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Metal ion function depends on the regulation of properties within the primary and second coordination spheres. An approach toward studying the structure−function relationships within the secondary coordination sphere is to construct a series of synthetic complexes having constant primary spheres but structurally tunable secondary spheres. This was accomplished through the development of hybrid urea−carboxamide ligands that provide varying intramolecular hydrogen bond (H-bond) networks proximal to a metal center. Convergent syntheses prepared ligands [(N‘-tert-butylureayl)-N-ethyl]-bis(N‘ ‘-R-carbamoylmethyl)amine (H41R) and bis[(N‘-tert-butylureayl)-N-ethyl]-(N‘ ‘-R-carbamoylmethyl)amine (H52R), where R = isopropyl, cyclopentyl, and (S)-(−)-α-methylbenzyl. The ligands with isopropyl groups H41iPr and H52iPr were combined with tris[(N‘-tert-butylureayl)-N-ethyl]amine (H6buea) and bis(N-isopropylcarbamoylmethyl)amine (H30iPr) to prepare a series of Co(II) complexes with varying H-bond donors. [CoIIH22iPr]- ...

The synthesis of the new multidentate tripodal compounds bis[(N′-tert-butylureido)-N-ethyl]-2-pyridylmethylamine (H41) and bis[(N′-tert-butylureido)-N-ethyl]-N-methylamine (H42) is described. These ligands contain two urea-ethylene arms that when deprotonated and bound to a metal ion, position two hydrogen bond donors near the metal center so that formation of intramolecular H-bonds with other coordinated species is possible. The complexes K[MII(H21)(η1-OAc)] and K[MII(H22)(η2-OAc)] (MII = Co and Fe) have been isolated and characterized. The multidentate ligands mediate the mode of acetate coordination: the [MII(H21)(η1-OAc)]− complexes have a monodentate coordination, whereas in [MII(H22)(η2-OAc)]− the acetate binds in a bidentate manner. X-Ray diffraction studies reveal that all complexes have trigonal bipyramidal coordination geometries with one of the acetate oxygen atoms being nearly trans to the amine nitrogen donor. All the complexes have relatively long M–O bond lengths in comparison with other MII–OAc complexes characterized previously. The complexes exhibit intramolecular H-bonds from the urea NH groups to one of the coordinated oxygen atoms of the acetate, causing a lengthening of the MII–OAc bond distances. The NH⋯O bond lengths and vibrational energies in these acetate complexes support weaker H-bonds than the H-bonding interactions in similar ligand complexes with hydroxo ligands.

The secondary coordination sphere in the active sites of metalloproteins is instrumental in controlling function. Non-covalent interactions, such as hydrogen bonds, are often used to create unique microenvironments around the metal ion(s). To duplicate these effects in synthetic complexes, first row transition metal complexes of the ligand bis[(tert-butyl)aminocarbonyl]-1,2-diaminoethane (H41) have been synthesized and structurally characterized. Twofold deprotonation of H41 affords the dianionic, bidentate ligand [H21]2−, which forms the four-coordinate complexes [MII(H21)2]2−. X-ray diffraction studies on [MII(H21)2]2− (M=Fe, Co, Zn) show that these complexes have pseudo-tetrahedral coordination geometry. H-bond donors from [H21]2− surround the metal centers in each complexes, and metrical data suggest that NH⋯M H-bonds are present in these complexes. The square-planar [NiII(H21)]2− has H-bond donors that span both faces of the coordination plane, forming intramolecular H-bonds between the [H21]2− ligands.

Convergent preparative routes to new urea-pyrazolate dinucleating ligands are described. Metal complexes of these ligands have hydrogen bond donors that are proximal to the metal centers that interact with other coordinated species. This is exemplified by Co(II) dimers with Co(II)-mu-Cl-Co(II) motifs, in which the chloro ligand is involved in four intramolecular hydrogen bonds. These noncovalent interactions appear to influence the Co(II)-Cl bonds, which are unusually long, having lengths greater than 2.5 A.

{Bis[(heterocycle)ethyl]amine}copper(I) complexes with a least one imidazole ligand react with 0.5 equiv. of dioxygen at −78 °C to give purple peroxo species. The dioxygen adduct of { N -2-[(2-pyridyl)ethyl]- N -2-[1-butyl- 2-imidazolyl)ethyl]amine}copper(I) tetrafluoroborate having one imidazole and one pyridine donor has absorption maxima at 332, 435 and 538 nm and is unreactive toward acid and triphenylphosphine at low temperature, characteristics that have been ascribed to μ-η 2 ,η 2 coordination. {Bis[2-(1-methyl-2-imidazolyl)ethyl]amine}copper(I) tetrafluoroborate ( 11 ) has been structurally characterized by X-ray crystallography and has the expected T-shape. Crystal data for 11 : monoclinic, a =9.2181(21), b =11.638(3), c =14.914(4) A; β=92.059(19)°; Z =4; space group= P 2 1 / c ; 1748 independent non-zero ( I >2.5σ( I ) reflections with 2θ between 2 and 50°; R =6.5%; R w =8.5%.

A partially-unlinked cavitand, derived from the condensation of acetaldehyde and resorcinol and having three ethylene bridges, functions as a monodentate ligand toward transition metal ions. Treatment of the cavitand with MCl 2 and a bidendate ligand (L) in the presence of NaOH led to isolation of metal complexes with the formula (cavitand) 2 ML (M=Co, Cu, Zn) or (cavitand) 2 ML 2 (M=Ni). The square-planar complexes of Cu(II) and Co(II), the tetrahedral complex of Zn(II), and the octahedral complex of Ni(II) were characterized spectroscopically and in one case by X-ray crystallography

The synthesis of a new tripodal tris(oxazoline) ligand, tris[4,4-dimethyl-2-(4,5-dihydrooxazolyl)]methylamine is described, and details of the X-ray crystal_structure of its Cu(I) complex are presented. The complex crystallizes as a dimer in the triclinic space group P 1 . Each Cu(I) ion is coordinated in a distorted trigonal geometry by two oxazoline groups from one tripod and a third oxazoline from the second ligand. The Cu(I)-Cu(I) distance is 5.7 A. The CO adduct of the complex exhibits ν(CO)= 2066 cm −1 .

New hybrid ligands containing combinations of pyrazole, pyridine, and imidazole have been prepared, and the reaction chemistry of their copper(I) derivatives has been studied. The dinucleating ligands provide three nitrogen donors to each metal ion, and each coordination unit is separated by a m-xylyl group. Except for the case where four of the donor groups are pyridyl, in which the xylyl spacer is hydroxylated, all of the complexes react via four-electron reduction of the dioxygen molecule to give bis(μ-hydroxy)copper(II) dimers

New polydentate ligands having (2-imidazolylethyl)amino and (2-benzimidazolylethyl)amino groups have been prepared via the imidate esters derived from N-(2-cyanoethyl)benzamides. These chelating ligands form stable copper(I) complexes that react with dioxygen at low temperature to give adducts presumed to be dinuclear peroxo complexes on the basis of the similarity of their electronic spectra with those for analogous pyridine-ligated species. A Schiff-base ligand derived from isophthalaldehyde and (aminoethyl)imidazole is hydroxylated when its copper(I) derivative is treated with dioxygen

A diverse group of copper-containing proteins carries out the transport and activation of the O2 molecule in biological systems.1–5 Extensive characterization of biomimetic analogs of two of those, namely hemocyanin and tyrosinase, has afforded a better understanding of the inorganic chemistry of peroxocopper complexes at the molecular level.6–12

New polydentate ligands having (2-imidazolylethyl)amino and (2-benzimidazolylethyl)amino groups have been prepared via the imidate esters derived from N-(2-cyanoethyl)benzamides. These chelating ligands form stable copper(I) complexes that react with dioxygen at low temperature to give adducts presumed to be dinuclear peroxo complexes on the basis of the similarity of their electronic spectra with those for analogous pyridine-ligated species. A Schiff-base ligand derived from isophthalaldehyde and (aminoethyl)imidazole is hydroxylated when its copper(I) derivative is treated with dioxygen

New hybrid ligands containing combinations of pyrazole, pyridine, and imidazole have been prepared, and the reaction chemistry of their copper(I) derivatives has been studied. The dinucleating ligands provide three nitrogen donors to each metal ion, and each coordination unit is separated by a m-xylyl group. Except for the case where four of the donor groups are pyridyl, in which the xylyl spacer is hydroxylated, all of the complexes react via four-electron reduction of the dioxygen molecule to give bis(μ-hydroxy)copper(II) dimers

New hybrid ligands containing pyrazole and pyridine have been prepared; and the reaction chemistry of their copper(I) derivatives has been studied. These dinucleating ligands provide three nitrogen donors to each metal ion, and a phenol or phenolate group to bridge between the metals. The reaction of the different dicopper(I) species with dioxygen follows patterns established previously for analogous pyridyl ligands; and peroxo and hydroperoxo adducts can be generated at low temperature

The preparation of new CoII-mu-OH-CoII dimers with the binucleating ligands 3,5-bis{bis[(N'-R-ureaylato)-N-ethyl]aminomethyl}-1H-pyrazolate ([H4PRbuam]5-, R=tBu, iPr) is described. The molecular structure of the isopropyl derivative reveals that each CoII center has a trigonal-bipyramidial coordination geometry, with a Co...Co separation of 3.5857(5) A. Structural and spectroscopic studies show that there are four hydrogen-bond (H-bond) donors near the CoII-micro-OH-CoII moiety; however, they are too far away to be form intramolecular H-bonds with the bridging hydroxo ligand. Treating [CoII2H4PRbuam(micro-OH)]2- with acetonitrile led to the formation of bridging acetamidato complexes, [CoII2H4PRbuam(micro-1,3-OC(NH)CH3)]2-; in addition, these CoII-micro-OH-CoII dimers hydrolyze ethyl acetate to form CoII complexes with bridging acetato ligands. The CoII-1,3-micro-X'-CoII complexes (X'=OAc-, [OC(NH)CH3]-) were prepared independently by reacting [CoII2H3PRbuam]2- with acetamide or [CoII2H4PRbuam]- with acetate. X-ray diffraction studies show that the orientation of the acetate ligand within the H-bonding cavity depends on the size of the R substituent appended from the urea groups. The tetradentate ligand 3-{bis[(N'-tert-butylureaylato)-N-ethyl]aminomethyl}-5-tert-butyl-1H-pyrazolato ([H2PtBuuam]3-) was also developed and its CoII-OH complex prepared. In the crystalline state, [CoIIH2PtBuuam(OH)]2- contains two intramolecular H-bonds between the urea groups of [H2PtBuuam]3- and the terminal hydroxo ligand. [nPr4N]2[CoIIH2PtBuuam(OH)] does not hydrate acetonitrile or hydrolyze ethyl acetate. In contrast, K2[CoIIH2PtBuuam(OH)] does react with ethyl acetate to produce KOAc; this enhanced reactivity is attributed to the presence of the K+ ions, which can possibly interact with the CoII-OH unit and ester substrate to assist in hydrolysis. However, K2[CoIIH2PtBuuam(OH)] was still unable to hydrate acetonitrile.

Metal ion function depends on the regulation of properties within the primary and second coordination spheres. An approach toward studying the structure-function relationships within the secondary coordination sphere is to construct a series of synthetic complexes having constant primary spheres but structurally tunable secondary spheres. This was accomplished through the development of hybrid urea-carboxamide ligands that provide varying intramolecular hydrogen bond (H-bond) networks proximal to a metal center. Convergent syntheses prepared ligands [(N'-tert-butylureayl)-N-ethyl]-bis(N' '-R-carbamoylmethyl)amine (H(4)1R) and bis[(N'-tert-butylureayl)-N-ethyl]-(N' '-R-carbamoylmethyl)amine (H(5)2R), where R=isopropyl, cyclopentyl, and (S)-(-)-alpha-methylbenzyl. The ligands with isopropyl groups H(4)1iPr and H(5)2iPr were combined with tris[(N'-tert-butylureayl)-N-ethyl]amine (H6buea) and bis(N-isopropylcarbamoylmethyl)amine (H(3)0iPr) to prepare a series of Co(II) complexes with varying H-bond donors. [CoIIH(2)2iPr]- (two H-bond donors), [CoIIH1iPr]- (one H-bond donor), and [CoII0iPr]- (no H-bond donors) have trigonal monopyramidal primary coordination spheres as determined by X-ray diffraction methods. In addition, these complexes have nearly identical optical and EPR properties that are consistent with S=3/2 ground states. Electrochemical studies show a linear spread of 0.23 V in anodic potentials (Epa) with [CoIIH(2)2iPr]- being the most negative at -0.385 V vs [Cp2Fe]+/[Cp2Fe]. The properties of [CoIIH3buea]- (H3buea, tris[(N'-tert-butylureaylato)-N-ethyl]aminato that has three H-bond donors) appears to be similar to that of the other complexes based on spectroscopic data. [CoIIH3buea]- and [CoIIH(2)2iPr]- react with 0.5 equiv of dioxygen to afford [CoIIIH3buea(OH)]- and [CoIIIH(2)2iPr(OH)]-. Isotopic labeling studies confirm that dioxygen is the source of the oxygen atom in the hydroxo ligands: [CoIIIH3buea(16OH)]- has a -(O-H) band at 3589 cm-1 that shifts to 3579 cm-1 in [CoIIIH3buea(18OH)]-; [CoIIIH(2)2iPr(OH)]- has -(16O-H)=3661 and -(18O-H)=3650 cm-1. [CoIIH1iPr]- does not react with 0.5 equiv of O2; however, treating [CoIIH1iPr]- with excess dioxygen initially produces a species with an X-band EPR signal at g=2.0 that is assigned to a Co-O2 adduct, which is not stable and converts to a species having properties similar to those of the CoIII-OH complexes. Isolation of this hydroxo complex in pure form was complicated by its instability in solution (kint=2.5x10-7 M min-1). Moreover, the stability of the CoIII-OH complexes is correlated with the number of H-bond donors within the secondary coordination sphere; [CoIIIH3buea(OH)]- is stable in solution for days, whereas [CoIIIH(2)2iPr(OH)]- decays with a kint=5.9x10-8 M min-1. The system without any intramolecular H-bond donors [CoII0iPr]- does not react with dioxygen, even when O2 is in excess. These findings indicate a correlation between dioxygen binding/activation and the number of H-bond donors within the secondary coordination sphere of the cobalt complexes. Moreover, the properties of the secondary coordination sphere affect the stability of the CoIII-OH complexes with [CoIIIH3buea(OH)]- being the most stable. We suggest that the greater number of intramolecular H-bonds involving the hydroxo ligand reduces the nucleophilicity of the CoIII-OH unit and reinforces the cavity structure, producing a more constrained microenvironment around the cobalt ion.

The presence of the Zn2+ ion dramatically enhances the inhibition of trypsin and tryptase by amidine-modified benzimidazole inhibitors via coordination to both the catalytically active Ser195 hydroxyl and His57 imidazole residues of the enzyme and the nitrogens of the amidine-modified benzimidazole inhibitor (Janc, J. W.; Clark, J. M.; Warne, R. L.; Elrod, K. C.; Katz, B. A.; Moore, W. R. Biochemistry 2000, 39, 4792-4800). Some new 5-amidino-2-substituted benzimidazoles were synthesized and compared to known related molecules to explore systematically the metal-mediated inhibition of bovine trypsin as a function of coordinating groups and metal ions. These compounds take advantage of the favorable interaction between the amidine group on one side of the inhibitor and the Asp189 carboxylate in the binding pocket of the enzyme. The 5-amidino-2-substituted benzimidazoles all demonstrated similar inhibition constants (Ki) of 20-50 microM in the absence of metal ions. In the presence of Zn2+, inhibition increased to varying extents, depending upon the group substituted at the 2 position of the benzimidazole. The largest increase in inhibition in the presence of Zn2+ was seen with (5-amidino-2-benzimidazolyl)-2-benzimidazolylmethane with an apparent inhibition constant (Ki') of 0.37 +/- 0.06 nM, giving a 59,000-fold increase in inhibition when Zn2+ is present. Other metal ions, including Mn2+, Sc3+, and Hg2+, also increased the inhibition by several of the benzimidazole derivatives synthesized. The compound bis(2-benzimidazolyl)methane (BBIM) was also examined because it lacks the amidine group that provides a favorable hydrogen-bonding interaction with Asp189 in the binding pocket of trypsin. In the absence of metal ions, BBIM did not have a detectable affinity for trypsin; however, in the presence of Zn2+, a Ki' of 127 +/- 3 nM was observed. This result demonstrates that an affinity for the enzyme in the absence of metal ions is not required for potent metal-mediated inhibition, greatly expanding the possibilities for metal mediation of nonmetalloenzymes.

Low-temperature oxygenation of {Cu[P(imiPr2)3]CH3CN}CF3SO3 affords a μ-η2:η2-peroxo adduct. Upon warming a dilute solution (

New hybrid ligands containing pyrazole and pyridine have been prepared; and the reaction chemistry of their copper(I) derivatives has been studied. These dinucleating ligands provide three nitrogen donors to each metal ion, and a phenol or phenolate group to bridge between the metals. The reaction of the different dicopper(I) species with dioxygen follows patterns established previously for analogous pyridyl ligands; and peroxo and hydroperoxo adducts can be generated at low temperature

After meeting several prerequisites, students enroll in a course that allows honors chemistry students to develop new experiments for future sections of regular students.

Binucleating ligands that provide three nitrogen donors, and in some cases a phenolate group, to each copper ion have been synthesized. Introduction of substituents to provide steric shielding of the presumed dioxygen-binding site in a previously-described complex prevents reaction of these new species with dioxygen. That these changes are not a direct consequence of steric effects is demonstrated by the synthesis of a Cu(II) derivative having a bridging acetate group. Thus, seemingly simple structural modifications of model systems for the hemocyanin active site may cause substantial changes in reactivity.

Les complexes binucleaires de phenolate pontes servent de modele pour des structures de site actif dans certaines formes des hemocyanine et tyrosinase; les spectres de resonance Raman de ces complexes sont etudies et compares a leurs analogues correspondants mononucleaires

The preparation of transition-metal thiolato complexes as synthetic biomimics1 has led to a resurgent interest in the synthesis of organic thiols and their derivatives. The compound 2,2′-dimercaptobiphenyl, 1, offers interesting possibilities as a ligand, and it has been used recently to displace iron-sulfur clusters from low molecular-weight Fe-S proteins.2 The two previous preparations for 1 require a coupling reaction of diazonium salts.3,4 Overall yields of 10%3 and 30%4 are made even less attractive by the need to precipitate copper by-products with H2S after the coupling step.

The reactions of a series of Cu(I) and Cu(II) complexes containing pyrazolyl or dimethylpyrazolyl residues in the ligands during the ionization process were studied by fast atom bombardment mass spectrometry. Complexes with a +1 charge produce intact cations. Those with a higher charge yield +1 cations by formal reduction or by clustering with anions, sometimes by several simultaneous processes. Neutral complexes are protonated to give +1 ions.

Synthese de bis{[(pyrazolyl-1)-2 ethyl] methylamino}-2,6 p-cresol et de son derive t-butyl-3 pyrazole. Preparation de complexes Cu(II)-azoture et Cu(I)-carbonyle. Proprietes magnetiques