New Monomeric Cobalt(II) and Zinc(II) Complexes of a Mixed N,S(alkylthiolate) Ligand:  Model Complexes of (His)(His)(Cys) Metalloprotein Active Sites

Abstract

The new N(2)S(alkylthiolate) ligand 2-methyl-1-[methyl-(2-pyridin-2-ylethyl)amino]propane-2-thiolate, PATH (1), has been prepared and reacted with zinc(II) and cobalt(II) to give the monomeric complexes [(PATH)ZnBr] (2), [(PATH)ZnNCS] (3), [(PATH)CoBr] (4), and [(PATH)CoNCS] (5). The molecular structures of 4 and 5 have been determined by X-ray diffraction. Each complex displays a distorted tetrahedral geometry at the metal center, with the PATH ligand providing the N(2)S(alkylthiolate) donors. These complexes are close structural mimics of the active site of metalloproteins with a His(2)Cys-M(II) site such as that found in peptide deformylase. Complexes 4 and 5 are the first examples of crystallographically characterized Co(II) complexes with an N(2)SL (L not equal N,S) donor set. Only one diastereomer for 2-5 is observed in the solid state, and simple molecular mechanics (Chem3D) calculations suggest this isomer is stable because of a favorable ligand conformation. NMR studies in the case of Zn(II) and UV-vis studies in the case of Co(II) provide strong evidence that their solid-state structures are retained in solution. Cyclic voltammetry reveals processes for both the Co(II/I) (4, - 1.51 V; 5, - 1.49 V) and Co(III/II) (4, + 0.9 V; 5, + 0.9 V) couples. The UV-vis data for the cobalt complexes are consistent with a monomeric, four-coordinate geometry regardless of the nature of the solvent (i.e., donating (MeOH, CH(3)CN) vs nondonating (CH(2)Cl(2))) and are compared with other cobalt complexes as well as cobalt-substituted His(2)Cys metalloproteins (peptide deformylase and blue-copper proteins). In addition, reaction of the bromide complexes 2 and 4 with hydroxide anion leads to the formation of 1:1 hydroxide:M(II) complexes which have been characterized in situ by (1)H NMR and UV-vis spectroscopy, respectively.

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

“…L 3 was first described by Goldberg et al and used for zinc chemistry unrelated to thiolate alkylation, [20][21][22] and these authors had already noted that the larger chelate ring size in relation to that provided by ligands like L 1 favors the formation of four-coordinate complexes. [21] We verified the ability of L 3 to form tetrahedral L·Zn-X complexes with soft donors X by preparing L 3 ·ZnCl from zinc chloride.…”

Mononuclear, Dinuclear, and Pentanuclear [{N,S(thiolate)}Iron(II)] Complexes: Nuclearity Control, Incorporation of Hydroxide Bridging Ligands, and Magnetic Behavior

“…In contrast, the [(tacn)Fe II (m-Cl) 3 Fe II (tacn)] + complex was determined to be weakly ferromagnetically coupled, with J = + + 11.6 cm…”

“…Traditional syntheses of (L) n M/OH complexes involve self-assembly [25][26][27][28] or substitution [29,30] reactions with excess OH À /H 2 O in protic solvents. Here we describe a new strategy involving aprotic conditions (THF) and a nearly stoichiometric amount of water to give the hydroxide-containing complexes [(Py 2 S) 4 Fe 5 (m-OH) 2 ](BF 4 ) 4 (3) and [(Py 2 S) 2 Fe 2 (m-OH)]BF 4 (4). Both of these complexes display unprecedented structural motifs for iron(ii).…”

“…+ ) have been studied in detail. [60,61] The [(thf)Fe II (mCl) 3 Fe II (thf)] + complex was found to be weakly antiferromagnetically coupled, with J = À4.6 cm…”

Cobalt(II) silanethiolato complexes with dimethylpyridines: crystal structures and spectroscopic studies

“…Relying on our earlier UV-Vis analysis of cobalt(II) silanethiolates with imidazoles as a co-ligand [10], we suppose that such models will be useful for the spectral studies of the active centers of other metalloproteins [10,[15][16][17][18], and this paper is the continuation of our research. Here, we describe the syntheses, structures and spectral analysis of three monomeric new cobalt(II) tri-tert-butoxysilanethiolates with dimethylpyridine co-ligands.…”