Bismuthine oxides

Tris(4-methylphenyl)bismuthine (0.482 g, 1 mmol) was added to a suspension of freshly prepared iodosobenzene (0.286 g, 1.3 mmol) in dry dichloromethane (30 ml) and the resulting mixture was sonicated at 35°C under argon on a commercial ultrasonic washing machine until the substrate was completely consumed (checked by TLC). After 2-3 h, the chalky suspension turned to a bright yellow solution of tris(4-methylphenyl)bismuthine oxide, which was quickly filtered through a Celite bed and used for further pmposes [94TL8197]. 

The most characteristic property of the bismuthine oxides is their oxidizing ability to convert activated alcohols, triphenylphosphine and hydrazobenzene to the corresponding ketones, oxide and azo compound, respectively. However, thioanisole and methyl octyl sulfide remain intact even after prolonged stirring with bismuthine oxide at ambient temperature [94TL8197] (Section 5.2.4). 

These oxidation reactions are performed under neutral conditions at ambient temperature, contrary to similar oxidations with organylantimony oxides which often need more severe conditions. The findings clearly show the difference in chemical behavior between bismuthine oxides and other orga-nylpnicogen oxides. It is likely that the chemical nature of organylbismuthine oxides depends considerably on its preparative procedures. For some time now, a similar phenomenon has been noticed with triphenylantimony oxide that exists in a dimeric, oligomeric or polymeric form. 

Acyl carbene equivalents The moderately stabilized RCOCH=BPhj ylides are generated from the tetrafluoroborate salts. These ylides react with aldehydes to give a,p-epoxy ketones, in contrast to the stibonium, arsonium, and phosphonium ylides, which afford enones. The weaker Bi-0 bond disfavors decomposition of the adducts into enones and the bismuthine oxides. 

There have been several reports of the formation of tertiary bismuthines by the action of free radicals on metallic bismuth. One method of generating the radicals iavolves cleavage of ethane or hexafluoroethane ia a radiofrequeacy glow discharge apparatus the radicals thus formed are allowed to oxidize the metal at — 196°C (53). Trimethylbismuthiae and tris(trifluoromethyl)bismuthine [5863-80-9], C BiF, have been obtained by this procedure. 

Tertiary bismuthines appear to have a number of uses in synthetic organic chemistry (32), eg, they promote the formation of 1,1,2-trisubstituted cyclopropanes by the iateraction of electron-deficient olefins and dialkyl dibromomalonates (100). They have also been employed for the preparation of thin films (qv) of superconducting bismuth strontium calcium copper oxide (101), as cocatalysts for the polymerization of alkynes (102), as inhibitors of the flammabihty of epoxy resins (103), and for a number of other industrial purposes. 

Studies of the electrochemical oxidation of trivalent organic As, Sb and Bi compounds have mainly been focused on oxidations of trisubstituted arsines and, to a smaller extent, on the oxidations of trisubstituted stibines, whereas only a few preparative studies of oxidations of trisubstituted bismuthines have been reported. 

TABLE 14. Half-wave potentials ( 1 2) chemically irreversible oxidation at Pt electrodes of trisubstituted arsines, stibines and bismuthines in MeCN°... 

The body shows decomposition if heated above 270° C. and burns in air with a reddish flame and the separation of lead oxide. It is moderately soluble in chloroform, benzene, or carbon bisulphide when hot, and difficultly soluble in alcohol, ether, ligroin, or acetic acid. If heated in a sealed tube with hydrochloric acid decomposition occurs, lead tetrachloride and benzene being produced. By the action of halogens or concentrated nitric acid two phenyl groups are split off, and a lead diphenyl dihalide or dinitrate formed. A similar action takes place with iodic acid, formic, acetic, trichloracetic, propionic, valeric, and p-nitrobenzoic acids. With metallic chlorides the following derivatives are formed arsenic trichloride — lead diphenyl dichloride and diphenyl arsenious chloride antimony trichloride — lead diphenyl dichloride and diphenylstibine chloride antimony penta-chloride — lead diphenyl dichloride and diphenylstibine trichloride bismuth tribromide —> lead diphenyl dichloride and diphenylchloro-bismuthine thallie chloride —> lead diphenyl dichloride and thallium diphenyl chloride tellurium tetrachloride —> lead diphenyl dichloride and tellurium diphenyl dichloride. 

Bismuthine (MeSi)2CHBiCl2 was treated with Na2[W(CO)s] to afford [ W(CO)5 3( 3- -Bi2)] and [W2(CO)8(/i-772-Bi2)(/r-BiMe)W(CO)5]. The structures of these compounds are shown in Figure 26. The latter complex features a Bi2 moiety bridging two tungsten ions. If the Bi—Bi bond is a single bond, the formal oxidation state of tungsten is +2. However, the Bi—Bi distance... 

Triarylbismuthine A -tosylimides react with benzaldehyde, benzoyl chloride and phenyl isocyanate to give A -tosylimine, A-tosylamide and A -tosylurea derivatives, respectively [91CL105] (Section 5.5.2.3). The imides oxidize secondary and benzylic alcohols to carbonyl compounds, sometimes accompanied by the concurrent formation of a diaryl(A -tosylamino)bismuthine [96JCR(S)24] (Section 5.2.4). When treated with acetic acid, the imides are converted to the corresponding triarylbismuth diacetates and sulfonamides (Scheme 3.9). 

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