Polynuclear and polymeric metal complexes based upon 1,2,4-triazolyl functionalized adamantanes

A series of coordination compounds [Cd₂(trad)₇Br₂][Cd(trad)Br₃]₂ (1), [Cd₃(trad)₆{N(CN)₂}₄(H₂O)₂](N(CN)₂)₂ (2), [{Cd₂(trad)₅}{Cd(N(CN)₂)₆}]·3CH₃OH (3), [{Cd₃(trad)₆(SeCN)₂}{Cd(SeCN)₄}₂] (4), [Cd₂(trad)₃(NCS)₄] (5), [Cd₃(tr₂ad)₃(μ-NCS)₃](NCS)₃ (6), [Cd₃(tr₂ad)₆](NO₃)₆·22H₂O (7), [Cu₃(tr₂ad)₄(SO₄)(H₂O)₃](SO₄)₂·34H₂O (8) and [Cu₂(OH)(tr₂ad)₂](NO₃)₃·4H₂O (9) (trad = 4-(adamantan-1-yl)-1,2,4-triazole; tr₂ad = 1,3-bis(1,2,4-triazol-4-yl)-adamantane) revealed the potential of 1,2,4-triazolyl functionalized adamantanes for design of metal-organic polymers incorporating polynuclear coordination units as multiconnected nodes. Structures 1-5 are based upon characteristic di- and trinuclear clusters involving triple triazole bridges [M(μ₂-trad)₃M] (M = Cd), while doubling of the ligand functionality (tr₂ad) allows integration of the clusters into 3D polymeric frameworks 6-9 (M = Cd, Cu).     

New phospholyl complexes of groups 4 and 6: Syntheses, characterisation and polymerisation studies

[M(P₃C₂^tBu₂)(CO)₃I] (M = Mo, 1, W, 2) have been synthesised and reacted with PCl₅ for oxidation study purposes. Compounds Ti(P₃C₂^tBu₂)(Ind)Cl₂], 3, and [Zr(P₃C₂^tBu₂)(Cp)Cl₂], 4, were detected spectroscopically, but showed to be too unstable to be isolated. A Ti(IV) complex, [Ti(P₃C₂^tBu₂)Cl₃], 5, has been formed from the reaction of [TiCl₄] with the base-free ligand K(P₃C₂^tBu₂), while the Ti(III) species, [Ti(P₃C₂^tBu₂) Cl₂(THF)], 6, was prepared from [TiCl₃(THF)₃]. Compounds 5 and 6 were studied as ethylene catalyst precursors after activation with MAO. In the studied conditions, complex 5 is the most active one with an activity of 2.2 × 10⁵ g(molTi [E] h)⁻¹, one order of magnitude higher than compound 6. The produced polymer is linear polyethylene.     

Ferrocenyl-substituted allenylidene complexes of chromium, molybdenum and tungsten: Synthesis, structure and reactivity

Bis(ferrocenyl)-substituted allenylidene complexes, [(CO)₅MCCCFc₂] (1a-c, Fc = (C₅H₄)Fe(C₅H₅), M = Cr (a), Mo (b), W (c)) were obtained by sequential reaction of Fc₂CO with Me₃Si-CCH, KF/MeOH, n-BuLi, and [(CO)₅M(THF)]. For the synthesis of related mono(ferrocenyl)allenylidene chromium complexes, [(CO)₅CrCCC(Fc)R] (R = Ph, NMe₂), three different routes were developed: (a) reaction of the deprotonated propargylic alcohol HCCC(Fc)(Ph)OH with [(CO)₅Cr(THF)] followed by desoxygenation with Cl₂CO, (b) Lewis acid induced alcohol elimination from alkenyl(alkoxy)carbene complexes, [(CO)₅CrC(OR)CHC(NMe₂)Fc], and (c) replacement of OMe in [(CO)₅CrCCC(OMe)NMe₂] by Fc. Complex 1a was also formed when the mono(ferrocenyl)allenylidene complex [(CO)₅CrCCC(Fc)NMe₂] was treated first with Li[Fc] and the resulting adduct then with SiO₂. The replacement route (c) was also applied to the synthesis of an allenylidene complex (7a) with a CC spacer in between the ferrocenyl unit and C_γ of the allenylidene ligand, [(CO)₅CrCCC(NMe₂)-CCFc]. The related complex containing a CHCH spacer (9a) was prepared by condensation of [(CO)₅CrCCC(Me)NMe₂] with formylferrocene in the presence of NEt₃. The bis(ferrocenyl)-substituted allenylidene complexes 1a-c added HNMe₂ across the C_α-C_β bond to give alkenyl(dimethylamino)carbene complexes and reacted with diethylaminopropyne by regioselective insertion of the CC bond into the C_β-C_γ bond to afford alkenyl(diethylamino)allenylidene complexes, [(CO)₅MCCC(NEt₂)CMeCFc₂]. The structures of 5a, 7a, and 9a were established by X-ray diffraction studies.     

Polypyrazolates of the heavier group 13 and 14 elements: A review

Heavy group 13 and 14 analogs of the poly(pyrazolyl)borates are the subject of this review. Within these, the most extensive research has been performed on the study of polypyrazolylgallates Me₂Ga(R₂pz)₂]⁻ (R = H or Me) and [MeGa(pz)₃]⁻, and their complexes with transition metals. In this review, the common features shared with the boron analogs are presented and contrasted. Other recently reported series of group 13 analogs are the alkali polypyrazolylaluminates Na[(R₂pz)₃] with R = Me, ^tBu; R′ = M. The complexes with one or two pyrazolyl ligands on aluminum display anagostic Al-CH₃?Na interactions, these interactions are persistent even if complexes were obtained from solutions with THF that normally coordinate alkali ions. The polypyrazolylsilane ligands Me₂Si(R₂pz)₂ and MeSi(R₂pz)₃ with R = H, Me are remarkably easy to obtain and isolate, in contrast is the fact that the carbon analogs are much harder to obtain and isolate in reasonable yields. Therefore it is surprising that the chemistry of the former ligands is not as developed as could be anticipated. Nevertheless there are examples of the use of these silanes as ligands with the following transition metals: Cr, Mn, Cu, Zn, Sc and Zr. The heavier group 14 analogs with Ge and Sn display coordination patterns with alkali and alkaline ions that resemble those observed with the borates and aluminates. The formation of cationic bimetallic cages of the type [E₂(R₂pz)₃]⁺ and neutral complexes [E₂(R₂pz)₄] has also been observed that can be consider formal isomers of the alkenes. The use of these compounds as ligands has been recently reported.     

4,5-Bis(diphenylphosphinoyl)-1,2,3-triazole ligand: Studies on metal complex formations in liquid-liquid distribution systems

The formation reactions of hydrophobic metal complexes of divalent typical element and transition metal ions with a novel chelating ligand containing N and O donor atoms, 4,5-bis(diphenylphosphinoyl)-1,2,3-triazole (L^TH), were investigated by the liquid-liquid distribution method carried out on metal ions between chloroform and aqueous solutions. The liquid-liquid distribution reaction formulae of metal ions via the formation of hydrophobic metal complexes were revealed, along with their equilibrium constants. Three types of hydrophobic mononuclear and binuclear metal complexes distributed into chloroform solutions were found, namely, ML₂ (M = Mg²⁺, Zn²⁺, Pb²⁺; L = L^T−), ML₂(HL) (M = Cd²⁺, Mn²⁺), and M₂L₃(OH) (M = Co²⁺, Ni²⁺, Cu²⁺). Linear free energy relationships were found between the equilibrium constants of the liquid-liquid distribution reactions and the stability constants of 1:1 complexes consisting of a divalent metal ion and a glycinate. These relationships suggest the chelate formation of N,O-coordination with a heterocyclic five-membered ring in the metal complexes with L^TH.     

Spectroscopic and magnetic properties of diethyl (pyridin-4-ylmethyl)phosphate (4-pmOpe) ligand with perchlorate transition metal salts. Crystal structure of [Cu(4-pmOpe)2(ClO4)2]

The perchlorate M(II) (M = Cu, Ni, Co) complexes with the diethyl (pyridin-4-ylmethyl)phosphate (4-pmOpe) ligand of the composition [M(4-pmOpe)₂ (H₂O)₂](ClO₄)₂ (M = Ni, Co) and [Cu(4-pmOpe)₂(ClO₄)₂] were prepared and studied. The ligand contains two donor atoms, i.e. pyridine nitrogen and phosphoryl oxygen atoms. In particular, the crystal structure of [Cu(4-pmOpe)₂(ClO₄)₂] was determined by the X-ray method. Its structure consists of a one-dimensional polymeric chain in which copper(II) ions are N,O-bridged by two 4-pmOpe organic ligands in a trans arrangement. Two perchlorate ions occupy the fifth and the sixth coordination sites. The Cu?Cu distance is 9.180 Å. The crystal packing is determined by the weak intermolecular C-H?O hydrogen contacts. The coordination compounds were identified and characterized by elemental analysis, spectroscopic and magnetic studies. Spectroscopic and magnetic results of the copper(II) compound are presented in the light of the crystal structure. The magnetic data indicate very weak intra- and interchain magnetic exchange interactions (J^’ = −0.43 and zJ^’ = 0.29 cm⁻¹, respectively). The spectroscopic and magnetic properties of the Co(II) and Ni(II) complexes indicate octahedral and polymeric structure of both compounds in which 4-pmOpe ligand also acts as N,O-bridge between metal ions.     

Synthesis and characterization of new ternary Cu(II)-polyamines-ATP complexes

Four new complexes of Cu(II) of stoichiometry [Cu(ATP)(polyamine)] containing as ligands the polyamines (PA) ethylenediamine, 1,3-diaminopropane, spermidine or spermine and adenosine 5′triphosphate were prepared from aqueous solution at pH 6. The synthesis, characterization, thermogravimetric, vibrational spectroscopy, electron paramagnetic resonance analyses are described and show that these complexes have similar molecular structures. The infrared spectra and the thermal analysis are briefly discussed based on the peculiarities of the complexes. The IR spectra of the ligands and their copper complexes were used to assign the various groups and compare the shifts due to complexation. The EPR parameters values for the complexes show that Cu(II) is complexed in a similar way in the four complexes. Similarity in the coordination mode of complexes in solid state has been determined and discussed. The data obtained suggest that the four complexes present one water molecule of hydration and are complexed through two oxygen atoms from ATP and through two nitrogen atoms of each polyamine.     

Synthesis, spectroscopy and thermal behavior of new lead(II) complexes derived from S-methyl/benzyldithiocarbazates (SMDTC/SBDTC): X-ray crystal structure of [Pb(SMDTC)(NO3)2]

Lead(II) complexes of S-methyldithiocarbazate (SMDTC), [Pb(SMDTC)(NO₃)₂] (1) and S-benzyldithiocarbazate (SBDTC), [Pb(SBDTC)(NO₃)₂] (2) have been synthesized for the first time and characterized by elemental analysis, IR and TGA techniques. The complexes were obtained by addition of the appropriate ligand to an aqueous ethanolic solution of lead(II) nitrate in 1:1 molar ratio. The X-ray crystal structure of complex 1 has been determined by single crystal X-ray diffractometry. In complex 1, lead(II) is in a nine coordinated sphere with seven oxygen atoms of the nitrate groups and thione sulfur, β-nitrogen of neutral bidentate NS chelating ligand. Three nitrate groups act as bidentate chelating whereas the fourth nitrate group is coordinating to the central lead(II) and at the same time it bridges with neighboring lead(II) atom. Coordination geometry of the central lead(II) atom has a tricapped trigonal prismatic arrangement with streochemically inactive lone pair. The lead atoms are linked into polymeric chains and these chains form twin polymeric ribbons linked through bridging oxygen atoms. The N-H?O hydrogen bond network between N_SMDTC and O_nitrate atom leads to self-assembled molecular conformation and stabilizes the crystal structure. The complex 2 with similar spectral and thermal behavior is expected to have a tricapped trigonal prismatic structure. The thermal behavior studies shows that the complexes start to decompose at relatively low temperature (ca. 110 °C) to give PbS residue.     

Shape complementarity of protein-protein complexes at multiple resolutions

Biological complexes typically exhibit intermolecular interfaces of high shape complementarity. Many computational docking approaches use this surface complementarity as a guide in the search for predicting the structures of protein-protein complexes. Proteins often undergo conformational changes to create a highly complementary interface when associating. These conformational changes are a major cause of failure for automated docking procedures when predicting binding modes between proteins using their unbound conformations. Low resolution surfaces in which high frequency geometric details are omitted have been used to address this problem. These smoothed, or blurred, surfaces are expected to minimize the differences between free and bound structures, especially those that are due to side chain conformations or small backbone deviations. Despite the fact that this approach has been used in many docking protocols, there has yet to be a systematic study of the effects of such surface smoothing on the shape complementarity of the resulting interfaces. Here we investigate this question by computing shape complementarity of a set of 66 protein-protein complexes represented by multiresolution blurred surfaces. Complexed and unbound structures are available for these protein-protein complexes. They are a subset of complexes from a nonredundant docking benchmark selected for rigidity (i.e. the proteins undergo limited conformational changes between their bound and unbound states). In this work, we construct the surfaces by isocontouring a density map obtained by accumulating the densities of Gaussian functions placed at all atom centers of the molecule. The smoothness or resolution is specified by a Gaussian fall-off coefficient, termed "blobbyness." Shape complementarity is quantified using a histogram of the shortest distances between two proteins' surface mesh vertices for both the crystallographic complexes and the complexes built using the protein structures in their unbound conformation. The histograms calculated for the bound complex structures demonstrate that medium resolution smoothing (blobbyness = -0.9) can reproduce about 88% of the shape complementarity of atomic resolution surfaces. Complexes formed from the free component structures show a partial loss of shape complementarity (more overlaps and gaps) with the atomic resolution surfaces. For surfaces smoothed to low resolution (blobbyness = -0.3), we find more consistency of shape complementarity between the complexed and free cases. To further reduce bad contacts without significantly impacting the good contacts we introduce another blurred surface, in which the Gaussian densities of flexible atoms are reduced. From these results we discuss the use of shape complementarity in protein-protein docking.     

Binding of HIV-1 TAR mRNA to a peptide nucleic acid oligomer and its conjugates with metal-ion-binding multidentate ligands

A peptide nucleic acid (PNA) oligomer and a series of PNA conjugates featuring covalently attached pendant 1,4,7,10-tetraazacyclododecane (cyclen) or bis((pyridin-2-yl)methyl)amine (DPA) moieties have been synthesized that are complementary to regions of the HIV-1 TAR messenger RNA stem-loop. Thermal denaturation studies, in conjunction win with native gel shift assays, suggest that the PNAs “invade” TAR to produce a mixture of two 1:1 PNA–TAR adducts, tentatively assigned as an “open-duplex” structure, in which the TAR stem-loop dissociates and the PNA hybridizes with its RNA complement via Watson–Crick base-pairing, and a triplex-type structure, in which the initially displaced RNA segment is bound to the PNA:RNA duplex through Hoogsteen base-pairing. Thermal denaturation experiments with the TAR sequence and single-stranded RNA and DNA oligonucleotides, both in the presence and in the absence of Zn²⁺ ions, show that the introduction of cyclen or DPA ligand arms into the PNA oligomer leads to a small but reproducible increase in the T _m values. This is attributed to hydrogen-bonding and/or electrostatic interactions between protonated forms of cyclen/DPA and the cognate RNA or DNA oligonucleotide targets. Contrary to expectations, the addition of Zn²⁺ ions did not further enhance duplex formation through binding of Zn(II)–cyclen or Zn(II)–DPA moieties to the complementary RNA or DNA. Native gel shift assays further confirmed the stability increase of the metal-free cyclen- and DPA-modified PNA hybrids as compared with a control PNA sequence. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.