Monomere Tripod–Zink-Thiolat-Komplexe

Abstract

Die Umsetzung des Pyrazolylborat‐Zink‐Komplexes TpCum,MeZn–OH mit den entsprechenden Thiolen lieferte die stabilen Komplexe TpCum,MeZn–SR (1: R = Ph, 2: R = CH2–Ph, 3: R = CH2–CH2–Ph) als weitere Vertreter dieser Verbindungsklasse. Aus dem Liganden Tris(benzimidazolylmethyl)amin (BIMA), Zinkperchlorat und dem entsprechenden Natriumthiolat bildeten sich die kationischen Komplexe (BIMA)Zn–SR (R = Ph, CH2Ph), die als [(BIMA)Zn–S–Ph] BPh4 (4) und [(BIMA)Zn–S–CH2Ph] ClO4 (5) isoliert wurden. Eine Strukturanalyse von 4 belegte die pseudotetraedrische Koordinationsgeometrie für diesen neuartigen Verbindungstyp.

Nucleophilic reaction by carbonic anhydrase model zinc compound: characterization of intermediates for CO2 hydration and phosphoester hydrolysis

“…The tetrahedral geometry around a zinc atom was slightly distorted, where the zinc was coordinated by three benzimidazole nitrogen atoms of and one oxygen atom of hydroxide ion with the bond angles around zinc atom 103.7(2)°-114.6(1)°( Table 2). The bond lengths of Zn-N1 2.015 (6) A, Zn-O1 2.047 (7) A are consistent with the literature data of tetrahedral zinc compounds [35,36,40,[45][46][47]. The location of the phenolic OH groups is located at two positions 5 and 6 of each benzene ring (Fig.…”

Polysulfido Chain in Binuclear Zinc(II) Complexes

“…It may be noted that Zn­(II)-bound thiolate ligands have been shown to undergo alkylation reactions in both biological systems and mononuclear zinc­(II) thiolate complexes following either a dissociative (two pathways) or an associative (σ-bond metathesis) mechanism, and a detailed discussion regarding the same is available in the literature . An appreciable number of studies on the mechanism of such an alkylation of coordinated thiolate ligands in mononuclear Zn­(II) complexes have already been reported in the literature. ,,,,− The mechanism has been shown to depend on the solvent polarity, hydrogen-bonding effect with the coordinated thiolates, identity of the alkylating agents, and other coligands bound to the Zn­(II) centers and may still remain inconclusive in some cases . Considering Lippard’s proposition regarding the relationship between the Zn–thiolate bond distances and dissociative versus associative mechanism, , we may anticipate that, because the Zn–S SPh distance in complex 4 is 2.337(1)–2.353(1) Å (longer than 2.30 Å), it may promote a dissociative mechanism.…”

“…The Zn centers in 4 reside in a distorted trigonal-bipyramidal geometry, with Zn–S SPh distances ranging from 2.337(1) to 2.353(1) Å, which are longer than the Zn–S distances reported for the mononuclear zinc complexes, [Zn­(SPh) 2 (2,9-Me 2 Phen)] [2.255(2)–2.257(4) Å], [Tm Ph ]­Zn­(SPh) [2.258(1) Å], where Tm Ph is the tris­(2-mercapto-1-phenylimidazolyl)­hydroborato ligand, and [Tp Ph ]­Zn­(SEt) [2.203(3) Å], where Tp Ph is hydrotris­(3-phenylpyrazolyl)­borate, but shorter, as expected, than the Zn–S distances of 2.426(2) and 2.433(2) Å in the thiolate-bridged binuclear Zn­(II) complex [Zn 2 ( N -Et-HPTB)­(μ 2 -SEt)] 2+ . The Zn–S distances in 4 [2.337(1)–2.353(1) Å] are, however, quite similar to that reported for the mononuclear complexes [Zn­(SPh) 4 ] 2– (2.35 Å) , and (BIMA)­Zn­(SPh) [2.328(1) Å], where BIMA is bis­(benzimidazolemethyl)­amine . The molecular structure of 6 in 6 (BPh 4 ) revealed a binuclear Zn­(II) unit, where each of the two five-coordinate Zn centers resides in a distorted trigonal-bipyramidal geometry with a Zn–Zn separation of 3.676 Å (Figure a).…”

“…79 The Zn−S distances in 4 [2.337(1)−2.353(1) Å] are, however, quite similar to that reported for the mononuclear complexes [Zn(SPh) 4 ] 2− (2.35 Å) 112,113 and (BIMA)Zn(SPh) [2.328(1) Å], where BIMA is bis-(benzimidazolemethyl)amine. 95 The molecular structure of 6 in 6(BPh 4 ) revealed a binuclear Zn(II) unit, where each of the two five-coordinate Zn centers resides in a distorted trigonalbipyramidal geometry with a Zn−Zn separation of 3.676 Å (Figure 2a). The two Zn(II) centers are bridged additionally by a S 5 2− unit with Zn−S distances of 2.380(1) and 2.388(1) Å, while the S−S distances within the bridging S 5 2− unit range from 2.033(2) to 2.054 (2) Å.…”

Thiolate exchange in [TmR]ZnSR′ complexes and relevance to the mechanisms of thiolate alkylation reactions involving zinc enzymes and proteins

“…On the basis of such studies, it is now recognized that zinc-thiolate alkylation may proceed via two mechanistic extremes that are dissociative and associative in nature. For example, (a) anionic [Zn(SPh) 4 ] 2À is alkylated by (MeO) 3 PO by a mechanism that is proposed to proceed via initial heterolytic thiolate dissociation [24,25], while (b) neutral derivatives such as [Tp RR 0 ]ZnSR [26][27][28][29], ½Phðpz Bu t ÞBt Bu t ZnSAr [30,31], ½HCðpz Me 2 Þ 2 ðCMe 2 SÞZnX [32,33], [HB(mim R ) 2 (pz)]ZnSR [34,35] and a series of other zinc thiolates [36][37][38][39][40][41][42][43], are proposed to undergo alkylation without prior dissociation of RS À . In this paper, we address further aspects relevant to zinc thiolate alkylation in model compounds by the use of the tris(2-mercapto-1-R-imidazolyl) , but this observation does not provide definitive evidence that the mechanism is associative since a dissociative reaction can also exhibit second-order kinetics if re-coordination of RS À to the zinc center competes with alkylation by MeI [69].…”