Zinc complexes of the N,N,S ligand (mercaptophenyl)(picolyl)amine

Abstract

The zinc complex chemistry of the tridentate thiol ligand N-(2-mercaptophenyl)(2-picolyl)amine (MPPAH) differs considerably from that of the aliphatic analogue N-(2-mercaptoethyl)(2-picolyl)amine reported previously. This is due to the lower basicity and hence bridging tendency of its aromatic thiolate function. With zinc salts of 0x0 anions the 1:l complexes (MPPA)ZnX (la-c: X = ONO,, OAc, OBz) are formed which according to spectroscopic data are monomeric while the halide (MPPA)ZnBr (2) seems to be polymeric. In the absence of coordinating anions the monomeric 2 : l complex (MPPA),Zn (3) results which according to a crystal structure determination contains tetrahedral zinc coordinated by one MPPA ligand in a tridentate fashion while the other is only monodentate and sulfur-bound. A similar NzS2 coordination can be deduced for the 1:l:l complex (MPPA)Zn(STrt) (4) resulting from ZnEt,, MPPAH and triphenylmethanethiol.The purpose of our investigations into the zinc complex chemistry of chelating ligands with N and S donors is twofold. Firstly we want to gain an understanding of the factors controlling their coordinative behaviour (stoichiometries, coordination numbers, thiolate bridging, stabilities, etc.). Secondly, we want to learn how to construct structural and possibly functional models of enzymes containing zinc in a ZnN,S, environment like liver alcohol dehydrogenase"], spinach carbonic anhydraseI21, or bovine aminolaevulinate dehydrataset31. In order to do t h s we screen known or newly synthesized polydentate amine-thiol ligands for their ligation behavior toward various zinc salts.In the previous paper of this seriesL41 we outlined our main objectivcs and the synthetic approach used to obtain zinc complexes in which the metal is placed into the right steric and electronic environment of N and S donors, the desirable ligand combinations being ZnN2SX, ZnN3SX, or ZnNS2X. In these combinations the N and S donors are meant to be provided by one chelating ligand while the group X represents a labile coligand or the substrate of a possible enzyme model. While many chelating ligands exist with the appropriate number of N and S donor functions it must be said that their use for the modelling of the abovementioned enzymes is still an open challenge, despite some impressive results obtained with alcohol dehydrogenase models r5 3 6].This paper reports on our investigations with another ligand suitable for the ZnN2SX combination. This ligand, N-(2-mercaptophenyl)(2-picolyl)amine (MPPAH) is the aromatic analogue of the aliphatic thiol N-(2-mercaptoethyl)(2-picoly1)amine (MEPAHjr4'. We foundL41 that MEPAH yields a puzzling variety of zinc complexes, a dominating feature of which is the tendency of thiolate bridging and hence oligomerization. We hoped that the more rigid nature of the aromatic NCCS unit in MPPAH and the lower basicity of its thiolate function would help to suppress this unfavorable property.

Zinc Thiolate Complexes of (N,N,S)‐Tridentate Ligands for the Modeling of Thiolate Alkylating Enzymes

“…Complex 3d shares these features with our (N 2 S-chelate)Zn-SR complex derived from the N 2 S-chelate ligand MPPA. [13] The Zn-N and Zn-S distances of the L 3 ·Zn-SR complexes are in the normal range, comparing well with those both in (N 2 Schelate) [12][13][14] and in (N 2 S-tripod)Zn-SR complexes. [23,24] The coordination pattern of zinc in complexes 3 is close enough to that in the thiolate alkylating enzymes to justify the investigation of alkylating reactions.…”

“…We are not aware of a model study employing such an NS 2 ligand, and so far just one type of such N 2 S ligands seems to have been used for thiolate alkylation in zinc complexes. [8,9] We have reported various tridentate N 2 S ligands [12][13][14][15] as well as pyrazolylborate-derived NS 2 [16] and N 2 S tripods. [17] While we have previously focused on modeling hydrolytic enzymes or alcohol dehydrogenase with their zinc complexes, we are at present using their zinc thiolate complexes for studies of thiolate alkylation.…”

A water-soluble multisite ionophore ligand bearing pyridine and aminothiophenol functionality. Synthesis, spectroscopy and electrochemistry of its complexes, and peripheral reactivity of the (E,E)M (M = Ni) complex with Pd2+ and Ag+

“…Initially, 2-(2¢-pyridylmethylamino)-benzenethiol, (2), was prepared by a two-step reaction sequence according to a published procedure [34][35][36]. The ligand (3) was prepared by the reaction between 2-(2-pyridylethylamino)-benzenethiol and (E,E)-dichloroglyoxime in THF with an excess of NaHCO 3 to neutralize HNO 3 formed during the reaction (Scheme 1).…”

Synthesis, Spectral Characterization and Electrochemical Properties of New vic-dioxime Complexes Bearing Carboxylate

“…Antiphenylchloroglyoxime was synthesized as described in the literature [18]. Anti-monochloroglyoxime was synthesized as described in the literature [19,20] and (E, E)-dichloroglyoxime was prepared by a reported procedure [21,22]. The elemental analyses were carried out in the Laboratory of the Scientific and Technical Research Council of Turkey (TUBITAK).…”