108202-20-6Relevant articles and documents
Remarkable substituent effects on the oxidizing ability of tetraarylbismuthonium tetrafluoroborates in alcohol oxidation
Matano, Yoshihiro,Suzuki, Takeshi,Iwata, Takaharu,Shinokura, Tomonori,Imahori, Hiroshi
, p. 1621 - 1628 (2009/05/06)
Substituent effects on the oxidizing ability of tetraarylbismuthonium tetrafluoroborates in alcohol oxidation are reported. Intermolecular and intramolecular competition experiments on geraniol oxidation by the combined use of tetraarylbismuthonium tetrafluoroborates and N,N,N′,N′- tetramethylguanidine (TMG) have revealed that the oxidizing ability of the bismuthonium salt increases by the introduction of methyl groups at the ortho position and an electron-withdrawing group at the para position of the aryl ligands. The intermolecular and intramolecular H/D kinetic isotope effects observed for the competitive oxidation of p-bromobenzyl alcohols have shown that the present oxidation reaction consists of fast pre-equilibrium leading to alkoxytetraarylbismuth(V) intermediates (first step) and α-hydrogen abstraction by the aryl ligand attached to the bismuth (second step). The experimental results demonstrate that the electron-deficient aryl ligands enhance the electrophilicity at the bismuth center to put forward the first step and that the bulky ligands destabilize the alkoxybismuth(V) intermediates to accelerate the second step. The newly explored mesityl- and 2,6- xylyltriarylbismuthonium salts have proven to convert primary and secondary alcohols to the corresponding carbonyl compounds with high efficiency under mild conditions. A remarkable steric effect of these oxidants has also been exhibited in the chemoselective oxidation between primary and secondary benzylic alcohols.
Synthesis, structure, and reactions of triaryl(methyl)bismuthonium salts
Matano, Yoshihiro
, p. 2258 - 2263 (2008/10/08)
Treatment of triarylbismuth difluorides 2 (Ar3BiF2; a, Ar = Ph; b, Ar = 4-MeC6H4; c, Ar = 4-MeOC6H4; d, Ar = 2-MeOC6H4) with methylboronic acid (3) in the presence of BF3·OEt2 in CH2Cl2 afforded the corresponding triaryl(methyl)bismuthonium tetrafluoroborates 4a-d ([Ar3MeBi+][BF4-]) in 42-91% yield. X-ray crystallographic analysis of compound 4d revealed that the bismuth center possesses a distorted tetrahedral geometry with C-Bi-C bond angles of 106.1(3)-113.6(3)° and Bi-C bond lengths of 2.182(7)-2.195(8) angstrom. Compound 4a transferred the methyl group to Ph3E (E = P, As, Sb), tris(4-methylphenyl)bismuthine, ROH (R = Me, Et, i-Pr, PhCH2), water, sodium benzenesulfinate, sodium benzoate, N,N-dimethylformamide (DMF), and thioacetamide to give the corresponding methylated products with a good recovery of triphenylbismuthine. The pseudo-first-order rate constant (kobsd = 2.9 × 10-4 s-1) observed for the reaction between 4a and benzyl alcohol (5d) was about twice as large as that (kobsd = 1.3 × 10-4 s-1) between MeOTf and 5d (in CDCl3 at 23°C; [4a] or [MeOTf] = 0.062 M; [5d] = 0.97 M). The observed reactivity of 4a clearly demonstrates the high nucleofugality of the triphenylbismuthonio group.
