[COSTRIBCTIOSFROM
THE PLASTICS
LABORATORY OF P R I S C E T O S
UNIVERSITP, P R I S C E l O N ,
s.J . ]
Alkylation of Ferrocene with a-Aryl Alcohols1 BY EBERHARD LV. NEUSEAND DANIELS.TRIFAN RECEIVEDAUGUST l i , 1961
A smooth condensation reaction can be achieved between ferrocene and secondary and tertiary aryl- and aryl-alkylcarbinols to give the corresponding aralkylferrocene derivatives in good t o excellent yields T h e condensations are conducted in the melt phase, using strong Lewis acids a s catalysts a t concentrations substantially lower t h a n for usual Friedel-Crafts reactions. T h e principal formation of either t h e mono- or disubstituted derivative is determined b y t h e reactant ratio Reduced reactivity and yield trends are observed with decreasingly aryl-substituted carbinols Relatively inert behavior is found for t-butyl alcohol and other aliphatic alcohols or deactivated monoaryl-alkylcarbinols under these reaction conditions.
Introduction densing ferrocene with the correspondingly subAs part of a general investigation of the self- stituted carbinols in the melt phase. As catalysts, condensation reactions of ferrocenylcarbinols lead- strong Lewis acids were used, anhydrous aluminum ing to polymeric products,2 it became of interest chloride being the most suitable compound. The to undertake the related study of the formation of concentrations required ranged from 3 to 20%12 aralkylferrocene derivatives via condensation re- and, hence, were substantially lower than comactions of benzenoid carbinols with the ferrocene monly applied in Friedel-Crafts reactions. In nucleus. To date only three ferrocene derivatives general, the reaction was found to be favored by bearing aralkyl substituents have been described increased temperature, but to minimize side rein the literature : triphenylmethylferrocene, 1,lI- actions and risk of partial decomposition, the syndiben~hydrylferrocene~-~ and 1,lt-di-(2-phenyl-2- theses were conducted a t the lowest temperatures propyl: -ferrocene.6 Kone of these was prepared required to obtain a homogeneous melt of the reby direct substitution on the ferrocene rings, their actants (usually 100-140'). For work-up, the Lyntheses all following multi-step reaction courses reaction products were extracted with appropriate with low-to-moderate over-all yields. The lack solvents and further isolated and purified by of data on direct substitution reactions in ferrocene chromatography or recrystallization. With the proper choice of the reactant ratio, chemistry is not surprising in view of the unfavorable course of the Friedel-Crafts reaction with the conversion could be directed toward the prinferrocene using alkyl or aryl halides as compared cipal formation of the monosubstituted or disubto acid chlorides and anhydrides. JlThile the latter stituted derivative. For the former, an excess of reactants give rapid, high-yield reactions with ferrocene proved necessary since, a t equimolar referrocene, the former were first considered as un- actant ratio, a tendency toward the siinultaneous feasible in this until more successful attempts formation of disubstituted products was always were reported by Nesmeyanov and c~-workers.g-~~observed. However, even here, mixtures of several alkylation The structural assignments of the condensation products were obtained requiring difficult separation products were based on elemental and infrared methods, and the yields of the individual substitu- analysis. M'herever feasible, they were corrobotion products were low, making this procedure rated by comparison with compounds reported in rather unsatisfactory for preparative purposes. the literature. Infrared analysis was also applied I t has now been found that under the proper to determine or corroborate the substitution reaction conditions, secondary and tertiary CY- scheme in the di-substituted derivatives, utilizing aralkylferrocene derivatives can be prepared by the fact that two strong bands near 9 and 10 p are direct substitution in good to excellent yields. characteristic of the presence of a t least one unThis work is described in the present paper. substituted ring in the ferrocene m ~ l e c u l e . ' ~This criterion, commonly referred to as the "'3-10 p Results and Discussion rule," has been successfully applied by numerous Synthesis of the above-mentioned aralkylfer- authors in discriminating between homo- and heterorocene compounds was brought about by con- annular substitution. 4 a 314--17 However, apparellt exceptions are known involving certain heteroan(1) This research was supported in part b y the Army. S a v y a n d Air nularly disubstituted compounds which exhibit Forre under Signal Corps Contract DA-039sc-78103. ( 2 ) In preparation. one or both of the 9 p and 10 I* bands.18 Therefore, l:C A S.Nesmeyanov a n d E. G. Perevalova, DokJady A k a d . .Yaiik .7 R . . 119, 288 (1958) ( 4 ) (a1 P 1.. Pauson, J . A m . C h e m SOC.,76, 2187 (19341; (11) I
