Molecular structures of tris(2-mercapto-1-tert-butylimidazolyl)hydroborato and tris(2-mercapto-1-adamantylimidazolyl)hydroborato sodium complexes: analysis of [TmR] ligand coordination modes and conformations

Abstract

The tris(mercaptoimidazolyl)hydroborato complexes, [κ(3)-S2H-Tm(Bu(t))]Na(THF)3 and [κ(3)-S2H-Tm(Ad)]Na(THF)3, which feature t-butyl and adamantyl substituents, have been synthesized via the reactions of the respective 1-R-1,3-dihydro-2H-imidazole-2-thiones with NaBH4 in THF (R = Bu(t), 1-Ad). X-ray diffraction studies indicate that the compounds are monomeric and that the [Tm(R)] ligands coordinate to the metal in a κ(3)-S2H manner via two of the sulfur donors and the hydrogen attached to boron, a combination that is unprecedented for sodium derivatives. Analysis of the tris(mercaptoimidazolyl)hydroborato compounds that are listed in the Cambridge Structural Database has allowed for the formulation of a set of criteria that enables κ(x)-S(x) and κ(x+1)-S(x)H coordination modes to be identified. Furthermore, the various κ(x)-S(x) and κ(x+1)-S(x)H coordination modes have also been analyzed with respect to the conformations of the [Tm(R)] ligands, which differ by rotation of the imidazolethione moieties about the B-N bond.

Exchange of alkyl and tris(2-mercapto-1-t-butylimidazolyl)hydroborato ligands between zinc, cadmium and mercury

“…The formation of [Tm Bu t ]ZnMe and [Tm Bu t ]CdMe by these reactions provides a useful method of synthesis from the sodium complex because [Tm Bu t ] 2 M may be generated via the reactions of [Tm Bu t ]Na 17,27 with MCl 2 (M = Zn, Cd), as illustrated in Scheme 2. Specifically, [Tm Bu t ]MMe can be obtained from [Tm Bu t ]Na in a single reaction flask via a two-step sequence that involves (i) treatment of 2 equivalents of [Tm Bu t ]Na with MCl 2 to generate [Tm Bu t ] 2 M, followed by (ii) treatment with Me 2 M to afford [Tm Bu t ]MMe (Scheme 3).…”

“…1 H NMR chemical shifts are reported in ppm relative to SiMe 4 (δ = 0) and were referenced internally with respect to the protio solvent impurity (δ = 7.16 for C 6 D 6 , 2.08 for C 7 D 8 , and 1.94 for CD 3 CN). 34 Me 2 Cd and Me 2 Zn were obtained from Strem, while [Tm Bu t ]Na, 17 , † [Tm Bu t ] 2 Zn, 22 [Tm Bu t ] 2 Cd, 23 [Tp Me 2 ] 2 Zn 28 and [Tm Bu t ]HgMe 24a were prepared by literature methods. CAUTION: Mercury and cadmium compounds are toxic, and appropriate safety precautions must be taken in handling these compounds .…”

“… † [Tm Bu t ]Na may be obtained in both solvated and non-solvated forms (see reference 17). The non-solvated form was used herein.…”

Synthesis and structural characterization of tris(2-mercapto-1-methylbenzimidazolyl)hydroborato cadmium halide complexes, {[TmMeBenz]Cd(μ-Cl)}2and [TmMeBenz]CdI: a rare example of cadmium in a trigonal bipyramidal sulfur-rich coordination environment

“…The molecular structures of the products, namely [Tm MeBenz ]CdI (Figure 1) and {[Tm MeBenz ]Cd(µ–Cl)} 2 (Figure 2), have been determined by single crystal X-ray diffraction, and while the [Tm MeBenz ] ligand exhibits the κ 3 -coordination mode that is commonly observed for [Tm R ] ligands, 20 a striking feature is that the iodide compound is a monomer, whereas the chloride derivative is a dimer with two µ–Cl bridges. Of note, the molecular structure of the chloroform solvate, {[Tm MeBenz ]Cd(µ–Cl)} 2 •6(CHCl 3 ), has also been determined and exhibits a similar structure for both of the crystallographically independent molecules (Figure 3 and Figure 4), thereby indicating that packing effects are not responsible for the dimeric structure of the chloride derivative.…”

Influence of benzannulation on metal coordination geometries: Synthesis and structural characterization of tris(2-mercapto-1-methylbenzimidazolyl)hydroborato cadmium bromide, {[TmMeBenz]Cd(μ-Br)}2

“…The tris (mercaptoimidazolyl)hydroborato class of ligands, [Tm R ], as introduced by Reglinski and Spicer, 1,2,3 has proven to be of much use in coordination chemistry by virtue of its ability to provide a well-defined [S 3 ] donor platform, which provides a valuable complement to Trofiomenko’s [ N 3 ] donor tris (pyrazolyl)hydroborato class of ligands. 4,5,6 For example, we have used [Tm R ] ligands both to ( i ) model aspects of metalloenzymes that feature sulfur-rich active sites and ( ii ) mimic the interactions of toxic metals such as mercury, cadmium and lead with cysteine thiolate groups.…”