The hitherto unknown compounds 2‐(2′‐thieny1)‐pyridine and methyl α‐picolyl sulphide have been synthesized. The stability constants of Ni2+, Cu2+ and Zn2+ complexes with these two substances and with pyridine, α‐picoline, β‐picoline, γ‐picoline, and 2‐phenylpyridine have been measured and are discussed. Evidence for the coordination of the sulphur atom in methyl α‐picolyl sulphide as well as in the aromatic 2‐(2′‐thieny1)‐pyridine is given. It is also shown that thiophene is able to coordinate to Cu2+.
(12. X I . 71)Szmnmary. The acidity constants of the six thienyl-and the three phenyl-pyridines, and the stability constants of the corresponding Cu2+ 1 : 1 complexes were dcterinined in aqueous solution ( I Y 0.1, NaCIO,; 25"). The basicity of the pyritlyl group is incrcascd by a shift of a thienyl or phenyl group in. the order 2 < 3 < 4 and the inlluence of the 2'-thicnyl group is greater than that of the 3'-thienyl group. The stability of the Cu2+ 1 : 1 complexes formed with 3-and 4-substitutecl pyridines is only dependcnt on their basicity, as is commonly observed for structurally related ligands and their complcxcs. Due to stcric hindrancc the complexes of the 2-substituted derivatives are less stnblc by about 1.5 log units. There is no evidence that the aromatic bonded sulfur of Z-(Z'-thien?-l)-pyritii~le participates in complex formation with Cu2+, in opposition t o an earlier claim [l].In the present work the acidity constants of the six thienylpyridines (I-VI), 2-, 3-, and 4-phenylpyridine, and 2-benzylpyridine, as well as the stability constants of their Cu2+ 1 :1 complexes were determined and compared3). The published constants of pyridine, 2-, 3-, and 4-niethylpyridine [l] are given with our data.Our aim was to show, if a possible steric hindrance in a-substituted pyridines is reflected in the stability of the Cu2+ 1:1 complcxcs. If so it should be possible to deduce whether or not the aromatic bonded sulfur, as present in a sterically favoured position in 2-(2'-thieny1)-pyridine (I) participates in chelate formation.Experimental. The six thicnylpyridines [Z], 2-[ 3 ] , 3- [4], and 4-1)henylpj.ridines [5] were synthesized as described. 2-Benzylpyridine was obtained from Dr. F . Ic'aschig GmbH, Ludwigshafcn am Ithein, Germany. All other materials wcrc from H u k a AG, Buchs, Switzerland.The apparatus and the procedurc of measuring and of eiraluating the experimental data arc dcscribetl in [l].The acidity constants of the ligands and the stability constants of the corresponding Cu2+ 1 : 1 complexes (sce Table) have bccn determined b y potcntiometric titrstion in aqueous solution ( I = 0.1, NaC10,; 25" for the measures with the ligands, for the Cu-complexcs part of the NaClO, was replaced by an excess of Cu(CIO,), with respect to the concentration of the ligand). On titrating solutions containing only Cu2+, care was taken that the stability constants were calculated only for the pH range for which hydrolysis of Cu2+ could be omitted. *) lnstitut fur Xnorganische Chcmie, Spitalstrasse 51, CH-4000 Bascl, Schweiz. 2)Dcpartment of Organic Chemistry, Zerniltclaan, Groningen, The Netherlands. 3,In 1964 Kahnzann, SzgeZ& ErZenvneyer [l] described the synthesis of a thienylpyridine to which thc structure of Z-(Z'-thienyl)-pyridinc was assigned. By synthesizing all six possible thicnylpyridincs Wynberg, van Bergen 6: Kellogg [Z] showed that thc isomer uscd by Kahrnann et al. [l] was actually 4-(2'-thienyl)-pyridine and not the bclicved 2-(2')-isomer. Hence, the results attributed t o 2-(2'-thienyl)-p~.ridine (I...
The hitherto unknown compounds 5‐(2‐Pyridyl)‐thiazole and 2‐(N‐Thioformyl‐ω‐aminoacetyl)‐pyridine have been synthesized. The stability constants of the Cu2+‐1:1‐complexes of 5‐(2‐Pyridyl)‐thiazole, 2‐(2‐Pyridyl)‐thiazole and 4‐(2‐Pyridyl)‐thiazole have been measured and are discussed. Evidence for the coordination of the sulphur atom in 5‐(2‐Pyridyl)‐thiazole is given.
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