Steric stabilization of a monomeric proalumatrane: experimental and theoretical studies

Treatment of tripodal tris(3-tert-butyl-2-hydroxy-5-methylbenzyl)amine (L) with 1 equiv of trimethylaluminum in toluene gave the stable proalumatrane (AlL) (1) [wherein L = tris(3-tert-butyl-5-methyl-2-oxidobenzyl)amine] featuring a distorted trigonal monopyramidal four-coordinate aluminum geometry. An analogous reaction uses the less sterically congested isomer of L, namely, tris(5-tert-butyl-2-hydroxy-3-methylbenzyl)amine provided dimeric (AlL')2 (2) [wherein L' = tris(5-tert-butyl-3-methyl-2-oxidobenzyl)amine], which contains two bridging alumatrane moieties possessing five-coordinate TBP aluminum geometries. Reaction of AlL with water provided the adduct H2O.AlL (3), a species that is representative of a coordinatively stabilized intermediate in the hydrolysis of an aluminum alkoxide. Theoretical calculations revealed that considerable stabilization energy is obtained by the coordination of a water molecule to the tetracoordinate aluminum in AlL and that this result is consistent with the postulate that the Lewis acidity of AlL exceeds that of boron trifluoride, despite the presence of the transannular N-->Al bond in AlL.     

The first example of a monomeric alumatrane

The novel five-coordinate aluminum adduct Me(2)HN. AlL (2) [wherein L = tris(2-oxy-3,5-dimethylbenzyl)amine] containing three six-membered rings has been characterized by spectroscopic and by X-ray means. This adduct of an alumatrane is the first structurally characterized monomeric alumatrane derivative, and unlike its parent alumatrane [Al(OCH(2)CH(2))(3)N](x), 2 is monomeric in the gas, solution, and solid states. The X-ray molecular structure of 2 reveals a tricyclic cage moiety of C(3) symmetry. The aluminum geometry is a slightly distorted trigonal bipyramid in which, quite unexpectedly, the metal atom is located somewhat below the plane formed by three equatorial oxygens and its Al-N(tertiary) bond is shorter than that in Me(3)N.AlH(3).NMe(3) (Heitsch, C. W.; Nordman, C. E.; Parry, R. W. Inorg. Chem. 1963, 2, 508).     

Homogeneous forced hydrolysis of aluminum through the thermal decomposition of urea

Homogeneous hydrolysis of aluminum by decomposition of urea in solution was achieved because the urea coordinates to the Al3+ in solution, forming [Al(H2O)5 (urea)]3+ and to a lesser extent [Al(H2O)4 (urea)2]3+. Upon hydrolysis more hydrolyzed monomeric species, [Al(H2O)5 (OH)]2+, [Al(H2O)4 (OH)2]+, [Al(H2O)4 (urea)(OH)]2+, and [Al(H2O)3 (urea)(OH)2]+, were formed, followed by trimeric species and the Al13 Keggin complex [AlO4Al12(OH)24(H2O)12]7+. The 27Al NMR spectra indicated the formation of other complexes in addition to the Al13 at the end of the hydrolysis reaction.     

Synthesis and structure of cyclic phosphate, phosphoramidate, phosphonates, and phosphonium salts. Phosphatrane formation

Reaction of tris(2-hydroxy-3,5-dimethylbenzyl)amine (6) with phosphorus reagents led to the formation of the phosphoramidate, N[CH2(Me2C6H2)O]2PO (1), the phosphate N[CH2(Me2C6H2)O]2[CH2(Me2C6H2)OH]P(O)(OPh) (2), the phosphonium salts N[CH2(Me2C6H2)O]3PMe+I- (3A) and N[CH2(Me2C6H2)O]3PMe+I3- (3B), and the phosphonates N[CH2(Me2C6H2)O]2[CH2(Me2C6H2)OH]P(O)Me (4) and N[CH2(Me2C6H2)O]2[CH2(Me2C6H2)OSiMe3]P(O)Me (5). X-ray analysis provided molecular structures for all of the compounds. The solid-state structural representations were supported in solution by an analysis of the NCH2 proton NMR patterns. The structures of 3A and 3B show the presence of phosphatranes with weak P-N donor interactions. These represent the first phosphatranes containing all six-membered rings. Variable temperature analysis of the 1H NMR spectra of 3A indicates fluxional behavior whereby a racemic mixture of the chiral phosphonium salt rapidly intraconverts at room temperature. The activation energy for the enantiomeric conversion of the clockwise and anticlockwise orientations of the propeller-like phosphatrane is 11.2 kcal/mol, which is compared to that of the isoelectronic silatrane N[CH2(Me2C6H2)O]3SiMe (E), 10.3 kcal/mol.     

Syntheses and characterization of mu,eta(1),eta(1)-3,5-di-tert-butylpyrazolato derivatives of aluminum

The 3,5-di-tert-butylpyrazolato (3,5-tBu(2)pz) derivatives of aluminum [(eta(1),eta(1)-3,5-tBu(2)pz)(mu-Al)R(1)R(2)](2) (R(1) = R(2) = Me 1; R(1) = R(2) = Et, 2; R(1) = R(2) = Cl, 3; R(1) = R(2) = I, 4; [(eta(2)-3,5-tBu(2)pz)(3)Al], 5; [Al(2)(eta(1),eta(1)-3,5-tBu(2)pz)(2)(mu-E)(C triple bond CPh)(2)] (E = S (6), Se (7), Te (8)) have been prepared in good yield. Compounds 1 and 2 were obtained by the reactions of H[3,5-tBu(2)pz] with Me(3)Al and Et(3)Al, respectively. Reaction of [(eta(1),eta(1)-3,5-tBu(2)pz)(mu-Al)H(2)](2) with the pyrazole H[3,5-tBu(2)pz] gave [(eta(2)-3,5-tBu(2)pz)(3)Al] (5). The reaction of [(eta(1),eta(1)-3,5-tBu(2)pz)(mu-Al)R(2)](2) (R = H, Me) and I(2) yielded 4, while the reaction of 1 equiv of K[3,5-tBu(2)pz] and AlCl(3) afforded 3. In addition, the reaction of [Al(2)(eta(1),eta(1)-3,5-tBu(2)pz)(2)(mu-E)H(2)] and HC triple bond CPh gave 6, 7, and 8. All compounds have been characterized by elemental analysis, NMR, and mass spectroscopy. The molecular structure analyses of compounds 1, 3, 6, and 7 by X-ray crystallography showed that complexes 1 and 3 are dimeric with two eta(1),eta(1)-pyrazolato groups in twisted conformation while 6 and 7 with two eta(1),eta(1)-pyrazolato groups display a boat conformation.     

(RO)(2)Ta[tris(2-oxy-3,5-dimethylbenzyl)amine]: structure and lactide polymerization activities

The novel atrane-like six-coordinate (RO)(2)TaL complexes [where R = Me or Et and L = tris(2-oxy-3,5-dimethylbenzyl)amine] containing three six-membered rings have been synthesized and characterized. The R = Me complex is the first group 5 representative of this class of compounds structurally characterized by X-ray means. Somewhat surprisingly, these compounds failed to function as single-site initiators for the polymerization of l-LA to isotactic PLA and rac-LA to atactic PLA, whereas Ta(OEt)(5) and two titanium analogues ROTiL (where R = 2,6-di-i-PrC(6)H(3) and i-Pr) as well as Ti(O-i-Pr)(4) were effective catalysts for both polymerizations.     

Crystal structure of [Al4(OH)6(H2O)12][Al(H2O)6]2Br12: a new polyaluminum compound

A vertex-shared tetrahedral [Al(4)(OH)(6)(H(2)O)(12)](6+) (Al(4)) and a disordered [Al(H(2)O)(6)](3+) (Al(1)) that coexist in a 1:2 ratio within each unit cell were observed in the structure of [Al(4)(OH)(6)(H(2)O)(12)][Al(H(2)O)(6)](2)Br(12), which crystallized in a cubic Fd3m space group from a spontaneously hydrolyzed solution of AlBr(3). The former is composed of four AlO(6) octahedra that are connected to each other by sharing three vertexes of each octahedron and form a large regular tetrahedron with ideal T(d) symmetry. The central Al(3+) ion of the latter is coordinated by 6 disordered OH(2) molecules, that form a core-shell structure with ideal D(3d) symmetry.     

Synthesis, crystal structure, and solid-state NMR spectroscopy of a new open-framework aluminophosphate (NH(4))(2)Al(4)(PO(4))(4)(HPO(4))xH(2)O

A new three-dimensional open-framework aluminophosphate (NH(4))(2)Al(4)(PO(4))(4)(HPO(4)).H(2)O (denoted AlPO-CJ19) with an Al/P ratio of 4/5 has been synthesized, using pyridine as the solvent and 2-aminopyridine as the structure-directing agent, under solvothermal conditions. The structure was determined by single-crystal X-ray diffraction and further characterized by solid-state NMR techniques. The alternation of the Al-centered polyhedra (including AlO(4), AlO(5), and AlO(6)) and the P-centered tetrahedra (including PO(4) and PO(3)OH) results in an interrupted open-framework structure with an eight-membered ring channel along the [100] direction. This is the first aluminophosphate containing three kinds of Al coordinations (AlO(4), AlO(5), and AlO(6)) with all oxygen vertexes connected to framework P atoms. (27)Al MAS NMR, (31)P MAS NMR, and (1)H --> (31)P CPMAS NMR characterizations show that the solid-state NMR techniques are an effective complement to XRD analysis for structure elucidation. Furthermore, all of the possible coordinations of Al and P in the aluminophosphates with an Al/P ratio of 4/5 are summarized. Crystal data: (NH(4))(2)Al(4)(PO(4))(4)(HPO(4))xH(2)O, monoclinic P2(1) (No. 4), a = 5.0568(3) A, b = 21.6211(18) A, c = 8.1724(4) A, beta = 91.361(4) degrees , V = 893.27(10) A(3), Z = 2, R(1) = 0.0456 (I > 2 sigma(I)), and wR(2) = 0.1051 (all data).     

The donor ability of the chelated carbonate ligand: protonation and metallation of [(L)Co(O2CO)]+ complexes in aqueous solution

The syntheses and X-ray structures of [Co(Me-tpa)O(2)COZnCl(3)], [Co(pmea)O(2)COZnCl(3)].H(2)O [Co(trpyn)O(2)COZn(OH(2))(4)OCO(2)Co(trpyn)](ZnCl(4))(2).H(2)O, [Co(trpyn)(O(2)COH)]ZnCl(4).3H(2)O and [Co(trpyn)(O(2)CO)]ClO(4) are reported (Me-tpa = [(6-methyl-2-pyridyl)methyl]bis(2-pyridylmethyl)amine, pmea = bis(2-pyridylmethyl)-2-(2-pyridylethyl)amine, trpyn = tris(2-(1-pyrazolyl)ethyl)amine). The chelated bicarbonate complex [Co(trpyn)(O(2)COH)]ZnCl(4).3H(2)O is isolated as a crystalline solid from an acidic solution of the parent carbonate [Co(trpyn)(O(2)CO)]ClO(4), and X-ray structural analysis shows that lengthening of the C[double bond, length as m-dash]O(exo) bond and shortening of the C-O(endo) bond accompanies protonation. The bimetallic complex [Co(Me-tpa)O(2)COZnCl(3)] results from the unexpected coordination of ZnCl(3)(-) to the exo O atom of a chelated carbonate ligand. This complex is obtained from both acidic and neutral solutions in which [Zn(2+)] = 1.0 M, while the structurally similar complex [Co(pmea)O(2)COZnCl(3)].H(2)O is isolated from an analogous neutral solution. The trimetallic complex [Co(trpyn)O(2)COZn(OH(2))(4)OCO(2)Co(trpyn)](ZnCl(4))(2).H(2)O crystallises on prolonged standing of [Co(trpyn)(O(2)CO)]ClO(4) in a neutral solution having [Zn(2+)] = 1.0 M. The Zn-O bond lengths in all three complexes are indicative of bonds of significant strength. DFT calculations show that the nature of the bonding interaction between the Co(iii) ion and the endo O atoms of the carbonate ligand remain essentially unaffected by coordination of Zn(2+) to the exo O atom. They also show that such coordination of Zn(2+) decreases the C-O(exo) bond order.     

Alkoxo, chlorido, and methyl derivatives of oxidomolybdenum(VI) complexes with tetradentate [O3N]-type ligands

Dioxomolybdenum(VI) complex [MoO₂(Heg)₂] (H₂eg = 1,2-ethanediol) reacts with phenolic ligand precursors tris(2-hydroxy-3,5-dimethylbenzyl)amine (H₃L^Me) and tris(2-hydroxy-3,5-di-tert-butylbenzyl)amine (H₃L^tBu) to form oxomolybdenum(VI) complexes of type [MoO(L^R) (Heg)]. The Heg ligand can be replaced by other alcohols (i.e. 2-aminoethanol, 2-amino-2-methylpropan-1-ol, 2-(dimethylamino)ethanol or allyl alcohol) in the reaction at refluxing toluene or at neat alcohol. Treatment of [MoO(L^R)(Heg)] with Me₃SiCl yields corresponding chlorido complexes [MoO(L^R)Cl]. These are also formed in the reaction of H₃L^R with [MoO₂Cl₂(dmf)₂]. The reaction of [MoO(L^R)Cl] with MeMgI yields air-stable monomethyl derivatives [MoO(L^R)(Me)]. X-ray analyses of [MoO(L^tBu)X] (X = Heg, 2-methyl-2-aminopropanolate anion or Cl) reveal that the ligand L^R has a tetradentate coordination through three oxygen donors and one nitrogen donor, which is located trans to the terminal oxo group. The sixth coordination site is occupied by an oxygen donor, a chlorido ligand or a methyl group.     

Synthesis and characterization of ethylbis(2-pyridylethyl)amineruthenium complexes and two different types of C-H bond cleavage at an ethylene arm

Ruthenium complexes bearing ethylbis(2-pyridylethyl)amine (ebpea), which has flexible -C(2)H(4)- arms between the amine and the pyridyl groups and coordinates to a metal center in facial and meridional modes, have been synthesized and characterized. Three trichloro complexes, fac-[Ru(III)Cl(3)(ebpea)] (fac-[1]), mer-[Ru(III)Cl(3)(ebpea)] (mer-[1]), and mer-[Ru(II)Cl(3){η(2)-N(C(2)H(5))(C(2)H(4)py)═CH-CH(2)py}] (mer-[2]), were synthesized using the Ru blue solution. Formation of mer-[2] proceeded via a C-H activation of the CH(2) group next to the amine nitrogen atom of the ethylene arm. Reduction reactions of fac- and mer-[1] afforded a triacetonitrile complex mer-[Ru(II)(CH(3)CN)(3)(ebpea)](PF(6))(2) (mer-[3](PF(6))(2)). Five nitrosyl complexes fac-[RuX(2)(NO)(ebpea)]PF(6) (X = Cl for fac-[4]PF(6); X = ONO(2) for fac-[5]PF(6)) and mer-[RuXY(NO)(ebpea)]PF(6) (X = Cl, Y = Cl for mer-[4]PF(6); X = Cl, Y = CH(3)O for mer-[6]PF(6); X = Cl, Y = OH for mer-[7]PF(6)) were synthesized and characterized by X-ray crystallography. A reaction of mer-[2] in H(2)O-C(2)H(5)OH at room temperature afforded mer-[1]. Oxidation of C(2)H(5)OH in H(2)O-C(2)H(5)OH and i-C(3)H(7)OH in H(2)O-i-C(3)H(7)OH to acetaldehyde and acetone by mer-[2] under stirring at room temperature occurred with formation of mer-[1]. Alternative C-H activation of the CH(2) group occurred next to the pyridyl group, and formation of a C-N bond between the CH moiety and the nitrosyl ligand afforded a nitroso complex [Ru(II)(N(3))(2){N(O)CH(py)CH(2)N(C(2)H(5))C(2)H(4)py}] ([8]) in reactions of nitrosyl complexes with sodium azide in methanol, and reaction of [8] with hydrochloric acid afforded a corresponding chloronitroso complex [Ru(II)Cl(2){N(O)CH(py)CH(2)N(C(2)H(5))C(2)H(4)py}] ([9]).     

Formation of a ruthenium(IV)-oxo complex by electron-transfer oxidation of a coordinatively saturated ruthenium(II) complex and detection of oxygen-rebound intermediates in C-H bond oxygenation

A coordinatively saturated ruthenium(II) complex having tetradentate tris(2-pyridylmethyl)amine (TPA) and bidentate 2,2'-bipyridine (bpy), [Ru(TPA)(bpy)](2+) (1), was oxidized by a Ce(IV) ion in H(2)O to afford a Ru(IV)-oxo complex, [Ru(O)(H(+)TPA)(bpy)](3+) (2). The crystal structure of the Ru(IV)-oxo complex 2 was determined by X-ray crystallography. In 2, the TPA ligand partially dissociates to be in a facial tridentate fashion and the uncoordinated pyridine moiety is protonated. The spin state of 2, which showed paramagnetically shifted NMR signals in the range of 60 to -20 ppm, was determined to be an intermediate spin (S = 1) by the Evans' method with (1)H NMR spectroscopy in acetone-d(6). The reaction of 2 with various oraganic substrates in acetonitrile at room temperature afforded oxidized and oxygenated products and a solvent-bound complex, [Ru(H(+)TPA)(bpy)(CH(3)CN)], which is intact in the presence of alcohols. The oxygenation reaction of saturated C-H bonds with 2 proceeds by two-step processes: the hydrogen abstraction with 2, followed by the dissociation of the alcohol products from the oxygen-rebound complexes, Ru(III)-alkoxo complexes, which were successfully detected by ESI-MS spectrometry. The kinetic isotope effects in the first step for the reaction of dihydroanthrathene (DHA) and cumene with 2 were determined to be 49 and 12, respectively. The second-order rate constants of C-H oxygenation in the first step exhibited a linear correlation with bond dissociation energies of the C-H bond cleavage.     

Evaluating the identity and diiron core transformations of a (μ-oxo)diiron(III) complex supported by electron-rich tris(pyridyl-2-methyl)amine ligands

The composition of a (μ-oxo)diiron(III) complex coordinated by tris[(3,5-dimethyl-4-methoxy)pyridyl-2-methyl]amine (R(3)TPA) ligands was investigated. Characterization using a variety of spectroscopic methods and X-ray crystallography indicated that the reaction of iron(III) perchlorate, sodium hydroxide, and R(3)TPA affords [Fe(2)(μ-O)(μ-OH)(R(3)TPA)(2)](ClO(4))(3) (2) rather than the previously reported species [Fe(2)(μ-O)(OH)(H(2)O)(R(3)TPA)(2)](ClO(4))(3) (1). Facile conversion of the (μ-oxo)(μ-hydroxo)diiron(III) core of 2 to the (μ-oxo)(hydroxo)(aqua)diiron(III) core of 1 occurs in the presence of water and at low temperature. When 2 is exposed to wet acetonitrile at room temperature, the CH(3)CN adduct is hydrolyzed to CH(3)COO(-), which forms the compound [Fe(2)(μ-O)(μ-CH(3)COO)(R(3)TPA)(2)](ClO(4))(3) (10). The identity of 10 was confirmed by comparison of its spectroscopic properties with those of an independently prepared sample. To evaluate whether or not 1 and 2 are capable of generating the diiron(IV) species [Fe(2)(μ-O)(OH)(O)(R(3)TPA)(2)](3+) (4), which has previously been generated as a synthetic model for high-valent diiron protein oxygenated intermediates, studies were performed to investigate their reactivity with hydrogen peroxide. Because 2 reacts rapidly with hydrogen peroxide in CH(3)CN but not in CH(3)CN/H(2)O, conditions that favor conversion to 1, complex 1 is not a likely precursor to 4. Compound 4 also forms in the reaction of 2 with H(2)O(2) in solvents lacking a nitrile, suggesting that hydrolysis of CH(3)CN is not involved in the H(2)O(2) activation reaction. These findings shed light on the formation of several diiron complexes of electron-rich R(3)TPA ligands and elaborate on conditions required to generate synthetic models of diiron(IV) protein intermediates with this ligand framework.     

Phosphorus-nitrogen donor interaction leading to atrane formation in phosphate and oxyphosphorane compositions. Implications for phosphoryl transfer enzymes(1)

Reaction of aminotriphenols, tris(2-hydroxy-3,5-dimethylbenzyl)amine (E) and tris(2- hydroxy-3-tert-butyl-5-methylbenzyl)amine (F), with triphenylphosphite, tris(p-methoxyphenyl)phosphite, or phenyldiphenoxyphosphane in the presence of N-chlorodiisopropylamine led to the isolation of tetraoxyphosphorane 1, pentaoxyphosphorane 3, phosphate-atrane 2, hexacoordinated pentaoxyphosphorane-atrane 4, and the first hexacoordinated tetraoxyphosphorane-atrane 5. X-ray analysis of 1-3 and 5 were obtained. NMR data is reported and supports that the atrane 4 has the same hexacoordinated structure as 5. Phosphate 2 reveals weak phosphorus-nitrogen donor action whereas the hexacoordinated atranes 4 and 5 have pronounced P-N coordination. The results are used to support amino acid donor action occurring at active sites of phosphoryl transfer enzymes. Increased strength of donor action in the higher-coordinate model activated state compared to that in the substrate phosphate composition should serve as a factor in enhancing enzyme reaction rates.     

Selective extraction of gallium from aluminum and indium using tripod phenolic ligands

Solvent extraction of trivalent group 13 metal cations such as aluminum, gallium and indium with tripod quadridentate phenolic ligand, tris(2-hydroxy-3,5-dimethylbenzyl)amine (H(3)tdmba), was investigated as fundamental study for their mutual separation. Gallium was extracted almost quantitatively as Ga(tdmba) (logK(ex)=-6.66+/-0.06 on using chloroform as extraction solvent), whereas aluminum and indium were hardly extracted due to steric hindrance on complexation of them with the ligand. The extracted Ga species was estimated as trigonal bipyramidal complex with one H(2)O molecule. Furthermore, extractability of Ga was increased by changing the ligand to more acidic tris(5-chloro-2-hydroxy-3-methylbenzyl)amine (H(3)tcmba) (logK(ex)=-6.18+/-0.18 on using dichloroethane as extraction solvent).     

Assembly of Carbohydrates on a Nickel(II) Center by Utilizing N-Glycosidic Bond Formation with Tris(2-aminoethyl)amine (tren). Syntheses and Characterization of [Ni{N-(aldosyl)-tren}(H(2)O)](2+), [Ni{N,N'-bis(aldosyl)-tren}](2+) and [Ni{N,N',N"-tris(aldosyl)-tren}](2+)

Reactions of [Ni(tren)(H(2)O)(2)]X(2) (tren = tris(2-aminoethyl)amine; X = Cl (1a), Br (1b); X(2) = SO(4) (1c)) with mannose-type aldoses, having a 2,3-cis configuration (D-mannose and L-rhamnose), afforded {bis(N-aldosyl-2-aminoethyl)(2-aminoethyl)amine}nickel(II) complexes, [Ni(N,N'-(aldosyl)(2)-tren)]X(2) (aldosyl = D-mannosyl, X = Cl (2a), Br (2b), X(2) = SO(4) (2c); aldosyl = L-rhamnosyl, X(2) = SO(4) (3c)). The structure of 1c was confirmed by X-ray crystallography to be a mononuclear [Ni(II)N(4)O(2)] complex with the tren acting as a tetradentate ligand (1c.2H(2)O: orthorhombic, Pbca, a = 15.988(2) ?, b = 18.826(4) ?, c = 10.359(4) ?, V = 3118 ?(3), Z = 8, R = 0.047, and R(w) = 0.042). Complexes 2a,c and 3c were characterized by X-ray analyses to have a mononuclear octahedral Ni(II) structure ligated by a hexadentate N-glycoside ligand, bis(N-aldosyl-2-aminoethyl)(2-aminoethyl)amine (2a.CH(3)OH: orthorhombic, P2(1)2(1)2(1), a = 16.005(3) ?, b = 20.095(4) ?, c = 8.361(1) ?, V = 2689 ?(3), Z = 4, R = 0.040, and R(w) = 0.027. 2c.3CH(3)OH: orthorhombic, P2(1)2(1)2(1), a = 14.93(2) ?, b = 21.823(8) ?, c = 9.746(2) ?, V = 3176 ?(3), Z = 4, R = 0.075, and R(w) = 0.080. 3c.3CH(3)OH: orthorhombic, P2(1)2(1)2(1), a = 14.560(4) ?, b = 21.694(5) ?, c = 9.786(2) ?, V = 3091 ?(3), Z = 4, R = 0.072, and R(w) = 0.079). The sugar part of the complex involves novel intramolecular sugar-sugar hydrogen bondings around the metal center. The similar reaction with D-glucose, D-glucosamine, and D-galactosamine, having a 2,3-trans configuration, resulted in the formation of a mono(sugar) complex, [Ni(N-(aldosyl)-tren)(H(2)O)(2)]Cl(2) (aldosyl = D-glucosyl (4b), 2-amino-2-deoxy-D-glucosyl (5a), and 2-amino-2-deoxy-D-galactosyl (5b)), instead of a bis(sugar) complex. The hydrogen bondings between the sugar moieties as observed in 2 and 3 should be responsible for the assembly of two sugar molecules on the metal center. Reactions of tris(N-aldosyl-2-aminoethyl)amine with nickel(II) salts gave the tris(sugar) complexes, [Ni(N,N',N"-(aldosyl)(3)-tren)]X(2) (aldosyl = D-mannosyl, X = Cl (6a), Br (6b); L-rhamnosyl, X = Cl (7a), Br (7b); D-glucosyl, X = Cl (9); maltosyl, X = Br (10); and melibiosyl, X = Br (11)), which were assumed to have a shuttle-type C(3) symmetrical structure with Delta helical configuration for D-type aldoses on the basis of circular dichroism and (13)C NMR spectra. When tris(N-rhamnosyl)-tren was reacted with NiSO(4).6H(2)O at low temperature, a labile neutral complex, [Ni(N,N',N"-(L-rhamnosyl)(3)-tren)(SO(4))] (8), was successfully isolated and characterized by X-ray crystallography, in which three sugar moieties are anchored only at the N atom of the C-1 position (8.3CH(3)OH.H(2)O: orthorhombic, P2(1)2(1)2(1), a = 16.035(4) ?, b = 16.670(7) ?, c = 15.38(1) ?, V = 4111 ?(3), Z = 4, R = 0.084, and R(w) = 0.068). Complex 8 could be regarded as an intermediate species toward the C(3) symmetrical tris(sugar) complexes 7, and in fact, it was readily transformed to 7b by an action of BaBr(2).     

Lanthanide(III) and group 13 metal ion complexes of tripodal amino phosphinate ligands

The tripodal amino-phosphinate ligands, tris(4-(phenylphosphinato)-3-benzyl-3-azabutyl)amine (H(3)ppba.2HCl.H(2)O) and tris(4-(phenylphosphinato)-3-azabutyl)amine (H(3)ppa.HCl.H(2)O) were synthesized and reacted with Al(3+), Ga(3+), In(3+) and the lanthanides (Ln(3+)). At 2 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(3)ppba)(2)](3+)(M = Al(3+), Ga(3+), In(3+), Ho(3+)-Lu(3+)) were isolated. The bicapped [Ga(H(3)ppba)(2)](NO(3))(2)Cl.3CH(3)OH was structurally characterized and was shown indirectly by various techniques to be isostructural with the other [M(H(3)ppba)(2)](3+) complexes. Also, at 2 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(4)ppba)(2)](5+)(M = La(3+)-Tb(3+)) were characterized, and the X-ray structure of [Gd(H(4)ppba)(2)](NO(3))(4)Cl.3CH(3)OH was determined. At 1 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(4)ppba)](4+)(M = La(3+)-Er(3+)) were isolated and characterized. Elemental analysis and spectroscopic evidence supported the formation of a 1 : 1 monocapped complex. Reaction of 1 : 1 ratios of H(3)ppa with Ln(3+) and In(3+) yielded complexes of the type [M(H(3)ppa)](3+)(M = La(3+)-Yb(3+)) but with Ga(3+), complex of the type [Ga(ppa)].3H(2)O was obtained. Reaction of 1 : 1 ratios of H(3)ppa with Ln(3+) and In(3+) yielded complexes of the type [M(H(3)ppa)](3+)(M = La(3+)-Yb(3+)) but with Ga(3+) a neutral complex [Ga(ppa)].3H(2)O was obtained. The formation of an encapsulated 1 : 1 complex is supported by elemental analysis and spectroscopic evidence.     

A sterically hindered N,N,O tripod ligand and its zinc complex chemistry

The new ligand bis(2-picolyl)(2-hydroxy-3,5-di-tert-butylbenzyl)amine (HL) was prepared from bis(2-picolyl)amine and 2,4-di-tert-butyl-6-(chloromethyl)phenol. It acts as a tetradentate N,N,O tripod ligand ensuring 5-fold coordination in all its zinc complexes L.Zn-X. The central complex of the series was [L.Zn(OH(2))]ClO(4) (1) obtained from zinc perchlorate. Together with the more labile complex L.Zn-C(2)H(5) (2), obtained from diethyl zinc, it was used as a starting material for ligand substitutions. In the presence of bases, 1 was converted to L.Zn-OH (3), [L.Zn(py)]ClO(4) (4), and [(L.Zn)(3)(mu(3)-CO(3))]ClO(4) (5). Metathetical reactions produced the neutral complexes L.Zn-X with X = Br (6), OAc (7), OC(6)H(5) (8), SC(6)H(5) (9), OP(O)(OPh)(2) (10), p-nitrophenolate (11), 1-methyluracilate (12), o-formylphenolate (13), and o-hydroxymethylphenolate (14). Structure determinations of 1, 5, 7, 10, 11, 13, and 14 confirmed the strictly monodentate attachment of all units X in L.Zn-X. The hydrolytic cleavage of tris(p-nitrophenyl) phosphate by 1 was investigated preparatively and kinetically. L.Zn-OH was found to be the hydrolytically active nucleophile. The second-order rate constant for the cleavage reaction was found to be slightly lower than the values for related systems, reflecting the steric hindrance in the tert-butyl-substituted ligand L.     

Novel iron(III) complexes of tripodal and linear tetradentate bis(phenolate) ligands: close relevance to intradiol-cleaving catechol dioxygenases

Four new iron(III) complexes of the bis(phenolate) ligands N,N-dimethyl-N',N'-bis(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine [H2(L1)], N,N-dimethyl-N',N'-bis(2-hydroxy-4-nitrobenzyl)ethylenediamine [H2(L2)], N,N'-dimethyl-N,N'-bis(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine [H2(L3)], and N,N'-dimethyl-N,N'-bis(2-hydroxy-4-nitrobenzyl)ethylenediamine [H2(L4)] have been isolated and studied as structural and functional models for the intradiol-cleaving catechol 1,2-dioxygenases (CTD). The complexes [Fe(L1)Cl] (1), [Fe(L2)(H2O)Cl] (2), [Fe(L3)Cl] (3), and [Fe(L4)(H2O)Cl] (4) have been characterized using absorption spectral and electrochemical techniques. The single-crystal X-ray structures of the ligand H2(L1) and the complexes 1 and 2 have been successfully determined. The tripodal ligand H2(L1) containing a N2O2 donor set represents the metal-binding region of the iron proteins. Complex 1 contains an FeN2O2Cl chromophore with a novel trigonal bipyramidal coordination geometry. While two phenolate oxygens and an amine nitrogen constitute the trigonal plane, the other amine nitrogen and chloride ion are located in the axial positions. In contrast, 2 exhibits a rhombically distorted octahedral coordination geometry for the FeN2O3Cl chromophore. Two phenolate oxygen atoms, an amine nitrogen atom, and a water molecule are located on the corners of a square plane with the axial positions being occupied by the other nitrogen atom and chloride ion. The interaction of the complexes with a few monodentate bases and phenolates and differently substituted catechols have been investigated using absorption spectral and electrochemical methods. The effect of substituents on the phenolate rings on the electronic spectral features and FeIII/FeII redox potentials of the complexes are discussed. The interaction of the complexes with catecholate anions reveals changes in the phenolate to iron(III) charge-transfer band and also the appearance of a low-energy catecholate to iron(III) charge-transfer band similar to catechol dioxygenase-substrate complexes. The redox behavior of the 1:1 adducts of the complexes with 3,5-di-tert-butylcatechol (H2DBC) has been also studied. The reactivities of the present complexes with H2DBC have been studied and illustrated. Interestingly, only 2 and 4 catalyze the intradiol-cleavage of H2DBC, the rate of oxygenation being much faster for 4. Also 2, but not 4, yields an extradiol cleavage product. The reactivity of the complexes could be illustrated not on the basis of the Lewis acidity of the complexes alone but by assuming that the product release is the rate-determining phase of the catalytic reaction.     

Non-oxo 5-coordinate and 6-coordinate vanadium(IV) complexes with their precursor [LV(III)(CH3OH)](0), where L = a trianionic aminetris(phenolate)-[N,O,O,O] donor ligand: a magnetostructural and EPR study

Ligating properties of a tripodal, potentially tetradentate aminetris(phenol) ligand, tris(2-hydroxy-3,5-di-tert-butylbenzyl)amine, H(3)L, containing [N,O,O,O] donor atoms toward the vanadium ions in +III and IV oxidation states have been studied. The structures of complexes 1 [LV(III)(CH(3)OH)](0), 2 [LV(IV)(OCH(3))](0) and 3 [LV(IV)(acac)](0) were determined by X-ray diffraction methods as having five-coordinate V(III), 1, five-coordinate non-oxo-vanadium(IV), 2, and six-coordinate non-oxo-vanadium(iv) 3, respectively. Compounds 1-3 were also studied with electrochemical methods, variable-temperature (2-295 K) magnetic susceptibility measurements and X-band electron paramagnetic resonance (EPR) spectroscopy. The electrochemical results of 2 and 3 suggest metal-centered oxidation, i.e. the generation of a V(V)-phenolate species. EPR investigations indicate a (d(xy))(1) ground state showing a considerable increase in the in-plane π-bonding, as is expected for a phenolate ligand.