[0.10]; η5-C5H4[0.12]) without the hydrocarbon spacer group are at higher energy than the parent compound.