Halogens, reactions with metal alkoxide

The reactions of metal alkoxides with halogens were investigated by Nesmeyanov et al. who observed that the reaction between titanium tetra-n-butoxide and chlorine or bromine yielded the dihalide dibutoxide coordinated with one mole of alcohol as TiX2(OBu)2.BuOH and n-butyl propionate. The reaction may be represented by... 

Nearly all the methods described in Chapter 2 have been applied for the preparation of uranium derivatives. The reaction of metallic uranium with alcohols in the presence of halogenes (method 1) doesn t lead, as it turned out, to homoleptic alkoxides, but is a facile route to alkoxide halides [79, 1669] ... 

When halocyclopropanes react with an alkali metal alkoxide in an organic solvent, elimination-addition reactions take place and result in formation of alkoxycyclopropanes. In most cases the overall reaction can be regarded as a simple substitution of a halogen atom by an alkoxy group (see Section 5.2.1.1.11.2.2.), but in some cases a double substitution is observed. The latter reaction occurred when 6,6-dichloro-3-thiabicyclo[3.1.0]hexane was treated with potassium fcr/-butoxide and gave l-tcrt-butoxy-e r/o-6-chloro-3-thiabicyclo[3.1.0]hexane (1) in 68% yield. The reaction is believed to take place via a strained cyclopropene intermediate, which is trapped by nucleophilic attack of the ferr-butoxide or by reaction with furan if present.Other 1,1-dichlorocyclopropanes react analogously under similar conditions, 22-724 jjyj jien an excess of base is used, a second elimination-addition... 

Halogens react with sodium with varying degrees of vigor. Sodium forms alkoxides and alkali metals with alkyl halides (Wurtz reaction), which are heterogeneous and probably very complex (alkanes) (Klemm et al. 2000). 

Anhydrous halogen derivatives of metals can be converted into metal alkoxides via reaction with either alkali metal alkoxides or with alcohols in the presence of ammonia. The reaction is usually carried out in other solvents than alcohols (hydrocarbon or ether ones) on cooling and with the amoimts of alcohols only slightly exceeding the stoichiometry. The reason is that oxo-alkoxides or oxo-alkoxide halides can otherwise be formed as impurities. This approach can be used successfully for synthesis of, for example, alkoxides of Sn(IV) [87], Bi (III) [114], and Fe(III) [82] ... 

A number of compounds of the types RSbY2 and R2SbY, where Y is an anionic group other than halogen, have been prepared by the reaction of dihalo- or halostibines with lithium, sodium, or ammonium alkoxides (118,119), amides (120), azides (121), carboxylates (122), dithiocarbamates (123), mercaptides (124,125), or phenoxides (118). Dihalo- and halostibines can also be converted to compounds in which an antimony is linked to a main group (126) or transition metal (127). 

Halogen-substituted arene chromium tricarbonyl complexes undergo nucleophilic substitution by alkoxide ions at a considerably enhanced rate over the free arene 39, 327, 444). The effect of the chromium tricarbonyl moiety on the rate of substitution of the arene is approximately equal to that of a -nitro group (39). Treatment of ethylbenzene chromium tricarbonyl with fcrf-butyl lithium followed by hydrolysis and decomposition of the resulting complexes with Ce(IV) yielded m- and p-ethyl-tcrt-butylbenzene along with some unsubstituted ethylbenzene (55). The reaction represents a novel nucleophilic displacement of a hydride ion and contrasts with the metalation reaction observed with w-butyl lithium (304). 

In the nickel(ll)-catalyzed NHK reaction, the first step is the reduction of Ni " to Ni that inserts into the halogen-carbon bond via an oxidative addition. The organonickel species transmetallates with Cr " to form the organochromium(lll) nucleophile, which then reacts with the carbonyl compound. To make the process environmentally benign, a chromium-catalyzed version was developed where a chlorosilane was used as an additive to silylate the chromium alkoxide species in order to release the metal salt from the product. The released Cr " is reduced to Cr " with manganese powder. 

---