Clare Kimblin

Tris(mercaptoimidazolyl)hydroborato complexes of cobalt and iron, [TmPh]2M (M=Fe, Co): structural comparisons with their tris(pyrazolyl)hydroborato counterparts

Abstract The tris(mercaptophenylimidazolyl)borate iron and cobalt complexes [TmPh]2M (M=Fe, Co) have been synthesized by reaction of [TmPh]Tl with MI2. Structural characterization by X-ray diffraction demonstrates that the potentially tridentate [TmPh] ligand binds through only two sulfur donors in these ‘sandwich’ complexes and that the ‘tetrahedral’ metal centers supplement the bonding by interactions with the two B–H groups. Comparison of the structures of [TmPh]2M (M=Fe, Co) with the related tris(pyrazolyl)borate [TpPh]2M counterparts indicates that the tris(mercaptoimidazolyl) ligand favors lower primary coordination numbers in divalent metal complexes. The trivalent complexes, {[TpPh]2Fe}[ClO4] and {[pzBmMe]2Co}I, however, exhibit octahedral coordination, with the ligands binding using their full complement of donor atoms.

The Synthesis and Structure of Tris [2-(1,4-diisopropylimidazolyl)]phosphine Zinc Nitrate, [PimPri 2 ]Zn(NO3)2: Structural Consequences of t-Butyl versus Isopropyl Substitution in Tris (imidazolyl) phosphine Zinc Complexes

The zinc complex [PimPr i 2 ]Zn(NO3)2has been synthesized by the reaction of tris[2-(1,4-diisopropylimidazolyl)] phosphine [PimPr i 2 ] with Zn(NO3)2 · 6(H2O). Comparison of the structure of [PimPr i 2 ]Zn(NO3)2 with its more heavily substituted analogue {[PimPr i Bu t ]Zn (NO3)} (NO3)demonstrates the rather dramatic structural consequences of replacing the t-butyl substituents in the 4-positions of the imidazolyl moieties with isopropyl groups. Specifically, [PimPr i 2 ]Zn(NO3)2 exists as a six-coordinate complex with both unidentate and bidentate nitrate ligands whereas {[PimPr i ,Bu t ]Zn(NO3)exists as an ion pair with a single nitrate ligand coordinated to zinc in an anisobidentate mode. [PimPr i 2 ]Zn(NO3)2 is orthorhombic, Pbca (No. 61), a = 18.870(4) A, b = 17.273(7) A, c = 20.641(4) A, V = 6758(3) A3, Z = 8.

Mononuclear tris(2-mercapto-1-arylimidazolyl)hydroborato complexes of zinc, [TmAr]ZnX: structural evidence that a sulfur rich coordination environment promotes the formation of a tetrahedral alcohol complex in a synthetic analogue of LADH

The tris(2-mercapto-1-mesitylimidazolyl)borate ligand, [TmMes]–, has been used to synthesize {[TmMes]Zn(HOMe)}+, a stable monomeric tetrahedral zinc–methanol complex which resembles the proposed alcohol intermediate in the catalytic cycle of the mechanism of action of liver alcohol dehydrogenase.

The synthesis and structure of {[PimPri,But]ZnOH}(ClO4): a tris(imidazolyl)phosphine zinc hydroxide complex and a proposed structural model for carbonic anhydrase

The zinc hydroxide complex {[Pimpri,But]ZnOH}(ClO4) is synthesized by the reaction of [Pimpri,But] with Zn(ClO4)2·6H2O; {[Pimpri,But]ZnOH}(ClO4) is the first structurally characterized monomeric zinc hydroxide complex supported by imidazole functionalities and is therefore an excellent structural model for the active site of carbonic anhydrase.

The synthesis and structural characterization of bis(mercaptoimidazolyl)(pyrazolyl)hydroborato and tris(mercaptoimidazolyl)hydroborato complexes of thallium(I) and thallium(III)

The bis(mercaptoimidazolyl)(pyrazolyl)hydroborato and tris(mercaptoimidazolyl)hydroborato ligands, [pzBmMe]− and [TmPh]−, have been used to prepare complexes of both thallium(I) and thallium(III), namely [pzBmMe]Tl, [pzBmMe]TlMe2, {[TmPh]2Tl}2 and {[TmPh]2Tl}[ClO4]. For example, reaction of [pzBmMe]Tl with Me2TlCl yields [pzBmMe]TlMe2, while reaction of [TmPh]Li with Tl(ClO4)3 yields {[TmPh]2Tl}[ClO4]. [pzBmMe]TlMe2, {[TmPh]2Tl}2 and {[TmPh]2Tl}[ClO4] have been structurally characterized by X-ray diffraction. Interestingly, for the monomeric thallium(III) derivatives, the pyrazolyl group does not coordinate to the thallium center in the dimethyl complex [pzBmMe]TlMe2, which is therefore fur-coordinate, whereas all the mercaptoimidazolyl groups coordinate to thallium in {[TmPh]2Tl}+, thereby resulting in a six-coordinate octahedral geometry.

Synthesis and molecular structures of a pair of tris(imidazolyl)phosphine cobalt–perchlorate complexes, {[PimPri2]Co(OClO3)}[ClO4] and {[PimPri2]Co(OH2)(HOMe)(OClO3)}[ClO4]

The cobalt–perchlorate complexes, {[PimPri2]Co(OClO3)}(ClO4) and {[PimPri2]Co(OH2)(HOMe)(OClO3)}(ClO4), have been synthesized via the reaction of tris[2-(1,4-diisopropylimidazolyl)]phosphine [PimPri2] with Co(ClO4)2·6H2O; the isolation of these species, as opposed to a hydroxide derivative {[PimPri2]CoOH}+, demonstrates the important role that steric interactions play in generating synthetic analogues for metal-substituted carbonic anhydrases.

Tris(imidazolyl)phosphine cobalt complexes: structural comparisons with isoelectronic tris(pyrazolyl)hydroborato analogues

The cobalt complexes {[PimPri,But]CoI}I and {[PimPri,But]Co(NO3)}NO3 are synthesized by the reaction of the sterically demanding tris[2-(1-isopropyl-4-tert-butylimidazolyl)]phosphine [PimPri,But] with CoI2 and Co(NO3)2, respectively; comparison of the structures of {[PimPri,But]M(NO3)}+(M = Co, Zn) with those of the structurally analogous, but neutral, tris(3-tert-butylpyrazolyl)hydroborato complexes [TpBut]M(NO3) illustrates that the charged complexes have a greater tendency to adopt bidentate coordination of the nitrate ligand.