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)

Abstract

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 L1 and L2 reacted with excess triethylborane to give L1BEt3 and 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 Pd0 complexes, namely, Pd(PPh3)4 and 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{μ‐SNC(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.

Non-Innocent Base Properties of 3- and 4-Pyridyl-dithia- and Diselenadiazolyl Radicals: The Effect ofN-Methylation

“…The chemistry and structural properties of DTDA and DSDA radicals have been extensively studied for many years. A wide range of 4-substituents have been explored with increasing interest in the introduction of ligands that can enhance or complement the coordination chemistry of the radical itself. ,, In principle, a 3- or 4-pyridyl ligand provides an effective secondary binding site for metal ions, but the basic nature of these ligands also introduces subtleties in the preparation of the radicals to which they are bound. Here, we have provided a detailed account of the preparation of 3-, 4-pyDTDA and their Se-based analogues using procedures that reflect the intermediacy of protonated radicals.…”

“…In contrast, the related 3-, 4-pyDTDA radicals have received relatively little attention. A number of metal complexes have been reported, , but information on the radicals themselves is sparse, and the corresponding 3,4-pyDSDA derivatives are, to date, unknown. The relative dearth of information on these particular radicals may stem in part from the presence of a basic nitrogen on the ligand, which has caused some difficulties in their isolation.…”

Cobalt Porphyrin–Thiazyl Radical Coordination Polymers: Toward Metal–Organic Electronics

“…In all of these materials, the DTDA moiety acts as a bidentate ligand with coordination to the metal occurring through both sulfur atoms (an η 2 -S–S binding mode). Examples of 4-(4′-pyridyl)-1,2,3,5-dithiadiazolyl (py-DTDA) acting as a Lewis base via the pyridyl nitrogen are uncommon but exist in the form of an adduct with triethylborane and in the complex fac -Mn­(CO) 3 Br­(py-DTDA) 2 . Reaction of these adducts with Pd(0) complexes resulted in cleavage of the S–S bond.…”