Synthesis, structure, and reactions of triaryl(methyl)bismuthonium salts

Treatment of triarylbismuth difluorides 2 (Ar3BiF2; a, Ar = Ph; b, Ar = 4-M eC6H4; c, Ar = 4-MeOC6H4; d,Ar = 2-MeOC6H4) with methylboronic acid (3) in the presence of BF3. OEt2 in CH2Cl2 afforded the corresponding triaryl(meth yl)bismuthonium tetrafluoroborates 4a-d ([Ar3MeBi+][BF4-]) in 42-91% yield. X-ray crystallographic analysis of compound 4d revealed that the bismuth c enter possesses a distorted tetrahedral geometry with C-Bi-C bond angles of 106.1(3)-113.6(3)degrees and Bi-C bond lengths of 2.182(7)-2.195(8) Angstr om. 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 ben zenesulfinate, sodium benzoate, N,N-dimethylformamide (DMF), and thioacetam ide to give the corresponding methylated products with a good recovery of t riphenylbismuthine. The pseudo-first-order rate constant (k(obsd) = 2.9 x 1 0(-4) s(-1)) observed for the reaction between 4a and benzyl alcohol (5d) w as about twice as large as that (k(obsd) = 13 X 10(-4) s(-1)) between MeOTf and 5d (in CDCl3 at 23 degrees C; [4a] or [MeOTf] = 0.062 M; [5d] = 0.97 M ). The observed reactivity of 4a clearly demonstrates the high nucleofugali ty of the triphenylbismuthonio group.