Diselenadiazolyl radicals

The selenium analogue [PhCNSeSeN] and cyano-functionalized diselenadiazolyl radicals adopt cofacial dimeric structures, e.g., 11.4 (E = Se), with unequal Se Se interactions of ca. 3.15 and 3.35 A. In the latter case the radical dimers are linked together by electrostatic CN Se contacts.Tellurium analogues of dithiadiazolyl radicals (or the corresponding cations) are unknown, but calculations predict that the radical dimers, e.g., 11.4 (E = Te), will be more strongly associated than the sulfur or selenium analogues. ... 

Figure 3 Cofacial dimer of the 1,2,3,5-diselenadiazolyl radical (21a) showing head-to-tail stacking.

Amidines (161) and tris(trimethylsilyl) amidines (162) react with a mixture of selenium and selenium tetrachloride to give U, 2,3,5-diselenadiazol-l-ylium chlorides (163), some of which are converted into other salts for characterization. These salts are reduced by triphenylantimony to give 1,2,3,5-diselenadiazolyl radicals (164) (Scheme 13). The salts (23) and (43a)-(43d) were thereby prepared and converted into the radicals (21a)-(21e) <89JA9276, 9UA582, 92CC1265, 92IC1802>. The... 

The structures of a series of 1,2,3-thiaselenazoles and 1,2,3-thiaselenazolyl and 1,2,3,5-diselenadiazolyl radicals have been studied extensively by X-ray diffraction. 

A, while that between the pairs is 3.383(6) A. The 7r-stacked arrays of cations are linked by centrosymmetric pairs of Se(2)—N(l ) contacts, thereby generating ribbons running along the y-direction. These four-center Se—N supramolecular synthons, which are common in diselenadiazolylium salts and diselenadiazolyl radicals, are likely to dominate the solid-state structures of reduced diselenazolyl materials. 

Fig. 3 The stacking of the difluorophenyl diselenadiazolyl radicals (2. E = Se) showing (a) the almost eclipsed stacking of diselenadiazolyl rings and (b) the offset stacking of the difluorophenyl rings Se. red N, blue F, yellow. (Adapted from Ref. [5].) (View this art in color at www.dekker.coin.)...

The solid-state characterization of the bifunctional radical [4,4 -(5-cyanobenzene)-l,3-bis(l,2,3,5-diselenadiazolyl)] 28 has been studied <1993CM820>. The crystal structure consists of stacks of diradicals running parallel to radical dimerization up and down the stack generates a zigzag arrangement, as seen in the related 1,3-phenylene structures. Along the stacking axis the mean intradimer Se-Se contact is 3.23 A, while the mean interdimer Se—Se distance is 3.91 A. 

Reaction of 1,2,3,5-disclcnadiazolyl radical 50 with Pd[PPh3]4 in THF gave the metal complex 208 in 72% yield (Equation 21) <1998NJC763>. The structure of complex 208 was determined by X-ray diffraction. The structure 208 reveals three Pd atoms bridged by two diselenadiazolyl ligands in which the Se-Se bond is formally cleaved. 

Cyanofuran-2-[l,2,3,5-diselenadiazolyl] 30 was prepared similarly (Scheme 54) <2001IC6820>. The cyano-furyl-functionalized persilylated amidine 330, prepared by the reaction of 2,5-dicyanofuran with lithium bistrimethyl-silylamide, was treated with 2 equiv of SeCl2, which was prepared in situ from Se and SeCU- The diselenadiazolylium chloride [30] [Cl] was reduced with triphenylantimony to give the radical 30 in 68% yield from compound 330. 

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