Triphenylmethyl tetrafluoroborate

C. 7 ricar6oni/Z[( 1,2,3,4,5-jj)-l-and 2-methoxy-2,4 -cydohexadien-l-yl]-irminimum volume of dichloromethane and 18 g. (0.072 mole) of tricarbonyl (1- and 2-methoxy-l,3-cyclohexadiene)iron dissolved in a like volume of dichloromethane is added. The resulting dark solution is left for 20-30 minutes and then added with stirring to three times its volume of ether (Note 21). The precipitate is collected and washed with ether to 5ueld 21-22 g. (87-91%) of product as yellow solid (Note 19). 

Harris et al. (3) used triphenylmethyl tetrafluoroborate to prepare the polypyridinium salt, (I), which was a stable conducting polymer when doped with TCNQ dianions. 

The parent system is prepared by oxidation of tetrahydrothiopyran with triphenylmethane and perchloric acid (66HCA2046) in high yield, and the method is applicable to the preparation of virtually all simple alkyl or aryl derivatives. In more complex cases, especially where the strong acid might cause elimination or isomerization side reactions, triphenylmethyl tetrafluoroborate may be used with the thiin precursor (equation 113) (78CL723). 

Although tricarbonylbutadieneiron (1) was prepared by Reihlen et a/.1 in 1930, some considerable time passed before the corresponding cyclohexadiene complex (2 equation 1) was reported.2 Fischer and Fischer described the conversion of (2) to the cationic cyclohexadienyliron complex (3 equation 1) by reaction with triphenylmethyl tetrafluoroborate in dichloromethane.3 This particular complex is extremely easy to prepare and isolate as the hydride abstraction reaction proceeds the product (3) crystallizes out. Precipitation is completed by pouring the reaction mixture into wet diethyl ether, the small amount of water present serving to destroy any excess triphenylmethyl tetrafluoroborate by conversion to triphe-nylmethanol. Filtration, followed by washing the residue with ether, gives pure dienyl complex. 

The 1,3-dioxolane and 1,3-dioxane systems are stable to an extremely wide range of reaction procedures provided that an acidic medium is avoided. Deprotection is effected under a wide variety of mild acid conditions such as, for example, aqueous tartaric acid,134 perchloric acid,135 or moist silica gel either alone or in the presence of oxalic or sulphuric acids.136 The mild oxidative cleavage reaction with triphenylmethyl tetrafluoroborate in dichloromethane is... 

In l,6,6aA4-trithiapentalenes or in l-oxa-6,6aA4-dithiapentalenes having a 3,4-propano bridge, triphenylmethyl tetrafluoroborate oxidizes the cyclohexane ring to a benzene ring with formation of a cation (7lAHC(l3)l6l,p. 198). 

Dienes are generally much less reactive when coordinated to transition metals than when in an uncoordinated state. An important discovery was thus made by Fischer and Fischer (86) in 1960 when they found that cyclo-hexadiene-iron tricarbonyl (XV) (formed from 1,3-cyclohexadiene and iron pentacarbonyl) undergoes hydride ion abstraction by triphenylmethyl tetrafluoroborate to form 7r-cyclohexadienyl-iron tricarbonyl tetra-fluoroborate (XVI) ... 

Although Able et al. (2, 8) had originally set out to prepare 7r-cyclo-heptatrienyl complexes of metals, the cycloheptatriene complexes they actually obtained served as key intermediates in forming the former complexes. In 1958 Dauben and Honnen (61) reported that cycloheptatriene-molybdenum tricarbonyl reacted with triphenylmethyl tetrafluoroborate in methylene chloride solution with abstraction of hydride ion from the molybdenum complex. The reaction products, obtained in nearly quantitative yields, were triphenylmethane and the 7r-cycloheptatrienyl complex [(7r-C7H7)Mo(CO)3]+BF4 . 

Because of the ready conversion of benzylidene acetals to acyloxonium ions, A-bromosuccinimide is not the only reagent used for effecting these types of reactions. In fact, Lewis acids may be used. In one example, illustrated in Scheme 6.25, triphenylmethyl tetrafluoroborate provides a convenient means of generating an acyloxonium ion in preparation for the introduction of a bromide [49]. As a final note, we should recognize that although the Hanessian-Hullar reaction depends on A-bromosuccinimide as both the ionizing and nucleophile... 

The benzodithiole (165) reacted with the indole derivative (166) in acetic acid to form the substitution products (167) (Scheme 35) <80BCJ166l>. Consecutive treatment of (167 R = H) with triphenylmethyl tetrafluoroborate and triethylamine afforded the dibenzo-l,4-dithia-6-azafulvalene (168) <80BCJ1661>. 

An effective route to the parent cation (33) using Meerwein s reagent, borohydride reduction followed by reaction with triphenylmethyl tetrafluoroborate is illustrative (Scheme 6) <86ZC138>. 

Triphenylmethyl tetrafluoroborate in methylene dichloride has a shift of +1-55 and is not affected by addition of tetrabutylammonium fluoride. Potassium tetrafluoroborate dissolved in liquid hydrogen fluoride at — 5°C had a shift of +T81, whereas boron trifluoride in... 

Similar hydride transfer reactions are possible for certain complex alkyls, where conversion into the olefin complex can be achieved by abstraction of H by triphenylmethyl tetrafluoroborate ... 

---