CHEMISTRY

Corresponding Member of the Academy of Sciences of the USSR G. A. RAZUVAEV, V. N. LATYAEVA
and L. I. VYSHINSKAYA

REACTIONS OF BENZOYL PEROXIDE WITH TITANOCENE DERIVATIVES

In our previous work it was indicated that biscyclopentadienyltitanium, \( \mathrm{C}_2\mathrm{Ti} \) (\( \mathrm{C}=\mathrm{C}_5\mathrm{H}_5 \)), is formed during the thermal decomposition of biscyclopentadienyldiphenyltitanium in alcoholic and benzene solutions. \( \mathrm{C}_2\mathrm{Ti} \) is a highly reactive compound, readily reacting with metal halides and alkyl halides with formation of the stable dichloride of titanocene \((^1)\). It is especially necessary to note the extreme sensitivity of \( \mathrm{C}_2\mathrm{Ti} \) to atmospheric oxygen.

It therefore seemed of interest to us to trace the interaction of biscyclopentadienyltitanium with acyl peroxides, which readily cleave the \( \mathrm{O—O} \) bond and are donors of acyloxy radicals.

The action of benzoyl peroxide on sandwich compounds has been described only in one example, the reaction with ferrocene. Under comparatively mild conditions (in benzene solution at \(78^\circ\)) complete destruction of the sandwich structure occurs, with formation of iron tribenzoate. The cyclopentadienyl groups evidently polymerize to a high-molecular compound \((^2)\).

In our case, in the interaction of benzoyl peroxide with \( \mathrm{C}_2\mathrm{Ti} \) in the cold in benzene or isopropyl alcohol solution, decomposition of the titanocene group did not occur. An instantaneous change in the color of the solution from dark green to bright yellow was observed; \( \mathrm{CO}_2 \) was not evolved during the reaction. The yellow crystalline product obtained in an atmosphere of dry nitrogen was the expected biscyclopentadienyltitanium dibenzoate:

\[ \mathrm{C}_2\mathrm{Ti} + (\mathrm{C}_6\mathrm{H}_5\mathrm{COO})_2 \rightarrow \mathrm{C}_2\mathrm{Ti}(\mathrm{OCOC}_6\mathrm{H}_5)_2 . \]

For identification of the previously undescribed \( \mathrm{C}_2\mathrm{Ti}(\mathrm{OCOC}_6\mathrm{H}_5)_2 \), a counter synthesis was carried out from titanocene dichloride and silver benzoate:

\[ \mathrm{C}_2\mathrm{TiCl}_2 + 2\mathrm{C}_6\mathrm{H}_5\mathrm{COOAg} \rightarrow \mathrm{C}_2\mathrm{Ti}(\mathrm{OCOC}_6\mathrm{H}_5)_2 + 2\mathrm{AgCl}. \]

The biscyclopentadienyltitanium dibenzoate thus obtained was characterized by elemental analysis, determination of molecular weight, melting point, and content of benzoate groups (Table 1). \( \mathrm{C}_2\mathrm{Ti}(\mathrm{OCOC}_6\mathrm{H}_5)_2 \) hydrolyzes extremely readily with decomposition of the molecule of the titanocene salt and formation of cyclopentadiene, the salt of benzoic acid, and titanic acid:

\[ \mathrm{C}_2\mathrm{Ti}(\mathrm{OCOC}_6\mathrm{H}_5)_2 + 2\mathrm{NaOH} + \mathrm{H}_2\mathrm{O} \rightarrow 2\mathrm{CH} + 2\mathrm{C}_6\mathrm{H}_5\mathrm{COONa} + \mathrm{H}_2\mathrm{TiO}_3 . \]

Upon alcoholysis in absolute isopropyl alcohol, cyclopentadiene, acetone, and benzoic acid were detected among the reaction products. In an atmosphere of moist air the molecule of titanocene dibenzoate loses two moles of cyclopentadiene and can be converted into dibenzoxytitanoxide \((^3)\):

\[ \mathrm{C}_2\mathrm{Ti}(\mathrm{OCOC}_6\mathrm{H}_5)_2 \xrightarrow{\mathrm{H}_2\mathrm{O}} 2\mathrm{CH} + \mathrm{O—Ti}(\mathrm{OCOC}_6\mathrm{H}_5)_2 . \]

The isolated solid infusible product was characterized by elemental analysis, as well as by the content of benzoate groups.

An analogous representative of compounds of the type $Ц_2Ti(OCOR)_2$ was obtained in the example of the reaction of titanocene dichloride with silver acetate:

\[ Ц_2TiCl_2 + 2CH_3COOAg \to Ц_2Ti(OCOCH_3)_2 + 2AgCl. \]

The yellow compound formed in this reaction, with m.p. 127–130°, corresponds by elemental analysis to biscyclopentadienyltitanium diacetate.

Alcoholysis of this compound in absolute isopropyl alcohol proceeded with cleavage of the acetate groups and partial formation of cyclopentadiene. A yellow amorphous substance, insoluble in organic solvents, whose structure has not been established, precipitated. Acetone was found in the isopropyl alcohol solution. Hydrolysis with dilute alkali proceeded completely, with formation of cyclopentadiene, acetic acid, and titanic acid.

The preparation of biscyclopentadienyltitanium dibenzoate in the interaction of $Ц_2Ti$ with benzoyl peroxide shows that, in contrast to ferrocene, the structure of titanocene remains unchanged under the reaction conditions. Therefore it seemed of interest to trace the action of acyl peroxides on organometallic compounds of tetravalent titanium.

For this purpose, the reaction of diphenylbiscyclopentadienyltitanium with benzoyl peroxide was carried out. In this case also, under mild conditions (in isopropyl alcohol solution at room temperature), an interesting displacement of phenyl radicals by the acyloxy groups of the peroxide occurs:

\[ Ц_2Ti(C_6H_5)_2 + (C_6H_5COO)_2 + CH_3CH(OH)CH_3 \to \]

\[ \to Ц_2Ti(OCOC_6H_5)_2 + 2C_6H_6 + CH_3COCH_3, \]

with formation of biscyclopentadienyltitanium dibenzoate. The phenyl radicals are converted into benzene by dehydrogenation of the alcohol to acetone.

On comparing the IR spectra of biscyclopentadienyltitanium acetate and benzoate with the initial $Ц_2TiCl_2$ and $Ц_2Ti(C_6H_5)_2$, the following absorption bands were found (in reciprocal centimeters): $Ц_2Ti(C_6H_5)_2$ 448; 459; 606; 690; 720; 770; 822; 886; 930; 990; 1024; 1076; 1286; $Ц_2TiCl_2$ 769; 814; 828; 872; 880; 930; 960; 1018; $Ц_2Ti(OCOCH_3)_2$ 404; 520; 600; 624; 822; 865; 1024; $Ц_2Ti(OCOC_6H_5)_2$ 720; 830; 865; 1024; 1068; 1132. The absorption bands 822–830 and 1018–1024 cm$^{-1}$, characteristic of all the compounds, should be assigned to vibrations of the cyclopentadienyl ring. The absorption band 865 cm$^{-1}$, absent from the spectra of $Ц_2Ti(C_6H_5)_2$ and $Ц_2TiCl_2$, may be assigned to vibrations of the Ti—O bond.

Experimental Part

All operations for isolation of compounds $Ц_2Ti(OCOR)_2$, where R = CH$_3$, C$_6$H$_5$, were carried out in an atmosphere of dry nitrogen.

Reaction of $Ц_2Ti$ with benzoyl peroxide. To a strongly cooled benzene or alcohol solution of $Ц_2Ti$, obtained beforehand from 1.66 g (0.005 mole) of $Ц_2Ti(C_6H_5)_2$ in 10 ml of solvent, a solution of 1.2 g (0.005 mole) of $(C_6H_5COO)_2$ was added dropwise. A sharp change in color from dark green to bright yellow was observed. From the solution, 0.8 g (0.002 mole) of $Ц_2Ti(OCOC_6H_5)_2$ with m.p. 185° was isolated. A mixed sample with the substance prepared by independent synthesis melted at 186°.

On hydrolysis of 0.21 g (0.0005 mole) of $Ц_2Ti(OCOC_6H_5)_2$ with 0.1 N alkali, 0.12 g (0.001 mole) of benzoic acid with m.p. 120° was isolated.

Reaction of $Ц_2Ti(C_6H_5)_2$ with benzoyl peroxide in isopropyl alcohol. 2.5 g (0.0075 mole) of $Ц_2Ti(C_6H_5)_2$ and 1.82 g (0.0075 mole) of $(C_6H_5COO)_2$ in 25 ml of isopropyl alcohol were shaken

at room temperature for 50 h. The yellow precipitate of \(\mathrm{C}_2\mathrm{Ti}(\mathrm{OCOC}_6\mathrm{H}_5)_2\) that formed was filtered off: its weight was 1.5 g, m.p. 188°.

On hydrolysis of 0.2 g (0.0005 mole) of the substance, 0.12 g (0.001 mole) of benzoic acid, m.p. 121°, was isolated.

Benzene was isolated from the solution in the form of m-dinitrobenzene (0.3 g), m.p. 90°, and acetone in the form of 2,4-dinitrophenylhydrazone (0.2 g), m.p. 126°.

Preparation of \(\mathrm{C}_2\mathrm{Ti}(\mathrm{OCOC}_6\mathrm{H}_5)_2\). 3.0 g (0.012 mole) of \(\mathrm{C}_2\mathrm{TiCl}_2\) and 5.53 g (0.024 mole) of \(\mathrm{C}_6\mathrm{H}_5\mathrm{COOAg}\) in 60 ml of benzene were stirred at room temperature for 10–15 min. During this time the color of the solution changed from red to orange-yellow. On dilution of the solution with petroleum ether, 2.0 g (0.0047 mole) of \(\mathrm{C}_2\mathrm{Ti}(\mathrm{OCOC}_6\mathrm{H}_5)_2\), m.p. 188–192° (with decomposition), precipitated. The substance is readily soluble in benzene, methylene chloride, and chloroform; sparingly soluble in alcohols and petroleum ether. The data of elemental analysis, molecular weight, and hydrolysis for the content of benzoate groups are given in Table 1.

Alcoholysis of \(\mathrm{C}_2\mathrm{Ti}(\mathrm{OCOC}_6\mathrm{H}_5)_2\). On partial hydrolysis of \(\mathrm{C}_2\mathrm{Ti}(\mathrm{OCOC}_6\mathrm{H}_5)_2\), a yellow infusible substance was isolated.

\[ \text{Found, \%: }\quad \mathrm{C}\ 54.70;\quad \mathrm{H}\ 3.59;\quad \mathrm{Ti}\ 16.36 \]

\[ \mathrm{C}_{12}\mathrm{H}_{10}\mathrm{TiO}_5.\qquad \text{Calculated, \%: }\quad \mathrm{C}\ 54.90;\quad \mathrm{H}\ 3.26;\quad \mathrm{Ti}\ 15.70 \]

1.0 g of \(\mathrm{C}_2\mathrm{Ti}(\mathrm{OCOC}_6\mathrm{H}_5)_2\) (0.0024 mole), m.p. 188°, in 53 ml of isopropyl alcohol, under a stream of dry oxygen, was kept for 3 h at 0°. The reaction mixture was distilled. Acetone was identified in the distillate (by formation of the 2,4-dinitrophenylhydrazone) and cyclopentadiene by formation of \(\mathrm{C}_5\mathrm{H}_5\mathrm{Tl}\) with thallous reagent. 0.35 g (0.0013 mole) of \(\mathrm{C}_5\mathrm{H}_5\mathrm{Tl}\) was isolated.

Preparation of \(\mathrm{C}_2\mathrm{Ti}(\mathrm{OCOCH}_3)_2\). 2.5 g (0.010 mole) of \(\mathrm{C}_2\mathrm{TiCl}_2\) and 5.0 g (0.030 mole) of \(\mathrm{CH}_3\mathrm{COOAg}\) in 60 ml of benzene were stirred for 15–20 min at room temperature. Dilution with petroleum ether gave 0.7 g (0.0024 mole) of \(\mathrm{C}_2\mathrm{Ti}(\mathrm{OCOCH}_3)_2\), m.p. 127–130° (with decomposition). The substance is readily soluble in benzene, methylene chloride, chloroform, and isopropyl alcohol, and sparingly soluble in petroleum ether. In air it decomposes with liberation of acetic acid. The elemental-analysis data are given in Table 1.

Table 1

* Average values of concordant analytical results are given.

Alcoholysis of \(\mathrm{C}_2\mathrm{Ti}(\mathrm{OCOCH}_3)_2\). 0.88 g (0.003 mole) of \(\mathrm{C}_2\mathrm{Ti}(\mathrm{OCOCH}_3)_2\) in 20 ml of isopropyl alcohol, at room temperature under a stream of dry nitrogen, was kept for several hours. During this time a yellow infusible precipitate (0.32 g) separated from the solution. Found, %: C 43.47; H 6.36; Ti 27.87.

The substance is insoluble in organic solvents and is destroyed by the action of alkali.

In the solution, 0.005 mole of acetic acid was determined. In addition, 0.12 g of acetone 2,4-dinitrophenylhydrazone, m.p. 126°, and 0.2 g of \( \mathrm{C_5H_5Tl} \) were isolated.

On hydrolysis of 0.46 g (0.0015 mole) of \( \mathrm{L_2Ti(OCOCH_3)_2} \) with 0.1 \(N\) KOH, 0.0027 mole of acetic acid, 0.15 g of \( \mathrm{H_2TiO_3} \), and cyclopentadiene were determined.

The authors express their gratitude to T. V. Guseva for carrying out the elemental analysis.

Scientific Research Institute of Chemistry
at Gorky State University
named after N. I. Lobachevsky

Received
20 II 1961

REFERENCES

1. G. A. Razuvaev, V. N. Latyaeva, L. I. Vyshinskaya, DAN, 134, 612 (1960).
2. Posakker, RZhKhim., 1959, No. 22, 78502.
3. J. D. Varga, R. C. Mehrotra, J. Pract. Chem., 8, 64 (1959).