Title

Transannular coupling reactions of 1,6-cyclodecadiyne and synthesis and characterization of pentamethylcyclopentadienyliron complexes with unsaturated hydrocarbon bridges

Date of Award

1997

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

Michael B. Sponsler

Keywords

Transannular coupling, Pentamethylcyclopentadienyliron, Unsaturated hydrocarbon bridges

Subject Categories

Organic Chemistry

Abstract

Iodine and bromine were discovered to be readily added to 1,6-cyclodecadiyne to regioselectively form transannular coupling products 1,5-diiodo-2,3,4,6,7,8-hexahydronaphthalene and the dibromo derivative respectively. Solvent-incorporation products were observed in the addition of iodine when the reaction was done in benzene, chlorobenzene, or methanol. Silver nitrate-assisted iodination of the cyclodiyne in methanol gave 1-iodo-5-methoxy-2,3,4,6,7,8-hexahydronaphthlene as a major product. Acid-catalyzed transannular hydration of the diyne led to a facile formation of 3,4,5,6,7,8-hexahydronaphthalene-1(2H)-one. A cyclic iodonium ion and a vinyl cation were proposed as intermediates in the iodination reaction pathway based on the controlled mechanistic studies. The diyne is also very reactive to 16-electron cationic iron complexes, white the diene diiodide can oxidatively add to tetrakis(triphenyl)palladiun complex.

Pentamethylcyclopentadienyl dicarbonyl iron anion Fp$\sp*$K reacted with cis-3,4-dichlorocyclobutene, producing ring-closed compounds, trans-3-chloro-4- (Cp$\sp*$(CO)$\sb2$Fe) -cyclobutene and (Cp$\sp*$(CO)$\sb2$Fe) $\sb2$-($\mu$-trans-3,4-cyclobutenediyl), and ring-opened compounds, (Cp$\sp*$(CO)$\sb2$Fe) -(CH=CH-CH=CCl) and (Cp$\sp*$(CO)$\sb2$Fe) $\sb2$-($\mu$-CH=CH-CH=CH), each isolated independently under different conditions. The closed-ring complexes underwent electrocyclic ring opening reactions to form the ring-opened complexes in quantitative yields. Photochemical reactions of (Cp$\sp*$(CO)$\sb2$Fe) $\sb2$-($\mu$-CH=CH-CH=CH) with $\eta\sp2$-bis(diphenylphosphino)ethane produced the pentamethylcyclopentadienyl butadiene-bridged diiron complex (Cp$\sp*$($\eta\sp2$-dppe)Fe) $\sb2$-($\mu$-CH=CH-CH=CH), which was characterized in its three oxidation state (neutral, cation, and dication). The X-ray structure of the neutral form was also determined.

The cyclic voltammogram of (Cp$\sp*(\eta\sp2$-dppe)Fe) $\sb2$-($\mu$-CH=CH-CH=CH) showed two single-electron reversible oxidation waves separated by 0.60 V. A large comproportionation constant ($1.42\times10\sp{10}$) was determined for the formation of radical cation complex ($\{$Cp$\sp*(\eta$-dppe)Fe$\}\sb2$-($\mu$ -CH=CH-CH=CH)) (PF$\sb6$). Mossbauer spectra characterize the radical cation and dication complex ($\{$Cp$\sp*(\eta\sp2$-dppe)Fe$\}\sb2$-($ \mu$-CH=CH-CH=CH)) (PF$\sb6\rbrack\sb2$ as isovalent complexes. Electronic spectra of the radical cation showed a narrow band at 505 nm from metal-ligand charge transfer and a strong broad solvent-independent band at 1427 nm assigned as an "intervalence transition", characteristic of mixed-valence complexes. The radical cation is classified as a nontrapped delocalized Robin-Day Class III mixed-valence complex with an effective coupling parameter, V$\rm\sb{ab}$ = 0.43 eV.

Instead of forming the expected $\mu$-$\rm C\sb2H\sb2$ olefin-bridged heterodinuclear complexes, reactions of iron acetylide Cp$\sp*$(dppe)Fe-C$\equiv$CH with hydrozirconium chloride, diisobutyl-aluminum hydride, and catecholborane led to the formation of C$\sb2$-bridged complexes Cp$\sp*$(dppe)Fe-C$\equiv$C-ZrClCp$\sb2$, Cp$\sp*$(dppe)Fe-C$\equiv$CAl$\rm\sp{i}$Bu$\sb2$, and Cp$\sp*$(dppe)Fe-C$\equiv$C-Bcat, respectively in high yields with the release of hydrogen gas as a by-product. A two-electron three-center mechanism is proposed for these reactions. Reaction of the iron acetylide with dimethylaminotrimethyltin gave the condensed product Cp$\sp*$(dppe)Fe-C$\equiv$C-SnMe$\sb3$ in quantitative yield.

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