Synthesis and chemistry of dithiadiazole free radicals [4-(4′-C5H4N)CN2S2] and [4-(3′-C5H4N)CN2S2];: X-ray crystal structures of [Pd3{μ-SNC(Ar′)NS-S,S′}2(PPh3)4] (Ar′=4′-C5H4N, 4′-C5H4NBEt3 and 3′-C5H4NBEt3)

Two new 1,2,3,5-dithiadiazoles, [4-(4'-C5H4N)CN2S2] (L-1) and [4-(3'-C5H4N)CN2S2] (L-2), With different pyridyl groups at the 4-position were prepared. As Lewis bases, the dithiadiazoles reacted with Lewis acids via their pyridyl groups to form acid-base adducts with retention of the five-membered dithiadiazole ring. Ligands L-1 and L-2 reacted with excess triethylborane to give (LBEt3)-B-1 and (LBEt3)-B-2 (1a and 1b) and with Mn(CO)(5)Br to give the fac-Mn(CO)(3)Br(L-1)(2) (2a) and fac-Mn(CO)(3)Br(L-2)(2) (2b) complexes. When reacted with Pd-0 complexes, namely, Pd(PPh3)(4) and a mixture of [Pd-2(dba)(3)] and dppf, the dithiadiazoles underwent ring-opening reaction by reductive cleavage of the S-S bond of the dithiadiazole ring. The resulting formation of Pd-S bonds gave the corresponding trinuclear complexes [Pd-3{mu-SNC(4'-C5H4N)NS-S,S'}(2)(PPh3}(4)] (3a), [Pd-3{mu-SNC(3'-C5H4N)NS-S,S'}(2)(PPh3)(4)] (3b), and [Pd-3{mu-SNC(4'-C5H4N)NS-S,S'}(2)(dppf)(2)] (4) [dba = dibenzylideneacetone, dppf = 1,1'-bis(diphenylphosphanyl)ferrocene]. Complexes 3a and 3b reacted with excess triethylborane to give the corresponding acid-base adducts [Pd-3(mu-SNC(4 '-C5H4NBEt3)NS-S,S'}(2)(PPh3)(4)] (5a) and [Pd-3{mu-SNC(3'-C5H4NBEt3)NS-S,S')(2)(PPh3)(4)] (5b.) Complex 3a reacted with Mn(CO)(5)Br to give {[Pd-3{mu-SNC(4'-C5H4N)NS-S,S}(2){PPh3)(4)][MnBr(CO)(3)]}(n) (6). The structures of 3a, 5a, and 5b were established by X-ray crystallography.