Synthesis and Chemistry of Dithiadiazole Free Radicals [4-(4'-C5H4N)CN2S2] and [4(3'-5H4N)CN2S2] X-ray crystal structures of Pd3 -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] (L1) and [4- (3'-C5H4N)CN2S2] (L2), 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 L1and L2reacted with excess triethylborane to give L1BEt3and L2BEt3(1a and 1b) and with Mn(CO)5Br to give the fac-Mn(CO)3Br(L1)2(2a) and fac-Mn(CO)3Br(L2)2(2b) complexes. When reacted with Pd0complexes, namely, Pd(PPh3)4and a mixture of [Pd2(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 [Pd3→μ-SNC (4'-C5H4N)NS-S,S'←2(PPh3)4] (3a), [Pd3→μ-SNC(3'- C5H4N)NS-S,S'←2(PPh3)4] (3b), and [Pd3→μ-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 [Pd3→μ-SNC(4'- C5H4NBEt3)NS-S,S'←2(PPh3)4] (5a) and [Pd3→μSNC(3'-C5H4NBEt3)NS- S,S'←2(PPh3)4] (5b.) Complex 3a reacted with Mn(CO)5Br to give →[Pd3→μ-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.