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Stoichiometric Schiff base condensations of sterically bulky primary amines with acenaphthenequinone yield isolable monoimines. In the presence of iron(II) chloride, the remaining ketone reacts with a second primary amine bearing a pendant donor atom to give asymmetric, tridentate, α-diimine complexes that possess remarkable structural variability. A series of NNP and NNS tridentate iron(II) complexes are prepared; these coordination compounds become active catalysts for ethylene oligomerization when activated with methylalumoxanes. X-ray crystallographic studies of the precatalyst complexes confirm that the ligand binds in a tridentate fashion. Correlations between the precatalyst solid-state structures and catalyst activity and α-olefin product distribution are explored.

In the absence of base, the reaction of [Fe{sup II}(TMCS)]PF{sub 6} (1, TMCS = 1-(2-mercaptoethyl)-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane) with peracid in methanol at -20 C did not yield the oxoiron(IV) complex (2, [Fe{sup IV}(O)(TMCS)]PF{sub 6}), as previously observed in the presence of strong base (KO{sup t}Bu). Instead, the addition of 1 equiv of peracid resulted in 50% consumption of 1. The addition of a second equivalent of peracid resulted in the complete consumption of 1 and the formation of a new species 3, as monitored by UV-vis, ESI-MS, and Moessbauer spectroscopies. ESI-MS showed 3 to be formulated as [Fe{sup II}(TMCS) + 2O]{sup +}, while EXAFS analysis suggested that 3 was an O-bound iron(II)-sulfinate complex (Fe-O = 1.95 {angstrom}, Fe-S = 3.26 {angstrom}). The addition of a third equivalent of peracid resulted in the formation of yet another compound, 4, which showed electronic absorption properties typical of an oxoiron(IV) species. Moessbauer spectroscopy confirmed 4 to be a novel iron(IV) compound, different from 2, and EXAFS (Fe{double_bond}O = 1.64 {angstrom}) and resonance Raman ({nu}{sub Fe{double_bond}O} = 831 cm{sup -1}) showed that indeed an oxoiron(IV) unit had been generated in 4. Furthermore, both infrared and Raman spectroscopy gave indications that 4 contains a metal-bound sulfinate moietymore » ({nu}{sub s}(SO{sub 2}) {approx} 1000 cm{sup -1}, {nu}{sub as}(SO{sub 2}) {approx} 1150 cm{sup -1}). Investigations into the reactivity of 1 and 2 toward H{sup +} and oxygen atom transfer reagents have led to a mechanism for sulfur oxidation in which 2 could form even in the absence of base but is rapidly protonated to yield an oxoiron(IV) species with an uncoordinated thiol moiety that acts as both oxidant and substrate in the conversion of 2 to 3.« less

We have synthesized and characterized, using X-ray crystallographic, spectroscopic, and computational techniques, a six-coordinate diazide Fe (3+) complex, LFe(N 3) 2 (where L is the tetradentate ligand 7-diisopropyl-1,4,7-triazacyclononane-1-acetic acid), that serves as a model of the azide adducts of Fe (3+) superoxide dismutase (Fe (3+)SOD). While previous spectroscopic studies revealed that two distinct azide-bound Fe (3+)SOD species can be obtained at cryogenic temperatures depending on protein and azide concentrations, the number of azide ligands coordinated to the Fe (3+) ion in each species has been the subject of some controversy. In the case of LFe(N 3) 2, the electronic absorption and magnetic circular dichroism spectra are dominated by two broad features centered at 21 500 cm (-1) (approximately 4000 M (-1) cm (-1)) and approximately 30 300 cm (-1) (approximately 7400 M (-1) cm (-1)) attributed to N3 (-) --> Fe (3+) charge transfer (CT) transitions. A normal coordinate analysis of resonance Raman (RR) data obtained for LFe(N 3) 2 indicates that the vibrational features at 363 and 403 cm (-1) correspond to the Fe-N 3 stretching modes (nu Fe-N3) associated with the two different azide ligands and yields Fe-N 3 force constants of 1.170 and 1.275 mdyne/A, respectively. RR excitation profile data obtained with laser excitation between 16,000 and 22,000 cm (-1) reveal that the nu Fe-N3 modes at 363 and 403 cm (-1) are preferentially enhanced upon excitation in resonance with the N 3 (-) --> Fe (3+) CT transitions at lower and higher energies, respectively. Consistent with this result, density functional theory electronic structure calculations predict a larger stabilization of the molecular orbitals of the more strongly bound azide due to increased sigma-symmetry orbital overlap with the Fe 3d orbitals, thus yielding higher N 3 (-) --> Fe (3+) CT transition energies. Comparison of our data obtained for LFe(N 3) 2 with those reported previously for the two azide adducts of Fe (3+)SOD provides compelling evidence that a single azide is coordinated to the Fe (3+) center in each protein species.

Two water-soluble phosphines, 3,7-diformyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane ( 1 , DFPTA) and 1-pyridylmethyl-3,5-diaza-1-azonia-7-phosphatricyclo[3.3.1.1]decane bromide ( 2 , [pymePTA]Br), have been respectively, prepared by reacting 1,3,5-triaza-7-phosphaadamantane (PTA) with formic anhydride and bromomethylpyridine. Compound 1 is only the second acyl derivative of PTA to be prepared while 2 is only the second derivative of PTA reported that contains an aromatic appendage. Both compounds were characterized by elemental analysis, FAB-MS, 1 H, 13 C, and 31 P NMR spectroscopy, and single crystal X-ray diffraction. This analysis showed that the formamide groups of 1 were in an anti confirmation in solution but in a syn confirmation in the solid state. The solubilities of 1 and 2 were examined in common organic solvents and water. It was found that 1.1 M aqueous solutions of 1 could be prepared while 2.4 M solutions of 2 were produced. The greater solubility of 2 was likely due to its ionic nature.

Complexes of the general formula cis-[MX2(PTA)2] (M = Pd, Pt; X = Cl, Br, I; PTA = 1,3,5-triaza-7-phosphaadamantane) were used to study the catalytic intramolecular hydroamination/cyclization of 4-pentyn-1-amine into 2-methyl-pyrroline in water, methanol, and dimethyl sulfoxide (DMSO). Kinetic data were measured via 1H NMR under homogeneous conditions at 50 °C and showed the following trends in rate: (i) Fastest rates were observed in D2O. (ii) The Pd complexes of this study produced faster rates than the Pt complexes. (iii) The identity of the halide had no effect on the catalytic rate. Cyclization by the catalytic precursor cis-[PdCl2(PTA)2] (4) in D2O was zero-order in substrate and first-order in metal complex with ΔH‡ = 20.0 ± 2.1 kcal/mol, ΔS‡ = −7.4 ± 6.3 cal/mol K, and Ea = 20.6 ± 2.1 kcal/mol. The acetylide complex, trans-[Pt(C C(CH2)3NH2)2(PTA)2] (6) precipitated from a catalytic mixture involving cis-[PtBr2(PTA)2] (2). Spectroscopic and kinetic studies indicated that 6 and its cis analog, 7, were the predominant species in solution and that they were both active catalysts for the cyclization reaction. These data, in conjunction with the rate trends, indicated that the mechanism of the Pd(II) and Pt(II) catalyzed hydroamination of terminal alkynylamines in aqueous solution followed a unique mechanism with cyclization of an acetylenic-amine ligand being rate determining.

The structural properties of the singly halogenated derivatives of CH(3)CN-BF(3) (X-CH(2)CN-BF(3): X = F, Cl, Br, I) have been investigated via single-crystal X-ray crystallography, solid-state infrared spectroscopy, and correlated electronic-structure theory. Taken together, these data illustrate large differences between the gas-phase and solid-state structures of these systems. Calculated gas-phase structures (B3PW91/aug-cc-pVTZ) of FCH(2)CN-BF(3), ClCH(2)CN-BF(3), and BrCH(2)CN-BF(3) indicate that the B-N dative bonds in these systems are quite weak, with distances of 2.422, 2.374, and 2.341 A, respectively. However, these distances, as well as other calculated structural parameters and normal-mode vibrational frequencies, indicate that the dative interactions do become slightly stronger in proceeding from F- to Br-CH(2)CN-BF(3). In contrast, solid-state structures for FCH(2)CN-BF(3), ClCH(2)CN-BF(3), and ICH(2)CN-BF(3) from X-ray crystallography all have B-N distances that are quite short, about 1.65 A. Thus, the B-N distances of the F- and Cl-containing derivatives contract by over 0.7 A upon crystallization. Large shifts in the vibrational modes involving motions of the BF(3) subunit parallel these structural changes. An X-ray crystal structure could not be determined for BrCH(2)CN-BF(3)(s), but the solid-state IR spectrum is consistent with those obtained previously for related complexes and suggests that the solid-state structure resembles those of the others, and in turn, implicates a large gas-solid structural difference for this species as well.

The water-soluble complex [Ir(COD)(PTA)3]Cl (1, PTA = 1,3,5-triaza-7-phosphaadamantane) was prepared by the reaction of [IrCl(COD)]2 with six equivalents of PTA under a nitrogen atmosphere. Compound 1 was fully characterized in solution and the solid state. 1 crystallized in the monoclinic space group C2/c with a = 29.648(9) A, b = 11.238(2) A, c = 19.930(2) A, and β = 96.55(2)°. Complex 1 and the related Ir(I) compounds, [IrCl(CO)(PTA)3] (2) and [Ir(CO)(PTA)4]Cl (3), were active catalysts in the intramolecular hydroamination of 4-pentyn-1-amine in water. This is the first reported study of the Ir(I) mediated transformation in aqueous media.

A combined synthetic/spectroscopic/computational approach has been employed to prepare and characterize a series of Fe(II)-thiolate complexes that model the square-pyramidal [Fe(II)(N(His))(4)(S(Cys))] structure of the reduced active site of superoxide reductases (SORs), a class of enzymes that detoxify superoxide in air-sensitive organisms. The high-spin (S = 2) Fe(II) complexes [(Me(4)cyclam)Fe(SC(6)H(4)-p-OMe)]OTf (2) and [FeL]PF(6) (3) (where Me(4)cyclam = 1,4,8,11-tetramethylcyclam and L is the pentadentate monoanion of 1-thioethyl-4,8,11-trimethylcyclam) were synthesized and subjected to structural, magnetic, and electrochemical characterization. X-ray crystallographic studies confirm that 2 and 3 possess an N(4)S donor set similar to that found for the SOR active site and reveal molecular geometries intermediate between square pyramidal and trigonal bipyramidal for both complexes. Electronic absorption, magnetic circular dichroism (MCD), and variable-temperature variable-field MCD (VTVH-MCD) spectroscopies were utilized, in conjunction with density functional theory (DFT) and semiemperical INDO/S-CI calculations, to probe the ground and excited states of complexes 2 and 3, as well as the previously reported Fe(II) SOR model [(L(8)py(2))Fe(SC(6)H(4)-p-Me)]BF(4) (1) (where L(8)py(2) is a tetradentate pyridyl-appended diazacyclooctane macrocycle). These studies allow for a detailed interpretation of the S--Fe(II) charge transfer transitions observed in the absorption and MCD spectra of complexes 1-3 and provide significant insights into the nature of Fe(II)-S bonding in complexes with axial thiolate ligation. Of the three models investigated, complex 3 exhibits an absorption spectrum that is particularly similar to the one reported for the reduced SOR enzyme (SOR(red)), suggesting that this model accurately mimics key elements of the electronic structure of the enzyme active site; namely, highly covalent Fe-S pi- and sigma-interactions. These spectral similarities are shown to arise from the fact that 3 contains an alkyl thiolate tethered to the equatorial cyclam ring, resulting in a thiolate orientation that is very similar to the one adopted by the Cys residue in the SOR(red) active site. Possible implications of our results with respect to the electronic structure and reactivity of SOR(red) are discussed.

Complexes of the general formula cis-[PtX2(PTA)2] (X = Cl, Br, I; PTA = 1,3,5-triaza-7-phosphaadamantane) were produced by the reaction of the water-soluble phosphine PTA with [MX2(COD)] (COD = 1,5-cyclooctadiene) under a nitrogen atmosphere. Compound 1 has previously been prepared by a different means and crystallographically characterized. Therefore, in order to fully compare 1–3, compounds 2 and 3 were studied both in solution and the solid state. Cis-[PtBr2(PTA)2] (2) crystallized in the monoclinic space group C2/c with a = 19.992(4) A, b = 9.741(2) A, c = 9.510(2) A, and β = 104.11(1)° while its iodide analog 3 crystallized as the HCl salt, cis-[PtI2(PTAH)2]Cl2, in the P2/n space group with a = 8.9043(1) A, b = 10.1131(1) A, c = 25.2173(1) A, and β = 90.245(1)°. Compounds 1, 2, and 3 were active catalysts in the intramolecular hydroamination of 4-pentyn-1-amine in water. This is the first reported study of this metal-mediated transformation in aqueous media.

This report describes the synthesis, structural characterization, and polymerization behavior of a series of chromium(III) complexes supported by bis(2-pyridylmethyl)alkylamine (BPA) ligands. The compounds are prepared in high yield by room-temperature reaction of the appropriate BPA ligand with CrCl3(THF)3. X-ray crystallographic studies reveal that the complexes' coordination geometries depend on the substituent at the 6-position of the pyridine ring. Unsubstituted ligands yield fac-{N-propyl-N,N-di(2-pyridylmethyl)amine}CrCl3 (6A) and fac-{N-hexyl-N,N-di(2-pyridylmethyl)amine}CrCl3(6B), whereas 6-methyl-substituted ligands produce mer-{N-propyl-N,N-di(6-methyl-2-pyridylmethyl)amine}CrCl3(6C) and mer-{N-hexyl-N,N-di(6-methyl-2-pyridylmethyl)amine}CrCl3 (6D). Moreover, ethylene polymerization studies indicate that, upon activation by methylalumoxane, the fac derivatives are 30−40 times more active than their mer counterparts.

A family of chromium complexes bearing tridentate pyridine-based ligands are disclosed as highly active precatalysts for the oligomerization of ethylene. The ligands are comprised of two distinct types: Type 1, in which both ketone groups of 2,6-diacetylpyridine are converted to imines to produce pyridine bisimine NNN ligands; and Type 2, in which only one ketone group of 2,6-diacetylpyridine is condensed with an aniline derivative to give monoimine NNO coordination sets. Ligands of either type are coordinated to chromium(II) or chromium(III) chlorides, and activation of the resultant complexes with methylaluminoxane (MAO) produces highly active ethylene oligomerization and polymerization catalysts. Catalysts of Type 1 (NNN set) generally produce 1-butene when only two ortho alkyl substituents are present but switch to making waxes or polyethylene when the size and/or number of ortho substituents are increased. Catalysts of Type 2 (NNO set) produce waxes and polyethylene under all of the substitution pat...

The reaction of the complex [Mo(OTf)(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (1) (OTf = trifluoromethylsulfonate; phen = 1,10-phenanthroline) with tetrabutylammonium fluoride trihydrate afforded the fluoride complex [MoF(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (2). The IR spectrum and the oxidation potential of 2 reflect the fact that its metal center is more electron-rich than that of the chloro analogue [MoCl(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)]. Compound 2 reacted with 1 affording the homobinuclear complex [[Mo(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)](2)(mu-F)][OTf] (3), with a fluoride bridge. Compound 2 also reacts with the species generated in situ by triflate abstraction from [M(OTf)(CO)(3)('N-N')] (M = Mn, Re; 'N-N' = 2,2'-bipyridine (bipy), phen) using NaBAr'(4) (Ar' = 3,5-bis(trifluoromethyl)phenyl), affording the heterobinuclear complexes [[Mo(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)](mu-F)[M(CO)(3)('N--N')]][BAr'(4)] (M = Mn, 'N-N' = bipy (4); M = Re, 'N-N' = phen (5)). All new compounds have been characterized by spectroscopic methods (IR and NMR) and, in the case of 1, 2, 3, and 4, also by means of X-ray diffraction analysis.

Divalent manganese, cobalt, nickel, and zinc complexes of 6-Ph(2)TPA (N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; [(6-Ph(2)TPA)Mn(CH(3)OH)(3)](ClO(4))(2) (1), [(6-Ph(2)TPA)Co(CH(3)CN)](ClO(4))(2) (2), [(6-Ph(2)TPA)Ni(CH(3)CN)(CH(3)OH)](ClO(4))(2) (3), [(6-Ph(2)TPA)Zn(CH(3)CN)](ClO(4))(2) (4)) and 6-(Me(2)Ph)(2)TPA (N,N-bis((6-(3,5-dimethyl)phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; [(6-(Me(2)Ph)(2)TPA)Ni(CH(3)CN)(2)](ClO(4))(2) (5) and [(6-(Me(2)Ph)(2)TPA)Zn(CH(3)CN)](ClO(4))(2) (6)) have been prepared and characterized. X-ray crystallographic characterization of 1A.CH(3)()OH and 1B.2CH(3)()OH (differing solvates of 1), 2.2CH(3)()CN, 3.CH(3)()OH, 4.2CH(3)()CN, and 6.2.5CH(3)()CN revealed mononuclear cations with one to three coordinated solvent molecules. In 1A.CH(3)()OH and 1B.2CH(3)()OH, one phenyl-substituted pyridyl arm is not coordinated and forms a secondary hydrogen-bonding interaction with a manganese bound methanol molecule. In 2.2CH(3)()CN, 3.CH(3)()OH, 4.2CH(3)()CN, and 6.2.5CH(3)()CN, all pyridyl donors of the 6-Ph(2)TPA and 6-(Me(2)Ph)(2)TPA ligands are coordinated to the divalent metal center. In the cobalt, nickel, and zinc derivatives, CH/pi interactions are found between a bound acetonitrile molecule and the aryl appendages of the 6-Ph(2)TPA and 6-(Me(2)Ph)(2)TPA ligands. (1)H NMR spectra of 4 and 6 in CD(3)NO(2) solution indicate the presence of CH/pi interactions, as an upfield-shifted methyl resonance for a bound acetonitrile molecule is present. Examination of the cyclic voltammetry of 1-3 and 5 revealed no oxidative (M(II)/M(III)) couples. Admixture of equimolar amounts of 6-Ph(2)TPA, M(ClO(4))(2).6H(2)O, and Me(4)NOH.5H(2)O, followed by the addition of an equimolar amount of acetohydroxamic acid, yielded the acetohydroxamate complexes [((6-Ph(2)TPA)Mn)(2)(micro-ONHC(O)CH(3))(2)](ClO(4))(2) (8), [(6-Ph(2)TPA)Co(ONHC(O)CH(3))](ClO(4))(2) (9), [(6-Ph(2)TPA)Ni(ONHC(O)CH(3))](ClO(4))(2) (10), and [(6-Ph(2)TPA)Zn(ONHC(O)CH(3))](ClO(4))(2) (11), all of which were characterized by X-ray crystallography. The Mn(II) complex 8.0.75CH(3)()CN.0.75Et(2)()O exhibits a dinuclear structure with bridging hydroxamate ligands, whereas the Co(II), Ni(II), and Zn(II) derivatives all exhibit mononuclear six-coordinate structures with a chelating hydroxamate ligand.

The spirolactone core of napalilactone and pathylactone A was synthesized in five steps from 2-methyl-2-cyclohexen-1-one or 2,3-dimethyl-2-cyclohexen-1-one. This spirolactone contains all of the carbon atoms and three of the four stereocenters of napalilactone and pathylactone A.

The synthesis of several chiral tropocoronands (6 and 7) has been accomplished. These compounds have been shown to complex with various metals. Tropocoronands that have been synthesized include H2(TC-3,cyhex) through H2(TC-6,cyhex) (6) and H2(TC-3,diphen) through H2(TC-6,diphen) (7). The route is short and the tropocoronands are easily purified by chromatography or recrystallization. Two other groups have been incorporated into tropocoronands, H2(TC-3,binap) (9) and H2(TC-6,pent) (10).

The first 1,3,5-triaza-7-phosphaadamantane (PTA) ligated iridium compounds have been synthesized. The reaction of PTA with [Ir(COD)Cl]2 (COD = 1,5-cyclooctadiene) under a CO atmosphere produces an inseparable mixture of [Ir(PTA)3(CO)Cl] (1) and the PTA analogue of Vaska's compound, [Ir(PTA)2(CO)Cl] (2). Compound 1 and [Ir(PTA)4(CO)]Cl (3) were prepared via ligand substitution reactions of PTA with Vaska's compound, trans-Ir(PPh3)2(CO)Cl, in absolute and 95% ethanol, respectively. Complex 3 crystallizes in the orthorhombic space group Pbca with a = 20.3619(4) A, b = 14.0345(3) A, c = 24.1575(5) A, and Z = 8. Single-crystal X-ray diffraction studies show that 3 has a trigonal bipyramidal structure in which the CO occupies an axial position. This is the first crystallographically characterized [IrP4(CO)]+ complex in which the CO is axially ligated. Compound 1 was converted into 3 by ligand substitution with 1 equiv of PTA in water. Interestingly, the reaction of 3 with excess NaCl did not result in the production of 1, but instead the formation of the dichloro species, [Ir(PTAH)2(PTA)2Cl2]Cl3 (4) (PTAH = protonated PTA). Dissolution of 1 or 3 in dilute HCl produced 4 and a dihydrido species, [Ir(PTAH)4(H)2]Cl5 (5), which were readily separated by inspection due to their different crystal habits. Compound 5 crystallizes in the triclinic space group P1 with a = 12.4432(9) A, b = 12.5921(9) A, c = 16.3231(12) A, alpha = 76.004(1) degrees, beta = 71.605(1) degrees, gamma = 69.177(1) degrees, and Z = 2. Complex 5 exhibits a distorted octahedral geometry with two hydride ligands in a cis configuration. A rationale consistent with these reactions is presented by consideration of the steric and electronic properties of the PTA ligand.

As part of an ongoing effort to rationally design new copper catalysts for olefin aziridination, a family of copper(II) complexes derived from new tetradentate macrocyclic ligands are synthesized, characterized both in the solid state and in solution, and screened for catalytic nitrene transfer reactivity with a representative set of olefins. The pyridylmethyl-appended diazacycloalkane ligands L6(py)2, L7(py)2, and L8(py)2 are prepared by alkylation of the appropriate diazacycloalkane (piperazine, homopiperazine, or diazacyclooctane) with picolyl chloride in the presence of triethylamine. The ligands are metalated with Cu(ClO4)(2).6H2O to provide the complexes [(L6(py)2)Cu(OClO3)]ClO4 (1), [(L7(py)2)Cu(OClO3)]ClO4 (2), and [(L8(py)2)Cu](ClO4)2 (3), which, after metathesis with NH4PF6 in CH3CN, afford [(L6(py)2)Cu(CH3CN)](PF6)2 (4), [(L7(py)2)Cu(CH3CN)](PF6)2 (5), and [(L8(py)2)Cu](PF6)2 (6). All six complexes are characterized by X-ray crystallography, which reveals that complexes supported by L6(py)2 and L7(py)2 (1, 2, 4, 5) adopt square-pyramidal geometries, while complexes 3 and 6, ligated by L8(py)2 feature tetracoordinate, distorted-square-planar copper ions. Tetragonal geometries in solution and d(x2 - y2), ground states are confirmed for the complexes by a combination of UV-visible and EPR spectroscopies. The divergent flexibility of the three supporting ligands influences the Cu(II)/Cu(I) redox potentials within the family, such that the complexes supported by the larger ligands L7(py)2 and L8(py)2 (5 and 6) exhibit quasi-reversible electron transfer processes (E1/2 approximately -0.2 V vs Ag/AgCl), while the complex supported by L6(py)2 (4), which imposes a rigid tetragonal geometry upon the central copper(II) ion, is irreversibly reduced in CH3CN solution. Complexes 4-6 are efficient catalysts (in 5 mol % amounts) for the aziridination of styrene with the iodinane PhINTs (in 80-90% yields vs PhINTs), while only 4 exhibits significant catalytic nitrene transfer reactivity with 1-hexene and cyclooctene.

Copper(I) complexes of 1,4-diisopropyl-7-R″-1,4,7-triazacyclononane (R″=2-pyridylmethyl, LPy; 6-methyl-2-pyridylmethyl, L6MePy; 5-methyl-2-pyridylmethyl, L5MePy; 6-phenyl-2-pyridylmethyl, L6PhPy; 2-quinolylmethyl, LQuin) were prepared and characterized by CHN analysis, NMR and FTIR spectroscopy, cyclic voltammetry, and mass spectrometry. An X-ray crystal structure of [L6PhPyCu]SbF6 was determined and compared to that previously reported for [LPyCu]O3SCF3; similar distorted trigonal bipyramidal geometries are adopted with the ligands coordinated in η4 fashion. The complexes [LCu]+ (L=LPy or LQuin) form adducts with CO(g) in which the heterocyclic appendage is displaced. With NO(g), [LPyCu]O3SCF3 reacts in a disproportionation process to yield N2O and [LPyCu(ONO)]O3SCF3, which was structurally defined by X-ray crystallography. Upon reaction with O2(g) at −75°C the Cu(I) complexes of LPy and L5MePy yield trans-1,2-peroxo species [LCuOOCuL]2+ as determined by UV–Vis and resonance Raman spectroscopy. In contrast, spectroscopy indicates that low temperature oxygenation of [L6PhPyCu]SbF6 yields a bis(μ-oxo)dicopper core, postulated to be capped by η3-L6PhPy (pyridyl appendage not coordinated). Decomposition of the trans-1,2-peroxo compounds results in hydroxylation of the ligand at the benzylic position of the heterocyclic appendage, but the bis(μ-oxo) complexes decay to give products resulting from N-dealkylation of the heterocycle arm. The different fates of the Cu(I) complexes of LPy and L5MePy versus that of L6PhPy upon oxygenation may be traced to the coordination of the heterocycle; in the former cases, the pyridyl unit remains coordinated, favoring trans-1,2-peroxo generation, whereas pyridyl dissociation facilitated by the sterically bulky 6-phenyl group on L6PhPy yields a [η3-L6PhPyCu]+ fragment amenable to bis(μ-oxo) core formation. The steric properties of the heterocyclic components of the ligands used in this study thus are important determinants of the reactivity of their Cu(I) complexes with small molecules.

Combined experimental and computational studies suggest that the iron-mediated aziridination of cis-1-phenylpropene proceeds along two mechanistic pathways that share a common imidoiron(IV) intermediate. One pathway involves a second species, proposed to be an azametallacyclobutane intermediate, which collapses to provide the syn-aziridine product. A second, parallel pathway is responsible for the formation of an anti-aziridine.

A new family of enantiomerically pure pyrazoles with a variety of substitutions on a key stereogenic center was synthesized from (R)-(+)-pulegone by a straightforward, large-scale route involving initial construction of the pyrazole ring via formylation/dehydration with hydrazine followed by ozonolysis to yield a readily functionalized ketone (5). Alkylation of 5 with a variety of Grignard reagents, dehydration, hydrogenation, and recrystallization afforded the set of new chiral pyrazoles (7a−c). Cis and/or trans diastereomers of one of these pyrazoles having a phenyl substituent (7a) were elaborated into enantiopure, multidentate C1-symmetric bis(pyrazolyl)diphenylborate (Tl[cis-Ph2Bppm]), C2-symmetric bis(pyrazolyl)methane (cis- and trans-Xpm), and C3-symmetric tris(pyrazolyl)phosphine oxide (cis- and trans-OPpm) and tris(pyrazolyl)hydroborate (K[trans-Tppm]) ligands. Interestingly, epimerization of the benzylic stereogenic center occurred during the synthesis of K[trans-Tppm], as determined by comparis...

Copper complexes of the new ligands1a LPiv and LRAmR‘ that comprise 1,4-diisopropyl-1,4,7-triazacyclononanes linked to secondary and tertiary amide groups were prepared and characterized, with a particular view toward evaluating amide structural, spectroscopic, and potential hydrogen-bonding influences of relevance to ongoing copper−dioxygen reactivity studies. X-ray crystal structures of the Cu(I) complexes [LCu(CH3CN)]X (L = LHAmMe, X = ClO4; L = LPiv, X = CF3SO3) revealed typical 4-coordinate geometries with the amide dangling free, while those of the Cu(II) compounds [LCuCl]X (L = LHAmMe, X = ClO4; L = LMeAmH, X = PF6) and [LPivCu(O3SCF3)]O3SCF3 showed 5-coordinate square pyramidal geometries with the amide coordinated to the metal via its carbonyl oxygen atom. Analysis of FTIR spectra of the aforementioned compounds and the carbon monoxide adducts [LMeAmR‘Cu(CO)]SbF6 (R‘ = H or Me) allowed (i) identification of signatures of amide structural features, hydrogen bonding, and metal coordination and (ii)...

The reactivity of dicopper(I) complexes of the ligands α,α‘-bis(4,7-diisopropyl-1,4,7-triazacyclononan-1-yl)-p- and m-xylene (p- and m-XYLiPr4) with dioxygen was examined by spectroscopic and rapid...

A series of CuII and ZnII complexes with new ligands having either one or two substituted phenolates appended to the 1,4,7-triazacyclononane frame were prepared and characterized by optical absorption, EPR, NMR, and/or resonance Raman spectroscopy, cyclic voltammetry, and, in eight cases, X-ray crystallography. Features of the active site geometries of the CuII−tyrosinate forms of galactose and glyoxal oxidases (GAO and GLO) were modeled by these complexes, including the binding of a redox-active phenolate and an exogenous ligand (Cl-, CH3CO2-, or CH3CN) in a cis-equatorial position of a square pyramidal metal ion. The role of the unique ortho S−C covalent bond between a cysteine (C228) and the equatorial tyrosinate (Y272) in the proteins was probed through an examination of the optical absorption and electrochemical properties of sets of similar complexes comprised of phenolate ligands with differing ortho substituents, including thioether groups. The o-alkylthio unit influences the PhO- → CuII LMCT tran...

Two compounds with novel connectivities, (Et2O)2Li[μ-E(SiMe3)2]2GaH2 (E = P (1), As (2)), formally lithium pnictidogallates, were synthesized in the reactions between LiGaH4 and E(SiMe3)3 in diethyl ether via trimethylsilane elimination. No reaction took place for E = N under comparable conditions. Structural characterizations showed 1 and 2 to be isomorphous in the solid state and feature the planar four-membered rings of the {Li[μ-E]2Ga} core.

Thiolate-ligated oxoiron(IV) centers are postulated to be the key oxidants in the catalytic cycles of oxygen-activating cytochrome P450 and related enzymes. Despite considerable synthetic efforts, chemists have not succeeded in preparing an appropriate model complex. Here we report the synthesis and spectroscopic characterization of [Fe IV (O)(TMCS)] + where TMCS is a pentadentate ligand that provides a square pyramidal N 4 (SR) apical , where SR is thiolate, ligand environment about the iron center, which is similar to that of cytochrome P450. The rigidity of the ligand framework stabilizes the thiolate in an oxidizing environment. Reactivity studies suggest that thiolate coordination favors hydrogen-atom abstraction chemistry over oxygen-atom transfer pathways in the presence of reducing substrates.

In an effort to provide precedence for postulated intermediates in copper-protein-mediated nitrite reduction, a series of novel complexes containing the CuI−NO2- unit, including monocopper(I), dicopper(I,I), and mixed valence dicopper(I,II) and copper(I)−zinc(II) species, were prepared, fully characterized, and subjected to reactivity studies designed to probe their ability to produce nitric oxide. Treatment of solutions of [LCu(CH3CN)]PF6 (L = Li-Pr3, 1,4,7-triisopropyl-1,4,7-triazacyclononane, or LBn3, 1,4,7-tribenzyl-1,4,7-triazacyclononane) in MeOH with excess NaNO2 yielded the novel dicopper(I,I) complexes [(LCu)2(μ-NO2)]PF6. The complex with L = Li-Pr3 was cleaved by PPh3 to afford [Li-Pr3Cu(PPh3)]PF6 and Li-Pr3Cu(NO2), a structural model for the substrate adduct of copper nitrite reductase. Oxidation of the dicopper(I,I) compound (L = Li-Pr3) with (Cp2Fe)(PF6) in CH2Cl2 yielded the deep red, mixed valent, dicopper(I,II) species [(Li-Pr3Cu)2(μ-NO2)](PF6)2, which was structurally characterized as its...

The results of experiments designed to probe the mechanism by which the bis(μ-oxo)dicopper complexes [(LCu)2(μ-O)2](ClO4)2 (L = 1,4,7-tribenzyl-, 1,4,7-triisopropyl-, and 1,4-diisopropyl-7-benzyl-1,4,7-triazacyclononane ligands; LBn3, LiPr3, and LiPr2Bn, respectively) decompose to products arising from macrocyclic ligand N-dealkylation are described. After removal of copper from the decomposed solutions, analysis of the organic products revealed N-dealkylated ligands and aldehyde or ketone, the oxygen atoms in the latter being derived from the bis(μ-oxo)dicopper core as shown by 18O-isotope labeling experiments. Thus, the overall N-dealkylation is akin to monooxygenase reactions carried out by various metalloenzymes such as cytochrome P450, dopamine β-monooxygenase, and peptidyl glycine α-amidating monooxygenase. Direct, intramolecular attack of the bis(μ-oxo)dicopper core at a ligand substituent C−H bond during the rate-determining step was indicated by the observed first-order kinetics, the results of H...

A compound previously reported (Harata et al. J. Am. Chem. Soc. 1994, 116, 10817) as the first structurally characterized example of a monocopper−superoxo complex is shown instead to be [(tppa)Cu(OH)]ClO4, a novel mononuclear hydroxide complex of copper stabilized by intramolecular hydrogen-bonding interactions. An X-ray crystal structure of the compound independently prepared from tppa, Cu(ClO4)2·6H2O, and aqueous NaOH is identical to that mistakenly attributed to the superoxo complex.

A description of the structure and bonding of novel bis(μ-oxo)dicopper complexes and their bis(μ-hydroxo)dicopper decomposition products was derived from combined X-ray crystallographic, spectroscopic, and ab initio theoretical studies. The compounds [(LCu)2(μ-O)2]X2 were generated from the reaction of solutions of [LCu(CH3CN)]X with O2 at −80 °C (L = 1,4,7-tribenzyl-1,4,7-triazacyclononane, LBn3; 1,4,7-triisopropyl-1,4,7-triazacyclononane, LiPr3; or 1-benzyl-4,7-diisopropyl-1,4,7-triazacyclononane, LiPr2Bn; X = variety of anions). The geometry of the [Cu2(μ-O)2]2+ core was defined by X-ray crystallography for [(d21-LBn3Cu)2(μ-O)2](SbF6)2 and by EXAFS spectroscopy for the complexes capped by LBn3 and LiPr3; notable dimensions include short Cu−O (∼1.80 A) and Cu···Cu (∼2.80 A) distances like those reported for analogous M2(μ-O)2 (M = Fe or Mn) rhombs. The core geometry is contracted compared to those of the bis(μ-hydroxo)dicopper(II) compounds that result from decomposition of the bis(μ-oxo) complexes upon...

The spirolactone core of napalilactone and pathylactone A was synthesized in five steps from 2-methyl-2-cyclohexen-1-one or 2,3-dimethyl-2-cyclohexen-1-one. This spirolactone contains all of the carbon atoms and three of the four stereocenters of napalilactone and pathylactone A.

A series of divalent metal flavonolate complexes of the general formula [(6-Ph(2)TPA)M(3-Hfl)]X (1-5-X; X = OTf(-) or ClO(4)(-); 6-Ph(2)TPA = N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II); 3-Hfl = 3-hydroxyflavonolate) were prepared and characterized by X-ray crystallography, elemental analysis, FTIR, UV-vis, (1)H NMR or EPR, and cyclic voltammetry. All of the complexes have a bidentate coordinated flavonolate ligand. The difference in M-O distances (Delta(M-O)) involving this ligand varies through the series, with the asymmetry of flavonolate coordination increasing in the order Mn(II) approximately Ni(II)Cu(II)Zn(II)Co(II). The hypsochromic shift of the absorption band I (pi--pi*) of the coordinated flavonolate ligand in 1-5-OTf (relative to that in free anion) increases in the order Ni(II)Mn(II)Cu(II)Zn(II), Co(II). Previously reported 3-Hfl complexes of divalent metals fit well with this ordering. (1)H NMR studies indicate that the 3-Hfl complexes of Co(II), Ni(II), and Zn(II) exhibit a pseudo-octahedral geometry in solution. EPR studies suggest that the Mn(II) complex 1-OTf may form binuclear structures in solution. The mononuclear Cu(II) complex 4-OTf has a distorted square pyramidal geometry. The oxidation potential of the flavonolate ligand depends on the metal ion present and/or the solution structure of the complex, with the Mn(II) complex 1-OTf exhibiting the lowest potential, followed by the pseudo-octahedral Ni(II) and Zn(II) 3-Hfl complexes, and the distorted square pyramidal Cu(II) complex 4-OTf. The Mn(II) complex [(6-Ph(2)TPA)Mn(3-Hfl)]OTf (1-OTf) is unique in the series in undergoing ligand exchange reactions in the presence of M(ClO(4))(2).6H(2)O (M = Co, Ni, Zn) in CD(3)CN to produce [(6-Ph(2)TPA)M(CD(3)CN)(n)](X)(2), [Mn(3-Hfl)(2).0.5H(2)O], and MnX(2) (X = OTf(-) or ClO(4)(-)). Under similar conditions, the 3-Hfl complexes of Co(II), Ni(II), and Cu(II) undergo flavonolate ligand exchange to produce [(6-Ph(2)TPA)M(CD(3)CN)(n)](X)(2) (M = Co, Ni, Cu; n = 1 or 2) and [Zn(3-Hfl)(2).2H(2)O]. An Fe(II) complex of 3-Hfl, [(6-Ph(2)TPA)Fe(3-Hfl)]ClO(4) (8), was isolated and characterized by elemental analysis, FTIR, UV-vis, (1)H NMR, cyclic voltammetry, and a magnetic moment measurement. This complex reacts with O(2) to produce the diiron(III) mu-oxo compound [(6-Ph(2)TPAFe(3Hfl))(2)(mu-O)](ClO(4))(2) (6).

The structurally characterized copper complex [(i-Pr3TACN)Cu(O2CCF3)2] (1) mediates nitrene transfer from PhINTs to olefins to form N-tosylaziridines in good to excellent yields, in catalytic amounts (0.5 mol %) 1 order of magnitude less than is required for other copper catalysts, such as [Cu(acac)2]. Nitrene transfer reactivity has also been observed with substituted styrenes, internal and terminal aliphatic olefins, and sulfides, suggesting that 1 may be a general nitrene transfer catalyst for use on organic synthesis.

Iron(II) complexes of polydentate nitrogen donor ligands catalyze the rapid aziridination of olefins by PhINTs.

This report describes the synthesis and characterization of metal halide complexes (M = Mn, Fe, Co) supported by a new family of pendant donor-modified alpha-diimine ligands. The donor (N, O, P, S) substituent is linked to the alpha-diimine by a short hydrocarbon spacer forming a tridentate, mer-coordinating ligand structure. The tridentate ligands are assembled from monoimine precursors, the latter being synthesized by selective reaction with one carbonyl group of the alpha-dione. While attempts to separately isolate tridentate ligands in pure form were unsuccessful, metal complexes supported by the tridentate ligand are readily synthesized in-situ, by forming the ligand in the presence of the metal halide, resulting in a metal complex which subsequently crystallizes out of the reaction mixture. Metal complexes with NNN, NNO, NNP and NNS donor sets have been prepared and examples supported by NNN, NNP and NNS ligands have been structurally characterized. In the solid state, NNN and NNP ligands coordinate in a mer fashion and the metal complexes possess distorted square pyramidal structures and high spin (S = 2) electronic configurations. Compounds with NNS coordination environments display a variety of solid state structures, ranging from those with unbound sulfur atoms, including chloride bridged and solvent ligated species, to those with sulfur weakly bound to the metal center. The extent of sulfur ligation depends on the donor ability of the crystallization solvent and the substitution pattern of the arylthioether substituent.

The first examples of mononuclear nitrogen/sulfur-ligated Co(II) alkoxide complexes, species of relevance to a reactive intermediate observed for Co(II)-substituted liver alcohol dehydrogenase, have been isolated and characterized by multiple methods including X-ray crystallography, EPR, paramagnetic (1)H NMR, and cyclic voltammetry.

New metal(II)-thiolate complexes supported by the tetradentate ligand 1,5-bis(2-pyridylmethyl)-1,5-diazacyclooctane (L(8)py(2)) have been synthesized and subjected to physical, spectroscopic, structural, and computational characterization. The X-ray crystal structures of these complexes, [L(8)py(2)M(S-C(6)H(4)-p-CH(3))]BPh(4) (M = Co, Ni, Zn), reveal distorted square-pyramidal divalent metal ions with four equatorial nitrogen donors from L(8)py(2) and axial p-toluenethiolate ligands. The reactions of the complexes with benzyl bromide produce isolable metal(II)-bromide complexes (in the cases of Co and Ni) and the thioether benzyl-p-tolylsulfide. This reaction is characterized by a second-order rate law (nu = k(2)[L(8)py(2)M(SAr)(+)][PhCH(2)Br]) for all complexes (where M = Fe, Co, Ni, or Zn). Of particular significance is the disparity between k(2) for M = Fe and Co versus k(2) for M = Ni and Zn, in that k(2) for M = Ni and Zn is ca. 10 times larger (faster) than k(2) for M = Fe and Co. An Eyring analysis of k(2) for [L(8)py(2)Co(SAr)](+) and [L(8)py(2)Ni(SAr)](+) reveals that the reaction rate differences are not rooted in a change in mechanism, as the reactions of these complexes with benzyl bromide exhibit comparable activation parameters (M = Co: DeltaH() = 45(2) kJ mol(-)(1), DeltaS() = -144(6) J mol(-)(1) K(-)(1); M = Ni: DeltaH() = 43(3) kJ mol(-)(1), DeltaS() = -134(8) J mol(-)(1) K(-)(1)). Electronic structure calculations using density functional theory (DFT) reveal that the enhanced reaction rate for [L(8)py(2)Ni(SAr)](+) is rooted in a four-electron repulsion (or a "filled/filled interaction") between a completely filled nickel(II) d(pi) orbital and one of the two thiolate frontier orbitals, a condition that is absent in the Fe(II) and Co(II) complexes. The comparable reactivity of [L(8)py(2)Zn(SAr)](+) relative to that of [L(8)py(2)Ni(SAr)](+) arises from a highly ionic zinc(II)-thiolate bond that enhances the negative charge density on the thiolate sulfur. DFT calculations on putative thioether-coordinated intermediates reveal that the Co(II)- and Zn(II)-thioethers exhibit weaker M-S bonding than Ni(II). These combined results suggest that while Ni(II) may serve as a competent replacement for Zn(II) in alkyl group transfer enzymes, turnover may be limited by slow product release from the Ni(II) center.

Superoxide reductase (SOR) is an Fe protein that catalyzes the reduction of superoxide to give H(2)O(2). Recently, the mutation of the Glu47 residue into alanine (E47A) in the active site of SOR from Desulfoarculus baarsii has allowed the stabilization of an iron-peroxo species when quickly reacted with H(2)O(2) [Math{\'e} et al. (2002) J. Am. Chem. Soc. 124, 4966-4967]. To further investigate this non-heme peroxo-iron species, we have carried out a M{\"o}ssbauer study of the (57)Fe-enriched E47A SOR from D. baarsii reacted quickly with H(2)O(2). Considering the M{\"o}ssbauer data, we conclude, in conjunction with the other spectroscopic data available and with the results of density functional calculations on related models, that this species corresponds to a high-spin side-on peroxo-Fe(3+) complex. This is one of the first examples of such a species in a biological system for which M{\"o}ssbauer parameters are now available: delta(/Fe) = 0.54 (1) mm/s, DeltaE(Q) = -0.80 (5) mm/s, and the asymmetry parameter eta = 0.60 (5) mm/s. The M{\"o}ssbauer and spin Hamiltonian parameters have been evaluated on a model from the side-on peroxo complex (model 2) issued from the oxidized iron center in SOR from Pyrococcus furiosus, for which structural data are available in the literature [Yeh et al. (2000) Biochemistry 39, 2499-2508]. For comparison, similar calculations have been carried out on a model derived from 2 (model 3), where the [CH(3)-S](1)(-) group has been replaced by the neutral [NH(3)](0) group [Neese and Solomon (1998) J. Am. Chem. Soc. 120, 12829-12848]. Both models 2 and 3 contain a formally high-spin Fe(3+) ion (i.e., with empty minority spin orbitals). We found, however, a significant fraction (approximately 0.6 for 2, approximately 0.8 for 3) of spin (equivalently charge) spread over two occupied (minority spin) orbitals. The quadrupole splitting value for 2 is found to be negative and matches quite well the experimental value. The computed quadrupole tensors are rhombic in the case of 2 and axial in the case of 3. This difference originates directly from the presence of the thiolate ligand in 2. A correlation between experimental isomer shifts for Fe(3+) mononuclear complexes with computed electron densities at the iron nucleus has been built and used to evaluate the isomer shift values for 2 and 3 (0.56 and 0.63 mm/s, respectively). A significant increase of isomer shift value is found upon going from a methylthiolate to a nitrogen ligand for the Fe(3+) ion, consistent with covalency effects due to the presence of the axial thiolate ligand. Considering that the isomer shift value for 3 is likely to be in the 0.61-0.65 mm/s range [Horner et al. (2002) Eur. J. Inorg. Chem., 3278-3283], the isomer shift value for a high-spin eta(2)-O(2) Fe(3+) complex with an axial thiolate group can be estimated to be in the 0.54-0.58 mm/s range. The occurrence of a side-on peroxo intermediate in SOR is discussed in relation to the recent data published for a side-on peroxo-Fe(3+) species in another biological system [Karlsson et al. (2003) Science 299, 1039-1042]., Comment: Biochemistry, American Chemical Society, 2004, pp.8815-25

Symmetric binding of nitrite via both O atoms to CuI [Cu--O = 2.191 (4) A] was observed. The copper coordination geometry is significantly distorted from tetrahedral, as evidenced by the angles P--Cu--P [127.75 (7) degrees] and O--Cu--O [56.7 (2) degrees].

A facile synthesis of 1,4,8-trimethylcyclam and a thioalkyl-pendant derivative are reported, and the X-ray crystal structure of a nickel(II) complex illustrates structural consequences of appending the thiolate donor onto the macrocycle.

We report the synthesis, structural and spectroscopic characterization, and magnetic and electrochemical studies of a series of iron(II) complexes of the pyridyl-appended diazacyclooctane ligand L(8)py(2), including several that model the square-pyramidal [Fe(II)(N(his))(4)(S(cys))] structure of the reduced active site of the non-heme iron enzyme superoxide reductase. Combination of L(8)py(2) with FeCl(2) provides [L(8)py(2)FeCl(2)] (1), which contains a trigonal-prismatic hexacoordinate iron(II) center, whereas a parallel reaction using [Fe(H(2)O)(6)](BF(4))(2) provides [L(8)py(2)Fe(FBF(3))]BF(4) (2), a novel BF(4)(-)-ligated square-pyramidal iron(II) complex. Substitution of the BF(4)(-) ligand in 2 with formate or acetate ions affords distorted pentacoordinate [L(8)py(2)Fe(O(2)CH)]BF(4) (3) and [L(8)py(2)Fe(O(2)CCH(3))]BF(4) (4), respectively. Models of the superoxide reductase active site are prepared upon reaction of 2 with sodium salts of aromatic and aliphatic thiolates. These model complexes include [L(8)py(2)Fe(SC(6)H(4)-p-CH(3))]BF(4) (5), [L(8)py(2)Fe(SC(6)H(4)-m-CH(3))]BF(4) (6), and [L(8)py(2)Fe(SC(6)H(11))]BF(4) (7). X-ray crystallographic studies confirm that the iron(II)-thiolate complexes model the square-pyramidal geometry and N(4)S donor set of the reduced active site of superoxide reductase. The iron(II)-thiolate complexes are high spin (S = 2), and their solutions are yellow in color because of multiple charge-transfer transitions that occur between 300 and 425 nm. The ambient temperature cyclic voltammograms of the iron(II)-thiolate complexes contain irreversible oxidation waves with anodic peak potentials that correlate with the relative electron donating abilities of the thiolate ligands. This electrochemical irreversibility is attributed to the bimolecular generation of disulfides from the electrochemically generated iron(III)-thiolate species.