Octahedral metallo-mesogens of chromium, molybdenum and tungsten with 1,4,7-trisubstituted 1,4,7-triazacyclononane and three carbonyl groups as ligands

Liquid crystalline complexes with chromium, molybdenum and with tungsten as metallic centres are reported. 1,4,7-Trisubstituted 1,4,7-triazacyclononane and three carbonyl groups are coordinated in an octahedral geometry. The observed mesophases are characterized as disordered rectangular columnar of a pyramidic type.     

Complexation of metal ions with TRAP (1,4,7-triazacyclononane phosphinic acid) ligands and 1,4,7-triazacyclononane-1,4,7-triacetic acid: phosphinate-containing ligands as unique chelators for trivalent gallium

Three phosphinic acid 1,4,7-triazacyclononane (TACN) derivatives bearing methylphosphinic (TRAP-H), methyl(phenyl)phosphinic (TRAP-Ph), or methyl(hydroxymethyl)phosphinic acid (TRAP-OH) pendant arms were investigated as members of a new family of efficient Ga(3+) chelators, TRAP ligands (triazacyclononane phosphinic acids). Stepwise protonation constants of ligands and stability constants of their complexes with Ga(3+), selected divalent metal, and Ln(3+) ions were determined by potentiometry. For comparison, equilibrium data for the metal ion-NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid) systems were redetermined. These ligands exhibit high thermodynamic selectivity for Ga(3+) over the other metal ions (log K(GaL) - log K(ML) = 7-9) and a selective complexation of smaller Mg(2+) over Ca(2+). Stabilities of the Ga(3+) complexes are dependent on the basicity of the donor atoms: [Ga(NOTA)] (log K(GaL) = 29.6) > [Ga(TRAP-OH)] (log K(GaL) = 23.3) > [Ga(TRAP-H)] (log K(GaL) = 21.9). The [Ga(TRAP-OH)] complex exhibits unusual reversible rearrangement of the "in-cage" N(3)O(3) complex to the "out-of-cage" O(6) complex. The in-cage complex is present in acidic solutions, and at neutral pH, Ga(3+) ion binds hydroxide anion, induces deprotonation and coordination of the P-hydroxymethyl group(s), and moves out of the macrocyclic cavity; the hypothesis is supported by a combination of results from potentiometry, multinuclear nuclear magnetic resonance spectrometry, and density functional theory calculations. Isomerism of the phosphinate Ga(3+) complexes caused by a combination of the chelate ring conformation, the helicity of coordinated pendant arms, and the chirality of the coordinated phosphinate groups was observed. All Ga(3+) complexes are kinetically inert in both acidic and alkaline solutions. Complex formation studies in acidic solutions indicate that Ga(3+) complexes of the phosphinate ligands are formed quickly (minutes) and quantitatively even at pH <2. Compared to common Ga(3+) chelators (e.g., 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) derivatives), these novel ligands show fast complexation of Ga(3+) over a broad pH range. The discussed TRAP ligands are suitable alternatives for the development of (68)Ga radiopharmaceuticals.     

Efficient plasmid DNA cleavage by copper(II) complexes of 1,4,7-triazacyclononane ligands featuring xylyl-linked guanidinium groups

Three new metal-coordinating ligands, L(1), L(2), and L(3), have been prepared by appending o-, m-, and p-xylylguanidine pendants, respectively, to one of the nitrogen atoms of 1,4,7-triazacyclononane (tacn). The copper(II) complexes of these ligands are able to accelerate cleavage of the P-O bonds within the model phosphodiesters bis(p-nitrophenyl)phosphate (BNPP) and [2-(hydroxypropyl)-p-nitrophenyl]phosphate (HPNPP), as well as supercoiled pBR 322 plasmid DNA. Their reactivity toward BNPP and HPNPP is not significantly different from that of the nonguanidinylated analogues, [Cu(tacn)(OH(2))(2)](2+) and [Cu(1-benzyl-tacn)(OH(2))(2)](2+), but they cleave plasmid DNA at considerably faster rates than either of these two complexes. The complex of L(1), [Cu(L(1)H(+))(OH(2))(2)](3+), is the most active of the series, cleaving the supercoiled plasmid DNA (form I) to the relaxed circular form (form II) with a k(obs) value of (2.7 ± 0.3) × 10(-4) s(-1), which corresponds to a rate enhancement of 22- and 12-fold compared to those of [Cu(tacn)(OH(2))(2)](2+) and [Cu(1-benzyl-tacn)(OH(2))(2)](2+), respectively. Because of the relatively fast rate of plasmid DNA cleavage, an observed rate constant of (1.2 ± 0.5) × 10(-5) s(-1) for cleavage of form II DNA to form III was also able to be determined. The X-ray crystal structures of the copper(II) complexes of L(1) and L(3) show that the distorted square-pyramidal copper(II) coordination sphere is occupied by three nitrogen atoms from the tacn ring and two chloride ions. In both complexes, the protonated guanidinium pendants extend away from the metal and form hydrogen bonds with solvent molecules and counterions present in the crystal lattice. In the complex of L(1), the distance between the guanidinium group and the copper(II) center is similar to that separating the adjacent phosphodiester groups in DNA (ca. 6 ?). The overall geometry of the complex is also such that if the guanidinium group were to form charge-assisted hydrogen-bonding interactions with a phosphodiester group, a metal-bound hydroxide would be well-positioned to affect the nucleophilic attack on the neighboring phosphodiester linkage. The enhanced reactivity of the complex of L(1) at neutral pH appears to also be, in part, due to the relatively low pK(a) of 6.4 for one of the coordinated water molecules.     

Synthesis, spectroscopic and structural characterisation of molybdenum, tungsten and manganese carbonyl complexes of tetrathio- and tetraseleno-ether ligands

A range of complexes of the binucleating tetrathio- and tetraseleno-ether ligands, 1,2,4,5-C₆H₂(CH₂EMe)₄ (E = S, L³ or Se, L⁴) or C(CH₂EMe)₄ (E = S, L⁵ or Se, L⁶) and of bidentate analogues 1,2-C₆H₂(CH₂EMe)₂ (E = S, L¹ or Se = L²) with molybdenum and tungsten carbonyls and manganese carbonyl chloride have been prepared, and characterised by IR and multinuclear NMR (¹H, ¹³C{¹H}, ⁷⁷Se, ⁵⁵Mn, ⁹⁵Mo) spectroscopy and mass spectrometry. Crystal structures are reported for [Mo(CO)₄(L²)], [Mo(CO)₄(L³)], [Mo(CO)₄(μ-L³)Mo(CO)₄], [Mo(CO)₄(L⁴)], [Mn(CO)₃Cl(μ-L³)Mn(CO)₃Cl], [Mo(CO)₄(μ-L⁵)Mo(CO)₄], [Mn(CO)₃Cl(L⁵)] and two forms (containing meso and DL diastereoisomers) of [W(CO)₄(L⁵)].     

Telluroamides and selenoamides: Complexes with chromium,molybdenum, and tungsten pentacarbonyls

Several new telluroamide and selenoamide group 6 metal complexes ( 2a–2f ), C₅H₉NOE-M(CO)₅, where E is Te or Se and M is Cr, Mo, or W, have been successfully synthesized by the reaction between PyM(CO)₅ and 4-(telluroformyl)morpholine ( 1a ) or 4-(selenoformyl)morpholine ( 1b ). The crystal structures of C₅H₉NOSe ( 1b ), C₅H₉NOTe-Cr(CO)₅ ( 2a ), and C₅H₉NOSe-Cr(CO)₅ ( 2d ) have been determined. The changes in the physical properties and structures between free ligands ( 1a , 1b ) and coordinated telluro- or selenocarbonyls (in complexes 2a–2f ) have been investigated. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:57–64, 1998     

Reactions of (di)manganese carbonyl ions with 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3TACN) in the gas phase

The gas-phase reactions of a series of (di)manganese carbonyl positive ions with 1,4,7-trimethyl-1,4,7-triazacyclononane (Me(3)TACN) have been examined with the aid of Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. The monomanganese carbonyl ions, [Mn(CO)(n)](+) (n = 2-5), react predominantly by ligand exchange and to a minor extent by electron transfer with the formation of the radical cation of Me(3)TACN. For the [Mn(CO)(n)](+) (n = 2-4) ions, the ligand exchange results in the exclusive formation of a [Mn(Me(3)TACN)](+) complex, whereas small amounts of [Mn(CO)(Me(3)TACN)](+) ions are also generated in the reactions of the [Mn(CO)(5)](+) ion. The [Mn(2)(CO)(n)](+) ions (n = 2, 4 and 5) react also by competing electron transfer and ligand exchange. The reaction of the [Mn(2)(CO)(2)](+) and [Mn(2)(CO)(4)](+) ions is associated with cleavage of the Mn--Mn bond as evidenced by the pronounced formation of [Mn(Me(3)TACN)](+) ions. For [Mn(2)(CO)(5)](+), the ligand exchange leads mainly to the formation of [Mn(2)(CO)(n)(Me(3)TACN)](+) (n = 1-3) ions. These primary product ions react subsequently by the incorporation of a second Me(3)TACN molecule to afford [Mn(2)(CO)(Me(3)TACN)(2)](+) and [Mn(2)(CO)(2)(Me(3)TACN)(2)](+) ions. Both of these latter species incorporate an oxygen molecule with formation of ions with the assigned composition of [Mn(2)(O(2))(CO)(Me(3)TACN)(2)](+) and [Mn(2)(O(2))(CO)(2)(Me(3)TACN)(2)](+).     

Diazabutadienes as σ,π-bridging ligands in binuclear molybdenum carbonyl complexes containing molybdenummolybdenum double bonds

Reduction of Mo(CO)₄ DAB (DAB = diazabutadiene) followed by oxidation with Mn(CO)₃BrDAB or HCl gives a small yield (15 to 25%) of complexes of the type Mo₂(CO)₆(DAB)₂, in which the two DAB ligands bridge a molybdenummolybdenum double bond and act as σ,π-donors.     

Trace-matrix separations for high-purity chromium,molybdenum and tungsten with cellulose collectors

Trace metals (20 elements) in high-purity chromium, molybdenum and tungsten are collected and preconcentrated by precipitation and adsorption on cellulose collectors. The compound methods allow the application of AAS and ICP-AES as determination methods for the production control of highly pure refractory metals under routine conditions.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria     

Reactions of chromium,molybdenum and tungsten carbonyls with a tetradentate schiff base

Interaction of metal carbonyls M(CO)₆ (M?=?Cr, Mo and W) with the tetradentate Schiff base bis(salicylaldehyde)phenylenediimine (salphenH₂) was studied in THF. Under reduced pressure, reaction of salphenH₂ with M(CO)₆ (M?=?Cr, Mo) yielded Cr(CO)₂(salphen) 1 and MoO(CO)(salphen) 2. The complexes MoO₂(salphenH)₂ 3 and W₂O₆(salphenH₂) 4 were isolated from reactions in air. All the complexes were characterized by elemental analysis, mass spectrometry and IR and ¹H?NMR spectroscopy. Spectroscopic studies of the reported complexes revealed the proposed structures. The UV-vis spectra of the complexes in different solvents showed bands due to either metal-to-ligand or ligand-to-metal charge transfer. Thermal properties of the chromium and molybdenum complexes were investigated by thermogravimetric techniques.     

Singlet diradical complexes of chromium, molybdenum, and tungsten with azo anion radical ligands from M(CO)6 precursors

The homoleptic diamagnetic complexes M(mer-L)(2), M = Cr, Mo,W (1a,b, 2a,b, and 4a,b), were obtained by reacting the hexacarbonyls M(CO)(6) with the tridentate ligands 2-[(2-N-arylamino)phenylazo]pyridine (HL = NH(4)C(5)N=NC(6)H(4)N(H)C(6)H(4)(H) (HL(a)) or NH(4)C(5)N=NC(6)H(4)N(H)C(6)H(4)(CH(3)) (HL(b))) in refluxing n-octane. In the case of M = Mo, the dinuclear compounds [Mo(L)(pap)](2)(mu-O) (3a,b) (pap = 2-(phenylazo)pyridine), were obtained as second products in moist solvent. X-ray diffraction analysis for Cr(L(b))(2) (1b), Mo(L(a))(2) (2a), and W(L(a))(2) (4a) reveals considerably distorted-octahedral structures with trans-positioned azo-N atoms and cis-positioned 2-pyridyl-N and anilido nitrogen atoms. Whereas the N(azo)-M-N(azo) angle is larger than 170 degrees, the other two trans angles are smaller, at about 155 degrees (M = Cr, 1b) or 146 degrees (M = Mo, W; 2a, 4a), due to the overarching bite of the mer-tridentate ligands. The bonds from M to the neutral 2-pyridyl-N atoms are distinctly longer by more than 0.08 A than those to the anilido or azo nitrogen atoms, reflecting negative charge on the latter. The N-N bond distances vary between 1.339(2) A for 1b and 1.373(3) A for 4a, clearly indicating the azo radical anion oxidation state. Considering the additional negative charge on anilido-N, the mononuclear complexes are thus formulated as M(IV)(L*(2-))(2). The diamagnetism of the complexes as shown by magnetic susceptibility and (1)H NMR experiments is believed to result from spin-spin coupling between the trans-positioned azo radical functions, resulting in a singlet diradical situation. The experimental structures are well reproduced by density functional theory calculations, which also support the overall electronic structure indicated. The dinuclear 3a with N-N distances of 1.348(10) A for L(a) and 1.340(9) A for pap is also formulated as an azo anion radical-containing molybdenum(IV) species, i.e., [Mo(IV)(L*(2-))(pap*-)](2)(mu-O). All compounds can be reversibly reduced; the Cr complexes 1a,b are also reversibly oxidized in two steps. Electron paramagnetic resonance spectroscopy indicates metal-centered spin for 1a+ and 1a- and g approximately 2 signals for 2a-, 3a+, 3a-, and 4a-. Spectroelectrochemistry in the UV-vis-NIR region showed small changes for the reduction of 2a, 3a, and 4a but extensive spectral changes for the reduction and oxidation of 1a.     

Coordination chemistry of chelating nitrogen ligands with tungsten carbonyl nitriles

The reactions of a series of Schiff base ligands (1–4) prepared by condensation of pyridine-2-carboxaldehyde and 2-X-anilines (X = F, Cl, Br, OMe) with W(CO)₃(RCN)₃ results in the formation of deeply coloured complexes W(CO)₃(1–4)(NCR) which readily react with carbon monoxide to afford W(CO)₄(1–4). The ligand 5, prepared from pyridine-2-carboxaldehyde and N,N-dimethylethylenediamine, coordinates to W(CO)₃ through the conjugated pyridine—imine chelate to afford complexes with a pendant dimethylamino group which reacts with electrophiles. Of the ligands studied, only the bis-amine, pyridine ligand 8, coordinates to W(CO)₃ in a tridentate manner. These reactions provide insight into the geometric and electronic factors which influence coordination of nitrogen containing ligands at a fac-tricarbonyl metal centre.     

Facile N-1 protection of cyclam, cyclen and 1,4,7-triazacyclononane

An exceptionally high yielding method for the tri-protection of cyclam and cyclen using ethyl trifluoroacetate is described. The selective reaction also applies to the di-protection of 1,4,7-triazacyclononane. The application of this method in the synthesis of AMD3100, a clinical candidate for stem cell mobilization is presented.     

N-heterocyclic carbenes as ligands in high-valent molybdenum and tungsten complexes

Oxometal complexes of molybdenum and tungsten in high oxidation states from stable adducts with 1,3-dimethylimidazoline-2-ylidene (L) 1. The first ‘carbene’ complexes of molybdenum(VI) [MoO₂Cl(L)₃]Cl (3a) and tungsten(VI) WO₂Cl₂(L)₂ (4b) are reported.     

Reactions of transiently formed nitrilium phosphanylide chromium,molybdenum, and tungsten complexes with heterocumulenes

Thermal decomposition of the 2H‐azaphosphirene metal complexes 1a–c in the presence of 1‐piperidinecarbonitrile and heterocumulene derivatives 3, 4 , and 5 yielded the Δ³‐1,3,2‐oxazaphospholene complexes 6c and the Δ³‐1,3,2‐thiazaphospholene complexes 7a–c as isolable products; the latter represent the first complexes of this ring system. It is remarkable that these trapping reactions of the nitrilium phosphanylide complexes 2a–c , which were formed as reactive intermediates, proceeded with high regio‐ and substrate selectivities. The complexes were isolated by column chromatography and characterized by elemental analysis, NMR spectroscopy and mass spectrometry. © 2002 John Wiley & Sons, Inc. Heteroatom Chem 13:72–76, 2002; DOI 10.1002/hc.1108     

The electrochemical reduction of arylmethoxycarbene complexes of chromium,molybdenum and tungsten

The reduction of a series of (arylmethoxycarbene)pentacarbonyltunsten(0) compounds was studied by cyclic voltammetry and a dependence of E_{$\text{1}\text{2}$} of the quasi-reversible voltammogram on the conformation of the aryl ring of the carbene complex was observed.     

Tmtacn, tacn, and triammine complexes of (eta 6-arene)OsII: syntheses, characterizations, and photosubstitution reactions (tmtacn = 1,4,7-trimethyl-1,4,7-triazacyclononane; tacn = 1,4,7-triazacyclononane)

A series of (eta 6-arene)OsII complexes containing the saturated nitrogen donor ligands tmtacn, tacn, and NH3 are prepared and characterized. The electrochemical properties and photochemical reactions of these complexes are studied, and the solid-state structures for [(eta 6-p-cymene)Os(tacn)](PF6)2 (1) and [(eta 6-p-cymene)Os(tmtacn)](PF6)2 (2) are determined. Single-crystal X-ray data: 1, orthorhombic, space group Pbca-D2h15 (No. 61), with a = 14.716(3) A, b = 17.844(3) A, c = 18.350(4) A, V = 4819(2) A3, and Z = 8; 2, monoclinic, space group C2-C2(3) (No. 5), with a = 17.322(4) A, b = 10.481(3) A, c = 15.049(4) A, beta = 98.72 degrees, V = 2701(1) A3, and Z = 4.     

Lanthanide complexes of new nonadentate imino-phosphonate ligands derived from 1,4,7-triazacyclononane: synthesis, structural characterisation and NMR studies

The polyamino ligand 1,4,7-tris(2-aminoethyl)-1,4,7-triazacyclononane (1) has been used to synthesise two new ligands by Schiff-base condensation with methyl sodium acetyl phosphonate to give ligand L and methyl sodium 4-methoxybenzoyl phosphonate to give ligand L1 in the presence of lanthanide ion as templating agent to form the complexes [Ln(L)] and [Ln(L1)](Ln = Y, La, Gd, Yb). Both ligands L and L1 have nine donor atoms comprising three amine and three imine N-donors and three phosphonate O-donors and form Ln(III) complexes in which the three pendant arms of the ligands wrap around the nine-coordinate Ln(III) centres. Complexes with Y(III), La(III), Gd(III) and Yb(III) have been synthesised and the complexes [Y(L)], [Gd(L)] and [Gd(L1)] have been structurally characterised. In all the complexes the coordination polyhedron about the lanthanide centre is slightly distorted tricapped trigonal prismatic with the two triangular faces of the prism formed by the macrocyclic N-donors and the phosphonate O-donors. Interestingly, given the three chiral phosphorus centres present in [Ln(L)] and [Ln(L1)] complexes, the three crystal structures reported show the presence of only one diastereomer of the four possible. 1H, 13C and 31P NMR spectroscopic studies on diamagnetic [Y(L)] and [La(L)] and on paramagnetic [Yb(L)] complexes indicate the presence in solution of all the four different diastereomers in varying proportions. The stability of complexes [Y(L)] and [Y(L1)] in D2O in both neutral and acidic media, and the relaxivity of the Gd(III) complexes, have also been investigated.