Symmetrical and Non‐symmetrical Pd (II) Pincer Complexes Bearing Mesoionic N‐heterocyclic Thiones: Synthesis, Characterizations and Catalytic Properties

Abstract

In contrast to well‐established symmetrical pincer complexes, non‐symmetrical metal pincers with the loss of C2v symmetry are much less studied. In this work, mesoionic NHTs (NHTs = N‐heterocyclic thiones), which can be viewed as the sulfur adducts of mesoionic carbenes, are incorporated into pincer complexes for the first time. Two symmetrical and non‐symmetrical phenylene‐bridged bis (NHT) compounds 3a/3b were synthesized as proligands via a “cycloaddition‐alkylation‐thionation” reaction sequence. In a case to access bis (NHT) compound 3c, N‐dealkylation reactions occurred. The carbene NMR signals of NHTs are only partially correlated to the π‐accepting abilities of carbenes, which is different from Bertrand's carbene‐phosphinidene system. The structural analysis of 3a/3b indicates that they possess C‐S partial double bonds. 3a and 3b served as the precursors to access two aryl anion‐linked [SCS/S′] pincer complexes 6a/6b. An external base proved to be essential for this cyclopalladation process. The catalytic properties of 6a/6b in the cycloisomerizations of alkynoic acids have been examined. Finally, non‐symmetrical complex 6a shows superior catalytic performance in such transformations contrasting to its symmetrical counterpart 6b.

Sulfur‐Containing 1,2,3‐Triazoles: Synthesis and Properties

“…[65][66][67][68][69][70][71][72][73][74] Some of 4-sulfanyl-1,2,3-triazoles, showing unique bioactivity and superior catalytic performance, were potentially applied as drugs and ligands. [16,75] 4-Sulfinyl-1,2,3triazoles, which were prepared by CuAAC, displayed fluorescence and anion binding performance. [76][77]…”

“…Until now, CuAAC, organocatalytic azide‐ketone [3+2] cycloaddition (OrgAKC) have been developed to obtain 4‐ sulfanyl‐1,2,3‐triazoles [65–74] . Some of 4‐sulfanyl‐1,2,3‐triazoles, showing unique bioactivity and superior catalytic performance, were potentially applied as drugs and ligands [16,75] . 4‐Sulfinyl‐1,2,3‐triazoles, which were prepared by CuAAC, displayed fluorescence and anion binding performance [76–77] …”

Azides in the Synthesis of Various Heterocycles

“…Firstly, the triazolium salts 165/166 were reacted with elemental sulfur in a base (KO t Bu and K 2 CO 3 ) non-symmetrical mesoionic bis (NHT) compound 168 the symmetrical analog 169 in good yields, 76% and 72%, respectively. Complexes 170-173 were formed with the treatment of 167 with elemental sulfur in the presence of K 2 CO 3 as a base (Scheme 66) [51]. Yoshida et al [52] reported that the double-click reaction between aryl azides and the diyne (183) afforded a regioisomeric mixture of bicyclo-adduct 184 (trans/cis) in an excellent yield.…”

“…Firstly, the triazolium salts 165/166 were reacted with elemental sulfur in a base (KO t Bu and K2CO3) nonsymmetrical mesoionic bis (NHT) compound 168 the symmetrical analog 169 in good yields, 76% and 72%, respectively. Complexes 170-173 were formed with the treatment of 167 with elemental sulfur in the presence of K2CO3 as a base (Scheme 66)[51].…”

High spin iron(ii) complexes based on imidazolyl- and 1,2,3-triazolyl-thione ligands and NCE (E = S, Se or BH3) co-ligands: effect of the S-functional group on the structural and magnetic properties

“…To the best of our knowledge this work is the first utilising the latter type of compound as ligand for iron( ii ), however, recently zinc( ii ) 23 and palladium( ii ) 24 complexes of related monodentate ligands have been reported. Nonetheless, the iron( ii ) complexes reported here containing NCE co-ligands are the first of its type.…”