CHEMISTRY

Academician A. N. NESMEYANOV, V. A. SAZONOVA, V. N. DROZD

REPLACEMENT OF HALOGEN IN BROMOFERROCENE BY AROMATIC AND HETEROCYCLIC RADICALS

As was shown in our laboratory, tetraphenylborocuprate pyridinate can be used for the phenylation of $\alpha,\beta$-unsaturated carbonyl compounds ($^1$). Studying halogen exchange in haloferrocenes in the presence of copper ions, we found that tetraphenylborocuprate pyridinate arylates bromoferrocene, with replacement of bromine by phenyl, at $130^\circ$, forming phenylferrocene.

\[ \mathrm{C_5H_5FeC_5H_4Br} \ \xrightarrow{\mathrm{CuB(C_6H_5)_4}}\ \mathrm{C_5H_5FeC_5H_4{-}C_6H_5}. \]

The reaction is accompanied by reduction of bromoferrocene to ferrocene and by the formation of a number of by-products—diferrocenyl and, probably, polyarylated ferrocenes, which were not studied in detail. It is more convenient to carry out the reaction using not pyridinate $\mathrm{CuB(C_6H_5)_4}$, but a mixture of $(\mathrm{C_6H_5})_4\mathrm{BK}$ ($^2$) and $\mathrm{Cu_2Br_2}$, which has almost no effect on the yield of phenylferrocene.

We applied this method to the preparation of $n$-tolylferrocene, as well as heterocyclylferrocenes, which cannot be obtained by the most commonly used method for the synthesis of arylferrocenes—arylation of ferrocene with aryldiazonium salts ($^{3,4}$). We succeeded in obtaining $\alpha$-thienylferrocene and N-indolylferrocene in yields of 81% and 35%, respectively, by heating bromoferrocene with a mixture of tetra-($\alpha$-thienyl)boropotassium ($^5$) and $\mathrm{Cu_2Br_2}$ and tetra-(indolyl-1)-boropotassium ($^6$) with $\mathrm{Cu_2Br_2}$ at $130^\circ$.

\[ \mathrm{C_5H_5FeC_5H_4Br} + \mathrm{KB}\left(\text{\(\alpha\)-thienyl}\right)_4 \ \xrightarrow{\mathrm{Cu_2Br_2}}\ \text{\(\alpha\)-thienylferrocene} \]

\[ \mathrm{C_5H_5FeC_5H_4Br} + \mathrm{KB}\left(\text{indolyl-1}\right)_4 \ \xrightarrow{\mathrm{Cu_2Br_2}}\ \text{N-indolylferrocene} \]

N-Pyrrylferrocene is formed in 17% yield upon heating bromoferrocene with a mixture of sodium pyrrole and $\mathrm{Cu_2Br_2}$.

\[ \mathrm{C_5H_5FeC_5H_4Br} + \text{sodium pyrrole} \ \xrightarrow{\mathrm{Cu_2Br_2}}\ \text{N-pyrrylferrocene} \]

The absence in the IR spectra of N-indolylferrocene and N-pyrrylferrocene of an absorption band at $3400$–$3440\ \mathrm{cm^{-1}}$, characteristic of the NH bond of the pyrrole ring, confirms their structure as N-substituted compounds.

Copper phenylacetylide reacts with bromoferrocene in boiling dimethylformamide, forming ferrocenylphenylacetylene.

Experimental Section

Phenylferrocene. a) A mixture of 0.3 g of bromoferrocene and 1.8 g of tetraphenylborocuprate pyridinate is heated under nitrogen at $125$–$130^\circ$ for 30 min; the reaction mixture is cooled and washed with ether. The ethereal sol-

The solution is washed with water, 10% $H_2SO_4$, again with water, dried over $MgSO_4$, the ether is distilled off, and the residue is chromatographed on $Al_2O_3$ in heptane: first a mixture of ferrocene and bromoferrocene is eluted, and then 0.17 g (57% of theory) of phenylferrocene, m.p. 110–111° (from alcohol), is obtained. Literature data: m.p. 110–111° (⁴). Other reaction products were not investigated.

b) A mixture of 0.2 g of bromoferrocene, 0.54 g of potassium tetraphenylborate, and 0.22 g of $Cu_2Br_2$, moistened with 0.8 ml of pyridine, is heated under nitrogen at 125–130° for 30 min. After analogous work-up, 0.11 g (56% of theory) of phenylferrocene, m.p. 110–111° (from alcohol), is obtained.

$p$-Tolylferrocene. In an analogous manner, from 0.2 g of bromoferrocene, 0.45 g of tetra-$p$-tolylsodium borate (⁷), and 0.17 g of $Cu_2Br_2$, 0.11 g (53% of theory) of $p$-tolylferrocene is obtained, m.p. 138–139° (from alcohol). Literature data: m.p. 139–140° (³).

$\alpha$-Thienylferrocene. In an analogous manner, from a mixture of 0.4 g of bromoferrocene, 0.65 g of tetra-($\alpha$-thienyl)potassium borate, and 0.25 g of $Cu_2Br_2$, moistened with 0.6 ml of pyridine, 0.32 g (81% of theory) of $\alpha$-thienylferrocene is obtained, m.p. 116.5–117.5° (from alcohol).

Found, %: C 62.85, 62.64; H 4.74, 4.56; Fe 20.80, 20.71; S 11.89, 11.94
$C_{14}H_{12}FeS$. Calculated, %: C 62.70; H 4.51; Fe 20.83; S 11.96

N-Pyrrylferrocene. A mixture of 0.5 g of bromoferrocene, 0.78 g of sodium pyrrolide, and 1.10 g of $Cu_2Br_2$ is heated under nitrogen at 120° for 30 min. The reaction mixture is cooled and washed with hot benzene. After distilling off the benzene, the residue is chromatographed on $Al_2O_3$; heptane first elutes 0.10 g of ferrocene, then a mixture of N-pyrrylferrocene and diferrocenyl, and then 0.15 g of diferrocenyl, which is better eluted with benzene. N-Pyrrylferrocene cannot be separated from diferrocenyl by chromatography on $Al_2O_3$ because of their close $R_f$ values; but after sublimation at 90°/13 mm, 0.08 g (17% of theory) of N-pyrrylferrocene is obtained, m.p. 83–83.5° (from alcohol).

Found, %: C 67.15, 67.28; H 5.39, 5.42; Fe 22.48, 22.50; N 5.50, 5.65
$C_{14}H_{13}FeN$. Calculated, %: C 66.96; H 5.22; Fe 22.24; N 5.58

N-Indolylferrocene. In an analogous manner to the first three experiments, from a mixture of 0.80 g of bromoferrocene, 1.60 g of tetra-(indolyl-1)potassium borate, and 0.56 g of $Cu_2Br_2$, moistened with 1.4 ml of pyridine, 0.32 g (35% of theory) of N-indolylferrocene is obtained, m.p. 89–90° (from alcohol).

Found, %: C 72.16, 71.93; H 5.08, 5.15; Fe 18.48, 18.31; N 4.79, 4.71
$C_{18}H_{15}FeN$. Calculated, %: C 71.78; H 5.02; Fe 18.55; N 4.65

Ferrocenylphenylacetylene. To a solution of 0.5 g of bromoferrocene in 10 ml of dimethylformamide, 1 g of copper phenylacetylide is added, and the mixture is boiled under nitrogen on an oil bath for 3 h. After cooling, the reaction mixture is diluted with water and filtered; the precipitate on the filter is washed with ether. The ether extracts are washed with 10% $H_2SO_4$, water, 10% KOH, water, and dried over $MgSO_4$. After removal of the ether, the residue is chromatographed on $Al_2O_3$ in heptane; first a mixture of bromoferrocene and ferrocene is eluted, and then ferrocenylphenylacetylene. Yield 0.26 g (48% of theory), m.p. 126–127° (from alcohol).

Found, %: C 75.34, 75.67; H 4.96, 5.08; Fe 19.47, 19.24
$C_{18}H_{14}Fe$. Calculated, %: C 75.55; H 4.93; Fe 19.52

Moscow State University
named after M. V. Lomonosov

Received
20 VII 1963

CITED LITERATURE

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