Synthesis and Chemistry of Dithiadiazole Free Radicals [4‐(4′‐C 5 H 4 N)CN 2 S 2 ] and [4‐(3′‐C 5 H 4 N)CN 2 S 2 ]; X‐ray Crystal Structures of [Pd 3 {μ‐SNC(Ar′)NS– S,S′ } 2 (PPh 3 ) 4 ] (Ar′ = 4′‐C 5 H 4 N, 4′‐C 5 H 4 NBEt 3 and 3′‐C 5 H 4 NBEt 3 )

Abstract Two new 1,2,3,5‐dithiadiazoles, [4‐(4′‐C 5 H 4 N)CN 2 S 2 ] ( L 1 ) and [4‐(3′‐C 5 H 4 N)CN 2 S 2 ] ( 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 L 1 BEt 3 and L 2 BEt 3 ( 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(PPh 3 ) 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 {μ‐SNC(4′‐C 5 H 4 N)NS‐ S,S′ } 2 (PPh 3 ) 4 ] ( 3a ), [Pd 3 {μ‐SNC(3′‐C 5 H 4 N)NS‐ S,S′ } 2 (PPh 3 ) 4 ] ( 3b ), and [Pd 3 {μ‐SNC(4′‐C 5 H 4 N)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 {μ‐SNC(4′‐C 5 H 4 NBEt 3 )NS‐ S,S′ } 2 (PPh 3 ) 4 ] ( 5a ) and [Pd 3 {μ‐SNC(3′‐C 5 H 4 NBEt 3 )NS‐ S,S′ } 2 (PPh 3 ) 4 ] ( 5b .) Complex 3a reacted with Mn(CO) 5 Br to give {[Pd 3 {μ‐SNC(4′‐C 5 H 4 N)NS‐ S,S′ } 2 (PPh 3 ) 4 ][MnBr(CO) 3 ]} n ( 6 ). The structures of 3a , 5a , and 5b were established by X‐ray crystallography.