Two-coordinate, homoleptic manganese(ii) primary terphenyl amido complexes: the effects of secondary coordination on geometry and Lewis base complexation

Exploring sulfur donor atom coordination chemistry with La(II), Nd(II), and Tm(II) using a terphenylthiolate ligand

To expand the range of donor atoms known to stabilize 4fn5d1 Ln(II) rare-earth metal (Ln) ions beyond the C, N, and O first row main group donor atoms, the Ln(III) sulfur donor terphenylthiolate iodide complexes, LnIII(SAriPr6)2I (AriPr6 = C6H3-2,6-(C6H2-2,4,6-iPr3)2, Ln = La, Nd) were reduced to form LnII(SAriPr6)2 complexes. These Ln(II) species were structurally characterized, analyzed by density functional theory (DFT) calculations, and compared to Tm(SAriPr6)2, which was synthesized from TmI2(DME)3.

Extremely bulky amide ligands in main group chemistry

The development of extremely sterically demanding, monodentate amide ligands facilitates the isolation of main group species with new and highly reactive coordination modes. An outstanding feature of these ligands is the ability to tune their steric demands. Reactivity investigations highlight the potential for small molecule activation chemistry and catalysis for these compounds.

Structure-based studies on the metal binding of two-metal-dependent sugar isomerases

Two-metal-dependent sugar isomerases are important in the synthesis of rare sugars. Many of their properties, specifically their metal dependency, have not been sufficiently explored. Here we used X-ray crystallography, site-directed mutagenesis, isothermal titration calorimetry and electron paramagnetic resonance spectroscopy to investigate the molecular determinants of the metal-binding affinity of l-rhamnose isomerase, a two-Mn(2+) -dependent isomerase from Bacillus halodurans (BHRI). The crystal structure of BHRI confirmed the presence of two metal ion-binding sites: a structural metal ion-binding site for substrate binding, and a catalytic metal ion-binding site that catalyzes a hydride shift. One conserved amino acid, W38, in wild-type BHRI was identified as a critical residue for structural Mn(2+) binding and thus the catalytic efficiency of BHRI. This function of W38 was explored by replacing it with other amino acids. Substitution by Phe, His, Lys, Ile or Ala caused complete loss of catalytic activity. The role of W38 was further examined by analyzing the crystal structure of wild-type BHRI and two inactive mutants of BHRI (W38F and W38A) in complex with Mn(2+) . A structural comparison of the mutants and the wild-type revealed differences in their coordination of Mn(2+) , including changes in metal-ligand bond length and affinity for Mn(2+) . The role of W38 was further confirmed in another two-metal-dependent enzyme: xylose isomerase from Bacillus licheniformis. These data suggest that W38 stabilizes protein-metal complexes and in turn assists ligand binding during catalysis in two-metal-dependent isomerases.

STRUCTURED DIGITAL ABSTRACT

BHRI and BHRI bind by x-ray crystallography (View interaction).

Silylamide complexes of chromium(II), manganese(II), and cobalt(II) bearing the ligands N(SiHMe2)2 and N(SiPhMe2)2

Bis(dimethylsilyl)amide and bis(dimethylphenylsilyl)amide complexes of the divalent transition metals chromium, manganese, and cobalt were synthesized. Dimeric, donor-free {Mn[N(SiHMe2)2]2}2 could be obtained via two different pathways, a salt metathesis route (utilizing MnCl2(thf)1.5 and LiN(SiHMe2)2) and a transsilylamination protocol (utilizing Mn[N(SiMe3)2]2(thf) and HN(SiHMe2)2). Addition of 1,1,3,3-tetramethylethylendiamine (tmeda) to {Mn[N(SiHMe2)2]2}2 yielded the monomeric adduct Mn[N(SiHMe2)2]2(tmeda). The syntheses of Cr[N(SiHMe2)2]2(tmeda), Co[N(SiMe3)2][N(SiHMe2)2](tmeda), and Co[N(SiHMe2)2]2(tmeda) were achieved by transsilylamination from Cr[N(SiMe3)2]2(tmeda) and {Co[N(SiMe3)2]2}2(μ-tmeda), respectively. Bis(dimethylphenylsilyl)amide complexes Mn[N(SiMe2Ph)2]2, Cr[N(SiMe2Ph)2]2, and Co[N(SiMe2Ph)2]2(thf) were obtained via salt metathesis employing MCl2(thf)x (M = Cr, Mn, Co) with equimolar amounts of LiN(SiMe2Ph)2 in n-hexane. Treatment of CrCl2 with LiN(SiMe2Ph)2 in thf gave Cr[N(SiMe2Ph)2]2(thf)2, featuring an almost square planar trans-coordination. All complexes were examined by elemental analyses, DRIFT and UV-vis spectroscopy, as well as X-ray structure analysis, paying particular attention to secondary M---SiH β-agostic and M---π(arene) interactions. Magnetic moments were determined by Evans' method.

catena-Poly[[[aqua-manganese(III)]-μ-(E)-5-bromo-N-[2-(5-bromo-2-oxidobenzyl-idene-amino)-4-nitro-phen-yl]-2-oxidobenzamidato] N,N-dimethyl-fomamide monosolvate]

The asymmetric unit of the title complex, {[Mn(C(20)H(10)Br(2)N(3)O(5))(H(2)O)]·(CH(3))(2)NCHO}(n), consists of one Mn(III) ion, one (E)-5-bromo-N-[2-(5-bromo-2-oxidobenzyl-idene-amino)-4-nitro-phen-yl]-2-oxidobenzamidate ligand (Schiff base), one water mol-ecule and an N,N-dimethyl-formamide mol-ecule. The coordination geometry around the Mn(III) ion is a distorted octa-hedron, being surrounded by two O and two N atoms from the Schiff base, which are positioned in the equatorial plane. The water mol-ecule and the O atom of the carbonyl group from the adjacent Mn(III) complex are situated at the axial positions, leading to a polymeric chain along the c axis. In the crystal, the complex and N,N-dimethyl-formamide mol-ecules are connected via O-H⋯O, C-H⋯O and C-H⋯Br hydrogen bonds, forming a three-dimensional network.