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) m F] ([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.

Approaches to analytical and synthetic electrochemistry in fluorous solvent-containing media

“…NMR spectra were acquired using a Bruker ARX-500 NMR with d 6 -acetone as the solvent. Ferrocene (Strem) was sublimed and 1,1 0 -bis-1H,1H,2H,2H-perfluorooctyl-ferrocene, here symbolized as 1,1 0 bis[2.8]ferrocene, 2, was provided by Prof. Russell Hughes of Dartmouth College [17]. The fluorous-tailed triphenylphosphine derivative P[C 6 H 4 (CH 2 ) 2 (CF 2 ) 5 (CF 3 )] 3 was provided by Dr. Berth-Jan Deelman of Utrecht University [18].…”

“…The reported [17] electrochemical behavior of two fluorous-tailed ferrocene derivatives in organic solvents with [NBu 4 ][PF 6 ] as the supporting electrolyte provide a ready comparison for results on 2 in the fluorous medium. Without a medium change, the E 1/2 of 2 is expected to be within experimental error of the values reported for 1,1 0 bis[2.6]ferrocene and 1,1 0 bis[2.10]ferrocene (0.034 V and 0.038 V vs. Fc, respectively).…”

“…In light of the fact that the [ [17], the difference is unlikely to involve changes in the innersphere activation barrier of the ferrocenyl compound. Rather, a medium effect is implied.…”

Fluorous Organometallic Chemistry

“…2), the reaction of a metal cyclopentadienide with a perfluoroalkyl iodide, gave complicated mixtures of products with the desired perfluoroalkyl cyclopentadienes (I) produced in poor yields. In contrast, Hughes and Trujillo [82] adapted Månsson's methodology [83] through the reaction of nickelocene with the appropriate iodide in the presence of triphenylphosphine, to give a series of mixtures of the respective double bond isomers. The dienes with the fluorous ponytail directly attached demonstrated very different properties to those containing the short ethylene spacer unit.…”

Selective mono- and di{(perfluoroalkyl)acylation} of ferrocene

“…Hence, it is of general interest to develop methods for the preparation of new perfluoroalkylated cyclopentadienes and their complexes with a spacer inserted between the cyclopentadienyl ring and the perfluoroalkyl chain that would shield the cyclopentadienyl ring from the inductive effect of the perfluoroalkyl chain. There has been some progress achieved in the recent years in the development of methods for the preparation of (perfluoroalkyl)alkylated cyclopentadienes by alkylation of cyclopentadienes with R f CH 2 CH 2 I but these procedures has been usually plagued by relatively low yields and selectivity [3,4].…”