SYNTHESIS AND PROPERTIES OF A SERIES OF PHENYLENE-BRIDGED BI-N-BISMUTHANES

A series of meta- and para-phenylene-bridged Bi(III)(n) and Bi(V)(n) c ompounds (n greater than or equal to 2) have been synthesized. Reactio n of Ph2BiX (X = Cl, OSO2CF3) with p-Li2C6H4, p-(BrMg)(2)C6H4, or p- a nd m-(Me2S . Cu)(2)C6H4 generated in situ from dibromobenzenes gave th e corresponding para- and meta-phenylene-bridged Bi-n-bismuthanes, Ph2 BiC6HeBiPh2 (2), Ph2BiC6H4Bi(Ph)C6H4BiPh2 (3), and Ph2BiC6H4Bi(Ph)C6H4 Bi(Ph)C6H4BiPh2 (4), in 2-30% yields. Bi-n-bismuthanes 2-4 were oxidat ively chlorinated by SO2Cl2 to yield the Bi-n-bismuth polychlorides 5- 7, in which all pentavalent bismuth atoms bore three aryl groups and t wo chlorine atoms. Compounds 2-7 showed lambda(max) at around 244-249 and 285-290 nm in the UV-vis spectra, suggesting that the phenylene br idges did not perturb significantly the sigma- and pi-transitions of t he aromatic systems in these bismuth oligomers. Ortho-lithiation direc ted by the sulfonyl group was employed for the one-pot preparation of highly branched Bi-n-bismuthanes; successive treatment of Ar3Bi 9a wit h 3 equiv of t-BuLi and Ar2BiI (10b) (Ar = 2-Et2NSO2C6H4) afforded m-p henylene-bridged Bi-n-bismuthanes, Ar2Ar'Bi (11a), ArAr'Bi-2 (12a), an d Ar'Bi-3 (13a) in 2-49% yields (Ar' = 3-Ar2Bi-2-Et2NSO2C6H3). Treatme nt of ortho-lithiated (2-t-BuSO2C6H4)(p-Tol)(2)Bi (14) with p-Tol(2)Bi Cl gave sulfone-substituted Bi-2-bismuthane 15, which was converted to the corresponding Bi-2-chlorodiarylbismuthane (16) by the Bi-C cleava ge reaction. An X-ray diffraction analysis of 16 showed that both bism uth centers have a distorted trigonal pyramidal geometry weakly coordi nated by the neighboring sulfonyl-oxygen atoms. The symmetrically bran ched Bi-4-bismuthane 13a was successfully converted to a dendritic, Bi -10-bismuthane 17 in 20% isolated yield by successive treatment with t -BuLi and 10b. The reaction between ortho-lithiated 9a and ArBiI2 (10c ) followed by GPC separation afforded two fractions of oligomeric Bi-n -bismuthanes, the vapor depression measurement of which revealed that the average numbers of the bismuth atoms present therein were 7 and 16 , respectively. UV-vis spectra of 9a, 11a, 12a, 13a, and 17 exhibited no bathochromic shift; the inefficient pi-electron delocalization woul d probably be due to the twisted geometry between aromatic rings, as i nferred from the X-ray structure of the related Bi-2-bismuthane 16. Th e extinction coefficients of these phenylene-bridged Bi-n-bismuthanes were found to increase with increasing number of bismuth atoms.