N–H⋯O hydrogen bonding interactions in tetrahedral [ZnS4] complexes of relevance to zinc enzymes: the synthesis, structures and reactivity of tris(2-mercapto-1-arylimidazolyl)hydroborato zinc(2-mercapto-1-arylimidazole) complexes, {[TmAr]Zn(mimAr)}[ClO4] (Ar=Ph, p-Tol)

New Tris(thioimidazolyl)borate Ligands and Some Zinc Complexes Thereof

“…Based on this observation, and on the similar non-coordination of the hydroxymethyl group in 24 (see below), it must be concluded that the hydroxymethyl function in 22 is also not coordinated to zinc. The same reasoning as above, together with the knowledge that the L·Zn units, unlike the TpZn units, easily bind uncharged nitrogen ligands, [3,5,12,13] led us to the application of 1-methyl-2-hydroxymethylimidazole. It was hoped that the coordination of both its 3-nitrogen and the hydroxymethyl oxygen to zinc would be favoured by the formation of a five-membered chelate ring.…”

“…We [3,4] and others [5][6][7][8][9] have tried to model the structure and function of these enzymes by applying tripodal scorpionate [10] ligands bearing one to three sulfur donors. During these studies Parkin's [5,8,11,12] and our own research group [3,13] have found that the sulfur-rich environment of the tris(thioimidazolyl)borate ligands (Tti R ) enables the attachment of quite unusual and biologically relevant coligands X at the zinc ion in an S 3 ZnX environment.…”

“…[14] Remarkably little metal complex chemistry has been done with them in the eight years since, either by Reglinski himself [15][16][17][18][19][20] or by other research groups. [3,5,8,[11][12][13][14][15][16][21][22][23][24][25] So far only methyl, [14] tert-butyl, [3] benzyl, [22] phenyl, [5] p-tolyl, [22] [ mesityl [5] and p-cumenyl substituents [3] have been attached at the N 1 nitrogens of the thioimidazolyl moieties, of which only tert-butyl and mesityl can be considered as sterically demanding.…”

Synthetic Bioinorganic Chemistry: Scorpionates Turn 50

“…The Ada DNA repair protein, which restores damaged DNA by abstracting a methyl group from a methylated nucleic base residue or phosphate group and transfers it to one of its own cysteine thiolate groups, also has a Zn(Cys) 4 core [134,135]. In this regard, the alkylation of well-defined zinc thiolate complexes has been studied by a number of researchers, including Lippard [136,137], Darensbourg [138], Vahrenkamp [139][140][141][142][143][144][145][146], Parkin [130,[147][148][149], Riordan [111,150], Carrano [151][152][153][154], Anders [155,156], and Ibrahim [157,158]. There appears to be mounting evidence that the methylation of zinc thiolates occurs by two distinct mechanisms: dissociative, in which a zinc-bound thiolate is released and then reacts with the electrophile, a pathway taking place in anionic complexes such as [Zn(SPh) 4 ] 2À [137], and associative, in which the methylating agent directly attacks the thiolate ligand still bound to the metal [112,159,160].…”

Benzannulated tris(2-mercapto-1-imidazolyl)hydroborato ligands: tetradentate κ4-S3H binding and access to monomeric monovalent thallium in an [S3] coordination environment

“…For example, we have utilized these ligands to model aspects of zinc enzymes with sulfur-rich active sites 4 and the mechanism of action of the protolytic cleavage of Hg–C bonds by organomercurial lyase ( MerB ). 5 One of the reasons for extensive use of these ligands is that they may be readily modified by incorporation of different 1-R substituents, thereby allowing facile modification of the steric and electronic properties of the ligand system.…”