Boron -iodide

Coordination compounds of boron bromide and boron iodide. D. R. Martin, Chem. Rev., 1948,42, 581-599 (33). 

Ammino-boron Tri-iodides.—Boron iodide and ammonia unite with development of heat. If dry ammonia gas is passed into a solution of boron tri-iodide in carbon tetrachloride, cooled to 0° C., a white amorphous substance of composition BI3.5NH3 is formed,3 which turns brown on exposure to light and is decomposed by water. This compound is capable of absorbing more ammonia, being transformed into a liquid of composition BI3.15NH3, which is exceedingly unstable and rapidly loses ammonia on exposure to air. These derivatives also are most probably mixtures of ammonium iodide and boron triamide. 

Boron-carbon bonds can be formed by redox reactions between boron iodides and organic iodides, e.g. ... 

Carbon tetraiodide has been prepared by the interaction of carbon tetrachloride and various metallic iodides, such as aluminum iodide, boron iodide, calcium iodide, and lithium iodide. The procedure here described makes use of readily available materials and involves the reaction of carbon tetrachloride with ethyl iodide in the presence of aluminum chloride. ... 

A soln. of boron iodide in pentane added to a soln. of triphenylmethyl iodide in methylene chloride -> triphenylcarbonium iodoborate. Y 91%.—The above salt and tropenium iodoborate are the first characterized salts of this anion reported. K. M. Harmon and F. E. Gummings, Am. Soc. 87, 539 (1965). 

Boron tri-iodide, Blj (BClj plus HI at red heat or I2 plus NaBH ), m.p. 43°C, b.p. 2iO°C. It has very similar properties to boron trichloride. 

Boron sub-iodide, B2I4, is prepared by the action of an electrical discharge on BI vapour. 

The iodination reaction can also be conducted with iodine monochloride in the presence of sodium acetate (240) or iodine in the presence of water or methanolic sodium acetate (241). Under these mild conditions functionalized alkenes can be transformed into the corresponding iodides. AppHcation of B-alkyl-9-BBN derivatives in the chlorination and dark bromination reactions allows better utilization of alkyl groups (235,242). An indirect stereoselective procedure for the conversion of alkynes into (H)-1-ha1o-1-alkenes is based on the mercuration reaction of boronic acids followed by in situ bromination or iodination of the intermediate mercuric salts (243). 

Both ( )- and (Z)-l-halo-l-alkenes can be prepared by hydroboration of 1-alkynes or 1-halo-l-alkynes followed by halogenation of the intermediate boronic esters (244,245). Differences in the addition—elimination mechanisms operating in these reactions lead to the opposite configurations of iodides as compared to bromides and chlorides. 

Conversion to a more facile, sulfur-derived, leaving group can be achieved by treatment with sodium thiosulfate or salts of thio and dithio acids (75,87). Under anhydrous conditions, boron tribromide converts the 3 -acetoxy group to a bromide whereas trimethyl silyl iodide gives good yields of the 3 -iodide (87,171,172). These 3 -halides are much more reactive, even when the carboxyl group is esterified, and can be displaced readily by cyano and by oxygen nucleophiles (127). 

Methane sulfonic acid, trifluoroacetic acid, hydrogen iodide, and other Brmnsted acids can faciUtate 3 -acetoxy displacement (87,173). Displacement yields can also be enhanced by the addition of inorganic salts such as potassium thiocyanate and potassium iodide (174). Because initial displacement of the acetoxy by the added salt does not appear to occur, the role of these added salts is not clear. Under nonaqueous conditions, boron trifluoride complexes of ethers, alcohols, and acids also faciUtate displacement (87,175). 

BCl, BBr, and BI undergo exchange reactions to yield mixed boron hahdes. Exchange reactions also occur with trialkyl, triaryl, trialkoxy, or triaryloxy boranes and with diborane. Anhydrous metal bromides and iodides can be prepared by the exchange reaction of the metal chloride or oxide and BBr or BI (21)-... 

Boron triiodide rapidly cleaves methyl ethers of o-, m-, or / -substituted aromatic aldehydes (0°, 25° 0.5-5 min 40-86% yield)." BI3 complexed with A/,A-diethylaniline is similarly effective, but benzyl ethers are converted to the iodide... 

Ethyl-2-methyl-3-(10,11) -dihydro-5H-dibenzo [a,d] cycloheptene-5-ylidene)-1 -pyrrolinium iodide (4.7 g) was dissolved in 7 cc of methanol. To this solution there were added 1.4 g of sodium boron hydride within about 80 minutes with stirring and stirring of the solution was continued for two hours to complete the reaction. The reaction mixture was acidified with 10% aqueous hydrochloric acid solution and then the methanol was distilled off. The residual solution was alkalized with 20% aqueous sodium hydroxide solution and extracted with ether. The ether layer was dried over magnesium sulfate and the ether was distilled off. The resulting residue was further distilled under reduced pressure to yield 2.0 g of 1-ethyl-2-methyl-3-(10,11 ) dihydro-5H-dibenzo[a,d]cycloheptene-5-ylidene)pyrrolidine (boiling point 167°C/4 mm Hg.). 

The authors used a synthesis of 9,9-spirobitluorenes 32 which was developed by Clarksen and Gomberg [60] and which includes the addition of biphenyl-2-yl-magnesium iodide to fluorenone and subsequent cyclization with protic acids. To obtain 2,2,, 7,7 -arylated 9,9-spirobifluorenes 33, 9,9-spirobifluorene (32) was tetrabrominated [58] to yield 34 followed by a Suzuki-type aryl-aryl cross-coupling with various oligoaryl and oligoheteroaryl boronic acids to obtain the 2,2, 7,7 -tetraarylated derivatives 33. 

Fluoride ion, and weak acids and bases do not interfere, but nitrate, nitrite, perchlorate, thiocyanate, chromate, chlorate, iodide, and bromide do. Since analysis of almost all boron-containing compounds requires a preliminary treatment which ultimately results in an aqueous boric acid sample, this procedure may be regarded as a gravimetric determination of boron. 

For a-benzyloxycyclohexaneacelaldehyde and 2-butenylstannanes, good chelation control was observed using zinc iodide and titanium(IV) chloride, but only weak synjanti selectivity. Better syn/anti selectivity was found using boron trifluoride-diethyl ether complex, but weak chelation control. Magnesium bromide gave excellent chelation control and acceptable syn/anli selectivity90. 

This 1,2-asymmetric induction has been attributed to stcric and stcrcoclectronic factors. Similarly, the cuprate additions to 4-alkylcyclopentenones l7 -19, and 4-alkylcyclohexcnones16 b-18 proceeded with very high trans diastereoselection. The copper iodide catalyzed addition of propylmagnesium bromide to 4-methyl-2-cyclohexenone gave a trans/cis ratio of 80 20, whereas the addition to 5-methyl-2-cyclohexenone produced a transjcis ratio of 93 72 3-Silyloxy system 3 gave the trans-adduct 4 on treatment with butylcopper-boron trifluoride reagent20. 

The structurally simplest silicon reagent that has been used to reduce sulphoxides is the carbene analog, dimethylsilylene (Me2Si )29. This molecule was used as a mechanistic probe and did not appear to be useful synthetically. Other silanes that have been used to reduce sulphoxides include iodotrimethylsilane, which is selective but unstable, and chlorotrimethylsilane in the presence of sodium iodide, which is easy to use, but is unselective since it cleaves esters, lactones and ethers it also converts alcohols into iodides. To circumvent these complications, Olah30 has developed the use of methyltrichlorosilane, again in the presence of sodium iodide, in dry acetonitrile (equation 8). A standard range of sulphoxides was reduced under mild conditions, with yields between 80 and 95% and with a simple workup process. The mechanism for the reaction is probably very similar to that given in equation (6), if the tricoordinate boron atoms in this reaction scheme are replaced... 

Olefin metathesis of vinylboronates [102] and allylboronates [103, 104] has been investigated over the past few years because organoboranes are versatile intermediates for organic synthesis. Cross metathesis of vinylboronate 108 and 2-butene 109, for example, yields the boronate 110, which can be converted to the corresponding vinyl bromide 111 with high Z selectivity. Vinyl iodides can be obtained analogously. It should be noted that vinyl bromides and vinyl... 

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