Brian M. Bridgewater

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 molecular structure of [TmPh]2Pb: a complex with an ‘inverted’ η4-coordination mode for the tris(2-mercapto-1-phenylimidazolyl)hydroborato ligand

Abstract The tris(2-mercaptoimidazolyl)borate lead complex, [TmPh]2Pb, may be synthesized by reaction of Pb(ClO4)2 with 2 equivalents of [TmPh]Li. The molecular structure of [TmPh]2Pb has been determined by X–ray diffraction, revealing that it possesses an unusual structure with an inverted η4-coordination mode for the [TmPh] ligand which includes a Pb···H–B interaction.

A zinc hydroxide complex of relevance to 5-aminolevulinate dehydratase: The synthesis, structure and reactivity of the tris(2-mercapto-1-phenylimidazolyl)hydroborato complex [TmPh]ZnOH

Abstract The tris(2-mercapto-1-phenylimidazolyl)hydroborato ligand, [TmPh], has been used to prepare [TmPh]ZnOH, the first structurally characterized terminal zinc hydroxide complex of a tridentate sulfur donor ligand; as such, [TmPh]ZnOH represents a good structural model for the zinc enzyme 5-aminolevulinate dehydratase (ALAD).

A non-classical hydrogen bond in the molybdenum arene complex [η6-C6H5C6H3(Ph)OH]Mo(PMe3)3: evidence that hydrogen bonding facilitates oxidative addition of the O–H bond

Mo(PMe3)6 reacts with 2,6-Ph2C6H3OH to give the eta 6-arene complex [eta 6-C6H5C6H3(Ph)OH]Mo(PMe3)3 which exhibits a non-classical Mo...H-OAr hydrogen bond; DFT calculations indicate that the hydrogen bonding interaction facilitates oxidative addition of the O-H bond to give [eta 6,eta 1-C6H5C6H3(Ph)O]Mo(PMe3)2H.

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.

A zinc thiolate species which mimics aspects of the chemistry of the Ada repair protein and matrix metalloproteinases: the synthesis, structure and reactivity of the tris(2-mercapto-1-phenylimidazolyl)hydroborato complex [TmPh]ZnSPh

The tris(2-mercapto-1-phenylimidazolyl)hydroborato ligand, [TmPh], has been used to prepare the zinc phenylthiolate derivative, [TmPh]ZnSPh, which provides a good structural model for zinc enzymes that possess [Zn(Cys)4] motifs; furthermore, the reactivity of the thiolate linkage in [TmPh]ZnSPh mimics the chemistry of the Ada protein and the activation mechanism of matrix metalloproteinases.

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.

Reactivity of Mo(PMe3)5H2 towards catecholborane: synthesis and structure of Mo(PMe3)4(η2-H2BCat)H

Abstract Mo(PMe 3 ) 5 H 2 reacts with catecholborane (CatBH) to give Mo(PMe 3 ) 4 (η 2 -H 2 BCat)H. Structural characterization by X-ray diffraction suggests that the complex is best represented as a borohydride complex, as opposed to a boryl-hydride derivative Mo(PMe 3 ) 4 (BCat)H 3 .

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.

Influence of a [Me2Si] ansa bridge on the barrier to rotation about the Zr–phenyl bond and on the generation and reactivity of benzyne intermediates: comparison of the structures and reactivity of [Me2Si(C5Me4)2]Zr(Ph)X and Cp*2Zr(Ph)X (X = H, Cl, Ph)

Comparison of the chemistry of [Me2Si(C5Me4)2]ZrPh2 and Cp*2ZrPh2 demonstrates that incorporation of a [Me2Si] ansa bridge reduces the barrier for both (i) rotation about the Zr–Ph bond and (ii) elimination of benzene to generate a benzyne intermediate; furthermore, the [Me2Si] ansa bridge promotes the reaction of two equivalents of MeCN with the benzyne intermediate {[Me2Si(C5Me4)2]Zr(η2-C6H4)}, whereas insertion of only one equivalent is observed with [Cp*2Zr(η2-C6H4)].