Ligand effects and dimer formation in dicoordinated copper(I) complexes

The dimers of dicoordinated Cu(I) complexes of the type [CuXL], where X^? = Cl^?, Br^?, I^?, or CN^? and L is a neutral ligand such as NH₃, PH₃, or CNCH₃, have been studied by means of ab initio and density functional calculations. The performance of density functional calculations using the hybrid B3LYP method has been compared with MP2 results. Ligand and conformational effects are analyzed for two types of dimers, notably those in which the monomers retain their linear conformation and associate through Cu–Cu contacts and those in which the X ligands act as bridges resulting in tricoordination of each Cu atom and a rhombic Cu₂X₂ core. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Pentadentate terpyridine-catechol linked ligands and their cobalt(III) complexes

A series of novel pentadentate terpyridine-catechol linked ligands were prepared, in which the terpyridine and catechol moieties were linked together by (CH2)n chains of different lengths (n = 4-6). Together with 1-methylimidazole, these ligands formed low-spin, six-coordinate Co(III) complexes. Two of the complexes (n = 4, 5) were characterized by X-ray crystallography [n = 4, monoclinic, P2(1)/c, a = 14.957(7) A, b = 10.585(9) A, c = 23.033(7) A, beta = 106.01(3) degrees, V = 3505(3) A3, Z = 4, R = 0.063; n = 5, monoclinic, P2(1)/c, a = 8.848(7) A, b = 15.78(1) A, c = 25.455(7) A, beta = 93.90(5) degrees, V = 3544(3) A3, Z = 4, R = 0.056], which revealed similar structures around the Co(III) centers but different conformations for the (CH2)n linkers. The (CH2)4 linker showed a straight, symmetric conformation whereas the (CH2)5 linker showed a curved conformation that allowed the accommodation of one extra CH2 unit, suggesting that the (CH2)4 linker presents the "best-fit" length for these complexes.     

Supramolecular interaction of ethylenediamine linked beta-cyclodextrin dimer and berberine hydrochloride by spectrofluorimetry and its analytical application

The supramolecular interaction of β-cyclodextrin dimer with berberine hydrochloride was studied in aqueous KH₂PO₄-H₃PO₄ buffer solution of pH 2.00 at room temperature by spectrofluorimetry. The apparent association constant of the complex was 1.53 × 10⁴ L mol⁻¹. Based on the significant enhancement of fluorescence intensity of supramolecular sandwich complexes, a spectrofluorimetric method with high sensitivity and selectivity was developed for the determination of berberine hydrochloride in aqueous solution in presence of ethylenediamine linked β-CD dimer. The linear range of the method was 12.8-1.00 × 10⁴ ng mL⁻¹ with the detection limit 3.6 ng mL⁻¹. There was no interference from the normally used in tablets and serum constituents. The proposed method was successfully applied to the determination of berberine hydrochloride in tablets and serum. And then it has a promising potential in therapeutic drug monitoring, pharmokinetis and clinical application.     

Pathway from chain to dimer in Cu(I) camphor hydrazone complexes

The chemical reactivity, molecular structure, and surface characteristics of Cu(I) camphor hydrazone compounds indicate that exist a structural pathway for conversion of coordination polymers into dimers and vice versa. By X-ray diffraction analysis two polymorphic forms of the chain compound [{CuCl}(2)(Me(2)NNC(10)H(14)O)](n) were identified that essentially differ in the structural arrangement and geometry of the non-linear copper atom. The characterization of the dimer complexes [{Cu(Me(2)NNC(10)H(14)O)}(2)(μ-X)(2)] (X = Cl or Br) was also achieved by X-ray diffraction analysis showing the unusual arrangement of the camphor hydrazone ligands that occupy the same side of the molecule. Bond lengths and torsion angles show that one of the polymorphic forms is structurally close to the related dimer. The surface composition of the coordination polymers [{CuX}(2)(YNC(10)H(14)O)](n) (X = Cl, Y = NMe(2), NH(2); X = Br, Y = NH(2)) and dimers [{Cu(Me(2)NNC(10)H(14)O)}(2)(μ-X)(2)] (X = Cl or Br) studied by X-ray Photoelectron Spectroscopy corroborate the molecular properties and the reactivity trend.     

Bis(ethylene)dithioformamidinium dihalides and their copper(I), silver(I) and gold(I) complexes

The bis(ethylene)dithioformamidinium dihalides (En₂Tu₂X₂, X = Cl(H₂O), Br, I), obtained by oxidation of ethylenethiourea, and their complexes MX.En₂Tu₂X₂ (M = Cu, X = Br[0.2 DMF]; M = Ag, X = Br; M = Au, X = Cl), 2MX. 1.5 En₂Tu₂X₂ (M = Cu, X = Cl[0.4 DMF]; M = Ag, X = I), MX. 1.5 En₂Tu₂X₂ (M = Cu, X = I; M = Au, X = Br), AgCl. 1.25 En₂Tu₂Cl₂, 4AgI. 1.5 En₂Tu₂I₂, AuI.2En₂Tu₂I₂, were prepared and studied by i.r. spectroscopy. The En₂Tu²⁺₂ ion is N-bonded to the metal ion. Some νMN and νMX bands are tentatively assigned.     

Solvent-free synthesis of bisferrocenylimines and their rhodium(I) complexes

The solvent-free reaction of ferrocenecarboxaldehyde and diaminoalkanes under solvent-free conditions gave bisferrocenylimines (L) in excellent yields. Cationic rhodium(I) complexes with the formulation [Rh(COD)(L)]ClO₄ were prepared by the reaction of [Rh(COD)Cl]₂ with the bisferrocenylimines in the presence of silver perchlorate. The compounds were characterised by NMR, IR, MS and elemental analysis. The X-ray crystal structures of two rhodium(I) complexes are also reported.     

Novel pincer complexes of Ag(I), coordination of toluene and their comparison with indium analogues

The bis(imino)pyridine scaffold provides for the synthesis and characterization of the unique Ag(I) pincer complexes [{ArN=CPh}(2)(NPh)]Ag(+)(OTf)(-) (Ar = 2,5-(t)Bu(2)C(6)H(3); 2,6-(i)Pr(2)C(6)H(3)). The similar covalent radii of Ag(I) and In(I), prompted a bonding comparison of these species with their In(I) analogues. Coordination of toluene to the Ag center revealed the stronger Lewis acidity of the metal site in these compounds relative to In(I) analogues.     

Light-induced geometrical changes in acyclic ruthenium(II) complexes and their ruthena-macrocyclic analogues

The two ligands 1 (4'-(3-anisylphenyl)-2,2';6',2' '-terpyridine) and 2 (2-mesityl-8-anisyl-1,10-phenanthroline) (Scheme 2) were synthesized and coordinated to ruthenium. The corresponding complexes Ru(1)(2)(L)n+, where L = Cl-, CH3CN, or C5H5N, have been fully characterized. Notably, the hindering mesityl group of the phenanthroline ligand was shown to lie opposite to the monodentate ligand L both in solution and in the solid state. Upon irradiation in acetonitrile or pyridine, quantitative isomerization of the complex occurred, which consisted of a 90 degrees rotation of the bidentate chelate. In the new isomers the mesityl group was shown to pi stack to the coordinated monodentate ligand with the anisyl group of the phen (1,10-phenanthroline) lying on the other side of the ruthenium atom. The back reaction was performed by heating the photochemical isomers of the complexes in DMSO and exchanging the DMSO with chloride anion, acetonitrile, or pyridine. The stability of the ruthenium(II)-pyridine bond was used in order to inscribe the Ru(terpy)(phen) motif in a molecular ring. Functionalization of the ligands and subsequent cyclization reaction on the complex were performed on the two isomers of Ru(1)(2)(C5H5N)2+. Four macrocyclic complexes including the Ru(terpy)(phen)(py)n+ moiety were obtained and characterized. A (CH2)18 alkane chain or polyethylene glycol chain formed the flexible part of the ruthena-macrocycles. Upon visible light irradiation a dramatic geometrical changeover of the cyclic complex took place, which could be reversed thermally.     

Silver(I) and mercury(II) complexes of meta- and para-xylyl linked bis(imidazol-2-ylidenes)

Mononuclear silver and mercury complexes bearing bis-N-heterocyclic carbene (NHC) ligands with linear coordination modes have been prepared and structurally characterised. The complexes form metallocyclic structures that display rigid solution behaviour. A larger metallocycle of the form [L₂Ag₂]²⁺ [where L = para-bis(N-methylimidazolylidene)xylylene] has been isolated from the reaction of para-xylylene-bis(N-methylimidazolium) chloride and Ag₂O. Reaction of silver- and mercury-NHC complexes with Pd(NCCH₃)₂Cl₂ affords palladium-NHC complexes via NHC-transfer reactions, the mercury case being only the second example of a NHC-transfer reaction using a mercury-NHC complex.     

8-Oxyquinolate iridium(I) complexes and their oxidative-addition reactions

The novel sixteen-electron complex [Ir(Oq)(COD)] (Oq = 8-oxyquinolate; COD = 1,5-cyclooctadiene) adds monodentate phosphines, phosphites or activated olefins irreversibly to give pentacoordinate iridium(I) complexes of the type [Ir(Oq)(COD)L] (L = PPh₃, P(OPh)₃, maleic anhydride or tetracyano-ethylene). Reaction of [Ir(Oq)(COD)] with some diphosphines leads to substitution products of the general formula [Ir(Oq)(diphos)] (diphos = 1,2-bis(diphenylphosphino)ethane or cis-1,2-bis(diphenylphosphino)ethylene). Carbon monoxide displaces the COD group from the complexes giving either [Ir(Oq)(CO)₂] or [Ir(Oq)(CO)L], and the latter undergo oxidative addition reactions with SnCl₄, Me₃SiCl, Me₃SnCl, MeI, allylbromide, PhCOCl, MeCOCl, Cl₂, Br₂, TlCl₃ and HCl leading to novel iridium(III) complexes.     

Hypoxia-targeting copper bis(selenosemicarbazone) complexes: comparison with their sulfur analogues

The first copper bis(selenosemicarbazone) complexes have been synthesized, using the ligands glyoxal bis(selenosemicarbazone), pyruvaldehyde bis(selenosemicarbazone), and 2,3-butanedione bis(selenosemicarbazone). Their spectroscopic properties indicate that they are structurally analogous to their well-known square-planar sulfur-containing counterparts, the copper bis(thiosemicarbazone) complexes. Spectroscopic comparison of the sulfur- and selenium-containing complexes provides insight into their electronic structure. The effects on spectroscopic and redox properties of replacing sulfur with selenium, and of successive addition of methyl groups to the ligand backbone, are rationalized in terms of their electronic structure using spin-unrestricted density functional calculations. These suggest that, like the sulfur analogues, the complexes have a very low-lying empty ligand-based pi-orbital immediately above the LUMO, while the LUMO itself has d(x2)-(y2) character (i.e., is the spin partner of the HOMO). Replacement of S by Se shifts the oxidation potentials much more than the reduction potentials, whereas alkylation of the ligand backbone shifts the reduction potentials more than the oxidation potentials. This suggests that oxidation and reduction involve spatially different orbitals, with the additional electron in the reduced species occupying the ligand-based pi-orbital rather than d(x2)-(y2). Density functional calculations on the putative singlet Cu(I)-reduced species suggest that this ligand pi-character could be brought about by distortion away from planarity during reduction, allowing the low-lying ligand pi-LUMO to mix into the d(x2)-(y2)-based HOMO. The analogy in the structure and reduction behavior between the sulfur- and selenium-containing complexes suggests that labeled with positron emitting isotopes of copper (Cu-60, Cu-62, Cu-64), the complexes warrant biological evaluation as radiopharmaceuticals for imaging of tissue perfusion and hypoxia.     

A new series of dinuclear Au(I) complexes linked by diethynylpyridine groups

A series of novel digold complexes incorporating ethynyl pyridine derivatives as a spacer unit, [(R(3)P)Au(C[triple bond]C)X(C[triple bond]C)Au(PR(3))] (R = Ph, X = 2,5-pyridine (1); R = Cy (cyclohexane), X = 2,5-pyridine (2); R = Ph, X = 2,6-pyridine (3); R = Ph, X = 2,5'-bipyridine (4); R = Ph, X = 2,6'-bipyridine (5)), has been synthesised. All the complexes have been characterised spectroscopically and the structures determined by single-crystal X-ray crystallography. The central (C[triple bond]C)(X)(C[triple bond]C) unit is essentially linear for complexes 1, 2 and 4 and kinked for complexes 3 and 5, but only in 1, with the shortest spacer group and the less bulky phosphine ligand, is there evidence of d(10)...d(10) Au...Au interactions (Au-Au 3.351(2) A). The solution UV/visible absorption and emission spectra for all the complexes are similar to those of the free ligands suggesting that the spectra are dominated by pi-pi* ligand-centred transitions and this is confirmed by DFT calculations.     

Dicarbonylrhodium(I) complexes of aminophenols and their catalytic carbonylation reaction

The complexes [Rh(CO)₂ClL]( 1 ), where L = 2‐aminophenol ( a ), 3‐aminophenol ( b ) and 4‐aminophenol ( c ), have been synthesized and characterized. The ligands are coordinated to the metal centre through an N‐donor site. The complexes 1 undergo oxidative addition ( OA ) reactions with various alkyl halides ( RX ) like CH₃I, C₂H₅I and C₆H₅CH₂Cl to produce Rh(III) complexes of the type [Rh(CO)(COR)XClL], where R = ? CH₃( 2 ), ? C₂H₅( 3 ), X = I; R = C₆H₅CH₂? and X = Cl ( 4 ). The OA reaction with CH₃I follows a two‐stage kinetics and shows the order of reactivity as 1b > 1c > 1a . The minimum energy structure and Fukui function values of the complexes 1a–1c were calculated theoretically using a DND basis set with the help of Dmol³ program to substantiate the observed local reactivity trend. The catalytic activity of the complexes 1 in carbonylation of methanol, in general, is higher (TON 1189–1456) than the species [Rh(CO)₂I₂]^? (TON 1159). Copyright © 2007 John Wiley & Sons, Ltd.     

Bonding and (hyper)polarizability in the sodium dimer

We report a conventional ab initio and density functional theory study of the polarizability (alpha(alphabeta)/e(2)a(0) (2)E(h) (-1)) and hyperpolarizability (gamma(alphabetagammadelta)/e(4)a(0) (4)E(h) (-3)) of the sodium dimer. A large [18s14p9d2f1g] basis set is thought to yield near-Hartree-Fock values for both properties: alpha=272.28, Deltaalpha=127.22 and gamma=2157.6 x 10(3) at R(e)=3.078 87 A. Electron correlation has a remarkable effect on the Cartesian components of gamma(alphabetagammadelta). Our best value for the mean is gamma=1460.1 x 10(3). The (hyper)polarizability shows very strong bond-length dependence. The effect is drastically different for the longitudinal and transverse components of the hyperpolarizability. The following first derivatives were extracted from high-level coupled cluster calculations: (dalpha/dR)(e)=54.1, (dDeltaalpha/dR)(e)=88.1e(2)a(0)E(h) (-1), and (dgamma/dR)(e)=210 x 10(3)e(4)a(0) (3)E(h) (-3). We associate the (hyper)polarizability to bonding effects between the two sodium atoms by introducing the differential property per atom Q(diff)/2 identical with (Q[Na(2)(X (1)Sigma(g) (+))]/2-Q[Na((2)S)]). The differential (hyper)polarizability per atom is predicted to be strongly negative for the dimer at R(e), as [alpha(Na(2))/2-alpha(Na)]=-33.8 and [gamma(Na(2))/2-gamma(Na)]=-226.3 x 10(3). The properties calculated with the widely used B3LYP and B3PW91 density functional methods differ significantly. The B3PW91 results are in reasonable agreement with the conventional ab initio values. Last, we observe that low-level ab initio and density functional theory methods underestimate the dipole polarizability anisotropy. Experimental data on this important property are highly desirable.     

Novel neutral octanuclear copper(I) complexes stabilized by pyridine linked bis(pyrazolate) ligands

Two novel, neutral, octanuclear copper(I) complexes displaying twisted-boat Cu(8) conformations and short Cu-Cu interactions have been synthesized from hydrothermal reactions; the complexes show unusual multiple band emissions.     

Cationic rhodium(I) and iridium(I,III) complexes of cinnamonitrile and their catalytic activities

Summary Reactions of cinnamonitrile (trans-PhCH=CHCN) with [M(ClO₄)(CO)(PPh₃)₂] (M=Rh or Ir) produce hydrogenation oftrans-PhCH=CHCN to PhCH₂CH₂CN at 100°C under 3 atm of hydrogen.     

Synthesis of chiral salen Mn(III) complexes covalently linked to Re(I)-based photosensitizers

Two Mn(III)Re(I) binuclear complexes were prepared as catalyst-photosensitizer models, in which the chiral pyrrolidine salen Mn(III) unit was covalently bonded to an Re(I) bipyridyl carbonyl moiety via a carboxamide linkage. The spectral and electrochemical properties of the Mn(III)Re(I) complexes were studied.     

Synthesis, characterisation and theoretical studies of amidinato-indium(I) and thallium(I) complexes: isomers of neutral group 13 metal(I) carbene analogues

The synthesis and characterisation of the monomeric amidinato-indium(I) and thallium(I) complexes, [M(Piso)].PisoH, M = In or Tl, Piso- = [ArNC(Bu(t))NAr]-, Ar = C6H3Pr(i)2-2,6, are reported. These complexes, in which the metal centre is chelated by the amidinate ligand in an N,eta3-arene-fashion, can be considered as isomers of four-membered group 13 metal(I) carbene analogues. Theoretical studies have compared the relative energies of both isomeric forms of a model complex, [In{PhNC(H)NPh}].     

1,4-dicyanobutene-bridged binuclear rhodium(I) complexes and their catalytic activities

Reactions of Rh(ClO₄)(CO)(PPh₃)₂ with dicyano olefins, cis-NCCHCH-CH₂CH₂CN (c-DC1B), rans-NCCHCHCH₂CH₂CN (t-DC1B), trans-NCCH₂CHCHCH₂CN (t-DC2B), and NCCH₂CH₂CH₂CN (DCB) produce the binuclear dicationic rhodium(I) complexes, [(CO)(PPh₃)₂RhNCACNRh-(PPh₃)₂(CO)](ClO₄)₂ (NCACN = c-DC1B 1), t-DC1B (2), t-DC2B (3), DCB (4). Complexes 1 and 2 are catalytically active for the hydrognation of c-DC1B and t-DC1B, respectively, to give DCB, while complex 3 catalyze the isomerization of t-DC2B to give c-DC1B and t-DC1B, and the hydrogenation of t-DC2B to DCB at 100°C.